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Title:
INTEGRATED PLASMONIC-FERROELECTRIC MATERIALS AND METHODS OF MAKING AND USE THEREOF
Document Type and Number:
WIPO Patent Application WO/2019/191208
Kind Code:
A1
Abstract:
Disclosed herein integrated plasmonic-ferroelectric materials and methods of making and methods of use thereof. The integrated plasmonic-ferroelectric materials comprise a ferroelectric particle and a plurality of plasmonic particles disposed on the ferroelectric particle and in physical contact with the ferroelectric particle.

Inventors:
WANG, Gufeng (1021 Main Campus Drive, 2nd FloorRaleigh, North Carolina, 27606, US)
MAGGARD, Paul A. (1021 Main Campus Drive, 2nd FloorRaleigh, North Carolina, 27606, US)
Application Number:
US2019/024248
Publication Date:
October 03, 2019
Filing Date:
March 27, 2019
Export Citation:
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Assignee:
NORTH CAROLINA STATE UNIVERSITY (1021 Main Campus Drive, 2nd FloorRaleigh, North Carolina, 27606, US)
International Classes:
H01L41/187; H01L41/00; H01L41/16
Foreign References:
US5935485A1999-08-10
Other References:
ORTIZ ET AL.: "Composite Ferroelectric and Plasmonic Particles for Hot Charge Separation and Photocatalytic Hydrogen Gas Production", ACS APPLIED ENERGY MATERIALS, vol. 1, no. 9, 29 August 2018 (2018-08-29), pages 4606 - 4616, XP055638693
Attorney, Agent or Firm:
NEAR, Rachel D. et al. (Meunier Carlin & Curfman LLC, 999 Peachtree Street NE,Suite 130, Atlanta Georgia, 30309, US)
Download PDF:
Claims:
CLAIMS

What is claimed is:

1. A integrated plasmonic-ferroelectric material comprising:

a ferroelectric particle; and

a plurality of plasmonic particles disposed on the ferroelectric particle and in physical contact with the ferroelectric particle.

2. The integrated plasmonic-ferroelectric material of claim 1, wherein the ferroelectric particle comprises AgNbCb, AgTaCb, BaTiCb, BafTbO , Bii2TiCho, BriTbO , BbTbCb, (Ba,Eu)Ti03, BaMnF4, BaFeF4, BaNiF4, BaCoF4, BaZnF4, BaMgF4, BaAhCri, BaGa204, BaxSri-xNb206, Ba2NaNb50i5, Bao.5Sro.5Nb206, BiSc03, BiFeCb, CaTi03, Cd2Nb207, Cs2ZnCl, Cs2CuCl, Cs2CoCl, Cs2CdCl, Cs2HgCl, Cs2ZnBr, Cs2CuBr, Cs2CoBr, Cs2CdBr, Cs2HgBr, Gd2(Mo04)3, GeTe, KNbCb, potassium sodium niobate, potassium tantalite niobate, KTiOP04, KTa03, K2Cd2(S04)3, KNbSbCb, KrZnCl.

K2CuCl, K2C0CI, K2CdCl, K2HgCl, K2ZnBr, K2CuBr, K2CoBr, K2CdBr, K2HgBr, NaNbCb, NaTaOs, Nao.sBio.sTiCb, (NH )2Cd2(S04)3, (NH )2ZnCl, (NH )2CuCl, (NH )2CoCl, (NH )2CdCl, (NH )2HgCl, (NH )2ZnBr, (NH )2CuBr, (NH )2CoBr, (NH )2CdBr, (NH )2HgBr, N13B7O13I, N13B7O13CI, La2Ti207, LiNbOs, PbTi03, lead zirconate titanate (PbZn-xTix03, PZT), (Pb,La)Ti03, (Pb,La)(Zr,Ti)03, PbZr03, PbHf03, lead scandium tantalate, PbiGesOi 1. PbNb206, PbTa206, Pb(Mg,Nb)03, Rb2ZnCl, Rb2CuCl, Rb2CoCl, Rb2CdCl, Rb2HgCl, Rb2ZnBr, Rb2CuBr, Rb2CoBr, Rb2CdBr, Rb2HgBr, Sri-xBaxNb206, SrAhCri, SrGa204, SrTi03, SrBi2Ta209, Tl2Cd2(S04)3, YMnCb, polyvinylidene fluoride, or combinations thereof.

3. The integrated plasmonic-ferroelectric material of claim 1 or claim 2, wherein the

ferroelectric particle comprises PbTiCb, lead zirconate titanate (PbZn-xTix03, PZT), or a combination thereof.

4. The integrated plasmonic-ferroelectric material of any one of claims 1-3, wherein the ferroelectric particle comprises PbZn-xTix03 wherein x is from 0 to less than 1, from 0.2 to 0.8, or from 0.4 to 0.6.

5. The integrated plasmonic-ferroelectric material of any one of claims 1-4, wherein the ferroelectric particle comprises PbTiCb.

6 The integrated plasmonic-ferroelectric material of any one of claims 1-5, wherein the ferroelectric particle has a shape that is substantially spherical, ellipsoidal, triangular, pyramidal, tetrahedral, cylindrical, rectangular, cuboidal, or cuboctahedral.

7. The integrated plasmonic-ferroelectric material of any one of claims 1-6, wherein the ferroelectric particle has a shape that is substantially rectangular, cuboidal, or cuboctahedral.

8. The integrated plasmonic-ferroelectric material of any one of claims 1-7, wherein the ferroelectric particle has an average particle size of from 10 nanometers (nm) to 1 millimeter (mm), from 125 nm to 5 microns, from 125 nm to 500 nm, or from 1 micron to 5 microns.

9. The integrated plasmonic-ferroelectric material of any one of claims 1-8, wherein the plurality of plasmonic particles comprises a plurality of metal particles comprising a metal selected from the group consisting of Au, Ag, Pt, Pd, Cu, Cr, Al, Cd, Zn, Ga, and combinations thereof.

10. The integrated plasmonic-ferroelectric material of any one of claims 1-9, wherein the plurality of plasmonic particles have an average particle size of from 5 nm to 50 microns, or from 5 nm to 1 micron.

11. The integrated plasmonic-ferroelectric material of any one of claims 1-10, wherein the plurality of plasmonic particles have a shape that is substantially spherical, ellipsoidal, triangular, pyramidal, tetrahedral, polygonal, cylindrical, rectangular, cuboidal, cuboctahedral, or a combination thereof.

12. The integrated plasmonic-ferroelectric material of any one of claims 1-11, wherein the plurality of plasmonic particles have a shape that is that is substantially spherical, ellipsoidal, cylindrical, or a combination thereof.

13. The integrated plasmonic-ferroelectric material of any one of claims 1-12, wherein the plurality of plasmonic particles comprise a plurality of rod shaped particles having an average length and an average diameter.

14. The integrated plasmonic-ferroelectric material of claim 13, wherein the average length of the plurality of rod shaped particles is from 5 nm to 1 micron.

15. The integrated plasmonic-ferroelectric material of claim 13 or claim 14, wherein the average diameter of the plurality of rod shaped particles is from 5 nm to 100 nm, from 5 nm to 50 nm, or from 10 nm to 20 nm.

16. The integrated plasmonic-ferroelectric material of any one of claims 13-15, wherein the plurality of rod shaped particles have an average aspect ratio of from greater than 1 to 200, from greater than 1 to 100, from greater than 1 to 50, from greater than 1 to 10, from greater than 1 to 6, or from 3 to 6.

17. The integrated plasmonic-ferroelectric material of any one of claims 13-16, wherein the each of the plurality of rod shaped particles comprise a first metal and each of the plurality of rod shaped particles have a first end and a second end, wherein the first end and the second end are capped with a second metal that is different than the first metal, such that the plurality of plasmonic particles comprise a plurality of end-capped rod shaped particles.

18. The integrated plasmonic-ferroelectric material of claim 15, wherein the first metal is selected from the group consisting of Au, Ag, Pt, Pd, Cu, Cr, Al, Cd, Zn, Ga, and combinations thereof.

19. The integrated plasmonic-ferroelectric material of claim 17 or claim 18, wherein the second metal is selected from the group consisting of Al, Ti, Cr, Mn, Fe, Co, Ni, Cu, Mo, Pd, Ag, Cd, Pt, Au, Zn, Ga, and combinations thereof.

20. The integrated plasmonic-ferroelectric material of any one of claims 17-19, wherein the first metal comprises Au and the second metal comprises Pt.

21. The integrated plasmonic-ferroelectric material of any one of claims 17-20, wherein the average ratio of the first metal to the second metal in the plurality of end-capped rod shaped particles is from 0.01 to 10.

22. The integrated plasmonic-ferroelectric material of any one of claims 1-21, further

comprising a plurality of co-catalyst particles disposed on the ferroelectric particle and in physical contact with the ferroelectric particle.

23. The integrated plasmonic-ferroelectric material of claim 22, wherein the plurality of co catalyst particles comprises a metal selected from the group consisting of Al, Ti, Cr, Mn, Fe, Co, Ni, Cu, Mo, Pd, Ag, Cd, Pt, Au, Zn, Ga, Pb, and combinations thereof.

24. The integrated plasmonic-ferroelectric material of claim 22 or claim 23, wherein the plurality of co-catalyst particles comprise Pt.

25. The integrated plasmonic-ferroelectric material of any one of claims claim 22-24, wherein the plurality of co-catalyst particles have an average particle size of from 10 nm to 50 nm.

26. The integrated plasmonic-ferroelectric material of any one of claims 22-25, wherein the plurality of co-catalysts particles have a shape that is substantially spherical, ellipsoidal, triangular, pyramidal, tetrahedral, polygonal, cylindrical, rectangular, cuboidal, cuboctahedral, or a combination thereof.

27. The integrated plasmonic-ferroelectric material of any one of claims 22-26, wherein the plurality of co-catalyst particles are substantially spherical in shape.

28. The integrated plasmonic-ferroelectric material of any one of claims 22-27, wherein the ferroelectric particle is present in an amount in the integrated plasmonic-ferroelectric material and wherein the plurality of co-catalyst particles are present in an amount of from 0.1 wt% to 10 wt%, from 0.1 wt% to 5 wt%, or from 0.5 wt% to 1 wt% based on the amount of the ferroelectric particle in the integrated plasmonic-ferroelectric material.

29. The integrated plasmonic-ferroelectric material of any one of claims 1-28, wherein the plurality of plasmonic particles have a surface plasmon resonance that overlaps with at least a portion of the solar spectrum.

30. The integrated plasmonic-ferroelectric material of any one of claims 1-29, wherein the ferroelectric particle has a bandgap that overlaps with at least a portion of the solar spectrum.

31. A method of making the integrated plasmonic-ferroelectric material of any one of claims 1-30, the method comprising disposing the plurality of plasmonic particles on the ferroelectric particle.

32. The method of claim 31, wherein the method further comprises making the ferroelectric particle.

33. The method of claim 31 or claim 32, wherein the method further comprises making the plurality of plasmonic particles.

34. The method of any one of claims 31-33, wherein the method further comprises disposing the plurality of co-catalyst particles on the ferroelectric particle.

35. The method of claim 34, wherein the method further comprises making the plurality of co-catalyst particles.

36. A method of use of the integrated plasmonic-ferroelectric materials of any one of claims 1-30, the method comprises using the integrated plasmonic-ferroelectric material as a photocatalyst.

37. The method of claim 36, wherein the method comprises using the integrated plasmonic- ferroelectric material as a photocatalyst for water purification, nitrogen fixation, ammonia production, hydrogen peroxide generation, or a combination thereof.

38. The method of claim 36 or claim 37, wherein the method comprises using the integrated plasmonic-ferroelectric material as a photocatalyst for photocatalytic nitrogen fixation by photocatalytically forming ammonia.

39. The method of claim 36, wherein the method comprises using the integrated plasmonic- ferroelectric material as a photocatalyst for photocatalytic fuel generation.

40. The method of claim 39, wherein the method comprises contacting the photocatalyst with a fuel precursor to form a mixture and illuminating the mixture with light that overlaps with at least a portion of the plasmon resonance of the plurality of plasmonic particles, thereby converting the fuel precursor to a fuel.

41. The method of claim 40, wherein the light overlaps with at least a portion of the bandgap of the ferroelectric particle.

42. The method of claim 40 or claim 41, wherein the light is provided by a light source, and the light source comprises an artificial light source or a natural light source.

43. The method of any one of claims 40-42, wherein the light comprises sunlight.

44. The method of any one of claims 40-43, wherein the fuel precursor comprises water.

45. The method of any one of claims 39-44, wherein the method comprises using the

integrated plasmonic-ferroelectric material as a photocatalyst for solar water splitting.

46. The method of any one of claims 40-43, wherein the fuel precursor comprises CCh and the method comprises using the integrated plasmonic-ferroelectric material as a photocatalyst for photochemical reduction of CCh.

47 The method of any one of claims 40-45, wherein the fuel comprises hydrogen and the method comprises using the integrated plasmonic-ferroelectric material as a photocatalyst for photocatalytic hydrogen generation.

Description:
INTEGRATED PLASMONIC-FERROELECTRIC MATERIALS AND METHODS OF MAKING AND USE THEREOF

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to U.S. Provisional Application No.

62/650,454 filed March 30, 2018, which is hereby incorporated herein by reference in its entirety.

BACKGROUND

Conventional semiconductors for hydrogen production absorb light to create electrons and holes (e.g.,“hot” charges), which diffuse to the surface of the semiconductor where reactions can then occur. However, conventional semiconductor-based catalysts for hydrogen production suffer from various limitations, such as, low light absorption, fast charge

recombination, large bandgaps (e.g., such that low energy photons cannot be used), and low overall efficiency for solar light conversion (<l%, while commercially viable efficiency is 10% or more).

Plasmonic nanoparticles are excellent light absorbers for harvesting solar energy, resulting in hot electrons that could potentially be utilized in photocatalytic hydrogen production. However, the hot electrons generated in localized surface plasmon resonance process have a very short lifetime and are challenging to be used efficiently.

Combinations of plasmonic particles with conventional semiconductors have been studied, but these combinations still suffer from low charge injection efficiency and low overall efficiency. The hot charges can flow back from the semiconductor to the metal, thereby lowering the charge injection efficiency. Therefore, efficient photocatalyst materials are still needed.

The compositions and methods discussed herein addresses these and other needs.

SUMMARY

In accordance with the purposes of the disclosed compositions and methods as embodied and broadly described herein, the disclosed subject matter relates to integrated plasmonic- ferroelectric materials and methods of making and methods of use thereof. The integrated plasmonic-ferroelectric materials comprise a ferroelectric particle and a plurality of plasmonic particles disposed on the ferroelectric particle and in physical contact with the ferroelectric particle.

In some examples, the ferroelectric particle comprises PbTiCb, lead zirconate titanate (PbZri-xTixCb, PZT), or a combination thereof. In some examples, the ferroelectric particle comprises PbTiCb. In some examples, the ferroelectric particle comprises lead zirconate titanate, PbZn-xTixCb (PZT), wherein x is from 0 to less than 1. The ferroelectric particle can have a shape that is substantially spherical, ellipsoidal, triangular, pyramidal, tetrahedral, cylindrical, rectangular, cuboidal, or cuboctahedral. In some examples, the ferroelectric particle can have a shape that is substantially rectangular, cuboidal, or cuboctahedral. The ferroelectric particle can have an average particle size of from 10 nm to 1 mm (e.g., from 125 nm to 5 microns, from 125 nm to 500 nm, or from 1 micron to 5 microns). In some examples, the ferroelectric particle has a bandgap that overlaps with at least a portion of the solar spectrum.

The plurality of plasmonic particles can comprise, for example, a plurality of metal particles comprising a metal selected from the group consisting of Au, Ag, Pt, Pd, Cu, Cr, Al,

Cd, Zn, Ga, and combinations thereof. In some examples, the plurality of plasmonic particles can comprise gold. The plurality of plasmonic particles can, for example, have a surface plasmon resonance that overlaps with at least a portion of the solar spectrum. The plurality of plasmonic particles can, for example, have an average particle size of from 5 nm to 50 microns (e.g., from 5 nm to 1 micron). The plurality of plasmonic particles can, for example, have a shape that is substantially spherical, ellipsoidal, triangular, pyramidal, tetrahedral, polygonal, cylindrical, rectangular, cuboidal, cuboctahedral, or a combination thereof. In some examples, the plurality of plasmonic particles can have a shape that is that is substantially spherical, ellipsoidal, cylindrical, or a combination thereof.

In some examples, the plurality of plasmonic particles can comprise a plurality of rod shaped particles having an average length and an average diameter. The average length of the plurality of rod shaped particles can, for example, be from 5 nm to 1 micron. The average diameter of the plurality of rod shaped particles can, for example, be from 5 nm to 100 nm (e.g., from 5 nm to 50 nm, or from 10 nm to 20 nm). In some examples, the plurality of rod shaped particles can be described by their aspect ratio, which, as used herein, is the length of a rod shaped particle divided by the diameter of a rod shaped particle. For example, the plurality of rod shaped particles can have an average aspect ratio from greater than 1 to 200 (e.g., from greater than 1 to 100, from greater than 1 to 50, from greater than 1 to 10, from greater than 1 to 6, or from 3 to 6).

In some examples, each of the plurality of rod shaped particles can comprise a first metal and each of the plurality of rod shaped particles can have a first end and a second end, wherein the first end and the second end are capped with a second metal that is different than the first metal, such that the plurality of plasmonic particles comprise a plurality of end-capped rod shaped particles. The first metal can, for example, be selected from the group consisting of Au, Ag, Pt, Pd, Cu, Cr, Al, Cd, Zn, Ga, and combinations thereof. The second metal can, for example, be selected from the group consisting of Al, Ti, Cr, Mn, Fe, Co, Ni, Cu, Mo, Pd, Ag, Cd, Pt, Au, Zn, Ga, and combinations thereof. In some examples, the first metal can comprise Au and the second metal can comprise Pt. The average ratio of the first metal to the second metal in the plurality of end-capped rod shaped particles can, for example, be from 0.01 to 10.

The integrated plasmonic-ferroelectric materials can, in some examples, further comprise a plurality of co-catalyst particles disposed on the ferroelectric particle and in physical contact with the ferroelectric particle. The plurality of co-catalyst particles can, for example, comprise a metal selected from the group consisting of Al, Ti, Cr, Mn, Fe, Co, Ni, Cu, Mo, Pd, Ag, Cd, Pt, Au, Zn, Ga, Pb, and combinations thereof. In some examples, the plurality of co-catalyst particles can comprise Pt. The plurality of co-catalyst particles can, for example, have an average particle size of from 10 nm to 50 nm. The plurality of co-catalyst particles can have a shape that is substantially spherical, ellipsoidal, triangular, pyramidal, tetrahedral, polygonal, cylindrical, rectangular, cuboidal, cuboctahedral, or a combination thereof. The plurality of co-catalyst particles can, for example, be substantially spherical in shape. In some examples, the plurality of co-catalyst particles can be present in an amount of from 0.1 wt% to 10 wt% based on the amount of the ferroelectric particle present in the integrated plasmonic-ferroelectric material (e.g., from 0.1 wt% to 5 wt%, or from 0.5 wt% to 1 wt%).

Also disclosed herein are methods of making the integrated plasmonic-ferroelectric materials described herein. For example, the integrated plasmonic-ferroelectric materials described herein can be made by a method comprising depositing the plurality plasmonic particles on the ferroelectric particle, thereby forming the integrated plasmonic-ferroelectric material. In some examples, the methods further comprise depositing the plurality of co-catalyst particles on the ferroelectric particle. In some examples, the methods can further comprise making the ferroelectric particle. In some examples, the methods can further comprise making the plurality of plasmonic particles. In some examples, the methods can further comprise making the plurality of co-catalyst particles.

Also disclosed herein are methods of use of the integrated plasmonic-ferroelectric materials described herein. For example, the integrated plasmonic-ferroelectric materials described herein can be used as a photocatalyst. In some examples, the integrated plasmonic- ferroelectric materials can be used as a photocatalyst for water purification, nitrogen fixation (e.g., ammonia production), or hydrogen peroxide generation (e.g., from water). For example, the integrated plasmonic-ferroelectric materials can be used as a photocatalyst for photocatalytic nitrogen fixation by photocatalytically forming ammonia.

Also disclosed herein are methods of using the integrated plasmonic-ferroelectric materials described herein as a photocatalyst for photocatalytic fuel generation. The methods can comprise, for example, contacting the photocatalyst with a fuel precursor to form a mixture and illuminating the mixture with light that overlaps with at least a portion of the plasmon resonance of the plurality of plasmonic particles, thereby converting the fuel precursor to a fuel. In some examples, the light overlaps with at least a portion of the bandgap of the ferroelectric particle. The light source can be a natural light source or an artificial light source. In some examples, the light comprises sunlight.

In some examples, the fuel precursor comprises water. The methods can, for example, comprise using the integrated plasmonic-ferroelectric material as a photocatalyst for solar water splitting.

In some examples, the fuel precursor can comprise CC and the method comprises using the integrated plasmonic-ferroelectric material as a photocatalyst for photochemical reduction of CCh.

In some examples, the fuel comprises hydrogen and the method comprises using the integrated plasmonic-ferroelectric material as a photocatalyst for photocatalytic hydrogen generation.

Additional advantages of the disclosed compositions and methods will be set forth in part in the description which follows, and in part will be obvious from the description. The advantages of the disclosed compositions and methods will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosed systems and methods, as claimed.

The details of one or more embodiments of the invention are set forth in the

accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying figures, which are incorporated in and constitute a part of this specification, illustrate several aspects of the disclosure, and together with the description, serve to explain the principles of the disclosure. Figure 1 is a schematic of the proposed integrated plasmonic-ferroelectric particle for hydrogen production. Ox: oxidant, e.g., H + or a sacrificial oxidant in a model redox reaction; Red: reductant, e.g. FEO, sacrificial agent, or other reductant in a model redox reaction; EF: Fermi level.

Figure 2 is a schematic of the charge injection from Au nanorods to PbTi03 via exposure to 976 nm light causing photo-reduction of hydrogen ions on the co-catalyst Pt islands on an integrated Au nanorod-PbTiCh material.

Figure 3 is a SEM image of“long” Au nanorods. Scale bar 100 nm.

Figure 4 is a SEM image of Pt-end-capped“long” Au nanorods. Pt:Au = 1 : 10. Scale bar: 200 nm.

Figure 5 is the UV-VIS spectra for the“long” AuNRs and the Pt end-capped“long” AuNRs.

Figure 6 is a SEM image of the“regular” Au nanorods. Scale bar: 300 nm.

Figure 7 is the UV-VIS spectrum of the“regular” Au nanorods.

Figure 8 is a SEM image of 40 nm Au spheres. Scale bar: 150 nm.

Figure 9 is the UV-VIS spectrum of 40 nm Au spheres.

Figure 10 is a SEM image of NaCl-fluxed PbTiCh ferroelectric particles with a dimension of ~ 250 nm. Scale bar: 1 pm.

Figure 11 is a SEM image of PbO-fluxed PbTiCh ferroelectric particles with a dimension of ~ 5 pm. Scale bar: 5 pm.

Figure 12 is the Powder X-ray Diffraction (PXRD) patterns of PbTi03 particles: (A) The theoretical PbTiCh PXRD pattern. (B) The PbO fluxed PbTiCh PXRD pattern. (C) The NaCl fluxed PbTiCh PXRD pattern.

Figure 13 is the diffuse reflectance spectra of NaCl-fluxed PbTiCh and PbO-fluxed PbTi03 particles.

Figure 14 is a SEM image of the Au nanorod/ferroelectric PbTi03 particles after the photon-driven reduction of Pt islands onto their surfaces under irradiation by 976 nm light. Scale bar: 500 nm.

Figure 15 is a SEM image of an enlarged area designated“1” in Figure 14 to show the Pt islands. Scale bar: 100 nm.

Figure 16 is a SEM image of an enlarged area designated“2” in Figure 14 to show the Pt islands. Scale bar: 100 nm. EDX scanning shows that a small area including Au nanorods and surrounding Pt islands contains Pb: 60.8 ± 0.4%, Ti: 14.5 ± 0.2%, O: 18.9 ± 0.3%, Au: 3.5 ± 0.2%, and Pt: 1.4 ± 0.2%, respectively. As a comparison, the PbTiCb particles before Pt reduction contain Pb: 65.8 ± 0.3%, Ti: 16.2 ± 0.2%, and O: 16.3 ± 0.2%, respectively.

Figure 17 is a SEM image of a control experiment for ferroelectric PbTiCh particles with no Au nanorods after irradiation by 976 nm light. Scale bar: 1 pm.

Figure 18 is a SEM image of Pt islands on ferroelectric particles deposited by photo reduction. NaCl-fluxed PbTiCh particles with a dimension of - 250 nm. Scale bar: 100 nm.

Figure 19 is a SEM image of Pt-ferroelectric particles impregnated with Pt end-capped Au nanorods, wherein ferroelectric particles are NaCl Fluxed PbTiCh particles (dimension: -125 nm). Scale bar: 500 nm.

Figure 20 is a SEM image of Pt-ferroelectric particles impregnated with Pt end-capped Au nanorods, wherein the ferroelectric particles are NaCl Fluxed PbTiCh particles (dimension: - 1 pm). Scale bar: 1 pm.

Figure 21 shows the results for the photocatalytic Eh gas production on integrated Pt- AuNR/micro-FE-Pt and Pt-AuNR/nano-FE-Pt particles. As a comparison, hydrogen gas production on Pt end-capped Au nanorods and Nano-FE-Pt particles are also shown.

Figure 22 is a SEM image of integrated particles comprising NaCl fluxed ferroelectric particles (size: -500 nm) with 40 nm Au nanospheres. Scale bar: 500 nm.

Figure 23 is a SEM image of integrated particles comprising NaCl fluxed ferroelectric particles (size: -500 nm) with“regular” Au nanorods. Scale bar: 1 pm.

Figure 24 is a SEM image of integrated particles comprising NaCl fluxed ferroelectric particles (size: -500 nm) with“long” Au nanorods. Scale bar: 300 nm.

Figure 25 shows the results for the photocatalytic Eh gas production as a function of time on various integrated AuNP/FE-Pt nanoparticles.

Figure 26 is a comparison of the photocatalytic Eh gas production on Pt-AuNR/FE-Pt versus AuNR/FE-Pt particles. Nano-ferroelectric: Prepared in a NaCl flux with sizes of - 250 nm.

Figure 27 shows the reaction kinetics for the photocatalytic Eh gas production on integrated Pt-AuNR/nano-FE-Pt particles under 976 nm light as a function of irradiation power. Nano-ferroelectric: PbTiCh nanoparticles prepared within a NaCl with a size of -250 nm.

Figure 28 shows the reaction rate for photocatalytic Eh gas production on integrated Pt- AuNR/nano-FE-Pt particles under 976 nm light as a function of irradiation power. Nano- ferroelectric: PbTiCh nanoparticles prepared within a NaCl with a size of -250 nm. Figure 29 shows the results for the photocatalytic Eh gas production kinetics on integrated Pt-AuNR/nano-FE-Pt particles under natural sun light. Nano-ferroelectric: PbTiCb nanoparticles prepared within a NaCl flux with sizes of - 250 nm. Average solar irradiation on the sample: -100 mW/cm 2 .

Figure 30 shows hydrogen production in a test tube using Pt end-capped Au nanorods.

DETAILED DESCRIPTION

The compositions and methods described herein may be understood more readily by reference to the following detailed description of specific aspects of the disclosed subject matter and the Examples included therein.

Before the present compositions and methods are disclosed and described, it is to be understood that the aspects described below are not limited to specific synthetic methods or specific reagents, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting.

Also, throughout this specification, various publications are referenced. The disclosures of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art to which the disclosed matter pertains. The references disclosed are also individually and specifically incorporated by reference herein for the material contained in them that is discussed in the sentence in which the reference is relied upon.

In this specification and in the claims that follow, reference will be made to a number of terms, which shall be defined to have the following meanings.

Throughout the description and claims of this specification the word“comprise” and other forms of the word, such as“comprising” and“comprises,” means including but not limited to, and is not intended to exclude, for example, other additives, components, integers, or steps.

As used in the description and the appended claims, the singular forms“a,”“an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to“a composition” includes mixtures of two or more such compositions, reference to “an agent” includes mixtures of two or more such agents, reference to“the component” includes mixtures of two or more such components, and the like.

“Optional” or“optionally” means that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where the event or circumstance occurs and instances where it does not. Ranges can be expressed herein as from“about” one particular value, and/or to“about” another particular value. By“about” is meant within 5% of the value, e.g., within 4, 3, 2, or 1% of the value. When such a range is expressed, another aspect includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as

approximations, by use of the antecedent“about,” it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint.

It is understood that throughout this specification the identifiers“first” and“second” are used solely to aid in distinguishing the various components and steps of the disclosed subject matter. The identifiers“first” and“second” are not intended to imply any particular order, amount, preference, or importance to the components or steps modified by these terms.

Integrated plasmonic-ferroelectric Materials

Disclosed herein are integrated plasmonic-ferroelectric materials. As used herein, an “integrated plasmonic-ferroelectric material” is a type of composite plasmonic-ferroelectric material comprising a ferroelectric particle and a plurality of plasmonic particles disposed on the ferroelectric particle and in physical contact (e.g., intimate physical contact) with the ferroelectric particle. For example, the integrated plasmonic-ferroelectric material can use electromagnetic radiation (e.g., light) to generate hot charges on at least a portion of the plurality of plasmonic particles and the hot charges can then be injected into the ferroelectric particle, thus integrating the features of the plurality of plasmonic particles and the ferroelectric particle into a functioning whole.

As used herein,“a ferroelectric particle” and“the ferroelectric particle” are meant to include any number of ferroelectric particles. Thus, for example“the ferroelectric particle” includes one or more ferroelectric particles. In some examples, the ferroelectric particle can comprise a plurality of ferroelectric particles.

The ferroelectric particle can comprise any suitable ferroelectric material. Examples of ferroelectric materials include, but are not limited to, AgNbCri. AgTaCri. BaTiCh, BaiTriO , Bi TiCho, Bi 4 Ti 3 0i2, BriThCh, (Ba,Eu)Ti0 3 , BaMnF 4 , BaFeF 4 , BaNiF 4 , BaCoF 4 , BaZnF 4 , BaMgF 4 , BaAhCri, BaGa 2 0 4 , Ba x Sri- x Nb206, Ba2NaNbsOi5, Bao.5Sro.5Nb206, BiScCh, BiFeCh, CaTi0 3 , Cd 2 Nb 2 07, Cs 2 ZnCl, Cs 2 CuCl, Cs 2 CoCl, Cs 2 CdCl, Cs 2 HgCl, Cs 2 ZnBr, Cs 2 CuBr, Cs2CoBr, Cs 2 CdBr, Cs2HgBr, Gd2(Mo0 4 ) 3 , GeTe, KNbCb, potassium sodium niobate (KxNai- x Nb0 3 ), potassium tantalite niobate (KTa x Nbi- x 0 3 ), KTiOPCri, KTaCh, K 2 Cd2(S0 4 ) 3 , KNbSriCh, K 2 ZnCl, K 2 CuCl, K2C0CI, K 2 CdCl, K 2 HgCl, K 2 ZnBr, K 2 CuBr, K 2 CoBr, K 2 CdBr, K 2 HgBr, NaNbCb, NaTaOs, NaasBio.sTiOs, (NH4) 2 Cd 2 (S04)3, (NH 4 ) 2 ZnCl, (NH 4 ) 2 CuCl, (NH 4 ) 2 CoCl, (NH 4 ) 2 CdCl, (NH 4 ) 2 HgCl, (NH 4 ) 2 ZnBr, (NH 4 ) 2 CuBr, (NH 4 ) 2 CoBr, (NH 4 ) 2 CdBr, (NH 4 ) 2 HgBr, N13B7O13I, N13B7O13CI, La 2 Ti 2 07, LiNb03, PbTi03, lead zirconate titanate (PbZri- x Ti x 03, PZT), (Pb,La)Ti03 (PLT), (Pb,La)(Zr,Ti)03 (PLZT), PbZr03, PbHf03, lead scandium tantalate (Pb(Sc x Tai- x )0 3 ), PbsGesOn, PbNbO, PbTa 2 Oe, Pb(Mg,Nb)0 3 (PMN), Rb 2 ZnCl, RteCuCl, Rb 2 CoCl, Rb 2 CdCl. Rb 2 HgCl, Rb 2 ZnBr. Rb 2 CuBr, Rb 2 CoBr, Rb 2 CdBr, Rb 2 HgBr, Sri- x Ba x Nb 2 0 6 , SrAl 2 04, SrGa 2 04, SrTi03, SrBi 2 Ta 2 09, Tl 2 Cd 2 (S04)3, YMn03, polyvinylidene fluoride (PVDF), or combinations thereof. In some examples, the ferroelectric particle comprises PbTiCb, lead zirconate titanate (PbZri- x Ti x 03, PZT), or a combination thereof. In some examples, the ferroelectric particle comprises PbTiCb.

In some examples, the ferroelectric particle comprises lead zirconate titanate, PbZri- x Ti x 03 (PZT), wherein x is from 0 to less than 1. For example, the ferroelectric particle can comprise PbZri- x Ti x 03 wherein x is 0 or more (e.g., 0.1 or more, 0.2 or more, 0.3 or more, 0.35 or more, 0.4 or more, 0.45 or more, 0.46 or more, 0.47 or more, 0.48 or more, 0.49 or more, 0.5 or more, 0.51 or more, 0.52 or more, 0.53 or more, 0.54 or more, 0.55 or more, 0.56 or more,

0.57 or more, 0.58 or more, 0.59 or more, 0.6 or more, 0.65 or more, 0.7 or more, 0.8 or more, or 0.9 or more). In some examples, the ferroelectric particle can comprise PbZn- x Ti x 03 wherein x is less than 1 (e.g., 0.9 or less, 0.8 or less, 0.7 or less, 0.65 or less, 0.6 or less, 0.59 or less, 0.58 or less, 0.57 or less, 0.56 or less, 0.55 or less, 0.54 or less, 0.53 or less, 0.52 or less, 0.51 or less, 0.5 or less, 0.49 or less, 0.48 or less, 0.47 or less, 0.46 or less, 0.45 or less, 0.4 or less, 0.35 or less, 0.3 or less, 0.2 or less, or 0.1 or less). The ferroelectric particle can comprise PbZri- x Ti x 03 wherein x can range from any of the minimum values described above to any of the maximum values described above. For example, the ferroelectric particle can comprise PbZn- x Ti x 03 wherein x is from 0 to less than 1 (e.g., from 0 to 0.5, from 0.5 to less than 1, from 0 to 0.2, from 0.2 to 0.4, from 0.4 to 0.6, from 0.6 to 0.8, from 0.8 to less than 1, from 0.2 to 0.8, from 0.3 to 0.7, or from 0.48 to 0.6).

The ferroelectric particle can comprise a particle of any shape. The ferroelectric particle can have an irregular shape, a regular shape, an isotropic shape, an anisotropic shape, or a combination thereof. In some examples, the ferroelectric particle can have an isotropic shape. In some examples, the ferroelectric particle can have an anisotropic shape. In some examples, the ferroelectric particle can have a shape that is substantially spherical, ellipsoidal, triangular, pyramidal, tetrahedral, cylindrical, rectangular, cuboidal, or cuboctahedral. In some examples, the ferroelectric particle can have a shape that is substantially rectangular, cuboidal, or cuboctahedral.

The ferroelectric particle can have an average particle size.“Average particle size” and “mean particle size” are used interchangeably herein, and generally refer to the statistical mean particle size of the particles in a population of particles. For example, the average particle size for a plurality of particles with a substantially spherical shape can comprise the average diameter of the plurality of particles. For a particle with a substantially spherical shape, the diameter of a particle can refer, for example, to the hydrodynamic diameter. As used herein, the

hydrodynamic diameter of a particle can refer to the largest linear distance between two points on the surface of the particle. For an anisotropic particle, the average particle size can refer to, for example, the average maximum dimension of the particle (e.g., the length of a rod shaped particle, the diagonal of a cube shape particle, the bisector of a triangular shaped particle, etc.) For an anisotropic particle, the average particle size can refer to, for example, the hydrodynamic size of the particle. Mean particle size can be measured using methods known in the art, such as evaluation by scanning electron microscopy, transmission electron microscopy, and/or dynamic light scattering.

The ferroelectric particle can, for example, have an average particle size of 10 nm or more (e.g., 15 nm or more, 20 nm or more, 25 nm or more, 30 nm or more, 35 nm or more, 40 nm or more, 45 nm or more, 50 nm or more, 60 nm or more, 70 nm or more, 80 nm or more, 90 nm or more, 100 nm or more, 125 nm or more, 150 nm or more, 175 nm or more, 200 nm or more, 225 nm or more, 250 nm or more, 300 nm or more, 350 nm or more, 400 nm or more, 450 nm or more, 500 nm or more, 600 nm or more, 700 nm or more, 800 nm or more, 900 nm or more, 1 micrometer (micron, pm) or more, 2 microns or more, 3 microns or more, 4 microns or more, 5 microns or more, 10 microns or more, 15 microns or more, 20 microns or more, 25 microns or more, 30 microns or more, 35 microns or more, 40 microns or more, 45 microns or more, 50 microns or more, 60 microns or more, 70 microns or more, 80 microns or more, 90 microns or more, 100 microns or more, 125 microns or more, 150 microns or more, 175 microns or more, 200 microns or more, 225 microns or more, 250 microns or more, 300 microns or more, 350 microns or more, 400 microns or more, 450 microns or more, 500 microns or more, 600 microns or more, 700 microns or more, 800 microns or more, or 900 microns or more). In some examples, the ferroelectric particle can have an average particle size of 1 millimeter (mm) or less (e.g., 900 microns or less, 800 microns or less, 700 microns or less, 600 microns or less, 500 microns or less, 450 microns or less, 400 microns or less, 350 microns or less, 300 microns or less, 250 microns or less, 225 microns or less, 200 microns or less, 175 microns or less, 150 microns or less, 125 microns or less, 100 microns or less, 90 microns or less, 80 microns or less, 70 microns or less, 60 microns or less, 50 microns or less, 45 microns or less, 40 microns or less, 35 microns or less, 30 microns or less, 25 microns or less, 20 microns or less, 15 microns or less, 10 microns or less, 5 microns or less, 4 microns or less, 3 microns or less, 2 microns or less, 1 micron or less, 900 nm or less, 800 nm or less, 700 nm or less, 600 nm or less, 500 nm or less, 450 nm or less, 400 nm or less, 350 nm or less, 300 nm or less, 250 nm or less, 225 nm or less, 200 nm or less, 175 nm or less, 150 nm or less, 125 nm or less, 100 nm or less, 90 nm or less, 80 nm or less, 70 nm or less, 60 nm or less, 50 nm or less, 45 nm or less, 40 nm or less, 35 nm or less, 30 nm or less, 25 nm or less, 20 nm or less, or 15 nm or less).

The average particle size of the ferroelectric particle can range from any of the minimum values described above to any of the maximum values described above. For example, the ferroelectric particle can have an average particle size of from 10 nm to 1 mm (e.g., from 10 nm to 100 nm, from 100 nm to 1 micron, from 1 micron to 10 microns, from 10 microns to 100 microns, from 100 microns to 1 mm, from 1 nm to 500 nm, from 500 nm to 1 micron, from 1 micron to 500 microns, from 500 microns to 1 mm, from 125 nm to 5 microns, from 125 nm to 500 nm, or from 1 micron to 5 microns). The average particle size of the ferroelectric particle can, for example, be measured using electron microscopy.

In some examples, the ferroelectric particle can comprise a plurality of ferroelectric particles, and the plurality of ferroelectric particles can be substantially monodisperse.

“Monodisperse” and“homogeneous size distribution,” as used herein, and generally describe a population of particles where all of the particles have the same or nearly the same particle size. As used herein, a monodisperse distribution refers to particle distributions in which 80% of the distribution (e.g., 85% of the distribution, 90% of the distribution, or 95% of the distribution) lies within 25% of the average particle size (e.g., within 20% of the average particle size, within 15% of the average particle size, within 10% of the average particle size, or within 5% of the average particle size).

In some examples, the ferroelectric particle has a bandgap that overlaps with at least a portion of the solar spectrum. The size, shape, and/or composition of the ferroelectric particle can be selected in view of a variety of factors. In some examples, the size, shape, and/or composition can be selected such that the ferroelectric particle has a bandgap that overlaps with at least a portion of the solar spectrum. In some examples, the size, shape, and/or composition of the ferroelectric particle can be selected in view of the intended use of the integrated plasmonic- ferroelectric materials. In some examples, the ferroelectric particle can comprise a plurality of ferroelectric particles and the plurality of ferroelectric particles can comprise: a first population of particles comprising a first material and having a first average particle size and a first particle shape; and a second population of particles comprising a second material and having a second average particle size and a second particle shape; wherein the first average particle size and the second average particle size are different, the first particle shape and the second particle shape are different, the first material and the second material are different, or a combination thereof. In some examples, the plurality of ferroelectric particles can comprise a mixture of a plurality of populations of particles, wherein each population of particles within the mixture has a different size, shape, composition, or combination thereof.

The plurality of plasmonic particles can comprise a plasmonic material. Examples of plasmonic materials include, but are not limited to, plasmonic metals (e.g., Au, Ag, Pt, Pd, Cu, Cr, Al, or a combination thereof), plasmonic semiconductors (e.g., silicon carbide), doped semiconductors (e.g., aluminum-doped zinc oxide), transparent conducting oxides, perovskites, metal nitrides, silicides, germanides, and two-dimensional plasmonic materials (e.g., graphene), and combinations thereof.

In some examples, the plurality of plasmonic particles can comprise a plurality of metal particles comprising a metal selected from the group consisting of Au, Ag, Pt, Pd, Cu, Cr, Al,

Cd, Zn, Ga, and combinations thereof. In some examples, the plurality of plasmonic particles can comprise gold. In some examples, the plurality of plasmonic particles can comprise an alloy.

In some examples, the each of the plurality of plasmonic particles can comprise a first metal and a second metal, wherein the first metal and the second metal are different, and wherein the first metal and the second metal are located in different areas of each of the plurality of plasmonic particles. In certain examples, the plurality of plasmonic particles can comprise a plurality of core-shell particles, wherein the core can comprise the first metal and the shell can comprise the second metal, and wherein the shell at least partially encapsulates the core. In some examples, the shell substantially encapsulates the core. In certain examples, each of the plurality of plasmonic particles can comprise a first population of particles comprising the first metal and a second population of particles comprising the second metal, wherein each of the particles in the first population of particles has a surface that is decorated with one or more of the particles in the second population of particles.

The plurality of plasmonic particles can have an average particle size.“Average particle size” and“mean particle size” are used interchangeably herein, and generally refer to the statistical mean particle size of the particles in a population of particles. For example, the average particle size for a plurality of particles with a substantially spherical shape can comprise the average diameter of the plurality of particles. For a particle with a substantially spherical shape, the diameter of a particle can refer, for example, to the hydrodynamic diameter. As used herein, the hydrodynamic diameter of a particle can refer to the largest linear distance between two points on the surface of the particle. For an anisotropic particle, the average particle size can refer to, for example, the average maximum dimension of the particle (e.g., the length of a rod shaped particle, the diagonal of a cube shape particle, the bisector of a triangular shaped particle, etc.) For an anisotropic particle, the average particle size can refer to, for example, the hydrodynamic size of the particle. Mean particle size can be measured using methods known in the art, such as evaluation by scanning electron microscopy, transmission electron microscopy, and/or dynamic light scattering.

In some examples, the plurality of plasmonic particles can have an average particle size of 5 nm or more (e.g., 10 nm or more, 15 nm or more, 20 nm or more, 25 nm or more, 30 nm or more, 35 nm or more, 40 nm or more, 45 nm or more, 50 nm or more, 60 nm or more, 70 nm or more, 80 nm or more, 90 nm or more, 100 nm or more, 125 nm or more, 150 nm or more, 175 nm or more, 200 nm or more, 225 nm or more, 250 nm or more, 300 nm or more, 350 nm or more, 400 nm or more, 450 nm or more, 500 nm or more, 600 nm or more, 700 nm or more, 800 nm or more, 900 nm or more, 1 micrometer (micron, pm) or more, 2 microns or more, 3 microns or more, 4 microns or more, 5 microns or more, 10 microns or more, 15 microns or more, 20 microns or more, 25 microns or more, 30 microns or more, 35 microns or more, or 40 microns or more). In some examples, the plurality of plasmonic particles can have an average particle size of 50 micrometers (microns, pm) or less (e.g., 45 microns or less, 40 microns or less, 35 microns or less, 30 microns or less, 25 microns or less, 20 microns or less, 15 microns or less, 10 microns or less, 5 microns or less, 4 microns or less, 3 microns or less, 2 microns or less, 1 micron or less, 900 nm or less, 800 nm or less, 700 nm or less, 600 nm or less, 500 nm or less, 450 nm or less, 400 nm or less, 350 nm or less, 300 nm or less, 250 nm or less, 225 nm or less, 200 nm or less, 175 nm or less, 150 nm or less, 125 nm or less, 100 nm or less, 90 nm or less, 80 nm or less,

70 nm or less, 60 nm or less, 50 nm or less, 45 nm or less, 40 nm or less, 35 nm or less, 30 nm or less, 25 nm or less, 20 nm or less, or 15 nm or less).

The average particle size of the plurality of plasmonic particles can range from any of the minimum values described above to any of the maximum values described above. For example, the plurality of plasmonic particles can have an average particle size of from 5 nm to 50 microns (e.g., from 5 nm to 100 nm, from 100 nm to 1 micron, from 1 micron to 10 microns, from 10 microns to 50 microns, from 5 nm to 500 nm, from 500 nm to 1 micron, from 1 micron to 50 microns, from 5 nm to 1 micron, or from 10 nm to 900 nm).

The plurality of plasmonic particles can comprise particles of any shape. In some examples, the plurality of plasmonic particles can have an irregular shape, a regular shape, an isotropic shape, an anisotropic shape, or a combination thereof. In some examples, the plurality of plasmonic particles can have an isotropic shape. In some examples, the plurality of plasmonic particles can have an anisotropic shape. The plurality of plasmonic particles can, for example, have a shape that is substantially spherical, ellipsoidal, triangular, pyramidal, tetrahedral, polygonal, cylindrical, rectangular, cuboidal, cuboctahedral, or a combination thereof. In some examples, the plurality of plasmonic particles can have a shape that is that is substantially spherical, ellipsoidal, cylindrical, or a combination thereof.

In some examples, the plurality of plasmonic particles can comprise a plurality of rod shaped particles having an average length and an average diameter. The average length of the plurality of rod shaped particles can, for example, be 5 nm or more (e.g., 10 nm or more, 15 nm or more, 20 nm or more, 25 nm or more, 30 nm or more, 35 nm or more, 40 nm or more, 45 nm or more, 50 nm or more, 60 nm or more, 70 nm or more, 80 nm or more, 90 nm or more, 100 nm or more, 125 nm or more, 150 nm or more, 175 nm or more, 200 nm or more, 225 nm or more, 250 nm or more, 300 nm or more, 350 nm or more, 400 nm or more, 450 nm or more, 500 nm or more, 600 nm or more, 700 nm or more, 800 nm or more, or 900 nm or more). In some examples, the average length of the plurality of rod shaped particles can be 1 micron or less (e.g., 900 nm or less, 800 nm or less, 700 nm or less, 600 nm or less, 500 nm or less, 450 nm or less, 400 nm or less, 350 nm or less, 300 nm or less, 250 nm or less, 225 nm or less, 200 nm or less, 175 nm or less, 150 nm or less, 125 nm or less, 100 nm or less, 90 nm or less, 80 nm or less, 70 nm or less, 60 nm or less, 50 nm or less, 45 nm or less, 40 nm or less, 35 nm or less, 30 nm or less, 25 nm or less, 20 nm or less, or 15 nm or less). The average length of the plurality of rod shaped particles can range from any of the minimum values described above to any of the maximum values described above. For example, the plurality of rod shaped particles can have an average length of from 5 nm to 1 micron (e.g., from 5 nm to 500 nm, from 500 nm to 1 micron, from 5 nm to 200 nm, from 200 nm to 400 nm, from 400 nm to 600 nm, from 600 nm to 800 nm, from 800 nm to 1 micron, from 5 nm to 900 nm, from 5 nm to 800 nm, or from 10 nm to 700 nm). The average diameter of the plurality of rod shaped particles can, for example, be 5 nm or more (e.g., 10 nm or more, 15 nm or more, 20 nm or more, 25 nm or more, 30 nm or more, 35 nm or more, 40 nm or more, 45 nm or more, 50 nm or more, 55 nm or more, 60 nm or more, 65 nm or more, 70 nm or more, 75 nm or more, 80 nm or more, 85 nm or more, or 90 nm or more). In some examples, the average diameter of the plurality of rod shaped particles can be 100 nm or less (e.g., 95 nm or less, 90 nm or less, 85 nm or less, 80 nm or less, 75 nm or less, 70 nm or less, 65 nm or less, 60 nm or less, 55 nm or less, 50 nm or less, 45 nm or less, 40 nm or less, 35 nm or less, 30 nm or less, 25 nm or less, 20 nm or less, or 15 nm or less). The average diameter of the plurality of rod shaped particles can range from any of the minimum values described above to any of the maximum values described above. For example, the plurality of rod shaped particles can have an average diameter of from 5 nm to 100 nm (e.g., from 5 nm to 50 nm, from 50 nm to 100 nm, from 5 nm to 20 nm, from 20 nm to 40 nm, from 40 nm to 60 nm, from 60 nm to 80 nm, from 80 nm to 100 nm, from 5 nm to 80 nm, from 5 nm to 40 nm, or from 10 nm to 20 nm).

In some examples, the plurality of rod shaped particles can be described by their aspect ratio, which, as used herein, is the length of a rod shaped particle divided by the diameter of a rod shaped particle. For example, the plurality of rod shaped particles can have an average aspect ratio of greater than 1 (e.g., 1.5 or more, 2 or more, 2.5 or more, 3 or more, 3.5 or more, 4 or more, 4.5 or more, 5 or more, 5.5 or more, 6 or more, 6.5 or more, 7 or more, 7.5 or more, 8 or more, 8.5 or more, 9 or more, 9.5 or more, 10 or more, 11 or more, 12 or more, 13 or more, 14 or more, 15 or more, 20 or more, 25 or more, 30 or more, 35 or more, 40 or more, 45 or more, 50 or more, 60 or more, 70 or more, 80 or more, 90 or more, 100 or more, 110 or more, 120 or more, 130 or more, 140 or more, or 150 or more). In some examples, the plurality of rod shaped particles can have an average aspect ratio of 200 or less (e.g., 190 or less, 180 or less, 170 or less, 160 or less, 150 or less, 140 or less, 130 or less, 120 or less, 110 or less, 100 or less, 90 or less, 80 or less, 70 or less, 60 or less, 50 or less, 45 or less, 40 or less, 35 or less, 30 or less, 25 or less, 20 or less, 15 or less, 14 or less, 13 or less, 12 or less, 11 or less, 10 or less, 9.5 or less, 9 or less, 8.5 or less, 8 or less, 7.5 or less, 7 or less, 6.5 or less, 6 or less, 5.5 or less, 5 or less, 4.5 or less, 4 or less, 3.5 or less, 3 or less, 2.5 or less, or 2 or less). The average aspect ratio of the plurality of rod shaped particles can range from any of the minimum values described above to any of the maximum values described above. For example, the plurality of rod shaped particles can have an average aspect ratio of from greater than 1 to 200 (e.g., from greater than 1 to 100, from greater than 1 to 50, from greater than 1 to 20, from greater than 1 to 10, from greater than 1 to 6, or from 3 to 6).

In some examples, each of the plurality of rod shaped particles can comprise a first metal and each of the plurality of rod shaped particles can have a first end and a second end, wherein the first end and the second end are capped with a second metal that is different than the first metal, such that the plurality of plasmonic particles comprise a plurality of end-capped rod shaped particles. The first metal can, for example, be selected from the group consisting of Au, Ag, Pt, Pd, Cu, Cr, Al, Cd, Zn, Ga, and combinations thereof. The second metal can, for example, be selected from the group consisting of Be, Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Ba, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and combinations thereof. In some examples, the second metal can comprise a metal selected from the group consisting of Al, Ti, Cr, Mn, Fe, Co, Ni, Cu, Mo, Pd, Ag, Cd, Pt, Au, Zn, Ga, and combinations thereof. In some examples, the first metal can comprise Au and the second metal can comprise

Pt.

The average ratio of the first metal to the second metal in the plurality of end-capped rod shaped particles can, for example, be 0.01 or more (e.g., 0.05 or more, 0.1 or more, 0.15 or more, 0.2 or more, 0.25 or more, 0.3 or more, 0.35 or more, 0.4 or more, 0.45 or more, 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, 0.9 or more, 1 or more, 1.5 or more, 2 or more, 2.5 or more, 3 or more, 3.5 or more, 4 or more, 4.5 or more, 5 or more, 6 or more, 7 or more, or 8 or more). In some examples, the average ratio of the first metal to the second metal in the plurality of end- capped rod shaped particles can be 10 or less (e.g., 9 or less, 8 or less, 7 or less, 6 or less, 5 or less, 4.5 or less, 4 or less, 3.5 or less, 3 or less, 2.5 or less, 2 or less, 1.5 or less, 1 or less, 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.45 or less, 0.4 or less, 0.35 or less, 0.3 or less, 0.25 or less, 0.2 or less, 0.15 or less, or 0.1 or less). The average ratio of the first metal to the second metal in the plurality of end-capped rod shaped particles can range from any of the minimum values described above to any of the maximum values described above. For example, the average ratio of the first metal to the second metal in the plurality of end-capped rod shaped particles can be from 0.01 to 10 (e.g., from 0.01 to 1, from 1 to 10, from 0.01 to 0.1, from 0.1 to 0.5, from 0.5 to 1, from 1 to 5, from 5 to 10, from 0.01 to 5, or from 0.1 to 9).

The plurality of plasmonic particles can, for example, have a surface plasmon resonance that overlaps with at least a portion of the solar spectrum. For example, the plurality of plasmonic particles can have a plasmon resonance at a wavelength of 520 nm or more (e.g., 550 nm or more, 600 nm or more, 650 nm or more, 700 nm or more, 750 nm or more, 800 nm or more, 850 nm or more, 900 nm or more, 950 nm or more, 1000 nm or more, 1050 nm or more, or 1100 nm or more). In some examples, the plurality of plasmonic particles can have a plasmon resonance at a wavelength or 1200 nm or less (e.g., 1150 nm or less, 1100 nm or less, 1050 nm or less, 1000 nm or less, 950 nm or less, 900 nm or less, 850 nm or less, 800 nm or less, 750 nm or less, 700 nm or less, 650 nm or less, or 600 nm or less). The plasmon resonance of the plurality of plasmonic particles can range from any of the minimum values described above to any of the maximum values described above. For example, the plurality of plasmonic particles can have a plasmon resonance at a wavelength (or wavelength region) of from 520 nm to 1200 nm (e.g., from 520 nm to 850 nm, from 850 nm to 1200 nm, from 520 nm to 560 nm, from 560 nm to 590 nm, from 590 nm to 635 nm, from 635 nm to 700 nm, from 700 nm to 1000 nm, from 1000 nm to 1200 nm, from 520 nm to 700 nm, from 700 nm to 1200 nm, or from 550 nm to 1150 nm).

The size, shape, and/or composition of the plurality of plasmonic particles can be selected in view of a variety of factors. In some examples, the size, shape, and/or composition of the plurality of plasmonic particles can be selected such that the plurality of plasmonic particles have a plasmon resonance at a wavelength or wavelength region of interest. In some examples, the size, shape, and/or composition can be selected such that the plurality of plasmonic particles have a plasmon resonance that overlaps with at least a portion of the solar spectrum. In some examples, the size, shape, and/or composition of the plurality of plasmonic particles can be selected such that the plurality of plasmonic particles have a plasmon resonance at one or more wavelengths from 500 nm to 1200 nm. In some examples, the size, shape, composition, and/or amount of the plurality of plasmonic particles can be selected in view of the intended use of the integrated plasmonic-ferroelectric materials.

In some examples, the plurality of plasmonic particles comprise: a first population of particles comprising a first material and having a first average particle size and a first particle shape; and a second population of particles comprising a second material and having a second average particle size and a second particle shape; wherein the first average particle size and the second average particle size are different, the first particle shape and the second particle shape are different, the first material and the second material are different, or a combination thereof. In some examples, the plurality of plasmonic particles can comprise a mixture of a plurality of populations of particles, wherein each population of particles within the mixture has a different size, shape, composition, or combination thereof.

The integrated plasmonic-ferroelectric materials can, in some examples, further comprise a plurality of co-catalyst particles disposed on the ferroelectric particle and in physical contact (e.g., intimate physical contact) with the ferroelectric particle. In some examples, at least one of the plurality of co-catalyst particles can be proximate to at least one of the plurality of plasmonic particles on the ferroelectric particle. In some examples, at least one of the plurality of co catalyst particles can be in electromagnetic contact with at least one of the plurality of plasmonic particles on the ferroelectric particle. In some examples, at least one of the plurality of co catalyst particles can be in physical contact with at least one of the plurality of plasmonic particles on the ferroelectric particle.

The plurality of co-catalyst particles can, for example, comprise a metal selected from the group consisting of Be, Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Sr, Y, Zr, Nb,

Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Ba, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and combinations thereof. In some examples, the plurality of co-catalyst particles can comprise a metal selected from the group consisting of Al, Ti, Cr, Mn, Fe, Co, Ni, Cu, Mo, Pd, Ag, Cd, Pt, Au, Zn, Ga, Pb, and combinations thereof. In some examples, the plurality of co-catalyst particles can comprise Pt.

The plurality of co-catalyst particles can, for example, have an average particle size of 10 nm or more (e.g., 15 nm or more, 20 nm or more, 25 nm or more, 30 nm or more, 35 nm or more, or 40 nm or more). In some examples, the plurality of co-catalyst particles can have an average particle size of 50 nm or less (e.g., 45 nm or less, 40 nm or less, 35 nm or less, 30 nm or less, 25 nm or less, 20 nm or less, or 15 nm or less). The average particle size of the plurality of co-catalyst particles can range from any of the minimum values described above to any of the maximum values described above. For example, the plurality of co-catalyst particles can have an average particle size of from 10 nm to 50 nm (e.g., from 10 nm to 30 nm, from 30 nm to 50 nm, from 10 nm to 20 nm, from 20 nm to 30 nm, from 30 nm to 40 nm, from 40 nm to 50 nm, or from 15 nm to 45 nm).

The plurality of co-catalyst particles can comprise a particle of any shape. The plurality of co-catalyst particles can have an irregular shape, a regular shape, an isotropic shape, an anisotropic shape, or a combination thereof. In some examples, the plurality of co-catalyst particles can have an isotropic shape. In some examples, the plurality of co-catalyst particles can have an anisotropic shape. In some examples, the plurality of co-catalyst particles can have a shape that is substantially spherical, ellipsoidal, triangular, pyramidal, tetrahedral, polygonal, cylindrical, rectangular, cuboidal, cuboctahedral, or a combination thereof. The plurality of co catalyst particles can, for example, be substantially spherical in shape.

In some examples, the plurality of co-catalyst particles can be present in an amount of 0.1 wt% or more based on the amount of ferroelectric particle present in the integrated plasmonic- ferroelectric material (e.g., 0.2 wt% or more, 0.3 wt% or more, 0.4 wt% or more, 0.5 wt% or more, 0.6 wt% or more, 0.7 wt% or more, 0.8 wt% or more, 0.9 wt% or more, 1 wt% or more,

1.5 wt% or more, 2 wt% or more, 2.5 wt% or more, 3 wt% or more, 3.5 wt% or more, 4 wt% or more, 4.5 wt% or more, 5 wt% or more, 6 wt% or more, 7 wt% or more, or 8 wt% or more). In some examples, the plurality of co-catalyst particles can be present in an amount of 10 wt% or less based on the amount of ferroelectric particle present in the integrated plasmonic-ferroelectric material (e.g., 9 wt% or less, 8 wt% or less, 7 wt% or less, 6 wt% or less, 5 wt% or less, 4.5 wt% or less, 4 wt% or less, 3.5 wt% or less, 3 wt% or less, 2.5 wt% or less, 2 wt% or less, 1.5 wt% or less, 1 wt% or less, 0.9 wt% or less, 0.8 wt% or less, 0.7 wt% or less, 0.6 wt% or less, 0.5 wt% or less, 0.4 wt% or less, or 0.3 wt% or less). The plurality of co-catalyst particles can be present in an amount that range from any of the minimum values described above to any of the maximum values described above. For example, the plurality of co-catalyst particles can be present in an amount of from 0.1 wt% to 10 wt% based on the amount of the ferroelectric particle present in the integrated plasmonic-ferroelectric material (e.g., from 0.1 wt% to 5 wt%, from 5 wt% to 10 wt%, from 0.1 wt% to 2 wt%, from 2 wt% to 4 wt%, from 4 wt% to 6 wt%, from 6 wt% to 8 wt%, from 8 wt% to 10 wt%, from 0.1 wt% to 8 wt%, from 0.1 wt% to 4 wt%, or from 0.5 wt% to 1 wt%).

The size, shape, composition, and/or amount of the plurality of co-catalyst particles can be selected in view of a variety of factors. In some examples, the size, shape, composition, and/or amount of the plurality of co-catalyst particles can be selected in view of the intended use of the integrated plasmonic-ferroelectric materials.

Methods of Making

Also disclosed herein are methods of making the integrated plasmonic-ferroelectric materials described herein. For example, the integrated plasmonic-ferroelectric materials described herein can be made by a method comprising depositing the plurality plasmonic particles on the ferroelectric particle, thereby forming the integrated plasmonic-ferroelectric material. In some examples, the methods further comprise depositing the plurality of co-catalyst particles on the ferroelectric particle. Depositing the plurality of plasmonic particles and/or the plurality of co-catalyst particles can, for example, comprise lithographic deposition (e.g., electron beam lithography, nanoimprinting, focused ion beam lithography, or a combination thereof), printing, spin coating, drop-casting, zone casting, dip coating, blade coating, spraying, vacuum filtration, slot die coating, curtain coating, or combinations thereof.

In some examples, the methods can further comprise making the ferroelectric particle. Methods of making ferroelectric particles are known in the art. In some examples, the methods can further comprise making the plurality of plasmonic particles. Methods of making plasmonic particles are known in the art. In some examples, the methods can further comprise making the plurality of co-catalyst particles. Methods of making co-catalyst particles are known in the art.

Methods of Use

Also disclosed herein are methods of use of the integrated plasmonic-ferroelectric materials described herein. For example, the integrated plasmonic-ferroelectric materials described herein can be used as a photocatalyst.

In some examples, the integrated plasmonic-ferroelectric materials can be used as a photocatalyst for water purification, nitrogen fixation (e.g., ammonia production), or hydrogen peroxide generation (e.g., from water). For example, the integrated plasmonic-ferroelectric materials can be used as a photocatalyst for photocatalytic nitrogen fixation by photocatalytically forming ammonia.

Also disclosed herein are methods of using the integrated plasmonic-ferroelectric materials described herein as a photocatalyst for photocatalytic fuel generation. The methods can comprise, for example, contacting the photocatalyst with a fuel precursor to form a mixture and illuminating the mixture with light that overlaps with at least a portion of the plasmon resonance of the plurality of plasmonic particles, thereby converting the fuel precursor to a fuel. In some examples, the light overlaps with at least a portion of the bandgap of the ferroelectric particle.

The light can, for example, be provided by a light source. The light source can be any type of light source. Examples of suitable light sources include natural light sources (e.g., sunlight) and artificial light sources (e.g., incandescent light bulbs, light emitting diodes, gas discharge lamps, arc lamps, lasers, etc.). In some examples, the light comprises sunlight.

In some examples, the fuel precursor comprises water. The methods can, for example, comprise using the integrated plasmonic-ferroelectric material as a photocatalyst for solar water splitting. In some examples, the fuel precursor can comprise CC and the method comprises using the integrated plasmonic-ferroelectric material as a photocatalyst for photochemical reduction of CCh.

In some examples, the fuel comprises hydrogen and the method comprises using the integrated plasmonic-ferroelectric material as a photocatalyst for photocatalytic hydrogen generation.

A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.

The examples below are intended to further illustrate certain aspects of the systems and methods described herein, and are not intended to limit the scope of the claims.

EXAMPLES

The following examples are set forth below to illustrate the methods and results according to the disclosed subject matter. These examples are not intended to be inclusive of all aspects of the subject matter disclosed herein, but rather to illustrate representative methods and results. These examples are not intended to exclude equivalents and variations of the present invention which are apparent to one skilled in the art.

Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperature, etc.) but some errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, temperature is in °C or is at ambient temperature, and pressure is at or near atmospheric. There are numerous variations and combinations of measurement conditions, e.g., component concentrations, temperatures, pressures and other measurement ranges and conditions that can be used to optimize the described process.

Example 1

Plasmonic nanoparticles are excellent light absorbers for harvesting solar energy, resulting in hot electrons that can be utilized in photocatalytic hydrogen production. However, the hot electrons generated in localized surface plasmon resonance process have a very short lifetime and are challenging to be used efficiently. Herein, using near IR light irradiation, it is shown that by combining gold nanorods with a ferroelectric material that possesses a large remanent electric dipole moment, hot charges generated on plasmonic particles can be injected into ferroelectric materials and drive the photocatalysis reaction. The efficiency of using hot electrons for photocatalytic reactions is enhanced, which improves the light-to-chemical energy conversion efficiencies by about one order of magnitude for the same amount of plasmonic particles being used.

Introduction

Molecular hydrogen is an attractive chemical energy carrier because it is clean, has a high energy density, and can be conveniently transported and stored (Navarro et al.

Photocatalytic Technologies, Advances in Chemical Engineering, eds H. I. DeLasa & B. S. Rosales, 2009, 36, 111-143; Sivula et al. Chemsuschem, 2011, 4, 432-449; Yuan et al. Energy & Environmental Science 2014, 7, 3934-3951; Li et al. Journal of Materials Chemistry A, 2015, 3, 2485-2534; Ingram et al. Journal of the American Chemical Society, 2011, 133, 5202-5205; Maeda et al. Nature, 2006, 440, 295-295). Using solar energy to produce hydrogen gas from water remains one of the most attractive yet challenging reactions in converting solar energy into chemical energy. To achieve hydrogen gas production from sunlight, photocatalysts are required. In general, a photocatalytic reaction consists of three steps: First, photoexcitation which leads to the generation of electron (e ) and hole (h + ) pairs. Second, the electrons and holes must be separated and then diffuse to the catalyst surfaces. Third, the electrons and holes react with adsorbed electron acceptors and donors, respectively, to complete the photocatalytic reaction. Hence, the photocatalytic efficiency is predominantly affected by three main factors: the amount of light absorption, charge separation efficiency, and surface reaction rates.

Semiconductors and semiconductor-based hybrid systems have been extensively studied and used as photocatalysts in hydrogen and/or oxygen production (Kawai et al. Journal of the Chemical Society-Chemical Communications, 1980, 694-695; Hoffmann et al. Chemical Reviews, 1995, 95, 69-96). The advantages of these systems include low cost, environmentally friendly nature, and excellent stability in aqueous solutions (Carp et al. Progress in Solid State Chemistry, 2004, 32, 33-177; Kim et al. Applied Catalysis B-Environmental, 2002, 35, 305- 315). However, the main limitations of semiconductor-based photocatalysts, e.g., TiCh and Fe203, are poor light absorption and fast recombination of charge carriers (e.g., at the ns time scale). In spite of efforts to improve these limitations, including doping (Asahi et al. Science, 2001, 293, 269-271), sensitization (Odobel et al. Journal of Physical Chemistry Letters, 2013, 4, 2551-2564), and surface treatment (Ma et al. Journal of Physical Chemistry C, 2013, 117, 24496-24502), the practical efficiency of semiconductor-based photocatalysts in converting solar energy to chemical energy remains < 1%, while a minimum solar-to-hydrogen efficiency of -10% is required for any system to be commercially viable (Hans-Joachim Lewerenz et al. Photoelectrochemical Water Splitting: Materials, Processes and Architectures, Royal Society of Chemistry, 2013).

Plasmonic particles have recently been employed as a component of photocatalytic systems due to their localized surface plasmon resonance (SPR), which can be described as the collective oscillation of conduction band electrons excited by light. At the surface plasmon resonance wavelength, the absorption cross-section of the particles is greatly enhanced, allowing efficient light harvesting in the visible to the near IR range. This is very important because the photon flux of the sun light is fairly low (e.g., at the -100 mW/cm 2 scale). Thus, using metallic plasmonic nanoparticles as antennas can greatly boost the efficiency of light absorption. More importantly, high-energy hot electrons are generated in the surface plasmon resonance process (Major et al. Journal of Physical Chemistry Letters, 2014, 5, 866-874; Brandt et al. Journal of Physical Chemistry Letters, 2016, 7, 3179-3185), which can participate in the chemical reaction on the particle surface (Adleman et al. Nano Letters, 2009, 9, 4417-4423; Fasciani et al. Org. Lett. 2011, 13, 204-207; Bueno Alejo et al. Catal. Sci. Technol. 2011, 1, 1506-1511; Liu et al. Nano Letters, 2011, 11, 1111-1116; Christopher et al. Nat. Chem. 2011, 3, 467-472; Warren et al. Energy & Environmental Science, 2012, 5, 5133-5146; Hoggard et al. ACS Nano, 2013, 7, 11209-11217; Mubeen et al. Nature Nanotechnology, 2013, 8, 247-251; Mukherjee et al. Nano Lett. 2013, 13, 240-247; Ha et al. Journal of the American Chemical Society, 2014, 136, COS MOS; Marchuk et al. Chemical Physics, 2014, 445, 95-104; Linic et al. Nature Materials, 2015, 14, 567-576). Herein, hot electrons refer to the excited electrons with energies above the Fermi level of the metal particle (Mukherjee et al. Nano Lett. 2013, 13, 240-247; Linic et al. Nature Materials, 2015, 14, 567-576). There are many studies showing that for plasmonic particle-based catalysts, the excitation of their surface plasmon resonance greatly enhances their catalytic activities (Adleman et al. Nano Letters, 2009, 9, 4417-4423; Fasciani et al. Org. Lett. 2011, 13, 204-207; Bueno Alejo et al. Catal. Sci. Technol. 2011, 1, 1506-1511; Liu et al. Nano Letters, 2011, 11, 1111-1116; Christopher et al. Nat. Chem. 2011, 3, 467-472; Warren et al. Energy & Environmental Science, 2012, 5, 5133-5146; Hoggard et al. ACS Nano, 2013, 7, 11209-11217; Mubeen et al. Nature Nanotechnology, 2013, 8, 247-251; Mukheijee et al. Nano Lett. 2013, 13, 240-247; Ha et al. Journal of the American Chemical Society, 2014, 136, 1398-1408; Marchuk et al. Chemical Physics, 2014, 445, 95-104; Linic et al. Nature Materials, 2015, 14, 567-576). It is generally believed that in many reactions, the surface plasmon resonance enhances the chemical reactions not merely through a photothermal effect (Adleman et al. Nano Letters, 2009, 9, 4417-4423; Fasciani et al. Org. Lett. 2011, 13, 204-207; Bueno Alejo et al. Catal. Sci. Technol. 2011, 1, 1506-1511) but involves hot charge injection from the particle surface to the adsorbates directly or indirectly, inducing the chemical reactions (Mukherjee et al. Nano Lett. 2013, 13, 240-247; Linic et al. Nature Materials, 2015, 14, 567-576; Haes et al. Journal of the American Chemical Society, 2006, 128, 10905-10914). Especially, the excited electron gas in the nanoparticle initially would adiabatically establish equilibrium with a mean temperature of several thousands of degrees. Thus, high energy hot electrons (i.e., photon energy much larger than that at the surface plasmon resonance frequency) are produced in the surface plasmon resonance process even when the particle is excited by low energy photons (Moskovits. Nature Nanotechnology, 2015, 10, 6-8). The generation of high energy hot electrons makes it possible for many catalytic reactions with high activation energy barriers to proceed.

However, hot electrons in metallic particles have a very short lifetime (e.g. in the femtosecond to picosecond time scale), which hinders their efficient use in driving chemical reactions. Herein, it was hypothesized that by combining plasmonic nanoparticles with ferroelectric (FE) particles that have a large remanent electric field, hot electrons generated in the plasmonic particles can be injected into the ferroelectric material and their lifetime extended by orders of magnitude. Thus, a new route of using these hot electrons will be enabled for photocatalysis (Figure 1).

Ferroelectric semiconductors, e.g. PbTiCh, have been extensively studied for their spontaneous electric polarization that can be reversed by an external field (Bonnell et al.

Ferroelectric Thin Films X, Materials Research Society Symposium Proceedings, eds S. R. Gilbert et al, 2002, 688, 317-328; Kalinin et al. Physical Review B, 2001, 63, 125411; Streiffer et al. Physical Review Letters, 2002, 89, 067601; Cai et al. Inorganic Chemistry, 2007, 46, 7423- 7427). Because of the spontaneous polarization, they are characterized with a polarization- dependent band bending, which lies close to the ferroelectric surface and promotes electron-hole pair separation. This is an attractive feature for photocatalytic reactions such as water splitting and significant promise has been shown for their photocatalytic activity (Amey et al. Journal of the American Ceramic Society, 2011, 94, 1483-1489). However, PbTiCh, for example, has a bandgap that falls at the edge of the visible range at ~2.7 eV and thus does not absorb light with a wavelength longer than -460 nm. By joining plasmonic particles with ferroelectric particles, visible to near IR light can be used to generate hot electrons, which can then be injected into the ferroelectric particles and their lifetime greatly extended.

Hot electron injection from plasmonic particles to semiconductors has been observed and the hybrid materials have been used in photovoltaic devices (Mubeen et al. Nature Nanotechnology, 2013, 8, 247-251; Atwater et al. Nature Materials, 2010, 9, 205-213; Clavero. Nature Photonics, 2014, 8, 95-103; Linic et al. Nature Materials, 2011, 10, 911-921; Thomann et al. Nano Letters, 2011, 11, 3440-3446) and photocatalysts (Christopher et al. Nat. Chem. 2011,

3, 467-472; Mukherjee et al. Nano Lett. 2013, 13, 240-247; Marimuthu et al. Science, 2013, 339, 1590-1593). The current challenge is that the injection efficiency is low for normal

semiconductors (Ma et al. Light-Science & Applications, 2016, 5, el60l7). The use of an internally polarized ferroelectric particle can enhance this charge injection process. Here, as an exemplary system, lead titanate (PbTiCh) is selected as the ferroelectric material because of its large, stable ferroelectric polarization and tunable conduction band energy that can be further used to facilitate charge injection, transport, and separation (Amey et al. Journal of the American Ceramic Society, 2011, 94, 1483-1489; Kakekhani et al. Surf. Sci. 2016, 650, 302-316;

Kakekhani et al. Journal of Materials Chemistry A, 2016, 4, 5235-5246; Wang et al. Nature Communications, 2016, 7, 10348; Cao et al. Journal of Materials Chemistry, 2012, 22, 12592- 12598; Qin et al. Applied Physics Letters, 2007, 91, 092904). The internal electric field of the ferroelectric is challenging to measure directly but was estimated theoretically to be on the order of -10 7 V/m (Kathan-Galipeau et al. Acs Nano, 2011, 5, 640-646). As a contrast, the maximum electric field of a coherent light source with an intensity of 1 W/cm 2 would be -3,000 V/m (estimated from / = 1/2 ecE^ ax . where e is permittivity, c is the speed of light). Thus, charge injection from the plasmonic particle to the ferroelectric particle can happen naturally.

Here, with near IR light irradiation that excites the plasmonic particle only, two different photocatalytically-driven reactions (i.e., Pt photo-reduction and hydrogen gas generation) were used to show that effective charge injection occurs on the ferroelectric particle surfaces. The efficiency of using hot electrons generated on plasmonic particles is enhanced by nearly one order of magnitude in hydrogen production. Thus, the integrated plasmonic-ferroelectric particles described herein represent a photocatalytic system that can achieve high efficiency in light absorption, electron-hole generation, and charge separation.

Experimental Section

Chemicals. HAuCL 3H 2 0 (99%), NaBH 4 (99%), AgNCh (99%), H 2 PtCl 4 (>99%), ascorbic acid (99%), CTAB (99%), 5-formyl-salicylic acid (5-FSA), hydrochloric acid (HC1, concentrated), Methanol (99%) were purchased from Sigma Aldrich and used as received. PbO (99.99%) and Ti0 2 (Anatase, 99.9%) were obtained from Alfa Aesar, Ward Hill, MA. Au nanoparticle (AuNP) synthesis.

Preparation of Au seeds: Au nanorods were synthesized using a previously reported seed-mediated method (Ortiz et al. The Journal of Physical Chemistry C, 2017, 121, 1876-1883). In a typical seed synthesis, 5.0 mL of 0.50 mM HAuCL solution was gently mixed with 5.0 mL of 0.20 M cetyltrimethylammonium bromide (CTAB) solution. Then, 600 pL of 10 mM freshly prepared NaBTB solution was introduced to the solution and mixed at with vigorous stirring for 2.0 minutes. The final solution was left undisturbed for 30 minutes prior to use.

Preparation of“regular” Au nanorods (aspect ratio ~4). A growth solution containing 10 mM 5-FSA and 50 mM CTAB was prepared (100 mL). Then, 1.92 mL of 10.0 mM AgNCb was added. After keeping the mixture undisturbed for 15 minutes, 100 mL of 1.0 mM HAuCL was mixed with the growth solution at a medium stirring speed for 90 min. Then, at drastic stirring conditions, 512 pL of 0.10 M ascorbic acid was added to the solution within 30 seconds. At the same stirring speed, 320 pL of previously synthesized gold seeds was added and the solution was stirred for an extra 30 s. The final solution was left undisturbed for 12 hours at room temperature. The final total Au concentration was -0.50 mM.

Preparation of“long” Au nanorods (aspect ratio ~5). Long Au nanorods were synthesized following the same procedure for the regular Au nanorods except that 2.0 mL of 1.0 M HC1 was added dropwise with stirring after HAuCL was introduced. The final total Au concentration was -0.50 mM.

Preparation of Pt End-Capped Au nanorods (Pt-AuNRs; Pt:Au = 1:10). To selectively coat Pt on the ends of Au nanorods with regular and higher aspect ratios, the same procedure was adopted as reported previously (Ortiz et al. The Journal of Physical Chemistry C, 2017, 121, 1876-1883). Briefly, 10 mL of fresh solution of regular Au nanorods or long Au nanorods was used. For Pt loading at a Pt:Au = 1: 10, 40.4 pL of 0.010 M HC1 was added to the Au nanorod solution at 35°C under mild stirring for 5.0 minutes, followed by the slow addition of 50 pL of 0.01 M FLPtCb in 5.0 min under mild stirring. Finally, 287 pL of freshly made 0.10 M ascorbic acid was added dropwise. The final solution was left undisturbed at 35°C for 8 hours. The solution color changed from light reddish pink to light purplish, indicating the reaction had taken place. The final total Au concentration was -0.50 mM.

Preparation of Au spheres: Au spheres capped with CTAB were synthesized using the same seeds for Au nanorod synthesis. In a typical Au sphere synthesis, 10 mL of 0.50 mM HAuCL solution was mixed with 10 mL of 0.20 M CTAB solution for 15 minutes. Then, 1.0 mL of 6.0 mM cold NaBFL solution was added under drastic stirring in 2.0 minutes. The final solution was allowed to age for 48 hours. The as synthesized Au nanospheres were 40 nm in diameter.

Preparation of PbTiCb. The flux synthesis of PbTiCb was performed by combining a stoichiometric mixture of PbO and TiC . The mixture was ground in acetone for 30 min before the addition of salt flux. For nano-ferroelectric (nano-FE) particles, NaCl salt flux was introduced in a flux-to-reactant molar ratio of 1 : 1. Meanwhile, for micro-ferroelectric (micro-FE) particles, PbO flux was added in a flux-to-reactant molar ratio of 1 : 1. After grinding, the reactant mixture was placed inside alumina crucibles and heated to l000°C inside a box furnace in air for a reaction time of 1.0 h. The crucibles were cooled to room temperature inside the furnace. The resulting powder was first washed with deionized water to remove the flux, then washed briefly in 1.0 M HNO3 to remove excess PbO flux, and finally dried overnight in an oven at 800°C. Fine homogeneous yellow powders of PbTi03 were obtained in high purity, as judged from powder X-ray diffraction.

The ferroelectric particles showed variability in their sizes and Eh production rates for each batch of synthesis. The nano-ferroelectric particles varied from -125 - 500 nm and the micro-ferroelectric particles varied from -1- 5 pm, respectively. Each batch of ferroelectric particles was characterized using SEM. An appropriate comparison of photocatalytic rates was only performed when the same batch of particles was used.

Pt deposition on PbTiCb through photo-reduction using white light (Pt-PbTiCb).

The ferroelectric particles were coated with 1% Pt islands (by weight) as surface co-catalysts using photochemical reduction. In a typical experiment, 300 mg of ferroelectric material was suspended in a 15 mL solution containing 16% methanol (v/v) and 15.0 pmol of Pt salt

(FEPtCE). The photo-reduction was carried out using an outer-irradiation type fused-silica reaction cell. The cell was irradiated for 4.0 hours with a 400 W Xe Arc lamp. The lamp output was -280-950 nm with a power density of 800 mW/cm 2 . The solution was stirred throughout the entire irradiation time. The final product was washed three times with DI water and re-suspended to a total volume of 15.0 mL of DI water. (Final concentrations: 20 mg/mL PbTiCh; total Pt concentration -1.0 mM.)

Au nanorod (or Pt end-capped Au nanorod) impregnation onto PbTiCb (or Pt- PbTiCb). The Au nanorods (either with or without Pt-end capping) solution was pre-cleaned 2-3 times using DI water to remove excessive ligands and resuspended in the same amount of solution. Next, 7.5 mL of the prepared PbTiCh or Pt-PbTiCh suspension was mixed with 7.5 mL of the clean Au nanorod (with or without Pt-end capping) solution. The solution was then placed in a glass vial and heated to 80°C, under constant stirring, overnight. The mixture dried up completely with the Au nanorods (with or without Pt-end capping) adsorbed on the PbTiCb or Pt-PbTiCb surface. The solids were stored for future use or immediately resuspended in DI water for Th production.

For Fh production, the solid was resuspended in 7.5 mL DI water and a part of the suspension was used in hydrogen production. (Concentrations: 20 mg/mL PbTiCb; Pt on PbTiCb -1.0 mM; total Au -0.50 mM; Pt on Au nanorod -0.050 mM.)

Photo-reduction of Pt on integrated Au nanorod/ferroelectric materials using 976 nm light. To observe the charge injection from Au nanorods to PbTiCb, the 976 nm light photo reduction was carried out on integrated Au nanorod-PbTiCb (Figure 2). The Au nanorod was first impregnated onto PbTiCb using the same procedure for impregnating Au nanorods onto Pt- PbTiCb.

The photo-reduction was then carried out using an outer-irradiation type fused-silica reaction cell. Integrated Au nanorod-PbTiCb (50 mg) was added to 2.5 mL of a binary mixture containing 1.0 mg/mL Pt salt and 400 pL methanol. The cell was irradiated for 1.0 hour with a continuous wave, 976 nm laser (MDL-III, Dragon lasers). The total output was set at 2000 mW with an irradiation area of 1.0 cm 2 (-1/5 of the solution was illuminated). (Concentrations: 20 mg/mL PbTiCb; total Pt -1.0 mM; total Au -0.5 mM; Pt on Au nanorod -0.05 mM. Note Pt was not completely reduced under this condition; a significant amount of Pt was still in the solution.)

Electron microscopy. Scanning electron microscopy (SEM) images were collected using an FEI Verios 460L field emission SEM (FESEM).

Photocatalytic Hydrogen Production. In photocatalytic ¾ production experiments, the impregnated Pt-AuNR/FE-Pt or AuNR/FE-Pt particles were re-suspended in DI water before use (Concentrations: 20 mg/mL PbTiCb; Pt on PbTiCb -1.0 mM; total Au -0.50 mM). First, 800 pL of an integrated particle solution was mixed with 500 pL of methanol and 1.2 mL DI water to form a 2.5 mL solution. The solution was then degassed by bubbling with nitrogen gas for 15 minutes. The solution was finally transferred to a quartz cell for irradiation. The quartz cell was connected to a thin, L-shaped tubing. The inside of the cell and tubing were purged with nitrogen for 15 minutes. A water droplet was used to seal the whole reaction chamber. The volume change was read from the movement of the droplet in the horizontal segment of the L-shaped tubing. After the photoreaction, the volume of the produced gas was re-read after the whole system was re-equilibrated at room temperature. The reported gas production volume was corrected for the temperature change during reaction. (Total materials used in the reaction: 16 mg ferroelectric material, Pt on ferroelectric 0.8 mhioΐ. ~0.4 mhioΐ Au, Pt on Au nanorods -0.04 mihoΐ).

A continuous wave, 976 nm laser (MDL-III, Dragon lasers) was used in hydrogen gas production. The total output was set at desired power (2000 mW, 1575 mW, 975 mW, or 250 mW). The irradiation area was -1 cm 2 . 1/5 of the solution was illuminated.

Gas chromatography of the photoreaction products. All gas chromatograms were taken using a SRI 8610C gas chromatograph with a 2.0 meter silica gel-packed column (1.0 mm internal diameter and 1/16 th outer diameter), a thermal conductivity detector, and nitrogen as the carrier gas.

Results and Discussion

Au nanorods and Pt-end-capped Au nanorods synthesis. To generate hot electrons,

Au nanorods (AuNRs) and Pt-end-capped Au nanorods (Pt-AuNRs) were used as the plasmonic nanoparticles. Au nanorods and Au nanorod-based particles are especially useful because: they are photo-stable; they are efficient in harvesting solar energies because of their large absorption coefficient (Kakekhani et al. Surf. Sci. 2016, 650, 302-316; Kakekhani et al. Journal of Materials Chemistry A, 2016, 4, 5235-5246; Hartland. Chemical Reviews, 2011, 111, 3858-3887; Ye et al. ACS Nano, 2012, 6, 2804-2817; Jing et al. Nano Lett., 2014, 14, 3674-3682); and they are excellent in producing high energy hot electrons from low energy visible-to-infrared photons through a fast charge carrier re-equilibrium process (Linic et al. Nature Materials, 2015, 14, 567- 576; Ortiz et al. ACS Appl. Mater. Interf. 2017, 9, 25962-25969). This can be especially important because semiconductor-based photocatalysts typically requires a band gap > 3.0 eV to efficiently catalyze the water splitting reaction due to many energy loss processes (Hans- Joachim Lewerenz et al. Photoelectrochemical Water Splitting: Materials, Processes and Architectures, Royal Society of Chemistry, 2013), while most of the solar irradiation is below this threshold. Thus, the use of Au nanorods allows the utilization of the energy deemed“less useful” and increases the attainable solar to chemical energy conversion efficiency.

Pt end-capped Au nanorods (Pt-AuNRs) with different aspect ratios can be synthesized by using 5-formyl salicylic acid as the organic modifier and by tuning the pH (Ortiz et al. The Journal of Physical Chemistry C, 2017, 121, 1876-1883). Herein,“long Au nanorods” (aspect ratio -5) were mainly used, which have a surface plasmon resonance wavelength of 850 nm when unmodified and 920 nm after Pt-end-capping (Figure 3-Figure 5). The long Au nanorods were chosen because their surface plasmon resonance wavelength had the best match with the light source used in the experiments (output at 976 nm). The“regular Au nanorods” (aspect ratio ~4, surface plasmon resonance 810 nm for unmodified particles, Figure 6 and Figure 7), and Au nanospheres (AuNSs) with a diameter of 40 nm (surface plasmon resonance 532 nm, Figure 8 and Figure 9) were used as controls.

While the Au nanorods themselves can absorb light and generate hot charge carriers, the motivation for investigating the Pt end-capped Au nanorods in addition to Au nanorods was two fold: (1) to compare the hydrogen gas production efficiency for Pt end-capped Au nanorods and integrated materials comprising Pt end-capped Au nanorods/ferroelectric particles; and (2) to achieve an optimal match so that the Au nanorods and the ferroelectric particles will have enhanced surface contact to facilitate the charge injection and separation. At a Pt:Au ratio of 1: 10, the nanorod ends are slightly expanded and less protected by the ligands (Ortiz et al. The Journal of Physical Chemistry C, 2017, 121, 1876-1883), which can provide specific contact points between the particles.

To demonstrate the charge injection from plasmonic particles to the ferroelectric oxide, and to exclude the possibility that the excited electrons are generated by excitation of the ferroelectric particles directly, near IR light irradiation at 976 nm was utilized, which has a significantly lower photon energy than the band gap of the PbTi03 at -460 nm.

The Au nanorods (as well as Pt end-capped Au nanorods) were then deposited on PbTiCb particles though wet impregnation method. The highly -faceted PbTiCb particles were synthesized in the form of either nano-particles (-125-500 nm, synthesized via NaCl flux), referred to herein as nano-ferroelectric (nano-FE) particles, or micro-particles (-1- 5 pm, synthesized PbO flux), referred to herein as micro-ferroelectric (micro-FE) particles (Amey et al. Journal of the American Ceramic Society, 2011, 94, 1483-1489). The bare ferroelectric particles were characterized using scanning electron microscopy (Figure 10, Figure 11,). The crystalline structure of the ferroelectric particles were characterized by powder X-ray diffraction (Figure 12). The bandgaps of the ferroelectric particles were characterized using UV-VIS diffuse reflectance spectroscopy (Figure 13).

Charge injection from Au nanorods to PbTiCb: Photochemical surface reduction of Pt using near IR light. The fundamental hypothesis is that the hot electrons generated on plasmonic particles will be injected into ferroelectric particles owing to their permanent electric polarization. To test whether charge injection occurs, the photon-induced reduction of Pt(IV) onto the integrated Au nanorod-ferroelectric particles was performed. The Au nanorods (no Pt) were used and impregnated onto bare micro-ferroelectric PbTiCh particles. The Au nanorods without Pt and the bare micro-ferroelectric particle (e.g., also without Pt) were used to avoid any confusion with photo-reduced Pt. Before impregnation, the Au nanorods were cleaned 3 times to remove excessive ligands on the particles. The suspension of the integrated particles was then exposed to 976 nm near IR light in the presence of aqueous FhPtCE and methanol as the sacrificial agent. The near IR light was from a laser expanded to have an irradiation area of -1.0 cm 2 , giving a power density of 2.0 W/cm 2 .

After irradiation under 976 nm light for 30 minutes, the particles were then characterized by SEM. As shown in the SEM images, Pt islands emerged on ferroelectric particle surface, with most of them located within a distance of -100 nm from the Au nanorods (Figure 14, Figure 15, Figure 16). This is strong supporting evidence that the hot electrons were injected from plasmonic particles to the ferroelectric particles, which drove the photochemical reduction of the Pt at the surfaces. Again, 976 nm near IR light has a photon energy well below the bandgap of the PbTiCh, so the excited electrons were not from the light absorption within the ferroelectric particles.

As a control, the experiment was repeated under the same conditions but in the absence of Au nanorods in the absence of Au nanorods, no Pt islands were found to deposit on the ferroelectric particle surface (Figure 17), indicating that charge injection takes place from the Au nanorod to ferroelectric particles.

Photocatalytic ¾ production: Enhanced rates for integrated Au nanorod and ferroelectric particles. The photocatalytic activities of the integrated plasmonic-ferroelectric particles were investigated under irradiation in aqueous solutions for the reduction of water to Eh. Au nanorods alone are poor catalysts although they are excellent light absorbers. By end capping Au nanorods with Pt, they become highly active for the production of hydrogen gas even when being illuminated with near IR photons (Ortiz et al. The Journal of Physical

Chemistry C, 2017, 121, 1876-1883). The initial Eh production rate (in the first 10 min) for the Pt end-capped Au nanorods was measured to be -0.25 pmol/min for -0.4 pmol total Au, which compares very favorably among all Au-based metallic nanoparticles (Zheng et al. Journal of the American Chemical Society, 2014, 136, 6870-6873). This shows that the Pt end-capped Au nanorods are efficient in absorbing low energy photons and converting them to hot electrons that can drive hydrogen production.

The integrated Pt end-capped Au nanorod and ferroelectric particles were similarly investigated for their photocatalytic activity for hydrogen gas production and compared to that for the Pt end-capped Au nanorods alone. The ferroelectric particles were first deposited with Pt islands (1 wt%) to serve as surface co-catalysts using a photochemical reduction reaction under white light irradiation (namely FE-Pt, Figure 18). The Pt co-catalyst islands can lower the kinetic barrier (i.e., overpotential) for hydrogen formation. The integrated particles were synthesized using the wet impregnation methods and annealed together at a low temperature of 80°C for surface attachment of the particles. Figure 19 and Figure 20 show that the Pt end-capped Au nanorods were distributed evenly over the nano-ferroelectric (average size -125 nm) and micro- ferroelectric (average size -1 pm) particle surfaces. The average loading of the Au nanorods on the ferroelectric particles were consistent with the expected values (Au nanorod: ferroelectric -0.6 for 125 nm nano-ferroelectric and -280 for 1 pm micro-ferroelectric, respectively). The Pt end-capped Au nanorods with an aspect ratio of 5 and Pt:Au = 1: 10 were used throughout, unless specified otherwise.

The integrated plasmonic and ferroelectric particles, using either nano-ferroelectric or micro-ferroelectric particles, were suspended in a solution containing methanol for Eh production and tested for their photocatalytic rates under 976 nm near IR light irradiation. Both the nano-ferroelectric and micro-ferroelectric integrated particles showed a significant amount of hydrogen production after light exposure, which was confirmed using gas chromatography. The other half of the reaction is the oxidation of the methanol to formaldehyde and/or formic acid, which was confirmed using Tollen’s test (Zoellner et al. Dalton. Trans., 2017, 46, 10657-10664). No significant amount of CO2 was detected among the product gases using gas chromatography.

The integrated Pt-AuNR/nano-ferroelectric-Pt particles gave a Eh production rate of 1.41 ± 0.40 pmol/min for a total of 12 runs using ferroelectric particles made from 3 different batches (Figure 21). In each experiment, a sample containing 16.0 mg ferroelectric, 0.80 pmol Pt on nano-ferroelectric, 0.40 pmol Au, and 0.040 pmol Pt on Au nanorods were used. This rate is compared to that of the pure metallic Pt end-capped Au nanorod particles (0.25 pmol/min,

Figure 21), where the total Au in both solutions (0.40 pmol Au) was kept constant in order to compare the efficiency of using the hot electrons generated from the Au nanorod particles. This result shows that the production rate was enhanced by a factor of 5.6, almost an order of magnitude when the ferroelectric particles are present.

Similarly, the Pt-AuNR/micro-FE-Pt particles also show an enhanced Eh production rate of 0.88 ± 0.27 pmol/min for 7 different experiments using different batches of ferroelectric particles (Figure 21). Thus, the production rate is enhanced by 3.5 times for the Pt-AuNR/micro- FE-Pt integrated particles compared to the Pt end-capped Au nanorods alone. The rate for the micro-ferroelectric integrated particles is lower than that for the nano-ferroelectric integrated particles, possibly because the total surface area of the micro-ferroelectric particles is ~ 10 times smaller than that of the nano-ferroelectric particles (discussed further below).

In the integrated particles, there was more Pt present over the integrated particles’ surfaces than was present in the Pt end-capped Au nanorods alone. However, this is desired so that the photocatalytic rates are not limited by the inherent surface activities of the ferroelectric oxide or the Au nanorods, but rather, only by the efficiency of generation of hot electrons and the charge injection between the Au nanorod and the ferroelectric particle. The experimental design confirms a scheme that can distribute these hot electrons onto multiple co-catalyst islands that are exposed to the solution. Thus, their lifetimes are extended and the solar to hydrogen conversion efficiency is enhanced in this system design.

The photon-driven catalytic activity of the integrated particles generally decreased over time and was lost after ~60 min. The possible reasons can be inferred from the observation of the sample solution: the integrated particles aggregated over time; the Au nanorods may also detach from the ferroelectric particles.

As a control experiment, the nano-ferroelectric-Pt particles (no Au nanorods or Pt end- capped Au nanorods) were also tested under 976 nm irradiation. Surprisingly, the Pt-nano- ferroelectric particles also produced hydrogen gas, but at a much smaller rate and the particles lost activity quickly. It is possible that the heating effect of the laser can also promote electrons from the valence band to the conduction band, which can thermally drive the reaction. However, this process is very inefficient and the hydrogen production rate is low.

Thus, together with the controls, the two photocatalytic reactions show that Au nanorods can inject hot electrons to ferroelectric particles upon irradiation; the excited electrons can participate in chemical reactions, e.g., producing fh. The enhancement of the hydrogen production rate supports the hypothesis of charge injection because of the permanent polarization inside the ferroelectric particle. Although in the experiments described herein, the interfacial contact between the plasmonic and the ferroelectric particles were not controlled in terms of the crystal facets, it is still not surprising to see this enhancement. One would envision that -half of the Au nanorods will deposit onto a surface that favors the charge injection while the other half will deposit onto a surface that is unfavorable for the charge injection. If the favorable combination enhances the overall production rate by many times, the net effect would still be a significant enhancement despite the production rate from other half of the nanoparticles being curbed or even nulled. Surface plasmon resonance involvement in hot electron generation. To further support that the hot electrons are generated on the plasmonic nanoparticles and being transported to the ferroelectric particle surface to participate reaction, the Au nanoparticles were used with different aspect ratios without the Pt end-capping. The photocatalytic activities were investigated for the nano-ferroelectric-Pt (average size 500 nm) impregnated with long Au nanorods, short Au nanorods, and Au nanospheres (40 nm in diameter) using 976 nm near IR light irradiation in aqueous solutions, as described above. To have a fair comparison, ferroelectric particles from the same batch were used.

Figure 22-Figure 24 are SEM images of the integrated particles with the gold

nanoparticles of three different shapes, i.e., 40 nm spheres, short nanorods, and long nanorods. The photocatalytic activity for hydrogen production as a function of time is plotted in Figure 25 for the three integrated particles. As can be seen in Figure 25, all three integrated particles showed activity. The initial reaction rates were 0.71 ± 0.20 pmol EE molecules/min, 0.46 ± 0.28 pmol EE molecules/min, and 0.09 ± 0.04 pmol EE molecules/min for the same amount of Au and ferroelectric particles in the first -10 min for long Au nanorods, regular Au nanorods, and 40 nm Au nanospheres, respectively. The standard deviation was obtained from 2-3 replicates. The trend of the reaction rates is consistent with the absorbance of these particles at 976 nm: from the long Au nanorods to regular Au nanorods, the absorbance decreased by almost half and the production rate also reduced by almost half; for the Au nanospheres, the absorbance at 976 nm is almost negligible and the production rate also becomes -10 times smaller. These experimental results strongly support that the particle surface plasmon resonance is involved in the light absorption and hydrogen gas generation, and that the hydrogen production happens

predominantly on the ferroelectric particle surface rather than on Au nanorod ends.

Integrated particles using Au nanorods or Pt end-capped Au nanorods? Integrated particles prepared from both Au nanorods and Pt end-capped Au nanorods (i.e., with and without the Pt end capping functionality) can greatly enhance the EE production rate as compared to metallic particles only. Generally, integrated particles using Pt end-capped Au nanorods have a production rate higher than those using Au nanorods without the Pt end-capping. The Pt- AuNR/nano-FE-Pt particles gave a EE production rate of 1.41 ± 0.40 pmol/min (12 runs using different ferroelectric particles) while the AuNR/nano-FE-Pt particles gave a rate of 0.81 ± 0.37 pmol/min (7 runs using different ferroelectric particles).

Since there is variability between the ferroelectric particles made from different batches, to have a direct and fair comparison, Figure 26 shows one example that both Au nanorod and Pt end-capped Au nanorod integrated particles were prepared with the same batch of nano- ferroelectric particles. The initial production rate was 1.69 ± 0.33 pmol EE/min for Pt-AuNR/FE- Pt and 0.88 ± 0.49 pmol EE/min for AuNR/FE-Pt integrated particles, respectively. The standard deviation was from 3~4 replicated runs. The hydrogen gas production rate is -two times higher for the Pt end-capped Au nanorod integrated particles. The higher production rate is not solely caused by the extra Pt on the Au nanorod ends, which is only -5% of the total Pt in the integrated particles. More likely, Pt serves as a bridge between the Au nanorods and the ferroelectric particles, thereby reducing the energy barrier for charge transfer.

Nano-ferroelectric or micro-ferroelectric particles? The ferroelectric particles showed variability in their sizes according to the flux reaction involving a PbO or a NaCl molten-salt, though the particles prepared in the NaCl flux were in the nanometer range (-125-500 nm) while the particles prepared in the PbO flux were in the micrometer range (-1-5 pm). Generally, the nano-ferroelectric integrated particles showed a higher reactivity (1.41 ± 0.40 pmol/min, 12 runs with different ferroelectric particles) than the micro-ferroelectric integrated particles (0.88 ± 0.27 pmol/min, 7 runs using different ferroelectric particles). There are a few possible reasons that can account this difference: (1) their exposed crystallographic surface facets show different rates of reactivity, and/or (2) the nanometer-sized ferroelectric particles have a large surface area per gram of the particles so that their reaction rate is higher.

Reaction rate as a function of irradiation power. The above results demonstrate that the integrated particles made of Pt end-capped Au nanorods and nano-ferroelectric-Pt particles exhibit high photocatalytic activities for the production of molecular hydrogen. To have a better understanding how surface plasmon resonance-generated hot electrons are involved in the photocatalytic reaction, the hydrogen production rate was measured as a function of the laser irradiation power on Pt-AuNRs/nano-FE-Pt particles. Figure 27 shows the reaction rates at different irradiation levels (0.25 W/cm 2 , 0.98 W/cm 2 , 1.6 W/cm 2 , and 2.0 W/cm 2 ). As the laser power increased from 0.25 W/cm 2 to 0.98 W/cm 2 , from 0.98 W/cm 2 to 1.6 W/cm 2 , and from 1.6 W/cm 2 to 2.0 W/cm 2 , the initial reaction rate increased from 0.14 ±0.04 pmol EE molecules/min to 0.58 ± 0.21 pmol EE molecules/min, from 0.58 ± 0.21 pmol EE molecules/min to 1.02 ± 0.26 pmol EE molecules/min, and from 1.02 ± 0.26 pmol EE molecules/min to 1.69 ± 0.33 pmol EE molecules/min, respectively. The standard deviation was obtained from 2-4 replicates. Thus, the initial reaction rate follows a non-linear relationship with respect to the irradiation power (Figure 28). A quadratic function rate = 2.93 c HE f- + 2.23 c 1 O 4 / ± 3.13 c 10 2 can satisfactorily fit the data ( R 2 = 0.992), where / is the irradiation intensity. Interestingly, this observed quadratic relationship is in direct contrast to the linear rate - power relationship for the same hydrogen reduction reaction observed on the Pt end-capped Au nanorods surface. In that case, it was suggested the chemical reaction, either the interfacial transfer of hot electrons from the nanoparticle to the reactant molecule or some photo-activated steps along the chemical reaction pathways, was the rate-limiting step for the hydrogen gas production; the surface hot electron concentration on Pt end-capped Au nanorods is linearly proportional to the photon flux under the experimental conditions. The second conclusion is, however, unexpected because the instantaneous temperature of an electron gas in a metal particle upon light absorption is dominated by the photon influx and increases linearly with respect to the irradiation laser power. The total number of hot electrons exceeding the Fermi level is linear. However, the total number of“high energy” hot electrons exceeding a large threshold value would increase non-linearly with respect to the temperature, or the photon flux, according to Fermi-Dirac distribution:

f (E ) = - - - exp[( E - E F ) / k B T ] + l (1 ) where /is the probability an energy level is filled; EF is the Fermi level; ke is the Boltzmann constant; T is the temperature. The linear rate-power relationship may be caused by the low activation energy of the hydrogen gas production reaction in the presence of methanol. Thus, even very low energy hot electrons can participate in the chemical reaction, giving a linear reaction rate - light intensity relationship.

Here, the non-linear relationship possibly suggests that the metal-semiconductor Schottky barrier plays an important role in selecting the“high energy” hot electrons to pass through the interface. That is, only when the hot electrons have an energy higher than the interfacial energy barrier can they be transferred to ferroelectric particle and participate in the chemical reaction. This energy barrier process will make the population of the hot electrons that participate in chemical reaction follow a non-linear relationship, whereas in the case of Pt end- capped Au nanorods alone, hot electrons can directly diffuse to the metal surface so that the hot electron population will be linearly proportional to the light intensity.

Photocatalytic ¾ production under Sunlight. All the experiments described above have been performed under near IR light irradiation at 976 nm. This wavelength was purposely selected in order to exclude the possibility that hot electrons are being generated from bandgap excitation within the ferroelectric particles directly. Thus, at 976 nm, all of the electrons participating in the chemical reactions are injected from the plasmonic Au nanorods. However, light in the entire UV -VIS-near IR spectrum can be used to generate hot electrons in plasmonic particles, as well as in the ferroelectric particles, and used to drive the photocatalytic reaction. To demonstrate this, the photocatalytic activity of the integrated Pt- AuNR/nano-FE-Pt particles was tested under natural sunlight in September, Raleigh, North Carolina, USA. Figure 29 shows ¾ gas production yield as a function of time. The experiments were carried out around noon, where the sun irradiance was measured to be -245 mW/cm 2 orthogonal to the ray direction. Considering the incident angle of the solar rays, the irradiation power on the sample was on the order of magnitude of -100 mW/cm 2 . At this irradiation level, the hydrogen gas was produced with an initial rate of 0.54 pmol/min. These experiments confirm that the nanoparticles are practically useful in producing ¾ gas from natural sun light.

Conclusions

In summary, these investigations have demonstrated that a photocatalyst formed by combining Pt end-capped- Au nanorods and ferroelectric PbTiCri particles, can produce hydrogen gas using light. The large permanent electric polarization of the ferroelectric particles can be utilized to extract hot electrons generated on a nearby plasmonic particle that is in contact with ferroelectric particle. Effective charge separation within the particle photocatalyst can be achieved, which can extend the lifetime of hot electrons by orders of magnitude and improve their efficiency in driving the chemical reaction. The photocatalyst system described herein takes advantage of a mechanism that effectively separate electrons and holes generated in a metal surface plasmon resonance process. The photocatalyst design shows that the efficiency of using hot electrons generated on plasmonic particles can be improved by - 5 times.

Example 2

Described herein are integrated materials that use a ferroelectric material as a substrate, which has a large remanent electric filed which can facilitate charge injection and separation. As such, an integrated material comprising a ferroelectric material and a plasmonic particle can trap the charges in the ferroelectric rather than allowing them to flow back to the metal. Further, the hot charges will be separated in the ferroelectric, further extending their lifetimes. These processes mean that the lifetime of the hot charges can be extended by -1,000,000 times in the integrated plasmonic-ferroelectric materials.

A integrated plasmonic-ferroelectric material comprising gold nanorods and a ferroelectric material that possesses a large remanent electric dipole moment, can use near IR light irradiation to generate hot charges on plasmonic particles which can be injected into the ferroelectric material and drive a photocatalysis reaction. The efficiency of using hot electrons for photocatalytic reactions is enhanced in the integrated plasmonic-ferroelectric materials, which improves the light-to-chemical energy conversion efficiencies by about one order of magnitude for the same amount of plasmonic particles being used.

Figure 30 shows hydrogen production in a test tube using the Pt end-capped Au nanorods.

The integrated plasmonic-ferroelectric materials described herein can enhance current water splitting efficiency by ~l order of magnitude, such that the efficiency of solar to chemical energy conversion efficiency would become viable.

Other advantages which are obvious and which are inherent to the invention will be evident to one skilled in the art. It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and is within the scope of the claims. Since many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

The methods of the appended claims are not limited in scope by the specific methods described herein, which are intended as illustrations of a few aspects of the claims and any methods that are functionally equivalent are intended to fall within the scope of the claims. Various modifications of the methods in addition to those shown and described herein are intended to fall within the scope of the appended claims. Further, while only certain

representative method steps disclosed herein are specifically described, other combinations of the method steps also are intended to fall within the scope of the appended claims, even if not specifically recited. Thus, a combination of steps, elements, components, or constituents may be explicitly mentioned herein or less, however, other combinations of steps, elements, components, and constituents are included, even though not explicitly stated.