Field of Invention Disclosed is the one-pot mass production method of nanoparticles. The present invention provides a facile method to manufacture nanoparticles, wherein the amount can be produced on a large scale and a surface functional agent may be optionally added to promote desired properties (e.g., hydrophilicity, hydrophobicity, bioconjugation and biocompatilbility). The method comprises of providing chemical compounds as precursors for the core of the nanoparticles, blending the chemical compounds into a solid powder and heating the blended material for thermolysis to take place. The nanoparticles produced have a diameter in the range of 1 to 100 nm.

Also disclosed are ultra-small nanoparticles which have a diameter in the range of 1 to 20 nm. These nanoparticles may be surface functionalized so that they can be used in information storage media, biomedical, catalysis, waste water treatment and seawater desalination.

Background

The listing or discussion of a prior-published document in this specification should not necessarily be taken as an acknowledgement that the document is part of the state of the art or is common general knowledge. Magnetic nanoparticles, particularly those made of spinel ferrite with a composition of MFe ₂ 0 ₄ (M = Fe, Mn, Ni or Co), have unique superparamagnetic, magnetoresistive and magneto-optical characteristics, and have shown great promise in a broad range of applications including biomedicine, information storage media, catalysis, waste water treatment and seawater desalination.

The specific applications of a functional nanoparticle material largely depend on its properties. By controlling the size and surface functionality, the properties of the magnetic ferrite nanoparticles can be tailored. Small-sized (<20 nm) magnetic nanoparticles have attracted great attention recently. For example, ultra-small (<10 nm) magnetic nanoparticles have attracted special attention because of their size-dependent properties. For example, when used as T1 contrast agents for magnetic resonance imaging, ultra-small magnetic ferrite nanoparticles are always needed. This is because the magnetic moment of ferrite nanoparticles decreases rapidly with size. As a result, smaller nanoparticles with reduced volume magnetic anisotropy and increased spin disorders show suppressed T2 effect and maximized T1 contrast effect. In addition, such ultra-small nanoparticles (e.g. super- hydrophilic iron oxide nanoparticles) can be used as efficient magnetically separable draw solutes in forward osmosis for seawater desalination. This is because a large percentage of the atoms in ultra-small nanoparticles are surface atoms, resulting in a high surface atoms/bulk atoms ratio and a large specific surface area, which are both useful in facilitating the conjugation of magnetic nanoparticles with hydrophilic molecules to achieve a high water flux. Other applications particularly suited to the use of such ultra-small magnetic nanoparticles include information storage media, catalysis and a wide range of biomedical applications.

The size and surface functionaiization of magnetic nanoparticles are also critical for their advanced applications. Surface functionaiization does not only serve to protect the magnetic nanoparticles against degradation, but can also be used for further functionalization/conjugation with molecules, such as catalytically active species and various drugs. In particular, surface functionaiization of magnetic nanoparticles with functional groups such as carboxyl groups can lead to high hydrophilicity for good aqueous dispersion, which is often required for biomedical applications, waste water treatment and seawater desalination. In addition to the ultra-small size and hydrophilicity discussed above, biocompatibility needs to be considered for magnetic nanoparticles, as this is very important for their use in biomedical applications. Therefore, it is of immense interest to find ways to fabricate ultra-small hydrophilic and biocompatible magnetic nanoparticles in large quantities.

Forward osmosis (FO) is an emerging technology that can produce clean water, green energy as well as enriching biomolecules such as protein. From a technical aspect, FO utilizes the osmotic pressure difference of two solutions separated by a semi-permeable membrane to draw water molecules from the less concentrated solution (feed solution) to the other solution (draw solution), while most solutes are rejected by the semi-permeable membrane. Compared to pressure-driven membrane processes and other water production techniques, FO provides unique advantages of high rejection of contaminants, low membrane fouling and, potentially, less operation energy. Besides the need for a semipermeable membrane with high water permeate and low reverse salt flux, the selection of a suitable draw solute is critical if one wishes to build a high- performance FO system for water reuse and seawater desalination. In general, a draw solute in FO for water production should fulfil the criteria of high osmolality to generate high osmotic pressures and be easily and efficiently separated from the obtained water. A variety of draw solutes have been explored for us in FO technology, but progress in finding useful draw solutes is well behind the development of FO membranes. For example, the use of chemical compounds such as ammonium bicarbonate and carbon dioxide can be used as draw solutes, both of which can induce reasonable FO fluxes, but their recovery involves heating, which is energy intensive. Other biocompatible molecules such as sugars have also been tested as draw solutes but their recovery is very difficult. Highly hydrophilic superparamagnetic nanoparticles have been recently investigated as a new type of draw solute and offer the advantages of easy recovery and low reverse flux compared to chemical compounds such as ammonium bicarbonate. In addition, with size in nanometer scale, superparamagnetic nanoparticles have a high surface-area-to-volume ratio, particularly when the size of the nanoparticles is less than 10 nm. Moreover, such hydrophilic nanoparticles can be recycled easily and can generate high osmotic pressures (and hence, high water flux) in FO, which will result in efficient water reclamation and seawater desalination purposes. However, there is a lack of a facile way for mass production of highly hydrophilic superparamagnetic nanoparticles, which greatly limits their application as draw solutes in FO processes.

Various synthetic routes have been used to fabricate magnetic ferrite nanoparticles, including coprecipitation, microemulsion, hydrothermal and thermal decomposition processes. The coprecipitation process always involves the mixing of ferrous (Fe ²⁺ ) and ferric (Fe ³⁺ ) salts, followed by coprecipitation of magnetic nanoparticles via addition of a reagent such as a base. The coprecipitation route is a facile way to prepare magnetic nanoparticles and is also well developed. However, a drawback of this route is that the final product is always a mixture of magnetite and maghemite due to the variations in the molar ratio of the iron salts.

The microemulsion process uses two immiscible phases (water and oil) with a surfactant, which can form a monolayer at the interface between the two phases. The particle size of the magnetic nanoparticles prepared from microemulsion can be controlled by varying the precursor composition. A drawback of the microemulsion- route is that extensively agglomerated nanoparticles are often generated. In addition, most magnetic nanoparticles obtained by this route are poorly crystalline or there is a need to use toxic/carcinogenic reducing agents such as hydrazine during the synthesis.

Hydrothermal synthesis involves the crystallisation of substances from high temperature aqueous solutions at high vapor pressures, and has been used to prepare magnetic nanoparticles. Although hydrothermal synthesis has the advantage of simplicity and can yield magnetic nanoparticles with high crystallinity, it always produces large (>100 nm) nanoparticles, which may display ferromagnetic behavior. To produce small magnetic nanoparticles, thermal decomposition of an organometallic iron species in high boiling organic solvents containing stabilizing surfactants at high temperature has been developed. The high temperature thermal decomposition route can produce magnetic nanoparticles with ultra-small size, but without further ligand exchange these nanoparticles often fail in forming colloidal solutions in aqueous media. In addition, complex steps and a large amount of high-boiling organic solvents are always required during the synthesis.

Therefore, based upon the above, a simple route to the mass production of ultra-small hydrophilic magnetic ferrite nanoparticies has yet to be developed.

Summary of the invention

We present a solvent-free thermolysis route to fabricate ultra-small magnetic ferrite nanoparticles. This versatile route provides unique advantages in mass production of ultra- small magnetic ferrite nanoparticles with good hydrophilicity and biocompatibility while eliminating the use of high boiling organic solvents and post ligand exchange.

The present invention provides a facile method to manufacture nanoparticles, wherein the amount can be produced on a large scale and a surface functional agent may be optionally added to promote desired properties (e.g., hydrophilicity, hydrophobicity, bioconjugation and biocompatibility). The method comprises of providing chemical compounds as precursors for the core of the nanoparticles, blending the chemical compounds into a solid powder and heating the blended material for thermolysis to take place. Depending on the precursors that are used, the core of the nanoparticles may be magnetic or superparamagnetic. The precursors used are one or more selected from the group comprising of iron (III) acetylacetonate, manganese(ll) acetylacetonate, nickel(ll) acetylacetonate, cobalt(lll) acetylacetonate, iron (III) chloride, iron (II) chloride, iron (III) nitrite, iron (II) nitrite, iron (III) sulfate, iron (II) sulfate, manganese(ll) chloride, manganese(ll) nitrite, manganese(ll) sulfate, nickel chloride, nickel nitrite, nickel sulfate, cobalt chloride, cobalt nitrite, cobalt sulfate and a mixture thereof. The core synthesized can be selected from one or more of the group comprising of Fe ₂ 0 ₃ , Fe ₃ 0 ₄ , Mn0 ₂ , Co ₃ 0 ₄ , NiO, XFe ₂ 0 , and a mixture thereof, where X can be Fe, Co, Ni or Mn. Heating can be conducted in the range of 100-500°C (e.g. 100-350°C) under air, nitrogen or argon condition.

In one aspect, the invention relates to a facile method with mass production capability for manufacturing superparamagnetic nanopartides.

In one aspect, this invention relates to spinel ferrite nanopartides with composition of XFe ₂ 0 ₄ (X =Fe, Mn, Ni, Co, Zn, etc), Z _a Y _(1-a) Fe ₂ 0 ₄ (Z = Mn, Zn, Fe, Co or Ni and Y = Zn, Ni, Fe, Mn or Co) or hexagonal crystal structured materials such as BaFe ₂ 0 ₉ . Small-sized magnetic ferrite nanopartides such as ultra-small iron oxide nanopartides are needed when used as 7 ^" _? contrast agents for magnetic resonance imaging/ Magnetic moment of iron oxide nanopartides declines rapidly as their size decreases due to the reduction in the volume magnetic anisotropy and spin disorders on the surface, resulting in suppressed T ₂ effect and maximized T-, contrast effect. These nanopartides can be used in a wide range of biomedical applications. Based on an MTT assay using MCF7 cells, the magnetic ferrite nanopartides show a good biocompatibility and do not affect cell morphology. They are also demonstrated for protein enrichment based on hydrophilicity induced forward osmosis, showing efficient enrichment for proteins of hemoglobin and albumin. These nanopartides comprise of a magnetic core and optionally, molecules or polymers bound to the core to functionalize the particles. In one embodiment, the nanopartides have a diameter of 1 to 100 nm. In one embodiment, the nanopartides have a diameter of 1 to 20 nm.

In one aspect, the invention relates to a facile method with mass production capability for manufacturing highly hydrophilic superparamagnetic nanopartides described herein. The inventors have conducted broad studies and researches to synthesize highly hydrophilic superparamagnetic nanopartides with mass production capability. These hydrophilic superparamagnetic nanopartides can be economically used in desalination, wastewater reclamation, as well as protein and pharmaceuticals concentration. In one aspect, the highly hydrophilic superparamagnetic nanopartides synthesized with the method of this invention are applied as a draw solute in forward osmosis (FO). The FO system includes contacting the highly hydrophilic superparamagnetic nanopartlcles solution described above with one side of membrane and contacting a feed solution to extract water from the feed solutions such as seawater, brackish water and pharmaceutical or protein solution through a FO process. When extracted water is accumulated to certain level, the superparamagnetic nanoparticle solution is re-concentrated by passing through external magnetic field and ultrafiltration. The re-generated superparamagnetic nanoparticles are recycled as draw solute in FO processes as described above.

In one aspect, this invention relates to highly hydrophilic superparamagnetic nanoparticles, which include a metal-based core and highly hydrophilic shell. The metal-based core may comprise of Fe ₂ 0 ₃ , Fe ₃ 0 ₄ , Mn0 ₂ , Co ₃ 0 ₄ , NiO or XFe ₂ 0 , or a mixture thereof, in which X is Fe, Co, Ni or Mn etc. The hydrophilic shell may comprise of hydrophilic sodium or potassium based small molecules or polymers. Examples of these are sodium, potassium and a mixture of other salts known to those skilled in the art.

In a first aspect of the invention, there is provided a method of synthesizing nanoparticles comprising: providing one or more core-precursor materials, preparing a solid powder by processing the one or more core-precursor materials and heating the solid powder to cause thermolysis.

In embodiments of this first aspect:

(a) the nanoparticles have a diameter in the range of 1 to 100 nm, optionally from 1 to 20 nm, such as from 1 to <10 nm (e.g. 1 to <10 nm);

(b) the method is capable of producing nanoparticles on a large scale. For example, the large scale is at least 500g, optionally at least 900 g, such as at least 1 kg;

(c) the nanoparticles have a magnetic or a superparamagnetic core;

(d) the one or more core-precursor materials are selected from the group comprising of barium chloride, barium sulfate and, more particularly, iron (III) acetylacetonate, manganese(ll) acetylacetonate, nickel(ll) acetylacetonate, cobalt(lll) acetylacetonate, iron (III) chloride, iron (II) chloride, iron (III) nitrite, iron (II) nitrite, iron (III) sulfate, iron (II) sulfate, manganese(ll) chloride, manganese(ll) nitrite, manganese(ll) sulfate, nickel chloride, nickel nitrite, nickel sulfate, cobalt chloride, cobalt nitrite, cobalt sulfate, barium chloride, barium sulfate and mixtures thereof;

(e) the synthesized magnetic or superparamagnetic core has a composition selected from one or more of the group comprising of Fe ₂ 0 ₃ , Fe ₃ 0 ₄ , Mn0 ₂ , Co ₃ 0 ₄ , NiO, XFe ₂ 0 ₄ , Z _a Y ₍₁ . _a) Fe ₂ 0 ₄ or hexagonal crystal structured materials such as BaFe ₂ 0 ₉ and a mixture thereof, where:

X is selected from Fe, Co, Ni, Mn and Zn;

Z is selected from Mn, Zn, Fe, Co and Ni;

Y is selected from Zn, Ni, Fe, Mn and Co; and

a is from 0 to 1 ;

(f) the method does not comprise adding a liquid to the solid powder;

(g) the heating is conducted in the range of 100-500°C under air, nitrogen or argon conditions, optionally from 250 to 400°C, such as from 270 to 350°C (e.g. from 300 to 350°C);

(h) the process further comprises providing one or more functional materials, where the one or more functional materials are mixed together with the one or more core- precursor materials to prepare the solid powder;

(i) the functional material is a hydrophilic or hydrophobic material, for example the hydrophilic functional material is one or more selected from the group consisting of , maleic acid and its salts, poly (maleic acid) and its salts, poly( ethylene glycol) and its salts, dimercaptosuccinic acid and its salts, dendrimers, polymer brushes, and hydrophilic amino acids and, more particularly, sodium citrate and/or the hydrophobic functional material is selected from one or more of the group consisting of alkanes, dioctyl sodium sulfosuccinate, hydrophobic amino acids, polylactic acid and, more particularly, octadecylamine and oleic acid;

G) when present, the functional material can be used in a molar ratio of from 1 :1 to 20:1 relative to the one or more core-precursor materials, optionally from 2:1 to 10:1 ;

(k) when a functional material is present, the heating step may comprise:

(1 ) heating the solid powder to a temperature of from 100 to less than 250°C; and

(2) increasing the temperature to from 270 to 350°C, for example, in step (a), the temperature is maintained for from 5 minutes to 1 hour and/or in step (b) the temperature is maintained from 30 minutes to 2 hours. Embodiments (a) to (k) may be individually or jointly combined with the first aspect of the invention. For the avoidance of doubt, all possible combinations of embodiments (a) to (k) with the aspect from which they depend are explicitly contemplated.

In a second aspect of the invention, there is provided a nanoparticle material comprising:

\ at least a core material selected from one or more of the group comprising of Fe ₂ 0 ₃ , Fe ₃ 0 ₄ , Mn0 ₂ , Co ₃ 0 ₄ , NiO, XFe ₂ 0 ₄ , Z _a Y ₍ i _-a) Fe ₂ 0 ₄ or hexagonal crystal structured materials such as BaFe ₁₂ 0i ₉ and a mixture thereof, where:

X is selected from Fe, Co, Ni, Mn and Zn;

Z is selected from Mn, Zn, Fe, Co and Ni;

Y is selected from Zn, Ni, Fe, Mn and Co; and

a is from 0 to 1 , and wherein

the nanoparticles have an average diameter of from 1 to 20 nm, optionally from 1 to 10 nm. In embodiments of this second aspect,

(aa) the core material is magnetic or superparamagnetic;

(bb) the nanoparticle further comprises a functional material attached to the core material (e.g. the functional material is a metal salt selected from one or more of the group comprising of sodium, potassium and mixtures thereof, optionally wherein the functional material is sodium citrate);

(cc) the functional material is a hydrophilic or hydrophobic material, for example the hydrophilic functional material is one or more selected from the group consisting of maleic acid and its salts, poly (maleic acid) and its salts, poly(ethylene glycol) and its salts, dimercaptosuccinic acid and its salts, dendrimers, polymer brushes, and hydrophilic amino acids and, more particularly, sodium citrate and/or the hydrophobic functional material is selected from one or more of the group consisting of alkanes, dioctyl sodium sulfosuccinate, hydrophobic amino acids, polylactic acid and, more particularly, octadecylamine and oleic acid (e.g. the functional material is a metal salt selected from one or more of the group comprising of sodium, potassium and mixtures thereof, optionally wherein the functional material is sodium citrate);

(dd) when the nanoparticle comprises the attachment of a hydrophilic functional material, the nanoparticle has a water flux value in the range of 1 to 40 L.m ^"2 .hr ^"1 when used as a draw solute in forward osmosis, wherein the feed solution is a saline solution having a measured osmolality of 1000 mOsm kg ^-1 .

Embodiments (aa) to (dd) may be individually or jointly combined with the second aspect of the invention. For the avoidance of doubt, all possible combinations of embodiments (aa) to (dd) with the aspect from which they depend are explicitly contemplated. In a third aspect of the invention, the nanoparticle material may be obtained or be obtainable using the processes described hereinbefore, particularly with reference to embodiments (a) to (k) and the first aspect of the invention (including all possible combinations thereof). In a fourth aspect of the invention, there is provided a use of a hydrophilic nanoparticle material according to the second aspect of the invention in a draw solute for forward osmosis. In an embodiment of this aspect, the nanoparticle has a water flux value in the range of 1 to 40 L.m ^"2 .hr ^"1 when used as a draw solute in forward osmosis, wherein the feed solution is a saline solution having a measured osmolality of 1000 mOsm kg ^-1 .

The following numbered clauses represent certain aspects and embodiments of the invention.

1. A method of synthesizing nanoparticles in large scale, comprising:

providing chemical compounds as precursors for a core;

blending the chemical compounds into a solid powder; and

heating the blended material for thermolysis to take place.

2. The method of clause 1 , wherein the nanoparticles have a diameter in the range of 1 to 100 nm.

3. The method of clause 1 or clause 2, wherein the nanoparticles have a magnetic core.

4. The method of any one of the preceding clauses, wherein the chemical compounds are one or more selected from the group comprising of iron (III) acetylacetonate, manganese(ll) acetylacetonate, nickel(ll) acetylacetonate, cobalt(lll) acetylacetonate, iron (III) chloride, iron (II) chloride, iron (III) nitrite, iron (II) nitrite, iron (III) sulfate, iron (II) sulfate, manganese(ll) chloride, manganese(ll) nitrite, manganese(ll) sulfate, nickel chloride, nickel nitrite, nickel sulfate, cobalt chloride, cobalt nitrite, cobalt sulfate and a mixture thereof.

5. The method of any one of the preceding clauses, wherein the magnetic core synthesized has a composition, selected from one or more of the group comprising of Fe ₂ 0 ₃ . Fe ₃ 0 ₄ , Mn0 ₂ , Co ₃ 0 _4l NiO, XFe ₂ 0 ₄ , or hexagonal crystal structured materials such as BaFei ₂ 0 ₁₉ and a mixture thereof, where X can be Fe, Co, Ni, Mn or Zn. 6. The method of any one of the preceding clauses, wherein the nanoparticles have a superparamagnetic core.

7. The method of any one of the preceding clauses, wherein the chemical compounds is one or more selected from the group comprising of iron (III) acetylacetonate, manganese(ll) acetylacetonate, nickel(ll) acetylacetonate, cobalt(lll) acetylacetonate, iron (III) chloride, iron (II) chloride, iron (III) nitrite, iron (II) nitrite, iron (III) sulfate, iron (II) sulfate, manganese(ll) chloride, manganese (II) nitrite, manganese(ll) sulfate, nickel chloride, nickel nitrite, nickel sulfate, cobalt chloride, cobalt nitrite, cobalt sulfate and a mixture thereof.

8. The method of claim 6, wherein the magnetic core synthesized has a composition selected from one or more of the group comprising of Fe ₂ 0 ₃ . Fe ₃ 0 ₄ , Mn0 ₂ , Go ₃ 0 ₄ , NiO, XFe ₂ 0 ₄ , or hexagonal crystal structured materials such as BaFe ₁₂ 0 ₉ and a mixture thereof, where X can be Fe, Co, Ni, Mn or Zn.

9. The method of any one of the preceding clauses, wherein the heating is conducted in the range of 100-500°C (e.g. from 100-350°C) under air, nitrogen or argon condition.

10. A superparamagnetic nanoparticle comprising:

a magnetic core; and

molecules or polymers bound to the core to functionalize the particle, wherein the magnetic core is formed using chemical compounds as precursors.

11. The nanoparticle of clause 10, wherein the magnetic core has a diameter in the range of 1 to 100 nm.

12. The nanoparticle of clause 10 or clause 11 , wherein the magnetic core has a diameter in the range of 1 to 20 nm. 13. The nanoparticle of any one of the clauses 10 to 12, wherein the functional molecules bound to the core are hydrophilic.

14. The nanoparticle of clause 3, wherein the functional molecules are selected from one or more of a group comprising of sodium, potassium and other salts and a mixture thereof. 15. The nanoparticle of any one of clauses 10 to 14, wherein the magnetic core synthesized has a composition selected from one or more of the group comprising of one or more of the group comprising of Fe ₂ 0 ₃ . Fe ₃ 0 ₄ , MnQ ₂ , Co ₃ 0 ₄ , NiO, XFe ₂ 0 ₄ , or hexagonal crystal structured materials such as BaFei ₂ 0 ₉ and a mixture thereof, where X can be Fe, Co, Ni, Mn or Zn.

16. The nanoparticle of anyone of clauses 10 to 15, wherein the chemical compounds are one or more selected from the group comprising of iron (III) acetylacetonate, manganese(ll) acetylacetonate, nickel(ll) acetylacetonate, cobalt(lll) acetylacetonate, iron (III) chloride, iron (II) chloride, iron (III) nitrite, iron (II) nitrite, iron (III) sulfate, iron (II) sulfate, manganese(ll) chloride, manganese (II) nitrite, manganese(ll) sulfate, nickel chloride, nickel nitrite, nickel sulfate, cobalt chloride, cobalt nitrite, cobalt sulfate and a mixture thereof.

17. The nanoparticle of any one of clauses 10 to 16, wherein the functional molecules bound to the core are hydrophobic.

18. The nanoparticle of clause 13, wherein the nanoparticle has a water flux value in the range of 1 to 40 L.m ^"2 .hr ^"1 when used as a draw solute in forward osmosis. Without further elaboration, it is believed that the above description has adequately enabled the present invention. The following examples are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever. All of the publications cited herein are hereby incorporated by reference in their entirety. Figures

Fig. 1 : Mass-production of highly hydrophilic superparamagnetic nanoparticles MNPs_SC. Fig. 2: TEM images of MNPs and MNPs_SC prepared with different NaCA: Fe(acac) ₃ ratios (n) labeled as MNPs_SCn (n is molar ratio of NaCA:Fe(acac) ₃ ).

Fig. 3: Powder XRD patterns of MNPs, MNPs_SC2, MNPs_SC5 and MNPs_SC10.

Fig. 4: VSM loops of the MNPs, MNPs_SC2, MNPs_SC5 and MNPs_SC10.

Fig. 5: Osmolality and hydrophilicity related aqueous solution dispersion of the MNPs and MNPs_SC10.

Fig. 6: (A) Hydrophilicity related aqueous dispersion of MNPs and MNPs_SC. (B) MNPs and MNPs_SC in a water/hexane system. After sonication, MNPs readily migrated into the hexane layer but MNPs_SC retained in the water layer. MNPs_SC refers to MNPs_SC10. Fig. 7: FO performance of MNPs_SC10 towards Dl and salt water. Each value was obtained by 4 separate measurements.

Fig. 8: (A) FO setup for protein enrichment (co-current cross flow of protein solution and MNPs_SC10 solution). (B) UV-vis spectra of protein hemoglobin solutions with different operation times. (C) Hemoglobin concentration vs. operation time. The inset of (C) shows the photos of hemoglobin solutions obtained at different operation times. (D) Albumin concentration vs. operation time. The inset of (D) shows the corresponding UV-vis spectra of the albumin solutions.

Fig. 9: Osmolality and photos of the nanoparticle dispersions before protein enrichment (MNPs_SC) and after regeneration via magnetic collection and ultrafiltration after the protein enrichment (MNPs_SC_Re).

Fig. 10: MTT cytotoxicity assay in using MCF7 cells following 24-hour exposure to various concentrations of MNPs and MNPs_SC10. Cell viability value was expressed as the percentage of absorbance observed relative to the control wells receiving only culture media. Fig. 11 : TEM images of magnetic nanoparticles of MnFe ₂ 0 ₄ . NiFe ₂ 0 ₄ and CoFe ₂ 0 ₄ fabricated using the same method as MNPs_SC10.

Fig. 12: Powder XRD patterns of the MNPs_SC and mixed metal ferrite nanoparticles of MnFe ₂ 0 ₄ , NiFe ₂ 0 ₄ , and CoFe ₂ 0 ₄ .

Fig. 13: Magnetic behaviours of MNPs_SC and metal ferrite nanoparticles of MnFe ₂ 0 ₄ , NiFe ₂ 0 ₄ , and CoFe ₂ 0 ₄ . The curves were measured using a vibrating sample magnetometer at 298 K. All M values were obtained by dividing the electromagnetic unit (emu) values by the total weight of nanoparticles (including the core and ligands).

Fig. 14: Synthesis and magnetic response of hydrophobic magnetic nanoparticles that were prepared by choosing suitable molecules such as octadecylamine.

Detailed Description

The solvent-free thermolysis route to fabricate ultra-small magnetic ferrite nanoparticles presented herein provides unique advantages in the large-scale production of nanoparticles while eliminating the use of high boiling organic solvents and post ligand exchange.

The method of synthesizing nanoparticles comprises providing one or more core-precursor materials, preparing a solid powder by processing the one or more core-precursor materials and heating the solid powder to cause thermolysis. This process does not require the addition of a solvent to assist the reaction and allows for the large-scale production (e.g. > 500g, such as >900g, such as >1 kg) of nanoparticles of various sizes. For example, the nanoparticles may have a diameter of from 1 to 100 nm, but the process may be particularly suited to the production of nanoparticles having a diameter size of from 1 to 20 nm, such as from 1 to <10 nm (e.g. from 1 to <10 nm). While the method may be used to make many different types of nanoparticles, the process is particularly useful in preparing nanoparticles that have a magnetic or a superparamagnetic core. Such nanoparticle cores may be prepared by the use of one or more core-precursor materials are selected from the group comprising of barium chloride, barium sulfate and, more particularly, iron (III) acetylacetonate, manganese(ll) acetylacetonate, nickel(ll) acetylacetonate, cobalt(lll) acetylacetonate, iron (III) chloride, iron (II) chloride, iron (III) nitrite, iron (II) nitrite, iron (III) sulfate, iron (II) sulfate, manganese(ll) chloride, manganese(ll) nitrite, manganese(ll) sulfate, nickel chloride, nickel nitrite, nickel sulfate, cobalt chloride, cobalt nitrite, cobalt sulfate, barium chloride, barium sulfate and mixtures thereof. When the above-mentioned core-precursor materials are used, the nanoparticle core formed by the process may have a composition selected from one or more of the group comprising of Fe ₂ 0 ₃ , Fe ₃ 0 ₄ , Mn0 ₂ , Co ₃ 0 ₄ , NiO, XFe ₂ 0 ₄ , Z _a Y _(1-a) Fe ₂ 0 ₄ or hexagonal crystal structured materials such as BaFei ₂ 0 ₁₉ and a mixture ^' thereof, where:

X is selected from Fe, Co, Ni, Mn and Zn;

Z is selected from Mn, Zn, Fe, Co and Ni (e.g. Z is Mn or Zn);

Y is selected from Zn, Ni, Fe, Mn and Co (e.g. Y is Zn or Ni); and

a is from 0 to 1.

The process described above may be conducted at a temperature of from 100-500°C under air, nitrogen or argon conditions, for example from 250 to 400°C, such as from 300 270 to 350°C (e.g. from 300 to 350°C). It will be appreciated the length of time needed to form the nanoparticles will vary and that the optimal amount of time for any given material is readily determinable by a skilled person. While the process may be conducted using the core-precursor materials only, it is also possible to add further materials to the process to prepare further nanoparticle materials. For example, one or more functional materials may be added to the core-precursor materials, where the one or more functional materials are mixed together with the one or more core- precursor materials to prepare the solid powder. Said functions materials may a hydrophilic or hydrophobic material. For example the hydrophilic functional material is one or more selected from the group consisting of maleic acid and its salts, poly(maleic acid) and its salts, poly(ethylene glycol) and its salts, dimercaptosuccinic acid and its salts, dendrimers, polymer brushes, and hydrophilic amino acids and, more particularly, sodium citrate and/or the hydrophobic functional material is selected from one or more of the group consisting of alkanes, dioctyl sodium sulfosuccinate, hydrophobic amino acids, polylactic acid and, more particularly, octadecylamine and oleic acid. When present, the functional material can be used in a molar ratio of from 1 :1 to 20:1 relative to the one or more core-precursor materials, optionally from 2:1 to 10:1.

When a functional material is present, the process of heating the solid powder may be modified. For example, the heating step may comprise:

(1 ) heating the solid powder to a temperature of from 100 to less than 250°C; and

(2) increasing the temperature to from 270 to 350°C. In certain examples, step (a), the temperature is maintained for from 5 minutes to 1 hour and/or in step (b) the temperature is maintained from 30 minutes to 2 hours. While not wishing to be bound to theory, it is speculated that the differential temperature ranges assist in producing the core nanoparticle material and in attaching the functional material to the core nanoparticle material.

It will be appreciated that, certain aspects of this invention relates to a method involving a one-pot mass production of highly hydrophilic superparamagnetic nanoparticles.

In one aspect, the highly hydrophilic superparamagnetic nanoparticles produced by this invention can be used as a draw solute in FO. There is also provided a nanoparticle material comprising a core material selected from one or more of the group comprising of Fe ₂ 0 ₃ , Fe ₃ 0 ₄ , Mn0 ₂ , Co ₃ 0 ₄ , NiO, XFe ₂ 0 ₄ , Z _a Y _{( -} a ₎ Fe ₂ 0 ₄ or hexagonal crystal structured materials such as BaFe ₂ 0 ₁₉ and a mixture thereof, where: X is selected from Fe, Co, Ni, Mn and Zn;

Z is selected from Mn, Zn, Fe, Co and Ni;

Y is selected from Zn, Ni, Fe, Mn and Co; and

a is from 0 to 1 , and wherein

the nanoparticles have an average diameter of from 1 to 20 nm, optionally from 1 to 10 nm.

As will be appreciated, the above-described nanoparticles may have a core material that is magnetic or superparamagnetic. The nanoparticle may also comprise a functional material attached to the core material. The functional material may be a hydrophilic or hydrophobic material, for example the hydrophilic functional material is one or more selected from the group consisting of , maleic acid and its salts, poly (maleic acid) and its salts, poly(ethylene glycol) and its salts, dimercaptosuccinic acid and its salts, dendrimers, polymer brushes, and hydrophilic amino acids and, more particularly, sodium citrate and/or the hydrophobic functional material is selected from one or more of the group consisting of alkanes, dioctyl sodium sulfosuccinate, hydrophobic amino acids, polylactic acid and, more particularly, octadecylamine and oleic acid (e.g. the functional material is a metal salt selected from one or more of the group comprising of sodium, potassium and mixtures thereof, optionally wherein the functional material is sodium citrate).

When the functional material is hydrophilic, the nanoparticle may be suitable for use as a draw solute in forward osmosis, amongst other things. Such hydrophilic nanoparticles may have a water flux value in the range of 1 to 40 Lm ^"2 .hr ^"1 when used as a draw solute in forward osmosis wherein the feed solution is a saline solution having a measured osmolality of 1000 mOsm kg ^-1 .

The forward osmosis process using the hydrophilic nanoparticles as the draw solution was conducted on a lab-scale circulating-filtration unit. A commercial TFC membrane (Hydration Technologies Inc.) was used as the FO membrane. Dl water, saline water (NaCI solution with a measured osmolality of 1000 mOsm kg ^-1 ), seawaters or waste waters were used as feed solutions. The cross-flow membrane module consists of two rectangular channels, one on each side of the membrane, with a frame configuration of 8.0 cm in length, 1.0 cm in width, and 0.25 cm in height, with feed and draw solutions flowing concurrently at the same velocity. The water permeation flux, _v (L m ^-2 h ^_1 , abbreviated as LMH), was calculated from the mass change of the feed solution as follows J _v = ml(pAAt), where Am (g) is the permeation water accumulated over a predetermined time At (h) during the duration of FO, A is the effective membrane surface area (m ² ), and p is the density of water.

Hydrophobic magnetic nanoparticles may be used as magnet-induced temporary superhydrophobic surfaces, which are required for use in oil-water separation, protection of electronic devices in a high moisture environment, controlling cell adhesion on substrate surface, reducing fluid resistance for aquaculture devices, and reduction of fluid drag in microfluidic devices. For many of these applications, superhydrophobicity is required only temporarily. It is required that a temporary superhydrophobic surface can be generated and removed easily on demand. Hydrophobic MNPs can generate such temporary superhydrophobic surfaces under remotely controllable magnetic fields. It will be appreciated that the nanoparticle material described hereinbefore may be obtained or be obtainable by using the processes described hereinbefore. The current invention addresses two most critical issues in existing approaches of using magnetic nanoparticles as draw solute for FO desalination: 1 ) Limited capability for mass production. Although magnetic nanoparticles have been explored as draw solution for FO, the slow and tedious process for the preparation of such nanoparticles (typically at gram scale per reaction) prohibits large-scale production and Induces high cost. This invention is based on a one-pot solid-state reaction and produces super-hydrophllic nanoparticles in kilogram, with the potential for even larger scale. Production at this scale will significantly lower the manufacturing cost. There has been report of synthesizing magnetic nanoparticles with kilogram scale in organic solvents involving multiple steps, but the particles are hydrophobic and not suitable for FO draw solution. 2) Low osmotic pressure and thus limited water flux for FO. Current available magnetic nanoparticle-based draw solution for seawater desalination can only allow water flux of 1-3 liter per square meter per hour (LMH). Our initial tests demonstrate that the nanoparticles prepared with our method can draw water from seawater at a high average water flux of 7.6 LMH. It is worth noting that this three-fold improvement in water flux is achieved by using as-synthesized nanoparticles.

EXAMPLES

Example embodiments of the disclosure will be better understood and readily apparent to one of ordinary skill in the art from the following example, and if applicable, in conjunction with the figures.

General Procedure 1

All magnetic nanocrystals were fabricated using a solventless thermolysis route. To synthesize functionalized magnetic iron oxide nanoparticles, an iron oxide precursor was mixed with a ligand material in solid form with different molar ratios via grinding or ball milling.

Then the mixed solid powder was put into a glass container, and was thermally treated.

Thermal treatment conditions were as follows: (1 ) from room temperature to 100-250°C at a rate of 10°C min ^"1 and retaining this temperature for half an hour, (2) increasing temperature to 270-350°C at a rate of 2°C min ^~1 and retaining this temperature for one hour, and (3) cooling to room temperature. To remove impurities, the as-prepared material was dispersed in deionised (Dl) water with a short time of sonication. Then acetone was added to the nanoparticle aqueous solution to precipitate the particles under centrifugation. The above cycle was repeated at least 3 times. Material characterizations

Physical Analysis

TEM images were recorded on a JEM-2100F electron microscope operating at an accelerating voltage of 200 kV. The corresponding particle size distribution histograms were plotted by counting 300 nanoparticles. X-ray diffraction (XRD) patterns were measured using an X-ray diffractometer (GADDS XRD system, Bruker AXS) with a CuKa source (λ = 1.54 A). X-ray photoelectron spectroscopy (XPS) characterizations were performed on a PHI Quantera X-ray photoelectron spectrometer with a chamber pressure of 5 x 10-9 torr, a spatial resolution of 30 pm and an Al cathode as the X-ray source to determine the composition of the nanoparticles. Thermogravimetric analysis (TGA) was conducted using a Perkin-Elmer TGA at a constant heating rate of 5 °C min ¹ from room temperature to 850°C in a nitrogen environment. For TGA measurements to monitor the formation process of the nanoparticles, the temperature-time profile was the same as the solventless thermolysis route used for the preparation of the magnetic nanoparticles. A vibrating sample magnetometer (VSM, LakeShore 450-10) was used to characterize the magnetic properties of nanoparticles. All the M values were calculated by dividing the magnetization value by the total mass of the sample. MTT assay

MCF7 human breast adenocarcinoma cell lines were grown in Dulbecco's modified Eagle's medium supplemented with 10% heat inactivated fetal bovine serum, 1 mM L-glutamine and 50 U mL ^_1 penicillin/streptomycin. Cells were seeded into a 96-well plate containing 200 μΙ_ media and cultured in a humidified incubator at 37°C with 5.0% C02. After 24 h, various concentrations of nanoparticles were added into each well. To provide reliable results, each concentration of nanoparticles was set in six wells. After 24 h incubation with nanoparticles, the medium was removed and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) (100 pL, 0.5 mg ml_-1 in media) was added into each well. Following incubation at 37 °C for 4 h, the medium was removed and the precipitated violet crystals were dissolved in

200 μΙ_ of dimethyl sulfoxide. The absorbance was measured at 570 nm using a BioTek microplate reader. The cell viability was assessed by the ratio of absorbance values from each group and the control group.

Protein enrichment

The experimental set-up of protein enrichment consists of a permeation cell with a rectangular channel (8.0 cm * 1.0 cm ^χ 0.25 cm, length ^χ width ^χ height) and a water permission membrane, two pumps and solution containers as shown in Figure 8A. The nanoparticle solution used here has an osmolarity much higher than that of protein solutions. The nanoparticle solution was used as the draw solution and the protein solution as the feed solution. Protein concentrations were obtained based on absorbance at 405 and 208 nm for hemoglobin and albumin, respectively.

Osmolality Measurements -

The osmolality of a solution was measured using a Wascor Vapor 5600 instrument. For the nanoparticle solutions, each solution was measured using a concentration of 0.45 mL/g.

Example 1 : Synthesis and characterization of hydrophilic superparamagnetic nanoparticles

In this example, superparamagnetic nanoparticles were synthesized. The materials used were Iron (III) acetylacetonate (Fe(acac) ₃ ), manganese(ll) acetylacetonate, nickel(ll) acetylacetonate, cobalt(lll) acetylacetonate and sodium citrate tribasic dehydrate from Sigma-Aldrich and acetone from Acros Organics. All the chemicals above were used as received.

The synthetic approach is a one-pot solid thermal production method that can manufacture superparamagnetic nanoparticles with mass production capability. Fe(acac) ₃ was mixed with sodium citrate tribasic dihydrate (NaCA) with a molar ratio (NaCA:Fe(acac) ₃ ) of 2:1 , 5:1 and 10:1 via grinding or ball milling to form a uniformly mixed solid powder, which was heated inside an oven under air conditions. The heating process was as follows:

1 ) heating the material from room temperature to 200°C, with a heating rate of 10°C/min 2) maintaining the200°C temperature for 30 min

3) heating from 200°C to 280°C, with a heating rate of 2°C/min 4) maintaining the 280°C for 60 min and then cooling the material down to room temperature.

The heating process is not limited to the procedure described above. With modification of the temperature or time, hydrophilic magnetic nanoparticles can still be fabricated.

The obtained powder was dissolved in water and sonicated for 15-30 min. Then acetone was added to the aqueous solution, resulting in precipitation that was separated via centrifugation. The black material was re-dissolved in water and re-precipitated by acetone followed by centrifugation. The above washing process was repeated a couple of times more to remove most residuals. The final product was redispersed in Dl water and used for further characterizations.

The mass production capability is demonstrated in Figure 1 , which shows that the process described herein can produce the described material on a kilogram scale.

The obtained product is abbreviated below as MNPs_SCx, where x is the molar ratio of NaCA to Fe(acac) ₃ expressed as a whole number. As a comparison, materials prepared without the use of NaCA but using the same procedure as that for Na_MNPs is abbreviated as MNPs.

The produced superparamagnetic nanoparticles were imaged using Transmission Electron Microscope (TEM, JEOL: JEM-2100F) by drying a dispersion of magnetic nanoparticles after further centrifugation on amorphous carbon coated copper grids, as shown in Figure 2. When measured by Scion Image software Scnlmage, The MNPs, MNPs_SC2, MNPs_SC5 and MNPs_SC10 were measured to have average diameter sizes of 15.9, 9.6, 5.7 and 3.5 nm, respectively. In addition, it was found that the nanoparticles were more uniform at higher molar ratios of sodium citrate/Fe(acac) ₃ . Powder X-ray diffraction (XRD) patterns of the nanoparticles show standard magnetite < (Fe304, PDF 01 -071-6336) crystal structure (Figure 3). The particle sizes were also estimated based on XRD peak broadening. For MNPs, MNPs_SC2, MNPs_SC5, MNPs_SC10, the calculated sizes were 19.6, 12.2, 6.3 and 4.4 nm, respectively, similar to those obtained from TEM images. Magnetic behavior of the magnetic nanoparticles was evaluated through a vibrating sample magnetometer (VSM, LakeShore 450-10) from -15 to 15 kOe at room temperature and the saturation magnetization values normalized to the mass of nanoparticles to yield the specific magnetization, M (emu/g) - the weight being based upon the total weight of the samples including the magnetic core and functional ligands. The specific magnetization for MNPs was 27.9 emu/g (28.2 emu/g or 92.2 emu/g of iron oxide; 30.6 wt% of iron oxide determined by TGA) and for MNPs_SCx ranged from 17.6 to 7.1 emu/g, respectively, as shown in Figure 4. No coericivity or remanence was observed by magnetic measurements. Figure 5 shows osmolality and hydrophilicity related aqueous solution dispersion of the magnetic nanoparticles. MNPs_SC10 can be well dispersed in aqueous solution and have an osmolality of 2870 mOsm/kg, which is much higher than that (450 mOsm/kg) for MNPs, indicating the highly hydrophilic nature of the nanoparticles. The hydrophilicity of the nanoparticles prepared with sodium citrate was also confirmed from aqueous dispersions of the samples (Figure 6). Initially, both MNPs and MNPs_SC10 samples could form a good dispersion in water after sonication. After one week, MNPs_SC10 remained as a stable dispersion. But for MNPs, most nanoparticles precipitated out. The different stability of the aqueous dispersions indicates the superior hydrophilicity of MNPs_SC10 than that of MNPs. In addition, it was found that when both aqueous dispersions were sonicated in the presence of hexane, MNPs readily migrated into hexane from water, while MNPs_SC10 remained in the water layer. This result further confirms the high hydrophilicity of the nanoparticles prepared with sodium citrate. Performance of synthesized superparamagnetic nanoparticles as draw solutes in FO

The performance of the MNPs_SC10 as draw solutes in the FO system was carried out on a lab-scale circulating filtration unit, composing a commercially available HTI membrane (Hydration Technologies Inc.) as the FO membrane and Dl/salt water as the feed solution. A crossflow permeation cell was designed with a rectangular channel on either side of the membrane, and the effective membrane surface area (A) is 8 cm ² . The velocities of both draw and feed solutions, which co-currently flowed through the permeation cell channel, were maintained at 6.4 cm/s during the FO testing. The water permeation flux J with units of L/(m ² h) abbreviated as LMH was calculated from the volume change of the feed solution using J = A V/(A A t), where Δ V (L) is the permeation water collected over a predetermined time Δ f (h) in the FO process duration and A has the unit of m ² MNPs_SC10 nanoparticles (2870 mOsm/kg) were tested in FO systems using Dl water (osmolality of 0 mOsm/kg) or salt water (0.6 M NaCI with an osmolality of 1200 mOsm/kg) as the feed-solution at room temperature and regenerated via magnetic separation and ultrafiltration. As displayed in Figure 7, using Dl water as the feed solution, water flux for MNPs_SC10 was 17.3 LMH at the 1st cycle run, and still retained 16.4 LMH at the 5th cycle. MNPs_SC10 provided a water flux of 6.8 and 4.9 LMH at the 1st and 5th cycle, respectively when using salt water as the feed solution. In comparison, under the same condition using Dl water as the feed solution, 0.6 M NaCI aqueous solution as the draw solution in FO only provides a water flux of 13.9 LMH.

Seawater was taken from Sentosa coast having an osmolality of 890 mOsm/kg was also tested using the above-mentioned system and the MNPs_SC10 nanoparticles. The nanoparticles providing an average water flux of 7.6 LMH.

Protein Enrichment

The ultra-small magnetic nanoparticles with high hydrophilicity and biocompatibility may find applications in diverse areas including biomedicine, seawater desalination, and protein enrichment. For protein production and analysis, protein enrichment is critical. Being a type of natural biopolymer consisting of one or more chains of amino acids, proteins are always sensitive to the environment. Thus, the development of an environmentally friendly process for protein enrichment is required. With high hydrophilicity and hence high osmolarity, the MNPs_SC10 nanoparticles were explored for protein enrichment based on an osmotically driven process with the setup shown in Figure 8. The setup contains a permeation cell with a rectangular channel (8.0 cm ^χ 1.0 cm x 0.25 cm) and a water permeable membrane, two pumps and solution containers. Since the average pore diameter of the membrane used here is about 0.5 nm that is significantly smaller than the diameter of both nanoparticles and protein molecules, they could not migrate across the membrane. The MNPs_SC10 solution used here has an osmolality of 2290 mOsm kg ^"1 (more dilute than that used in the test conducted above), much higher than that of the protein solution (<100 mOsm kg ^"1 ). Thus, with a significant difference in osmolality, water in the protein solution can be extracted spontaneously by the nanoparticle dispersion driven by the osmotic pressure difference across the membrane. In this work, hemoglobin, an iron-containing oxygen transport metalloprotein, and albumin, a globular protein to regulate the colloidal osmotic pressure of blood, were used. The protein concentrations were obtained based on the corresponding absorbance intensities at 405 and 208 nm for hemoglobin and albumin, respectively. As shown in Figure 8B and C, for both proteins, their concentrations gradually increased with time. The concentration increased from 0.12 to 0.36 g L ^"1 for hemoglobin after 3.5 h; and from 0.25 to 0.71 g L ^"1 for albumin after 4 h, demonstrating successful and efficient protein enrichment. More importantly, the adsorption peak for both hemoglobin and albumin remained unchanged after the enrichment, suggesting that the conformational structure of the proteins was retained. This observation further confirms that the osmotically driven process is environmentally friendly and the MNPs_SC10 nanoparticles are a kind of green agent for protein enrichment. In addition, after protein enrichment, the MNPs_SC10 can be easily regenerated by magnetic separation together with ultrafiltration for re-use (Figure 9).

Biocompatabliity of synthesized superparamagnetic nanoparticles

To evaluate the biocompatibility of the prepared magnetic nanoparticles, in particular to verify whether any toxicity resulting from the synthetic methodology, MNPs and MNPs_SC10 were investigated in vitro using human cells including MCF7 human breast adenocarcinoma cells and Hela cells as the model. The cell viability was monitored using the 3-(4,5- dimethylthlazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay using MCF7, a colorimetric assay that is popular to monitor cell viability by measuring the cleavage of the MTT via activity of cellular enzymes in living cells. Cell viability value was expressed as percentage of absorbance observed relative to the control cells receiving only culture media. From the cell viability for MNPs and MNPs_SC1 Owith different concentrations ranging from 0 to 1.0 mg ml ^"1 It could be found that cells retained 95% and 88% viability for MNPs_SC10 concentration of 0.3 and 1.0 mg ml ^"1 , respectively, but only 52% and 26% viability for MNPs at the same concentrations (Figure 10), suggesting that MNPs_SC10were much more biocompatible than MNPs. Other Metals as Part of the Ferrite Nanoparticle

The one-pot solid thermal reaction method of Example 1 was also successfully used to synthesize other magnetic nanoparticles including MnFe ₂ 0 ₄ , NiFe ₂ 0 and CoFe ₂ 0 ₄ with TEM images provided in Figure 11 (i.e. Fe(acac) ₃ was mixed with M(acac) ₂ (M= Mn, Ni and Co) and sodium citrate tribasic dihydrate in the appropriate rations via grinding or ball-milling, and was thermally treated with the same procedure of Example 1 ). For example, when preparing MnFe ₂ 0 ₄ , a molar ratio of 1 :2 of the Mn and Fe precursor comounds were used. The TEM images show that all these ferrite nanoparticles have uniform particle size. The average sizes are 4.5, 3.8 and 3 _: 6 nm for MnFe ₂ 0 , NiFe ₂ 0 ₄ and CoFe ₂ 0 , respectively. Clear lattice fringes are revealed by HRTEM images, indicating the high crystallinity of the nanoparticles. Energy dispersive spectroscopy (EDS) line scan results confirm the compositions of the ferrite nanoparticles. The crystal structures of the ferrite nanoparticles were also investigated by XRD with results provided in Figure 12. All samples exhibit inverse spinel structure of metal ferrites. The magnetic properties of the ferrite nanoparticles were investigated using VSM at room temperature. All magnetization curves display a well-defined magnetic behaviour (Figure 13). Example 2: Synthesis and characterization of hydrophobic magnetic nanoparticles

In this example, hydrophobic superparamagnetic nanoparticles are synthesized. Materials used were Iron (III) acetylacetonate (Fe(acac) ₃ , manganese(ll) acetylacetonate, nickel(ll) acetylacetonate, cobalt(lll) acetylacetonate and octadecylamine and hexane. All the chemicals above were used as received. The synthesis steps are the same as that of the hydrophilic magnetic nanoparticles with details as follows.

Fe(acac) ₃ was mixed with octadecylamine with a molar ratio (octadecylamine/ Fe(acac) ₃ ) of 10 via grinding or ball milling to form a uniformly mixed solid powder, which was heated inside an oven under air condition. The heating process was: 1 ) from room temperature to 200°C with a heating rate of 10 °C/min, 2) staying at 200°C for 30 min, 3) from 200°C to 280°C with a heating rate of 2°C/min, 4) staying at 280°C for 60 min) cooling down to room temperature. The synthesis process and the magnetic response of the hydrophobic magnetic nanoparticles were provided in Figure 14.

Again, it is highlighted that the heating process is not limited to the procedure described above and the molar ratio of Fe(acac)3/octadecylamine can be changed. The obtained powder was dissolved in hexane and sonicated for 15 min. Then acetone was added to the hexane solution, resulting in precipitation that was separated via centrifugation. The black was re-dissolved in hexane and re-precipitated by acetone followed by centrifugation. The above washing process was repeated a couple of times to remove most residuals. The final product was redispersed in hexane and for further characterizations. Said compounds are useful in magnet-induced temporary superhydrophobic surfaces.