STRUCTURE FOR CO2 ACTIVATION

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority of U.S. Provisional Patent Application No. 62/666,225 filed May 3, 2018, which is hereby incorporated by reference in its entirety.

BACKGROUND

Field of the Invention

[0002] The invention generally concerns catalysts for the adsorption and/or activation of carbon dioxide (CO2). In particular the catalyst are mesoporous carbon nitrides and are operable under ambient conditions and provide for CO2 adsorption and/or activation.

Description of the Related Art

[0003] It is well known that CO2 emissions are responsible of the global warming effect. One of the strategies to decrease the CO2 emissions into the atmosphere is to use the CO2 as feedstock. For this reason, many researchers tried to activate or capture the CO2 molecule. However, due to the high stability of this molecule, the CO2 activation is extremely challenging and a new kind of catalyst need to be developed. In other hand, a new class of MCN with high surface areas and tunable mesoscale pore diameters has been considered for a large spectrum of potential applications in the fields of catalysis, gas adsorption, and energy conversion due to their unique electronic, optical, and basic properties (Lakhi et ah, Chem. Soc. Rev., 2:2017, DOI: l0.l039/c6cs00532b; Wang et ah, Nat. Mater. 2009, 8:76; Zheng et ah, Energy Environ. Sci., 2012, 5:6717). The synthesis of MCN has been realized via hard-templating approach using mesoporous silica as a sacrificial template. Recently, intensive research has been reported not only to develop various structural and textural properties for high surface areas, different pore sizes, uniform morphology but also to control surface functionalities, nitrogen contents, and band gaps and positions (Talapaneni et ah, ChemSusChem, 2012, 5:700; Jin et ah, Angew. Chem. Int. Ed., 2009, 48:7884; Zhong et al., Sci. Rep., 2015, 5: 12901; Lakhi et ah, RSC Adv., 2015, 5:40183). However, although the reported MCN materials have showed textural features for various catalytic performances and gas adsorption capacities, additional MCNs with high nitrogen contents and small band gaps is still required for improving MCN performance. SUMMARY

[0004] Catalysts and processes have been developed that provide a solution to the economic and energy inefficiency problems associated with processing of carbon dioxide (CO2). In particular, catalyst and processes for the CO2 adsorption and/or activation have been developed that work at lower temperatures as well as lower pressures.

[0005] Certain embodiments are directed to a mesoporous carbon nitride (MCN) material comprising a three-dimensional carbon nitride matrix having a bimodal mesopore distribution. The mesoporous MCN can have a first pore size distribution of 1, 2, 3, 4, 5 nm to 6, 7, 8, 9, 10 nm and a second pore size distribution of greater than 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 nanometer (nm) to 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30 nm. In particular aspects the mesoporous MCN can have a first pore size distribution of 1 nm to 10 nm and a second pore size distribution of greater than 10 nanometer (nm) to 30 nm. The mesoporous MCN material can have a uniform pore size of 2 nm to 5 nm, preferably 3 nm to 4 nm, along the [ 100] direction of the matrix. The term“uniform pore size” refers to population of pores having a narrow standard deviation, for example, the standard deviation of pore size can be less than 5%, or less than 2%, or less than 1% (i.e., 0.01 to 5, 2, or 1%). The mesoporous MCN material can have a carbon to nitrogen ratio of 0.45, 0.5. 0.55 to 0.65,0.7, 0.75, a specific surface area of 250, 260, 270, 280, or 290 m ² /g to 300, 310, 320, 330, 340, or 350 m ² /g, and a total pore volume of 0.25, 0.3, 0.35 cm ³ /g to 0.4, 0.45, 0.5 cm ³ /g. In particular aspects the mesoporous MCN material can have a carbon to nitrogen ratio of 0.5 to 0.7, a specific surface area of 250 m ² /g to 350 m ² /g, and a total pore volume of 0.3 cm ³ /g to 0.5 cm ³ /g. In a more particular aspect the mesoporous MCN material can have a carbon to nitrogen ratio of about 0.67, a surface area of 290 m ² /g to 310 m ² /g, and a total pore volume of about 0.42 cm ³ /g. A mesoporous MCN material described herein can adsorb carbon dioxide (CO2) at 8 mmol/gcat. to 10 mmol/gcat. at 0°C and a pressure of 1 to 5, or about 3 MPa. The mesoporous MCN matrix can be an aminoguanidine or an amino- 1,2, 4-triazole based polymeric matrix. In certain aspects the MCN matrix is (i) an aminoguanidine and urea or formaldehyde based co-polymeric matrix or (ii) an amino- 1,2, 4-triazole and urea or formaldehyde based co-polymeric matrix. The mesoporous MCN material can have a rZ-spacing of 8.5 to 9.5, preferably about 8.7 to about 9.2, or more preferably about 8.9 or about 9.1 and a cell parameter (ao) of 18 to 21 nm, preferably 19.5 nm to 20.8 nm , more preferably 20.5 to 20.7 nm. The matrix can comprise 70 wt.% to 80 wt.% of C-N=C, 15 wt.% to 20 wt.% of C=C groups, 5 wt.% to 8 wt.% C-N-H, based on the total weight of the MCN material. In certain embodiments the mesoporous MCN material is a CO2 activation catalyst.

[0006] Certain embodiments are directed to processes for carbon dioxide (CO2) adsorption. The process can include contacting a mesoporous carbon nitride (MCN) material as described herein with a feed stream comprising CO2, wherein at least a portion of the CO2 is adsorbed by the mesoporous MCN material. In certain aspects 7 mmol/gmat. to 10 mmol/gmat. of CO2 is adsorbed by the mesoporous MCN material at a temperature of 0°C and a pressure of 1 to 5 MPa, preferably 3 MPa. In particular aspects the adsorbed CO2 is activated.

[0007] Certain embodiments are directed to methods of producing a mesoporous carbon nitride (MCN) material as described herein. The methods of producing can include: (a) contacting a calcined KIT-5 silica template with an aqueous solution comprising a MCN precursor material having -NH2 groups to form a mixture; (b) polymerizing the precursor material and forming a MCN polymeric material/KIT-5 composite; (c) carbonizing the MCN polymeric material/KIT-5 composite; and (d) removing the KIT-5 silica template to obtain the mesoporous MCN material and optionally drying the obtained material. The polymerizing step (b) can include: heating the mixture to a first temperature of 90 to H0°C, preferably about l00°C; and increasing the temperature to 150 to l70°C, preferably about l60°C. The carbonizing step (c) can incluse heating the mesoporous MCN material/KIT-5 composite to 400°C to 600°C, preferably about 500°C under an inert gas atmosphere. The MCN-precursor material can have -NH2 groups comprises aminoguanidine or amino- 1,2, 4-triazole, preferably amino- 1,2, 4-triazole. The aqueous mixture can further include urea or formaldehyde. The method can further include producing the calcined KIT-5 silica template, the method comprising: (i) obtaining an aqueous solution comprising, water, a hydrophilic non-ionic polymeric surfactant, and tetraethyl orthosilicate (TEOS); (ii) heating the solution at a temperature of 30°C to 50°C, preferably 35°C to 40°C, (iii) increasing the temperature to l30°C to l80°C, preferably l40°C to l60°C, to form a KIT-5 silica template/polymer composite; and (iv) calcining KIT-5 silica template/polymer composite at 400°C to 800°C, preferably 500°C to 600°C, to form the KIT-5 silica template.

[0008] Cage type mesoporous carbon nitride, MCN nanocage, with bimodal porous structure was successfully prepared from KIT-5 silica as hard template synthesized at l50°C and amino triazole as a single precursor. The MCN nanocage had biomodal mesoporous structure with pore diameters centered at 3.4 nm and 15-20 nm and high surface areas of 300.97 m ² /g with 3D cubic mesoporous structure. In addition, the MCN nanocage prepared using amino triazole had high nitrogen content with a C/N ratio of 0.67, which is lower than theoretical C/N ratio of 0.75. Furthermore, the MCN nanocage showed excellent CO2 uptake capacity of 8.67 mmol/g at the temperature of 0°C and pressure of 30 bar. This MCN material is a bimodal MCN nanocage with highly ordered structure and high nitrogen content produced by carbonization of amino triazloe precursor and KIT-5 silica template.

[0009] Other embodiments of the invention are discussed throughout this application. Any embodiment discussed with respect to one aspect of the invention applies to other aspects of the invention as well and vice versa. Each embodiment described herein is understood to be embodiments of the invention that are applicable to all aspects of the invention. It is contemplated that any embodiment discussed herein can be implemented with respect to any method or composition of the invention, and vice versa. Furthermore, compositions and kits of the invention can be used to achieve methods of the invention.

[0010] The use of the word“a” or“an” when used in conjunction with the term“comprising” in the claims and/or the specification may mean“one,” but it is also consistent with the meaning of“one or more,”“at least one,” and“one or more than one.”

[0011] Throughout this application, the term“about” is used to indicate that a value includes the standard deviation of error for the device or method being employed to determine the value.

[0012] The use of the term“or” in the claims is used to mean“and/or” unless explicitly indicated to refer to alternatives only or the alternatives are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and“and/or.”

[0013] As used in this specification and claim(s), the words“comprising” (and any form of comprising, such as“comprise” and“comprises”),“having” (and any form of having, such as “have” and“has”),“including” (and any form of including, such as“includes” and“include”) or“containing” (and any form of containing, such as“contains” and“contain”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

[0014] In the context of the present invention, at least twenty embodiments are now described. Embodiment 1 is a mesoporous carbon nitride (MCN) material. The material includes a three-dimensional carbon nitride matrix having a bimodal mesopore distribution. Embodiment 2 is the mesoporous MCN material of embodiment 1, having a first pore size distribution of 1 nm to 10 nm and a second pore size distribution of greater than 10 nanometer (nm) to 30 nm. Embodiment 3 is the mesoporous MCN material of any one of embodiments 1 to 2, having a uniform pore size of 2 nm to 5 nm, preferably 3 nm to 4 nm, along the [100] direction of the matrix. Embodiment 4 is the mesoporous MCN material any one of embodiments 1 to 3, having a carbon to nitrogen ratio of 0.5 to 0.7, a specific surface area of 250 m2/g to 350 m2/g, and a total pore volume of 0.3 cm3/g to 0.5 cm3/g. Embodiment 5 is the mesoporous MCN material of embodiment 4, having a carbon to nitrogen ratio of about 0.67, a surface area of 290 m2/g to 310 m2/g, and a total pore volume of about 0.42 cm3/g. Embodiment 6 is the mesoporous MCN material of any one of embodiments 1 to 5, capable of adsorbing carbon dioxide (C02) at 8 mmol/gcat. to 10 mmol/gcat. at 0°C and a pressure of 1 to 5, or about 3 MPa. Embodiment 7 is the mesoporous MCN material of any one of embodiments 1 to 6, wherein the MCN matrix is an aminoguanidine or an amino- 1,2, 4-triazole based polymeric matrix. Embodiment 8 is the mesoporous MCN material of any one of embodiments 1 to 7, wherein the MCN matrix is (i) an aminoguanidine and urea or formaldehyde based co-polymeric matrix or (ii) an amino- 1,2, 4-triazole and urea or formaldehyde based co-polymeric matrix. Embodiment 9 is the mesoporous MCN material of any one of embodiments 1 to 8, wherein the material is a C02 activation catalyst. Embodiment 10 is the mesoporous MCN material of any one of embodiments 1 to 9, wherein the MCN matrix has a d-spacing of 8.5 to 9.5, preferably about 8.7 to about 9.2, or more preferably about 8.9 or about 9.1 and a cell parameter (aO) of 18 to 21 nm, preferably 19.5 nm to 20.8 nm , more preferably 20.5 to 20.7 nm. Embodiment 11 is the mesoporous MCN material of any one of embodiments 1 to 10, wherein the matrix includes 70 wt.% to 80 wt.% of C-N=C, 15 wt.% to 20 wt.% of C=C groups, 5 wt.% to 8 wt.% C-N-H, based on the total weight of the MCN material.

[0015] Embodiment 12 is a process for carbon dioxide (C02) adsorption. This process includes the steps of contacting the mesoporous carbon nitride (MCN) material of any one of embodiments 1 to 11 with a feed stream containing C02, wherein at least a portion of the C02 is adsorbed by the mesoporous MCN material. Embodiment 13 is the process of embodiment 12, wherein 7 mmol/gmat. to 10 mmol/gmat. of C02 is adsorbed by the mesoporous MCN material at a temperature of 0°C and a pressure of 1 to 5 MPa, preferably 3 MPa. Embodiment 14 is the process of any one of embodiments 12 to 13, wherein the adsorbed C02 is activated.

[0016] Embodiment 15 is a method of producing the mesoporous carbon nitride (MCN) material of any one of embodiments 1 to 11. This method includes the steps of (a) contacting a calcined KIT-5 silica template with an aqueous solution comprising a MCN precursor material having -NH2 groups to form a mixture; (b) polymerizing the precursor material and forming a MCN polymeric material/KIT-5 composite; (c) carbonizing the MCN polymeric material/KIT-5 composite; and (d) removing the KIT-5 silica template to obtain the mesoporous MCN material and optionally drying the obtained material.

[0017] Embodiment 16 is the method of embodiment 15, wherein polymerizing step (b) includes heating the mixture to a first temperature of 90 to 1 l0°C, preferably about l00°C; and increasing the temperature to 150 to l70°C, preferably about l60°C. Embodiment 17 is the method of embodiment 16, wherein carbonizing step (c) includes heating the mesoporous MCN material/KIT-5 composite to 400°C to 600°C, preferably about 500°C under an inert gas atmosphere. Embodiment 18 is the method of any one of embodiments 15 to 17, wherein the MCN-precursor material having -NH2 groups comprises aminoguanidine or amino- 1, 2,4- triazole, preferably amino- 1,2, 4-triazole. Embodiment 19 is the method of any one of embodiments 15 to 18, wherein the aqueous mixture further comprises urea or formaldehyde. Embodiment 20 is the method of any one of embodiments 15 to 18, further comprising producing the calcined KIT-5 silica template, the method the steps of: (i) obtaining an aqueous solution containing, water, a hydrophilic non-ionic polymeric surfactant, and tetraethyl orthosilicate (TEOS); (ii) heating the solution at a temperature of 30°C to 50°C, preferably 35°C to 40°C, (iii) increasing the temperature to l30°C to l80°C, preferably l40°C to l60°C, to form a KIT-5 silica template/polymer composite; and (iv) calcining KIT-5 silica template/polymer composite at 400°C to 800°C, preferably 500°C to 600°C, to form the KIT- 5 silica template.

[0018] Other obj ects, features and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating specific embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

DESCRIPTION OF THE DRAWINGS

[0019] The following drawings form part of the present specification and are included to further demonstrate certain aspects of the present invention. The invention may be better understood by reference to one or more of these drawings in combination with the detailed description of the specification embodiments presented herein.

[0020] FIG. 1. Representation of the replica approach. [0021] FIGs. 2A-B. (A) Low angle and (B) high angle powder XRD patterns of the MCN nanocage.

[0022] FIGs. 3A-B. (A) N2 adsorption-desorption isotherms and (B) pore size distribution of the MCN nanocage.

[0023] FIGs. 4A-C. (A) SEM image, (B) high-resolution TEM image and (C) EELS spectrum of the MCN nanocage.

[0024] FIGs. 5A-B. (A) XPS survey and (B) high-resolution Cls and Nls spectra of the MCN nanocage.

[0025] FIG. 6. FTIR-ATR spectrum of the MCN nanocage.

[0026] FIGs. 7A-B. .(A) C K-edge and (B) N K-edge NEXAFS spectra of the (a) MCN nanocage and (b) non-porous g-C3N ₄ prepared by dicyandiamide at 550°C.

[0027] FIG. 8. CO2 adsorption isotherm of the MCN nanocage at 0°C and pressure up to 30 bar.

DESCRIPTION

[0028] The following discussion is directed to various embodiments of the invention. The term“invention” is not intended to refer to any particular embodiment or otherwise limit the scope of the disclosure. Although one or more of these embodiments may be preferred, the embodiments disclosed should not be interpreted, or otherwise used, as limiting the scope of the disclosure, including the claims. In addition, one skilled in the art will understand that the following description has broad application, and the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to intimate that the scope of the disclosure, including the claims, is limited to that embodiment.

[0029] Since mesoporous carbon nitrides (MCN) were discovered in 2005, a new class of MCN with 2- or 3 -dimensional structure and large pore diameters has been reported with potential applications in the fields of catalysis, gas adsorption, and energy conversion due to their unique textural and surface features, optical and electronic properties (Lakhi et ak, Chem. Soc. Rev., 2016 (in press); Wang et ak, Nat. Mater. 2009, 8:76; Zheng et ak, Energy Environ. Sci., 2012, 5:6717). In general, MCN materials with different structures and pore diameters can be synthesized through various mesoporous silica as a sacrificial template. More recently, 3- dimensional structured MCNs with large pore size, high surface area, and uniform morphology have been reported (Talapaneni et ak, ChemSusChem, 2012, 5:700; Jin et ak, Angew. Chem. Int. Ed., 2009, 48:7884; Zhong et al., Sci. Rep., 2015, 5: 12901; Lakhi et al., RSC Adv., 2015, 5:40183; Lakhi et al., Catal. Today, 2015, 243:209). However, although the reported MCN materials have showed unique textural parameters for various catalytic performances and gas adsorption capacities, novel MCN with new structure and high nitrogen contents is still required for improving their performance.

[0030] An MCN nanocage has been prepared with ordred high surface area through a KIT- 5 silica template by using triazole as a high nitrogen CN precursor. Furthermore, the inventors investigated CO2 uptake adsorption capacity of the preapred MCN nanocage for application in CO2 capture and photocatalytic reduction of the CO2 molecules into useful chemicals.

[0031] Preliminary periodic DFT calculations suggest that defective carbon nitride can chemisorb and activate CO2 at room and/or mild temperature. In particular, the activation of CO2 to a bent geometry seems to be feasible in presence of high concentration of primary and secondary amino groups (NH2 and NH) because of the formation of multiple H-bonds between the molecule and the carbon nitride framework. The computational results suggest also a relatively easy CO2 desorption process due to moderate binding energy. The identified defect- engineered carbon nitride material seems to be promising for CO2 capture as it represents a compromise between the other sorbent materials associated to physical or chemical adsorption mechanism. Based on the computational conclusion, a strategy has been elaborated in order to enhance the number of -NH2 species and their accessibility. In order to enhance the -NH2 species, different CN precursor like aminoguanidine or amino 1,2, 4-triazole can be used as monomers. The addition of a co-monomer like urea or formaldehyde can also modify the structure of the polymer and enhance the target species. Because polymerization occur between -NH/-NH2 species, and -N/-NH species for the aminoguanidine and the amino 1,2,4 triazole respectively, the number of -NH2 species should significantly be enhanced by using these monomers.

[0032] Typically, mesoporous materials, like SBA-15, KIT-6, and FDU-12 are used as hard templates. The pore volume of those materials is filled by the CN precursors. Then, a thermal treatment is applied for polymerization. After this step, the silica template is removed by an appropriate treatment. The morphology of the final material is the replica of the silica mesoporosity. By applying this approach, it should be possible to facilitate the accessibility of the -NH2 species and enhance the CO2 reactivity. A. MCN Materials

[0033] The structural information on the MCN nanocage was investigated by powder XRD measurements. As shown in FIG. 2A, MCN nanocage show intense (111) and broader (200) diffraction pakes at low angle region, indicating highly ordered structure with the symmetry of the cubic space group of Fm3m. The cubic cell parameter ao was determined to be a 20.67 calculated using the equation of ao = chn^3. It reveals that the prepared MCN nanocage is highly ordered three-dimensional cage type mesostructure. The turbostratic ordering of graphitic CN wall structure is also observed from the diffraction peak at 27.3° in the high angle XRD pattern (FIG. 2B).

[0034] Textural properties of the MCN nanocage were confirmed by N2 adsorption- desorption analysis. As shown in FIG. 3 A, the N2 isotherms of MCN nanocage show typical type IV according to the IUPAC classification with Hl hysteresis loops. A high BET surface area of 300.97 m ² /g and a high total pore volume of 0.42 cm ³ /g was achieved. The bimodal porosity, resulting from the removal of F127 and silica from the walls, exhibits two maximum pore diameters at 3.4 nm and 17.4 nm, respectively (FIG. 3B). It is expected that this biomodal textural properties of MCN nanocage could reduce the diffusion resistance for the facile mass transportation of CO2 capture and reduction.

[0035] The prepared MCN nanocage exhibit spherical morphology with a single particle size of ca. 50-100 nm (FIG 4A). FIG. 4B shows the high-resolution TEM image of the MCN nanocage. The uniform pore size of the order of 3-4 nm along the [100] direction was clearly observed. A regular arrangement of bright spots also reveals that the mesoporous material is of the 3D cage type symmetry.

[0036] Furthermore, electron energy loss spectroscopy (EELS) and X-ray photoelectron spectroscopy (XPS) analyses were also carried out in order to understand the bonding character of C and N network in the wall structure of MCN nanocage. According to the EEL spectrum of the MCN nanocage (FIG. 4C), the C-K edges and N-K edges were observed. The peaks at 280.0 eV and 378.0 eV are attributed to the ls-p* electron transitions, indicating that sp ² graphitic carbon is bonded to nitrogen in the CN wall structure. The signals located at 286.0 eV and 386 eV can be assigned to the ls-s* electron transitions on sp ³ carbon species.

[0037] As shown in FIG. 5 and Table 2, XPS measurements reveal further details about molecular structure. The C/N ratio calculated from the survey spectra is found to be ca. 0.67, which is slightly lower than the stoichiometric C/N ratio of 0.75 for the typical non-porous carbon nitrides with an ideal composition of C3N4. The chemical composition of this new MCN nanocage with high nitrogen content is determined to be C3N4.51 based on the atomic weight percentages from the XPS data. The Cls spectra of both materials show mainly one carbon species with a binding energy of 287.7 eV, which is corresponding to the C-N=C coordination. According to the literature (Thomas et al., ./. Mater. Chem ., 2008, 18, 4893), the Nls spectra can be deconvoluted as four different binding energies: main signal of C-N=C group at 398.3 eV, tertiary nitrogen of N-3C group at 400.1 eV, amino functions carrying hydrogen (C-NH2 group) at 401.4 eV, and N=N bonding configuration at 403.5 eV. It is found that the area percentages with respect to C-N=C and C-NH2 groups are more than 74 % and 5 %, respectively.

[0038] FTIR-ATR spectrum shows symmetric and anti-phase N=N vibrations (740-790 cm ') as well as C=N (1321 cm ¹ ) and N=N (1421 cm ¹ ) stretching bonds (FIG. 6). Interestingly, the C-NFh scissoring band was clearly seen at 1550 cm ¹ . Another band at 1574 cm ¹ was attributed to typical graphite-like C-N bond framework.

[0039] Furthermore, synchrotron-based near-edge X-ray absorption fine structure (NEXAFS) was investigated to understand the chemical bonding nature of MCN nanocage by comparing the non-porous graphitic carbon nitride (g-C3N4) prepared by dicyandiamide at 550°C. In the carbon K-edge NEXAFS spectra (FIG. 6A), MCN nanocage clearly show characteristic resonances of graphitic carbon nitride including 7t*c=c (Cl) at 285.6 eV, 7I*C-N-C (C2) at 288.0 eV, o*c-c (C3) at around 294 eV, and structural defects. In nitrogen K-edge region (FIG. 6B), the MCN nanocage also show two typical p* resonances at 399.4 and 402.3 eV, which is corresponding to aromatic C-N-C coordination in one tri-s-triazine heteroring (Nl) and N-3C bridging among three tri-s-triazine moieties (N2), respectively (Zheng et al, Nat. Commun. 2014, 5:3783, doi: l0. l038/ncomms4783). As compared with non-porous g- C3N4, the prepared MCN nanocage was characterized to be a mesoporous carbon nitride material with graphitic bonding structure.

[0040] The CO2 adsorption capacity was evaluated at high pressure up to 30 bar and temperatures of 0°C. As well reported in the literature (Lakhi et al., RSC Adv., 2015, 5:40183; Lakhi et al., Catal. Today, 2015, 243 :209), the CO2 molecules having Lewis acidic property is easily captured inside nanopore channel of the Lewis basic MCN materials through acid-base neutralization reaction. As shown in FIG. 6 and Table 1, the CO2 adsorption capacity of the MCN nanocage achieved up to 8.67 mmol/g. This result is mainly attributed to both high content of nitrogen including-NH and -NH ₂ groups and well-developed cage-type mesoporous structure.

Table 1. Textural parameters, C/N ratio, and CO2 adsorption of the MCN nanocage.

MCN

20.68 9.01 300.97 3.4/17.4 0.42 0.67 8.67

nanocage _

a The cell parameter calculated from low-angle XRD patterns (Fig. 1) using < _¾ > = <2ii 3.

b Pore diameters derived from the adsorption branches of the isotherms by using the BJH method. ^c Total pore volumes estimated from the adsorbed amount at a relative pressure of p/po = 0.99.

d Total pore volumes estimated from the adsorbed amount at a relative pressure of p/po = 0.99.

e CO2 adsorption measured at 0°C and 30 bar using dry CO2 gas.

Table 2. XPS spectra deconvolution of the MCN nanocage.

[0041] The inventors have demonstrated for the first time the preparation of bimodal MCN nanocage material with highly ordered and 3D cubic-structure by using KIT-5 silica as a hard template and 3 -amino- 1,2, 4-triazole as a CN precursor. The BET surface area is 300.97 m ² /g and total pore volume is 0.42 cm ³ /g. Intesrtingly, the biomodal mesopore sizes of MCN nanocage were centered at 3.4 nm and 15-20 nm. From the XPS data, the stoichiometric C/N ratio was turn out to be 0.67 with high nitrogen content. Based on the excellent CO2 capture capacity (8.67 mmol/g), the presentr bimodal MCN nanocage material can be used as superior nitrogen-rich adsorbents for CO2 capture and conversion.

B. Process for Producing MCN materials

[0042] A KIT-5 template can be produced by first obtaining a polymerization solution including a triblock copolymer dispersed in an aqueous hydrogen chloride solution with tetraethyl orthosilicate (TEOS) to form a polymerization mixture. In a second step the polymerization mixture can be reacted by heating at a predetermined synthesis temperature to form a KIT-5 template, wherein the predetermined temperature determines the pore size of the KIT-5 template. The polymerization mixture can be heated at a synthesis temperature of about 100 to 200°C, or any value or range there between ( e.g ., 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 143, 142, 143, 144, 145,

146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 163, 164,

165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175, 176, 177, 178, 179, 180, 181, 182, 183,

184, 185, 186, 187, 188, 189, 190, 191, 192, 193, 194, 195, 196, 197, 198, or l99°C). For the general formula KIT-5-X, X represents the incubation temperature. For example, in certain aspects the polymerization mixture can be heated at a synthesis temperature of about 100, 130, or l50°C to yield corresponding KIT-5 templates denoted KIT-5-100, KIT-5-130, and KEG-5- 150, respectively. Preferably, the incubation temperature is l50°C. The formed KIT-5 template can then be dried at 90°C to 1 l0°C, preferably l00°C. In a final step, the dried KIT- 5 template can be ethanol washed and in certain aspects not subjected to calcination temperatures.

[0043] In particular aspects, two and a half grams of Pluronic F127 is dissolved in 120 g of deionized water and 5.25 g of concentric HC1 solution. Twelve grams of tetraethoxy silane (TEOS) is quickly added into the mixture and stirred at 40°C for 24 hr. The solution is then heated at 150°C for 24 hr for hydrothermal reaction. The resulting white solid product is filtered and then calcined at 550°C to remove the surfactant.

[0044] Preparation ofMCN nanocage using 3-amino-1, 2, 4-triazole. Mesoporous carbon nitride material can be formed by nanocasting using a template as prepared above, e.g. , KIT-5 template. Nanocasting is a technique used to form a periodic mesoporous framework using a hard template to produce a negative replica of the hard template structure. A molecular precursor can be infiltrated into the pores of the hard template and subsequently polymerized within the pores of the hard template. Then the hard template can be removed by a suitable method. This nanocasting route is advantageous because no cooperative assembly processes between the template and the precursors are required. A hard template can be a mesoporous silica. In one aspect, the mesoporous silica can be KIT-5, MCM-41, SBA-15, TUD-l, HMM- 33, etc ., or derivatives thereof prepared in similar manners from tetraethyl orthosilicate (TEOS) or (3-mercaptopropyl) trimethoxysilane (MPTMS). In certain aspect, the mesoporous silica is a 3D-cubic Fm3m silica, such as KIT-5 which contains interpenetrating cylindrical pore systems.

[0045] In a typical synthesis, 3.0 g of 3 -amino- 1,2, 4-triazole (3 AT) dissolved in deionized water (2.0 g) was added to 1 g of KIT-5-150 silica template. The mixture was homogeneously blended and then placed in a programmed oven at l00°C for 6 hr and further heated at l60°C for another 6 hr. The resulting composite was heated up to 500°C with a ramping rate of 3°C / min and kept at this temperature for 5 hr under constant nitrogen flow for carbonization process. The KIT-5- 150 template was then thoroughly removed using a HF solution (5 wt%).

C. Carbon Dioxide Capture

[0046] Carbon dioxide capture techniques can be divided into post-combustion capture, pre- combustion capture, and oxy-fuel capture according to stages at which carbon dioxide is captured. The carbon dioxide capture techniques can also be divided into membrane separation, liquid phase separation, and solid phase separation techniques according to the principles of carbon dioxide capture. The membrane separation techniques use separation membranes to concentrate carbon dioxide, the liquid phase separation techniques use liquid absorbents such as amines or aqueous ammonia, and the solid phase separation techniques use solid phase adsorbents such as MCN materials described herein.

[0047] Embodiments of the current invention employ MCN materials described herein as absorbents for CO2 and/or catalyst for conversion of CO2 to other organic compounds. In certain embodiments, the capture of carbon dioxide and the reduction of the captured carbon dioxide to produce organic products may be preferably achieved in a device incorporating the MCN materials described herein.

[0048] A device, apparatus, or system can incorporate the described material, and can be used for capture of carbon dioxide and conversion of the captured carbon dioxide to organic products. The system can include a feed source supplying a CO2 containing source, reactor containing an MCN material as described herein, and a product outlet for collection and processing of reaction products. The reactor can capture carbon dioxide (CO2) and reduce carbon dioxide into products or product intermediates. The MCN material in the reactor can capture at least a portion of the introduced carbon dioxide where the CO2 can be reduced producing a product mixture, where the product mixture includes organic products.

[0049] The carbon dioxide can be obtained from any source, such as an exhaust stream from fossil-fuel burning power or industrial plants, from geothermal or natural gas wells or the atmosphere itself.