WO2019021157A1

WO2019021157A1 - Carbon nitride materials for co2 adsorption

Info

Publication number: WO2019021157A1
Application number: PCT/IB2018/055470
Authority: WO
Inventors: In Young Kim; Jessica SCARANTO; Khalid Albahily; Ugo RAVON; Ajayan Vinu
Original assignee: Sabic Global Technologies B.V.
Priority date: 2017-07-24
Filing date: 2018-07-23
Publication date: 2019-01-31

Abstract

CO2 adsorbent materials that include two-dimensional (2-D) and/or three-dimensional (3-D) nitrogen rich material compositions capable of adsorbing CO2 are described. The structures can include a tetrazole moiety. The CO2 adsorbent materials can have an atomic nitrogen to atomic carbon (N:C) ratio of 1.35 to 2.35. Methods of making and use of the CO2 adsorbent materials are also described.

Description

CARBON NITRIDE MATERIALS FOR C0₂ ADSORPTION

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority of U.S. Provisional Patent Application No. 62/536,284 filed July 24, 2017, and U.S. Provisional Patent Application No. 62/536,294 filed July 24, 2017. The entire contents of each of the above-referenced disclosures are specifically incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0002] The invention generally concerns a nitrogen rich material for adsorption of CO2. In particular, the nitrogen rich material includes a two dimensional (2-D) carbon nitride structure having an atomic nitrogen to atomic carbon (N:C) ratio of 1.36:2.28 or a 3-D carbon nitride structure having an atomic nitrogen to atomic carbon (N:C) ratio of 1.4:2.35 or both.

2. Description of Related Art

[0003] The emission of CO2 through the burning of fossil fuels and industrial activities is one of the maj or contributors to global warming. An effective way to reduce CO2 emission is to adsorb CO2 followed by its conversion to hydrocarbon fuels. Highly porous materials such as zeolites, metal-organic frameworks, and activated carbons have attracted great interest for CO2 adsorption. However, production of metal-based materials such as zeolites and metal organic frameworks are associated with high cost. Although the cost of activated carbons is low, pure carbons do not exhibit any catalytic activities for CO2 conversion. Interestingly, many researchers have reported that incorporation of nitrogen into carbon can greatly improve the catalytic activity of the resultant catalyst due to enhanced π bonding in the framework. In one instance, graphitic carbon nitride (g-C₃N₄), which has higher nitrogen content as compared to nitrogen-doped carbon, shows good activities for CO2 adsorption as well as CO2 conversion. However, it is still challenging to improve the activities of carbon nitrides for CO2 adsorption and conversion since reported studies on carbon nitride have a restricted chemical composition of C3N4.

[0004] Mesoporous carbon nitrides (MCN-1 and MCN-7) have been synthesized and used for CO2 capture. By way of example, Lakhi et al., (RSC Adv., 2015, 5:40183; Catal. Today, 2015, 243 :209; and Chem. Soc. Rev., 2017, 46:72-101) describes mesoporous carbon nitrides made from ethylenediamine and carbon tetrachloride precursors. These carbon nitrides exhibited a CO2 adsorption ability of 10.5-16.5 mmol/g at 30 bar and 273 K. In other attempts to increase the photocatalytic activity of graphitic(g)-C3N4 towards CO2, composites of graphene and g-C₃N₄ have been made. For example, Ong et al. (Chem Commun., 2015, 51 :858) describes a sandwich- like g-C3N4-graphene composite system, where CO2 molecules could adsorb onto the graphene surface with π-π interactions, which resulted in the destabilization and activation of CO2 molecules, thus leading to the photocatalytic reduction of CO2 on the graphene sheets.

[0005] There remains an opportunity for improved CO2 materials particularly those that adsorb CO2 and can be used in chemical reactions that involve CO2 as a reagent.

SUMMARY OF THE INVENTION

[0006] A discovery has been made that address some of the problems associated with adsorption of CO2 by carbon nitride (CN) materials. The solution is premised on a 2-D and/or 3- D nitrogen rich materials that have an atomic nitrogen to carbon (N:C) ratio between 1.36 and 2.28 or 1.4 and 2.35, respectively. The CN material can include a tetrazole moiety and/or an amino-tetrazole moiety. Without wishing to be bound by theory, it is believed that the use of the carbon nitride materials of the current invention results in 2-D and/or 3-D carbon nitride materials having adsorption capacity and can be used in chemical processes as a source of CO and/or CO2. Notably, the adsorption can be done in the absence of graphitic carbon nitride and/or without making composite materials.

[0007] In some aspects of the invention, 2-D and 3-D nitrogen rich carbon nitride materials are described. The 3-D nitrogen rich CN materials can include a three-dimensional carbon nitride structure having an atomic N:C ratio of 1.4 to 2.35 or any range or value there between (e.g., 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, or 2.35). The 2-D nitrogen rich CN materials can include a two-dimensional carbon nitride structure having an atomic N:C ratio of 1.36 to 2.28 (e.g., 1.36, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, or 2.28). The 2-D and/or 3-D carbon nitride structure can include one or more tetrazole moieties and/or one or more substituted tetrazole moieties. In certain aspects, the tetrazole moiety is derived from an amino-tetrazole compound (e.g., 5-amino-lH- tetrazole, 1,5-diamino-lH-tetrazole, l,5-(aminomethyl)tetrazole, or l-(3-aminophenyl)tetrazole, or combinations thereof). The 3-D carbon nitride materials of the present invention can be porous or non-porous. A porous 3-D carbon nitride material of the present invention can have an average pore diameter of 2 nm to 20 nm, including all ranges and values there between. In certain aspects, the average pore diameter is 3 nm to 12 nm. A 2-D carbon nitride material of the present invention can have an average pore diameter of 2 nm to 20 nm, including all ranges and values there between. In certain aspects, the average pore diameter is 3 nm to 6.5 nm. In certain aspects, the material can have a surface area of 50 to 500 m²/g. In certain aspects, the surface area of the CN material is 200 m²/g to 310 m²/g. In certain aspects, the carbon nitride structure can include one or more functional groups (e.g., an amino group). 2D carbon nitride materials of the present invention have their primary pores interconnected with the micropores, thus forming a 2D porous structure instead of ID structure. Notably, the 2D carbon materials of the present invention 2D p6mm symmetry as determined using X-ray diffraction techniques owing to the unique porous structure. The 2-D material can have a rod type morphology. In certain aspects, the carbon nitride structure can include one or more functional groups (e.g., an amino group). In particular aspects the material has a band gap of 2.5 to 3.0 eV, preferably 2.75 to 2.85 eV.

[0008] In another aspect of the present invention, methods of synthesizing the 2-D and/or 3-D carbon nitride material of the present invention are described. A method can include (a) contacting a 2-D or 3-D hard template with an aqueous amino tetrazole solution forming a templated reaction mixture; (b) heating the templated reaction mixture to a temperature between 40 to 200 °C to forma CN/template composite; (d) heating composite at a temperature of 250 °C to 400 °C to form a carbon nitride/template complex; and (e) removing the template forming a 2-D or 3-D carbon nitride material of the present invention. Step (b) heating can include (i) heating the templated reaction mixture to a temperature between 40 °C to 120 °C, preferably between 80 °C and 120 °C to form a first heated reaction mixture, (ii) optionally cooling the first heated reaction mixture, and (iii) heating the reaction mixture to a temperature of 130 °C and 200 °C, preferably 140 °C to 180 °C. Step (c) heating can include heating the CN/template composite in an inert gaseous atmosphere (e.g., a nitrogen, helium or argon atmosphere). In certain aspects, the method can further include bringing the composite to temperature using a ramping rate of 1, 2, 3, to 4 °C/min, preferably 3 °C/min. In certain aspects, the amino tetrazole can be 5-amino-lH-tetrazole, 1,5- diamino-lH-tetrazole, l,5-(aminomethyl)tetrazole, or l-(3-aminophenyl)tetrazole or combinations thereof. The template can be a silica template. The 2-D template can be a mesoporous silica template. The silica template can be a calcined silica template or an ethanol washed silica template. In certain aspects, the 2-D template can be SBA-15, or MCM41 template. In a further aspect, the 2-D template can be removed from the 2-D carbon nitride material/template complex by contacting the 2-D carbon nitride material/template complex with hydrogen fluoride. In certain aspects, the 3-D silica template is a porous silica template. In certain aspects, the 3-D silica template can be KIT-6, KIT-5, SBA-15, or FDU-12 template. The 2-D and/or 3-D silica templates can be a calcined silica template or an ethanol washed silica template. In a further aspect, the template can be removed by contacting the carbon nitride material/template complex with hydrogen fluoride.

[0009] In another embodiment of the present invention, processes to capture CO2 are described. A CO2 capture process can include contacting the 2-D CN material or the present invention, the 3-D CN material of the present invention or both with a CO2 containing feed source and adsorbing CO2 in or on the carbon nitride structure. In certain aspects, the adsorbed CC /carbon nitride material can be used in chemical processes as a source of CO and/or CO2. Non-limiting examples of chemical processes include epoxidations, carboxylation, carbonate reactions and the like.

[0010] In an aspect of the present invention 20 embodiments are described. Embodiment 1 is a CO2 adsorbent carbon nitride (CN) material comprising a two dimensional (2-D) carbon nitride structure having an atomic nitrogen to atomic carbon (N:C) ratio of 1.36: 1 to 2.28: 1 or a 3-D carbon nitride structure having an atomic nitrogen to atomic carbon (N:C) ratio of 1.4: 1 to 2.35: 1 or both. Embodiment 2 is the material of embodiment 1, wherein the 2-D, 3-D, or both carbon nitride structures comprise a tetrazole moiety and/or an amino tetrazole moiety. Embodiment 3 is the material of any one of embodiments 1 to 2, wherein the tetrazole moiety or amino tetrazole moiety are derived from amino tetrazole precursor of: 5-amino-lH-tetrazole; 1,5-diamino-lH- tetrazole; l,5-(aminomethyl)tetrazole; or l-(3-aminophenyl)tetrazole, or mixtures thereof. Embodiment 4 is the material of any one of embodiments 1 to 3, wherein the 2-D carbon nitride material is has a nanorod morphology. Embodiment 5 is the material of embodiment 4, wherein the material has an average pore diameter of 2 to 20 nm, preferably 3 to 12 nm. Embodiment 6 is the material of any one of embodiments 1 to 5, wherein the carbon nitride material has surface area of 50 to 500 m²/g, preferably 200 to 310 m²/g. Embodiment 7 is the material of embodiment 1, wherein the 3-D carbon nitride material is porous. Embodiment 8 is the material of embodiment 1, wherein the 3-D carbon nitride material is non-porous. Embodiment 9 is the material of any one of embodiments 1 to 8, wherein the 2-D, 3-D, or both carbon nitride structure comprises functional groups. Embodiment 10 is the material of embodiment 9, wherein the functional groups are amino groups.

[0011] Embodiment 11 is a method of synthesizing the 2-D or 3-D carbon nitride (CN)material of any one of embodiments 1 to 10, the method comprising: (a) contacting a 2-D or 3-D template with an aqueous amino tetrazole solution forming a templated reaction mixture; (b) heating the templated reaction mixture to a temperature between 40 and 200 °C to form a CN/template composite; (c) heating the CN/template composite to a temperature of 250 to 400 °C, forming a 2-D or 3-D carbon nitride material/template complex; and (d) removing the template, forming a 2-D or 3-D carbon nitride material. Embodiment 12 is the method of embodiment 11, wherein the step (b) heating comprises: (i) heating the templated reaction mixture to a temperature between 40 °C to 200 °C, preferably between 80 °C and 120 °C to form a first heated reaction mixture; (ii) optionally cooling the first heated reaction mixture; and (iii) heating the reaction mixture to a temperature of 40 °C and 200 °C, preferably 140 °C to 180 °C to form a carbon nitride material/template complex; and the step (c) heating is performed in an inert atmosphere, preferably, a nitrogen atmosphere. Embodiment 13 is the method of any one of embodiments 11 to 12, wherein the amino tetrazole is 5-amino-lH-tetrazole, 1,5-diamino-lH-tetrazole, 1,5- (aminomethyl)tetrazole, or l-(3-aminophenyl)tetrazole, or combinations thereof. Embodiment 14 is the method of any one of embodiments 11 to 13, wherein the template is a silica template, preferably a porous silica template. Embodiment 15 is the method of embodiment 14, wherein the silica template is a KIT-6, a KIT-5, a SBA-15, or a FDU-12 template. Embodiment 16 is the method of any one of embodiments 11 to 13, wherein the 2-D template is a mesoporous silica template, preferably a MCM41 template. Embodiment 17 is the method of any one of embodiments 14 or 16, wherein the silica template is a calcined silica template or an ethanol washed silica template. Embodiment 18 is the method of any one of embodiments 11 to 17, wherein step (d) removing comprises contacting the hard template/tetrazole-based carbon nitride product with hydrogen fluoride or an alcohol solvent, preferably ethanol.

[0012] Embodiment 19 is a CO2 capture process comprising contacting the CO2 adsorbent carbon nitride material any one of embodiments 1 to 10 with a CO2 containing feed source and adsorbing CO2 in or on the carbon nitride structure. Embodiment 20 is the process of embodiment 19, further comprising providing the CO2 adsorbed carbon nitride material to a chemical process

[0013] 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 of the invention can be used to achieve methods of the invention.

[0014] The following includes definitions of various terms and phrases used throughout this specification. [0015] The phrase "nitrogen rich" refers to carbon nitrides having more nitrogen atoms than graphitic carbon nitrides having the general formula of C3N4.

[0016] The use of the words "a" or "an" when used in conjunction with any of the terms "comprising," "including," "containing," or "having" in the claims, 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."

[0017] The terms "about" or "approximately" are defined as being close to as understood by one of ordinary skill in the art. In one non-limiting embodiment, the terms are defined to be within 10%, preferably within 5%, more preferably within 1%, and most preferably within 0.5%. [0018] The term "substantially" and its variations are defined to include ranges within 10%, within 5%, within 1%, or within 0.5%.

[0019] The terms "inhibiting" or "reducing" or "preventing" or "avoiding" or any variation of these terms, when used in the claims and/or the specification includes any measurable decrease or complete inhibition to achieve a desired result.

[0020] The term "effective," as that term is used in the specification and/or claims, means adequate to accomplish a desired, expected, or intended result.

[0021] 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.

[0022] The 2-D and/or 3-D nitrogen rich materials of the present invention can "comprise," "consist essentially of," or "consist of particular ingredients, components, compositions, etc. disclosed throughout the specification. With respect to the transitional phase "consisting essentially of," in one non-limiting aspect, a basic and novel characteristic of the 2-D and 3-D nitrogen rich materials of the present invention are their abilities to adsorb CO2.

[0023] Other objects, 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.

BRIEF DESCRIPTION OF THE DRAWINGS [0024] 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.

[0025] FIG. 1 shows reaction schematics of prior art to make carbon nitride materials and a schematic of amino-tetrazoles used to make the CN materials of the present invention.

[0026] FIG. 2A is a schematic of a representation of method to produce the 2-D nitrogen rich materials of the present invention. [0027] FIG. 2B is a schematic of a representation of method to produce the 3-D nitrogen rich materials of the present invention.

[0028] FIG. 3 shows X-ray diffraction patterns (XRD) patterns of 3-D nitrogen based materials of the present invention made from a calcined templating agent at (left) low angle and (right) high angle regions.

[0029] FIG. 4 shows XRD patterns of 3-D nitrogen based materials of the present invention made from an ethanol washed templating agent at (left) low angle and (right) high angle regions.

[0030] FIG. 5 shows FTIR spectra of 3-D nitrogen based materials of the present invention with (left spectra) and without an ethanol wash (right specta) and of 5-amino-lH-tetrazole precursor material.

[0031] FIG. 6A-B shows X-ray photon spectroscopy (XPS) survey Cls and Nls spectra of 3- D nitrogen based materials of the present invention with and without a ethanol wash.

[0032] FIG. 7 shows near-edge X-ray Absroption fine structrure ( EXAFS) spectra for (left) C and (right) N K-edge 3-D nitrogen based materials of the present invention with and without a ethanol wash (a-f), bulk (non-porous) amino tetrazole-based carbon nitride (g) and bulk g-C₃N₄ (h).

[0033] FIG. 8 shows scanning electron microscopy (SEM) images of 3-D nitrogen based materials of the present invention with and without a ethanol wash.

[0034] FIG. 9 shows a transmission electron microscopy (TEM) image of 3-D nitrogen based materials of the present invention made using a KIT6-150 template without an ethanol wash.

[0035] FIG. 10 shows UV-Vis spectra of 3-D nitrogen based materials of the present invention made from KIT6-150 template without or with an ethanol wash.

[0036] FIG. 11 shows nitrogen (N₂) absorption-desorption isotherms of 3-D nitrogen based materials of the present invention with and without a ethanol wash. [0037] FIGS. 12A and 12B show CO2 adsoprtion isotherms of 2-D and 3D CN materials of the present invention. FIG. 12A shows CO2 adsorption isotherms of 2-D nitrogen based materials of hte present invention using a SBA15 templated (calcined at 130 °C (bottom curve), 150 °C (middle curve) and 180 °C (top curve)) tetrazole based materials at 0 °C and (right) comparision of CO2 adsorption isotherms of SBA15 calcined at 150 °C at 0 °C (diamonds) and 10 °C (squares). FIG. 12 B shows (Left) CO2 adsorption isotherms of 3-D nitrogen based materials of the present invention using a KIT6-180 template (bottom curve, squares), a KIT6-150 template (circles), and a KIT6-130 template (hexagons) at 0 °C, and (right) comparision of CO2 adsorption isotherms of 3-D nitrogen based materials of the present invention made using a KIT6-150 template without an ethanol wash at 0 °C (top curve) and 10 °C (bottom curve).

DETAILED DESCRIPTION OF THE INVENTION

[0038] A discovery has been made that provides a possible solution to CO2 capture using carbon nitride materials. The discovery is premised on a 2-D and/or 3-D carbon nitride materials that are nitrogen rich. The nitrogen rich material carbon nitrides of the present invention can be synthesized through, for example, a templating-replication method using a 2-D or 3-D template and a tetrazole compound as a carbon nitride precursor. The resulting 3-D tetrazole- or amino- tetrazole-based carbon nitrides can exhibit an atomic nitrogen to carbon (N/C) ratio in the range of about 1.40 to about 2.35 and the resulting tetrazole- or amino-tetrazole-based 2-D carbon nitrides can exhibit an atomic nitrogen to carbon (N/C) ratio in the range of about 1.36 to about 2.28, indicating nitrogen rich materials as compared to graphitic carbon nitride and/or bulk carbon nitride material. Fourier transformed infrared spectra of amino tetrazole-based carbon nitrides of the present invention include N-H and N=N bonding features, which can be attributed to amino tetrazole and/or tetrazole moieties in the materials. The 2-D and 3-D amino tetrazole-based carbon nitrides can show higher capacity for CO2 adsorption than that of graphitic carbon nitride. The increased CO2 absorptivity of 2-D and/or 3-D amino tetrazole-based carbon nitride can be attributed to its enhanced basicity upon the formation of carbon nitride structure. Taking into account the high CO2 adsorption capacity and 2-D or 3-D pores of amino tetrazole-based carbon nitrides, the carbon nitrides can be used to capture CO2 and subsequently be used as CO and/or CO2 source in chemical reactions.

[0039] Based on periodic density functional theory (DFT) calculations, chemically modified or defective (e.g., having imperfections in their structure) carbon nitride materials can chemisorb and activate CO2 at room and/or mild temperature. In particular, the activation of CO2 to a bent geometry is feasible in the 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.

[0040] Taking into account the fact that the chemical composition of a carbon nitride can be dependent on the nitrogen composition of the precursor, nitrogen-rich carbon nitride materials of the present invention can be synthesized using a precursor with high nitrogen content. For example, referring to the structures in FIG. 1, the amino tetrazole compounds include at least 3 C- N bonds and 3 N-N bonds as compared to the prior art using dicyandiamide (3 C-N bonds, O N- N bonds) or triazine (4 C-N bonds, O N-N bonds). Thus, the band gap of carbon nitride can be tuned for CO2 conversion upon the formation of tetrazole-based polymer. Without wishing to be bound by theory, it is believed that nitrogen lone pairs can play a role as a strong basic center and assist in anchoring the acidic CO2 molecules. The 2-D and/or 3-D porous structure of carbon nitride derived from 2-D or 3-D templating agents, respectively can provide a beneficial effect in shortening transport pathway of CO2 molecules, electrons, and holes to increase the activities of carbon nitride for CO2 adsorption and subsequent use in chemical reactions.

A. Nitrogen-Rich 2-D and 3-D Carbon Nitride Materials

[0041] Embodiments of the current invention include materials having a 2-D carbon nitride structure formed from an amino tetrazole precursor material and having an atomic nitrogen to atomic carbon (N:C) ratio of 1.36:2.28 or a 3-D carbon nitride structure formed from an amino tetrazole precursor material and having an N:C ratio of 1.4:2.35, or combinations of the 2-D and 3-D materials. The resulting materials can each adsorb CO2. Non-limiting examples of amino tetrazole precursors can include 5-amino-lH-tetrazole, 1,5-diamino-lH-tetrazole, 1,5- (aminomethyl)tetrazole, or l-(3-aminophenyl)tetrazole, or combinations thereof. The three- dimensional carbon nitride material can be a porous carbon nitride or a non-porous carbon nitride. A porous 2-D and 3-D nitrogen rich materials of the present invention can have an average pore diameter of 2, 3, 4, 5, 6, 7, 8, 9, or 10 to 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 nm, including all ranges and values there between. In certain aspects, the average pore diameter can be 3 to 12 nm or the 3-D CN material and 3 to 6.5 nm for the 2-D CN material. The specific surface area of the 2-D and 3-D CN materials of the present invention can be from 50 to 500 m²g^_1, 100 to 400 m²g^" 200 to 350 or greater than, equal to, or between any two of 50, 75, 100, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, 185, 190, 195, 200, 205, 210, 215, 220, 225, 230, 235, 240, 245, 250, 255, 260, 265, 270, 275, 280, 285, 290, 295, 300, 305, 310, 315, 320, 330, 340, 350, 360, 370, 380, 390, 400, 450, and 500 m²g^_1- In certain aspects, the specific surface area of the 2-D and/or 3-D CN materials is 200 m²/g to 310 m²/g. In certain aspects, the nitrogen rich material of the present invention can include functional groups. Non-limiting examples of functional groups include primary amines (-NH) and secondary amines (-NH2).

[0042] The nitrogen rich carbon nitride materials can be characterized by SEM/EDS, XPS, XRD, and FTIR as well as other methods. Bulk crystallinity may be determined by powder X- ray diffraction (XRD). Bulk compositional analysis can be derived from combined CHN combustion and ICP/AA results. Composite thermal stability may be determined using thermogravimetric-differential thermal analysis. Surface coordinated molecular species and structural modifications of the carbon nitride framework can be probed with FTIR spectroscopic methods. At the molecular level, the carbon nitride material can be assessed for dispersion, homogeneity, and compositional purity by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Higher resolution structural, compositional, and nanoscale diffraction data may be obtained using transmission electron microscopy (TEM). Scanning X-ray photoelectron spectrometer (XPS, includes Auger and ultraviolet photoelectron spectroscopies) can identify oxidation states and local surface chemistry. B. Methods of Making 2-D and 3-D Carbon Nitride Materials of the Present Invention

[0043] The nitrogen rich materials of the present invention can be made through a templating process to produce the 2-D or 3-D structure. The nitrogen rich CN materials can be formed using nanocasting methodology that employs a template. Nanocasting is a technique to form a 2-D or 3-D framework using a hard template to produce a negative replica of the hard template structure. By way of example, a molecular precursor can be infiltrated into the pores of the template and subsequently polymerized within the pores of the template at elevated temperatures. Then the 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 needed. A template (e.g., a hard template) can be a mesoporous silica material. 3-D templating materials include mesoporous materials, like SBA-15 and MCM41. 2-D templating materials include mesoporous materials, like SBA-15, KIT-6, and FDU-12. The templating materials can be made as exemplified in the Examples, described in the specification or purchased from commercial sources (e.g., SigmaMillipore, U. S.A.).

[0044] In some embodiments, mesoporous silica templates can be produced by reacting tetraethyl orthosilicate with a template made of micellar rods. The resulting template can be a collection of nano-sized spheres or rods that are filled with a regular arrangement of pores. The template can then be removed by washing with a solvent adjusted to the proper pH. Mesoporous particles can also be synthesized using a simple sol-gel method such as the Stober process, or a spray drying method. Tetraethyl orthosilicate can also be used with an additional polymer monomer (as a template). Other precursors can include (3-mercaptopropyl)trimethoxysilane (MPTMS). The pore volume of these materials can be filled by carbon nitride precursors and subsequently polymerized within the pores of the hard template. After polymerization, the silica template can be removed by an appropriate treatment. The morphology of the final material can be a replica of the hard template as shown in FIGS. 2A (2-D) and 2B (3-D). This nanocasting route provides the advantage of not relying on a cooperative assembly processes between the template and the precursors. Moreover, nanocasting can be performed in non-aqueous media. By applying this approach, it is possible to facilitate the accessibility of the NH2 species and enhance the CO2 adsorption. [0045] Certain embodiments of the invention are directed to methods of synthesizing a 2-D or 3-D carbon nitride material formed from an amino-tetrazole precursor. One or more of the following steps can be used in the synthesis. In a first step, a template can be contacted with an aqueous amino-tetrazole solution forming a templated reaction mixture. In certain aspects, the silica template can be a porous silica template. The silica template can be a calcined silica template or an ethanol washed silica template. In certain aspects the amino tetrazole precursor is 5-amino- lH-tetrazole; 1,5-diamino-lH-tetrazole; l,5-(aminomethyl)tetrazole; or l-(3- aminophenyl)tetrazole.

[0046] In a second step, templated reaction mixture can be heated to a temperature between 40, 50, 60, 70, 80, 90, 125 °C, including all values and ranges there between; preferably between 80 and 120 °C, for at least 1, 2, 3, 4 to 5, 6, 7, or at least 8 hours, including all values and ranges there between. The first heated reaction mixture can be optionally cooled to about 30 °C to 80 °C. The heated or cooled reaction mixture can then be heated to a temperature of 130 °C, 140 °C, 150 °C, 160 °C, 170 °C, 180 °C, 190 °C, 200 °C, including all values and ranges there between; preferably 140 °C to 180 °C for 1, 2, 3, 4 to 5, 6, 7, 8 hours, including all values there between, forming a composite. Heating the composite at a temperature of 250, 275, 300 to 325, 350, 375, 400 °C, including all values and ranges there between, for 1, 2, 3, 4 to 5, 6, 7, 8 hours, forming a template/tetrazole-based carbon nitride product. In certain aspects, the method further comprises bringing the composite to temperature using a ramping rate of 1, 2, 3, to 4 °C/min, preferably 3 °C/min under constant inert gas (e.g., nitrogen) flow. The template can be removed by contacting the hard template/tetrazole-based carbon nitride product with hydrogen fluoride. Removing the template forms the 2-D or 3-D CN material of the present invention.

C. Use of the Nitrogen Rich Carbon Nitride Materials of the Present Invention

[0047] The 2-D CN materials, the 3-D CN materials or a mixture thereof can be used to adsorb CO2 as exemplified, in a non-limiting manner, in the Examples. One example of a CO2 capture process includes an absorption unit that receives a C02-containing feedstock that can come from a variety of sources such as power plant flue gas. In certain aspects, the absorption unit can include a 2-D CN structure or a 3-D CN structure of the current invention, or both. The absorption of CO2 by the 2-D and/or 3-D CN materials of the present invention can produce a C02-depleted product stream. A non-limiting example of CO2 capture can be process in which CO2 is removed either from flue gases after combustion of a carbon based fuel or the removal of and processing of carbon before combustion.

[0048] Certain embodiments, the 2-D CN material, the 3-D CN material, or a blend thereof with adsorbed CO2 can be used in chemical reactions to produce compounds that include an oxygen or a CO moiety to produce epoxides, carbonates, polycarbonates, alcohols, carboxylic acid, aldehydes and the like.

Examples

[0049] The present invention will be described in greater detail by way of specific examples. The following examples are offered for illustrative purposes only, and are not intended to limit the invention in any manner. Those of skill in the art will readily recognize a variety of noncritical parameters which can be changed or modified to yield essentially the same results.

[0050] Materials. Tetraethyl orthosilicate (TEOS), aminoguanidine hydrochloride and triblock copolymer poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (Pluronic PI 23, molecular weight 5800 g mol^"1, EO20PO70EO20), which were obtained from SigmaMillipore (U.S. A). Ethanol and hydrofluoric acid (HF) were purchased from Wako Pure Chemical Industries (U.S.A.). All the chemicals were used without further purification. Doubly deionized water has been used throughout the synthesis process.

EXAMPLE 1

(Preparation of mesoporous 2D SBA-15 silica template)

[0051] Pluronic P123 (4 g) and HC1 solution (37 wt%, 120 g) were dissolved in water and stirred at 40 °C followed by addition of tetraethoxysilane (8.6 g) after 2 h. The solution was aged with stirring at 40 °C for 24 h. Hydrothermal treatment was applied to solution at various temperatures including 130 °C, 150 °C, and 180 °C for 48 h. Two processes were applied to remove the surfactant. In the first method, silica was calcined at 540 °C under air flow for 24 h. In the second method, silica was throughly washed with ethanol 4-5 times. The silica hydrothermally treated at 130 °C, 150 °C, and 180 °C was denoted as SBA15-130, SBA15-150 and SBA15-180, respectively.

EXAMPLE 2

(Synthesis of 2-D mesoporous CN materials From Templated 5-amino-lH-tetrazole)

[0052] 2-D amino tetrazole-based carbon nitrides were prepared using SBA15 and 5-amino- lH-tetrazole as a hard template and a precursor, respectively. 5-Amino-lH-tetrazole (3.14 g) was dissolved in deionized water (3.0 g) and mixed until homogeneous to form a reactant mixture. The reactant mixture was placed in a programmed oven at 100 °C for 6 h and subsequently heated at 160 °C for another 6 h to form a composite. The resulting composite was carbonized by heating the composite to 400 °C with a ramping rate of 3 °C/min and held at the final temperature for 5 h under a constant nitrogen flow. The silica template was removed using HF treatment followed by drying at 100 °C. The resulting 2-D carbon nitride materials were denoted as SBA15-130-cal- tetrazole (Example 2A), SBA15-150-cal-tetrazole (Example 2B), and SB Al 5- 180-cal -tetrazole (Example 2C) for carbon nitrides prepared from calcined templates of SBA15-130, SBA15-150, and SBA15-180, respectively, from Example 1. 2-D carbon nitride materials denoted as SBA15- 130-EtOH-tetrazole (Example 2D), SBA15-150-EtOH-tetrazole (Example 2E), and SBA15-180- EtOH-tetrazole (Example 2F) were prepared from ethanol washed templates of SBA15-130, SBA15-150, and SBA15-180, respectively from Example 1.

EXAMPLE 3

(Preparation of mesoporous 3-D KIT-6 silica template)

[0053] Pluronic P123 (4 g) and HC1 solution (37 wt%) were dissolved in water. «-Butanol (4 g) was added into the solution and stirred at 35 °C followed by addition of tetraethoxysilane (8.6 g) after lh. The solution was aged with stirring at 35 °C for 24 h. The hydrothermal treatment was applied for this solution at various temperatures including 130 °C, 150 °C, and 180 °C for 24 h. Two processes were applied to remove the surfactant. In the first method, silica was calcined at 540 °C under air flow for 24 h. In the second method, silica was throughly washed with ethanol 4-5 times. The hydrothermally treated ( 130 °C, 150 °C, and 180 °C) silica template was denoted as KIT6-130, KIT6-150 and KIT6-180, respectively.

EXAMPLE 4

(Synthesis of 3-D mesoporous CN materials From Templated 5-amino-lH-tetrazole)

[0054] 3-D amino tetrazole-based carbon nitrides were prepared using KIT6 and 5-amino-lH- tetrazole as a hard template and a precursor, respectively. 5-Amino-lH-tetrazole (3.14 g) was dissolved in deionized water (3.0 g) and mixed until homogeneous to form a reactant mixture. The reactant mixture was placed in a programmed oven at 100 °C for 6 h and subsequently heated at 160 °C for another 6 h to form a composite. The resulting composite was carbonized by heating the composite to 400 °C with a ramping rate of 3 °C/min and held at the final temperature for 5 h under a constant nitrogen flow. The silica template was removed using HF treatment followed by drying at 100 °C. The resulting 3-D carbon nitride materials were denoted as KIT6-130-cal- tetrazole (Example 4A), KIT6-150-cal -tetrazole (Example 4B), and KIT6- 180-cal -tetrazole (Example 4C) for carbon nitrides prepared from calcined templates of KIT6-130, KIT6-150, and KIT6-180, respectively, from Example 3. 3-D carbon nitride materials denoted as KIT6-130- EtOH-tetrazole (Example 4D), KIT6-150-EtOH-tetrazole (Example 4E), and KIT6-180-EtOH- tetrazole (Example 4F) were prepared from ethanol washed templates of KIT6-130, KIT6-150, and KIT6-180, respectively from Example 3.

EXAMPLE 5

(Characterization of 2-D and 3-D Carbon Nitride Materials of the present invention) [0055] XRD: Powder XRD patterns of the Examples 2 and 4 catalysts were characterized with low angle powder XRD carried out on a PANalytical Empyream platform (PANalytical B.V., the Netherlands) diffractometer using Bragg-Brentano geometry. The measurements were collected using Cu Κ_α radiation from a sealed tube source operating at 40 kV and 40 mA, a fixed divergence slit of 0.1° and a PIXcel^3D detector. The scan rate used was 0.01 °/sec. The low angle measurements were done in the 2 Theta range 0.1° to 5° and wide angle measurements were from 5° to 60°. The ordering of the porous structure of amino tetrazole-based 3-D carbon nitride materials along with the parent silica template were analyzed by means of powder XRD.

[0056] 2-D CN materials. The ordering of the porous structure of amino tetrazole-based 2-D carbon nitride materials along with the parent silica template were analyzed by means of powder XRD. As shown in FIG. 3 A and FIG. 4A, all the samples exhibited XRD patterns with an intense peak at the small angle region. This peak can be indexed to correspond to the (100) and (110) Bragg reflection of a of a hexagonal symmetry with the P6mm space group, which is an indication of a highly ordered 2-D mesoporous system. The (100) Bragg reflection of the carbon nitrides shifted towards the lower angle upon increasing the hydrothermal reaction temperature from 130 °C to 180 °C. Taking into account the fact that <i-spacing of (100) plan is proportional to pore size in highly ordered mesoporous structure, it was determined that the pore diameter of 2-D mesoporous carbon nitride was successfully controlled.

[0057] All 2-D carbon nitride samples exhibited a distinct peak at 26.7° coressponding to (002) plane of graphitic carbon nitride, indicating a successful polymerization of 5-amino-lH-tetrazole. Thus, a polymerized carbon nitride was prepared with a amino tetrazole compound as a precursor. The d(oo2) value of 2-D carbon nitride materials of the present invention was 0.34 nm, which was determined to be larger than that of g-C₃N₄ (0.32 nm). From, the expanded ί¾₀₀₂> value of present carbon nitrides, it was determined that of amine group in the interlayer of the carbon nitride sheet was present in the structure. [0058] 3-D CN Materials. As shown in FIG. 3B and FIG. 4B, all the samples exhibited XRD patterns with an intense peak at the small angle region. This peak can be indexed to correspond to the (211) Bragg reflection of a cubic symmetry with t ela3d space group, which is an indication of a highly ordered mesoporous system. The (211) Bragg reflection of the carbon nitrides shifted towards the lower angle upon increasing the hydrothermal reaction temperature from 130 °C to 180 °C. On the basis of least square fitting, <i-spacings of (211) plane are determined as 7.36 nm, 8.83 nm, 9.20 nm, 8.83 nm, 9.20 nm, and 9.40 nm for KIT6-130-cal-tetrazole, KIT6-150-cal- tetrazole, KIT6-180-cal-tetrazole, KIT6-130-EtOH-tetrazole, KIT6-150-EtOH-tetrazole, and KIT6-180-EtOH-tetrazole, respectively. Taking into account the fact that <i-spacing of (211) plan is proportional to pore size in highly ordered mesoporous structure, it was determined that the pore diameter of 3-D mesoporous carbon nitride was successfully controlled.

[0059] All 3-D carbon nitride samples exhibited a distinct peak at 26.9° coressponding to (002) plane of graphitic carbon nitride, indicating a successful polymerization of 5-amino-lH-tetrazole. Thus, a polymerized carbon nitride was prepared with a amino tetrazole compound as a precursor. The d(oo2) value of carbon nitride materials of the present invention was 0.33 nm, which was determined to be larger than that of g-C₃N₄ (0.32 nm). From, the expanded ο2) value of present carbon nitrides, it was determined that of amine group in the interlayer of the carbon nitride sheet was present in the structure. [0060] FTIR: FTIR spectra of the Examples 2 and 4 catalysts were recorded by using a Nicolet Magna-IR 750 (Thermo Fisher Scientific, U.S.A.) fitted with a MTEC Model 300 Photoacoustic (METC Photoacoustics, Inc., U.S.A.) measuring 256 scans, at a resolution of 8 cm^"1, and a mirror velocity of 0.158 cm/s which equates to a sampling depth of about 22 microns.

[0061] The FTIR spectra of amino tetrazole-based carbon nitrides are displayed in FIG. 5 (2- D) and 5B (3-D0. The peaks in the region v = 730-780 cm^"1 were attributed to the synphase and antiphase vibrations of N=N of the tetrazole ring. The peak at 810 cm^"1 corresponded to condensed C-N heterocycle mode of the tetrazole ring. All of the carbon nitride materials of the present invention show similar peak intensities for vibration modes of N=N and condensed C-N heterocycles. In comparison, g-C₃N₄ has a stronger C-N heterocycles mode than N=N modes. From these results, it was determined that a tetrazole moiety was present in the carbon nitride 2- D and 3-D structures. For the 2-D CN materials, the peaks at v = 1321 and 1421 cm^"1 were attributed to C-N and N=N stretching bonds, respectively. Another band appearing at v = 1574 cm^"1 was attributed to an aromatic C=N band. In addition, bands at v = 890 and 2168 cm ^{D 1} were attributed to N-C=N and N=C=N stretchings. From these spectroscopic results, it was determined that 2-D carbon nitride structure included an amino tetrazole-based polymer matrix. For the 3-D CN materials, the peaks at v = 3000-3500 cm^"1 were attributed to the N-H stretching of NFh groups attached to the sp² hybridized carbon. The peaks at v = 3000-3500 cm^-1 were attributed to the N-H stretching of NFh groups attached to the sp² hybridized carbon. .In addition, bands at v = 890 and 2168 cm^"1 were attributed to N-C=N and N=C=N stretchings. From these spectroscopic results, it was determined that 3-D carbon nitride structure included an amino tetrazole-based polymer matrix.

[0062] XPS: X-ray spectroscopy measurements of the Examples 2 and 4 carbide nitride materials was acquired using a Kratos Axis ULTRA X-ray Photoelectron Spectrometer (Kratos Analytical, a Shimadzu Group Company, United Kingdom) incorporating a 165 mm hemispherical electron energy analyzer. The incident radiation was Monochromatic Al K_a X-rays (1486.6 eV) at 225 W (15 kV, 15 ma). Survey (wide) scans were taken at analyzer pass energy of 160 eV and multiplex (narrow) high resolution scans at 20 eV. Survey scans were carried out over 1200-0 eV binding energy range with 1.0 eV steps and a dwell time of 100 ms. To account for the charging effect, all the spectra were referred to the CI s peak at 284.5 eV.

[0063] 2-D materials. Table 1 lists the XPS results of SBA15-130-cal-tetrazole, SBA15-150- cal-tetrazole, SBA15-180-cal-tetrazole, SBA15-130-EtOH-tetrazole, SBA15-150-EtOH-tetrazole and SBA15-180-EtOH-tetrazole. The carbon nitrides material exhibited N/C ratios in range of 1.36-2.28. In contrast, g-C₃N₄ has a N:C ratio of 1.33. This result strongly underscores the successful synthesis of highly nitrogen-rich carbon nitride. Cls spectra in FIG. 6 shows the two peaks at 287.7 and 284.6 eV. The major C peak at 288 eV is identified as N-C=N and the weaker one at 284.6 eV corresponds to C-C=C. Notably, all the carbon nitride materials of the present invention show N-C=N bonding (77-90% peak area). This is in contrast to g-C₃N₄, which has a -60% peak area of N-C=N bonding. From this, it was determined that present 2-D carbon nitrides are composed of amino tetrazole moieties. Interestingly, the C-H bonding feature appears at 286.4 eV in the Cls spectra of all 2-D carbon nitride materials prepared with ethanol -washed SBA15, had C-H bonding. Nls peak of all the materials was deconvoluted to three peaks corresponding to (i) C-N=C, (ii) tertiary N, and (iii) quaternary N. All the 2-D carbon nitride materials showed identical deconvoluted spectra, underscoring that their N bonding features were the same regardless of the templates used.

Table 1

[0064] 3-D CN materials. Table 2 lists the XPS results of KIT6-130-cal-tetrazole, KIT6-150- cal-tetrazole, KIT6-180-cal-tetrazole, KIT6-130-EtOH-tetrazole, KIT6-150-EtOH-tetrazole and KIT6-180-EtOH-tetrazole. The carbon nitrides material exhibited N/C ratios in range of 1.40- 2.35. In contrast, g-C₃N₄ has a N:C ratio of 1.33. This result strongly underscores the successful synthesis of highly nitrogen-rich carbon nitride. Cls spectra in FIG. 6A-B shows the two peaks at 287.7 and 284.6 eV. The major C peak at 288 eV is identified as N-C=N and the weaker one at 284.6 eV corresponds to C-C=C. Notably, all the carbon nitride materials of the present invention show a N-C=N bonding (77-90% peak area). This is in contrast to g-C₃N₄, which has a -60% peak area of N-C=N bonding. From this, it was determined that present carbon nitrides are composed of amino tetrazole moieties. Interestingly, the C-H bonding feature appears at 286.4 eV in the Cls spectra of all 3-D carbon nitride materials prepared with ethanol-washed KIT6, had C-H bonding. With increasing the temperature of hydrothermal reaction for silica template, the content of C-H bonding was enhanced. On the basis of this result, it was determined that amino tetrazole-based carbon nitride-carbon composites were formed by using ethanol-washed KIT6 templates. Nls peak of all the materials was deconvoluted to three peaks corresponding to (i) C- N=C, (ii) tertiary N, and (iii) quaternary N. All the 3-D carbon nitride materials showed identical deconvoluted spectra, underscoring that their N bonding features were the same regardless of the templates used.

Table 2

[0065] NEXAFS The electron configuration of amino tetrazole-based carbon nitrides were probed by near-edge X-ray absorption fine structure (NEXAFS) analysis were acquired on the soft X-ray spectroscopy beamline at the Australian Synchrotron (Victoria, Australia), which is equipped with a hemispherical electron analyzer and a microchannel plate detector that enables a simultaneous recording of the total electron yield and partial electron yield. The raw NECAFS data were normalized to the photoelectron current of the photon beam, measured on an Au grid. [0066] 2-D materials. In carbon K-edge EXAFS spectra, the 2-D carbon nitride materials of Example 2 showed characteristic transitions including oi_s→ π_2ρ ^*οε at 284.7 eV and oi_s→ 2_P ^*c-N-c at 288.3 eV. As compared with g-C₃N₄, all of the 2-D carbon nitride materials had a blue shift of Gis→ π 2_P ^*c=c transition, underscoring the successful engineering of the electronic configuration of carbon nitrides upon formation of the amino tetrazole moiety of carbon nitride structure. In the nitrogen K-edge NEXAFS spectra, the 2-D carbon nitride materials of Example 2 showed a transition at 400.6 eV, which was attributed to oi_s→ π_2ρ*Ν-Η transition. From this evidence, it was determined that amino tetrazole moieties were in carbon nitride matrix.

[0067] 3-D materials. In carbon K-edge NEXAFS spectra, the 3-D carbon nitride materials of Example 2 showed characteristic transitions including oi_s→ π_2ρ ^*οε at 285.0 eV and oi_s→ π_2ρ ^*ε- N-c at 288.0 eV. As compared with g-C₃N₄, all of the 3-D carbon nitride materials had a blue shift of Gis→ 2p*c=c transition, underscoring the successful engineering of the electronic configuration of carbon nitrides upon formation of the amino tetrazole moiety of carbon nitride structure. The 3-D carbon nitride materials prepared with ethanol-washed KIT6 templates (Examples 2D-2F) showed a novel transition at 288.5 eV, suggesting the existence of additional carbon species with 3-D carbon nitride materials. This result was correlated with the XPS results. In the nitrogen K- edge NEXAFS spectra, the 3-D carbon nitride materials of Example 2 showed a transition at 400.2 eV, which was attributed to oi_s→ π_2ρ*Ν-Η transition. From this evidence, it was determined that amino tetrazole moieties were in carbon nitride matrix. [0068] SEM and TEM. Morphology of the Examples 2 and 4 catalysts were observed on a ZEISS 500 VP FE-SEM (Zeiss, Germany) and 2100F JEOL HR-TEM (JEOL U.S. A, Inc., U.S.A.). SEM images of the Example 2 and 4 samples are depicted in FIG. 8 A and FIG 8B. From the SEM images, it was determined that the 2-D and 3-D carbon nitride materials had an irrigular morphology composed of small nanoparticles. Highly ordered pore structure of the 2-D 3-D carbon nitride materials was observed in transmission electron microscopy (TEM) images (FIGS. 9A (2-D) and 9B (3B)).

[0069] UV-Vis. UV-Vis absorption spectra of the Examples 2 and 4 catalysts were recorded by using UV-3600 plus UV/VIS/NIR spectrophotometer (220-2600 nm) from Shimadzu. Instrument is equipped with a diffuse reflectance integrating sphere coated with BaS0₄, which served as a standard. Thickness of the quartz optical cell was 5 mm. The band gap of the materials were calculated using Tauc Plot method. Band gap data of Example 2 3-D carbon nitride materials was obtaind. FIG. 10A shows the UV-vis spectra of SBA15-130-cal-tetrazole, SBA15-150-cal- tetrazole, SB Al 5- 180-cal -tetrazole, SBA15-130-EtOH-tetrazole, SBA15-150-EtOH-tetrazole and SBA15-180-EtOH-tetrazole 2-D CN materials. All of the 2-D carbon nitride materials prepared using calcined SBA15 template had a bandgap of 2.75 eV to 2.85 eV. FIG. 10B shows the UV-vis spectra of KIT6-130-cal-tetrazole, KIT6-150-cal-tetrazole, KIT6-180-cal-tetrazole, KIT6-130-EtOH-tetrazole, KIT6-150-EtOH-tetrazole and KIT6-180-EtOH-tetrazole. All of the 3- D carbon nitride materials prepared using calcined KIT6 template had a bandgap of 2.7 eV, and the 3-D carbon nitride materials prepared ethanol-washed KIT6 templates had bandgap of 2.4 eV. Thus, from these results it was shown that the tuning of the band gap can be acheived by the methods of the present invention.

[0070] Textural parameters. Textural parameters and mesoscale ordering (d(2ii) spacing, unit cell size, surface area, pore volume and pore diameter) of the Examples 2 and 4 carbon nitride materials were determined from nitrogen adsorption-desorption isotherms using a Micromeritics ASAP 2040 sorption analyzer (Micromeritics Instruments, U.S. A) at -196 °C. All samples were out-gassed for 12 hrs at high temperatures under vacuum (ρ<1 ^χ 10-5 h.Pa) in the degas port of the adsorption analyzer. The specific surface area was calculated using the Brunauer-Emmett-Teller (BET) method. The pore size distributions were obtained from either adsorption or desorption branches of the isotherms using Barrett- Joy ner-Halenda (BJH) method. FIGS. 11A (2-D) and 11B (3-D) show the N2 adsorption-desorption isotherms. All samples show type IV adsorption isotherms according to the IUPAC classification and feature of capillary condensation with a small hysterisis in the mesopores, which indicated the presence of well-ordered mesopores in the samples. [0071] The textural parameters of the 2-D carbon nitride materials are summarized in Table 3. The highly ordered 2-D carbon nitride materials has BET surface areas of 208-306 m²/g with pore diameter of 3.1-6.1 nm. With increasing pore diameter of the 2-D carbon nitride materials of the present invention, their BET surface areas are increased. Thus, tuning of the pore size of the 2-D carbon nitride materials was achieved. Since the 2-D carbon nitride materials of the present invention exhibited high surface areas, large pore volumes, and high nitrogen content, these materials were expected to be good adsorbents for CO2 adsorption.

Table 3

Sample No. Surface Area (m²g^_1) Pore Diameter (nm)

2A 208 3.5

2B 261 5.4

2C 244 6.1

2D 286 3.1

2E 306 5.2

2F 219 6.1 [0072] The textural parameters of the 3-D carbon nitride materials are summarized in Table 4. The highly ordered 3-D carbon nitride materials has BET surface areas of 218-305 m²/g with pore diameter of 3.1-11.3 nm. With increasing pore diameter of the 3-D carbon nitride materials of the present invention, their BET surface areas are increased. Thus, tuning of the pore size of hte 3-D carbon nitride materials was achieved. Notably, the 3-D carbon nitride prepared with KIT6- 130 silica templates (Samples 4 A and 4D) had mesopores with large pore diameter of about 10.0-11.3 nm. The formation of large pores was ascribed to a collapse of small pores in KIT6. Thus, bimodal mesoporous 3-D carbon nitride materials can be obtained using the methods of the invention. Since the 3-D carbon nitride materials of the present invention exhibited high surface areas, large pore volumes, and high nitrogen content, these materials were expected to perform as good adsorbents for CO2 adsorption.

Table 4

EXAMPLE 5

(CO2 Adsorption Ability of the Carbon Nitride Materials of the Present Invention)

[0073] CO2 adsorption ability of the Examples 2 and 4 nitride materials was evaluated at high pressure up to 30 bar (3.0 Mpa) and a temperatures of 0 °C, 10 °C, and 25 °C. FIG. 12 shows the relationship between the amount of CO2 adsorbed and pressure for Samples 2A-C and Samples 4A-C. [0074] 2-D CN materials. From the data, it was determined that of the 2-D CN material, the SBA15-180-cal-tetrazole registered the highest CO2 adsorption capacity of 9.0 mmol/g at 0 °C and 30 bar whereas SBA15-130-cal-tetrazole and SBA15-150-cal-tetrazole display capacities of 5.6 and 8.0 mmol/g under indentical temperature and pressure conditions. The effect of temperature on the adsorption capacity is investigated for SBA15-180-cal-tetrazole. The slightly decreased CO2 adsorption capacity at 10 °C is attributed to the increased entropy of CO2 at elevated temperature. Although the CO2 adsorption capacity at 10 °C of SBA15-150-cal-tetrazole is sinficantly decreased at 30 bar, high capcitance of SBA15-180-cal-tetrazole is maintained up to 20 bar. Present experimental findings strongly demonstrate that amino tetrazole-based carbon nitride is very promissing CO2 adsorbents at low and high pressure. [0075] 3-D CN materials. From the data, it was determined that, of the 3-D CN materials, KIT6-150-cal-tetrazole had the highest CO2 adsorption capacity of 10.5 mmol/g at 0 °C and 30 bar (3.0 Mpa) while KIT6-130-cal-tetrazole (Sample 4 A) and KIT6-180-cal-tetrazole (Sample 4C) had CO2 adsorption capacities of 8.8 mmol/g and 8.7 mmol/g, respectively under indentical temperature and pressure conditions. The effect of temperature on the adsorption capacity was investigated for KIT6-150-cal-tetrazole. The CO2 adsorption capacity at 10 °C of KIT6-150-cal- tetrazole was slightly decreased at 3.0 Mpa, however, high capacitance of KIT6-150-cal-tetrazole was maintained up to 2.0 MPa at the same temperature. From the results, it was determined that 2-D and 3-D carbon nitride materials of the present invention were excellent CO2 adsorbents at low pressure and high pressure. Notably, all of that present CO2 adsorption capacity was higher as compared to triazine-based carbon nitrides.

Claims

1. A CO2 adsorbent carbon nitride (CN) material comprising a two dimensional (2-D) carbon nitride structure, a 3-D carbon nitride structure having an atomic N:C ratio of 1.4: 1 to 2.35: 1, or both, wherein each CN material has an atomic nitrogen to atomic carbon (N:C) ratio of 1.36: 1 to 2.35: 1.

2. The material of claim 1, wherein the 2-D, 3-D, or both carbon nitride structures comprise a tetrazole moiety and/or an amino tetrazole moiety.

3. The material of claim 2, wherein the tetrazole moiety or amino tetrazole moiety are derived from an amino tetrazole precursor selected from the group consisting of: 5- amino-lH-tetrazole; 1,5-diamino-lH-tetrazole; l,5-(aminomethyl)tetrazole; l-(3- aminophenyl)tetrazole, or mixtures thereof.

4. The material of claim 1, wherein the 2-D carbon nitride material is has a nanorod morphology and a N:C ratio of 1.36: 1 to 2.28: 1.

5. The material of claim 1, wherein the 3-D carbon nitride material has an atomic N:C ratio of 1.4: 1 to 2.35: 1.

6. The material of claim 1, wherein the 2-D material has an average pore diameter of 3 to 6.5 nm

7. The material of claim 1, wherein 3-D carbon nitride material has an average pore diameter of 3 to 12 nm.

8. The material of claim 1, wherein the carbon nitride material has surface area of 50 to 500 m²/g, preferably 200 to 310 m²/g.

9. The material of claim 1, wherein the 3-D carbon nitride material is porous.

10. The material of claim 1, wherein the 3-D carbon nitride material is non-porous.

11. A method of synthesizing the 2-D or 3-D carbon nitride (CN)material of any one of claims 1 to 10, the method comprising:

(a) contacting a 2-D or 3-D template with an aqueous amino tetrazole solution forming a templated reaction mixture;

(b) heating the templated reaction mixture to a temperature between 40 and 200 °C to form a CN/template composite; (c) heating the CN/template composite to a temperature of 250 to 400 °C, forming a 2-D or 3-D carbon nitride material/template complex; and

(d) removing the template, forming a 2-D or 3-D carbon nitride material.

12. The method of claim 11, wherein the step (b) heating comprises:

(i) heating the templated reaction mixture to a temperature between 40 °C to 200 °C, preferably between 80 °C and 120 °C to form a first heated reaction mixture;

(ii) optionally cooling the first heated reaction mixture; and

(iii) heating the reaction mixture to a temperature of 40 °C and 200 °C, preferably 140 °C to 180 °C to form a carbon nitride material/template complex; and

the step (c) heating is performed in an inert atmosphere, preferably, a nitrogen atmosphere.

13. The method of any one of claims 11 to 12, wherein the amino tetrazole is 5-amino-lH- tetrazole, 1,5-diamino-lH-tetrazole, l,5-(aminomethyl)tetrazole, or l-(3- aminophenyl)tetrazole, or combinations thereof.

14. The method of any one of claims 11 to 13, wherein the template is a silica template, preferably a porous silica template.

15. The method of claim 14, wherein the silica template is a KIT-6, a KIT-5, a SBA-15, or a FDU-12 template.

16. The method of any one of claims 11 to 13, wherein the 2-D template is a mesoporous silica template, preferably a MCM41 template.

17. The method of any one of claims 14 or 16, wherein the silica template is a calcined silica template or an ethanol washed silica template.

18. The method of any one of claims 11 to 17, wherein step (d) removing comprises contacting the hard template/tetrazole-based carbon nitride product with hydrogen fluoride or an alcohol solvent, preferably ethanol.

19. A CO2 capture process comprising contacting the CO2 adsorbent carbon nitride material any one of claims 1 to 10 with a CO2 containing feed source and adsorbing CO2 in or on the carbon nitride structure. The process of claim 19, further comprising providing the CO2 adsorbed carbon nitride material to a chemical process.