WO2019211675A1

WO2019211675A1 - Nitrogen-rich 3d mesoporous carbon nitrides: graphitic c 3n 6 derived from 3-amino-1,2,4-triazole with urea via calcination-free kit-6 silica templates

Info

Publication number: WO2019211675A1
Application number: PCT/IB2019/052183
Authority: WO
Inventors: Dae-Hwan Park; Kripal S. LAKHI; Jessica SCARANTO; Khalid Albahily; Ugo RAVON; Ajayan Vinu
Original assignee: Sabic Global Technologies B.V.
Priority date: 2018-05-03
Filing date: 2019-03-18
Publication date: 2019-11-07

Abstract

Certain embodiments are directed to a mesoporous carbon nitride (MCN) material that is complementary to an ethanol washed, calcination free (uncalcined) KIT-6 silica template, the MCN having a three-dimensional MCN matrix with –NH2 groups and an average pore diameter of 3 nanometers (nm) to 4 nm.

Description

NITROGEN-RICH 3D MESOPOROUS CARBON NITRIDES: GRAPHITIC CsNe DERIVED FROM 3-AMINO-l,2,4-TRIAZOLE WITH UREA VIA CALCINATION-

FREE KIT-6 SILICA TEMPLATES

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority of U.S. Provisional Patent Application

No. 62/666,215 filed May 3, 2018, which is hereby incorporated by reference in its entirety.

BACKGROUND

I. Field of the Invention

[0002] The invention generally concerns materials for the capture and/or catalysis of carbon dioxide (CO2). In particular the materials adsorb CO2 and aid in the management of greenhouse gas emission.

II. Description of the Related Art

[0003] It is well known that CO2 emissions contribute to global warming, /. e. , the greenhouse effect. One of the strategies to decrease the CO2 emissions into the atmosphere is to capture and use the CO2 as a feedstock. For this reason, many researchers tried to activate or capture the CO2 molecule. However, due to the high stability of this molecule, CO2 activation is extremely challenging and additional catalyst need to be developed.

[0004] A new class of high surface area, tunable pore diameter mesoporous carbon nitride (MCN) 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 al. Chem. Soc. Rev., 2016 (in press); Wang et ah, Nat. Mater. 2009, 8:76; Zheng et al., 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 MCN structural and textural properties, such as high surface area, different pore size, uniform morphology, but also to control surface functionalities, nitrogen content, band gaps, and position (Talapaneni et al., ChemSusChem, 2012, 5:700; Jin et al., Angew. Chem. Int. Ed., 2009, 48:7884; Zhonget al., Sci. Rep., 2015, 5: 12901 ; Lakhi et al., RSC Adv., 2015, 5:40183). However, although the reported MCN materials have showed textural features for various catalytic performances and gas adsorption capacities, they are deficient in regard to high nitrogen content and small band gaps that are needed for improved performance. SUMMARY

[0005] Additional MCN materials and processes have been developed that provide a solution to the economic and energy inefficiency problems associated with CO2 capture and catalysis. In particular, materials, catalysts, and processes for CO2 adsorption have been developed that work at lower temperatures as well as lower pressures.

[0006] Certain embodiments are directed to a mesoporous carbon nitride (MCN) material complementary to an ethanol washed KIT-6 silica template, the MCN having a three- dimensional MCN matrix with -NH2 groups and an average pore diameter of 3 nanometers (nm) to 4 nm. An ethanol washed KIT-6 silica template is not exposed to calcination conditions prior to MCN formation. In certain aspects the MCN material can have a carbon to nitrogen ratio of 0.45 to 0.55, a surface area of 235 m²/g to 255 m²/g, and a total pore volume of 0.20 cm³/g to 0.3 cm³/g. In a particular aspect the mesoporous MCN material can have a carbon to nitrogen ratio of about 0.48, a surface area of 245 m²/g to 250 m²/g, and a total pore volume of about 0.26 cm³/g. The mesoporous MCN material can be capable of adsorbing carbon dioxide (CO2) at 6 mmol/g to 7 mmol/g at 0 °C and a pressure of 1 to 5, or about 3 MPa.

[0007] In a further aspect the mesoporous MCN material can have a carbon to nitrogen ratio of 0.55 to 0.65, a surface area of 175 m²/g to 225 m²/g, and a total pore volume of 0.25 cm³/g to 0.35 cm³/g, more particularly a carbon to nitrogen ratio of about 0.59, a surface area of 200 m²/g to 210 m²/g, and a total pore volume of about 0.28 cm³/g. The mesoporous MCN material can be capable of adsorbing carbon dioxide (CO2) at 5 mmol/g to 6 mmol/g at a temperature of 0°C and a pressure of 1 to 5, or about 3 MPa.

[0008] In certain aspects the mesoporous MCN material can have a MCN matrix having a rZ-spacing of 8.60 to 9.9, preferably about 8.65 to about 9.81, or more preferably about 9.19 or about 9.81.

[0009] In certain aspects the mesoporous MCN material can have an aminoguanidine or an amino- 1,2, 4-triazole based polymeric matrix. In a further aspect the mesoporous MCN material can have a MCN matrix that 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.

[0010] In certain aspects the mesoporous MCN material is a CO2 activation catalyst.

[0011] Certain embodiments are directed to a process for carbon dioxide (CO2) adsorption, the process comprising: contacting the mesoporous carbon nitride (MCN) material of any one of the present invention with a feed stream comprising CO2, wherein at least a portion of the CO2 is adsorbed by the mesoporous MCN material. In certain aspects the process 5 mmol/g to 6 mmol/g of CO2 is adsorbed by the mesoporous MCN material at a temperature of 0°C and a pressure of 30 bar. In a particular aspect the adsorbed CO2 is activated.

[0012] Still other embodiments are directed to methods of producing the mesoporous carbon nitride (MCN) material, the method comprising: (a) contacting an ethanol washed KIT- 6 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-6 composite; (c) carbonizing the MCN polymeric material/KIT-6 composite; and (d) removing the ethanol washed KIT-6 silica template to obtain the mesoporous MCN material and optionally drying the obtained material. In certain aspects polymerizing step (b) comprises (i)heating the mixture to a first temperature of 90 to H0°C, preferably about l00°C for 4 to 8 hours, preferably, 6 hours; and (ii) increasing the temperature to 150 to l70°C, preferably about l60°C, for 4 to 8 hours, preferably 6 hours. In another aspect the carbonizing step (c) comprises heating the mesoporous MCN material/KIT-6 composite to 400 °C to 600 °C, preferably about 500 °C, for 3 to 7 hours, preferably about 5 hours under an inert gas atmosphere. The method can further include producing the ethanol washed KIT-6 silica template, the method comprising: (a) obtaining a solution comprising amphiphilic triblock copolymer and tetraethyl orthosilicate (TEOS); (b) heating the solution at a temperature of 75 °C to 200 °C, preferably 100 °C to 150 °C, for 12 to 36 hours, preferably about 24 hours, to form a non-calcined KIT-6 silica template/triblock copolymer composite; and (c) removing the triblock copolymer and any surfactant from the composite to obtain the ethanol washed KIT-6 silica template. In certain aspects the removing step (c) comprises contacting the ethanol washed KIT-6 silica template/triblock copolymer composite with an alcoholic solution, preferably an ethanol solution. The method can also include contacting the ethanol washed KIT-6 silica template/triblock copolymer composite with the alcoholic solution at ambient temperature for 1 to 5 hours, preferably 2 to 4 hours, or more preferably about 3 hours at 20 to 40 °C.

[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 made by the methods of the invention can be used to achieve methods of the invention.

A. Definitions

[0014] The term“ethanol washed template” or“calcination free template” refers to a hard template that has not been subjected to calcination conditions prior to MCN formation. For example, a KIT-6 template, a SDU-15 template or the like.

[0015] The term“calcination” is understood to refer to a temperature treatment in which the starting materials combine to form a microstructure of crystallites, in which the volatile components, for example, water of crystallization, are removed, and in which a mechanically stable solid body that undergoes scarcely any change in volume during further heat treatment is formed.

[0016] The processes and carbon nitride materials of the present invention can“comprise,” “consist essentially of,” or“consist of’ particular ingredients, components, compositions, etc. disclosed throughout the specification.

[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 terms “wt.%”, “vol.%”, or“mol.%” refers to a weight percentage of a component, a volume percentage of a component, or molar percentage of a component, respectively, based on the total weight, the total volume of material, or total moles, that includes the component. In a non-limiting example, 10 grams of component in 100 grams of the material is 10 wt.% of component.

[0022] 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.

[0023] 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.”

[0024] The methods to prepare the 3-D mesoporous CN 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 methods to prepare the 3-D mesoporous CN materials of the present invention is the use of an uncalcined template.

[0025] 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.”

[0026] 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

[0027] 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.

[0028] FIGS. 1A and IB. Representations of the replica approach using an uncalcined SDU-15 template (1A) and an uncalcined KIT-6 template (1B) [0029] FIGS. 2A-B. (A) Low angle and (B) high angle powder XRD patterns of the (a) MCN-T-X and (b) MCN-TU-X materials, where T is 3 -amino- 1,2, 4-triazole, TU is 3-amino- 1,2, 4-triazole and urea, and X is temperature template synthesis tempearature.

[0030] FIGS. 3A-B. (A) N2 adsorption-desorption isotherms and (B) pore size distribution of the (a) MCN-T-X and (b) MCN-TU-X materials.

[0031] FIGS. 4A-B. (A) High-resolution TEM images and (B) EELS spectrum of the MCN-TU-150.

[0032] FIGS. 5A-B. (A) XPS survey and (B) high-resolution Cls and Nls spectra of the (a) MCN-T-150 and (b) MCN-TU-150.

[0033] FIG. 6. FTIR-ATR spectra of the (a) MCN-T-150 and (b) MCN-TU-150.

[0034] FIGS. 7A-B. (A) C K-edge and (B) N K-edge NEXAFS spectra of the MCN-T-X and MCN-TU-X at the KIT-6 synthetic temperature of (a) 100, (b) 130, (c) 150, and (d) non- porous g-C3N₄ prepared by dicyandiamide at 550 °C.

[0035] FIGS. 8A-B. CO2 adsorption isotherms of the (A) MCN-T and (B) MCN-TU materials at 0 °C and pressure up to 30 bar.

DESCRIPTION

[0036] 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 the presence of a 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 a relatively easy CO2 desorption process due to moderate binding energy. The identified defect- engineered carbon nitride material seems then to be promising for CO2 capture as it represents a compromise between the other sorbent materials associated to physical or chemical adsorption mechanisms. Based on the computational conclusion, a strategy was employed 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 (T or AT) can be used as a monomer alone or in combination with a co-monomer. The addition of a co-monomer like urea or formaldehyde can also modify the structure of the polymer and enhance the target species. [0037] Because polymerization occurs 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. However, because CN is non porous, another aspect of the catalyst synthesis needs to be study, the morphology control. Indeed, working on the morphology, should facilitate the accessibility of the active site to the reactant. In this work, morphology control study is carried out by using a replica approach as shown in FIGS. 1A and 1B. Referring to FIG. 1B, template 10 ( e.g ., calcined KIT-6) can include canal 12 and pores 14. Canal 12 is representative of the pore volume of template 10. Pores 14 can be filled corresponding carbon nitride precursor material 16 to form a template/carbon nitride precursor material. By way of example, an aqueous solution of 3- amino- 1,2, 4-triazole can be added to a an uncalcined KIT-6. The template/carbon nitride precursor material can undergo a thermal treatment to polymerize the precursor inside the pore of the material to form uncalcined template/CN composite 16 having canal 12 and polymerized CN material 18. Uncalcined template/CN composite 16 can be subjected to conditions sufficient to dissolve the template 10 (e.g., KIT-6), and form mesoporous carbon nitride material 20 of the present invention. By way of example, uncalcined template 10 can be dissolved using an HF treatment, a very high alkaline solution, or any other dissolution agent capable of removing the uncalcined template and not dissolving the CN framework. The kind of uncalcined template and the CN precursor used influence the characteristics of the final material. By way of example, various uncalcined KIT-6 with various pore diameters can be used as templates. In certain aspects, the pore size of the uncalcined KIT-6 template can be tuned and 3 -amino- 1,2, 4-triazole can be used to produce a high nitrogen content.

[0038] 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 to polymerize the precursor. After this step, the silica template is removed by an appropriate treatment. The morphology of the final material is the negative replica of the silica mesoporous morphology, resulting in a mesoporous carbon nitride (MCN). By applying this approach, it is possible to facilitate the accessibility of the -NH2 species and enhance the CO2 reactivity. The starting mesoporous silica is an important parameter in the characteristics of the resulting MCN.

A. MCN material

[0039] The MCN material produced by the methods described herein can be characterized at least in terms of carbon/nitrogen ratio, porosity, surface area, and CO2 adsorption capacity. [0040] In certain aspects MCN materials show reflection peaks at low angle region, which is indexed as the (211) diffractions of Ia3d symmetry with rZ-spacings from 8.65 and 9.49 to 9.19 and 9.81, respectivley, indicating highly ordered and three-dimensional (3D) porous mesostructures. Mesoscale textural features of the preapred MCN materials were confirmed by Nz adsorption-desorption analysis demonstrating N2 isotherms having a type IV curve with Hl hysteresis loops, indicating the presence of well-ordered mesopores with high surface areas, large pore volumes and tunable pore diameters in all of the prepared MCN materials. The Brunauer-Emmett-Teller (BET) surface area of the MCN materials can be from about 95, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190 to about 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350 m²/g, in certain instance the BET surface area is 246.65 m²/g. The mesopore sizes of the prepared materials exhibit highly uniform and narrow size distributions, and are gradually increased with increase in the pore diameters of the KIT-6-150- EW templates used. The maximum pore diameter can be from about 3.0, 3.1, 3.2, 3.3 3.4, 3.5 to about 3.6, 3.7, 3.8, 3.9, 4.0 nm (incuding all values and ragnes there between), in certain aspects pore diameter can be about 3.21 nm to 3.69 nm.

[0041] Electron energy loss spectroscopy (EELS) and X-ray photoelectron spectroscopy (XPS) analyses can be used to characterize the materials as well. An EEL spectrum of the material can be used to observe the C-K edges and N-K edges. The peaks at 283.0 eV and 381.6 eV are attributed to the ls-p* electron transitions, indicating that sp² graphitic carbon is bonded to nitrogen in the CN wall structure. The signals located at 289.9 eV and 398 eV can be assigned to the ls-s* electron transitions on sp³ carbon species (Thomas et ah, ./. Mater. Chem., 2008, 18:4893).

[0042] The materials can have a C/N ratio of 0.45, 0.50 to 0.55, 0.60 (including all values and ranges there between), and in certain instances 0.48 and 0.59. The prepared materials have high nitrogen contents with chemical formulas of“C3N5.03” and“C3N6.14”, for example.

[0043] The Cls spectra of the materials show mainly one carbon species with a binding energy of 287.7 eV, which corresponds to the C-N=C coordination. The Nls spectra can be deconvoluted as four different binding energies: (i) a main signal of C-N=C group at 398.3 eV, (ii) a tertiary nitrogen of N-3C group at 400.1 eV, (iii) an amino function carrying hydrogen (C-NFh group) at 401.4 eV, and (iv) a N=N bonding configuration at 403.5 eV.

[0044] Fourier transform infrared spectroscopy - attenuated total reflectance (FTIR-ATR) spectra of the materials showed symmetric and anti-phase N=N vibrations (740 - 790 cm ¹) as well as C=N (1321 cm ¹) and N=N (1421 cm ¹) stretching bonds. Interestingly, the C-NH2 scissoring band was clearly seen at 1550 cm ¹. Another band at 1574 cm ¹ was attributed to typical graphite-like C-N bond. The nitrogen content can be confirmed by bands intensities of N=N and C=N.

[0045] Synchrotron-based near-edge X-ray absorption fine structure (NEXAFS) can be performed to further probe chemical bonding nature of the developed MCN materials by comparing the non-porous graphitic carbon nitride (g-C3N₄) prepared by dicyandiamide at 550°C. In the carbon K-edge NEXAFS spectra MCN materials show characteristic resonances of graphitic carbon nitride including p* c=c (Cl) at 285.4 eV, 7I*C:-N-C (C2) at 288.0 eV, o*c-c (C3) at around 293 eV, and structural defects. In nitrogen K-edge region MCN materials also show two typical p* resonances at 399.3 and 402.3 eV, which corresponds 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). As compared with non-porous g-C3N₄, the MCN materials are well-defined nitrogen-rich mesoporous graphitic carbon nitride materials. As can be seen from the nitrogen K-edge NEXAFS spectra, an increased intensity of N2 resonance in the all MCN-EU-X materials reveals that the addition of urea induced highly networked graphitic structure with N-3C bridging framework, which is in agreement with the XPS results. The CN framework is also relatively highly cross-linked through the KIT-6 silica synthesized at 150 degree.

[0046] The CO2 adsorption capacity the MCN material can be determined at pressures up to 30 bar and temperatures of 0°C. As reported in the literature (Lakhi et al., 2015, 5:40183; Lakhi et al., Catal. Today, 2015, 243 :209), the CO2 molecules with Lewis acidic property is highly likely to be adsorbed inside the mesopore channel of the Lewis basic MCN materials through acid-base neutralization reaction. CO2 adsorption capacity can range from about, at most, or at least 2.8, 3.0, 3.2, 3.4, 3.6, 3.8, 4.0, 4.2, 4.4, 4.6, 4.8, 5.0, 5.2, 5.4, 5.6, 5.8, 6.0, 6.2, 6.4, 6.6, 6.8 7.0 mmol/g, including all values and ranges there between. In certain aspects the CO2 adsorption capacity is 5.63 mmol/g to 6.76 mmol/g.

[0047] MCN material described herein are highly ordered, 3D structured MCN materials with tunable pore diamters and high nitrogen content produced by nanocasting calcination-free KIT-6 silica as a hard templates with 3 -amino- 1,2, 4-triazole (T or 3AT) or 3 -amino- 1, 2,4- triazole (T or 3AT) and urea (U). From the results on the CO2 adsorption capacity, it is concluded that the MCN materials can serve as a photocatalyst for the CO2 capture and conversion into valuable chemicals with hydrogen produced through water splitting under visible light.

B. Process for Producing Mesoporous Carbon Nitride 3-Amino-l, 2, 4, triazole

(MCN-T) and Mesoporous Carbon Nitride 3-Amino-l, 2, 4, triazole / Urea (MCN

TU) Materials

[0048] Highly ordered mesoporous carbon nitride materials (MCN) with high nitrogen contents can be prepared by using 3 -amino- 1,2, 4-triazole (T or 3AT) as a single carbon nitride precursor or a combination of 3 -amino- 1,2, 4-triazole and urea as double CN precursors by forming a replica of an ethanol -washed KIT-6 silica (KIT-6-EW) as a template. The ethanol washed KIT-6 template is a KIT-6 template that is not calcined prior to the CN polymerization reaction, as is thus a calcination free template.

1. Silica Template

[0049] A KIT-6 template can be produced by first obtaining a polymerization solution including an amphiphilic triblock copolymer dispersed in an aqueous hydrogen chloride solution with 1 -butanol and 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-6 template, wherein the predetermined temperature determines the pore size of the KIT-6 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 199 °C). For the general formula KIT-6-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-6 templates denoted KIT-6-100, KIT-6-130, and KIT-6-150, respectively. Preferably, the incubation temperature is l50°C. The formed KIT-6 template can then be dried at 90°C to H0°C, preferably l00°C. In a final step, the dried KIT-6 template can be ethanol washed and in certain aspects not subjected to calcination temperatures. 2. Mesoporous Carbon Nitride (MCN) Material

[0050] Mesoporous carbon nitride material can be formed by nanocasting using a template as prepared above, e.g ., calcination free KIT-6 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-6, 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 Ia3d symmetric silica, such as KIT-6 which contains interpenetrating cylindrical pore systems.

[0051] In particular aspects ethanol washed KIT-6 (KIT-6-EW) silica templates are not subjected to calcination (calcination-free, or non-calcined templates) prior to use in the nanocasting process. The KIT-6-EW template can be synthesized with different pore diameters by hydrothermal reactions at different temperatures, e.g, 100, 130, and l50°C (KIT-6-EW- 100, etc.) as described above.

[0052] It is of particular note that: (i) MCN-T-150 and MCN-T-150 materials using KEG-6- EW-150 silica prepared at the temperature of l50°C had the highest specific surface areas (231.44 m²/g and 246.65 m²/g) and the largest pore diameters (3.21 nm and 3.69 nm) with I a 3d symmetry and well-ordered 3D mesoporous structure; (ii) the MCN-TU-150 prepared by triazole mixed with urea had a very high nitrogen content with a C/N ratio of 0.48, which is lower than a C/N ratio of 0.59 for MCN-T-150 prepared by triazole only and a theoretical C/N ratio of 0.75 for typical non-porous carbon nitride; and (iii) the nitrogen-rich MCN-TU-150 material with a chemical formula of C3N6.14 showed the highest CO2 adsorption capacity of 6.76 mmol/g at the temperature of 0°C and pressure of 30 bar.

C. Use of MCN-T and MCN-TU for Carbon Dioxide Capture

[0053] 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.

[0054] Embodiments of the current invention employ MCN materials described herein as absorbents for CO2 and/or catalyst for conversion of C02 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.

[0055] 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 C02 can be reduced producing a product mixture, where the product mixture includes organic products.

[0056] 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.

D. Examples

[0057] The following examples as well as the figures are included to demonstrate preferred embodiments of the invention. It should be appreciated by those of skill in the art that the techniques disclosed in the examples or figures represent techniques discovered by the inventors to function well in the practice of the invention, and thus can be considered to constitute preferred modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention. EXAMPLE 1

PREPARATION OF NITROGEN-RICH 3D ME SOPOROUS CARBON NITRIDES

VIA CALCINATION-FREE KIT-6 SILICA TEMPLATES

1. Methods

[0058] Preparation of KIT-6-X-EW silica templates. Pluronic P123 (4 g) and HC1 solution (37 wt%) were dissolved in water n-butanol (4 g) was added and stirred at 35°C for 1 hr. 8.6 g of tetraethoxy silane (TEOS) was then dropped into the homogeneous clear solution. After stirring at 35°C for 24 hr, the solution was hydrothermally treated at 100, 130, and 150 °C for 24 hr. KIT-6-X-EW silica templates were obtained after washing with an ethanol solution at ambient temperature for 3 hr to remove the P123 surfactant. The‘X’ and‘EW’ indicate the temperature of the hydrothermal treatment and the ethanol washing, respectively.

[0059] Preparation ofMCN using 3-amino-l ,2,4-triazole (3AT) with urea. MCN materials were prepared using KIT-6-X-EW and 3 -amino- 1,2, 4-triazole (T or 3AT, C₂H₄N₄) with or without urea (EG, CH₄N₂O). In a typical synthesis, 3 AT (3.0 g) dissolved in deionized water (3.0 g) was added to KIT-6-X-EW (1.0 g) along with addition of urea (3.0 g). The mixture was homogeneously mixed and then placed in a programmed oven at 100 °C for 6 hr and further heated at 160 °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. The KIT-6-X-EW silica templates were then removed through treatment with 5 wt% HF solution, filtered, washed with ethanol, and dried at 100 °C. The MCN materials were labelled as MCN-T-X (without urea) or MCN-TU-X (with urea), where X indicates the synthesis temperature of the KIT-6-X-EW silica.

[0060] Catalyst characterization. The KIT-6-X-EW silica templates were suceesfully prepared according to the typical synthetic procedure combined with ethanol washing process for the extraction of P123 surfactant. To the inventors knowledge, no report has appeared in a scientific journal on the ethanol-washed calcination-free KIT-6 silica even though a series of reports on calcination-free SBA-15 silicas with different pore diameters and controlled rod morpology have been published (Lakhi et ah, , RSC Adv., 2015, 5:40183). Three silica tempates with different pore diameters, KIT-6-100-EW, KIT-6-130-EW, and KIT-6-150-EW, were used as templates for the synthesis of MCN-T-X and MCN-TU-X having a high nitrogen content using 3AT as a single CN precursor and 3AT with urea as double CN precursors, respectivley. 2. Results

[0061] The information on the ordering and graphitic structure of the MCN materials was obtained by powder XRD measurements. As shown in FIG. 2A, both MCN-T and MCN-TU materials show reflection peaks at low angle region, which is indexed as the (211) diffractions of Ia3d symmetry with rZ-spacings from 8.65 and 9.49 to 9.19 and 9.81, respectivley. These data indicate that the present MCN materials are highly ordered and three-dimensional (3D) porous mesostructures. The diffraction peaks at 27.3° in high angle region were also observed for all the materials (FIG. 2B), confirming the turbostratic ordering of graphitic CN wall structure. Interstingly, such graphitic nature of MCN-T is the same as that obtained for nonporous CN-T using 3 AT only carbonized in the absence of silica template, which indicates that the CN wall structure of the porous materials was able to be formed at relativley low temperature inside the mesopore channel of the KIT-6-EW silica templates through the effect of pore confinement.

[0062] Mesoscale textural features of the preapred MCN materials were confirmed by N2 adsorption-desorption analysis. As shown in FIG. 3 A, the N2 isotherms of both MCN-T and MCN-TU show type IV curve with Hl hysteresis loops, indicating the presence of well-ordered mesopores with high surface areas, large pore volumes and tunable pore diameters in all of the prepared MCN materials. The BET surface area was increased up to 231.44 m²/g for MCN-T- 150 sample and 246.65 m²/g for MCN-TU-150 sample. As can be seen in FIG. 3B, the mesopore sizes of the prepared materials exhibit highly uniform and narrow size distributions, and are gradually increased with increase in the pore diameters of the KIT-6-150-EW templates used. The maximum pore diameter of MCN-T-150 and MCN-TU-150 were 3.21 nm and 3.69 nm, respectively. Textural parameters of the prepared MCN materials are also summarized in Table 1. It is worthy to note that the shape of the isotherm and capillary condensation step for both MCN-T-150 and MCN-TU-150 samples are relativley quite narrow compared to those of corresponding 100 and 130 samples. This indicates that the KIT-6-150-EW silica template with the largest pore diameter were able to achieve the perfect replication with high cross- linking of CN precursors, 3AT and urea, during the carbonization process. This result is in agreement with the highly-ordered 3D structure observed in the low angle XRD patterns.

[0063] FIG. 4A shows the high-resolution TEM image of the MCN-TU-150 sample. The uniform pore size of the order of 3 to 4 nm along the [100] direction was clearly observed, which is consistent with the pore size distribution obtained from the N2 adsorption measurements. 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-T-150 and MCN-TU-150. According to the EEL spectrum of the MCN-TET- 150 (FIG. 4B), the C-K edges and N-K edges were observed. The peaks at 283.0 eV and 381.6 eV are attributed to the ls-p* electron transitions, indicating that sp² graphitic carbon is bonded to nitrogen in the CN wall structure. The signals located at 289.9 eV and 398 eV can be assigned to the ls-s* electron transitions on sp³ carbon species (Thomas et ah, J. Mater. Chem ., 2008, 18:4893).

[0064] 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. 0.59 for MCN-T-150 and 0.48 for MCN-TET-150, which is lower than the C/N ratio of 0.75 for the typical non-porous carbon nitrides with a nominal composition of C3N4. These results also confirm that the prepared materials have high nitrogen contents with chemical formulas of “C3N5.03” for MCN-T-150 and“CsNe.n” for MCN-TU-150, respectively.

[0065] The Cls spectra of both materials show mainly one carbon species with a binding energy of 287.7 eV, which corresponds to the C-N=C coordination. The Nls spectra can be deconvoluted as four different binding energies: (i) a main signal of C-N=C group at 398.3 eV, (ii) a tertiary nitrogen of N-3C group at 400.1 eV, (iii) an amino function carrying hydrogen (C-NFh group) at 401.4 eV, and (iv) a N=N bonding configuration at 403.5 eV. It is found that the area percentages with respect to C-N=C and C-NFh groups calculated in the MCN- TU-150 prepared by combining 3AT with urea are higher than those of MCN-T-150 material prepared by 3 AT only.

[0066] As represented in FIG. 6, FTIR-ATR spectra of all materials showed symmetric and anti-phase N=N vibrations (740 - 790 cm ¹) as well as C=N (1321 cm ¹) and N=N (1421 cm ¹) stretching bonds. 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. The nitrogen contents in the MCN-TU-150 was relatively higher than that of MCN-T-150, which was confirmed by bands intensities of N=N and C=N at the sample of 3 AT combined with urea represented relatively higher than those of 3 AT only.

[0067] The inventors also investigated synchrotron-based near-edge X-ray absorption fine structure (NEXAFS) to further probe chemical bonding nature of the developed MCN materials by comparing the non-porous graphitic carbon nitride (g-C3N4) prepared by dicyandiamide at 550°C. In the carbon K-edge NEXAFS spectra (FIG. 7A), both MCN-T and MCN-TU materials show characteristic resonances of graphitic carbon nitride including 7i*c-c (C l) at 285.4 eV, *C-N-C (C2) at 288.0 eV, o*c-c (C3) at around 293 eV, and structural defects. In nitrogen K-edge region (FIG. 7B), both MCN-T and MCN-TU materials also show two typical p* resonances at 399.3 and 402.3 eV, which corresponds 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). As compared with non-porous g- C3N4, the prepared MCN-T and MCN-TU materials turned out to be well-defined nitrogen-rich mesoporous graphitic carbon nitride materials. More importantly, as can be seen from the nitrogen K-edge NEXAFS spectra, an increased intensity of N2 resonance in the all MCN-TU- X materials reveals that the addition of urea induced highly networked graphitic structure with N-3C bridging framework, which is in agreement with the XPS results. The CN framework was also relatively highly cross-linked through the KIT-6 silica synthesized at 150 degree.

[0068] The CO2 adsorption capacity for all samples with tunable pore diameters and high nitrogen content was investigated at high pressures up to 30 bar and temperatures of 0°C. As reported in the literature (Lakhi et al., 2015, 5 :40183; Lakhi et al., Catal. Today, 2015, 243 :209), the CO2 molecules with Lewis acidic property is highly likely to be adsorbed inside the mesopore channel of the Lewis basic MCN materials through acid-base neutralization reaction. As represented in FIG. 6 and Table 1, the CO2 adsorption capacity achieved and varied depending on the tunable pore diameters and specific surface area, and even NFh functional groups. The highest CO2 adsorption capacity was recorded as a 5.63 mmol/g for MCN-T-150 and 6.76 mmol/g for MCN-TU-150 material.

Table 1. Textural parameters, C/N ratio, and CO2 adsorption of the MCN-T and MCN-TU materials using KIT-6-X-EW silica templates. flo D SBET Dpore V total C0₂

C/N^d

[nm] [nml^a im²/gl [nml^b [cm³/g [mmol/g]⁶

MCN-T-100 21.19 8.65 107.61 3.01 0.16 0.85 3.63

MCN-T-130 22.07 9.01 97.46 3.03 0.27 0.71 5.07

MCN-T-150 22.51 9.19 205.45 3.21 0.28 0.59 5.63

MCN-TU-100 23.25 9.49 141.79 3.13 0.19 0.84 2.83

MCN-TU-130 23.00 9.39 231.44 3.46 0.26 0.70 3.80

MCN-TU-150 24.03 9.81 246.65 3.69 0.26 0.48 6.76

a The cell parameter calculated from low-angle XRD paterns (FIGS. 2A-B) using ao = 6 211.

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-T-150 and MCN-TU-150.

[0069] In summary, the inventors have demonstrated the preparation of highly ordered and

3D structured MCN materials with tunable pore diamters and high nitrogen content by using enthaol -washed calcination-free KIT-6 silica as a hard templates and 3 -amino- 1,2, 4-triazole (T or 3 AT) by combining with urea (U) as double CN precursors. The MCN-T-150 and MCN- TU-150 materials prepared by KIT-6-150-EW silica showed the highest specific surface areas (231.44 m²/g and 246.65 m²/g) and nitrogen contents (C3N5.03 and C3N6.14). The addition of urea induced the highly cross-linked N-3C bridging network among three (tri-s-triazine) moieties. From the results on the CO2 adsorption capacity, it is also concluded that the MCN- TU-150 materials (6.76 mmol/g at 0 °C and 30 bar) can serve as a highly promising photocatalyst for the CO2 capture and conversion into valuable chemicals with hydrogen produced through water splitting under visible light.

[0070] Although embodiments of the present application and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the embodiments as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the above disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein can be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.

Claims

1. A method of producing a mesoporous carbon nitride (MCN) material, the method comprising:

(a) contacting an ethanol washed KIT-6 silica template with an aqueous solution comprising a MCN precursor material having -NTh groups to form a mixture;

(b) polymerizing the precursor material and forming a MCN polymeric material/KIT-6 composite;

(c) carbonizing the MCN polymeric material/KIT-6 composite; and

(d) removing the ethanol washed KIT-6 silica template to obtain the MCN material and optionally drying the obtained material.

2. The method of claim 2, wherein polymerizing step (b) comprises (i) heating the mixture to a first temperature of 90 to 110 °C, preferably about 100 °C for 4 to 8 hours, preferably, 6 hours; and (ii) increasing the temperature to 150 to 170 °C, preferably about 160 °C, for 4 to 8 hours, preferably 6 hours.

3. The method of claim 1, wherein carbonizing step (c) comprises heating the mesoporous MCN material/KIT-6 composite to 400 °C to 600 °C, preferably about 500 °C, for 3 to 7 hours, preferably about 5 hours under an inert gas atmosphere.

4. The method of any one of claims 1 to 3, further comprising producing the ethanol washed KIT-6 silica template, the method comprising:

(a) obtaining a solution comprising amphiphilic triblock copolymer and tetraethyl orthosilicate (TEOS);

(b) heating the solution at a temperature of 75 °C to 200 °C, preferably 100 °C to 150

°C, for 12 to 36 hours, preferably about 24 hours, to form a non-calcined KIT- 6 silica template/triblock copolymer composite; and

(c) removing the triblock copolymer from the composite to obtain the ethanol washed

KIT-6 silica template.

5. The method of claim 4, wherein removing step (c) comprises contacting the ethanol washed KIT-6 silica template/triblock copolymer composite with an alcoholic solution, preferably an ethanol solution.

6. The method of claim 5, comprising contacting the ethanol washed KIT-6 silica

template/triblock copolymer composite with the alcoholic solution at ambient temperature for 1 to 5 hours, preferably 2 to 4 hours, or more preferably about 3 hours at 20 to 40 °C.

7. The method of claim 1, wherein the MCN precursor is an amino- 1,2, 4-triazole and urea or formaldehyde.

8. The method of claim 7, wherein obtained MCN has a three-dimensional MCN matrix with -NTb groups and an average pore diameter of 3 nanometers (nm) to 4 nm, a carbon to nitrogen ratio of 0.45 to 0.55, a surface area of 235 m²/g to 255 m²/g, and a total pore volume of 0.20 cm³/g to 0.3 cm³/g.

9. The method of claim 8, wherein the obtained MCN has a carbon to nitrogen ratio of about 0.48, a surface area of 245 m²/g to 250 m²/g, and a total pore volume of about 0.26 cm³/g.

10. The method of claim 9, wherein the obtained MCN has capable of adsorbing carbon dioxide (CO2) at 6 mmol/g to 7 mmol/g at 0 °C and a pressure of 1 to 5, or about 3 MPa.

11. The method of claim 1, wherein the MCN precursor is an amino- 1,2, 4-triazole.

12. The method of claim 11, wherein the obtained MCN has a carbon to nitrogen ratio of 0.55 to 0.65, a surface area of 175 m²/g to 225 m²/g, and a total pore volume of 0.25 cm³/g to 0.35 cm³/g.

13. The method of claim 12, wherein the obtained MCN has a carbon to nitrogen ratio of about 0.59, a surface area of 200 m²/g to 210 m²/g, and a total pore volume of about 0.28 cm³/g.

14. The method of claim 11, wherein the obtained MCN is capable of adsorbing carbon dioxide (CO2) at 5 mmol/g to 6 mmol/g at a temperature of 0 °C and a pressure of 1 to 5, or about 3 MPa.

15. The method of claim 1, wherein the obtained MCN has a 3-D matrix having a d- spacing of 8.60 to 9.9, preferably about 8.65 to about 9.81, or more preferably about 9.19 or about 9.81.

16. A process for carbon dioxide (CO2) adsorption, the process comprising:

contacting the mesoporous carbon nitride (MCN) material obtained by any one of claims 1 to 15 with a feed stream comprising CO2, wherein at least a portion of the CO2 is adsorbed by the mesoporous MCN material.

17. The process of claim 16, wherein 5 mmol/g to 6 mmol/g of CO2 is adsorbed by the mesoporous MCN material at a temperature of 0°C and a pressure of 30 bar.

18. The process of claim 16, wherein the adsorbed CO2 is activated.