A method for preparing mesoporous tubular carbon nitride

Abstract

A method for preparing mesoporous tubular carbon nitride rich in mesoporous tubular carbon nitride co-modified with intralayer / interlayer co-confined single-atom Tm and C vacancy co-modification includes: 1) mechanically mixing melamine and urea precursors uniformly, wherein the molar ratio of melamine to urea is 1:23-1:19; then pressing this mixture into cylindrical tablets using a tablet press and placing them in a covered alumina boat, followed by pyrolysis in a muffle furnace at 550±20℃ for 4±1h, and collecting the product after grinding; 2) uniformly dispersing the above product with thulium chloride hexahydrate in deionized water, rapidly freezing the resulting suspension in liquid nitrogen and drying it in a freeze dryer to obtain a semi-finished product; 3) placing the above semi-finished product in a covered quartz boat, and then annealing it in a tube furnace at 300±20℃ for 3±1h, followed by centrifugal washing and freeze drying to obtain the final product. Its application in photocatalysis yields excellent results.

Description

Technical Field

[0001] This invention belongs to the field of new materials technology. It relates to the preparation of mesoporous tubular carbon nitride, and more particularly to a method for preparing mesoporous tubular carbon nitride rich in intralayer / interlayer co-confined rare earth single-atom Tm co-modification with C vacancy. Background Technology

[0002] Single-atom modification involves anchoring atomically dispersed metals onto a support material to obtain single-atom modified materials. In recent years, single-atom modified materials have demonstrated superior performance in certain reactions due to their unique coordination structures, electronic properties, and site-specific activity. Furthermore, since single-atom materials can achieve near-maximum atom utilization efficiency, the amount of metal used can be significantly reduced, thus contributing to lower material costs and more efficient resource utilization, which is particularly important for noble and rare earth metals. These advantages have led to widespread interest in single-atom materials in electrochemistry, photochemistry, organic synthesis, and biomedicine. Especially in photocatalysis, single metal atoms supported on semiconductor photocatalysts not only serve as active sites for photocatalytic reactions, but their unique geometric and electronic properties also enhance the inherent activity of each metal active site, resulting in significant catalytic activity and selectivity that cannot be achieved on metal surfaces. Therefore, single-atom modified materials are not only ideal emerging photocatalytic materials but also provide an excellent platform for exploring catalytic structure-performance relationships and studying catalytic mechanisms at the atomic scale. Among numerous single-atom photocatalytic materials, carbon nitride-based single-atom photocatalysts are a widely studied class of materials. This is mainly due to the ease of synthesis, elemental abundance, low cost, high stability, and tunable morphology of the carbon nitride support. More importantly, it possesses an ultra-high content of Lewis base pyridine nitrogen, which can effectively interact with strong Lewis acid metal atoms to form metal-nitrogen coordination structures, thus aiding in the dispersion and stabilization of metal atoms. However, in terms of morphology, carbon nitrides obtained through conventional synthesis methods are generally bulk or relatively thick sheets. Even nanosheets prepared through various exfoliation methods often suffer from low specific surface areas due to van der Waals forces, hindering the uniform loading of metal atoms. Template methods can yield carbon nitrides with high specific surface areas and specific porous tubular morphologies. This morphology not only provides ample loading sites for metal atoms but also facilitates reactant adsorption and gas molecule transport. Simultaneously, the nano-confinement effect generated by the porous tubular structure helps stabilize active metal atoms spatially, thereby promoting the stable conduct of the photocatalytic reaction. However, template methods typically require cumbersome etching processes and consume additional materials, making them both troublesome and wasteful, and unsuitable for future industrial applications. Therefore, exploring template-free methods for the simple preparation of carbon nitride carrier materials with high specific surface area and porous tubular structures is essential. Furthermore, regarding the spatial location of single atoms, current methods for synthesizing single-atom modified carbon nitride nanomaterials mainly fall into two categories: "intra-layer confined single atoms" and "inter-layer confined single atoms." "Intra-layer confined single atoms" involve introducing metal single atoms into the π-conjugated plane of carbon nitride, increasing its in-plane conductivity, thereby enhancing in-plane charge transfer and improving photocatalytic performance.The term "interlayer confined single-atom" refers to introducing single-atom metals into the interlayer space of carbon nitride. This improves interlayer electron transfer and thus enhances photocatalytic performance through metal-nitrogen charge transfer channels formed between the single atom and adjacent carbon nitride layers. Furthermore, research shows that introducing specific defects into carbon nitride can trap electrons, suppress photogenerated charge radiative recombination, and simultaneously serve as active centers for some photocatalytic reactions, promoting their favorable occurrence. However, the key challenge facing most carbon nitride-based single-atom photocatalysts remains the low catalytic efficiency caused by insufficient and inefficient active sites. Yet, almost no synthetic method can simultaneously confine single atoms within and between layers and introduce defects to modify carbon nitride to enhance photocatalytic performance. Therefore, it is essential to develop a simple, efficient, energy-saving method for preparing porous tubular carbon nitride with high activity and selectivity through the design of co-modified defects using confined single atoms within and between layers. Summary of the Invention

[0003] The purpose of this invention is to provide a method for preparing mesoporous tubular carbon nitride rich in intralayer / interlayer co-confined single-atom Tm and C vacancy co-modification. This method prepares porous tubular carbon nitride nanomaterials with intralayer / interlayer co-confined atomic-level dispersion of Tm and C vacancy co-modification through unique and simple operation steps.

[0004] The technical solution of this invention is that the method involves using only two precursor materials—melamine and urea—adding them to a mortar in a molar ratio of 1:23 to 1:19, mechanically grinding them evenly, and then using a tablet press to compress the mixture into tablets approximately [size missing]. The cylindrical slices were then subjected to a pyrolysis step to obtain the precursor. The pyrolysis conditions were 550±20℃ in a muffle furnace for 4±1h. The product was collected after grinding.

[0005] Thulium chloride hexahydrate and the above pyrolysis products were uniformly dispersed in deionized water at a mass ratio of 1:11000-1:9. The resulting suspension was rapidly frozen in liquid nitrogen, followed by freeze-drying to obtain a semi-finished product. The semi-finished product was then annealed in a tube furnace under a 5% H2 / Ar atmosphere at 300±20℃ for 3±1 h. Finally, after centrifugation, washing, and freeze-drying, porous tubular carbon nitride nanomaterials with co-confined intralayer / interlayer single-atom Tm and C vacancy co-modification were obtained. This method only requires simple grinding, pressing, pyrolysis, and impregnation annealing steps, while general strategies such as exfoliation or template methods often require lengthy and cumbersome operations and generally cannot form a structure in which intralayer / interlayer co-confined single atoms and C vacancies coexist.

[0006] The key to this method is: (1) mechanically mixing two precursor materials—appropriate amounts of melamine and urea—in a dry atmosphere, pressing them into tablets under appropriate pressure, and then placing them in a muffle furnace for pyrolysis; (2) uniformly dispersing appropriate amounts of thulium chloride hexahydrate and the above pyrolysis products in deionized water, freeze-drying them into semi-finished products, and then placing them in a tube furnace under a 5% H2 / Ar atmosphere for further annealing. This simple preparation method may be applied to the synthesis of porous tubular carbon nitride nanomaterials with in-layer / inter-layer co-constrained single metal atoms and defect co-modification from the pyrolysis products of a mixture of appropriate amounts of metal salts and appropriate amounts of melamine and urea. The principle for the amount of melamine and urea used is: the molar ratio of melamine to urea is 1:23-1:19. The principle for the pressure and tablet size when using a tablet press is: the pressure range is 48-80 MPa, and the tablet size is approximately The cylindrical shape. The principle for the amount of pyrolysis products used in the compression of metal salts with melamine and urea mixtures is: the mass ratio of metal elements in the metal salt to the pyrolysis products is 1:25000-49:1000.

[0007] This invention provides an application for mesoporous tubular carbon nitride nanomaterials co-modified with intralayer / interlayer co-confined single-atom Tm and C vacancy, specifically, the use of mesoporous tubular carbon nitride nanomaterials co-modified with intralayer / interlayer co-confined single-atom Tm and C vacancy for photocatalysis. Results show that the construction of multiple active Tm sites within and between layers effectively promotes CO2 adsorption and activation, significantly reducing the formation energy of the reaction intermediate *COOH. Simultaneously, the presence of C vacancies further enhances the activation ability of Tm sites for CO2. Moreover, the construction of intralayer Tm sites, interlayer Tm-N charge transfer channels, and C vacancies significantly enhances the separation and transfer of photogenerated carriers. Furthermore, the porous tubular structure also promotes favorable photocatalytic reactions. Therefore, mesoporous tubular carbon nitride nanomaterials co-modified with intralayer / interlayer co-confined single-atom Tm and C vacancy are excellent photocatalytic materials. Their application in the photocatalytic reduction of carbon dioxide yields promising results.

[0008] The porous tubular carbon nitride nanomaterials prepared in this way, which are co-modified with single-atom Tm and C vacancies, can be used in the field of photocatalysis, such as photocatalytic carbon dioxide reduction.

[0009] The beneficial effects of this invention are as follows: Urea and melamine are mechanically mixed uniformly, compressed into tablets, and placed in an alumina boat. The precursor is obtained through a one-step pyrolysis process, which is simple and convenient. Urea, another raw material, is inexpensive, stable, and non-toxic. Simultaneously, the precursor is impregnated with thulium chloride hexahydrate to obtain a semi-finished product. This product is then annealed again, centrifuged, washed, and freeze-dried to obtain porous tubular carbon nitride nanomaterials with co-modified intralayer / interlayer co-confined single-atom Tm and C vacancies. This structure is highly beneficial for photocatalysis. Furthermore, the formation of single atoms promotes the efficient utilization of metal resources. Figure 9-10 That explains it. Attached Figure Description

[0010] Figure 1 These are X-ray diffraction (XRD) patterns of products with different Tm single-atom contents according to embodiments of the present invention. The products of the present invention are denoted as TCN-Cv / Tm-Y, where Y = 1, 2, or 3, representing the actual mass of thulium chloride hexahydrate added during the synthesis process. Cv represents a C vacancy, which is generated along with the introduction of Tm. The actual masses of thulium chloride hexahydrate added during the synthesis process are: 3 mg for TCN-Cv / Tm-1, 6 mg for TCN-Cv / Tm-2, and 9 mg for TCN-Cv / Tm-3. Porous tubular pure carbon nitride (TCN) without Tm modification is used as a comparison. The figures show that Tm was successfully incorporated into carbon nitride without changing the crystal phase, and no Tm-related impurity phases were generated.

[0011] Figure 2 (a) is a scanning electron microscope (SEM) image of the product of an embodiment of the present invention, for comparison. Figure 2 (b) is a SEM image of pure carbon nitride (TCN) without Tm modification. It can be seen that the product has a porous tubular structure and the Tm modification has basically not changed the morphology.

[0012] Figure 3 (a) is a transmission electron microscope (TEM) image of the product of the embodiment of the present invention, for comparison. Figure 3 (b) is a TEM image of pure carbon nitride (TCN) without Tm. It can be further seen that the product has a porous tubular structure and that the Tm modification has almost no effect on the morphology.

[0013] Figure 4 (a)-(f) are spherical aberration electron microscope (AC-HAADF-STEM) images of the product in the embodiments of the present invention. Figure 4 (a) and the corresponding element mapping diagram ( Figure 4 (b)-(f)) indicates that Tm is uniformly distributed in the form of single atoms on the porous tubular carbon nitride matrix.

[0014] Figure 5 This is the Fourier transform infrared (FTIR) spectrum of the product in an embodiment of the present invention. Figure 5 (a) Electron paramagnetic resonance (EPR) spectrum ( Figure 5 (b) and X-ray photoelectron spectroscopy (XPS) plots Figure 5 (c)-(f)) Blocky pure carbon nitride (CN) without Tm and porous tubular pure carbon nitride (TCN) are used as comparisons to show that the prepared product has a cyano structure and the introduction of Tm is accompanied by the formation of C vacancies. At the same time, Tm in the product carries a partial positive charge.

[0015] Figure 6 These are synchrotron radiation test analysis diagrams of the products in this embodiment of the invention, showing the X-ray absorption near-edge structure spectrum (…). Figure 6 (a) Fourier transform extended X-ray absorption fine structure spectrum ( Figure 6 (b) Wavelet transform-extended X-ray absorption fine structure spectroscopy Figure 6 (c)-(e)) and the extended X-ray absorption fine structure spectra of the product and their fitting curves ( Figure 6 (f)) The analysis results further show that Tm in the product is distributed in the form of single atoms and carries a partial positive charge. Tm single atoms are confined in the carbon nitride layer and between layers. Tm is only bonded to N and is coordinated with 6 N atoms.

[0016] Figure 7 The image shows the ultraviolet-visible absorption spectrum of the product in this embodiment of the invention. Analysis of the image shows that the band gap of the product is 2.79 eV.

[0017] Figure 8 These are the N2 adsorption-desorption curves and pore size distribution curves of the products in the embodiments of the present invention.

[0018] Figure 9 The photocatalytic activity of the product in this embodiment of the invention in reducing carbon dioxide to produce CO and CH4. Figure 9 In the table, (a), (b), and (c) represent the activity of TCN-Cv / Tm-Y corresponding to three products with different Tm contents and C vacancy modifications, respectively. CN represents the activity of blocky pure carbon nitride, and TCN represents the activity of porous tubular pure carbon nitride.

[0019] Figure 10 This is a stability diagram of the photocatalytic carbon dioxide reduction cycle of the product in the embodiment of the present invention. Detailed Implementation

[0020] The following steps: (1) The molar ratio of melamine to urea is in the range of 1:23-1:19. For example, in the case of 10g urea and 1g melamine, the amount of melamine is approximately 7.92896 mmol, the amount of urea is approximately 0.16650 mol, and the molar ratio of melamine to urea is approximately 1:21. The principle of a molar ratio of melamine to urea between 1:23 and 1:19 may be applied to the synthesis of other porous tubular carbon nitride nanomaterials co-constrained by single metal atoms and defects within / between layers.

[0021] Place an appropriate amount of urea and melamine in an agate mortar and grind for several tens of minutes to mix them evenly.

[0022] Place an appropriate amount of the above homogeneous mixture into a tableting mold, and use a tableting machine to compress it into tablets of approximately [size missing]. The cylindrical sheet, with a pressure range of 48-80 MPa, may be used to synthesize other porous tubular carbon nitride nanomaterials that are co-constrained by single metal atoms and defects within / between layers.

[0023] After the melamine and urea precursor were mechanically mixed evenly, the mixture was pressed into cylindrical tablets using a tablet press and placed in a covered alumina boat. The tablets were then pyrolyzed in a muffle furnace at 550±20℃ for 4±1h at a heating rate of 5℃ / min. After the reaction was completed, the tablets were allowed to cool naturally to room temperature. The product was then ground and collected.

[0024] The cylindrical tablets were placed in a covered alumina boat and pyrolyzed in a muffle furnace at about 550°C for about 4 hours, with a heating rate of 5°C / min. After the reaction was completed, the tablets were allowed to cool naturally to room temperature, and the product was collected after grinding.

[0025] (2) The above product was uniformly dispersed with thulium chloride hexahydrate in deionized water to obtain a suspension, which was then rapidly frozen in liquid nitrogen and dried in a freeze dryer to obtain a semi-finished product.

[0026] Specifically: Disperse an appropriate amount of the above pyrolysis product in an appropriate amount of deionized water by ultrasonication for several tens of minutes, and add an appropriate amount of thulium chloride hexahydrate aqueous solution dropwise under vigorous magnetic stirring, and then continue stirring for 3±1h to obtain a uniformly dispersed light yellow suspension.

[0027] The above pale yellow suspension was rapidly frozen in liquid nitrogen and then dried in a freeze dryer for 4-7 days to obtain a semi-finished product.

[0028] (3) The above semi-finished products are placed in a covered quartz boat and then annealed in a tube furnace at 300±20℃ for 3±1h, followed by centrifugal washing and freeze drying.

[0029] The mass ratio of thulium chloride hexahydrate to the aforementioned pyrolysis products is in the range of 1:11000-1:9, and the mass ratio of metal Tm element to pyrolysis products is between 1:25000-49:1000. For example, in the case of 100 mg of pyrolysis products and 6 mg of thulium chloride hexahydrate, the mass ratio of thulium chloride hexahydrate to pyrolysis products is 3:50, and the mass ratio of metal element Tm element to pyrolysis products is approximately 1:38. The mass ratio of metal salt to pyrolysis products is between 1:11000-1:9. The mass ratio of metal element in metal salt to pyrolysis products is between 1:25000-49:1000. This principle may be applicable to the synthesis of other porous tubular carbon nitride nanomaterials with intralayer / interlayer co-confined single metal atoms and defect co-modification.

[0030] An appropriate amount of the above semi-finished product was placed in a covered quartz boat, and then placed in a tube furnace for annealing at 300±20℃ for about 3 hours. The heating rate was 5℃ / min, the atmosphere was 5% H2 / Ar, and the gas flow rate was 80±5mL / min. After the reaction was completed, the product was naturally cooled to room temperature, and then removed and collected.

[0031] The above-mentioned tubular furnace annealing product was washed several times with anhydrous ethanol and deionized water, and then freeze-dried in a freeze dryer for 4-7 days. This yielded a mesoporous tubular carbon nitride nanomaterial rich in mesoporous tubular structures co-modified with rare earth single-atom Tm and C vacancy within / between layers. Its application in photocatalysis yielded excellent results.

[0032] (1) Under dry conditions, weigh 10g of urea and 1g of melamine and place them in an agate mortar. Grind them thoroughly for 40 minutes to obtain a uniformly mixed powder of white urea and melamine precursors.

[0033] (2) Place approximately 2.2 g of the above-mentioned homogeneous precursor mixture into a tableting mold, and use a tableting machine at 72 MPa to compress the mixture into tablets with a size of approximately Cylindrical sheet;

[0034] (3) The covered alumina boat containing the above precursor mixture cylindrical sheet was placed in a muffle furnace and pyrolyzed at 550°C for 4 hours with a heating rate of 5°C / min. After the reaction was completed, it was naturally cooled to room temperature and the pale yellow product was collected after grinding.

[0035] (4) Disperse about 100 mg of the above precursor mixture pyrolysis product in 30 mL of deionized water by sonication for 30 min to obtain a pale yellow suspension.

[0036] (5) Under vigorous magnetic stirring, 300, 600 and 900 μL of thulium chloride hexahydrate aqueous solution (10 mg / mL) were added dropwise to the above pale yellow suspension, and then stirred continuously for 3 h to obtain a pale yellow suspension containing thulium chloride that was evenly dispersed.

[0037] (6) The above pale yellow suspension containing thulium chloride was rapidly frozen in liquid nitrogen and then dried in a freeze dryer for 4-7 days to obtain a semi-finished product.

[0038] (7) Place about 50 mg of the above semi-finished product in a covered quartz boat, then place it in a tube furnace under a 5% H2 / Ar atmosphere and anneal it at 300°C for 3 h. The heating rate is 5°C / min and the gas flow rate is 80 mL / min. After the reaction is completed, allow it to cool naturally to room temperature, remove the product and collect it.

[0039] (8) The above-mentioned tubular furnace annealing product was washed several times with anhydrous ethanol and deionized water, and then freeze-dried in a freeze dryer for 4-7 days to obtain mesoporous tubular carbon nitride nanomaterials co-modified with intra- and inter-layer co-confined rare earth single-atom Tm and C vacancy. The porous tubular carbon nitride nanomaterials co-modified with intra- and inter-layer co-confined single-atom Tm and C vacancy obtained in this way can achieve good results when used for photocatalysis.

[0040] The products were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), spherical aberration electron microscopy (AC-HAADF-STEM), Fourier transform infrared spectroscopy (FTIR), electron paramagnetic resonance spectroscopy (EPR), X-ray photoelectron spectroscopy (XPS), Shanghai Synchrotron Radiation Facility (SSRF), ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS), fully automated specific surface area and porosity analyzer, and inductively coupled plasma atomic emission spectrometry (ICP-OES).

[0041] Figure 1 The images show XRD patterns of products with different Tm single-atom contents in embodiments of the present invention, with pure porous tubular carbon nitride (TCN) as a comparison. It can be seen from the images that Tm was successfully incorporated into carbon nitride without changing the crystal phase or generating any impurity phases related to Tm.

[0042] Table 1 shows the ICP-OES test results of the products in the embodiments of the present invention. The actual Tm single-atom loading of different products can be seen from the table. The results obtained for 300, 600, and 900 μL of thulium chloride hexahydrate are as follows: the actual Tm content is 0.79 wt% for TCN-Cv / Tm-1, 1.65 wt% for TCN-Cv / Tm-2, and 2.56 wt% for TCN-Cv / Tm-3, respectively.

[0043] Figure 2 (a) is a scanning electron microscope (SEM) image of the product of an embodiment of the present invention, for comparison. Figure 2(b) is a SEM image of pure carbon nitride (TCN) without Tm modification. It can be seen that the product has a porous tubular structure and the Tm modification has basically not changed the morphology.

[0044] Figure 3 (a) is a TEM image of the product of an embodiment of the present invention, for comparison. Figure 3 (b) is a TEM image of pure carbon nitride (TCN) without Tm. It can be further seen that the product has a porous tubular structure and that the Tm modification has almost no effect on the morphology.

[0045] Figure 4 (a)-(f) are AC-HAADF-STEM images of the products in the embodiments of the present invention. Figure 4 (a) and the corresponding element mapping diagram ( Figure 4 (b)-(f)) indicates that Tm is uniformly distributed on the carbon nitride matrix in the form of isolated atoms.

[0046] Figure 5 This is the FTIR image of the product in the embodiment of the present invention. Figure 5 (a)), EPR diagram ( Figure 5 (b) and XPS graph ( Figure 5 (c)-(f)) Blocky pure carbon nitride (CN) without Tm and porous tubular pure carbon nitride (TCN) are used as comparisons to show that the prepared product has a cyano structure and the introduction of Tm is accompanied by the formation of C vacancies. At the same time, Tm in the product carries a partial positive charge.

[0047] Figure 6 The diagram shows the synchrotron radiation test analysis of the product in this embodiment of the invention. The analysis further shows that Tm in the product is distributed in the form of single atoms and carries a partial positive charge. Tm single atoms are confined both inside and between layers of carbon nitride. At the same time, Tm is only coordinated with N, and the coordination number is 6.

[0048] Figure 7 The image shows the UV-Vis absorption spectrum of the product. Analysis of the image reveals that the band gap of the product is 2.79 eV. By comparing Tm-free bulk pure carbon nitride (CN) and porous tubular pure carbon nitride (TCN), it is shown that the modification of single-atom Tm and C vacancies has little effect on the light-harvesting ability of pure carbon nitride.

[0049] Figure 8 The figures show the N2 adsorption-desorption curves and pore size distribution curves of the product in this embodiment of the invention. It can be seen from the figures that the specific surface area of ​​the product has increased to a certain extent compared with pure carbon nitride, and the pores in the product are mainly mesoporous.

[0050] For example, a photocatalytic CO2 reduction experiment was conducted using the porous tubular carbon nitride nanocatalyst prepared in the examples, which was co-modified with intra-layer / inter-layer co-confined rare earth single-atom Tm and C vacancies. Specifically, approximately 5 mg of the photocatalyst was weighed and uniformly dispersed in a 3.14 cm³ medium. 2 The catalyst was placed on a perforated quartz glass plate and placed in a glass reaction vessel. The total volume of the reaction system was approximately 460 mL, and the light source was a 300 W xenon lamp. High-purity CO2 gas was then introduced into the reaction system to purge the air and bring the pressure in the reaction system to standard atmospheric pressure. Then, 400 μL of deionized water was injected into the reaction system as a reducing agent. After the catalyst had adsorbed and balanced the reactant molecules in the dark for several hours, the light was turned on. Subsequently, at regular intervals, about 1 mL of gas was taken from the reaction system and injected into a gas chromatograph to analyze the amount of CO and CH4 produced.

[0051] The evolution of CO and CH4 yields over time and the product yields are as follows: Figure 9 As shown in the figure. The results indicate that the porous tubular carbon nitride nanocatalyst co-modified with intra- and inter-layer co-confined rare earth single-atom Tm and C vacancies exhibits superior photocatalytic CO2 reduction activity compared to bulk pure carbon nitride (CN) and porous tubular pure carbon nitride (TCN). While effectively improving activity, the product still maintains high selectivity in the photocatalytic reduction of CO2 to CO. Figure 9 ).

[0052] The product's photocatalytic CO2 reduction stability is as follows Figure 10 As shown in the figure, the porous tubular carbon nitride nanocatalyst with intra-layer / inter-layer co-confined rare earth single-atom Tm and C vacancy co-modification exhibits excellent stability for photocatalytic reduction of CO2.

[0053] Table 1 Explanation

[0054] Table 1 shows the ICP-OES test results of the products in the embodiments of the present invention. The table shows the actual Tm single-atom loading of different products. The actual Tm contents are: TCN-Cv / Tm-1 is 0.79 wt%, TCN-Cv / Tm-2 is 1.65 wt%, and so on.

[0055] The TCN-Cv / Tm-3 ratio is 2.56 wt%.

[0056] Table 1 shows the content of the metal element Tm in the catalysts synthesized in the examples.

[0057]

[0058] The above description is merely a specific embodiment of the present invention; however, the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing mesoporous tubular carbon nitride rich in intralayer / interlayer co-confined single-atom Tm-co-modified C vacancy, characterized in that, The process includes the following steps: (1) mechanically mixing melamine and urea precursors uniformly, wherein the molar ratio of melamine to urea is 1:23-1:19; then pressing the mixture into cylindrical tablets using a tablet press and placing them in a covered alumina boat, followed by pyrolysis reaction in a muffle furnace at 550±20 ℃ for 4±1 h, and collecting the product after grinding; (2) uniformly dispersing the product with thulium chloride hexahydrate in deionized water, rapidly freezing the resulting suspension in liquid nitrogen and drying it in a freeze dryer to obtain a semi-finished product; (3) placing the above semi-finished product in a covered quartz boat, and then annealing it in a tube furnace at 300±20 ℃ for 3±1 h. h, after centrifugation, washing and freeze-drying, yields mesoporous tubular carbon nitride rich in intralayer / interlayer co-confined single-atom Tm-co-C vacancy co-modification; the mass ratio of the thulium chloride hexahydrate and the above precursor mixture pyrolysis product is 1:11000-1:9, and the mass ratio of metal Tm element in the metal salt to the pyrolysis product is 1:25000-49:1000.

2. The preparation method according to claim 1, characterized in that, Mechanical mixing involves placing appropriate amounts of urea and melamine precursors in an agate mortar and grinding for several tens of minutes to obtain a white, uniformly mixed powder of urea and melamine.

3. The preparation method according to claim 1, characterized in that: Place an appropriate amount of a homogeneous mixture of urea and melamine into a tableting mold, and use a tableting machine to press the mixture into cylindrical tablets with a size of Ø18 mm × 7 mm. The pressure range for pressing the precursor mixture into cylindrical tablets is 48-80 MPa.

4. The preparation method according to any one of claims 1-2, characterized in that: A covered alumina boat containing cylindrical sheets of precursor mixture was placed in a muffle furnace and pyrolyzed at 550±20 °C for 4 h with a heating rate of 5 °C / min. After the reaction was completed, the alumina boat was allowed to cool naturally to room temperature, and the product was collected after grinding.

5. The preparation method according to claim 1, characterized in that: A suitable amount of the above precursor mixture pyrolysis product was ultrasonically dispersed in a suitable amount of deionized water for several tens of minutes to obtain a pale yellow suspension.

6. The preparation method according to claim 1, characterized in that: Weighing, grinding, and tableting were all performed in a dry environment.

7. The preparation method according to claim 5, characterized in that: Under vigorous magnetic stirring, an appropriate amount of thulium chloride hexahydrate aqueous solution was added dropwise to the above pale yellow suspension, and then stirred continuously for 3±1 h to obtain a pale yellow suspension containing thulium chloride that was evenly dispersed.

8. The preparation method according to claim 7, characterized in that: The above-mentioned pale yellow suspension containing thulium chloride was rapidly frozen in liquid nitrogen and then dried in a freeze dryer for 4-7 days to obtain a semi-finished product.

9. The preparation method according to claim 8, characterized in that: An appropriate amount of the above semi-finished product was placed in a covered quartz boat, and then placed in a tube furnace under a 5% H2 / Ar atmosphere and annealed at 300±20 ℃ for 3 h. The heating rate was 5℃ / min and the gas flow rate was 80±5 mL / min. After the reaction was completed, the product was naturally cooled to room temperature, removed and collected. The tube furnace annealed product was washed several times with anhydrous ethanol and deionized water, and then placed in a freeze dryer for 4-7 days to obtain mesoporous tubular carbon nitride rich in intralayer / interlayer co-confined single atom Tm co-modified C vacancy.

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