Composite photocatalyst based on surface-aminated carbon nitride and preparation method and application thereof

Abstract

The application belongs to the technical field of catalysts, and particularly relates to a composite photocatalyst based on surface-aminoated carbon nitride and a preparation method and application thereof. The preparation method comprises the following steps: firstly, placing bulk carbon nitride in a tube furnace and performing heat treatment under the action of oxygen to peel off single-layer or oligolayer carbon nitride nanosheets; then, ultrasonically dispersing the carbon nitride nanosheets and urea into ethylene glycol to obtain surface-aminoated carbon nitride nanosheets through solvothermal reaction; and finally, depositing a metal cocatalyst on the surface of the carbon nitride to obtain the composite photocatalyst based on surface-aminoated carbon nitride. The metal cocatalyst obtained by the application has a strong interaction between metal particles and the surface-aminoated carbon nitride nanosheets of the carrier, can promote the separation and transmission of photo-generated carriers, can improve the utilization rate of metal atoms in the photocatalytic reaction, and exhibits extremely excellent photocatalytic performance under visible light.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalyst preparation, in particular to a composite photocatalyst based on surface aminated carbon nitride and a preparation method and application thereof. BACKGROUND

[0002] Photocatalytic technology has been widely researched and developed in recent years due to its advantages such as high efficiency, green and non-polluting, and direct utilization of solar energy, especially in a series of environmental and energy fields such as degradation of pollutants, water splitting to produce hydrogen and oxygen, reduction of carbon dioxide, and organic synthesis. As a visible light responsive photocatalyst, graphite phase carbon nitride has high stability, simple synthesis method, and two-dimensional layered structure, and has attracted widespread attention from researchers in the field of photocatalysis. Graphite phase carbon nitride with a two-dimensional layered structure is stacked together, which is commonly referred to as "bulk" carbon nitride. However, the bulk carbon nitride photocatalyst has many defects, and the recombination probability of photo-generated carriers is high under light irradiation, resulting in low photocatalytic performance, which limits its practical application in the field of photocatalysis.

[0003] In photocatalytic reactions, cocatalysts play a crucial role in improving the activity and stability of photocatalysts, such as improving the separation efficiency of electrons and holes at the interface, reducing the activation energy of surface reactions, providing active sites for reactions, and inhibiting the occurrence of reverse reactions. Therefore, by loading cocatalysts, especially metal cocatalysts (such as platinum, gold, copper, etc.), the photocatalytic performance of carbon nitride can be greatly improved. Due to the lack of sufficient active sites on the surface of bulk carbon nitride, the interaction between the metal and the carbon nitride is weak after the metal is deposited on the surface of the carbon nitride, and the transfer probability of photo-generated carriers is low, making it difficult to fully utilize the advantages of metal cocatalysts.

[0004] Therefore, it is of great significance to optimize the structure of the surface of bulk carbon nitride, improve the metal-support interaction, and design an efficient composite photocatalyst based on carbon nitride. SUMMARY

[0005] One of the purposes of the present application is to provide a preparation method of a composite photocatalyst based on surface aminated carbon nitride, which can greatly enhance the metal-support interaction, realize effective separation and transmission of photo-generated carriers, and improve the utilization rate of metal atoms in photocatalytic reactions, thereby significantly enhancing the performance of carbon nitride photocatalysts.

[0006] To achieve the above purpose, the following technical solution is adopted: a preparation method of a composite photocatalyst based on surface aminated carbon nitride, comprising the following steps:

[0007] S1, placing bulk carbon nitride in a tube furnace and performing heat treatment at 480-580℃ in high-purity oxygen to obtain single-layer or oligolayer structured carbon nitride nanosheets;

[0008] S2, dispersing the carbon nitride nanosheets prepared in step S1 into ethylene glycol, and adding urea to continue uniform dispersion, wherein the mass ratio of urea to carbon nitride nanosheets is (0.1-2.0):1, to obtain a mixed suspension; performing a solvothermal reaction on the mixed suspension at 120-200℃, and obtaining surface-aminoated carbon nitride nanosheets by centrifugation, washing, and drying;

[0009] S3, dispersing the surface-aminoated carbon nitride nanosheets into deionized water, and then mixing with an aqueous metal precursor solution, wherein the mass ratio of metal in the aqueous metal precursor solution to the surface-aminoated carbon nitride nanosheets is (0.1-10):100, and the mixture is stirred and reacted at 60-100℃, and then freeze-dried, and the dried powder is placed in a tube furnace to perform thermal reduction under the action of hydrogen at 200-600℃, to obtain the surface-aminoated carbon nitride-based composite photocatalyst.

[0010] Further improvement of the preparation method of the surface-aminoated carbon nitride-based composite photocatalyst:

[0011] Preferably, in step S1, the purity of the high-purity oxygen is >99.99%, and the heat treatment time is 5-30 min.

[0012] Preferably, in step S2, the dispersion concentration of the carbon nitride nanosheets in ethylene glycol is 1-3 mg / ml, and the solvothermal reaction time is 1-24 h.

[0013] Preferably, in step S3, the metal precursor in the aqueous metal precursor solution is a single metal water-soluble salt or a combination of two or more metal water-soluble salts.

[0014] Preferably, the metal in the metal water-soluble salt is one of noble metals Au, Pt, Pd, Ag or non-noble metals Fe, Cu, Co, Ni, and the water-soluble salt is a chloride, a nitrate, a sulfate, or a sulfite.

[0015] Preferably, in step S3, the mixture is stirred and reacted at 60-100℃ for 2-12 h.

[0016] Preferably, in step S3, the thermal reduction time is 1-6 h.

[0017] Preferably, in step S3, the hydrogen action is a high-purity hydrogen atmosphere with a purity >99.99%, or a mixed hydrogen and inert gas atmosphere.

[0018] The second object of the present application is to provide a surface-aminoated carbon nitride-based composite photocatalyst prepared by the preparation method described in any one of the above.

[0019] The third object of the present application is to provide a use of the above-mentioned composite photocatalyst based on surface-ammoniated g-C3N4 in photocatalytic reactions such as water splitting and carbon dioxide reduction.

[0020] The present application has the following advantages over the prior art:

[0021] The present application provides a preparation method of a composite photocatalyst based on surface-ammoniated g-C3N4. First, bulk g-C3N4 is exfoliated into monolayer or oligolayer g-C3N4 nanosheets by heat treatment, then the surface of g-C3N4 is ammoniated by a solvothermal reaction with urea, and finally a metal cocatalyst is deposited on the surface of g-C3N4, thereby obtaining a composite photocatalyst based on surface-ammoniated g-C3N4. Compared with bulk g-C3N4, the solvothermal reaction of monolayer or oligolayer g-C3N4 with urea can greatly improve the degree of surface ammoniation of g-C3N4. Compared with unammoniated g-C3N4 nanosheets, the g-C3N4 nanosheets after ammoniation have stronger interaction with metals, and the metal cocatalyst particles are smaller, which can effectively promote the separation and transport of photo-generated carriers and fully exert the advantages of the metal cocatalyst, thereby significantly enhancing the photocatalytic performance of g-C3N4.

[0022] The metal cocatalyst obtained by the present application has strong interaction between metal particles and surface-ammoniated g-C3N4 nanosheets on the support surface, which can promote the separation and transport of photo-generated carriers and improve the utilization rate of metal atoms in photocatalytic reactions, and exhibit extremely excellent photocatalytic performance under visible light. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 Transmission electron microscope images of the surface-ammoniated g-C3N4 composite photocatalysts synthesized for Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3.

[0024] Figure 2 Infrared spectra of bulk g-C3N4, Example 1, Comparative Example 1 and Comparative Example 2.

[0025] Figure 3 High-resolution XPS spectra of element Pt in Example 1, Comparative Example 2 and Comparative Example 5.

[0026] Figure 4 High-resolution XPS spectra of element N in bulk g-C3N4, Example 1 and Comparative Example 2.

[0027] Figure 5 Performance of bulk g-C3N4, surface-ammoniated g-C3N4 nanosheets, Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4 and Comparative Example 5 in photocatalytic hydrogen production under visible light.

[0028] Figure 6 Stability of the composite photocatalyst synthesized in Example 1 in photocatalytic hydrogen production.

[0029] Figure 7 High-resolution transmission electron microscopy image of the metal Au and Cu co-loaded surface-aminoated carbon nitride composite photocatalyst synthesized for Example 3.

[0030] Figure 8 Performance of bulk carbon nitride, Example 3, Comparative Example 6 and Comparative Example 7 in photocatalytic reduction of carbon dioxide under visible light. DETAILED DESCRIPTION

[0031] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application is further described in detail below in combination with examples, and all other examples obtained by those of ordinary skill in the art without making any creative efforts on the basis of the examples in the present application all belong to the scope of protection of the present application.

[0032] Example 1

[0033] The present embodiment provides a preparation method of a surface-aminoated carbon nitride composite photocatalyst, which specifically comprises the following steps:

[0034] Example 1

[0035] The present embodiment provides a preparation method of a surface-aminoated carbon nitride composite photocatalyst, which specifically comprises the following steps:

[0036] S1, 10g of melamine powder is weighed into a 100mL ceramic crucible with a lid, which is moved into an air muffle furnace, and heated from room temperature to 550℃ at a heating rate of 5℃ / min, and kept for 2h. After cooling to room temperature, the sintered product is fully ground to obtain a light yellow bulk carbon nitride (abbreviated as g-C3N4).

[0037] S2, 0.2g of bulk carbon nitride powder (abbreviated as g-C3N4) is weighed and placed in a tube furnace, high-purity oxygen (purity >99.99%) is introduced, and annealing heat treatment is carried out at 500℃ for 10min to obtain carbon nitride nanosheets with single-layer or oligolayer structure, with a yield of about 30%;

[0038] S3, 50mg of carbon nitride nanosheets prepared in step S2 is dispersed in 30mL of ethylene glycol for 30min, and then 20mg of urea is added for further ultrasonic dispersion for 30min, with a mass ratio of urea to carbon nitride nanosheets of 0.4, to obtain a mixed suspension;

[0039] The mixed suspension is transferred to a stainless steel reaction kettle containing a 100mL polytetrafluoroethylene liner, and reacted at 160℃ for 6h. The product after reaction is centrifuged, washed and dried to obtain surface-aminoated carbon nitride nanosheets (abbreviated as C3N4-amino).

[0040] S4, 100 mg of surface-aminoated carbon nitride nanosheets were weighed and dispersed in 60 mL of deionized water by ultrasonic dispersion. Then a certain amount of chloroplatinic acid aqueous solution (the mass of Pt was 0.5 mg) was added, and the reaction was stirred at 70°C for 6 h. After freeze-drying of the product, the dried powder was placed in a tube furnace and annealed at 200°C for 2 h under the action of high-purity hydrogen (purity > 99.99%), to obtain a metal Pt-loaded surface-aminoated carbon nitride composite photocatalyst. The loading amount of Pt was 0.5 wt%.

[0041] Example 2

[0042] The present embodiment provides a preparation method of a surface-aminoated carbon nitride-based composite photocatalyst, which specifically comprises the following steps:

[0043] S1, 0.3 g of bulk carbon nitride powder prepared in step S1 of Example 1 was placed in a tube furnace, high-purity oxygen (purity > 99.99%) was introduced, and annealing heat treatment was carried out at 480°C for 15 min to obtain single-layer or oligolayer structure carbon nitride nanosheets, with a yield of about 25%;

[0044] S2, 100 mg of carbon nitride nanosheets prepared in step S1 were dispersed in 60 mL of ethylene glycol by ultrasonic dispersion for 45 min; then 100 mg of urea was added and ultrasonic dispersion was continued for 45 min, and the mass ratio of urea to carbon nitride was 1.0, to obtain a mixed suspension;

[0045] The mixed suspension was transferred to a stainless steel reaction kettle containing a 100 mL polytetrafluoroethylene liner, and reacted at 180°C for 4 h. The product after reaction was obtained by centrifugation, washing and drying to obtain surface-aminoated carbon nitride nanosheets (abbreviated as C3N4-amino);

[0046] S3, 100 mg of surface-aminoated carbon nitride nanosheets were weighed and dispersed in 45 mL of deionized water by ultrasonic dispersion. Then a certain amount of chloroauric acid aqueous solution (the mass of Au was 1.5 mg) was added, and the reaction was stirred at 60°C for 8 h. After freeze-drying of the product, the dried powder was placed in a tube furnace and annealed at 300°C for 1 h under the action of high-purity hydrogen (purity > 99.99%), to obtain a metal Au-loaded surface-aminoated carbon nitride composite photocatalyst. The loading amount of Au was 1.5 wt%.

[0047] Example 3

[0048] The present embodiment provides a preparation method of a surface-aminoated carbon nitride-based composite photocatalyst, which specifically comprises the following steps:

[0049] S1, 0.1 g of the bulk g-C3N4 powder prepared in step S1 of Example 1 was weighed and placed in a tube furnace, high-purity oxygen (purity > 99.99%) was introduced, and annealing heat treatment was carried out at 550°C for 5 min to obtain single-layer or oligolayer structure g-C3N4 nanosheets, with a yield of about 20%;

[0050] S2, 60 mg of the g-C3N4 nanosheets prepared in step S1 was weighed and dispersed in 40 mL of ethylene glycol for 30 min; then 120 mg of urea was added and ultrasonic dispersion was continued for 45 min, with a mass ratio of urea to g-C3N4 of 2.0, to obtain a mixed suspension;

[0051] The mixed suspension was transferred to a stainless steel reaction kettle containing a 100 mL polytetrafluoroethylene liner, and reacted at 140°C for 9 h. The product after reaction was obtained by centrifugation, washing and drying to obtain surface-aminoated g-C3N4 nanosheets (abbreviated as C3N4-amino);

[0052] S3, 100 mg of the surface-aminoated g-C3N4 nanosheets was weighed and ultrasonically dispersed in 45 mL of deionized water. Then a certain amount of copper nitrate and chloroauric acid aqueous solution (the amount of Au was 0.3 mg, and the amount of Cu was 0.6 mg) was added, and the reaction was stirred at 80°C for 2 h. After freeze-drying of the product, the dried powder was placed in a tube furnace, and under the action of hydrogen / nitrogen mixed gas (80% N2 / 20% H2), annealing was carried out at 500°C for 2 h to obtain a surface-aminoated g-C3N4 composite photocatalyst co-loaded with metal Au and Cu. The loading amount of Au was 0.3 wt%, and the loading amount of Cu was 0.6 wt%.

[0053] In order to better reflect the advantages of the present application, we compare the samples synthesized by the following comparative examples.

[0054] Comparative Example 1

[0055] This comparative example refers to Example 1, except that the bulk g-C3N4 is not peeled into g-C3N4 nanosheets by step S1, but is directly surface-aminoated by step S2 and Pt nanoparticles are deposited by step S3.

[0056] Comparative Example 2

[0057] This comparative example refers to Example 1, except that after the bulk g-C3N4 is peeled into g-C3N4 nanosheets by step S1, it is not subjected to the aminoation treatment of step S2, but is directly subjected to the deposition of Pt nanoparticles by step S3.

[0058] Comparative Example 3

[0059] This comparative example refers to Example 1, except that the bulk g-C3N4 is not subjected to the treatment of steps S1 and S2, but is directly subjected to the deposition of Pt nanoparticles by step S3.

[0060] Comparative Example 4

[0061] This comparative example refers to Example 1, except that bulk carbon nitride is first exfoliated into carbon nitride nanosheets by step S1, and then the carbon nitride nanosheets are ultrasonically dispersed with urea in ethylene glycol, without a solvothermal reaction, and Pt nanoparticles are directly deposited by step S3.

[0062] Comparative Example 5

[0063] This comparative example refers to Example 1, except that the Pt nanoparticles synthesized by step S3 after the bulk carbon nitride is treated by step S1 and step S2 are not subjected to hydrogen thermal reduction.

[0064] Comparative Example 6

[0065] This comparative example refers to Example 3, except that step S3 only loads Pt nanoparticles, obtaining a metal Pt-loaded surface-aminated carbon nitride composite photocatalyst. Among them, the loading amount of Pt is 0.5wt%.

[0066] Comparative Example 7

[0067] This comparative example refers to Example 3, except that step S3 only loads Cu nanoparticles, obtaining a metal Cu-loaded surface-aminated carbon nitride composite photocatalyst. Among them, the loading amount of Cu is 0.2wt%.

[0068] The photocatalysts obtained in the above examples and comparative examples are evaluated for their performance under visible light by photocatalytic decomposition of water and reduction of carbon dioxide. The light source is a PLS-SXE300D type xenon lamp and a UV420 type filter (Beijing Polifilm Technology Co., Ltd.). The gas chromatograph is a Kexiao 1690C type, equipped with a thermal conductivity detector, an FID detector and a methane conversion furnace, and the carrier gas is high-purity nitrogen. The steps of the photocatalytic decomposition of water to produce hydrogen reaction are as follows: weigh 5 mg of the photocatalyst powder and add it to 100 mL of a 10 vol% triethanolamine aqueous solution, stir uniformly, and then seal the photocatalytic reactor. High-purity nitrogen is introduced to purge the reactor at a flow rate of 50 milliliters per minute to eliminate residual gases in the reactor, and then the photocatalytic reaction is started. The steps of the photocatalytic reduction of carbon dioxide reaction are as follows: weigh 50 mg of the photocatalyst powder and add it to a carbon dioxide-filled quartz glass reactor, and inject 2 mL of deionized water, and then start the photocatalytic reaction.

[0069] Figure 1Transmission electron microscopy (TEM) images of the surface-aminated carbon nitride composite photocatalysts synthesized in Examples 1, 1, 2, and 3. Statistical analysis showed that the Pt nanoparticles loaded on the carbon nitride surface had diameters of 0.97, 1.76, 2.1, and 3.8 nm, respectively. Smaller Pt nanoparticle diameters indicate stronger interactions between Pt and the supported carbon nitride. In Comparative Example 3, the bulk carbon nitride support was neither exfoliated into carbon nitride nanosheets nor surface-aminated, resulting in very weak interactions between the loaded Pt and the bulk carbon nitride. In Example 1, the bulk carbon nitride support was first exfoliated into carbon nitride nanosheets and then surface-aminated, leading to strong interactions between the loaded Pt and the surface-aminated carbon nitride nanosheets. In Comparative Example 2, although the bulk carbon nitride support was exfoliated into carbon nitride nanosheets, the lack of surface-amination resulted in weak interactions between the loaded Pt and the supported carbon nitride nanosheets. For Comparative Example 1, although the bulk carbon nitride was not exfoliated into carbon nitride nanosheets, its metal-support interaction was superior to that of Comparative Examples 2 and 3 after surface amination modification. Furthermore, the smaller the particle size of the Pt nanoparticles, the larger their specific surface area, which improves the utilization rate of surface Pt atoms in the photocatalytic reaction, thereby enhancing the performance of the photocatalyst.

[0070] Figure 2 Infrared spectra of bulk carbon nitride, Example 1, Comparative Example 1, and Comparative Example 2. 3000-3500 cm⁻¹ -1 The broad peak at the specified location corresponds to the NH bond vibration on the carbon nitride surface, i.e., the degree of surface amination. For bulk carbon nitride, Example 1, Comparative Example 1, and Comparative Example 2, the transmittance of NH bond vibration was 78.8%, 71.3%, 77.1%, and 78.3%, respectively. The results indicate that the carbon nitride nanosheets without surface amination modification have a weak degree of surface amination; although the bulk carbon nitride underwent surface amination modification, its actual amination degree was also weak due to severe aggregation; only when the bulk carbon nitride was exfoliated into carbon nitride nanosheets before surface amination modification could the degree of surface amination be significantly enhanced.

[0071] Figure 3 and Figure 4 The images show high-resolution XPS spectra of Pt and N in bulk carbon nitride, Example 1, Comparative Example 2, and Comparative Example 5, respectively. Figure 3 Comparative Example 2 synthesized Pt nanoparticles with Pt 0 The metallic form is loaded onto the surface of carbon nitride nanosheets, and the characteristic peak at 70.8 eV corresponds to Pt. 0 4f 7 / 2 Energy levels. For Example 1, the Pt nanoparticles also used Pt... 0The metal state form is supported on the surface of the support. Compared with Comparative Example 2, the 4f 0 energy level of Pt 7 / 2 in Example 1 is red-shifted to 71.0 eV. At the same time, in Comparative Example 5, Pt is mainly supported on the surface of the surface-aminated g-C3N4 in the form of metal state Pt 0 , but a certain amount of oxidized Pt 2+ also exists. A large number of literatures show that, compared with oxidized Pt 2+ , Pt 0 nanoparticles in the metal state are active site centers in the photocatalytic hydrogen production reaction. Therefore, it is necessary to perform hydrogen thermal reduction on Comparative Example 5 to eliminate as much oxidized Pt 2+ as possible (corresponding to Example 1). According to the XPS spectrum of N element in Figure 4 , the binding energy of N element in Example 1 and Comparative Example 2 is red-shifted compared with bulk g-C3N4, and the red-shift amplitude of N element in Example 1 is greater. Combined with the results of Figure 1 , Figure 2 , Figure 3 and Figure 4 , only when the bulk g-C3N4 is exfoliated into g-C3N4 nanosheets and then surface-aminated, can the interaction between metal Pt and the support g-C3N4 be significantly improved.

[0072] Figure 5 The photocatalytic hydrogen production performance of bulk g-C3N4, surface-aminated g-C3N4 nanosheets, Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4 and Comparative Example 5 under visible light. For bulk g-C3N4, the hydrogen production rate is only 18.2 pmol / h. For surface-aminated g-C3N4 nanosheets, the hydrogen production rate is slightly increased to 20.8 pmol / h. Since the surfaces of bulk g-C3N4 and surface-aminated g-C3N4 nanosheets lack active sites for hydrogen production, their photocatalytic hydrogen production efficiency is very low. When metal Pt is supported on the surface of the support g-C3N4, the hydrogen production rate is greatly enhanced. For Example 1, the hydrogen production rate is increased to 1157.5 pmol / h, which is 63.6 times that of bulk g-C3N4. For Comparative Example 5, since a small amount of oxidized Pt 2+The hydrogen production rate of the prepared composite photocatalyst is 915.2 pmol / h, which is lower than that of Example 1. For Comparative Example 1, the bulk-phase carbon nitride is loaded with Pt nanoparticles after direct amination, and the hydrogen production activity of the prepared composite photocatalyst is reduced to 841.2 pmol / h. For Comparative Example 2, the carbon nitride nanosheets are not surface-aminated, and the hydrogen production rate of the prepared composite photocatalyst is further reduced to 720.1 pmol / h. When the bulk-phase carbon nitride is neither exfoliated into carbon nitride nanosheets nor surface-aminated, the hydrogen production rate of the prepared composite photocatalyst is the lowest, only 681.4 eV. In addition, for Comparative Example 4, the carbon nitride nanosheets are mixed with urea, and the surface amination degree is weak due to the absence of a solvothermal reaction, and the hydrogen production rate of the prepared composite photocatalyst is 807.6 pmol / h, which is not only significantly lower than that of Example 1, but also lower than that of Comparative Example 5 and Comparative Example 1. Therefore, only when the bulk-phase carbon nitride is first exfoliated into carbon nitride nanosheets, then surface-aminated, and finally hydrogen-reduced with Pt nanoparticles, can a high-efficiency photocatalytic hydrogen production material be obtained.

[0073] Figure 6 The stability of the composite photocatalyst synthesized in Example 1 in photocatalytic hydrogen production. After 4 rounds of 16 h photocatalytic reaction, the photocatalytic hydrogen production rate is basically not significantly reduced, indicating that the composite photocatalyst synthesized in Example 1 has good photocatalytic stability.

[0074] Figure 7 The high-resolution transmission electron microscopy image of the surface-aminated carbon nitride composite photocatalyst loaded with metal Au and Cu synthesized in Example 3. According to statistics, the average particle size of the nanoparticles is about 1.3 nm, and the lattice fringe 0.217 nm corresponds to the structure of AuCu alloy (0.2355x1 / 3+0.2087x2 / 3=0.217), indicating that Au and Cu are loaded on the surface of the surface-aminated carbon nitride nanosheets in the form of an alloy.

[0075] Figure 8The performance of bulk C3N4, Example 3, Comparative Example 6 and Comparative Example 7 in photocatalytic reduction of carbon dioxide under visible light. For bulk C3N4, the product is mainly CO with a yield of 0.54 pmol / hg and a CO selectivity of 94.7%. When Cu is loaded on the surface of the surface-aminated C3N4 nanosheets, the CO yield is increased to 1.71 pmol / hg, but the CH4 yield is also increased from 0.03 to 0.15 pmol / hg, and the CO selectivity is 91.9%. For the composite photocatalyst with Au loading, the CO yield and selectivity are 1.27 pmol / hg and 90.7%, respectively. When AuCu alloy is loaded on the surface of the surface-aminated C3N4 nanosheets, the CO yield is greatly increased to 3.26 pmol / hg, while the CH4 yield is suppressed to 0.04 pmol / hg, and the CO selectivity is increased to 98.8%, indicating that the composite photocatalyst of surface-aminated C3N4 with Au and Cu co-loading synthesized in Example 3 has good performance in photocatalytic reduction of carbon dioxide.

[0076] Those skilled in the art will understand that the above description is only several specific embodiments of the present application, not all embodiments. It should be noted that many modifications and improvements can also be made by those of ordinary skill in the art, and all modifications and improvements that do not exceed the scope of the claims should be considered as the protection scope of the present application.

Claims

1. A method for preparing a composite photocatalyst based on surface-aminated carbon nitride, characterized by, The method comprises the following steps: S1, placing bulk g-C3N4 in a tube furnace, and performing heat treatment in high-purity oxygen at 480-580 °C to obtain single-layer or oligolayer g-C3N4 nanosheets; S2, dispersing the g-C3N4 nanosheets obtained in step S1 in ethylene glycol, and then adding urea to uniformly disperse, wherein the mass ratio of urea to g-C3N4 nanosheets is (0.1-2.0):1, to obtain a mixed suspension; performing a solvothermal reaction on the mixed suspension at 120-200 °C, and obtaining surface-aminoated g-C3N4 nanosheets by centrifugation, washing, and drying; S3, dispersing the surface-aminoated g-C3N4 nanosheets in deionized water, and then mixing with a metal precursor aqueous solution, wherein the mass ratio of metal in the metal precursor aqueous solution to the surface-aminoated g-C3N4 nanosheets is (0.1-10):100, and performing stirring reaction on the mixed solution at 60-100 °C, followed by freeze-drying, and then placing the dried powder in a tube furnace to perform thermal reduction in a hydrogen atmosphere at 200-600 °C, to obtain a surface-aminoated g-C3N4-based composite photocatalyst.

2. The method for preparing a composite photocatalyst based on surface-aminated carbon nitride according to claim 1, characterized by, In step S1, the purity of the high-purity oxygen is >99.99%, and the heat treatment time is 5-30 min.

3. The method for preparing a composite photocatalyst based on surface-aminated carbon nitride according to claim 1, characterized by, In step S2, the dispersion concentration of the g-C3N4 nanosheets in ethylene glycol is 1-3 mg / mL, and the solvothermal reaction time is 1-24 h.

4. The method for preparing a composite photocatalyst based on surface-aminated carbon nitride according to claim 1, characterized by, In step S3, the metal precursor in the metal precursor aqueous solution is a single metal water-soluble salt or a combination of two or more metal water-soluble salts.

5. The method for preparing a composite photocatalyst based on surface-aminated carbon nitride according to claim 4, characterized by, The metal in the metal water-soluble salt is one of noble metals Au, Pt, Pd, and Ag, or non-noble metals Fe, Cu, Co, and Ni, and the water-soluble salt is a chloride, a nitrate, a sulfate, or a sulfite.

6. The method for preparing a composite photocatalyst based on surface-aminated carbon nitride according to claim 1, characterized by, In step S3, the mixed solution is stirred and reacted at 60-100 °C for 2-12 h.

7. The method for preparing a composite photocatalyst based on surface-aminated carbon nitride according to claim 1, characterized by, In step S3, the thermal reduction time is 1-6 h.

8. The method for preparing a composite photocatalyst based on surface-aminated carbon nitride according to claim 1, characterized by, In step S3, the hydrogen atmosphere is a high-purity hydrogen atmosphere with a purity of >99.99%, or a mixed atmosphere of hydrogen and an inert gas.

9. A surface-aminoated g-C3N4-based composite photocatalyst prepared by the preparation method of any one of claims 1-8.

10. Use of the surface-aminoated g-C3N4-based composite photocatalyst of claim 9 in a photocatalytic reaction.

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