A composite photocatalyst loaded with single-atom metal and its preparation method and application

Abstract

The present invention belongs to the field of catalyst technology, and specifically relates to a composite photocatalyst loaded with single-atom metal, and a preparation method and application thereof, wherein the preparation method comprises: (1) fully impregnating carbon nitride nanosheets into a nitrogen-containing precursor solution and then freeze-drying; (2) obtaining carbon nitride nanosheets with nitrogen-rich surfaces under the action of ammonia + hydrogen and inductively coupled low-temperature plasma; (3) loading a metal precursor onto the surface of the nitrogen-rich carbon nitride nanosheets according to an equal volume impregnation method and then vacuum drying; (4) obtaining a carbon nitride composite photocatalyst containing a single-atom metal co-catalyst through a discharge reaction under the action of hydrogen low-temperature plasma. The catalyst has high yield, high loading rate of single-atom metal, and very good photocatalytic stability between samples of different batches, and is suitable for future batch preparation.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and in particular relates to a composite photocatalyst loaded with single-atom metals, and a preparation method and application thereof. Background Art

[0002] Using photocatalytic technology to decompose water to produce hydrogen and degrade pollutants is one of the effective strategies to solve the energy crisis and environmental pollution. As a visible light responsive photocatalyst, graphite phase carbon nitride has the characteristics of high stability, simple synthesis method, and two-dimensional layered structure, and has attracted extensive attention from researchers in the field of photocatalysis. However, the single carbon nitride photocatalyst has a high probability of recombination of photogenerated carriers under light, and its performance in decomposing water to produce hydrogen and degrading pollutants is relatively low, which limits its practical application in the field of photocatalysis.

[0003] In photocatalytic reactions, the loading of metal co-catalysts can effectively improve the performance of carbon nitride. Generally, in order to improve the utilization rate of precious metals, the size of precious metal nanoparticles needs to be reduced. When the size of metal particles is reduced to the single-atom level, the utilization rate of metal atoms can be maximized. For single-atom metals, their active sites are composed of isolated metal atoms and carriers, and their catalytic performance is highly dependent on the structure of the carrier.

[0004] When single-atom metals are loaded onto the surface of carbon nitride, carbon nitride can be regarded as an extended ligand and coordinated with dispersed single-atom metals, such as metal-nitrogen coordination, to achieve the fixation of metal particles on the carbon nitride carrier in an atomic-level dispersed manner. The preparation methods of single-atom metal-loaded carbon nitride composite photocatalysts are mainly impregnation method, coprecipitation method, hydrothermal reduction method, etc., and their loading amount is usually very low (<0.5wt%). At the same time, due to the lack of sufficient coordination active sites on the surface of carbon nitride, metal particles can easily agglomerate into nanoclusters or nanoparticles, affecting their photocatalytic performance and not suitable for mass production. Therefore, it is urgent to develop a method with a large loading amount and suitable for mass preparation of single-atom metal-based carbon nitride composite photocatalysts. Summary of the invention

[0005] One of the purposes of the present invention is to provide a method for preparing a composite photocatalyst loaded with single-atom metals that is efficient and suitable for large-scale preparation. The preparation method can achieve gram-level or even kilogram-level large-scale preparation, and the loading amount of the single-atom metal co-catalyst can reach 10wt%.

[0006] To achieve the above object, the present invention adopts the following technical solution: a method for preparing a composite photocatalyst loaded with single-atom metal, comprising the following steps:

[0007] S1, immersing carbon nitride nanosheets having a two-dimensional layered structure into an aqueous solution of a nitrogen-containing precursor, stirring the mixture sufficiently, and then freeze-drying the mixture to obtain a mixed powder 1;

[0008] S2, placing the mixed powder 1 obtained in step S1 in a reaction chamber of an inductively coupled low-temperature plasma device, and performing a discharge reaction in a mixed atmosphere of ammonia and hydrogen to obtain carbon nitride nanosheets with nitrogen-rich surfaces;

[0009] S3, immersing an equal volume of the nitrogen-rich carbon nitride nanosheets into a metal precursor solution, and then drying the mixture under vacuum at a low temperature to obtain a mixed powder 2;

[0010] S4. Place the mixed powder 2 obtained in step S3 in a reaction chamber of an inductively coupled low-temperature plasma device, and conduct a discharge reaction in a hydrogen atmosphere to obtain a composite photocatalyst loaded with single-atom metals on a preparation scale of gram to kilogram levels.

[0011] Preferably, the nitrogen-containing precursor in step S1 is one or a combination of two or more of ammonia water, urea or hydrazine hydrate.

[0012] Preferably, the concentration of the aqueous solution of the nitrogen-containing precursor in step S1 is 5-15 mol / L, and the nitrogen-containing precursor is one or a combination of two or more of ammonia water, urea or hydrazine hydrate.

[0013] Preferably, the stirring temperature in step S1 is 60-100° C., and the stirring time is 6-24 h.

[0014] Preferably, in the mixed atmosphere of ammonia and hydrogen in step S2, the volume content of ammonia is 5%-15%, and the volume content of hydrogen is 85%-95%.

[0015] Preferably, the power of the discharge reaction in step S2 is 20-200W, the discharge time is 15-60min, and the vacuum degree is 20-50Pa.

[0016] Preferably, the metal precursor of the metal precursor solution in step S3 is one or a combination of two or more water-soluble salts of Au, Pt, Pd, Ag, Fe, Cu, Co, and Ni, and the water-soluble salt is one or a combination of two or more chlorides, nitrates, sulfates, and sulfites.

[0017] Preferably, the mass ratio of the total amount of metal in the metal precursor solution in step S3 to the carbon nitride nanosheets in step S1 is (0.1-10):100.

[0018] Preferably, the power of the discharge reaction in step S4 is 0-20 W and not 0, the discharge time is 0-5 min and not 0, and the vacuum degree is 5-10 Pa.

[0019] The second object of the present invention is to provide a composite photocatalyst loaded with single-atom metal prepared by the above preparation method.

[0020] The third object of the present invention is to provide a use of the above-mentioned composite photocatalyst loaded with single-atom metal in photocatalytic reactions such as decomposition of water.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The preparation method provided by the present invention firstly mixes carbon nitride nanosheets with nitrogen-containing precursors, obtains carbon nitride nanosheets with nitrogen-rich surfaces through inductively coupled low-temperature plasma discharge reaction, and then places the nanosheets in a metal precursor solution for equal volume immersion and then obtains a composite photocatalyst loaded with single-atom metal through low-temperature plasma discharge reaction. Equal volume immersion means that the volume of immersion water is equal to the saturated water absorption of the catalyst. When the carbon nitride nanosheets after surface nitrogen enrichment treatment are mixed with metal precursors, they can provide stronger metal-N coordination, so that metal particles are loaded on the carbon nitride surface in single-atom form, which can effectively prevent metal particles from agglomerating into metal clusters or metal nanoparticles, and the metal loading can reach 10wt%, realizing gram-level or even kilogram-level large-scale preparation.

[0023] (2) The present invention solves the problem of low photocatalytic performance of carbon nitride. The prepared composite photocatalyst loaded with single-atom metals has metal co-catalyst particles uniformly loaded on the surface of nitrogen-rich carbon nitride nanosheets in single-atom form, which can give full play to the atomic utilization of the metal co-catalyst and show extremely excellent photocatalytic performance under visible light. The particle size of the single-atom metal co-catalyst is 0.1-0.2nm, and the photocatalytic stability between samples from different batches is very good. By adjusting the type of metal precursor, the preparation of a variety of composite photocatalysts based on single-atom metal co-catalysts can be achieved.

[0024] (3) The present invention mainly utilizes an inductively coupled low-temperature plasma device to synthesize composite photocatalysts loaded with single-atom metals. The experimental device is relatively simple and the reaction conditions are mild. It can realize the batch preparation of single-atom co-catalysts, improve production efficiency, reduce reaction costs, and is conducive to the promotion and application of this synthesis method. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The Pt / C prepared in Example 1 3 N 4 Spherical aberration-corrected high-angle dark-field scanning transmission electron microscopy image.

[0026] Figure 2 The Pt / C prepared in Example 1 3 N 4 Spherical aberration-corrected high-angle dark-field scanning transmission electron microscopy image.

[0027] Figure 3 The Pt / C prepared in Example 13 N 4 Extended X-ray absorption fine structure spectrum.

[0028] Figure 4 Pt / C prepared in Comparative Example 5 3 N 4 Spherical aberration-corrected high-angle dark-field scanning transmission electron microscopy image.

[0029] Figure 5 The Pt / C obtained in Comparative Example 2 3 N 4 High-resolution transmission electron microscopy image.

[0030] Figure 6 The Pt / C obtained in Comparative Example 3 3 N 4 High-resolution transmission electron microscopy image.

[0031] Figure 7 The Pt / C obtained in Comparative Example 4 3 N 4 High-resolution transmission electron microscopy image.

[0032] Figure 8 The performance of the photocatalysts obtained in Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4 and Comparative Example 5 in decomposing water to produce hydrogen under visible light.

[0033] Fig. 9 The different batches of Pt / C obtained in Example 1 3 N 4 Performance of water splitting to produce hydrogen under visible light. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention.

[0035] The manufacturer of the inductively coupled low-temperature plasma device used in the following embodiments is Anhui Beiyike Equipment Technology Co., Ltd., and the model is BTF-1200C-S-SL-PECVD. It should be explained that the low temperature in the inductively coupled low-temperature plasma device is a relative concept. In other plasma technologies, such as arc discharge plasma, the temperature of the central plasma can reach several thousand degrees. In the inductively coupled plasma technology, depending on the discharge power, such as tens of watts to two or three hundred watts, the temperature of the central plasma may only be tens of degrees to one or two hundred degrees, so it is called "low temperature" plasma.

[0036] Example 1

[0037] This embodiment provides a method for preparing a composite photocatalyst loaded with a single metal atom, which specifically comprises the following steps:

[0038] S1, weighing 1 g of graphite phase carbon nitride nanosheet powder, adding it to 50 mL of concentrated ammonia solution (ammonia concentration is 28 wt%), stirring at 80° C. for 12 h, and freeze-drying to obtain a mixed powder 11;

[0039] S2, placing the mixed powder 11 in the reaction chamber of the inductively coupled low-temperature plasma device, and introducing 12% by volume NH 3 +88% H 2 Mix the gas, remove the gas in the device, turn on the vacuum pump to evacuate to 25Pa, the discharge power is 100W, and the discharge time is 45min. After the discharge reaction is completed, carbon nitride nanosheet powder with nitrogen-rich surface is obtained;

[0040] S3, slowly add H 2 PtCl 6 The aqueous solution (concentration of 25 g / L) was immersed in equal volumes, H 2 PtCl 6 The mass ratio of Pt contained in the aqueous solution to the carbon nitride nanosheet powder in step S1 is 0.1:100. After the impregnation is completed, the mixture is dried under vacuum at 60° C. for 24 hours to obtain a mixed powder 12;

[0041] S4, placing the mixed powder 12 in the reaction chamber of the inductively coupled low-temperature plasma device again, and introducing high-purity H 2 , remove the gas in the device, turn on the vacuum pump to evacuate to 5 Pa, the discharge power is 15 W, and the discharge time is 3 min. After the discharge reaction is completed, 0.1 wt% single-atom Pt-loaded carbon nitride nanosheet powder is obtained.

[0042] Example 2

[0043] This embodiment provides a method for preparing a composite photocatalyst loaded with a single metal atom, which specifically comprises the following steps:

[0044] S1, weighing 0.1 g of graphite phase carbon nitride nanosheet powder, adding it to 20 mL of urea aqueous solution (urea concentration is 35 wt%), stirring at 60° C. for 18 h, and freeze-drying to obtain a mixed powder 21;

[0045] S2, placing the mixed powder 21 in the reaction chamber of the inductively coupled low-temperature plasma device, and introducing 10% by volume NH 3 +90%H 2Mix the gas, remove the gas in the device, turn on the vacuum pump to evacuate to 30Pa, the discharge power is 60W, and the discharge time is 30min. After the discharge reaction is completed, carbon nitride nanosheet powder with nitrogen-rich surface is obtained;

[0046] S3, slowly add HAuCl 4 The aqueous solution (concentration of 25 g / L) was immersed in equal volumes, and HAuCl 4 The mass ratio of Au contained in the aqueous solution to the carbon nitride nanosheet powder in step S1 is 0.5:100. After the impregnation is completed, the mixture is dried under vacuum at 70° C. for 16 h to obtain a mixed powder 22;

[0047] S4, placing the mixed powder 22 in the reaction chamber of the inductively coupled low-temperature plasma device again, and introducing high-purity H 2 , remove the gas in the device, turn on the vacuum pump to evacuate to 8 Pa, the discharge power is 10 W, and the discharge time is 4 min. After the discharge reaction is completed, 0.5 wt% single-atom Au-loaded carbon nitride nanosheet powder is obtained.

[0048] Example 3

[0049] This embodiment provides a method for preparing a composite photocatalyst loaded with a single metal atom, which specifically comprises the following steps:

[0050] S1, weighing 100 g of graphite phase carbon nitride nanosheet powder, adding it to 2000 mL of ammonia aqueous solution (ammonia concentration is 24 wt%), stirring at 70° C. for 24 h, and freeze-drying to obtain a mixed powder 31;

[0051] S2, placing the mixed powder 31 in the reaction chamber of the inductively coupled low-temperature plasma device, and introducing 15% by volume NH 3 +85% H 2 Mix the gas, remove the gas in the device, turn on the vacuum pump to evacuate to 20Pa, the discharge power is 200W, and the discharge time is 60min. After the discharge reaction is completed, carbon nitride nanosheet powder with nitrogen-rich surface is obtained;

[0052] S3, adding Cu(NO 3 ) 2 The aqueous solution (concentration of 300 g / L) was immersed in equal volumes of Cu(NO 3 ) 2 The mass ratio of Cu contained in the aqueous solution to the carbon nitride nanosheet powder in step S1 is 10:100. After the impregnation is completed, the mixture is dried under vacuum at 80° C. for 24 hours to obtain a mixed powder 32;

[0053] S4, placing the mixed powder 32 in the reaction chamber of the inductively coupled low-temperature plasma device again, and introducing high-purity H 2 , remove the gas in the device, turn on the vacuum pump to evacuate to 5 Pa, the discharge power is 18 W, and the discharge time is 3 min. After the discharge reaction is completed, 10 wt% single-atom Cu-loaded carbon nitride nanosheet powder is obtained.

[0054] Example 4

[0055] This embodiment provides a method for preparing a composite photocatalyst loaded with a single metal atom, which specifically comprises the following steps:

[0056] S1, weighing 20 g of graphite phase carbon nitride nanosheet powder, adding it to 2000 mL of hydrazine aqueous solution (hydrazine hydrate concentration is 24 wt%), stirring at 60° C. for 12 h, and freeze-drying to obtain a mixed powder 41;

[0057] S2, placing the mixed powder 41 in the reaction chamber of the inductively coupled low-temperature plasma device, and introducing 15% by volume NH 3 +85% H 2 Mix the gas, remove the gas in the device, turn on the vacuum pump to evacuate to 40Pa, the discharge power is 150W, and the discharge time is 20min. After the discharge reaction is completed, carbon nitride nanosheet powder with nitrogen-rich surface is obtained.

[0058] S3, slowly add HAuCl 4 and AgNO 3 A mixed aqueous solution (HAuCl 4 and AgNO 3 The concentration of HAuCl was 25 g / L. 4 and AgNO 3 The mass ratios of Au, Ag and the carbon nitride nanosheet powder in step S1 contained in the mixed aqueous solution are 1:100 and 2:100, and after the impregnation is completed, the mixture is dried under vacuum at 50° C. for 12 hours to obtain a mixed powder 42;

[0059] S4, placing the mixed powder 42 in the reaction chamber of the inductively coupled low-temperature plasma device again, and introducing high-purity H 2 , remove the gas in the device, turn on the vacuum pump to evacuate to 5 Pa, the discharge power is 12 W, and the discharge time is 3 minutes. After the discharge reaction is completed, 1wt% Au single atom and 2wt% Ag single atom co-loaded carbon nitride nanosheet powder is obtained.

[0060] Comparative Example 1

[0061] This comparative example refers to Example 1, except that the carbon nitride nanosheets were immersed in ammonia water and NH3 / H 2 After plasma reduction, no Pt is loaded on its surface. This method only obtains nitrogen-rich C 3 N 4 Powder, only steps S1 and S2, no steps S3 and S4.

[0062] Comparative Example 2

[0063] The specific preparation steps of this comparative example refer to those of Example 1, except that the carbon nitride nanosheets are not subjected to nitrogen enrichment treatment, but are directly reduced by equal volume impregnation and inductively coupled low temperature plasma. 3 N 4 Powder, only steps S3 and S4 of the preparation method, without steps S1 and S2.

[0064] Comparative Example 3

[0065] The specific preparation steps of this comparative example refer to those of Example 1, except that: the carbon nitride nanosheets are immersed in ammonia water and freeze-dried without being subjected to NH 3 +H 2 The Pt / C obtained by this method was then reduced by equal volume impregnation and inductively coupled low temperature plasma reduction. 3 N 4 Powder, only steps S1, S3 and S4 of the preparation method, without step S2.

[0066] Comparative Example 4

[0067] The specific preparation steps of this comparative example refer to those of Example 1, except that: the carbon nitride nanosheets are directly soaked in NH 3 +H 2 The Pt / C obtained by this method was then reduced by equal volume impregnation and inductively coupled low temperature plasma reduction. 3 N 4 Powder, only steps S2, S3 and S4 of the preparation method, without step S1.

[0068] Comparative Example 5

[0069] The specific preparation steps of this comparative example refer to those of Example 1, with the only difference being that the discharge power in step S4 exceeds 20W, and the actual discharge power is 25W.

[0070] Photocatalytic water decomposition was used to evaluate the performance of the photocatalysts obtained in the above embodiments and comparative examples under visible light. The specific steps of the photocatalytic water decomposition reaction for hydrogen production are as follows: (1) Weigh 5 mg of photocatalyst powder and add it to 100 mL of an aqueous solution containing 10 vol% triethanolamine. After stirring evenly, seal the photocatalytic reactor. Pass high-purity nitrogen gas and purge the reactor at a flow rate of 50 ml per minute to eliminate the residual gas in the reactor. Then start the photocatalytic reaction. The light source is a PLS-SXE300D xenon lamp and a UV420 filter (Beijing Bofeilai Technology Co., Ltd.). At regular intervals, a gas chromatograph is used to detect the production of hydrogen during the reaction online.

[0071] Figure 1 and Figure 2 The Pt / C obtained in Example 1 3 N 4 Spherical aberration corrected high-angle dark field scanning transmission electron microscope image. It can be seen from the figure that the monodisperse bright spots are evenly dispersed on the substrate, and no agglomeration of the monodisperse bright spots is observed. These bright spots can be attributed to Pt atoms. Therefore, Pt is uniformly loaded on C in the form of single atoms. 3 N 4 The surface of the nanosheets. By statistically analyzing the size distribution of Pt, more than 99% of the Pt particles are less than 0.2nm. The extended X-ray absorption fine structure (EXAFS) spectroscopy was used to study the single-atom Pt on C 3 N 4 The coordination environment and local structure in the nanosheet carrier are analyzed. Figure 3 L of Pt 3 Fourier transform results of edge EXAFS, the comparison sample is the standard sample H 2 PtCl 6 and Pt sheets. Figure 3 As shown, the Pt / C prepared in Example 1 3 N 4 In the FT-EXAFS curve, there is only one strong FT peak, located at About, lower than the standard sample H 2 PtCl 6 and Pt film and It shows that Pt is located in C 3 N 4 The Pt-N chemical bond is formed by coordinating with the N in the five-membered ring of the nanosheet support, which is consistent with the results reported in the literature. Therefore, by nitrogen-enriching the carbon nitride nanosheets, we successfully bound the single-atom Pt in the carbon nitride skeleton and prepared a highly dispersed and stable single-atom Pt co-catalyst.

[0072] The Pt / C obtained in Comparative Examples 2, 3, 4 and 5 was3 N 4 The powders were also analyzed by high-resolution transmission electron microscopy or spherical aberration-corrected high-angle dark-field scanning transmission electron microscopy. Figure 4 The Pt / C obtained in Comparative Example 5 3 N 4 Spherical aberration corrected high angle dark field scanning transmission electron microscope image of the powder. Comparative Example 5 Compared with Example 1, the discharge power of step S4 is increased to 25W. When the discharge power of step S4 exceeds 20W, the size of Pt increases to 0.4-0.6nm, that is, Pt is no longer loaded on the surface of the carbon nitride nanosheet in the form of a single atom, but in the form of a cluster, indicating that when the discharge power of step S4 exceeds 20W, it will cause the agglomeration of Pt single atoms, and therefore it is not suitable for the synthesis of single-atom Pt. Figure 5 , Figure 6 and Figure 7 The distribution is the Pt / C obtained in Comparative Example 2, Comparative Example 3 and Comparative Example 4 3 N 4 High-resolution transmission electron microscopy image of the powder. It can be seen from the figure that when Pt / C 3 N 4 During the preparation, without simultaneously going through step S1 and step S2 in the preparation method, Pt is mainly loaded on the carbon nitride surface in the form of nanoparticles. The average particle sizes of the Pt nanoparticles obtained in Example 2, Comparative Example 3 and Comparative Example 4 are 1.67nm, 1.38nm and 1.12nm respectively. Therefore, the present invention obtains Pt / C with uniform loading of single-atom Pt through the four steps in the preparation method. 3 N 4 powder.

[0073] Figure 8 The performance of photocatalysts obtained in Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4 and Comparative Example 5 in decomposing water to produce hydrogen under visible light. For carbon nitride nanosheets that have not been treated in any way, the hydrogen production rate is only 7.2 μmol / h. When the carbon nitride nanosheets are treated with nitrogen enrichment, the hydrogen production rate of the sample of Comparative Example 1 obtained does not change significantly, indicating that the nitrogen enrichment treatment does not affect the performance of carbon nitride photocatalytic hydrogen production. The single-atom Pt-loaded carbon nitride composite photocatalyst prepared by the present invention has a hydrogen production rate significantly increased to 942.5 μmol / h, which is 130.9 times that of the carbon nitride nanosheets, indicating that the loading of single-atom Pt greatly improves the atomic utilization rate of Pt and enhances the performance of carbon nitride photocatalytic water decomposition to produce hydrogen. For Comparative Example 5, when Pt is loaded on the surface of carbon nitride in the form of atomic clusters, its hydrogen production rate is 674.8 μmol / h, which is lower than the Pt / C loaded with single-atom Pt. 3 N 4For Comparative Examples 2, 3 and 4, when Pt was loaded on the carbon nitride surface in the form of nanoparticles, the hydrogen production rates were 375.4, 386.7 and 460.1 μmol / h, respectively, which were not only lower than the Pt / C supported by single-atom Pt, but also lower than the Pt / C supported by single-atom Pt. 3 N 4 Photocatalyst, also lower than Pt / C supported by atomic cluster Pt 3 N 4 Photocatalyst. Therefore, the single-atom Pt-loaded carbon nitride composite photocatalyst prepared by the present invention exhibits extremely excellent photocatalytic performance of hydrogen production by water splitting under visible light.

[0074] In order to further verify the advantages of the present invention in preparing composite photocatalysts loaded with single-atom metals, we synthesized 10 batches of samples according to the scheme of Example 1 and studied their photocatalytic water splitting performance. Fig. 9 The hydrogen production rates of the 10 batches of samples were 942.5, 931.6, 907.5, 924.6, 912.6, 928.8, 939.5, 901.4, 897.6 and 917.5 μmol / h, respectively. The fluctuation of the hydrogen production rate by photolysis of water was less than 5%, indicating that the Pt / C synthesized in different batches 3 N 4 Photocatalysts are very stable and can be prepared on a gram or even kilogram scale.

[0075] Those skilled in the art should understand that the above are only some specific embodiments of the present invention, rather than all embodiments. It should be noted that for those of ordinary skill in the art, many modifications and improvements can be made, and all modifications or improvements that do not exceed the scope of protection of the present invention should be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a composite photocatalyst loaded with single-atom metals, It is characterized in that The following steps are involved: S1, immersing carbon nitride nanosheets having a two-dimensional layered structure into an aqueous solution of a nitrogen-containing precursor, stirring the mixture sufficiently, and then freeze-drying the mixture to obtain a mixed powder 1; S2, placing the mixed powder 1 obtained in step S1 in a reaction chamber of an inductively coupled low-temperature plasma device, and performing a discharge reaction in a mixed atmosphere of ammonia and hydrogen, wherein the power of the discharge reaction is 20-200 W, the discharge time is 15-60 min, and the vacuum degree is 20-50 Pa, to obtain carbon nitride nanosheets with nitrogen-rich surface; S3, immersing an equal volume of nitrogen-rich carbon nitride nanosheets into a precursor solution of metal Pt, and then drying at low temperature and vacuum to obtain a mixed powder 2; S4. Place the mixed powder 2 obtained in step S3 in the reaction chamber of an inductively coupled low-temperature plasma device, and conduct a discharge reaction in a hydrogen atmosphere, wherein the power of the discharge reaction is 0-20 W and not 0, the discharge time is 0-5 min and not 0, and the vacuum degree is 5-10 Pa, to obtain a composite photocatalyst loaded with single-atom metals on a preparation scale of gram to kilogram level.

2. The method for preparing the composite photocatalyst loaded with single-atom metal according to claim 1, It is characterized in that The concentration of the aqueous solution of the nitrogen-containing precursor in step S1 is 5-15 mol / L, and the nitrogen-containing precursor is one or a combination of two or more of ammonia water, urea or hydrazine hydrate.

3. The method for preparing the composite photocatalyst loaded with single-atom metal according to claim 1, It is characterized in that The stirring temperature in step S1 is 60-100° C. and the stirring time is 6-24 h.

4. The method for preparing the composite photocatalyst loaded with single-atom metal according to claim 1, It is characterized in that In step S2, the volume content of ammonia in the mixed atmosphere of ammonia and hydrogen is 5%-15%, and the volume content of hydrogen is 85%-95%.

5. The method for preparing the composite photocatalyst loaded with single-atom metal according to claim 1, It is characterized in that In step S3, the precursor of metal Pt is a water-soluble salt of metal Pt, and the water-soluble salt is one or a combination of two or more of chloride, nitrate, sulfate, and sulfite.

6. The method for preparing the composite photocatalyst loaded with single-atom metal according to claim 1, It is characterized in that The mass ratio of the total amount of metal in the metal precursor solution in step S3 to the carbon nitride nanosheets in step S1 is (0.1-10):

100.

7. A composite photocatalyst loaded with single-atom metal prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the composite photocatalyst loaded with single-atom metal as claimed in claim 7 in a photocatalytic reaction.

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