Preparation method and application of non-noble metal single atom catalyst

Abstract

The disclosure discloses a preparation method and application of a non-noble metal single atom catalyst, and belongs to the technical fields of chemistry, chemical engineering and material science. According to the disclosure, cheap raw materials and simple method are used to prepare the single atom catalyst. In essence, metal is anchored on light-absorbing carrier in a single atom form under irradiation to produce the single atom catalyst. In the disclosure, the non-noble metal single atom catalyst is prepared by using a photochemical synthetic route for the first time. The single atom catalyst synthesized in the disclosure is dispersed on the surface of photoactive substance. Using nickel single atom as a co-catalyst in photocatalytic water splitting to produce hydrogen, the cost is low and the catalytic efficiency is greatly improved compared with other types of non-noble metal modified composite photocatalysts.

Claims

1. A preparation method of a non-noble metal single atom catalyst, comprising: (aa) mixing by ultrasound 0.1 mL of a 12.5 mg/mL nickel acetate aqueous solution, 5 mL of absolute methanol, 5 mL of water, and 30 mg of a nitrogen carbide nanosheet in the reaction vessel, (bb) degassing the reaction vessel with nitrogen; (cc) illuminating the reaction vessel with a 300 W xenon lamp for 1, 2, or 3 hours; and (dd) performing a solid-liquid separation, followed by washing with deionized water and with ethanol, and drying to obtain the non-noble metal single atom catalyst, wherein the photoactive carrier is a photoactive substance whose electrons can undergo transition or be excited to produce reductive photo-generated electrons under irradiation, wherein the electron donor reagent is a substance that does not undergo a chemical reaction with the photoactive carrier and the metal source under dark conditions, and wherein the electron donor reagent reacts with a hole or oxidizing substances generated when electrons transition or are excited by the photoactive carrier under irradiation to provide electrons.

2. The preparation method according to claim 1, wherein a light source excites the photoactive carrier and is matched with the photoactive carrier in energy level, and wherein the light source provides wavelengths within a wavelength range of 200 nm to 1300 nm.

3. The preparation method according to claim 1, further comprising adding to the reaction vessel a hole trapping agent dispersed or dissolved in a solvent.

4. The preparation method according to claim 1, wherein the cadmium sulfide nanorod is prepared by a hydrothermal method, which comprises: adding 2.5 g of hydrated cadmium chloride, thiourea, and ethylenediamine into a high-pressure reactor, exposing to heat in an oven at 160 C. for 48 hours, cooling to room temperature, filtering to obtain a yellow solid, washing the yellow solid with deionized water and with ethanol, and drying in an oven at 60 C. to obtain the cadmium sulfide nanorod.

5. The preparation method according to claim 1, wherein the carbon nitride nanosheet is prepared by a calcination method, comprises the following steps: weighing and adding 1 gram of dicyandiamide and 5 grams of ammonium chloride into a mortar, and grinding to the dicyandiamide and the ammonium chloride to obtain a ground solid; covering the ground solid in a crucible, and heating the crucible in a muffle furnace at 550 C. for 4 hours at a heating rate of 3 C. min.sup.1.

6. The preparation method according to claim 1, wherein the ultrasonic dispersion time is 1 minute.

7. The preparation method according to claim 1, wherein the degassing is performed for 30 to 40 minutes.

8. The method according to claim 1, wherein the cadmium sulfide nanorod is prepared by: adding 20.25 mmol of cadmium chloride hemipentahydrate, 40.75 mmol of thiourea, and 60 mL of ethylenediamine into a 100 mL high-pressure reactor to obtain a reaction mixture, heating the reaction mixture in an oven at 160 C. for 48 hours; cooling the reaction mixture to room temperature; washing with deionized water and ethanol; and drying in at 60 C. for 12 hours to obtain the cadmium sulfide nanorod.

9. The preparation method according to claim 1, wherein the carbon nitride nanosheet is prepared by: adding 1 g of dicyandiamide and 5 g of ammonium chloride into a mortar, mixing thoroughly by grinding to obtain a ground solid; covering the ground solid in a crucible; and heating the crucible at 550 C. for 4 hours at a rate of 3 C. min.sup.1 to obtain the carbon nitride nanosheet.

Description

BRIEF DESCRIPTION OF FIGURES

(1) FIG. 1 is the XRD patterns of cadmium sulfide nanorod and Ni.sub.1/cadmium sulfide nanorod composite catalyst in Example 1.

(2) FIG. 2 is the transmission electron microscope image of the Ni.sub.1/cadmium sulfide nanorod composite catalyst in Example 1.

(3) FIG. 3 is the transmission electron microscope energy dispersive X-ray spectrum of the Ni.sub.1/cadmium sulfide nanorod composite catalyst in Example 1.

(4) FIG. 4 is the X-ray absorption near-edge structure spectrum of the Ni.sub.1/cadmium sulfide nanorod composite catalyst in Example 1.

(5) FIG. 5A is the multi-element full spectrum of the Ni.sub.1/cadmium sulfide nanorod composite catalyst in Example 1.

(6) FIG. 5B is the Ni spectrum of the Ni.sub.1/cadmium sulfide nanorod composite catalyst in Example 1.

(7) FIG. 5C is the Cd spectrum of the Ni.sub.1/cadmium sulfide nanorod composite catalyst in Example 1.

(8) FIG. 5D is the S spectrum of the Ni.sub.1/cadmium sulfide nanorod composite catalyst in Example 1.

(9) FIG. 6 is the photocatalytic hydrogen production test diagram of Ni.sub.1/cadmium sulfide nanorod composite catalyst in Example 2 under visible irradiation.

(10) FIG. 7 is the photocatalytic hydrogen production test diagram of the Ni.sub.1/cadmium sulfide nanorod composite catalyst in Example 2 under outdoor sunirradiation.

(11) FIG. 8 is the XRD patterns of carbon nitride nanosheet and nickel single atom/carbon nitride nanosheet composite catalyst in Example 4.

(12) FIG. 9 is the transmission electron microscope image of the nickel single atom/carbon nitride nanosheet composite catalyst in Example 4.

(13) FIG. 10 is the high angle annular dark field-scanning transmission electron microscope image of the nickel single atom/carbon nitride nanosheet composite catalyst in Example 4.

(14) FIG. 11 is the X-ray absorption near-edge structure spectrum of the nickel single atom/carbon nitride nanosheet composite catalyst in Example 4.

(15) FIG. 12A is the multi-element full spectrum of the nickel single atom/carbon nitride nanosheet composite catalyst in Example 4.

(16) FIG. 12B is the Ni spectrum of the nickel single atom/carbon nitride nanosheet composite catalyst in Example 4.

(17) FIG. 12C is the C spectrum of the nickel single atom/carbon nitride nanosheet composite catalyst in Example 4.

(18) FIG. 12D is the N spectrum of the nickel single atom/carbon nitride nanosheet composite catalyst in Example 4.

(19) FIG. 13 is the cyclic hydrogen production test diagram of nickel single atom/carbon nitride nanosheet composite catalyst in Example 5 under simulated sunirradiation.

(20) FIG. 14 is the photocatalytic hydrogen production test diagram of the nickel single atom/carbon nitride nanosheet composite catalyst in Example 5 under outdoor sunirradiation.

(21) FIG. 15 is a diagram showing a reaction mechanism of the disclosure.

(22) FIG. 16 is the photocatalytic hydrogen production test diagram of a Co.sub.1/CN catalyst in Example 7 under simulated sunirradiation.

(23) FIG. 17 is a photocatalytic hydrogen production test diagram of a Ni.sub.1/CN catalyst reduced by hydrogen in Comparative Example 5 under simulated sunirradiation.

DETAILED DESCRIPTION

(24) The disclosure is described in detail below.

(25) As shown in FIG. 15, the reaction mechanism of the disclosure specifically includes the steps that water molecules are first adsorbed on CdS in an aqueous solution, CdS nanorod absorbs irradiation to generate photo-generated electron-hole pairs under irradiation, then photogenerated electrons are transferred to the surface of the CdS nanorod for reducing H.sup.+ to produce H.sub.2, and Ni.sup.2+ is combined with remaining OH.sup. to finally form Ni(II) loaded on CdS; in addition, electron donor reagent is used to provide electrons to combine with remaining photo-generated holes, and finally, an entire photoreduction process is completed. Therefore, the catalyst prepared in the disclosure has NiO bond rather than NiNi bond, has no metal component aggregation state (no NiNi bond), and is a single atom catalyst.

(26) In order to more specifically illustrate the method of the disclosure, examples of the disclosure are given below, but the application of the disclosure is not limited to these aspects.

Example 1: Preparation of Nickel Single Atom/Cadmium Sulfide Nanorod Composite Catalyst

(27) The nickel single atom/cadmium sulfide composite catalyst is prepared by the following method.

(28) (1) 20.25 mmol of cadmium chloride hemipentahydrate, 40.75 mmol of thiourea and 60 mL of ethylenediamine were added into a 100 mL high-pressure reactor, and placed in an oven at 160 C. for 48 hours. The reactor was cooled to room temperature under natural conditions, The yellow solid was obtained by washing with deionized water 10 times and washed with ethanol 2 times, and dried in an oven at 60 C. for 12 hours, namely cadmium sulfide nanorod.

(29) (2) 50 mg of cadmium sulfide nanorod was added into a 25 mL flask, and 1 mL of a nickel acetate aqueous solution (12.5 mg/mL), 1 mL of a thiourea aqueous solution (38 mg/mL) and 8 mL of deionized water were then added. Ultrasonic dispersion treatment was performed for 1 minute, and then degassing was performed with nitrogen for 40 minutes to remove oxygen in a reaction system.

(30) (3) After degassing, the flask was irradiated under a 300 W xenon lamp for 20 minutes. The solid was obtained by centrifugation, washing with deionized water 5 times and washing with ethanol 2 times, and dried under nitrogen flow, namely nickel single atom/cadmium sulfide nanorod composite catalyst.

(31) X-ray diffraction spectra (XRD) (shown in FIG. 1), transmission electron microscope (TEM) images (shown in FIG. 2), energy dispersive X-ray spectrum (EDX) (shown in FIG. 3), X-ray absorption near-edge structure spectrum (XANES) (shown in FIG. 4) and X-ray photoelectron spectra (XPS) (shown in FIG. 5A, FIG. 5B, FIG. 5C and FIG. 5D) of the prepared photocatalyst are obtained. It can be seen that there is divalent nickel element on the cadmium sulfide nanorod, but there are no corresponding X-ray diffraction signals and TEM images, and there is nickel-oxygen bond, but no nickel-nickel bonds. It is proven that nickel on the catalyst prepared in this example is in the form of single metal atom.

Example 2: Catalytic Activity of Nickel Single Atom/Cadmium Sulfide Nanorod Composite Catalyst

(32) 2 mg of cadmium sulfide obtained in step (1) of Example 1, 10 mL of lactic acid and 40 mL of water were added into a 100 mL photocatalytic reactor. After ultrasonic treatment for 30 seconds, degassing with nitrogen for 1 hour to remove oxygen in a system, the photocatalytic reactor was irradiated under a 300 W Xenon lamp (equipped with a 420 nm cut-off optical filter). Produced hydrogen in the reaction was detected by thermal conductivity-gas chromatography. After the reaction was performed for 6 hours, the hydrogen production rate was 4.8 mmol.Math.g.sup.1.Math.h.sup.1.

(33) 2 mg of cadmium sulfide obtained in step (1) of Example 1, 10 mL of lactic acid and 40 mL of water were added into a 100 mL photocatalytic reactor. After ultrasonic treatment for 30 seconds, degassing with nitrogen for 1 hour to remove oxygen in a system, the photocatalytic reactor was irradiated under a 300 W Xenon lamp (equipped with a 420 nm cut-off optical filter). Produced hydrogen in the reaction was detected by thermal conductivity-gas chromatography. After the reaction was performed for 6 hours, the hydrogen production rate was 142.7 mmol.Math.g.sup.1.Math.h.sup.1 and was about 30 times higher than that of the cadmium sulfide nanorod.

(34) 1 mg of the Ni.sub.1/CdS NRs composite catalyst in Example 1, 9.0 g of sodium sulfide nonahydrate, 6.6 g of anhydrous sodium sulfite and 50 mL of deionized water were added into a 100 mL photocatalytic reactor. After ultrasonic treatment for 30 seconds, degassing with nitrogen for 1 hour to remove oxygen in a system, the photocatalytic reactor was irradiated under a 300 W Xenon lamp (equipped with a 420 nm cut-off optical filter). Produced hydrogen in the reaction was detected by thermal conductivity-gas chromatography. Degas every two hours to remove the produced hydrogen, and then irradiation treatment was continued. After the reaction was performed for 16 hours, the catalytic activity was still not reduced significantly. A photocatalytic hydrogen production test diagram of the Ni.sub.1/CdS NRs composite catalyst under visible irradiation is shown in FIG. 6.

(35) 1 mg of the Ni.sub.1/CdS NRs composite catalyst in Example 1, 9.0 g of sodium sulfide nonahydrate, 6.6 g of anhydrous sodium sulfite and 50 mL of deionized water were added into a 100 mL photocatalytic reactor. After ultrasonic treatment for 30 seconds, degassing with nitrogen for 1 hour to remove oxygen in a system, the photocatalytic reactor was irradiated under outdoor sunirradiation. The thermal conductivity-gas chromatography was used to detect hydrogen produced in the reaction every 2 hours, and then irradiation treatment was continued. After the reaction was performed for 6 hours, the hydrogen production can reach as high as 900 mmol.Math.g.sup.1. A photocatalytic hydrogen production test diagram of the Ni.sub.1/CdS NRs composite catalyst under outdoor sunirradiation is shown in FIG. 7.

(36) It can be seen that Ni.sub.1/CdS NRs prepared in this example have many advantages, such as simple preparation method, efficient photocatalytic hydrogen production rate, good stability and low cost. The cost can be greatly reduced when Ni.sub.1/CdS NRs are applied to industrial production, and Ni.sub.1/CdS NRs is a novel catalytic material with a good prospect in industrial photocatalytic production of hydrogen.

Example 3

(37) (1) 20.25 mmol of cadmium chloride hemipentahydrate, 40.75 mmol of thiourea and 60 mL of ethylenediamine were added into a 100 mL high-pressure reactor, and placed in an oven at 160 C. for 48 hours. The reactor was cooled to room temperature under natural conditions, The yellow solid was obtained by washing with deionized water 10 times and washed with ethanol 2 times, and dried in an oven at 60 C. for 12 hours, namely cadmium sulfide nanorod.

(38) (2) 50 mg of cadmium sulfide nanorod, 1 mL of a thiourea aqueous solution (38 mg/mL) and 8 mL of deionized water were added into a 25 mL flask. Ultrasonic dispersion treatment was performed for 1 minute, and then degassing was performed with nitrogen for 40 minutes to remove oxygen in a reaction system.

(39) (3) After degassing, the flask was irradiated under a 300 W xenon lamp for 5, 10, 15 or 20 minutes. The solid was obtained by centrifugation, washing with deionized water 5 times and washing with ethanol 2 times, and dried under nitrogen flow.

(40) It can be determined through tests that all the prepared catalysts are nickel single atom/cadmium sulfide nanorod composite catalysts. The contents (mass percentage) of nickel in the nickel single atom/cadmium sulfide nanorod composite catalysts obtained under different irradiation times are tested. The contents of nickel in the catalysts obtained after irradiation for 5, 10, 15 or 20 minutes are 0.61%, 1.25%, 2.13% and 2.85%, respectively. It can be seen that the content of metal single atoms in the catalyst can be adjusted by changing the irradiation time.

Example 4: Preparation of a Nickel Single Atom/Carbon Nitride Nanosheet Composite Catalyst

(41) A nickel single atom/carbon nitride nanosheet composite catalyst is prepared by the following method.

(42) (1) 1 g of dicyandiamide and 5 g of ammonium chloride were added into a mortar, and thoroughly mixed by grinding; the obtained solid after grinding was placed in a crucible with a cover; the crucible was placed in a muffle furnace, and heated at 550 C. for 4 hours at a rate of 3 C. min.sup.1 to obtain a irradiation yellow solid, namely carbon nitride nanosheet.

(43) (2) 30 mg of the carbon nitride nanosheet, 0.1 mL of nickel acetate aqueous solution (12.5 mg/mL), 5 mL of anhydrous methanol and 5 mL of deionized water were added into a 25 mL flask. Ultrasonic dispersion treatment was performed for 1 minute, and then degassing was performed with nitrogen for 40 minutes to remove oxygen in the reaction system.

(44) (3) After degassing, the flask was irradiated under a 300 W xenon lamp for 3 hours. The solid was obtained by centrifugation, washing with deionized water 5 times and washing with ethanol 2 times, and dried under nitrogen flow, namely nickel single atom/carbon nitride nanosheet composite catalyst (Ni.sub.1/CN).

(45) X-ray diffraction spectra (XRD) (shown in FIG. 8), transmission electron microscope (TEM) image (shown in FIG. 9), high angle annular dark field-scanning transmission electron microscope (HAADF-STEM) image (shown in FIG. 10), X-ray absorption near-edge structure (XANES) spectra (shown in FIG. 11) and X-ray photoelectron (XPS) spectra (shown in FIG. 12A, FIG. 12B, FIG. 12C and FIG. 12D) of the prepared photocatalyst are obtained. It can be seen that there is divalent nickel element on carbon nitride, but there are no corresponding X-ray diffraction signals and Ni nanoparticles in TEM images. There is single nickel atom in the HAADF-STEM image and nickel-oxygen bond, but no nickel-nickel bonds from XANES spectra. It is proven that nickel on the carbon nitride nanosheet prepared in this example is in the form of single metal atom.

Example 5: Catalytic Activity of a Nickel Single Atom/Carbon Nitride Nanosheet

(46) 5 mg of the carbon nitride nanosheet obtained in step (1) of Example 4, 2 mL of triethanolamine and 8 mL of water were added into a 25 mL flask. Ultrasonic treatment was performed for 30 seconds, and degassing was performed with nitrogen for 1 hour to remove oxygen in a system. The flask was irradiated under a 300 W xenon lamp (equipped with an AM 1.5 optical filter). The produced hydrogen was detected by thermal conductivity-gas chromatography. The hydrogen production rate was 2.3 mol.Math.g.sup.1.Math.h.sup.1.

(47) 5 mg of the Ni.sub.1/CN composite catalyst obtained in Example 4, 2 mL of triethanolamine and 8 mL of water were added into a 25 mL flask. Ultrasonic treatment was performed for 30 seconds, and degassing was performed with nitrogen for 1 hour to remove oxygen in a system. The flask was irradiated under a 300 W xenon lamp (equipped with an AM 1.5 optical filter). The produced hydrogen was detected by thermal conductivity-gas chromatography. The hydrogen production rate was 16500 mol.Math.g.sup.1.Math.h.sup.1 and was about 7174 times higher than that of the carbon nitride nanosheet.

(48) 5 mg of the Ni.sub.1/CN composite catalyst in Example 4, 2 mL of triethanolamine and 8 mL of water were added into a 25 mL flask. Ultrasonic treatment was performed for 30 seconds, and degassing was performed with nitrogen for 1 hour to remove oxygen in a system. The flask was irradiated under a 300 W xenon lamp (equipped with an AM 1.5 optical filter). The produced hydrogen was detected by thermal conductivity-gas chromatography. The thermal conductivity-gas chromatography was used to detect hydrogen produced in the reaction every 1 hour, and degassing was performed every 4 hours (one cycle) to remove hydrogen in the reaction system, and then irradiation treatment was continued. After the reaction was performed for 32 hours, the catalytic activity was still not reduced significantly.

(49) 5 mg of the Ni.sub.1/CN composite catalyst in Example 4, 2 mL of triethanolamine and 8 mL of water were added into a 25 mL flask. Ultrasonic treatment was performed for 30 seconds, and degassing was performed with nitrogen for 1 hour to remove oxygen in a system. The flask was irradiated under outdoor sunirradiation. The produced hydrogen was detected by thermal conductivity-gas chromatography every 2 hours and removed by degassing, and then irradiation treatment was continued. After the reaction was performed for 6 hours, the hydrogen production can reach as high as 11.8 mmol.Math.g.sup.1.

(50) It can be seen that Ni.sub.1/CN composite catalyst prepared in this example have many advantages, such as simple preparation method, efficient photocatalytic hydrogen production rate, good stability and low cost. The cost can be greatly reduced when Ni.sub.1/CdS NRs are applied to industrial production, and Ni.sub.1/CdS NRs is a novel catalytic material with a good prospect in industrial photocatalytic production of hydrogen.

Example 6

(51) When the irradiation time is 1 hour and 2 hours respectively, other operations and steps are the same as those in Example 4, and nickel single atom/carbon nitride nanosheet composite catalysts are prepared.

(52) The contents (mass percentage) of nickel in the nickel single atom/carbon nitride nanosheet composite catalysts obtained under different irradiation times are tested. The contents of nickel in the catalysts obtained after irradiation for 1, 2 or 3 hours (Example 4) are 0.05%, 0.03% and 0.21%, respectively. It can be seen that the content of metal single atoms in the catalyst can be adjusted by changing the irradiation time.

Example 7

(53) (1) 30 mg of the carbon nitride nanosheet, 0.1 mL of cobalt acetate aqueous solution (12.5 mg/mL), 5 mL of anhydrous methanol and 5 mL of deionized water were added into a 25 mL flask. Ultrasonic dispersion treatment was performed for 1 minute, and then degassing was performed with nitrogen for 40 minutes to remove oxygen in the reaction system. The flask was irradiated under a 300 W xenon lamp for 3 hours. The solid was obtained by centrifugation, washing with deionized water 5 times and washing with ethanol 2 times, and dried under nitrogen flow, namely cobalt single atom/carbon nitride nanosheet composite catalyst (Co.sub.1/CN).

(54) (2) 5 mg of the carbon nitride nanosheet obtained in step (1) of Example 4, 2 mL of triethanolamine and 8 mL of water were added into a 25 mL flask. Ultrasonic treatment was performed for 30 seconds, and degassing was performed with nitrogen for 1 hour to remove oxygen in a system. The flask was irradiated under a 300 W xenon lamp (equipped with an AM 1.5 optical filter). The produced hydrogen was detected by thermal conductivity-gas chromatography. The hydrogen production rate was 2.3 mol.Math.g.sup.1.Math.h.sup.1.

(55) (3) 5 mg of the Co.sub.1/CN composite catalyst obtained in step (1) of Example 7, 2 mL of triethanolamine and 8 mL of water were added into a 25 mL flask. Ultrasonic treatment was performed for 30 seconds, and degassing was performed with nitrogen for 1 hour to remove oxygen in a system. The flask was irradiated under a 300 W xenon lamp (equipped with an AM 1.5 optical filter). The produced hydrogen was detected by thermal conductivity-gas chromatography. The hydrogen production rate was 708.9 mol.Math.g.sup.1.Math.h.sup.1.

(56) According to test results shown in FIG. 16, after the reaction was performed for 1 hour, the hydrogen production rate of Co.sub.1/CN reached 708.9 mol.Math.g.sup.1.Math.h.sup.1, and the hydrogen production rate of CN without Co loaded was only 2.3 mol.Math.g.sup.1.Math.h.sup.1.

Example 8

(57) The light-absorbing carriers in Examples 1 and 4 were changed into TiO.sub.2, BiOX (where X is Cl, Br or I), CdX (where X is S, Se or Te), BiWO.sub.6, BiVO.sub.4, Cu.sub.2O, C.sub.3N.sub.4, ZnO, ZnS, ZnSe, zinc oxide-ruthenium oxide (ZnORuO.sub.2), gallium sulfide (CuGaS.sub.2), gallium phosphide (GaP) or gallium arsenide (GaAs), and the metal was changed into iron, cobalt, copper, manganese, zinc, aluminum, chromium, molybdenum or tungsten. Single metal atom catalysts can be obtained by adjusting conditions, and good catalytic performance can also be achieved. More details are not described here.

Comparative Example 1

(58) In order to verify the necessity of the electron donor reagent in the disclosure, a control experiment without the electron donor reagent was carried out.

(59) (1) 20.25 mmol of cadmium chloride hemipentahydrate, 40.75 mmol of thiourea and 60 mL of ethylenediamine were added into a 100 mL high-pressure reactor, and placed in an oven at 160 C. for 48 hours. The reactor was cooled to room temperature under natural conditions, The yellow solid was obtained by washing with deionized water 10 times and washed with ethanol 2 times, and dried in an oven at 60 C. for 12 hours, namely cadmium sulfide nanorod.

(60) (2) 50 mg of cadmium sulfide nanorod, 1 mL of a nickel acetate aqueous solution (12.5 mg/mL), 9 mL of deionized water were added into a 25 mL flask. Ultrasonic dispersion treatment was performed for 1 minute, and then degassing was performed with nitrogen for 40 minutes to remove oxygen in a reaction system.

(61) (3) After degassing, the flask was irradiated under a 300 W xenon lamp for 20 minutes. The solid was obtained by centrifugation, washing with deionized water 5 times and washing with ethanol 2 times, and dried under nitrogen flow. Relevant characterizations showed that the prepared material was not single atom catalyst.

(62) Similarly, no nickel single atom composite catalyst could be prepared by using the preparation method in Example 4 when methanol was changed into equal volume of water.

(63) It can be seen that the electron donor reagent in the disclosure is necessary for preparation of the single atom catalyst.

Comparative Example 2

(64) Common non-photoactive carrier materials such as Y-type molecular sieves, porous alumina, porous silica, coal-based activated carbon, biomass activated carbon, carbon fibers, carbon nanotubes, nickel acetate solution, thiourea solution and deionized water were mixed by ultrasound. After degassing with nitrogen, the mixture was irradiated under a 300 W xenon lamp for 20-100 minutes, but no non-noble metal single atom could be deposited on these non-photoactive carriers through the photochemical method similar to Example 1.

(65) It can be seen that in order to prepare the non-noble metal single atom catalyst in the disclosure, it is necessary to add the photoactive carrier whose electrons can undergo transition or be excited to generate reductive photo-generated electrons under irradiation.

Comparative Example 3

(66) When thiourea in Example 1 was changed into a sodium borohydride aqueous solution (1 mL, 19 mg/mL) with higher reduction property and other operation steps and methods were the same as those in Example 1, non-noble metal single atom catalyst could not be prepared.

(67) When methanol in Example 4 was changed into hydrazine hydrate and other operation steps and methods were the same as those in Example 4, non-noble metal single atom catalyst could not be prepared.

(68) It can be seen that selection of the electron donor reagent is also very important. The electron donor reagent required in the disclosure cannot undergo chemical reaction with the photoactive carrier and the metal source under dark, but can undergo a reaction with hole or oxidizing substances generated when electrons undergo transition or are excited of photoactive carrier under irradiation to provide electrons.

Comparative Example 4

(69) It is found that non-noble metal single atom catalyst could not be prepared through the experiment process in Example 1 without irradiation. It is indicated that irradiation is also necessary for preparation of the single atom catalyst in the disclosure.

Comparative Example 5

(70) In order to verify the effect of the obtained single atom catalyst reduced by high-temperature hydrogen, this control experiment was carried out.

(71) (1) 0.2 g of the Ni.sub.1/CN composite catalyst obtained in Example 4 was added into a porcelain boat, placed in a tube furnace and heated at a heating rate of 10 C./min under a 5% H.sub.2/Ar mixed gas atmosphere and then kept at 300 C. for 1 hour to obtain a solid, namely Ni.sub.1/CN composite material reduced by hydrogen.

(72) (2) 5 mg of the Ni.sub.1/CN composite catalyst obtained in Example 4, 2 mL of triethanolamine and 8 mL of water were added into a 25 mL flask. Ultrasonic treatment was performed for 30 seconds, and degassing was performed with nitrogen for 1 hour to remove oxygen in a system. The flask was irradiated under a 300 W xenon lamp (equipped with an AM 1.5 optical filter). The produced hydrogen was detected by thermal conductivity-gas chromatography. The hydrogen production rate was 16500 mol.Math.g.sup.1.Math.h.sup.1.

(73) (3) 5 mg of the Ni.sub.1/CN composite catalyst reduced by hydrogen obtained in step (1) of Comparative Example 5, 2 mL of triethanolamine and 8 mL of water were added into a 25 mL flask. Ultrasonic treatment was performed for 30 seconds, and degassing was performed with nitrogen for 1 hour to remove oxygen in a system. The flask was irradiated under a 300 W xenon lamp (equipped with an AM 1.5 optical filter). The produced hydrogen was detected by thermal conductivity-gas chromatography. The hydrogen production rate was 62.9 mol.Math.g.sup.1.Math.h.sup.1.

(74) According to test results shown in FIG. 17, it can be seen that after the reaction is performed for 6 hours, the hydrogen production rate of the Ni.sub.1/CN composite material reduced by hydrogen is only 62.9 mol.Math.g.sup.1.Math.h.sup.1 and is only 0.38% of that (16500 mol.Math.g.sup.1.Math.h.sup.1) of unreduced Ni.sub.1/CN. It is indicated that the single atom catalyst with a positive valence obtained in the disclosure is highly active and is better than a reduced simple substance.