Photocatalytic material, preparation method and application thereof, and method for preparing hydrogen by photocatalytic decomposition of ammonia

Abstract

The application relates to the technical field of photocatalysis, and discloses a kind of photocatalytic material and its preparation and application, a kind of photocatalytic ammonia decomposition hydrogen production method.A kind of photocatalytic material, wherein the photocatalytic material includes nitrogen, carbon, phosphorus, non-noble metal and noble metal, the photocatalytic material has carbon nitride covalent skeleton, phosphorus and noble metal exist in the form of doping in carbon nitride covalent skeleton, the non-noble metal is loaded in the form of oxide outside carbon nitride covalent skeleton;The non-noble metal is selected from at least one of iron, cobalt and nickel, and the noble metal is selected from at least one of ruthenium, platinum and palladium.The photocatalytic material contains carbon nitride doped with phosphorus and noble metal, and co-modified with non-noble metal, which can improve the activity and stability of photocatalytic ammonia decomposition hydrogen production.

Description

Technical Field

[0001] The present invention relates to the technical field of photocatalysis, and in particular to a photocatalytic material, its preparation and application, and a method for producing hydrogen by photocatalytic decomposition of ammonia. Background Art

[0002] Developing ammonia as a hydrogen storage medium can bridge the gap between renewable energy, hydrogen energy, and traditional industries, creating a comprehensive "ammonia-hydrogen" green circular economy that aligns with my country's energy structure: "clean and efficient ammonia synthesis → safe and low-cost ammonia storage and transportation → carbon-free and efficient 'ammonia-hydrogen' utilization." This is of great significance for ensuring national energy and environmental security and sustainable socioeconomic development. Furthermore, developing ammonia as a clean and efficient new energy source not only achieves energy conservation and emission reduction in the traditional synthetic ammonia industry, but also bridges the gap between renewable energy and new energy industries, promising enormous application prospects.

[0003] Ammonia decomposition is an endothermic reaction. Conventional systems typically require reaction temperatures above 500-800°C, resulting in high energy consumption and high risk. Therefore, the development of catalytic materials for ammonia decomposition driven by renewable energy is urgent. Photocatalytic technology using semiconductor materials can directly capture solar energy to drive high-value-added chemicals. Using only inexpensive and abundant non-precious metals (copper and iron), a research team from Rice University, Syzygy Plasmonics Inc., and Princeton University has created a room-temperature, light-driven catalyst that converts ammonia into clean-burning hydrogen using only the energy of light. Among common semiconductor photocatalysts, carbon nitride (CN) has a stable structure, excellent physicochemical properties, and a wide spectral response range, making it an important application in photocatalytic water splitting, pollutant degradation, and hydrogen production from ammonia decomposition. However, the inherent photogeneration of CN limits its efficiency. Furthermore, conventional synthesis methods have certain drawbacks, making it difficult to obtain non-precious metal-phosphorus co-modified CN materials with high overall performance.

[0004] Chinese patent application CN106492870A discloses a metal oxide-doped photocatalyst composed of a composite of a metal oxide and a non-metal oxide carbon nitride, wherein the metal oxide is selected from at least one of yttrium oxide, zirconium oxide, niobium oxide, molybdenum oxide, technetium oxide, ruthenium oxide, rhodium oxide, palladium oxide, silver oxide, and cadmium oxide. The preparation method comprises the following steps: Step 1: dispersing a compound containing a non-metallic element in a first dispersant, adding a nitrogen-containing organic compound to the system, mixing the mixture uniformly, removing the first dispersant, and then calcining the mixture to obtain a non-metallic element-doped graphite carbon nitride; Step 2: mixing the non-metallic element-doped graphite carbon nitride obtained in Step 1 with the metal oxide, adding a second dispersant (organic solvent) for dispersion, mixing the mixture uniformly, removing the second dispersant, and then calcining the mixture at high temperature. Step 1 is performed in a liquid phase system, and Step 2 is performed in an organic solvent, such as ethanol. The photocatalyst is used to degrade azo dyes. However, the synthesis process requires the use of organic solvents, which can cause environmental pollution or health hazards, making it unsuitable for large-scale production. Summary of the Invention

[0005] The present invention aims to overcome the problems of the prior art by providing a photocatalytic material, its preparation and application, and a method for photocatalytic ammonia decomposition to produce hydrogen. The photocatalytic material comprises carbon nitride doped with phosphorus and a precious metal and co-modified with a non-precious metal, which can enhance the activity and stability of photocatalytic ammonia decomposition to produce hydrogen.

[0006] In order to achieve the above-mentioned purpose, the first aspect of the present invention provides a photocatalytic material, wherein the photocatalytic material includes nitrogen, carbon, phosphorus, non-precious metals and precious metals, the photocatalytic material has a carbon nitride covalent skeleton, phosphorus and precious metals are present in the carbon nitride covalent skeleton in the form of doping, and the non-precious metals are loaded outside the carbon nitride covalent skeleton in the form of oxides; the non-precious metals are selected from at least one of iron, cobalt and nickel, and the precious metals are selected from at least one of ruthenium, platinum and palladium.

[0007] A second aspect of the present invention provides a method for preparing a photocatalytic material, wherein the method comprises the following steps:

[0008] (1) mixing a nitrogen-containing organic compound with a phosphorus source and a noble metal source, and then performing rotary evaporation drying, a first roasting, and freeze drying, wherein the noble metal is selected from at least one of ruthenium, platinum, and palladium;

[0009] (2) mixing the product obtained in step (1) with a non-noble metal source in the presence of a solvent, wherein the non-noble metal is at least one of iron, cobalt and nickel;

[0010] (3) Under a protective atmosphere, the product obtained in step (2) is subjected to a second calcination, wherein the second calcination comprises first keeping the temperature at 100-200° C. for 0.5-2 h, and then heating to 210-350° C. for 1-2 h.

[0011] The third aspect of the present invention provides a photocatalytic material prepared by the preparation method described in the second aspect.

[0012] A fourth aspect of the present invention provides a use of the photocatalytic material described in the first aspect or the third aspect in a photocatalytic ammonia decomposition reaction to produce hydrogen.

[0013] A fifth aspect of the present invention provides a method for producing hydrogen by photocatalytic decomposition of ammonia, wherein the method comprises: in the presence of a photocatalytic material and visible light, decomposing the reaction raw material ammonia, wherein the photocatalytic material is the photocatalytic material described in the first aspect or the third aspect.

[0014] The photocatalytic material provided by the present invention utilizes phosphorus and noble metal doping and non-noble metal co-modification of carbon nitride to increase the semiconductor's own carrier density. At the same time, the doping energy level is used to regulate the light absorption performance. This can overcome the serious carrier recombination problem of the single carbon nitride semiconductor itself, and significantly improve the activity and stability of photocatalytic ammonia decomposition to produce hydrogen.

[0015] The photocatalytic material provided by the present invention increases the number of surface active sites by in-situ introduction of phosphorus doping, non-noble metals and noble metal-modified carbon nitride, so that the catalytic material exhibits excellent performance in ammonia decomposition to produce hydrogen, which can further improve the conversion efficiency.

[0016] The preparation method provided by the present invention involves doping phosphorus and noble metal elements into a carbon nitride precursor to produce phosphorus- and noble metal-containing carbon nitride, and then achieving co-doping with non-noble metals through in-situ synthesis, so that phosphorus and noble metals are present in the carbon nitride covalent skeleton in the form of doping, and the non-noble metals are loaded outside the carbon nitride covalent skeleton. The preparation method is simple and easy to control, and the carbon nitride structure is complete. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is the X-ray diffraction pattern (XRD) of the photocatalytic material of Example 1.

[0018] Figure 2 This is a high-resolution transmission electron microscope image of the photocatalytic material of Example 1. DETAILED DESCRIPTION

[0019] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0020] A first aspect of the present invention provides a photocatalytic material, wherein the photocatalytic material includes nitrogen, carbon, phosphorus, non-precious metals and precious metals, the photocatalytic material has a carbon nitride covalent skeleton, phosphorus and precious metals are present in the carbon nitride covalent skeleton in the form of doping, and the non-precious metals are loaded outside the carbon nitride covalent skeleton in the form of oxides; the non-precious metals are selected from at least one of iron, cobalt and nickel, and the precious metals are selected from at least one of ruthenium, platinum and palladium.

[0021] In the present invention, through the synergistic modification of the carbon nitride skeleton by phosphorus, non-precious metal elements, and precious metal elements, the electronic structure of the carbon nitride itself can be regulated, the number of surface active sites of the photocatalytic material can be increased, the charge transfer can be accelerated, and the efficiency of hydrogen production by ammonia decomposition can be improved.

[0022] In the present invention, iron is calculated as Fe2O3, nickel is calculated as NiO, and cobalt is calculated as Co3O4.

[0023] The inventors discovered that the nitrogen-to-carbon ratio in existing carbon nitride-based photocatalytic materials is difficult to control. The carbon content in carbon nitride is high, typically 0.8-0.85:1, which is detrimental to improving the efficiency of the photocatalytic material in hydrogen production from ammonia decomposition. Preferably, the molar ratio of carbon to nitrogen in the photocatalytic material, calculated as an element, is 0.7-0.8:1, more preferably 0.74-0.76:1.

[0024] In the present invention, the molar ratio of carbon to nitrogen is measured by X-ray fluorescence spectrometry.

[0025] In the present invention, preferably, the mass ratio of nitrogen calculated as carbon nitride to the non-noble metal calculated as oxide is 100:2-8, more preferably 100:3-6.

[0026] In the present invention, preferably, the mass ratio of nitrogen calculated as carbon nitride to the precious metal calculated as an element is 100:0.1-2, more preferably 100:0.2-0.8.

[0027] In the present invention, preferably, the mass ratio of nitrogen calculated as carbon nitride to the phosphorus calculated as an element is 100:0.5-10, more preferably 100:3-8.

[0028] In the above preferred case, it is beneficial to increase the number of surface active sites of the photocatalytic material and accelerate charge transfer, thereby improving the efficiency of photocatalytic ammonia decomposition to produce hydrogen.

[0029] In the present invention, preferably, the mass ratio of the precious metal to phosphorus, calculated as elements, is 0.05-0.5:1, more preferably 0.05-0.18:1. This preferred embodiment has the advantage of optimizing the ratio to control light absorption performance and free carrier density, thereby improving the efficiency of hydrogen production from ammonia decomposition.

[0030] In the present invention, the content of each component in the photocatalytic material is obtained by X-ray fluorescence spectrum analysis during the preparation of the catalytic material.

[0031] In the present invention, the presence of a carbon nitride covalent skeleton in the photocatalytic material is demonstrated by X-ray diffraction testing. Preferably, the X-ray diffraction pattern of the photocatalytic material exhibits typical carbon nitride diffraction peaks at 2θ of 13.6° and 27.2°, and lacks obvious diffraction peaks of phosphorus and precious metals, demonstrating that the photocatalytic material has a carbon nitride covalent skeleton structure, and that phosphorus and precious metals are present in the carbon nitride covalent skeleton in the form of dopants.

[0032] In the present invention, phosphorus and noble metals are present in the carbon nitride covalent skeleton in the form of doping, which means that phosphorus replaces the carbon element in the carbon nitride skeleton, and the noble metal is located in the carbon nitride triazine ring cavity and coordinated with nitrogen.

[0033] In the present invention, the non-noble metal is loaded outside the carbon nitride covalent skeleton in the form of oxides, which means that the non-noble metal oxide is loaded on the carbon nitride skeleton in the form of nanoparticles or clusters.

[0034] In the present invention, the free carrier density of the photocatalytic material can be increased by combining phosphorus, noble metals and non-noble metal elements, thereby improving the efficiency of hydrogen production by decomposing ammonia. Preferably, the free carrier density of the photocatalytic material is (2-6)×10 22 cm -3 , more preferably (3-5)×10 22 cm -3 The advantages of adopting this preferred embodiment are that the carrier density is optimized, which helps separate and transport photogenerated charges and improves the photocatalytic efficiency.

[0035] A second aspect of the present invention provides a method for preparing a photocatalytic material, wherein the method comprises the following steps:

[0036] (1) mixing a nitrogen-containing organic compound with a phosphorus source and a noble metal source, and then performing rotary evaporation drying, a first roasting, and freeze drying, wherein the noble metal is selected from at least one of ruthenium, platinum, and palladium;

[0037] (2) mixing the product obtained in step (1) with a non-noble metal source in the presence of a solvent, wherein the non-noble metal is at least one of iron, cobalt and nickel;

[0038] (3) Under a protective atmosphere, the product obtained in step (2) is subjected to a second calcination, wherein the second calcination comprises first keeping the temperature at 100-200° C. for 0.5-2 h, and then heating to 210-350° C. for 1-2 h.

[0039] The preparation method of the photocatalytic material provided by the present invention first prepares a carbon nitride precursor containing phosphorus and precious metals, so that the phosphorus and precious metals exist in the carbon nitride covalent skeleton in the form of doping, and then realizes co-doping of non-precious metals through in situ synthesis, so that the non-precious metals exist in the form of oxides outside the carbon nitride covalent skeleton. The preparation method is simple and easy to control.

[0040] In the present invention, the nitrogen-containing organic compound refers to an organic compound containing both carbon and nitrogen, in particular, a nitrogen-containing small molecule organic compound that can be decomposed during the roasting process, which can simultaneously provide a nitrogen source and a carbon source during the first roasting process. The present invention has a wide range of choices for the nitrogen-containing organic compound, and conventional substances in the art can be used. Preferably, in step (1), the nitrogen-containing organic compound is selected from at least one of melamine, dicyandiamide and urea, and is more preferably melamine.

[0041] In the present invention, the phosphorus source can be selected from a wide range of types, as long as it can provide phosphorus. Preferably, in step (1), the phosphorus source is an alkali metal phosphate and / or an alkali metal hypophosphite, more preferably sodium hypophosphite and / or potassium hypophosphite.

[0042] In the present invention, the type of precious metal source can be selected from a wide range, as long as it can provide non-precious metal elements. Preferably, in step (1), the precious metal source is a soluble salt of a precious metal, more preferably a soluble inorganic salt of a precious metal, and even more preferably at least one selected from the group consisting of a nitrate, sulfate, and chloride of a precious metal.

[0043] In the present invention, preferably, in step (1), the conditions for the rotary evaporation drying include: a temperature of 40-80°C, more preferably 60-70°C.

[0044] In the present invention, the conditions for the first calcination are selected over a wide range. Preferably, in step (1), the temperature is 300-700°C, the time is 3-6 hours, and the heating rate is 2-10°C / min. Further preferably, in step (1), the conditions for the first calcination include: a temperature of 500-600°C, a time of 4-5 hours, and a heating rate of 2-5°C / min.

[0045] In the present invention, preferably, the first calcination is carried out under an inert atmosphere, and the gas flow rate of the inert atmosphere is 20-100 mL / min relative to 20 g of the nitrogen-containing organic compound in step (1).

[0046] In the present application, the conditions for freeze-drying are selected in a wide range. Preferably, in step (1), the conditions for freeze-drying include: temperature of -50℃ to -20℃, and time of 20-48h. The inventors of the present application have found in research that drying at a low-temperature freezing temperature enables phosphorus and noble metal to be doped in-situ into the carbon nitride skeleton, and when the drying temperature is not within the above-mentioned preferred range, too high a drying temperature may cause noble metal particles to agglomerate, and too low a drying temperature may result in high energy consumption.

[0047] In the present application, preferably, the method further comprises washing the calcined product obtained after the first calcination before freeze-drying. In the present application, the type of the washing agent used for washing is not particularly limited, and the washing agent commonly defined in the art is suitable for use in the present application, such as water and / or ethanol. In the present application, the mode of washing is not particularly limited, and for example, water and ethanol can be used for washing, respectively. In the present application, the number of times of washing is not particularly limited, as long as the sodium phosphate impurities generated in the calcination can be removed, and preferably, the number of times of washing is such that the content of sodium phosphate impurities in the calcined product is <0.2wt%.

[0048] In the present application, the type of the non-noble metal source is selected in a wide range, as long as it can provide non-noble metal elements. Preferably, in step (2), the non-noble metal source is a soluble salt of non-noble metal, preferably a soluble inorganic salt of non-noble metal, and further preferably at least one selected from the group consisting of nitrate, sulfate and chloride of non-noble metal.

[0049] In the present application, the order of mixing of the components in step (2) is not particularly limited, and the product obtained in step (1) can be dispersed in a solvent first, and then the non-noble metal source is added, or the product obtained in step (1) and the non-noble metal source can be dissolved in solvents, respectively, and then mixed.

[0050] In the present application, the type of the solvent is selected in a wide range, as long as the dissolution of the components is achieved. Preferably, in step (2), the solvent is water. Preferably, step (2) does not use an organic solvent, and the synthesis process is green and environmentally friendly, which is conducive to large-scale production.

[0051] In the present application, the formation of the graphite phase carbon nitride structure is achieved by segmental calcination and regulation of the reaction conditions in different calcination stages. Preferably, the second calcination comprises first holding at 150-200℃ for 0.5-1.5h, and then heating to 250-350℃ for 1.5-2h. The segmental calcination in the above range is advantageous for promoting the exfoliation of the carbon nitride interlayer structure and forming the graphite phase structure; when one-stage calcination is used, it is not conducive to the formation of the ultrathin interlayer structure; when the temperature of the second calcination is not in the above preferred range, the temperature of the second calcination is too high, which may lead to the agglomeration of the interlayer structure, and the temperature of the second calcination is too low, which may lead to the difficulty in forming the graphite phase structure, and is not conducive to the improvement of the photocatalytic efficiency.

[0052] In the present application, preferably, in step (3), the conditions of the second calcination comprise a heating rate of 2-10℃ / min.

[0053] In the present application, the protective atmosphere refers to a gas that does not participate in the reaction, and is used to avoid the introduction of oxygen during calcination. Preferably, the protective atmosphere is provided by at least one of nitrogen, argon and helium. The present application has a wide selection range for the flow rate of the protective atmosphere. Preferably, the gas flow rate of the protective atmosphere is 20-100mL / min.

[0054] In the present application, preferably, the mass ratio of the nitrogen-containing organic compound calculated based on carbon nitride to the non-noble metal source calculated based on oxide is 100:2-8, and further preferably 100:3-6.

[0055] In the present application, preferably, the mass ratio of the nitrogen-containing organic compound calculated based on carbon nitride to the noble metal source calculated based on element is 100:0.1-2, and further preferably 100:0.2-0.8.

[0056] In the present application, preferably, the mass ratio of the nitrogen-containing organic compound calculated based on carbon nitride to the phosphorus source calculated based on element is 100:0.5-10, and further preferably 100:3-8.

[0057] In the present application, preferably, the mass ratio of the noble metal source to the phosphorus source calculated based on element is 0.05-0.5:1, and further preferably 0.05-0.18:1.

[0058] The third aspect of the present application provides a photocatalytic material prepared by the preparation method of the second aspect.

[0059] The fourth aspect of the present application provides an application of the photocatalytic material of the first aspect or the third aspect in a photocatalytic ammonia decomposition reaction for hydrogen production.

[0060] A fifth aspect of the present invention provides a method for producing hydrogen by photocatalytic decomposition of ammonia, wherein the method comprises: in the presence of a photocatalytic material and visible light, decomposing the reaction raw material ammonia, wherein the photocatalytic material is the photocatalytic material described in the first aspect or the third aspect.

[0061] In the present invention, preferably, the reaction raw material ammonia is provided by an ammonia aqueous solution, and the concentration of the ammonia aqueous solution is 0.01-0.1 mol / L.

[0062] In the present invention, preferably, the conditions for the decomposition reaction include: a reaction temperature of 0.5-40° C., and an amount of the photocatalytic material of 0.02-0.1 g relative to 0.01 mol of an aqueous ammonia solution.

[0063] The present invention will be described in detail below through examples. In the following examples, unless otherwise specified, all raw materials used are commercially available.

[0064] In the present invention, the content of each component in the photocatalytic material is obtained by X-ray fluorescence spectrum analysis during the preparation of the catalytic material.

[0065] Example 1

[0066] (1) 30 g of melamine, 5 g of sodium hypophosphite, and 0.17 g of ruthenium trichloride were weighed and dispersed in 50 mL of water. After thorough mixing, the mixture was dried by rotary evaporation at 60 ° C. The resulting product was calcined at 550 ° C in an argon atmosphere for 4 h at a heating rate of 5 ° C per minute. The gas flow rate was 40 mL / min relative to 20 g of melamine. After cooling, the resulting product was washed three times with water and ethanol (the content of sodium phosphate impurities in the product was 0.1 wt%), dispersed in 50 mL of water, and freeze-dried at -40 ° C for 24 h to obtain a phosphorus- and noble metal-doped carbon nitride precursor.

[0067] (2) Add 2.5 g of ferric nitrate nonahydrate to the phosphorus- and noble metal-doped carbon nitride precursor obtained in step (1), and grind and mix thoroughly;

[0068] (3) The product obtained in step (2) was subjected to a programmed temperature calcination treatment, wherein the temperature rise program was room temperature-150°C (1h)-300°C (1.5h), the temperature rise rate was 5°C per minute, the calcination atmosphere was argon, and the gas flow rate was 40mL / min. After cooling, the photocatalytic material was obtained.

[0069] Figure 1 This is the X-ray diffraction pattern of the photocatalytic material. It can be seen that typical carbon nitride characteristic peaks appear at 13.2° and 27.8°, proving that the carbon nitride structure is intact. Figure 2The high resolution transmission electron microscopy image of the photocatalytic material shows that the sample mainly exists in the form of two-dimensional graphite sheet layer structure, and no obvious particles or clusters are observed in the sample, indicating that the noble metal ruthenium and phosphorus are highly dispersed and exist in the form of doping in the carbon nitride skeleton.

[0070] Example 2

[0071] (1) 30 g of melamine, 5 g of sodium hypophosphite and 0.12 g of ruthenium trichloride were weighed and dispersed in 50 mL of water, and after being fully mixed, they were dried by rotary evaporation at 60°C. The obtained product was calcined in an argon atmosphere at 520°C for 4 h, with a heating rate of 5°C per minute, and the gas flow rate was 40 mL / min relative to 20 g of melamine. After cooling, the obtained product was washed with water and ethanol for 3 times respectively (the content of sodium hypophosphite impurity in the product was 0.1% by weight), then dispersed in 50 mL of water and freeze-dried at -40°C for 24 h, to obtain a phosphorus and noble metal doped carbon nitride precursor;

[0072] (2) The phosphorus and noble metal doped carbon nitride precursor obtained in step (1) was mixed with 2.5 g of iron nitrate nonahydrate by grinding;

[0073] (3) The product obtained in step (2) was subjected to programmed temperature calcination treatment, with a temperature program of room temperature-150°C (1 h)-300°C (1.5 h), a heating rate of 5°C per minute, an argon atmosphere, and a gas flow rate of 40 mL / min. After cooling, the photocatalytic material was obtained.

[0074] Example 3

[0075] (1) 30 g of melamine, 5 g of sodium hypophosphite and 0.12 g of ruthenium trichloride were weighed and dispersed in 50 mL of water, and after being fully mixed, they were dried by rotary evaporation at 60°C. The obtained product was calcined in an argon atmosphere at 520°C for 4 h, with a heating rate of 5°C per minute, and the gas flow rate was 40 mL / min relative to 20 g of melamine. After cooling, the obtained product was washed with water and ethanol for 3 times respectively (the content of sodium hypophosphite impurity in the product was 0.1% by weight), then dispersed in 50 mL of water and freeze-dried at -40°C for 24 h, to obtain a phosphorus and noble metal doped carbon nitride precursor;

[0076] (2) The phosphorus and noble metal doped carbon nitride precursor obtained in step (1) was mixed with 2.5 g of iron nitrate nonahydrate by grinding;

[0077] (3) The product obtained in step (2) was subjected to programmed temperature calcination treatment, with a temperature program of room temperature-150°C (1 h)-300°C (1.5 h), a heating rate of 5°C per minute, an argon atmosphere, and a gas flow rate of 40 mL / min. After cooling, the photocatalytic material was obtained.

[0078] Example 4

[0079] (1) 30 g of melamine, 0.5 g of sodium hypophosphite, and 0.02 g of ruthenium trichloride were weighed and dispersed in 50 mL of water. After thorough mixing, the mixture was dried by rotary evaporation at 60 ° C. The resulting product was calcined at 550 ° C in an argon atmosphere for 4 h at a heating rate of 5 ° C per minute. The gas flow rate was 40 mL / min relative to 20 g of melamine. After cooling, the resulting product was washed three times with water and ethanol (the content of sodium phosphate impurities in the product was 0.05 wt%), dispersed in 50 mL of water, and freeze-dried at -40 ° C for 26 h to obtain a phosphorus- and noble metal-doped carbon nitride precursor.

[0080] (2) adding 0.5 g of ferric nitrate nonahydrate to the phosphorus-containing carbon nitride precursor obtained in step (1), and grinding and mixing thoroughly;

[0081] (3) The product obtained in step (2) was subjected to a programmed temperature calcination treatment, wherein the temperature rise program was room temperature-200°C (0.5h)-300°C (1.5h), the temperature rise rate was 5°C per minute, the calcination atmosphere was argon, the gas flow rate was 40mL / min, and the photocatalytic material was obtained after cooling.

[0082] Example 5

[0083] (1) 30 g of melamine, 10 g of sodium hypophosphite, and 0.41 g of ruthenium trichloride were weighed and dispersed in 60 mL of water. After thorough mixing, the mixture was dried by rotary evaporation at 60°C. The resulting product was calcined at 550°C in an argon atmosphere for 4 h at a heating rate of 5°C per minute. The gas flow rate was 40 mL / min relative to 20 g of melamine. After cooling, the resulting product was washed three times with water and ethanol (the content of sodium phosphate impurities in the product was 0.12 wt%), dispersed in 50 mL of water, and freeze-dried at -40°C for 20 h to obtain a phosphorus- and noble metal-doped carbon nitride precursor.

[0084] (2) Add 2.0 g of ferric nitrate nonahydrate to the phosphorus- and noble metal-doped carbon nitride obtained in step (1), and grind and mix thoroughly;

[0085] (3) The product obtained in step (2) was subjected to a programmed temperature calcination treatment, wherein the temperature rise program was room temperature-150°C (1h)-300°C (1.5h), the temperature rise rate was 5°C per minute, the calcination atmosphere was argon, and the gas flow rate was 40mL / min. After cooling, the photocatalytic material was obtained.

[0086] Example 6

[0087] (1) 30 g of melamine, 5 g of sodium hypophosphite and 0.17 g of ruthenium trichloride were weighed and dispersed in 50 mL of water, mixed thoroughly, and then dried by rotary evaporation at 60°C. The obtained product was calcined in an argon atmosphere at 650°C for 3 h, with a temperature increase rate of 10°C per minute, and a gas flow rate of 40 mL / min relative to 20 g of melamine. After cooling, the obtained product was washed with water and ethanol for 3 times respectively (the content of sodium hypophosphite impurities in the product was 0.07% by weight), and then dispersed in 50 mL of water and freeze-dried at -40°C for 22 h to obtain a phosphorus and noble metal doped carbon nitride precursor;

[0088] (2) The phosphorus and noble metal doped carbon nitride precursor obtained in step (1) was mixed with 2.5 g of iron nitrate nonahydrate by grinding thoroughly;

[0089] (3) The product obtained in step (2) was subjected to programmed temperature calcination treatment, with a temperature increase program of room temperature - 100°C (1 h) - 220°C (1.5 h), a temperature increase rate of 5°C per minute, and an argon atmosphere with a gas flow rate of 40 mL / min. After cooling, a photocatalytic material was obtained.

[0090] Example 7

[0091] (1) 30 g of melamine, 5 g of sodium hypophosphite and 0.17 g of ruthenium trichloride were weighed and dispersed in 50 mL of water, mixed thoroughly, and then dried by rotary evaporation at 60°C. The obtained product was calcined in an argon atmosphere at 650°C for 3 h, with a temperature increase rate of 10°C per minute, and a gas flow rate of 40 mL / min relative to 20 g of melamine. After cooling, the obtained product was washed with water and ethanol for 3 times respectively (the content of sodium hypophosphite impurities in the product was 0.07% by weight), and then dispersed in 50 mL of water and freeze-dried at -40°C for 22 h to obtain a phosphorus and noble metal doped carbon nitride precursor;

[0092] (2) The phosphorus and noble metal doped carbon nitride precursor obtained in step (1) was mixed with 2.5 g of iron nitrate nonahydrate by grinding thoroughly;

[0093] (3) The product obtained in step (2) was subjected to programmed temperature calcination treatment, with a temperature increase program of room temperature - 100°C (1 h) - 220°C (1.5 h), a temperature increase rate of 5°C per minute, and an argon atmosphere with a gas flow rate of 40 mL / min. After cooling, a photocatalytic material was obtained.

[0094] Example 8

[0095] (1) 30 g of melamine, 5 g of sodium hypophosphite, and 0.17 g of chloroplatinic acid were weighed and dispersed in 50 mL of water. After thorough mixing, the mixture was dried by rotary evaporation at 60°C. The resulting product was calcined at 550°C in an argon atmosphere for 4 h at a heating rate of 5°C per minute. The gas flow rate was 40 mL / min relative to 20 g of melamine. After cooling, the resulting product was washed three times with water and ethanol (the content of sodium phosphate impurities in the product was 0.1 wt%), dispersed in 50 mL of water, and freeze-dried at -40°C for 24 h to obtain a phosphorus- and noble metal-doped carbon nitride precursor.

[0096] (2) adding 1.9 g of nickel nitrate hexahydrate to the phosphorus- and noble metal-doped carbon nitride precursor obtained in step (1), and grinding and mixing thoroughly;

[0097] (3) The product obtained in step (2) was subjected to a programmed temperature calcination treatment, wherein the temperature rise program was room temperature-150°C (1h)-300°C (1.5h), the temperature rise rate was 5°C per minute, the calcination atmosphere was argon, and the gas flow rate was 40mL / min. After cooling, the photocatalytic material was obtained.

[0098] Comparative Example 1

[0099] (1) 30 g of melamine and 5 g of sodium hypophosphite were weighed and dispersed in 50 mL of water. After thorough mixing, the mixture was dried by rotary evaporation at 60°C. The resulting product was calcined at 550°C in an argon atmosphere for 4 h at a heating rate of 5°C per minute. The gas flow rate was 40 mL / min relative to 20 g of melamine. After cooling, the resulting product was washed three times with water and ethanol (the content of sodium phosphate impurities in the product was 0.1 wt%), dispersed in 50 mL of water, and freeze-dried at -40°C for 24 h to obtain a phosphorus-doped carbon nitride precursor.

[0100] (2) adding 2.5 g of ferric nitrate nonahydrate to the phosphorus-doped carbon nitride precursor obtained in step (1), and grinding and mixing thoroughly;

[0101] (3) The product obtained in step (2) was subjected to a programmed temperature calcination treatment, wherein the temperature rise program was room temperature-150°C (1h)-300°C (1.5h), the temperature rise rate was 5°C per minute, the calcination atmosphere was argon, and the gas flow rate was 40mL / min. After cooling, the photocatalytic material was obtained.

[0102] Comparative Example 2

[0103] 30g of melamine, 5g of sodium hypophosphite, and 0.17g of ruthenium trichloride were dispersed in 50mL of water, mixed thoroughly, and dried by rotary evaporation at 60°C. The resulting product was calcined at 550°C in an argon atmosphere for 4 hours at a heating rate of 5°C per minute (at a gas flow rate of 40mL / min relative to 20g of melamine). After cooling, the resulting product was washed three times with water and ethanol (the sodium phosphate impurity content in the product was 0.1% by weight), then dispersed in 50mL of water and freeze-dried at -40°C for 24 hours to obtain phosphorus- and precious metal-doped carbon nitride.

[0104] Comparative Example 3

[0105] (1) 30 g of melamine and 5 g of sodium hypophosphite were weighed and dispersed in 50 mL of water. After thorough mixing, the mixture was dried by rotary evaporation at 60°C. The resulting product was calcined at 550°C in an argon atmosphere for 4 h at a heating rate of 5°C per minute. The gas flow rate was 40 mL / min relative to 20 g of melamine. After cooling, the resulting product was washed three times with water and ethanol (the content of sodium phosphate impurities in the product was 0.1 wt%), dispersed in 50 mL of water, and freeze-dried at -40°C for 24 h to obtain a phosphorus-doped carbon nitride precursor.

[0106] (2) Add 2.5 g of ferric nitrate nonahydrate and 0.17 g of ruthenium trichloride to the phosphorus-doped carbon nitride precursor obtained in step (1), and grind and mix thoroughly;

[0107] (3) The product obtained in step (2) was subjected to a programmed temperature calcination treatment, wherein the temperature rise program was room temperature-150°C (1h)-300°C (1.5h), the temperature rise rate was 5°C per minute, the calcination atmosphere was argon, and the gas flow rate was 40mL / min. After cooling, the photocatalytic material was obtained.

[0108] Comparative Example 4

[0109] 5 g of sodium hypophosphite was dispersed in 50 mL of water, and 30 g of melamine was added to the system. After mixing evenly, the mixture was dried by rotary evaporation at 60 ° C. The resulting product was then calcined at 550 ° C in an argon atmosphere for 4 h, with a heating rate of 5 ° C per minute and a gas flow rate of 40 mL / min relative to 20 g of melamine to obtain phosphorus-doped carbon nitride; phosphorus-doped carbon nitride was mixed with 0.5 g of ferric oxide and 0.11 g of ruthenium dioxide, and 50 mL of ethanol was added to disperse the mixture. After mixing evenly, the mixture was dried by rotary evaporation at 60 ° C. The resulting product was then calcined at 550 ° C in an argon atmosphere for 4 h, with a heating rate of 5 ° C per minute and a gas flow rate of 40 mL / min to obtain a photocatalytic material.

[0110] Comparative Example 5

[0111] (1) 30 g of melamine, 5 g of sodium hypophosphite, and 0.17 g of ruthenium trichloride were weighed and dispersed in 50 mL of water. After thorough mixing, the mixture was dried by rotary evaporation at 60°C. The resulting product was calcined at 550°C in an argon atmosphere for 4 h at a heating rate of 5°C per minute and a gas flow rate of 40 mL / min relative to 20 g of melamine. After cooling, the resulting product was washed three times with water and ethanol (the content of sodium phosphate impurities in the product was 0.15% by weight), dispersed in 50 mL of water, and freeze-dried at -40°C to obtain phosphorus- and precious metal-doped carbon nitride.

[0112] (2) Add 2.5 g of ferric nitrate nonahydrate to the phosphorus- and noble metal-doped carbon nitride obtained in step (1), and grind and mix thoroughly;

[0113] (3) The product obtained in step (2) was subjected to a programmed temperature calcination treatment, wherein the temperature rise program was room temperature to 300°C (4h), the temperature rise rate was 5°C per minute, the calcination atmosphere was argon, and the gas flow rate was 40mL / min. After cooling, the photocatalytic material was obtained.

[0114] The contents of the components in the above-mentioned photocatalytic materials are shown in Table 1, and the property parameters are shown in Table 2.

[0115] Table 1

[0116]

[0117] Table 2

[0118]

[0119]

[0120] As can be seen from the above table, the photocatalytic material provided by the present invention has a good visible light absorption range and a large free carrier density, which is beneficial to improving the efficiency of photocatalytic ammonia decomposition to produce hydrogen.

[0121] Application of photocatalytic ammonia decomposition to produce hydrogen

[0122] The photocatalytic materials prepared in the above embodiments and comparative examples were used in the photocatalytic ammonia decomposition and hydrogen production reaction under simulated sunlight. The activity test was carried out using an online vacuum photocatalytic reaction device, and the light source was a 300W xenon lamp. The reaction conditions were: 0.1g of catalytic material, 100mL of 0.1mol / L ammonia solution, and a reaction temperature of 5°C. After the start of the reaction, samples were taken every hour to measure the average rate within 6 hours. The products were analyzed by chromatography equipped with a hydrogen flame ionization detector and a thermal conductivity cell detector, and quantified using a pre-determined standard curve. The reaction mainly produces two products, namely N2 and H2, and a small amount of O2 from the water decomposition side reaction. The reaction results are shown in Table 3.

[0123] Table 3

[0124]

[0125]

[0126] As can be seen from the table above, the photocatalytic material provided by the present invention has good performance in hydrogen production by decomposing ammonia, and the hydrogen generation rate can reach 1307.4 μmol g -1 h -1 Compared with Example 1, in Comparative Example 3, both the noble metal ruthenium and the non-noble metal iron were doped outside the carbon nitride skeleton structure. The hydrogen generation rate of the photocatalytic material prepared in Comparative Example 3 was only 373.8 μmol g when used for ammonia decomposition to produce hydrogen. -1 h -1 Compared with Example 1, the second calcination in step (3) of Comparative Example 5 uses a single-stage calcination to prepare the photocatalytic material. There are more hydrogen bonds and interlayer stacking between carbon nitrides, resulting in a low free carrier density, serious charge recombination, and poor activity. The photocatalytic material prepared in Comparative Example 5 has a hydrogen generation rate of only 270.3 μmol g when used for ammonia decomposition to produce hydrogen. -1 h -1 .

[0127] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A photocatalytic material, characterized in that: The photocatalytic material comprises nitrogen, carbon, phosphorus, non-noble metals and noble metals, wherein the photocatalytic material has a carbon nitride covalent skeleton, phosphorus and noble metals are present in the carbon nitride covalent skeleton in the form of doping, and the non-noble metals are loaded outside the carbon nitride covalent skeleton in the form of oxides; The non-noble metal is selected from at least one of iron, cobalt and nickel, and the noble metal is selected from at least one of ruthenium, platinum and palladium; The free carrier density of the photocatalytic material is (2-6)×10 22 cm -3 ; In the photocatalytic material, the molar ratio of carbon to nitrogen, calculated as elements, is 0.7-0.8:1; A method for preparing a photocatalytic material, wherein the method comprises the following steps: (1) mixing a nitrogen-containing organic compound with a phosphorus source and a noble metal source, and then performing rotary evaporation drying, a first roasting, and freeze drying; (2) mixing the product obtained in step (1) with a non-noble metal source in the presence of a solvent; (3) Under a protective atmosphere, the product obtained in step (2) is subjected to a second roasting, wherein the second roasting comprises first keeping the temperature at 100-200°C for 0.5-2h, and then heating to 210-350°C and keeping the temperature for 1-2h.

2. The photocatalytic material according to claim 1, wherein In the photocatalytic material, the molar ratio of carbon to nitrogen is 0.74-0.76:1, calculated as elements.

3. The photocatalytic material according to claim 1 or 2, wherein The mass ratio of nitrogen calculated as carbon nitride to the non-noble metal calculated as oxide is 100:2-8.

4. The photocatalytic material according to claim 3, wherein The mass ratio of nitrogen calculated as carbon nitride to the non-noble metal calculated as oxide is 100:3-6.

5. The photocatalytic material according to claim 1 or 2, wherein The mass ratio of nitrogen calculated as carbon nitride to the precious metal calculated as an element is 100:0.1-2.

6. The photocatalytic material according to claim 5, wherein The mass ratio of nitrogen calculated as carbon nitride to the precious metal calculated as an element is 100:0.2-0.

8.

7. The photocatalytic material according to claim 1 or 2, wherein The mass ratio of nitrogen calculated as carbon nitride to phosphorus calculated as an element is 100:0.5-10.

8. The photocatalytic material according to claim 7, wherein The mass ratio of nitrogen calculated as carbon nitride to phosphorus calculated as an element is 100:3-8.

9. The photocatalytic material according to claim 1 or 2, wherein Calculated on an element basis, the mass ratio of the noble metal to phosphorus is 0.05-0.5:

1.

10. The photocatalytic material according to claim 9, wherein Calculated on an element basis, the mass ratio of the noble metal to phosphorus is 0.05-0.18:

1.

11. The photocatalytic material according to claim 1 or 2, wherein In the X-ray diffraction pattern of the photocatalytic material, typical carbon nitride diffraction peaks appear at 2θ of 13.6° and 27.2°.

12. The photocatalytic material according to claim 1 or 2, wherein The free carrier density of the photocatalytic material is (3-5)×10 22 cm -3 .

13. The method for preparing the photocatalytic material according to claim 1, wherein: The method comprises the following steps: (1) mixing a nitrogen-containing organic compound with a phosphorus source and a noble metal source, followed by rotary evaporation drying, a first roasting, and freeze drying, wherein the noble metal is at least one selected from the group consisting of ruthenium, platinum, and palladium; (2) mixing the product obtained in step (1) with a non-noble metal source in the presence of a solvent, wherein the non-noble metal is selected from at least one of iron, cobalt and nickel; (3) Under a protective atmosphere, the product obtained in step (2) is subjected to a second roasting, wherein the second roasting comprises first keeping the temperature at 100-200°C for 0.5-2h, and then heating to 210-350°C and keeping the temperature for 1-2h.

14. The method according to claim 13, wherein: In step (1), the nitrogen-containing organic compound is selected from at least one of melamine, dicyandiamide and urea.

15. The method according to claim 14, wherein In step (1), the phosphorus source is an alkali metal phosphate and / or an alkali metal hypophosphite.

16. The method according to claim 15, wherein In step (1), the phosphorus source is sodium hypophosphite and / or potassium hypophosphite.

17. The method according to any one of claims 13 to 16, wherein: In step (1), the noble metal source is a soluble salt of a noble metal.

18. The method according to claim 17, wherein In step (1), the noble metal source is a soluble inorganic salt of a noble metal.

19. The method according to claim 18, wherein In step (1), the noble metal source is selected from at least one of nitrates, sulfates and chlorides of noble metals.

20. The method according to any one of claims 13 to 16, wherein: In step (1), the conditions for the rotary evaporation drying include: a temperature of 40-80°C.

21. The method according to claim 20, wherein In step (1), the conditions for the rotary evaporation drying include: a temperature of 60-70°C.

22. The method according to any one of claims 13 to 16, wherein: In step (1), the conditions for the first calcination include: a temperature of 300-700°C, a time of 3-6 hours, and a heating rate of 2-10°C / min.

23. The method according to claim 22, wherein In step (1), the conditions for the first calcination include: a temperature of 500-600°C, a time of 4-5 hours, and a heating rate of 2-5°C / min.

24. The method according to any one of claims 13 to 16, wherein: The first calcination is carried out under an inert atmosphere, and the gas flow rate of the inert atmosphere is 20-100 mL / min relative to 20 g of the nitrogen-containing organic compound in step (1).

25. The method according to any one of claims 13 to 16, wherein: In step (1), the freeze-drying conditions include: temperature of -50°C to -20°C, and time of 20-48 hours.

26. The method according to any one of claims 13 to 16, wherein: In step (2), the non-precious metal source is a soluble salt of a non-precious metal.

27. The method according to claim 26, wherein In step (2), the non-precious metal source is a soluble inorganic salt of a non-precious metal.

28. The method according to claim 27, wherein In step (2), the non-precious metal source is selected from at least one of nitrates, sulfates and chlorides of non-precious metals.

29. The method according to any one of claims 13 to 16, wherein: In step (2), the solvent is water.

30. The method according to any one of claims 13 to 16, wherein: In step (3), the second roasting includes first keeping the temperature at 150-200°C for 0.5-1.5 hours, and then heating to 250-350°C and keeping the temperature for 1.5-2 hours.

31. The method according to any one of claims 13 to 16, wherein: In step (3), the conditions for the second calcination include: a heating rate of 2-10°C / min.

32. The method according to any one of claims 13 to 16, wherein: The protective atmosphere is provided by at least one of nitrogen, argon and helium.

33. The method according to any one of claims 13 to 16, wherein: The mass ratio of the nitrogen-containing organic compound calculated as carbon nitride to the non-noble metal source calculated as oxide is 100:2-8.

34. The method according to claim 33, wherein The mass ratio of the nitrogen-containing organic compound calculated as carbon nitride to the non-noble metal source calculated as oxide is 100:3-6.

35. The method according to any one of claims 13 to 16, wherein: The mass ratio of the nitrogen-containing organic compound calculated as carbon nitride to the precious metal source calculated as an element is 100:0.1-2.

36. The method according to claim 35, wherein The mass ratio of the nitrogen-containing organic compound calculated as carbon nitride to the noble metal source calculated as an element is 100:0.2-0.

8.

37. The method according to any one of claims 13 to 16, wherein: The mass ratio of the nitrogen-containing organic compound calculated as carbon nitride to the phosphorus source calculated as an element is 100:0.5-10.

38. The method according to claim 37, wherein The mass ratio of the nitrogen-containing organic compound calculated as carbon nitride to the phosphorus source calculated as an element is 100:3-8.

39. The method according to any one of claims 13 to 16, wherein: Calculated by elements, the mass ratio of the noble metal source to the phosphorus source is 0.05-0.5:

1.

40. The method of claim 39, wherein Calculated on an element basis, the mass ratio of the noble metal source to the phosphorus source is 0.05-0.18:

1.

41. Use of the photocatalytic material according to any one of claims 1 to 12 in a photocatalytic ammonia decomposition reaction to produce hydrogen.

42. A method for producing hydrogen by photocatalytic decomposition of ammonia, wherein: The method comprises: in the presence of a photocatalytic material and visible light, performing a decomposition reaction on ammonia as a reaction raw material, wherein the photocatalytic material is the photocatalytic material according to any one of claims 1 to 12.

43. The method according to claim 42, wherein The reaction raw material ammonia is provided by an ammonia solution, and the concentration of the ammonia solution is 0.01-0.1 mol / L.

44. The method according to claim 42 or 43, wherein The conditions for the decomposition reaction include: a reaction temperature of 0.5-40° C., and an amount of the photocatalytic material of 0.02-0.1 g relative to 0.01 mol of ammonia solution.

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