Biomass-derived in-situ nitrogen and phosphorus doped carbon material supported iron-based catalysts, preparation and use thereof

Abstract

The application discloses a biomass-derived in-situ nitrogen and phosphorus doped carbon material loaded iron-based catalyst and a preparation and application thereof. The preparation method comprises the following steps: weighing biomass, crushing and grinding the biomass to below 200 meshes, adding a solvent, adding an iron-containing aqueous solution after the biomass is fully dispersed and activated, uniformly stirring and mixing, magnetically stirring at 20-50 DEG C for 8-15 h, adjusting PH to be greater than 9 by using an alkaline reagent, forming a gel, freezing and drying the gel, then performing microwave treatment, performing hydrothermal reaction, filtering and washing to obtain a precursor, drying the precursor, high-temperature calcining under an inert atmosphere, and cooling to obtain a biomass-derived in-situ nitrogen and phosphorus doped carbon material loaded iron-based photocatalyst. The application provides an application of the biomass-derived in-situ nitrogen and phosphorus doped carbon material loaded iron-based photocatalyst in photocatalytic reduction of CO2, and the photocatalyst has good cycle stability and high yield of target products.

Description

Technical Field

[0001] This invention relates to iron-based catalysts supported on biomass-derived in-situ nitrogen-phosphorus-doped carbon materials, their preparation, and their application in photocatalytic reduction of CO2. Background Technology

[0002] The excessive use of fossil fuels has led to CO2 emissions exceeding nature's capacity to process them, causing global warming and threatening the environment and ecosystems. Much research has focused on reducing CO2 emissions, capturing CO2, and converting and utilizing CO2. Converting CO2 into high-value fuels or chemicals plays a crucial role in addressing energy supply and environmental pollution issues, and researchers typically employ thermocatalysis, electrocatalysis, and photocatalysis. Compared to thermocatalysis and electrocatalysis, photocatalytic CO2 reduction technology, which uses ultraviolet or visible light to drive the generation of photoelectrons, offers advantages such as mild operating conditions, low energy consumption, and being environmentally friendly and pollution-free, attracting widespread attention from researchers.

[0003] However, single semiconductor materials generally suffer from problems such as excessively wide or narrow band gaps, insufficient light absorption or photoresponse range, easy recombination of photogenerated electron pairs, poor conductivity, and insufficient negative electrode potential for CO2 reduction, resulting in poor photocatalytic activity and weak stability. Many studies have aimed to enhance light absorption, modulate band gaps, increase defect structures, alter or modify active centers, accelerate electron transfer, suppress photogenerated electron pair recombination, and strengthen substrate molecule activation and adsorption by constructing heterojunctions, plasma modification, composite carbon materials, or porous materials, thereby improving photocatalytic activity. For example, Chinese patent (202110057935.3) achieved a lower band gap than pure CdS by compositing CdS with MOF-808 and RGO, thus improving the photocatalytic performance of CdS. Chinese patent (202011108636.X) used modified nitrogen-containing defect-structured graphitic carbon nitride (gC3N) to achieve similar results. x A Z-type composite catalyst for photocatalytic nitrogen fixation and ammonia production was obtained by combining iron oxide (Fe2O3). However, it still faces problems such as low photocatalytic activity, severe photocorrosion, and poor catalyst stability.

[0004] Carbon materials are acid-resistant and have good electrical conductivity. They can be used as carriers to effectively disperse active components. In particular, the use of heteroatom-doped carbon materials can significantly improve the electronic structure of carbon materials, forming an electronic structure with uneven charge distribution. This not only enhances the adsorption and activation ability of substrate molecules, but also regulates the electron density of active components.

[0005] In summary, the technical problem to be solved by this invention is:

[0006] A method for preparing a mixed-valence iron-based photocatalytic material supported on a biomass-derived in-situ nitrogen-phosphorus-doped carbon material was developed. The photocatalytic material prepared by this method can be applied in the photocatalytic reduction of carbon dioxide, and has high photocatalytic performance and good stability. Summary of the Invention

[0007] One of the objectives of this invention is to provide a method for preparing iron-based photocatalysts supported on biomass-derived in-situ nitrogen-phosphorus-doped carbon materials, in order to overcome the problems of high cost, complicated steps, uneven doping, and high environmental pressure in existing methods for preparing nitrogen-phosphorus-doped carbon materials, which use organic or inorganic chemical reagents as raw materials or activators.

[0008] The second objective of this invention is to provide an iron-based photocatalyst supported on a biomass-derived in-situ nitrogen-phosphorus-doped carbon material.

[0009] The third objective of this invention is to provide an application of an iron-based photocatalyst supported on a biomass-derived in-situ nitrogen-phosphorus-doped carbon material in the photocatalytic reduction of CO2.

[0010] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0011] In a first aspect, the present invention provides a method for preparing an iron-based photocatalyst supported on a biomass-derived in-situ nitrogen-phosphorus-doped carbon material, comprising the following steps:

[0012] Weigh biomass, crush and grind it to below 200 mesh, add solvent, and after the biomass is fully dispersed and activated, add an iron-containing aqueous solution. The solute in the iron-containing aqueous solution is ferric salt and / or ferrous salt with a total concentration of 0.5-3 mol / L. After stirring and mixing evenly, stir magnetically at 20-50℃ for 8-15 h, then adjust the pH to >9 with an alkaline reagent to form a gel. Freeze-dry the gel, then microwave it at 400-800W for 3-5 min, and then hydrothermally react it at 160-200℃ for 8-15 h. Filter and wash to obtain the precursor. After drying the precursor, heat it to 700-950℃ in an inert gas atmosphere at a heating rate of 3-15℃, calcine it for 0.5-2.5 h, and cool it to obtain a biomass-derived in-situ nitrogen-phosphorus-doped carbon material supported iron-based photocatalyst.

[0013] The biomass is selected from one or more of glucose, sucrose, brown sugar, soybean flour, Escherichia coli, yeast, humus, and distiller's grains;

[0014] The alkaline reagent is any one or more of the following: 1-6M ammonia water, 1-6M sodium hydroxide aqueous solution, 1-6M potassium hydroxide aqueous solution, 1-6M sodium carbonate aqueous solution, and 1-6M sodium bicarbonate aqueous solution.

[0015] The feeding ratio of the biomass, solvent and iron-containing aqueous solution is (2-10)g:(2-25)g:(10-40)mL.

[0016] Preferably, the biomass is one of the following: a mixture of distiller's grains, yeast, soybean flour and humus in a mass ratio of 1:1, or a mixture of distiller's grains and brown sugar in a mass ratio of 5:1.

[0017] Preferably, the solvent is selected from any one of water, ethanol, 1-5 vol% glutaraldehyde aqueous solution, 1-5 vol% formaldehyde aqueous solution, and 1-5 vol% acetone aqueous solution. More preferably, the solvent is selected from any one of water, 5 vol% glutaraldehyde aqueous solution, 3 vol% formaldehyde aqueous solution, and 5 vol% acetone aqueous solution.

[0018] Preferably, the ferric salt is any one or more of ferric chloride, ferric sulfate, and ferric nitrate, and the ferrous salt is any one or more of ferrous chloride, ferrous sulfate, ferrous acetate, and ferrous oxalate. More preferably, the solute in the iron-containing aqueous solution is a ferrous salt, even more preferably any one of ferrous chloride, ferrous sulfate, and ferrous oxalate, and most preferably ferrous chloride.

[0019] Preferably, the alkaline reagent is any one or more of the following: 4-6M ammonia water, 4-6M sodium hydroxide aqueous solution, 4-6M potassium hydroxide aqueous solution, 4-6M sodium carbonate aqueous solution, and 4-6M sodium bicarbonate aqueous solution.

[0020] Preferably, the feeding ratio of the biomass, solvent and iron-containing aqueous solution is (5-10)g:(20-30)g:15mL.

[0021] Preferably, the biomass is fully dispersed and activated by the following method: weighing the biomass, crushing and grinding it to below 200 mesh (more preferably 100-200 mesh), adding solvent, sonicating for 3-5 minutes, and then letting it stand for 30-60 minutes.

[0022] Preferably, the freeze-drying is performed under vacuum at -10 to -50°C for 8 to 12 hours.

[0023] Preferably, the washing process involves first washing with deionized water until neutral, and then thoroughly washing with ethanol.

[0024] Preferably, the precursor is dried at 80–100°C.

[0025] Preferably, the temperature is raised to 750–850°C in a nitrogen atmosphere at a rate of 3–10°C / min, and calcined for 1–2 hours. More preferably, the temperature is raised to 750–850°C in a nitrogen atmosphere at a rate of 5–10°C / min, and calcined for 1–2 hours.

[0026] A particularly preferred embodiment of the present invention is as follows: the biomass is distiller's grains or yeast; the solvent is a 3% formaldehyde aqueous solution, a 5% glutaraldehyde aqueous solution, or a 5% acetone aqueous solution; the iron-containing aqueous solution is a 1.5M ferrous chloride aqueous solution; and the alkaline reagent is a 5M KOH aqueous solution or a 5M ammonia solution. The mixture is heated to 750-850°C at a rate of 3-10°C / min under a nitrogen atmosphere and calcined for 1-2 hours. The feed ratio of the biomass, solvent, and iron-containing aqueous solution is 5-10 g:20 g:15 mL. The most preferred embodiment is as follows: the biomass is distiller's grains; the solvent is a 3% formaldehyde aqueous solution; the iron-containing aqueous solution is a 1.5M ferrous chloride aqueous solution; and the alkaline reagent is a 5M KOH aqueous solution or a 5M ammonia solution. The mixture is heated to 850°C at a rate of 8-10°C / min under a nitrogen atmosphere and calcined for 1-1.5 hours. The feed ratio of the biomass, solvent, and iron-containing aqueous solution is 5-10 g:20 g:15 mL.

[0027] Another preferred embodiment of the present invention is as follows: the biomass is a mixture of soybean flour and humus in a mass ratio of 1:1; the solvent is water; the iron-containing aqueous solution is a 2.0M ferrous oxalate aqueous solution; the alkaline reagent is 6M ammonia water; the mixture is heated to 750°C at a rate of 5°C / min in a nitrogen atmosphere and calcined for 2 hours; the feed ratio of the biomass, solvent and iron-containing aqueous solution is 6g:30g:15mL.

[0028] In a second aspect, the present invention provides an iron-based photocatalyst supported on a biomass-derived in-situ nitrogen-phosphorus-doped carbon material prepared according to the preparation method described in the first aspect.

[0029] The biomass-derived in-situ nitrogen-phosphorus-doped carbon material supported iron-based photocatalyst of the present invention simultaneously contains zero-valent, divalent, and trivalent iron.

[0030] Thirdly, the present invention provides the application of the iron-based photocatalyst supported on the biomass-derived in-situ nitrogen-phosphorus-doped carbon material described in the second aspect in the photocatalytic reduction of CO2.

[0031] Preferably, the specific operating steps of the application are as follows: weigh the biomass-derived in-situ nitrogen-phosphorus-doped carbon material loaded with iron-based photocatalyst and sodium bicarbonate and put them into a reaction vessel, slowly add sulfuric acid, stir to make them evenly dispersed, and generate CO2 and water in situ; then react under visible light for 1 to 3 hours to generate CO and methane.

[0032] Preferably, the catalyst can achieve high yields of CO and methane.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] (1) This invention uses biomass containing carbon, nitrogen and phosphorus elements as raw material to obtain nitrogen and phosphorus co-doped carbon materials. After the biomass is mixed with iron salt, the in-situ nitrogen and phosphorus doped carbon materials are obtained by various heat treatments using the "one-pot method" to support mixed valence state iron-based photocatalytic materials. The raw materials are widely available and the cost is low. The preparation method is simple and green.

[0035] (2) No additional nitrogen or phosphorus source is required during the preparation process. There are no reducing agents or chemical activators. The operation is simple and convenient, with little pollution, and it is suitable for large-scale production and application.

[0036] (3) The combination of freeze-drying technology, microwave heat treatment, hydrothermal and pyrolysis technologies, etc., assists crystal growth and biomass pore protection, which provides a guarantee for the formation of the catalyst's phase structure.

[0037] (4) During the preparation process of this invention, there is an interaction between biomass and metal ions, and a heterojunction is formed between carbon materials and iron oxides and multivalent iron oxides. In particular, the in-situ formation of zero-valent iron facilitates rapid electron transfer, which constructs a multi-site synergistic effect of the catalyst. This is beneficial to the separation between electrons and holes, making electrons transfer and utilization more efficient. Furthermore, the introduction of nitrogen and phosphorus doped carbon materials increases the specific surface area of ​​the catalyst, which is more conducive to the adsorption of substrate molecules.

[0038] (5) The nitrogen and phosphorus doped carbon material supported on mixed valence state iron-based photocatalytic material obtained by the method of the present invention has excellent performance, is magnetic, and can be used as a photocatalyst to reduce CO2 to carbon monoxide and methane. It has good cycle stability and high yield of target product. Attached Figure Description

[0039] Figure 1 The image shows a SEM image of the nitrogen-phosphorus-doped carbon material supported on a mixed-valence iron-based photocatalyst prepared in Example 1. The image shows that the material has a rod-like morphology.

[0040] Figure 2 The image shows a TEM image of the nitrogen-phosphorus-doped carbon material loaded with mixed-valence iron-based photocatalyst prepared in Example 1. The image shows that the particles in the material are loaded or embedded in the carbon layer. High-magnification TEM reveals that the particles are polycrystalline metal elements and metal oxides.

[0041] Figure 3 The image shows the X-ray diffraction pattern of the nitrogen-phosphorus-doped carbon material supported on the mixed-valence iron-based photocatalyst prepared in Example 1. The pattern shows that the material contains elemental iron, iron phosphide, ferrous oxide, iron(II) oxide, and ferric oxide.

[0042] Figure 4 The image shows the Raman spectrum of the nitrogen-phosphorus doped carbon material supported on the mixed-valence iron-based photocatalyst prepared in Example 1. The image shows that the material contains graphitic carbon and amorphous carbon, as well as Fe-O and Fe-Fe bonds.

[0043] Figure 5 The image shows the XPS plot of the nitrogen-phosphorus-doped carbon material supported on mixed-valence iron-based photocatalyst prepared in Example 1, where a: broad spectrum; b: fine spectrum of Fe 2p; the figure shows that the material contains C, N, O, P and Fe elements, including elemental iron, iron phosphide, ferrous oxide, iron(II,III) oxide and iron(III) oxide.

[0044] Figure 6 The image shows the EDS elemental mapping of the nitrogen-phosphorus-doped carbon material supported on the mixed-valence iron-based photocatalyst prepared in Example 1, with C, N, O, P and Fe elements and their contents. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described below in conjunction with the accompanying drawings and preferred embodiments, but the scope of protection of this invention is not limited thereto:

[0046] Unless otherwise specified, the biomass used in the examples is distiller's grains, and the biomass is crushed and ground to 100-200 mesh. Unless otherwise specified, the solvent is a 3 vol% formaldehyde aqueous solution. The amounts used in the photocatalytic reduction of CO2 are as follows: sodium bicarbonate 0.84 g, 2M sulfuric acid 3.5 mL.

[0047] Example 1

[0048] 1. A method for preparing a nitrogen-phosphorus-doped carbon material-supported mixed-valence iron-based photocatalytic material:

[0049] Weigh 5g of biomass (its elemental composition is shown in Table 1), add 20g of solvent, sonicate for 5min, let stand for 35min, add 15mL of ferrous chloride (1.5mol / L), stir and mix evenly, magnetically stir at 40℃ for 11h, adjust the pH to greater than 9 with 5mol / L KOH to form a gel, vacuum dry at -50℃ for 10h, microwave in a microwave oven (power 500W) for 3min, then add 10mL of deionized water to the mixture and transfer to a hydrothermal reactor for hydrothermal treatment at 200℃ for 10h to obtain a solid-liquid mixture. After vacuum filtration, wash with deionized water until neutral, wash 5 times with ethanol, and dry the obtained solid in a vacuum oven at 100℃. Then transfer it to a tube furnace and heat it to 850℃ at a rate of 10℃ / min in a nitrogen atmosphere for 1.5h. After cooling, obtain a black powder, take it out, grind and sieve (100 mesh), and the prepared catalyst 1.

[0050] Table 1 shows the relative content of each element in the biomass of Example 1.

[0051] element Wt% C 50 N 10 O 30 P 6 Mg 0.01 Na 0.21 K 3.38 Cl 0.4 total 100.00

[0052] Figure 1 The image shows an SEM image of catalyst 1 prepared in Example 1, which shows that the material has a rod-like morphology.

[0053] Figure 2 The image shows a TEM image of catalyst 1 prepared in Example 1. The image shows that the particles in the material are loaded or embedded in the carbon layer. High-magnification TEM reveals that the particles are polycrystalline metal elements and metal oxides.

[0054] Figure 3 The image shows the X-ray diffraction pattern of catalyst 1 prepared in Example 1, which indicates that the material contains elemental iron, ferric phosphide, ferrous oxide, iron(II) oxide and ferric oxide.

[0055] Figure 4 The image shows the Raman spectrum of catalyst 1 prepared in Example 1, which indicates the presence of graphitic carbon and amorphous carbon in the material, as well as Fe-O and Fe-Fe bonds.

[0056] Figure 5 The image shows the XPS plot of catalyst 1 prepared in Example 1, which shows that the material contains C, N, O, P and Fe elements, including elemental iron, ferric phosphide, ferrous oxide, iron(II) oxide and ferric oxide.

[0057] Figure 6 The image shows the EDS elemental mapping analysis of catalyst 1 prepared in Example 1, with C, N, O, P and Fe elements and their contents.

[0058] 2. Application of catalyst 1 in photocatalytic carbon dioxide reduction reaction.

[0059] Weigh 0.02g of catalyst 1, add sodium bicarbonate (0.84g), evacuate the vacuum, and then add 3.5mL of 2M sulfuric acid to produce CO2 and water in situ.

[0060] Then, the reaction was carried out under light (simulated sunlight by a 300W xenon lamp) for 2 hours.

[0061] After completing the experiment, 0.5 mL of gas was extracted from the tube, and the peak area was detected using a gas chromatograph (GC-14C). The yields of CH4 and CO were calculated, and the calculated yields of CH4 and CO were 3.4 μmol g. -1 h -1 and 2.8 μmol g -1 h -1 .

[0062] Catalyst 1 was recovered and recycled, and the results are shown in Table 2:

[0063] Table 2 Catalyst 1 Recycling

[0064] frequency <![CDATA[CO production rate (μmolh -1 g -1 )]]> <![CDATA[CH4 production rate (μmolh -1 g -1 )]]> 1 2.8 3.4 2 2.8 3.4 3 2.8 3.4 4 2.8 3.4 5 2.8 3.4 6 2.8 3.4

[0065] Comparative Example 1

[0066] 1. A method for preparing a nitrogen-phosphorus-doped carbon material-supported mixed-valence iron-based photocatalytic material:

[0067] Weigh 5g of biomass, add 20g of solvent, sonicate for 5min, let stand for 35min, add 15mL of ferric chloride (1.5mol / L), stir and mix evenly, magnetically stir at 40℃ for 11h, adjust pH to greater than 9 with 5mol / L KOH to form a gel, vacuum dry at -50℃ for 10h, microwave in a microwave oven (500W) for 3min, then transfer the mixture with 10mL of deionized water to a hydrothermal reactor and hydrothermally heat at 200℃ for 10h to obtain a solid-liquid mixture, filter under reduced pressure, wash with deionized water until neutral, wash 5 times with ethanol, dry the obtained solid in a vacuum oven at 100℃, transfer to a tube furnace, heat to 850℃ at a rate of 10℃ / min in a nitrogen atmosphere, calcine for 1.5h, cool to obtain a black powder, take it out, grind and sieve (100 mesh), thus preparing catalyst 2.

[0068] 2. Application of catalyst 2 in photocatalytic carbon dioxide reduction reaction.

[0069] Weigh 0.02g of catalyst 2, add sodium bicarbonate (0.84g), evacuate the vacuum, and then add 3.5mL of 2M sulfuric acid to produce CO2 and water in situ. Then react under light (simulated sunlight by a 300W xenon lamp) for 2 hours.

[0070] After completing the experiment, 0.5 mL of gas was extracted from the tube, and the peak area was detected using a gas chromatograph (GC-14C). The yields of CH4 and CO were calculated, and the calculated yields of CH4 and CO were 2.7 μmol g. -1 h -1 and 1.5 μmol g -1 h -1 .

[0071] Comparative Example 2

[0072] 1. A method for preparing a nitrogen-phosphorus-doped carbon material-supported mixed-valence iron-based photocatalytic material:

[0073] Weigh 5g of sucrose, add 20g of solvent, sonicate for 5min, let stand for 35min, add 15mL of ferrous chloride (1.5mol / L), stir and mix evenly, magnetically stir at 40℃ for 11h, adjust pH to greater than 9 with 5mol / L KOH to form a gel, vacuum dry at -50℃ for 10h, microwave in a microwave oven (500W) for 3min, then transfer the mixture with 10mL of deionized water to a hydrothermal reactor and hydrothermally heat at 200℃ for 10h to obtain a black solid-liquid mixture. After vacuum filtration, wash with deionized water until neutral, wash 5 times with ethanol, and dry the resulting solid in a vacuum oven at 100℃. Then transfer it to a tube furnace and calcine at 850℃ in a nitrogen atmosphere at a rate of 10℃ / min for 1.5h. After cooling, obtain a black powder, take it out, grind and sieve (100 mesh). The prepared catalyst 3.

[0074] 2. Application of catalyst 3 in photocatalytic carbon dioxide reduction reaction.

[0075] Weigh 0.02g of catalyst 3, add sodium bicarbonate (0.84g), evacuate the vacuum, and then add 3.5mL of 2M sulfuric acid to produce CO2 and water in situ.

[0076] Then, the reaction was carried out under light (simulated sunlight by a 300W xenon lamp) for 2 hours.

[0077] After completing the experiment, 0.5 mL of gas was extracted from the tube, and the peak area was detected using a gas chromatograph (GC-14C). The yields of CH4 and CO were calculated, and the calculated yields of CH4 and CO were 1.0 μmol g. -1 h -1 and 0.5 μmol g -1 h -1 .

[0078] Comparative Example 3

[0079] 1. A method for preparing an iron-based photocatalytic material:

[0080] 20g solvent, sonicated for 5min, left to stand for 35min, 15mL ferrous chloride (1.5mol / L) added, stirred and mixed evenly, magnetically stirred at 40℃ for 11h, pH adjusted to greater than 9 with 5mol / L KOH to form a green gel, vacuum dried at -50℃ for 10h, microwaved in a microwave oven (500W) for 3min, then the mixture with 10mL deionized water was transferred to a hydrothermal reactor and hydrothermally heated at 200℃ for 10h to obtain a mixture, filtered under reduced pressure, washed with deionized water until neutral, washed 5 times with ethanol, the obtained solid was dried in a vacuum oven at 100℃, transferred to a tube furnace, heated to 850℃ at a rate of 10℃ / min in a nitrogen atmosphere, calcined for 1.5h, cooled to obtain a black powder, taken out and ground and sieved (100 mesh), the prepared catalyst 4.

[0081] 2. Application of catalyst 4 in photocatalytic carbon dioxide reduction reaction.

[0082] Weigh 0.02g of catalyst 4, add sodium bicarbonate (0.84g), evacuate the vacuum, and then add 3.5mL of 2M sulfuric acid to produce CO2 and water in situ.

[0083] Then, the reaction was carried out under light (simulated sunlight by a 300W xenon lamp) for 2 hours.

[0084] After completing the experiment, 0.5 mL of gas was extracted from the tube, and the peak area was detected using a gas chromatograph (GC-14C). The yields of CH4 and CO were calculated, and the calculated yields of CH4 and CO were 0.1 μmol g. -1 h -1 and 0.2 μmol g -1 h -1 .

[0085] Based on Example 1, the heat treatment conditions were varied as shown in Comparative Examples 4-6.

[0086] Comparative Example 4

[0087] 1. A method for preparing a nitrogen-phosphorus-doped carbon material-supported mixed-valence iron-based photocatalytic material:

[0088] Weigh 5g of biomass, add 20g of solvent, sonicate for 5min, let stand for 35min, add 15mL of ferrous chloride (1.5mol / L), stir and mix evenly, magnetically stir at 40℃ for 11h, adjust pH to greater than 9 with 5mol / L KOH to form a gel, vacuum dry the mixture at -50℃ for 10h, then transfer the mixture with 10mL of deionized water to a hydrothermal reactor and hydrothermally heat at 200℃ for 10h to obtain a solid-liquid mixture, filter under reduced pressure, wash with deionized water until neutral, wash 5 times with ethanol, dry the obtained solid in a vacuum oven at 100℃, transfer to a tube furnace, heat to 850℃ at a rate of 10℃ / min in a nitrogen atmosphere, calcine for 1.5h, cool to obtain a black powder, take it out, grind and sieve (100 mesh), the prepared catalyst 5.

[0089] 2. Application of catalyst 5 in photocatalytic carbon dioxide reduction reaction.

[0090] Weigh 0.02g of catalyst 5, add sodium bicarbonate (0.84g), evacuate the vacuum, and then add 3.5mL of 2M sulfuric acid to produce CO2 and water in situ.

[0091] Then, the reaction was carried out under light (simulated sunlight by a 300W xenon lamp) for 2 hours.

[0092] After completing the experiment, 0.5 mL of gas was extracted from the tube, and the peak area was detected using a gas chromatograph (GC-14C). The yields of CH4 and CO were calculated, and the calculated rates of CH4 and CO production were 0.2 μmol g. -1 h -1 and 0.9 μmol g -1 h -1 .

[0093] Comparative Example 5

[0094] 1. A method for preparing a nitrogen-phosphorus-doped carbon material-supported mixed-valence iron-based photocatalytic material:

[0095] Weigh 5g of biomass, add 20g of solvent, sonicate for 5min, let stand for 35min, add 15mL of ferrous chloride (1.5mol / L), stir and mix evenly, magnetically stir at 40℃ for 11h, adjust pH to greater than 9 with 5mol / L KOH to form a gel, vacuum dry at -50℃ for 10h, microwave in a microwave oven (power 500W) for 3min to obtain a black solid-liquid mixture, filter under reduced pressure, wash with deionized water until neutral, wash 5 times with ethanol, dry the obtained solid in a vacuum oven at 100℃, transfer to a tube furnace, heat to 850℃ at a rate of 10℃ / min in a nitrogen atmosphere, calcine for 1.5h, cool to obtain a black powder, take out, grind and sieve (100 mesh), the prepared catalyst 6.

[0096] 2. Application of Catalyst 6 in photocatalytic carbon dioxide reduction reaction.

[0097] Weigh 0.02g of catalyst 6, add sodium bicarbonate (0.84g), evacuate the vacuum, and then add 3.5mL of 2M sulfuric acid to produce CO2 and water in situ.

[0098] Then, the reaction was carried out under light (simulated sunlight by a 300W xenon lamp) for 2 hours.

[0099] After completing the experiment, 0.5 mL of gas was extracted from the tube, and the peak area was detected using a gas chromatograph (GC-14C). The yield of CH4 or CO was calculated, and the calculated rates of CH4 and CO production were 0 μmol / g. -1 h -1 and 0.2 μmol g -1 h -1 .

[0100] Comparative Example 6

[0101] 1. A method for preparing a nitrogen-phosphorus-doped carbon material-supported mixed-valence iron-based photocatalytic material:

[0102] Weigh 5g of biomass, add 20g of solvent, sonicate for 5min, let stand for 35min, add 15mL of ferrous chloride (1.5mol / L), stir and mix evenly, magnetically stir at 40℃ for 11h, adjust pH to greater than 9 with 5mol / L KOH to form a gel, vacuum dry at -50℃ for 10h, transfer to a tube furnace, and then heat to 850℃ at a rate of 10℃ / min in a nitrogen atmosphere, calcine for 1.5h, cool to obtain black powder, take out and grind and sieve (100 mesh), the prepared catalyst 7.

[0103] 2. Application of Catalyst 7 in photocatalytic carbon dioxide reduction reaction.

[0104] Weigh 0.02g of catalyst 7, add sodium bicarbonate (0.84g), evacuate the vacuum, and then add 3.5mL of 2M sulfuric acid to produce CO2 and water in situ.

[0105] Then, the reaction was carried out under light (simulated sunlight by a 300W xenon lamp) for 2 hours.

[0106] After completing the experiment, 0.5 mL of gas was extracted from the tube, and the peak area was detected using a gas chromatograph (GC-14C). The yields of CH4 and CO were calculated, and the calculated yields of CH4 and CO were 1.7 μmol g. -1 h -1 and 0.9 μmol g -1 h -1 .

[0107] Table 3 Influence of Heat Treatment Method

[0108] Heat treatment <![CDATA[CH4 production rate (μmolg -1 h -1 )]]> <![CDATA[CO production rate (μmol g -1 h -1 )]]> Example 1 Microwave + Hydrothermal + Pyrolysis 3.4 2.8 Comparative Example 4 Hydrothermal + Pyrolysis 0.2 0.9 Comparative Example 5 Microwave + Pyrolysis 0 0.2 Comparative Example 6 pyrolysis 1.7 0.9

[0109] Example 2

[0110] 1. A method for preparing a nitrogen-phosphorus-doped carbon material-supported mixed-valence iron-based photocatalytic material:

[0111] Weigh 3g of soybean flour and 3g of humic matter, add 30g of water, sonicate for 5min, let stand for 40min, add 15mL of ferrous oxalate (2.0mol / L), stir and mix evenly, magnetically stir at 40℃ for 10h, adjust pH to greater than 9 with 6mol / L ammonia water to form a gel, vacuum dry at -50℃ for 10h, microwave in a microwave oven (power 500W) for 5min, then transfer the mixture with 10mL of deionized water to a hydrothermal reactor and hydrothermally heat at 200℃ for 10h to obtain a solid-liquid mixture, filter under reduced pressure, wash with deionized water until neutral, wash 5 times with ethanol, dry the obtained solid in a vacuum oven at 80℃, transfer to a tube furnace, heat to 650℃ at a rate of 5℃ / min in a nitrogen atmosphere, calcine for 2h, cool to obtain a black powder, take it out, grind and sieve (100 mesh), the prepared catalyst 8.

[0112] 2. Application of catalyst 8 in photocatalytic carbon dioxide reduction reaction.

[0113] Weigh 0.02g of catalyst 8, add sodium bicarbonate (0.84g), evacuate the vacuum, and then add 3.5mL of 2M sulfuric acid to produce CO2 and water in situ.

[0114] Then, the reaction was carried out under light (simulated sunlight by a 300W xenon lamp) for 3 hours.

[0115] After completing the experiment, 0.5 mL of gas was extracted from the tube, and the peak area was detected using a gas chromatograph (GC-14C). The yields of CH4 and CO were calculated, and the calculated yields of CH4 and CO were 1.4 μmol g. -1 h -1 and 0.8 μmol g -1 h -1 .

[0116] Example 3

[0117] 1. A method for preparing a nitrogen-phosphorus-doped carbon material-supported mixed-valence iron-based photocatalytic material:

[0118] Weigh 3g of soybean flour and 3g of humic matter, add 30g of water, sonicate for 5min, let stand for 40min, add 15mL of ferrous oxalate (2.0mol / L), stir and mix evenly, magnetically stir at 40℃ for 10h, adjust pH to greater than 9 with 6mol / L ammonia water to form a gel, vacuum dry at -50℃ for 10h, microwave in a microwave oven (power 500W) for 5min, then transfer the mixture with 10mL of deionized water to a hydrothermal reactor and hydrothermally heat at 200℃ for 10h to obtain a black solid-liquid mixture, filter under reduced pressure, wash with deionized water until neutral, wash 5 times with ethanol, dry the obtained solid in a vacuum oven at 80℃, transfer to a tube furnace, heat to 750℃ at a rate of 5℃ / min in a nitrogen atmosphere, calcine for 2h, cool to obtain a black powder, take it out, grind and sieve (100 mesh), the prepared catalyst 9.

[0119] 2. Application of Catalyst 9 in photocatalytic carbon dioxide reduction reaction.

[0120] Weigh 0.02g of catalyst 9, add sodium bicarbonate (0.84g), evacuate the vacuum, and then add 3.5mL of 2M sulfuric acid to produce CO2 and water in situ.

[0121] Then, the reaction was carried out under light (simulated sunlight by a 300W xenon lamp) for 3 hours.

[0122] After the experiment, 0.5 mL of gas was extracted from the tube, and the peak area was detected using a gas chromatograph (GC-14C). The yields of CH4 and CO were calculated, and the calculated yields of CH4 and CO were 3.0 μmol g. -1 h -1 and 2.4 μmol g -1 h -1 .

[0123] Example 4

[0124] 1. A method for preparing a nitrogen-phosphorus-doped carbon material-supported mixed-valence iron-based photocatalytic material:

[0125] Weigh 3g of soybean flour and 3g of humic matter, add 30g of water, sonicate for 5min, let stand for 40min, add 15mL of ferrous oxalate (2.0mol / L), stir and mix evenly, magnetically stir at 40℃ for 10h, adjust pH to greater than 9 with 6mol / L ammonia water to form a gel, vacuum dry at -50℃ for 10h, microwave in a microwave oven (power 500W) for 5min, then transfer the mixture with 10mL of deionized water to a hydrothermal reactor and hydrothermally heat at 200℃ for 10h to obtain a black solid-liquid mixture, filter under reduced pressure, wash with deionized water until neutral, wash 5 times with ethanol, dry the obtained solid in a vacuum oven at 80℃, transfer to a tube furnace, heat to 850℃ at a rate of 5℃ / min in a nitrogen atmosphere, calcine for 2h, cool to obtain a black powder, take it out, grind and sieve (100 mesh), thus preparing catalyst 10.

[0126] 2. Application of Catalyst 10 in photocatalytic carbon dioxide reduction reaction.

[0127] Weigh 0.02g of catalyst 10, add sodium bicarbonate (0.84g), evacuate the vacuum, and then add 3.5mL of 2M sulfuric acid to produce CO2 and water in situ.

[0128] Then, the reaction was carried out under light (simulated sunlight by a 300W xenon lamp) for 3 hours.

[0129] After completing the experiment, 0.5 mL of gas was extracted from the tube, and the peak area was detected using a gas chromatograph (GC-14C). The yields of CH4 and CO were calculated, and the calculated yields of CH4 and CO were 0.9 μmol g. -1 h -1 and 1.5 μmol g -1 h -1 .

[0130] Example 5

[0131] 1. A method for preparing a nitrogen-phosphorus-doped carbon material-supported mixed-valence iron-based photocatalytic material:

[0132] Weigh 3g of soybean flour and 3g of humus, add 30g of water, sonicate for 5min, let stand for 40min, add 15mL of ferrous oxalate (2.0mol / L), stir and mix evenly, magnetically stir at 40℃ for 10h, adjust pH to greater than 9 with 6mol / L ammonia water to form a gel, microwave in a microwave oven (power 500W) for 5min, then vacuum dry the mixture at -50℃ for 10h, then transfer the mixture with 10mL of deionized water to a hydrothermal reactor and hydrothermally heat at 200℃ for 10h to obtain a solid-liquid mixture, filter under reduced pressure, wash with deionized water until neutral, wash 5 times with ethanol, dry the obtained solid in a vacuum oven at 80℃, transfer to a tube furnace, heat to 750℃ at a rate of 5℃ / min in an argon atmosphere, calcine for 2h, cool to obtain a black powder, take it out, grind and sieve (100 mesh), thus preparing catalyst 11.

[0133] 2. Application of catalyst 11 in photocatalytic carbon dioxide reduction reaction.

[0134] Weigh 0.02g of catalyst 11, add sodium bicarbonate (0.84g), evacuate the vacuum, and then add 3.5mL of 2M sulfuric acid to produce CO2 and water in situ.

[0135] Then, the reaction was carried out under light (simulated sunlight by a 300W xenon lamp) for 3 hours.

[0136] After the experiment, 0.5 mL of gas was extracted from the tube, and the peak area was detected using a gas chromatograph (GC-14C). The yields of CH4 and CO were calculated, and the calculated yields of CH4 and CO were 3.0 μmol g. -1 h -1 and 2.4 μmol g -1 h -1 .

[0137] Table 4. Effect of pyrolysis conditions

[0138]

[0139]

[0140] Example 6

[0141] 1. A method for preparing a nitrogen-phosphorus-doped carbon material-supported mixed-valence iron-based photocatalytic material:

[0142] Weigh 5g of distiller's grains and 1g of brown sugar, add 20g of water, sonicate for 5min, let stand for 40min, add 15mL of ferric nitrate (1.5mol / L), stir and mix evenly, magnetically stir at 30℃ for 13h, adjust the pH to greater than 9 with 4mol / L ammonia water to form a gel, vacuum dry at -50℃ for 10h, microwave in a microwave oven (power 500W) for 5min, then transfer the mixture with 10mL of deionized water to a hydrothermal reactor and hydrothermally heat at 180℃ for 12h to obtain a solid-liquid mixture, filter under reduced pressure, wash with deionized water until neutral, wash 5 times with ethanol, dry the obtained solid in a vacuum oven at 80℃, transfer to a tube furnace, heat to 750℃ at a rate of 3℃ / min in an argon atmosphere, calcine for 2h, cool to obtain a black powder, take it out, grind and sieve (100 mesh), thus preparing catalyst 12.

[0143] 2. Application of catalyst 12 in photocatalytic carbon dioxide reduction reaction.

[0144] Weigh 0.02g of catalyst 12, add sodium bicarbonate (0.84g), evacuate the vacuum, and then add 3.5mL of 2M sulfuric acid to produce CO2 and water in situ.

[0145] Then, the reaction was carried out under light (simulated sunlight by a 300W xenon lamp) for 3 hours.

[0146] After the experiment, 0.5 mL of gas was extracted from the tube, and the peak area was detected using a gas chromatograph (GC-14C). The yields of CH4 and CO were calculated, and the calculated yields of CH4 and CO were 2.1 μmol g. -1 h -1 and 3.0 μmol g -1 h -1 .

[0147] Example 7

[0148] 1. A method for preparing a nitrogen-phosphorus-doped carbon material-supported mixed-valence iron-based photocatalytic material:

[0149] Weigh 5g of distiller's grains and 1g of brown sugar, add 20g of water, sonicate for 5min, let stand for 40min, add 15mL of ferric nitrate (1.5mol / L), stir and mix evenly, magnetically stir at 30℃ for 13h, adjust pH to greater than 9 with 2mol / L ammonia water to form a gel, vacuum dry at -50℃ for 10h, microwave in a microwave oven (power 500W) for 5min, then transfer the mixture with 10mL of deionized water to a hydrothermal reactor and hydrothermally heat at 180℃ for 12h to obtain a black solid-liquid mixture, filter under reduced pressure, wash with deionized water until neutral, wash 5 times with ethanol, dry the obtained solid in a vacuum oven at 80℃, transfer to a tube furnace, heat to 750℃ at a rate of 3℃ / min in an argon atmosphere, calcine for 2h, cool to obtain a black powder, take it out, grind and sieve (100 mesh), thus preparing catalyst 13.

[0150] 2. Application of catalyst 13 in photocatalytic carbon dioxide reduction reaction.

[0151] Weigh 0.02g of catalyst 13, add sodium bicarbonate (0.84g), evacuate the vacuum, and then add 3.5mL of 2M sulfuric acid to produce CO2 and water in situ.

[0152] Then, the reaction was carried out under light (simulated sunlight by a 300W xenon lamp) for 3 hours.

[0153] After completing the experiment, 0.5 mL of gas was extracted from the tube, and the peak area was detected using a gas chromatograph (GC-14C). The yields of CH4 and CO were calculated, and the calculated yields of CH4 and CO were 0.7 μmol g. -1 h -1 and 2.4 μmol g -1 h -1 .

[0154] Example 8

[0155] 1. A method for preparing a nitrogen-phosphorus-doped carbon material-supported mixed-valence iron-based photocatalytic material:

[0156] Weigh 5g of distiller's grains and 1g of brown sugar, add 20g of water, sonicate for 5min, let stand for 40min, add 15mL of ferric nitrate (1.5mol / L), stir and mix evenly, magnetically stir at 30℃ for 13h, adjust the pH to greater than 9 with 6mol / L ammonia water to form a gel, vacuum dry at -50℃ for 10h, microwave in a microwave oven (power 500W) for 5min, then transfer the mixture with 10mL of deionized water to a hydrothermal reactor and hydrothermally heat at 180℃ for 12h to obtain a solid-liquid mixture, filter under reduced pressure, wash with deionized water until neutral, wash 5 times with ethanol, dry the obtained solid in a vacuum oven at 80℃, transfer to a tube furnace, heat to 750℃ at a rate of 3℃ / min in an argon atmosphere, calcine for 2h, cool to obtain a black powder, take it out, grind and sieve (100 mesh), thus preparing catalyst 14.

[0157] 2. Application of catalyst 14 in photocatalytic carbon dioxide reduction reaction.

[0158] Weigh 0.02g of catalyst 14, add sodium bicarbonate (0.84g), evacuate the vacuum, and then add 3.5mL of 2M sulfuric acid to produce CO2 and water in situ.

[0159] Then, the reaction was carried out under light (simulated sunlight by a 300W xenon lamp) for 3 hours.

[0160] After completing the experiment, 0.5 mL of gas was extracted from the tube, and the peak area was detected using a gas chromatograph (GC-14C). The yields of CH4 and CO were calculated, and the calculated yields of CH4 and CO were 0.6 μmol g. -1 h -1 and 2.3 μmol g -1 h -1 .

[0161] Example 9

[0162] 1. A method for preparing a nitrogen-phosphorus-doped carbon material-supported mixed-valence iron-based photocatalytic material:

[0163] Weigh 5g of distiller's grains and 1g of brown sugar, add 20g of water, sonicate for 5min, let stand for 40min, add 15mL of ferric nitrate (1.5mol / L), stir and mix evenly, magnetically stir at 30℃ for 13h, adjust the pH to greater than 9 with 2mol / L sodium hydroxide to form a gel, vacuum dry at -50℃ for 10h, microwave in a microwave oven (power 500W) for 5min, then transfer the mixture with 10mL of deionized water to a hydrothermal reactor and hydrothermally heat at 180℃ for 12h to obtain a solid-liquid mixture, filter under reduced pressure, wash with deionized water until neutral, wash 5 times with ethanol, dry the obtained solid in a vacuum oven at 80℃, transfer to a tube furnace, heat to 750℃ at a rate of 3℃ / min in an argon atmosphere, calcine for 2h, cool to obtain a black powder, take it out, grind and sieve (100 mesh), thus preparing catalyst 15.

[0164] 2. Application of Catalyst 15 in photocatalytic carbon dioxide reduction reaction.

[0165] Weigh 0.02g of catalyst 15, add sodium bicarbonate (0.84g), evacuate the vacuum, and then add 3.5mL of 2M sulfuric acid to produce CO2 and water in situ.

[0166] Then, the reaction was carried out under light (simulated sunlight by a 300W xenon lamp) for 3 hours.

[0167] After completing the experiment, 0.5 mL of gas was extracted from the tube, and the peak area was detected using a gas chromatograph (GC-14C). The yields of CH4 and CO were calculated, and the calculated yields of CH4 and CO were 0.9 μmol g. -1 h -1 and 2.3 μmol g -1 h -1 .

[0168] Example 10

[0169] 1. A method for preparing a nitrogen-phosphorus-doped carbon material-supported mixed-valence iron-based photocatalytic material:

[0170] Weigh 5g of distiller's grains and 1g of brown sugar, add 20g of water, sonicate for 5min, let stand for 40min, add 15mL of ferric nitrate (1.5mol / L), stir and mix evenly, magnetically stir at 30℃ for 13h, adjust the pH to greater than 9 with 2mol / L sodium carbonate to form a gel, vacuum dry at -50℃ for 10h, microwave in a microwave oven (power 500W) for 5min, then transfer the mixture with 10mL of deionized water to a hydrothermal reactor and hydrothermally heat at 180℃ for 12h to obtain a solid-liquid mixture, filter under reduced pressure, wash with deionized water until neutral, wash 5 times with ethanol, dry the obtained solid in a vacuum oven at 80℃, transfer to a tube furnace, heat to 750℃ at a rate of 3℃ / min in an argon atmosphere, calcine for 2h, cool to obtain a black powder, take it out, grind and sieve (100 mesh), thus preparing catalyst 16.

[0171] 2. Application of Catalyst 16 in photocatalytic carbon dioxide reduction reaction.

[0172] Weigh 0.02g of catalyst 16, add sodium bicarbonate (0.84g), evacuate the vacuum, and then add 3.5mL of 2M sulfuric acid to produce CO2 and water in situ.

[0173] Then, the reaction was carried out under light (simulated sunlight by a 300W xenon lamp) for 3 hours.

[0174] After completing the experiment, 0.5 mL of gas was extracted from the tube, and the peak area was detected using a gas chromatograph (GC-14C). The yields of CH4 and CO were calculated, and the calculated yields of CH4 and CO were 1.0 μmol g. -1 h -1 and 2.2 μmol g -1 h -1 .

[0175] Example 11

[0176] 1. A method for preparing a nitrogen-phosphorus-doped carbon material-supported mixed-valence iron-based photocatalytic material:

[0177] Weigh 5g of distiller's grains and 1g of brown sugar, add 20g of water, sonicate for 5min, let stand for 40min, add 15mL of ferric nitrate (1.5mol / L), stir and mix evenly, magnetically stir at 30℃ for 13h, adjust the pH to greater than 9 with 2mol / L sodium carbonate to form a gel, vacuum dry at -50℃ for 10h, microwave in a microwave oven (power 500W) for 5min, then transfer the mixture with 10mL of deionized water to a hydrothermal reactor and hydrothermally heat at 180℃ for 12h to obtain a solid-liquid mixture, filter under reduced pressure, wash with deionized water until neutral, wash 5 times with ethanol, dry the obtained solid in a vacuum oven at 80℃, transfer to a tube furnace, heat to 750℃ at a rate of 3℃ / min in an argon atmosphere, calcine for 2h, cool to obtain a black powder, take it out, grind and sieve (100 mesh), thus preparing catalyst 17.

[0178] 2. Application of Catalyst 17 in photocatalytic carbon dioxide reduction reaction.

[0179] Weigh 0.02g of catalyst 17, add sodium bicarbonate (0.84g), evacuate the vacuum, and then add 3.5mL of 2M sulfuric acid to produce CO2 and water in situ.

[0180] Then, the reaction was carried out under light (simulated sunlight by a 300W xenon lamp) for 3 hours.

[0181] After completing the experiment, 0.5 mL of gas was extracted from the tube, and the peak area was detected using a gas chromatograph (GC-14C). The yields of CH4 and CO were calculated, and the calculated yields of CH4 and CO were 0.6 μmol g. -1 h -1 and 2.5 μmol g -1 h -1 .

[0182] Table 5. Effects of Alkali Type and Concentration

[0183] Alkali (concentration) <![CDATA[CH4 production rate (μmolg -1 h -1 )]]> <![CDATA[CO production rate (μmolg -1 h -1 )]]> Example 6 Ammonia (4M) 2.1 3.0 Example 7 Ammonia (2M) 0.7 2.4 Example 8 Ammonia (6M) 0.6 2.3 Example 9 Sodium hydroxide (2M) 0.9 2.3 Example 10 Sodium carbonate (2M) 1.0 2.2 Example 11 Sodium bicarbonate (2M) 0.6 2.5

[0184] Example 12

[0185] 1. Cyclic experiment of catalyst 1 in photocatalytic carbon dioxide reduction reaction.

[0186] The catalyst from Example 1 was recovered, washed several times with 30 mL each of ethanol and deionized water, dried in a vacuum oven, and then the photocatalytic carbon dioxide reduction reaction from Example 1 was repeated in a cyclic experiment. After six cycles, the yields of CH4 and CO were calculated. Analysis revealed that the rates of CH4 and CO production were 3.4 μmol g, respectively. -1 h -1 and 2.8 μmol g -1 h -1(As shown in Table 2).

[0187] Example 13

[0188] 1. A method for preparing a nitrogen-phosphorus-doped carbon material-supported mixed-valence iron-based photocatalytic material:

[0189] Weigh 10g of yeast, add 20g of 5% acetone aqueous solution, sonicate for 5min, let stand for 35min, add 15mL of ferrous chloride (1.5mol / L), stir and mix evenly, magnetically stir at 40℃ for 11h, adjust pH to greater than 9 with 5mol / L ammonia water to form a green gel, vacuum dry at -50℃ for 10h, microwave in a microwave oven (power 500W) for 3min, then transfer the mixture with 10mL of deionized water to a hydrothermal reactor and hydrothermally heat at 150℃ for 10h to obtain a solid-liquid mixture, filter under reduced pressure, wash with deionized water until neutral, wash 5 times with ethanol, dry the obtained solid in a vacuum oven at 100℃, transfer to a tube furnace, heat to 850℃ at a rate of 8℃ / min in a nitrogen atmosphere, calcine for 1h, cool to obtain a black powder, take it out, grind and sieve (100 mesh), thus preparing catalyst 18.

[0190] 2. Application of Catalyst 18 in photocatalytic carbon dioxide reduction reaction.

[0191] Weigh 0.03g of catalyst 18, add sodium bicarbonate (0.84g), evacuate the vacuum, and then add 3.5mL of 2M sulfuric acid to produce CO2 and water in situ.

[0192] Then, the reaction was carried out under light (simulated sunlight by a 300W xenon lamp) for 2 hours.

[0193] After the experiment, 0.5 mL of gas was extracted from the tube, and the peak area was detected using a gas chromatograph (GC-14C). The yields of CH4 and CO were calculated, and the calculated yields of CH4 and CO were 3.0 μmol g. -1 h -1 and 2.7 μmol g -1 h -1 .

[0194] Example 14

[0195] 1. A method for preparing a nitrogen-phosphorus-doped carbon material-supported mixed-valence iron-based photocatalytic material:

[0196] Weigh 10g of soybean flour, add 20g of 5% acetone aqueous solution, sonicate for 5min, let stand for 35min, add 15mL of ferrous chloride (1.5mol / L), stir and mix evenly, magnetically stir at 40℃ for 11h, adjust pH to greater than 9 with 5mol / L ammonia water to form a green gel, vacuum dry at -50℃ for 10h, microwave in a microwave oven (power 500W) for 3min, then transfer the mixture with 10mL of deionized water to a hydrothermal reactor and hydrothermally heat at 150℃ for 10h to obtain a solid-liquid mixture, filter under reduced pressure, wash with deionized water until neutral, wash 5 times with ethanol, dry the obtained solid in a vacuum oven at 100℃, transfer to a tube furnace, heat to 850℃ at a rate of 8℃ / min in a nitrogen atmosphere, calcine for 1h, cool to obtain a black powder, take it out, grind and sieve (100 mesh), the prepared catalyst 19.

[0197] 2. Application of Catalyst 19 in photocatalytic carbon dioxide reduction reaction.

[0198] Weigh 0.03g of catalyst 19, add sodium bicarbonate (0.84g), evacuate the vacuum, and then add 3.5mL of 2M sulfuric acid to produce CO2 and water in situ.

[0199] Then, the reaction was carried out under light (simulated sunlight by a 300W xenon lamp) for 2 hours.

[0200] After completing the experiment, 0.5 mL of gas was extracted from the tube, and the peak area was detected using a gas chromatograph (GC-14C). The yields of CH4 and CO were calculated, and the calculated yields of CH4 and CO were 1.0 μmol g. -1 h -1 and 1.4 μmol g -1 h -1 .

[0201] Example 15

[0202] 1. A method for preparing a nitrogen-phosphorus-doped carbon material-supported mixed-valence iron-based photocatalytic material:

[0203] Weigh 10g of humic material, add 20g of 5% acetone aqueous solution, sonicate for 5min, let stand for 35min, add 15mL of ferrous chloride (1.5mol / L), stir and mix evenly, magnetically stir at 40℃ for 11h, adjust pH to greater than 9 with 5mol / L ammonia water to form a green gel, vacuum dry at -50℃ for 10h, microwave in a microwave oven (power 500W) for 3min, then transfer the mixture with 10mL of deionized water to a hydrothermal reactor and hydrothermally heat at 150℃ for 10h to obtain a solid-liquid mixture, filter under reduced pressure, wash with deionized water until neutral, wash 5 times with ethanol, dry the obtained solid in a vacuum oven at 100℃, transfer to a tube furnace, heat to 850℃ at a rate of 8℃ / min in a nitrogen atmosphere, calcine for 1h, cool to obtain a black powder, take it out, grind and sieve (100 mesh), thus preparing catalyst 20.

[0204] 2. Application of Catalyst 20 in photocatalytic carbon dioxide reduction reaction.

[0205] Weigh 0.03g of catalyst 20, add sodium bicarbonate (0.84g), evacuate the vacuum, and then add 3.5mL of 2M sulfuric acid to produce CO2 and water in situ.

[0206] Then, the reaction was carried out under light (simulated sunlight by a 300W xenon lamp) for 2 hours.

[0207] After completing the experiment, 0.5 mL of gas was extracted from the tube, and the peak area was detected using a gas chromatograph (GC-14C). The yields of CH4 and CO were calculated, and the calculated yields of CH4 and CO were 1.5 μmol g. -1 h -1 and 2.0 μmol g -1 h -1 .

[0208] Example 16

[0209] 1. A method for preparing a nitrogen-phosphorus-doped carbon material-supported mixed-valence iron-based photocatalytic material:

[0210] Weigh 10 g of distiller's grains, add 20 g of 5% acetone aqueous solution, ultrasonicate for 5 min, let stand for 35 min, add 15 mL of ferrous chloride (1.5 mol / L), stir to mix evenly, stir magnetically at 40 °C for 11 h, adjust the pH to greater than 9 with 5 mol / L ammonia water to form a green gel, vacuum dry it at -50 °C for 10 h, place it in a microwave oven (power 500 W) and microwave for 3 min, then transfer the mixture added with 10 mL of deionized water to a hydrothermal reaction kettle and hydrothermal react at 150 °C for 10 h to obtain a solid-liquid mixture. After vacuum filtration, wash it with deionized water until neutral and wash it with ethanol 5 times. The obtained solid is dried in a vacuum oven at 100 °C, transferred to a tube furnace, and then heated to 850 °C at a rate of 8 °C / min in a nitrogen atmosphere and calcined for 1 h. After cooling, a black powder is obtained, taken out and ground and sieved (100 mesh), and the prepared catalyst 21 is obtained.

[0211] 2. Application of catalyst 21 in photocatalytic carbon dioxide reduction reaction.

[0212] Weigh 0.03 g of catalyst 21, add sodium bicarbonate (0.84 g), evacuate, and then add 3.5 mL of 2 M sulfuric acid to in-situ generate CO2 and water.

[0213] Then react under illumination (simulated sunlight by a 300 W xenon lamp) for 2 h.

[0214] After completing the experiment, extract 0.5 mL of the gas in the tube, detect the peak area with a gas chromatograph (GC-14C), calculate the CH4 or CO yield, and through analysis and calculation, the rates of producing CH4 and CO are 3.0 μmol g -1 h -1 and 2.9 μmol g -1 h -1 .

[0215] Example 17

[0216] 1. Preparation method of a nitrogen and phosphorus doped carbon material supported mixed-valence iron-based photocatalytic material:

[0217] Weigh 10g of glucose, add 20g of 5% acetone aqueous solution, sonicate for 5min, let stand for 35min, add 15mL of ferrous chloride (1.5mol / L), stir and mix evenly, magnetically stir at 40℃ for 11h, adjust pH to greater than 9 with 5mol / L ammonia water to form a green gel, vacuum dry at -50℃ for 10h, microwave in a microwave oven (power 500W) for 3min, then transfer the mixture with 10mL of deionized water to a hydrothermal reactor and hydrothermally heat at 150℃ for 10h to obtain a solid-liquid mixture, filter under reduced pressure, wash with deionized water until neutral, wash 5 times with ethanol, dry the obtained solid in a vacuum oven at 100℃, transfer to a tube furnace, heat to 850℃ at a rate of 8℃ / min in a nitrogen atmosphere, calcine for 1h, cool to obtain a black powder, take it out, grind and sieve (100 mesh), thus preparing catalyst 22.

[0218] 2. Application of catalyst 22 in photocatalytic carbon dioxide reduction reaction.

[0219] Weigh 0.03g of catalyst 22, add sodium bicarbonate (0.84g), evacuate the vacuum, and then add 3.5mL of 2M sulfuric acid to produce CO2 and water in situ.

[0220] Then, the reaction was carried out under light (simulated sunlight by a 300W xenon lamp) for 2 hours.

[0221] After completing the experiment, 0.5 mL of gas was extracted from the tube, and the peak area was detected using a gas chromatograph (GC-14C). The yields of CH4 and CO were calculated, and the calculated yields of CH4 and CO were 2.5 μmol g. -1 h -1 and 2.1 μmol g -1 h -1 .

[0222] Table 6. Effects of different biomass

[0223] biomass <![CDATA[CH4 production rate (μmolg -1 h -1 )]]> <![CDATA[CO production rate (μmolg -1 h -1 )]]> Example 13 yeast 3.0 2.7 Example 14 Soy flour 1.0 1.4 Example 15 humus 1.5 2.0 Example 16 Distillers' grains 3.0 2.9 Example 17 glucose 0.5 1.0 Comparative Example 3 none 0.1 0.2

[0224] Example 18

[0225] 1. A method for preparing a nitrogen-phosphorus-doped carbon material-supported mixed-valence iron-based photocatalytic material:

[0226] Weigh 10g of distiller's grains, add 20g of 5% glutaraldehyde aqueous solution, sonicate for 5min, let stand for 35min, add 15mL of ferrous chloride (0.5mol / L), stir and mix evenly, magnetically stir at 40℃ for 11h, adjust pH to greater than 9 with 5mol / L ammonia water to form a green gel, vacuum dry at -50℃ for 10h, microwave in a microwave oven (power 500W) for 3min, then transfer the mixture with 10mL of deionized water to a hydrothermal reactor and hydrothermally heat at 200℃ for 10h to obtain a solid-liquid mixture, filter under reduced pressure, wash with deionized water until neutral, wash 5 times with ethanol, dry the obtained solid in a vacuum oven at 100℃, transfer to a tube furnace, heat to 750℃ at a rate of 3℃ / min in a nitrogen atmosphere, calcine for 2h, cool to obtain a black powder, take it out, grind and sieve (100 mesh), the prepared catalyst 23.

[0227] 2. Application of catalyst 23 in photocatalytic carbon dioxide reduction reaction.

[0228] Weigh 0.03g of catalyst 23, add sodium bicarbonate (0.84g), evacuate the vacuum, and then add 3.5mL of 2M sulfuric acid to produce CO2 and water in situ.

[0229] Then, the reaction was carried out under light (simulated sunlight by a 300W xenon lamp) for 2 hours.

[0230] After completing the experiment, 0.5 mL of gas was extracted from the tube, and the peak area was detected using a gas chromatograph (GC-14C). The yields of CH4 and CO were calculated, and the calculated yields of CH4 and CO were 0.6 μmol g. -1 h -1 and 0.8 μmol g -1 h -1 .

[0231] Example 19

[0232] 1. A method for preparing a nitrogen-phosphorus-doped carbon material-supported mixed-valence iron-based photocatalytic material:

[0233] Weigh 10g of distiller's grains, add 20g of 5% glutaraldehyde aqueous solution, sonicate for 5min, let stand for 35min, add 15mL of ferrous chloride (1.5mol / L), stir and mix evenly, magnetically stir at 40℃ for 11h, adjust pH to greater than 9 with 5mol / L ammonia water to form a green gel, vacuum dry at -50℃ for 10h, microwave in a microwave oven (power 500W) for 3min, then transfer the mixture with 10mL of deionized water to a hydrothermal reactor and hydrothermally heat at 200℃ for 10h to obtain a solid-liquid mixture, filter under reduced pressure, wash with deionized water until neutral, wash 5 times with ethanol, dry the obtained solid in a vacuum oven at 100℃, transfer to a tube furnace, heat to 750℃ at a rate of 3℃ / min in a nitrogen atmosphere, calcine for 2h, cool to obtain a black powder, take it out, grind and sieve (100 mesh), the prepared catalyst 24.

[0234] 2. Application of catalyst 24 in photocatalytic carbon dioxide reduction reaction.

[0235] Weigh 0.03g of catalyst 24, add sodium bicarbonate (0.84g), evacuate the vacuum, and then add 3.5mL of 2M sulfuric acid to produce CO2 and water in situ.

[0236] Then, the reaction was carried out under light (simulated sunlight by a 300W xenon lamp) for 2 hours.

[0237] After completing the experiment, 0.5 mL of gas was extracted from the tube, and the peak area was detected using a gas chromatograph (GC-14C). The yields of CH4 and CO were calculated, and the calculated yields of CH4 and CO were 2.9 μmol g. -1 h -1 and 3.0 μmol g -1 h -1 .

[0238] Example 20

[0239] 1. A method for preparing a nitrogen-phosphorus-doped carbon material-supported mixed-valence iron-based photocatalytic material:

[0240] Weigh 10g of distiller's grains, add 20g of 5% glutaraldehyde aqueous solution, sonicate for 5min, let stand for 35min, add 15mL of ferrous chloride (2.5mol / L), stir and mix evenly, magnetically stir at 40℃ for 11h, adjust pH to greater than 9 with 5mol / L ammonia water to form a green gel, vacuum dry at -50℃ for 10h, microwave in a microwave oven (power 500W) for 3min, then transfer the mixture with 10mL of deionized water to a hydrothermal reactor and hydrothermally heat at 200℃ for 10h to obtain a black solid-liquid mixture, filter under reduced pressure, wash with deionized water until neutral, wash 5 times with ethanol, dry the obtained solid in a vacuum oven at 100℃, transfer to a tube furnace, heat to 750℃ at a rate of 3℃ / min in a nitrogen atmosphere, calcine for 2h, cool to obtain a black powder, take it out, grind and sieve (100 mesh), the prepared catalyst 25.

[0241] 2. Application of catalyst 25 in photocatalytic carbon dioxide reduction reaction.

[0242] Weigh 0.03g of catalyst 25, add sodium bicarbonate (0.84g), evacuate the vacuum, and then add 3.5mL of 2M sulfuric acid to produce CO2 and water in situ.

[0243] Then, the reaction was carried out under light (simulated sunlight by a 300W xenon lamp) for 2 hours.

[0244] After completing the experiment, 0.5 mL of gas was extracted from the tube, and the peak area was detected using a gas chromatograph (GC-14C). The yields of CH4 and CO were calculated, and the calculated yields of CH4 and CO were 0.5 μmol g. -1 h -1 and 2.3 μmol g -1 h -1 .

[0245] Example 21

[0246] 1. A method for preparing a nitrogen-phosphorus-doped carbon material-supported mixed-valence iron-based photocatalytic material:

[0247] Weigh 10g of distiller's grains, add 20g of 5% glutaraldehyde aqueous solution, sonicate for 5min, let stand for 35min, add 15mL of ferrous sulfate (1.5mol / L), stir and mix evenly, magnetically stir at 40℃ for 11h, adjust pH to greater than 9 with 2mol / L sodium hydroxide to form a gel, vacuum dry at -50℃ for 10h, microwave in a microwave oven (power 500W) for 3min, then transfer the mixture with 10mL of deionized water to a hydrothermal reactor and hydrothermally heat at 200℃ for 10h to obtain a solid-liquid mixture, filter under reduced pressure, wash with deionized water until neutral, wash 5 times with ethanol, dry the obtained solid in a vacuum oven at 100℃, transfer to a tube furnace, heat to 750℃ at a rate of 5℃ / min in a nitrogen atmosphere, calcine for 2h, cool to obtain a black powder, take it out, grind and sieve (100 mesh), the prepared catalyst 26.

[0248] 2. Application of catalyst 26 in photocatalytic carbon dioxide reduction reaction.

[0249] Weigh 0.03g of catalyst 26, add sodium bicarbonate (0.84g), evacuate the vacuum, and then add 3.5mL of 2M sulfuric acid to produce CO2 and water in situ.

[0250] Then, the reaction was carried out under light (simulated sunlight by a 300W xenon lamp) for 2 hours.

[0251] After completing the experiment, 0.5 mL of gas was extracted from the tube, and the peak area was detected using a gas chromatograph (GC-14C). The yields of CH4 and CO were calculated, and the calculated yields of CH4 and CO were 2.8 μmol g. -1 h -1 and 3.0 μmol g -1 h -1 .

[0252] Example 22

[0253] 1. A method for preparing a nitrogen-phosphorus-doped carbon material-supported mixed-valence iron-based photocatalytic material:

[0254] Weigh 10g of distiller's grains, add 20g of 5% glutaraldehyde aqueous solution, sonicate for 5min, let stand for 35min, add 15mL of ferric chloride (1.5mol / L), stir and mix evenly, magnetically stir at 40℃ for 11h, adjust pH to greater than 9 with 2mol / L sodium hydroxide to form a gel, vacuum dry at -50℃ for 10h, microwave in a microwave oven (power 500W) for 3min, then transfer the mixture with 10mL of deionized water to a hydrothermal reactor and hydrothermally heat at 200℃ for 10h to obtain a solid-liquid mixture, filter under reduced pressure, wash with deionized water until neutral, wash 5 times with ethanol, dry the obtained solid in a vacuum oven at 100℃, transfer to a tube furnace, heat to 750℃ at a rate of 5℃ / min in a nitrogen atmosphere, calcine for 2h, cool to obtain a black powder, take it out, grind and sieve (100 mesh), the prepared catalyst 27.

[0255] 2. Application of catalyst 27 in photocatalytic carbon dioxide reduction reaction.

[0256] Weigh 0.03g of catalyst 27, add sodium bicarbonate (0.84g), evacuate the vacuum, and then add 3.5mL of 2M sulfuric acid to produce CO2 and water in situ.

[0257] Then, the reaction was carried out under light (simulated sunlight by a 300W xenon lamp) for 2 hours.

[0258] After completing the experiment, 0.5 mL of gas was extracted from the tube, and the peak area was detected using a gas chromatograph (GC-14C). The yields of CH4 and CO were calculated, and the calculated yields of CH4 and CO were 2.8 μmol g. -1 h -1 and 3.0 μmol g -1 h -1 .

[0259] Example 23

[0260] 1. A method for preparing a nitrogen-phosphorus-doped carbon material-supported mixed-valence iron-based photocatalytic material:

[0261] Weigh 10g of distiller's grains, add 20g of 5% glutaraldehyde aqueous solution, sonicate for 5min, let stand for 35min, add 15mL of ferric sulfate (1.5mol / L), stir and mix evenly, magnetically stir at 40℃ for 11h, adjust pH to greater than 9 with 2mol / L sodium hydroxide to form a gel, vacuum dry at -50℃ for 10h, microwave in a microwave oven (power 500W) for 3min, then transfer the mixture with 10mL of deionized water to a hydrothermal reactor and hydrothermally heat at 200℃ for 10h to obtain a solid-liquid mixture, filter under reduced pressure, wash with deionized water until neutral, wash 5 times with ethanol, dry the obtained solid in a vacuum oven at 100℃, transfer to a tube furnace, heat to 750℃ at a rate of 5℃ / min in a nitrogen atmosphere, calcine for 2h, cool to obtain a black powder, take it out, grind and sieve (100 mesh), the prepared catalyst 28.

[0262] 2. Application of catalyst 28 in photocatalytic carbon dioxide reduction reaction.

[0263] Weigh 0.03g of catalyst 28, add sodium bicarbonate (0.84g), evacuate the vacuum, and then add 3.5mL of 2M sulfuric acid to produce CO2 and water in situ.

[0264] Then, the reaction was carried out under light (simulated sunlight by a 300W xenon lamp) for 2 hours.

[0265] After the experiment, 0.5 mL of gas was extracted from the tube, and the peak area was detected using a gas chromatograph (GC-14C). The yields of CH4 and CO were calculated, and the calculated yields of CH4 and CO were 1.2 μmol g. -1 h -1 and 1.1 μmol g -1 h -1 .

[0266] Example 24

[0267] 1. A method for preparing a nitrogen-phosphorus-doped carbon material-supported mixed-valence iron-based photocatalytic material:

[0268] Weigh 10g of distiller's grains, add 20g of 5% glutaraldehyde aqueous solution, sonicate for 5min, let stand for 35min, add 15mL of ferrous oxalate (1.5mol / L), stir and mix evenly, magnetically stir at 40℃ for 11h, adjust pH to greater than 9 with 2mol / L sodium hydroxide to form a gel, vacuum dry at -50℃ for 10h, microwave in a microwave oven (power 500W) for 3min, then transfer the mixture with 10mL of deionized water to a hydrothermal reactor and hydrothermally heat at 200℃ for 10h to obtain a solid-liquid mixture, filter under reduced pressure, wash with deionized water until neutral, wash 5 times with ethanol, dry the obtained solid in a vacuum oven at 100℃, transfer to a tube furnace, heat to 750℃ at a rate of 5℃ / min in a nitrogen atmosphere, calcine for 2h, cool to obtain a black powder, take it out, grind and sieve (100 mesh), the prepared catalyst 29.

[0269] 2. Application of catalyst 29 in photocatalytic carbon dioxide reduction reaction.

[0270] Weigh 0.03g of catalyst 29, add sodium bicarbonate (0.84g), evacuate the vacuum, and then add 3.5mL of 2M sulfuric acid to produce CO2 and water in situ.

[0271] Then, the reaction was carried out under light (simulated sunlight by a 300W xenon lamp) for 2 hours.

[0272] After completing the experiment, 0.5 mL of gas was extracted from the tube, and the peak area was detected using a gas chromatograph (GC-14C). The yields of CH4 and CO were calculated, and the calculated yields of CH4 and CO were 2.2 μmol g. -1 h -1 and 1.8 μmol g -1 h -1 .

[0273] Example 25

[0274] 1. A method for preparing a nitrogen-phosphorus-doped carbon material-supported mixed-valence iron-based photocatalytic material:

[0275] Weigh 10g of distiller's grains, add 20g of 5% glutaraldehyde aqueous solution, sonicate for 5min, let stand for 35min, add 15mL of ferric nitrate (1.5mol / L), stir and mix evenly, magnetically stir at 40℃ for 11h, adjust pH to greater than 9 with 2mol / L sodium hydroxide to form a gel, vacuum dry at -50℃ for 10h, microwave in a microwave oven (power 500W) for 3min, then transfer the mixture with 10mL of deionized water to a hydrothermal reactor and hydrothermally heat at 200℃ for 10h to obtain a solid-liquid mixture, filter under reduced pressure, wash with deionized water until neutral, wash 5 times with ethanol, dry the obtained solid in a vacuum oven at 100℃, transfer to a tube furnace, heat to 750℃ at a rate of 5℃ / min in a nitrogen atmosphere, calcine for 2h, cool to obtain a black powder, take it out, grind and sieve (100 mesh), the prepared catalyst 30.

[0276] 2. Application of catalyst 30 in photocatalytic carbon dioxide reduction reaction.

[0277] Weigh 0.03g of catalyst 30, add sodium bicarbonate (0.84g), evacuate the vacuum, and then add 3.5mL of 2M sulfuric acid to produce CO2 and water in situ.

[0278] Then, the reaction was carried out under light (simulated sunlight by a 300W xenon lamp) for 2 hours.

[0279] After completing the experiment, 0.5 mL of gas was extracted from the tube, and the peak area was detected using a gas chromatograph (GC-14C). The yields of CH4 and CO were calculated, and the calculated yields of CH4 and CO were 1.1 μmol g. -1 h -1 and 1.0 μmol g -1 h -1 .

[0280] Table 7. Effects of different iron salts and concentrations

[0281]

[0282]

[0283] Comparative Example 8

[0284] 1. A method for preparing a nitrogen-phosphorus-doped carbon material-supported mixed-valence iron-based photocatalytic material:

[0285] Weigh 5g of biomass, add 20g of solvent, sonicate for 5min, let stand for 35min, add 15mL of ferrous chloride (1.5mol / L), stir and mix evenly, magnetically stir at 40℃ for 11h, adjust pH to greater than 9 with 5mol / L KOH to form a green gel, microwave it in a microwave oven (500W) for 3min, then transfer the mixture with 10mL of deionized water to a hydrothermal reactor and hydrothermally heat at 200℃ for 10h to obtain a solid-liquid mixture, filter under reduced pressure, wash with deionized water until neutral, wash 5 times with ethanol, dry the obtained solid in a vacuum oven at 100℃, transfer it to a tube furnace, heat it to 850℃ at a rate of 10℃ / min in a nitrogen atmosphere, calcine for 1.5h, cool to obtain a black powder, take it out, grind and sieve (100 mesh), and the prepared catalyst 31.

[0286] 2. Application of catalyst 31 in photocatalytic carbon dioxide reduction reaction.

[0287] Weigh 0.02g of catalyst 31, add sodium bicarbonate (0.84g), evacuate the vacuum, and then add 3.5mL of 2M sulfuric acid to produce CO2 and water in situ.

[0288] Then, the reaction was carried out under light (simulated sunlight by a 300W xenon lamp) for 2 hours.

[0289] After completing the experiment, 0.5 mL of gas was extracted from the tube, and the peak area was detected using a gas chromatograph (GC-14C). The yields of CH4 and CO were calculated, and the calculated yields of CH4 and CO were 2.7 μmol g. -1 h -1 and 2.1 μmol g -1 h -1 .

Claims

1. A method for preparing an iron-based photocatalyst supported on a biomass-derived in-situ nitrogen-phosphorus-doped carbon material, characterized in that: The preparation method includes the following steps: Weigh out biomass, crush and grind it to below 200 mesh, add solvent, and after the biomass is fully dispersed and activated, add an iron-containing aqueous solution. The solute in the iron-containing aqueous solution is ferric salt and / or ferrous salt with a total concentration of 0.5~3 mol / L. After stirring and mixing evenly, stir magnetically at 20~50℃ for 8~15 h, then adjust the pH to >9 with an alkaline reagent to form a gel. Freeze-dry the gel, then microwave it at 400~800 W for 3~5 min, and then hydrothermally react it at 160~200℃ for 8~15 h. Filter and wash to obtain the precursor. After drying the precursor, it is heated to 700-950 °C in an inert gas atmosphere at a heating rate of 3-15 °C and calcined for 0.5-2.5 h. After cooling, a biomass-derived in-situ nitrogen-phosphorus-doped carbon material supported iron-based photocatalyst is obtained. The biomass-derived in-situ nitrogen-phosphorus-doped carbon material supported iron-based photocatalyst contains zero-valent, divalent, and trivalent iron. The biomass is one of the following: ① distiller's grains, ② a mixture of soybean flour and humus in a mass ratio of 1:1, ③ a mixture of distiller's grains and brown sugar in a mass ratio of 5:1; The solvent is selected from any one of water, ethanol, 1-5 vol% glutaraldehyde aqueous solution, 1-5 vol% formaldehyde aqueous solution, and 1-5 vol% acetone aqueous solution; The alkaline reagent is any one or more of the following: 1-6 M ammonia water, 1-6 M sodium hydroxide aqueous solution, 1-6 M potassium hydroxide aqueous solution, 1-6 M sodium carbonate aqueous solution, and 1-6 M sodium bicarbonate aqueous solution. The feeding ratio of the biomass, solvent and iron-containing aqueous solution is (2~10)g:(2~25)g:(10~40)mL.

2. The preparation method according to claim 1, characterized in that: The ferric salt is any one or more of ferric chloride, ferric sulfate, and ferric nitrate, and the ferrous salt is any one or more of ferrous chloride, ferrous sulfate, ferrous acetate, and ferrous oxalate.

3. The preparation method according to claim 2, characterized in that: The solute in the iron-containing aqueous solution is a ferrous salt.

4. The preparation method according to claim 1, characterized in that: The temperature was increased to 750-850 °C at a rate of 3-10 °C / min in a nitrogen atmosphere, and calcined for 1-2 h.

5. The preparation method according to claim 4, characterized in that: The temperature was increased to 750-850 °C at a rate of 5-10 °C / min in a nitrogen atmosphere, and calcined for 1-2 h.

6. The preparation method according to claim 1, characterized in that: The biomass is distiller's grains, the solvent is a 3 vol% formaldehyde aqueous solution, a 5 vol% glutaraldehyde aqueous solution, or a 5 vol% acetone aqueous solution, the iron-containing aqueous solution is a 1.5 M ferrous chloride aqueous solution, and the alkaline reagent is a 5 M KOH aqueous solution or a 5 M ammonia solution. During the preparation process, the temperature is raised to 750-850 ℃ at a rate of 3-10 ℃ / min in a nitrogen atmosphere and calcined for 1-2 h. The feed ratio of the biomass, solvent, and iron-containing aqueous solution is 5-10 g: 20 g: 15 mL.

7. The preparation method according to claim 6, characterized in that: The biomass is distiller's grains, the solvent is a 3 vol% formaldehyde aqueous solution, the iron-containing aqueous solution is a 1.5 M ferrous chloride aqueous solution, and the alkaline reagent is a 5 M KOH aqueous solution or a 5 M ammonia solution. During the preparation process, the temperature is raised to 850 °C at a rate of 8-10 °C / min in a nitrogen atmosphere and calcined for 1-1.5 h. The feed ratio of the biomass, solvent, and iron-containing aqueous solution is 5-10 g: 20 g: 15 mL.

8. The preparation method according to claim 1, characterized in that: The biomass is a mixture of soybean flour and humus in a mass ratio of 1:

1. The solvent is water. The iron-containing aqueous solution is a 2.0M ferrous oxalate aqueous solution. The alkaline reagent is 6M ammonia water. During the preparation process, the temperature is raised to 750℃ at a rate of 5℃ / min in a nitrogen atmosphere and calcined for 2 h. The feed ratio of biomass, solvent and iron-containing aqueous solution is 6g:30g:15mL.

9. A biomass-derived in-situ nitrogen-phosphorus-doped carbon material supported iron-based photocatalyst prepared by any one of the preparation methods described in claims 1-8.

10. The application of the biomass-derived in-situ nitrogen-phosphorus-doped carbon material supported iron-based photocatalyst in photocatalytic reduction of CO2 as described in claim 9.

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