Preparation method and application of Fe3O4 / g-C3N4 self-circulation photo-Fenton catalyst with p-n structure

Abstract

The application relates to the technical field of photo-Fenton catalysts, in particular to a preparation method and application of a self-circulation photo-Fenton catalyst with a p-n structure Fe3O4 / g-C3N4. The catalyst comprises a p-type semiconductor structure Fe3O4 and an n-type semiconductor structure g-C3N4 matrix; the n-type semiconductor structure g-C3N4 matrix is prepared by adopting triazine organic matter as raw material through a thermal polymerization method; and the p-type semiconductor structure Fe3O4 is formed on the surface of the g-C3N4 by combining photo irradiation treatment with pyrolysis treatment. The self-circulation photo-Fenton catalyst with the p-n structure Fe3O4 / g-C3N4 has a larger specific surface area and a wider sunlight utilization wavelength range, higher photo-generated electron density and stable hydrogen peroxide generation capacity, and higher conversion efficiency of the self Fe 2+ / Fe 3+ .

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of photo-Fenton catalysts, in particular, and more particularly to a preparation method and application of a Fe3O4 / g-C3N4 self-circulation photo-Fenton catalyst with p-n structure. BACKGROUND

[0002] Photocatalytic technology has become one of the important technologies in the field of organic pollutant treatment due to its high efficiency and no secondary pollution. Among various advanced oxidation technologies, photo-Fenton technology has attracted much attention due to its high efficiency, controllability, and no secondary pollution. However, common photo-Fenton catalysts need to add additional oxidants and iron sources, such as hydrogen peroxide (Y. Zhao, S. Kang, L. Qin, W. Wang, T. Zhang, S. Song, S. Komarneni, Self-assembled gels of Fe-chitosan / montmorillonite nanosheets: Dye degradation by the synergistic effect of adsorption and photo-Fenton reaction, Chemical Engineering Journal, 379 (2020) 122322.) and ferrous chloride (J. Sun, T. Xue, L. Cui, J. Liu. Bibonding Constructing Coordinatively Unsaturated Zn i+ (0<i<2) Sites for Enhanced Photo-Fenton Activity. Advanced Sustainable Systems, 7 (2023), 2300116.), which has the disadvantages of high cost, easy formation of iron sludge, and low efficiency in alkaline environment, which seriously limits the practical application of photo-Fenton technology. Therefore, there is an urgent need to develop a self-circulation photo-Fenton catalyst with wide practicality and stability to meet the needs of actual large-scale production and application. SUMMARY

[0003] In view of the deficiencies of the above-mentioned photo-Fenton catalyst, the present application aims to provide a preparation method of a Fe3O4 / g-C3N4 self-circulation photo-Fenton catalyst with p-n structure, which can be directly applied to the degradation of organic pollutants by Fenton reaction without adding additives (oxidants, iron sources), solving the problems of the need to add additional oxidants and iron sources, harsh pH conditions and easy formation of iron sludge of the existing photo-Fenton catalyst. The preparation method of the present application is simple in process and environmentally friendly, and the obtained Fe3O4 / g-C3N4 self-circulation photo-Fenton catalyst with p-n structure exhibits excellent catalytic degradation activity.

[0004] In order to achieve the above-mentioned purpose, the technical scheme of the present application is as follows:

[0005] The present application provides a preparation method of a Fe3O4 / g-C3N4 self-circulation photo-Fenton catalyst with p-n structure, which comprises a p-type semiconductor structure Fe3O4 and an n-type semiconductor structure g-C3N4 matrix; the n-type semiconductor structure g-C3N4 matrix is prepared by thermal polymerization method using triazine organic matter as raw material; and the p-type semiconductor structure Fe3O4 is formed on the surface of g-C3N4 by photo irradiation treatment combined with pyrolysis treatment in an inert atmosphere.

[0006] As a preferred, the method comprises the following steps:

[0007] Step 1: mixing triazine organic matter with ammonia water and then placing in a reaction furnace for heat treatment to obtain g-C3N4 powder;

[0008] Step 2: dispersing the g-C3N4 powder obtained in step 1 in a metal Fe salt solution to obtain a suspension A, stirring the suspension A under light irradiation conditions, centrifuging and ultrasonic washing to obtain a solid, and then drying to obtain a g-C3N4 powder loaded with metal Fe ions;

[0009] Step 3: grinding the g-C3N4 powder loaded with metal Fe ions obtained in step 2 and dispersing in a ligand solution to obtain a suspension B, stirring, centrifuging, ultrasonic washing to obtain a solid, and then drying to obtain a g-C3N4 matrix composite material with mixed valence Fe 3+ / Fe 2+ ;

[0010] Step 4: grinding the g-C3N4 matrix composite material with mixed valence Fe 3+ / Fe 2+ obtained in step 2 and placing in a tube furnace for pyrolysis treatment in an inert atmosphere to obtain a Fe3O4 / g-C3N4 self-circulation photo-Fenton catalyst with p-n structure.

[0011] As preferred, in step 1, the triazine organic matter is one or more of urea, melamine, thiourea, thiocyanic acid; the nitrogen-containing triazine compound can generate g-C3N4 with a porous structure through simple heat treatment, and g-C3N4 can oxidize water to hydrogen peroxide under light conditions.

[0012] As preferred, in step 1, the mass ratio of the triazine organic matter to ammonia water is 10:3.

[0013] As preferred, in step 1, the heat treatment temperature is 450-550℃, the heat treatment time is 1-5h, and the heating rate is 0.5-20℃ / min; the molecular structure of the triazine organic matter contains multiple stable aromatic ring structures, and sufficient energy is required for decomposition, so higher temperature and heating rate will cause the molecular structure of the triazine organic matter to decompose rapidly, thereby destroying the framework and structure of g-C3N4 and affecting the performance of the catalyst in generating hydrogen peroxide.

[0014] As preferred, in step 2, the concentration of g-C3N4 in the suspension A is 1-20g / L.

[0015] As preferred, in step 2, the metal Fe salt includes one or more of ferric chloride, ferric nitrate, and ferric carbonate; the metal Fe ions in the metal Fe salt solution can coordinate with N in g-C3N4. 3+ 3+ The metal Fe ions in the metal Fe salt solution have high ion stability and are not easily oxidized.

[0016] As preferred, in step 2, the solvent of the metal Fe salt solution is one or more of deionized water, methanol, and ethanol, and the concentration of the metal Fe salt solution is 1mmol / L-2mol / L.

[0017] As preferred, in step 2, the stirring time is 3-24h.

[0018] As preferred, in step 2, the drying temperature is 40-70℃, and the drying time is 3-24h; if the drying time is too long or the temperature is too high, the metal Fe is easy to form other oxides, nitrides, or carbides of Fe.

[0019] As preferred, in step 2, the light wavelength of the light irradiation treatment is 200-1100nm, the power is 300W, and the distance between the light source and the upper surface of the solution is 5cm; if the light wavelength is too short or too long, the power is too low or too high, or the distance between the light source and the upper surface of the solution is too large, the utilization rate of g-C3N4 matrix to photons will be reduced, which cannot make it completely combine with the iron source, and the distance between the light source and the upper surface of the solution is too close, which is easy to produce thermal effects and affect the reaction.

[0020] ​As preferred, in step 3, the concentration of the g-C3N4 loaded with Fe ions in the suspension B is 1-20 g / L.

[0021] As preferred, in step 3, the ligand includes one of 2-methyl imidazole, N,N-dimethylformamide, carboxylate of terephthalic acid, phosphonate, imidazole acid salt and phenolic acid ester.

[0022] As preferred, in step 3, the solvent of the ligand solution is one or more of deionized water, methanol and ethanol, the solvent of the ligand solution is the same as that of the Fe salt solution, and the concentration of the ligand solution is 1 mmol / L-2 mol / L.

[0023] As preferred, in step 3, the stirring time is 3-24 h.

[0024] As preferred, in step 3, the drying temperature is 30-60℃, and the drying time is 3-24 h; if the drying time is too long or the temperature is too high, the Fe is easy to form other oxides, nitrides or carbides of Fe.

[0025] As preferred, in step 3, the centrifugal speed is 2000-12000 rpm, and the time is 2-20 min; the stirring speed is 100-1000 rpm; and the solvent for ultrasonic washing is one or more of deionized water, methanol and ethanol, and the washing is performed 1-5 times.

[0026] As preferred, in step 4, the inert atmosphere includes one or more of nitrogen, argon and helium; the pyrolysis under the protection of the inert atmosphere can effectively protect the skeleton structure of the g-C3N4, reduce the reaction process of oxygen and the Fe source, and help to form the p-n heterostructure.

[0027] As preferred, in step 4, the pyrolysis temperature is 350-550℃, and the pyrolysis time is 1-5 h.

[0028] Another aspect of the present application provides an application of the Fe3O4 / g-C3N4 self-circulation photo-Fenton catalyst with the p-n structure prepared by the above preparation method, which is used for degrading organic pollutants in wastewater, including one or more of dyes, phenolic compounds, chlorinated hydrocarbons, brominated hydrocarbons and benzene series substances.

[0029] As preferred, the application includes the following steps: adding the Fe3O4 / g-C3N4 self-circulation photo-Fenton catalyst with the p-n structure into a solution containing the organic pollutants, and after reaching the adsorption equilibrium, allowing it to react under light irradiation; the wavelength of the light is 200-1200 nm.

[0030] The present application has the following beneficial effects:

[0031] 1) Through the green and environmentally friendly light irradiation and simple and easy to operate pyrolysis method, the Fe3O4 with p-type semiconductor properties is formed on the surface of the n-type semiconductor structure g-C3N4, and the Fe3O4 / g-C3N4 self-circulation light Fenton catalyst with p-n structure is obtained.

[0032] 2) The selected raw materials such as nitrogen-containing organic matter, metal Fe salt and nitrogen-containing ligand are cheap and easy to obtain, the preparation method of the patent is simple and easy to operate, low in cost, and can realize large-scale production.

[0033] 3) The obtained Fe3O4 / g-C3N4 self-circulation light Fenton catalyst with p-n structure has a large specific surface area and a wide sunlight utilization wavelength range, compared with the g-C3N4 matrix, the obtained catalyst has a higher photoelectron density and a stable hydrogen peroxide generation capacity, and the obtained catalyst has a higher conversion efficiency of Fe 2+ / Fe 3+ .

[0034] 4) The obtained Fe3O4 / g-C3N4 self-circulation light Fenton catalyst with p-n structure is applied to treat wastewater solution containing organic pollutants, the g-C3N4 matrix can oxidize water to hydrogen peroxide under light, and Fe3O4 can provide iron source, without adding additional oxidizing agent and Fe source, realizing self-circulation Fenton efficient and rapid degradation of organic pollutants in wastewater, having great potential, and showing wide application prospect in future environmental governance, water resource purification and regeneration fields. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 XRD spectra of the samples of Example 1, Comparative Example 3, Comparative Example 5, Comparative Example 6;

[0036] Figure 2 SEM spectrum of the sample of Example 1;

[0037] Figure 3 TEM spectrum of the sample of Example 1;

[0038] Figure 4 UV-Vis absorption spectrum and Tauc spectrum of the samples of Example 1, Comparative Example 1, Comparative Example 6;

[0039] Figure 5 Fe 2p XPS spectrum of the samples of Example 1 and Comparative Example 1, (a) is Example 1, (b) is Comparative Example 1;

[0040] Figure 6 Transient photocurrent spectrum of the samples of Example 1, Example 2, Comparative Example 1 and Comparative Example 6;

[0041] Figure 7 Mott-Schottky curves of the samples of Example 1, Comparative Example 3, Comparative Example 5 and Comparative Example 6, (a) is Example 1, (b) is Comparative Example 6, (c) is Comparative Example 3, (d) is Comparative Example 5;

[0042] Figure 8 N2gas adsorption / desorption curves of the samples of Example 1 and Comparative Example 6, (a) is Example 1, (b) is Comparative Example 6;

[0043] Figure 9 The test results of the content of hydrogen peroxide in the aqueous solution after the sample of Example 1 was irradiated in the aqueous solution for 1 h. DETAILED DESCRIPTION

[0044] The present application will be described in detail below with reference to the accompanying drawings and specific examples. The following examples will help those skilled in the art to further understand the present application, but do not limit the present application in any form. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present application. These all belong to the protection scope of the present application.

[0045] The formula for calculating the efficiency of the catalyst in the photofenton degradation of methylene blue in the examples is as follows:

[0046] Degradation efficiency = (C0-C t )·100 / C0 = (A0-A t )·100 / A0

[0047] Wherein C0and C t represent the initial concentration and the concentration at time t of the methylene blue aqueous solution, respectively.

[0048] Example 1

[0049] A preparation method of a Fe3O4 / g-C3N4 self-circulation photofenton catalyst with p-n structure, comprising the following steps:

[0050] 1) Weigh 15 grams of urea and 5 milliliters of ammonia water (mass concentration of 25%-28%) and mix thoroughly, then place in a 50ml crucible, heat to 550℃ at a heating rate of 1℃ / min in air atmosphere, and keep the temperature at this temperature for 1h, then naturally cool to room temperature, grind the obtained yellow block into powder, and obtain a graphite phase carbon nitride (g-C3N4) matrix powder;

[0051] 2) Take 16.22 g of iron chloride solid and add to 100 ml of anhydrous methanol solution (AR, ≥99%), ultrasonic for 5 min, so that the iron chloride solid is fully dissolved, i.e. a dark red methanol solution of iron chloride is obtained; at room temperature, take 5 g of yellow g-C3N4 matrix powder and add to the methanol solution of iron chloride, and place on a magnetic stirrer with a rotation speed of 500 rpm for stirring for 12 h, while a xenon lamp light source with a wavelength of 200-1100 nm and a power of 300 W is placed 5 cm away from the liquid surface; after continuous irradiation for 12 h, the suspension is centrifuged at 12000 rpm by a centrifuge, and then washed with anhydrous ethanol and deionized water respectively for 4 times to obtain a solid, and finally the obtained product is placed in a vacuum drying oven, with a temperature of 50°C, and dried for 12 h to obtain a g-C3N4 material loaded with Fe ions;

[0052] 3) Take 8.00 g of 2-methylimidazole solid and add to 100 ml of anhydrous methanol solution (AR, ≥99%), ultrasonic for 25 min, so that the 2-methylimidazole solid is fully dissolved, i.e. a transparent colorless methanol solution of 2-methylimidazole is obtained; at room temperature, the g-C3N4 material loaded with Fe ions is dispersed in the 2-methylimidazole solution, and placed on a magnetic stirrer with a rotation speed of 500 rpm for stirring for 12 h, and then the suspension is centrifuged at 12000 rpm by a centrifuge, and then washed with anhydrous ethanol and deionized water respectively for 4 times to obtain a solid, and then placed in a vacuum drying oven, with a temperature of 50°C, and dried for 12 h to obtain a g-C3N4 matrix composite material with mixed valence Fe 3+ / Fe 2 + ;

[0053] 4) Take 5 g of the g-C3N4 matrix composite material with mixed valence Fe 3+ / Fe 2+ , and place in a 40 ml reaction boat, and add to a tube furnace, and heat to 550°C at a heating rate of 1°C / min under a nitrogen atmosphere, and keep at this temperature for 1 h, and then naturally cool to room temperature, and further grind the obtained dark reddish-brown powder to obtain a p-n structure Fe3O4 / g-C3N4 self-circulation photo-Fenton catalyst.

[0054] Example 2

[0055] A preparation method of a p-n structure Fe3O4 / g-C3N4 self-circulation photo-Fenton catalyst, comprising the following steps:

[0056] 1) Take 15 g of urea and 5 ml of ammonia water, mix thoroughly, and then place in a 50 ml crucible. Heat to 550°C at a rate of 1°C / min in an air atmosphere, and keep at this temperature for 1 h. Then cool naturally to room temperature. Grind the resulting yellow block into powder to obtain a g-C3N4 matrix powder;

[0057] 2) Take 8.11 g of iron chloride solid and add to 100 ml of anhydrous methanol solution (AR, ≥99%). Ultrasonic for 5 min to dissolve the iron chloride solid thoroughly, to obtain a dark red methanol solution of iron chloride. At room temperature, take 5 g of yellow g-C3N4 matrix powder and add to the methanol solution of iron chloride. Place on a magnetic stirrer with a rotation speed of 500 rpm and stir for 12 h. At the same time, place a xenon lamp light source with a wavelength of 200-1100 nm and a power of 300 W at a distance of 5 cm from the liquid surface. After 12 h of continuous irradiation, centrifuge the suspension at 12000 rpm, and then wash the solid with anhydrous ethanol and deionized water respectively for 4 times. Finally, place the resulting product in a vacuum drying oven, at a temperature of 50°C, and dry for 12 h, to obtain a g-C3N4 material loaded with Fe ions;

[0058] 3) Take 4.00 g of 2-methylimidazole solid and add to 100 ml of anhydrous methanol solution (AR, ≥99%). Ultrasonic for 25 min to dissolve the 2-methylimidazole solid thoroughly, to obtain a transparent colorless methanol solution of 2-methylimidazole. At room temperature, disperse the g-C3N4 material loaded with Fe ions in the 2-methylimidazole solution, and place on a magnetic stirrer with a rotation speed of 500 rpm and stir for 12 h. Then centrifuge the suspension at 12000 rpm, and then wash the solid with anhydrous ethanol and deionized water respectively for 4 times. Then place in a vacuum drying oven, at a temperature of 50°C, and dry for 12 h, to obtain a g-C3N4 matrix composite material with mixed valence Fe 3+ / Fe 2 + ;

[0059] 4) Take 5 g of the g-C3N4 matrix composite material with mixed valence Fe 3+ / Fe 2+ , and place in a 40 ml reaction boat. Add to a tube furnace, and heat to 550°C at a rate of 1°C / min in a nitrogen atmosphere, and keep at this temperature for 1 h. Then cool naturally to room temperature. Further grind the resulting dark red-brown powder to obtain a p-n structure Fe3O4 / g-C3N4 self-circulation photo-Fenton catalyst.

[0060] Example 3

[0061] A preparation method of a Fe3O4 / g-C3N4 self-circulation photo-Fenton catalyst with p-n structure, comprising the following steps:

[0062] 1) 15 g of urea and 5 ml of ammonia water were mixed and then placed in a 50 ml crucible, and heated to 550℃ at a heating rate of 1℃ / min in an air atmosphere, and then kept at this temperature for 1 h, and then naturally cooled to room temperature, and the obtained yellow block was ground into powder, thereby obtaining a graphite phase carbon nitride (g-C3N4) matrix powder;

[0063] 2) 16.22 g of iron chloride solid was added to 100 ml of anhydrous methanol solution (AR, ≥99%), and ultrasonicated for 5 min to fully dissolve the iron chloride solid, thereby obtaining a dark red methanol solution of iron chloride; 5 g of yellow g-C3N4 matrix powder was added to the methanol solution of iron chloride at room temperature, and stirred on a magnetic stirrer at a rotation speed of 500 rpm for 12 h, and a xenon lamp light source with a wavelength of 200-1100 nm and a power of 300 W was placed 5 cm away from the liquid surface; after continuous irradiation for 12 h, the suspension was centrifuged at 12000 rpm, and then washed with anhydrous ethanol and deionized water for 4 times respectively to obtain a solid, and finally the obtained product was placed in a vacuum drying oven at a temperature of 50℃ for drying for 12 h, thereby obtaining a g-C3N4 material loaded with Fe ions;

[0064] 3) 8.00 g of 2-methylimidazole solid was added to 100 ml of anhydrous methanol solution (AR, ≥99%), and ultrasonicated for 25 min to fully dissolve the 2-methylimidazole solid, thereby obtaining a transparent colorless methanol solution of 2-methylimidazole; the g-C3N4 material loaded with Fe ions was dispersed in the 2-methylimidazole solution at room temperature, and stirred on a magnetic stirrer at a rotation speed of 500 rpm for 12 h, and then the suspension was centrifuged at 12000 rpm, and then washed with anhydrous ethanol and deionized water for 4 times respectively to obtain a solid, and then placed in a vacuum drying oven at a temperature of 50℃ for drying for 12 h, thereby obtaining a g-C3N4 matrix composite material with mixed valence Fe 3+ / Fe 2 + ;

[0065] 4) 5 g of the g-C3N4 matrix composite material with mixed valence Fe 3+ / Fe 2+ was placed in a 40 ml reaction boat, and then added into a tube furnace, and heated to 350℃ at a heating rate of 1℃ / min in a nitrogen atmosphere, and then kept at this temperature for 1 h, and then naturally cooled to room temperature, and the obtained dark red-brown powder was further ground and refined, thereby obtaining a Fe3O4 / g-C3N4 self-circulation photo-Fenton catalyst with p-n structure.

[0066] Comparative Example 1

[0067] The difference from Example 1 is only that the g-C3N4 matrix powder is added to the mixed solution of ferric chloride under stirring in the dark condition to obtain the Fe3O4 / g-C3N4 photo-Fenton catalyst.

[0068] Comparative Example 2

[0069] The difference from Example 2 is only that the g-C3N4 matrix powder is added to the mixed solution of ferric chloride under stirring in the dark condition to obtain the Fe3O4 / g-C3N4 photo-Fenton catalyst.

[0070] Comparative Example 3

[0071] The difference from Example 1 is only that the g-C3N4 matrix composite material with mixed valence Fe 3+ / Fe 2+ is pyrolyzed under air to obtain the Fe3O4 / g-C3N4 photo-Fenton catalyst.

[0072] Comparative Example 4

[0073] The difference from Example 2 is only that the g-C3N4 matrix composite material with mixed valence Fe 3+ / Fe 2+ is pyrolyzed under air to obtain the Fe3O4 / g-C3N4 photo-Fenton catalyst.

[0074] Comparative Example 5

[0075] 1) 16.22 g of ferric chloride solid was weighed into 100 ml of anhydrous methanol solution (AR, ≥99%), and ultrasonic was applied for 5 min to make the ferric chloride solid fully dissolved, i.e. a dark red methanol solution of ferric chloride was obtained; 8.00 g of 2-methylimidazole solid was weighed into 100 ml of anhydrous methanol solution (AR, ≥99%), and ultrasonic was applied for 25 min to make the 2-methylimidazole solid fully dissolved, i.e. a transparent colorless methanol solution of 2-methylimidazole was obtained; at room temperature, the dark red methanol solution of ferric chloride and the transparent colorless methanol solution of 2-methylimidazole were placed on a magnetic stirrer with a rotation speed of 500 rpm for stirring for 12 h, then the suspension was centrifuged at 12000 rpm, and then the solid was washed with anhydrous ethanol and deionized water respectively for 4 times by ultrasonic to obtain a solid, and finally the obtained product was placed in a vacuum drying box with a temperature of 50 °C for drying for 12 h to obtain a dark red composite material;

[0076] 2) Take 5 grams of dark red composite material and place it in a 40 ml reaction boat, add it to the tube furnace, heat to 550℃ at a rate of 1℃ / min under nitrogen atmosphere, and keep it at this temperature for 1h, then naturally cool to room temperature, further grinding, to obtain black p-type Fe3O4 powder.

[0077] Comparative Example 6

[0078] Take 15g urea and 5ml ammonia water, mix thoroughly, then place in a 50ml crucible, heat to 550℃ at a rate of 1℃ / min under air atmosphere, and keep it at this temperature for 1h, then naturally cool to room temperature, grind the resulting yellow block into powder, to obtain graphite phase carbon nitride (g-C3N4) powder.

[0079] The p-n structure Fe3O4 / g-C3N4 self-circulation photo-Fenton catalyst prepared in the above examples is characterized by XRD, TEM, SEM, XPS, N2 gas adsorption / desorption, UV-visible absorption spectrum, transient photocurrent test and Mott-Schottky curve test, etc.

[0080] Figure 1 (a), (b), (c), (d) in FIG. 1 are respectively the XRD spectra of Fe3O4 / g-C3N4 photo-Fenton catalyst in Comparative Example 3, p-n structure Fe3O4 / g-C3N4 self-circulation photo-Fenton catalyst in Example 1, g-C3N4 powder in Comparative Example 6 and p-type Fe3O4 powder in Comparative Example 5. The characteristic peaks of g-C3N4 matrix in the XRD of Fe3O4 / g-C3N4 photo-Fenton catalyst in Comparative Example 3 disappear, and Fe3O4 phase is the main component, which shows that nitrogen can protect the framework structure of g-C3N4 matrix during pyrolysis; the XRD spectrum of p-n structure Fe3O4 / g-C3N4 self-circulation photo-Fenton catalyst has both the characteristic peaks of metal oxide and g-C3N4 matrix, which shows that Fe3O4 / g-C3N4 is successfully synthesized.

[0081] Figure 2 FIG. 2 is the SEM spectrum of p-n structure Fe3O4 / g-C3N4 self-circulation photo-Fenton catalyst in Example 1 of the present application. It can be seen that the p-n structure Fe3O4 / g-C3N4 self-circulation photo-Fenton catalyst presents a loose block or lamellar structure.

[0082] Figure 3 FIG. 3 is the TEM spectrum of p-n structure Fe3O4 / g-C3N4 self-circulation photo-Fenton catalyst in Example 1 of the present application. It can be seen that the g-C3N4 matrix presents a porous structure, and a large number of spherical Fe3O4 nanoparticles are distributed on the surface of the matrix.

[0083] Figure 4 (a), (b), (c) are UV-Vis absorption spectra and corresponding Tauc plots of g-C3N4 powder of Comparative Example 6, Fe3O4 / g-C3N4 self-circulation photo-Fenton catalyst with p-n structure of Example 1, and Fe3O4 / g-C3N4 photo-Fenton catalyst of Comparative Example 1, respectively. By comparison, it can be seen that the Fe3O4 / g-C3N4 self-circulation photo-Fenton catalyst with p-n structure has the largest sunlight utilization range of about 200-850 nm, and has the narrowest band gap of 2.64 eV, which is conducive to improving the carrier lifetime and degradation efficiency of the catalyst.

[0084] Figure 5 (a) and Figure 5 (b) are Fe 2p XPS spectra of Fe3O4 / g-C3N4 self-circulation photo-Fenton catalyst with p-n structure of Example 1 and Fe3O4 / g-C3N4 photo-Fenton catalyst of Comparative Example 1, respectively. By comparison, it can be seen that Fe 2+ and Fe 3+ exist in the catalysts, and the Fe 2+ content of the Fe3O4 / g-C3N4 self-circulation photo-Fenton catalyst with p-n structure is higher, which helps to obtain higher photo-Fenton degradation efficiency.

[0085] Figure 6 (a), (b), (c), (d) are transient photocurrent spectra of Fe3O4 / g-C3N4 self-circulation photo-Fenton catalyst with p-n structure of Example 1 and Example 2, Fe3O4 / g-C3N4 photo-Fenton catalyst of Comparative Example 1, and g-C3N4 powder of Comparative Example 6, respectively. As can be seen from the results, the Fe3O4 / g-C3N4 self-circulation photo-Fenton catalyst with p-n structure has the largest current density under light, which proves that it has the highest charge density under light, which helps to improve the photo-Fenton degradation efficiency.

[0086] Figure 7 (a)-(d) are Mott-Schottky curves of Fe3O4 / g-C3N4 self-circulation photo-Fenton catalyst with p-n structure of Example 1, g-C3N4 powder of Comparative Example 6, Fe3O4 / g-C3N4 photo-Fenton catalyst of Comparative Example 3, and Comparative Example 5, respectively. As can be seen from the results, the Fe3O4 / g-C3N4 self-circulation photo-Fenton catalyst with p-n structure has the structure characteristics of p-type semiconductor and n-type semiconductor at the same time, which shows that the p-n structure Fe3O4 / g-C3N4 self-circulation photo-Fenton catalyst is successfully synthesized.

[0087] Figure 8(a) and (b) are N2 gas adsorption / desorption curves of the p-n structure Fe3O4 / g-C3N4 self-cycling photo-Fenton catalyst in Example 1 and the g-C3N4 powder in Comparative Example 6, respectively. The results show that the specific surface area of the p-n structure Fe3O4 / g-C3N4 self-cycling photo-Fenton catalyst is increased by about 10% after light irradiation and thermal structure, which can effectively increase the contact area of the reaction solution and the catalyst, and is conducive to the occurrence of the self-cycling photo-Fenton reaction.

[0088] Figure 9 The test results of the hydrogen peroxide content in the aqueous solution after the p-n structure Fe3O4 / g-C3N4 self-cycling photo-Fenton catalyst in Example 1 is irradiated in the aqueous solution for 1 h. Before the test, the supernatant after the reaction is added to the color developing liquid composed of 0.4 mol / L potassium iodide and 0.1 mol / L aqueous solution of phthalic acid for color developing treatment for 0.5 h. The results show that the p-n structure Fe3O4 / g-C3N4 self-cycling photo-Fenton catalyst can produce about 6 μmol / L of hydrogen peroxide in the aqueous solution under light irradiation, which can effectively realize the self-cycling Fenton reaction. -1 h -1

[0089] Table 1 is the photo-Fenton degradation efficiency of the p-n structure Fe3O4 / g-C3N4 self-cycling photo-Fenton catalyst in Examples 1-2 and the Fe3O4 / g-C3N4 photo-Fenton catalyst in Comparative Examples 1-6 on the aqueous solution containing methylene blue within 1 h. It can be observed from the results that the p-n structure Fe3O4 / g-C3N4 self-cycling photo-Fenton catalyst in Example 1 has the highest photo-Fenton degradation efficiency.

[0090] Table 2 is a comparison of the redox conversion efficiency of Fe2+ / Fe3+ of the p-n structure Fe3O4 / g-C3N4 self-cycling photo-Fenton catalyst in Examples 1-2 and the Fe3O4 / g-C3N4 photo-Fenton catalyst in Comparative Examples 1-6 in 0.1 mol / L aqueous solution of potassium chloride. It can be known from the results that the p-n structure Fe3O4 / g-C3N4 self-cycling photo-Fenton catalyst in Example 1 has the optimal redox potential of iron and the largest redox current, proving that it has the best redox conversion efficiency of Fe2+ / Fe3+, which helps to improve the self-cycling photo-Fenton degradation efficiency. Comparative Example 6 is a pure g-C3N4 catalyst, which cannot occur the redox process of Fe2+ / Fe3+. 3+ 2+ 3+ 2+ 3+ 2+

[0091] Table 1 Comparison of self-cycling photo-Fenton degradation efficiency of samples in Examples 1-2 and Comparative Examples 1-6 in methylene blue solution within 1 h​​​​​​​

[0092] Number Photofenton degradation methylene blue efficiency (%) Example 1 85.0％ Example 2 56.4％ Example 3 58.3％ Comparative Example 1 48.3％ Comparative Example 2 40.2％ Comparative Example 3 33.7％ Comparative Example 4 22.3％ Comparative Example 5 2.6％ Comparative Example 6 28.8％

[0093] Table 2 Sample self-Fe oxidation-reduction conversion efficiency comparison of Example 1-2 and Comparative Example 1-5 samples in 0.1 mol / L potassium chloride solution 3+ / Fe 2+

[0094]

[0095]

[0096] The above descriptions are only preferred embodiments of the present application, and are not intended to limit the present application in other forms. Any person skilled in the art can modify or change the above disclosed technical contents into equivalent embodiments with equivalent changes. However, any simple modification, equivalent change and modification of the above embodiments without departing from the technical solution of the present application, and according to the technical essence of the present application, still belong to the protection scope of the technical solution of the present application.​

Claims

1. A method for preparing a self-circulating photo-Fenton catalyst with a pn structure Fe3O4 / g-C3N4, characterized in that: The catalyst comprises a p-type semiconductor structure Fe3O4 and an n-type semiconductor structure g-C3N4 matrix; the n-type semiconductor structure g-C3N4 matrix is ​​prepared by thermal polymerization using organic materials as raw materials; the p-type semiconductor structure Fe3O4 is formed on the surface of g-C3N4 by photoirradiation followed by pyrolysis under an inert atmosphere. The preparation method includes the following steps: Step 1: The organic matter is mixed with ammonia water and then placed in a reaction furnace for heat treatment to obtain g-C3N4 powder; the organic matter is one or more of urea, melamine, thiourea, and trithiocyanate. Step 2: Disperse the g-C3N4 powder obtained in Step 1 in a metal Fe salt solution to obtain suspension A. Stir suspension A under light irradiation, centrifuge and ultrasonically wash to obtain solid, and then dry to obtain g-C3N4 powder loaded with metal Fe ions. Step 3: The g-C3N4 powder loaded with Fe ions obtained in Step 2 is ground and dispersed in a ligand solution to obtain suspension B. After stirring, centrifugation, and ultrasonic washing, a solid is obtained, which is then dried to obtain Fe with mixed valence states. 3+ / Fe 2+ g-C3N4 matrix composite material; the ligand is 2-methylimidazole; Step 4: The Fe obtained in Step 3 with mixed valence states... 3+ / Fe 2+ The g-C3N4 matrix composite material was ground and placed in a tube furnace for pyrolysis under an inert atmosphere to obtain a pn structure Fe3O4 / g-C3N4 self-circulating photo-Fenton catalyst.

2. The preparation method according to claim 1, characterized in that: In step 1, the mass ratio of the organic matter to ammonia is 10:

3.

3. The preparation method according to claim 1, characterized in that: In step 1, the heat treatment temperature is 450-550℃, the heat treatment time is 1-5 h, and the heating rate is 0.5-20℃ / min.

4. The preparation method according to claim 1, characterized in that: In step 2, the concentration of g-C3N4 in suspension A is 1-20 g / L; The metal Fe salt includes one or more of ferric chloride, ferric nitrate, and ferric carbonate; The solvent for the Fe metal salt solution is one or more of deionized water, methanol, and ethanol, and the concentration of the Fe metal salt solution is 1 mmol / L-2 mol / L. The stirring time is 3-24 hours; The drying temperature is 40-70℃, and the drying time is 3-24 h.

5. The preparation method according to claim 1, characterized in that: In step 2, the wavelength of the light used for the light irradiation treatment is 200-1100 nm, the power is 300 W, and the distance between the light source and the upper surface of the solution is 5 cm.

6. The preparation method according to claim 1, characterized in that: In step 3, the concentration of g-C3N4 loaded with metal Fe ions in suspension B is 1-20 g / L; The solvent of the ligand solution is one or more of deionized water, methanol, and ethanol, and the concentration of the ligand solution is 1 mmol / L-2 mol / L; The stirring time is 3-24 hours; The drying temperature is 30-60℃, and the drying time is 3-24 h; The centrifugation speed is 2000-12000 rpm, and the time is 2-20 min; The stirring speed is 100-1000 rpm; The ultrasonic cleaning solvent is one or more of deionized water, methanol, and ethanol, and the washing is performed 1-5 times.

7. The preparation method according to claim 1, characterized in that: In step 4, the inert atmosphere includes one or more of nitrogen, argon, and helium; The pyrolysis temperature is 350-550℃, and the pyrolysis time is 1-5 h.

8. The application of a pn-structured Fe3O4 / g-C3N4 self-circulating photo-Fenton catalyst prepared by the method according to any one of claims 1-7, characterized in that: This is used to degrade organic pollutants in wastewater, including one or more of dyes, phenolic compounds, chlorinated hydrocarbons, bromine hydrocarbons, and benzene compounds.

9. The application according to claim 8, characterized in that: Includes the following steps: A self-circulating photo-Fenton catalyst with a pn structure, Fe3O4 / g-C3N4, was added to a solution containing organic pollutants. After reaching adsorption equilibrium, the catalyst was allowed to react under light irradiation with a wavelength of 200-1200 nm.

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