Photocatalyst for degrading organic pollutants and preparation method thereof

Abstract

The invention belongs to the technical field of water pollution treatment, and relates to a photocatalyst for organic pollutant degradation and a preparation method thereof, and the preparation method specifically comprises the following steps: 1, mixing gelatin, NaCl and water, stirring, carrying out high temperature calcination under nitrogen protection, and cooling to obtain g-C3N4; 2, ZnO, g-C3N4 and an alcoholic solution are mixed and subjected to ultrasonic treatment, then biomass charcoal is added, ultrasonic treatment continues to be conducted, filtering is conducted, filter residues are dried to be constant in weight, then high-temperature calcination is conducted, and after natural cooling, a g-C3N4-biomass charcoal-ZnO composite photocatalyst is obtained; the three components of g-C3N4, ZnO and biomass charcoal have a synergistic effect, the biomass charcoal adsorbs and enriches pollutants, ZnO / g-C3N4 heterojunction generates active oxygen species, the degradation efficiency of organic matters is remarkably improved, and the limitation that a traditional catalyst is single in function is broken through.

Description

Technical Field

[0001] The present invention belongs to the technical field of water pollution treatment, and relates to a photocatalyst for degrading organic pollutants and a preparation method thereof. Background Art

[0002] With the development of urbanization and industrialization, industrial pollutants such as azo dyes, agrochemicals, personal care products, pharmaceutical products, and aromatic compounds are continuously discharged into water bodies, and water pollution has become a worldwide problem. These harmful pollutants have low biodegradability, poor stability, high toxicity, and will remain in the environment for a long time, thus having a huge impact on the environment and human health.

[0003] Ways such as adsorption, photocatalysis, and photo-Fenton can effectively remove pollutants in water bodies. Among them, the photocatalytic oxidation method has attracted much attention due to its low cost and high efficiency. However, traditional photocatalysts have the following defects: 1) Traditional photocatalysts (such as TiO2, ZnO) mainly rely on ultraviolet light excitation, have low utilization rate of visible light (only accounting for 4-5% of the solar spectrum), narrow light response range, and cannot make full use of solar energy, resulting in low degradation efficiency. 2) The carrier recombination rate of single-component photocatalysts (such as pure g-C3N4) is high (>80%), and photo-generated electrons and holes recombine quickly, reducing the generation of active free radicals, and the catalytic activity is limited. It needs to be improved by noble metal loading or complex modification, with high costs. 3) Existing nanocatalysts are prone to agglomeration and difficult to separate. For example, TiO2 powder is difficult to recycle, and the problem of photocorrosion (such as ZnO is easily dissolved under light) leads to poor stability, low reuse rate of photocatalysts, increased treatment costs, and easy to cause secondary pollution. 4) Traditional preparation methods are difficult to regulate the porous structure, resulting in a small specific surface area of the catalyst, insufficient exposure of active sites, weak pollutant adsorption capacity, and low catalytic efficiency. 5) The preparation of composite catalysts mostly relies on high-temperature calcination or complex template methods (such as mesoporous SiO2 templates), with high energy consumption and cumbersome steps, and it is difficult for large-scale production.

[0004] Therefore, it has become an urgent problem to provide a photocatalyst for degrading organic pollutants with high catalytic efficiency, easy recovery, and low preparation cost. Summary of the Invention

[0005] In order to solve the above problems, the present invention provides a photocatalyst for degrading organic pollutants and a preparation method thereof, specifically including the following steps:

[0006] Step 1: Mix a zinc source and an iron source in a Fe / Zn molar ratio of 1:20, disperse them in a solvent with a solid-liquid mass ratio of 1:20, react at 180 - 200 °C for 2 - 3 h to obtain a ZnO precursor. Heat the ZnO precursor to 300 - 350 °C at a heating rate of 5 °C / min, hold for 1 - 1.5 h, then heat to 500 - 600 °C at a heating rate of 2 °C / min, and hold for 2 - 2.5 h to obtain nano-ZnO.

[0007] Preferably, the solvent is a glycerol - aqueous solution or an ethylene glycol - aqueous solution. In the glycerol - aqueous solution, the volume ratio of glycerol to water is 4:1, and in the ethylene glycol - aqueous solution, the volume ratio of ethylene glycol to water is 3:1.

[0008] Preferably, the zinc source is Zn(CH3COO)2·2H2O, and the iron source is Fe(NO3)3·9H2O.

[0009] Step 2: Crush the biomass to 70 - 80 mesh, mix it with an acid solution in a mass ratio of 1:4, soak at 50 - 60 °C and 100 - 120 rpm for 30 - 40 min, take it out and dry the surface moisture, then carbonize at 600 - 700 °C for 2 - 3 h to obtain biomass carbon.

[0010] Preferably, the biomass is one or more of wood, straw, grains, and nut shells.

[0011] Preferably, the acid solution is a phosphoric acid solution with a mass fraction of 15% - 20% or an acetic acid solution with a mass fraction of 25% - 30%.

[0012] Step 3: Mix gelatin, NaCl, and water in a mass ratio of 1:3:100, stir at 50 - 60 °C and 120 - 150 rpm for 1 - 2 h, then react at 180 - 200 °C for 12 - 14 h to obtain a composite gel. Take out the composite gel and dry the surface moisture, then vacuum dry at -30 - 50 °C for 20 - 24 h to obtain a precursor. Heat the precursor to 500 - 600 °C at a heating rate of 5 °C / min under nitrogen protection, and calcine at a constant temperature for 4 - 5 h, and obtain g-C3N4 after cooling.

[0013] Step 4: Crush nano-ZnO, biomass carbon, and g-C3N4 respectively, pass through a 100 - 150 mesh sieve. Mix ZnO, g-C3N4, and an alcohol solution with a solid-liquid mass ratio of 1:20, sonicate at 50 - 60 kHz for 30 - 40 min, then add biomass carbon and continue to sonicate for 30 - 40 min. Filter, dry the filter residue at 60 - 70 °C to constant weight, then heat to 300 - 400 °C at a heating rate of 5 °C / min and calcine for 1 - 1.5 h, and obtain the g-C3N4 - biomass carbon - ZnO composite photocatalyst after natural cooling.

[0014] Preferably, the mass ratio of nano-ZnO, biomass carbon, and g-C3N4 is (20-35):(50-70):(10-15).

[0015] Preferably, the alcohol solution is an ethanol solution with a volume fraction of 30-50% or a PEG-400 solution with a volume fraction of 2-3%.

[0016] The mechanism of preparing g-C3N4 from gelatin is that the gelatin molecular chain is rich in various amino acids, such as glycine, proline, and hydroxyproline, and its -C-NH-C- structural unit undergoes dehydration and decarboxylation reactions at high temperatures (500-600°C). The specific paths include:

[0017] Amino condensation: The amino group (-NH2) of glycine dehydrates with the carboxyl group (-COOH) of the adjacent chain to form a -C=N- bond;

[0018] Cyclization reaction: Continuous amino groups and imino groups (-NH-) generate a triazine ring (C3N3) through a six-membered ring transition state, forming the basic structural unit of g-C3N4;

[0019] Layered stacking: NH3 and H2O released during the pyrolysis process act as gas templates, prompting the triazine rings to form a two-dimensional sheet structure through π-π stacking.

[0020] The mechanism of action of NaCl and gelatin is that during the hydrothermal pretreatment stage (180-200°C), gelatin molecules are adsorbed on the surface of solid NaCl crystals through hydrogen bonds to form a three-dimensional interpenetrating network structure. At this time, NaCl acts as a rigid template, guiding the directional arrangement of gelatin molecules through van der Waals forces and electrostatic interactions, providing a space-confined environment for subsequent pyrolysis.

[0021] During the calcination process under nitrogen protection at 550°C, partial ion dissociation occurs on the surface of the NaCl crystal (Na + and Cl - ). Na + can be embedded between the layers of g-C3N4 through ion exchange to form a Na-N coordination bond, while Cl - combines with the uncondensed amino groups, inhibits the excessive formation of interlayer hydrogen bonds, fills the interlayer voids, and after cooling, NaCl is removed by washing with water, leaving through channels.

[0022] Gases such as CO2 and H2O released during the pyrolysis of gelatin expand in the gaps of the NaCl crystal, forming a stress gradient. Solid NaCl acts as a rigid support framework, restricting the gas escape path, and finally forming through channels with a diameter of 50-200 nm.

[0023] The present invention has the following advantages:

[0024] (1) By combining g-C3N4 with ZnO, a heterostructure is formed, broadening the light absorption range to the full spectrum and promoting electron-hole separation simultaneously, thus solving the problems of narrow light response and high carrier recombination rate of traditional catalysts.

[0025] (2) As a porous carrier, biomass carbon supports ZnO and g-C3N4 to prevent agglomeration. The rigid skeleton of biomass carbon provides physical support. Nano-ZnO is strongly bonded to the carbon matrix through calcination, reducing photocorrosion. If the biomass contains Fe, efficient recovery can be achieved through magnetic separation, overcoming the deficiencies of difficult recovery and poor stability of traditional catalysts.

[0026] (3) The present invention utilizes the thermal decomposition gas expansion of NaCl template and gelatin to form through pores and mesoporous structures, significantly increasing the specific surface area, providing abundant adsorption sites and reaction interfaces, and compensating for the defects of small specific surface area and insufficient active sites of traditional catalysts.

[0027] (4) The present invention uses biomass carbon and gelatin as raw materials, combines high-temperature calcination and solvent control, significantly reduces energy consumption, and has no toxic by-products, solving the problems of relying on precious metals and high energy consumption in the prior art for preparation.

[0028] (5) The three components of g-C3N4, ZnO and biomass carbon in the present invention act synergistically. Biomass carbon adsorbs and enriches pollutants, and the ZnO / g-C3N4 heterojunction generates reactive oxygen species (·OH, O2 - ), significantly improving the degradation efficiency of organic matter and breaking through the limitations of the single function (only adsorption or catalysis) of traditional catalysts. Detailed implementation manners

[0029] The technical solutions in the embodiments of the invention are described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0030] Example 1

[0031] Step 1: Mix Zn(CH3COO)2·2H2O and Fe(NO3)3·9H2O according to the molar ratio of Fe / Zn of 1:20, and disperse them in a glycerol-water solution with a solid-liquid mass ratio of 1:20. React at 200°C for 2.5 h to obtain a ZnO precursor. Heat the ZnO precursor to 350°C at a heating rate of 5°C / min, hold for 1.5 h, and then heat to 550°C at a heating rate of 2°C / min and hold for 2.5 h to obtain nano-ZnO. The volume ratio of glycerol to water is 4:1.

[0032] Step 2: Crush the walnut shells to 75 mesh, mix them with acetic acid solution with a mass fraction of 30% at a mass ratio of 1:4, soak them at 55°C and 120 rpm for 35 min, take them out and dry the surface moisture, and carbonize them at 650°C for 2.5 h to obtain biomass carbon.

[0033] Step 3: Mix gelatin, NaCl and water at a mass ratio of 1:3:100, stir at 55°C and 150 rpm for 1.5 h, then react at 200°C for 12 h to obtain a composite gel. Take out the composite gel and dry the surface moisture, vacuum dry it at -40°C for 24 h to obtain a precursor. The precursor is heated to 550°C at a rate of 5°C / min under nitrogen protection and calcined at a constant temperature for 4 h, and g-C3N4 is obtained after cooling.

[0034] Step 4: Crush nano-ZnO, biomass carbon and g-C3N4 respectively, and pass through a 120-mesh sieve. Mix ZnO, g-C3N4 and ethanol solution with a volume fraction of 40%, and the solid-liquid mass ratio is 1:20. Ultrasonic at 60 kHz for 30 min, then add biomass carbon and continue ultrasonic for 30 min. Filter, dry the filter residue at 65°C to constant weight, then heat it to 350°C at a rate of 5°C / min and calcine for 1.5 h. After natural cooling, a g-C3N4-biomass carbon-ZnO composite photocatalyst is obtained. The mass ratio of the nano-ZnO, biomass carbon and g-C3N4 is 3:6:1.

[0035] Test Example 1

[0036] Prepare methylene blue solution with a concentration of 10 mg / L, and set five groups of treatments to carry out photocatalysis on the methylene blue solution. Treatment 1: Use ZnO prepared in Example 1; Treatment 2: Use g-C3N4 prepared in Example 1; Treatment 3: Use pure anatase nano-titanium dioxide (TiO2) photocatalyst purchased from Hangzhou Hengge Nano Technology Co., Ltd.; Treatment 4: Use the composite photocatalyst prepared in Example 1; Treatment 5: Use the composite photocatalyst prepared in Example 1.

[0037] Among them, the catalyst dosage for Treatments 1-5 is 1 g / L, and the light source is a 300 W xenon lamp. For Treatments 1-4, the degradation rate of methylene blue is measured after 60 min of illumination, and for Treatment 5, the degradation rate of methylene blue is measured after 30 min of illumination. The results are shown in Table 1.

[0038] Table 1

[0039] Illumination time (min) Degradation rate (%) Remarks Treatment 1 60 45 Traditional catalyst, prone to agglomeration during the catalytic process Treatment 2 60 52 High carrier recombination rate Treatment 3 60 65 Strong dependence on ultraviolet light Treatment 4 60 96 Full-spectrum response, efficient adsorption-catalysis Treatment 5 30 82 Rapid degradation, significantly improving the degradation rate

[0040] The g-C3N4-biomass carbon-ZnO composite photocatalyst prepared by the present invention has a degradation rate of up to 96% for methylene blue within 60 minutes, which is significantly better than pure ZnO, pure g-C3N4 and commercial TiO2. Its advantages are as follows:

[0041] 1. Heterogeneous structure: broaden the light absorption range to the full spectrum and promote electron-hole separation.

[0042] 2. Porous carrier: biomass carbon inhibits aggregation and increases the specific surface area

[0043] 3. Synergistic effect: adsorption-catalysis synergy to rapidly enrich and degrade pollutants.

[0044] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A preparation method of a photocatalyst for degrading organic pollutants, characterized in that, It includes the following steps: Step 1: Mix and stir gelatin, NaCl and water, then react at 150 - 200 °C to obtain a composite gel. Take out the composite gel and dry the surface moisture, then vacuum dry to obtain a precursor. The precursor is calcined at a constant temperature of 500 - 600 °C under nitrogen protection, and after cooling, g-C3N4 is obtained; Step 2: Crush and sieve nano-ZnO, biomass carbon and g-C3N4 respectively. Mix ZnO, g-C3N4 and an alcohol solution, perform ultrasonic treatment, then add biomass carbon and continue ultrasonic treatment. Filter, dry the filter residue to a constant weight, and then calcine at a constant temperature of 300 - 400 °C. After natural cooling, a g-C3N4-biomass carbon-ZnO composite photocatalyst is obtained.

2. The preparation method of a photocatalyst for degrading organic pollutants according to claim 1, wherein In Step 1, the mass ratio of the gelatin, NaCl and water is 1:3:

100.

3. The preparation method of a photocatalyst for degrading organic pollutants according to claim 1, characterized in that, In Step 2, the mass ratio of the nano-ZnO, biomass carbon and g-C3N4 is (20 - 35):(50 - 70):(10 - 15).

4. The preparation method of a photocatalyst for degrading organic pollutants according to claim 1, characterized in that, In Step 2, the solid-liquid mass ratio of ZnO, g-C3N4 and the alcohol solution is 1:

20.

5. The preparation method of a photocatalyst for degrading organic pollutants according to claim 1, characterized in that, The alcohol solution in Step 2 is an ethanol solution with a volume fraction of 30 - 50% or a PEG-400 solution with a volume fraction of 2 - 3%.

6. The preparation method of a photocatalyst for degrading organic pollutants according to claim 1, wherein, The preparation method of the nano-ZnO in Step 2 is to mix a zinc source and an iron source at an Fe / Zn molar ratio of 1:20, disperse them in a solvent, react at 180 - 200 °C for 2 - 3 h to obtain a ZnO precursor, calcine the ZnO precursor at a constant temperature of 300 - 350 °C for 1 - 1.5 h, and then calcine at a constant temperature of 500 - 600 °C for 2 - 2.5 h to obtain nano-ZnO.

7. The preparation method of a photocatalyst for degrading organic pollutants according to claim 6, characterized in that, The solvent is a glycerol-water solution or an ethylene glycol-water solution. The volume ratio of glycerol to water in the glycerol-water solution is 4:1, and the volume ratio of ethylene glycol to water in the ethylene glycol-water solution is 3:

1.

8. The preparation method of a photocatalyst for degrading organic pollutants according to claim 6, characterized in that, The zinc source is Zn(CH3COO)2·2H2O, and the iron source is Fe(NO3)3·9H2O.

9. The preparation method of a photocatalyst for degrading organic pollutants according to claim 1, characterized in that, The preparation method of the biomass carbon in Step 2 is to crush the biomass, mix it with an acid solution and soak it, take it out and dry the surface moisture, and carbonize it at 600 - 700 °C for 2 - 3 h to obtain biomass carbon.

10. The g-C3N4-biomass carbon-ZnO composite photocatalyst prepared by the method according to any one of claims 1 - 9.