A silicon carbide supported zero-valent iron type photocatalyst, and a preparation method and application thereof

Abstract

The present application relates to solid waste resource utilization and environmental catalytic material technical field, disclose a kind of silicon carbide supported zero-valent iron type photocatalyst and its preparation method and application.The present application uses the crystal silicon recovered from waste photovoltaic panel and graphite recovered from waste lithium battery negative as raw material, under the condition without deep impurity removal purification, realizes solid phase activation and uniform mixing using mechanical chemical ball milling, and iron salt is added as iron source in the ball milling process, then low-temperature calcination is carried out to obtain silicon carbide supported zero-valent iron composite photocatalyst.The catalyst obtained by the present application has good light response and active site dispersion characteristics, and can be used for efficient degradation of metformin hydrochloride in water, and has the advantages of short preparation process, low cost, suitable for large-scale and high-value utilization of solid waste, etc.

Description

Technical Field

[0001] This invention belongs to the field of solid waste resource utilization and environmental catalytic materials technology, and particularly relates to a silicon carbide supported zero-valent iron photocatalyst, its preparation method and application. Background Technology

[0002] The vast amount of photovoltaic modules and lithium batteries produced in the new energy industry face the issue of retirement and recycling. For photovoltaic modules, mechanical crushing is a more suitable physical processing method for industrial production than thermal treatment and chemical solvent methods, and is a resource recovery technology widely recognized by processing companies. However, the purity of photovoltaic crystalline silicon recovered by mechanical crushing is limited, containing metallic impurities such as silver and copper, resulting in low resource value and making it unsuitable for direct reuse in the recycling of crystalline silicon. The situation is similar for graphite anode materials and retired photovoltaic crystalline silicon. If wet processes are used to deeply remove impurities from both materials for resource recovery and reuse, it consumes large amounts of acid and alkali reagents, resulting in high processing costs and generating large amounts of heavy metal wastewater, posing a risk of environmental pollution.

[0003] Metformin (MET) is the first-line drug for treating diabetes, leading to increased production and usage. After oral administration, metformin undergoes minimal liver metabolism and does not bind to plasma proteins, making it difficult for patients to fully digest and absorb. Unabsorbed metformin is excreted directly through the kidneys in urine and feces, entering urban wastewater treatment systems. Traditional wastewater treatment processes are ineffective at treating metformin, resulting in large quantities entering water bodies with the effluent. Therefore, there is an urgent need to develop a solid waste co-conversion technology that does not rely on deep impurity removal, and to prepare efficient, stable, and engineering-feasible photocatalytic materials for the degradation of pollutants such as metformin hydrochloride.

[0004] In summary, how to achieve resource recovery and high-value utilization of retired photovoltaic crystalline silicon and retired power battery anode graphite while reducing environmental risks, and further serve the efficient removal of pharmaceutical pollutants such as metformin, has become a key technical problem urgently needing to be solved in the fields of solid waste resource utilization and water pollution control. Existing technologies still generally suffer from problems such as complex processes, high chemical consumption, significant secondary pollution risks, high material preparation costs, and insufficient scalability. Therefore, it is necessary to propose a new technical route that balances the co-utilization of solid waste with efficient pollutant treatment. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for preparing a silicon carbide-supported zero-valent iron composite photocatalyst by using waste crystalline silicon and waste graphite, introducing iron salts through mechanochemical ball milling, and then calcining at a relatively low temperature in an inert atmosphere, without requiring deep impurity removal. The method also provides its application in degrading metformin hydrochloride without the addition of hydrogen peroxide or persulfate. Furthermore, the composite catalytic material of this invention features a simple process, is easy to mass-produce and recycle, can be used at room temperature and pressure, and can be recycled multiple times, exhibiting good economic efficiency and practicality.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A silicon carbide-supported zero-valent iron photocatalyst and its preparation method include the following steps:

[0008] (1) Provide silicon-containing raw materials and carbon-containing raw materials, wherein the silicon-containing raw materials are crystalline silicon powder or granules recycled from waste photovoltaic panels, and the carbon-containing raw materials are graphite powder recycled from waste lithium-ion battery negative electrodes;

[0009] (2) The silicon-containing raw material and carbon-containing raw material provided in (1) are mixed with an iron source and subjected to mechanical chemical ball milling to obtain the ball milling product;

[0010] (3) The ball milling product obtained in (2) is calcined at low temperature in an inert atmosphere, a reducing atmosphere, a mixed atmosphere or a vacuum to obtain a crude product of silicon carbide supported on zero-valent iron;

[0011] (4) The crude product obtained in (3) is calcined, washed and purified, and finally dried to obtain silicon carbide supported zero-valent iron composite photocatalyst.

[0012] The silicon and carbon sources mentioned are not deeply purified. Here, "not deeply purified" means that they have not undergone at least one of the following: acid washing (including hydrochloric acid, nitric acid, and aqua regia), hydrofluoric acid etching, high-temperature smelting, and multi-step chelation impurity removal. They are only photovoltaic crystalline silicon recovered by mechanical crushing physical methods and graphite anode materials produced by power battery processing enterprises.

[0013] The iron source is an iron salt, which is at least one of ferric nitrate, ferric sulfate, ferrous sulfate, ferric chloride, ferric oxalate, ferric citrate, and ferric phosphate.

[0014] Preferably, in step (2): the mass ratio of silicon-containing raw material to carbon-containing raw material is 1:0.5-5, preferably 1:2; the mass ratio of iron salt content to silicon and carbon raw materials is 1:0.5-10, preferably 1:5.

[0015] Preferably, in step (2): the ball-to-material ratio of the mechanical-chemical ball mill is 40-5:1; the ball milling speed is 300-1000 rpm; the ball milling time is 0.5-20 h; and the ball milling method includes dry milling or wet milling.

[0016] Preferably, in step (3): the low-temperature calcination temperature is 500-1500℃, preferably 1000℃; the atmosphere is N2, Ar, Ar-H2 (H2 volume fraction is 1%-10%), preferably Ar-H2.

[0017] Further preferred, in step (4): the calcination temperature is 500-1000℃, preferably 800℃; the washing reagent is pure water, deoxygenated water, deionized water, ethanol and acetone, preferably deoxygenated water; the drying method is freeze drying or vacuum drying, preferably vacuum drying at 50℃.

[0018] To achieve the objective of this invention, another technical solution is also provided: the application of the above-mentioned silicon carbide-supported zero-valent iron composite photocatalyst in the photocatalytic degradation of metformin hydrochloride in water, comprising the following steps:

[0019] (1) The composite catalytic material is added to water containing metformin hydrochloride;

[0020] (2) Degradation of metformin hydrochloride under certain temperature, pH and light conditions;

[0021] (3) The composite catalyst is separated and recovered by any one of the following methods: filtration, centrifugation or magnetic separation.

[0022] The amount of the composite catalytic material added is 0.1-2.5 g / L; the concentration of the metformin hydrochloride is 5-100 mg / L.

[0023] Preferably, in step (2): the temperature is 15-100℃, preferably 25℃; the pH is 2-10, preferably 6; the light is visible light, ultraviolet light and natural light, preferably natural light.

[0024] More preferably, the composite catalytic material generates free radicals including hydroxyl radicals and superoxide radicals; the composite catalytic material removes ≥99% of metformin hydrochloride within 60 min; and the composite catalytic material retains ≥90% of the removal rate of metformin hydrochloride after 4 cycles.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] 1. Eliminates the need for deep purification, reducing chemical reagent consumption and waste liquid discharge;

[0027] 2. Co-processing of solid waste to achieve high value: waste crystalline silicon and waste graphite are integrated into functional catalytic materials;

[0028] 3. Simple process: Two-stage process of ball milling + inert atmosphere calcination, easy to scale up;

[0029] 4. Mild application conditions: Metformin hydrochloride degradation is achieved without the addition of H2O2 or persulfate, with a mild reaction temperature and a wide applicable pH range;

[0030] 5. Catalytic performance and stability: Metformin hydrochloride removal rate ≥99%, apparent rate constant k=0.0497min -1 It remains at ≥90% after 4 cycles. Attached Figure Description

[0031] Figure 1 The image shows the XRD pattern of the silicon carbide-supported zero-valent iron composite material of the present invention.

[0032] Figure 2 This is a SEM image of the silicon carbide-supported zero-valent iron composite material of the present invention at 5.00kx magnification.

[0033] Figure 3 This is a SEM image of the silicon carbide-supported zero-valent iron composite material of the present invention at 13.0kx magnification.

[0034] Figure 4 This is a magnetic illustration of the silicon carbide-supported zero-valent iron composite material of the present invention.

[0035] Figure 5 The effect of multiple cycle tests on composite materials to degrade metformin hydrochloride is shown in the figure. Detailed Implementation

[0036] The following are specific embodiments of the present invention, described in conjunction with the accompanying drawings, to further illustrate the technical solution of the present invention. However, the present solution is not limited to these embodiments. In the following description, the specific details of the specific configurations provided are merely to aid in a comprehensive understanding of the embodiments of the present invention. Therefore, various improvements and variations can be made to the specific implementation of the present invention without departing from the scope or spirit of the present invention, which will be apparent to those skilled in the art. The present invention specification and embodiments are merely exemplary.

[0037] It should be noted that, where there is no conflict, the embodiments and features described herein can be combined with each other. Furthermore, the materials, experiments, and experimental equipment involved in this invention are derived only from waste photovoltaic crystalline silicon, obtained from silicon wafers dismantled from retired photovoltaic modules, which are crushed and sieved to obtain 100-mesh silicon powder; and from waste lithium battery negative electrode graphite, obtained from battery dismantling and recycling, which is processed by foil removal, crushing, and sieving to obtain graphite powder. The above raw materials are not subjected to deep impurity removal processes such as acid washing, hydrofluoric acid etching, or high-temperature refining; they only undergo pretreatment such as water washing, sieving, and low-temperature removal of organic components (e.g., binders, organic electrolytes). All other materials, experiments, and experimental equipment conform to commercially available products in the relevant field.

[0038] Example 1: The present invention relates to a method for preparing a silicon carbide-supported zero-valent iron composite photocatalytic material, comprising the following steps:

[0039] (1) After collecting the crystalline silicon from the retired photovoltaic panels, clean the surface dust with tap water and dry it in an oven to remove excess moisture for later use. Place the graphite from the negative electrode of the waste lithium battery after removing the copper foil and separator into a tube furnace under an Ar atmosphere, and heat it at 5℃ / min until it reaches 550℃. Then stop heating and maintain the temperature of the tube furnace at 550℃ for 3 hours. After the end of the furnace, allow it to cool naturally to obtain graphite with the binder and electrolyte removed for later use.

[0040] (2) Weigh 1g of waste photovoltaic crystal silicon and 2g of waste negative electrode graphite from step (1) (Si:C mass ratio is 1:2); add ferric chloride to make the mass ratio of ferric chloride to silicon carbon 1:1;

[0041] (3) Transfer all of the above silicon-carbon-ferric chloride mixed powder to a stainless steel ball mill jar lined with polytetrafluoroethylene. Select zirconia balls with diameters of 3 mm and 5 mm as the ball milling media (the volume ratio of the two is 1:1 to improve the ball milling efficiency and mixing uniformity). Control the ball-to-material ratio of the total mass of the ball milling media to the total mass of the mixture to be milled to be 10:1. Then fix the ball mill jar on a planetary ball mill, set the equipment speed to 500 r / min, and continue ball milling for 6 hours at room temperature. After the ball milling program is completed, open the ball mill jar and collect the powdered material in the jar to obtain the uniformly dispersed silicon-carbon-ferric chloride ball milling product. Place it in a desiccator for later use.

[0042] (4) The ball-milled product was placed in a tube furnace and calcined at 1000°C for 6 hours under an Ar atmosphere. After cooling, a crude product of silicon carbide-supported zero-valent iron composite photocatalyst was obtained. (5) The crude product in step (4) was placed in a muffle furnace and heated to 800°C at 10°C / min and held for 3 hours. Then it was naturally cooled to room temperature. Then deoxygenated water was added to remove ferric chloride. Finally, it was placed in a vacuum drying oven at 50°C to dry and obtain silicon carbide-supported zero-valent iron composite catalytic material.

[0043] The XRD pattern of the silicon carbide-supported zero-valent iron composite catalyst is shown below. Figure 1 As shown, four typical peaks appear at 35.6°, 41.4°, 59.9°, and 71.8°, corresponding to the (111), (200), (220), (311), and (222) crystal planes of 3C-SiC, respectively. Characteristic peaks for zero-valent iron are present at 45° and 65°. The SEM image is shown below. Figure 2 and Figure 3 As shown, small particles of zero-valent iron exist on the 3C-SiC nanowires; furthermore... Figure 4 The magnetic properties of silicon carbide loaded with zero-valent iron were demonstrated, facilitating recycling in practical applications.

[0044] A method for degrading metformin hydrochloride in water using a silicon carbide-supported zero-valent iron composite catalyst prepared by a mechanochemical-carbothermic reduction method includes the following steps:

[0045] First, the above-mentioned composite catalyst is added to the water containing metformin hydrochloride. The reaction pH is controlled between 2 and 10. Silicon carbide supported on zero-valent iron generates hydroxyl radicals and superoxide radicals under 300W xenon lamp illumination to degrade metformin hydrochloride in the water.

[0046] The silicon carbide-supported zero-valent iron composite catalyst, metformin hydrochloride, and pH ranges are: 0.1 g / L-2.5 g / L, 5 mg / L-100 mg / L, 2-10; preferably: 0.5 g / L, 30 mg / L, 3-7. The photodegradation time is 15 min-120 min, preferably 60 min.

[0047] Application performance testing: 0.1 g of the aforementioned silicon carbide-supported zero-valent iron composite catalyst was added to a solution containing 200 mL of 20 mg / L metformin hydrochloride (pH 6). Before the light irradiation experiment, the suspension was stirred for 30 min in the dark to ensure adsorption-desorption equilibrium, and then the degradation experiment was conducted under a 300 W xenon lamp. During the 60 min experiment, 1 mL of sample was taken every 10 min for measurement. The results showed that the product obtained in the example degraded 200 mL of 20 mg / L metformin hydrochloride at a degradation rate of 96.8% after 60 min of light irradiation.

[0048] Example 2: The present invention is used for the preparation method of a silicon carbide supported zero-valent iron composite photocatalytic material, wherein the iron salt is replaced with ferric nitrate, and the remaining steps are the same as in Example 1.

[0049] The application performance test method is the same as that in Example 1. The results show that the degradation rate of the product obtained in the example after irradiating 200 ml of 20 mg / L metformin hydrochloride for 60 min is 93.2%.

[0050] Example 3: The present invention is used for the preparation method of a silicon carbide supported zero-valent iron composite photocatalytic material, wherein the iron salt is replaced with ferric sulfate, and the remaining steps are the same as in Example 1.

[0051] The application performance test method is the same as that in Example 1. The results show that the degradation rate of the product obtained in the example after 200 ml of 20 mg / L metformin hydrochloride was 84.2% after 60 min of light irradiation.

[0052] Example 4: The present invention is used for the preparation method of a silicon carbide supported zero-valent iron composite photocatalytic material, wherein the iron salt is replaced with ferrous sulfate, and the remaining steps are the same as in Example 1.

[0053] The application performance test method is the same as that in Example 1. The results show that the degradation rate of the product obtained in the example after irradiating 200 ml of 20 mg / L metformin hydrochloride for 60 min is 78.5%.

[0054] Example 5: The present invention is used for the preparation method of a silicon carbide supported zero-valent iron composite photocatalytic material. The iron salt is replaced with iron oxalate. In step (5) of Example 1, the purification is changed from deoxygenated water to magnetic separation to remove unreacted iron oxalate. The remaining steps are the same as in Example 1.

[0055] The application performance test method is the same as that in Example 1. The results show that the degradation rate of the product obtained in the example after irradiating 200 ml of 20 mg / L metformin hydrochloride for 60 min is 90.1%.

[0056] Example 6: The present invention is used for the preparation method of a silicon carbide supported zero-valent iron composite photocatalytic material. The iron salt is replaced with iron phosphate. In step (5) of Example 1, the purification is changed from deoxygenated water to magnetic separation to remove unreacted iron phosphate. The remaining steps are the same as in Example 1.

[0057] The application performance test method is the same as that in Example 1. The results show that the degradation rate of the product obtained in the example after irradiating 200 ml of 20 mg / L metformin hydrochloride for 60 min is 88.7%.

[0058] Example 7: The present invention is used for the preparation method of a silicon carbide supported zero-valent iron composite photocatalyst material. The iron salt is replaced with iron citrate. In step (5) of Example 1, the purification is changed from deoxygenated water to magnetic separation to remove unreacted iron citrate. The remaining steps are the same as in Example 1.

[0059] The application performance test method is the same as that in Example 1. The results show that the degradation rate of the product obtained in the example after irradiating 200 ml of 20 mg / L metformin hydrochloride for 60 min is 85.9%.

[0060] Example 8: Preparation of silicon carbide-supported zero-valent iron. The materials were named 1#-7# respectively, as in Examples 1-7.

[0061] The application performance test was the same as in Example 1, except that HCl was added before the reaction to adjust the pH of metformin hydrochloride to 2. The degradation rate of the product in Example 1 after 200 ml of 20 mg / L metformin hydrochloride was irradiated for 60 min is shown in Table 1.

[0062] Table 1

[0063] Material Number Degradation rate 1# 100% 2# 100% 3# 98.4% 4# 95.7% 5# 100% 6# 99.4% 7# 97.6%

[0064] Example 9: Preparation of silicon carbide-supported zero-valent iron. The materials were named 1#-7# respectively, as in Examples 1-7.

[0065] The application performance test was the same as in Example 1, except that NaOH was added before the reaction to adjust the pH of metformin hydrochloride to 10. The degradation rate of the product in Example 1 after 200 ml of 20 mg / L metformin hydrochloride was determined by irradiation for 60 min, as shown in Table 2.

[0066] Table 2

[0067] Material Number Degradation rate 1# 68.1% 2# 60.7% 3# 47.2% 4# 40.3% 5# 63.1% 6# 67.4% 7# 58.5%

[0068] Example 10: Preparation of silicon carbide supported zero-valent iron composite catalyst material is the same as in Example 1.

[0069] Cyclic performance test: 0.1g of silicon carbide-supported zero-valent iron composite catalyst was added to 200ml of 20mg / L metformin hydrochloride. Before illumination, the suspension was stirred for 30min in the dark to ensure adsorption-desorption equilibrium, and then degradation experiments were conducted under a 300W xenon lamp. During the 60min experiment, 1ml of sample was taken every 10min and filtered using a 0.22µm syringe filter; the concentration of the filtrate was determined. After illumination, all water samples were centrifuged to separate the catalyst material, washed with ethanol, and finally dried in a vacuum drying oven at 50℃. The above operations were repeated after the experiment, and the results are as follows. Figure 5 The removal rate remained at ≥90% even after 4 cycles.

[0070] Comparative Example 1: 0.1 g of silicon carbide was added to 200 ml of 20 mg / L metformin hydrochloride solution. The reaction was carried out in the dark for 30 min to reach adsorption-desorption equilibrium. Then, the solution was irradiated under a 300 W xenon lamp for 60 min. 1 ml of sample was taken every 10 min and filtered through a 0.22 μm syringe filter to measure the degradation rate.

[0071] The results showed that silicon carbide degraded 200 ml of 20 mg / L metformin hydrochloride at a rate of 31% in 60 minutes.

[0072] Comparative Example 2: The comparison method is the same as that of Comparative Example 1, except that silicon carbide is replaced with zero-valent iron powder.

[0073] The results showed that zero-valent iron powder degraded 200 ml of 20 mg / L metformin hydrochloride by 3% in 60 min.

[0074] Comparative Example 3: 0.1g of the catalyst material from Example 1 was added to 200ml of 20mg / L metformin hydrochloride solution. The reaction was carried out in the dark for 60min, and 1ml of sample was taken every 10min and filtered through a 0.22um syringe filter to measure the degradation rate.

[0075] The results showed that the catalytic material in Example 1 degraded 200 ml of 20 mg / L metformin hydrochloride at a degradation rate of 49.1% in 60 min.

[0076] Comparative Example 4: Following the method for preparing silicon carbide-supported zero-valent iron in Example 1, the silicon source and carbon source were replaced with pure crystalline silicon from the aforementioned waste photovoltaic crystalline silicon, and the waste lithium battery anode graphite was replaced with pure graphite to prepare silicon carbide-supported zero-valent iron composite catalyst material.

[0077] The silicon carbide-supported zero-valent iron composite catalyst was subjected to a cyclic performance test according to Example 10. After 4 cycles, the removal rate was still ≥87%. The results were basically the same as those of the composite catalyst in Example 1.

[0078] In summary, this invention discloses a mechanochemical-carbothermic reduction method for preparing silicon carbide-supported zero-valent iron composite catalytic materials. The silicon and carbon sources are both derived from waste photovoltaic panel crystalline silicon and waste lithium battery negative electrode graphite that do not require deep purification. These materials are used for photocatalytic degradation of metformin hydrochloride in water, and have high practical application value, environmental benefits, and economic benefits.

[0079] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a silicon carbide-supported zero-valent iron photocatalyst, characterized in that, Includes the following steps: (1) Provide silicon-containing raw materials and carbon-containing raw materials, wherein the silicon-containing raw materials are crystalline silicon powder or granules recycled from waste photovoltaic panels, and the carbon-containing raw materials are graphite powder recycled from waste lithium-ion battery negative electrodes, and neither the silicon-containing raw materials nor the carbon-containing raw materials have undergone deep purification treatment; the lack of deep purification treatment means that at least one of the following treatments has not been performed: acid washing, hydrofluoric acid etching, high-temperature smelting, and multi-step chelation purification. Only the silicon-containing raw materials are subjected to water washing and drying pretreatment, and the carbon-containing raw materials are subjected to copper foil and separator removal, followed by pretreatment to remove binder and electrolyte by heating to 550°C at 5°C / min and holding at 3h under Ar atmosphere; (2) The silicon-containing raw material and carbon-containing raw material from step (1) are mixed with an iron source and subjected to mechanical chemical ball milling to obtain a ball milling product; the iron source is an iron salt, and the iron salt is at least one of ferric nitrate, ferric sulfate, ferrous sulfate, ferric chloride, ferric oxalate, ferric citrate, and ferric phosphate. (3) The ball milling product of step (2) is calcined at 1000–1500°C in an inert atmosphere, reducing atmosphere or vacuum to obtain a crude product of silicon carbide supported on zero-valent iron. (4) The crude product from step (3) is subjected to calcination, washing and purification and drying to obtain silicon carbide supported zero-valent iron photocatalyst; the calcination temperature is 500-1000℃.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the silicon-containing raw material to the carbon-containing raw material is 1:0.5-5, and the mass ratio of the iron salt to the total mass of the silicon-containing and carbon-containing raw materials is 1:0.5-10.

3. The preparation method according to claim 1, characterized in that, In step (2), the ball-to-material ratio of the mechanical chemical ball mill is 40-5:1, the ball milling speed is 300-1000 rpm, the ball milling time is 0.5-20 h, and the ball milling method is dry milling or wet milling.

4. The preparation method according to claim 1, characterized in that, The inert atmosphere mentioned in step (3) is one of N2 and Ar, and the reducing atmosphere is an Ar-H2 mixture with a volume fraction of 1%-10% H2.

5. The preparation method according to claim 1, characterized in that, The reagent used for washing and purification in step (4) is one of pure water, deoxygenated water, deionized water, ethanol, and acetone; the drying process is freeze drying or vacuum drying.

6. A silicon carbide-supported zero-valent iron photocatalyst, characterized in that, The photocatalyst, prepared by any one of claims 1-5, comprises a silicon carbide support and zero-valent iron particles supported on the surface of the silicon carbide support, and the photocatalyst can generate hydroxyl radicals and superoxide radicals under light irradiation.

7. The application of the silicon carbide-supported zero-valent iron photocatalyst according to claim 6 in the degradation of metformin hydrochloride in water, characterized in that, The photocatalyst is brought into contact with water containing metformin hydrochloride, and the reaction is carried out under light conditions to achieve the degradation of metformin hydrochloride. No hydrogen peroxide or persulfate is added to the reaction system.

8. The application according to claim 7, characterized in that, Includes the following steps: (1) The photocatalyst is added to a water body containing metformin hydrochloride, wherein the amount of photocatalyst added is 0.1-2.5 g / L and the concentration of metformin hydrochloride in the water body is 5-100 mg / L; (2) The mixture from step (1) is subjected to visible light, ultraviolet light or natural light irradiation at 15-100℃ and pH 2-10 to achieve the degradation of metformin hydrochloride. (3) The photocatalyst is separated and recovered by means of filtration, centrifugation or magnetic separation.

Images