A multi-electrode photoelectrocatalytic device and its application in high-concentration wastewater treatment.

Abstract

This application discloses a multi-electrode photoelectrocatalytic device and its application in the treatment of high-concentration wastewater. The photoelectrocatalytic device includes a main reaction tank, an electrode fixing cover, wires, a photoanode, a photocathode, and an electrode cathode. The photoanode is a WO3 electrode; the photocathode is a MIL-101(Fe)-CC electrode, which activates hydrogen peroxide; and the electrode cathode is a PTFE / TiO2 / Ni-MOF / PDA@C electrode, which generates hydrogen peroxide. The treatment system and method of this invention have good treatment effects on both heavy metals and organic pollutants, and exhibit high chemical stability.

Description

Technical Field

[0001] This application relates to the field of high-efficiency photoelectrocatalysis technology, specifically to the construction of a three-electrode photoelectrocatalysis device based on dual photoelectrodes, and its application in chromium-containing wastewater and organic wastewater. Background Technology

[0002] Taking the heavy metal chromium (Cr(VI)) as an example, it is widely used in industries such as electroplating and metal processing. Cr(VI)-containing pollutants are easily released into natural water bodies due to their high solubility and toxicity, threatening human and ecosystem health. For chromium-containing wastewater, the common practice is to reduce the toxic Cr(VI) to Cr(III), which can reduce its toxicity by more than 100 times. Optonic pollutants (OPs), such as ciprofloxacin (CIP), are frequently detected in groundwater, surface water, domestic sewage, livestock wastewater, and agricultural wastewater due to their poor biodegradability. Furthermore, residual CIP in the ecosystem can induce the emergence of drug-resistant bacteria and bioaccumulation in the food chain. Exploring efficient and environmentally friendly methods to remove pollutants from water has become particularly urgent.

[0003] Photoelectrocatalysis (PEC) technology, which leverages the advantages of both photocatalysis and electrocatalysis, utilizes an electric field to promote electron migration and further hinder the recombination of photogenerated carriers. By applying an external bias voltage, combining electrochemical methods with traditional physical or chemical modification procedures for photocatalysts can significantly improve overall catalytic efficiency.

[0004] For example, the applicant disclosed a self-biased dual-photoelectrode system in a previous invention patent application (publication number CN109160575A), in which the dual photoelectrodes include a photocathode and a photoanode; the photocathode is an N-Zn-MOF photocathode, and the photoanode is an Fe-MOF photoanode. In the self-biased dual-photoelectrode system disclosed in publication number CN 113277594A, the dual photoelectrodes include a photocathode and a photoanode, with the photoanode being a BiVO4 / NH2MIL125 photoanode and the photocathode being a NiO photocathode. However, the performance of these systems is generally low, only capable of processing μM concentrations of Cr(VI), and unable to effectively process high concentrations (mM) of pollutants. Summary of the Invention

[0005] This application constructs a three-electrode system based on a dual-photoelectrode system by adding a carbon-containing electrode as the cathode. The research revealed that for direct anodic reactions, the removal rate of sparingly soluble compounds increases when a highly oxidizing anode is used, and the generated ·OH induces oxidation reactions. Furthermore, the reduction of dissolved oxygen to form H₂O₂ is only efficiently achieved on certain cathode materials (including mercury, gold, or carbon). Therefore, this application aims to generate H₂O₂ by adding a carbon-containing electrode to the cathode. The H₂O₂ generated in the system cannot directly participate in the degradation of pollutants; instead, an activation process is required to convert it into oxidative free radicals. This activation can be achieved through a Fenton-like reaction induced by photo-promoted Fe(III) / Fe(II) cycles. Additionally, using an iron-containing electrode can help reduce pollution in the treated water.

[0006] Metal-organic frameworks (MOFs) have become an attractive class of porous hybrid materials. In recent decades, iron-based MOFs (Fe-MOFs) have received increasing attention because Fe is non-toxic, abundant in crustal minerals, and often proven to be a catalytically active center. The corresponding mechanism is mainly related to the photoexcitation of Fe-O clusters and the transfer of electrons from O(II) to Fe(III). The treatment system of this application, in a visible light-driven photo-Fenton system, allows Fe(III) in Fe-MOFs to be reduced to Fe(II), and can be efficiently used to treat complex water pollution.

[0007] Dopamine (DA) can self-assemble to form tightly adhered polydopamine (PDA) films on the surfaces of most solid materials, especially under mild reaction conditions and with simple operation. In metallic systems, PDA plays multiple roles under light, acting as a light-absorbing substance, an electron transport acceptor, and an adhesion interface, thereby enhancing photocatalytic activity.

[0008] Ni-MOF materials have attracted much attention due to their relative stability, low cost, and non-toxicity, as well as their excellent performance in lithium-ion batteries and catalysis. Nickel, a transition metal, serves as an excellent redox active site, exhibiting superior electrochemical and redox properties compared to other elements. However, the photocatalytic activity of pure Ni-MOFs is limited by the ease with which photogenerated carriers recombine. PDA modification can enhance the photoelectrocatalytic activity of Ni-MOFs by accelerating the transfer of photogenerated electrons and increasing light absorption.

[0009] Titanium dioxide (TiO2) has been widely used as an excellent catalyst material due to its advantages such as simple preparation, low cost, large active sites, and non-toxicity. However, TiO2 nanoparticles are prone to aggregation, have small size, and are difficult to recycle, which reduces their photocatalytic efficiency and causes secondary pollution. A multilayered, sheet-like two-dimensional Ni-MOF is used to support TiO2 nanoparticles, forming a non-uniform hierarchical structure. The high specific surface area of ​​Ni-MOF enhances the photodegradation ability of TiO2, thereby improving the overall photoelectrocatalytic performance of the system.

[0010] Furthermore, the water stability of MOF materials has long been considered crucial for their practical applications. Numerous studies have shown that the hydrolytic stability of MOFs can be enhanced by improving the hydrophobicity of their internal pore surfaces and / or external crystal surfaces. By loading a hydrophobic coating onto the electrode surface, a waterproof surface and inherent porosity can be provided, enabling the electrode to be used more broadly in fields such as wastewater treatment and fuel purification. Polytetrafluoroethylene (PTFE) possesses excellent acid and alkali resistance, high-temperature resistance, corrosion resistance, and a low coefficient of friction. Immersing the synthesized electrode in a PTFE solution significantly improves the electrode's hydrophobicity and stability.

[0011] Based on the above analysis, this application provides a method for constructing a three-electrode photoelectrocatalytic system, including a high-efficiency hydrogen peroxide generation unit: PTFE / TiO2 / Ni-MOF / PDA@C cathode; a high-efficiency hydrogen peroxide activation unit: MIL-101(Fe)-CC photocathode and WO3 photoanode, and provides the application of this system in the removal of Cr(VI) and CIP.

[0012] A three-electrode photoelectrocatalytic device based on dual photoelectrodes includes a main reaction cell, an electrode fixing cover, and wires. It also includes a photoanode, a photocathode, and an electrocathode placed on the electrode fixing cover and extending into the main reaction cell. The photoanode is connected to the positive output terminal of a power supply via wires, and the photocathode and electrocathode are respectively connected to the cathode output terminal of the power supply via wires.

[0013] The photoanode is a WO3 electrode;

[0014] The photocathode is a MIL-101(Fe)-CC electrode;

[0015] The cathode is a PTFE / TiO2 / Ni-MOF / PDA@C electrode;

[0016] The fabrication process of the PTFE / TiO2 / Ni-MOF / PDA@C electrode includes:

[0017] (1) Dissolve dopamine hydrochloride (PDA) in Tris-HCl aqueous solution to obtain solution A. Place carbon cloth or carbon felt in solution A and sonicate to obtain PDA@C.

[0018] (2) Dissolve nickel chloride hexahydrate, terephthalic acid and polyvinylpyrrolidone in ethanol to obtain solution B. Immerse the dried PDA@C in solution B and add sodium hydroxide solution dropwise. Heat in a water bath. The electrode obtained after the reaction is denoted as Ni-MOF / PDA@C.

[0019] (3) TiO2 nanoparticles and dopamine hydrochloride (PDA) are uniformly dispersed in Tris-HCl aqueous solution to obtain solution C. The Ni-MOF / PDA@C is immersed in solution C and heated in a water bath. The electrode obtained after the reaction is named TiO2 / Ni-MOF / PDA@C.

[0020] (4) The TiO2 / Ni-MOF / PDA@C is immersed in a polytetrafluoroethylene dispersion suspension. After the reaction is completed, the electrode is dried to obtain the PTFE / TiO2 / Ni-MOF / PDA@C.

[0021] In the three-electrode system constructed in this application, upon light irradiation, the photoanode generates photocharge, and photogenerated electrons are transferred to the cathode via an applied bias voltage, activating molecular oxygen to generate H₂O₂. The generated H₂O₂ is then activated through multiple pathways to form ·OH reaction species: Fe 2+ The electrode binds to H₂O₂ via a Fenton-like mechanism, which is a key source of ·OH. Simultaneously, photo-excited electrons at the electrode can also reduce H₂O₂ to release ·OH. Furthermore, photo-excited electrons can preemptively bind Fe. 2+ Converted to Fe 3+ Accelerate Fe 2+ / Fe 3+ The continuous cycle of photoelectrons promotes the stable conversion of H2O2 into ·OH, while the continuous consumption of photoelectrons, in turn, facilitates the effective separation of photogenerated electron-hole pairs. Consequently, contaminants such as Cr(VI) and CIP in the solution are removed via ·OH. In this way, each electrode has its independent function while working synergistically, resulting in simple and efficient operation. This avoids the problems associated with the difficult recovery of traditional powder photocatalysts.

[0022] Several alternative methods are provided below, but they are not intended as additional limitations on the overall solution above. They are merely further additions or optimizations. Provided there are no technical or logical contradictions, each alternative method can be combined individually with respect to the overall solution above, or multiple alternative methods can be combined with each other.

[0023] Optionally, the electrodes prepared in each step are dried at room temperature before proceeding to the next step.

[0024] Optionally, in solution A, the mass-to-volume ratio of dopamine hydrochloride to Tris-HCl aqueous solution is 0.1g-0.2g:90mL-180mL; the concentration of the Tris-HCl aqueous solution is 10mM and pH=8.5.

[0025] Furthermore, in solution A, the mass-to-volume ratio of dopamine hydrochloride and Tris-HCl aqueous solution is 0.1 g: 90 mL.

[0026] Optionally, in solution B, the mass-to-volume ratio of nickel chloride hexahydrate, terephthalic acid, polyvinylpyrrolidone, and ethanol is 0.89g–1.78g: 0.623g–1.246g: 0.5g–1g: 40mL–80mL; and the ethanol is anhydrous ethanol.

[0027] Furthermore, in solution B, the mass-to-volume ratio of nickel chloride hexahydrate, terephthalic acid, polyvinylpyrrolidone, and ethanol is 0.89 g: 0.623 g: 0.5 g: 40 mL.

[0028] Optionally, in solution C, the mass-to-volume ratio of titanium dioxide, dopamine hydrochloride, and Tris-HCl aqueous solution is 0.025g–0.05g: 0.05g–0.1g: 50mL–100mL; the concentration of the Tris-HCl aqueous solution is 10mM and the pH is 8.5.

[0029] Furthermore, in solution C, the mass-to-volume ratio of titanium dioxide, dopamine hydrochloride, and Tris-HCl aqueous solution is 0.025 g: 0.05 g: 50 mL.

[0030] Optionally, the polytetrafluoroethylene dispersion suspension contains 2% polytetrafluoroethylene by mass.

[0031] Optionally, in step (2), the water bath heating conditions are: heating at 40-60℃ for 3-5 hours. Further, water bath heating at 50℃ for 4 hours.

[0032] Optionally, in step (3), the water bath heating conditions are: heating at 40–60°C for 0.5–1.5 hours. Further, heating at 50°C for 1 hour.

[0033] Optionally, the concentration of the sodium hydroxide solution is 1–1.5 mol / L (preferably 1.25 mol / L); the volume ratio of the added sodium hydroxide solution to ethanol is 1:4. Polyvinylpyrrolidone contains an amide structure in its molecular structure, which can be hydrolyzed in sodium hydroxide solution to the corresponding amine and sodium carboxylate salts.

[0034] Optionally, the carbon cloth or carbon felt used should be 2×2cm in size. 2 .

[0035] Optionally, the WO3 electrode is prepared as follows:

[0036] Sodium tungstate dihydrate was dissolved in deionized water, and then hydrochloric acid was added dropwise to obtain a mixture that produced a white precipitate. Simultaneously, ammonium oxalate monohydrate was dissolved in deionized water and stirred at room temperature to obtain an ammonium oxalate solution. The ammonium oxalate solution was added to the mixture and stirred continuously to obtain a transparent solution D. Solution D was then transferred to a polytetrafluoroethylene (PTFE) liner, and FTO (Fluoropolymer Oxide) was immersed with its conductive side facing down and leaned against the inner wall of the PTFE container for hydrothermal reaction. After the hydrothermal reaction was completed and the FTO was dried, it was placed in a muffle furnace for annealing, and the resulting material was the WO3 electrode.

[0037] Optionally, when preparing solution D, the mass-to-volume ratio of sodium tungstate dihydrate, ammonium oxalate monohydrate, and deionized water is 0.250 g–0.5 g : 0.235 g–0.47 g : 30 mL–60 mL. The deionized water refers to the total amount of deionized water in mixture D.

[0038] Furthermore, when preparing solution D, the mass-volume ratio of sodium tungstate dihydrate, ammonium oxalate monohydrate, and deionized water is 0.250 g: 0.235 g: 30 mL.

[0039] Optionally, when preparing the photoelectric anode, the hydrothermal reaction temperature is 140℃~150℃, the reaction time is 8h~10h, the annealing temperature is 500℃~550℃, and the annealing time is 60min~90min.

[0040] Optionally, when fabricating the photoanode, the FTO has a size of 2×5cm. 2 Thickness 2.2mm, resistance 7 ohms; WO3 growth area 2×2cm 2 .

[0041] Optionally, the preparation of the MIL-101(Fe)-CC electrode:

[0042] Ferric chloride hexahydrate and terephthalic acid were mixed in N,N-dimethylformamide to obtain a deep orange solution E. The obtained deep orange solution E was transferred to a polytetrafluoroethylene liner and subjected to a hydrothermal reaction. After the reaction was completed, the solution was vacuum dried to obtain MIL-101(Fe) powder. The obtained MIL-101(Fe) powder was added to a mixed solution of ethanol, water and Nafion solution, ultrasonically dispersed, and then drop-coated onto carbon cloth to obtain the MIL-101(Fe)-CC electrode.

[0043] Optionally, when preparing solution E, the mass-to-volume ratio of ferric chloride hexahydrate, terephthalic acid, and N,N-dimethylformamide is: 0.675g~1.35g : 0.206g~0.412g : 15mL~30mL.

[0044] Furthermore, when preparing solution E, the mass-to-volume ratio of ferric chloride hexahydrate, terephthalic acid, and N,N-dimethylformamide is 0.675 g : 0.206 g : 15 mL.

[0045] Optionally, the mass-to-volume ratio of MIL-101(Fe) powder to ethanol, water and Nafion solution is 3 mg MIL-101(Fe): 250 μL ethanol: 250 μL water: 10 μL Nafion solution.

[0046] Optionally, the ethanol is anhydrous ethanol; the water is deionized water; and the Nafion solution is a 5% Nafion ethanol solution.

[0047] Optionally, when preparing the photocathode, the hydrothermal reaction temperature is 100℃~120℃ and the reaction time is 20h~24h.

[0048] Optionally, the photoanode and photocathode are placed side by side on the battery fixing cover, with the photocathode placed parallel to the rear side of the photocathode; the load surfaces of the photocathode and photoanode both face the visible light source, and the incident visible light rays penetrate the photocathode and photoanode perpendicularly; and the distance between the photocathode and photoanode is 0.3cm to 0.5cm.

[0049] Optionally, the load surfaces of the photoanode and photocathode are located in the same row, and the photocathode and photocathode are located in the same column.

[0050] Optionally, the distance between the electric cathode and the photocathode is 0.4 to 0.6 cm, preferably 0.5 cm.

[0051] Most preferably, the photoanode is prepared by the following method:

[0052] 0.250 g of sodium tungstate dihydrate was dissolved in 30 mL of deionized water; then 10 mL of 3M hydrochloric acid was added dropwise to obtain a white precipitate; simultaneously, 0.235 g of ammonium oxalate monohydrate was dissolved in 30 mL of deionized water and stirred at room temperature for 30 min; the solution was added to the white precipitate and stirred continuously for 1 h to obtain a transparent solution; then this solution was transferred to a 100 mL polytetrafluoroethylene (PTFE) liner; the FTO conductive glass was ultrasonically cleaned sequentially with acetone, ethanol, and deionized water, and finally dried, then immersed and leaned against the inner wall of the PTFE container with the conductive side facing down; it was sealed and placed in an oven and reacted at 140 °C for 8 h; the dried FTO was then annealed in a muffle furnace at 500 °C for 1 h to obtain the WO3 film.

[0053] Most preferably, the method for preparing the photocathode is as follows:

[0054] 0.675 g of ferric chloride hexahydrate and 0.206 g of terephthalic acid were mixed in 15 mL of N,N-dimethylformamide and then sonicated for 15 min to ensure dissolution. The resulting deep orange solution was transferred to a polytetrafluoroethylene liner and heated in an oven at 110 °C for 20 h. The solid product was obtained by centrifugation and washed twice with N,N-dimethylformamide and ethanol, respectively. Finally, the product was vacuum dried overnight at 60 °C to obtain MIL-101(Fe). 3 mg of MIL-101(Fe) was added to 250 μL of ethanol, 250 μL of water and 10 μL of Nafion solution and sonicated for 40 min. 80 μL of the sonicated solution was drop-coated onto a 2 × 2 cm carbon cloth, and the drop-coating was repeated four times to obtain the MIL-101(Fe)-CC cathode.

[0055] Most preferably, the method for preparing the cathode is as follows:

[0056] (1) Place the carbon felt (2cm×2cm) in 90mL of Tris-HCl aqueous solution (10mM, pH=8.5) containing dopamine hydrochloride (0.1g), sonicate for 15min, and label it as PDA@C);

[0057] (2) The dried PDA@C was immersed in a 40 mL ethanol solution containing nickel chloride hexahydrate (3.75 mmol), terephthalic acid (3.75 mol) and polyvinylpyrrolidone (0.5 g). 10 mL of 1.25 mol / L sodium hydroxide solution was added dropwise to the above solution. The solution was then heated in a water bath at 50 °C for 4 h and labeled as Ni-MOF / PDA@C.

[0058] (3) Titanium dioxide nanoparticles (0.025 g) and dopamine hydrochloride (0.05 g) were uniformly dispersed in 50 mL of Tris-HCl aqueous solution (10 mM, pH = 8.5); Ni-MOF / PDA@C was immersed in the prepared solution and heated at 50 °C for 1 h, and labeled as TiO2 / Ni-MOF / PDA@C;

[0059] (4) Immerse TiO2 / Ni-MOF / PDA@C in a 2% polytetrafluoroethylene dispersion suspension solution for 1 hour, and after drying, label it as PTFE / TiO2 / Ni-MOF / PDA@C.

[0060] This application also provides a method for treating heavy metals and organic pollutants in wastewater using the aforementioned three-electrode photoelectrocatalytic device, wherein the heavy metal is Cr(VI) and the organic pollutant is at least one selected from ciprofloxacin, tetracycline hydrochloride, norfloxacin, and phenol, comprising:

[0061] Wastewater containing the heavy metals and organic pollutants is placed in the main reaction tank. The photoanode, photocathode, and electrocathode are fixed on the electrode fixing cover and connected to the power source with wires. Sodium sulfate buffer solution is used as electrolyte. The mixture is stirred in the dark until adsorption equilibrium is reached. Then, the visible light source and the power source are turned on simultaneously to photocatalytically degrade the heavy metals and pollutants.

[0062] Optionally, the distance between the photoanode and the photocathode is 0.3cm to 0.5cm.

[0063] Optionally, the organic pollutant is ciprofloxacin or tetracycline hydrochloride.

[0064] Optionally, the visible light illuminance is 80 mW / cm². 2 ~120mW / cm 2 .

[0065] Optionally, the applied voltage is 0.1-2V.

[0066] Optionally, stirring in the dark until adsorption equilibrium is reached takes about 30 minutes.

[0067] Optionally, the duration of visible light irradiation and simultaneous application of voltage is 30–120 min.

[0068] Optionally, the concentration of Cr(VI) in the wastewater is 80 μM to 1 mM, the concentration of organic pollutants is 10 mg / L to 40 mg / L, and the concentration of the sodium sulfate buffer solution is 0.1 M.

[0069] Optionally, when treating wastewater containing hexavalent chromium, the pH value needs to be adjusted to 3, while the original pH value is 5-6.

[0070] Furthermore, the light source is a 300W xenon lamp, and the light intensity is adjusted to 100mW / cm². 2 An additional 2V bias voltage is applied.

[0071] Optionally, the H2O2 concentration of the system can be determined using the DPD (N,N-diethyl-p-phenylenediamine) / POD (horseradish peroxidase) method.

[0072] Optionally, the content of hexavalent chromium in the solution is determined by diphenylcarbazide spectrophotometry. The content of ciprofloxacin is detected by high-performance liquid chromatography.

[0073] The purpose of this application is to construct a three-electrode photoelectrocatalytic system, in which the three electrodes have different functions. Hydrogen peroxide is generated through the PTFE / TiO2 / Ni-MOF / PDA@C photocathode, and the hydrogen peroxide is activated through the MIL-101(Fe)-CC photocathode to generate ·OH. The ·OH is then used to remove hexavalent chromium and ciprofloxacin from the solution. This provides a novel method for treating pollutants, with better versatility and practicality.

[0074] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0075] (1) Unlike traditional dual-electrode systems, this application separates the hydrogen peroxide generation unit and the activation unit, and hydrogen peroxide can be generated or activated in a directional manner by adding or removing electrodes.

[0076] (2) The three-electrode system constructed in this application has high photoelectrocatalytic performance and is easy to recycle.

[0077] (3) The three-electrode system constructed in this application mainly uses ·OH to remove hexavalent chromium and ciprofloxacin from the solution without the need to add sacrificial agents, providing a new method for treating pollutants.

[0078] (4) The three-electrode system constructed in this application can efficiently treat high-concentration Cr(VI) wastewater at the mM level, and can remove 100% of Cr(VI) from 1mM (57.5mg / L) wastewater within 1 hour. Attached Figure Description

[0079] Figure 1 and Figure 2 The images show a top view and a 3D structural schematic diagram of the WO3|MIL-101(Fe)-CC|PTFE / TiO2 / Ni-MOF / PDA@C three-electrode system of this application.

[0080] Figure 3 Photocurrent curves at different fabrication stages of the cathode PTFE / TiO2 / Ni-MOF / PDA@C in this application.

[0081] Figure 4 This is a bar chart showing the hydrogen peroxide generation at the photoanode and different cathodes in this application.

[0082] Figure 5 This is a bar chart showing the removal of hexavalent chromium from the photoanode and different cathodes in this application.

[0083] Figure 6 This is a bar chart showing the removal of ciprofloxacin from the photoanode and different cathodes in this application.

[0084] Figure 7 This is a bar chart showing the removal of hexavalent chromium at different concentrations in the three-electrode system of this application.

[0085] Figure 8 This is a bar chart showing the removal of different organic pollutants in the three-electrode system of this application.

[0086] Figure 9 This is a bar chart of the hexavalent chromium removal cycle experiment of the three-electrode system of this application. Detailed Implementation

[0087] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0088] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0089] This application provides a method for constructing a three-electrode photoelectrocatalytic system. The three-electrode system includes a main reaction cell, an electrode fixing cap 1, wires, a photoanode 2, a photocathode 3, and an electrode cathode 4. The three-electrode system includes a high-efficiency hydrogen peroxide generation unit: a PTFE / TiO2 / Ni-MOF / PDA@C electrode cathode; a high-efficiency hydrogen peroxide activation unit: a MIL-101(Fe)-CC photocathode and a WO3 photoanode; and provides the application of this system in the removal of Cr(VI) and CIP. The photoanode and photocathode are placed side-by-side on the battery fixing cap, and the electrode cathode is placed parallel to the rear of the photocathode; the photoanode is connected to the positive terminal of the power supply via wires, and the photocathode and electrode cathode are respectively connected to the cathode of the power supply via wires, as shown below. Figure 1 and Figure 2 As shown.

[0090] Cr(VI) solution and ciprofloxacin (CIP) solution were used as target pollutants. A three-electrode system was constructed using WO3 as the photoanode, PTFE / TiO2 / Ni-MOF / PDA@C (cathode), and MIL-101(Fe)-CC (photocathode) as dual cathodes. The reaction was carried out in a 50 mL transparent quartz reactor using a 300 W xenon lamp as the light source, with the light intensity adjusted to 100 mW / cm². 2An external bias voltage of 2V was applied, and the electrolyte was a 0.1M Na₂SO₄ solution. The initial Cr(VI) concentration was set to 1mM, and the solution pH was set to 3; the initial CIP concentration was 10mg / L, and the pH was not adjusted. After a dark reaction of 30 min, the lamp was turned on and the voltage was applied. Cr(VI) was determined by diphenylcarbazide spectrophotometry, and the CIP concentration was determined by high-performance liquid chromatography.

[0091] The following is a description using specific embodiments:

[0092] Example 1

[0093] The construction of a three-electrode photoelectrocatalytic system is as follows. The raw materials used in the examples are all commercially available products and have not undergone further purification.

[0094] The preparation method of WO3 photoelectric anode is as follows:

[0095] 0.250 g of sodium tungstate dihydrate was dissolved in 30 mL of deionized water, and then 10 mL of 3M hydrochloric acid was added dropwise to obtain a white precipitate. Simultaneously, 0.235 g of ammonium oxalate monohydrate was dissolved in 30 mL of deionized water and stirred at room temperature for 30 min. The resulting solution was added to the white precipitate, and the mixture was stirred continuously for 1 h to obtain a transparent solution. This transparent solution was then transferred to a 100 mL polytetrafluoroethylene (PTFE) liner. The FTO conductive glass was ultrasonically cleaned sequentially with acetone, ethanol, and deionized water, and then dried. It was then immersed in the PTFE container and leaned against the inner wall with the conductive side facing down. The container was sealed and placed in an oven at 140 °C for 8 h. The dried FTO was then annealed in a muffle furnace at 500 °C for 1 h to obtain a WO3 thin film, which is the WO3 photoanode.

[0096] The preparation method of MIL-101(Fe)-CC photocathode is as follows:

[0097] 0.675 g of ferric chloride hexahydrate and 0.206 g of terephthalic acid were mixed in 15 mL of N,N-dimethylformamide and then sonicated for 15 min to ensure dissolution. The resulting deep orange solution was transferred to a polytetrafluoroethylene liner and heated in an oven at 110 °C for 20 h. The solid product was obtained by centrifugation and washed twice with N,N-dimethylformamide and ethanol, respectively. Finally, the product was vacuum dried overnight at 60 °C to obtain MIL-101(Fe).

[0098] Add 3 mg of MIL-101(Fe) to a mixed solution of 250 μL ethanol, 250 μL water and 10 μL Nafion, and sonicate for 40 min. Take 80 μL of the sonicated solution and drop it onto a 2×2 cm carbon cloth, repeating the dropping process four times to obtain a MIL-101(Fe)-CC cathode.

[0099] The preparation method of PTFE / TiO2 / Ni-MOF / PDA@C cathode is as follows:

[0100] (1) Place the carbon felt (2cm×2cm) in 90mL of Tris-HCl aqueous solution (10mM, pH=8.5) containing dopamine hydrochloride (0.1g), sonicate for 15min, and label it as PDA@C.

[0101] (2) PDA@C dried at room temperature for 12 h was immersed in 40 mL of ethanol solution containing nickel chloride hexahydrate (3.75 mmol), terephthalic acid (3.75 mol) and polyvinylpyrrolidone (0.5 g), and 1.25 mol / L sodium hydroxide solution (10 mL) was added dropwise to the above solution. Then it was heated in a water bath at 50 °C for 4 h and labeled as Ni-MOF / PDA@C.

[0102] (3) Titanium dioxide nanoparticles (0.025 g) and dopamine hydrochloride (0.05 g) were uniformly dispersed in 50 mL of Tris-HCl aqueous solution (10 mM, pH = 8.5). The Ni-MOF / PDA@C obtained in step (2) was dried at room temperature for 12 h, immersed in the solution prepared in this step, and heated at 50 °C for 1 h, and labeled as TiO2 / Ni-MOF / PDA@C.

[0103] (4) The TiO2 / Ni-MOF / PDA@C was dried at room temperature for 12 hours and then immersed in a 2% polytetrafluoroethylene dispersion suspension solution for 1 hour. After drying, it was labeled as PTFE / TiO2 / Ni-MOF / PDA@C.

[0104] Example 2

[0105] Using the cathodes from different preparation stages in Example 1 as working electrodes, platinum sheets as counter electrodes, and Ag / AgCl electrodes as reference electrodes, the transient photocurrent responses of different electrodes were tested. Figure 3 With the loading of Ni-MOF and TiO2, the photocurrent gradually increases, and with the introduction of the hydrophobic coating PTFE, its photoelectric properties are further improved. This shows that the loading of the hydrophobic coating can significantly enhance the photoelectric performance of the electrode, further proving the rapid separation of photoexcited charge carriers.

[0106] The PTFE / TiO2 / Ni-MOF / PDA@C cathode prepared in this application exhibits a photocurrent of 11 μA / cm in a 0.1 M Na2SO4-Na2SO3 mixed solution. 2 This is significantly higher than the photocurrent of 0.06 μA / cm² of the N-Zn-MOF-0.5 cathode (CN109160575A). 2 .

[0107] Example 3

[0108] Adopting such Figure 1 and Figure 2 The three-electrode system shown investigated the H2O2 production of different electrode systems, and the results are as follows: Figure 4 As shown, by coating the catalyst surface with the hydrophobic polymer PTFE, more O2 can be captured near the active sites, thus achieving a high H2O2 yield. However, due to the activation effect of MIL-101(Fe), the H2O2 yield of the WO3|MIL-101(Fe)-CC system is only 37 μM. In the three-electrode system, hydrogen peroxide is continuously generated and activated through the cathode and photocathode, ultimately resulting in an H2O2 yield of 190 μM.

[0109] Example 4

[0110] Targeting Cr(VI) and CIP as pollutants, the following methods were employed: Figure 1 and Figure 2 The apparatus shown was used to test the reducing and oxidizing properties of the system. The initial Cr(VI) concentration was 1 mM, and the solution pH was 3; the initial CIP concentration was 10 mg / L, and the pH was not adjusted. The results are as follows: Figure 5 and Figure 6 As shown, the three-electrode system can completely remove contaminants within the reaction time. However, when the H2O2 production unit (PTFE / TiO2 / Ni-MOF / PDA@C) or the H2O2 activation unit (MIL-101(Fe)-CC) is missing, the catalytic efficiency of the system decreases significantly, demonstrating the superiority of the system in this application.

[0111] Example 5

[0112] Adopting such Figure 1 and Figure 2 The three-electrode system shown was used to investigate the reducing power of the system for Cr(VI) solutions of different concentrations. The results are as follows: Figure 7 The reducing power gradually increases with increasing Cr(VI) concentration. Without the addition of any sacrificial agent, this three-electrode system can effectively reduce 100% of an 80 μM Cr(VI) solution within 30 min; and can remove 100% of a 1 mM (57.5 mg / L) Cr(VI) solution within 1 h.

[0113] Meanwhile, comparisons revealed that the three-electrode system of this application, under an applied bias voltage of 2V and by adjusting the solution pH to 3, can reduce 98% of 80μM Cr(VI) within 30 minutes without a sacrificial agent, and completely remove 1mM Cr(VI) within 60 minutes. In contrast, the two-electrode system of CN109160575A removes Cr(VI) at a concentration of 60-80μM, requires an irradiation time of 120-180 minutes, and includes 2M EDTA-2Na as a capture agent. The two-electrode system of CN 113277594A removes Cr(VI) at a concentration of 20-160μM, requires an irradiation time of 120-300 minutes, and requires 120 minutes to completely remove 80μM Cr(VI) at pH=3. Therefore, overall, the three-electrode system constructed in this application exhibits significantly improved photoelectrocatalytic performance.

[0114] Example 6

[0115] To further verify the oxidation performance of the three-electrode system of this application, the oxidation capacity of the system for phenol, tetracycline hydrochloride, and norfloxacin was tested, with the concentration of the pollutants fixed at 10 mg / L. The results are as follows: Figure 8 As shown, within 120 minutes, the system exhibited high removal efficiency for pollutants, completely removing ciprofloxacin and tetracycline hydrochloride, removing 90% of norfloxacin, and even achieving an 80% removal rate for phenol. The overall photoelectrocatalytic performance was significantly improved.

[0116] Example 7

[0117] To investigate the reusability and stability of the WO3|MIL-101(Fe)-CC|PTFE / TiO2 / Ni-MOF / PDA@C system of this application, ten consecutive Cr(VI) reduction experiments were conducted, and the results are as follows: Figure 9 As shown in the figure. After each reaction, the electrode was washed with deionized water and dried. The electrode exhibited good stability, decreasing by only 7% after ten reactions, indicating the high chemical stability of the system.

[0118] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A three-electrode photoelectrocatalytic device based on dual photoelectrodes, comprising a main reaction cell, an electrode fixing cover, and wires, characterized in that, It also includes a photoanode, a photocathode, and an electric cathode placed on the electrode fixing cover and extending into the main reaction tank. The photoanode is connected to the positive output terminal of the power supply through a wire, and the photocathode and the electric cathode are respectively connected to the cathode output terminal of the power supply through wires. The photoanode is a WO3 electrode; the WO3 electrode is prepared as follows: Sodium tungstate dihydrate was dissolved in deionized water, and then hydrochloric acid was added dropwise to obtain a mixture that produced a white precipitate; at the same time, ammonium oxalate monohydrate was dissolved in deionized water and stirred at room temperature to obtain an ammonium oxalate solution. Ammonium oxalate solution was added to the mixture, and the mixture was stirred continuously to obtain a transparent solution D; The solution D is then transferred to a polytetrafluoroethylene (PTFE) liner. The FTO is then immersed with its conductive side facing down and leaned against the inner wall of the PTFE container for hydrothermal reaction. After the hydrothermal reaction is completed and the FTO is dried, it is placed in a muffle furnace for annealing. The resulting material is the WO3 electrode. The photocathode is a MIL-101(Fe)-CC electrode; the preparation of the MIL-101(Fe)-CC electrode: Ferric chloride hexahydrate and terephthalic acid were mixed in N,N-dimethylformamide to obtain a deep orange solution E. The obtained deep orange solution E was transferred to a polytetrafluoroethylene liner and subjected to a hydrothermal reaction. After the reaction was completed, the solution was dried under vacuum to obtain MIL-101(Fe) powder. The obtained MIL-101(Fe) powder was added to a mixed solution of ethanol, water and Nafion solution, ultrasonically dispersed and then drop-coated onto carbon cloth to obtain the MIL-101(Fe)-CC electrode. The cathode is a PTFE / TiO2 / Ni-MOF / PDA@C electrode; The fabrication process of the PTFE / TiO2 / Ni-MOF / PDA@C electrode includes: (1) Dissolve dopamine hydrochloride PDA in Tris-HCl aqueous solution to obtain solution A. Place carbon cloth or carbon felt in solution A and sonicate to obtain PDA@C. (2) Dissolve nickel chloride hexahydrate, terephthalic acid and polyvinylpyrrolidone in ethanol to obtain solution B. Immerse the dried PDA@C in solution B and add sodium hydroxide solution. Heat in a water bath. The electrode obtained after the reaction is named Ni-MOF / PDA@C. (3) TiO2 nanoparticles and dopamine hydrochloride PDA are uniformly dispersed in Tris-HCl aqueous solution to obtain solution C. The Ni-MOF / PDA@C is immersed in solution C and heated in a water bath. The electrode obtained after the reaction is named TiO2 / Ni-MOF / PDA@C. (4) The TiO2 / Ni-MOF / PDA@C is immersed in a polytetrafluoroethylene dispersion suspension. After the reaction is completed, the electrode is dried to obtain the PTFE / TiO2 / Ni-MOF / PDA@C electrode. In solution A, the mass-to-volume ratio of dopamine hydrochloride to Tris-HCl aqueous solution is 0.1 g~0.2 g: 90 mL~180 mL; the concentration of the Tris-HCl aqueous solution is 10 mM and the pH is 8.

5. In solution B, the mass-to-volume ratio of nickel chloride hexahydrate, terephthalic acid, polyvinylpyrrolidone, and ethanol is 0.89 g~1.78 g : 0.623 g~1.246 g : 0.5 g~1 g : 40 mL~80 mL; the ethanol is anhydrous ethanol; the concentration of the sodium hydroxide solution is 1~1.5 mol / L; the volume ratio of sodium hydroxide solution added to ethanol is 1:

4. In solution C, the mass-to-volume ratio of titanium dioxide, dopamine hydrochloride, and Tris-HCl aqueous solution is 0.025 g~0.05 g : 0.05 g~0.1 g : 50 mL~100 mL; the concentration of the Tris-HCl aqueous solution is 10 mM and the pH is 8.

5. The polytetrafluoroethylene dispersion suspension contains 2% polytetrafluoroethylene by mass.

2. The three-electrode photoelectrocatalytic device according to claim 1, characterized in that, In step (2): the water bath heating conditions are: heating at 40~60℃ for 3~5 hours; In step (3), the conditions for water bath heating are: heating at 40~60℃ for 0.5~1.5h.

3. The three-electrode photoelectrocatalytic device according to claim 1, characterized in that, The photocathode and photoelectrode are placed side by side on the battery cover, with the photoelectrode placed parallel to the rear of the photocathode. The load surfaces of both the photocathode and photoanode face the visible light source, and the incident visible light rays penetrate the photocathode and photoanode perpendicularly. The distance between the photocathode and photoanode is 0.3 cm to 0.5 cm.

4. A method for treating heavy metals and organic pollutants in wastewater using the three-electrode photoelectrocatalytic device of claim 1, wherein the heavy metal is Cr(VI) and the organic pollutant is at least one selected from ciprofloxacin, tetracycline hydrochloride, norfloxacin, and phenol, characterized in that... include: Wastewater containing the heavy metals and organic pollutants is placed in the main reaction tank. The photoanode, photocathode, and electrocathode are fixed on the electrode fixing cover and connected to the power supply with wires. Sodium sulfate buffer solution is used as electrolyte. The mixture is stirred in the dark until adsorption equilibrium is reached. Then, the visible light source and power supply are turned on to photocatalytically degrade the heavy metals and pollutants.

5. The method according to claim 4, characterized in that, The distance between the photoanode and the photocathode is 0.3 cm to 0.5 cm.

6. The method according to claim 4, characterized in that, The organic pollutant is ciprofloxacin or tetracycline hydrochloride.

7. The method according to claim 4, characterized in that, Visible light intensity is 80 mW / cm 2 ~120 mW / cm 2 The applied voltage is 0-2 V; The visible light irradiation time and voltage application time are 30~120 min.

8. The method according to claim 4, characterized in that, The concentration of Cr(VI) in the wastewater is 80 μM to 1 mM, the concentration of organic pollutants is 10 mg / L to 40 mg / L, and the concentration of the sodium sulfate buffer solution is 0.1 M.

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