A method for removing organic matter from water using an electrochemically coupled ozone system based on LDH-loaded graphite felt cathode

Abstract

The present invention discloses a method for removing organic matter in water by using an electrochemically coupled ozone system based on an LDH-loaded graphite felt cathode, comprising: using MFe-LDH / GF as a cathode, wherein M is Cu, Mn, CO or Ni, using a platinum sheet as an anode, the reaction solution comprising pollutants and an electrolyte, wherein the electrolyte is Na2SO4, adding two electrodes to the reaction solution, and charging gaseous ozone into the reaction solution, adjusting the pH of the reaction solution to 3-9, and charging current into the two electrodes, thereby constructing an electrochemically coupled ozone system to remove pollutants. This method can improve HO • yield, thereby enhancing the removal of organic pollutants.

Description

Technical Field

[0001] The invention belongs to the field of catalytic ozone oxidation and organic matter removal, and particularly relates to a method for removing organic matter in water by using an electrochemically coupled ozone system based on an LDH-loaded graphite felt cathode. Background Art

[0002] With the rapid development of modern industry and the widespread use of chemicals, a large amount of organic wastewater generated by industry, agriculture, medicine, and human activities has not been effectively treated. Discharged into natural water bodies, it has caused serious chemical pollution to available water resources. These synthetic organic pollutants are generally chemically stable, highly toxic, and bioaccumulative, making them difficult to effectively remove through conventional water treatment processes such as flocculation, filtration, and biological action. Advanced oxidation treatment technologies, such as advanced oxidation, are often required to meet treatment requirements.

[0003] Electrochemically coupled ozone technology is an emerging advanced oxidation process for water treatment that combines electrochemistry and ozone. The carbon-based cathode in the system can cleverly reduce O2 in the mixed gas produced by the ozone generator to H2O2, thereby inducing a peroxidation reaction between H2O2 and O3 to generate a large amount of HO • , which makes up for the shortcomings of low electrochemical oxidation treatment efficiency and poor ozone oxidation mineralization rate. In addition, compared with electrochemical oxidation, electro-Fenton oxidation and O3 / H2O2 technologies, electrochemically coupled ozone not only significantly improves the removal efficiency of pollutants, but also reduces the safety risks of H2O2 during transportation and storage, making it a safer and more convenient water treatment technology.

[0004] The invention patent application with publication number CN113184951A discloses a modification method and application of a graphite felt cathode suitable for an electro-ozonation system. The process includes pre-treatment to remove impurities on the surface of the graphite felt, and anodizing the graphite felt in a neutral sodium sulfate electrolyte, thereby increasing the hydrophilicity of the graphite felt and the content of oxygen-containing functional groups on the surface, and increasing the active sites for oxygen reduction to hydrogen peroxide. This increases the production of hydrogen peroxide in the electro-ozonation system and enhances the removal capacity of oxalic acid. It is worth noting that although increasing the content of oxygen-containing functional groups on the surface of the graphite felt will lead to an increase in ozone catalytic sites, the modified graphite felt in the electro-ozonation system is protected by the cathode current, which greatly reduces the corrosion damage of ozone to the electrode surface and enhances the stability of the electrode.

[0005] Publication number CN113371798A discloses a method for removing chemical oxygen demand in wastewater by ozone-coupled electro-Fenton catalysis. In the system for removing chemical oxygen demand in wastewater by electro-Fenton catalysis, the anode uses a passive anode and iron as a contact double anode, and the cathode uses graphite felt; or the anode uses iron as the anode and the cathode uses graphite felt; or the passive anode and the cathode use iron and graphite felt as a contact double cathode. The electrolyte is the sewage to be degraded to construct an electro-Fenton system, a constant direct current is connected externally, and an external ozone generator is used to supply ozone to the cathode.

[0006] However, compared with the carbon cathode material commonly used in the electrochemical coupled ozone technology disclosed in the above patent application, the function is relatively simple, which only plays the role of generating H2O2, and the H2O2 diffused into the solution will inevitably participate in the HO • Therefore, it is necessary to develop a functional carbon cathode that can catalyze H2O2 and O3 to strengthen the electrochemical coupling of the ozone system HO • The yield and utilization rate of the product can be improved, and the removal effect of organic pollutants can be enhanced. Summary of the Invention

[0007] The present invention provides a method for removing organic matter from water by electrochemically coupled ozone system based on LDH loaded graphite felt cathode, which can improve the efficiency of HO • yield, thereby enhancing the removal of organic pollutants.

[0008] The present invention provides a method for removing organic matter in water using an electrochemically coupled ozone system based on an LDH-loaded graphite felt cathode, comprising:

[0009] MFe-LDH / GF is used as the cathode, where M is Cu, Mn, CO or Ni, and a platinum sheet is used as the anode. The reaction solution includes pollutants and an electrolyte, and the electrolyte is Na2SO4. Two electrodes are added to the reaction solution, and gaseous ozone is charged into the reaction solution. The pH of the reaction solution is adjusted to 3-9, and current is charged into the two electrodes to construct an electrochemically coupled ozone system to remove pollutants.

[0010] Preferably, MFe-LDH / GF is used as the cathode, wherein M is Cu. Since Cu has a higher electroactive area, it can more effectively inhibit the generation of H2O2 and generate more O2 •- Reacts with ozone to form more HO • , in order to further improve the removal efficiency of organic matter.

[0011] Preferably, the pH of the reaction solution is 5-7. The present invention controls the pH value of the reaction solution so that an appropriate amount of metal is dissolved to participate in the generation of HO •reaction, while reducing the dissolution of metals due to too low pH values, which can cause structural collapse during long-term catalysis and affect the reaction stability.

[0012] Preferably, the density of the current charged into the two electrodes is 2-5 mA / cm 2 .

[0013] Preferably, the concentration of the gaseous ozone is 15-60 mg / L, and the flow rate of the gaseous ozone is 100-300 mL / min.

[0014] Preferably, in the reaction solution, the concentration of Na2SO4 is 30-70 mmol / L, and the concentration of pollutants is 30-60 mg / L.

[0015] Preferably, the pollutant is oxalic acid, pyruvic acid or acetic acid.

[0016] Since small molecule organic acids (such as oxalic acid, pyruvic acid, and acetic acid) have extremely low reaction rates with ozone and are common degradation products in the treatment of organic wastewater using advanced oxidation technologies, they restrict the degree of mineralization of organic wastewater. Therefore, in the specific embodiment of the present invention, oxalic acid is selected as a model pollutant to evaluate the removal efficiency of organic matter by the electrochemically coupled ozone system.

[0017] Preferably, H2SO4 and NaOH are added to the reaction solution to adjust the pH value, wherein the concentration of H2SO4 is 0.05-0.2 mol / L, and the concentration of NaOH is 0.05-0.2 mol / L.

[0018] Preferably, the preparation method of the MFe-LDH / GF comprises:

[0019] The LDH mother solution was prepared by fully dissolving Fe(NO3)3·9H2O, M(NO3)2·xH2O, CO(NH2)2 and NH4F in ultrapure water, wherein the mass concentrations of Fe(NO3)3·9H2O, M(NO3)2·xH2O, CO(NH2)2 and NH4F were 9-23 g / L, 13-26 g / L, 20-35 g / L and 1-3 g / L, respectively;

[0020] Graphite felt is added to the LDH mother liquor to obtain a mixed solution, and the mixed solution is subjected to a hydrothermal reaction at a temperature of 90-120° C. and a reaction time of 8-16 hours. After the reaction is completed, the MFe-LDH / GF is obtained by suction filtration, washing, and drying.

[0021] The present invention controls the reaction temperature and reaction time to ensure that urea is fully decomposed, avoids the collapse of the layered structure caused by excessively high temperature, and prevents the formation of a large amount of ammonia gas decomposed into a complex with M ions, which is not conducive to the formation of the LDH catalyst. The present invention controls the concentration of each substance input to ensure the formation of LDH crystals and reduce impurity generation and metal outflow.

[0022] Preferably, the present invention achieves the best removal effect on organic pollutants by controlling the molar ratio of Fe and M to 2:1 to 3:1, and the mass concentrations of CO(NH2)2 and NH4F to 28.5 g / L and 2.1 g / L, respectively.

[0023] Preferably, the graphite felt is added to the LDH mother liquor, and the surface of the graphite felt is washed with acetone and ultrapure water in sequence, dried, and baked. The above operations are performed to remove oil stains and impurities on the surface of the graphite felt.

[0024] Preferably, the reacted material is repeatedly ultrasonically cleaned with ethanol and ultrapure water until the cleaning solution is neutral.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention uses MFe-LDH / GF as cathode to inhibit the generation of H2O2 and generate a large amount of O2 •- Instead of H2O2, it reacts with ozone to form HO • , which weakens the effect of H2O2 on HO • At the same time, the present invention controls the pH value of the reaction solution so that part of the metal is dissolved and reacts with ozone to obtain HO • Therefore, based on the above two points, the method provided by the present invention will greatly improve the removal efficiency of organic matter. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 X-ray diffraction patterns of GF and CuFe-LDH / GF cathodes provided in Example 1 of the present invention;

[0028] Figure 2 Scanning electron microscope images of the CuFe-LDH powder and the CuFe-LDH / GF cathode provided in Example 1 of the present invention;

[0029] Figure 3 Schematic diagram of the reaction device of the electrochemically coupled ozone system provided in Example 2 of the present invention;

[0030] Figure 4 Graph showing the effects of ozone oxidation, anodic oxidation, and electrochemically coupled ozone systems with different cathodes on the removal of oxalic acid provided in Examples 2-5 of the present invention and Comparative Examples 1-2;

[0031] Figure 5 The electrochemically active areas of different LDH cathodes provided in Examples 2-5 of the present invention;

[0032] Figure 6 This is a diagram showing the effect of the quenching agent provided in Example 6 of the present invention on the removal efficiency of oxalic acid;

[0033] Figure 7 This is a graph showing the effect of the metal molar ratio and preparation temperature on the oxalic acid removal efficiency provided in Example 7 of the present invention;

[0034] Figure 8 This is a diagram showing the effect of solution pH on oxalic acid removal efficiency provided in Example 8 of the present invention;

[0035] Figure 9 The stability of OA removal by the EP system with CuFe-LDH / GF as cathode provided in Example 9 of the present invention;

[0036] Figure 10 This is a diagram showing the removal effect of dissolved organic carbon in nanofiltration concentrated water by ozone oxidation and electrochemically coupled ozone systems with different cathodes provided in Example 10 of the present invention.

[0037] Specific embodiment

[0038] The layered double hydroxide (LDH) employed in the present invention is a type of octahedral, two-dimensional clay structure with multiple metal layers and adjustable interlayer anions. It has a wide range of applications in catalysis, adsorption, and drug delivery. Therefore, using an LDH-loaded carbon cathode, which boasts high catalytic activity and a large specific surface area, helps enhance the utilization efficiency of H₂O₂ and O₃ in electrochemically coupled ozone systems, promotes the formation of active species, and accelerates the removal of organic pollutants.

[0039] The present invention will be further described and illustrated below with reference to the accompanying drawings and specific embodiments. The technical features of each embodiment of the present invention may be combined accordingly without conflict.

[0040] Example 1

[0041] A CuFe-LDH / GF cathode suitable for an electrochemically coupled ozone system comprises the following synthesis steps:

[0042] (1) Cut the purchased commercial graphite felt into 2 cm × 4 cm pieces and wash them with acetone and ultrapure water for 20 min respectively to remove surface oil and impurities. Then put them into a constant temperature drying oven at 60 °C and dry them for 24 h before use.

[0043] (2) Dissolve 0.808 g Fe(NO3)3·9H2O, 1.449 g Cu(NO3)2·3H2O, 2 g CO(NH2)2, and 0.247 g NH4F in 70 mL of ultrapure water to obtain LDH mother solution.

[0044] (3) Immerse the spare graphite felt in step (1) in the LDH mother liquor in step (2) to expel the bubbles in the pores of the graphite felt. Then transfer the LDH mother liquor and the graphite felt to a stainless steel reactor containing a polytetrafluoroethylene liner and place it in an oven. Set the reaction temperature and time to 90°C and 12 h, respectively. After the reaction, separate the LDH powder and the LDH-loaded graphite felt by filtration, and repeatedly ultrasonically clean the material with ethanol and ultrapure water until the cleaning solution is neutral. Place the cleaned LDH-loaded graphite felt in a vacuum drying oven at 50°C and dry it. It is represented as CuFe-LDH / GF. The cathode has the following characteristics:

[0045] like Figure 1 As shown in the figure, the diffraction peak at 26.3° belongs to the 002 plane of graphite felt (GF), and the diffraction peaks at 11.5°, 23.1°, 34.1°, and 38.7° correspond to the (003), (006), (012), and (015) crystal planes of the CuFe-LDH / GF cathode, respectively, indicating that CuFe-LDH was successfully synthesized and loaded on the graphite felt surface. In addition, Cu2(OH)2CO3 crystals (JCPDF#01-072-8421) were also found on the CuFe-LDH / GF cathode. This is because urea releases CO2 while providing an alkaline source during the hydrothermal synthesis process, resulting in the combination of metal ions and carbonates, thereby forming a malachite structure. Figure 2 (a) and (b) show that the CuFe-LDH powder presents a typical layered structure, which appears as small particles and flakes after being loaded on graphite felt, further indicating that the CuFe-LDH / GF cathode was successfully synthesized.

[0046] Table 1 shows the specific surface area and pore parameters of GF and CuFe-LDH / GF. It can be seen that after GF was modified by CuFe-LDH loading, the BET specific surface area increased by 0.61 m 2 / g, which is beneficial to improving the adsorption capacity of the cathode. In addition, the average pore diameter of GF is small, mainly micropores, while the average pore diameter of CuFe-LDH / GF is large, which is conducive to the diffusion of reactants to the catalytic sites and promotes the mass transfer efficiency between the cathode and the solution.

[0047] Table 1 Specific surface area and pore parameters

[0048] GF CuFe-LDH / GF <![CDATA[BET(m 2 / g)]]> 0.96 1.57 <![CDATA[Micropore area (m 2 / g)]]> 0.66 0.69 <![CDATA[Total pore volume (cm 3 / g)]]> 0.0014 0.0070 Average pore diameter (nm) 5.73 17.80

[0049] Example 2

[0050] This example investigates the removal effect of oxalic acid by electrochemically coupled ozone system with CuFe-LDH / GF as cathode. Figure 3 . The ozone generator uses high-purity oxygen as the gas source. The generated gaseous O3 is analyzed by an ozone detector for concentration and then introduced into the reaction tank through a microporous aeration head. A magnetic stirrer is used to evenly dissolve the gaseous O3 in the reaction liquid, and a water bath is used to control the reaction temperature. The gas outlet of the reaction tank is connected to an ozone decomposer to destroy the undissolved gaseous O3. A DC power supply is used to provide a constant current density. All gas conduits in the reaction device are made of ozone-resistant rubber tubes. Specifically, the following steps are included:

[0051] (1) The CuFe-LDH / GF in Example 1 was used as a cathode and a platinum sheet (2×4 cm) was used as an anode. The distance between the cathode and the anode was 2 cm.

[0052] (2) The reaction solution volume was 400 mL, which contained 30 mg / L oxalic acid and 50 mmol / L Na2SO4. The initial pH of the solution was adjusted to 7 using 0.1 mol / L H2SO4 and 0.1 mol / L NaOH. The gas phase ozone concentration was adjusted to 30 mg / L and the gas flow rate was adjusted to 200 mL / min. -1 , the water bath temperature was adjusted to 25°C.

[0053] (3) Use a DC power supply to provide a current density of 2 mA / cm 2 , set the power-on time to 20 min, extract 1 mL of reaction solution at the predetermined time, and detect the remaining oxalic acid concentration in the water by high performance liquid chromatography.

[0054] like Figure 4 As shown, the removal rate of oxalic acid in this embodiment is 91.2%.

[0055] Comparative Example 1

[0056] like Figure 4 As shown, without turning on the ozone generator and with the remaining steps consistent with Example 2, almost no oxalic acid could be removed within 20 minutes by relying solely on the oxidation action of the platinum anode. Without applying current and with the remaining steps consistent with Example 2, only 7.0% of oxalic acid could be removed within 20 minutes by relying on the oxidation action of ozone. The results show that the electrochemically coupled ozone system with CuFe-LDH / GF as the cathode is much more effective in removing oxalic acid than the combined efficiency of anodic oxidation and ozone oxidation alone.

[0057] Comparative Example 2

[0058] like Figure 4As shown, the graphite felt (GF) in step 1 of Example 1 was used instead of the CuFe-LDH / GF cathode, and the remaining steps were consistent with Example 2. 46.8% of oxalic acid could be removed within 20 min, but it was much lower than the electrochemically coupled ozone system with CuFe-LDH / GF as the cathode.

[0059] Example 3-Example 5

[0060] In Examples 3 to 5, MnFe-LDH / GF, CoFe-LDH / GF and NiFe-LDH / GF were used as cathodes instead of CuFe-LDH / GF in Example 2. The electrochemically coupled ozone systems constructed in Examples 3 to 5 all showed good oxalic acid removal capabilities, but were still lower than the electrochemically coupled ozone system with CuFe-LDH / GF as the cathode, indicating that the divalent metal selection of the LDH-loaded graphite felt cathode in the system affects the oxalic acid removal efficiency. Figure 5 (a)-(f) Cyclic voltammetry curves at different scan rates show that the CuFe-LDH / GF cathode has the highest double-layer capacitance (10200 μF) among the four Fe-based LDH cathodes, indicating that it has the highest electroactive area, which is conducive to the occurrence of cathode reduction reaction and the formation of active species.

[0061] The preparation methods for the MnFe-LDH / GF, CoFe-LDH / GF, and NiFe-LDH / GF cathodes were similar to those for the CuFe-LDH / GF cathode. Based on the molar ratio of divalent metals (e.g., Cu, Mn, Co, Ni) to trivalent metals (Fe) in the LDH preparation process of 0.006 mol:0.002 mol, the Cu(NO₃)₂·3H₂O in Example 1 was replaced with 1.506 g of Mn(NO₃)₂·4H₂O, 1.746 g of Co(NO₃)₂·6H₂O, and 1.744 g of Ni(NO₃)₂·6H₂O, respectively.

[0062] Example 6

[0063] This example explores the mechanism of oxalic acid removal by an electrochemically coupled ozone system using CuFe-LDH / GF as the cathode, specifically comprising the following steps:

[0064] (1) The CuFe-LDH / GF in Example 1 was used as a cathode and a platinum sheet (2×4 cm) was used as an anode. The distance between the cathode and the anode was 2 cm.

[0065] (2) The reaction solution volume was 400 mL, which contained 30 mg / L oxalic acid and 50 mmol / L Na2SO4 as electrolytes. The initial pH of the solution was adjusted to 7 using 0.1 mol / L H2SO4 and 0.1 mol / L NaOH. The gas phase ozone concentration was adjusted to 30 mg / L and the gas flow rate was adjusted to 200 mL / min. -1 , the water bath temperature was adjusted to 25°C. 20 mmol / L tert-butyl alcohol was added as HO • quencher, 20 mmol / L chloroform as O2 •- quencher.

[0066] (3) Use a DC power supply to provide a current density of 2 mA / cm 2 , set the power-on time to 20 min, extract 1 mL of reaction solution at the predetermined time, and detect the remaining oxalic acid concentration in the water by high performance liquid chromatography.

[0067] like Figure 6 As shown in the figure, after adding 20 mmol / L TBA to the system, the degradation efficiency of oxalic acid was significantly inhibited, and the removal rate dropped from 91.2% to 13.2%, indicating that HO • It is the main active species for the degradation of oxalic acid. After adding 20 mmol / L chloroform to the system, the removal rate of oxalic acid decreased by 61.6%, indicating that O2 •- It is also an important active species in the degradation of oxalic acid. •- The redox potential of oxalic acid is only 1.0 V, which is almost incapable of oxidizing oxalic acid. • It plays an extremely important role in the formation process.

[0068] In addition, when only O2 was introduced and current was applied without ozone, the GF cathode produced 11 mg / L of H2O2 within 20 min, while the H2O2 production of the CuFe-LDH / GF cathode was only 1.6 mg / L. The above results indicate that the loading of CuFe-LDH changes the reduction path of O2 on the GF cathode, and the O2 generated on the cathode is •- Instead of H2O2, it reacts with ozone to form HO • (Formula 1-3), which weakens the effect of H2O2 on HO • The quenching effect of oxalic acid was greatly improved.

[0069] (1)

[0070] (2)

[0071] (3)

[0072] Example 7

[0073] This example investigates the effects of the preparation parameters of the CuFe-LDH / GF cathode on the removal of oxalic acid, specifically comprising the following steps:

[0074] (1) CuFe-LDH / GF cathodes with different Cu:Fe molar ratios (total metal content 0.008 mol) were prepared using the same steps as in Example 1. Except for the different amounts of metal salts added during the preparation of the LDH mother liquor, the remaining steps were the same. When the Cu:Fe molar ratios were 0:1, 1:1, 2:1, 3:1, 4:1, and 1:0, the amounts of Fe(NO3)3·9H2O and Cu(NO3)2·3H2O added were 3.232 g and 0 g, 1.616 g and 0.966 g, 1.077 g and 1.288 g, 0.808 g and 1.449 g, 0.646 g and 1.546 g, and 0 g and 1.933 g, respectively.

[0075] (2) CuFe-LDH / GF cathodes with different synthesis temperatures were prepared using the steps in Example 1. Except for the synthesis temperatures being 70°C, 90°C, 120°C, and 140°C, the remaining steps were the same.

[0076] (3) The CuFe-LDH / GF prepared in this example was used as the cathode and a platinum sheet (2×4 cm) was used as the anode. The distance between the cathode and the anode was 2 cm. The reaction solution volume was 400 mL, which contained 30 mg / L oxalic acid and 50 mmol / L Na2SO4 as electrolytes. The initial pH of the solution was adjusted to 7 using 0.1 mol / L H2SO4 and 0.1 mol / L NaOH. The gaseous ozone concentration was adjusted to 30 mg / L and the gas flow rate was adjusted to 200 mL / min. -1 , the water bath temperature was adjusted to 25°C.

[0077] (4) Use a DC power supply to provide a current density of 2 mA / cm 2 , set the power-on time to 20 min, extract 1 mL of reaction solution at the predetermined time, and detect the remaining oxalic acid concentration in the water by high performance liquid chromatography.

[0078] like Figure 7As shown in the figure, under the condition of keeping the total amount of metals unchanged during the preparation process, the GF cathode loaded with Cu or Fe alone has a relatively poor effect on removing oxalic acid in the electrochemically coupled ozone system, which is 75.4% and 78.8% respectively, but still higher than the unloaded GF cathode (46.8%). When the two metal elements are added, the molar ratio of Cu to Fe is 2:1 or 3:1, which is consistent with the optimal M reported in the literature. 2+ With M 3+ As the preparation temperature increased from 70°C to 120°C, the removal rate of oxalic acid increased from 67.8% to more than 90%. This is because the higher preparation temperature can accelerate the decomposition of urea, causing the pH of the solution to rise rapidly, thereby more effectively forming the LDH catalyst. Further increasing the temperature to 140°C significantly reduced the removal rate of oxalic acid, which may be because the high temperature caused the collapse of the layered structure, thereby affecting the catalytic activity of LDH. In addition, during the preparation process, it was found that when the temperature was 90°C or 120°C, the filtrate after the preparation was colorless, while the filtrate at 140°C was dark blue. This is because the high temperature caused urea to decompose a large amount of ammonia (NH3), which eventually formed a copper ammonia complex ([Cu(NH3)4] 2+ ), which is not conducive to the formation of LDH catalyst. Therefore, the optimal Cu:Fe molar ratio of CuFe-LDH / GF cathode is 3:1, and the optimal hydrothermal temperature is 120℃.

[0079] Example 8

[0080] Since solution pH is a key influencing factor in the electrochemically coupled ozone system, this example investigates the effect of solution pH on oxalic acid removal in an electrochemically coupled ozone system using CuFe-LDH / GF as the cathode, specifically comprising the following steps:

[0081] (1) The CuFe-LDH / GF in Example 1 was used as a cathode and a platinum sheet (2×4 cm) was used as an anode. The distance between the cathode and the anode was 2 cm.

[0082] (2) The reaction solution volume was 400 mL, which contained 30 mg / L oxalic acid and 50 mmol / L Na2SO4 as electrolytes. The initial pH of the solution was adjusted to 3-11 using 0.1 mol / L H2SO4 and 0.1 mol / L NaOH. The gas phase ozone concentration was adjusted to 30 mg / L and the gas flow rate was adjusted to 200 mL / min. -1 , the water bath temperature was adjusted to 25°C.

[0083] (3) Use a DC power supply to provide a current density of 2 mA / cm 2, set the power-on time to 20 min, extract 1 mL of reaction solution at the predetermined time, and detect the remaining oxalic acid concentration in the water by high performance liquid chromatography.

[0084] like Figure 8 As shown in the figure, when the initial pH of the solution is 3.0, the removal rate of oxalic acid by the system of the present invention is close to 100% within 20 minutes. As the pH of the solution increases to 5.0-9.0, the removal rate of oxalic acid is 86.0%-92.6%. When the initial pH of the solution rises to 11.0, the removal rate of oxalic acid is only about 20%. This is because O3 is difficult to accumulate and CO3 2- HO • In general, the system of the present invention exhibits good oxalic acid removal ability in the solution pH range of 3.0-9.0, improving the problem of poor performance of conventional electrochemical coupling systems under acidic conditions.

[0085] Example 9

[0086] This example investigates the stability of an electrochemically coupled ozone system using CuFe-LDH / GF as a cathode for removing oxalic acid, specifically comprising the following steps:

[0087] (1) The CuFe-LDH / GF in Example 1 was used as a cathode and a platinum sheet (2×4 cm) was used as an anode. The distance between the cathode and the anode was 2 cm.

[0088] (2) The reaction solution volume was 400 mL, which contained 30 mg / L oxalic acid and 50 mmol / L Na2SO4 as electrolytes. The initial pH of the solution was adjusted to 7.0 using 0.1 mol / L H2SO4 and 0.1 mol / L NaOH. The gas phase ozone concentration was adjusted to 30 mg / L and the gas flow rate was adjusted to 200 mL / min. -1 , the water bath temperature was adjusted to 25°C.

[0089] (3) Use a DC power supply to provide a current density of 2 mA / cm 2 , set the power-on time to 20 min, extract 1 mL of reaction solution at the predetermined time, and detect the remaining oxalic acid concentration in the water by high performance liquid chromatography.

[0090] like Figure 9 As shown in the figure, the removal rate of oxalic acid did not decrease significantly after the CuFe / GF cathode was reused for 5 times. In addition, the leaching amount of Cu and Fe elements in the repeated experiments was <0.06 mg·L -1, meeting the National Standard for Drinking Water Quality (GB5749-2022). The excellent stability of the EP-CuFe / GF system can be attributed to two factors: firstly, the high Ksp of the Cu or Fe hydroxides in the LDH makes them difficult to dissolve under neutral conditions; secondly, cathodic protection prevents the surface structure of the CuFe / GF cathode from being damaged by O₃. Therefore, EP-CuFe / GF can continuously and efficiently degrade oxalic acid under neutral conditions, laying the foundation for the practical application of this technology.

[0091] Example 10

[0092] This example investigates the removal effect of an electrochemically coupled ozone system using CuFe-LDH / GF as the cathode on actual wastewater, specifically comprising the following steps:

[0093] (1) The CuFe-LDH / GF in Example 1 was used as a cathode and a platinum sheet (2×4 cm) was used as an anode. The distance between the cathode and the anode was 2 cm.

[0094] (2) Municipal nanofiltration concentrated water was selected as the target wastewater, and its basic physical and chemical properties are shown in Table 2. The reaction liquid volume was 400 mL, the gas phase ozone concentration was adjusted to 30 mg / L, and the gas flow rate was adjusted to 200 mL / min. -1 , the water bath temperature was adjusted to 25°C.

[0095] Table 2 Basic physical and chemical properties of municipal nanofiltration brine

[0096] index parameter index parameter Water temperature / ℃ 15 Chroma / degree < 5 Turbidity / NTU 0.032 pH 7.7 Visible to the naked eye none <![CDATA[UV 254 ]]> 0.184 <![CDATA[DOC(mg·L -1 )]]> 16.38 <![CDATA[Conductivity (μs·cm -1 )]]> 1191 <![CDATA[Inorganic carbon (mg·L -1 )]]> 44.52 Redox potential (mV) -57

[0097] (3) Use a DC power supply to provide a current density of 2 mA / cm 2 , set the power-on time to 20 min, extract 5 mL of reaction solution at the predetermined time, and use the TOC analyzer to detect the remaining total dissolved organic carbon (DOC) in the water.

[0098] like Figure 10 As shown in the data, within a 60-minute treatment time, the DOC removal efficiencies for ozone oxidation, the electrochemically coupled ozone system with GF as the cathode, and the electrochemically coupled ozone system with CuFe-LDH / GF as the cathode were 35.9%, 53.1%, and 61.6%, respectively. These results demonstrate that the proposed system has high organic matter removal capabilities in actual wastewater treatment and exhibits promising potential for practical application.

[0099] In summary, the electrochemically coupled ozone system based on CuFe-LDH loaded graphite felt cathode proposed in the present invention effectively combines the advantages of electrochemical oxidation and ozone oxidation, makes up for the shortcomings of low electrochemical oxidation treatment efficiency and poor ozone oxidation mineralization rate, and weakens the effect of H2O2 on HO in conventional electrochemically coupled ozone system. • The quenching effect of HO • It is a relatively clean and efficient advanced oxidation technology for water treatment.

[0100] In electrochemically coupled ozone systems, relatively little research has been conducted on functionalized carbon cathodes, primarily focusing on loading nanocarbon materials or metal oxides. These processes often require high-temperature calcination, potentially leading to secondary contamination and material deformation. The method of the present invention utilizes a mild hydrothermal synthesis method for LDH loading, which is relatively simple and produces a relatively stable cathode material.

[0101] The graphite felt cathode material used in the method provided in the specific embodiment of the present invention is inexpensive and easily available. The modified graphite felt cathode maintains good stability in the system. After being recycled for 5 times, the oxalic acid removal efficiency remains above 90%, and the mass concentration of leached Fe and Cu elements is less than <0.06 mg / L, which is lower than the national "Standard for Drinking Water Quality" (GB5749-2022).

[0102] Compared with electrochemical oxidation, ozone oxidation and the electrochemically coupled ozone system with unmodified graphite felt as the cathode, the electrochemically coupled ozone system based on CuFe-LDH / GF cathode used in this method has a significant improvement in the removal rate of organic matter.

[0103] The embodiment described above is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Persons skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent substitution or equivalent transformation falls within the scope of protection of the present invention.

Claims

1. A method for removing organic matter from water using an electrochemically coupled ozone system based on an LDH-loaded graphite felt cathode, characterized in that: include: MFe-LDH / GF is used as the cathode, where M is Cu, Mn, CO or Ni, and a platinum sheet is used as the anode. The reaction solution includes pollutants and an electrolyte, and the electrolyte is Na2SO4. Two electrodes are added to the reaction solution, and gaseous ozone is charged into the reaction solution. The pH of the reaction solution is adjusted to 3-9, and current is charged into the two electrodes to construct an electrochemically coupled ozone system to remove pollutants.

2. The method for removing organic matter from water using an electrochemically coupled ozone system based on an LDH-loaded graphite felt cathode according to claim 1, characterized in that: MFe-LDH / GF was used as the cathode, where M was Cu.

3. The method for removing organic matter from water using an electrochemically coupled ozone system based on an LDH-loaded graphite felt cathode according to claim 1, characterized in that: The pH of the reaction solution is 5-7.

4. The method for removing organic matter from water using an electrochemically coupled ozone system based on an LDH-loaded graphite felt cathode according to claim 1, characterized in that: The density of the current charged to the two electrodes is 2-5 mA / cm 2 .

5. The method for removing organic matter from water using an electrochemically coupled ozone system based on an LDH-loaded graphite felt cathode according to claim 1, characterized in that: The concentration of the gaseous ozone is 15-60 mg / L, and the flow rate of the gaseous ozone is 100-300 mL / min.

6. The method for removing organic matter from water using an electrochemically coupled ozone system based on an LDH-loaded graphite felt cathode according to claim 1, characterized in that: In the reaction solution, the concentration of Na2SO4 is 30-70 mmol / L, and the concentration of pollutants is 30-60 mg / L.

7. The method for removing organic matter from water using an electrochemically coupled ozone system based on an LDH-loaded graphite felt cathode according to claim 1 or 6, characterized in that: The pollutant is oxalic acid, pyruvic acid or acetic acid.

8. The method for removing organic matter from water using an electrochemically coupled ozone system based on an LDH-loaded graphite felt cathode according to claim 1, characterized in that: H2SO4 and NaOH were added to the reaction solution to adjust the pH value, wherein the concentration of H2SO4 was 0.05-0.2 mol / L, and the concentration of NaOH was 0.05-0.2 mol / L.

9. The method for removing organic matter from water using an electrochemically coupled ozone system based on an LDH-loaded graphite felt cathode according to claim 1, characterized in that: The preparation method of the MFe-LDH / GF comprises: Fe(NO3)3·9H2O, M(NO3)2·3H2O, CO(NH2)2 and NH4F are fully dissolved in ultrapure water to obtain LDH mother solution, wherein the mass concentrations of Fe(NO3)3·9H2O, M(NO3)2·3H2O, CO(NH2)2 and NH4F are 9-23 g / L, 13-26 g / L, 20-35 g / L and 1-3 g / L, respectively; Graphite felt is added to the LDH mother liquor to obtain a mixed solution, and the mixed solution is subjected to a hydrothermal reaction at a temperature of 90-120° C. and a reaction time of 8-16 hours. After the reaction is completed, the MFe-LDH / GF is obtained by suction filtration, washing, and drying.

10. The method for removing organic matter from water using an electrochemically coupled ozone system based on an LDH-loaded graphite felt cathode according to claim 1, characterized in that: Graphite felt was added into LDH mother liquor, and the surface of the graphite felt was cleaned with acetone and ultrapure water in sequence, and then dried and baked.

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