Titanium-based metal oxide coating electrode, preparation method of titanium-based metal oxide coating electrode and application of titanium-based metal oxide coating electrode in electro-catalytic degradation of landfill leachate

Abstract

The invention discloses a titanium-based metal oxide coating electrode, a preparation method thereof and application of the titanium-based metal oxide coating electrode in electrocatalytic degradation of landfill leachate, the electrode is a Ti / RuO2 / IrO2-SnO2 coating electrode, and the preparation method of the titanium-based metal oxide coating electrode comprises the following steps: by taking a titanium plate as a substrate, pretreating, then coating with an acid solution containing a Ru source, an Ir source and a Sn source, drying and roasting, and repeating the coating, drying and roasting process for 5-20 times, thereby obtaining the titanium-based metal oxide coating electrode. And finally, annealing treatment is carried out, and preparation is completed. The Ti / RuO2 / IrO2-SnO2 coating electrode is used as an anode material, coconut shell biochar is used as a particle electrode to construct a three-dimensional aeration electro-catalytic reactor, the three-dimensional aeration electro-catalytic reactor is used for enhancing treatment of landfill leachate, especially tetracycline antibiotics (tc) including tetracycline (TC), tetracycline (OTC) and tetracycline chloride (CTC), and the three-dimensional aeration electro-catalytic reactor has the advantages of being easy to operate, high in treatment efficiency, low in energy consumption and the like, and has a good application prospect. The method is suitable for controlling and degrading tetracycline antibiotics in landfill leachate.

Description

Technical Field

[0001] The invention relates to the field of wastewater treatment, in particular to a titanium-based metal oxide coating electrode, a preparation method thereof and application thereof in electrocatalytic degradation of landfill leachate. Background Art

[0002] During the sedimentation and biodegradation process of landfills, a large amount of leachate containing humus, ammonia nitrogen (NH3-N) and chemical pollutants will be produced. The enrichment of chemical pollutants (such as antibiotics) in the leachate will further increase the long-term spread of drug-resistant genes and drug-resistant bacteria, thus seriously affecting the ecosystem. Among them, tetracycline antibiotics (TCs), such as tetracycline (TC), over-the-counter (OTC) and chlorotetracycline (CTC) have a very high detection frequency. The misuse of antibiotics not only leads to drug resistance, but also reduces the number of sensitive microbial communities and generally affects the activities of global microbial communities, ultimately posing a potential threat to humans. Therefore, effective treatment strategies must be adopted to control and remove antibiotics in landfill leachate.

[0003] Filtration, coagulation / flocculation / sedimentation have proven to be relatively ineffective methods for antibiotic removal, and subsequent treatment steps such as ozone oxidation and biological treatment are usually required to further remove pollutants. Activated sludge technology (AST) mainly removes antibiotic compounds through adsorption and biodegradation processes. They are all conventional treatment processes in wastewater treatment plants. However, studies have shown that traditional treatment methods can only remove part of the antibiotics. In summary, new alternatives have emerged - advanced oxidation processes (AOPs), which use intermediate free radicals with high reactivity and low selectivity to degrade antibiotics. AOPs are a promising technology for removing antibiotics from wastewater due to their high efficiency and stability.

[0004] Electrochemical oxidation (EO) is a representative process of AOPs, which can effectively degrade persistent organic pollutants and has the advantages of fast reaction and simple operation. With the improvement of EO, three-dimensional electrocatalytic oxidation has received considerable attention. Suspended particle electrodes are introduced into two-dimensional (2D) electrochemical systems. These particles act as microelectrodes and can be regarded as anodes or cathodes on different surfaces. Indeed, these microelectrodes diffused in the solution extend the reaction surface from the two-dimensional electrode to the entire system, thereby promoting mass transfer and electrocatalysis. The properties of the electrode and the electroactive species determine the kinetics, selectivity and efficiency of the electrochemical process. Recently, dimensionally stable anodes (DSAs) like this have also been used as alternatives to boron-doped diamond (BDD) and graphene-based systems. The presence of mixed metal oxide coatings provides inherent catalytic properties and enhanced stability. The main difference between DSA and other electrodes such as BDD and graphene is that direct and indirect oxidation occur simultaneously, with higher stability and special electrocatalytic properties. Foreign scientists compared Ti / PbO2 and Ti / Pt / PbO 2 The behavior of electrodes during TC and OTC electrooxidation. The current intensity observed on the platinum-coated electrode is 100 times that observed on the Ti / PbO 2 electrode, but the antibiotic degradation efficiency of the Ti / PbO 2 anode is slightly higher. Domestic scientists designed a cylindrical reactor with a Ti / RuO 2 / IrO 2 anode and a graphite rod cathode, using volcanic rock as a particle electrode. Under low pressure (4V) and acidic conditions, the removal rate of norfloxacin in volcanic rock is greater than 85% (40 min). In addition, the addition of particle electrodes has higher catalytic activity. Particle electrodes such as activated carbon, metals, and their oxides are still limited in practical applications due to high preparation costs, complex processes, and large usage amounts.

[0005] Biochar (BC), as an economical and environmentally friendly carbon material, has broad application prospects in environmental remediation due to its excellent physical and chemical properties, low cost, and abundant carbon source. However, at present, there are few reports on using biochar as a particle electrode.

[0006] The present invention aims to provide an economical, efficient, and easy-to-operate method for treating tetracycline antibiotics in landfill leachate. By preparing a Ti / RuO 2 / IrO 2 -SnO 2 anode and using coconut shell biochar as a particle electrode, efficient degradation of tetracycline antibiotics in leachate is achieved. This method not only improves the treatment efficiency, reduces the operating cost, but also has good stability and durability, which has important practical significance for alleviating the environmental pressure of antibiotic pollution. Summary of the Invention

[0007] Aiming at the problems existing in the prior art, the purpose of the design of the present invention is to provide a titanium-based metal oxide coated electrode, its preparation method, and its application in electrocatalytic degradation of landfill leachate. The efficient treatment technology for degrading tetracycline in wastewater of the present invention has the characteristics of economy, efficiency, and easy operation, and is suitable for the control and degradation of tetracycline wastewater.

[0008] The present invention is achieved through the following technical solutions:

[0009] A preparation method of a titanium-based metal oxide coated electrode, the electrode being a Ti / RuO 2 / IrO 2 -SnO 2 coated electrode, and its preparation method includes the following steps:

[0010] 1) Pretreatment: The titanium substrate plate is subjected to pretreatment steps of polishing and degreasing in sequence, and then immersed in an oxalic acid aqueous solution with a mass fraction of 5 - 20% for heating and etching to increase the surface roughness of the substrate, which is beneficial to the bonding of the subsequent coating and the substrate, and a pretreated titanium substrate plate is obtained;

[0011] 2) Coating: An acidic solution of Ru source, Ir source and Sn source is prepared as a precursor coating solution. The molar ratio of Ru source, Ir source and Sn source is 4 - 6:1:3 - 5. The solvent of the precursor coating solution is a methanol - concentrated hydrochloric acid mixed solution with a volume ratio of 3 - 5:1, and the mass concentration of the concentrated hydrochloric acid is 30 - 36%. The precursor coating solution is evenly coated on the pretreated titanium substrate plate with a coating rod;

[0012] 3) Drying and roasting: After the coating in step 2), drying is carried out to completely evaporate the solvent on the surface of the titanium substrate plate, and then it is placed in a muffle furnace for roasting treatment;

[0013] 4) Repeat the above processes of coating, drying and roasting for 5 - 20 times, and finally annealing treatment is carried out.

[0014] Further, the specific process of step 1) pretreatment is as follows:

[0015] S1 Polishing: The titanium substrate plate is polished successively with 400 - mesh and 800 - mesh sandpapers to remove the surface oxide layer and make it more uniform and smooth;

[0016] S2 Degreasing: Ultrasonic cleaning is carried out with pure water to remove surface metal debris and other impurities, and then it is boiled in a NaOH aqueous solution with a mass fraction of 5 - 15% for 1 - 2.5 h to remove oil stains;

[0017] S3 Acid etching: The degreased titanium substrate plate is immersed in an oxalic acid aqueous solution with a mass fraction of 5 - 20% for heating and etching. The heating temperature is 80 - 90 °C and the heating time is 1 - 2.5 h.

[0018] Further, in step 2), the Ru source is RuCl 3 , the Ir source is H 2 IrCl 6 ·xH 2 O, the Sn source is SnCl 4 , and the molar ratio of Ru source, Ir source and Sn source is 5 - 5.5:1:3.5 - 4.

[0019] Further, the roasting temperature in step 3) is 450 - 550 °C and the roasting time is 5 - 20 min.

[0020] Further, the annealing temperature in step 4) is 450 - 550 °C and the annealing time is 1 - 2 h.

[0021] A titanium-based metal oxide coated electrode prepared by the present invention, RuO 2 / IrO 2 -SnO 2 The loading amount of the coating on the titanium substrate plate is 2-5 mg / cm 2 .

[0022] The application of the described titanium-based metal oxide coated electrode in the electrocatalytic degradation of landfill leachate. For the degradation of landfill leachate, a three-dimensional electrocatalytic oxidation system is used. The anode uses the described titanium-based metal oxide coated electrode. The anode and the cathode are fixedly arranged in parallel in the electrolytic cell. Granular electrodes are filled between the anode and the cathode. A nano-aeration disk is installed near the cathode to introduce oxygen-containing gas. The fine and uniform atomization of the oxygen-containing gas is more conducive to the generation of cathode free radicals. Using the described landfill leachate as the electrolyte and introducing it into the electrolytic cell, stirring is started to fully disperse the granular electrodes. The electrode distance between the cathode and the anode is controlled at 3-5 cm for electrocatalytic degradation reaction. Among them, the particle size of the granular electrode is 0.88-2.36 mm, the dosage of the granular electrode in the electrolyte of the electrolytic cell is 3-11 g / L, and the current density is 10-50 mA / cm 2 , and the pH of the electrolyte is adjusted to be between 5 and 10.

[0023] Furthermore, the organic matter in the described landfill leachate contains antibiotic pollutants, and its COD is within 1500±100 mg / L, NH 3 -N is within 1000±100 mg / L. The cathode is selected as a titanium plate, and the granular electrode is selected as coconut shell biochar;

[0024] The pH of the electrolyte is adjusted to 9-10, and the electrocatalytic oxidation degradation reaction is carried out under the condition that the temperature is 25±2 °C, and the current density is 20-30 mA / cm 2 ;

[0025] KCl is also added to the described electrolyte as an electrolyte, and the concentration of the electrolyte KCl is 50-150 mg / L.

[0026] Furthermore, the described antibiotic pollutants include at least one of tetracycline (TC), oxytetracycline (OTC), and chlortetracycline (CTC), and the total concentration of the described antibiotic pollutants is within 30 mg / L.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1) It can significantly improve the ability of the three-dimensional aeration electrocatalytic reactor (3D-AER) to degrade humus in leachate, especially the treatment ability for tetracycline antibiotics (TC), including tetracycline (TC), oxytetracycline (OTC), and chlortetracycline (CTC).

[0029] 2) Compared with traditional advanced oxidation technologies (such as ozone oxidation, hydrogen peroxide oxidation, etc.), this technology achieves efficient COD removal through electrocatalytic degradation, while avoiding the use of a large amount of chemical reagents, reducing the treatment cost and energy consumption.

[0030] 3) By using the Ti / RuO 2 / IrO 2 -SnO 2 coated electrode as the anode material, combined with a three-dimensional electrocatalytic oxidation system, can maintain a high removal efficiency under different conditions, showing good stability. The Ti / RuO 2 / IrO 2 -SnO 2 coated electrode of the present invention has better catalytic activity than electrodes such as ruthenium-iridium-platinum, and can simultaneously achieve good degradation effects on COD, NH 3 -N and refractory antibiotic pollutants.

[0031] 4) The present invention relates to waste coconut shells, belonging to the preparation technology of "treating waste with waste" and sustainable development, effectively solving the problem of high-value utilization of coconut shells, and having good economic and environmental benefits. Brief Description of the Drawings

[0032] Figure 1 is the comparison result of the removal rates of COD, NH 3 -N, TC, OTC and CTC by the "ruthenium-iridium-tin" electrode in Example 1 and the "ruthenium-iridium-platinum" electrode in Comparative Example 1 during 3 hours of electrocatalysis.

[0033] Figure 2 is the influence result of different pH values on the removal rates of COD and NH 3 -N in Example 2 of the present invention.

[0034] Figure 3 is the influence result of different pH values on the removal rates of three kinds of tetracyclines in Example 2 of the present invention.

[0035] Figure 4 is the influence result of different current densities on the removal rates of COD and NH 3 -N in Example 2 of the present invention.

[0036] Figure 5 is the influence result of different current densities on the removal rates of three kinds of tetracyclines in Example 2 of the present invention.

[0037] Figure 6 is the influence result of different KCl concentrations on the removal rates of COD and NH 3 -N in Example 2 of the present invention.

[0038] Figure 7It is the influence result of different KCl concentrations on the removal rates of three kinds of tetracyclines in Example 2 of the present invention.

[0039] Figure 8 It is the influence result of different CBC dosing concentrations on the removal rates of COD and NH 3 -N in Example 2 of the present invention.

[0040] Figure 9 It is the influence result of different CBC dosing concentrations on the removal rates of three kinds of tetracyclines in Example 2 of the present invention.

[0041] Figure 10 It is the influence result of different CBC particle sizes on the removal rates of COD and NH 3 -N in Example 2 of the present invention.

[0042] Figure 11 It is the influence result of different CBC particle sizes on the removal rates of three kinds of tetracyclines in Example 2 of the present invention.

[0043] Figure 12 It is the influence result of different electrode spacings on the removal rates of COD and NH 3 -N in Example 2 of the present invention.

[0044] Figure 13 It is the influence result of different electrode spacings on the removal rates of three kinds of tetracyclines in Example 2 of the present invention.

[0045] Figure 14 It is the electrocatalytic degradation reaction effect under the optimal conditions in Example 3 of the present invention. Detailed implementation manners

[0046] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, those of ordinary skill in the art, under the inspiration of the present invention and without departing from the purpose and scope protected by the claims of the present invention, can also make many forms, all of which belong to the scope of protection of the present invention.

[0047] Example 1:

[0048] A titanium-based metal oxide coated electrode, namely a Ti / RuO 2 / IrO 2 -SnO 2 coated electrode, and its preparation method includes the following steps:

[0049] 1) Polishing: Use 400-mesh and 800-mesh sandpapers to polish the titanium substrate plate (with dimensions of 60 mm × 40 mm × 2 mm) in sequence to remove the surface oxide layer and make it more uniform and smooth.

[0050] 2) Degreasing: Ultrasonically clean the titanium substrate plate with pure water for 5 minutes to remove metal debris and other impurities, and then boil it in a 10% NaOH aqueous solution by mass for 2 h to remove oil stains.

[0051] 3) Acid etching: Immerse the degreased titanium substrate plate in a 10% oxalic acid aqueous solution by mass for heating and etching. The heating temperature is 90 °C and the heating time is 2 h to increase the surface roughness of the substrate, which is beneficial to the bonding between the subsequent coating and the substrate.

[0052] 4) Coating: Weigh RuCl 3 , H 2 IrCl 6 ·xH 2 O and SnCl 4 according to the molar ratio of Ru, Ir, and Sn of 5.5:1:3.9. The molar amount of RuCl 3 is 1.129 mmol, which is dissolved in 4 mL of anhydrous methanol, added to 1 mL of concentrated hydrochloric acid (mass fraction 36%), and ultrasonically treated for 20 minutes to obtain a precursor coating solution. The precursor coating solution is evenly coated on the pretreated titanium substrate plate with a coating rod. The precursor coating solution is coated on both sides of the titanium substrate plate, and the coating amount per side is 140 μL.

[0053] 5) Drying: Dry the coated titanium substrate plate at 100 °C until the surface solvent is completely evaporated.

[0054] 6) Calcination: Place the dried titanium substrate plate in a muffle furnace at 500 °C for calcination for 10 minutes, and then take it out and cool it to room temperature. Repeat the above coating, drying, and calcination processes 10 times, and finally anneal at 500 °C for 1 h to obtain a Ti / RuO 2 / IrO 2 -SnO 2 coating electrode. The loading amount of RuO 2 / IrO 2 -SnO 2 on the titanium substrate plate is about 3.69 mg / cm 2 .

[0055] The electrocatalytic degradation device in the present invention is as follows: The electrolytic cell is a cylindrical plexiglass container with a bottom diameter of 8 cm and a height of 15 cm. There are overflow holes for sampling designed on the side, the aperture of the overflow hole is 1 cm, the distance between the electrode sheet slots on the top cover is 3 - 5 cm, and a slot is opened every 0.5 cm. The anode is selected as the Ti / RuO 2 / IrO 2 -SnO 2The coated electrode, the cathode is selected as a titanium plate, and the effective sizes of both are length × width × thickness = 60 mm × 40 mm × 2 mm. The cathode and the anode are arranged in parallel and facing each other and are respectively erected in the electrolytic cell. A nano-aeration disk is installed near the cathode to introduce oxygen-containing gas. The fine and uniform atomization of the oxygen-containing gas is more conducive to the generation of cathode free radicals. Coconut shell charcoal is used as the particle electrode and is filled between the anode and the cathode. The anode and the cathode are connected to a DC regulated power supply through wires. The electrolytic cell is placed on a magnetic stirrer, and a magnetic stir bar is placed in the electrolytic cell. Under the action of the magnetic stirrer, the magnetic rotor is driven to fully stir the landfill leachate so that the reaction can operate efficiently.

[0056] The Ti / RuO prepared in Example 1 2 / IrO 2 -SnO 2 The coated electrode is applied to the electrocatalytic treatment of landfill leachate, and the steps are as follows:

[0057] S1 Prepare simulated landfill leachate: Using water as the solvent, the components in the water include humic acid HA, ammonium sulfate (NH 4 ) 2 SO 4 , sodium bicarbonate NaHCO 3 , tetracycline TC, oxytetracycline OTC and chlortetracycline CTC. Among them, humic acid provides COD, ammonium sulfate provides ammonium nitrogen, and sodium bicarbonate is used as a component of the buffer solution. In the simulated landfill leachate, the concentrations of TC, OTC and CTC are all 10 mg / L, the COD value is regulated to be 1258 mg / L, the NH 3 -N content is 963 mg / L, and the concentration of sodium bicarbonate NaHCO 3 is 2750 mg / L.

[0058] S2 Electrocatalytic reaction: Using the above electrocatalytic degradation device, using the simulated landfill leachate prepared in step S1 as the electrolyte, the volume of the electrolyte is 500 mL, and an electrolyte KCl with a final concentration of 100 mg / L is added thereto. Coconut shell charcoal is used as the particle electrode, the cathode is selected as a titanium plate, and the anode is selected as the Ti / RuO 2 / IrO 2 -SnO 2 coated electrode. 50 sccm of air is introduced through the nano-aeration disk. The electrocatalytic reaction conditions are controlled as follows: the pH of the electrolyte is 8, the addition concentration of coconut shell charcoal CBC in the electrolyte is 7 g / L, the particle size of coconut shell charcoal CBC is 1.40 - 1.70 mm, and the distance between the cathode and the anode is 3 cm. According to the above electrocatalytic conditions, the electrocatalytic oxidation degradation reaction is carried out at a temperature of 25 ± 2 °C, and the current density is controlled at 30 mA / cm 2 , and the electrocatalytic reaction time is 3 h.

[0059] According to the experimental process of the above steps S1 - S2, the Ti / RuO of Example 1 2 / IrO 2 -SnO 2 coated electrode (abbreviated as "ruthenium - iridium - tin" electrode) at 3 h of electrocatalysis, the comparison results of the removal rates of COD, NH 3 -N, TC, OTC and CTC are shown in the dotted - line graph results corresponding to "ruthenium - iridium - tin" in Figure 1 .

[0060] Comparative Example 1:

[0061] The preparation of a "ruthenium - iridium - platinum" electrode includes the following steps:

[0062] 1) Pretreatment: Pretreat the titanium substrate plate (with dimensions of 60 mm×40 mm×2 mm), that is, perform operations of polishing, degreasing and acid - etching in sequence, and the operation steps repeat the treatment process of steps 1 - 3) of Example 1.

[0063] 2) Platinum plating: The electro - deposition process of platinum plating is carried out in a single - chamber double - layer cell with a constant - temperature water bath at 65 °C. Using the titanium substrate plate pretreated in step 1) as the cathode and a platinum plate as the anode, the electro - deposition solution is an aqueous solution of chloroplatinic acid at 20 g / L, the current density is 250 mA cm -2 , the electrolysis time is 10 minutes, and after electroplating, it is washed with deionized water and dried.

[0064] 3) Coating: Weigh RuCl 3 and H 2 IrCl 6 ·xH 2 O according to the molar ratio of Ru:Ir of 5.5:1, where the molar amount of RuCl 3 is 1.129 mmol, dissolve it in 4 mL of anhydrous methanol, add it to 1 mL of concentrated hydrochloric acid (mass fraction 36%), and ultrasonicate for 20 minutes to obtain a precursor coating solution. The precursor coating solution is evenly coated on the pretreated titanium substrate plate with a coating rod. Coat the precursor coating solution on both sides of the titanium substrate plate, and the coating amount per side is 140 microliters.

[0065] 4) Drying: Dry the coated titanium substrate plate at 100 °C until the surface solvent is completely evaporated.

[0066] 5) Calcination: Place the dried titanium substrate plate in a muffle furnace at 500 °C for 10 minutes, then take it out and cool it to room temperature. Repeat the above coating, drying and calcination processes 10 times, and finally anneal at 500 °C for 1 hour.

[0067] The "ruthenium-iridium-platinum" electrode of Comparative Example 1 was applied to the electrocatalytic treatment of landfill leachate. The operation process repeated the steps S1 - S2 of Example 1, with the only difference being "replacing the ruthenium-iridium-tin electrode of Example 1 with the ruthenium-iridium-platinum electrode of Comparative Example 1", and the other conditions remaining unchanged. Thus, when the "ruthenium-iridium-platinum" electrode of Comparative Example 1 was electrocatalyzed for 3 h, the comparison results of the removal rates of COD, NH 3 -N, TC, OTC, and CTC are shown in the dotted line graph results corresponding to "ruthenium-iridium-platinum" in Figure 1 .

[0068] From Figure 1 it can be seen that under the same conditions, the treatment effect of the ruthenium-iridium-tin anode is better than that of the ruthenium-iridium-platinum anode.

[0069] Example 2:

[0070] Using the Ti / RuO 2 / IrO 2 -SnO 2 coated electrode prepared in Example 1, applied to the electrocatalytic treatment of landfill leachate, and the electrocatalytic reaction process repeated the steps S1 - S2 of Example 1, with the only difference being to investigate the effects of different electrolyte pH, current density, KCl concentration, particle electrode dosing concentration, particle electrode particle size, and anode-cathode distance respectively.

[0071] The influence results of different pH on the removal rates of COD and NH 3 -N are shown in Figure 2 , and the influence results of different pH on the removal rates of the three tetracyclines are shown in Figure 3 .

[0072] pH is a key factor in the catalytic degradation process, which affects the formation of free radicals and the reaction mechanism. The influence of different pH conditions on the removal rates of COD and NH 3 -N is as shown in Figure 2 . Under the initial conditions, the current density is 30 mA / cm 2 , the potassium chloride concentration is 100 mg / L, the CBC dosage is 7 g / L, the CBC particle size is 1.40 - 1.70 mm, and the electrode distance is 3 cm. When pH = 5, the COD removal rate reaches 90.4%, while the NH 3 -N removal rate is only 10.28%. As the pH increases, the COD removal rate first decreases and then increases, showing a turning point at pH = 7. On the contrary, the removal rate of NH 3 -N increases with the increase of pH value. When pH = 10, the removal rates of COD and NH 3The removal rates of -N both reached their maximum values (73.98% and 58.52%). Meanwhile, the removal rates of OTC, TC, and CTC under this condition were 85.65%, 87.44%, and 64.46% respectively. Therefore, we selected a pH of 10 as the optimized parameter for the subsequent reaction.

[0073] The effects of different current densities on the removal rates of COD and NH 3 -N are shown in Figure 4 , and the effects of different current densities on the removal rates of the three tetracyclines are shown in Figure 5 .

[0074] The current density affects the electron transfer rate between electrons and the solution. The experimental conditions were pH = 8, potassium chloride concentration 100 mg / L, CBC dosage 7 g / L, CBC particle size 1.40 - 1.70 mm, and electrode spacing 3 cm. See Figure 4 , as the current density increased, the removal rate of COD first increased and then decreased. The maximum removal rate of COD was 67.35%, and at this time the removal rate of NH 3 -N was 60.69% (current density = 30 mA / cm 2 ), indicating that an appropriate current density promoted the oxidation of organic compounds. Corresponding to the current density = 30 mA / cm 2 , the removal rates of OTC, TC, and CTC were 88.86%, 89.91%, and 72.86% respectively ( Figure 5 ). Therefore, 30 mA / cm 2 was the preferred object for subsequent research.

[0075] The effects of different KCl concentrations on the removal rates of COD and NH 3 -N are shown in Figure 6 , and the effects of different KCl concentrations on the removal rates of the three tetracyclines are shown in Figure 7 .

[0076] During the process of pollutant removal, the concentration of the electrolyte affects the conductivity and energy consumption of the solution. In some cases, the electrochemistry of the electrolyte can determine the kinetics and degradation pathways. The initial conditions were pH = 8, current density 30 mA / cm 2 , CBC dosage 7 g / L, CBC particle size 1.40 - 1.70 mm, and electrode spacing 3 cm. When the potassium chloride concentration was 100 mg / L, the removal rates of COD and NH 3 -N reached a turning point, and the maximum removal rates were 77.30% and 64.45% respectively ( Figure 6 ). Correspondingly, the removal rates of OTC, TC, and CTC were 85.43%, 88.95%, and 80.97% respectively ( Figure 7)。The potassium chloride concentration of 100 mg / L was used as the subsequent reaction parameter for 3D-AER.

[0077] The effects of different CBC dosing concentrations on the removal rates of COD and NH 3 -N are shown in Figure 8 , and the effects of different CBC dosing concentrations on the removal rates of three tetracyclines are shown in Figure 9 . The experimental conditions were pH = 8, current density 30 mA / cm 2 , potassium chloride concentration 100 mg / L, CBC particle size 1.40 - 1.70 mm, and electrode spacing 3 cm. Obviously, when the CBC dosage was 7 g / L, the removal rates of COD and NH3-N both reached their peaks (77.38% and 61.78%). In this example, the removal rates of OTC, TC, and CTC were 82.15%, 87.77%, and 84.22% respectively. Therefore, the dosage of the particle electrode was set at 7 g / L.

[0078] The effects of different CBC particle sizes on the removal rates of COD and NH 3 -N are shown in Figure 10 , and the effects of different CBC particle sizes on the removal rates of three tetracyclines are shown in Figure 11 .

[0079] The experimental conditions were pH = 8, current density 30 mA / cm 2 , potassium chloride concentration 100 mg / L, CBC dosage 7 g / L, and electrode spacing 3 cm. Generally speaking, as the CBC particle size increased, the removal rates of COD and NH 3 -N showed an upward trend, and the treatment effect of 1.7 - 2.36 mm CBC was the best, with the removal rates of COD and NH 3 -N reaching 70.42% and 60.80% respectively ( Figure 10 ). In this example, the removal rates of OTC, TC, and CTC were 85.79%, 88.90%, and 78.56% respectively ( Figure 11 ). The reason is that the small particle size of the particle electrode leads to an increase in its quantity, and frequent collisions are likely to cause short circuits, resulting in low current efficiency. Therefore, selecting an appropriate particle size can improve the mass transfer efficiency of the material.

[0080] The effects of different electrode spacings on the removal rates of COD and NH 3 -N are shown in Figure 12 , and the effects of different electrode spacings on the removal rates of three tetracyclines are shown in Figure 13 .

[0081] The distance between the electrodes affects the electric field strength of the solution, thereby affecting the removal of pollutants. The experimental conditions were pH = 8, current density 30 mA / cm 2, the potassium chloride concentration is 100 mg / L, the CBC dosage is 7 g / L, and the CBC particle size is 1.40 - 1.70 mm. From Figure 12 It can be seen that the degradation efficiency of COD and NH 3 -N in 3D-AER decreases with the increase of the electrode spacing, and the maximum removal rates are 79.84% and 65.88% respectively (the electrode spacing is 3 cm). In this example, the removal rates of OTC, TC, and CTC are 87.46%, 86.58%, and 81.88% respectively ( Figure 13 ). The smaller the inter-plate spacing, the greater the electric field strength, the better the mass transfer effect in the solution, and the higher the removal rate of TC within a certain time. Increasing the spacing between the electrode plates will reduce the removal effect. Due to the smaller potential difference, the particle electrode far from the particle electrode has lower activity, thus reducing the CE and removal efficiency and increasing the EC. Therefore, 3 cm is the optimal parameter.

[0082] Example 3:

[0083] Using the Ti / RuO prepared in Example 1 2 / IrO 2 -SnO 2 coated electrode, applied to the electrocatalytic treatment of landfill leachate, the steps S1 - S2 of Example 1 are repeated in the electrocatalytic reaction process, the difference is only that: the electrocatalytic reaction is carried out under the optimal conditions, that is, the electrolyte pH = 10, the current density is 30 mA / cm 2 , the potassium chloride concentration is 100 mg / L, the CBC dosage is 7 g / L, the CBC particle size is 1.7 - 2.36 mm, the electrode spacing is 3 cm, the electrocatalytic oxidation degradation reaction is carried out under the condition of a temperature of 25 ± 2 °C, and the electrocatalytic reaction time is 3 h.

[0084] Under the above optimal conditions, it has a good treatment effect on denitrification and decarbonization in the leachate. The removal rates of COD, NH3-N, TC, OTC, and CTC reach 82.76%, 66.02%, 86.58%, 87.46%, and 81.88% respectively (see Figure 14 ).

Claims

1. A method for preparing a titanium-based metal oxide coating electrode, characterized in that The electrode is a Ti / RuO2 / IrO2-SnO2 coated electrode, and its preparation method comprises the following steps: 1) Pretreatment: The titanium substrate plate is subjected to the pretreatment steps of polishing and degreasing in sequence, and then immersed in a 5-20% by mass oxalic acid aqueous solution for heating and etching to increase the surface roughness of the substrate, which is beneficial to the bonding of the subsequent coating and the substrate, thereby obtaining a pretreated titanium substrate plate; 2) coating: preparing an acidic solution of Ru source, Ir source and Sn source as a precursor coating solution, wherein the molar ratio of Ru source, Ir source and Sn source is 4-6:1:3-5, the solvent of the precursor coating solution is a methanol-concentrated hydrochloric acid mixture with a volume ratio of 3-5:1, and the mass concentration of the concentrated hydrochloric acid is 30-36%, and the precursor coating solution is evenly coated on the pretreated titanium substrate plate with a coating rod; 3) Drying and calcining: After step 2) coating, the titanium substrate is dried to completely evaporate the solvent on the surface of the titanium substrate, and then placed in a muffle furnace for calcination; 4) Repeat the above coating, drying and calcining process 5-20 times, and finally perform annealing.

2. The method for preparing a titanium-based metal oxide coating electrode according to claim 1, characterized in that The specific process of step 1) pretreatment is as follows: S1 polishing: Use 400-grit and 800-grit sandpaper to polish the titanium substrate in turn to remove the surface oxide layer and make it more uniform and smooth; S2 Degreasing: Use pure water to ultrasonically clean to remove metal debris and other impurities on the surface, and then boil in a 5-15% mass fraction NaOH aqueous solution for 1-2.5h to remove oil stains; S3 Acid Etching: Immerse the degreased titanium substrate in an aqueous solution of oxalic acid with a mass fraction of 5-20% and heat and etch it. The heating temperature is 80-90° C. and the heating time is 1-2.5 hours.

3. The method for preparing a titanium-based metal oxide coating electrode according to claim 1, characterized in that In step 2), the Ru source is RuCl3, the Ir source is H2IrCl6·xH2O, the Sn source is SnCl4, and the molar ratio of the Ru source, the Ir source and the Sn source is 5-5.5:1:3.5-4.

4. The method for preparing a titanium-based metal oxide coating electrode according to claim 1, characterized in that Step 3) The calcination temperature is 450-550°C and the calcination time is 5-20min.

5. The method for preparing a titanium-based metal oxide coating electrode according to claim 1, characterized in that Step 4) The annealing temperature is 450-550°C and the annealing time is 1-2h.

6. A titanium-based metal oxide coating electrode prepared by the method according to any one of claims 1 to 5, wherein the loading amount of the RuO2 / IrO2-SnO2 coating on the titanium substrate is 2-5 mg / cm 2 .

7. Use of a titanium-based metal oxide coating electrode as claimed in claim 6 in electrocatalytic degradation of landfill leachate.

8. The use according to claim 7, characterized in that A three-dimensional electrocatalytic oxidation system is used to degrade landfill leachate. The anode uses the titanium-based metal oxide coating electrode. The anode and the cathode are fixed in parallel in the electrolytic cell. A granular electrode is filled between the anode and the cathode. A nano-aeration plate is installed near the cathode to allow oxygen-containing gas to be introduced. The fine and uniform atomization of the oxygen-containing gas is more conducive to the generation of cathode free radicals. The landfill leachate is used as the electrolyte and introduced into the electrolytic cell. Stirring is started to fully disperse the granular electrode. The distance between the cathode and the anode is controlled to be 3-5 cm to perform the electrocatalytic degradation reaction. The particle size of the granular electrode is 0.88-2.36 mm, the dosage of the granular electrode in the electrolyte of the electrolytic cell is 3-11 g / L, and the current density is 10-50 mA / cm 2 , the pH of the electrolyte is adjusted to between 5-10.

9. The use according to claim 8, characterized in that The organic matter in the landfill leachate contains antibiotic pollutants, the COD is within 1500±100 mg / L, the NH3-N is within 1000±100 mg / L, the cathode is a titanium plate, and the particle electrode is coconut shell biochar; The pH of the electrolyte was adjusted to 9-10, and the electrocatalytic oxidation degradation reaction was carried out at a temperature of 25±2°C and a current density of 20-30 mA / cm 2 ; KCl is also added into the electrolyte as an electrolyte, and the concentration of the electrolyte KCl is 50-150 mg / L.

10. The use according to claim 9, characterized in that The antibiotic pollutants include at least one of tetracycline TC, oxytetracycline OTC and chlortetracycline CTC, and the total concentration of the antibiotic pollutants is within 30 mg / L.

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