Platinum-plated ruthenium iridium series titanium-based electrode, preparation method thereof and application of platinum-plated ruthenium iridium series titanium-based electrode in electro-catalytic treatment of complex matrix landfill leachate

Abstract

The invention discloses a platinum-plated ruthenium iridium series titanium-based electrode, a preparation method of the platinum-plated ruthenium iridium series titanium-based electrode and application of the platinum-plated ruthenium iridium series titanium-based electrode in electrocatalytic treatment of complex matrix landfill leachate. And then the surface of the platinum intermediate layer of the titanium substrate is coated with a ruthenium-iridium-loaded composite metal oxide to form a surface ruthenium-iridium active layer, the obtained electrode is Pt-Ti / RuO2-IrO2, and the thickness of the surface ruthenium-iridium active layer is 5-25 [mu] m. According to the invention, the titanium-based electrode plate is plated with platinum and coated with the ruthenium-iridium coating, so that the dosage of precious metal Pt is reduced, the electrocatalytic activity is improved, the peeling of the coating is reduced, the efficiency of degrading landfill leachate is greatly improved, and the stability of the electrocatalytic reaction of the electrode is high.

Description

Technical Field

[0001] The present invention relates to the field of wastewater treatment, and more specifically to a platinum-plated ruthenium-iridium titanium-based electrode, a preparation method thereof, and an application thereof in electrocatalytic treatment of complex matrix landfill leachate. Background Art

[0002] Sanitary landfill is a widely recognized and accepted method of treating solid waste today. However, sanitary landfill will inevitably produce leachate, which has the characteristics of complex water quality and high chromaticity. It is rich in organic matter, ammonia nitrogen, heavy metals and other toxic substances, and has an unbalanced nutrient ratio. Landfills can be divided into three types according to age: young (age <5 years old), middle-aged (age between 5 and 10 years old) and mature leachate (age >10 years old). The composition and properties of leachate change with the time of landfill. Young leachate has a lower pH value and a higher BOD value. 5 The concentration of COD is high, the ammonia nitrogen content is low (<400 mg / L), and the pH of mature landfill leachate is close to neutral, BOD 5 and COD concentration is reduced, with low BOD 5 / COD ratio (<0.1), high concentration of ammonia (>1000mg / L). Therefore, in comparison, mature landfill leachate has more difficult-to-degrade substances, which is a difficult problem to degrade today.

[0003] Tetracycline antibiotics (TC), including tetracycline, oxytetracycline, chlortetracycline, and doxycycline, have been widely used in human medicine, animal / crop rejuvenation, and diseases. A large number of unused or expired drugs are directly disposed of in solid waste without any specific treatment and disposal process. Due to its low metabolic degradation rate, 95% of TC is washed away and eventually enters various environments through sewage systems, surface runoff, etc., resulting in its widespread presence in the environment with concentrations ranging from μg / L to mg / L. This has led to the discovery of a large number of tetracycline drugs in landfill leachate. The accumulation and spread of tetracycline antibiotics in the environment through the food chain pose a significant risk to both humans and ecosystems. Therefore, it is necessary to find efficient methods to degrade tetracycline.

[0004] Treatment technologies for landfill leachate include biodegradation, physical separation, and chemical reactions. However, no method can remove all pollutants at the same time. For example, due to the stubborn nature of organic carbon in the leachate of aged landfills, biological processes may not achieve good results. At the same time, high concentrations of ammonia nitrogen and heavy metals in the leachate of aged landfills have a strong inhibitory effect on microorganisms. Advanced oxidation processes (AOPs) are often used to overcome the limitations of traditional technologies and are a better choice for treating landfill leachate. Among them, electrochemical oxidation has become one of the most popular and effective AOPs for treating various types of wastewater, especially in the field of treating landfill leachate. Two-dimensional electrochemical technology (2DET) is the basic form of electrochemical oxidation process, but it has defects such as high energy consumption, low treatment efficiency, low space-time yield, and mass transfer limitations. In order to solve these problems, researchers have developed three-dimensional electrochemical technology (3DET) in recent years, the core of which is to use particle electrodes to fill the space between the two planar electrodes of 2DET. Compared with 2DET, 3DET has significant advantages in conductivity, catalysis, electrode surface area, mass transfer efficiency and current efficiency. After the electric field is applied, the particle electrode is polarized and charged to form a microelectrode, and the redox reaction on the surface and nearby can be carried out. At present, various types of particle electrodes have been used in 3DET, including granular activated carbon (GAC), modified GAC, biochar, clay minerals, slag and metal materials (Fe, Cu, Al, etc.). Among them, biochar particle electrodes are produced by pyrolysis of biomass waste and have attracted much attention because of their rich active sites and functional groups such as quinoline and phenolic hydroxyl groups, environmental protection and low price. In the current era, it has great development potential and is expected to replace traditional materials.

[0005] Electrochemical oxidation treatment of landfill leachate generally relies on strong oxidants (such as OH) produced at the anode, active anodes with low oxygen evolution overpotential (such as IrO 2 、RuO 2 , Pt) will form superoxide with high oxidation ability on the surface, thereby degrading pollutants. The anode material plays a decisive role in the efficiency and speed of the electrochemical reaction and is the core element of the advancement of electrochemical oxidation technology. The ideal anode material must have good mechanical properties, electrochemical stability and corrosion resistance. In the research on electrochemical oxidation of late-stage landfill leachate, commonly used anode materials are ruthenium, iridium, titanium oxide-based anodes, platinum anodes, titanium-based lead dioxide anodes and diamond anodes. Platinum-plating titanium-based electrode plates and coating them with ruthenium-iridium coatings not only reduces the amount of precious metal Pt used and improves the electrocatalytic activity, but also reduces the peeling of the coating, greatly improving the efficiency of degrading landfill leachate. Summary of the invention

[0006] In view of the above-mentioned technical problems existing in the prior art, the object of the present invention is to provide a method for treating complex matrix landfill leachate and high concentration of emerging pollutants therein, which has the characteristics of high efficiency, easy operation, high number of repeated uses of electrode plates, and is suitable for the control and degradation of wastewater.

[0007] The technical solution adopted by the present invention is as follows:

[0008] A platinum-plated ruthenium-iridium titanium-based electrode is firstly electroplated with platinum on the surface of the titanium substrate to form a platinum intermediate layer, and then a ruthenium-iridium composite metal oxide is coated on the surface of the platinum intermediate layer of the titanium substrate to form a surface ruthenium-iridium active layer. The obtained electrode is Pt-Ti / RuO 2 -IrO 2 ,in:

[0009] The thickness of the surface ruthenium-iridium active layer is 5-25 μm, preferably 10-15 μm, and the molar ratio of ruthenium to iridium atoms is 0.4-2.5:1, preferably 2.0-2.5:1.

[0010] The platinum intermediate layer is formed by electroplating as follows: the titanium substrate is the cathode, the platinum plate is the anode, an acidic aqueous solution of chloroplatinic acid is used as the electrolyte, and an electrodeposition reaction is carried out at a temperature of 30-70° C. The current density of the electrodeposition reaction is 100-400 mA / cm 2 , the deposition time is 10-40min, so that a platinum coating is deposited on the surface of the titanium substrate; in the acidic aqueous solution of chloroplatinic acid, the concentration of chloroplatinic acid is 10-30g / L, and the concentration of HCl is 7-10M.

[0011] The method for preparing a platinum-ruthenium-iridium-based titanium-based electrode comprises the following steps:

[0012] 1) The titanium substrate is sequentially treated by surface sandblasting, alkaline washing and degreasing, and oxalic acid etching to obtain a uniform rough surface, and a pretreated titanium substrate is obtained for standby use;

[0013] 2) using an acidic aqueous solution of chloroplatinic acid as an electrolyte, the titanium substrate pretreated in step 1) as a cathode, and the platinum plate as an anode, and performing an electrodeposition reaction at a temperature of 30-70° C. for a deposition time of 10-40 minutes to deposit a platinum coating on the surface of the titanium substrate;

[0014] 3) After the reaction is completed, the platinum-plated titanium substrate is taken out, washed with deionized water, dried, and then heated at 150-400° C. for 30-120 min;

[0015] 4) preparing an acidic solution of ruthenium salt and iridium salt as a precursor coating liquid, and applying the precursor coating liquid evenly on the surface of the platinum coating of the titanium substrate with a coating rod, then drying to evaporate the solvent, transferring to a muffle furnace for thermal oxidation treatment to form a ruthenium-iridium surface active layer, and repeating the above coating and thermal oxidation operations until the thickness of the ruthenium-iridium surface active layer reaches the target result.

[0016] Further, the specific process of step 1) pretreatment is as follows:

[0017] S1: The titanium substrate has a purity of greater than 99% by mass. The titanium substrate is sandblasted with diamond powder and then ultrasonically cleaned with deionized water to remove metal grit and debris on the surface of the substrate;

[0018] S2: immersing the titanium substrate in a NaOH aqueous solution with a concentration of 20-100 mg / L and treating at a temperature of 60-85° C. for 30-90 min to remove the oil film on the surface of the titanium substrate;

[0019] S3: The titanium substrate after alkaline washing and degreasing is rinsed with deionized water, and then immersed in an oxalic acid aqueous solution with a mass fraction of 5-20%, heated to boiling reflux, and etched for 60-150 minutes to improve the surface activity of the titanium substrate;

[0020] S4: After etching, the titanium substrate is rinsed with deionized water, and then placed in an oxalic acid aqueous solution with a mass fraction of 0.5-2%, and stored for later use.

[0021] Furthermore, the electrolyte of step 2) is prepared by dissolving chloroplatinic acid and HCl solution in water, the concentration of chloroplatinic acid is 10-30 g / L, the concentration of HCl is 7-10 M, and the current density of the electrodeposition reaction is 100-400 mA / cm 2 , preferably 200-250mA / cm 2 .

[0022] Furthermore, in step 3), the heating temperature is 250-300° C., and the heating time is 60-90 min.

[0023] Further, in step 4), the molar ratio of ruthenium to iridium atoms in the precursor coating solution is 0.4-2.5:1, preferably 2.0-2.5:1, and the solvent of the precursor coating solution is a mixture of methanol and concentrated hydrochloric acid in a volume ratio of 3-5:1, and the mass concentration of the concentrated hydrochloric acid is 30-36%;

[0024] Furthermore, in step 4), the temperature of the thermal oxidation treatment in the muffle furnace is 450-550° C., and the time is 10-60 min.

[0025] The present invention also discloses the use of the platinum-ruthenium-iridium-based titanium-based electrode in the electrocatalytic treatment of complex matrix garbage leachate. A three-dimensional electrocatalytic oxidation system is used to degrade the complex matrix garbage leachate. The anode adopts the platinum-ruthenium-iridium-based titanium-based electrode. The anode and the cathode are fixed in parallel in an electrolytic cell. A granular electrode is filled between the anode and the cathode. The complex matrix garbage leachate is introduced into the electrolytic cell as an electrolyte. 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 an electrocatalytic degradation reaction. The particle size of the granular electrode is 0.85-2.36 mm, preferably 1.70-2.00 mm. The dosage of the granular electrode in the electrolyte of the electrolytic cell is 5-11 g / L, preferably 7-8 g / L. The current density is 20-50 mA / cm 2 , preferably 30±5mA / cm 2 , the pH of the electrolyte is adjusted to between 3-11.

[0026] Furthermore, the organic matter in the complex matrix landfill leachate contains antibiotic pollutants, which may be tetracycline TC, and the COD of the complex matrix landfill leachate is within 1100±100 mg / L, NH 3 -N is within 1000±100mg / L, pH is 5±0.15, the cathode is a titanium plate with a purity of more than 99%, and the particle electrode is coconut shell carbon.

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

[0028] (1) The present invention uses three-dimensional electrocatalytic oxidation technology to efficiently degrade landfill leachate and high-concentration tetracycline therein, has high efficiency and stable performance, is easy to use, and is suitable for the control and degradation of landfill leachate and tetracycline.

[0029] (2) The electrode of the present invention utilizes the synergistic effect of the platinum intermediate layer and the surface ruthenium iridium active layer to greatly improve the effect of electrocatalytic degradation of landfill leachate. COD and tetracycline TC are both well electrocatalytically removed. The application effect of the electrode of the present invention in catalytic degradation of landfill leachate is significantly better than that of the existing commercially available tin-antimony-titanium electrode Ti / SnO 2 -Sb 2 O 5 and commercially available ruthenium-iridium-tin electrode Ti / RuO 2 -IrO 2 -SnO 2 , which has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic structural diagram of a three-dimensional electrocatalytic oxidation system for degrading tetracycline in wastewater provided by the present invention.

[0031] Figure 2 The scanning electron microscope images are of the microscopic morphology of the platinum-ruthenium-iridium-based titanium-based electrode plate; (a), (b), and (c) are before the electrocatalytic reaction at different magnifications; (d), (e), and (f) are after 100 times of electrocatalytic degradation of landfill leachate and high-concentration tetracycline therein at different magnifications.

[0032] Figure 3 When applied to the electrocatalytic treatment of landfill leachate, the anode is respectively the platinum-ruthenium-iridium-based titanium-based electrode of Example 1, the commercially available tin-antimony-titanium electrode Ti / SnO 2 -Sb 2 O 5 and commercially available ruthenium-iridium-tin electrode Ti / RuO 2 -IrO 2 -SnO 2 , and the comparison results of COD degradation of landfill leachate within 180 minutes.

[0033] Figure 4 When applied to the electrocatalytic treatment of landfill leachate, the anode is respectively the platinum-ruthenium-iridium-based titanium-based electrode Pt-Ti / RuO 2 -IrO 2 , Ruthenium-iridium-based titanium-based electrode Ti / RuO of Example 2 2 -IrO 2 , and the comparison results of COD degradation of landfill leachate within 180 minutes.

[0034] Figure 5 When applied to the electrocatalytic treatment of landfill leachate, the anode is respectively the platinum-ruthenium-iridium-based titanium-based electrode Pt-Ti / RuO 2 -IrO 2 , Ruthenium-iridium-based titanium-based electrode Ti / RuO of Example 2 2 -IrO 2 , and the comparison results of ammonia nitrogen degradation in landfill leachate within 180 minutes.

[0035] Figure 6 It is the result of the influence of different factors on catalytic degradation; (a: pH, b: current density, c: particle dosage, d: particle diameter, e: plate spacing, f: overall effect).

[0036] Figure 7 It is a three-dimensional fluorescence analysis of landfill leachate at different electrocatalytic times in a three-dimensional electrocatalytic oxidation system; (A: 0min, B: 45min; C: 90min; D: 180min).

[0037] Figure 8a The degradation mechanism of landfill leachate and high concentration tetracycline in the three-dimensional electrocatalytic oxidation system was analyzed. 2 O 2Variation of production amount with electrocatalytic time;

[0038] Figure 8b The results of the degradation mechanism of landfill leachate and high-concentration tetracycline in the three-dimensional electrocatalytic oxidation system are compared after 180 minutes of electrocatalysis at different tert-butyl alcohol probe dosages in the electrolyte.

[0039] Figure 8c The electron paramagnetic resonance image of the electrolyte after 45 minutes of electrocatalysis when analyzing the degradation mechanism of landfill leachate and its high concentration of tetracycline in the three-dimensional electrocatalytic oxidation system. DETAILED DESCRIPTION

[0040] The present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0041] The commercially available tin-antimony-titanium electrode Ti / SnO used in the embodiments of the present invention is 2 -Sb 2 O 5 , Commercially available ruthenium iridium tin electrode Ti / RuO 2 -IrO 2 -SnO 2 , all purchased from Suzhou Shuer Titanium Industrial Technology Co., Ltd., with dimensions of length × width × thickness = 60mm × 40mm × 2mm.

[0042] Commercially available tin-antimony-titanium electrode Ti / SnO 2 -Sb 2 O 5 The preparation method is that the Sn and Sb precursor solutions are brushed with thermal decomposition method, the molar ratio of Sn and Sb in the precursor solution is 9:1, and the precursor solution is brushed on the surface of the titanium electrode and calcined at a high temperature of 550°C. 2 -Sb 2 O 5 The coating thickness is 12-15 μm.

[0043] Commercially available ruthenium iridium tin electrode Ti / RuO 2 -IrO 2 -SnO 2 The preparation method is as follows: Ru, Ir and Sn precursor solutions are coated on the surface of the titanium electrode, the molar ratio of Ru, Ir and Sn in the precursor solution is 2:2:1, and after drying, they are calcined at high temperature to form RuO on the surface of the titanium electrode. 2 -IrO 2 -SnO 2 The RuO coating on the titanium electrode surface 2 -IrO 2 -SnO 2 The coating thickness is 12-15 μm.

[0044] Example 1

[0045] The schematic diagram of the structure of the three-dimensional electrocatalytic oxidation system for degrading tetracycline in wastewater provided by the present invention is shown in Figure 1 The electrolytic cell is a cylindrical organic glass container with a bottom diameter of 8 cm and a height of 15 cm. The side is designed with an overflow hole for sampling with a hole diameter of 1 cm. The spacing between the electrode slots on the top cover is 3 to 5 cm, and a slot is opened every 0.5 cm. The slots opened on the top cover of the electrolytic cell also facilitate the contact between the outside air and the electrolyte in the electrolytic cell. The anode is selected as a platinum-ruthenium-iridium titanium-based electrode (Pt-Ti / RuO 2 -IrO 2 The cathode is a cheap and easily available titanium metal plate with a purity of more than 99%. The effective dimensions of both are length × width × thickness = 60mm × 40mm × 2mm. The cathode and anode are arranged in parallel and opposite to each other and stand upright in the electrolytic cell. Coconut shell charcoal is used as a granular electrode and filled between the anode and cathode. The cathode and cathode are connected to a DC regulated power supply through wires. The electrolytic cell is placed on a magnetic stirrer, and a stirring magnet 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 run efficiently.

[0046] The preparation process of platinum-ruthenium-iridium-based titanium-based electrode is as follows:

[0047] (1) Pretreatment of titanium substrate: The surface of the titanium substrate with a purity of 99% is sandblasted with diamond powder, and then ultrasonically washed with deionized water for 30 minutes to remove metal gravel and debris on the surface of the substrate, and then rinsed with deionized water after the ultrasonic treatment. Prepare 500 ml of NaOH solution with a concentration of 50 mg / L, place the pretreated titanium substrate in it, set the water bath temperature to 80°C, and continue for 60 minutes to remove the oil film on the surface of the titanium substrate. Prepare 500 ml of 10% oxalic acid aqueous solution by mass, rinse the titanium substrate after alkaline washing and degreasing with deionized water, then place it in a 10% oxalic acid solution, heat to boiling, and etch for 120 minutes to increase the surface activity. After etching, rinse the titanium substrate with deionized water and place it in a 1% oxalic acid solution (wt) for later use.

[0048] (2) Platinum electroplating on titanium substrate: Use chloroplatinic acid solution (20g / LH 2 PtCl 6 The substrate was platinized with an aqueous solution composed of 8.2M HCl, and the chloroplatinic acid solution was used as an electrolyte and poured into a single-chamber double-layer battery in a constant temperature water bath. A Ti substrate with a size of 60 mm×40 mm×2 mm was used as a cathode, two platinum plates were used as anodes, and the current density was 250 mA / cm 2The constant temperature water bath is set at 65°C. The single-chamber double-layer battery is provided with an external circulation pipeline to circulate the electrolyte to promote the deposition of platinum. The deposition time is 20 minutes. Due to the low operating temperature, there will be no gas precipitation to cause pinholes on the coating surface. Then, the platinum-coated titanium substrate is taken out and ultrasonically rinsed with deionized water to remove the surface acid and unreacted H 2 PtCl 6 The surface moisture of the platinum-coated titanium substrate was dried in an oven at a constant temperature of 60°C, the electrode was heat treated at 300°C for 60 minutes, and then cooled to room temperature to obtain a platinum-coated titanium substrate.

[0049] (3) Preparation and coating of precursor coating liquid: Weigh 0.693g of ruthenium trichloride and 0.738g of iridium chloride hexahydrate so that the molar ratio of ruthenium to iridium is 7:3, dissolve in 4ml of methanol and 1ml of concentrated hydrochloric acid (mass fraction 36%), and ultrasonicate for 20min to obtain a precursor liquid. Use a pipette to aspirate the coating liquid, and use a coating rod to evenly apply 400μL of the coating liquid on the surface of the platinum-plated titanium substrate in step (2), place it under an infrared lamp until the surface solvent is completely evaporated, and then place it in a muffle furnace for thermal oxidation at 500°C for 30min, and then cool to room temperature. Repeat the coating and thermal oxidation 10 times to further load RuO on the surface of the platinum-plated titanium substrate. 2 -IrO 2 Active layer, RuO 2 -IrO 2 The thickness of the active layer is about 15 μm, and the platinum-ruthenium-iridium titanium-based electrode Pt-Ti / RuO is prepared. 2 -IrO 2 .

[0050] The SEM images of the platinum-ruthenium-iridium-based titanium-based electrode prepared in Example 1 of the present invention at different magnifications are as follows: Figure 2 As shown in the sub-figures (a), (b), and (c), there are cloud-like stacking or discontinuous layers on the surface, which is formed by excessive liquid coating. There are also some concave pits on the surface of the electrode sheet, which are not exposed titanium substrates, but are formed by the lower thickness of ruthenium, iridium and platinum. At a magnification of 2.00k, there are a small number of fine cracks on the surface of the electrode sheet, which are formed during the stress relief process. These cracks will cause the electrolyte to penetrate into the surface of the titanium substrate during the reaction, promote the oxidation of titanium, and thus cause the coating to peel off, but the cracks of this electrode plate are fewer and finer than those of commercially available electrode plates.

[0051] The platinum-ruthenium-iridium-based titanium-based electrode prepared in Example 1 is applied to electrocatalytic treatment of landfill leachate, and the steps are as follows:

[0052] S1 Preparation of simulated landfill leachate: The landfill leachate uses simulated leachate, with water as the solvent. The components in the water include humic acid HA, ammonium sulfate (NH 4) 2 SO 4 , Tetracycline TC, Sodium bicarbonate NaHCO 3 , leachate COD is 1100mg / L, NH 3 -N is 1000 mg / L, and the pH is 7.8±0.15, in which humic acid provides COD, ammonium sulfate provides ammonium nitrogen, sodium bicarbonate is a component of the buffer solution, and tetracycline is a high-concentration antibiotic pollutant in the simulated landfill leachate.

[0053] Wherein, the concentration of each component in the simulated landfill leachate is: humic acid 1400 mg / L, sodium bicarbonate 2750 mg / L, tetracycline 20 mg / L, and ammonium sulfate 10000 mg / L.

[0054] S2 electrocatalytic reaction: Figure 1 The device shown in the figure uses coconut shell charcoal as a particle electrode, a titanium plate with a purity of 99.99% as a cathode, and a platinum-ruthenium-iridium-based titanium-based electrode prepared in Example 1 as an anode. The simulated landfill leachate prepared in step S1 is used as an electrolyte of 500 mL. The operating conditions are pH = 7.8 (actual pH, not adjusted), and the current density = 30 mA / cm 2 , coconut shell charcoal particle size = 1.70-2.00 mm, dosage = 7 g / L, cathode and anode plate spacing = 3 cm. Under this random condition, the effect of the anode on the degradation of simulated landfill leachate was investigated.

[0055] The platinum-plated ruthenium-iridium-based titanium-based electrode prepared in Example 1 is used for electrocatalytic treatment of landfill leachate. After a single reaction of 3 hours in the above step S2, the side reaction substances on the platinum-plated ruthenium-iridium-based titanium are cleaned, and the electrode is placed in an ultrasonic machine and ultrasonicated in deionized water for 30 minutes, then rinsed with deionized water and dried in a 60°C constant temperature oven. The obtained electrode is used for repeated electrocatalytic operation of the next batch, and fresh electrolyte is replaced for the next batch of electrocatalytic reactions. After the platinum-plated ruthenium-iridium-based titanium-based electrode of Example 1 is repeatedly reacted 100 times (the electrocatalytic reaction time for each batch is 3 hours), its SEM pictures at different magnifications are as follows Figure 2 As shown in (d), (e) and (f), the cloud-like layer structure still exists, the surface is relatively smooth, and the amount of coating missing is small.

[0056] Comparative Example 1:

[0057] Commercially available tin-antimony-titanium electrode Ti / SnO 2 -Sb 2 O 5 , applied to the electrocatalytic treatment of landfill leachate, the experimental steps are the same as steps S1-S2 of Example 1, the only difference is that "the platinum-plated ruthenium-iridium titanium-based electrode of Example 1 is replaced by a commercially available tin-antimony-titanium electrode Ti / SnO 2 -Sb2 O 5 ”, the other conditions remain unchanged.

[0058] Comparative Example 2:

[0059] Commercially available ruthenium-iridium-tin electrode Ti / RuO 2 -IrO 2 -SnO 2 , applied to the electrocatalytic treatment of landfill leachate, the experimental steps are the same as steps S1-S2 of Example 1, the only difference is that "the platinum-plated ruthenium-iridium titanium-based electrode of Example 1 is replaced by a commercially available ruthenium-iridium-tin electrode Ti / RuO 2 -IrO 2 -SnO 2 ”, the other conditions remain unchanged.

[0060] When applied to the electrocatalytic treatment of landfill leachate, the anode is respectively the platinum-plated ruthenium-iridium titanium-based electrode of Example 1, the commercially available tin-antimony-titanium electrode Ti / SnO 2 -Sb 2 O 5 and commercially available ruthenium-iridium-tin electrode Ti / RuO 2 -IrO 2 -SnO 2 According to the method of Example 1, electrocatalytic treatment was carried out, and the COD degradation of the landfill leachate within 180 minutes was compared. Figure 3 ,from Figure 3 It can be seen that the maximum COD removal rate of the platinum-ruthenium-iridium-based titanium-based electrode of Example 1 is 45.58% at 45 minutes within the 3-hour treatment time. 2 -Sb 2 O 5 The COD removal rate is 27.078%. The commercially available ruthenium iridium tin electrode Ti / RuO 2 -IrO 2 -SnO 2 The COD removal rate was 20.07%. The commercially available tin-antimony-titanium electrode Ti / SnO 2 -Sb 2 O 5 and commercially available ruthenium-iridium-tin electrode Ti / RuO 2 -IrO 2 -SnO 2 The maximum COD removal rates are 39.53% and 30.74% respectively, indicating that the platinum-ruthenium-iridium-based titanium-based electrode plated in Example 1 of the present invention has a greater electrocatalytic oxidation ability.

[0061] Example 2

[0062] Example 2 Preparation of ruthenium-iridium-based titanium-based electrode, the preparation of the electrode in Example 1 was repeated, the only difference being that "the step of electroplating platinum on the titanium substrate in step (2) was omitted", and the other conditions remained unchanged, and finally a ruthenium-iridium-based titanium-based electrode Ti / RuO was prepared. 2 -IrO 2 .

[0063] When applied to the electrocatalytic treatment of landfill leachate, the anode is respectively the platinum-ruthenium-iridium-based titanium-based electrode Pt-Ti / RuO 2 -IrO 2 , Ruthenium-iridium-based titanium-based electrode Ti / RuO of Example 2 2 -IrO 2 According to the method of Example 1, electrocatalytic treatment was carried out, and the COD degradation of the landfill leachate within 180 minutes was compared. Figure 4 ,from Figure 4 It can be seen that the maximum COD removal rate of the platinum-plated ruthenium-iridium-based titanium-based electrode of Example 1 is 45.58% at 45 minutes within a 3-hour treatment time. The COD removal rate of the ruthenium-iridium-based titanium-based electrode of Example 2 with the same coating thickness at the same time is only 26.47%, and its maximum COD removal rate within 180 minutes is only 30.20%.

[0064] The anodes are respectively the platinum-plated ruthenium-iridium titanium-based electrodes Pt-Ti / RuO 2 -IrO 2 , Ruthenium-iridium-based titanium-based electrode Ti / RuO of Example 2 2 -IrO 2 The results of the comparison of ammonia nitrogen degradation in landfill leachate within 180 min are shown in Figure 5 As shown, from Figure 5 It can be seen that the electrode of Example 1 has a higher ammonia nitrogen degradation effect than the electrode of Example 2, which is about 7% higher.

[0065] Figure 4 In the figure, the ordinate of the dotted line graph is the COD removal rate, and the ordinate of the bar graph is the COD content.

[0066] Figure 5 In the figure, the vertical axis corresponding to the dotted line graph is the ammonia nitrogen removal rate, and the vertical axis corresponding to the bar graph is the ammonia nitrogen content.

[0067] Example 3

[0068] The anode is the platinum-plated ruthenium-iridium titanium-based electrode Pt-Ti / RuO of Example 1. 2 -IrO 2The catalytic electrochemical reaction was carried out according to the electrocatalytic operating conditions of Example 1, except that the experimental conditions of the single factor experiment were changed. The experimental conditions of the single factor change were one of the following: pH (3-11), current density (20-50 mA / cm 2 ), coconut shell charcoal particle size (0.88-2.36mm), coconut shell charcoal dosage (5-11g / L) and electrode spacing (3-5cm), the effects of different factors on catalytic degradation are shown in the table. Figure 6 . Figure 6 In each sub-graph, the vertical axis of the dot-line graph corresponds to the removal rate, and the vertical axis of the bar graph corresponds to the COD or TC content.

[0069] The effect of different initial pH on the degradation performance of simulated landfill leachate is shown in Figure 6 As shown in the figure (a), when the pH is 3-7, the COD removal rate drops rapidly, from 98.91% to 50.50%. When the pH is 8, the COD removal rate rises to 61.90%. When the pH rises to 11, the COD removal rate shows a downward trend again, falling to 38.02%. This result shows that acidic conditions are more conducive to the removal of COD in the leachate. Because under acidic conditions, a large amount of free H + More easily with O in the air 2 The effect of generating H 2 O 2 , which improves the oxidation capacity of the system; under alkaline conditions, H generated on the surface of the particle electrode 2 O 2 Easy in OH － It decomposes rapidly under the action of humic acid, resulting in a decrease in its surface oxidation ability. And under alkaline conditions, humic acid will be weakly adsorbed on the electrode plate, thereby reducing the efficiency of the electrochemical reaction. In this system, the removal rate of tetracycline is not very sensitive to the initial pH value of the solution (3.0 to 11.0). The effect of pH on the TC removal rate of the system is significantly smaller than that on the COD removal rate. In general, TC is easily removed in an alkaline environment. When the pH value is 3-6, the TC removal rate increases from 65.32% to 73.07%, and when the pH value is 7, the TC removal rate decreases to 64.88%. When the pH is raised to 11 again, the TC removal rate increases, and the fluctuation is not obvious, up to 79.73%. Comprehensive comparison pH = 5 is a more preferred pH value in this system.

[0070] A large number of studies have shown that in reactions involving electrochemical processes, potential difference drives electron transfer, and electron transfer is the key to electrooxidation. Therefore, current density is an important parameter for evaluating the efficiency of three-dimensional electrocatalytic systems in treating landfill leachate. Figure 6 As shown in the sub-diagram (b), the higher the applied current density, the higher the power consumption and cost, so 30 mA / cm2 of current density.

[0071] The particle electrode increases the reaction efficiency of the electrochemical system and adjusts the electrochemical reaction area, thereby affecting the reaction efficiency. Therefore, the dosage of the particle electrode affects the removal effect of organic pollutants. The experiment set the particle dosage of 5, 7, 9, and 11 mg / L to explore its effect on the degradation effect. Figure 6 The sub-graph (c) shows that when the particle dosage increases, the COD removal rate shows a trend of first rising and then falling and maintaining stability. The worst effect occurs when the dosage is 5g / L, with a removal rate of 71.62%, and the best dosage is 7g / L, at which the removal rate is 80.81%. The effect of dosage on TC removal rate is not significant, with a minimum of 67.46% and a maximum of 71.84%. Considering the cost and treatment effect factors, the dosage is selected as 7mg / L, at which the COD and TC removal rates are 80.81% and 68.31% respectively.

[0072] The influence of three-dimensional particles on three-dimensional electrocatalytic systems is also reflected in the particle size. To this end, this experiment studied the influence of different particle sizes (0.85-1mm, 1.00-1.18mm, 1.18-1.40mm, 1.40-1.70mm, 1.70-2.00mm, 2.00-2.36mm). The particle size of the particle electrode fluctuates between 70.58% and 80.81% on the removal rate of COD in the system, showing a trend of first decreasing, then increasing, and then decreasing. It has little effect on the degradation of TC. Too large or too small particle size of the particle electrode is not conducive to the degradation of COD. The smaller the particle size, the more particles there are under the same dosage, and it is easier for particles to collide and cause short circuits. In addition, the small size of the particle electrode makes it difficult to recycle, which is not conducive to use in circulating wastewater. When the particle size is too large, the flow rate between wastewater particles increases, and due to the small specific surface area of ​​the particle electrode, the oxidation reaction ability of the particle electrode surface is weakened, which will cause poor electrolysis effect. In addition, the possibility of sedimentation will increase, resulting in a decrease in the effective number of particle electrodes. After comprehensive comparison, 1.70-2.00 mm is selected as the appropriate particle size.

[0073] In electrochemical experiments, the distance between electrodes plays a key role. It directly affects the size of the reactor resistance, which in turn affects the power consumption required by the system. If the distance between the plates is too narrow, the electric field strength may be too high, which may cause electric field breakdown at the moment of power-on, thereby shortening the service life of the electrode. If the distance between the electrodes is too large, it will increase the distance of material transfer, and at the same time cause part of the electrical energy to be converted into heat energy and other non-target side reactions, thereby increasing energy consumption. Figure 6The sub-figure (e) shows that the removal rates of COD and TC in the landfill leachate have the same trend, showing a trend of first increasing and then decreasing. The best plate spacing condition for degrading pollutants is 4 cm.

[0074] Figure 6 Figure (f) shows the overall degradation effect under the optimal conditions within 3 hours of degradation. At this time, the COD removal rate is 90.25% and the TC removal rate is 72.41%. At this time, the optimal operating conditions of the three-dimensional electrocatalytic system are: pH = 5, current density 30mA / cm 2 The particle dosage is 7g / L, the particle size is 1.70-2.00mm, the plate spacing is 4cm, the COD removal rate is 90.25% within 3 hours, and the TC removal rate is 72.41%.

[0075] Example 4

[0076] A three-dimensional electrocatalytic system (i.e., 3D-ECO) was constructed according to Example 3, and an electrocatalytic reaction was carried out according to the optimal reaction conditions of Example 3, and the degradation mechanism of the system was studied. In order to further explore the mechanism, a two-dimensional electrocatalytic system (i.e., 2D-ECO) was introduced for comparison. The difference between the two-dimensional electrocatalytic system and the three-dimensional electrocatalytic system was only that "no particle electrode was introduced", and the other conditions were the same, that is, the difference between the two-dimensional electrocatalytic system and the three-dimensional electrocatalytic system was whether coconut shell charcoal was added.

[0077] Three-dimensional fluorescence spectroscopy is often used to understand the degradation pathways of different fluorescent functional groups. Generally, the fluorescence EEM spectrum can be divided into four typical regions according to the position of the fluorescence peak. Region I is associated with aromatic proteins (such as tyrosine) with excitation (Ex) / emission (Em) wavelengths of <250nm / <380nm. Region II is associated with fulvic acid-like substances with Ex / Em of <250nm / <380nm. Region III is associated with soluble microbial byproduct-like substances at Ex / Em of 250-280nm / <380nm. Region IV is associated with humic acid-like organic matter at Ex / Em of >250nm / >380nm. Figure 7 As shown in Figure 2, a distinct peak A was identified at Ex / Em of 460nm / 550nm, which was attributed to humic acid-like substances. Figure 7 (B) After treatment with the 3D-ECO system, the fluorescence intensity associated with humic substances increased from 1250 ( Figure 7 (A)) decreased to 850, which means that the humus concentration decreased. For the 3D-ECO system treatment for 90min ( Figure 7 (C)) and 3D-ECO system 180min( Figure 7(D)) The fluorescence intensity of the effluent after further reduction to 800 and 450, respectively, indicating that humus-like substances were effectively removed. These results are consistent with the removal data of organic matter such as COD.

[0078] In existing studies, the 3D-ECO system consisting of titanium-based active electrodes and three-dimensional carbon-based particles can generate H in situ in the presence of oxygen. 2 O 2 .H 2 O 2 It can also be formed by the dimerization of M(·OH), which can occur near the anode surface or in the entire reaction system. 2 O 2 This is one of the reasons why the system indirectly oxidizes humic acid.

[0079] O 2 +2H + +2e - →H 2 O 2

[0080] 2M(·OH)→2M+H 2 O 2

[0081] 2·OH→H 2 O 2

[0082] Comparison of H in 3D-ECO and 2D-ECO systems 2 O 2 content, Figure 8a It shows that the 3D-ECO system has extremely high H in the electrolyte at the beginning (treatment time 15min). 2 O 2 The content was twice that of the 2D-ECO system. It reached its peak at 166.31 mg / L at 30 min of treatment time, and then slowly decreased until the H content in the electrolyte reached 1.5 h of treatment time. 2 O 2 The content of H2O2 reaches a balance state and stabilizes at about 135 mg / L. This may be because in the early stage of the electrochemical reaction, due to the high current density, the rate of oxygen reduction reaction is fast, resulting in the generation rate of hydrogen peroxide being greater than its consumption rate. 2 O 2 Then, due to H 2 O 2 The self-decomposition and the electrode plates being adsorbed and blocked by various side reaction products on the surface lead to mass transfer limitation and H 2 O 2The content of H in the electrolyte decreased. In the 2D-ECO system, the H 2 O 2 The content reached a maximum value of 144.18 mg / L. This caused the 3D system to produce more H than the 2D system. 2 O 2 The reasons for the rapid and high content are: (1) The porous structure of the coconut shell charcoal surface greatly increases the contact area between the electrode and the electrolyte, and there are more reaction sites; (2) The coconut shell charcoal surface changes the local environment, such as pH value, ion concentration, etc.; (3) The addition of coconut shell charcoal is equivalent to adding multiple micro-electrolytic cells, providing a shorter electron transfer path and enhancing mass transfer efficiency.

[0083] The active oxidizing substances in the system play a major indirect oxidative role. According to existing research, ·OH is the active oxidant in this experimental system. In order to confirm the degradation mechanism of the system, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) was used as a spin trapping agent for EPR measurement. DMPO can capture ·OH, ·SO 4 - , O 2·- The free radicals with shorter life spans have different characteristic peaks. When the electrocatalytic degradation time is 45 minutes, the COD removal rate is the highest, so the electrolyte is taken out at this time and mixed with the spin capture reagent, and the mixing volume ratio is 1:1.2. Figure 8c The ratio spectrum of the DMPO-OH adduct, which shows a four-line signal with an intensity ratio of 1:2:2:1, proves the generation of ·OH. Its generation and mechanism of action are hypothesized as follows: On the surface of the active anode-plated platinum-ruthenium-iridium-titanium-based electrode plate (referred to as M), heterogeneously adsorbed hydroxyl radicals (M(·OH)) are formed by the oxidation of water. For the active anode, the hydroxyl radicals interact strongly with the electrode surface to form advanced oxides or superoxides (MO). When the M surface has an oxidation state higher than the standard potential for oxygen evolution, MO forms chemically adsorbed "active oxygen". It becomes a carrier for electrochemical conversion, thereby affecting the evolution of oxygen and affecting efficiency as a side reaction.

[0084] M+H 2 O→M(·OH)+H + +e -

[0085] M(·OH)→MO+H + +e -

[0086] MO+R→M+RO

[0087] At the same time, physically adsorbed M(·OH) or free M(·OH)) reacts directly with organic molecules, leading to their electrochemical incineration (producing CO2 and water).

[0088] aM(·OH)+R→M+mCO 2 +nH 2 O+H + +e -

[0089] In the formula, R is an organic compound containing m carbon atoms, and it requires a = (2m + n) oxygen atoms to be completely mineralized into CO 2 .

[0090] Unfortunately, the following side reactions occur simultaneously, affecting the efficiency of electrocatalytic treatment.

[0091] M(·OH)→M+1 / 2O 2 +H + +e -

[0092] In this study, a free radical quenching experiment was also established. Figure 8b As shown in the figure, the inhibitory effect of adding TBA at a final concentration of 3, 6, and 9 mg / L in the electrolyte on TC was negligible, only inhibiting 2%. This result proves that ·OH does not play a major role in the degradation of TC in this system.

[0093] In addition to the indirect oxidation by free radicals, non-radical routes can also lead to electrochemical degradation. 1 O 2 ) is the main potential reactive oxygen species in the non-radical pathway, so tetramethylpiperidinyl oxide (TEMP) was used as a spin trap to verify. Figure 8c It is shown that when TEMP is used as a spin trapping agent, a typical triple peak signal (a N =17.0G), indicating 1 O 2 It may be the main reaction substance for the degradation of TC, which is mainly co-produced through the following reactions.

[0094] H 2 O 2 + ·OH→H 2 O+HO 2 ·

[0095] HO 2 +HO 2 · →H 2 O 2 + 1 O 2 .

Claims

1. A platinum-ruthenium-iridium-based titanium-based electrode, characterized in that First, platinum is electroplated on the surface of the titanium substrate to form a platinum intermediate layer, and then a ruthenium-iridium composite metal oxide is coated on the surface of the platinum intermediate layer of the titanium substrate to form a surface ruthenium-iridium active layer. The obtained electrode is Pt-Ti / RuO2-IrO2, wherein: The thickness of the surface ruthenium-iridium active layer is 5-25 μm, preferably 10-15 μm, and the molar ratio of ruthenium to iridium atoms is 0.4-2.5:1, preferably 2.0-2.5:

1.

2. A platinum-ruthenium-iridium-based titanium-based electrode as claimed in claim 1, characterized in that The platinum intermediate layer is formed by electroplating as follows: the titanium substrate is the cathode, the platinum plate is the anode, an acidic aqueous solution of chloroplatinic acid is used as the electrolyte, and an electrodeposition reaction is carried out at a temperature of 30-70° C. The current density of the electrodeposition reaction is 100-400 mA / cm 2 , the deposition time is 10-40min, so that a platinum coating is deposited on the surface of the titanium substrate; in the acidic aqueous solution of chloroplatinic acid, the concentration of chloroplatinic acid is 10-30g / L, and the concentration of HCl is 7-10M.

3. The method for preparing a platinum-ruthenium-iridium-based titanium-based electrode according to claim 1, characterized in that The following steps are involved: 1) The titanium substrate is sequentially treated by surface sandblasting, alkaline washing and degreasing, and oxalic acid etching to obtain a uniform rough surface, and a pretreated titanium substrate is obtained for standby use; 2) using an acidic aqueous solution of chloroplatinic acid as an electrolyte, the titanium substrate pretreated in step 1) as a cathode, and the platinum plate as an anode, and performing an electrodeposition reaction at a temperature of 30-70° C. for a deposition time of 10-40 minutes to deposit a platinum coating on the surface of the titanium substrate; 3) After the reaction is completed, the platinum-plated titanium substrate is taken out, washed with deionized water, dried, and then heated at 150-400° C. for 30-120 min; 4) preparing an acidic solution of ruthenium salt and iridium salt as a precursor coating liquid, and applying the precursor coating liquid evenly on the surface of the platinum coating of the titanium substrate with a coating rod, then drying to evaporate the solvent, transferring to a muffle furnace for thermal oxidation treatment to form a ruthenium-iridium surface active layer, and repeating the above coating and thermal oxidation operations until the thickness of the ruthenium-iridium surface active layer reaches the target result.

4. The method for preparing a platinum-ruthenium-iridium-based titanium-based electrode as claimed in claim 3, characterized in that The specific process of step 1) pretreatment is as follows: S1: The titanium substrate has a purity of greater than 99% by mass. The titanium substrate is sandblasted with diamond powder and then ultrasonically cleaned with deionized water to remove metal grit and debris on the surface of the substrate; S2: immersing the titanium substrate in a NaOH aqueous solution with a concentration of 20-100 mg / L and treating at a temperature of 60-85° C. for 30-90 min to remove the oil film on the surface of the titanium substrate; S3: The titanium substrate after alkaline washing and degreasing is rinsed with deionized water, and then immersed in an oxalic acid aqueous solution with a mass fraction of 5-20%, heated to boiling reflux, and etched for 60-150 minutes to improve the surface activity of the titanium substrate; S4: After etching, the titanium substrate is rinsed with deionized water, and then placed in an oxalic acid aqueous solution with a mass fraction of 0.5-2%, and stored for later use.

5. The method for preparing a platinum-ruthenium-iridium-based titanium-based electrode as claimed in claim 3, characterized in that The electrolyte of step 2) is prepared by dissolving chloroplatinic acid and HCl solution in water, the concentration of chloroplatinic acid is 10-30g / L, the concentration of HCl is 7-10M, and the current density of the electrodeposition reaction is 100-400mA / cm 2 , preferably 200-250mA / cm 2 .

6. The method for preparing a platinum-ruthenium-iridium-based titanium-based electrode as claimed in claim 3, characterized in that Step 3) The heating temperature is 250-300°C and the heating time is 60-90min.

7. The method for preparing a platinum-ruthenium-iridium-based titanium-based electrode as claimed in claim 3, characterized in that In step 4), the molar ratio of ruthenium to iridium atoms in the precursor coating solution is 0.4-2.5:1, preferably 2.0-2.5:1, and the solvent of the precursor coating solution is a mixture of methanol and concentrated hydrochloric acid in a volume ratio of 3-5:1, and the mass concentration of the concentrated hydrochloric acid is 30-36%.

8. The method for preparing a platinum-ruthenium-iridium-based titanium-based electrode as claimed in claim 3, characterized in that In step 4), the temperature of thermal oxidation treatment in the muffle furnace is 450-550° C. and the time is 10-60 min.

9. The use of a platinum-ruthenium-iridium-based titanium-based electrode in electrocatalytic treatment of complex matrix landfill leachate as claimed in claim 1, characterized in that A three-dimensional electrocatalytic oxidation system is used to degrade complex matrix landfill leachate, wherein the anode is the platinum-ruthenium-iridium titanium-based electrode, the anode and the cathode are fixed in parallel in the electrolytic cell, and a particle electrode is filled between the anode and the cathode. The complex matrix landfill leachate is used as the electrolyte and introduced into the electrolytic cell, stirring is started to fully disperse the particle electrode, and the electrode spacing between the cathode and the anode is controlled to be 3-5 cm to perform an electrocatalytic degradation reaction, wherein the particle size of the particle electrode is 0.85-2.36 mm, preferably 1.70-2.00 mm, the amount of the particle electrode added to the electrolyte of the electrolytic cell is 5-11 g / L, preferably 7-8 g / L, and the current density is 20-50 mA / cm 2 , preferably 30±5mA / cm 2 , the pH of the electrolyte is adjusted to between 3-11.

10. The use according to claim 9, characterized in that The organic matter in the complex matrix landfill leachate contains antibiotic pollutants, the COD is within 1100±100 mg / L, the NH3-N is within 1000±100 mg / L, the pH is 5±0.15, the cathode is a titanium plate with a purity of more than 99%, and the particle electrode is coconut shell carbon.

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