Preparation method of doped DSA electrode

Abstract

The invention belongs to the field of electrocatalytic oxidation, and provides a preparation method of a doped DSA electrode. The method comprises the following steps: pretreating a DSA matrix; a tin, lead and rare earth element alloy layer is electrically deposited; and preparing the porous doped oxide through anodic oxidation. The process is simple, coating or sintering is not needed, and steps are reduced by 50% or above; a water-based solution is used in the whole process, and organic solvent pollution is avoided; the electrode bonding force is good, and the bonding strength of the alloy layer and the substrate is larger than 20 MPa; cost is low, precious metal consumption is reduced by 80%, and raw material cost is reduced by 40%; the catalytic efficiency is high, the specific surface area reaches 50-100 m / g, and the phenol degradation rate exceeds 90%; and the service life is long, and stable operation is carried out for more than 1000 hours in an acceleration test. The method is suitable for the fields of industrial wastewater treatment, electrochemical synthesis and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of electro-catalytic oxidation, and relates to a preparation method of a doped DSA electrode. BACKGROUND

[0002] With the rapid development of modern industry, the amount of industrial wastewater discharged is increasing, which contains a large amount of refractory organic pollutants (such as phenols, halogenated hydrocarbons, dyes, etc.), posing a serious threat to the environment and human health. Traditional water treatment methods (such as biological treatment, adsorption) are often inefficient, while electro-catalytic oxidation technology as an advanced oxidation process can produce strong oxidizing free radicals (such as.OH), directly mineralizing pollutants into CO2 and H2O, and has the advantages of high efficiency and no secondary pollution.

[0003] DSA electrode is the core component of electro-catalytic oxidation system, and its performance directly affects the treatment effect. The existing DSA electrode mostly uses titanium or stainless steel substrate, and the coating is noble metal oxide (such as IrO2, RuO2) or transition metal oxide (such as SnO2, PbO2). The preparation methods include thermal decomposition method, sol-gel method, electrodeposition method, etc. For example, the patent with publication number CN109292918A uses noble metal coating and high-temperature sintering, resulting in high cost (noble metal accounts for more than 60% of the cost), poor adhesion, and VOCs pollution caused by organic solvent volatilization. The patent with publication number CN113562815A reduces pollution by using electrodeposition, but the process is complex, an intermediate layer needs to be treated, and the amount of noble metal is still high.

[0004] The main problems of the prior art include: the noble metal coating is expensive, which limits large-scale application; the process is complicated, involving multi-step coating and sintering, and the energy consumption is high; the use of organic solvents causes environmental pollution and health risks; the electrode adhesion is weak, easy to peel off, and the service life is short.

[0005] Therefore, the application aims to develop a green, simple and low-cost preparation method of doped DSA electrode, which overcomes the above defects by alloy co-deposition and rare earth doping. SUMMARY

[0006] The technical problem to be solved by the application is to provide a preparation method of a doped DSA electrode, so as to solve the problems of large amount of noble metal, complex process and environmental pollution in the prior art.

[0007] The technical scheme of the application is as follows:

[0008] A preparation method of a doped DSA electrode, the steps are as follows:

[0009] (1) substrate pretreatment;

[0010] (2) Electrodeposition alloy layer: an alloy layer of tin, lead and rare earth elements is electrodeposited on the surface of the substrate by electrodeposition method, the substrate obtained in step (1) is used as cathode, graphite or platinum sheet is used as anode, the formula of the electrodeposition solution is 30-50 g / L tin salt, 20-40 g / L lead salt, 5-15 g / L rare earth element salt and 40-60 g / L complexing agent, the water bath temperature is 20-40 ℃, the stirring speed is 100-300 rpm, the current density is 5-15 mA / cm2, the electrodeposition time is 10-30 min, and the substrate with uniform alloy layer is obtained;

[0011] (3) Preparation of porous doped oxide by anodization: the substrate with uniform alloy layer obtained in step (2) is subjected to anodization by using a two-electrode system, the substrate with uniform alloy layer is used as anode, and graphite sheet is used as cathode, in 0.5-3 mol / L NaOH solution or H2SO4 solution, the water bath temperature is controlled at 20-40 ℃, the voltage is 3-10 V, and the anodization time is 5-15 min, to form a porous doped DSA electrode, the thickness of the oxide layer thereon is 1-10 μm, and the specific surface area is greater than 50 m 2 / g.

[0012] In step (1), the specific process of the substrate pretreatment is as follows: the substrate is a metal substrate of titanium or stainless steel, the substrate is mechanically polished by using 400#, 800# and 1200# SiC water sandpaper in sequence, so that the surface roughness Ra is 0.1-0.5 μm; then the polished substrate is ultrasonically treated in 1-5 mol / L NaOH solution at a temperature of 20-30 ℃ for 10-20 min, the ultrasonic frequency is 40 kHz; then the substrate is immersed in a mixed solution of 2 mol / L hydrochloric acid and 0.5 mol / L hydrofluoric acid with a volume ratio of 20:1 for 10-15 min, to remove the oxide film; finally, the metal substrate is washed with deionized water for 3-5 times, and dried by cold air, the humidity is controlled below 30%.

[0013] In step (2), the tin salt is stannous chloride and / or stannous sulfate;

[0014] The lead salt is one or more than two kinds of mixture of lead nitrate, lead sulfate and lead acetate;

[0015] The rare earth element salt is one or more than two kinds of mixture of cerium salt, lanthanum salt and scandium salt, the cerium salt is cerium sulfate and / or cerium nitrate, the lanthanum salt is lanthanum chloride and / or lanthanum sulfate, and the scandium salt is scandium sulfate, the doping amount of the rare earth element salt is 1-5% of the total mass of the alloy layer, preferably 2-3%;

[0016] The complexing agent is one of sodium citrate, ammonium citrate and potassium pyrophosphate or a mixture of two or more thereof, and the concentration in the electrodeposition solution is 45-55 g / L.

[0017] In step (2), the current density for electrodeposition is 8-12 mA / cm 2 , and the pH value of the electrodeposition solution is controlled at 2-4.

[0018] In step (3), the anodic oxidation solution is a 1-2 mol / L NaOH solution, the voltage is 5-8 V, and the oxidation time is 8-12 min.

[0019] After step (3), a post-treatment step is further included, i.e., the electrode after anodic oxidation is washed with deionized water and dried at 60-80 ℃ for 30 min.

[0020] The rare earth element salt is dissolved in deionized water in advance, and the concentration is 0.1-0.5 mol / L, and then added to the electrodeposition solution.

[0021] The alloy layer comprises Sn-Pb-RE, wherein the content of Sn is 40-60 wt%, the content of Pb is 35-60 wt%, and RE is a rare earth element with a content of 1-5 wt%.

[0022] The oxide layer mainly comprises SnO2, PbO2 and rare earth oxides.

[0023] The doped DSA electrode prepared by the above method is used for electrocatalytic oxidation of wastewater treatment, and the degradation efficiency of organic pollutants (such as phenol and dye) is increased by 30-50%, and the service life of the electrode is prolonged to more than 1000 hours.

[0024] In step (2), the equipment for electrodeposition includes a constant potential instrument, a water bath and a stirrer, and the control precision is ±0.1 ℃ and ±1 rpm.

[0025] The present application has the following beneficial effects:

[0026] (1) The process is simple, and coating or sintering is not needed, and more than 50% of steps are reduced;

[0027] (2) It is green and environmentally friendly, and water-based solutions are used throughout the process without organic solvent pollution;

[0028] (3) The electrode has good bonding force, and the bonding strength of the alloy layer to the substrate is greater than 20 MPa;

[0029] (4) The cost is low, the amount of noble metal is reduced by 80%, and the cost of raw materials is reduced by 40%;

[0030] (5) The catalytic efficiency is high, the specific surface area is 50-100 m² / g, and the degradation rate of phenol is more than 90%;

[0031] (6) Long service life, stable operation for more than 1000 hours in accelerated test.

[0032] The application is suitable for the fields of industrial wastewater treatment and electrochemical synthesis. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 Surface topography of Example 1.

[0034] Figure 2 Surface topography of Example 2.

[0035] Figure 3 Surface topography of Example 3.

[0036] Figure 4 Surface topography of Example 4.

[0037] Figure 5 Surface topography of Example 5.

[0038] Figure 6 Surface topography of Example 6.

[0039] Figure 7 Surface topography of Comparative Example 1.

[0040] Figure 8 Surface topography of Comparative Example 2. DETAILED DESCRIPTION

[0041] The specific embodiments of the application are further illustrated in the following description in conjunction with the accompanying drawings and technical solutions.

[0042] Example 1

[0043] A preparation method of a doped DSA electrode, the steps are as follows:

[0044] (1) Substrate pretreatment: titanium substrate (size 10 cm x 10 cm x 1 mm) is selected, and is mechanically polished with 400#, 800#, and 1200# SiC water sandpaper in sequence to make the surface roughness Ra 0.2 μm; then the polished substrate is put into a 3 mol / L NaOH solution, and is ultrasonically treated at 25℃ for 15 min (ultrasonic power 100 W); then the substrate is soaked in a mixed solution of hydrochloric acid (2 mol / L) and hydrofluoric acid (0.5 mol / L) with a volume ratio of 20:1 for 12 min; finally, the substrate is washed with deionized water for 4 times, and is blown dry by cold air, with the humidity controlled at 30%.

[0045] (2) Electrodeposition of alloy layer: the pretreated titanium substrate is used as a cathode, a graphite sheet (area 20 cm 2) for anode, the composition of the electrodeposition solution is 35 g / L SnCl2 (purity 99.5%), 25 g / L Pb(NO3)2, 8 g / L Ce2(SO4)3, 50 g / L sodium citrate, and the pH is adjusted to 3.0 with dilute sulfuric acid; the water bath temperature is 25 °C, the stirring speed is 200 rpm, the current density is 10 mA / cm2, and the electrodeposition time is 20 min; after deposition, the thickness of the alloy layer is about 5 μm, and the composition analysis shows that Sn accounts for 55 wt%, Pb accounts for 35 wt%, and Ce accounts for 5 wt%.

[0046] (3) Anodic oxidation: the alloy layer-titanium substrate is used as anode, and graphite sheet is used as cathode, in 1.5 mol / L NaOH solution, at 25 °C, the voltage is 6 V, and the oxidation time is 10 min; after oxidation, the thickness of the porous oxide layer is 3 μm.

[0047] Electrode performance test: in the electro-catalytic oxidation reaction, the degradation rate of 100 mg / L phenol solution is 95%, and the electrode life is 1200 hours.

[0048] Example 2

[0049] The same as example 1, but the stainless steel substrate (304 stainless steel) is used, the alkali concentration in the pretreatment is changed to 2 mol / L NaOH; the rare earth salt in the electrodeposition solution is changed to 10 g / L LaCl3; and the anodic oxidation voltage is 8 V. Result: the alloy layer has better adhesion, and the degradation rate is 92%.

[0050] Example 3

[0051] The same as example 1, but the electrodeposition current density is changed to 8 mA / cm 2 , and the oxidation time is 8 min. Result: the porous structure is more uniform.

[0052] Example 4

[0053] The tin salt in the electrodeposition solution is changed to 40 g / L SnSO4, the lead salt is changed to 30 g / L Pb(CH3COO)2, and the rare earth salt is changed to 12 g / L Sc2(SO4)3; the anodic oxidation solution is changed to 1 mol / L H2SO4, the voltage is 4 V, and the time is 12 min. Result: the oxide layer is more stable, and it is suitable for high-acidity wastewater.

[0054] Example 5

[0055] Post-treatment is added: after anodic oxidation, the electrode is dried at 70 °C for 30 min. Result: the stability of the electrode is improved, and the life is extended to 1500 hours.

[0056] Example 6

[0057] The rare earth elements are mixed (5 g / L of Ce and 5 g / L of La), and good performance is shown, with a degradation rate of 85-95%.

[0058] Comparative Example 1

[0059] Without rare earth element: the electrodeposition solution only contains SnCl2 and Pb(NO3)2, and other conditions are the same as Example 1. Result: the electrode catalytic efficiency is reduced by 20%, and the service life is only 600 hours, which shows the key role of rare earth doping.

[0060] Comparative Example 2

[0061] Using traditional thermal decomposition method: coating noble metal IrO2 coating, sintering at 500℃. Result: the cost increases by 300%, and there is VOCs emission, and the adhesion is poor.

[0062] Theoretical explanation

[0063] In the application, the doping of rare earth elements (such as Ce, La) can adjust the electronic structure of the oxide, increase the generation rate of.OH, improve the electrode catalytic efficiency, and improve the degradation rate; the porous structure of the co-deposited alloy layer increases the specific surface area and increases more active sites, thereby improving the catalytic efficiency. Experiments show that the doping of rare earth elements can reduce the charge transfer resistance by 30%.

[0064] In summary, the method of the application is simple, environmentally friendly, and efficient, and is suitable for industrial application.

Claims

1. A method for preparing a doped DSA electrode, characterized in that, The steps are as follows: (1) substrate pretreatment; (2) Electrodeposited alloy layer: an alloy layer of tin, lead and rare earth elements is co-deposited on the surface of the substrate by electrodeposition method, the substrate obtained in step (1) is used as cathode, graphite or platinum sheet is used as anode, the formula of the electrodeposition solution is 30-50 g / L tin salt, 20-40 g / L lead salt, 5-15 g / L rare earth element salt and 40-60 g / L complexing agent, the water bath temperature is 20-40 ℃, the stirring speed is 100-300 rpm, the current density is 5-15 mA / cm 2 Under the conditions, the electrodeposition time is 10-30 min, and the substrate with uniform alloy layer is obtained; (3) Preparing porous doped oxide by anodic oxidation: using two electrode system to anodize the substrate with uniform alloy layer obtained in step (2), taking the substrate with uniform alloy layer as anode and graphite sheet as cathode, in 0.5-3 mol / L NaOH solution or H2SO4 solution, controlling water bath temperature to be 20-40℃, voltage to be 3-10V and anodic oxidation time to be 5-15 min, forming DSA electrode with micrometer porous structure, the thickness of oxide layer on the electrode is 1-10 μm, and the specific surface area is greater than 50 m2 / g. 2 / g.

2. The preparation method of the doped DSA electrode according to claim 1, characterized in that, In step (1), The specific process of the substrate pretreatment is as follows: the metal substrate is titanium or stainless steel, and the substrate is mechanically polished with 400#, 800# and 1200# SiC water sandpaper in sequence to make the surface roughness Ra be 0.1-0.5 μm; then the polished substrate is ultrasonically treated in a 1-5 mol / L NaOH solution at a temperature of 20-30 ℃ for 10-20 min at an ultrasonic frequency of 40 kHz; then the substrate is immersed in a mixed solution of concentrated hydrochloric acid with a concentration of 2 mol / L and concentrated hydrofluoric acid with a concentration of 0.5 mol / L at a volume ratio of 20:1 for 10-15 min to remove the oxide film; finally, the metal substrate is rinsed with deionized water for 3-5 times and blown dry with cold air, and the humidity is controlled below 30%.

3. The preparation method of the doped DSA electrode according to claim 1, characterized in that, In step (2), The tin salt is stannous chloride and / or stannous sulfate; The lead salt is one or more than two kinds of mixture of lead nitrate, lead sulfate and lead acetate; The rare earth element salt is one or more than two kinds of mixture of cerium salt, lanthanum salt and scandium salt, the cerium salt is cerium sulfate and / or cerium nitrate, the lanthanum salt is lanthanum chloride and / or lanthanum sulfate, and the scandium salt is scandium sulfate, and the doping amount of the rare earth element salt is 1-5% of the total mass of the alloy layer; The complexing agent is one or more than two kinds of mixture of sodium citrate, ammonium citrate and potassium pyrophosphate.

4. The preparation method of the doped DSA electrode according to claim 1, characterized in that, In step (2), The current density for electrodeposition is 8-12 mA / cm 2 The pH value of the electrodeposition solution is controlled at 2-4.

5. The preparation method of the doped DSA electrode according to claim 1, characterized in that, In step (3), The anodic oxidation solution is a 1-2 mol / L NaOH solution, the voltage is 5-8 V, and the oxidation time is 8-12 min.

6. The method of claim 1, wherein the doped DSA electrode is prepared by, After step (3), a post-treatment step is further included: the electrode after anodic oxidation is rinsed with deionized water and dried at 60-80 ℃ for 30 min.

7. The method of claim 1, wherein the doped DSA electrode is prepared by, The rare earth element salt is dissolved in deionized water in advance, and the concentration is 0.1-0.5 mol / L, and then added to the electrodeposition solution.

8. The method of claim 1, wherein the doped DSA electrode is prepared by, The composition of the alloy layer is Sn-Pb-RE, wherein the content of Sn is 40-60 wt%, the content of Pb is 35-60 wt%, and RE is a rare earth element with a content of 1-5 wt%.

9. The method of claim 1, wherein the doped DSA electrode is prepared by, The main components of the oxide layer are SnO2, PbO2 and rare earth oxides.

10. The doped DSA electrode obtained by the preparation method of claims 1-9 is used for electrocatalytic oxidation of wastewater treatment.

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