Preparation method and application of copper-iron bimetallic / graphite felt composite electrode derived from MOF-74 precursor

Abstract

The application relates to a preparation method and application of a copper-iron bimetal / graphite felt composite electrode derived from a MOF-74 precursor, and relates to the technical field of electrochemical catalytic oxidation water treatment.The graphite felt is used as a matrix, copper-iron-MOF-74 precursors are uniformly distributed on the surface of the graphite felt through a one-step solvothermal method, and then the copper-iron-MOF-74 precursors grown on the surface are calcined by adopting a high-temperature calcination method, so that a composite electrode modified by copper-iron bimetal active substances is obtained.Compared with the graphite felt which is not modified by copper-iron bimetal, when the graphite felt modified by the copper-iron bimetal active substances is used as a cathode material, the electric activation and the transition metal activation are synergized, the activation efficiency of persulfate is improved, the degradation capacity for pesticide wastewater can be obviously improved under acidic, neutral and weak alkaline conditions, the method is simple, convenient and controllable, the reaction system is stable, the catalyst does not need to be recovered, there is no subsequent pollution problem, and therefore the method has a good application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemical catalytic oxidation water treatment, and in particular to a preparation method of a composite electrode modified by a copper-iron bimetallic active substance on the basis of a MOF-74 precursor and application of the electrode as a cathode in an electro-activated persulfate advanced oxidation process. BACKGROUND

[0002] Advanced oxidation processes (AOPs) play an important role in the management of ecosystems such as pollutant degradation, in-situ chemical oxidation of contaminated soil, and wastewater treatment due to the generation of strong oxidizing free radicals. The commonly used ·OH is very effective in removing organic matter and other complex biomass such as sludge and lignocellulose, however, ·OH requires an acidic environment (pH 2-4) to function, and the instability of H2O2 greatly reduces its practical significance.

[0003] In recent years, persulfate has been widely used as a substitute for H2O2 in AOPs. Oxidation technology based on SO4 ·- has many advantages, and permonosulfate (PMS) and peroxymonosulfate (PDS) are strong oxidizing agents. The half-life of SO4 ·- is 3-4×10 -5 s, which is much longer than the half-life of ·OH (2×10 -8 s), so it has more opportunities to react with pollutants. Once the persulfate is activated, very active SO4 ·- is generated. Compared with ·OH (2.8V), SO4 ·- has a higher oxidation potential of 2.5-3.1V, which can oxidize pollutants into harmless CO2 and H2O, and has a wider pH range. In addition, the advanced oxidation technology based on SO4 ·- has the advantages of easy availability of raw materials, low price, high removal rate of persistent and stable organic pollutants, mild reaction conditions, and various activation methods of persulfate. The core of this technology is to improve the activation efficiency of persulfate. The methods for activating persulfate include thermal activation, photoactivation, transition metal activation, ultrasonic activation, alkaline activation, electrochemical activation, and combined activation.

[0004] Metal-organic frameworks (MOFs) are composed of metal-containing units and organic linkers, and utilize strong bonding to produce an open crystalline framework with permanent porosity. The most attractive features of MOFs are crystalline properties, tunable structure, large porosity (up to 90% free volume), ultra-high specific surface area (up to 10400 m 2 ·g -1 ), large pore size (9.8 nm), and low density (0.13 g·cm -3Due to the space confinement effect, MOFs-based materials applied in sulfate radical-based AOPs (SR-AOPs) can inhibit the release of metal ions compared with other commonly used PMS-activated homogeneous and / or heterogeneous catalysts. More importantly, the unique porous structure in MOFs-based materials provides a possible pathway for the penetration of active molecules, which is of great significance for increasing mass transfer and improving the removal efficiency of pollutants.

[0005] Graphite felt is an electrode material with three-dimensional structure, good electrical conductivity, high tensile strength, large specific surface area, and obvious advantages over other carbon electrodes. The present application uses graphite felt as a substrate material, and directly loads copper iron-MOF-74 (CuFe-MOF-74) precursors on the graphite felt electrode modified by anodic oxidation through in-situ solvothermal synthesis method to prepare a CuFe-MOF-74 modified graphite felt. The composite electrode is calcined in a nitrogen atmosphere to obtain a copper iron bimetallic active material modified electrode, which is used as a cathode in the electro-activated persulfate advanced oxidation process, and is used for the electro-activated persulfate oxidation degradation of pesticide wastewater in a wide pH range, so as to realize efficient degradation of pollutants and broaden the pH range of the reaction. Thus, a wastewater treatment technology is proposed, which combines electro-activation with transition metal activation in a synergistic way to promote the activation of persulfate. SUMMARY

[0006] The present application aims to provide a preparation method of a composite electrode modified by copper iron bimetallic active material based on MOF-74 precursor. The synthesis process of the present application is simple, convenient and controllable. The prepared electrode is applied in the electro-activated persulfate advanced oxidation process in a wide pH range, improves the utilization efficiency of persulfate in the reaction solution, and further generates more sulfate radicals to completely remove pesticide wastewater.

[0007] The specific preparation method of the composite electrode is as follows:

[0008] (1) Cut the graphite felt into a uniform specification, immerse the graphite felt in anhydrous ethanol solution, and then put it into an ultrasonic cleaner for ultrasonic cleaning for 30-60 min; then immerse and ultrasonic clean with deionized water to remove the residual anhydrous ethanol on the surface of the graphite felt, and obtain the graphite felt with surface oil stains and impurities removed; put the washed graphite felt into an 80℃ oven for drying, and reserve;

[0009] (2) Use the graphite felt treated in step (1) as an anode, use 50mM sodium sulfate solution as an electrolyte, and anodically modify at room temperature with a constant current of 40-100mA for 5-30 minutes, then wash with deionized water and put it into an 80℃ oven for drying and reserving;

[0010] (3) 0-2.5 mM ferrous sulfate heptahydrate, 0-2.5 mM copper nitrate trihydrate, 1.5 mM 2,5-dihydroxyterephthalic acid completely dissolved in a solution of DMF: ethanol: deionized water in a volume ratio of 1:1:1 to obtain a copper-iron-MOF-74 precursor solution; the contents of ferrous sulfate and copper nitrate are 0 at different times; preferably the molar ratio of copper to iron is 3:1-1:3.

[0011] (4) The graphite felt subjected to anodic oxidation modification treatment obtained in step (2) is placed in the copper-iron-MOF-74 precursor solution obtained in step (3) and placed in a polytetrafluoroethylene reaction kettle, reacted at a temperature of 80-140℃ for 24 h, naturally cooled to room temperature, and then sequentially washed with ethanol and deionized water to obtain a copper-iron-MOF-74 loaded graphite felt, which is dried for standby use;

[0012] (5) The copper-iron-MOF-74 loaded graphite felt obtained in step (4) is placed in a high-temperature atmosphere furnace and pyrolyzed at 300-700℃ in a nitrogen atmosphere for 2 h to obtain a copper-iron bimetallic active substance modified graphite felt composite electrode, i.e. a copper-iron bimetallic / graphite felt composite electrode.

[0013] The final copper-iron bimetallic / graphite felt composite electrode loaded substance includes CuFe2O4, Cu 0 .

[0014] The copper-iron bimetallic / graphite felt composite electrode obtained by the above preparation method is applied as a cathode in an electrically activated persulfate advanced oxidation process, which removes atrazine refractory pesticide wastewater by adding copper-iron transition metal activated persulfate to the electrically activated persulfate, and the degradation process is carried out at a wide pH range of 2-9; the reaction temperature is 25℃, the current density is 2 mA / cm 2 .

[0015] Compared with the prior art, the present application has the following excellent effects:

[0016] 1. The substrate graphite felt of the present application is low in price, has increased hydrophilicity and surface particle attachments after anodic oxidation modification treatment in step (2), is conducive to loading more bimetallic active substances, and greatly improves the removal efficiency of pollutants.

[0017] 2. In the present application, MOF-74 precursor is used as a self-sacrificial template, successfully loads copper-iron bimetallic active substances on the surface of graphite felt, and can remove 200 ml of 10 mg / L atrazine solution at a removal rate of 100% within 20 min in an electrically activated persulfate system; this method is simple, convenient and controllable, and overcomes the problem of uneven dispersion of oxides caused by traditional coating and impregnation methods.

[0018] 3. The degradation of pollutants in the process of the present application does not require an external catalyst, there is no catalyst recovery problem, and the stability is good.

[0019] 4. In the present application, the copper-iron bimetallic active substance is loaded on the graphite felt, which is equivalent to increasing the copper-iron transition metal activation on the basis of the electro-activated persulfate, and the two synergies improve the utilization efficiency of the persulfate and generate more sulfate radicals, which can quickly and completely degrade pollutants. Atrazine pollutants can be efficiently removed under acidic, neutral, and weak alkaline conditions. Moreover, the method is simple to make, easy to control, and the reaction system is stable, without the need for catalyst recovery and subsequent pollution problems, so it has good application prospects. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The scanning electron microscope images of the pretreated graphite felt electrode prepared for Comparative Example 1 and the copper-iron bimetallic active substance modified graphite felt electrode prepared in Example 1. ((A) is Comparative Example 1, and (B) is Example 1).

[0021] Figure 2 The XRD result graph of the graphite felt electrode prepared for Comparative Example 2 and the copper-iron bimetallic active substance modified graphite felt electrode prepared in Example 1.

[0022] Figure 3 The degradation effect of atrazine in the electro-activated persulfate system of the anodically oxidized modified electrode prepared for Comparative Example 3 and the copper-iron bimetallic active substance modified composite electrode prepared in Example 1.

[0023] Figure 4 The degradation effect of atrazine in the electro-activated persulfate system of the composite electrode prepared in Example 2 using different molar ratios of bimetallic.

[0024] Figure 5 The degradation effect of atrazine in the electro-activated persulfate system of the copper-iron bimetallic active substance modified composite electrode under different current densities in Example 3.

[0025] Figure 6 The degradation effect of atrazine in the electro-activated persulfate system of the copper-iron bimetallic active substance modified composite electrode under different pH conditions in Example 4. DETAILED DESCRIPTION

[0026] The following will be described in conjunction with the drawings and specific examples, but the present application is not limited to the following examples.

[0027] Example 1

[0028] (1) Graphite felt (area size 2 cm x 5 cm) was sequentially immersed in anhydrous ethanol, ultrapure water and ultrasonic cleaned to remove oil stains and impurities on the surface of the graphite felt, and dried in an oven at 80°C for standby;

[0029] (2) Subsequently, the graphite felt treated in step (1) was used as an anode and oxidized and modified in a 200 ml 50 mM sodium sulfate solution at a constant current of 80 mA at room temperature for 20 minutes;

[0030] (3) 1.5 mM of 2,5-dihydroxyterephthalic acid, 1.67 mM of copper nitrate trihydrate, and 0.83 mM of ferrous sulfate heptahydrate were added to a solution (60 mL) containing DMF: ethanol: deionized water in a volume ratio of 1:1:1 to completely dissolve, obtaining a MOF-74 precursor growth solution.

[0031] (4) The graphite felt obtained in step (2) was immersed in the growth solution prepared in step (3), and the growth solution was moved to a 100 ml polytetrafluoroethylene reactor and stored in a 100°C constant temperature oven for 24 h. The obtained copper-iron-MOF-74 modified graphite felt electrode was naturally cooled to room temperature, sequentially washed with anhydrous ethanol and ultrapure water, and dried at 80°C overnight;

[0032] (5) The copper-iron-MOF-74 modified graphite felt electrode obtained in step (4) was placed in a high-temperature atmosphere furnace and pyrolyzed at 500°C in a nitrogen atmosphere for 2 h, obtaining a copper-iron bimetallic active material modified composite electrode material.

[0033] (6) The electrode prepared above was used as a cathode, a platinum sheet was used as an anode, 0.05 M sodium sulfate was used as an electrolyte, and 0.4 mM sodium persulfate was used, I = 2 mA / cm 2 , pH = 5.8, 200 ml of atrazine wastewater with a concentration of 10 mg / L was degraded, as shown in curve b in FIG. 1, the removal rate of atrazine wastewater reached 100% at 20 min. Figure 3

[0034] Example 2

[0035] The specific preparation process is the same as that of Example 1, but in step (3), the total moles of copper and iron metals are controlled at 2.5 mmol, and the ratio of copper and iron metals is 3:1, 2:1, 1:1, 1:2, and 1:3, respectively. The electrode prepared above was used as a cathode, a platinum sheet was used as an anode, 0.05 M sodium sulfate was used as an electrolyte, and 0.4 mM sodium persulfate was used, I = 2 mA / cm 2 , pH = 5.8, 200 ml of atrazine wastewater with a concentration of 10 mg / L was degraded, as shown in curve b in FIG. 1, the removal rate of atrazine wastewater reached 100% at 20 min. Figure 4 When the ratio of copper and iron is 2:1, the removal rate of atrazine wastewater is best, reaching 100%.​

[0036] Example 3

[0037] The specific preparation process is the same as Example 1, but in step (6), the electrode prepared under the above conditions is used as the cathode, a platinum plate is used as the anode, 0.05M sodium sulfate is used as the electrolyte, and the sodium persulfate salt is 0.4mM, I = 0, 1.5, 2, 2.5, 4mA / cm 2 , pH = 5.8, 200ml of atrazine wastewater with a concentration of 10mg / L is degraded, and at 20min, the removal rate of atrazine is 100%. Figure 5 When I = 2mA / cm 2 , the removal rate of atrazine wastewater is best, reaching 100%.

[0038] Example 4

[0039] The specific preparation process is the same as Example 1, but in step (6), the electrode prepared under the above conditions is used as the cathode, a platinum plate is used as the anode, 0.05M sodium sulfate is used as the electrolyte, and the sodium persulfate salt is 0.4mM, I = 2mA / cm 2 , pH = 2, 4, 5.8, 7, 9, 200ml of atrazine wastewater with a concentration of 10mg / L is degraded, and at 20min, the removal rate of atrazine is 100%. Figure 6 When the pH is 2-9, i.e., under acidic, neutral, and weak alkaline conditions, atrazine wastewater can be efficiently degraded, thereby significantly widening the pH range applicable to the process.

[0040] Comparative Example 1

[0041] The specific preparation process is the same as Example 1, except that steps (2), (3), (4), (5), and (6) are omitted, i.e., the graphite felt is not anodically oxidized and modified with copper-iron bimetallic active substances, but only pretreated. The copper-iron bimetallic modified electrode prepared in Example 1 is characterized.

[0042] As shown in FIG. 1 Figure 1 (B), after pretreatment, anodic oxidation modification, and copper-iron bimetallic modification, the graphite felt surface has many spinel-shaped particles, increasing the specific surface area of the graphite felt and providing more activation sites for persulfate activation, thereby greatly improving the activation capacity of persulfate.

[0043] Comparative Example 2

[0044] The specific preparation process is the same as Example 1, except that steps (5) and (6) are omitted, i.e., the copper-iron-MOF-74 modified graphite felt electrode is not calcined at high temperature. The copper-iron bimetallic modified electrode prepared in Example 1 is characterized.

[0045] As Figure 2 shown, after high-temperature calcination of the copper-iron-MOF-74 modified graphite felt electrode, its main active component is CuFe2O4, Cu 0 On the basis of electro-activated persulfate, by increasing the copper-iron bimetallic active component, using Fe 3+ , Fe 2+ , Cu 2+ , Cu + for transition metal activation, realizing persulfate dual activation, increasing the production of sulfate radicals, accelerating the degradation of atrazine wastewater, and improving the removal efficiency of atrazine wastewater.

[0046] Comparative Example 3

[0047] The specific preparation process is the same as Example 1, except that steps (3), (4), and (5) are omitted, and the purpose is not to load copper-iron bimetallic active substances on the surface of the graphite felt, but only to modify the graphite felt by anodic oxidation; the electrode prepared under the above conditions is used as the cathode, platinum sheet is used as the anode, 0.05M sodium sulfate is used as the electrolyte, sodium persulfate is 0.4mM, I = 2mA / cm 2 , pH = 5.8, and 200ml of atrazine wastewater with a concentration of 10mg / L is degraded. The results of Comparative Example 3 and Example 1 are shown in Figure 3 As shown, from the removal rate of atrazine wastewater, the degradation of atrazine wastewater by the graphite felt electrode modified by copper-iron bimetallic active substances reached 100% in 20min, while the degradation of atrazine wastewater by the graphite felt electrode without copper-iron bimetallic active substances was only 31.9% in 20min. It can be seen that on the basis of electro-activated persulfate, increasing transition metal activation can greatly improve the utilization rate of persulfate, produce more sulfate radicals, and further accelerate the degradation of atrazine wastewater.

Claims

1. A method for preparing a copper-iron bimetallic / graphite felt composite electrode derived from MOF-74 precursors, characterized in that, Comprising the following steps: (1) Cut the graphite felt into a uniform size, immerse the graphite felt completely in anhydrous ethanol solution, and then place it in an ultrasonic cleaner for ultrasonic cleaning for 30-60 min; then immerse it in deionized water for ultrasonic cleaning to remove the residual anhydrous ethanol on the surface of the graphite felt, and obtain the graphite felt with surface oil stains and impurities removed; place the washed graphite felt in an 80℃ oven for drying, ready for use; (2) Use the graphite felt treated in step (1) as the anode, use 50 mM sodium sulfate solution as the electrolyte, and modify it by anodic oxidation at a constant current of 40-100 mA at room temperature for 5-30 min, then wash it with deionized water and place it in an 80℃ oven for drying, ready for use; (3) Dissolve 0-2.5 mM ferrous sulfate heptahydrate, 0-2.5 mM copper nitrate trihydrate, and 1.5 mM 2,5-dihydroxyterephthalic acid in a solution of DMF:ethanol:deionized water in a volume ratio of 1:1:1 to obtain a MOF-74 precursor solution; (4) Place the graphite felt modified by anodic oxidation obtained in step (2) in the MOF-74 precursor solution obtained in step (3) in a polytetrafluoroethylene reactor, and react at a temperature of 80-140℃ for 24 h, then sequentially wash it with ethanol and deionized water after natural cooling to room temperature, to obtain copper-iron-MOF-74 loaded graphite felt, which is dried and ready for use; (5) Place the copper-iron-MOF-74 loaded graphite felt obtained in step (4) in a high-temperature atmosphere furnace, pyrolyze it in a nitrogen atmosphere at 300-700℃ for 2 h, to obtain a copper-iron bimetallic active material modified graphite felt composite electrode, i.e. a copper-iron bimetallic / graphite felt composite electrode; The copper-iron molar ratio in step (3) is 3:1-1:

3.

2. A method of preparing a copper-iron bimetallic / graphite felt composite electrode derived from MOF-74 precursors according to claim 1, characterized in that, The main metallic active component of the prepared copper-iron bimetallic / graphite felt composite electrode is CuFe2O4, Cu 0 .

3. A copper-iron bimetallic / graphite felt composite electrode derived from a MOF-74 precursor, prepared according to the method of claim 1 or 2.

4. Use of a copper-iron bimetallic / graphite felt composite electrode derived from a MOF-74 precursor, prepared according to the method of claim 1 or 2, in an electrically activated persulfate advanced oxidation process.

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