A method for preparing and using a catalytic electrode

Abstract

The application discloses a preparation method and application of a catalytic electrode. In the application, a graphene oxide dispersion solution of N,N-dimethylformamide is used to replace a solution of ethyl acetate by means of a wet spinning machine to synthesize graphene oxide fibers; the obtained graphene oxide fibers are broken into short fibers in an ethanol aqueous solution, filtered through gauze, and then the ethanol aqueous solution on the fibers is volatilized and evaporated to obtain sheet-shaped graphene oxide; the obtained sheet-shaped graphene oxide is reduced in hydrazine hydrate N2H4 to obtain sheet-shaped reduced graphene oxide rGO; and the rGO is reduced in an argon atmosphere to obtain a catalytic electrode based on reduced graphene oxide. The catalytic electrode can activate persulfate to degrade organic pollutants through a kind of primary cell effect, thereby avoiding the harm of direct injection of persulfate into water to aquatic organisms, and avoiding the toxic risk of residual powder catalyst in the environment.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of material engineering and environmental engineering, and relates to a preparation method and application of a catalytic electrode. BACKGROUND

[0002] The decoupled oxidation process, which separates the oxidant with biological toxicity and the wastewater to be treated by the principle of the primary battery, has been proved to have certain potential in degrading the refractory organic pollutants in water. The decoupled oxidation process is that, after the catalytic electrode contacts with the oxidant and the pollutants in the wastewater to be treated, the potential difference formed at both ends promotes the directional transfer of electrons, and finally leads to the degradation of the pollutants. A suitable catalytic electrode is the key to initiate the process. At present, the preparation of the catalytic electrode is achieved by loading nanoparticle powder on a conductive substrate through an adhesive. The introduction of the adhesive not only may reduce the conductivity of the overall electrode and affect the accessibility of the active sites, but also leads to the falling off of the nanoparticles, thereby affecting the stability of the catalytic electrode. Therefore, it is necessary to develop an integrated catalytic electrode to avoid the problems of the composite catalytic electrode. Graphene oxide has the property of dehydration self-crosslinking, i.e. has the potential to form a self-supporting integrated electrode. The reduced graphene oxide obtained after the reduction of graphene oxide can have high conductivity and high specific surface area, and can be modified by the selection of the reduction method, thereby further improving the performance of the catalytic electrode.

[0003] The integrated catalytic electrode based on reduced graphene oxide designed and prepared in the present application can activate peroxysulfate to degrade organic pollutants by the primary battery-like effect, thereby avoiding the harm of direct peroxysulfate injection into water to aquatic organisms and the toxicity risk of residual powder catalyst in the environment. SUMMARY

[0004] The present application provides a preparation method of a catalytic electrode and application of degrading organic pollutants in wastewater, which utilizes the integrated catalytic electrode to activate peroxysulfate, and generates a potential difference between peroxysulfate and organic pollutants in the spatially separated double chambers, so as to have better catalytic degradation of pollutants.

[0005] The treatment conditions of the present application are as follows: a synthesis method of a catalytic electrode based on reduced graphene oxide, comprising the following steps:

[0006] 1) graphene oxide fibers are synthesized by replacing the solution of ethyl acetate with a graphene oxide dispersion solution dissolved in N,N-dimethylformamide using a wet spinning machine;

[0007] 2) after the graphene fibers obtained in step 1) are broken into short fibers in an ethanol aqueous solution and filtered through gauze, the ethanol aqueous solution on the fibers is volatilized and dried to obtain sheet-shaped graphene oxide;

[0008] 3) reducing the obtained sheet-like graphene oxide in hydrazine hydrate N2H4 to obtain sheet-like reduced graphene oxide rGO;

[0009] 4) reducing the obtained rGO in argon atmosphere to obtain sheet-like nitrogen-doped reduced graphene oxide rGO-R.

[0010] The reduced graphene oxide-based catalytic electrode synthesized in the application can activate potassium peroxodisulfate and generate a potential difference between the peroxodisulfate and the organic pollutants in the spatially separated double chambers, on the one hand, can quickly activate peroxodisulfate, generate a larger potential difference to promote the electron migration of the organic pollutants to the peroxodisulfate, and efficiently degrade the organic pollutants, on the other hand, can avoid the ecological environmental risk brought by peroxodisulfate, and make it better applied in the field of water pollution control.

[0011] In step 1), the N,N-dimethylformamide is dissolved in the graphene oxide dispersion liquid with a concentration of 0-10 mg / mL (further preferably 1-10 mg / mL), and most preferably 4 mg / mL.

[0012] In step 2), the volume ratio of ethanol in the ethanol aqueous solution is 0-100% (further preferably 10%-100%), and most preferably 95%.

[0013] The length of the short fibers is 0-5 cm (further preferably 0.1-5 cm), and most preferably 0.5 cm.

[0014] The ratio of the amount of sheet-like graphene oxide to hydrazine hydrate is 50-70 mg: 0.1-1 mL.

[0015] The mass ratio of the sheet-like graphene oxide to hydrazine hydrate is 1:(1-20), and further preferably 1:5.

[0016] In step 3), the reduction time of the sheet-like graphene oxide in hydrazine hydrate is 2-6 h, and further preferably 5 hours.

[0017] The reduction time of the rGO in argon atmosphere is 1-3 h, and further preferably 1 h.

[0018] Specifically, the synthesis method of the reduced graphene oxide-based catalytic electrode specifically comprises: 15 mL of 4 mg / mL N,N-dimethylformamide is dissolved in an oxidized graphene dispersion liquid to replace the solution of ethyl acetate with a wet spinning machine to synthesize graphene oxide fibers. Then, the above-mentioned 60 mg graphene fibers are broken into short fibers of 0.5 cm in a 95% volume percentage ethanol aqueous solution, filtered through gauze, and then the ethanol aqueous solution on the fibers is volatilized and dried to obtain sheet-shaped graphene oxide. Subsequently, the obtained 60 mg sheet-shaped graphene oxide is reduced in 0.3 mL of hydrazine N2H4 to obtain sheet-shaped reduced graphene oxide rGO. Finally, the sheet-shaped nitrogen-doped reduced graphene oxide rGO-R is obtained by reducing for 1 h in an argon atmosphere.

[0019] The application of the reduced graphene oxide-based catalytic electrode device for degrading organic pollutants by utilizing the galvanic effect in degrading organic pollutants specifically comprises:

[0020] Two pieces of 1 cm*1 cm (length* width) sheet-shaped catalytic electrodes are placed in the cathode and anode chambers of an H-shaped electrolytic cell separated by a proton exchange membrane as the cathode and anode, respectively, wherein the cathode chamber contains 40 mL of 10 mM potassium peroxodisulfate solution, and the anode chamber contains 40 mL of 5 mu M organic pollutant solution, the cathode and anode are connected by a copper wire, and the organic pollutant is bisphenol A, and the catalytic reaction is carried out.

[0021] Compared with the prior art, the application has the following outstanding features and beneficial effects:

[0022] (1) The catalytic electrode synthesized by the method can quickly activate peroxodisulfate, and the cathode chamber potential is increased to 0.88 V.

[0023] (2) The reduced graphene oxide-based catalytic electrode activates peroxodisulfate, and the potential difference of about 0.6 V generated at the cathode and anode is the key driving force for oxidative degradation.

[0024] (3) The method uses reduced graphene oxide as the raw material of the catalytic electrode, and the reduced graphene oxide is a non-metallic carbon material with a large specific surface area and abundant active sites, which can completely avoid the toxicity risk caused by metal ion leaching.

[0025] (4) Through the mechanism analysis of the reaction, the rGO-R / peroxodisulfate catalytic degradation of organic pollutants system is a decoupling oxidation mechanism. It is proved that the system can avoid adding peroxodisulfate to the water to be treated, and thus avoid the oxidative damage and toxicity risk of peroxodisulfate to the water organisms.

[0026] (5) The application selects graphene oxide with dehydration self-crosslinking property as raw material of catalytic electrode, and obtains the catalytic electrode based on reduced graphene oxide by hydrazine hydrate reduction and high-temperature reduction in sequence. The morphology structure characterization shows that the catalytic electrode is in graphene sheet layer structure. The experimental results show that the mechanism of the catalytic electrode in activating potassium peroxodisulfate to degrade organic pollutants is not free radical oxidation (such as ·OH and SO4·- oxidation), but decoupling oxidation mechanism. The reaction mechanism drives the directional migration of electrons from organic pollutants to peroxodisulfate through the potential difference between peroxodisulfate and organic pollutants in the spatially separated double-chamber, and finally leads to the oxidative degradation of organic pollutants and the reduction decomposition of peroxodisulfate, which can avoid adding peroxodisulfate to the water body to be treated, and further avoid the oxidative damage and toxicity risk of peroxodisulfate to water organisms. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 Fig. 1 is a scanning electron microscope (SEM) image of rGO and rGO-R, wherein a-d are SEM images of rGO, and e-h are SEM images of rGO-R.

[0028] Figure 2 Fig. 2 is a transmission electron microscope (TEM) image of rGO and rGO-R, wherein a-b are TEM images of rGO, and c-d are TEM images of rGO-R.

[0029] Figure 3 Fig. 3 is an X-ray diffraction (XRD) spectrum of rGO and rGO-R.

[0030] Figure 4 Fig. 4 is a reaction schematic diagram of activated PDS degrading BPA.

[0031] Figure 5 Fig. 5 is an adsorption kinetics curve of rGO and rGO-R on bisphenol A (BPA); Fig. 6 is a kinetics curve of rGO and rGO-R catalyzing peroxodisulfate (PDS) to degrade bisphenol A; Fig. 7 is an adsorption kinetics curve of rGO and rGO-R on PDS; and Fig. 8 is a kinetics curve of PDS oxidation in the process of rGO and rGO-R catalyzing PDS to degrade bisphenol A.

[0032] Figure 6 Fig. 9 is an EPR spectrum of rGO-R activating PDS to degrade organic pollutants, wherein a, b and c are EPR spectra of rGO-R activating PDS to degrade organic pollutants; and d is a quenching effect diagram of methanol (MeOH) and tert-butyl alcohol (TBA) on sulfate radicals and hydroxyl radicals in the reaction of rGO-R catalyzing PDS to degrade BPA.

[0033] Figure 7a is cyclic voltammogram of BPA on rGO; b is cyclic voltammogram of PDS on rGO; c is cyclic voltammogram of BPA on rGO-R; d is cyclic voltammogram of PDS on rGO-R.

[0034] Figure 8 a is open circuit potential curve with or without PDS or BPA on rGO; b is chronoamperogram at different potentials with or without BPA on rGO; c is open circuit potential curve with or without PDS or BPA on rGO-R; d is chronoamperogram at different potentials with or without BPA on rGO-R. DETAILED DESCRIPTION

[0035] The present application is further described in detail by the following examples in conjunction with the accompanying drawings.

[0036] (1) Process of the method of the present application

[0037] The graphene oxide dispersion liquid of 15 mL N,N-dimethylformamide (wherein the concentration of N,N-dimethylformamide is 4 mg / mL) is replaced with a solution of ethyl acetate to synthesize graphene oxide fiber by using a wet spinning machine. After the above-mentioned 60 mg graphene fiber is broken into short fibers of 0.5 cm in a 95% volume percentage ethanol aqueous solution, the ethanol aqueous solution on the fiber is filtered through gauze and evaporated to dryness to obtain sheet-shaped graphene oxide. Then, the obtained 60 mg sheet-shaped graphene oxide is reduced in 0.3 mL hydrazine hydrate N2H4 for 3 h to obtain sheet-shaped reduced graphene oxide rGO. Finally, sheet-shaped nitrogen-doped reduced graphene oxide rGO-R is obtained by reduction in an argon atmosphere for 1 h.

[0038] Two pieces of sheet-shaped catalytic electrodes of 1 cm*1 cm (length* width) are placed in the cathode and anode chambers of an H-shaped electrolytic cell separated by a proton exchange membrane as the cathode and anode, wherein the cathode chamber contains 40 mL of 10 mM potassium peroxodisulfate solution and the anode chamber contains 40 mL of 5 μM organic pollutant solution, the cathode and anode are connected by copper wire, and the organic pollutant is bisphenol A, and a catalytic reaction is carried out.

[0039] The concentration detection method of bisphenol A is as follows: 0.5 mL of the reaction membrane after a predetermined time interval is detected for residual bisphenol A on a high performance liquid chromatograph, and the liquid phase conditions are methanol: water = 70:30.

[0040] The detection method of PDS (potassium peroxodisulfate) is as follows: 0.1 mL of the sample solution is mixed with 4.9 mL of potassium iodide solution (concentration of 10 mM) after a predetermined time interval, and then placed for 20 minutes, and then detected by ultraviolet spectrophotometry, and the detection wavelength is 352 nm.

[0041] (2) Effects obtained by this example

[0042] The scanning electron microscope (SEM) image of the catalytic electrode is shown in Figure 1 (a-d) are the electron microscope images of the synthesized rGO at different scales, and (e-h) are the electron microscope images of the synthesized rGO at different scales, both of which can be seen as a layered structure. After high-temperature calcination of rGO, rGO-R is obtained, and the fiber structure is still retained without obvious fracture, as shown in Figure 1 b, c, f and g, the size of the single fiber shrinks.

[0043] The transmission electron microscope (TEM) image of the catalytic electrode is shown in Figure 2 (a-b) are the electron microscope images of the synthesized rGO at different scales, and (c-d) are the electron microscope images of the synthesized rGO at different scales, and there is no obvious difference between the two materials, both of which show a sheet shape with wrinkles.

[0044] The X-ray diffraction pattern of the catalytic electrode is shown in Figure 3 The rGO reduced only by hydrazine hydrate has obvious diffraction peaks near 2θ = 23.8° and 43.1°, corresponding to the (002) and (100) planes of graphite, respectively. After high-temperature reduction at 1100°C, rGO-R still has the diffraction peaks of the (002) and (100) planes of graphite, and the diffraction peak of the (002) plane obviously shifts to a high angle (2θ = 26.4°) and the diffraction peak is more sharp. This is because high-temperature reduction further removes the functional groups of graphene oxide, making the interlayer spacing smaller and the π-π conjugated structure in the graphene lattice restored.

[0045] The schematic diagram of the catalytic electrode activating PDS (potassium peroxodisulfate) and BPA (bisphenol A) is shown in Figure 4 The cathode chamber and the anode chamber are separated by a proton exchange membrane, and contain PDS solution and BPA solution, respectively, and the catalytic electrode is connected as the cathode and anode by wires.

[0046] As shown in Figure 5As shown, by comparing the concentration of BPA (bisphenol A) and PDS (potassium peroxodisulfate) in different systems, it is shown that rGO-R has a better adsorption and removal effect on BPA. Figure a shows that within two hours, rGO has almost no adsorption capacity for BPA, and rGO-R can adsorb about 20% of BPA. After connecting the cathode and anode with wires, rGO shows poor BPA removal capacity, and only 6% of BPA is removed after two hours; while rGO-R shows higher catalytic degradation capacity, and completely removes BPA within two hours. Similarly, in order to evaluate the activation capacity of rGO and rGO-R on PDS in the decoupling oxidation process, a low concentration of PDS solution is selected for experiment, and the results are shown in figures c and d. The concentration change curve of PDS shows that rGO and rGO-R have no obvious adsorption capacity for PDS, but rGO-R has stronger PDS activation capacity in the decoupling oxidation system, so that about 8% of PDS is decomposed in the reaction.

[0047] As shown in Figure 6 , Figure 6 , the free radicals possibly existing in the system are detected by electron paramagnetic resonance technology and the addition of a capture agent. DMPO dissolved in the aqueous phase is a probe for SO4 ·- and · ·OH, as shown in figure a, a high concentration of PDS can generate trace amounts of SO4 ·- and · ·OH through self-decomposition, and the intensity of SO4 ·- and ·OH decreases after the addition of rGO-R, indicating that rGO-R does not activate PDS to generate SO4·- and ·OH. DMPO and TEMP dissolved in the methanol phase are probes for O2 ·- and 1 , as can be seen from figures b and c, O2 ·- and 1 is not generated in the system. In order to exclude the influence of SO4 ·- and · ·OH on BPA degradation, methanol and tert-butyl alcohol are selected as quenching agents for these two kinds of free radicals and added to the degradation system, and the results show that neither SO4 ·- nor ·OH plays a role in the degradation of BPA.

[0048] The cyclic voltammogram of the catalytic electrode is shown in Figure 7 . For rGO, the addition of reactants does not cause redox peaks to appear on the curve. However, for rGO-R, compared with the electrolyte without reactants, after the addition of BPA, an obvious oxidation peak appears on the curve, and after the addition of PDS, an obvious reduction peak appears. This indicates that under the potential drive of -0.2V-1.0V, BPA can undergo oxidation on rGO-R and PDS can undergo reduction on rGO-R.

[0049] Open-circuit potential and chronocurrent of catalytic electrode in different systems, such as Figure 8 As shown in Figure a, for the rGO electrode, the addition of BPA and PDS results in a 0.1V potential difference between the anode and cathode in the corresponding two-chamber degradation reaction. Figure b shows that this potential difference is insufficient to induce oxidative degradation of BPA on rGO. Figure c shows that for the rGO-R electrode, the addition of BPA and PDS results in a larger potential difference (0.59V) between the anode and cathode in the corresponding two-chamber degradation reaction. Using the potential measured in c, applying a constant potential to rGO-R yields the chronoamperometry curve shown in d. When the applied potential is constant at 0.30V (equivalent to the potential of rGO-R itself), the current response shows no significant change regardless of the presence or absence of BPA. However, when the applied potential is constant at 0.86V (equivalent to the stable potential after rGO-R contacts PDS), the current in the BPA-containing system is significantly increased compared to the system without BPA, indicating that the high potential after rGO-R contacts PDS is sufficient for electron exchange between BPA and the catalytic electrode surface.

Claims

1. Use of a device for degrading organic pollutants using a galvanic-like effect for degrading organic pollutants, characterized in that, Specifically comprising: Two pieces of sheet-shaped catalytic electrodes are placed in the cathode and anode chambers of an H-shaped electrolytic cell separated by a proton exchange membrane as the cathode and anode, wherein the cathode chamber contains potassium peroxodisulfate solution and the anode chamber contains organic pollutant solution, and the cathode and anode are connected by a copper wire for catalytic reaction; The preparation method of the sheet-shaped catalytic electrode comprises the following steps: 1) The graphene oxide dispersion liquid of N, N-dimethylformamide is replaced with a solution of ethyl acetate to synthesize graphene oxide fibers by using a wet spinning machine; 2) The graphene oxide fibers obtained in step 1) are broken into short fibers in an ethanol aqueous solution, filtered through gauze, and then the ethanol aqueous solution on the fibers is volatilized and dried to obtain sheet-shaped graphene oxide; 3) The sheet-shaped graphene oxide obtained in step 2) is reduced in hydrazine N2H4 to obtain sheet-shaped reduced graphene oxide rGO; 4) The rGO obtained in step 3) is reduced in an argon atmosphere to obtain sheet-shaped nitrogen-doped reduced graphene oxide rGO-R, which is a sheet-shaped catalytic electrode based on reduced graphene oxide.

2. Use according to claim 1, characterized in that, In step 1), the concentration of N, N-dimethylformamide in the graphene oxide dispersion liquid of N, N-dimethylformamide is 1-10 mg / mL.

3. Use according to claim 1, characterized in that, In step 2), the volume percentage of the ethanol aqueous solution is 10%-100%.

4. Use according to claim 1, characterized in that, In step 2), the length of the short fibers is 0.1-5 cm.

5. The use according to claim 1, characterized in that, In step 3), the ratio of the amount of sheet-shaped graphene oxide to hydrazine is 50-70 mg: 0.1-1 mL.

6. Use according to claim 1, characterized in that, In step 3), the reduction time of the sheet-shaped graphene oxide in hydrazine is 2-6 h.

7. The use according to claim 1, characterized in that, In step 4), the reduction time of the rGO in an argon atmosphere is 1-3 h.

8. The use according to claim 1, characterized in that, The organic pollutant is bisphenol A.

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