Copper Integrated Electrode with Convertible Oxidation State and Preparation Method and Application Method thereof

Abstract

A copper integrated electrode with a convertible oxidation state, a preparation method and an application method are provided. The preparation process is based on an electrochemically induced self-growth method. Copper foam is used as a precursor, soaked in a graphene oxide solution, dried, calcined at high temperature and annealed, and then treated with an alkali solution to obtain the copper integrated electrode with the convertible oxidation state. The working electrode prepared by the nano-catalytic material of the present invention has good denitrification performance in the environmental field, which can achieve nearly 100% nitrate removal rate, nearly 100% nitrogen selectivity and long-term stability. These properties are due to the prepared working electrode having an oxidizable copper (I, II/0, I), oxygen vacancy (O) and a one-dimensional nanowire structure. The structure can regulate the adsorption and reduction of intermediate products, resulting in nearly 100% nitrate removal rate and nearly 100% nitrogen selectivity.

Claims

1. A preparation method of a copper integrated electrode with a convertible oxidation state, comprising the following steps: 1) cutting a copper foam into a copper foam strip, and washing the copper foam strip with ethanol and acetone to remove surface impurities of the copper foam strip to obtain a washed copper foam strip; 2) drying the washed copper foam strip obtained in step 1) at room temperature to obtain a dried copper foam strip, and immersing the dried copper foam strip in a graphene oxide solution with a concentration of 0.1 mg/mL-10 mg/mL for 1 min-10 min, covering a surface of the dried copper foam strip with a carbon layer to obtain a carbon coated copper foam strip, transferring the carbon coated copper foam strip to a constant temperature oven, and drying the carbon coated copper foam strip for 1 h-10 h at 50° C.-100° C. to obtain a copper foam carrier; 3) calcining the copper foam carrier obtained in step 2) for 1 h-5 h at 200° C.-500° C. in a tubular furnace with an argon atmosphere to obtain a C—Cu electrode substrate; 4) after cutting the C—Cu electrode substrate obtained in step 3) to a size of 1 cm×1 cm to obtain a trimmed C—Cu electrode substrate, cleaning the trimmed C—Cu electrode substrate 2-3 times with ultrapure water to obtain a first washed C—Cu electrode substrate, placing the first washed C—Cu electrode substrate in an alkali solution with a concentration of 0.1 M-1 M for a CV scanning for 1-400 cycles in a voltage range of −1 V-+1 V by a cyclic voltammetry to obtain a treated C—Cu electrode substrate, then cleaning the treated C—Cu electrode substrate 2-3 times with ultrapure water again to obtain a second washed C—Cu electrode substrate and drying the second washed C—Cu electrode substrate to obtain the copper integrated electrode with the convertible oxidation state.

2. The preparation method according to claim 1, wherein a concentration of a graphene oxide in the graphene oxide solution is 0.1 mg/mL-5 mg/mL; a preparation method of the graphene oxide solution comprises the following steps: M1: adding 2 g of graphite powder with a particle size of 325 mesh into concentrated sulfuric acid containing K2S208 and P2O5 for a uniform mixing to obtain a first mixed solution, heating the first mixed solution to 80° C. and keeping the first mixed solution at 80° C. for a first reaction under reflux and stirring for 5 h to obtain a first mixture, after the first reaction is completed, pouring the first mixture into 500 mL of pure water for stirring, mixing and putting aside to form a first precipitate, and filtering the first precipitate through a 0.2 μm filter membrane to obtain a first filtered precipitate, and then washing the first filtered precipitate with pure water to obtain a first washed precipitate, and drying the first washed precipitate in the air to obtain a pre-oxidized graphite; M2: adding the pre-oxidized graphite obtained in step M1 into 120 mL of concentrated sulfuric acid in a state of ice bath to obtain a second mixture, slowly adding 25 g of KMnO.sub.4 at 4° C.-6° C. into the second mixture under a constant stirring to obtain a third mixture, continuing to stir the third mixture at 35° C. for 4 h, then slowly adding 250 mL of deionized water into the third mixture to obtain a second mixed solution for a second reaction at a temperature below 50° C. to obtain a fourth mixture; M3: adding 1 L of deionized water to the fourth mixture obtained in step M2 to obtain a third mixed solution, then slowly adding 30 mL of a hydrogen peroxide solution with a mass fraction of 30% dropwise into the third mixed solution to obtain a fourth mixed solution, fully stirring the fourth mixed solution for a third reaction to obtain a second precipitate, washing the second precipitate with 1 L of dilute hydrochloric acid with a volume ratio of 1:10 to remove unreacted KMnO.sub.4 on the second precipitate to obtain a second washed precipitate, and then washing the second washed precipitate with 1 L of deionized water to remove residual dilute hydrochloric acid on the second washed precipitate to obtain a fifth mixture; M4: filtering the fifth mixture obtained in step M3 to obtain a graphene oxide solid, dissolving the graphene oxide solid with deionized water to prepare a graphene oxide solution with a mass fraction of 0.5%; M5: dialyzing continuously the graphene oxide solution obtained in step M4 for 1 week to remove residual metal ion impurities to obtain a dialyzed graphene oxide solution, performing a suction filtration on the dialyzed graphene oxide solution to obtain graphene oxide solid powder, and preparing the graphene oxide solid powder into a graphene oxide solution with a first predetermined concentration, then stripping a graphene material in the graphene oxide solution with the first predetermined concentration by an ultrasonic method to finally obtain a graphene oxide solution with a second predetermined concentration in a uniform light yellow and clear state.

3. The preparation method according to claim 1, wherein the alkali solution is a NaOH solution.

4. The preparation method according to claim 1, wherein the voltage range of the cyclic voltammetry in step 4) is −0.5 V-+0.85 V.

5. A copper integrated electrode with a convertible oxidation state prepared by the preparation method according to claim 1, wherein the copper integrated electrode is a single metal copper self-supporting Cu.sub.2O nanowires electrode.

6. An application method of the copper integrated electrode with the convertible oxidation state according to claim 5 in a denitrification treatment of a water body containing nitrate, comprising: forming a three-electrode system using the copper integrated electrode with the convertible oxidation state as a working electrode, a platinum electrode as a counter electrode, and an Ag/AgCl electrode as a reference electrode; and placing the three-electrode system in the water body containing the nitrate for the denitrification treatment.

7. The application method according to claim 6, wherein a concentration of the nitrate in the water body containing the nitrate is 10 mgN/L-300 mgN/L.

8. The application method according to claim 6, wherein a mixed electrolyte of Na.sub.2SO.sub.4 and NaCl is used in the three-electrode system.

9. The application method according to claim 8, wherein in the mixed electrolyte of the Na.sub.2SO.sub.4 and the NaCl, a concentration of the Na.sub.2SO.sub.4 is 0.06 mol/L-0.2 mol/L, and a concentration of the NaCl is 0.01 mol/L-0.05 mol/L.

10. The application method according to claim 6, wherein an applied voltage of the denitrification treatment is −1.1 V-−1.5 V, and a denitrification time is 1 h-28 h.

11. The copper integrated electrode according to claim 5, wherein a concentration of a graphene oxide in the graphene oxide solution is 0.1 mg/mL-5 mg/mL; a preparation method of the graphene oxide solution comprises the following steps: M1: adding 2 g of graphite powder with a particle size of 325 mesh into concentrated sulfuric acid containing K2S208 and P2O5 for a uniform mixing to obtain a first mixed solution, heating the first mixed solution to 80° C. and keeping the first mixed solution at 80° C. for a first reaction under reflux and stirring for 5 h to obtain a first mixture, after the first reaction is completed, pouring the first mixture into 500 mL of pure water for stirring, mixing and putting aside to form a first precipitate, and filtering the first precipitate through a 0.2 μm filter membrane to obtain a first filtered precipitate, and then washing the first filtered precipitate with pure water to obtain a first washed precipitate, and drying the first washed precipitate in the air to obtain a pre-oxidized graphite; M2: adding the pre-oxidized graphite obtained in step M1 into 120 mL of concentrated sulfuric acid in a state of ice bath to obtain a second mixture, slowly adding 25 g of KMnO.sub.4 at 4° C.-6° C. into the second mixture under a constant stirring to obtain a third mixture, continuing to stir the third mixture at 35° C. for 4 h, then slowly adding 250 mL of deionized water into the third mixture to obtain a second mixed solution for a second reaction at a temperature below 50° C. to obtain a fourth mixture; M3: adding 1 L of deionized water to the fourth mixture obtained in step M2 to obtain a third mixed solution, then slowly adding 30 mL of a hydrogen peroxide solution with a mass fraction of 30% dropwise into the third mixed solution to obtain a fourth mixed solution, fully stirring the fourth mixed solution for a third reaction to obtain a second precipitate, washing the second precipitate with 1 L of dilute hydrochloric acid with a volume ratio of 1:10 to remove unreacted KMnO.sub.4 on the second precipitate to obtain a second washed precipitate, and then washing the second washed precipitate with 1 L of deionized water to remove residual dilute hydrochloric acid on the second washed precipitate to obtain a fifth mixture; M4: filtering the fifth mixture obtained in step M3 to obtain a graphene oxide solid, dissolving the graphene oxide solid with deionized water to prepare a graphene oxide solution with a mass fraction of 0.5%; M5: dialyzing continuously the graphene oxide solution obtained in step M4 for 1 week to remove residual metal ion impurities to obtain a dialyzed graphene oxide solution, performing a suction filtration on the dialyzed graphene oxide solution to obtain graphene oxide solid powder, and preparing the graphene oxide solid powder into a graphene oxide solution with a first predetermined concentration, then stripping a graphene material in the graphene oxide solution with the first predetermined concentration by an ultrasonic method to finally obtain a graphene oxide solution with a second predetermined concentration in a uniform light yellow and clear state.

12. The copper integrated electrode according to claim 5, wherein the alkali solution is a NaOH solution.

13. The copper integrated electrode according to claim 5, wherein the voltage range of the cyclic voltammetry in step 4) is −0.5 V-+0.85 V.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The present invention will be described in more detail below based on embodiments and drawings, where,

[0033] FIG. 1 is a scanning electron microscope (SEM) image of Cu.sub.2O nanowires in embodiment 1 of the present invention;

[0034] FIG. 2 is a diagram showing the cyclic stability of the Cu.sub.2O nanowires for nitrate removal and nitrogen selectivity in embodiment 1 of the present invention;

[0035] FIG. 3 is an SEM image of Cu.sub.2O nanowires-100 in embodiment 2 of the present invention;

[0036] FIG. 4 is an SEM image of Cu.sub.2O nanocrystals in embodiment 3 of the present invention;

[0037] FIG. 5 is an SEM image of Cu.sub.2O octahedrons in embodiment 4 of the present invention;

[0038] FIG. 6 is an SEM image of Cu.sub.2O cubes in embodiment 5 of the present invention;

[0039] FIG. 7 is a diagram showing the nitrate removal rates and the nitrogen selectivities of the Cu.sub.2O nanowires obtained by embodiment 1, the Cu.sub.2O nanowires-100 obtained by embodiment 2 and the Cu.sub.2O nanocrystals obtained by embodiment 3 of the present invention; and

[0040] FIG. 8 is a diagram showing the nitrate (with different concentrations) removal rates and the nitrogen selectivities of the Cu.sub.2O nanowires obtained by embodiment 1, the Cu.sub.2O octahedrons obtained by embodiment 4 and the Cu.sub.2O cubes obtained by embodiment 5 of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] The technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the drawings of the embodiments of the present invention, and it will be apparent that the described embodiments are only a part of the embodiments of the present invention, and not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the present invention.

[0042] Embodiment 1

[0043] A preparation method of a copper integrated electrode with a convertible oxidation state provided by the present embodiment includes the following steps:

[0044] copper foam is cut into strips and washed with ethanol and acetone to remove surface impurities;

[0045] the copper foam is soaked in a 1 mg/mL graphene oxide solution for 1 min, placed in a 60° C. oven, dried for 2 h, then taken out and calcined in a tubular furnace at 300° C. for 2 h;

[0046] the calcined sample is put in a 0.1 M NaOH solution, and a CV scanning is performed for 200 cycles in a voltage range of −0.2 V-+0.9 V to form a self-supporting Cu.sub.2O nanowires electrode, which is the copper integrated electrode with the convertible oxidation state in the present embodiment.

[0047] A preparation method of the graphene oxide solution adopts an improved Hummers-Offeman chemical oxidation method, including the following steps:

[0048] M1: 2 g of graphite powder with a particle size of 325 mesh is added into concentrated sulfuric acid containing K.sub.2S.sub.2O.sub.8 and P.sub.2O.sub.5, mixed uniformly, heated to 80° C. and a reaction system is kept at 80° C. for reflux and stirring for 5 h, after the reaction is completed, an obtained mixture is poured into 500 mL of pure water, stirred, mixed and put aside to form a precipitate, and then the precipitate is filtered through a 0.2 μm filter membrane, the precipitate obtained by filtration is washed with pure water, and dried in the air to obtain a pre-oxidized graphite;

[0049] M2: the pre-oxidized graphite obtained in step M1 is added into 120 mL of concentrated sulfuric acid in a state of ice bath, 25 g of KMnO.sub.4 is slowly added at 4° C.-6° C. with constant stirring, and stirred continuously at 35° C. for 4 h, then 250 mL of deionized water is slowly added and the chemical reaction is continued at a temperature below 50° C.;

[0050] M3: 1 L of deionized water is added to the mixture obtained in step M2, then 30 mL of hydrogen peroxide solution with a mass fraction of 30% is slowly and dropwise added, after the reaction is completed under full stirring, the precipitate is washed with 1 L of dilute hydrochloric acid with a volume ratio of 1:10 to remove unreacted KMnO.sub.4, and then washed with 1 L of deionized water to remove residual dilute hydrochloric acid;

[0051] M4: the mixture obtained in step M3 is filtered to obtain a graphene oxide solid, the graphene oxide solid is dissolved with deionized water to prepare a graphene oxide solution with a mass fraction of 0.5%;

[0052] M5: the graphene oxide solution obtained in step M4 is dialyzed continuously for 1 week to remove residual metal ion impurities, a solution obtained after dialysis is subjected to a suction filtration, and obtained solid powder is prepared into a graphene oxide solution with a concentration of 1 mg/mL, then a graphene material in the graphene oxide solution is stripped by an ultrasonic method to finally obtain the graphene oxide solution with the concentration of 1 mg/mL in a uniform light yellow and clear state.

[0053] The present embodiment also provides an application method of applying the self-supporting Cu.sub.2O nanowires electrode to electrocatalytic denitrification in a water body containing nitrate. The self-supporting Cu.sub.2O nanowires electrode obtained above is directly used as a working electrode, a platinum electrode is used as a counter electrode, and an Ag/AgCl electrode is used as a reference electrode to form a three-electrode system. The three-electrode system is placed in the water body containing the nitrate for a denitrification treatment.

[0054] A concentration of the nitrate in the water body containing the nitrate is 100 mgN/L. In the mixed electrolyte of Na.sub.2SO.sub.4 and NaCl, a concentration of the Na.sub.2SO.sub.4 is 0.1 mol/L, and a concentration of the NaCl is 0.02 mol/L. An applied voltage is −1.3 V, and a denitrification time is 18 h.

[0055] FIG. 1 shows that Cu.sub.2O nanowires have a one-dimensional nanowire structure, which provides a high specific surface area.

[0056] FIG. 2 shows that after 10 consecutive cycles of electrocatalytic denitrification, the rate constant of nitrate nitrogen remains unchanged, while the removal capacity of nitrate decreases slightly, indicating that the catalyst can maintain good reaction power and cycling stability.

[0057] Electrochemical treatment technology refers to a series of physical and chemical reactions occur in a specialized reaction vessel with the assistance of electrode or external electric field, so as to realize the degradation effect on wastewater pollutants. Electrochemical treatment process does not need to add any pharmaceutical reagents, and it will not pollute the environment, so it is called “environment-friendly” technology. When the copper integrated electrode with the convertible oxidation state provided by the present invention is used for electrochemical denitrification in the water body containing the nitrate, various kinds of free radicals are generated in the solution. These free radicals have strong oxidizability and effectively remove the impurities in sewage. The denitrification is realized under the action of H.sub.2 generated by electrolysis during the electrochemical denitrification and the nitrate in sewage. NO.sub.3-N is an electron acceptor, and the product is non-toxic and tasteless N.sub.2.

[0058] When the nitrate ions in the aqueous solution are adsorbed on the surface of the copper integrated electrode with the convertible oxidation state, the nitrate in the water passes through the surface of the electrode, with 2 electrons transferring firstly to form NO.sub.3.sup.2−, then 1 electron transferring to form NO, and finally 2 electrons transferring through the copper integrated electrode to form N.sub.2. A total of 5 electrons are transferred during the process of converting nitrate in the water body into N.sub.2, and the selective reduction and denitrification treatment of the nitrate in the water body is achieved by the copper integrated electrode with the convertible oxidation state, which is environmentally friendly and does not need to add other additives. Moreover, the raw materials for electrode preparation are cheap and easy to obtain, the preparation process is simple, and the denitrification efficiency is remarkable.

[0059] Embodiment 2

[0060] The difference between the present embodiment and embodiment 1 is that in a preparation method of a copper integrated electrode with a convertible oxidation state of the present embodiment, a CV scanning is performed for 100 cycles.

[0061] FIG. 3 shows that the obtained electrode Cu.sub.2O nanowires-100 cycles maintains a nanowire structure, but lengths of the Cu.sub.2O nanowires are shorter than lengths of the Cu.sub.2O nanowires in embodiment 1.

[0062] Embodiment 3

[0063] The difference between the present embodiment and embodiment 1 is that the CV scanning is not performed in a preparation method of a copper integrated electrode with a convertible oxidation state of the present embodiment.

[0064] FIG. 4 shows that only the nanocrystals are formed in the obtained electrode Cu.sub.2O nanowires, which provides guidance for the subsequent directional growth of the nanowires.

[0065] Embodiment 4

[0066] The difference between the present embodiment and embodiment 1 is that in a preparation method of a copper integrated electrode with a convertible oxidation state of the present embodiment, the obtained Cu.sub.2O nanowires are firstly acid washed with acetic acid, and then an electrochemical CV scanning is performed on the Cu.sub.2O nanowires for 200 cycles.

[0067] FIG. 5 shows that the obtained electrode Cu.sub.2O nanowires are Cu.sub.2O octahedrons.

[0068] Embodiment 5

[0069] The difference between the present embodiment and embodiment 1 is that in a preparation method of a copper integrated electrode with a convertible oxidation state of the present embodiment, the obtained Cu.sub.2O nanowires are firstly acid washed with hydrochloric acid, and then an electrochemical CV scanning is performed on the Cu.sub.2O nanowires for 200 cycles.

[0070] FIG. 6 shows that the surface of the obtained electrode Cu.sub.2O nanowires is Cu.sub.2O cube morphology.

[0071] FIG. 7 shows that compared with the Cu.sub.2O nanowires-100 and the Cu.sub.2O nanocrystals, the obtained electrode Cu.sub.2O nanowires have higher nitrate removal rate and nitrogen selectivity.

[0072] FIG. 8 shows that compared with the Cu.sub.2O octahedrons and the Cu.sub.2O cubes, the obtained electrode Cu.sub.2O nanowires have higher nitrate removal rate and nitrogen selectivity.

[0073] Embodiment 6

[0074] The difference between the present embodiment and embodiment 1 is that in a preparation method of the present embodiment, the copper foam is soaked in a 0.1 mg/mL graphene oxide solution for 5 min, placed in a 50° C. oven, dried for 1 h, then taken out and calcined in a tubular furnace at 200° C. for 5 h;

[0075] the calcined sample is put in a 0.5 M NaOH solution, and a CV scanning is performed for 1 cycle in a voltage range of −1 V-+1 V.

[0076] When the copper integrated electrode obtained in the present embodiment used as the working electrode is applied in the water body containing the nitrate for a denitrification treatment, a concentration of the nitrate in the water body containing the nitrate is 200 mgN/L; in the mixed electrolyte of Na.sub.2SO.sub.4 and NaCl, a concentration of the Na.sub.2SO.sub.4 is 0.06 mol/L, and a concentration of the NaCl is 0.05 mol/L; an applied voltage is −1.1 V, and a denitrification time is 28 h.

[0077] Embodiment 7

[0078] The difference between the present embodiment and embodiment 1 is that in a preparation method of the present embodiment, the copper foam is soaked in a 10 mg/mL graphene oxide solution for 10 min, placed in a 100° C. oven, dried for 10 h, then taken out and calcined in a tubular furnace at 500° C. for 1 h;

[0079] the calcined sample is put in a 0.5 M NaOH solution, and a CV scanning is performed for 400 cycles in a voltage range of −0.5 V-+0.85 V.

[0080] When the copper integrated electrode obtained in the present embodiment used as the working electrode is applied in the water body containing the nitrate for a denitrification treatment, a concentration of the nitrate in the water body containing the nitrate is 300 mgN/L; in the mixed electrolyte of Na.sub.2SO.sub.4 and NaCl, a concentration of the Na.sub.2SO.sub.4 is 0.2 mol/L, and a concentration of the NaCl is 0.01 mol/L; an applied voltage is −1.5 V, and a denitrification time is 1 h.

[0081] Embodiment 8

[0082] The difference between the present embodiment and embodiment 1 is that in a preparation method of the present embodiment, the copper foam is soaked in a 5 mg/mL graphene oxide solution.

[0083] The above description of the embodiments is to facilitate the understanding and application of the present invention by those skilled in the art. Those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative labor. Therefore, the present invention is not limited to the embodiments here, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention shall be within the scope of protection of the present invention.