Copper-zinc dual active site organic composite catalyst, electrode and application thereof in electrocatalytic reduction of nitrate nitrogen

Abstract

The application discloses a copper-zinc double active site organic composite catalyst, an electrode and application of the copper-zinc double active site organic composite catalyst and the electrode in electrocatalytic reduction of nitrate nitrogen. The application first disperses phthalocyanine copper and phthalocyanine zinc respectively by ultrasonic, then re-composites to form coupling between Cu-Zn, and then is adsorbed to carbon material to form the copper-zinc double active site organic composite catalyst. The catalyst reduces nitrate by copper-zinc synergistic electrocatalysis, copper-zinc sites preferentially adsorb and reduce low-reaction-energy-ladder intermediate species respectively, and can effectively improve the activity of electrocatalytic reduction of nitrate and the selectivity of ammonia nitrogen. The copper-zinc double active site organic composite catalyst has obvious improvement in the activity and the selectivity of ammonia nitrogen compared with single phthalocyanine copper or phthalocyanine zinc catalyst, and has better ammonia production effect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrochemistry, and particularly relates to a copper-zinc dual active site organic composite catalyst, an electrode and application thereof in electrocatalytic reduction of nitrate nitrogen. BACKGROUND

[0002] Ammonia is an important chemical commonly used in the agricultural, plastic, pharmaceutical and other industries. The large-scale synthesis and application of ammonia greatly improves the yield of crops, while the Haber-Bosch process commonly used for synthesizing ammonia has problems such as excessive energy consumption and high carbon emission. Nitrate nitrogen widely exists in surface and underground water and has a certain threat to human health. Therefore, using electrochemical catalysis to produce ammonia from nitrate nitrogen in natural water bodies is a green and efficient technical route, which can realize the reduction of nitrate nitrogen to ammonia nitrogen and resource utilization.

[0003] The electrocatalytic reduction catalyst is the current research focus, and in recent years, the molecular catalyst has become a new field of catalytic science research due to the advantages of convenient atomic design, simple structure-activity relationship and high atomic utilization rate. SUMMARY

[0004] Therefore, the purpose of the present application is to provide a copper-zinc dual active site organic composite catalyst, an electrode and application thereof in electrocatalytic reduction of nitrate nitrogen, which can effectively improve the activity of electrocatalytic reduction of nitrate and the selectivity of ammonia nitrogen.

[0005] To achieve the above purpose, the present application provides the following technical solutions:

[0006] The present application provides a preparation method of a copper-zinc dual active site organic composite catalyst, comprising the following steps

[0007] (1) ultrasonic dispersion of copper phthalocyanine in a solvent to obtain solution A;

[0008] (2) ultrasonic dispersion of zinc phthalocyanine in the same solvent to obtain solution B;

[0009] (3) heating solution A and applying ultrasonic, and dropping solution B into solution A to form a mixed solution C;

[0010] (4) ultrasonic dispersion of carbon-based powder material in the same solvent to form an ink-like dispersion liquid, dropping mixed solution C into the dispersion liquid under ultrasonic state, stirring for a period of time, and then filtering and drying to obtain a copper-zinc dual active site organic composite catalyst.

[0011] As a preferred technical solution, in step (1), the undispersed particles are removed by centrifugal separation when the copper phthalocyanine is ultrasonic dispersed in the solvent to obtain solution A.

[0012] As a preferred technical solution, in the step (2), when the zinc phthalocyanine is ultrasonically dispersed in the same solvent, the undispersed particles are removed by centrifugal separation to obtain solution B.

[0013] As a preferred technical solution, the solvent is one or more of N,N-dimethylformamide, ethanol, methanol and acetonitrile.

[0014] As a preferred technical solution, in the step (3), solution A and solution B are mixed according to a mass ratio of copper phthalocyanine to zinc phthalocyanine of 1:0.1-1.

[0015] As a preferred technical solution, in the step (3), the heating temperature is 30-60 DEG C.

[0016] As a preferred technical solution, in the step (4), the carbon-based powder material is one or more of carbon black, graphene and carbon nanotube.

[0017] As a preferred technical solution, in the step (4), the stirring speed is 400-600 rpm, and the stirring time is 1-2 hours.

[0018] The application also provides a copper-zinc dual active site organic composite catalyst prepared by the preparation method.

[0019] The application also provides a copper-zinc dual active site organic composite catalyst electrode, which is prepared by mixing and dispersing the copper-zinc dual active site organic composite catalyst in a solvent and then uniformly coating the mixture on carbon paper.

[0020] The application also provides an application of the copper-zinc dual active site organic composite catalyst electrode in electrocatalytic reduction of nitrate nitrogen.

[0021] The application has the following beneficial effects:

[0022] The copper phthalocyanine and zinc phthalocyanine are first ultrasonically dispersed, then coupled between Cu and Zn, and then adsorbed on the carbon material to form a copper-zinc dual active site organic composite catalyst, which electrocatalytically reduces nitrate by the synergistic effect of copper and zinc, and the copper and zinc sites preferentially adsorb and reduce low-energy barrier intermediate species, thereby effectively improving the activity of electrocatalytic reduction of nitrate and the selectivity of ammonia nitrogen. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to make the purpose, technical scheme and beneficial effects of the application clearer, the application provides the following drawings for description:

[0024] In order to make the purpose, technical scheme and beneficial effects of the application clearer, the application provides the following drawings for description:Figure 1 TEM image of the copper-zinc dual active site organic composite catalyst electrode prepared in Example 1.

[0025] Figure 2 SEM image of the copper-zinc dual active site organic composite catalyst electrode prepared in Example 1.

[0026] Figure 3 Nitrate nitrogen and product distribution over time in the electrocatalytic reduction of nitrate reaction of the copper-zinc dual active site organic composite catalyst electrode prepared in Example 1.

[0027] Figure 4 Nitrate nitrogen and product distribution over time in the electrocatalytic reduction of nitrate reaction of the copper-zinc dual active site organic composite catalyst electrode prepared in Example 2.

[0028] Figure 5 Nitrate nitrogen and product distribution over time in the electrocatalytic reduction of nitrate reaction of the copper-zinc dual active site organic composite catalyst electrode prepared in Example 3.

[0029] Figure 6 Nitrate nitrogen and product distribution over time in the electrocatalytic reduction of nitrate reaction of the copper phthalocyanine catalyst electrode prepared in Comparative Example 1.

[0030] Figure 7 Nitrate nitrogen and product distribution over time in the electrocatalytic reduction of nitrate reaction of the zinc phthalocyanine catalyst electrode prepared in Comparative Example 2. DETAILED DESCRIPTION

[0031] The present application will be further described in conjunction with the following drawings and specific examples so that it can be better understood and implemented by those skilled in the art, but the examples are not intended to limit the present application.

[0032] The methods used in the following examples are conventional methods unless otherwise specified. The materials or reagents required in the following examples are commercially available unless otherwise specified.

[0033] Example 1: Copper-zinc dual active site organic composite catalyst electrode

[0034] (1) 20.0 mg of copper phthalocyanine was dissolved in 20.0 mL of ethanol and ultrasonicated until completely dispersed. Undispersed particles were removed by centrifugal separation at 4000 rpm to obtain a blue solution A;

[0035] (2) 20.0 mg of zinc phthalocyanine was dissolved in 20.0 mL of ethanol and ultrasonicated until completely dispersed. Undispersed particles were removed by centrifugal separation at 4000 rpm to obtain a light blue solution B;

[0036] (3) Solution A is heated to 40°C and 60 kHz ultrasound is applied, then solution B is slowly dripped into solution A to form mixed solution C, wherein the mass ratio of A to B solution is 1:0.1;

[0037] (4) 10.0 mg of carbon black is ultrasonically dispersed in 20.0 ml of ethanol to form an ink-like dispersion solution, solution C is slowly dripped into it under 60 kHz ultrasound, and magnetic stirring is carried out at 400 rpm for 2 hours, then filtered and dried to obtain a copper-zinc dual active site organic composite catalyst;

[0038] (5) The copper-zinc dual active site organic composite catalyst is added to an ethanol solution and mixed, then Nafion is added as a binder, and ultrasonic is applied until it forms a uniform ink; under the heating of an infrared lamp, the catalyst ink is evenly applied to both sides of the carbon paper to obtain a copper-zinc dual active site organic composite catalyst electrode.

[0039] The TEM and SEM images of the copper-zinc dual active site organic composite catalyst electrode prepared in Example 1 are shown in Figure 1 and Figure 2 As can be seen from the figures, the copper phthalocyanine particles and zinc phthalocyanine particles are stacked together by adsorption or conjugation.

[0040] Example 2: Copper-zinc dual active site organic composite catalyst electrode

[0041] (1) 20.0 mg of copper phthalocyanine is dissolved in 20.0 mL of ethanol and ultrasonically dispersed until completely dispersed, then centrifuged at 4000 rpm to remove undispersed particles to obtain blue solution A;

[0042] (2) 20.0 mg of zinc phthalocyanine is dissolved in 20.0 mL of ethanol and ultrasonically dispersed until completely dispersed, then centrifuged at 4000 rpm to remove undispersed particles to obtain light blue solution B;

[0043] (3) Solution A is heated to 40°C and 60 kHz ultrasound is applied, then solution B is slowly dripped into solution A to form mixed solution C, wherein the mass ratio of A to B solution is 1:0.3;

[0044] (4) 10.0 mg of carbon black is ultrasonically dispersed in 20.0 ml of ethanol to form an ink-like dispersion solution, solution C is slowly dripped into it under 60 kHz ultrasound, and magnetic stirring is carried out at 400 rpm for 2 hours, then filtered and dried to obtain a copper-zinc dual active site organic composite catalyst;

[0045] (5) The copper-zinc dual active site organic composite catalyst is added to an ethanol solution and mixed, then Nafion is added as a binder, and ultrasonic is applied until it forms a uniform ink; under the heating of an infrared lamp, the catalyst ink is evenly applied to both sides of the carbon paper to obtain a copper-zinc dual active site organic composite catalyst electrode.

[0046] Example 3: Copper-zinc dual active site organic composite catalyst electrode

[0047] (1) 20.0 mg of copper phthalocyanine was dissolved in 20.0 mL of ethanol and ultrasonically dispersed until completely dispersed, and centrifuged at 4000 rpm to remove undispersed particles to obtain a blue solution A;

[0048] (2) 20.0 mg of zinc phthalocyanine was dissolved in 20.0 mL of ethanol and ultrasonically dispersed until completely dispersed, and centrifuged at 4000 rpm to remove undispersed particles to obtain a light blue solution B;

[0049] (3) Solution A was heated to 40°C and 60 kHz ultrasound was applied, and then solution B was slowly dripped into solution A to form a mixed solution C, wherein the mass ratio of A to B solution was 1:0.5;

[0050] (4) 10.0 mg of carbon black was ultrasonically dispersed in 20.0 mL of ethanol to form an ink-like dispersion, and solution C was slowly dripped into it under 60 kHz ultrasound, and magnetically stirred at 400 rpm for 2 hours, and then filtered and dried to obtain a copper-zinc dual active site organic composite catalyst;

[0051] (5) The copper-zinc dual active site organic composite catalyst was added to an ethanol solution and mixed, and Nafion was added as a binder, and ultrasonically dispersed until it formed a uniform ink; under the heating of an infrared lamp, the catalyst ink was evenly applied to both sides of the carbon paper to obtain a copper-zinc dual active site organic composite catalyst electrode.

[0052] Comparative Example 1: Copper phthalocyanine catalyst electrode

[0053] (1) 20.0 mg of copper phthalocyanine was dissolved in 20.0 mL of ethanol and ultrasonically dispersed until completely dispersed, and centrifuged at 4000 rpm to remove undispersed particles to obtain a blue solution A;

[0054] (2) 10.0 mg of carbon black was ultrasonically dispersed in 20.0 mL of ethanol to form an ink-like dispersion, and solution A was slowly dripped into it under 60 kHz ultrasound, and magnetically stirred at 400 rpm for 2 hours, and then filtered and dried to obtain a copper phthalocyanine catalyst;

[0055] (3) The copper phthalocyanine catalyst was added to an ethanol solution and mixed, and Nafion was added as a binder, and ultrasonically dispersed until it formed a uniform ink; under the heating of an infrared lamp, the catalyst ink was evenly applied to both sides of the carbon paper to obtain a copper phthalocyanine catalyst electrode.

[0056] Comparative Example 2: Zinc phthalocyanine catalyst electrode

[0057] (1) 20.0 mg zinc phthalocyanine was dissolved in 20.0 mL ethanol and ultrasonically dispersed until completely dispersed, and then centrifuged at 4000 rpm to remove undispersed particles to obtain a light blue solution B;

[0058] (2) 10.0 mg carbon black was weighed and ultrasonically dispersed in 20.0 mL ethanol to form an ink-like dispersion liquid, and solution B was slowly added dropwise under ultrasonic state at 60 kHz, and then stirred at 400 rpm for 2 hours, and then filtered and dried to obtain a zinc phthalocyanine catalyst;

[0059] (3) The zinc phthalocyanine catalyst was added to an ethanol solution and mixed, and Nafion was added as a binder, and then ultrasonically dispersed until a uniform ink was formed; under the heating of an infrared lamp, the catalyst ink was uniformly applied to both sides of the carbon paper to obtain a zinc phthalocyanine catalyst electrode.

[0060] Removal effect of the catalyst on the pollutant nitrate

[0061] (1) The specific steps for building the denitration reaction device are as follows:

[0062] a) The denitration reaction electrolytic tank is an H-shaped electrolytic tank, the anode chamber and the cathode chamber are separated by a cation exchange membrane (Nafion-117), the volume of the two chambers is 150 mL, and sodium sulfate (50 mM) is added to the anode chamber and the cathode chamber as electrolyte, the volume is 100 mL, and nitrogen is passed for 10 min before the reaction; then 1 mL of a pipette is used to add a nitrate nitrogen stock solution to the cathode electrolytic chamber, and the initial concentration is 100 mg / L, and a B-type magnetic stirrer is added for stirring;

[0063] b) According to the principle of three-electrode system, the circuit of the electrocatalytic denitration device is built, the counter electrode is a platinum sheet electrode (30 mm x 30 mm), the reference electrode is a reversible hydrogen electrode, and the working electrode is a copper-zinc double active site organic composite catalyst electrode prepared according to Examples 1-3, a phthalocyanine copper catalyst electrode prepared according to Comparative Example 1, and a phthalocyanine zinc catalyst electrode prepared according to Comparative Example 2;

[0064] c) The evaluation of the denitration reaction effect is carried out by detecting the concentration of pollutants, intermediate products and end products by gas ultraviolet spectrophotometer (UV1000).

[0065] (2) The operation of the denitration reaction device is as follows:

[0066] a) The entire denitration experimental device is placed in a constant temperature water bath magnetic stirrer at 25°C, the stirring rate is 400 rpm, and the stirring is kept uniform;

[0067] b) The parameters of the electrochemical workstation are set, the chronamperometry program is selected, the voltage is set to -0.85 V, and the electrocatalytic reduction of nitrate reaction program is started.

[0068] (3) Determining the denitration reaction activity, the steps are as follows:

[0069] a) At 0 min, 60 min, 120 min, 180 min, 240 min of reaction, using a glass syringe to sample (about 2.5 ml) from the reaction solution in the cathode chamber, and taking 1 ml sample to 25 ml in a colorimetric tube;

[0070] b) Using a UV spectrophotometer (UV1000) to determine the concentration of nitrate nitrogen, ammonia nitrogen and nitrite nitrogen at wavelengths of 220 nm, 420 nm and 540 nm, respectively;

[0071] c) The removal rate of nitrate (η) = (1-C t / C0)*100%;

[0072] The selectivity of ammonia nitrogen S NH4+ is expressed as: S NH4+ =C NH4+ / (C0-C t )*100%;

[0073] Wherein, C NH4+ represents the concentration of NH4 + -N after electrolysis t time (mg L -1 ), C0 represents the initial concentration of NO3 - -N (mg L -1 ); C t represents the concentration of NO3 - -N at t time (mg L -1 ).

[0074] The working electrode uses the copper-zinc double active site organic composite catalyst electrode prepared in Examples 1-3, the copper phthalocyanine catalyst electrode prepared in Comparative Example 1 and the zinc phthalocyanine catalyst electrode prepared in Comparative Example 2, respectively, and the nitrate electrocatalytic reduction reaction is carried out according to the above steps, and the nitrate nitrogen and product distribution change with time in the nitrate electrocatalytic reduction reaction are as follows: Figures 3 to 7As shown in the results, when the copper-zinc dual active site organic composite catalyst electrode prepared in Example 1 was used as the working electrode, the removal rate of nitrate nitrogen continued to rise, and after 4 hours of reaction, the removal rate reached 92.8%, and the selectivity of NH3 was 96.3%. The removal rate of nitrate nitrogen and the selectivity of NH3 of the copper-zinc dual active site organic composite catalyst electrodes prepared in Examples 2 and 3 were close to that of Example 1. Under the same conditions, when the copper phthalocyanine catalyst electrode prepared in Comparative Example 1 was used as the working electrode, the removal rate was 59.2%, and the selectivity of NH3 was 60.8%; when the zinc phthalocyanine catalyst electrode prepared in Comparative Example 2 was used as the working electrode, the removal rate was 55.4%, and the selectivity of NH3 was 56.2%. It was proved that the copper-zinc dual active site organic composite catalyst electrode prepared in Examples 1-3 had higher activity and ammonia production selectivity than the copper phthalocyanine catalyst electrode prepared in Comparative Example 1 and the zinc phthalocyanine catalyst electrode prepared in Comparative Example 2.

[0075] The working electrode was the copper-zinc dual active site organic composite catalyst electrode prepared in Example 1, and the electrocatalytic reduction of nitrate was carried out according to the above steps. In addition, the voltage setting conditions were changed, and the value of the voltage was set to -0.65 V, -0.75 V, -0.85 V, -0.95 V, and -1.05 V, respectively, and 5 reactions were carried out. The results of the electrocatalytic reduction of nitrate by the copper-zinc dual active site organic composite catalyst electrode under different voltages are shown in Table 1. As the voltage increased, the removal rate of nitrate increased, the selectivity of ammonia nitrogen gradually increased, and the byproduct of nitrite gradually decreased.

[0076] Table 1 Removal rate of nitrate and selectivity of ammonia nitrogen under different voltages

[0077] Voltage (V) -0.65 -0.75 -0.85 -0.95 -1.05 Removal efficiency (η) % 83.2 88.6 92.8 98.6 99.8 Ammonia nitrogen selectivity (S) % 85.4 89.7 96.3 98.8 99.9

[0078] The working electrode was the copper-zinc dual active site organic composite catalyst electrode prepared in Example 1, and the electrocatalytic reduction of nitrate was carried out according to the above steps. In addition, the voltage setting conditions were changed, and the value of the voltage was set to -0.65 V, -0.75 V, -0.85 V, -0.95 V, and -1.05 V, respectively, and 5 reactions were carried out. The results of the electrocatalytic reduction of nitrate by the copper-zinc dual active site organic composite catalyst electrode under different voltages are shown in Table 1. As the voltage increased, the removal rate of nitrate increased, the selectivity of ammonia nitrogen gradually increased, and the byproduct of nitrite gradually decreased.

[0079] Table 2 Removal efficiency and selectivity of ammonia of repeated reactions of the same electrode for 5 times

[0080] Nitrate concentration (mg / L) 1 2 3 4 5 Removal efficiency (η) % 92.8 93.4 91.6 94.5 92.6 Ammonia nitrogen selectivity (S) % 96.3 96.8 95.8 97.5 95.6

[0081] The above examples are only preferred examples for fully illustrating the present application, and the protection scope of the present application is not limited thereto. Any equivalent replacement or transformation made by the person skilled in the art on the basis of the present application is within the protection scope of the present application. The protection scope of the present application is subject to the claims.

Claims

1. Use of a copper-zinc dual active site organic composite catalyst electrode in electrocatalytic reduction of nitrate, characterized in that: The preparation method of the copper-zinc dual active site organic composite catalyst electrode comprises the following steps: (1) ultrasonic dispersion of copper phthalocyanine in a solvent to obtain solution A; (2) ultrasonic dispersion of zinc phthalocyanine in the same solvent to obtain solution B; (3) heating solution A to a temperature of 30-60°C and applying ultrasonic waves, and dropping solution B into solution A, the mass ratio of copper phthalocyanine to zinc phthalocyanine being 1:0.1-0.3, to form a mixed solution C; (4) ultrasonic dispersion of carbon-based powder material in the same solvent to form an ink-like dispersion liquid, and dropping the mixed solution C into the dispersion liquid under ultrasonic waves, stirring for a period of time, and then filtering and drying to obtain a copper-zinc dual active site organic composite catalyst; the carbon-based powder material is one or more of carbon black, graphene, or carbon nanotubes; (5) mixing and dispersing the copper-zinc dual active site organic composite catalyst with a binder in a solvent, and then uniformly coating the mixture on carbon paper to obtain a copper-zinc dual active site organic composite catalyst electrode.

2. Use of a copper-zinc bi-active site organic composite catalyst electrode according to claim 1 for the electrocatalytic reduction of nitrate, characterized in that: In step (1), the undispersed particles are removed by centrifugal separation when ultrasonic dispersion of copper phthalocyanine in a solvent to obtain solution A; in step (2), the undispersed particles are removed by centrifugal separation when ultrasonic dispersion of zinc phthalocyanine in the same solvent to obtain solution B.

3. Use of a copper-zinc bi-active site organic composite catalyst electrode according to claim 1 for the electrocatalytic reduction of nitrate, characterized in that: The solvent in step (1) is one or more of N,N-dimethylformamide, ethanol, methanol, and acetonitrile.

4. Use of a copper-zinc bi-active site organic composite catalyst electrode according to claim 1 for the electrocatalytic reduction of nitrate, characterized in that: In step (3), the heating temperature is 30-60°C.

5. Use of a copper-zinc bi-active site organic composite catalyst electrode according to claim 1 for the electrocatalytic reduction of nitrate, characterized in that: In step (4), the stirring speed is 400-600 rpm, and the stirring time is 1-2 hours.

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