An electrocatalyst for reducing nitrate to nitrogen under strong acid conditions and a preparation method thereof

Abstract

The application discloses an electrocatalyst for reducing nitrate to nitrogen under strong acid condition and a preparation method thereof. The electrocatalyst is a tin dioxide material with rich polymorphism, and the specific component of the material is SnO2. The preparation method is that stannous chloride and ammonium fluoride are used to obtain a tin dioxide precursor through a hydrothermal method, and then the precursor is treated under an acid condition by using a pulse current method to obtain the electrocatalyst. The application solves the problem of low efficiency in the process of removing nitrate pollutants by electrocatalysis. Meanwhile, the electrocatalyst can maintain high stability under strong acid condition, and no nitrite is generated, so the electrocatalyst has certain commercial and practical application value.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electrocatalytic materials, and particularly relates to an electrocatalyst for reducing nitrate to nitrogen under strong acid conditions and a preparation method thereof. BACKGROUND

[0002] With the rapid development of industrial and agricultural technology, a large amount of nitrate (NO3 - ) waste is produced. NO3 - pollutants in groundwater can accumulate in the ecosystem, posing a great threat to the environment and human health. Generally speaking, traditional methods for removing excess nitrate have problems such as low selectivity, slow kinetics, harsh conditions, and high cost. In this regard, using renewable electricity to selectively reduce NO3 - to N2 is an ideal method for managing global nitrogen balance, with advantages such as environmental protection, sustainability, and high product selectivity.

[0003] Although significant progress has been made in the development of NO3RR electrocatalysts, current studies to verify their performance are basically carried out in neutral or alkaline media. Due to the serious corrosion of metal electrodes, electrochemical nitrate removal in strong acid media has so far received little attention. In fact, many strong acid wastewater from industries such as electroplating, semiconductor manufacturing, and metal pickling contain high concentrations of NO3 - . More importantly, compared with neutral / alkaline environments, NO3RR in acidic environments has the following unique advantages: i) Practical wastewater treatment cathodes operating in neutral / alkaline media will encounter serious problems such as the formation of undesirable inorganic scales (such as Ca(OH)2 / CaCO3 and Mg(OH)2), which can be avoided in strong acid media. ii) Strong acid media provide extremely high ionic conductivity, enabling NO3RR to operate at low voltage, with low energy consumption and compact system design. iii) Compared with neutral / alkaline conditions, the use of strong acid media can effectively suppress the production of byproduct NO2 - , thereby simplifying subsequent separation, purification, and acidification steps.

[0004] On the other hand, strong acid media can provide extremely high ionic conductivity, enabling NO3RR to operate at low voltage, with low energy consumption and safety, which is conducive to compact and simple system design. Combined with the non-scaling catalytic process, it has a great significance for practical application in the field of electrochemical nitrate removal. SUMMARY

[0005] The purpose of the present application is to solve the problems of poor activity and insufficient stability of tin-based oxide catalysts in the process of electrochemical removal of nitrate under strong acid conditions; the catalyst prepared by treating two-dimensional tin-based oxides using the pulse current method has abundant polycrystalline structures and two-dimensional morphology.

[0006] In one aspect of the present application, an electrocatalyst for reducing nitrate to nitrogen under strong acid conditions is provided. According to an embodiment of the present application, the electrocatalyst is a tin-based oxide, which is a polycrystalline structure with a stoichiometric ratio of Sn and O being 1:2, and the chemical formula is SnO2.

[0007] In another aspect of the present application, a method for preparing an electrocatalyst for reducing nitrate to nitrogen under strong acid conditions is provided. According to an embodiment of the present application, the method comprises the following steps:

[0008] (1) placing dry carbon cloth into a mixed solution of tin salt and ammonium fluoride, stirring, and then performing ultrasonic cleaning;

[0009] (2) loading the solution and the carbon cloth obtained in step (1) into a reaction kettle to perform high-pressure hydrothermal reaction to obtain a conductive electrode, and then performing water washing and drying to obtain a tin source precursor electrode;

[0010] (3) treating the tin source precursor electrode obtained in step (2) in an acidic electrolyte by pulse current method to obtain the electrocatalyst.

[0011] In addition, the method for preparing an electrocatalyst for reducing nitrate to nitrogen under strong acid conditions according to the above-mentioned embodiment of the present application can further have the following additional technical features:

[0012] In some embodiments of the present application, in step (1), the carbon cloth is first subjected to ultrasonic cleaning and then dried.

[0013] In some embodiments of the present application, the carbon cloth is subjected to ultrasonic cleaning in a cleaning environment of acetone, ethanol and water, respectively, and the ultrasonic time is 10-40 min; the drying temperature is 50-70°C, and the drying time is 3-9 h.

[0014] In some embodiments of the present application, in step (1), the tin salt is stannous chloride dihydrate, and the mass ratio of the tin salt to ammonium fluoride ranges from 3:1 to 2:1; the stirring time is 10-50 min, and the ultrasonic time is 10-50 min.

[0015] In some embodiments of the present application, in step (2), the temperature of the hydrothermal reaction is 160-200°C, and the time is 6-18 h; the drying temperature is 50-70°C, and the drying time is 3-9 h.

[0016] In some embodiments of the present application, in step (3), the acidic electrolyte is a mixed solution of 0.4-0.6 mol / L sulfuric acid and 0.05-0.15 mol / L sodium nitrate, the pulse voltage is (–0.652~–1.652) to –0.152 vs. mercury(II) sulfate reference electrode, and the pulse time is 6000-8000 s.

[0017] In another aspect of the present application, the present application provides a method for reducing nitrate to nitrogen gas under strong acid conditions. According to an embodiment of the present application, the method comprises the following steps: reducing nitrate to nitrogen gas by using the electrocatalyst as a cathode catalyst in an acidic single-chamber electrolytic cell.

[0018] In addition, the method for reducing nitrate to nitrogen gas under strong acid conditions according to the above-mentioned embodiments of the present application can also have the following additional technical features:

[0019] In some embodiments of the present application, during the process of reducing nitrate to nitrogen gas by using the electrocatalyst as a cathode catalyst, the applied voltage of the cathode is –0.05-0.25 V compared to the standard electrode potential, the reaction time is 3-9 h, the counter electrode used is a platinum sheet electrode, and the reference electrode is a mercury(II) sulfate electrode.

[0020] Compared with the prior art, the present application has the following beneficial effects:

[0021] 1) The electrocatalyst for reducing nitrate to nitrogen gas under strong acid conditions prepared by the two-step method of hydrothermal method + pulse voltage treatment has a rich polycrystalline structure and excellent performance and outstanding stability of reducing nitrate to N2 under low voltage conditions in strong acid conditions.

[0022] 2) The preparation process of the present application is green and pollution-free, the method is simple and has characteristics, the prepared catalyst can be mass-produced, the raw material cost is low, the catalytic process device is safe and easy to design, and it has great significance for the practical application in the field of electrochemical removal of nitrate.

[0023] 3) The tin-based oxide electrode integrated with carbon cloth has a nitrate conversion rate of 96.5% and a nitrogen gas selectivity of 88.4% at a voltage of –0.2 V vs. RHE in an acidic single-chamber electrolytic cell; the tin-based oxide electrode integrated with carbon cloth is stably operated for 10 cycles at a voltage of –0.2 V vs. RHE, and each cycle is 2 h. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The pulse current diagram of the electrocatalyst for reducing nitrate to nitrogen gas under strong acid conditions in Example 1 of the present application;

[0025] Figure 2The magnified plot of pulse current of the electrocatalyst for reducing nitrate to nitrogen under strong acid condition in Example 1 of the present application;

[0026] Figure 3 The XRD pattern of the electrocatalyst for reducing nitrate to nitrogen under strong acid condition in Example 1 of the present application;

[0027] Figure 4 The SEM pattern of the electrocatalyst for reducing nitrate to nitrogen under strong acid condition in Example 1 of the present application;

[0028] Figure 5 The TEM pattern of the electrocatalyst for reducing nitrate to nitrogen under strong acid condition in Example 1 of the present application;

[0029] Figure 6 The high-angle annular dark field pattern of the electrocatalyst for reducing nitrate to nitrogen under strong acid condition in Example 1 of the present application;

[0030] Figure 7 The polarization curve pattern of nitrate reduction of Application Example 1 and Comparative Example 2 of the present application;

[0031] Figure 8 The plot of conversion rate and selectivity of nitrate under different voltages during the process of nitrate reduction in Application Example 1 of the present application;

[0032] Figure 9 The plot of cycle stability under the voltage of -0.2V (V vs. RHE) during the process of nitrate reduction in Application Example 1 of the present application. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0034] Example 1

[0035] A preparation method of an electrocatalyst for reducing nitrate to nitrogen under strong acid condition, comprising the following steps:

[0036] (1) The cut hydrophilic carbon cloth is sequentially ultrasonically cleaned in acetone, ethanol and water for 40 minutes, 20 minutes and 10 minutes respectively, and then is placed in a drying oven for drying at a drying temperature of 60℃ for 6 hours;

[0037] (2) Prepare a 30 mL mixed solution of stannous chloride dihydrate and ammonium fluoride, wherein the mass of stannous chloride dihydrate is 0.65 g and the mass of ammonium fluoride is 0.386 g. Then put the carbon cloth into the mixed solution of stannous chloride and ammonium fluoride, and then stir and sonicate for 30 min.

[0038] (3) The clear solution obtained in step (2) and carbon cloth are put into a 50ml reactor for hydrothermal reaction at a temperature of 180℃ for 12h to obtain a conductive electrode. The conductive electrode is then washed with water three times and then dried in an oven to obtain a tin source precursor electrode at a drying temperature of 60℃ for 6h.

[0039] (4) The tin source precursor electrode was treated in an acidic electrolyte by pulse current method to obtain an electrocatalyst that reduces nitrate to nitrogen gas attached to the surface of carbon cloth. The acidic electrolyte was a mixed solution of 0.5M sulfuric acid and 0.1M sodium nitrate. The pulse voltage was -1.152 (pulse width 4.5s) to -0.152 (pulse width 0.5s) V vs. Hg / Hg2SO4, and the pulse time was 7000s.

[0040] like Figure 1 As shown, the magnitude of the current in the electrocatalyst changes significantly during the pulse process; for example... Figure 2 As shown, the current magnitude of the electrocatalyst is significantly increased in the latter part of the pulse process compared to the former part.

[0041] like Figure 3 As shown, the phase of the electrocatalyst is SnO2. Figure 4 As shown, the electrocatalyst has a morphology of two-dimensional nanosheets. Figure 5 As shown, the electrocatalyst consists of coarse nanosheets composed of nanoparticles. Figure 6 As shown, the electrocatalyst exhibits a rich polycrystalline structure.

[0042] Example 2

[0043] A method for preparing an electrocatalyst for reducing nitrate ions to nitrogen gas under strong acid conditions includes the following steps:

[0044] (1) The cut hydrophilic carbon cloth was ultrasonically cleaned in acetone, ethanol and water in sequence for 40 minutes, 20 minutes and 10 minutes respectively. Then it was placed in a drying oven to dry at 60°C for 6 hours.

[0045] (2) configuration 30 mL of stannous chloride dihydrate and ammonium fluoride mixed solution, wherein the mass of stannous chloride dihydrate is 0.65 g, the mass of ammonium fluoride is 0.386 g, then the carbon cloth is put into the stannum and ammonium fluoride mixed solution, then stirring, ultrasonic, stirring time is 30 min, ultrasonic time is 30 min;

[0046] (3) the clear solution obtained in step (2) and carbon cloth are loaded into a 50 ml reaction kettle for hydrothermal reaction, the temperature is 180℃, the time is 12h, a conductive electrode is obtained, then the obtained conductive electrode is washed with water three times, then dried in an oven to obtain a tin source precursor electrode, the drying temperature is 60℃, the drying time is 6h;

[0047] (4) the tin source precursor electrode is treated in an acidic electrolyte by pulse current method to obtain an electrocatalyst for reducing nitrate to nitrogen, wherein the acidic electrolyte is a mixed solution of 0.5M sulfuric acid and 0.1M sodium nitrate, the pulse voltage is -0.652 (pulse width 4.5s) to -0.152 (pulse width 0.5s) V vs. Hg / Hg2SO4, and the pulse time is 7000s.

[0048] Example 3

[0049] A method for preparing an electrocatalyst for reducing nitrate to nitrogen under strong acid conditions, comprising the following steps:

[0050] (1) the cut hydrophilic carbon cloth is ultrasonically cleaned in acetone, ethanol and water in sequence, the ultrasonic time is 40 minutes, 20 minutes and 10 minutes respectively, and then is placed in a drying oven for drying, the drying temperature is 60℃, and the drying time is 6 hours;

[0051] (2) configuration 30 mL of stannous chloride dihydrate and ammonium fluoride mixed solution, wherein the mass of stannous chloride dihydrate is 0.65 g, the mass of ammonium fluoride is 0.386 g, then the carbon cloth is put into the stannum and ammonium fluoride mixed solution, then stirring, ultrasonic, stirring time is 30 min, ultrasonic time is 30 min;

[0052] (3) the clear solution obtained in step (2) and carbon cloth are loaded into a 50 ml reaction kettle for hydrothermal reaction, the temperature is 180℃, the time is 12h, a conductive electrode is obtained, then the obtained conductive electrode is washed with water three times, then dried in an oven to obtain a tin source precursor electrode, the drying temperature is 60℃, the drying time is 6h;

[0053] (4) The tin source precursor electrode is treated in an acidic electrolyte by pulse current method to obtain an electrocatalyst for reducing nitrate to nitrogen, wherein the acidic electrolyte is a mixed solution of 0.5 M sulfuric acid and 0.1 M sodium nitrate, the pulse voltage is -1.652 (pulse width 4.5 s) to -0.152 (pulse width 0.5 s) V vs. Hg / Hg2SO4, and the pulse time is 7000 s.

[0054] Application Example 1

[0055] A method for reducing nitrate to nitrogen under strong acid conditions, comprising the following steps:

[0056] In an acidic single-chamber electrolytic cell, the electrolyte is a mixed solution of 0.5 M sulfuric acid and 0.02 M sodium nitrate, the carbon cloth attached with the electrocatalyst of Example 1 is used as a cathode catalytic electrode, different constant potential voltages are applied, the anode is a platinum sheet electrode, and the reference electrode is a mercury sulfate reference electrode.

[0057] The constant potential test under different voltages is carried out, the voltages are -0.05, -0.1, -0.15, -0.2, and -0.25 V vs. RHE, the time is 6 h, the continuous stirring at 300 rpm is maintained during the test, and the electrochemical workstation used is Chenhua chi660e. The obtained electrolyte is collected and diluted, and a quantitative result is obtained by using a UV spectrophotometer (Mettler UV-3000S). As shown in Figure 8 , under the voltage of -0.2 V vs. RHE, the conversion rate of nitrate is 96.5%, and the selectivity of nitrogen is 88.4%, which has good performance. Subsequently, 10 constant potential performance tests were carried out under the condition of -0.2 V vs. RHE, each for 6 h to evaluate the stability of the catalyst. As shown in Figure 9 , the graph shows that the electrocatalyst prepared in Example 1 has good electrochemical stability.

[0058] Comparative Example 1

[0059] A method for preparing an electrocatalyst for reducing nitrate to nitrogen under strong acid conditions, comprising the following steps:

[0060] (1) First, the cut hydrophilic carbon cloth is ultrasonically cleaned in acetone, ethanol, and water for 40 minutes, 20 minutes, and 10 minutes, respectively, and is placed in a drying oven for drying at 60°C for 6 hours;

[0061] (2) configuration 30 mL of a mixed solution of stannous chloride dihydrate and ammonium fluoride, wherein the mass of stannous chloride dihydrate is 0.65 g, and the mass of ammonium fluoride is 0.386 g, then the carbon cloth is placed in the mixed solution of tin and ammonium fluoride, then stirring, ultrasonic, stirring time is 30 min, ultrasonic time is 30 min;

[0062] (3) the clear solution obtained in step (2) and the carbon cloth are loaded into a 50 ml reaction kettle for hydrothermal reaction, the temperature is 180℃, the time is 12h, to obtain a conductive electrode; then the obtained conductive electrode is washed with water three times, then dried in an oven to obtain the sample, the drying temperature is 60℃, the drying time is 6h.

[0063] Comparative Example 2

[0064] The method for reducing nitrate to nitrogen under strong acid conditions is only different from application example 1 in that the electrocatalyst prepared in comparative example 1 is used as a cathode catalytic electrode.

[0065] As shown in Figure 7 , compared with the electrocatalyst prepared in comparative example 1, the electrocatalyst prepared in example 1 can significantly improve the current density of the reduction of nitrate to nitrogen.

[0066] Through the comparison between application example 1 and comparative example 2 of the present application, it is illustrated that the electrocatalyst prepared in example 1 has strong performance of electrocatalytic reduction of nitrate to nitrogen under strong acid conditions, and maintains high stability, while the electrocatalyst prepared in comparative example 1 has poor nitrate reduction performance, and the current density is much lower than that of the electrocatalyst prepared in example 1; and the electrocatalyst prepared in example 1 has good conversion rate and selectivity of nitrate reduction to nitrogen due to the existence of its rich polycrystalline structure.

[0067] The above is only an example and description of the present application, and those skilled in the art can make various modifications or supplements to the described specific embodiments or use similar ways to replace, as long as the modifications or supplements do not deviate from the structure of the present application or exceed the scope defined by the present claims, and should belong to the protection scope of the present application.

Claims

1. A method for preparing an electrocatalyst for reduction of nitrate to nitrogen under strong acid conditions, characterized by, The method comprises the following steps: (1) placing dry carbon cloth into a mixed solution of tin salt and ammonium fluoride, stirring, and then performing ultrasonic treatment; (2) placing the solution and the carbon cloth obtained in step (1) into a reaction kettle to perform high-pressure hydrothermal reaction to obtain a conductive electrode, then performing water washing on the conductive electrode, and then performing drying to obtain a tin source precursor electrode; (3) performing pulse current treatment on the tin source precursor electrode obtained in step (2) in an acidic electrolyte to obtain the electrocatalyst, wherein the electrocatalyst is a tin-based oxide, the oxide is a polycrystalline structure, the stoichiometric ratio of Sn and O is 1:2, and the chemical formula is SnO2.

2. The method for preparing an electrocatalyst for reducing nitrate to nitrogen under strong acid conditions according to claim 1, characterized in that: In step (1), the carbon cloth is first subjected to ultrasonic cleaning, and then dried.

3. A method of preparing an electrocatalyst for reduction of nitrate to nitrogen under strong acid conditions according to claim 2, characterized in that: The carbon cloth is subjected to ultrasonic cleaning in a cleaning environment of acetone, ethanol and water, and the ultrasonic time is 10-40 min; the drying temperature is 50-70 DEG C, and the drying time is 3-9 h.

4. The method of claim 1, wherein the method is characterized by: In step (1), the tin salt is stannous chloride dihydrate, the mass ratio of the tin salt to ammonium fluoride ranges from 3:1 to 2:1, the stirring time is 10-50 min, and the ultrasonic time is 10-50 min.

5. The method of claim 1, wherein the method is characterized by: In step (2), the hydrothermal reaction temperature is 160-200 DEG C, and the time is 6-18 h; the drying temperature is 50-70 DEG C, and the drying time is 3-9 h.

6. The method of claim 1, wherein the method is characterized by: In step (3), the acidic electrolyte is a mixed solution of 0.4-0.6 mol / L sulfuric acid and 0.05-0.15 mol / L sodium nitrate, the counter electrode is a platinum sheet electrode, the pulse voltage is (-0.652 ~ -1.652) to -0.152 vs. mercury(I) sulfate reference electrode, and the pulse time is 6000-8000 s.

7. An electrocatalyst prepared by the preparation method of any one of claims 1-6.

8. A method of reducing nitrate to nitrogen gas under strong acid conditions, characterized in that, The method comprises the following steps: reducing nitrate to nitrogen in an acidic single-chamber electrolytic cell by using the electrocatalyst of claim 7 as a cathode catalyst.

9. The method of reducing nitrate to nitrogen gas under strong acid conditions according to claim 8, wherein: The applied voltage of the cathode is -0.05-0.25 V vs. standard electrode potential, the reaction time is 3-9 h, the counter electrode used is a platinum sheet electrode, and the reference electrode is a mercury(I) sulfate electrode.

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