Electrocatalyst for reducing nitrate into nitrogen under strong acid condition and preparation method thereof

Abstract

The invention discloses an electrocatalyst for reducing nitrate into nitrogen under a strong acid condition and a preparation method thereof.The electrocatalyst is a stannic oxide material rich in polycrystals, the specific component of the material is SnO2, and the preparation method comprises the steps that stannous chloride and ammonium fluoride are subjected to a hydrothermal method to obtain a stannic oxide precursor; and treating the precursor under an acidic condition by using a pulse current method. The problem that the efficiency is low in the electro-catalysis nitrate pollutant removal process is solved. And meanwhile, the electrocatalyst can keep relatively high stability under a strong acid condition, does not generate nitrite, and has certain commercial and practical application values.

Description

Technical Field

[0001] The invention relates to the application field of electrocatalytic materials, and in particular to an electrocatalyst for reducing nitrate to nitrogen under strong acid conditions and a preparation method thereof. Background Art

[0002] With the rapid development of industrial and agricultural technology, a large amount of nitrate (NO3 - ) Waste. NO3 in groundwater - Pollutants can accumulate in ecosystems, posing a huge threat to the environment and human health. In general, traditional methods for removing excess nitrates have problems such as low selectivity, slow kinetics, harsh conditions, and high costs. In this regard, using renewable electricity to convert NO3 - Selective reduction to N2 is an ideal approach to manage the global nitrogen balance with the advantages of being environmentally friendly, sustainable and with high product selectivity.

[0003] Despite the significant progress in the development of NO3RR electrocatalysts, current studies to verify their performance are essentially conducted in neutral or alkaline media. Electrochemical nitrate removal in strongly acidic media has received little attention so far due to the severe corrosion of metal electrodes. In fact, many strongly acidic wastewaters from industries such as electroplating, semiconductor manufacturing, and metal pickling contain high concentrations of NO3RR. - More importantly, NO3RR in acidic environment has the following unique advantages compared to neutral / alkaline environment: i) Actual wastewater treatment cathodes operating in neutral / alkaline media encounter serious problems, such as the formation of undesirable inorganic scale (e.g., 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, allowing NO3RR to operate at low voltage, with low energy consumption and compact system design. iii) Compared to neutral / alkaline conditions, the use of strong acid media can effectively suppress the byproduct NO2 - The production of , thereby simplifying the subsequent separation, purification and acidification steps.

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

[0005] The purpose of the present invention is to solve the problem that tin-based oxide catalysts have poor activity and insufficient catalyst stability during the electrochemical removal of nitrates under strong acid conditions; the catalyst prepared by treating two-dimensional tin-based oxides using a pulse current method has a rich polycrystalline structure and a two-dimensional morphology.

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

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

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

[0009] (2) placing the solution obtained in step (1) and the carbon cloth into a reactor for high-pressure hydrothermal reaction to obtain a conductive electrode, then washing the conductive electrode with water, and then drying it to obtain a tin source precursor electrode;

[0010] (3) treating the tin source precursor electrode obtained in step (2) by a pulse current method in an acidic electrolyte 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 embodiment of the present invention may also have the following additional technical features:

[0012] In some embodiments of the present invention, in step (1), the carbon cloth is firstly ultrasonically cleaned and then dried.

[0013] In some embodiments of the present invention, the carbon cloth is ultrasonically cleaned in acetone, ethanol and water cleaning environments, respectively, with the ultrasonic time being 10-40 minutes respectively; the drying temperature is 50-70° C., and the drying time is 3-9 hours.

[0014] In some embodiments of the present invention, in step (1), the tin salt is stannous chloride dihydrate, the mass ratio of the tin salt to ammonium fluoride is in the range of 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 invention, in step (2), the temperature of the hydrothermal reaction is 160-200° C., and the time is 6-18 h; the temperature of the drying is, and the drying time is 3-9 h.

[0016] In some embodiments of the present invention, 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 to -1.652) to -0.152 vs. mercurous sulfate reference electrode, and the pulse time is 6000-8000 s.

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

[0018] In addition, the method for reducing nitrate to nitrogen under strong acid conditions according to the above embodiment of the present invention may also have the following additional technical features:

[0019] In some embodiments of the present invention, in the process where the electrocatalyst acts as a cathode catalyst to reduce nitrate to nitrogen, 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 electrode, and the reference electrode is a mercurous sulfate electrode.

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

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

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

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

[0024] Figure 1 This is a pulse current diagram of the electrocatalyst for reducing nitrate to nitrogen under strong acid conditions in Example 1 of the present invention;

[0025] Figure 2This is an enlarged view of the pulse current diagram of the electrocatalyst for reducing nitrate to nitrogen under strong acid conditions in Example 1 of the present invention;

[0026] Figure 3 is an XRD diagram of the electrocatalyst for reducing nitrate to nitrogen under strong acid conditions in Example 1 of the present invention;

[0027] Figure 4 This is a SEM image of the electrocatalyst for reducing nitrate to nitrogen under strong acid conditions in Example 1 of the present invention;

[0028] Figure 5 This is a TEM image of the electrocatalyst that reduces nitrate to nitrogen under strong acid conditions in Example 1 of the present invention;

[0029] Figure 6 This is a high-angle annular dark field image of the electrocatalyst that reduces nitrate to nitrogen under strong acid conditions in Example 1 of the present invention;

[0030] Figure 7 The polarization curves of nitrate reduction of Application Example 1 and Comparative Example 2 of the present invention are shown;

[0031] Figure 8 The graphs are the conversion rate and selectivity of nitrate at different voltages during the nitrate reduction process in Application Example 1 of the present invention;

[0032] Fig. 9 This is a cycle stability diagram at a voltage of –0.2 V (V vs. RHE) during the nitrate reduction process in Application Example 1 of the present invention. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] Example 1

[0035] A method for preparing an electrocatalyst for reducing nitrate to nitrogen under strong acid conditions comprises the following steps:

[0036] (1) The cut hydrophilic carbon cloth was ultrasonically cleaned in acetone, ethanol and water in turn, with the ultrasonic time being 40 minutes, 20 minutes and 10 minutes respectively, and then placed in a drying oven for drying at a drying temperature of 60° C. for 6 hours;

[0037] (2) preparing 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 placing the carbon cloth in the mixed solution of tin and ammonium fluoride, and then stirring and ultrasonicating, the stirring time is 30 min, and the ultrasonication time is 30 min;

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

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

[0040] like Figure 1 As shown, the magnitude of the current of the electrocatalyst changes significantly during the pulse process; Figure 2 As shown, the current magnitude of the electrocatalyst in the latter part of the pulse process is significantly larger than that in the former part.

[0041] like Figure 3 As shown in Figure 2, the phase of the electrocatalyst is SnO2. Figure 4 As shown in Figure 2, the morphology of the electrocatalyst is a two-dimensional nanosheet. Figure 5 As shown, the electrocatalyst nanoparticles consist of rough nanosheets. Figure 6 As shown, the electrocatalyst has a rich polycrystalline structure.

[0042] Example 2

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

[0044] (1) The cut hydrophilic carbon cloth was ultrasonically cleaned in acetone, ethanol and water in turn, with the ultrasonic time being 40 minutes, 20 minutes and 10 minutes respectively, and then placed in a drying oven for drying at a drying temperature of 60° C. for 6 hours;

[0045] (2) preparing 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 placing the carbon cloth in the mixed solution of tin and ammonium fluoride, and then stirring and ultrasonicating, the stirring time is 30 min, and the ultrasonication time is 30 min;

[0046] (3) The clear solution obtained in step (2) and the carbon cloth are placed in a 50 ml reactor for hydrothermal reaction at a temperature of 180° C. for 12 h to obtain a conductive electrode, and then the conductive electrode is washed three times with water and then dried in an oven to obtain a tin source precursor electrode at a drying temperature of 60° C. for 6 h;

[0047] (4) treating the tin source precursor electrode in an acidic electrolyte by a pulse current method to obtain a final 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 -0.652 (pulse width 4.5 s) to -0.152 (pulse width 0.5 s) V vs. Hg / Hg2SO4, and the pulse time is 7000 s.

[0048] Example 3

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

[0050] (1) The cut hydrophilic carbon cloth was ultrasonically cleaned in acetone, ethanol and water in turn, with the ultrasonic time being 40 minutes, 20 minutes and 10 minutes respectively, and then placed in a drying oven for drying at a drying temperature of 60° C. for 6 hours;

[0051] (2) preparing 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 placing the carbon cloth in the mixed solution of tin and ammonium fluoride, and then stirring and ultrasonicating, the stirring time is 30 min, and the ultrasonication time is 30 min;

[0052] (3) The clear solution obtained in step (2) and the carbon cloth are placed in a 50 ml reactor for hydrothermal reaction at a temperature of 180° C. for 12 h to obtain a conductive electrode, and then the conductive electrode is washed three times with water and then dried in an oven to obtain a tin source precursor electrode at a drying temperature of 60° C. for 6 h;

[0053] (4) treating the tin source precursor electrode in an acidic electrolyte by a pulse current method to obtain a final 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] The method for reducing nitrate to nitrogen under strong acid conditions comprises the following steps:

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

[0057] The constant potential test was carried out at different voltages, namely –0.05, –0.1, –0.15, –0.2, and –0.25 V vs. RHE, for 6 hours, with continuous stirring at 300 rpm. The electrochemical workstation used was Chenhua chi660e. The obtained electrolyte was collected and diluted, and the quantitative results were obtained using a UV spectrophotometer (Mepta UV-3000S). The results are shown in Figure 8 As shown in the figure, at a voltage of –0.2 V vs. RHE, the nitrate conversion rate was 96.5% and the nitrogen selectivity was 88.4%, which showed good performance. Subsequently, 10 constant potential performance tests were conducted at –0.2 V vs. RHE, each for 6 h to evaluate the stability of the catalyst. The results are shown in the figure. Fig. 9 As shown, the figure illustrates 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 comprises the following steps:

[0060] (1) First, the cut hydrophilic carbon cloth was ultrasonically cleaned in acetone, ethanol and water in turn, with the ultrasonic time being 40 minutes, 20 minutes and 10 minutes respectively, and then placed in a drying oven for drying at a temperature of 60°C for 6 hours;

[0061] (2) preparing 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 placing the carbon cloth in the mixed solution of tin and ammonium fluoride, and then stirring and ultrasonicating, the stirring time is 30 min, and the ultrasonication time is 30 min;

[0062] (3) The clear solution obtained in step (2) and the carbon cloth are placed in a 50 ml reactor for hydrothermal reaction at a temperature of 180° C. for 12 h to obtain a conductive electrode; the conductive electrode is then washed three times with water and then dried in an oven at a drying temperature of 60° C. for 6 h to obtain the sample.

[0063] Comparative Example 2

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

[0065] like Figure 7 As shown, compared with the electrocatalyst prepared in Comparative Example 1, the electrocatalyst prepared in Example 1 can significantly increase the current density of nitrate reduction to nitrogen.

[0066] By comparing Application Example 1 of the present invention with Comparative Example 2, it is shown that: the electrocatalyst prepared in Example 1 has a strong electrocatalytic reduction performance of nitrate to nitrogen under strong acid conditions and maintains a high stability, while the electrocatalyst prepared in Comparative Example 1 has a 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 a better conversion rate and selectivity of nitrate reduction to nitrogen due to the presence of its rich polycrystalline structure.

[0067] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the structure of the present invention or exceed the scope defined by the claims, they shall all fall within the protection scope of the present invention.

Claims

1. An electrocatalyst for reducing nitrate to nitrogen under strong acid conditions, characterized in that: The electrocatalyst is a tin-based oxide, which has a polycrystalline structure, wherein the stoichiometric ratio of Sn to O is 1:2, and the chemical formula is SnO2.

2. A method for preparing an electrocatalyst for reducing nitrate to nitrogen under strong acid conditions as claimed in claim 1, characterized in that: The following steps are involved: (1) placing the dry carbon cloth in a mixed solution of tin salt and ammonium fluoride, stirring, and then performing ultrasonic cleaning; (2) placing the solution obtained in step (1) and the carbon cloth into a reactor for high-pressure hydrothermal reaction to obtain a conductive electrode, then washing the conductive electrode with water, and then drying it to obtain a tin source precursor electrode; (3) treating the tin source precursor electrode obtained in step (2) by a pulse current method in an acidic electrolyte to obtain the electrocatalyst.

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

4. The method for preparing an electrocatalyst for reducing nitrate to nitrogen under strong acid conditions according to claim 3, characterized in that: The carbon cloth is ultrasonically cleaned in the cleaning environments of acetone, ethanol and water, respectively, and the ultrasonic time is 10-40 minutes respectively; the drying temperature is 50-70° C., and the drying time is 3-9 hours.

5. The method for preparing an electrocatalyst for reducing nitrate to nitrogen under strong acid conditions according to claim 2, characterized in that: In step (1), the tin salt is stannous chloride dihydrate, and the mass ratio of the tin salt to ammonium fluoride is in the range of 3:1 to 2:1; the stirring time is 10-50 min, and the ultrasonic time is 10-50 min.

6. The method for preparing an electrocatalyst for reducing nitrate to nitrogen under strong acid conditions according to claim 2, characterized in that: In step (2), the temperature of the hydrothermal reaction is 160-200° C., and the time is 6-18 h; the temperature of the drying is 50-70° C., and the time is 3-9 h.

7. The method for preparing an electrocatalyst for reducing nitrate to nitrogen under strong acid conditions according to claim 2, characterized in that: 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 electrode, the pulse voltage is (-0.652 to -1.652) to -0.152 vs. mercurous sulfate reference electrode, and the pulse time is 6000-8000 s.

8. A method for reducing nitrate to nitrogen under strong acid conditions, characterized in that: The method comprises the following steps: in an acidic single-chamber electrolytic cell, using the electrocatalyst according to claim 1 as a cathode catalyst to reduce nitrate to nitrogen.

9. The method for reducing nitrate to nitrogen under strong acid conditions according to claim 8, characterized in that: The applied voltage of the cathode is -0.05-0.25V compared to the standard electrode potential, the reaction time is 3-9h, the counter electrode used is a platinum electrode, and the reference electrode is a mercurous sulfate electrode.

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