Copper-modified wheel-type tungsten phosphate, preparation method thereof and application of copper-modified wheel-type tungsten phosphate in ammonia production through reduction of electro-catalytic nitrite

Abstract

The invention relates to copper-modified wheel-type tungsten phosphate, a preparation method of the copper-modified wheel-type tungsten phosphate and application of the copper-modified wheel-type tungsten phosphate in production of ammonia through electro-catalysis of nitrite reduction, and provides the copper-modified wheel-type tungsten phosphate, the preparation method of the copper-modified wheel-type tungsten phosphate and application of the copper-modified wheel-type tungsten phosphate in production of ammonia through electro-catalysis of nitrite reduction. According to the invention, the transition metal copper is introduced on the basis of K28Li5 [H7P8W48O184] 92H2O (hereinafter referred to as P8W48). K12Li13 [Cu20Cl (OH) 24 (H2O) 12 (P8W48O184)]. 22H2O (hereinafter referred to as Cu20P8W48) is formed through self-assembling and positioning, and the K12Li13 [Cu20Cl (OH) 24 (H2O) 12 (P8W48O184)]. 22H2O is applied to reduction of nitrite through electro-catalysis to prepare ammonia.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrocatalysis, and particularly relates to copper-modified wheel-shaped tungstophosphate, a preparation method thereof, and an application thereof in electrocatalytic reduction of nitrite to ammonia. A specific compound is formed by self-assembly coordination and applied to electrocatalytic reduction of nitrite to ammonia to improve electrocatalytic efficiency and ammonia production rate. Background Art

[0002] Excessive nitrite emissions are widespread in industrial wastewater and groundwater systems. This not only disrupts the global nitrogen cycle but also induces human health problems. For example, ferrous ions in hemoglobin are easily oxidized by nitrite, resulting in damage to red blood cells and their ability to transport oxygen, thus causing methemoglobinemia. The imbalance of the nitrogen cycle and the effective treatment of nitrite in water are major and urgent challenges of this century. The traditional chemical reduction method reduces nitrite to nitrogen by adding reducing agents such as sulfite. This method has problems such as easy inactivation of the catalyst and secondary pollution. Ammonia has a high energy density (4.32 kW·h·L -1 ), and is one of the most common industrial chemicals.

[0003] Ammonia (NH3) plays a key role in many fields and can be used as a fertilizer, energy source, carrier, and chemical precursor for synthesizing various nitrogen-containing compounds. The demand for NH3 has steadily increased to the level of billions of tons, while the global annual production of NH3 is approximately 180 million tons. More than 90% of ammonia production is mainly based on the Haber-Bosch process, which requires high operating pressures (20 - 30 MPa) and high temperatures (300 - 500 °C), increasing global energy consumption (2 - 5%; ≥8.6 EJ·year -1 ) and CO2 emissions (400 - 450 Mt·yr -1 ). Therefore, electrochemical nitrogen reduction reaction (N2RR) has become a promising strategy for sustainable production of NH3. However, despite extensive research over the past few decades, due to the inherently low efficiency of N2RR, its practical applications are still limited. This is because the N≡N bond dissociation energy is relatively high (941 kJ·mol -1 ) and the solubility of gaseous N2 in aqueous electrolytes is poor (0.66 mM under general environmental conditions). To address the challenges posed by N2RR, electrocatalytic nitrite reduction reaction (NO2RR) has recently attracted extensive attention because its N=O bond dissociation energy is weaker (204 kJ·mol -1 ) and its solubility is significantly higher. In addition, due to the rich content of NO 2- ions in different wastewater sources. NO 2-Direct conversion to NH3 provides an innovative approach for both sustainable NH3 production and wastewater treatment. Due to the complex six-electron, eight-proton reaction pathway of nitrite reduction and the intense competitive reaction with hydrogen release at similar potentials, the development of efficient and stable catalysts has become the top priority.

[0004] Copper-based catalysts have become a research hotspot due to their outstanding performance in electrocatalytic conversion of nitrite to ammonia, along with their low cost and rich variety. A variety of copper-based catalysts have been studied and reported. For example, Abdallah et al. designed a porous copper electrode with a large surface area by electrodepositing copper on nickel-modified graphite felt (GF); Zhang et al. reported anchoring monodisperse copper metal nanoparticles on reduced graphene oxide (rGO) through a simple electrochemical co-deposition method; Chen et al. prepared a catalyst of Pd-Cu supported on N-doped coral-like three-dimensional porous carbon nanostructure by a simple surfactant co-assembly method. These materials can all efficiently and mildly reduce nitrite to ammonia. However, the reduction of nitrite is a multi-electron transfer process. But the electronic structure of copper atoms makes the gain and loss of electrons relatively slow in redox reactions, thus affecting the efficiency and rate of electron transfer.

[0005] Polyoxometalates (POMs) are a class of polynuclear metal-oxygen cluster compounds formed by high-valent early transition metals (Mo, W, V, Nb, Ta) and oxygen. Due to their structural diversity and property tunability, they have received extensive and continuous attention in more and more fields. POMs are also known as "electronic sponges" and have the unique ability to enrich, store, and release electrons, and can undergo rapid reversible multi-electron redox reactions without structural changes. Due to this unique redox property, POMs have been reported to participate in various electrochemical processes including hydrogen evolution reaction, oxygen reduction, and carbon dioxide reduction reaction, promoting and regulating electron transfer, and enhancing the redox kinetics of the electrode process. Recently, a small amount of literature has also reported the application of POMs in electrocatalytic nitrite reduction. Among them, the Dawson-type derived high-nuclear wheel-shaped tungsten oxide cluster P8W48 has excellent stability in a wide pH range and good electrocatalytic activity for ammonia production by reducing nitrite. We noticed that the interior of the P8W48 ring is an oxygen-rich surface with strong coordination ability, so we considered introducing copper active sites into the interior of this cyclic POMs, which can not only achieve highly dispersed copper active sites but also realize the synergistic catalysis of copper and P8W48 for nitrite reduction. Summary of the Invention

[0006] Technical problems to be solved: The present invention provides a copper-modified wheel-shaped tungsten phosphate, its preparation method, and its application in electrocatalytic ammonia production by reducing nitrite. The present invention uses K 28 Li5[H7P8W48 O 184 ·92H2O (hereinafter referred to as P8W 48 ), a transition metal copper is introduced. Through self-assembly coordination, K 12 Li 13 [Cu 20 Cl(OH) 24 (H2O) 12 (P8W 48 O 184 )]·22H2O (hereinafter referred to as Cu 20 P8W 48 ) is prepared and applied to electrocatalytic reduction of nitrite to ammonia.

[0007] Technical solution: Application of copper-modified wheel-shaped tungstophosphate K 12 Li 13 [Cu 20 Cl(OH) 24 (H2O) 12 (P8W 48 O 184 )]·22H2O in electrocatalytic reduction of nitrite to produce ammonia.

[0008] Application of copper-modified wheel-shaped tungstophosphate K 12 Li 13 [Cu 20 Cl(OH) 24 (H2O) 12 (P8W 48 O 184 )]·22H2O in the preparation of electrode materials.

[0009] An electrode material contains copper-modified wheel-shaped tungstophosphate K 12 Li 13 [Cu 20 Cl(OH) 24 (H2O) 12 (P8W 48 O 184 )]·22H2O.

[0010] The above-mentioned copper-modified wheel-shaped tungstophosphate K 12 Li 13 [Cu 20 Cl(OH) 24 (H2O) 12 (P8W 48 O 184 )]·22H2O is prepared by the following method: Dissolve the copper source in the lithium acetate solution and add K 28 Li5[H7P8W 48 O 184·92H2O (KLiP8W 48 ) is prepared by heating the above solution at 70 - 100 °C for 0.5 - 2 hours.

[0011] The concentration of lithium acetate is 1 mol / L and the pH is 6; the copper source is CuCl2·2H2O; the molar ratio of LiOOCCH3, CuCl2·2H2O and K 28 Li5[H7P8W 48 O 184 ·92H2O (KLiP8W 48 ) is 20:0.6:0.025.

[0012] The above K 28 Li5[H7P8W 48 O 184 ·92H2O (KLiP8W 48 ) is prepared by the following method: Dissolve 40 g of Na2WO3·2H2O in 140 mL of deionized water, add 60 mL of 85 wt.% H3PO4 solution dropwise, reflux the resulting yellow-green solution at 110 °C for 5 - 13 h, and let the solution cool; add 40 g of KCl to the cooled solution, collect the precipitate and redissolve it in water; crystallize the solution at 5 °C; dry the crystals at 80 °C to obtain K6[α-P2W 18 O 62 ·14H2O (P2W 18 ); Dissolve 83 g of K6[α-P2W 18 O 62 ·14H2O (P2W 18 ) in 300 mL of water, add 200 mL of an aqueous solution containing 48.4 g of tris(hydroxymethyl)aminomethane, stir and then add 80 g of KCl. After complete dissolution, add 55.3 g of K2CO3, stir until a white precipitate appears, filter by suction, wash with ethanol, and air-dry to obtain K 12 [P2W 12 O 48 ·24H2O (P2W 12 ); Dissolve 14 g of K 12 [P2W 12 O 48 ·24H2O (P2W 12 ) in 500 mL of 1 M lithium acetate solution, let it stand to form white needle-like crystals, filter and collect, wash with water, and air-dry to obtain K 28 Li5[H7P8W 48 O 184 ·92H2O (KLiP8W 48 ).

[0013] The electrode was prepared by the following method: K 12 Li 13 [Cu 20 Cl(OH) 24 (H2O) 12 (P8W 48 O 184 )]·22H2O and carbon black were dispersed in a solution containing ethanol and Nafion by ultrasonic treatment, and the solution was taken and dropped onto a glassy carbon electrode to prepare a working electrode.

[0014] The specific preparation method of the electrode material was as follows: 4 mg of K 12 Li 13 [Cu 20 Cl(OH) 24 (H2O) 12 (P8W 48 O 184 )]·22H2O and 1 mg of carbon black were dispersed in a solution containing 950 μL of ethanol and 50 μL of Nafion by ultrasonic treatment, and 5 μL of the solution was taken and dropped onto a glassy carbon electrode with a diameter of 3 mm to prepare a working electrode.

[0015] Application of the above electrode material in electrocatalytic reduction of nitrite to ammonia.

[0016] An electrochemical system containing the above electrode material.

[0017] Beneficial effects: The present invention provides a preparation method of a wheel-shaped twenty-core copper-containing polyoxometalate K 12 Li 13 [Cu 20 Cl(OH) 24 (H2O) 12 (P8W 48 O 184 )]·22H2O electrode material, and deeply evaluates its performance in electrocatalytic production of ammonia from nitrite to address the problem of nitrite pollution in environmental water bodies. This polyacid combines both copper sites with excellent electrocatalytic activity and P8W 48 polyacid units with multi-electron storage and transfer capabilities. It can not only achieve the monodispersion of copper sites but also improve the selectivity of ammonia production. First, the catalyst was prepared into an electrode, and in a neutral electrolyte containing nitrite, the ammonia production performance was tested at different working potentials in an H-type electrolytic cell through an electrochemical workstation. At different potentials, the electrode had different degrees of catalytic response activity. Among them, the Faraday efficiency reached the highest at 92.42% at -0.6 V vs. RHE, and the yield could reach 0.2128 mmol h -1 mgcat -1 . Description of the Drawings

[0018] Figure 1 is Cu 20 P8W 48 Single crystal diagram of (a) single crystal physical object. It is synthesized by the method provided in Example 1. The wheel-shaped tungstophosphate is coordinated with the copper source. We can clearly see blue block crystals. (b) Single crystal ball-and-stick structure diagram. Through the atomic ball-and-stick model, we can intuitively understand the structure of polyoxometalate. Blue - copper; yellow - tungsten; purple - phosphorus; red - oxygen; green - chlorine.

[0019] Figure 2 is Cu 20 P8W 48 Experimental values and theoretical values of X-ray powder diffraction data of. It can be seen that the peak positions of the experimental values and theoretical values of the X-ray powder diffraction of the crystal are consistent, indicating that the crystal structure analysis is accurate and the synthesized crystal has a high purity. It proves the feasibility of the method in Example 1.

[0020] Figure 3 is Cu 20 P8W 48 Infrared spectrum of. Polyoxoanion Cu in about 2 wt.% KBr particles 20 P8W 48 The FT-IR spectrum of shows that all characteristic spectral bands of the POM structure exist in the range of 1200 - 400 cm -1 . The vibration peaks at 1017, 1090, and 1121 cm -1 belong to the P-O stretching spectral band, while the vibration peaks in the range of 1000 - 500 cm -1 belong to the W-O vibration spectral band. It further verifies the successful synthesis of Cu 20 P8W 48 .

[0021] Figure 4 is Cu 20 P8W 48 XPS full spectrum of. (a) Figure X PS measurement confirms that the binding energies of the Cu 2p 3 / 2 and 2p 1 / 2 peaks are located at 934.00 and 954.20 eV respectively, corresponding to the +2 valence state of the Cu center in the cluster. (b) The figure shows the high-resolution XPS spectrum of P 2p, where the signal at 133.5 eV is attributed to the P 2p orbital. (c) The figure shows the W4f spectrum, where the signals at 37.9 and 35.70 eV are attributed to W 6+ 4f 5 / 2 and W 6+ 4f 7 / 2 . (d) The figure is the full spectrum.

[0022] Figure 5 Standard curve of ammonia with 0.1 M PBS as the stock solution. (a) UV-visible absorption spectra of ammonia at different concentrations. (b) Standard calibration curve of ammonia. The operation is carried out according to the preparation method of the ammonia standard curve provided in Example 5. The preparation method of the stock solution is prepared with reference to the method provided in Example 2.

[0023] Figure 6 Standard curve of hydrazine with 0.1 M PBS as the stock solution. (a) UV-visible absorption spectra of hydrazine at different concentrations. (b) Standard calibration curve of hydrazine. The operation is carried out according to the preparation method of the hydrazine standard curve provided in Example 5.

[0024] Figure 7 Slurry, catalyst electrode and H-type electrolytic cell for electrochemical testing. The specific method for preparing the slurry is carried out according to the method provided in Example 3; the preparation of the catalyst electrode refers to the method provided in Example 3; the assembly of the H-type electrolytic cell and the correct use of the electrode are carried out according to the method provided in Example 4. The electrochemical testing method used refers to the specific testing steps provided in Example 4.

[0025] Figure 8 For Cu 20 P8W 48 、P8W 48 Linear sweep voltammetry curve in 0.1 M PBS containing 0.1 M NO 2- . At negative potentials, we can clearly see a reduction peak of Cu 20 P8W 48 , corresponding to the reduction of nitrite. Compared with the reduction peak of P8W 48 , only a smaller potential needs to be applied.

[0026] Figure 9 For Cu 20 P8W 48 Faraday efficiency and yield of ammonia at different potentials. An obvious volcano-type trend can be seen. As the potential increases, the Faraday efficiency of ammonia also increases and reaches a maximum at -0.6 V vs. RHE, which is 92.42%. The yield reaches 0.2128 mmol·h -1 mgcat -1 . The yield and Faraday efficiency are calculated through the standard curve obtained by testing in Example 5.

[0027] Figure 10 For Cu 20 P8W 48 Chronoamperometry (CA) curves at different potentials. As the potential increases, it can be clearly seen that the current density increases. The specific testing method refers to the chronoamperometry testing method in Example 4.

[0028] Figure 11 is Cu 20 P8W 48 UV absorption curves of ammonia production at different potentials. As the potential increases, the UV absorption curve of ammonia also shows an increasing trend, which is the same as the theoretical expectation. The UV colorimetric test is operated by the ammonia colorimetric method provided in Example 5 and detected by UV-visible absorption spectroscopy ((UV-vis, Shimadzu UVmini-1280 spectrophotometer).

[0029] Figure 12 is Cu 20 P8W 48 UV absorption curves of hydrazine at different potentials. It can be seen that no hydrazine is produced. The UV colorimetric test is operated by the hydrazine colorimetric method provided in Example 5 and detected by UV-vis.

[0030] Figure 13 is for Cu at -0.6V 20 P8W 48 for cyclic testing. Ten cyclic tests at -0.6V are shown, and the results show that there is no obvious change in NH3 production and FE.

[0031] Figure 14 is the comparative sample P8W 48 , (a) is the physical picture of P8W 48 , presenting white needles, is the precursor of Cu 20 P8W 48 The successful synthesis of Cu 20 P8W 48 crystals further verifies the accuracy of P8W 48 . (b) is the Faraday efficiency and yield of ammonia of P8W 48 at different potentials. Compared with Cu 20 P8W 48 , both the Faraday efficiency and the yield are significantly lower. The optimal potential of the experiment requires a larger voltage compared to Cu 20 P8W 48 , and the optimal Faraday efficiency is 75%. The yield is 0.15 mmol·h -1 mgcat -1 . Experiments prove that introducing copper active sites into the interior of this cyclic POMs can not only achieve the highly dispersed copper active sites, but also realize the synergistic catalysis of copper and P8W 48 for nitrite reduction.

[0032] Figure 15As a comparative sample copper source, copper dichloride dihydrate (a) Physical picture of copper dichloride dihydrate, which is the copper source. (b) Faraday efficiency and yield of ammonia at different potentials for the single copper source. Due to the easy agglomeration characteristics of the single copper source, the catalytic active sites are unevenly exposed, resulting in low yield and Faraday efficiency. The test results show that the optimal Faraday efficiency is 42.44%. The yield is 0.06185 mmol·h -1 mgcat -1 . The efficiency is low. Experiments have proved that after coordination with phosphotungstic acid, copper atoms are fully exposed in the cavity of the wheel-shaped tungsten-oxygen cluster. The catalytic activity of copper towards nitrite is fully exerted. Specific embodiments

[0033] The present invention will be further described below in conjunction with specific embodiments.

[0034] Example 1

[0035] Cu 20 P8W 48 Synthesis

[0036] The steps include:

[0037] S1. Dissolve the copper source in the lithium acetate solution and add P8W 48 .

[0038] S2. Heat the above solution at 80 °C for 1 hour. Cool to room temperature and filter.

[0039] Preferably, in step S1, prepare 20 mL of lithium acetate buffer solution with a concentration of 1 mol / L. Adjust the pH with acetic acid to pH 6.

[0040] Preferably, use copper dichloride dihydrate as the copper source, weigh 0.60 mmol, that is, 0.1 g.

[0041] Preferably, add 0.025 mmol of P8W 48 , that is, 0.37 g.

[0042] Preferably, in step S2, heat in a water bath for 1 hour, cool to room temperature and filter, and evaporate and crystallize the filtrate in an open beaker.

[0043] P8W 48 Synthesize according to the following method:

[0044] S1. Synthesis of K6[α-P2W 18 O 62 ·14H2O (P2W 18 )

[0045] Dissolve 40 g of Na2WO3·2H2O in 140 mL of deionized water. After heating to complete dissolution, add 60 mL of 85 wt.% H3PO4 solution dropwise using a constant pressure dropping funnel. The resulting yellow-green solution is refluxed at 110 °C for 5 - 13 h. After the reflux process is completed, let the solution cool naturally. Next, add 40 g of KCl to the cooled solution to produce a light green precipitate. Collect the precipitate and redissolve it in water. Then, let the solution stand overnight at 5 °C to crystallize. Finally, dry the crystals at 80 °C.

[0046] S2, K 12 [P2W 12 O 48 ·24H2O (P2W 12 ) synthesis

[0047] Dissolve 83 g of P2W 18 in 300 mL of water. Add an aqueous solution containing 48.4 g of tris(hydroxymethyl)aminomethane in 200 mL. Stir for half an hour, add 80 g of KCl. After complete dissolution, add 55.3 g of K2CO3 and stir for 15 minutes. A white precipitate appears. Filter by suction, wash with ethanol, and air dry.

[0048] S3, K 28 Li5[H7P8W 48 O 184 ·92H2O (P8W 48 ) synthesis

[0049] Dissolve 14 g of P2W 12 in 500 mL of 1 M lithium acetate buffer solution. White needle-like crystals appear after one week and are filtered and collected after two weeks, washed with water, and air dried.

[0050] Example 2

[0051] The present invention provides electrocatalytic reduction of nitrite in a neutral electrolyte.

[0052] Preparation of the electrolyte: Using potassium dihydrogen phosphate as the solute, adjust the pH to 7 with potassium hydroxide to prepare a potassium dihydrogen phosphate buffer solution (PBS) (pH = 7). Using PBS as the mother liquor, prepare a 0.1 M nitrite solution.

[0053] Example 3

[0054] Fabrication of the working electrode: Dissolve 5 mg of the catalyst (4 mg of Cu 20 P8W 48(+1 mg carbon black) was dispersed in 950 μL of ethanol and 50 μL of Nafion solution by sonication for 1 hour. 5 μL of the well-dispersed catalyst ink was dropped onto a glassy carbon electrode with a diameter of 3 mm to prepare a working electrode. After natural drying, it was directly used for electrochemical measurement.

[0055] Comparative Example 1: The difference between this comparative example and Example 1 is the use of P8W 48 as the catalyst. P8W 48 is the precursor of Cu 20 P8W 48 is a simple wheel-shaped tungsten-based polyoxoacid without introducing copper atoms for coordination. The synthesis steps refer to the synthesis method of P8W 48 in Example 1. Its electrochemical testing method is similar to that of Cu 20 P8W 48 Similar, the electrode preparation uses P8W 48 as the catalyst.

[0056] Comparative Example 2: The difference between this comparative example and Example 1 is the use of a copper source (copper dichloride dihydrate) as the catalyst. Copper dichloride dihydrate provides the copper source for Cu 20 P8W 48 In the lithium acetate buffer solution, copper dichloride dihydrate provides twenty copper atoms for each P8W 48 to form a coordinated wheel-shaped copper-containing anionic oxygen cluster. This comparative example uses a separate copper source as the catalyst.

[0057] Example 4

[0058] All electrochemical tests were carried out on an electrochemical workstation (CHI 760E, Shanghai Chenhua), and electrolysis was carried out using a typical H-type electrolytic cell. An Ag / AgCl, a Pt, and a glassy carbon electrode dropped with the catalyst were used as the reference electrode, the counter electrode, and the working electrode, respectively. The working electrode and Ag / AgCl were located in the cathode electrolytic cell, the foil electrode was located in the anode electrolytic cell, and they were separated by a nafion 117 proton exchange membrane in the middle. 50 mL of an electrolyte containing 0.1 M nitrite was poured into each of the cathode chamber and the anode chamber. The preparation of the electrolyte refers to Example 2. The usage example of the electrode refers to Figure 7 .. The corresponding electrode clips were used to connect to the corresponding electrodes. Then electrochemical tests were carried out. The methods of electrochemical tests were mainly linear sweep voltammetry test and chronoamperometry.

[0059] The nafion 117 membrane needs to be activated. Before each use, it was first boiled in 5% sulfuric acid for one hour, then boiled in 5% hydrogen peroxide solution for one hour, and finally boiled in deionized water for one hour. Usually, it was soaked in deionized water for storage.

[0060] Under neutral (pH = 7) test conditions, the potential of the reversible hydrogen electrode relative to the reference electrode Ag / AgCl is converted to the potential relative to RHE by formula (1-1):

[0061] E (RHE) = E (Ag / AgCl) + 0.0592 × pH + 0.197 V (1-1)

[0062] Linear sweep voltammetry test

[0063] Linear sweep voltammetry is to control the electrode potential to change at a constant rate, that is, continuous linear change, while measuring the response current passing through the electrode. Taking the reduction reaction as an example, the potential starts to scan in the negative direction. At the beginning, there is no reduction current. As the potential shifts negatively, the reduction current gradually appears and increases. When the potential shifts to a more negative value, the current further increases. At this time, the electrode reaction is mainly controlled by the interfacial charge transfer kinetics. In the present invention, linear sweep voltammetry test is carried out at a potential of 0.1 V / s. The scanning range is from 0.6 V vs RHE to -1.0 V vs RHE.

[0064] Chronocoulometry test

[0065] Chronocoulometry belongs to the constant potential method, which means applying a large step potential to the working electrode (jumping from a potential where no faradaic reaction occurs to a potential where an electrochemical reaction occurs, and recording the relationship between the electrode current and time under the potential step. In the present invention, five different reduction potentials are used, with an interval of 0.1 V vs RHE. The range is from -0.4 V vs RHE to -0.8 V vs RHE.

[0066] Example 5

[0067] Product detection

[0068] Detection of ammonia

[0069] The electrocatalyzed sample solution is colored by the indophenol blue colorimetric method, and the NH3 content in the electrolyte is measured by UV-vis. To ensure that the absorbance is in the same range and improve the accuracy of the results. Different volumes of the tested sample solution, 50, 100, and 200 μL, are collected from the cathode chamber of the electrolytic cell and diluted to 1 mL with 0.1 M PBS solution. Then, 1 mL of the color reagent (1 M NaOH solution containing 5 wt.% salicylic acid and 5 wt.% sodium citrate), 0.5 mL of the oxidant (0.05 M sodium hypochlorite solution), and 100 μL of the catalyst (1 wt.% sodium nitroprusside solution) are added in sequence. The above mixed solution is stored in the dark at room temperature for 2 h, and the absorbance value at 655 nm is measured by UV-vis, and the NH3 content in the sample solution is calculated according to the standard curve.

[0070] Standard curve of NH3 under neutral conditions

[0071] A series of concentration gradients (0.01, 0.02, 0.03, 0.05, 0.1 mM) of NH4 were prepared based on 0.1 M PBS solution. + The solution was colored according to the above method (without dilution), and then the absorbance was measured by UV-vis. With the concentration of NH4 + as the abscissa and the absorbance at 655 nm as the ordinate, a standard curve was obtained after linear fitting, and the equation was y = 8.616x + 0.0026, R 2 = 0.99957.

[0072] Detection of hydrazine

[0073] The Watt-Chrisp method was used to color the sample solution after electrocatalysis. The color development principle is as follows: Hydrazine reacts with dimethylbenzaldehyde in an acidic environment of concentrated hydrochloric acid to form a yellow product, namely the quinoid compound p-dimethylaminobenzylhydrazone. The absorbance of this product was detected by UV-vis, and quantitative analysis was carried out according to the absorbance value. To ensure that the absorbance is in the same range and improve the accuracy of the results. Different volumes of 50, 100, and 200 μL of the tested sample solution were collected from the cathode chamber of the electrolytic cell and diluted to 5 mL with 0.1 M PBS solution. Then 5 mL of the color reagent (4 g of PDAB dissolved in 20 mL of concentrated hydrochloric acid and 200 mL of ethanol) was added. The above mixed solution was stored in the dark at room temperature for 15 min, and the absorbance value at 460 nm was measured by UV-vis, and the content of hydrazine in the sample solution was calculated according to the standard curve.

[0074] Standard curve of hydrazine under neutral conditions

[0075] A series of electrolyte solutions of hydrazine with concentration gradients (0, 2, 4, 6, 8, 10 μM) were prepared based on 0.1 M PBS solution. Subsequently, the ultraviolet absorption spectra of these standard gradient concentration electrolyte solutions were detected by ultraviolet spectrophotometry. By measuring the absorbance at 460 nm and combining with the standard concentration of hydrazine. A standard curve y = 0.02701x + 0.0077, R 2 = 0.99932 was obtained after linear fitting.

[0076] The above embodiments describe the preferred embodiments of the present invention and do not limit the present invention. Without departing from the spirit or scope of the present invention, technical improvements and equivalent substitutions made by relevant technical personnel to the present invention are all within the protection scope of the present invention.

Claims

1. Application of copper-modified wheel-shaped tungstophosphate K 12 Li 13 [Cu 20 Cl(OH) 24 (H2O) 12 (P8W 48 O 184 )]·22H2O in electrocatalytic reduction of nitrite to ammonia.

2. Application of Copper-Modified Wheel-Type Tungstophosphate K 12 Li 13 [Cu 20 Cl(OH) 24 (H2O) 12 (P8W 48 O 184 )]·22H2O in the Preparation of Electrode Materials.

3. An electrode material, characterized in that, Copper-modified wheel-shaped tungsten phosphate K 12 Li 13 [Cu 20 Cl(OH) 24 (H2O) 12 (P8W 48 O 184 )]·22H2O。 4. The electrode material according to claim 3, wherein The copper-modified wheel-shaped tungstophosphate K 12 Li 13 [Cu 20 Cl(OH) 24 (H2O) 12 (P8W 48 O 184 )]·22H2O is prepared by the following method: Dissolve the copper source in a lithium acetate solution, and add K 28 Li5[H7P8W 48 O 184 ·92H2O (KLiP8W 48 ), and heat the above solution at 70 - 100 °C for 0.5 - 2 hours to obtain it.

5. The electrode material according to claim 4, wherein The concentration of lithium acetate is 1 mol / L and the pH is 6; the copper source is CuCl2·2H2O; the molar ratio of LiOOCCH3, CuCl2·2H2O and K 28 Li5[H7P8W 48 O 184 ·92H2O (KLiP8W 48 ) is 20:0.6:0.

025.

6. The electrode material according to claim 5, wherein The K 28 Li5[H7P8W 48 O 184 ·92H2O (KLiP8W 48 ) is prepared by the following method: Dissolve 40 g of Na2WO3·2H2O in 140 mL of deionized water, add dropwise 60 mL of 85 wt.% H3PO4 solution, reflux the resulting yellowish-green solution at 110 °C for 5 - 13 h, and let the solution cool; 40 g of KCl was added to the cooled solution, the precipitate was collected and redissolved in water; the solution was crystallized at 5 °C; the crystals were dried at 80 °C to obtain K6[α-P2W 18 O 62 ·14H2O (P2W 18 ); 83 g of K6[α-P2W 18 O 62 ·14H2O (P2W 18 ) was dissolved in 300 mL of water, 200 mL of an aqueous solution containing 48.4 g of tris(hydroxymethyl)aminomethane was added, after stirring, 80 g of KCl was added, after complete dissolution, 55.3 g of K2CO3 was added, stirred until a white precipitate appeared, filtered by suction, washed with ethanol, and air-dried to obtain K 12 [P2W 12 O 48 ·24H2O (P2W 12 ); 14 g of K 12 [P2W 12 O 48 ·24H2O (P2W 12 ) was dissolved in 500 mL of 1 M lithium acetate solution, allowed to stand to form white needle-like crystals, collected by filtration, washed with water, and air-dried to obtain K 28 Li5[H7P8W 48 O 184 ·92H2O (KLiP8W 48 ).

7. The electrode material according to claim 3, wherein The electrode is prepared by the following method: K 12 Li 13 [Cu 20 Cl(OH) 24 (H2O) 12 (P8W 48 O 184 )]·22H2O and carbon black are dispersed in a solution containing ethanol and Nafion by ultrasonic treatment, and the solution is dropped onto a glassy carbon electrode to form a working electrode.

8. The electrode material according to claim 7, wherein The preparation method is as follows: 4 mg of K 12 Li 13 [Cu 20 Cl(OH) 24 (H2O) 12 (P8W 48 O 184 )]·22H2O and 1 mg of carbon black are dispersed in a solution containing 950 μL of ethanol and 50 μL of Nafion by ultrasonic treatment. Then, 5 μL of the solution is dropped onto a glassy carbon electrode with a diameter of 3 mm to prepare a working electrode.

9. Use of the electrode material according to any one of claims 3-8 in electrocatalytic reduction of nitrite to ammonia.

10. An electrochemical system, characterized in that Containing the electrode material according to any one of claims 3-8.

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