Method for the oxidation of urea by chloroxyl radical and hydrogen production

Abstract

A method for oxidizing urea with chloroxygen radicals to produce hydrogen is disclosed. The method involves assembling a TiO2-modified WO3 electrode and an Sb-SnO2 electrode with their catalytic active surfaces facing each other, leaving a 3-8 mm gap as a pre-photoanode. A SiPVC post-photoanode is used to assemble a composite photoanode. Simulated sunlight is used as the light source, sodium chloride as the chloride ion source, urea solution as the substrate, sodium sulfate as the electrolyte solution, and the composite photoanode as the anode. Nickel-iron hydroxide-modified copper nanowire foam is used as the cathode, with SiPVC providing the self-bias voltage, thus forming a photoelectrochemical system. This invention, based on novel electrode materials and a composite photoanode assembly method, enhances the rapid and efficient generation of chloroxygen radicals (ClO·), promoting urea decomposition and strengthening hydrogen production at the cathode.

Description

Technical Field

[0001] This invention relates to a technology in the field of photoelectrocatalysis, specifically a method for oxidizing urea with chloroxygen free radicals to produce hydrogen. Background Technology

[0002] Urea is the main component of urine, and it is a major source of nitrogenous pollutants in domestic sewage, as well as a neglected source of hydrogen. However, the decomposition of urea to produce hydrogen suffers from poor selectivity and slow kinetics. To address these issues, existing technologies oxidize urea with hydroxyl radicals to produce hydrogen, but urea is easily oxidized to nitrates rather than nitrogen; existing technologies also oxidize urea with ClO· to ​​produce hydrogen, but the production rate of ClO· is slow. Summary of the Invention

[0003] This invention addresses the problem of slow ClO· generation rate in existing urea oxidation and hydrogen production processes by proposing a method for urea oxidation and hydrogen production using chloroxygen free radicals. Based on novel electrode materials and composite photoanode assembly, this method enhances the rapid and efficient generation of ClO· by chloroxygen free radicals (ClO·), thereby oxidizing urea into nitrogen and simultaneously producing hydrogen.

[0004] This invention is achieved through the following technical solution:

[0005] This invention relates to a method for oxidizing urea with chloroxygen radicals to produce hydrogen. A TiO2-modified WO3 electrode is used to generate hydroxyl radicals, and an Sb-SnO2 electrode is used to oxidize chloride ions to generate active chlorine. The catalytically active surfaces of the TiO2-modified WO3 electrode and the Sb-SnO2 electrode are positioned opposite each other with a 3-8 mm gap to serve as a pre-photoanode. This gap allows for further reaction between the hydroxyl radicals and active chlorine to generate a high concentration of ClO·. SiPVC is used as a post-photoanode. A composite photoanode is assembled from the pre-photoanode and the post-photoanode. Simulated sunlight is used as the light source, sodium chloride as the chloride ion source, urea solution as the substrate, sodium sulfate as the electrolyte solution, and the composite photoanode as the anode. Copper nanowire foam modified with nickel-iron hydroxide is used as the cathode, with SiPVC providing self-bias. This forms a photoelectrochemical system that enhances the generation of ClO· in the composite photoanode, promotes the decomposition of urea, and strengthens the generation of hydrogen at the cathode.

[0006] The simulated sunlight is preferably 100 mW / cm². -2 .

[0007] The preferred chloride ion source has a sodium chloride concentration of 0.05-0.125 mol / L.

[0008] The urea solution is preferably prepared at a concentration of 20–35 mg / L.

[0009] The sodium sulfate is an electrolyte solution, preferably with a concentration of 0.05–0.1 mol / L.

[0010] The nickel-iron hydroxide-modified copper nanowire foam copper is obtained by growing Cu(OH)2 nanowires in situ on the surface of the foam copper sheet and then heating it to obtain a CuO nanowire foam copper electrode; using the CuO nanowire foam copper electrode as the cathode and Pt as the counter electrode, it is placed in a sodium sulfate solution for electroreduction reaction to obtain a Cu nanowire foam copper electrode; then using the Cu nanowire foam copper electrode as the cathode and Pt as the counter electrode, it is placed in a mixed solution of Ni(NO3)2 and FeSO4 for electrodeposition to obtain a nickel-iron hydroxide-modified copper nanowire foam copper cathode.

[0011] The TiO2-modified WO3 electrode is obtained by thoroughly mixing ammonium metatungstate tetrahydrate, concentrated hydrochloric acid and hydrogen peroxide, transferring the mixture to a high-pressure autoclave lined with polytetrafluoroethylene, calcining fluorine-doped tin oxide (FTO) as a carrier to obtain a WO3 film, and then passing it through a water bath of a mixed aqueous solution of ammonium fluorotitanate and boric acid to obtain the TiO2-modified WO3 electrode.

[0012] The Sb-SnO2 electrode is obtained by dispersing tin tetrachloride pentahydrate, antimony trichloride and polyethylene glycol in isopropanol, mixing them to obtain a precursor slurry, spin-coating it onto a carrier and heating it.

[0013] The Sb-SnO2 electrode is preferably generated through multiple spin coating and heating processes.

[0014] Technical effect

[0015] This invention utilizes the TiO2-modified WO3 electrode in the pre-anode to generate hydroxyl radicals and the Sb-SnO2 electrode to generate active chlorine. The TiO2-modified WO3 and Sb-SnO2 electrodes are positioned face-to-face as the pre-anode, with a gap between them to allow the generated hydroxyl radicals and active chlorine to further react and convert into high-concentration ClO·. This facilitates the efficient oxidation of urea solution into carbon dioxide and nitrogen by ClO·. Based on this design, the pre-anode and post-anode are further assembled into a composite photoanode. The post-anode provides a self-bias voltage to enhance the generation of ClO· in the composite photoanode, resulting in an extremely high concentration of ClO·, which directly reacts with urea to convert into nitrogen and CO2. The use of a copper nanowire foam copper cathode modified with nickel-iron hydroxide for efficient hydrogen evolution further significantly improves the hydrogen evolution efficiency. Simultaneously, the self-bias voltage provided by the post-anode also enhances the hydrogen production reaction on the cathode. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of ClO· generated by the composite photoanode in Example 1;

[0017] Figure 2 This is a schematic diagram of ClO· generated by the photoanode in Comparative Example 1 of Example 1;

[0018] Figure 3 This is a comparison of the free radical capture results in Example 1 and Control Example 1;

[0019] Figure 4 This is a diagram showing the results of urea decomposition and hydrogen production in the photoelectrochemical cell in Example 1.

[0020] In the figure: a shows the trend of nitrogen content changing over time during the urea decomposition process in the photoelectrochemical cell; b shows the trend of hydrogen production changing during the urea decomposition process in the photoelectrochemical cell.

[0021] Figure 5 This is a comparison diagram of different anodes and cathodes for Example 1 and the control group;

[0022] In the figure: a shows the trend of total nitrogen over time under different photoanodes, where the cathode is a copper nanowire foam copper cathode modified with nickel-iron hydroxide, and the light intensity is 100 mW cm⁻¹. -2 The concentrations of sodium chloride and sodium sulfate are both 0.075 mol / L; b represents the hydrogen production under different cathodes, where the anode is a composite photoanode with a light intensity of 100 mW / cm². -2 The concentration of sodium chloride is 0.075 mol / L, and the concentration of sodium sulfate is 0.075 mol / L. Detailed Implementation

[0023] Example 1

[0024] This embodiment relates to a method for oxidizing urea with chloroxygen radicals to produce hydrogen. A TiO2-modified WO3 electrode is used to generate hydroxyl radicals, and an Sb-SnO2 electrode is used to oxidize chloride ions to generate active chlorine. The catalytic active surfaces of the TiO2-modified WO3 electrode and the Sb-SnO2 electrode are positioned opposite each other with a 5mm gap to serve as a pre-photoanode. This gap allows for further reaction between the hydroxyl radicals and active chlorine to generate a high concentration of ClO·. Si PVC is used as a post-photoanode. A composite photoanode is assembled from the pre-photoanode and the post-photoanode. Simulated sunlight at 100mW / cm² is used. -2 The photoelectrochemical system consists of a light source, a sodium chloride concentration of 0.075 mol / L as the chloride ion source, a urea solution concentration of 30 mg / L as the substrate, a sodium sulfate concentration of 0.075 mol / L as the electrolyte solution, a composite photoanode as the anode, and nickel-iron hydroxide-modified copper nanowire foam copper as the cathode. A self-bias voltage is provided by Si PVC to form a photoelectrochemical system, which enhances the generation of ClO· in the composite photoanode, promotes the decomposition of urea, and enhances the generation of hydrogen on the cathode.

[0025] The preparation method of the TiO2-modified WO3 electrode is as follows: 1g of ammonium metatungstate tetrahydrate is mixed with 93ml of deionized water, 3ml of analytical grade concentrated hydrochloric acid and 4ml of 30% hydrogen peroxide and stirred for 1 hour until completely dissolved. Then, the solution is transferred to a polytetrafluoroethylene-lined autoclave. Transparent fluorine-doped tin oxide (FTO) glass is placed at a certain angle to the wall of the polytetrafluoroethylene lining with the conductive side facing down. The autoclave is heated at 160℃ for 4 hours and then naturally cooled. Next, it is calcined at 500℃ for 2 hours to generate a WO3 film on the FTO surface. Then, the WO3 film is placed in a mixed aqueous solution of 15mmol / L ammonium fluorotitanate and 75mmol / L boric acid and heated in a constant temperature bath at 40℃ for 6 hours. After washing and drying, a partially transparent TiO2-modified WO3 electrode is obtained.

[0026] The preparation method of the Sb-SnO2 electrode is as follows: 1.4g of tin tetrachloride pentahydrate, 0.4g of antimony trichloride and 1g of polyethylene glycol are dissolved in 20mL of isopropanol by ultrasonic treatment; using transparent fluorine-doped tin oxide (FTO) glass as a substrate, the electrode is spin-coated for 15 seconds at 800rpm; then, it is heated on a hot plate at 350℃ for more than 5 minutes; the above spin-coating process is repeated 10 times, and the electrode is annealed at 500℃ for two hours to obtain a partially transparent Sb-SnO2 electrode;

[0027] The nickel-iron hydroxide-modified copper nanowire foamed copper cathode is prepared by the following method: Cleaned foamed copper is immersed in a mixed aqueous solution containing 2.5 mol / L sodium hydroxide and 0.125 mol / L ammonium persulfate for 6 minutes to grow Cu(OH)₂ nanowires in situ on the surface of the foamed copper. After washing with water, the Cu(OH)₂ nanowire foamed copper is placed in a muffle furnace and heated at 180°C for 180 minutes to obtain a CuO nanowire foamed copper electrode. Using the CuO nanowire foamed copper as the cathode and Pt as the counter electrode, it is placed in a solution containing 1 mol / L sodium hydroxide and 0.125 mol / L ammonium persulfate. In a sodium sulfate solution of L, an electroreduction reaction was carried out for 30 minutes with an external bias voltage of -1.0V vs. Ag / AgCl to obtain a Cu nanowire foam copper electrode. Using the Cu nanowire foam copper electrode as the cathode and Pt as the counter electrode, a mixed solution of 0.15 mol / L Ni(NO3)2 and 0.15 mol / L FeSO4 was used as the electrolyte. A potential of -1.0V vs. Ag / AgCl was applied for 90 seconds. The electrode was then washed with deionized water and dried in air to obtain a nickel-iron hydroxide modified copper nanowire foam copper cathode.

[0028] The aforementioned photoelectrochemical system achieved a final total nitrogen removal rate of 94.7% and simultaneously generated 169.1 μmol of hydrogen gas. See the results below. Figure 4 .

[0029] Compare with Example 1

[0030] As a control, under the same conditions as in Example 1, the photoanode was assembled using TiO2-modified WO3-Si PVC-Sb-SnO2 (see connection method). Figure 2 The specific effects are shown in Table 1.

[0031] Table 1 Comparison of parameters between Example 1 and Control Example 1

[0032] project This embodiment Compare with Example 1 Cathode type Composite photoanode <![CDATA[WO3-SiPVC-Sb-SnO2 modified with TiO2]]> reaction time 120min 120min Total nitrogen removal rate 94.9％ 70.5％

[0033] Figure 3 This example compares the TN removal efficiency of Example 1 and Control Example 1, using tert-butanol and bicarbonate as free radical scavengers respectively. Tert-butanol can simultaneously scavenge hydroxyl radicals and ClO·, while bicarbonate is only sufficient to scavenge hydroxyl radicals. Figure 3 The results showed that the concentration of hydroxyl radicals was low and the concentration of ClO· was high in Example 1, indicating that the hydroxyl radicals in Example 1 mainly reacted with active chlorine to generate ClO·.

[0034] Compare with Example 2

[0035] As a control, under the condition that other conditions remain unchanged in Example 1, the catalytic active surfaces of the TiO2-modified WO3 electrode and the Sb-SnO2 electrode have a gap of 1 mm, the reaction time is 120 min, and the total nitrogen removal rate is 65.3%.

[0036] Compare with Example 3

[0037] As a control, under the condition that other conditions remained unchanged in Example 1, the TiO2-modified WO3 electrode and the Sb-SnO2 electrode had a 15 mm gap between their catalytic active surfaces, a reaction time of 120 min, and a total nitrogen removal rate of 55.1%.

[0038] Control group 4

[0039] Figure 5 (a) is a control showing the change of total nitrogen removal over time when the front photoanode is a TiO2-modified WO3 electrode and a Sb-SnO2 electrode, respectively, while other conditions remain unchanged in Example 1. Figure 5 (b) is a comparison of hydrogen production when the cathodes are copper sheet, copper foam, platinum sheet, platinum carbon catalyst, and copper nanowire, respectively, while other conditions remain unchanged in Example 1.

[0040] The results shown in Example 1 and the control demonstrate that the photoelectrochemical system constructed in this example can generate a higher ClO· concentration, enabling rapid and efficient degradation of urea and simultaneous generation of hydrogen.

[0041] Example 2

[0042] This embodiment relates to a method for oxidizing urea with chloroxygen radicals to produce hydrogen. A TiO2-modified WO3 electrode is used to generate hydroxyl radicals, and an Sb-SnO2 electrode is used to oxidize chloride ions to generate active chlorine. The catalytic active surfaces of the TiO2-modified WO3 electrode and the Sb-SnO2 electrode are positioned opposite each other with a 3mm gap to serve as a pre-photoanode. This gap allows for further reaction between the hydroxyl radicals and active chlorine to generate a high concentration of ClO·. Si PVC is used as a post-photoanode. A composite photoanode is assembled from the pre-photoanode and the post-photoanode. Simulated sunlight at 100mW / cm² is used. -2 The photoelectrochemical system consists of a light source, a sodium chloride concentration of 0.125 mol / L as the chloride ion source, a urea solution concentration of 20 mg / L as the substrate, a sodium sulfate concentration of 0.05 mol / L as the electrolyte solution, a composite photoanode as the anode, and nickel-iron hydroxide-modified copper nanowire foam copper as the cathode. A self-bias voltage is provided by Si PVC to form a photoelectrochemical system, which enhances the generation of ClO· in the composite photoanode, promotes the decomposition of urea, and enhances the generation of hydrogen on the cathode.

[0043] The preparation method of the TiO2-modified WO3 electrode is the same as in Example 1.

[0044] The preparation method of the Sb-SnO2 electrode is the same as in Example 1.

[0045] The nickel-iron hydroxide-modified copper nanowire foam copper cathode is the same as in Example 1.

[0046] The photoelectrochemical system achieved a final total nitrogen removal rate of 93.1% and simultaneously generated 162.2 μmol of hydrogen gas.

[0047] Example 3

[0048] This embodiment relates to a method for oxidizing urea with chloroxygen radicals to produce hydrogen. A TiO2-modified WO3 electrode is used to generate hydroxyl radicals, and an Sb-SnO2 electrode is used to oxidize chloride ions to generate active chlorine. The catalytic active surfaces of the TiO2-modified WO3 electrode and the Sb-SnO2 electrode are positioned opposite each other with an 8mm gap to serve as a pre-photoanode. This gap allows for further reaction between the hydroxyl radicals and active chlorine to generate a high concentration of ClO·. Si PVC is used as a post-photoanode. A composite photoanode is assembled from the pre-photoanode and the post-photoanode. Simulated sunlight at 100mW / cm² is used. -2 The photoelectrochemical system consists of a light source, a sodium chloride concentration of 0.05 mol / L as the chloride ion source, a urea solution concentration of 35 mg / L as the substrate, a sodium sulfate concentration of 0.1 mol / L as the electrolyte solution, a composite photoanode as the anode, and nickel-iron hydroxide-modified copper nanowire foam copper as the cathode. A self-bias voltage is provided by Si PVC to form a photoelectrochemical system, which enhances the generation of ClO· in the composite photoanode, promotes the decomposition of urea, and enhances the generation of hydrogen on the cathode.

[0049] The preparation method of the TiO2-modified WO3 electrode is the same as in Example 1.

[0050] The preparation method of the Sb-SnO2 electrode is the same as in Example 1.

[0051] The nickel-iron hydroxide-modified copper nanowire foam copper cathode is the same as in Example 1.

[0052] The photoelectrochemical system achieved a final total nitrogen removal rate of 90.1% and simultaneously generated 153.2 μmol of hydrogen gas.

[0053] Compared with existing technologies, this method arranges the TiO2-modified WO3 electrode and the Sb-SnO2 electrode with their catalytic active surfaces facing each other and leaving a certain gap, which allows the hydroxyl radicals generated in the gap to react with the active chlorine to further convert into ClO·. This process is promoted by a self-biased electrode, which greatly promotes the denitrification and hydrogen production of urea.

[0054] The above-described specific implementations can be partially adjusted by those skilled in the art in different ways without departing from the principles and purpose of the present invention. The scope of protection of the present invention is defined by the claims and is not limited to the above-described specific implementations. All implementation schemes within the scope of the claims are bound by the present invention.

Claims

1. A method for the oxidation of urea by hydroxyl radicals and the production of hydrogen, characterized in that, Hydroxyl radicals are generated using a TiO2-modified WO3 electrode, and chloride ions are oxidized to generate active chlorine using an Sb-SnO2 electrode. The catalytic active surfaces of the TiO2-modified WO3 electrode and the Sb-SnO2 electrode are positioned opposite each other with a gap of 3-8 mm to serve as a pre-photoanode. The gap is used for further reaction of hydroxyl radicals and active chlorine to generate high concentrations of ClO·. SiPVC is used as a post-photoanode, and a composite photoanode is assembled from the pre-photoanode and the post-photoanode. Simulated sunlight is used as the light source, sodium chloride as the chloride ion source, urea solution as the substrate, sodium sulfate as the electrolyte solution, and the composite photoanode as the anode. Copper nanowire foam modified with nickel-iron hydroxide is used as the cathode, and SiPVC provides the self-bias voltage to form a photoelectrochemical system. This system enhances the generation of ClO· in the composite photoanode, promotes the decomposition of urea, and enhances the generation of hydrogen on the cathode.

2. The method of claim 1 wherein the chloroxyl radical oxidizes urea and produces hydrogen gas. The simulated sunlight has an intensity of 100 mW / cm². -2 .

3. The method of claim 1 wherein the chloroxyl radical oxidizes urea and produces hydrogen, characterized by, The chloride ion source has a sodium chloride concentration of 0.05-0.125 mol / L.

4. The method of claim 1 wherein the chloroxyl radical oxidizes urea and produces hydrogen, characterized by, The urea solution has a concentration of 20–35 mg / L.

5. The method of claim 1 wherein the chloroxyl radical oxidizes urea and produces hydrogen, characterized by, The sodium sulfate is an electrolyte solution with a concentration of 0.05–0.1 mol / L.

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