Preparation of Zn-doped Cu2O material and its application in the photoelectrocatalytic co-reduction of CO2 and nitrate to synthesize urea.

Abstract

The application belongs to the technical field of photoelectrocatalytic co-reduction of carbon dioxide (CO2) and nitrate (NO3 ‑ ) to synthesize urea, and relates to a preparation method of Zn-doped Cu2O material and application of the Zn-doped Cu2O material in photoelectrocatalytic co-reduction of CO2 and NO3 ‑ ) to synthesize urea. The preparation method comprises the following steps: dissolving copper salt and zinc salt in deionized water to form a mixed solution, adding a chelating agent and then heating and reacting, adding an alkali solution and a weak reducing agent to react, and after the reaction is completed, performing separation, washing and drying to obtain a Zn-doped Cu2O catalyst. The catalyst can be used in photoelectrocatalytic co-reduction of CO2 and NO3 ‑ ) to synthesize urea. Compared with undoped Cu2O, the introduction of Zn elements is beneficial to improving the electronic structure and interface charge transport behavior of the catalyst, promoting the adsorption and activation of reactants and the separation of photo-generated carriers, so that the performance of the urea synthesis reaction is improved.

Description

Technical Field

[0001] This invention pertains to the photoelectrocatalysis of carbon dioxide (CO2) and nitrate (NO3). - This research relates to the field of co-reduction synthesis of urea, specifically a method for preparing Zn-doped Cu2O material, and its application in photoelectrocatalysis of CO2 and NO3. - Application in the co-reduction synthesis of urea. Background Technology

[0002] In recent years, the greenhouse effect and climate change caused by massive CO2 emissions have become increasingly prominent, profoundly impacting ecosystems and human health. The high-value conversion and utilization of CO2 has become an important research direction in the environmental and energy fields. Simultaneously, large amounts of nitrates emitted during agricultural production and fossil fuel combustion enter water bodies, causing severe eutrophication and threatening the aquatic ecological environment. Therefore, achieving the synergistic resource conversion of CO2 and nitrogen-containing pollutants has significant environmental importance and application value. Photoelectrochemical conversion (PEC) technology can drive chemical reactions under the combined action of light and applied bias voltage, offering advantages such as mild reaction conditions, green energy utilization, and strong reaction controllability, showing promising application prospects in CO2 reduction and nitrogen-containing pollutant conversion. (The text then abruptly shifts to a seemingly unrelated topic about CO2 and NO3 conversion.) - Using CN as a reaction substrate, urea can be synthesized through CN coupling reaction, which not only enables the high-value utilization of carbon and nitrogen resources, but also the obtained urea has high economic value as an important agricultural fertilizer and chemical raw material.

[0003] Cu₂O is a p-type semiconductor material that is abundant, low-cost, and possesses a direct band gap (1.9–2.2 eV), showing promising application potential in photoelectrocatalytic synthesis reactions. However, practical applications of Cu₂O still suffer from problems such as severe carrier recombination, limited light absorption and charge separation efficiency, and insufficient structural stability, thus limiting its application in photoelectrocatalysis of CO₂ and NO₃. - Applications in the co-reduction synthesis of urea. Elemental doping is considered one of the effective strategies for controlling the electronic structure and surface reaction behavior of semiconductors. By introducing Zn, it is beneficial to control the local electronic structure and interfacial charge transport behavior of Cu2O, thereby improving the reactant adsorption activation and carrier separation efficiency during the reaction process. Therefore, developing a structurally stable and highly active Zn-doped Cu2O photoelectrocatalyst material is crucial for improving the photoelectrocatalytic synthesis of CO2 and NO3. - The performance of co-reduction synthesis of urea is of great significance. Summary of the Invention

[0004] For current photoelectrocatalysis of CO2 and NO3 -The co-reduction synthesis of urea suffers from problems such as severe carrier recombination, insufficient reactivity, and poor stability in the catalyst. This invention provides a Zn-doped Cu₂O material and its preparation method, and further provides its application in photoelectrocatalysis of CO₂ and NO₃⁻. - Its application in the co-reduction synthesis of urea aims to improve the catalytic activity and stability of the urea synthesis reaction.

[0005] The technical solution of the present invention is as follows: Zn element is introduced into the synthesis of Cu2O by hydroxyl-assisted synthesis. By controlling factors such as solvent ratio, reaction temperature and reaction time, Zn-doped Cu2O material is synthesized.

[0006] The Zn-doped Cu₂O photocatalytic material prepared in this invention retains the original crystal structure and morphology of Cu₂O. Simultaneously, the local electronic structure and surface reaction characteristics of the material are modulated through Zn doping, thereby improving the separation and transport efficiency of photogenerated carriers and enhancing the reaction of CO₂ and NO₃⁻. - It enhances the adsorption and activation capabilities, and further improves the performance of photoelectrocatalytic synthesis of urea.

[0007] The method for preparing Zn-doped Cu2O optoelectronic materials provided by this invention includes the following steps: (1) Dissolve the copper salt and zinc salt in deionized water and stir to form a homogeneous mixed solution; (2) Add a chelating agent to the mixture and continue stirring; (3) Heat the resulting solution and maintain it at the set temperature; (4) Add an alkaline solution to the reaction system and continue stirring; (5) Then add a weak reducing agent and continue the reaction for a certain period of time; (6) After the reaction is complete, the product is separated, washed and dried to obtain Zn-doped Cu2O optoelectronic material.

[0008] Preferably, the copper salt in step (1) is one or more of copper sulfate, copper nitrate or copper chloride, and the zinc salt is one or more of zinc nitrate, zinc sulfate or zinc chloride.

[0009] Preferably, in step (1), the molar ratio of copper salt to zinc salt is 99:1 to 85:15, and the total number of moles is 0.002 to 0.01 mol.

[0010] Preferably, the chelating agent in step (2) is ethylenediaminetetraacetic acid (EDTA), and the total volume of the mixed solution is 30-60 mL.

[0011] Preferably, the heating temperature in step (3) is 50~70℃. o C Preferably, the alkaline solution added in step (4) is a sodium hydroxide solution with a concentration of 0.6 ~ 6.8 mol / L and an addition volume of 20 ~ 30 mL.

[0012] Preferably, the weak reducing agent in step (5) is hydroquinone, and the reaction time is 1-2 h.

[0013] Preferably, in step (6), the product is washed with ethanol and deionized water in an alternating washing manner for 3 to 8 times; then it is vacuum dried at 60 to 80°C for 6 to 12 h to obtain Zn-doped Cu2O photocatalyst.

[0014] This invention also provides the application of the Zn-doped Cu2O material prepared by the above method in the photoelectrocatalytic synthesis of urea, wherein the material, under illumination and external polarization conditions, reacts with CO2 and NO3. - The reaction substrate is used for CN coupling reaction to achieve urea synthesis.

[0015] Preferably, the volume fraction of the CO2 gas is 15% to 99.99%.

[0016] Preferably, the NO3 - The concentration ranges from 10 to 500,000 ppm.

[0017] Preferably, the urea synthesis reaction is carried out in an apparatus consisting of an H-type quartz reactor, a three-electrode system, a proton exchange membrane, a light source system, an electrochemical workstation, and a gas supply system.

[0018] Preferably, the three-electrode system includes a working electrode coated with the Zn-doped Cu2O material, an Ag / AgCl (KCl saturated) reference electrode, and a Pt counter electrode.

[0019] Preferably, the working electrode uses FTO conductive glass as a substrate, and the catalyst loading is 0.05 mg / cm³. 2 .

[0020] Preferably, the proton exchange membrane is a Nafion 117 proton exchange membrane.

[0021] Preferably, the light source system is a xenon lamp light source (AM 1.5 G) equipped with a filter, with a power of 300 W and a wavelength range of 400 ~ 700 nm.

[0022] Preferably, the gas supply system comprises CO2 and a gas flow meter, with a CO2 gas flow rate of 20 cm³ / h. 3 / min.

[0023] Preferably, 30 mL of 0.1 mol / L KNO3 solution is added to both the cathode chamber and the anode chamber, wherein the cathode chamber uses a CO2-saturated KNO3 solution.

[0024] Preferably, the urea catalytic synthesis reaction is carried out at room temperature for 2 hours.

[0025] The beneficial effects of this invention are as follows: This invention innovatively employs a Zn element doping strategy to regulate Cu2O for photoelectrocatalysis of CO2 and NO3. - Co-reduction synthesis of urea. The introduction of Zn element is beneficial to improving the local electronic structure and interfacial charge transport behavior of the material, enhancing its adsorption and activation ability for intermediates related to CO2 and CN coupling reactions, and promoting the separation and migration of photogenerated carriers, thereby improving the catalytic performance of the urea synthesis reaction. Meanwhile, the material of this invention can be used with different CO2 concentrations and NO3... - They all exhibited good catalytic activity under various concentration conditions, demonstrating good application potential and industrial application prospects. Attached Figure Description

[0026] Figure 1 The XRD patterns are of Cu2O in Comparative Example 1, Cu2O-Zn-1% in Example 1, Cu2O-Zn-5% in Example 2, Cu2O-Zn-10% in Example 3, and Cu2O-Zn-15% in Example 4.

[0027] Figure 2 The images show the SEM morphology of Cu2O-Zn-1% obtained in Example 1, Cu2O-Zn-5% obtained in Example 2, Cu2O-Zn-10% obtained in Example 3, and Cu2O-Zn-15% obtained in Example 4.

[0028] Figure 3 This is the EDS energy spectrum of Cu2O-Zn-5% obtained in Example 2 of the present invention.

[0029] Figure 4 XPS-Zn 2p plots of Cu2O-Zn-1% obtained in Example 1, Cu2O-Zn-5% obtained in Example 2, Cu2O-Zn-10% obtained in Example 3, and Cu2O-Zn-15% obtained in Example 4 of the present invention.

[0030] Figure 5 EIS diagrams of Cu2O-Zn-1% obtained in Example 1, Cu2O-Zn-5% obtained in Example 2, Cu2O-Zn-10% obtained in Example 3, and Cu2O-Zn-15% obtained in Example 4 of the present invention.

[0031] Figure 6This is a comparison chart showing the performance of Cu2O obtained in Comparative Example 1, Cu2O-Zn-1% of Example 1, Cu2O-Zn-5% of Example 2, Cu2O-Zn-10% of Example 3, and Cu2O-Zn-15% of Example 4 in synthesizing urea under the same reaction conditions.

[0032] Figure 7 This is a comparison chart showing the performance of the byproduct ammonia of Cu2O obtained in Comparative Example 1, Cu2O-Zn-1% of Example 1, Cu2O-Zn-5% of Example 2, Cu2O-Zn-10% of Example 3, and Cu2O-Zn-15% of Example 4 under the same reaction conditions.

[0033] Figure 8 This is a comparison chart showing the performance of the byproduct nitrite ions of Cu2O obtained in Comparative Example 1, Cu2O-Zn-1% of Example 1, Cu2O-Zn-5% of Example 2, Cu2O-Zn-10% of Example 3, and Cu2O-Zn-15% of Example 4 under the same reaction conditions.

[0034] Figure 9 The graph shows the cyclic stability test performance of Cu2O-Zn-5% obtained in Example 2 of this invention.

[0035] Figure 10 This is a standard curve for detecting the urea and ammonia content synthesized in Examples 1 to 4 using the urease method of the present invention.

[0036] Figure 11 This is a standard curve for detecting the nitrite content synthesized in Examples 1 to 4 using the Griess method of the present invention. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The following embodiments are only used to illustrate the present invention and are not intended to limit the scope of protection of the present invention. All equivalent substitutions, improvements and modifications made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0038] Example 1: Preparation of 1% Zn-doped Cu2O (Cu2O-Zn-1%) material.

[0039] (1) Dissolve CuSO4·5H2O and Zn(NO3)2·6H2O in 30 mL of deionized water at a molar ratio of 99:1. Then add 0.2942 g of EDTA, stir well, and heat to 55°C. o C forms a complex solution, then 25 mL of 3.96 M NaOH solution is added, and stirring is continued for 5 minutes. Afterwards, 0.5 g of hydroquinone is added to the mixture, and the solution is stirred at 55°C.o Continue stirring at temperature C for 1 hour.

[0040] (2) After the reaction was complete, the precipitate was obtained by centrifugation and washed three times alternately with ethanol and deionized water to remove unreacted precursors and byproducts. The resulting precipitate was placed at 60°C. o The sample was dried in a vacuum drying oven at C to obtain a powder sample, denoted as Cu2O-Zn-1.

[0041] Example 2: Preparation of 5% Zn-doped Cu2O (Cu2O-Zn-5%) material.

[0042] (1) Dissolve CuSO4·5H2O and Zn(NO3)2·6H2O in 30 mL of deionized water at a molar ratio of 95:5. Then add 0.2942 g of EDTA, stir well, and heat to 55°C. o C forms a complex solution, then 25 mL of 3.96 M NaOH solution is added, and stirring is continued for 5 minutes. Afterwards, 0.5 g of hydroquinone is added to the mixture, and the solution is stirred at 55°C. o Continue stirring at temperature C for 1 hour.

[0043] (2) After the reaction was complete, the precipitate was obtained by centrifugation and washed three times alternately with ethanol and deionized water to remove unreacted precursors and byproducts. The resulting precipitate was placed at 60°C. o The sample was dried in a vacuum drying oven at C to obtain a powder sample, which was denoted as Cu2O-Zn-5%.

[0044] Example 3 Preparation of 10% Zn-doped Cu2O (Cu2O-Zn-10%) material.

[0045] (1) Dissolve CuSO4·5H2O and Zn(NO3)2·6H2O in 30 mL of deionized water at a molar ratio of 90:10. Then add 0.2942 g of EDTA, stir well, and heat to 55°C. o C forms a complex solution, then 25 mL of 3.96 M NaOH solution is added, and stirring is continued for 5 minutes. Afterwards, 0.5 g of hydroquinone is added to the mixture, and the solution is stirred at 55°C. o Continue stirring at temperature C for 1 hour.

[0046] (2) After the reaction was complete, the precipitate was obtained by centrifugation and washed three times alternately with ethanol and deionized water to remove unreacted precursors and byproducts. The resulting precipitate was placed at 60°C. o The sample was dried in a vacuum drying oven at C to obtain a powder sample, which was denoted as Cu2O-Zn-10%.

[0047] Example 4: Preparation of 15% Zn-doped Cu2O (Cu2O-Zn-15%) material.

[0048] (1) Dissolve CuSO4·5H2O and Zn(NO3)2·6H2O in 30 mL of deionized water at a molar ratio of 85:15. Then add 0.2942 g of EDTA, stir well, and heat to 55°C. o C forms a complex solution, then 25 mL of 3.96 M NaOH solution is added, and stirring is continued for 5 minutes. Afterwards, 0.5 g of hydroquinone is added to the mixture, and the solution is stirred at 55°C. o Continue stirring at temperature C for 1 hour.

[0049] (2) After the reaction was complete, the precipitate was obtained by centrifugation and washed three times alternately with ethanol and deionized water to remove unreacted precursors and byproducts. The resulting precipitate was placed at 60°C. o The sample was dried in a vacuum drying oven at C to obtain a powder sample, which was denoted as Cu2O-Zn-15%.

[0050] Comparative Example 1: Preparation of Cu2O Material (1) Dissolve CuSO4·5H2O and Zn(NO3)2·6H2O in 30 mL of deionized water at a molar ratio of 100:0. Then add 0.2942 g of EDTA, stir well, and heat to 55°C. o C forms a complex solution, then 25 mL of 3.96 M NaOH solution is added, and after stirring for 5 minutes, 0.5 g of hydroquinone is added to the mixed solution, and the solution is heated to 55 °C. o Stirring was continued at C for 1.0 h to ensure the full progress of the reduction reaction, while controlling the doping degree and distribution of Zn.

[0051] (2) The precipitate was obtained by centrifugation and washed three times with ethanol and deionized water to remove unreacted precursors and byproducts; the final precipitate was placed at 60°C. o The dried sample was obtained using a vacuum drying oven at C. The resulting powder sample is denoted as Cu2O-ecto.

[0052] Experimental Example 1: Setup of the photoelectrocatalytic urea synthesis reaction apparatus and reaction conditions This experiment designed and constructed a dedicated photoelectrocatalytic device. The device consists of an H-type quartz reactor, a three-electrode system, a proton exchange membrane, a light source system, an electrochemical workstation, and a gas supply system. The specific configuration is as follows: a. H-type quartz reactor The device uses an H-type quartz reactor as the reaction platform, which consists of two independent reaction chambers, serving as the cathode chamber and the anode chamber respectively (30 mL of 0.1 M KNO3 as the electrolyte). Because the reactor is made of quartz, it has excellent light transmittance, ensuring that the light emitted from the light source is uniformly distributed throughout the reaction system, thereby stimulating the photoelectric activity of the catalyst.

[0053] b. Three-electrode system The experiment employed a standard three-electrode configuration to achieve precise electrochemical control: Working electrode: an FTO glass slide coated with catalyst was used as the working electrode, with a catalyst loading of 0.05 mg / cm³. 2 Installed in the cathode chamber, it is mainly responsible for absorbing light energy and participating in the reaction of CO2 and NO3. - The reduction reaction. Counter electrode: A platinum sheet is used as the counter electrode due to its excellent conductivity and chemical stability, ensuring electronic balance and stable current output during the reaction. Reference electrode: An Ag / AgCl electrode is selected as the reference electrode to provide a stable reference potential, providing an accurate benchmark for electrochemical testing.

[0054] c. Proton exchange membrane The anode and cathode reaction chambers are effectively isolated by a Nafion 117 proton exchange membrane.

[0055] d. Light source system The device is equipped with an AM 1.5 G standard xenon lamp (300 W) as a light source to simulate sunlight, and features a filter that utilizes a light source in the range of 400–700 nm. The xenon lamp provides uniform and stable illumination conditions, ensuring that the catalyst is fully excited and can exert its photoelectrocatalytic function under illumination.

[0056] e. Electrochemical workstation The entire system is controlled and monitored by a high-precision electrochemical workstation. The workstation is set to a fixed voltage of -0.4 V vs. Ag / AgCl for 7200 s.

[0057] f. Gas supply system The device is equipped with a dedicated gas supply system for introducing CO2 gas (99.99% purity) into the cathode chamber. This system precisely controls the gas flow rate (20 cm⁻¹) using a gas flow meter. 3 ·min 1 This ensures that the CO2 in the electrolyte reaches saturation before the reaction, providing a sufficient carbon source for the subsequent reduction reaction.

[0058] Experiment Example 2: Detection Experiment of Products from Photocatalytic Urea Synthesis Reaction a. Urea detection experiment Specifically, take 0.2 mL of 5 mg·mL⁻¹. 1 The urease solution was thoroughly mixed with 1.8 mL of electrolyte after reacting for 2 hours and then added to a colorimetric bottle. The water bath was set to 40°C. o C. Stir the mixed solution for 40 min. Then, develop the color using the indophenol blue method, and calculate the concentration of NH3 in the electrolyte. The decomposition process involves urea in the electrolyte being decomposed into CO2 and two NH3 molecules by urease. The total number of moles in the electrolyte (m) 脲酶 ), represented as 2m 尿素 +m 氨 , of which 2m 尿素 This represents the number of moles of ammonia produced during decomposition. Therefore, m 尿素 =(m 脲酶 m 氨 ) / 2.

[0059] d. Detection experiment of byproduct NH3 Take 2 mL of the electrolyte after the reaction into a test tube, add 2 mL of colorimetric solution A (500 mL of deionized water containing 20 g sodium hydroxide, 25 g salicylic acid, and 28.487 g sodium citrate), mix well, then add 1 mL of colorimetric solution B (100 mL of deionized water containing 6.2 g sodium hypochlorite), mix well, then add 0.2 mL of colorimetric solution C (100 mL of deionized water containing 1 g sodium nitrosoferricyanide), mix the above mixture thoroughly, and let it stand for 2 h to carry out the colorimetric reaction.

[0060] By detecting the absorbance at 660 nm using UV-Vis in the range of 400 nm to 750 nm, the specific parameters were obtained. The absorbance of NH4 could then be calculated. + The content of NH4 in 0.1 M KNO3. + The standard curve of content is as follows Figure 10 As shown, Y = 0.4784X + 0.0601, R 2 = 0.9999, indicating a good fit.

[0061] c. Byproduct NO2 - Detection experiment Take 1 mL of the electrolyte after the reaction, add 2 mL of deionized water and mix well. Then add 1 mL of colorimetric reaction solution A (50 mL of deionized water contains 0.1 g of N-1-naphthyl ethylenediamine hydrochloride and 1 g of sulfonamide). Stir the mixture well and let it stand for 15 minutes to complete the colorimetric reaction.

[0062] Experiments were conducted using UV-Vis in the 400 nm to 700 nm range to obtain specific parameters of the absorbance at 540 nm. NO2 can then be calculated from these parameters. - The concentration of NO2 in 0.1 M KNO3. - The standard curve of content is as follows Figure 11 As shown, Y = 0.0443X + 0.00874, R 2 = 0.9993 and good fit.

[0063] Experimental Example 3: X-ray Powder Diffraction Analysis The crystal structures of the materials obtained in Comparative Example 1 and Examples 1-4 of this invention were characterized using a Japanese XRD-7000S powder diffractometer.

[0064] Depend on Figure 1 The results show that the key peaks of the Zn-doped Cu₂O catalyst are consistent with those in the JCPDS standard card (PDF#05-0667), indicating that the synthesized Cu₂O-Zn catalyst has a distinct Cu₂O phase and good crystallinity. Furthermore, magnification of its characteristic peaks reveals that the peak positions at (111) and (200) are significantly shifted to the right compared to the (111) and (200) peaks of pure Cu₂O, with a shift angle <0.1°. o This indicates that Zn ions have been successfully doped into the Cu2O lattice.

[0065] Experiment Example 4: Scanning Electron Microscopy (SEM) Characterization Analysis The morphology of the products from Examples 1, 2, 3, and 4 of this invention was characterized using a Hitachi SU8010 ultra-high resolution field emission scanning electron microscope (USA). The results are shown in [reference needed]. Figure 2 .

[0066] Figure 2 SEM results showed that all doped samples exhibited a polyhedral structure, with its unique (110) / (100) / (111) ternary heterojunction structure, which remained intact after Zn doping. Notably, as the Zn doping ratio increased from 1% to 15%, the sample particle size remained stable within 1 µm, the surface roughness did not change significantly, and no obvious lattice distortion was observed. This finding indicates that the electronic structure of materials can be independently controlled through elemental doping without destroying their advantageous morphological characteristics.

[0067] Experimental Example 5: Transmission Electron Microscopy (TEM) Characterization and Analysis The material of Example 2 of this invention was observed and TEM images and energy dispersive spectroscopy (EDS) elemental distribution were acquired using a JEM 2100F transmission electron microscope. The results are shown in [reference needed]. Figure 3 .

[0068] Figure 3 The EDS results showed that Zn (green) exhibited a diffuse distribution on the Cu2O surface (compared to Cu and O), and its spatial distribution trajectory completely overlapped with that of Cu (red) and O (blue) elements and was uniformly distributed, indicating that Zn was uniformly distributed in the Cu2O lattice at the atomic scale and did not form zinc clusters or zinc oxide particles.

[0069] Experimental Example 6: X-ray photoelectron spectroscopy (XPS) analysis The X-ray photoelectron spectra (XPS) of the products from Examples 1–4 were recorded on a Thermo Scientific ESCALAB 250Xi X-ray photoelectron spectrometer. The shifts in all binding energies were calibrated using the C 1s level at 284.8 eV. See the results below. Figure 4 .

[0070] From the high-resolution XPS spectrum of Zn 2p ( Figure 4 As can be seen, the products of Examples 1 to 4 all exhibit two symmetrical peaks at 1021.4 eV and 1044.8 eV, corresponding to the Zn 2p3 / 2 and Zn 2p1 / 2 energy levels, respectively. This confirms the presence of Zn in Zn-doped Cu2O. 2+ Combining with oxygen.

[0071] Experimental Example 7: Electrochemical Impedance Spectroscopy (EIS) Analysis Using a CHE 660E electrochemical workstation, with 0.5 M Na₂SO₄ solution as the electrolyte and an AC voltage of 1000 Hz and 5 mV amplitude, the EIS spectra of the comparative examples and products from Examples 1-4 were obtained. The results are shown in [reference needed]. Figure 5 .

[0072] from Figure 5 It can be observed that the Cu₂O-Zn-5% catalyst exhibits the smallest semi-circular radius in the Nyquist plot, indicating that this material has the lowest charge transfer resistance, significantly superior to samples with other doping ratios. This also confirms that 5% Zn doping can effectively improve the charge transport kinetics of Cu₂O catalysts at the electrode / electrolyte interface. Compared with undoped pure Cu₂O catalysts, Zn doping reduces interfacial charge transfer resistance, fully demonstrating that the introduction of Zn can significantly improve the electron transport channels on the catalyst surface.

[0073] Experimental Example 8: Photoelectrocatalysis of CO2 and NO3 using the materials from the examples and comparative examples as catalysts - Comparative experiment on the synthesis of urea.

[0074] The urea synthesis performance of Cu2O catalysts with different proportions of Zn doping is as follows: Figure 7 As shown, it can be observed that the FE and yield of urea synthesis using Cu2O catalysts with different Zn doping ratios first increase and then decrease with increasing Zn doping ratio. That is, the Cu2O-Zn-5% catalyst has the highest performance, with an FE of 42.4 ± 1.2% and a yield of 4.32 ± 0.17 mmol·g. cat. 1 ·h 1 The yields were 2.7 times (FE) and 4.5 times (yield) of the undoped product, respectively. The results indicate that the introduction of 5% Zn effectively enhances the adsorption of key intermediates and promotes CN coupling to urea. (See attached figures). Figure 6 .

[0075] Experimental Example 9: Photoelectrocatalysis of CO2 and NO3 using the materials from the examples and comparative examples as catalysts - A comparative experiment on the performance of ammonia, a byproduct of urea synthesis, was conducted. The results are shown in [link to experiment]. Figure 7 .

[0076] from Figure 7 It can be seen that the evolution of the byproduct ammonia is mirrored that of urea. Its FE and yield show a trend of first decreasing and then increasing with the increase of Zn doping ratio. That is, the performance of Cu2O-Zn-5% catalyst in ammonia synthesis is the lowest, indicating that 5% Zn doping can effectively suppress the synthesis of byproduct ammonia.

[0077] Experimental Example 10: Photoelectrocatalysis of CO2 and NO3 using the materials from the examples and comparative examples as catalysts. - NO2, a byproduct of urea synthesis Performance comparison experiments, results are shown in [link to results]. Figure 8 .

[0078] from Figure 8 It can be seen that the byproduct NO2 The formation of [a specific catalyst] exhibits a non-monotonic variation characteristic, with no linear correlation between its FE and yield and the Zn doping ratio; however, both FE and yield remain at low levels. The results indicate that the Cu₂O-Zn-5% catalyst can synergistically achieve dual optimization of target product activity enhancement and side reaction suppression. This is because the introduction of Zn reconstructs the electronic structure of the catalyst surface, enhancing the adsorption of key intermediates while weakening the activity of competitive nitrogen reduction.

[0079] Experimental Example 11: Cyclic Stability Test of Cu2O-Zn-5% Catalyst To investigate the reaction stability of Cu2O-Zn-5% under long-term experimental conditions, this invention conducted an uninterrupted photoelectrocatalytic urea synthesis experiment. The electrolytes in the cathode and anode chambers were replenished every 2 hours, and other reaction conditions remained consistent with those in Experiment 7. The results are detailed below. Figure 9 .

[0080] from Figure 9 As can be seen, at a potential of -0.4 V vs. Ag / AgCl, the catalyst exhibits excellent cycling stability: the average Faradaic efficiency remains at 30.68%, and the urea yield remains stable at 3.17 mmol·g⁻¹. cat. 1 ·h 1 Despite a slight performance degradation observed after the 13th cycle, its overall stability was significantly better than that of the undoped Cu₂O-ecto catalyst. This result effectively confirms the role of Zn doping in enhancing the structural stability of the catalyst.

[0081] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing Zn-doped Cu₂O material, characterized in that, Includes the following steps: (1) Dissolve copper salt and zinc salt in deionized water to prepare a mixed solution containing copper ions and zinc ions; (2) Add a chelating agent to the mixed solution and stir until homogeneous; (3) Heat the solution obtained in step (2) to 50~70℃ and keep it warm; (4) Add sodium hydroxide solution to the insulated solution and continue stirring to react; (5) Add a weak reducing agent to the system obtained in step (4) and continue the reaction for 1-2 h; (6) The reaction product was separated into solid and liquid components and washed with ethanol and deionized water. Then it was vacuum dried at 60-80℃ for 6-12 h to obtain Zn-doped Cu2O catalyst.

2. The preparation method according to claim 1, characterized in that: In step (1), the copper salt is any one of copper sulfate, copper nitrate or copper chloride; the zinc salt is any one of zinc nitrate, zinc sulfate or zinc chloride; the total amount of copper salt and zinc salt is 0.002 to 0.01 mol, and the molar ratio of copper salt to zinc salt is 99:1, 95:5, 90:10 and 85:

15.

3. The preparation method according to claim 1, characterized in that, In step (2), the chelating agent is ethylenediaminetetraacetic acid (EDTA).

4. The preparation method according to claim 1, characterized in that, In step (4), the concentration of the sodium hydroxide solution is 0.6–6.8 mol / L, the added volume is 20–30 mL, and the stirring time is 5 min.

5. The preparation method according to claim 1, characterized in that, In step (5), the weak reducing agent is hydroquinone; after the hydroquinone is added, the reaction continues for 60 min.

6. A Zn-doped Cu₂O material, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 5.

7. The Zn-doped Cu₂O material according to claim 6 in the photoelectrocatalysis of CO₂ and NO₃⁻ Application in the co-reduction synthesis of urea.

8. The application according to claim 7, characterized in that, During the reaction, the volume fraction of CO2 ranged from 15% to 99.99%, and the gas flow rate was 20 cm³. 3 / min.

9. The application according to claim 7, characterized in that, The photoelectrocatalysis of CO2 and NO3 The co-reduction synthesis of urea was carried out in a device consisting of an H-type quartz reactor, a three-electrode system, a proton exchange membrane, a light source system, an electrochemical workstation, and a gas supply system. The three-electrode system included an FTO conductive glass working electrode coated with a Zn-doped Cu2O catalyst, an Ag / AgCl reference electrode, and a Pt counter electrode. The proton exchange membrane was a Nafion 117 proton exchange membrane. The light source system was a xenon lamp equipped with a filter, with illumination conditions of AM 1.5G, a power of 300 W, and a wavelength range of 400–700 nm.

10. The application according to claim 7, characterized in that, The concentration of the KNO3 solution is 0.1 mol / L, and the volume is 30 mL. The cathode chamber is filled with a CO2-saturated KNO3 solution. The reaction is carried out at room temperature for 2 h.

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