A method for electrocatalytic reduction of carbon dioxide and nitrate to synthesize urea

Abstract

The application discloses a method for synthesizing urea by electrocatalytic reduction of carbon dioxide and nitrate. The method synthesizes indium tin sulfide (In4SnS8) with nanosheet structure by hydrothermal method, in which tin (Sn) is doped into indium sulfide (In2S3). The working electrode is prepared by using the In4SnS8 catalyst, carbon dioxide is used as carbon source, and nitrate solution is used as nitrogen source. Urea is synthesized by reaction under the action of the catalyst and electrolyte. The catalyst is simple in preparation process, and has remarkable catalytic effect. The method realizes sustainable production of urea by using carbon dioxide and nitrate under environmental conditions.

Description

Technical Field

[0001] This invention relates to the field of electrocatalysis technology, specifically to a method for the electrocatalytic reduction of carbon dioxide and nitrate to synthesize urea. Background Technology

[0002] Urea, a nitrogen-based fertilizer, plays a crucial role in increasing crop yields and ensuring the food supply for humanity. Currently, the industrial synthesis of urea is carried out through a two-step process: first, the production of ammonia (NH3), followed by the reaction of NH3 with carbon dioxide (CO2). Both processes operate under harsh conditions, rely on non-renewable energy sources, account for 2% of global energy consumption, and emit excessive amounts of carbon dioxide into the atmosphere. Therefore, current urea synthesis methods fall far short of meeting the needs of sustainable social development. In contrast, electrosynthesis can use renewable energy to convert raw materials into high-value-added chemicals, enabling the sustainable production of urea.

[0003] For decades, various human activities have released reactive nitrogen and carbon dioxide into the environment, causing an imbalance in the global nitrogen and carbon cycle. Nitrates (NO3) - Release is also one of the most harmful consequences, as it can leach from the soil, contaminating groundwater and surface water, leading to eutrophication and ecosystem disturbance. Carbon dioxide, as a greenhouse gas, also poses a significant threat to the environment. In this context, electrocatalytic CN-coupling driven by renewable electricity presents a promising alternative to the traditional Haber-Bosch method and the subsequent Bosch-Meiser process. Direct and sustainable urea synthesis undoubtedly has a positive impact on maintaining the global nitrogen and carbon balance.

[0004] Recent studies have shown that, under environmental conditions, the electrochemical reduction of CO2 and NO3 can... - Urea can be synthesized efficiently using various methods, such as Bi / BiVO4, BiFeO3 / BiVO4, Te-doped Pd nanocrystals, FeNi diatomic catalysts, and ZnO vacancies, for the electrochemical co-reduction synthesis of electrochemical urea from carbon dioxide and nitrate (or nitrogen). Despite some progress, the electrosynthesis of urea from carbon dioxide and nitrate under environmental conditions remains far from practical application and faces significant challenges. Summary of the Invention

[0005] To address the shortcomings mentioned in the background art, this invention provides a method for the electrocatalytic reduction of carbon dioxide and nitrate to synthesize urea. The electrocatalyst used in this method has a stable structure, a simple preparation process, and low cost, and can efficiently reduce carbon dioxide and nitrate to urea.

[0006] To achieve the above objectives, the technical problem to be solved by the present invention is addressed by the following technical solution:

[0007] One objective of this invention is to provide a method for preparing In4SnS8 nanosheets, comprising the following steps:

[0008] (1) Dissolve indium chloride tetrahydrate (InCl3·4H2O) in deionized water, then add thioacetamide (C2H5NS) and tin dichloride dihydrate (SnCl2·2H2O), and stir to obtain a precursor solution;

[0009] (2) Transfer the precursor solution stirred in step (1) to a polytetrafluoroethylene reactor, and then place it in an oven for hydrothermal reaction;

[0010] (3) After the hydrothermal reaction in step (2) is completed, cool to room temperature, wash and centrifuge the obtained substance to obtain the sample;

[0011] (4) The sample obtained in step (3) is placed in an oven to dry, and finally, In4SnS8 with nanosheet structure is obtained.

[0012] Preferably, in step (1), the molar ratio of InCl3·4H2O, C2H5NS and SnCl2·2H2O is 1:2:0.05.

[0013] Preferably, in step (1), the stirring time can be 20 to 60 minutes.

[0014] Preferably, the deionized water in step (2) has a conductivity of 10 to 18.3 MΩ·cm and a volume of 20 to 40 mL.

[0015] Preferably, in step (2), the hydrothermal reaction temperature can be 150-200℃, the time can be 5-10h, and the volume of the polytetrafluoroethylene reactor can be 25-50mL.

[0016] Preferably, in step (3), the solvent used for washing is selected from at least one of deionized water, ethanol, acetone and their mixtures.

[0017] Preferably, in step (3), the centrifugation step has a rotation speed of 3000-11000 rpm and a time of 5-30 min.

[0018] Preferably, the drying in step (4) can be vacuum drying, and the temperature of vacuum drying can be 60-80°C and the time can be 5-20h.

[0019] The second objective of this invention is to provide an In4SnS8 nanosheet prepared according to the aforementioned preparation method.

[0020] The third objective of this invention is to provide the application of the aforementioned In4SnS8 nanosheets in the electrocatalytic preparation of urea, comprising the following steps:

[0021] In the above electrochemical catalytic system, urea is synthesized by reacting carbon dioxide as the carbon source and nitrate solution as the nitrogen source under the action of In4SnS8 nanosheet catalyst and electrolyte.

[0022] The electrolyte can be a potassium nitrate solution or a mixed solution of potassium nitrate and potassium bicarbonate, wherein the concentration of potassium nitrate is 0.05-0.1 mol / L, the concentration of potassium bicarbonate is 0.05-1 mol / L, and the volume of electrolyte is 20-40 mL.

[0023] A three-electrode system was adopted, with the above-mentioned electrode materials as the working electrode, the Ag / AgCl electrode as the reference electrode, and the platinum column electrode as the counter electrode.

[0024] An H-type glass electrolytic cell is used as the reaction apparatus, with a reaction potential of -0.1 to -1.5V (relative to the standard hydrogen electrode), specifically -0.35 to -0.75V (relative to the standard hydrogen electrode); the reaction time can be 0.5 to 24 hours, specifically 2 hours.

[0025] The beneficial effects of the technical solution of this invention are as follows:

[0026] (1) The catalytic electrode material provided by the present invention has a stable structure and a simple preparation process, and can be used to convert carbon dioxide and nitrate into valuable urea.

[0027] (2) The catalytic electrode material provided by this invention has excellent electrocatalytic performance for urea synthesis, and the urea yield can reach 74.76 μg / h / mg. cat The Faraday efficiency reached a maximum of 19.52%.

[0028] (3) This invention uses greenhouse gas carbon dioxide as a carbon source and nitrate, which is common in wastewater, as a nitrogen source, which is of great significance for establishing a resource-saving and environmentally friendly human society. Attached Figure Description

[0029] Figure 1 The X-ray diffraction pattern of the In4SnS8 nanosheets obtained in Example 1 of this invention;

[0030] Figure 2 This is a low-magnification transmission electron microscope image of the In4SnS8 nanosheets obtained in Example 1 of the present invention;

[0031] Figure 3 This is a high-magnification transmission electron microscope image of the In4SnS8 nanosheets obtained in Example 1 of the present invention;

[0032] Figure 4 The elemental analysis diagram of the In4SnS8 nanosheets obtained in Example 1 of this invention;

[0033] Figure 5 The image shows the ultraviolet spectrum of the urea standard solution used in the electrocatalytic synthesis of urea in Example 2 of this invention.

[0034] Figure 6 This is the standard curve for the electrocatalytic synthesis of urea in Example 2 of the present invention;

[0035] Figure 7 This is a yield diagram of the electrocatalytic synthesis of urea from In4SnS8 nanosheets in Example 2 of the present invention;

[0036] Figure 8 This is a Faraday efficiency diagram of the electrocatalytic synthesis of urea from In4SnS8 nanosheets in Example 2 of the present invention. Detailed Implementation

[0037] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments and illustrations.

[0038] Example 1

[0039] Preparation of In4SnS8 nanosheets:

[0040] 1 mmol InCl3·4H2O was dissolved in 30 mL of deionized water, followed by the addition of 2 mmol C2H5NS and 0.05 mmol SnCl2·2H2O. After stirring for 30 minutes, the mixture was transferred to a 50 mL polytetrafluoroethylene (PTFE) reactor and placed in an oven. The reaction temperature was set to 160 °C, and the reaction time was 6 h. After cooling to room temperature, the sample was washed at least three times with deionized water and ethanol. The washed sample was then placed in a vacuum oven and left to stand for 12 h. Finally, nanosheet-structured In4SnS8 was obtained.

[0041] The structure of In4SnS8 nanosheets was characterized, and the results are as follows:

[0042] Figure 1 All the diffraction peaks that appeared in the In4SnS8 sample corresponded one by one to the diffraction peaks of pure In4SnS8, thus proving that the present invention has successfully prepared pure In4SnS8. Figure 2 The nanosheet morphology of the In4SnS8 sample is shown. Figure 3 The lattice spacing of 0.324 nm corresponds to the (311) crystal plane of In4SnS8; Figure 4 This indicates that In, Sn, and S elements are uniformly distributed on the surface of the In4SnS8 sample.

[0043] The above results prove that the present invention successfully prepared In4SnS8 nanosheets.

[0044] Example 2

[0045] Application study of the In4SnS8 sample prepared in Example 1 as a catalyst in electrocatalytic urea synthesis:

[0046] a. The electrocatalytic synthesis performance of urea was tested using a standard three-electrode system on an electrochemical workstation. First, the working electrode was pretreated: 4 mg of In₄SnS₈ catalyst was dispersed in 500 μL of ethanol containing 20 μL of 5 wt% Nafion, and sonicated for 1 h to prepare In₄SnS₈ catalyst ink; then, 50 μL of the catalyst ink was dropped onto 1 cm × 1 cm carbon paper to obtain the working electrode. A platinum column electrode was used as the counter electrode, and Ag / AgCl as the reference electrode. CO₂ was continuously bubbled into 30 mL of 0.1 MkNO₃ electrolyte, and an H-type glass electrolytic cell was used as the reaction apparatus.

[0047] b. After bubbling CO2 into the electrolyte for 30 min, maintain a constant potential for 2 h at -0.35V, -0.45V, -0.55V, -0.65V, and -0.75V (relative to the standard hydrogen electrode). The conversion formula between the electrode potential and the standard hydrogen electrode (RHE) is: E(vs.RHE)=E(vs.Ag / AgCl)+0.197V+0.0596×pH.

[0048] c. Urea content test: The urea detection method is the diacetyl monooxime method. The principle is that urea and diacetyl monooxime condense under acidic conditions under the catalysis of ferric ions, and in the presence of thioaminourea, a red 4,5-dimethyl-2-oximidazolium compound is generated. The color intensity is directly proportional to the urea content. Specifically, 1 mL of the electrolyte after 2 hours of reaction at each potential is taken, and 2 mL of sample 1 colorimetric reaction solution (200 mL containing 20 mL phosphoric acid, 60 mL concentrated sulfuric acid, and 20 mg FeCl3) and 1 mL of sample 2 colorimetric reaction solution (100 mL containing 0.5 g diacetyl monooxime and 10 mg thioaminourea) are added. The mixture is incubated at 100℃ for 20 minutes and then allowed to stand for 30 minutes. Subsequently, a UV-Vis spectrophotometer is used to scan the spectrum in the range of 450 nm to 600 nm. Figure 5 Record the absorbance value at 525 nm and analyze it using a standard curve. Figure 6 The concentration of urea can then be obtained, and its yield and Faraday efficiency can be calculated according to the formula. The maximum urea yield of 74.76 μg / h / mg was achieved at -0.65V (relative to the standard hydrogen electrode). cat The highest Faraday efficiency is 19.52%, such as Figure 7 , Figure 8As shown.

[0049] Formula for urea yield in electrocatalytic urea synthesis:

[0050] UreaYield(μg / h / mg cat )=(C×V) / (t×m)

[0051] Where C is the concentration of urea produced, V is the volume of electrolyte, t is the time of electrocatalytic reaction, and m is the catalyst loading.

[0052] The Faraday efficiency (FE) formula for electrocatalytic urea synthesis:

[0053] FE(%)=nFCV / 60.06×Q×100%

[0054] Where F is the Faraday constant, Q is the amount of charge, C is the concentration of urea produced, V is the volume of the electrolyte, and n is the number of electrons transferred in the electrochemical reaction.

[0055] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for synthesizing urea by electrocatalytic reduction of carbon dioxide and nitrate, characterized in that: Includes the following steps: Step 1: Dissolve indium chloride tetrahydrate (InCl3·4H2O) in deionized water, then add thioacetamide (C2H5NS) and tin dichloride dihydrate (SnCl2·2H2O), stir to obtain a precursor solution, wherein the molar ratio of InCl3·4H2O, C2H5NS and SnCl2·2H2O is 1:2:0.05, and the volume of deionized water is 20-40 mL; Step 2: The precursor solution is transferred to a polytetrafluoroethylene (PTFE) reactor and then placed in an oven for hydrothermal reaction. After the reaction is completed, the mixture is cooled to room temperature, and the resulting material is washed, centrifuged, and dried to obtain the In4SnS8 catalyst for the electrocatalytic reduction of carbon dioxide and nitrate to synthesize urea. The hydrothermal reaction temperature is 150–200 °C, the time is 5–10 h, and the volume of the PTFE reactor is 25–50 mL, thus preparing In4SnS8 nanosheets. Step 3: Using carbon dioxide as the carbon source and nitrate solution as the nitrogen source, urea is synthesized through reaction in the presence of In4SnS8 nanosheet catalyst and electrolyte.

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