Application of basic zinc carbonate in photocatalytic CO2 reduction

Abstract

The application discloses application of basic zinc carbonate in photocatalytic reduction of CO2, and a product of the photocatalytic reduction of CO2 is CO. The application uses the basic zinc carbonate, and can reduce the CO2 into CO through a photocatalytic reaction without a sacrificial agent and a cocatalyst, saves reagents required in a photocatalytic CO2 reduction process, and has simple use conditions. The basic zinc carbonate is used in the photocatalytic reduction of CO2 under a 300W high-pressure xenon lamp for 5h, and an average generation rate of CO is 1.61umol g –1 h –1 -1h-1. The basic zinc carbonate also has good stability and repeatability in a cyclic reaction test.

Description

Technical Field

[0001] This invention belongs to the field of photocatalysis technology, specifically relating to the application of basic zinc carbonate in photocatalytic CO2 reduction. Background Technology

[0002] The combustion of carbon dioxide-intensive fossil fuels results in a large amount of CO2 emissions. Converting CO2 into high-value-added chemicals is one way to reduce CO2 emissions.

[0003] Photocatalytic CO2 reduction is an artificial photosynthesis process that uses photoelectrons to reduce CO2 into high-value-added products such as CO and CH4. Currently, traditional semiconductor photocatalysts such as TiO2, ZnO, Fe2O3, g-C3N4, WC, CeO2, and BiVO4 are widely used in CO2 reduction research. However, these materials require hole sacrificial agents during the CO2 reduction process, and some materials also require co-catalysts. The use of hole sacrificial agents and co-catalysts leads to additional energy consumption. Therefore, there is a need to find new materials that do not require hole sacrificial agents and co-catalysts for CO2 reduction. Summary of the Invention

[0004] The purpose of this invention is to provide the application of basic zinc carbonate in photocatalytic CO2 reduction, so as to solve at least one of the above-mentioned technical problems.

[0005] In a first aspect, the present invention provides the application of basic zinc carbonate in photocatalytic CO2 reduction, wherein the product of the photocatalytic CO2 reduction is CO.

[0006] The basic zinc carbonate of the present invention can reduce CO2 to CO through photocatalytic reaction without sacrificial agents and co-catalysts, saving the reagents required for the photocatalytic CO2 reduction process, with simple usage conditions, and also exhibits high selectivity of basic zinc carbonate for CO in photocatalytic CO2 reduction.

[0007] In some embodiments, the molecular formula of basic zinc carbonate is Zn5(OH)6(CO3)2.

[0008] In some embodiments, the method for using basic zinc carbonate for photocatalytic CO2 reduction includes the following steps:

[0009] 20–40 mg of basic zinc carbonate was dispersed in 300–500 μL of water to obtain a mixture. The mixture was then uniformly drop-coated onto quartz glass and dried at 50–70 °C for 1–2 h to obtain a Zn5(OH)6(CO3)2 film loaded on quartz glass.

[0010] After placing the quartz glass in a reactor containing 10-15 mL of water, the reactor was evacuated to a pressure of 0.1 kPa. Then, 99.999% CO2 gas was introduced to a pressure of 80 kPa. This process was repeated three times. The reactor was then placed under a 300 W high-pressure xenon lamp for 1-10 hours.

[0011] In some embodiments, the method of using basic zinc carbonate for photocatalytic CO2 reduction can be as follows: 30 mg of basic zinc carbonate is dispersed in 400 μL of water to obtain a mixture, the mixture is uniformly drop-coated onto a 3 cm × 3 cm quartz glass, and then dried at 60 °C for 1 h to obtain a Zn5(OH)6(CO3)2 film loaded on the quartz glass.

[0012] After placing the quartz glass in a reactor containing 10 mL of water, the reactor was evacuated to a pressure of 0.1 kPa. Then, 99.999% CO2 gas was introduced to a pressure of 80 kPa. This process was repeated three times. The reactor was then placed under a 300 W high-pressure xenon lamp for 5 hours.

[0013] In some embodiments, Zn5(OH)6(CO3)2 can be prepared by the following steps:

[0014] S1. Dissolve Na2CO3 in deionized water and stir for 10-30 minutes to obtain Na2CO3 solution;

[0015] S2. Dissolve Zn(NO3)2·6H2O in deionized water and stir for 10-30 min to obtain an aqueous solution of Zn(NO3)2·6H2O.

[0016] S3. Add an aqueous solution of Zn(NO3)2·6H2O dropwise to a Na2CO3 solution and stir for 5–7 hours. Centrifuge the solution and wash the precipitate with deionized water and anhydrous ethanol, respectively, and centrifuge 3–10 times to obtain a solid. Then dry the solid at 50–70°C for 10–12 hours to obtain Zn5(OH)6(CO3)2.

[0017] The molar ratio of Na2CO3 to Zn(NO3)2·6H2O is (2.5~4):(1~2).

[0018] 5Zn was co-precipitated at room temperature 2+ +2CO3 2- +6OH - →Zn5(OH)6(CO3)2↓ Zn5(OH)6(CO3)2 is prepared by a simple method with low production cost, and the obtained Zn5(OH)6(CO3)2 has a nanosheet structure.

[0019] In some embodiments, the Na2CO3 solution can be prepared by dissolving 0.3–1.3 g of Na2CO3 in 40–60 mL of deionized water and stirring.

[0020] In some embodiments, the aqueous solution of Zn(NO3)2·6H2O can be prepared by dissolving 0.21 to 2.92 g of Zn(NO3)2·6H2O in 5 to 15 mL of deionized water and stirring.

[0021] In some embodiments, in step S1, the volume of deionized water can be 50 mL and the stirring time can be 20 min.

[0022] In some embodiments, in step S2, the volume of deionized water can be 10 mL and the stirring time can be 20 min.

[0023] In some embodiments, in step S3, the drying is vacuum drying, the drying temperature can be 60°C, and the drying time can be 12 hours.

[0024] In some embodiments, in step S3, the volume of deionized water and anhydrous ethanol can be 10-20 mL. More preferably, the volume of deionized water and anhydrous ethanol can be 10 mL.

[0025] In some embodiments, in step S3, the centrifugation process can be performed by centrifuging at a speed of 8000 to 10000 rpm for 3 to 5 minutes.

[0026] The beneficial effects of this invention are as follows:

[0027] The basic zinc carbonate of this invention has hydroxide ions in its structure that can alter the band structure and valence band oxidation potential of zinc materials, improving charge separation efficiency and rate. It reduces CO2 to CO via photocatalysis without the need for hole sacrificial agents or co-catalysts. This not only demonstrates the high selectivity of basic zinc carbonate for CO in photocatalytic CO2 reduction but also saves reagents required for the photocatalytic CO2 reduction process, simplifying the application conditions. The average CO production rate of Zn5(OH)6(CO3)2 under a 300W high-pressure xenon lamp for 5 hours was 1.61 μmol g. –1 h –1 It also showed good stability and repeatability in the 50-hour cyclic reaction test. Attached Figure Description

[0028] Figure 1 The XRD pattern of Zn5(OH)6(CO3)2 prepared in Example 1 of this invention;

[0029] Figure 2The XPS analysis fitting results are for Zn5(OH)6(CO3)2 prepared in Example 1 of this invention. Figure 2 (a) is the full XPS spectrum of Zn5(OH)6(CO3)2. Figure 2 (b) is the O 1s XPS plot. Figure 2 (c) is the Zn 2p XPS plot. Figure 2 (d) is the C 1s XPS plot;

[0030] Figure 3 (a) is a SEM image of Zn5(OH)6(CO3)2 prepared in Example 1 of this invention. Figure 3 (b) is Figure 3 (a) enlarged view, Figure 3 (c) is a TEM image of Zn5(OH)6(CO3)2 prepared in Example 1 of the present invention;

[0031] Figure 4 (a) is the UV-diffuse reflectance spectrum of Zn5(OH)6(CO3)2 prepared in Example 1; Figure 4 (b) is Figure 4 (a) Enlarged view; Figure 4 (c) is the band gap diagram of Zn5(OH)6(CO3)2 prepared in Example 1; Figure 4 (d) is the Mott-Schottky diagram of Zn5(OH)6(CO3)2 prepared in Example 1;

[0032] Figure 4 (e) shows the band structure calculation results of Zn5(OH)6(CO3)2 prepared in Example 1; Figure 4 (f) is the photoluminescence spectrum of Zn5(OH)6(CO3)2 prepared in Example 1;

[0033] Figure 5 The results of the photocatalytic CO2 reduction test in Experimental Example 1 of this invention are as follows. Figure 5 (a) is a graph showing the results of the photocatalytic reaction of Zn5(OH)6(CO3)2 from 0 to 5 h. Figure 5 (b) is a comparison chart of CO production under different conditions. Figure 5 (c) is a CO precipitation-time diagram. Detailed Implementation

[0034] The present invention will now be described in further detail with reference to the accompanying drawings, but the embodiments of the present invention are not limited thereto. The raw materials and reagents involved in the following embodiments are all commercially available.

[0035] Example 1

[0036] This embodiment provides a method for preparing Zn5(OH)6(CO3)2, including the following steps:

[0037] 1.272 g of Na₂CO₃ (0.012 mol) was added to 50 mL of deionized water and stirred with a magnetic stirrer for 20 min to obtain a Na₂CO₃ solution. Then, 2.38 g of Zn(NO₃)₂·6H₂O (0.008 mol) was added to 10 mL of deionized water and stirred with a magnetic stirrer for 20 min to obtain an aqueous solution of Zn(NO₃)₂·6H₂O. The aqueous solution of Zn(NO₃)₂·6H₂O was then added dropwise to the Na₂CO₃ solution and stirred at room temperature for 6 h. The mixture was then centrifuged at 9000 rpm for 3 min. The precipitate obtained by centrifugation was washed with 10 mL of anhydrous ethanol and 10 mL of deionized water, respectively, and centrifuged three times, 3 min each time. The solid obtained after centrifugation was then dried in a vacuum oven at 60 °C for 12 h to obtain a white sample.

[0038] XRD analysis was performed on the white sample obtained in Example 1, and the results are as follows: Figure 1 As shown. From Figure 1 It can be seen that the diffraction peaks located at 13.05, 16.42, 22.16, 24.24, 28.28, 31.29, 32.91, 34.88, 36.18, 38.35, 40.56, 43.69, 47.31, 50.75, 54.04, 58.04, 59.53, 63.64, 66.64, 68.09, and 73.20 can be indexed to Zn5(OH)6. The crystal planes of (CO3)2 (PDF#No.72-1100) are (200), (001), (111), (310), (020), (220), (021), (221), (112), (511), (402), (421), (222), (003), (800), (332), (223), (622), (731), (532), (640). The good crystal plane matching between the two indicates that the white sample is Zn5(OH)6(CO3)2, verifying the successful preparation of Zn5(OH)6(CO3)2 in Example 1.

[0039] X-ray photoelectron spectroscopy (XPS) analysis was performed on Zn5(OH)6(CO3)2 from Example 1. The obtained XPS peaks were fitted, and the results are as follows: Figure 2 As shown, Figure 2 (a) is the full XPS spectrum of Zn5(OH)6(CO3)2. Figure 2 (b) is the O 1s XPS plot. Figure 2 (c) is the Zn 2p XPS plot. Figure 2 (d) is the C 1s XPS plot. From Figure 2 (b) It can be seen that the peaks with binding energies at 530.6 eV and 535.4 eV correspond to the core energy level O1s. The first peak is related to the oxygen vacancy in the Zn5(OH)6(CO3)2 structure, and the second peak belongs to the oxygen of the hydroxyl anion. From Figure 2 (c) It can be seen that in the core energy level Zn 2p, the peaks at 1020.9, 1025.2, and 1041.1 eV are similar to those at Zn(OH)2 in Zn 2p. 1 / 2 The peaks at 1022.9 eV and 1046.4 eV are related to Zn 2p 1 / 2 This is related to the ·OH groups attached to Zn ions. The peak with a binding energy of 1044.1 eV is associated with ZnCO3. From Figure 2 (d) It can be seen that in the C1s core energy level, characteristic peaks of OCC, CO, COC and CC appear at binding energies of 289.6 eV, 286.3 eV and 284.8 eV, respectively. Among them, the peaks of 284.8 eV and 286.3 eV belong to hydrocarbons and carbon-oxygen pollutants, respectively, and the peak of 289.6 eV belongs to C in carbonates. This indicates that Zn5(OH)6(CO3)2 is highly carbonized and confirms that there are free and anchored carbonates in the layered structure of Zn5(OH)6(CO3)2.

[0040] The morphology of Zn5(OH)6(CO3)2 prepared in Example 1 was characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the results are as follows: Figure 3 As shown in (a) to (c). From Figure 3 It can be seen that the Zn5(OH)6(CO3)2 prepared in Example 1 has a nanosheet structure.

[0041] To investigate the optical bandgap properties of Zn5(OH)6(CO3)2, ultraviolet-diffuse reflectance spectroscopy (UV-Vis DRS), bandgap (Tauc), Mott-Schottky (MS), and photoluminescence (PL) spectroscopy were performed. The results are as follows: Figure 4 As shown in (a) to (f).

[0042] from Figure 4 In the UV-diffuse reflectance spectrum of (a), a high absorption edge can be observed between 200-250 nm and a low absorption edge between 250-375 nm in Zn5(OH)6(CO3)2. The low absorption edge is characterized by... Figure 4As can also be clearly observed in (b), studies have shown that the high absorption edge (200-250 nm) is characteristic of the basic zinc carbonate band gap energy (5.1 eV), while the low absorption edge (250-375 nm) indicates the trace presence of Smithsonite (ZnCO3), which is attributed to Zn5(OH)6(CO3)2 in CO3. 2- The n-π* and π-π* electronic transitions in Zn₅(OH)₆(CO₃)₂ and the Zn-O CT transition in Zn₅(OH)₆(CO₃)₂. From Figure 4 (c) It can be seen that the optical band gap of Zn5(OH)6(CO3)2 is 3.5eV.

[0043] Mott-Schottky analysis was used to further verify the accurate conduction band energy (ECB) and valence band energy (EVB) of Zn5(OH)6(CO3)2, and the results are as follows: Figure 4 As shown in (d). From Figure 4 (d) It can be seen that Zn5(OH)6(CO3)2 exhibits n-type semiconductor characteristics with a positive slope. From Figure 4 (d) further yields a flat-band potential (Efb) of -0.55 eV (vs. RHE) and a conduction band minimum (CBM) for Zn5(OH)6(CO3)2. Furthermore, based on... Figure 4 (a) Obtain the estimated Eg value of UV-Vis absorption and perform band structure calculations based on... Figure 4 The results in (e) determine the position of the maximum valence band (VBM) of Zn5(OH)6(CO3)2. Since the ECB position is typically about -0.2V negative than Efb, and the ECB of Zn5(OH)6(CO3)2 is more negative than the reduction potential required for many CO2 reduction products, the ECB of Zn5(OH)6(CO3)2 is above the CO2 / CO reduction potential, indicating that the photocatalytic reduction of CO2 to CO by Zn5(OH)6(CO3)2 is thermodynamically feasible. The oxidation potential of Zn5(OH)6(CO3)2 is 4.35 eV. Generally, the higher the oxidation potential, the stronger the oxidizing ability of the generated holes, which is also conducive to the formation of ·OH. Meanwhile, since the EVB of Zn5(OH)6(CO3)2 is below the oxidation potential of H2O / H2O2, it indicates that the photooxidation of H2O to H2O2 by Zn5(OH)6(CO3)2 is thermodynamically feasible. The above results indicate that photocatalytic redox reactions of Zn5(OH)6(CO3)2 are thermodynamically feasible and have the potential to reduce CO2 to CO.

[0044] The carrier dynamics of semiconductors are closely related to their photocatalytic performance. To investigate the carrier dynamics of Zn5(OH)6(CO3)2, steady-state photoluminescence (PL) spectroscopy analysis was performed on Zn5(OH)6(CO3)2. The results are as follows: Figure 4As shown in (f). From Figure 4 (f) It can be seen that Zn5(OH)6(CO3)2 exhibits a fluorescence emission peak at approximately 360 nm when excited by 295 nm light.

[0045] Example 2

[0046] This embodiment provides a method for preparing Zn5(OH)6(CO3)2, including the following steps:

[0047] 0.318 g of Na₂CO₃ (0.003 mol) was added to 50 mL of deionized water and stirred with a magnetic stirrer for 20 min to obtain a Na₂CO₃ solution. Then, 0.595 g of Zn(NO₃)₂·6H₂O (0.002 mol) was added to 10 mL of deionized water and stirred with a magnetic stirrer for 20 min to obtain an aqueous solution of Zn(NO₃)₂·6H₂O. The Zn(NO₃)₂·6H₂O aqueous solution was then added dropwise to the Na₂CO₃ solution, and the mixture was stirred at room temperature for 6 h. The mixture was then centrifuged at 9000 rpm for 3 min. The precipitate obtained by centrifugation was washed with 10 mL of anhydrous ethanol and 10 mL of deionized water, respectively, and centrifuged three times, 3 min each time. The solid obtained after centrifugation was then dried in a vacuum oven at 60 °C for 12 h to obtain a white sample. The white sample was analyzed by XPS and characterized by SEM. The results were compared with those obtained by... Figure 1 and Figure 3 The results were the same, indicating the successful preparation of Zn5(OH)6(CO3)2.

[0048] Example 3

[0049] This embodiment provides a method for preparing Zn5(OH)6(CO3)2, including the following steps:

[0050] 0.3 g of Na₂CO₃ was added to 40 mL of deionized water and stirred with a magnetic stirrer for 10 min to obtain a Na₂CO₃ solution. Then, 0.2104 g of Zn(NO₃)₂·6H₂O was added to 5 mL of deionized water and stirred with a magnetic stirrer for 10 min to obtain an aqueous solution of Zn(NO₃)₂·6H₂O. The Zn(NO₃)₂·6H₂O aqueous solution was then added dropwise to the Na₂CO₃ solution. The mixture was stirred at room temperature for 5 h and centrifuged at 9000 rpm for 3 min. The precipitate obtained by centrifugation was washed with 10 mL of anhydrous ethanol and 10 mL of deionized water, respectively, and centrifuged three times, 3 min each time. The solid obtained after centrifugation was then dried in a vacuum oven at 50 °C for 10 h to obtain a white sample. The white sample was analyzed by XPS and characterized by SEM. The results were compared with those obtained by... Figure 1 and Figure 3The results were the same, indicating the successful preparation of Zn5(OH)6(CO3)2.

[0051] Example 4

[0052] This embodiment provides a method for preparing Zn5(OH)6(CO3)2, including the following steps:

[0053] 1.3 g of Na₂CO₃ was added to 70 mL of deionized water and stirred with a magnetic stirrer for 30 min to obtain a Na₂CO₃ solution. Then, 2.9187 g of Zn(NO₃)₂·6H₂O was added to 15 mL of deionized water and stirred with a magnetic stirrer for 300 min to obtain an aqueous solution of Zn(NO₃)₂·6H₂O. The Zn(NO₃)₂·6H₂O aqueous solution was then added dropwise to the Na₂CO₃ solution, and the mixture was stirred at room temperature for 7 h. The mixture was then centrifuged at 9000 rpm for 3 min. The precipitate obtained by centrifugation was washed with 10 mL of anhydrous ethanol and 10 mL of deionized water, respectively, and centrifuged three times, 3 min each time. The solid obtained after centrifugation was then dried in a vacuum oven at 70 °C for 12 h to obtain a white sample. The white sample was analyzed by XPS and characterized by SEM. The results were compared with those obtained by... Figure 1 and Figure 3 The results were the same, indicating the successful preparation of Zn5(OH)6(CO3)2.

[0054] Experimental Example 1

[0055] This experimental example tests the photocatalytic CO2 reduction of Zn5(OH)6(CO3)2 prepared in Example 1. The photocatalytic CO2 reduction reaction is carried out in a gas-solid heterogeneous reaction mode.

[0056] 30 mg of Zn₅(OH)₆(CO₃)₂ was dispersed in 400 μL of H₂O, and the mixture was then uniformly drop-coated onto a 3 cm × 3 cm quartz glass substrate. The substrate was then vacuum-dried at 60 °C for 1 h to prepare a Zn₅(OH)₆(CO₃)₂ photocatalyst film. The quartz glass was held in place by a support and placed in a 150 mL reactor containing 10 mL of H₂O for photocatalytic CO₂ reduction testing. The results are as follows: Figure 5 As shown in (a) to (c).

[0057] The photocatalytic CO2 reduction test was conducted using the Labsolar-6A photochemical reaction system at Beijing Pofilai Technology Co., Ltd. The gaseous products generated during the test were detected online using a GC8860 gas chromatograph from Agilent Technologies, equipped with a HayeSep Q column (8ft × 0.125in. × 2mm) and a MolSieve 5A molecular sieve (8ft × 0.125in. × 2mm). The column was connected to a thermal conductivity (TCD) detector and a flame ionization (FID) detector to ensure the detection of all products. First, the entire system was evacuated to 0.1 kPa to remove air, then 99.999% high-purity CO2 was introduced to 80 kPa, followed by another evacuation. After three cycles, the system pressure was controlled at 80 kPa. Finally, the reaction system was placed under a 300W high-pressure xenon lamp (PLS SXE300UV) for photocatalytic CO2 reduction. The high-pressure xenon lamp was turned on for long-term illumination. The system automatically took a sample every hour and passed it into the gas chromatograph for online detection. After the reaction was completed, a standard curve was prepared using standard gases, and the gas yield produced by the reaction was calculated using the external standard method.

[0058] The results showed that Zn5(OH)6(CO3)2 prepared in Example 1 was reduced to CO by CO after irradiation with a 300W xenon lamp in a photocatalytic reaction system filled with CO2 and H2O, and no other gaseous products were detected. Figure 5 (a) It can be seen that during the 5-hour photoreaction of Zn5(OH)6(CO3)2, the CO production gradually increases, with an average CO production rate of 1.61 μmol g. –1 h –1 Blank tests were performed separately for Zn5(OH)6(CO3)2 and for no light exposure. The results are as follows. Figure 5 As shown in (b), it can be seen that in the absence of a catalyst and light irradiation, only a negligible trace amount of CO can be detected after 5 hours of reaction, indicating that CO production is solely due to Zn5(OH)6(CO3)2 under light irradiation. The long-term stability of Zn5(OH)6(CO3)2 was evaluated through cyclic testing, and the CO precipitation changes over time as shown in the figure. Figure 5 As shown in (c), the CO production gradually increased during the 10 cycles, indicating that Zn5(OH)6(CO3)2 exhibits good stability and repeatability. In a continuous cyclic experiment conducted under a 300W high-pressure xenon lamp for 50 hours, the average CO production rate was 3.22 μmol g / L. –1 h –1 .

[0059] The above descriptions are merely some embodiments of the present invention. Those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. The application of basic zinc carbonate in photocatalytic CO2 reduction, wherein the product of the photocatalytic CO2 reduction is CO; the method for using basic zinc carbonate for photocatalytic CO2 reduction includes the following steps: Disperse 20-40 mg of basic zinc carbonate in 300-500 μL of water to obtain a mixture. The mixture is then uniformly drop-coated onto quartz glass and dried at 50-70 °C for 1-2 h to obtain a Zn5(OH)6(CO3)2 film loaded on quartz glass. After placing the quartz glass in a reactor containing 10-15 mL of water, evacuate the reactor to a pressure of 0.1 kPa, then introduce CO2 gas with a volume fraction of 99.999% to a pressure of 80 kPa. Repeat this process three times, and then place the reactor under a 300 W high-pressure xenon lamp for 1-10 hours.

2. The application according to claim 1, characterized in that, The molecular formula of the basic zinc carbonate is Zn5(OH)6(CO3)2.

3. The application according to claim 1, characterized in that, The method for using basic zinc carbonate for photocatalytic CO2 reduction includes the following steps: 30 mg of basic zinc carbonate was dispersed in 400 μL of water to obtain a mixture. The mixture was then uniformly drop-coated onto quartz glass and dried at 60 °C for 1 h to obtain a Zn5(OH)6(CO3)2 film loaded on quartz glass. After placing the quartz glass in a reactor containing 10 mL of water, the reactor was evacuated to a pressure of 0.1 kPa. Then, 99.999% CO2 gas was introduced to a pressure of 80 kPa. This process was repeated three times. The reactor was then placed under a 300 W high-pressure xenon lamp for 5 hours.

4. The application according to claim 2, characterized in that, The preparation method of Zn5(OH)6(CO3)2 includes the following steps: S1. Dissolve Na2CO3 in deionized water and stir for 10-30 minutes to obtain Na2CO3 solution; S2. Dissolve Zn(NO3)2·6H2O in deionized water and stir for 10~30 min to obtain an aqueous solution of Zn(NO3)2·6H2O. S3. Add the aqueous solution of Zn(NO3)2·6H2O dropwise to the Na2CO3 solution and stir for 5-7 hours. Centrifuge and wash the precipitate obtained by centrifugation with 10-20 mL of deionized water and anhydrous ethanol respectively and centrifuge 3-10 times to obtain the solid. Then dry the solid at 50-70℃ for 10-12 hours to obtain the product. The molar ratio of Na2CO3 to Zn(NO3)2·6H2O is (2.5~4):(1~2).

5. The application according to claim 4, characterized in that, The Na2CO3 solution is prepared by dissolving 0.3-1.3g of Na2CO3 in 40-60mL of deionized water and stirring for 10-30min. The Zn(NO3)2·6H2O aqueous solution is prepared by dissolving 0.21-2.92g of Zn(NO3)2·6H2O in 5-15mL of deionized water and stirring for 10-30min.

6. The application according to claim 4, characterized in that, In step S1, the volume of deionized water is 50 mL and the stirring time is 20 min; in step S2, the volume of deionized water is 10 mL and the stirring time is 20 min; in step S3, the drying temperature is 60℃, the drying time is 12 h, and the volume of deionized water and anhydrous ethanol is 10 mL.

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