Application of CeO2 / ZIF-67 Catalyst in Piezoelectrocatalysis

Abstract

The present invention relates to the field of piezoelectric catalysis technology, and specifically discloses the application of CeO2 / ZIF-67 in piezoelectric catalysis. Through simple in-situ growth, a CeO2 / ZIF-67 catalyst is successfully constructed. By compounding CeO2, the piezoelectric effect of the metal-organic framework ZIF-67 can be enhanced, the carrier transport ability can be improved, and thus its piezoelectric catalytic performance can be improved. In particular, when the ratio of CeO2 to ZIF-67 is 1:60, hexavalent chromium is reduced within 40 minutes, providing an effective strategy for constructing highly active piezoelectric catalysts.

Description

Technical Field

[0001] The present invention belongs to the technical field of piezocatalysis, and particularly relates to the application of a CeO2 / ZIF-67 catalyst in piezocatalysis. Background Art

[0002] Recently, piezocatalysis based on piezoelectric materials has been emerging as a progressive strategy for solving environmental problems. When mechanical force is applied, piezoelectric materials generate polarized positive and negative charges on both sides of the catalyst surface, and then form an internal electric field, separating electrons and holes, thus inhibiting the recombination of carriers. Although much effort has been made in the innovation of piezocatalysts, most piezocatalysts still suffer from weak piezopolarization and insufficient catalytic active sites, which seriously restricts the performance of piezocatalysis. Therefore, developing new strategies to improve piezocatalytic efficiency is crucial for achieving a breakthrough in piezocatalysis. Summary of the Invention

[0003] The object of the present invention is to provide the application of a CeO2 / ZIF-67 catalyst in piezocatalysis. Metal-organic frameworks (MOF) materials are self-assembled from organic ligands and metal ions, and have characteristics such as ultra-large specific surface area, high porosity, high transition metal content, low density, and adjustable chemical structure. These promising properties have prompted researchers to apply these materials to catalysis, electrochemistry, and oxidation reactions. Generally, MOF materials with ferroelectric properties can be used in the piezocatalytic process. The present invention selects ZIF-67 loaded with CeO2 in a specific ratio, and the obtained CeO2 / ZIF-67 catalyst is used for piezocatalytic reduction of hexavalent chromium, showing extremely high piezocatalytic degradation efficiency, achieving the purpose of removing organic pollutants and heavy metal ions in industrial wastewater.

[0004] In order to achieve the object of the present invention, the specific technical solution adopted is as follows:

[0005] The application of a CeO2 / ZIF-67 catalyst in piezocatalysis for piezocatalytic reduction of hexavalent chromium, wherein the application method of the CeO2 / ZIF-67 catalyst includes: adding the CeO2 / ZIF-67 catalyst to a hexavalent chromium salt solution, and allowing the CeO2 / ZIF-67 catalyst to fully adsorb hexavalent chromium under dark conditions, and then performing a piezocatalytic reaction.

[0006] Furthermore, the preparation method of the CeO2 / ZIF-67 catalyst includes the following steps:

[0007] Disperse CeO2 in methanol, ultrasonicate until it is evenly suspended and dispersed, then stir, add PVP during stirring, add Co(NO3)2 solution dropwise after uniform dispersion (generally after 15 minutes), and then mix the prepared 2-methylimidazole solution with it. After sufficient stirring and dispersion (generally stirring for 1 hour), let stand at room temperature until sufficient reaction occurs (generally let stand for about 12 hours), collect and dry to obtain a white powdery CeO2 / ZIF-67 catalyst. The molar ratio of CeO2 to added Co ions is 1:30-120, preferably 1:60.

[0008] As a preferred embodiment, the standing time is 12-14 hours. The synthesis conditions are simple and easy to operate, fast and efficient, energy-saving and environmentally friendly, and good stability.

[0009] The purification steps in the preparation of CeO2 / ZIF-67 catalyst include: collecting the white precipitate by centrifugation, washing it with methanol and deionized water several times, and then drying it under vacuum overnight to obtain a white powder.

[0010] Furthermore, the drying temperature is 45 to 65° C., and the drying time is 12 to 16 hours.

[0011] Furthermore, the piezoelectric catalytic reaction is carried out under light and ultrasound conditions, with an ultrasound power of 240 W and a reaction time of 40 min.

[0012] Compared with the prior art, the present application has achieved the following beneficial effects: for the first time, the present application uses a CeO2 / ZIF-67 catalyst in a specific ratio as a piezoelectric catalyst. The CeO2 / ZIF-67 catalyst in a specific ratio has better conductivity, higher polarizability, more active centers and better piezoelectric catalytic performance. Its catalytic performance reaches or even exceeds that of existing piezoelectric catalysts, and it exhibits ultra-high piezoelectric catalytic activity in the piezoelectric catalytic reduction of hexavalent chromium. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is the XRD diagram of the catalysts in Example 1, Example 2, Example 3, Example 4, Example 5 and Comparative Example 1 and Comparative Example 2.

[0014] Figure 2 This is the transmission electron microscopy of the CeO2 / ZIF-67 catalyst in Example 1.

[0015] Figure 3 It is a performance diagram of the catalyst reducing hexavalent chromium in Example 1, Example 2, Example 3, Example 4, Example 5 and Control Example 1 and Control Example 2.

[0016] Figure 4 This is a performance diagram of Example 6, which is a catalyst reduction performance diagram of hexavalent chromium only under ultrasonic conditions.

[0017] Figure 5 This is Example 7, which is a performance graph of the catalyst for reducing hexavalent chromium only under light conditions.

[0018] Figure 6 This is the equilibrium curve graph of the addition of different scavengers in Example 8, Example 9, and Example 10 for the catalyst to reduce hexavalent chromium. Detailed implementation manners

[0019] The present invention is not limited to the following specific implementation manners. Those of ordinary skill in the art can implement the present invention in other various specific implementation manners according to the content disclosed in the present invention, or those that adopt the design structure and idea of the present invention and make simple changes or modifications all fall within the protection scope of the present invention. It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0020] The present invention is further described in detail below in conjunction with embodiments:

[0021] The present invention is described in detail below in conjunction with specific embodiments.

[0022] The degradation efficiency is calculated according to the following formula:

[0023] R = (C C0) / C0 * 100%

[0024] R: Degradation efficiency

[0025] C0: Initial concentration

[0026] C: Concentration after the degradation reaction.

[0027] Example 1

[0028] Disperse 8.6 mg of CeO2 in 20 ml of methanol, ultrasonicate for 30 min, then stir, and add 1 g of pvp during stirring. After 15 minutes, slowly add dropwise the Co(NO3)·6H2O solution (0.873 g, 5 ml). Then mix it with the prepared 2-methylimidazole solution (0.984 g, 5 ml). Stir for 1 h, let it stand for 12 h, collect and dry to obtain a white powder.

[0029] Weigh 10 mg of the catalyst and 30 mL of a 30 mg / L hexavalent chromium solution, stir for 60 min under dark conditions to reach the adsorption-desorption equilibrium, and reduce it under light and ultrasonic conditions for 40 min. Take samples every 5 min, measure the absorbance, calculate the degradation efficiency, and after analysis and calculation, the degradation efficiency is 93.0%.

[0030] Example 2

[0031] Compared with Example 1, the difference lies in that the dosage of CeO2 is changed to 4.3 mg during the preparation process, and other preparation methods are the same as those in Example 1.

[0032] The application method is the same as that in Example 1, and the reduction efficiency of hexavalent chromium at 30 mg / L in 30 mL is 87%.

[0033] Example 3

[0034] Compared with Example 1, the difference lies in that the dosage of CeO2 is changed to 17.2 mg during the preparation process, and other preparation methods are the same as those in Example 1.

[0035] The application method is the same as that in Example 1, and the reduction efficiency of the CeO2 / ZIF-67 catalyst prepared in Example 3 for hexavalent chromium at 30 mg / L in 30 mL is 77%.

[0036] Example 4

[0037] Compared with Example 1, the difference lies in that the dosage of CeO2 is changed to 34.4 mg during the preparation process, and other preparation methods are the same as those in Example 1.

[0038] The application method is the same as that in Example 1, and the reduction efficiency of the catalyst prepared in Example 4 for hexavalent chromium at 30 mg / L in 30 mL is 74%.

[0039] Example 5

[0040] Compared with Example 1, the difference lies in that the dosage of CeO2 is changed to 68.8 mg during the preparation process, and other preparation methods are the same as those in Example 1.

[0041] The application method is the same as that in Example 1, and the reduction efficiency of the catalyst prepared in Example 5 for hexavalent chromium at 10 mg / L in 30 mL is 51.0%.

[0042] Example 6

[0043] Compared with Example 1, the difference lies in that ultrasonic reduction is carried out for 40 min in a dark environment, and other preparation methods are the same as those in Example 1.

[0044] The application method is the same as that in Example 1, and the reduction efficiency of the catalyst prepared in Example 6 for hexavalent chromium at 30 mg / L in 30 mL is 58%.

[0045] Example 7

[0046] Compared with Example 1, the difference lies in that no ultrasonic treatment is carried out under light conditions, and other preparation methods are the same as those in Example 1.

[0047] The application method is the same as that in Example 1, and the reduction efficiency of the catalyst prepared in Example 7 for hexavalent chromium at 30 mg / L in 30 mL is 31%.

[0048] Example 8

[0049] Test the active groups in the piezoelectric degradation and reduction processes and conduct capture experiments. The specific steps are as follows:

[0050] Weigh 10 mg of the catalyst in Example 1 and 0.270 g of potassium persulfate, disperse them in 30 mL of 30 mg / L hexavalent chromium solution, stir for 60 min under dark conditions to reach adsorption-desorption equilibrium, reduce for 40 min under ultrasound, take samples every 5 min, calculate the degradation efficiency by measuring the absorbance, and the calculated degradation efficiency is 87% through analysis.

[0051] Example 9

[0052] Compared with Example 8, the difference is that 100 μL of isopropanol is added during the reaction process, and other preparation methods are the same as in Example 8. The reduction efficiency of the catalyst prepared in Example 1 for 30 mL of 30 mg / L hexavalent chromium is 80%.

[0053] Example 10

[0054] Compared with Example 8, the difference is that 0.18 g of p-benzoquinone is added during the reaction process, and other preparation methods are the same as in Example 8. The reduction efficiency of the catalyst prepared in Example 1 for 30 mL of 30 mg / L hexavalent chromium is 8%.

[0055] Control Example 1

[0056] Prepare a Co(NO3)2·6H2O solution (0.873 g, 5 ml). Then mix the prepared 2-methylimidazole solution (0.984 g, 5 ml) with it. Stir for 1 h, let it stand for 12 h, collect and dry to obtain white powder ZIF-67.

[0057] Weigh 10 mg of ZIF-67 and add it to 30 mL of 30 mg / L hexavalent chromium solution, stir for 60 min under dark conditions to reach adsorption-desorption equilibrium, degrade for 40 min under ultrasound, take samples every 5 min, calculate the degradation efficiency by measuring the absorbance, and the calculated degradation efficiency is 29% through analysis.

[0058] Control Example 2

[0059] Compared with Control Example 1, the difference is that 10 mg of CeO2 in Example 1 is weighed and added to 30 mL of 30 mg / L hexavalent chromium solution, and other preparation methods are the same as in Control Example 1.

[0060] The application method is the same as in Control Example 1. The reduction efficiency of the catalyst prepared in Control Example 2 for 30 mL of 30 mg / L hexavalent chromium is 2%.

[0061] Control Example 3

[0062] Compared with Example 1, the difference lies in that the obtained catalyst is calcined at 400 °C, and other preparation methods are the same as those in Example 1.

[0063] The application method is the same as that in Example 1. The reduction efficiency of the CeO2 / ZIF-67 catalyst prepared in Comparative Example 3 for 30 mL of 30 mg / L hexavalent chromium is 23%.

[0064] To further prove the stability of the CeO2 / ZIF-67 catalyst, XRD and XPS of the fresh and used catalysts of Example 1 were tested and compared. There is no obvious difference in the crystal structure between the recycled and fresh catalysts. The XPS spectrum shows that the surface chemical composition of the recycled CeO2 / ZIF-67 catalyst has not changed. The above results all prove that the CeO2 / ZIF-67 catalyst has good stability.

[0065] As described above, only the specific preferred embodiments of the present invention are provided, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and its concept of the present invention, makes equivalent substitutions or changes, and should be covered within the protection scope of the present invention.

Claims

1. Application of a CeO2 / ZIF-67 catalyst in piezoelectric catalysis, characterized in that: For piezoelectric reduction of hexavalent chromium, the application method includes: adding a catalyst to a hexavalent chromium salt solution, allowing the CeO2 / ZIF-67 catalyst to fully adsorb hexavalent chromium under dark conditions, and then performing a piezoelectric catalytic reaction; the piezoelectric catalytic reaction is carried out under light and ultrasonic conditions; The preparation method of the CeO2 / ZIF-67 catalyst includes the following steps: Disperse CeO2 in methanol, ultrasonicate until uniformly suspended and dispersed, then stir, add pvp during stirring, after uniformly dispersing, dropwise add Co(NO3)2 solution, then mix the prepared 2-methylimidazole solution with it, after fully stirring and dispersing, let it stand until fully reacted, collect and dry to obtain a white powdery CeO2 / ZIF-67 catalyst, and the molar ratio of CeO2 to the added Co ions is 1:30 - 120.

2. Use of the CeO2 / ZIF-67 catalyst according to claim 1 in piezoelectric catalysis, characterized in that: The molar ratio of CeO2 to the added Co ions is 1:

60.

3. Use of the CeO2 / ZIF-67 catalyst according to claim 1 in piezoelectric catalysis, characterized in that: The standing time is 12 - 14h.

4. Use of the CeO2 / ZIF-67 catalyst according to claim 1 in piezoelectric catalysis, characterized in that: The purification step in the preparation steps of the CeO2 / ZIF-67 catalyst includes: collecting the white precipitate by centrifugation, washing it several times with methanol and deionized water, and then drying it overnight in vacuum to obtain a white powder.

5. Use of the CeO2 / ZIF-67 catalyst according to claim 4 in piezoelectric catalysis, characterized in that: The drying temperature is 45 - 65 °C, and the drying time is 12 - 16h.

6. The application of the CeO2 / ZIF-67 catalyst according to claim 5 in piezoelectric catalysis, characterized in that: The piezoelectric catalytic ultrasonic power is 240W, and the piezoelectric catalytic reaction time is 40min.

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