In-situ titanium-doped ZIF-8 nanosol catalyst and its preparation method and application

Abstract

The present invention relates to an in-situ titanium-doped ZIF-8 nanosol catalyst, a preparation method, and an application thereof. The method comprises: dissolving a titanium source and a zinc source in a solvent, mixing, and obtaining a first solution; dissolving 2-methylimidazole in a solvent to obtain a second solution; adding the first solution to the second solution, and obtaining titanium-doped ZIF-8 after the reaction is complete; and dispersing the titanium-doped ZIF-8 in a dispersant to obtain a titanium-doped ZIF-8 nanosol. Compared with the prior art, the present invention improves the photocatalytic activity, thereby improving the catalytic efficiency and enhancing the degradation rate and degradation effect of organic pollutants.

Description

Technical Field

[0001] The invention belongs to the technical field of photocatalytic degradation of organic pollutants and relates to an in-situ titanium-doped ZIF-8 nanosol catalyst and a preparation method and application thereof. Background Art

[0002] With rapid economic development, rapid population growth, and advancing industrialization, environmental pollution is becoming increasingly severe. Traditional physical, chemical, and biological methods for treating environmental pollution suffer from high operating costs, low removal efficiency, and complex processes. Photocatalytic technology, with its relatively low cost, simple equipment, and easy operation, has been widely studied in environmental treatment.

[0003] Since 1972, when A. Fujishima and K. Honda (Fujishima, A. et al, Journal of Photochemistry and Photobiology C: Photochemistry Reviews 2000, 1(1), 1-21) discovered that titanium dioxide can decompose water into hydrogen and oxygen under light conditions, semiconductor metal oxides have attracted extensive research and application. In photocatalytic technology, photocatalysts can generate active species such as hydroxyl radicals and superoxide radicals under light irradiation, which can remove difficult-to-treat organic matter, pathogens, etc. Photocatalysis can widely remove persistent organic compounds and microorganisms in water, and is green, environmentally friendly and practical. As research continues to deepen, people have discovered some new photocatalytic materials, such as metal-organic frameworks (MOFs) and heteropoly acids.

[0004] MOFs are organic-inorganic network structures formed by covalent bonds between metal ions / metal clusters and organic ligands. Zeolitic imidazolate frameworks (ZIFs), a subcategory of MOFs, have been extensively studied in gas storage, molecular sieves, photocatalysis, and other fields due to their tunable pore size, chemical stability, and thermal stability. ZIF-8, a member of the zeolitic imidazolate family, is produced by reacting zinc as a metal source and 2-methylimidazole as a ligand in an organic solvent. ZIF-8 can maintain its crystallinity and porosity in various solutions, and its pore size and structure are easily adjustable, making it more susceptible to modification. Due to its unique chemical properties and physical structure, ZIF-8 provides a wide range of ideas for its application in the field of catalysis, making it a research hotspot.

[0005] Although the monometallic ZIF-8 material has high catalytic activity, its activity in most photocatalytic reactions is limited due to its large band gap (4.9-5.2 eV), which limits the application of ZIF-8 in the field of photocatalysis. By introducing transition metals into the framework, the photocatalytic activity of ZIF-8 can be enhanced, thereby producing a bimetallic catalytic system with heterogeneous active sites. Thanh et al. (Thanh, MT et al, Journal of Porous Materials 2017, 25 (3), 857-8691) introduced the iron source Fe 2+ Directly introduced into ZIF-8 to form Fe-ZIF-8, the material's absorption of visible light is increased, thereby increasing the material's photocatalytic activity and improving the photocatalytic efficiency. Mphuthi et al. (Mphuthi, LE et al, Journal of Inorganic and Organometallic Polymers and Materials 2022, 32(7), 2664-2678) replaced the metal centers in ZIF-8 and ZIF-67 by Ti(IV) exchange to form bimetallic Ti-ZIFs, and compared with ZIF-8 and ZIF-67, Ti-ZIFs showed higher photocatalytic activity.

[0006] Patent CN108855220A discloses a titanium dioxide-doped ZIF, its preparation method, and application. The preparation method comprises the following steps: mixing titanium dioxide nanoparticles with a solvent under ultrasonic conditions, then mixing with a cobalt source solution, adding 2-methylimidazole and the solvent under stirring conditions, stirring, performing a hydrothermal reaction, centrifuging, and drying to obtain the titanium dioxide-doped ZIF; the molar ratio of the titanium dioxide nanoparticles to the cobalt source is (1-2):4.

[0007] Patent CN109499620A discloses a method for preparing a TiO2 / ZIF-8 composite photocatalyst, comprising the following steps: placing a mixed solution of a soluble zinc salt, 2-methylimidazole and a first organic solvent in a high-pressure reactor for heating to react, deprotonating the 2-methylimidazole and self-assembling with zinc ions into ZIF-8, filtering, washing, drying, and then grinding to obtain ZIF-8 powder; allowing a hydrolyzable titanium source to undergo a hydrolysis reaction with water in a second organic solvent to obtain a first solution containing nano-titanium dioxide; concentrating the first solution to increase the concentration of the nano-titanium dioxide sol to obtain a second solution; and adding the ZIF-8 powder to the second solution, fully mixing through ultrasonic oscillation, filtering, washing, and drying to obtain the TiO2 / ZIF-8 composite photocatalyst.

[0008] The above patents all use a titanium source as a precursor of titanium dioxide and then introduce the ZIF-8 skeleton. The reaction steps are complicated and the reaction temperature is high. Summary of the Invention

[0009] The purpose of the present invention is to overcome at least one defect of the above-mentioned prior art and to provide an in situ titanium-doped ZIF-8 nanosol catalyst and its preparation method and application. The present invention improves the photocatalytic activity, thereby improving the catalytic efficiency and improving the degradation rate and degradation effect of organic pollutants.

[0010] The purpose of the present invention can be achieved by the following technical solutions:

[0011] One of the technical solutions of the present invention is to provide a method for preparing an in-situ titanium-doped ZIF-8 nanosol catalyst, the method comprising the following steps:

[0012] (1) dissolving a titanium source and a zinc source in a solvent respectively, and mixing them evenly after they are completely dissolved to obtain a first solution;

[0013] (2) dissolving 2-methylimidazole in a solvent to obtain a second solution;

[0014] (3) slowly adding the first solution dropwise to the second solution, obtaining a precipitate after the reaction is completed, and centrifuging and washing to obtain titanium-doped ZIF-8 (Ti-ZIF-8);

[0015] (4) Uniformly dispersing titanium-doped ZIF-8 in a dispersant to obtain titanium-doped ZIF-8 nanosol.

[0016] Furthermore, the preparation temperature is room temperature.

[0017] Furthermore, the reaction time in step (3) is 3-12 hours.

[0018] Furthermore, in step (1), the molar ratio of the titanium source to the zinc source is 1:(4-19).

[0019] Furthermore, in step (3), the molar ratio of 2-methylimidazole to the metal source is 8:1.

[0020] Furthermore, in step (1), the concentration of the titanium source is 0.004-0.016 mol / L, the concentration of the zinc source is 0.064-0.076 mol / L (concentration before mixing), and the concentration of 2-methylimidazole in step (2) is 0.30-0.36 mol / L.

[0021] Furthermore, in step (1), the titanium source includes titanium sulfate, titanium tetrachloride, isopropyl titanate, tetrabutyl titanate or tetraethyl titanate, and the zinc source includes zinc nitrate, zinc sulfate or zinc chloride.

[0022] Furthermore, the solvent and dispersant are both selected from one or two of water, ethanol, methanol and N,N-dimethylformamide (DMF).

[0023] One of the technical solutions of the present invention is to provide an in-situ titanium-doped ZIF-8 nano-sol catalyst prepared by the method described above, wherein the catalyst is in a sol state.

[0024] One of the technical solutions of the present invention is to provide an application of an in-situ titanium-doped ZIF-8 nanosol catalyst, wherein the catalyst is applied to photocatalytic degradation of organic pollutants.

[0025] As a preferred technical solution, the catalyst is used for photocatalytic degradation of organic dyes.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The present invention in situ dopes titanium atoms into the ZIF-8 lattice to form bimetallic catalytic active centers, providing more active sites, reducing the photogenerated electron-hole recombination rate, and increasing the specific surface area and pore size of the catalyst, providing more diffusion channels for reactants and products, thereby improving the catalytic efficiency of the system;

[0028] (2) The catalyst of the present invention is in a sol state. Since the sol particle size is small, the specific surface area is large, and it is easy to adsorb the substances to be degraded, the degradation ability can be improved;

[0029] (3) The present invention uses a simple method to prepare the Ti-ZIF-8 catalyst, the reaction temperature is room temperature, the reaction time is short, the preparation conditions are mild, the cost is low, and the composite catalyst has stable properties, a large surface area, and good dispersibility;

[0030] (4) The catalyst of the present invention has a good degradation rate and degradation effect on organic pollutants. It is a green and environmentally friendly composite catalyst that improves the absorption and utilization of ultraviolet light and accelerates the degradation rate of organic pollutants. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 X-ray diffraction patterns of the catalysts in Examples 1 to 3 of the present invention and the comparative example;

[0032] Figure 2 The infrared spectra of the catalysts in Examples 1 to 3 of the present invention and the comparative example are shown;

[0033] Figure 3 The ultraviolet diffuse reflectance spectra of the catalysts in Examples 1 to 3 of the present invention and the comparative example are shown;

[0034] Figure 4The graphs are for the degradation of methylene blue by the catalysts in Examples 1 to 3 of the present invention and the comparative example;

[0035] Figure 5 The kinetic curves of the catalysts for methylene blue in Examples 1 to 3 of the present invention and the comparative example are shown;

[0036] Figure 6 Graph showing the specific surface areas of the catalysts in Examples 1 to 3 of the present invention and the comparative example;

[0037] Figure 7 The pore size distribution diagram of the catalysts in Examples 1 to 3 of the present invention and the comparative example;

[0038] Figure 8 The following are scanning electron microscope images of the catalysts in Examples 1 to 3 of the present invention and the comparative example. DETAILED DESCRIPTION

[0039] The present invention is described in detail below with reference to specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0040] Unless otherwise specified, the equipment used in the following examples are all conventional equipment in the art; the reagents used are all commercially available products or prepared by conventional methods in the art unless otherwise specified. Anything not described in detail in the following examples can be achieved by conventional experimental means in the art.

[0041] In this embodiment, there is no particular limitation on the amount of the dispersant used, as long as it can completely disperse the precipitated product. The solid content of the sol obtained each time is different.

[0042] Example 1:

[0043] An in-situ titanium-doped ZIF-8 nanosol catalyst and a preparation method thereof, the specific steps are as follows:

[0044] 0.096 g (0.0004 mol) of titanium sulfate (Ti(SO4)2) and 1.07 g (0.0036 mol) of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) were respectively dissolved in 50 mL of ethanol, stirred at room temperature until completely dissolved and mixed evenly to prepare solution A; 2.6 g (0.032 mol) of 2-methylimidazole was dissolved in 100 mL of ethanol to prepare solution B; solution A was slowly added dropwise to solution B, and the reaction was stirred at room temperature for 6 hours. The molar ratio of titanium source, zinc source and 2-methylimidazole was 0.1:0.9:8. After the reaction, the white precipitate was collected by centrifugation and washed with ethanol 2-3 times to obtain 10% titanium-doped ZIF-8 (Ti-ZIF-8); 10% Ti-ZIF-8 was evenly dispersed in water to obtain 10% Ti-ZIF-8 sol.

[0045] An application and testing method of an in-situ titanium-doped ZIF-8 nanosol catalyst, the specific steps are as follows:

[0046] To 60 mL of methylene blue (MB, 45 mg / L) solution, 10% Ti-ZIF-8 sol (0.417 g / L, 25 mg of solid content of 10% Ti-ZIF-8 sol) was added. The mixture was stirred in the dark for 30 minutes. The reaction was carried out at room temperature using a photoreactor with a 30W LED lamp as the visible light source and a magnetic stirrer. 1 mL of sample was centrifuged and diluted threefold every 5 minutes, and then tested in a UV-visible spectrophotometer to verify the catalyst's degradation effect on MB.

[0047] Example 2:

[0048] An in-situ titanium-doped ZIF-8 nanosol catalyst and a preparation method thereof are substantially the same as those of Example 1, except that the amount of Ti(SO4)2 is 0.048 g (0.0002 mol), the amount of Zn(NO3)2·6H2O is 1.14 g (0.0038 mol), and the molar ratio of the titanium source, zinc source, and 2-methylimidazole is 0.05:0.95:8, to obtain a 5% Ti-ZIF-8 sol.

[0049] Example 3:

[0050] An in-situ titanium-doped ZIF-8 nanosol catalyst and a preparation method thereof are substantially the same as those of Example 1, except that the amount of Ti(SO4)2 is 0.192 g (0.0008 mol), the amount of Zn(NO3)2·6H2O is 0.96 g (0.0032 mol), and the molar ratio of the titanium source, zinc source, and 2-methylimidazole is 0.2:0.8:8, to obtain a 20% Ti-ZIF-8 sol.

[0051] Example 4:

[0052] An in-situ titanium-doped ZIF-8 nanosol catalyst and a preparation method thereof are basically the same as those in Example 1, except that the titanium source is tetraethyl titanate.

[0053] Example 5:

[0054] An in-situ titanium-doped ZIF-8 nanosol catalyst and a preparation method thereof are basically the same as those in Example 1, except that the titanium source is isopropyl titanate.

[0055] Example 6:

[0056] An in-situ titanium-doped ZIF-8 nanosol catalyst and a preparation method thereof are substantially the same as those in Example 1, except that the zinc source is zinc sulfate.

[0057] Example 7:

[0058] An in-situ titanium-doped ZIF-8 nanosol catalyst and a preparation method thereof are substantially the same as those in Example 1, except that the zinc source is zinc chloride.

[0059] Example 8:

[0060] An in-situ titanium-doped ZIF-8 nanosol catalyst and a preparation method thereof are substantially the same as those in Example 1, except that the titanium source, the zinc source, and 2-methylimidazole are separately dissolved in a 50% ethanol-water solution.

[0061] The application and testing methods of the catalysts prepared in Examples 4 to 8 are the same as those in Example 1, and the test results are not much different from those in Example 1.

[0062] Comparative Example:

[0063] A ZIF-8 nanosol catalyst and a preparation method thereof, the specific steps are as follows:

[0064] 3.0 g (0.01 mol) of Zn(NO3)2·6H2O was dissolved in 50 mL of ethanol, stirred at room temperature until completely dissolved and mixed evenly to prepare solution A; 6.5 g (0.08 mol) of 2-methylimidazole was dissolved in 100 mL of ethanol to prepare solution B; solution A was slowly added dropwise to solution B, and stirred at room temperature for 6 hours. The molar ratio of zinc source to 2-methylimidazole was 1:8. After the reaction was completed, the white precipitate was collected by centrifugation and washed with ethanol 2-3 times to obtain ZIF-8; ZIF-8 was evenly dispersed in water to obtain ZIF-8 sol.

[0065] An application of a ZIF-8 nanosol catalyst and a testing method thereof, the specific steps are as follows:

[0066] ZIF-8 sol (0.417 g / L, 25 mg of solid content of ZIF-8 sol) was added to 60 mL of MB (45 mg / L) solution and stirred in the dark for 30 minutes. The reaction was carried out at room temperature using a photoreactor with a 30W LED lamp as the visible light source and a magnetic stirrer. 1 mL of sample was centrifuged and diluted three times every 5 minutes, and tested in a UV-visible spectrophotometer to verify the catalyst's degradation effect on MB.

[0067] like Figure 1 As shown in Figure 3, the basic structure of ZIF-8 crystals does not change after titanium is doped into them.

[0068] like Figure 2 As shown, the infrared spectrum of Ti-ZIF-8 after titanium doping is similar to that of ZIF-8, indicating that the functional groups of ZIF-8 have not changed after titanium doping; and compared with ZIF-8, no new absorption peaks are generated, indicating that no new chemical bonds are generated during the doping process.

[0069] like Figure 3 As shown in the figure, Ti-ZIF-8 can improve the absorption of ultraviolet light by ZIF-8, thereby achieving a better catalytic degradation effect.

[0070] like Figure 4 As shown in the figure, the photocatalytic degradation efficiency of Ti-ZIF-8 is better than that of ZIF-8. After 30 minutes of illumination, the degradation efficiencies of 5%, 10%, and 20% Ti-ZIF-8 and ZIF-8 are 88.4%, 94.0%, 94.4%, and 70.1%, respectively. The degradation efficiency increases with the increase of titanium doping amount. However, when the titanium content is increased to 20%, the degradation efficiency does not increase significantly. The reason is that the active center gradually shifts from Zn 2+ Transfer to Ti 4+ On, and Ti 4+ The activity is not as good as Zn 2+ .

[0071] like Figure 5 As shown in the data, the photocatalytic reaction rate of Ti-ZIF-8 is better than that of ZIF-8. After 30 minutes of illumination, the rate constants of 5%, 10% and 20% Ti-ZIF-8 and ZIF-8 are 0.07187, 0.08669, 0.09368 and 0.03527, respectively. With the increase of titanium doping amount, the rate constant also increases.

[0072] like Figure 6As shown, both 10% Ti-ZIF-8 and ZIF-8 have microporous structures, and the adsorption capacity of Ti-ZIF-8 is slightly larger than that of ZIF-8, which improves the adsorption of MB by the catalyst and increases the contact area between the catalyst and MB, thereby improving the catalytic efficiency of the catalyst.

[0073] like Figure 7 As shown in the figure, the pore size of Ti-ZIF-8 is slightly larger than that of ZIF-8, which can provide more diffusion channels for reactants and products, thereby improving the catalytic efficiency.

[0074] like Figure 8 As shown in the figure, Ti-ZIF-8 has a relatively regular cubic structure, a relatively smooth surface, and an average particle size of 60 nm.

[0075] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A method for preparing an in-situ titanium-doped ZIF-8 nanosol catalyst, characterized in that: The method comprises the following steps: (1) dissolving a titanium source and a zinc source in a solvent respectively, and mixing them to obtain a first solution; (2) dissolving 2-methylimidazole in a solvent to obtain a second solution; (3) adding the first solution to the second solution, and obtaining titanium-doped ZIF-8 after the reaction is completed; (4) dispersing titanium-doped ZIF-8 in a dispersant to obtain titanium-doped ZIF-8 nanosol; The preparation temperature was room temperature; In step (1), the titanium source includes titanium sulfate, titanium tetrachloride, isopropyl titanate, tetrabutyl titanate or tetraethyl titanate, and the zinc source includes zinc nitrate, zinc sulfate or zinc chloride; Titanium atoms are in situ doped into the ZIF-8 lattice to form bimetallic catalytic active centers, providing more active sites, reducing the photogenerated electron-hole recombination rate, and increasing the specific surface area and pore size of the catalyst, providing more diffusion channels for reactants and products, thereby improving the catalytic efficiency of the system.

2. The method for preparing an in-situ titanium-doped ZIF-8 nanosol catalyst according to claim 1, wherein: The reaction time in step (3) is 3-12 h.

3. The method for preparing an in-situ titanium-doped ZIF-8 nanosol catalyst according to claim 1, wherein: In step (1), the molar ratio of the titanium source to the zinc source is 1:(4-19).

4. The method for preparing an in-situ titanium-doped ZIF-8 nanosol catalyst according to claim 1, wherein: In step (3), the molar ratio of 2-methylimidazole to the metal source is 8:

1.

5. The method for preparing an in-situ titanium-doped ZIF-8 nanosol catalyst according to claim 1, wherein: In step (1), the concentration of the titanium source is 0.004-0.016 mol / L, the concentration of the zinc source is 0.064-0.076 mol / L, and the concentration of 2-methylimidazole in step (2) is 0.30-0.36 mol / L.

6. The method for preparing an in-situ titanium-doped ZIF-8 nanosol catalyst according to claim 1, characterized in that: The solvent and dispersant are both selected from one or two of water, ethanol, methanol and N,N-dimethylformamide.

7. An in-situ titanium-doped ZIF-8 nanosol catalyst prepared by the method according to any one of claims 1 to 6, characterized in that: The catalyst is in a sol state.

8. Use of the in-situ titanium-doped ZIF-8 nanosol catalyst as claimed in claim 7, characterized in that: The catalyst is used for photocatalytic degradation of organic pollutants.

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