A ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material and its preparation method

Abstract

This invention discloses a ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material and its preparation method. First, TiO2 nanosheets and ZIF-8 nanoparticles are prepared. Then, AgBr particles are prepared. During the co-deposition process of AgBr particle preparation, the prepared TiO2 nanosheets are added first, so that the TiO2 nanosheets coat the surface of the AgBr particles, with the AgBr particles forming the core and the TiO2 nanosheets forming the inner shell structure coating the AgBr particles. Subsequently, ZIF-8 nanoparticles are added, surrounding and binding to the inner shell structure of the TiO2 nanosheets to form an outer shell structure. Finally, the prepared ZIF-8 / AgBr / TiO2 heterojunction forms a core-double-shell structure. The synergistic effect of the three components improves the photocatalytic efficiency and response rate.

Description

Technical Field

[0001] This invention relates to the field of photocatalytic materials, specifically to a ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material and its preparation method. Background Technology

[0002] As a key multifunctional material, Ag-based semiconductor photocatalysts possess suitable band gaps and can fully utilize solar energy. To date, AgBr, with its high visible light response, has been considered an excellent photocatalyst. However, AgBr itself is rarely used as a catalyst due to its poor light absorption and the easy recombination of photogenerated electron-hole pairs. To improve the photocatalytic activity of AgBr, selecting a suitable semiconductor to couple with it to form a heterojunction is one of the effective techniques for enhancing photocatalytic performance. Studies have shown that TiO2 is a good candidate for synthesizing semiconductor heterojunctions with higher photocatalytic activity.

[0003] Chinese patent CN104607214B ​​discloses a method for preparing a visible light-responsive AgBr / TiO2 catalyst. The method uses titanate, anhydrous ethanol, CTAB, silver nitrate, and deionized water as raw materials. First, titanate and anhydrous ethanol are mixed. Then, a mixed aqueous solution of CTAB and silver nitrate is added dropwise to the titanate solution. After thorough mixing, a hydrothermal reaction is carried out. The products obtained from the hydrothermal reaction are washed with deionized water and ethanol by centrifugation, dried, and finally calcined to obtain the AgBr / TiO2 catalyst. While the preparation method is simple, the AgBr / TiO2 photocatalyst exhibits a degradation rate of Rhodamine B of only 29.3%–73.2% after 120 min of photocatalytic degradation. This indicates that the catalytic efficiency and response rate of the AgBr / TiO2 catalyst still need improvement. Summary of the Invention

[0004] To improve the catalytic efficiency and response rate of photocatalysts, this application provides a ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material and its preparation method.

[0005] In a first aspect, the present invention provides a method for preparing a ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material, which is achieved by the following technical solution:

[0006] A method for preparing a ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material includes the following steps:

[0007] Preparation of TiO2 nanosheets: Tetrabutyl titanate and hydrofluoric acid were mixed and subjected to a hydrothermal reaction. After the reaction was completed, the precipitate was washed and dried to prepare TiO2 nanosheets.

[0008] Preparation of ZIF-8 nanoparticles: Zinc nitrate hexahydrate was dissolved in methanol to obtain solution A, and 2-methylimidazole was dissolved in methanol to obtain solution B. Then, solutions A and B were mixed and stirred to react. After the reaction was completed, the precipitate was collected by centrifugation. The precipitate was washed and dried to prepare ZIF-8 nanoparticles.

[0009] Preparation of ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material: The prepared TiO2 nanosheets were dispersed in AgNO3 solution, KBr solution was added, and the reaction was carried out. Then, the prepared ZIF-8 nanoparticles were added. After the reaction was completed, the precipitate was washed and dried to prepare the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material.

[0010] Optionally, in the step of preparing TiO2 nanosheets, the volume ratio of tetrabutyl titanate to hydrofluoric acid is 10-40 mL: 1-5 mL, the hydrothermal reaction temperature is 160-200 °C, and the time is 20-28 h.

[0011] Optionally, the prepared TiO2 nanosheets have a thickness of 5–15 nanometers and a particle size of 50–100 nanometers.

[0012] Optionally, in the step of preparing ZIF-8 nanoparticles, the mass-to-volume ratio of zinc nitrate hexahydrate to methanol in solution A is 1.5–2.0 g: 20–40 mL, the mass-to-volume ratio of 2-methylimidazole to methanol in solution B is 3.5–4.5 g: 20–40 mL, the volume ratio of solution A to solution B is 20–40 mL: 20–40 mL, the stirring speed of solution A and solution B is 400–2000 r / min, the stirring time is 1–3 h, the precipitation time is 2–12 h, and the centrifugation speed is 2000–10000 rpm.

[0013] Optionally, the particle size of the prepared ZIF-8 nanoparticles is 300–500 nanometers.

[0014] Optionally, in the step of preparing the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material, the concentration of AgNO3 solution is 5-12 mg / mL, the concentration of KBr solution is 10-15 mg / mL, the volume ratio of KBr solution to AgNO3 solution is 10-30 mL: 20-60 mL, and the mass-volume ratio of ZIF-8 nanoparticles, TiO2 nanosheets and AgNO3 solution is 20-200 mg: 50-100 mg: 20-60 mL.

[0015] Optionally, in the prepared ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material, the mass ratio of ZIF-8, AgBr and TiO2 is 1~6:8~12:1~6.

[0016] Optionally, in the step of preparing the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalyst material, the mass ratio of ZIF-8, AgBr and TiO2 is 1 to 5:10:2.

[0017] Optionally, the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material has a core-double shell structure, with AgBr particles forming the core, TiO2 nanosheets coating the surface of AgBr particles to form the inner shell, and ZIF-8 nanoparticles surrounding and binding to the TiO2 inner shell to form the outer shell. The particle size ratio of ZIF-8, AgBr and TiO2 is 300-500 nm: 1000-2000 nm: 50-100 nm.

[0018] Secondly, this application provides a ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material, which is obtained by the aforementioned preparation method of the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material.

[0019] In summary, this application includes at least one of the following beneficial technical effects:

[0020] 1. The preparation method of ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material provided by the present invention is easy to control and simple to prepare.

[0021] 2. The method for preparing the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material provided by the present invention first prepares TiO2 nanosheets and ZIF-8 nanoparticles, then prepares AgBr particles. During the co-deposition process of preparing AgBr particles, the prepared TiO2 nanosheets are first added, so that the TiO2 nanosheets coat the surface of the AgBr particles, with the AgBr particles forming the core and the TiO2 nanosheets forming the inner shell structure coating the AgBr particles. Subsequently, ZIF-8 nanoparticles are added, and the ZIF-8 nanoparticles surround and bind to the TiO2 inner shell structure. The resulting ZIF-8 / AgBr / TiO2 heterojunction forms a core-double-shell structure. The ZIF-8 nanoparticles in the outer shell are porous, possessing excellent specific surface area and adsorption capacity, enabling them to rapidly capture and adsorb pollutants, providing numerous active sites, and exhibiting transparency and photocatalytic activity. Combined with TiO2 to form a heterojunction structure, the Ag ions in the internal AgBr particles can rapidly transfer charge carriers and generate a plasmonic resonance effect, suppressing electron-hole recombination and improving charge separation efficiency. The synergistic effect of these three elements enhances photocatalytic efficiency and response rate.

[0022] 3. The ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material provided by this invention has a specific ratio of mass and particle size of ZIF-8 nanoparticles, AgBr particles, and TiO2 nanosheets. When the mass ratio of ZIF-8 nanoparticles, AgBr particles, and TiO2 nanosheets is 1-5:10:2, and the particle size ratio is 300-500 nm:1000-2000 nm:50-100 nm, better photocatalytic efficiency and response rate are obtained. Taking 0.05 g of the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material prepared by this invention and adding it to 100 ml of a 20 mg / L Rhodamine B solution for photocatalytic degradation, the degradation rate can reach more than 81.4% after 30 min of light irradiation, more preferably 86.9%, and most preferably 93.2%. Attached Figure Description

[0023] Figure 1 This is an X-ray diffraction pattern of the TiO2 powder prepared in Example 1;

[0024] Figure 2 This is a transmission electron microscope (TEM) image of the TiO2 powder prepared in Example 1;

[0025] Figure 3 This is an X-ray diffraction pattern of the ZIF-8 powder prepared in Example 1;

[0026] Figure 4 Here is a scanning electron microscope image of the ZIF-8 powder prepared in Example 1;

[0027] Figure 5 This is the X-ray diffraction pattern of the ZIF-8 / AgBr / TiO2 composite material prepared in Example 1;

[0028] Figure 6 This is a scanning electron microscope image of the ZIF-8 / AgBr / TiO2 composite material prepared in Example 1;

[0029] Figure 7 The degradation curve of Rhodamine B by the photocatalyst in Example 1 under simulated visible light irradiation is shown.

[0030] Figure 8 The degradation curve of Rhodamine B by the photocatalyst in Example 2 under simulated visible light irradiation is shown.

[0031] Figure 9 The degradation curve of Rhodamine B by the photocatalyst in Example 3 under simulated visible light irradiation is shown.

[0032] Figure 10 This is a scanning electron microscope image of the ZIF-8 powder prepared in Comparative Example 1.

[0033] Figure 11This is a scanning electron microscope image of the ZIF-8 / AgBr / TiO2 composite material prepared in Comparative Example 2.

[0034] Figure 12 This is a scanning electron microscope image of the ZIF-8 / AgBr / TiO2 composite material prepared in Comparative Example 3.

[0035] Figure 13 This is a scanning electron microscope image of the ZIF-8 / AgBr / TiO2 composite material prepared in Comparative Example 4.

[0036] Figure 14 This is a scanning electron microscope image of the ZIF-8 / AgBr / TiO2 composite material prepared in Comparative Example 5. Detailed Implementation

[0037] AgBr exhibits high visible light response. However, due to its poor absorption of visible light and the easy recombination of photogenerated electron-hole pairs, AgBr is rarely used as a standalone catalyst. To improve the photocatalytic activity of AgBr, coupling it with a suitable semiconductor to form a heterojunction is an effective technique. Studies have shown that TiO2 is a good candidate for synthesizing semiconductor heterojunctions with higher photocatalytic activity. During long-term research, the inventors discovered that the lack of visible light activity in TiO2 leads to low photocatalytic performance and response rate in AgBr / TiO2 composites. To further improve the photocatalytic activity and response rate of AgBr / TiO2 materials, the inventors constructed a ZIF-8 / AgBr / TiO2 multi-element heterojunction photocatalyst by adding a zeolite imidazole ester framework 8 (ZIF-8) to AgBr / TiO2 materials. Through long-term research, the inventors of this invention discovered that TiO2 nanosheets with specific geometric dimensions prepared by a specific preparation process can achieve excellent matching and combination with AgBr particles of specific particle size, exhibiting good dispersibility and large contact area. ZIF-8 has high specific surface area and adsorption performance, and can also improve the charge separation efficiency when combined with AgBr / TiO2. The resulting ternary heterogeneous composite photocatalyst has good photocatalytic activity and a fast catalytic response rate. Furthermore, the inventors surprisingly discovered that the multi-component heterojunction on the aforementioned specific structure, under specific mass and particle size ratios of ZIF-8, AgBr, and TiO2, exhibits optimal photocatalytic activity and response rate. The ternary heterocomposite photocatalyst forms a specific core-double-shell structure, with AgBr particles forming the core, TiO2 nanosheets coating the surface of the AgBr particles to form the inner shell, and ZIF-8 nanoparticles surrounding and binding to the TiO2 inner shell to form the outer shell. ZIF-8 nanoparticles have a porous structure with excellent specific surface area and adsorption capacity, enabling them to rapidly capture and adsorb pollutants, providing a large number of active sites, and possessing transparency and photocatalytic activity. When combined with TiO2 to form a heterojunction structure, the Ag ions of the internal AgBr particles can rapidly transfer electrons and generate a plasmonic resonance effect, inhibiting electron-hole recombination and improving charge separation efficiency. The synergistic effect of the three enhances photocatalytic efficiency and response rate.

[0038] Specifically, this invention provides a method for preparing a ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material, comprising the following steps:

[0039] Preparation of TiO2 nanosheets: Tetrabutyl titanate and hydrofluoric acid were mixed and subjected to a hydrothermal reaction. After the reaction was completed, the precipitate was washed and dried to prepare TiO2 nanosheets.

[0040] Preparation of ZIF-8 nanoparticles: Zinc nitrate hexahydrate was dissolved in methanol to obtain solution A, and 2-methylimidazole was dissolved in methanol to obtain solution B. Then, solutions A and B were mixed and stirred to react. After the reaction was completed, the precipitate was collected by centrifugation. The precipitate was washed and dried to prepare ZIF-8 nanoparticles.

[0041] Preparation of ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material: The prepared TiO2 nanosheets were dispersed in AgNO3 solution, KBr solution was added, and the reaction was carried out. Then, the prepared ZIF-8 nanoparticles were added. After the reaction was completed, the precipitate was washed and dried to prepare the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material.

[0042] In some embodiments of the present invention, in the step of preparing TiO2 nanosheets, the volume ratio of tetrabutyl titanate to hydrofluoric acid is 10-40 mL: 1-5 mL, preferably 20-30 mL: 2-4 mL; the hydrothermal reaction temperature is 160-200 °C, preferably 170-190 °C; and the time is 20-28 h, preferably 22-26 h.

[0043] In some embodiments of the present invention, the prepared TiO2 nanosheets have a thickness of 5–15 nanometers and a particle size of 50–100 nanometers.

[0044] In some embodiments of the present invention, in the step of preparing ZIF-8 nanoparticles, the mass-to-volume ratio of zinc nitrate hexahydrate to methanol in solution A is 1.5–2.0 g: 20–40 mL, preferably 1.7–1.8 g: 25–35 mL; the mass-to-volume ratio of 2-methylimidazole to methanol in solution B is 3.5–4.5 g: 20–40 mL, preferably 3.8–4.1 g: 25–35 mL; the volume ratio of solution A to solution B is 20–40 mL: 20–40 mL, preferably 25–35 mL: 25–35 mL; the stirring speed for the reaction of solution A and solution B is 400–2000 r / min, preferably 600–1000 r / min; the stirring time is 1–3 h; the precipitation time is 2–12 h, preferably 3–6 h; and the centrifugation rate is 2000–10000 rpm, preferably 5000–9000 rpm.

[0045] In some embodiments of the present invention, the particle size of the prepared ZIF-8 nanoparticles is 300-500 nanometers.

[0046] In some embodiments of the present invention, in the step of preparing the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material, the concentration of AgNO3 solution is 5-12 mg / mL, preferably 8-10 mg / mL; the concentration of KBr solution is 10-15 mg / mL, preferably 11-13 mg / mL; the volume ratio of KBr solution to AgNO3 solution is 10-30 mL:20-60 mL, preferably 15-25 mL:35-45 mL; the mass-volume ratio of ZIF-8 nanoparticles, TiO2 nanosheets and AgNO3 solution is 20-200 mg:50-100 mg:20-60 mL, preferably 35-200 mg:60-90 mg:35-45 mL.

[0047] In some embodiments of the present invention, the mass ratio of ZIF-8, AgBr and TiO2 in the prepared ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material is 1-6:8-12:1-6.

[0048] In some embodiments of the present invention, in the step of preparing ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material, the mass ratio of ZIF-8, AgBr and TiO2 is 1 to 5:10:2.

[0049] In some embodiments of the present invention, the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material has a core-double shell structure, with AgBr particles forming the core, TiO2 nanosheets coating the surface of the AgBr particles to form the inner shell, and ZIF-8 nanoparticles surrounding and bonding to the TiO2 inner shell to form the outer shell. The particle size ratio of ZIF-8, AgBr and TiO2 is 300-500 nm: 1000-2000 nm: 50-100 nm.

[0050] This invention provides a ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material, which is obtained by the aforementioned preparation method of the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material.

[0051] Unless otherwise specified, all raw materials used in this invention are commercially available.

[0052] The present invention will be further described in detail below with reference to the embodiments.

[0053] Example 1

[0054] Preparation of TiO2 nanosheets: 25 mL of tetrabutyl titanate was placed in a 100 mL reaction vessel. Then, while stirring at 800 r / min, 3 mL of hydrofluoric acid (40 wt%) was added dropwise. Stirring was continued at the same speed for 15 min until homogeneous. The reaction vessel was then placed in a forced-air drying oven for hydrothermal reaction at 180℃ for 24 h. After the oven cooled to room temperature, the reaction vessel was opened, and the upper yellow liquid was removed. The precipitate was then washed three times with anhydrous ethanol and deionized water, respectively. Finally, the washed precipitate was dried to constant weight to obtain the sample powder.

[0055] Figure 1 The X-ray diffraction pattern of the sample powder obtained in this step is shown below. Figure 1 The X-ray diffraction characteristic peaks correspond to TiO2, confirming that the prepared sample powder is TiO2 powder. Figure 2 This is a transmission electron microscope (TEM) image of the sample powder from this step. Figure 2 It can be seen that the TiO2 powder has a regular nanosheet structure, with a thickness of 5-15 nanometers and a particle size of 50-100 nanometers.

[0056] Preparation of ZIF-8 nanoparticles: 1.76 g of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) was dissolved in 30 mL of methanol (purity ≥99.9%) to obtain solution A. 3.89 g of 2-methylimidazole (purity 99wt%) was dissolved in 30 mL of methanol (purity ≥99.9%) to obtain solution B. Solution B was then added to solution A and stirred at 800 r / min for 2 hours. After stirring, the mixture was allowed to precipitate for 4 hours. The white powder precipitate was collected by centrifugation at 8000 rpm. The precipitate was washed three times with methanol and three times with deionized water, and then dried to constant weight to obtain the sample powder.

[0057] Figure 3 The X-ray diffraction pattern of the sample powder obtained in this step is shown below. Figure 3 The X-ray diffraction characteristic peaks can be seen to correspond to ZIF-8, which confirms that the prepared sample powder is ZIF-8 powder. Figure 4 Here is a scanning electron microscope (SEM) image of the sample powder from this step. Figure 4 It can be seen that ZIF-8 powder has a regular nanoparticle structure, and the particle size of ZIF-8 nanoparticles is 300-500 nanometers.

[0058] Preparation of ZIF-8 / AgBr / TiO2 heterojunction composite photocatalyst material: 0.3397 g AgNO3 was placed in 40 mL of deionized water and stirred until homogeneous to prepare an AgNO3 solution with a concentration of 8.5 mg / mL. 0.238 g KBr was placed in 20 mL of deionized water and stirred until homogeneous to prepare a KBr solution with a concentration of 11.9 mg / mL. 0.0751 g of the prepared TiO2 nanosheets were dispersed in the AgNO3 solution and stirred at 800 r / min for 30 min. Then, the KBr solution was added dropwise to the AgNO3 solution, and the mixture was stirred in the dark for 30 min at a stirring speed of 800 r / min. The mixture was then sonicated for 30 min at a sonication frequency of 40 kHz. Finally, 0.11265 g of the prepared material was added. ZIF-8 nanoparticles were stirred for 30 minutes at a speed of 800 r / min, followed by sonication for another 30 minutes. After the stirring was completed, the precipitate was washed three times with deionized water and dried to constant weight to prepare a ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material, wherein the mass ratio of ZIF-8, AgBr and TiO2 was 3:10:2.

[0059] Figure 5 The X-ray diffraction pattern of the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalyst material in this step is shown below. Figure 5 It can be seen from the data that the diffraction characteristic peaks of this X-ray correspond to ZIF-8, AgBr and TiO2, respectively. Figure 6 This is a scanning electron microscope (SEM) image of the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalyst material from this step. Figure 6 As can be seen, the structure of the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalyst material is a core-double shell structure. AgBr particles form the core, TiO2 nanosheets coat the surface of AgBr particles to form the inner shell, and ZIF-8 nanoparticles surround and bind to the TiO2 inner shell to form the outer shell. The particle size ratio of ZIF-8, AgBr and TiO2 is 300-500 nm: 1000-2000 nm: 50-100 nm.

[0060] Catalytic performance test:

[0061] A photocatalytic experiment was conducted on 100 ml of 20 mg / L Rhodamine B using 0.05 g of photocatalyst. The degradation rate was tested by stirring the solution in the dark for 45 min to reach adsorption equilibrium, and then measuring the absorbance using a UV-Vis spectrophotometer. The absorbance at this point was recorded as C0. Samples were taken every 5 min under 300 W xenon lamp (AM1.5) irradiation to simulate visible light, and the absorbance C was measured. The concentration change was analyzed in conjunction with a standard curve to obtain the degradation curve.

[0062] To facilitate comparison, the specific preparation methods for AgBr and AgBr / TiO2 composite materials are as follows:

[0063] Preparation of AgBr: 0.3397 g AgNO3 was placed in 40 mL of deionized water and stirred until homogeneous to prepare AgNO3 solution. 0.238 g KBr was placed in 20 mL of deionized water and stirred until homogeneous to prepare KBr solution. Then, the KBr solution was added dropwise to the AgNO3 solution. The mixture was stirred in the dark for 30 min at a stirring speed of 800 r / min, followed by sonication for 30 min at a sonic frequency of 40 kHz. After the treatment, the precipitate was washed three times with deionized water and dried to constant weight to obtain AgBr.

[0064] Preparation of AgBr / TiO2 composite material: 0.3397 g AgNO3 was placed in 40 mL of deionized water and stirred until homogeneous to prepare AgNO3 solution. 0.238 g KBr was placed in 20 mL of deionized water and stirred until homogeneous to prepare KBr solution. 0.0751 g of the prepared TiO2 nanosheets were dispersed in the AgNO3 solution and stirred at 800 r / min for 30 min. Then, the KBr solution was added dropwise to the AgNO3 solution and stirred in the dark for 30 min at a stirring speed of 800 r / min. The mixture was then sonicated for 30 min at a sonic frequency of 40 kHz. After the treatment, the precipitate was washed three times with deionized water and dried to constant weight to obtain AgBr / TiO2 composite material with a mass ratio of AgBr to TiO2 of 10:2.

[0065] The catalytic performance of the prepared ZIF-8, AgBr, TiO2, AgBr / TiO2 composite materials and ZIF-8 / AgBr / TiO2 heterojunction composite photocatalysts were tested, and the degradation curves were obtained as follows: Figure 7 As shown, from Figure 7 It can be seen that the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalyst material can achieve a degradation rate of 93.2% for Rhodamine B after 30 minutes of degradation, while the degradation rates of ZIF-8, AgBr, TiO2, and AgBr / TiO2 composite materials are 39.3%, 43%, 28.1%, and 70.5%, respectively.

[0066] Example 2

[0067] The difference between Example 2 and Example 1 is that in the step of preparing ZIF-8 / AgBr / TiO2 composite material in Example 2, the amount of ZIF-8 nanoparticles added is 0.03755g, that is, the mass ratio of ZIF-8, AgBr and TiO2 is 1:10:2, and the rest of the preparation steps are the same as in Example 1.

[0068] The degradation curves of the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalyst material prepared in Example 2 were measured as follows: Figure 8 As shown, from Figure 8 As can be seen from Example 2, the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material prepared can achieve a degradation rate of 81.4% of Rhodamine B in 30 minutes, which is significantly higher than that of ZIF-8, AgBr, TiO2 and AgBr / TiO2 composite materials.

[0069] Example 3

[0070] The difference between Example 3 and Example 1 is that in the step of preparing ZIF-8 / AgBr / TiO2 composite material in Example 3, the amount of ZIF-8 nanoparticles added is 0.18775g, that is, the mass ratio of ZIF-8, AgBr and TiO2 is 5:10:2, and the rest of the preparation steps are the same as in Example 1.

[0071] The degradation curve of the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalyst material prepared in Example 3 was measured as follows: Figure 9 As shown, from Figure 9 As can be seen from Example 3, the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material can achieve a degradation rate of 86.9% for Rhodamine B after 30 minutes of degradation, which is significantly higher than that of ZIF-8, AgBr, TiO2 and AgBr / TiO2 composite materials.

[0072] Comparative Example 1:

[0073] The difference between Comparative Example 1 and Example 2 is as follows: In Comparative Example 1, after stirring the reaction for 2 hours, no precipitation occurred. The white powder precipitate was collected by centrifugation at 8000 rpm. The precipitate was washed three times each with methanol and deionized water, and then dried to constant weight to obtain the sample powder. The remaining preparation steps were the same as in Example 2. The scanning electron microscope image of the ZIF-8 nanoparticles is shown below. Figure 10 As shown, the particle size of ZIF-8 nanoparticles is 300–900 nm. The particle size ratio of ZIF-8, AgBr, and TiO2 in the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalyst material prepared in Comparative Example 1 is 300–900 nm: 1000–2000 nm: 50–100 nm.

[0074] Comparative Example 2:

[0075] The steps for preparing TiO2 nanosheets and ZIF-8 nanoparticles in Comparative Example 2 were the same as in Example 2, except that the steps for preparing the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalyst material were as follows: 0.3397 g of AgNO3 was placed in 40 mL of deionized water and stirred until homogeneous to prepare an AgNO3 solution with a concentration of 8.5 mg / mL. 0.238 g of KBr was placed in 20 mL of deionized water and stirred until homogeneous to prepare a KBr solution with a concentration of 11.9 mg / mL. Subsequently, the KBr solution was added dropwise to the AgNO3 solution, and the mixture was stirred in the dark for 30 min at a stirring speed of 800 r / min. Then, it was sonicated for 30 min at a sonication frequency of 40 kHz. Finally, 0.0751 g of the prepared material was taken... TiO2 nanosheets and 0.03755g ZIF-8 nanoparticles were dispersed in the mixed solution, stirred at 800r / min for 30min, and then sonicated for 30min. After the mixture was stirred, the precipitate was washed three times with deionized water and dried to constant weight to prepare the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material, wherein the mass ratio of ZIF-8, AgBr and TiO2 was 1:10:2.

[0076] Figure 11 This is a scanning electron microscope (SEM) image of the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalyst material from this step. Figure 11 It is not clear whether TiO2 nanosheets are coated on the surface of AgBr particles.

[0077] Comparative Example 3:

[0078] The steps for preparing TiO2 nanosheets and ZIF-8 nanoparticles in Comparative Example 3 were the same as in Example 2, except that the steps for preparing the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalyst material were as follows: 0.3397 g of AgNO3 was placed in 40 mL of deionized water and stirred until homogeneous to prepare an AgNO3 solution with a concentration of 8.5 mg / mL. 0.238 g of KBr was placed in 20 mL of deionized water and stirred until homogeneous to prepare a KBr solution with a concentration of 11.9 mg / mL. Subsequently, the KBr solution was added dropwise to the AgNO3 solution, and the mixture was stirred in the dark for 30 min at a stirring speed of 800 r / min, followed by ultrasonic treatment for 30 min at a ultrasonic frequency of 40 kHz. Then, 0.0751 g of the prepared TiO2 nanosheets were dispersed in the mixed solution, stirred at 800 r / min for 30 min, and ultrasonicated for another 30 min. Finally, 0.03755 g of the prepared... ZIF-8 nanoparticles were added to the mixed solution, stirred at 800 r / min for 30 min, and then sonicated for another 30 min. After the reaction, the precipitate was washed three times with deionized water and dried to constant weight to prepare the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material, wherein the mass ratio of ZIF-8, AgBr and TiO2 was 1:10:2.

[0079] Figure 12 This is a scanning electron microscope (SEM) image of the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalyst material from this step. Figure 12 The morphology of the ZIF-8 sample could not be clearly observed, and the distribution of TiO2 nanosheets was not uniform.

[0080] Comparative Example 4:

[0081] The steps for preparing TiO2 nanosheets and ZIF-8 nanoparticles in Comparative Example 4 were the same as in Example 2, except that the steps for preparing the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalyst material were as follows: 0.3397 g of AgNO3 was placed in 40 mL of deionized water and stirred until homogeneous to prepare an AgNO3 solution with a concentration of 8.5 mg / mL. 0.238 g of KBr was placed in 20 mL of deionized water and stirred until homogeneous to prepare a KBr solution with a concentration of 11.9 mg / mL. Subsequently, the KBr solution was added dropwise to the AgNO3 solution, and the mixture was stirred in the dark for 30 min at a stirring speed of 800 r / min. Then, it was sonicated for 30 min at a sonication frequency of 40 kHz. Then, 0.03755 g of the prepared ZIF-8 nanoparticles were dispersed in the mixed solution, stirred at 800 r / min for 30 min, and sonicated for another 30 min. Finally, 0.0751 g of the prepared ZIF-8 / AgBr / TiO2 heterojunction composite photocatalyst material was dispersed in the mixed solution. TiO2 nanosheets were added to the mixed solution, stirred at 800 r / min for 30 min, and then sonicated for another 30 min. After the reaction, the precipitate was washed three times with deionized water and dried to constant weight to prepare the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material, wherein the mass ratio of ZIF-8, AgBr and TiO2 was 1:10:2.

[0082] Figure 13 This is a scanning electron microscope (SEM) image of the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalyst material from this step. Figure 13 Aggregation of TiO2 nanosheets was observed.

[0083] Comparative Example 5:

[0084] Preparation of ZIF-8 / AgBr / TiO2 heterojunction composite photocatalyst material: 0.3397 g AgNO3 was placed in 40 mL of deionized water and stirred until homogeneous to prepare an AgNO3 solution with a concentration of 8.5 mg / mL. 0.238 g KBr was placed in 20 mL of deionized water and stirred until homogeneous to prepare a KBr solution with a concentration of 11.9 mg / mL. 0.03755 g of the prepared ZIF-8 nanoparticles were dispersed in the AgNO3 solution and stirred at 800 r / min for 30 min. Then, the KBr solution was added dropwise to the AgNO3 solution. The mixture was stirred in the dark for 30 min at a stirring speed of 800 r / min, followed by ultrasonic treatment for 30 min at a frequency of 40 kHz. Finally, 0.0751 g of the prepared... TiO2 nanosheets were stirred for 30 minutes at a speed of 800 r / min, followed by sonication for another 30 minutes. After the stirring was completed, the precipitate was washed three times with deionized water and dried to constant weight to prepare the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material, wherein the mass ratio of ZIF-8, AgBr and TiO2 was 1:10:2.

[0085] Figure 14 This is a scanning electron microscope (SEM) image of the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalyst material from this step. Figure 14 TiO2 nanosheets and ZIF-8 particles are not clearly visible in the image.

[0086] The photocatalytic performance of the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic materials prepared in Comparative Examples 1-5 was tested using the same method as in Example 2. The degradation rate of Rhodamine B by the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic materials prepared in Comparative Examples 1-5 after 30 min of degradation was found to be less than the degradation rate of 81.4% in Example 2.

[0087] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A method for preparing a ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material, characterized in that, Includes the following steps: Preparation of TiO2 nanosheets: Tetrabutyl titanate and hydrofluoric acid were mixed and subjected to a hydrothermal reaction. After the reaction was completed, the precipitate was washed and dried to prepare TiO2 nanosheets. The thickness of the prepared TiO2 nanosheets was 5-15 nm and the particle size was 50-100 nm. Preparation of ZIF-8 nanoparticles: Zinc nitrate hexahydrate was dissolved in methanol to obtain solution A, and 2-methylimidazole was dissolved in methanol to obtain solution B. Then, solutions A and B were mixed and stirred to react. After the reaction was completed, the precipitate was collected by centrifugation. The precipitate was washed and dried to prepare ZIF-8 nanoparticles. The particle size of the prepared ZIF-8 nanoparticles is 300~500 nanometers; Preparation of ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material: The prepared TiO2 nanosheets were dispersed in AgNO3 solution, KBr solution was added, and the reaction was carried out. Then, the prepared ZIF-8 nanoparticles were added. After the reaction was completed, the precipitate was washed and dried to prepare ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material. In the steps of preparing the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material, the concentration of AgNO3 solution was 8.5 mg / mL, the concentration of KBr solution was 11.9 mg / mL, the volume ratio of KBr solution to AgNO3 solution was 20 mL:40 mL, and the mass-volume ratio of ZIF-8 nanoparticles, TiO2 nanosheets and AgNO3 solution was 112.65 mg:75.1 mg:40 mL. In the prepared ZIF-8 / AgBr / TiO2 heterojunction composite photocatalyst material, the mass ratio of ZIF-8, AgBr and TiO2 is 3:10:2; The ZIF-8 / AgBr / TiO2 heterojunction composite photocatalyst material has a core-double-shell structure. AgBr particles form the core, TiO2 nanosheets coat the surface of AgBr particles to form the inner shell, and ZIF-8 nanoparticles surround and bind to the TiO2 inner shell to form the outer shell. The particle size ratio of ZIF-8, AgBr and TiO2 is 300~500nm:1000~2000nm:50~100nm.

2. The preparation method of the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material according to claim 1, characterized in that, In the preparation of TiO2 nanosheets, the volume ratio of tetrabutyl titanate to hydrofluoric acid was 25 mL: 3 mL, the hydrothermal reaction temperature was 180 °C, and the reaction time was 24 h.

3. The preparation method of the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material according to claim 1, characterized in that, In the steps for preparing ZIF-8 nanoparticles, the mass-to-volume ratio of zinc nitrate hexahydrate to methanol in solution A was 1.76 g:30 mL, the mass-to-volume ratio of 2-methylimidazole to methanol in solution B was 3.89 g:30 mL, the volume ratio of solution A to solution B was 30 mL:30 mL, the stirring speed of solutions A and B was 800 r / min, the stirring time was 2 h, the precipitation time was 4 h, and the centrifugation speed was 8000 rpm.

4. A ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material, obtained by the preparation method of the ZIF-8 / AgBr / TiO2 heterojunction composite photocatalytic material according to any one of claims 1 to 3.

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