Bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst and preparation method and application thereof

Abstract

This invention discloses a bismuth oxychloride / zirconium-based metal-organic framework (MOF) composite photocatalyst, its preparation method, and its applications. The preparation method includes: mixing zirconium salt, bismuth salt, terephthalic acid, and an organic solvent and carrying out a solvothermal reaction to obtain the bismuth oxychloride / zirconium-based MOF composite photocatalyst. The bismuth oxychloride / zirconium-based MOF composite photocatalyst prepared by this invention via a one-step solvent method possesses advantages such as large specific surface area, high porosity, numerous active sites, fast photogenerated carrier separation and migration rates, high photocatalytic activity, high stability, and high photocatalytic efficiency, making it widely applicable for treating heavy metal pollution in the environment. Furthermore, the preparation method of this invention greatly simplifies the preparation process and improves preparation efficiency, offering advantages such as convenient synthesis, simple operation, and no secondary pollution to the environment. It meets practical production needs, is suitable for large-scale preparation, and is convenient for industrial application.

Description

Technical Field

[0001] This invention belongs to the field of photocatalysis, specifically relating to a bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst, its preparation method, and its application. Background Technology

[0002] Compared to wastewater contaminated with organic pollutants, the treatment of wastewater contaminated with heavy metals is far more difficult. Heavy metal pollutants are difficult to biodegrade but can accumulate in living tissues and be passed through the food chain, making it difficult to effectively treat water bodies contaminated with heavy metals in a short period. Wastewater contaminated with heavy metals, especially chromium, is particularly difficult to treat. Chromium salts are a major product series in my country's inorganic chemical industry, widely used in electroplating of metal surfaces, metallurgical processes, textile industry, wood preservation, and chemical synthesis. For example, in the leather industry, the tanning process mainly uses chromium tanning. However, in this method, only about 60% of the chromium reacts with the leather, while about 40% is discharged, resulting in a large amount of chromium-containing wastewater. In natural aquatic environments, chromium compounds mainly exist in two forms: high-valence Cr(VI) and low-valence Cr(III). Cr(VI) is a highly water-soluble (approximately 1680 g / L), highly toxic, and highly mobile heavy metal ion that can be transmitted through drinking water and the food chain, and is easily absorbed by the human body. Cr(III), on the other hand, is less toxic and readily precipitates from water as Cr(OH)3. Cr(VI) is more than 100 times more toxic than Cr(III), and it poses carcinogenic and mutagenic risks to humans and animals. The International Agency for Research on Cancer has identified Cr(VI) compounds as one of the three major carcinogens for humans. The World Health Organization stipulates that the Cr(VI) content in wastewater should be ≤0.05 mg / L, and my country's environmental standards allow for a Cr(VI) content in water below 0.05 mg / L.

[0003] Currently, the main methods for treating heavy metal-contaminated wastewater include membrane separation, adsorption, ion exchange, electrolysis, and chemical precipitation. However, each of these methods has its drawbacks: membrane separation is costly; adsorption is inefficient and has a short lifespan; ion exchange requires stringent operating conditions; electrolysis is energy-intensive; and chemical precipitation is inefficient and generates secondary pollution, making it unsuitable for practical application. Therefore, finding a simple and easy-to-implement method to effectively treat heavy metal-contaminated wastewater is of great significance.

[0004] In recent years, photocatalysis technology has attracted widespread attention as an environmentally friendly, efficient, and low-cost technology. Among them, metal-organic frameworks (MOFs), with their semiconductor properties, tunable porous structures, and numerous active sites, are considered ideal photocatalysts for water purification. Compared with traditional semiconductor photocatalysts, MOF photocatalysts have several unique advantages. First, the porous structure of MOFs can promote the diffusion of reactants and products; second, the porous structure of MOFs can expose as many substrate-bound catalytic active sites as possible; and finally, MOF photocatalysts are easily modified by covalent bonds through post-synthetic methods, thus facilitating the adjustment of their light absorption properties or the introduction of additional catalytic active centers. Among the many MOFs, zirconium-based metal-organic frameworks (Zr-MOFs, represented by the UIO-66 series) with high acid-base stability are considered promising MOF materials for practical applications. However, single-component MOF photocatalysts generally suffer from poor visible light response, low photogenerated electron-hole separation efficiency, low activity, and limited stability. Therefore, composite photocatalysts based on MOFs have attracted more attention. However, the preparation of most of these composite photocatalysts requires two or more synthetic steps, which is detrimental to improving preparation efficiency. Furthermore, the preparation process is complex, costly, time-consuming, and labor-intensive. The resulting composite photocatalysts also suffer from poor photocatalytic activity, severely limiting their widespread application. Therefore, finding a bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst with a large specific surface area, numerous active sites, fast photogenerated carrier separation and migration rates, high photocatalytic activity, high stability, and high photocatalytic efficiency, along with a convenient, simple, and environmentally friendly preparation method, is of great significance for the effective removal of heavy metal pollutants from the environment. Summary of the Invention

[0005] The technical problem to be solved by this invention is to overcome the shortcomings of the prior art and provide a bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst with large specific surface area, high porosity, many active sites, fast separation and migration rate of photogenerated carriers, high photocatalytic activity, high stability, and high photocatalytic efficiency. It also provides a simple and efficient preparation method and an application of the above-mentioned bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst in the treatment of heavy metal wastewater.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution.

[0007] A method for preparing a bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst includes the following steps:

[0008] S1. Mix zirconium salt, bismuth salt, terephthalic acid and organic solvent to obtain a mixed solution;

[0009] S2. The mixed solution obtained in step S1 is subjected to a solvothermal reaction, washed, soaked, and dried to obtain a bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst.

[0010] The above preparation method can be further improved by step S1 as follows:

[0011] S1-1. Mix zirconium salt and organic solvent, and sonicate to obtain solution A;

[0012] S1-2. Add bismuth salt to solution A and sonicate to obtain solution B;

[0013] S1-3. Add terephthalic acid to solution B and sonicate to obtain a mixed solution.

[0014] In a further improvement to the above preparation method, the molar ratio of zirconium salt to bismuth salt is ≤5.5∶1, the molar ratio of terephthalic acid to zirconium salt is 1~1.25∶1, the ratio of zirconium salt to organic solvent is 1.2mmol∶40mL~60mL, the zirconium salt is zirconium tetrachloride, the bismuth salt is bismuth nitrate pentahydrate, and the organic solvent is dimethylformamide.

[0015] In a further improvement to the above preparation method, in step S1-1, the ultrasound time is 5 min to 30 min; in step S1-2, the ultrasound time is 5 min to 10 min; and in step S1-3, the ultrasound time is 5 min to 10 min.

[0016] In a further improvement to the above preparation method, the molar ratio of zirconium salt to bismuth salt is 2 to 4:1.

[0017] In a further improvement to the above preparation method, in step S2, the temperature of the solvothermal reaction is 110℃~140℃, and the reaction time is 24h~48h; the washing involves centrifuging three times each with ethanol and methanol, with centrifugation at 4000rpm for 5min~10min; the soaking involves soaking in methanol for 24h~32h, with centrifugation every 4h~6h during the soaking process, followed by ultrasonication for 30min~60min; the drying temperature is 60℃~70℃, and the drying time is 12h~18h, with vacuum drying.

[0018] As a general technical concept, the present invention also provides a bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst prepared by the above-described preparation method.

[0019] The above-mentioned bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst is further improved by including a zirconium-based metal-organic framework material, wherein bismuth oxychloride is supported on the zirconium-based metal-organic framework material, and the zirconium-based metal-organic framework material is UIO-66.

[0020] As a general technical concept, the present invention also provides an application of the above-mentioned bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst in the treatment of heavy metal wastewater.

[0021] The above-mentioned application, further improved, includes the following steps: mixing bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst with heavy metal wastewater, stirring, and after reaching adsorption equilibrium, carrying out a photocatalytic reduction reaction under light irradiation to complete the treatment of heavy metal wastewater; the amount of bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst added is 0.15g to 0.3g per liter of heavy metal wastewater.

[0022] In a further improvement to the above application, the heavy metal in the wastewater is chromium, the initial concentration of chromium in the wastewater is ≤15mg / L, the initial pH value of the wastewater is 4-6, the stirring speed is 600r / min-800r / min, the stirring time is 30min-45min, and the photocatalytic reduction reaction time is 1h-2h.

[0023] Compared with the prior art, the advantages of the present invention are as follows:

[0024] (1) To address the shortcomings of existing zirconium-based metal-organic framework (MOF) composite photocatalysts, such as complex preparation processes and low photocatalytic activity, this invention creatively proposes a method for preparing a bismuth oxychloride / zirconium-based MOF composite photocatalyst. Using zirconium salt, bismuth salt, and terephthalic acid as raw materials, the bismuth oxychloride / zirconium-based MOF composite photocatalyst is prepared via a one-step solvent method. In this invention, the addition of bismuth salt during the preparation of the zirconium-based MOF (UIO-66) significantly increases the specific surface area and the number of voids in the composite photocatalyst, thereby enhancing its adsorption capacity and exposing more active sites. Simultaneously, by loading bismuth oxychloride (BiOCl) onto the zirconium-based MOF (UIO-66) via a one-step solvent method, a heterojunction system is successfully constructed, which helps reduce the recombination rate of photogenerated electron-hole pairs, improves electron utilization, and achieves excellent photocatalytic performance. Therefore, a bismuth oxychloride / zirconium-based MOF composite photocatalyst with a large specific surface area, high porosity, and numerous active sites can be prepared via a one-step solvent method. Compared to the monomeric UIO-66 and the multi-step synthesized BiOCl / UIO-66 composite photocatalyst, the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst prepared by the method of this invention has a larger specific surface area, higher porosity, and more active sites, and exhibits better photocatalytic activity. Therefore, it is more conducive to the treatment of heavy metal pollutants and ultimately achieves efficient and rapid removal of heavy metal pollutants (such as Cr(VI)) from the environment, meeting practical application needs and showing broad prospects in the field of photocatalysis. Furthermore, the method of this invention greatly simplifies the preparation process, improves preparation efficiency, and has advantages such as convenient synthesis, simple operation, and no secondary pollution to the environment. It meets practical production needs, is suitable for large-scale preparation, and is easy to industrialize.

[0025] (2) This invention also provides a bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst, comprising UIO-66 and bismuth oxychloride nanosheets, wherein the bismuth oxychloride nanosheets are supported on UIO-66. In the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst of this invention, UIO-66 has the advantages of large specific surface area and high porosity, making it a good support; BiOCl belongs to the V-VI-VII ternary semiconductor oxide system, is tetragonal, and [Bi2O2] 2+ Layers and double layers [Cl] -With its staggered arrangement and the Cl atom bilayer connected by van der Waals forces, and a band gap energy of approximately 3.2 eV, BiOCl is an indirect semiconductor. The transition of photogenerated electrons from the valence band to the conduction band requires a certain k-space distance, which to some extent reduces the recombination rate of photogenerated electron-hole pairs. Therefore, it is a promising photocatalyst. The bismuth oxychloride (BiOCl) / zirconium-based metal-organic framework (UIO-66) composite photocatalyst possesses advantages such as large specific surface area, high porosity, numerous active sites, fast separation and migration rates of photogenerated carriers, high photocatalytic activity, high stability, and high photocatalytic efficiency. It can be widely used to treat heavy metal pollution in the environment, demonstrating significant application value and promising prospects.

[0026] (3) This invention also provides an application of bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst in the treatment of heavy metal wastewater. By mixing the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst with heavy metal wastewater for photocatalytic reduction, efficient reduction treatment of heavy metals can be achieved. This method has advantages such as simple process, convenient operation, simple equipment, low cost, good reduction effect, and cleanliness without pollution. It can be widely used to remove heavy metal pollutants from water bodies and has high application and commercial value. Taking Cr(VI) as an example, using the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst for 60 minutes of photocatalytic reduction, the removal rate of Cr(VI) reached as high as 93.67%, achieving efficient reduction treatment of Cr(VI) and meeting practical application requirements. Attached Figure Description

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0028] Figure 1 The images show scanning electron microscope (SEM) images of the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst (0.42BOCU-1) prepared in Example 1, the UIO-66 catalyst (UIO-66) prepared in Comparative Example 1, and the UIO-66 / BiOCl composite photocatalyst (BOCU-2) prepared in Comparative Example 2, where (a) is UIO-66, (b) is 0.42BOCU-1, and (c) is BOCU-2.

[0029] Figure 2The X-ray diffraction patterns of the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalysts (0.22BOCU-1, 0.42BOCU-1, 0.62BOCU-1, 0.82BOCU-1 and 1.02BOCU-1) prepared in Example 1, the UIO-66 catalyst (UIO-66) prepared in Comparative Example 1, and the UIO-66 / BiOCl composite photocatalyst (BOCU-2) prepared in Comparative Example 2 are shown.

[0030] Figure 3 This is an electron transmission microscope image of the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst (0.42BOCU-1) prepared in Example 1 of the present invention.

[0031] Figure 4 Fourier transform infrared spectra of the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst (0.42BOCU-1) prepared in Example 1 of the present invention, the UIO-66 catalyst (UIO-66) prepared in Comparative Example 1, and the UIO-66 / BiOCl composite photocatalyst (BOCU-2) prepared in Comparative Example 2.

[0032] Figure 5 The N2 adsorption-desorption curves are shown for the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst (0.42BOCU-1) prepared in Example 1, the UIO-66 catalyst (UIO-66) prepared in Comparative Example 1, and the UIO-66 / BiOCl composite photocatalyst (BOCU-2) prepared in Comparative Example 2.

[0033] Figure 6 The UV-Vis diffuse reflectance spectra of the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst (0.42BOCU-1) prepared in Example 1, the UIO-66 catalyst (UIO-66) prepared in Comparative Example 1, and the UIO-66 / BiOCl composite photocatalyst (BOCU-2) prepared in Comparative Example 2.

[0034] Figure 7 The photoluminescence spectra of the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst (0.42BOCU-1) prepared in Example 1 of the present invention, the UIO-66 catalyst (UIO-66) prepared in Comparative Example 1, and the UIO-66 / BiOCl composite photocatalyst (BOCU-2) prepared in Comparative Example 2 are shown.

[0035] Figure 8The photocurrent response spectra of the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst (0.42BOCU-1) prepared in Example 1, the UIO-66 catalyst (UIO-66) prepared in Comparative Example 1, and the UIO-66 / BiOCl composite photocatalyst (BOCU-2) prepared in Comparative Example 2 are shown.

[0036] Figure 9 The electrochemical impedance spectroscopy (EIS) spectra of the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst (0.42BOCU-1) prepared in Example 1, the UIO-66 catalyst (UIO-66) prepared in Comparative Example 1, and the UIO-66 / BiOCl composite photocatalyst (BOCU-2) prepared in Comparative Example 2 are shown.

[0037] Figure 10 The image shows the removal effect of hexavalent chromium by the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalysts (0.22BOCU-1, 0.42BOCU-1, 0.62BOCU-1, 0.82BOCU-1 and 1.02BOCU-1) in Example 2 of this invention.

[0038] Figure 11 The image shows the removal effect of hexavalent chromium by the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst (0.42BOCU-1), UIO-66 catalyst (UIO-66), and UIO-66 / BiOCl composite photocatalyst (BOCU-2) in Example 2 of this invention.

[0039] Figure 12 The image shows the removal effect of bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst (0.42BOCU-1) on different concentrations of hexavalent chromium in Example 3 of this invention.

[0040] Figure 13 The image shows the removal effect of hexavalent chromium by the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst (0.42BOCU-1) under different pH conditions in Example 4 of this invention. Detailed Implementation

[0041] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention. All materials and instruments used in the following embodiments are commercially available.

[0042] Example 1:

[0043] A method for preparing a bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst includes the following steps:

[0044] (1) Add 0.2796 g of zirconium tetrachloride (ZrCl4) to 40 mL of dimethylformamide (DMF) and sonicate for 30 min to dissolve ZrCl4 in DMF.

[0045] (2) Add 0.42 mmol of bismuth nitrate pentahydrate (Bi(NO3)2·5H2O) and 0.1993 g of terephthalic acid (H2BDC) to the ZrCl4 solution obtained in step (1) and sonicate for 5 min to mix them evenly to obtain a mixed solution.

[0046] (3) Transfer the mixed solution obtained in step (2) into the 100mL reactor liner, seal it, put it into the reactor shell, tighten it, place it in a drying oven, and carry out a solvothermal reaction at 120℃ for 24h to obtain a grayish-white powder.

[0047] (4) The grayish-white powder obtained in step (3) was centrifuged and washed three times with ethanol and methanol respectively. The centrifugation was performed at 4000 rpm for 5 min. After each centrifugation, the solvent was changed and the powder was mixed evenly with a high-speed mixer before the next centrifugation and washing operation was performed. After centrifugation and washing, the powder was soaked in methanol and centrifuged every 4 h. After changing the solvent, the powder was sonicated for 30 min. After repeating this process 6 times, the powder was vacuum dried at 60℃ for 12 h to obtain the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst, denoted as 0.42BOCU-1.

[0048] The bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst prepared in the embodiments of the present invention includes a zirconium-based metal-organic framework material UIO-66, on which BiOCl nanosheets are loaded.

[0049] In this embodiment, the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst has a porous structure, and the introduction of Bi salt during its preparation greatly increases the porosity of the composite material.

[0050] In this embodiment, different bismuth oxychloride / zirconium-based metal-organic framework composite photocatalysts were also prepared. Their preparation methods were basically the same as those of the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst (0.42BOCU-1). The only difference was that in step (2), the amount of bismuth nitrate pentahydrate used was 0.22 mmol, 0.62 mmol, 0.82 mmol, and 1.02 mmol, respectively. The corresponding bismuth oxychloride / zirconium-based metal-organic framework composite photocatalysts were named 0.22BOCU-1, 0.62BOCU-1, 0.82BOCU-1, and 1.02BOCU-1, respectively.

[0051] Comparative Example 1:

[0052] A method for preparing a UIO-66 catalyst is basically the same as the preparation method in Example 1, except that: in Comparative Example 1, the amount of bismuth nitrate pentahydrate is 0, that is, no bismuth nitrate pentahydrate is added.

[0053] The UIO-66 catalyst prepared in Comparative Example 1 is denoted as UIO-66.

[0054] Comparative Example 2:

[0055] A two-step synthesis method for a UIO-66 / BiOCl composite photocatalyst includes the following steps:

[0056] 0.0955 g of the UIO-66 catalyst prepared in Comparative Example 1 was added to 50 mL of ultrapure water and sonicated for 30 min. Then, 0.0820 g of KCl was added and the mixture was magnetically stirred at 600 rpm for 1 h. Then, 0.5335 g of bismuth nitrate pentahydrate was added, and the pH was adjusted to 6.0 with NaOH solution. After magnetic stirring for another 1 h, the mixture was transferred to the lining of a 100 mL reactor, sealed, placed inside the outer shell of the reactor, tightened, and placed in a forced-air drying oven for hydrothermal reaction at 120 °C for 24 h. The resulting white powder was washed 8 to 10 times with ultrapure water, filtered, and dried in a forced-air drying oven at 60 °C for 12 h to obtain the UIO-66 / BiOCl composite photocatalyst.

[0057] The UIO-66 / BiOCl composite photocatalyst prepared in Comparative Example 2 is designated as BOCU-2.

[0058] Figure 1 The images show scanning electron microscope (SEM) images of the bismuth oxychloride / zirconium-based metal-organic framework (BOCU-1) prepared in Example 1, the UIO-66 catalyst (UIO-66) prepared in Comparative Example 1, and the UIO-66 / BiOCl composite photocatalyst (BOCU-2) prepared in Comparative Example 2, where (a) is UIO-66, (b) is 0.42BOCU-1, and (c) is BOCU-2. Table 1 shows that the bismuth oxychloride / zirconium-based metal-organic framework (BOCU-1), UIO-66 catalyst (UIO-66), and UIO-66 / BiOCl composite photocatalyst (BOCU-2) all exhibit good crystallinity. The bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst (0.42BOCU-1) of the present invention has BiOCl nanosheets loaded on UIO-66 particles; at the same time, bismuth nitrate pentahydrate is added during the preparation of the zirconium-based metal-organic framework (UIO-66), so that UIO-66 is transformed from a regular polyhedron to an irregular sphere.

[0059] Figure 2The X-ray diffraction patterns of the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalysts (0.22BOCU-1, 0.42BOCU-1, 0.62BOCU-1, 0.82BOCU-1 and 1.02BOCU-1) prepared in Example 1, the UIO-66 catalyst (UIO-66) prepared in Comparative Example 1, and the UIO-66 / BiOCl composite photocatalyst (BOCU-2) prepared in Comparative Example 2 are shown. Figure 3 This is an electron transmission microscope image of the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst (0.42BOCU-1) prepared in Example 1 of this invention. Figure 2 As can be seen from the XRD pattern, the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst of this invention exhibits characteristic peaks of UIO-66 and BiOCl (JCPDS 06-0249), respectively, indicating the successful preparation of the composite photocatalyst. Figure 3 As can be seen, (b), (c), and (d) represent the (110), (101), and (001) crystal planes of BiOCl, respectively. In the XRD pattern, the 12.04° peak of the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst of the present invention corresponds to the (001) crystal plane, the 25.90° peak corresponds to the (101) crystal plane, and the 32.54° peak corresponds to the (110) crystal plane. This further proves the successful preparation of the composite photocatalyst.

[0060] Figure 4 The Fourier transform infrared (FTIR) spectra of the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst (0.42BOCU-1) prepared in Example 1, the UIO-66 catalyst (UIO-66) prepared in Comparative Example 1, and the UIO-66 / BiOCl composite photocatalyst (BOCU-2) prepared in Comparative Example 2 are shown below. Figure 4 It can be known that 1573cm -1 and 1400cm -1 Corresponding to the asymmetric and symmetric stretching of OCO in the organic linker terephthalic acid, respectively; 10¹⁸ cm -1 Corresponding to the coordination bond between the Zr cluster and the organic linker terephthalic acid; 549 cm -1 The presence of the Bi-O bond in BiOCl indicates the successful preparation of the composite photocatalyst.

[0061] Figure 5The N2 adsorption-desorption curves are shown for the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst (0.42BOCU-1) prepared in Example 1, the UIO-66 catalyst (UIO-66) prepared in Comparative Example 1, and the UIO-66 / BiOCl composite photocatalyst (BOCU-2) prepared in Comparative Example 2. The physicochemical properties of the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst, the UIO-66 catalyst, and the UIO-66 / BiOCl composite photocatalyst are shown in Table 1. Figure 5 As shown in Table 1, compared with the UIO-66 catalyst (UIO-66) and the UIO-66 / BiOCl composite photocatalyst (BOCU-2), the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst (0.42BOCU-1) of the present invention has a larger specific surface area and more active sites, which is beneficial to improving the photocatalytic activity of the composite photocatalyst.

[0062] Table 1 Physicochemical properties of bismuth oxychloride / zirconium-based metal-organic framework composite photocatalysts, UIO-66 catalysts, and UIO-66 / BiOCl composite photocatalysts

[0063] sample <![CDATA[Specific surface area (m 2 / g)]]> Aperture (nm) <![CDATA[Pore volume (cm 3 / g)]]> UIO-66 579.283 3.407 0.4681 0.42BOCU-1 1530.821 3.067 0.7156 BOCU-2 441.003 3.391 0.2403

[0064] Figure 6 The images show the UV-Vis diffuse reflectance spectra of the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst (0.42BOCU-1) prepared in Example 1, the UIO-66 catalyst (UIO-66) prepared in Comparative Example 1, and the UIO-66 / BiOCl composite photocatalyst (BOCU-2) prepared in Comparative Example 2. Figure 6 It can be seen that the introduction of BiOCl has little effect on the light absorption range of the photocatalyst.

[0065] Figure 7 The images show the photoluminescence spectra of the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst (0.42BOCU-1) prepared in Example 1, the UIO-66 catalyst (UIO-66) prepared in Comparative Example 1, and the UIO-66 / BiOCl composite photocatalyst (BOCU-2) prepared in Comparative Example 2. Figure 7 It can be seen that the greater the intensity in the spectrum, the greater the recombination rate of photogenerated electron-hole pairs in the photocatalyst. The order of the recombination rates of photogenerated electron-hole pairs among the three materials is: UIO-66 > BOCU-2 > 0.42BOCU-1.

[0066] Figure 8The images show the photocurrent response spectra of the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst (0.42BOCU-1) prepared in Example 1, the UIO-66 catalyst (UIO-66) prepared in Comparative Example 1, and the UIO-66 / BiOCl composite photocatalyst (BOCU-2) prepared in Comparative Example 2. Figure 8 It can be seen that the higher the current density in the spectrum, the higher the separation efficiency of photogenerated electron-hole pairs. The order of separation efficiency of photogenerated carriers in the three materials is: 0.42BOCU-1>BOCU-2>UIO-66.

[0067] Figure 9 The electrochemical impedance spectroscopy (EIS) spectra of the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst (0.42BOCU-1) prepared in Example 1, the UIO-66 catalyst (UIO-66) prepared in Comparative Example 1, and the UIO-66 / BiOCl composite photocatalyst (BOCU-2) prepared in Comparative Example 2 are shown. Figure 9 It can be seen that the larger the radius of the arc in the spectrum, the greater the carrier migration impedance of the photocatalyst. The order of the mobility of photogenerated carriers in the three materials is: 0.42BOCU-1>BOCU-2>UIO-66.

[0068] Combination Figures 6-9 It is known that the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst (0.42BOCU-1) of the present invention has excellent photogenerated carrier separation and mobility, and thus has the best photocatalytic activity.

[0069] Example 2:

[0070] An application of a bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst in the reduction of heavy metal pollution, specifically, using the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst to reduce hexavalent chromium (Cr(VI)) in water, includes the following steps:

[0071] Take 20 mg of the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalysts (0.22BOCU-1, 0.42BOCU-1, 0.62BOCU-1, 0.82BOCU-1 and 1.02BOCU-1) prepared in Example 1, the UIO-66 catalyst (UIO-66) prepared in Comparative Example 1, and the UIO-66 / BiOCl composite photocatalyst (BOCU-2) prepared in Comparative Example 2, and add them to 100 mL of hexavalent chromium solution with an initial concentration of 10 mg / L. Mix well and stir at 600 r / min for 30 min in the dark to allow the photocatalysts to reach adsorption equilibrium. Then, carry out the photocatalytic reduction reaction for 60 min under the irradiation of a 32 W ultraviolet lamp to complete the reduction treatment of hexavalent chromium in the water.

[0072] During the photocatalytic reduction reaction, 1 mL of sample was taken every 15 min. The absorbance of hexavalent chromium in the solution was measured by the diphenylcarbazide spectrophotometer method according to the national standard GB7467-87, and the reduction efficiency was calculated.

[0073] Figure 10 This image shows the removal effect of bismuth oxychloride / zirconium-based metal-organic framework composite photocatalysts (0.22BOCU-1, 0.42BOCU-1, 0.62BOCU-1, 0.82BOCU-1, and 1.02BOCU-1) on hexavalent chromium in Example 2 of this invention. Figure 10 It can be seen that the removal rates of hexavalent chromium by 0.22BOCU-1, 0.42BOCU-1, 0.62BOCU-1, 0.82BOCU-1 and 1.02BOCU-1 of the present invention are 73.24%, 93.67%, 83.01%, 78.46% and 67.72%, respectively. It is evident that the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst (0.42BOCU-1) has the best photocatalytic reduction effect on hexavalent chromium.

[0074] Figure 11 The images show the removal efficiency of hexavalent chromium by the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst (0.42BOCU-1), UIO-66 catalyst (UIO-66), and UIO-66 / BiOCl composite photocatalyst (BOCU-2) in Example 2 of this invention. Figure 11 It can be seen that after 1 hour of illumination, the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst (0.42BOCU-1) of the present invention achieved a removal rate of 93.67% for hexavalent chromium, while the removal rates of 10 mg / L hexavalent chromium by the monomer material UIO-66 and the two-step synthesized UIO-66 / BiOCl composite photocatalyst (BOCU-2) were 42.68% and 44.94%, respectively. This indicates that the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst of the present invention can significantly improve the removal efficiency of heavy metals (such as hexavalent chromium). Compared with UIO-66 and BOCU-2, the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst (0.42BOCU-1) of the present invention has a larger specific surface area and more active sites, thus exhibiting stronger adsorption and reduction capabilities; at the same time, it has superior photogenerated carrier separation and mobility, resulting in better photocatalytic activity of the composite photocatalyst, ultimately achieving efficient and thorough removal of heavy metal pollutants (such as Cr(VI)).

[0075] Example 3:

[0076] An application of a bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst in the reduction of heavy metal pollution, specifically, using the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst to reduce hexavalent chromium (Cr(VI)) in water, includes the following steps:

[0077] Take 20 mg of the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst (0.42 BOCU-1) prepared in Example 1, and add it to hexavalent chromium solutions with initial concentrations of 10 mg / L, 15 mg / L, and 20 mg / L (volume 100 mL), respectively. Mix well and stir at 600 r / min for 30 min in the dark (dark room) to allow the photocatalyst to reach adsorption equilibrium. Then, carry out the photocatalytic reduction reaction for 60 min under 32 W ultraviolet lamp irradiation to complete the reduction treatment of hexavalent chromium in the water.

[0078] Figure 12 This image shows the removal effect of the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst (0.42BOCU-1) on hexavalent chromium of different concentrations in Example 3 of this invention. Figure 12 It can be seen that after 1 hour of illumination, the removal rates of hexavalent chromium by the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst (0.42BOCU-1) of the present invention for initial concentrations of 10 mg / L, 15 mg / L and 20 mg / L were 93.67%, 73.55% and 58.01%, respectively. It is evident that the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst of the present invention has a good removal effect on hexavalent chromium solutions of different concentrations. In particular, the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst of the present invention has a better removal effect on low-concentration heavy metal polluted wastewater.

[0079] Example 4:

[0080] An application of a bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst in the reduction of heavy metal pollution, specifically, using the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst to reduce hexavalent chromium (Cr(VI)) in water, includes the following steps:

[0081] Six 20 mg portions of the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst (0.42 BOCU-1) prepared in Example 1 were added to hexavalent chromium solutions with pH values ​​of 2, 3, 4, 5, 6, and 8, respectively (the volume of the solution was 100 mL and the initial concentration was 10 mg / L). The solutions were mixed evenly and stirred at 600 r / min for 30 min in the dark (dark room) to allow the photocatalyst to reach adsorption equilibrium. The photocatalytic reduction reaction was carried out under 32 W ultraviolet lamp irradiation for 60 min to complete the reduction treatment of hexavalent chromium in the water.

[0082] Figure 13This image shows the removal effect of the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst (0.42BOCU-1) on hexavalent chromium under different pH conditions in Example 4 of this invention. Figure 13 It can be seen that after 1 hour of illumination, the removal rates of hexavalent chromium by the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst (0.42BOCU-1) of the present invention were 60.13%, 68.98%, 97.00%, 92.90%, 84.07%, and 58.49% respectively under pH conditions of 2, 3, 4, 5, 6, and 8. This shows that the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst of the present invention has a wide applicable pH range and has a good removal effect on hexavalent chromium under different pH conditions. In particular, the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst of the present invention has a better removal effect on hexavalent chromium in the pH range of 4 to 6.

[0083] In summary, the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst prepared by this invention has advantages such as large specific surface area, high porosity, multiple active sites, fast separation and migration rate of photogenerated carriers, high photocatalytic activity, high stability, and high photocatalytic efficiency. It can be widely used to treat heavy metal pollution in the environment and has good application value and application prospects.

[0084] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention using the methods and techniques disclosed above, or modify them into equivalent embodiments with equivalent changes, without departing from the spirit and technical essence of the present invention. Therefore, any simple modifications, equivalent substitutions, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall still fall within the protection scope of the technical solutions of the present invention.

Claims

1. A method for preparing a bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst, characterized in that, Includes the following steps: S1. A mixed solution is obtained by mixing zirconium salt, bismuth salt, terephthalic acid, and an organic solvent, specifically as follows: S1-1. Mix zirconium salt and organic solvent, and sonicate to obtain solution A; the zirconium salt is zirconium tetrachloride. S1-2. Add bismuth salt to solution A and sonicate to obtain solution B; S1-3. Add terephthalic acid to solution B and sonicate to obtain a mixed solution; the molar ratio of zirconium salt to bismuth salt is 2-4:1; the molar ratio of terephthalic acid to zirconium salt is 1-1.25:

1. S2. The mixed solution obtained in step S1 is subjected to a solvothermal reaction, washed, soaked, and dried to obtain a bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst.

2. The method for preparing the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst according to claim 1, characterized in that, The ratio of zirconium salt to organic solvent is 1.2 mmol: 40 mL to 60 mL, the bismuth salt is bismuth nitrate pentahydrate, and the organic solvent is dimethylformamide; In step S1-1, the ultrasound duration is 5 min to 30 min; In steps S1-2, the ultrasound duration is 5 min to 10 min; In steps S1-3, the ultrasound duration is 5 min to 10 min.

3. The method for preparing the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst according to claim 1 or 2, characterized in that, In step S2, the temperature of the solvothermal reaction is 110℃~140℃, and the reaction time is 24h~48h; the cleaning is performed by centrifuging with ethanol and methanol three times in sequence, and the centrifugation is performed by centrifuging at 4000rpm for 5min~10min; the soaking is performed by soaking in methanol for 24h~32h, during which centrifugation is performed every 4h~6h, followed by ultrasonication for 30min~60min; the drying temperature is 60℃~70℃, the drying time is 12h~18h, and the drying is performed under vacuum.

4. A bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst prepared by the method described in any one of claims 1 to 3, characterized in that, The invention includes a zirconium-based metal-organic framework material, wherein bismuth oxychloride is loaded onto the zirconium-based metal-organic framework material, and the zirconium-based metal-organic framework material is UIO-66.

5. The application of the bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst as described in claim 4 in the treatment of heavy metal wastewater.

6. The application according to claim 5, characterized in that, The process includes the following steps: mixing bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst with heavy metal wastewater, stirring, and after reaching adsorption equilibrium, carrying out a photocatalytic reduction reaction under light irradiation to complete the treatment of heavy metal wastewater; the amount of bismuth oxychloride / zirconium-based metal-organic framework composite photocatalyst added is 0.15g to 0.3g per liter of heavy metal wastewater.

7. The application according to claim 6, characterized in that, The heavy metal in the wastewater is chromium, the initial concentration of chromium in the wastewater is ≤15mg / L, the initial pH value of the wastewater is 4-6, the stirring speed is 600r / min-800r / min, the stirring time is 30min-45min, and the photocatalytic reduction reaction time is 1h-2h.

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