Z-type CdWO4 / Bi2WO6 catalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of antibiotic wastewater treatment, and particularly relates to a Z-type CdWO4 / Bi2WO6 catalyst as well as a preparation method and application thereof. The catalyst is formed by loading CdWO4 particles on a Bi2WO6 nanosheet unit. The Z-type CdWO4 / Bi2WO6 catalyst is prepared by adopting a hydrothermal process, the photo-generated charge separation efficiency and the sulfadiazine degradation rate of the catalyst are remarkably improved through energy band structure regulation and interface optimization, and meanwhile, the catalyst has excellent structural stability and recycling performance. The Z-type heterojunction is constructed by accurately controlling integration of CdWO4 and a Bi2WO6 substrate, and the Z-type CdWO4 / Bi2WO6 catalyst is high in light adsorption capacity, high in electron hole separation efficiency, stable in material structure, fast in photon-generated carrier transmission and capable of effectively inhibiting recombination of photon-generated carriers.

Description

Technical Field

[0001] The invention belongs to the technical field of antibiotic wastewater treatment, and particularly relates to a Z-type CdWO4 / Bi2WO6 catalyst and a preparation method and application thereof. Background Art

[0002] With rising living standards, the demand for antibiotics has steadily increased. However, this unregulated use has triggered a series of adverse consequences. First, overuse of antibiotics accelerates the emergence and proliferation of drug-resistant strains, significantly reducing the efficacy of conventional antimicrobial therapies. Second, the increasing resistance of pathogens can compromise clinical treatment outcomes, often requiring higher doses or more effective therapeutic agents. More critically, antibiotics accumulate in the environment through bioaccumulation in the food chain, posing long-term toxic risks to human health. A prime example is sulfadiazine, an antibiotic widely used in agriculture. Its molecular structure consists of aromatic and pyrimidine rings, forming a highly stable framework that significantly hinders biodegradation. Furthermore, the unique electronic properties of the sulfonamide group create a dual protective mechanism: it not only limits the activity of free radicals but also slows photolysis and chemical degradation. The combined effect of these recalcitrant mechanisms leads to the persistent accumulation of these compounds in environmental media such as surface water and soil, ultimately creating a "chemical time bomb" that threatens ecological integrity and public health.

[0003] Current treatment technologies for sulfadiazine wastewater can be categorized into three main categories: biological treatment, physicochemical methods, and advanced oxidation processes. While each of these processes has its advantages, they often suffer from inadequate targeted destruction of the aromatic pyrimidine ring structure within the sulfadiazine molecule and low mineralization efficiency. Furthermore, during degradation, more difficult-to-decompose sulfonamide analogs, such as N4-acetylated derivatives, are easily generated, posing a risk of secondary pollution. In this context, photocatalysis, a key branch of advanced oxidation systems, has attracted considerable attention due to its environmental friendliness and high degradation potential. This technology, driven by light energy, can degrade pollutants at ambient temperature and pressure, theoretically without causing secondary hazards, making it a highly promising green treatment option. However, existing photocatalytic systems suffer from two significant drawbacks: first, most catalysts are limited to ultraviolet wavelengths, resulting in low solar energy utilization; second, the rapid recombination of photogenerated carriers severely limits catalytic efficiency. Therefore, catalyst modification to overcome the limitations of the light response range and improve carrier separation efficiency has become a key research direction in this field. For sulfadiazine, enhancing the ability to decompose the aromatic pyrimidine ring, the efficiency of free radical attack, and the mineralization capacity is crucial.

[0004] Among emerging semiconductor photocatalysts, Bi2WO6 stands out for its inherent visible-light response (band gap ~2.67 eV), representing a significant advancement over traditional UV-dependent catalysts such as TiO2. This material exhibits remarkable properties, including non-toxicity, robust chemical stability, and operability under ambient conditions, making it a sustainable candidate for solar-driven environmental remediation. However, practical implementation requires overcoming key challenges, particularly inefficient charge carrier separation and limited active site accessibility. Meanwhile, advances in tungstate material research have highlighted the potential of CdWO4, whose monoclinic wolframite-type crystal structure (space group P2 / c) confers a unique electronic configuration. This material's wide band gap (~3.8 eV) imparts exceptional redox potential to photogenerated carriers, manifesting in conduction band electrons exhibiting enhanced reduction capabilities. This structural configuration promotes anisotropic charge transport within the WO-Cd polyhedral network, achieving electron mobilities significantly exceeding those of conventional photocatalytic systems. Summary of the Invention

[0005] To address the challenges of existing photocatalysts, such as weak visible light response, high carrier recombination rates, and insufficient sulfadiazine degradation efficiency, this paper proposes a Z-type heterojunction CdWO4 / Bi2WO6 catalyst, its preparation method, and application. Through band structure manipulation and interface optimization, this catalyst significantly improves the efficiency of photogenerated charge separation and sulfadiazine degradation, while also exhibiting excellent structural stability and recyclability. A Z-type heterojunction is constructed by precisely controlling the integration of CdWO4 and Bi2WO6 substrates. The interface structure leverages the complementary optoelectronic properties of the two materials, effectively combining the visible light responsiveness of Bi2WO6 with the strong reduction potential of CdWO4 to create spatially distinct redox-active domains. This configuration achieves synergistic improvements in multiple performance metrics: enhanced light absorption through an interfacial charge transfer mechanism, directional carrier migration facilitated by the WO-Cd / WO-Bi bonding structure, minimizing recombination losses, and targeted generation of oxidized species within the stable aromatic pyrimidine molecular framework capable of sulfadiazine degradation.

[0006] In order to achieve the above object, the technical solution of the present invention is as follows: On one hand, the present invention provides a Z-type CdWO4 / Bi2WO6 catalyst, which is composed of CdWO4 particles supported on Bi2WO6 nanosheet units.

[0007] In the above technical solution, further, in the catalyst, the content of CdWO4 particles is 1~4wt%.

[0008] Another aspect of the present invention provides a method for preparing the above-mentioned Z-type CdWO4 / Bi2WO6 catalyst, comprising the following steps: (1) dissolving Na2WO4·2H2O in deionized water, adding Bi(NO3)3·5H2O, magnetically stirring, then transferring to an autoclave for reaction, naturally cooling to room temperature after the reaction is completed, centrifuging, washing, and drying to obtain Bi2WO6 microspheres; (2) immersing the Bi2WO6 microspheres obtained in step (1) in a Cd(NO3)2·4H2O aqueous solution, then calcining to obtain the Z-type CdWO4 / Bi2WO6 catalyst.

[0009] In the above technical solution, further, in step (1), the mass ratio of Na2WO4·2H2O and Bi(NO3)3·5H2O is (2-3):(7-8).

[0010] In the above technical solution, further, in step (1), the reaction temperature is 110-130℃, and the reaction time is 20-24 hours.

[0011] In the above technical solution, further, in step (1), the drying temperature is 70℃, and the drying time is 8-12 hours.

[0012] In the above technical solution, further, in step (2), the mass ratio of Bi2WO6 microspheres and Cd(NO3)2·4H2O is (8-10):(1-1.6); The concentration of the Cd(NO3)2·4H2O aqueous solution is 0.05-0.08 g / mL.

[0013] In the above technical solution, further, in step (2), the immersion temperature is room temperature, and the immersion time is 12-14 hours.

[0014] In the above technical solution, further, in step (2), the calcination temperature is 530-550℃, and the calcination time is 2-4 hours.

[0015] In the above technical solution, further, the preparation method specifically comprises the following steps: 1) dissolving 0.2-0.3 g of Na2WO4·2H2O in 80-100 mL of deionized water, adding 0.7-0.8 g of Bi(NO3)3·5H2O to the solution, obtaining a transparent solution under magnetic stirring, transferring the mixture to a 100 mL capacity autoclave, then heating at 110-130℃ for 20-24 hours, centrifuging the obtained precipitate after the autoclave is naturally cooled to room temperature, then washing with ethanol and distilled water multiple times, then drying at 70℃ for 8-12 hours to obtain Bi2WO6 microspheres; 2) Soaking 0.8-1 g of the Bi2WO6 microspheres obtained in step 1) in an aqueous solvent solution containing 2 mL of Cd(NO3)2·4H2O at a concentration of 0.05-0.08 g / mL, allowing the mixture to stand at room temperature for 12-14 hours, and then calcining it at 530-550°C for 2-4 hours to obtain the Z-type CdWO4 / Bi2WO6 catalyst.

[0016] The present invention also provides an application of the Z-type CdWO4 / Bi2WO6 catalyst in photocatalytic degradation of sulfadiazine.

[0017] In the above technical solution, 10 to 30 mg of Z-type CdWO4 / Bi2WO6 catalyst powder is further added to 50 to 100 mL of a sulfadiazine solution containing a concentration of 5 to 10 mg / L, dispersed in a quartz tube, and ultrasonicated in an ultrasonic machine for 30 to 60 minutes to form a uniform suspension. The suspension is allowed to stand in the dark for 25 to 35 minutes to measure the physical adsorption efficiency of the catalyst. The solution is then irradiated with a xenon lamp to simulate sunlight under magnetic stirring, and the flow of cooling water is ensured to maintain the reaction container at 25 to 35°C. The absorbance of the solution in the 257 nm ultraviolet diffuse reflectance spectrum is measured every 30 minutes of irradiation. The irradiation is performed for 150 to 180 minutes and the data is recorded. The concentration of the remaining sulfadiazine solution in the solution is obtained by using the relationship between absorbance and concentration according to the Lambert-Beer law, and the degradation efficiency is then calculated.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. The Z-type CdWO4 / Bi2WO6 catalyst of the present invention is composed of CdWO4 particles supported on Bi2WO6 nanosheet units.

[0019] 2. The Z-type CdWO4 / Bi2WO6 binary catalyst of the present invention has strong light absorption capacity and high electron-hole separation efficiency. This is mainly due to the direct Z-type heterojunction material, which forms a Z-type heterojunction at the phase interface without the introduction of a conductive medium. The key to forming a Z-type heterojunction is the material's suitable band structure and band matching. This material structure is stable, photogenerated carriers are transported quickly, and recombination of photogenerated carriers can be effectively suppressed.

[0020] 3. Compared with traditional photocatalysts, the Z-type CdWO4 / Bi2WO6 catalyst of the present invention has better visible light absorption performance and a degradation efficiency of up to 84%, which greatly improves the photocatalytic degradation of sulfadiazine. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1X-ray diffraction patterns of CdWO4 in Comparative Example 1, Bi2WO6 in Comparative Example 2, and CdWO4 / Bi2WO6-X samples in Examples 1-4; Figure 2 Scanning electron microscope images of CdWO4 of comparative example 1, Bi2WO6 of comparative example 2, and CdWO4 / Bi2WO6-3 of example 3, as well as mapping images of CdWO4 / Bi2WO6-3 of example 3, (a)-(b) are scanning electron microscope images of Bi2WO6, (c)-(d) are scanning electron microscope images of CdWO4, (e)-(f) are scanning electron microscope images of CdWO4 / Bi2WO6-3, and (g)-(k) are element mapping images of CdWO4 / Bi2WO6-3; Figure 3 X-ray photoelectron energy diagram of the CdWO4 / Bi2WO6X-3 sample in Example 3, (a) is the total X-ray photoelectron spectrum, (b) is the Bi 4f fine spectrum, (c) is the Cd 3d fine spectrum, (d) is the W 4f fine spectrum, and (e) is the O 1s fine spectrum; Figure 4 The infrared spectra of the samples in Examples 1-4 and Comparative Example 1-2 and the fluorescence spectra of the samples in Comparative Example 1-2 and Example 3 are shown in Figures 1-4 and 1-2, and (b) is the fluorescence spectra of the samples in Comparative Example 1-2 and Example 3; Figure 5 The UV-visible diffuse reflectance spectra of the samples in Examples 1-4 and Comparative Example 1-2, and the optical band gap diagrams of the samples in Comparative Example 1-2 and Example 3, (a) is the UV-visible diffuse reflectance spectra of the samples in Examples 1-4 and Comparative Example 1-2, and (b) is the optical band gap diagram of the samples in Comparative Example 1-2 and Example 3; Figure 6 The cyclic voltammetry curves of the samples in Examples 1-4 and Comparative Examples 1-2 and the fitting curves between current density and potential scan rate, (a) is the cyclic voltammetry curve of the sample of Comparative Example 2, (b) is the cyclic voltammetry curve of the sample of Comparative Example 1, (c) is the cyclic voltammetry curve of the sample of Example 1, (d) is the cyclic voltammetry curve of the sample of Example 2, (e) is the cyclic voltammetry curve of the sample of Example 3, (f) is the cyclic voltammetry curve of the sample of Example 4, and (g) is the fitting curve between current density and potential scan rate; Figure 7 The linear sweep voltammetry curves of the samples in Examples 1-4 and Comparative Examples 1-2 are shown in Figures 1-4 and 1-2, respectively. (a) is a curve of the sample under dark conditions, and (b) is a curve of the sample under visible light irradiation conditions. Figure 8For the comparison of the degradation rates of sulfadiazine of the samples of Examples 1-4 and Comparative Examples 1-2, (a) is a sulfadiazine degradation rate curve, and (b) is a pseudo-first-order kinetic equation curve; Figure 9 The degradation principle of the Z-type CdWO4 / Bi2WO6 of the application. DETAILED DESCRIPTION

[0022] The following non-limiting examples can make those skilled in the art more fully understand the application, but do not limit the application in any way. Unless otherwise specified, the experimental methods used in the application are conventional methods, and the experimental apparatus, materials, reagents, etc. used can be obtained from commercial channels.

[0023] A Z-type CdWO4 / Bi2WO6 catalyst, which is composed of CdWO4 particles supported on Bi2WO6 nanosheet units.

[0024] The preparation method of the above-mentioned Z-type CdWO4 / Bi2WO6 catalyst comprises the following steps: (1) Dissolve Na2WO4·2H2O in deionized water, add Bi(NO3)3·5H2O, magnetically stir, then transfer to an autoclave for reaction, after the reaction is completed, naturally cool to room temperature, centrifuge, wash, dry, and obtain Bi2WO6 microspheres; (2) Dip the Bi2WO6 microspheres obtained in step (1) in a Cd(NO3)2·4H2O aqueous solution, then calcine, and obtain a Z-type CdWO4 / Bi2WO6 catalyst; In step (1), the mass ratio of Na2WO4·2H2O to Bi(NO3)3·5H2O is (2-3):(7-8); In step (1), the reaction temperature is 110-130°C, and the reaction time is 20-24 hours; In step (1), the drying temperature is 70°C, and the drying time is 8-12 hours; In step (2), the mass ratio of Bi2WO6 microspheres to Cd(NO3)2·4H2O is (8-10):(1-1.6); and the concentration of the Cd(NO3)2·4H2O aqueous solution is 0.05-0.08 g / mL; In step (2), the dipping temperature is room temperature, and the dipping time is 12-14 hours; In step (2), the calcination temperature is 530-550°C, and the calcination time is 2-4 hours.

[0025] Application of the above-mentioned Z-type CdWO4 / Bi2WO6 catalyst: 50 mg of Z-type CdWO4 / Bi2WO6 powder was added to 100 mL of a solution containing 20 mg / L sulfadiazine, dispersed in a quartz tube, and ultrasonicated in an ultrasonic machine for 30 minutes to form a uniform suspension. The suspension was allowed to stand in the dark for 30 minutes to measure the physical adsorption efficiency of the catalyst. The solution was then irradiated with a xenon lamp to simulate sunlight under magnetic stirring. During this period, the flow of cooling water was ensured to keep the reaction container at 25°C. The absorbance of the solution in the 257 nm ultraviolet diffuse reflectance spectrum was measured every 30 minutes of irradiation. The data was recorded for 180 minutes. The Lambert-Beer law was used to determine the concentration of the remaining sulfadiazine solution in the solution using the relationship between absorbance and concentration, and the degradation efficiency was then calculated.

[0026] Example 1 (1) 0.2940 g of Na2WO4·2H2O was dissolved in 80 mL of deionized water. 0.7900 g of Bi(NO3)3·5H2O was added to the solution to obtain a transparent solution under magnetic stirring. The mixture was transferred to a 100 mL autoclave and then heated at 120°C for 24 h. After the autoclave was naturally cooled to ambient temperature, the obtained precipitate was centrifuged and subsequently washed with ethanol and distilled water several times. It was then dried at 70°C for 8 h to obtain Bi2WO6 microspheres. (2) 1 g of Bi2WO6 microspheres obtained in step (1) were immersed in 2 mL of a 0.05 g / mL Cd(NO3)2·4H2O aqueous solution at room temperature for 12 h. Subsequently, the microspheres were calcined at 550 °C for 4 h. The obtained sample was designated as CdWO4 / Bi2WO6-1, in which the content of CdWO4 particles was 1 wt%.

[0027] Example 2 (1) 0.2940 g of Na2WO4·2H2O was dissolved in 80 mL of deionized water. 0.7900 g of Bi(NO3)3·5H2O was added to the solution to obtain a transparent solution under magnetic stirring. The mixture was transferred to a 100 mL autoclave and then heated at 120 °C for 24 h. After the autoclave was naturally cooled to ambient temperature, the obtained precipitate was centrifuged and subsequently washed with ethanol and distilled water several times. It was then dried at 70 °C for 8 h to obtain Bi2WO6 microspheres. (2) 1 g of Bi2WO6microspheres obtained in step (1) was immersed in 2 mL of Cd(NO3)2»4H2O aqueous solution with a concentration of 0.06 g / mL at room temperature for 12 hours, and then calcined at 550°C for 4 hours to obtain a sample, which was recorded as CdWO4 / Bi2WO6-2, wherein the content of CdWO4particles was 2 wt%.

[0028] Example 3 (1) 0.2940 g of Na2WO4»2H2O was dissolved in 80 mL of deionized water, and then 0.7900 g of Bi(NO3)3»5H2O was added into the solution to obtain a transparent solution under magnetic stirring. The mixture was transferred into a 100 mL capacity autoclave, and then heated at 120°C for 24 hours. After the autoclave was naturally cooled to ambient temperature, the obtained precipitate was centrifuged, and then washed with ethanol and distilled water for several times, and then dried at 70°C for 8 hours to obtain Bi2WO6microspheres; (2) 1 g of Bi2WO6microspheres obtained in step (1) was immersed in 2 mL of Cd(NO3)2»4H2O aqueous solution with a concentration of 0.07 g / mL at room temperature for 12 hours, and then calcined at 550°C for 4 hours to obtain a sample, which was recorded as CdWO4 / Bi2WO6-3, wherein the content of CdWO4particles was 3 wt%.

[0029] Example 4 (1) 0.2940 g of Na2WO4»2H2O was dissolved in 80 mL of deionized water, and then 0.7900 g of Bi(NO3)3»5H2O was added into the solution to obtain a transparent solution under magnetic stirring. The mixture was transferred into a 100 mL capacity autoclave, and then heated at 120°C for 24 hours. After the autoclave was naturally cooled to ambient temperature, the obtained precipitate was centrifuged, and then washed with ethanol and distilled water for several times, and then dried at 70°C for 8 hours to obtain Bi2WO6microspheres; (2) 1 g of Bi2WO6microspheres obtained in step (1) was immersed in 2 mL of Cd(NO3)2»4H2O aqueous solution with a concentration of 0.08 g / mL at room temperature for 12 hours, and then calcined at 550°C for 4 hours to obtain a sample, which was recorded as CdWO4 / Bi2WO6-4, wherein the content of CdWO4particles was 4 wt%.

[0030] Comparative Example 1 0.2940 g of Na2WO4·2H2O was dissolved in 80 mL of deionized water, and 0.2364 g of Cd(NO3)2·4H2O was added to this solution to obtain a transparent solution under magnetic stirring. The mixture was transferred to a 100 mL autoclave and then heated at 120°C for 24 hours. After the autoclave was naturally cooled to ambient temperature, the obtained precipitate was centrifuged and subsequently washed with ethanol and distilled water several times, and then dried at 70°C for 8 hours to obtain pure CdWO4.

[0031] Comparative Example 2 0.2940 g of Na2WO4·2H2O was dissolved in 80 mL of deionized water, and 0.7900 g of Bi(NO3)3·5H2O was added to this solution to obtain a transparent solution under magnetic stirring. The mixture was transferred to a 100 mL autoclave and then heated at 120°C for 24 hours. After the autoclave was naturally cooled to ambient temperature, the obtained precipitate was centrifuged and subsequently washed with ethanol and distilled water several times, and then dried at 70°C for 8 hours to obtain pure Bi2WO6.

[0032] Result analysis: Figure 1 The X-ray diffraction patterns of the CdWO4 in Comparative Example 1, the Bi2WO6 in Comparative Example 2, and the CdWO4 / Bi2WO6 samples with different CdWO4 particle contents in Examples 1-4 are shown in the 2θ range of 10-80. As can be seen from the figure, all peaks in the diffraction pattern are precisely aligned with the standard card Bi2WO6 phase (PDF#73-1126) and CdWO4 phase (PDF#84-0038). For the CdWO4 / Bi2WO6 sample, the diffraction peaks appear at 2θ of 28.79°, 33.83°, 47.22°, and 56.03°, corresponding to the (014), (020), (220), and (208) crystal planes of Bi2WO6, respectively. In addition, the diffraction peaks at 2θ values ​​of 29.62°, 36.87°, and 48.21° are related to the (110), (002), and (200) crystal planes of CdWO4. This XRD pattern confirms the coexistence of Bi2WO6 and CdWO4 phases in the CdWO4 / Bi2WO6 sample. Therefore, it can be inferred that the CdWO4 / Bi2WO6 material obtained in the present invention is a composite of pure Bi2WO6 and CdWO4.

[0033] Figure 2The following are scanning electron micrographs of CdWO4 from Comparative Example 1, Bi2WO6 from Comparative Example 2, and CdWO4 / Bi2WO6-3 from Example 3, as well as a mapping image of CdWO4 / Bi2WO6-3 from Example 3. (a)-(b) are scanning electron micrographs of Bi2WO6, (c)-(d) are scanning electron micrographs of CdWO4, (e)-(f) are scanning electron micrographs of CdWO4 / Bi2WO6-3, and (g)-(k) are elemental mapping images of CdWO4 / Bi2WO6-3. The photocatalytic activity of the CdWO4 / Bi2WO6 material can be enhanced to a certain extent. After composite formation, both Bi2WO6 and CdWO4 have increased surface active sites, enabling them to absorb more photons, thereby enhancing their photocatalytic activity. Furthermore, the material's mesoporous structure enhances the mobility of organic molecules. The elemental mapping image of the CdWO4 / Bi2WO6 material shows the uniform dispersion of Bi, Cd, W and O elements throughout the compound, indicating the presence of Bi, Cd, W and O elements in the CdWO4 / Bi2WO6 material, proving that the CdWO4 / Bi2WO6 material is a composite of pure Bi2WO6 and CdWO4.

[0034] Figure 3 The X-ray photoelectron energy spectrum of the CdWO4 / Bi2WO6-3 sample in Example 3 is shown in Figure 3. (a) is the overall X-ray photoelectron spectrum, (b) is the Bi 4f fine spectrum, (c) is the Cd 3d fine spectrum, (d) is the W 4f fine spectrum, and (e) is the O 1s fine spectrum. These XPS results further confirm the coexistence of Bi2WO6 and CdWO4 in the CdWO4 / Bi2WO6 photocatalyst.

[0035] Figure 4 The infrared spectra of all samples in Examples 1-4 and Comparative Examples 1-2, as well as the fluorescence spectra of CdWO4 in Comparative Example 1, Bi2WO6 in Comparative Example 2, and CdWO4 / Bi2WO6-3 in Example 3, (a) is the infrared spectra of all samples, (b) is the fluorescence spectra of Bi2WO6, CdWO4, and CdWO4 / Bi2WO6-3. The presence of atmospheric water causes the stretching vibration peak (3415 cm) corresponding to the hydroxyl group (-OH) to appear in the samples. -1 ) and bending vibration peaks (2358 cm -1 ). 1620 cm -1 , 1225cm -1 and 1078 cm -1 The significant peaks at 3415 cm represent the stretching vibration of the WOW bridge oxygen bond, the stretching vibration of the Bi-O bond, and the stretching vibration of the WO bond. -1and 2358 cm -1 The characteristic peaks of CdWO4 / Bi2WO6 can be detected, and it can be determined that CdWO4 / Bi2WO6 is composed of Bi2WO6 and CdWO4.

[0036] Figure 5 The following are the UV-visible diffuse reflectance spectra of all samples in Examples 1-4 and Comparative Examples 1-2, as well as the optical band gap diagrams of CdWO4 in Comparative Example 1, Bi2WO6 in Comparative Example 2, and CdWO4 / Bi2WO6-3 in Example 3. (a) is the UV-visible diffuse reflectance spectra of all samples, and (b) is the optical band gap diagram of Bi2WO6, CdWO4, and CdWO4 / Bi2WO6-3. CdWO4 exhibits an absorption edge at approximately 385 nm. In contrast, pristine Bi2WO6 exhibits considerable absorption in the visible light wavelength range, with an absorption band edge observed at approximately 440 nm, indicating its responsiveness to visible light. Compared to pure Bi2WO6, the composite catalyst exhibits increased absorption intensity in the 360-460 nm wavelength range, extending the visible light absorption range. The band gap of Bi2WO6 is 2.63 eV, the band gap of CdWO4 is 2.86 eV, and the band gap of the composite material CdWO4 / Bi2WO6-3 is 2.38 eV, which is lower than that of Bi2WO6, indicating that the composite sample can utilize sunlight more effectively and is beneficial to improving the performance of photocatalysis.

[0037] Figure 6 The cyclic voltammetry curves of all samples in Examples 1-4 and Comparative Examples 1-2 and the fitting curves between current density and potential scan rate, (a) is the cyclic voltammetry curve of the sample of Comparative Example 2, (b) is the cyclic voltammetry curve of the sample of Comparative Example 1, (c) is the cyclic voltammetry curve of the sample of Example 1, (d) is the cyclic voltammetry curve of the sample of Example 2, (e) is the cyclic voltammetry curve of the sample of Example 3, (f) is the cyclic voltammetry curve of the sample of Example 4, and (g) is the fitting curve between current density and potential scan rate. CdWO4 / Bi2WO6-3 dl 0.131 mF / cm 2 , higher than the pure sample, indicating that the composite catalyst has increased active sites and improved photocatalytic efficiency. Furthermore, compared with other catalysts at different concentrations, the intrinsic hydrogen evolution activity per unit ECSA of CdWO4 / Bi2WO6-3 is enhanced. Therefore, the CdWO4 / Bi2WO6-3 catalyst significantly improves the photoelectrochemical performance.

[0038] Figure 7The linear sweep voltammetry curves of all samples in Examples 1-4 and Comparative Examples 1-2 are shown. (a) is the curve of all samples under dark conditions, and (b) is the curve of all samples under visible light irradiation conditions. It is observed that the CdWO4 / Bi2WO6 composite material exhibits a higher current than the pure sample under both dark and visible light irradiation. In addition, it is obvious that the photocurrent measurements of all samples irradiated with visible light are higher than the values ​​measured under dark conditions. Among all the synthesized photocatalysts, CdWO4 / Bi2WO6-3 of Example 3 exhibits the highest photocurrent. A high photocurrent generally indicates that the sample is able to generate and transport photoexcited carriers under light. In addition, this result further confirms that the CdWO4 / Bi2WO6 of the present invention can effectively limit the recombination of photogenerated electron-hole pairs and help improve photocatalytic activity.

[0039] Application Example 1 To 100 mL of a 20 mg / L sulfadiazine solution, 50 mg of Z-type CdWO4 / Bi2WO6 powder was added. The mixture was dispersed in a quartz tube and sonicated for 30 minutes to form a uniform suspension. The suspension was then allowed to stand in the dark for 30 minutes to allow for adsorption to determine the catalyst's physical adsorption efficiency. The solution was then irradiated with a xenon lamp to simulate sunlight under magnetic stirring. Cooling water was continuously flowing to maintain the reaction vessel at 25°C. The absorbance of the solution at 257 nm was measured every 30 minutes. The data were recorded for 180 minutes. Using the Lambert-Beer law, the relationship between absorbance and concentration was used to determine the concentration of the remaining sulfadiazine in the solution, and thus the degradation efficiency.

[0040] Figure 8Comparison of the sulfadiazine degradation rates of the catalysts obtained in Examples 1-4 and Comparative Examples 1-2. The time course of sulfadiazine degradation on different catalysts under simulated sunlight irradiation is shown in (a) as a graph of sulfadiazine degradation rates, and (b) as a graph of pseudo-first-order kinetic equations. All catalysts exhibited photodegradation ability for sulfadiazine, with the CdWO4 / Bi2WO6-3 catalyst showing the highest photocatalytic degradation efficiency. Clearly, all CdWO4 / Bi2WO6 catalysts exhibited improved degradation efficiency for sulfadiazine antibiotic wastewater compared to Bi2WO6 and CdWO4. After 180 minutes of visible light irradiation, the degradation efficiencies of sulfadiazine on pure Bi2WO6, pure CdWO4, CdWO4 / Bi2WO6-1, CdWO4 / Bi2WO6-2, CdWO4 / Bi2WO6-3, and CdWO4 / Bi2WO6-4 catalysts were 68%, 17%, 70%, 72%, 84%, and 82%, respectively. In summary, the degradation efficiency of the catalyst of the present invention for antibiotic wastewater is still higher than that of the pure sample. However, it was also found that the degradation efficiency did not increase with the continuous increase of catalyst concentration, indicating that the appropriate concentration can form an efficient heterojunction interface between the two and effectively inhibit the recombination of electrons and holes.

[0041] Figure 9 This is the degradation principle of the Z-type CdWO4 / Bi2WO6 of the present invention. Before the formation of the nanoheterostructure, the Fermi levels of Bi2WO6 and CdWO4 align with their respective CB and VB energy levels. When Bi2WO6 and CdWO4 are in close contact, the Fermi level of Bi2WO6 shifts upward, while that of CdWO4 shifts downward, ultimately aligning their Fermi levels at the same position. As the Fermi levels shift, the Bi2WO6 conduction band and the CdWO4 valence band approach each other, bending downward while the CdWO4 valence band shifts upward. This facilitates electron flow from the Bi2WO6 conduction band to the CdWO4 conduction band. Under visible light irradiation, electrons in the VB are excited and move to the CB, leaving an equal number of holes in the VB. When the Bi2WO6 conduction band electrons and the CdWO4 valence band holes recombine, the number of holes in the Bi2WO6 valence band equals the number of electrons in the CdWO4 conduction band. Because the electron potential in CdWO4 CB is higher than O2 / ·O2 - More negative, can react with O2 to form O2 - , and O2 - Species can mineralize SDZ. The holes in the valence band of Bi2WO6 have great potential and oxidation strength, which enables them to oxidize OH- to ·OH radicals and directly mineralize SDZ. Therefore, CdWO4 / Bi2WO6-3 has high photocatalytic performance, which effectively hinders the recombination of electron-hole pairs and promotes ·O2 - Species and cavity formation.

[0042] The above-described embodiments are only preferred embodiments of the present invention, and are not intended to be all feasible embodiments of the present invention. Any obvious modifications made by a person skilled in the art without departing from the principles and spirit of the present invention should be considered to be included within the scope of protection of the claims of the present invention.

Claims

1. A Z-type CdWO4 / Bi2WO6 catalyst, characterized in that: It is composed of CdWO4 particles loaded on Bi2WO6 nanosheet units.

2. The Z-type CdWO4 / Bi2WO6 catalyst according to claim 1, characterized in that In the catalyst, the content of CdWO4 particles is 1-4 wt%.

3. A method for preparing the Z-type CdWO4 / Bi2WO6 catalyst according to any one of claims 1-2, characterized in that: The following steps are involved: (1) Na2WO4·2H2O was dissolved in deionized water, Bi(NO3)3·5H2O was added, and the mixture was stirred magnetically. The mixture was then transferred to an autoclave for reaction. After the reaction was completed, the mixture was naturally cooled to room temperature, centrifuged, washed, and dried to obtain Bi2WO6 microspheres. (2) The Bi2WO6 microspheres obtained in step (1) are impregnated in a Cd(NO3)2·4H2O aqueous solution and then calcined to obtain the Z-type CdWO4 / Bi2WO6 catalyst.

4. The preparation method according to claim 3, characterized in that In step (1), the mass ratio of Na2WO4·2H2O and Bi(NO3)3·5H2O is (2~3):(7~8).

5. The preparation method according to claim 3, characterized in that In step (1), the reaction temperature is 110-130° C., and the reaction time is 20-24 hours.

6. The preparation method according to claim 3, characterized in that In step (1), the drying temperature is 70°C and the drying time is 8 to 12 hours.

7. The preparation method according to claim 3, characterized in that In step (2), the mass ratio of Bi2WO6 microspheres to Cd(NO3)2·4H2O is (8~10):(1~1.6); The concentration of Cd(NO3)2·4H2O aqueous solution is 0.05~0.08g / mL.

8. The preparation method according to claim 3, characterized in that In step (2), the immersion temperature is room temperature and the immersion time is 12 to 14 hours.

9. The preparation method according to claim 3, characterized in that In step (2), the calcination temperature is 530-550° C., and the calcination time is 2-4 hours.

10. Use of the Z-type CdWO4 / Bi2WO6 catalyst according to any one of claims 1 to 2 in photocatalytic degradation of sulfadiazine.

Images