CdS QDs / Bi2WO6 / g-C3N4 double heterojunction photocatalyst, and preparation method and application thereof

Abstract

The application belongs to the technical field of sewage treatment, and particularly relates to a CdS QDs / Bi2WO6 / g-C3N4 double heterojunction photocatalyst and a preparation method and application thereof. The preparation method comprises the following steps: adding Bi2WO6 / g-C3N4 catalyst and cadmium salt into a solvent to perform ultrasonic dispersion and stirring, and then adding an alcohol solution containing a sulfur source to perform water bath reaction; and the product is collected by centrifugation, washed and dried to obtain the CdS QDs / Bi2WO6 / g-C3N4 double heterojunction photocatalyst. The CdS QDs / Bi2WO6 / g-C3N4 double heterojunction photocatalyst is synthesized by adopting a solvothermal reaction and a chemical in-situ growth technology under mild conditions. The method is simple in operation, low in cost and mild in reaction conditions, the obtained photocatalyst is high in visible light degradation activity of antibiotics, good in stability and fast in speed, and has good degradation effects on levofloxacin, norfloxacin and terramycin hydrochloride, and the degradation rate is more than 80%.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst, its preparation method, and its application. Background Technology

[0002] Antibiotic wastewater is known for its high organic matter concentration and significant fluctuations in water quality and quantity, making it one of the most difficult industrial wastewaters to treat. Currently, commonly used treatment methods include biological methods, electrochemical methods, ionizing irradiation (CN201711329143.7), and adsorption methods (CN201911182741.5). It is worth noting that purely physical treatment often serves only as a pretreatment measure (CN201710259259.1), aiming to improve the biodegradability of the wastewater, but rarely directly achieving water quality standards. Furthermore, photocatalytic degradation has attracted attention due to its relatively low cost. For example, Liu Zhifeng et al. achieved good results in treating antibiotics using a silver phosphate / bismuth sulfide / bismuth oxide dual Z-type photocatalyst (CN201811392023.6), but the treatment cycle was relatively long. While biological methods are low-cost, their long treatment cycles limit their practical application. Adsorption or filtration methods can only temporarily collect antibiotics but cannot degrade them. Electrochemical methods are ineffective in treating low-concentration antibiotic wastewater and are energy-intensive. Photocatalysis utilizes sunlight to excite semiconductor catalysts, generating photogenerated charge carriers that react with water or dissolved oxygen to produce reactive substances such as hydroxyl radicals and superoxide radicals. These reactive substances can effectively degrade antibiotic molecules. Relatively speaking, photocatalysis is a highly efficient, low-energy-consumption, and more thorough method for treating antibiotic wastewater.

[0003] Based on the above background, this invention has successfully developed a low-cost photocatalyst with low photogenerated carrier recombination rate, superior photocatalytic performance, strong stability and wide degradation range by constructing a dual heterostructure, which is expected to be widely used in the field of industrial antibiotic wastewater treatment. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, the primary objective of this invention is to provide a method for preparing a CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst. This preparation process is simple, the reaction conditions are mild, and the resulting photocatalyst exhibits good degradation effects on antibiotics, providing a new solution for the treatment of industrial antibiotic wastewater and showing broad application prospects.

[0005] The second objective of this invention is to provide the above-mentioned CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst, which has a low photogenerated carrier recombination rate, high photocatalytic performance, good stability, and good degradation effect on levofloxacin, norfloxacin, and oxytetracycline hydrochloride.

[0006] A third objective of this invention is to provide an application of the above-mentioned CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst.

[0007] To achieve the aforementioned first objective, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing a CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst includes the following steps: adding Bi2WO6 / g-C3N4 catalyst and cadmium salt to a solvent for ultrasonic dispersion and stirring, then adding an alcohol solution containing a sulfur source for water bath reaction; collecting the product by centrifugation, washing and drying to obtain the final product.

[0009] This invention synthesizes a CdSQDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst by employing a solvothermal reaction and a mild in-situ chemical growth technique. This method is simple to operate, the reaction conditions are mild, and the resulting catalyst has broad application prospects in the field of photocatalysis.

[0010] As a preferred embodiment of the present invention, the ratio of the Bi2WO6 / g-C3N4 catalyst to the cadmium salt is 1g:(3-14)mmol.

[0011] By precisely controlling the ratio of Bi2WO6 / g-C3N4 to cadmium salt, the distribution and loading of CdS QDs on the Bi2WO6 / g-C3N4 surface can be optimized, thereby forming a more uniform and dense double heterojunction structure, which is beneficial to the effective separation and transport of photogenerated carriers and improves photocatalytic efficiency.

[0012] As a preferred embodiment of the present invention, the amount of cadmium salt and sulfur source added is such that the molar ratio of Cd atoms to S atoms is 1:(1.1-1.2).

[0013] By strictly controlling the molar ratio of Cd atoms to S atoms, the generation amount and size distribution of CdS QDs can be precisely controlled, which helps to form uniform and monodisperse CdS QDs, thereby improving their coverage and loading efficiency on the Bi2WO6 / g-C3N4 surface, thus optimizing the structure of the double heterojunction and ensuring a tight interfacial contact between CdS and Bi2WO6 / g-C3N4.

[0014] As a preferred embodiment of the present invention, the mass ratio of CdS QDs to Bi2WO6 / g-C3N4 in the CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst is (0.5-2):1.

[0015] By controlling the amounts of Bi2WO6 / g-C3N4, cadmium salt, and sulfur source in the above technical solution, the mass ratio of CdS QDs to Bi2WO6 / g-C3N4 in the CdSQDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst prepared by the present invention is (0.5-2):1, more preferably 0.5:1, 0.625:1, 0.75:1, 0.875:1, 1:1, and 2:1.

[0016] As a preferred embodiment of the present invention, the cadmium salt is any one of (CH3COO)2Cd·2H2O, CdCl2, and Cd(NO3)2; the sulfur source is any one of thioacetamide, thiourea, and sodium sulfide.

[0017] As a preferred embodiment of the present invention, the ultrasonic dispersion time is 10-15 min; the stirring temperature is 60-90℃ and the stirring time is 8-15 min.

[0018] Controlling the ultrasonic dispersion time to within 10-15 minutes ensures uniform dispersion of cadmium salt and Bi2WO6 / g-C3N4 in the solvent. This facilitates uniform loading of CdS QDs onto the Bi2WO6 / g-C3N4 surface, preventing agglomeration and thus improving the performance of the dual heterojunction photocatalyst. Controlling the stirring temperature and time ensures the uniformity of CdS QDs on the Bi2WO6 / g-C3N4 surface. 2+ Sufficient contact with Bi2WO6 / g-C3N4 prepares the material for the subsequent sulfidation reaction. Furthermore, appropriate ultrasonic dispersion and stirring conditions can accelerate the reaction process and shorten the preparation cycle.

[0019] As a preferred embodiment of the present invention, the heating reaction is carried out at a temperature of 60-90°C for 1-2 hours.

[0020] By controlling the temperature and reaction time, not only can the complete sulfidation reaction and optimized growth of CdS quantum dots be promoted, but the interfacial bonding force between CdS quantum dots and Bi2WO6 / g-C3N4 can also be enhanced, thereby forming a more compact and uniform double heterojunction structure and improving the degradation efficiency and activity of the photocatalyst.

[0021] As a preferred embodiment of the present invention, the mass ratio of g-C3N4 to Bi2WO6 in the g-C3N4 / Bi2WO6 catalyst is (0.05-2):1; the preparation process of the g-C3N4 / Bi2WO6 catalyst includes: adding tungstate and g-C3N4 to a hexadecyltrimethylammonium bromide solution, ultrasonically dispersing, then adding bismuth salt for hydrothermal reaction, and centrifuging, washing, and drying to obtain the catalyst.

[0022] As a preferred embodiment of the present invention, the tungstate is sodium tungstate, potassium tungstate, or ammonium tungstate; the bismuth salt is any one of bismuth nitrate, bismuth oxynitrate, bismuth chloride, bismuth oxychloride, bismuth acetate, and bismuth formate; the hydrothermal reaction is carried out at a temperature of 100-160°C for 12-36 hours.

[0023] To achieve the second objective mentioned above, the technical solution adopted by the present invention is as follows:

[0024] A CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst was prepared using the preparation method described in the first objective of this invention.

[0025] To achieve the third objective mentioned above, the technical solution adopted by the present invention is as follows:

[0026] An application of a CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst for the photocatalytic degradation of antibiotic pollutants in water.

[0027] As a preferred embodiment of the present invention, the antibiotic contaminant may be tetracycline, levofloxacin, norfloxacin, or oxytetracycline hydrochloride.

[0028] As a preferred embodiment of the present invention, the concentration of the antibiotic pollutants in the water is 10-80 mg / L, and the addition ratio of the CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst in the antibiotic wastewater is (0.5-1) g / L.

[0029] As a preferred embodiment of the present invention, the light intensity of the photocatalytic degradation is 300-500 mW / cm². 2 The temperature is 25-35℃ and the time is 10-60 minutes.

[0030] Through the above technical solution, the CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst of the present invention is mixed with antibiotic wastewater, stirred under dark conditions, and after reaching adsorption equilibrium, photocatalytic reaction is carried out under light conditions to complete the degradation treatment of antibiotic pollutants.

[0031] The present invention has the following advantages over the prior art:

[0032] 1. This invention synthesizes a CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst using a solvothermal reaction and mild-condition in-situ chemical growth technique. Specifically, the Bi2WO6 / g-C3N4 catalyst and an appropriate amount of cadmium salt are added to a solvent and dispersed evenly. Then, an alcohol solution containing a sulfur source is added, and CdS QDs are generated in situ under mild conditions, forming a tight dual heterojunction structure with the Bi2WO6 / g-C3N4 catalyst. This method is simple to operate, has mild reaction conditions, and is low in cost. The resulting photocatalyst exhibits good degradation effects on antibiotics, providing a new solution for the treatment of industrial antibiotic wastewater and showing broad application prospects.

[0033] 2. The CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst synthesized in this invention exhibits high activity, good stability, and fast degradation rate of antibiotics under visible light. It shows good degradation effects on levofloxacin, norfloxacin, oxytetracycline hydrochloride, and tetracycline, with a degradation rate of over 80%.

[0034] 3. The CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst synthesized in this invention has good universality for antibiotic degradation, providing a new idea and method for the development of new high-efficiency visible light photocatalysts. It has great practical application prospects in the field of photocatalytic treatment of antibiotic wastewater. Attached Figure Description

[0035] Figure 1 This is a TEM image of the CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst of the present invention;

[0036] Figure 2 This invention demonstrates the free radical capture activity of the CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst for the degradation of tetracycline.

[0037] Figure 3 The figures are Mott-schottky curves for Bi2WO6, CdS QDs and g-C3N4, where (a), (b) and (c) correspond to Bi2WO6, CdS QDs and g-C3N4 respectively.

[0038] Figure 4 This is a diagram illustrating the photocatalytic mechanism of the CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst of the present invention.

[0039] Figure 5 This is a comparison of the degradation activities of tetracycline on the CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst obtained in Example 1 of the present invention and the comparative catalysts obtained in Comparative Examples 1-3.

[0040] Figure 6 The photodegradation activity of the CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst obtained in Example 1 of this invention for various antibiotics;

[0041] Figure 7 This paper presents the changes in absorbance of various antibiotics over time during the degradation of various antibiotics by the CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst of the present invention. Among them, (a), (b), (c), and (d) correspond to oxytetracycline hydrochloride, norfloxacin, levofloxacin, and tetracycline, respectively. Detailed Implementation

[0042] The technical solution of the present invention will be further described below with reference to specific embodiments. However, those skilled in the art should understand that the following embodiments are only for illustrating the present invention and should not be regarded as limiting the present invention. Specific conditions not specified in the embodiments are performed according to conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the reagents or instruments used are all conventional products obtained through commercial channels.

[0043] Example 1

[0044] A method for preparing a CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst includes the following steps:

[0045] (1) Melamine and NH4Cl were mixed in a mass ratio of 1:1, ground thoroughly, and placed in a 50 mL crucible in a muffle furnace. The temperature was raised from room temperature to 550 °C and held for 4 h (heating rate of 5 °C / min). After cooling to room temperature and grinding, the crucible containing the powder was placed back into the muffle furnace, and the temperature was raised again to 550 °C (heating rate of 5 °C / min) and held for 2 h. After the powder cooled to room temperature, it was washed several times alternately with distilled water and anhydrous ethanol, and then dried in an oven at 60 °C to obtain g-C3N4.

[0046] (2) Prepare a homogeneous solution by mixing 25 mg of hexadecyltrimethylammonium bromide (CTAB) with 40 mL of deionized water. After the solution becomes clear, add 0.1649 g of Na2WO4·2H2O and stir until dissolved. Then add 0.25 g of g-C3N4 obtained in step (1) and ultrasonically disperse for 30 min. Next, add 0.4851 g of Bi(NO3)3·5H2O and stir for 2 h. Transfer the mixture to a polytetrafluoroethylene reactor and place it in an electric heating drying oven at 120 °C for hydrothermal treatment for 24 h. After cooling to room temperature, wash and dry the product to obtain the Bi2WO6 / g-C3N4 catalyst.

[0047] (3) Take 0.2g of Bi2WO6 / g-C3N4 catalyst and add it to 35mL of ethanol. Then add 0.1845g of Cd(CH3COO)2·2H2O and disperse it by ultrasonication for 10min. Then stir it in a water bath at 70℃ for 10min. Then add a homogeneous solution of 0.0515g of thioacetamide (TAA) and 15mL of ethanol under vigorous stirring. Continue to react in a water bath at 80℃ for 1h. After cooling to room temperature, centrifuge, wash and dry at 60℃ to obtain CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst.

[0048] This embodiment also provides a CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst, which is prepared by the above method.

[0049] Example 2

[0050] A method for preparing a CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst includes the following steps:

[0051] (1) Urea and NH4Cl were mixed in a mass ratio of 3:1, ground thoroughly, and placed in a 50 mL crucible in a muffle furnace. The temperature was raised from room temperature to 520 °C and held for 3 h (heating rate 3 °C / min). After cooling to room temperature and grinding, the crucible containing the powder was placed back into the muffle furnace, and the temperature was raised again to 520 °C (heating rate 3 °C / min) and held for 2 h. After the powder cooled to room temperature, it was washed several times alternately with distilled water and anhydrous ethanol, and then dried in an oven at 60 °C to obtain g-C3N4.

[0052] (2) Prepare a homogeneous solution by mixing 30 mg of hexadecyltrimethylammonium bromide (CTAB) with 50 mL of deionized water. After the solution becomes clear, add 0.1810 g of K2WO4·2H2O and stir until dissolved. Then add 0.25 g of g-C3N4 obtained in step (1) and ultrasonically disperse for 30 min. Next, add 50 mL of ethanol solution of BiCl3 (with a mass of 0.3153 g of BiCl3) and stir vigorously for 2 h. Transfer the mixture to a polytetrafluoroethylene reactor and place it in an electric heating drying oven at 120 °C for hydrothermal treatment for 24 h. After cooling to room temperature, wash and dry the product to obtain the Bi2WO6 / g-C3N4 catalyst.

[0053] (3) Take 0.2g of Bi2WO6 / g-C3N4 catalyst and add it to 35mL of ethanol. Then add 0.1845g of Cd(CH3COO)2·2H2O and disperse it by ultrasonication for 15min. Then stir it in a 60℃ water bath for 15min. Then add a homogeneous solution of 0.0515g of thioacetamide (TAA) and 15mL of ethanol under vigorous stirring. Continue to react in a 60℃ water bath for 2h. After cooling to room temperature, centrifuge, wash and dry at 60℃ to obtain CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst.

[0054] This embodiment also provides a CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst, which is prepared by the above method.

[0055] Example 3

[0056] A method for preparing a CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst includes the following steps:

[0057] (1) Melamine and NH4Cl were mixed in a mass ratio of 1:1, ground thoroughly, and placed in a 50 mL crucible in a muffle furnace. The temperature was raised from room temperature to 550 °C and held for 4 h (heating rate of 5 °C / min). After cooling to room temperature and grinding, the crucible containing the powder was placed back into the muffle furnace, and the temperature was raised again to 550 °C (heating rate of 5 °C / min) and held for 2 h. After the powder cooled to room temperature, it was washed several times alternately with distilled water and anhydrous ethanol, and then dried in an oven at 60 °C to obtain g-C3N4.

[0058] (2) Prepare a homogeneous solution by mixing 35 mg of hexadecyltrimethylammonium bromide (CTAB) with 40 mL of deionized water. After the solution becomes clear, add 0.1649 g of Na2WO4·2H2O and stir until dissolved. Then add 0.5 g of g-C3N4 obtained in step (1) and ultrasonically disperse for 30 min. Next, add 0.4851 g of Bi(NO3)3·5H2O and stir for 2 h. Transfer the mixture to a polytetrafluoroethylene reactor and place it in an electric heating drying oven at 120 °C for hydrothermal treatment for 24 h. After cooling to room temperature, wash and dry the product to obtain Bi2WO6 / g-C3N4.

[0059] (3) Take 0.2g Bi2WO6 / g-C3N4 and add it to 35mL of ethanol. Then add 0.2768g of Cd(CH3COO)2·2H2O and disperse it by ultrasonication for 15min. Then stir it in a 90℃ water bath for 8min. Then add a homogeneous solution of 0.0773g of thioacetamide (TAA) and 15mL of ethanol under vigorous stirring. Continue to react in a 90℃ water bath for 1h. After cooling to room temperature, centrifuge, wash and dry at 60℃ to obtain CdS QDs / Bi2WO6 / g-C3N4 double heterojunction photocatalyst.

[0060] This embodiment also provides a CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst, which is prepared by the above method.

[0061] Example 4

[0062] A method for preparing a CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst includes the following steps:

[0063] (1) Urea and NH4Cl were mixed in a mass ratio of 3:1, ground thoroughly, and placed in a 50 mL crucible in a muffle furnace. The temperature was raised from room temperature to 520 °C and held for 3 h (heating rate 3 °C / min). After cooling to room temperature and grinding, the crucible containing the powder was placed back into the muffle furnace, and the temperature was raised again to 520 °C (heating rate 3 °C / min) and held for 2 h. After the powder cooled to room temperature, it was washed several times alternately with distilled water and anhydrous ethanol, and then dried in an oven at 60 °C to obtain g-C3N4.

[0064] (2) Prepare a homogeneous solution by mixing 30 mg of hexadecyltrimethylammonium bromide (CTAB) with 50 mL of deionized water. After the solution becomes clear, add 0.1810 g of K2WO4·2H2O and stir until dissolved. Then add 0.5 g of g-C3N4 obtained in step (1) and ultrasonically disperse for 30 min. Next, add 50 mL of ethanol solution of BiCl3 (with a mass of 0.3153 g of BiCl3) and stir vigorously for 2 h. Transfer the mixture to a polytetrafluoroethylene reactor and place it in an electric heating drying oven at 120 °C for hydrothermal treatment for 24 h. After cooling to room temperature, wash and dry the product to obtain Bi2WO6 / g-C3N4.

[0065] (3) Take 0.2g Bi2WO6 / g-C3N4 and add it to 35mL of ethanol. Then add 0.738g of Cd(CH3COO)2·2H2O and disperse it by ultrasonication for 10min. Then stir it in an 80℃ water bath for 10min. Then add a homogeneous solution of 0.206g of thioacetamide (TAA) and 20mL of ethanol under vigorous stirring. Continue to react in a 70℃ water bath for 2h. After cooling to room temperature, centrifuge, wash and dry at 60℃ to obtain CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst.

[0066] This embodiment also provides a CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst, which is prepared by the above method.

[0067] Comparative Example 1

[0068] The difference between Comparative Example 1 and Example 1 is that step (1) is omitted and g-C3N4 is not added in step (2), that is, pure Bi2WO6 is prepared by the same method as step (2) of Example 1; then Bi2WO6 / g-C3N4 in step (3) of Example 1 is replaced with pure Bi2WO6 to obtain CdS QDs / Bi2WO6 catalyst.

[0069] Comparative Example 2

[0070] The difference between Comparative Example 2 and Example 1 is that step (2) is omitted, and Bi2WO6 / g-C3N4 in step (3) of Example 1 is replaced with g-C3N4 to obtain CdS QDs / g-C3N4 catalyst.

[0071] Comparative Example 3

[0072] The difference between Comparative Example 3 and Example 1 is that step (3) is omitted, thus obtaining the Bi2WO6 / g-C3N4 catalyst.

[0073] Comparative Example 4

[0074] The difference between Comparative Example 4 and Example 1 is that steps (1) and (2) are omitted, and Bi2WO6 / g-C3N4 is not added to ethanol in step (3). That is, pure CdS QDs are prepared by the method of step (3) in Example 1.

[0075] Experimental Example 1: Structural Characterization

[0076] 1. The specific surface area, pore size and pore volume parameters of g-C3N4 prepared in step (1) of Example 1, pure Bi2WO6 prepared in Comparative Example 1, pure CdSQDs prepared in Comparative Example 4, Bi2WO6 / g-C3N4 prepared in Comparative Example 3 and CdS QDs / Bi2WO6 / g-C3N4 prepared in Example 1 are shown in Table 1.

[0077] Table 1. Specific surface area, pore size, and pore volume parameters of various catalysts

[0078] Catalysts <![CDATA[Specific surface area (m 2 g -1 )]]> Aperture (nm) <![CDATA[Pore volume (cm 3 g -1 )]]> <![CDATA[g-C3N4]]> 82.57 34.65 0.753 <![CDATA[Bi2WO6]]> 41.67 27.48 0.220 CdS QDs 91.23 32.16 0.652 <![CDATA[Bi2WO6 / g-C3N4]]> 60.40 27.23 0.358 <![CDATA[CdS QDs / Bi2WO6 / g-C3N4]]> 75.14 29.46 0.371

[0079] 2. TEM image of the CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst obtained in Example 1 is shown below. Figure 1 As shown.

[0080] Experimental Example 2

[0081] To investigate the free radical scavenging activity of the CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst obtained in Example 1 of this invention for degrading tetracycline, ascorbic acid was used to capture ·O2. - Ammonium oxalate is used to capture h + Isopropanol was used to capture ·OH. The specific test method was as follows: the CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst obtained in Example 1 was added to 100 mL of water containing 50 mg / L tetracycline, and different free radical scavengers were added. The mixture was stirred in the dark for 30 min to reach adsorption and desorption equilibrium. The photocatalytic degradation experiment was conducted under irradiation with a 300W xenon lamp equipped with a 400 nm cutoff filter, with a light intensity of 345 mW / cm². 2 At specific time intervals, take 3 mL of the degradation solution, centrifuge thoroughly, collect the supernatant, filter it through a 0.22 μm filter, and then measure the absorbance of the solution at the characteristic wavelength of the pollutant using a UV-Vis spectrophotometer. Record the change in absorbance of the pollutant solution with light exposure time. See [link to test results]. Figure 2 .

[0082] from Figure 2 The free radical capture experiment results clearly show that the degradation rate of tetracycline decreased only slightly after the addition of isopropanol and ammonium oxalate, while the degradation rate dropped sharply to 1.55% after the addition of ascorbic acid. This indicates that the degradation rate of tetracycline by O2 during photocatalytic degradation is significantly reduced. - Plays the most crucial role, h + It also participates in the degradation of tetracycline to some extent. The order of contribution of the three to the photodegradation reaction can be expressed as: ·O2 - h + >·OH.

[0083] Experimental Example 3

[0084] To further investigate the photocatalytic mechanism of the CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst prepared in this invention, electrochemical tests were performed on its constituent components—Bi2WO6, CdS QDs, and g-C3N4. Based on the Mott-Schottky curves and valence band spectroscopy results, the conduction and valence band positions of the three semiconductors were determined. The results are detailed below. Figure 3 and Figure 4 .

[0085] Figure 3 Mott-Schottky curves for Bi2WO6, CdS QDs, and g-C3N4. Figure 4 This is a diagram illustrating the photocatalytic mechanism of the CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst. Due to the difference in conduction band potential between g-C3N4 and CdS QDs compared to O2 / ·O2... - The potential is more negative, and the electrons in their respective conduction bands can reduce the O2 adsorbed on the catalyst surface to ·O2, which has strong oxidizing power. - This process further decomposes antibiotics into non-toxic small molecules. Similarly, because the valence band potential of Bi2WO6 is only +2.36 eV, lower than that of H2O / ·OH (+2.4 eV), holes in its valence band cannot generate ·OH and can only migrate to the surface of Bi2WO6 to oxidize organic pollutants into small molecules. When the catalyst is photoexcited, under the influence of its built-in electric field, photogenerated holes from g-C3N4 and CdS QDs recombine with photogenerated electrons from Bi2WO6 at the contact interface, thereby extending the photogenerated electron lifetime of g-C3N4 and CdS QDs and generating more ·O2. - Therefore, it can degrade various antibiotics more efficiently, exhibiting... Figure 4 The dual heterojunction catalytic mechanism is shown.

[0086] Test Example 4

[0087] To investigate the effectiveness of the catalysts obtained in Examples 1-4 and Comparative Examples 1-3 in removing antibiotic pollutants from antibiotic wastewater, the catalysts obtained in Examples 1-4 and Comparative Examples 1-3 were added to antibiotic wastewater with a tetracycline concentration of 50 mg / L. The addition ratio of each catalyst group was 0.5 g / L, and the mixture was stirred at 1000 rpm until homogeneous. The specific experimental method was the same as in Experiment 2, except that a free radical scavenger was not added. The degradation activity results of each catalyst group for tetracycline are as follows: Figure 5 As shown.

[0088] like Figure 5As shown, after 12 min of photocatalytic degradation, compared with the degradation rates of tetracycline by the CdS QDs / Bi2WO6 catalyst, CdS QDs / g-C3N4 catalyst, and Bi2WO6 / g-C3N4 catalyst obtained in Comparative Examples 1-3 (70.6%, 72.4%, and 40.2%, respectively), the degradation rate of tetracycline by the CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst prepared in this invention was significantly higher, reaching 80.9%. This is because a chemical reaction occurs between CdS QDs, Bi2WO6, and Bi2WO6 / g-C3N4. Figure 1 The unique dual heterostructure shown effectively promotes the separation and migration of photogenerated electron-hole pairs, reduces the recombination probability, and thus significantly improves photocatalytic activity. This charge separation mechanism not only prolongs the lifetime of photogenerated carriers but also enhances the redox capacity of the catalyst, enabling more tetracycline molecules to be photocatalytically degraded.

[0089] The above results indicate that the CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst prepared in this invention exhibits excellent performance in tetracycline degradation, with fast degradation rate and high degradation efficiency, and has potential application value in environmental pollution control.

[0090] Experimental Example 5

[0091] To demonstrate the degradation versatility of the CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst of this invention and the change in absorbance of each antibiotic over time during degradation, the CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst obtained in Example 1 was added to wastewater containing tetracycline, levofloxacin, norfloxacin, and oxytetracycline hydrochloride, respectively. The concentrations of tetracycline, levofloxacin, norfloxacin, and oxytetracycline hydrochloride in the wastewater were all 0.5 g / L. The photodegradation activity of various antibiotics was tested using the method described in Example 4. The results are shown in [link to example]. Figure 6 The changes in absorbance of various antibiotics over time during the degradation of various antibiotics by the CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst are shown in the figure. Figure 7 .

[0092] from Figure 6 As can be seen from the above, the CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst prepared in this invention has excellent degradation activity for tetracycline, levofloxacin, norfloxacin and oxytetracycline hydrochloride within 12 min, with a degradation rate of not less than 80%, indicating that the CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst of this invention has good universality for antibiotic degradation.

[0093] Figure 7 This figure shows the change in absorbance of various antibiotics over time during the degradation of various antibiotics by the CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst. (a), (b), (c), and (d) correspond to oxytetracycline hydrochloride, norfloxacin, levofloxacin, and tetracycline, respectively. Figure 7 It can be seen that during the dark-state adsorption-desorption equilibrium before illumination, the absorption peaks of various antibiotics, such as levofloxacin, did not shift significantly under the action of the catalyst, indicating that the adsorption process did not alter the structure of the antibiotics. However, after irradiation with the light for 2-3 minutes, the absorbance of various antibiotic solutions showed a sharp decrease at wavelengths of approximately 275 nm and 357 nm, and the positions of the absorption peaks shifted significantly with the extension of illumination time. This demonstrates the effective degradation of various antibiotics by the CdS QDs / Bi2WO6 / g-C3N4 dual heterojunction photocatalyst of this invention.

[0094] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. The basic principles and main features of the present invention have been described above with specific implementation schemes. Based on the present invention, some modifications or substitutions can be made, but these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of protection claimed by the present invention.

Claims

1. A method for preparing a CdS QDs / Bi 2 WO 6 / g-C 3 N 4 double heterojunction photocatalyst, characterized in that, The method comprises the following steps: The Bi2WO6 / g-C3N4 catalyst and the cadmium salt are added into a solvent for ultrasonic dispersion and stirring, and then an alcohol solution containing a sulfur source is added for water bath reaction; the product is collected by centrifugation, and is washed and dried to obtain the product; The adding amount of the cadmium salt and the sulfur source is a molar ratio of Cd atoms to S atoms of 1: (1.1-1.2) ; The temperature of the water bath reaction is 60-90 DEG C, and the time is 1-2 h.

2. The method for preparing CdS QDs / Bi2WO6 / g-C3N4 double heterojunction photocatalyst according to claim 1, characterized in that, The Bi2WO6 / g-C3N4 catalyst and the cadmium salt are added into a solvent for ultrasonic dispersion and stirring, and then an alcohol solution containing a sulfur source is added for water bath reaction; the product is collected by centrifugation, and is washed and dried to obtain the product; 3. The method for preparing CdS QDs / Bi2WO6 / g-C3N4 double heterojunction photocatalyst according to claim 1, characterized in that, The mass ratio of CdS QDs to Bi2WO6 / g-C3N4 in the CdS QDs / Bi2WO6 / g-C3N4 double heterojunction photocatalyst is (0.5-2) :

1.

4. The method for preparing CdS QDs / Bi2WO6 / g-C3N4 double heterojunction photocatalyst according to claim 1, characterized in that, The cadmium salt is any one of (CH3COO)2Cd·2H2O, CdCl2 and Cd(NO3)2; and the sulfur source is any one of thioacetamide, thiourea and sodium sulfide.

5. The method for preparing CdS QDs / Bi2WO6 / g-C3N4 double heterojunction photocatalyst according to claim 1, characterized in that, The ultrasonic dispersion time is 10-15 min; the stirring temperature is 60-90 DEG C, and the time is 8-15 min.

6. The method for preparing CdS QDs / Bi2WO6 / g-C3N4 double heterojunction photocatalyst according to claim 1, characterized in that, The mass ratio of g-C3N4 to Bi2WO6 in the Bi2WO6 / g-C3N4 catalyst is (0.05-2) : 1; and the preparation process of the Bi2WO6 / g-C3N4 catalyst comprises the following steps: a tungstate and g-C3N4 are added into a cetyltrimethylammonium bromide solution, ultrasonic dispersion is carried out, then a bismuth salt is added for hydrothermal reaction, and the product is collected by centrifugation, washed and dried to obtain the product.

7. A CdS QDs / Bi2WO6 / g-C3N4 double heterojunction photocatalyst, characterized in that, The preparation method is prepared by using the preparation method in any one of claims 1-6.

8. Use of the CdS QDs / Bi2WO6 / g-C3N4 bi-heterojunction photocatalyst according to claim 7, characterized in that, The method is used for photocatalytic degradation of antibiotic pollutants in water.

Images