Bromine-modified zinc tin oxide photocatalyst and preparation method and application thereof

Abstract

This invention relates to the field of photocatalytic materials technology, and discloses a bromine-modified zinc tin oxide photocatalyst, its preparation method, and its application. The method includes dissolving L-tryptophan, SnCl4·5H2O, and Zn(Ac)2·2H2O in deionized water to obtain a first mixture; adding NaBr to the first mixture to obtain a second mixture; adding anhydrous sodium carbonate to the second mixture and then carrying out a hydrothermal reaction; and centrifuging, washing, and drying the product after the hydrothermal reaction to obtain the target catalyst. This invention introduces NaBr into the synthesis system, promoting the entry of bromine into the crystal interior, inducing lattice contraction and a reduction in interplanar spacing. This change in microstructure shortens the internal charge transport path and improves the charge separation efficiency of the photocatalyst. Combined with L-tryptophan to control the reaction rate, this ultimately enhances the photocatalytic degradation rate of volatile organic compounds.

Description

Technical Field

[0001] This invention relates to the field of photocatalytic materials technology, specifically to a bromine-modified zinc tin oxide photocatalyst, its preparation method, and its application. Background Technology

[0002] Zinc tin oxide, as an inorganic semiconductor material, has potential applications in the photocatalytic degradation of volatile organic compounds. However, existing unmodified zinc tin oxide photocatalysts generally suffer from long internal charge transport paths, resulting in low separation efficiency of photogenerated charges, which directly limits the photocatalytic degradation rate of volatile organic compounds.

[0003] To improve catalytic performance, researchers have attempted to modify semiconductor materials by doping. However, in practice, it is often difficult to precisely balance the relationship between the dopant ratio and the stability of the original crystal structure, and there is a lack of effective means to simultaneously control morphology and reaction rate. This can easily lead to the destruction of the material's crystal phase, making it impossible to guarantee a high degradation conversion rate for the final product.

[0004] In addition, some existing photocatalyst synthesis processes have drawbacks such as complicated preparation procedures and difficulty in controlling reaction conditions, resulting in poor crystal quality of the obtained products or the formation of impurity phases, making it difficult to replace existing processes to provide a stable and reliable source of degradation materials. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a bromine-modified zinc tin oxide photocatalyst, its preparation method, and its application. This solves the problem that the long internal charge transport path of unmodified zinc tin oxide photocatalysts leads to low charge separation efficiency, resulting in insufficient degradation reaction rate and final conversion rate of volatile organic compounds.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] The first aspect of this invention provides a bromine-modified zinc tin oxide photocatalyst, the raw materials for which include L-tryptophan, SnCl4·5H2O, Zn(Ac)2·2H2O and NaBr;

[0008] The proportions were controlled as follows: the molar ratio of L-tryptophan, SnCl4·5H2O and Zn(Ac)2·2H2O was 1.96:0.63:1.2;

[0009] The ratio of the number of moles of NaBr to the total number of moles of SnCl4·5H2O and Zn(Ac)2·2H2O is 0.1 to 0.75.

[0010] Adding NaBr to the reaction system allows bromine to enter the zinc-tin oxide crystal, inducing internal arrangement changes and lattice contraction. The microstructural changes manifest as a shift in the diffraction peak angle of the (311) crystal plane to higher angles, accompanied by a decrease in interplanar spacing. This shrinkage in interplanar spacing optimizes the internal charge transport path, improving the charge separation efficiency of the zinc-tin oxide material. Furthermore, the combination of L-tryptophan as a morphology modifier and ligand to control the reaction rate enhances the degradation activity of the photocatalyst.

[0011] Preferably, the ratio of the number of moles of NaBr to the total number of moles of SnCl4·5H2O and Zn(Ac)2·2H2O is 0.122.

[0012] Preferably, the (311) crystal plane diffraction peak angle of the bromine-modified zinc tin oxide photocatalyst is between 33.85° and 34.16°.

[0013] Preferably, the (311) interplanar spacing of the bromine-modified zinc tin oxide photocatalyst is 0.256 nm.

[0014] A second aspect of this invention provides a method for preparing a bromine-modified zinc tin oxide photocatalyst, comprising the following steps:

[0015] L-tryptophan, SnCl4·5H2O and Zn(Ac)2·2H2O were dissolved in deionized water to prepare the first mixture.

[0016] Add NaBr to the first mixture and mix and stir to obtain the second mixture;

[0017] Anhydrous sodium carbonate was added to the second mixture as a precipitant, and after thorough stirring, it was placed in a hydrothermal reactor to carry out the hydrothermal reaction.

[0018] The product after the hydrothermal reaction was centrifuged, washed, and dried to collect the bromine-modified zinc tin oxide photocatalyst.

[0019] Preferably, the hydrothermal reaction temperature is set to 120°C and the hydrothermal reaction time is set to 24 hours.

[0020] Preferably, when preparing the first mixture, the ratio of the number of moles of SnCl4·5H2O added to the volume of deionized water is controlled to be 0.0252 mmol / ml.

[0021] Preferably, when adding anhydrous sodium carbonate, the molar ratio of anhydrous sodium carbonate to SnCl4·5H2O is limited to 7.25:0.63.

[0022] Preferably, the product after the hydrothermal reaction is naturally cooled to room temperature before centrifugation.

[0023] A third aspect of this invention provides the application of a bromine-modified zinc tin oxide photocatalyst in the degradation of volatile organic compounds. The photocatalyst, after being coated and dried to form a thin film, is placed in a reactor containing volatile organic compound gases and subjected to a photocatalytic reaction under ultraviolet light irradiation. Changes in gas concentration are monitored and recorded to obtain the degradation results.

[0024] This invention provides a bromine-modified zinc tin oxide photocatalyst, its preparation method, and its application. It possesses the following beneficial effects:

[0025] 1. This invention introduces NaBr into the zinc-tin oxide preparation system, promoting the entry of bromine into the crystal interior and inducing lattice contraction, resulting in a decrease in interplanar spacing. This alteration of the microstructure shortens the charge transport path within the photocatalyst, improves charge separation efficiency, and enhances the photocatalytic degradation rate of volatile organic compounds.

[0026] 2. This invention controls the chemical reaction rate by limiting the ratio range of the molar number of NaBr to the total molar number of SnCl4·5H2O and Zn(Ac)2·2H2O, and by utilizing L-tryptophan as a morphology modifier and ligand. The synergistic effect among the formulation components achieves crystal fine-tuning while maintaining the stability of the original crystal phase, ensuring that the photocatalyst has a high degradation conversion rate.

[0027] 3. This invention provides a clear method for preparing photocatalysts by combining dissolution and stirring, the addition of anhydrous sodium carbonate precipitation, and a constant-temperature hydrothermal treatment process. The synthesis process is easy to control, and the obtained product has good crystal quality and is free of impurity phases, providing a stable and reliable material source for the degradation of volatile organic compounds. Attached Figure Description

[0028] Figure 1 The X-ray diffraction (XRD) patterns and ZSO standard charts of the comparative examples and Examples 1-5 of the present invention are shown.

[0029] Figure 2 Figure (a) is a high-resolution transmission electron microscope image of the comparative example of the present invention, and Figure (b) is a low-magnification transmission electron microscope image of the comparative example of the present invention.

[0030] Figure 3 Figure (a) is a high-resolution transmission electron microscope image of Example 2 of the present invention, and Figure (b) is a low-magnification transmission electron microscope image of Example 2 of the present invention.

[0031] Figure 4 The images show the photocatalytic degradation activity test results for toluene in Examples 1-5 and the comparative examples of the present invention. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Unless otherwise specified, all reagents and instruments used in the embodiments of this invention can be purchased from the market.

[0034] This invention utilizes SnCl4·5H2O, Zn(Ac)2·2H2O, NaBr, and L-tryptophan as raw materials to prepare a bromine-modified zinc tin oxide photocatalyst via hydrothermal synthesis. Under hydrothermal synthesis conditions, this invention effectively incorporates bromine into the zinc tin oxide crystal lattice. The mechanism and catalytic principle of this preparation strategy specifically include: in terms of coordination and nucleation control, L-tryptophan acts as a morphology regulator and ligand, complexing with tin ions provided by SnCl4·5H2O and zinc ions provided by Zn(Ac)2·2H2O. This complexation controls the reaction rate in the reaction system, and, in conjunction with the synergistic effect of the hydrothermal reaction conditions, maintains the crystal phase stability of the target product, zinc tin oxide, and avoids the formation of impurity phases.

[0035] Regarding lattice doping and shrinkage, in a hydrothermal treatment environment, bromide ions generated by the dissociation of NaBr participate in the construction of the crystal network. The intervention of bromide ions into the crystal interior induces lattice shrinkage, which is manifested in the phase characterization as the (311) crystal plane diffraction peak shifting to higher angles (e.g., between 33.85° and 34.16°), directly reflecting the degree of lattice shrinkage induced by bromine doping. In terms of improving photocatalytic performance, lattice shrinkage reduces the interplanar spacing (e.g., the (311) crystal plane spacing is reduced to 0.256 nm), shortening the physical path for photogenerated electrons and holes to migrate from the lattice interior to the surface. The optimization of the microcrystalline structure directly improves the charge separation efficiency of zinc-tin oxide materials. The separated charges participate in the catalytic reaction, thereby improving the reaction rate and final conversion rate of the synthesized photocatalytic material in the degradation of organic pollutants.

[0036] In the hydrothermal synthesis preparation in the reactor, deionized water was used as the medium. Mixing and stirring facilitated the dissolution and complexation reactions of L-tryptophan, SnCl4·5H2O, and Zn(Ac)2·2H2O in water. L-tryptophan acted as a morphology modifier and ligand to control the reaction rate of the metal ions. The addition of NaBr ensured that bromide ions were uniformly dispersed in the complexation system. The addition of anhydrous sodium carbonate as a precipitant induced the formation of an amorphous precursor from the complexed metal ions. In the subsequent hydrothermal reaction at 120°C, the precursor underwent dehydration, rearrangement, and crystallization. The dispersed bromide ions were effectively incorporated into the zinc tin oxide crystalline network, completing lattice doping and shrinkage fine-tuning.

[0037] The specific hydrothermal reaction temperature and time conditions of this invention are as follows: hydrothermal synthesis is carried out at 120°C for 24 hours. Controlling the hydrothermal synthesis temperature and time within a suitable range helps ensure the high crystallinity of the zinc-tin oxide catalyst, allowing the precursors to react fully and preventing the destruction of the crystal phase. If the hydrothermal reaction temperature is too low or the holding time is too short, there is insufficient energy to promote complete crystal growth, and the product will contain unreacted precursors. If the hydrothermal reaction temperature is too high or the holding time is too long, it will not only increase energy consumption but also cause excessive grain agglomeration and growth, which is detrimental to maintaining the size of the catalyst material.

[0038] In some embodiments of the present invention, controlling the molar ratio of NaBr addition within a suitable range of 0.1 to 0.75 (preferably 0.122) can effectively regulate the internal structure of the material, ensuring that the obtained bromine-modified zinc tin oxide photocatalyst exhibits excellent degradation performance for volatile organic compounds such as toluene. If the ratio is too low, significant lattice shrinkage cannot be induced, and the charge transport path cannot be effectively shortened. If the ratio is too high, the photocatalytic activity of the material will decline, even approaching the level of the unmodified sample, affecting the catalytic degradation performance of the material. Furthermore, controlling the initial concentration of tin salt during the preparation of the mixture avoids excessively rapid nucleation leading to uneven particle size or decreased yield. Limiting the molar ratio of the precipitant anhydrous sodium carbonate to the tin source ensures that the metal cations are completely precipitated into the solid phase, avoiding component imbalance caused by liquid phase residue.

[0039] In some embodiments of the present invention, the prepared material is further subjected to post-treatment: after the hydrothermal reaction is completed, it is allowed to cool naturally to room temperature. This process gently releases the internal stress of the crystals grown under high temperature and high pressure, preventing defects from forming in the crystals due to a sudden drop in temperature. Subsequent centrifugation, washing, and drying operations remove soluble byproducts remaining on the surface of the material, resulting in a solid catalyst powder with a complete microstructure.

[0040] In other embodiments of the present invention, multiple characterization experiments and tests have demonstrated that, compared to conventional unmodified zinc tin oxide, the bromine-modified zinc tin oxide photocatalyst prepared by the present invention exhibits a significantly higher degradation and removal rate of toluene under ultraviolet light than the unmodified sample. Therefore, the present invention also provides the application of the bromine-modified zinc tin oxide photocatalyst in the degradation of volatile organic compounds such as toluene.

[0041] Its specific catalytic degradation process and mechanism include: the light energy absorption stage, in which the film with bromine-modified zinc tin oxide photocatalyst is placed in an environment containing volatile organic compounds such as toluene, and photon energy is input into the material system by turning on the light source such as ultraviolet high-pressure mercury lamp to irradiate the catalyst surface; the charge separation and surface migration stage, based on the lattice contraction effect caused by bromine doping during the catalyst preparation process, the interplanar spacing of the crystal (311) is reduced.

[0042] The reduction in interplanar spacing shortens the transport distance for photogenerated electrons and holes from the crystal interior to the material surface. This reduced transport distance decreases the probability of recombination of positive and negative charges during migration, improves overall charge separation efficiency, and ensures that charge carriers reach the catalyst surface. During the oxidative degradation stage, thanks to the shortened internal charge transport path and improved charge separation efficiency, charge carriers accumulated on the surface participate in the redox process under light irradiation, catalyzing the degradation of volatile organic compounds such as toluene adsorbed in the environment. Ultimately, this results in a significant improvement in the material's photocatalytic activity, reaction rate, and final conversion rate.

[0043] The following provides a further description of the bromine-modified zinc tin oxide photocatalyst, its preparation method, and its application.

[0044] Examples 1-5:

[0045] Example 1:

[0046] This embodiment provides a method for preparing a bromine-modified zinc tin oxide photocatalyst, comprising the following steps:

[0047] 1.96 mmol L-tryptophan, 0.63 mmol SnCl4·5H2O and 1.2 mmol Zn(Ac)2·2H2O were placed in a reaction vessel and dissolved in 25 ml of deionized water to obtain the first mixture.

[0048] Then, 0.015 g of NaBr was added to the first mixture and stirred to obtain the second mixture;

[0049] Then, 7.25 mmol of anhydrous sodium carbonate was added to the second mixture as a precipitant. After thorough stirring, the final mixture was transferred to a hydrothermal reactor and subjected to a hydrothermal reaction at 120°C for 24 hours.

[0050] After the reaction is complete, allow it to cool naturally to room temperature, centrifuge to collect the solid precipitate, and wash and dry the solid precipitate to obtain the target product, bromine-modified zinc tin oxide photocatalyst.

[0051] Example 2:

[0052] This embodiment provides a method for preparing a bromine-modified zinc tin oxide photocatalyst, comprising the following steps:

[0053] 1.96 mmol L-tryptophan, 0.63 mmol SnCl4·5H2O and 1.2 mmol Zn(Ac)2·2H2O were placed in a reaction vessel and dissolved in 25 ml of deionized water to obtain the first mixture.

[0054] Then, 0.023 g of NaBr was added to the first mixture and stirred to obtain the second mixture;

[0055] Then, 7.25 mmol of anhydrous sodium carbonate was added to the second mixture as a precipitant. After thorough stirring, the final mixture was transferred to a hydrothermal reactor and subjected to a hydrothermal reaction at 120°C for 24 hours.

[0056] After the reaction is complete, allow it to cool naturally to room temperature, centrifuge to collect the solid precipitate, and wash and dry the solid precipitate to obtain the target product, bromine-modified zinc tin oxide photocatalyst.

[0057] Example 3:

[0058] This embodiment provides a method for preparing a bromine-modified zinc tin oxide photocatalyst, comprising the following steps:

[0059] 1.96 mmol L-tryptophan, 0.63 mmol SnCl4·5H2O and 1.2 mmol Zn(Ac)2·2H2O were placed in a reaction vessel and dissolved in 25 ml of deionized water to obtain the first mixture.

[0060] Then, 0.045g of NaBr was added to the first mixture and stirred to obtain the second mixture;

[0061] Then, 7.25 mmol of anhydrous sodium carbonate was added to the second mixture as a precipitant. After thorough stirring, the final mixture was transferred to a hydrothermal reactor and subjected to a hydrothermal reaction at 120°C for 24 hours.

[0062] After the reaction is complete, allow it to cool naturally to room temperature, centrifuge to collect the solid precipitate, and wash and dry the solid precipitate to obtain the target product, bromine-modified zinc tin oxide photocatalyst.

[0063] Example 4:

[0064] This embodiment provides a method for preparing a bromine-modified zinc tin oxide photocatalyst, comprising the following steps:

[0065] 1.96 mmol L-tryptophan, 0.63 mmol SnCl4·5H2O and 1.2 mmol Zn(Ac)2·2H2O were placed in a reaction vessel and dissolved in 25 ml of deionized water to obtain the first mixture.

[0066] Then, 0.075 g of NaBr was added to the first mixture and stirred to obtain the second mixture;

[0067] Then, 7.25 mmol of anhydrous sodium carbonate was added to the second mixture as a precipitant. After thorough stirring, the final mixture was transferred to a hydrothermal reactor and subjected to a hydrothermal reaction at 120°C for 24 hours.

[0068] After the reaction is complete, allow it to cool naturally to room temperature, centrifuge to collect the solid precipitate, and wash and dry the solid precipitate to obtain the target product, bromine-modified zinc tin oxide photocatalyst.

[0069] Example 5:

[0070] This embodiment provides a method for preparing a bromine-modified zinc tin oxide photocatalyst, comprising the following steps:

[0071] 1.96 mmol L-tryptophan, 0.63 mmol SnCl4·5H2O and 1.2 mmol Zn(Ac)2·2H2O were placed in a reaction vessel and dissolved in 25 ml of deionized water to obtain the first mixture.

[0072] Then, 0.113 g of NaBr was added to the first mixture and stirred to obtain the second mixture;

[0073] Then, 7.25 mmol of anhydrous sodium carbonate was added to the second mixture as a precipitant. After thorough stirring, the final mixture was transferred to a hydrothermal reactor and subjected to a hydrothermal reaction at 120°C for 24 hours.

[0074] After the reaction is complete, allow it to cool naturally to room temperature, centrifuge to collect the solid precipitate, and wash and dry the solid precipitate to obtain the target product, bromine-modified zinc tin oxide photocatalyst.

[0075] Comparative example:

[0076] The difference from Example 2 is that NaBr was not added; otherwise, they are the same.

[0077] Test Example 1-3:

[0078] Test Example 1:

[0079] This test example provides X-ray diffraction tests on the zinc tin oxide photocatalyst samples prepared in Examples 1 to 5 and comparative examples.

[0080] Test steps:

[0081] The photocatalyst samples prepared in Examples 1 to 5 and the comparative examples were used as test objects.

[0082] The powder sample was tested using an X-ray diffractometer, and the spectral data of diffraction intensity (au) as a function of diffraction angle 2θ (degree) were recorded. The diffraction angle was determined according to Bragg's formula. The calculation shows that, Represents the interplanar spacing. It represents the Bragg angle (i.e., the angle between the incident X-ray and the crystal plane). Represents the diffraction series. This represents the wavelength of the incident X-ray.

[0083] The obtained test spectrum was compared and analyzed with the Zn2SnO4 (JCPDS74-2184) standard card to check whether there were impurity phases in the sample.

[0084] Test data:

[0085] Table 1. Summary of diffraction peak angles of the (311) crystal plane for each sample

[0086] Sample Name (311) Crystal plane diffraction peak angle (°) Comparative Example 33.84 Example 1 34.04 Example 2 34.16 Example 3 34.04 Example 4 33.85 Example 5 33.91

[0087] Test conclusion:

[0088] Combination Figure 1 Compared with the data in Table 1, Figure 1 XRD patterns of comparative examples and Examples 1-5, and ZSO standard cards. From Figure 1 As can be seen from the figure, the standard diffraction peak positions of Zn2SnO4 (JCPDS74-2184) are marked at the bottom. Among them, the diffraction peak angle of the (311) crystal plane in the comparative example is 33.84°. The XRD test results show that no detectable impurity peaks appeared in the sample, indicating that the sample has good crystal quality and phase purity. Compared with the Br-doped sample, the positions and intensities of the main diffraction peaks did not change significantly, and no new diffraction signals appeared. This indicates that the introduction of an appropriate amount of Br did not cause significant damage to the crystal structure and maintained the crystal phase stability of Zn2SnO4.

[0089] According to the Bragg equation, it was observed that after adding NaBr in different mass ratios, the diffraction peak angles of the ZSO-Brx (bromine-modified zinc tin oxide) samples shifted from low to high angles. Specifically, the diffraction peak angle of the (311) crystal plane in Example 1 was 34.04°, in Example 2 it was 34.16°, in Example 3 it was 34.04°, in Example 4 it was 33.85°, and in Example 5 it was 33.91°. Furthermore, as the NaBr molar ratio increased from 10% to 75%, the peak shift angle gradually increased, confirming the successful introduction of Br and the resulting lattice contraction.

[0090] Test Example 2:

[0091] This test example provides microstructure characterization tests for the zinc tin oxide photocatalyst samples prepared in Example 2 and the comparative example.

[0092] Test steps:

[0093] The photocatalyst samples prepared in the comparative example and Example 2 were used as experimental subjects. The microstructure of the samples was characterized by transmission electron microscopy (TEM, JEM-2010), and low-magnification and high-resolution transmission electron microscopy images were obtained.

[0094] In low-magnification transmission electron microscopy images, the morphological features of the sample are observed using a 10nm scale.

[0095] High-resolution lattice fringes were observed in high-resolution transmission electron microscopy images, and interplanar spacing was measured.

[0096] Test data:

[0097] Table 2. Summary of interplanar spacing data for each (311) sample

[0098] Sample Name Crystal plane index Interplanar spacing (nm) Comparative Example （311） 0.265 Example 2 （311） 0.256

[0099] Test conclusion:

[0100] Combination Figure 2 , Figure 3 Compared with the data in Table 2, Figure 2 and Figure 3 This is a TEM (Transmission Electron Microscopy) test image. Among them, Figure 2 Sub-image (a) is a high-resolution transmission electron microscope image for comparison. Figure 2The sub-image in (b) is a low-magnification transmission electron microscope image of the comparative example (the image includes a 10 nm scale bar). Figure 3 The sub-image in (a) is a high-resolution transmission electron microscope image from Example 2. Figure 3 The sub-figure in (b) is a low-magnification transmission electron microscope image of Example 2 (the figure includes a 10 nm scale bar).

[0101] Characterization revealed the presence of two types of high-resolution lattice fringes. Figure 2 As can be seen from subfigure (a), the lattice spacing measured in the comparative example is 0.265 nm (i.e., d(311) = 0.265 nm, where d represents the interplanar spacing); from Figure 3 As shown in subfigure (a), the lattice spacing measured in Example 2 was 0.256 nm (i.e., d(311) = 0.256 nm). The lattice spacings of 0.265 nm and 0.256 nm belong to the (311) plane of ZSO (zinc tin oxide). The decrease in the interplanar spacing from 0.265 nm to 0.256 nm reflects the change in the internal arrangement of the crystal. The phenomenon of reduced spacing is consistent with the phenomenon of the diffraction peak angle shifting to a higher angle in XRD (X-ray diffraction) tests, confirming that Br was successfully introduced and caused lattice shrinkage.

[0102] In practical research and observation on the photocatalytic degradation of volatile organic compounds, the microcrystalline structure of inorganic semiconductor materials is directly related to the internal charge transport path. The reduction in interplanar spacing verifies the successful introduction of Br element, and the optimization of the microcrystalline structure further improves the charge separation efficiency of ZSO material. The transmission electron microscopy characterization results of Example 2 confirm that Br doping to achieve lattice fine-tuning is a reliable path to optimize the photocatalytic performance of zinc tin oxide. This microstructure optimization lays a solid structural foundation for the subsequent material to exhibit excellent photocatalytic activity (improved reaction rate and final conversion rate) when degrading organic pollutants under 300W ultraviolet high-pressure mercury lamp irradiation.

[0103] Test Example 3:

[0104] This test example provides a toluene degradation activity test for the zinc tin oxide photocatalyst samples prepared in Examples 1 to 5 and comparative examples.

[0105] Test steps:

[0106] The 0.4g catalyst sample was divided into four portions (0.1g each) using a small amount of ethanol solution. Each portion was evenly coated onto four glass slides and then placed in an oven to dry and form a thin film.

[0107] These slides were then placed in a reactor measuring 200mm × 100mm × 17mm, and a 300W ultraviolet high-pressure mercury lamp was placed directly above the reactor as the light source.

[0108] Three gas detectors are used to monitor the flow rates of toluene, dry air, and humid air while the air generator is running.

[0109] During the photocatalytic reaction, the instantaneous concentration changes of VOCs (volatile organic compounds) in the reaction chamber at the ppm level were monitored online using a photoacoustic spectrometer (GASERA ONE, USA). When the photoacoustic spectrometer detected that the toluene gas was stable at 50 ppm in the dark, this concentration was recorded as the concentration of C7H8 (toluene) gas in the reaction chamber at adsorption equilibrium under dark conditions. .

[0110] Turn on the mercury lamp and set the illumination time to 60 minutes. Use a photoacoustic spectrometer to observe the real-time changes in the concentrations of CO2, H2O, and C7H8 gases inside the reactor, and record the real-time concentration of C7H8 gas under illumination. .

[0111] C7H8 gas removal rate (ŋ%) according to Calculate the toluene gas removal rate.

[0112] Test data:

[0113] Table 3. Summary of toluene removal rates by photocatalytic degradation for each sample

[0114] Sample Name Toluene degradation rate (%) Comparative Example 67.3 Example 1 88.3 Example 2 94.7 Example 3 86.3 Example 4 84.7 Example 5 68.5

[0115] Test conclusion:

[0116] Combination Figure 4 Analyze the data in Table 3. Figure 4 The vertical axis represents toluene concentration, and the horizontal axis represents degradation time (minutes). The vertical axis scale includes 0, 20, 40, 60, 80, 100, and 120, and the horizontal axis scale includes 0, 10, 20, 30, 40, 50, and 60. The graph contains six curves with data points: purple dots represent the comparative example, pink dots represent Example 1, orange dots represent Example 2, green dots represent Example 3, blue dots represent Example 4, and red dots represent Example 5.

[0117] from Figure 4The curve trend and the data in Table 3 show that the removal rate of C7H8 increases with the increase of illumination time. In the comparative example, the toluene removal rate was approximately 67.3% within 60 minutes of illumination. The photocatalytic activity of the material was enhanced after adding different mass ratios of NaBr. Specifically, the toluene degradation rate was 88.3% in Example 1, 94.7% in Example 2, 86.3% in Example 3, and 84.7% in Example 4. Example 2 exhibited the best catalytic performance.

[0118] The photocatalytic degradation test results show that the introduction of Br element improves the charge separation efficiency of ZSO material. Under the aforementioned light source irradiation, bromine-modified zinc tin oxide exhibits superior photocatalytic activity compared to unmodified ZSO, with improved reaction rates and final conversion rates in the degradation of organic pollutants.

[0119] at the same time, Figure 4 Table 3 also shows that in Example 5, due to the increased amount of NaBr added, the toluene degradation rate dropped to 68.5%, close to the level of the unmodified sample. Controlling the proportion of NaBr added affects the material's performance. L-Tryptophan, as a morphology modifier and ligand, is used to control the reaction rate. Combined with the synergistic effect of hydrothermal reaction conditions, the synthesized photocatalytic material exhibits improved reaction rate and final conversion rate in the degradation of organic pollutants, demonstrating practical application value in environmental purification.

Claims

1. A bromine-modified zinc tin oxide photocatalyst, characterized in that, It is prepared by reacting raw materials containing the following proportions: L-tryptophan, SnCl4·5H2O, Zn(Ac)2·2H2O and NaBr; The molar ratio of L-tryptophan, SnCl4·5H2O, and Zn(Ac)2·2H2O is 1.96:0.63:1.

2. The ratio of the number of moles of NaBr to the total number of moles of SnCl4·5H2O and Zn(Ac)2·2H2O is 0.1 to 0.

75.

2. The bromine-modified zinc tin oxide photocatalyst according to claim 1, characterized in that, The ratio of the number of moles of NaBr to the total number of moles of SnCl4·5H2O and Zn(Ac)2·2H2O is 0.

122.

3. The bromine-modified zinc tin oxide photocatalyst according to claim 1, characterized in that, The diffraction peak angle of the (311) crystal plane of the bromine-modified zinc tin oxide photocatalyst is between 33.85° and 34.16°.

4. The bromine-modified zinc tin oxide photocatalyst according to claim 1, characterized in that, The (311) interplanar spacing of the bromine-modified zinc tin oxide photocatalyst is 0.256 nm.

5. A method for preparing a bromine-modified zinc tin oxide photocatalyst, characterized in that, The application of the bromine-modified zinc tin oxide photocatalyst as described in any one of claims 1-4 includes the following steps: L-tryptophan, SnCl4·5H2O and Zn(Ac)2·2H2O were dissolved in deionized water to obtain the first mixture. Add NaBr to the first mixture and stir to obtain the second mixture; Anhydrous sodium carbonate was added to the second mixture as a precipitant, and after thorough stirring, a hydrothermal reaction was carried out. The product after the hydrothermal reaction was centrifuged, washed, and dried to obtain the bromine-modified zinc tin oxide photocatalyst.

6. The preparation method according to claim 5, characterized in that, The hydrothermal reaction was carried out at a temperature of 120°C for 24 hours.

7. The preparation method according to claim 5, characterized in that, When preparing the first mixture, the ratio of the number of moles of SnCl4·5H2O added to the volume of deionized water is 0.0252 mmol / ml.

8. The preparation method according to claim 5, characterized in that, When the anhydrous sodium carbonate is added, the molar ratio of the anhydrous sodium carbonate to the SnCl4·5H2O is 7.25:0.

63.

9. The preparation method according to claim 5, characterized in that, Before centrifugation, the product of the hydrothermal reaction was naturally cooled to room temperature.

10. The application of a bromine-modified zinc tin oxide photocatalyst as described in any one of claims 1-4 in the degradation of volatile organic compounds.

Images