SnS2 / SnO2 planar heterojunction photocatalyst and preparation method and application thereof

Abstract

The application discloses a SnS2 / SnO2 planar heterojunction photocatalyst and a preparation method and application thereof, wherein the SnS2 / SnO2 planar heterojunction photocatalyst is a two-dimensional layered structure, and oxygen is uniformly distributed on the layered surface of the SnS2 / SnO2 planar heterojunction photocatalyst and the inside of the connection between layers. The SnS2 / SnO2 planar heterojunction as the photocatalyst is applied to removal reactions of methyl orange and hexavalent chromium under visible light, and excellent redox photocatalytic activity is exhibited. In addition, in the cycle test, the SnS2 / SnO2 material also has high stability, and provides a possibility for continuous photocatalytic removal of pollutants in a water environment. The SnS2 / SnO2 planar heterojunction photocatalyst provided by the application can be recycled multiple times, has low cost and simple process, and has large-scale application prospects.

Description

Technical Field

[0001] This invention belongs to the field of photocatalyst technology, and relates to a SnS2 / SnO2 planar heterojunction photocatalyst, its preparation method, and its application. Background Technology

[0002] Faced with water pollution problems in modern society, photocatalysis technology holds promise for effectively addressing this issue by utilizing solar energy to purify wastewater. Stable, inexpensive, and high-performance semiconductor photocatalysts are fundamental to photocatalytic applications, among which titanium dioxide is used for wastewater treatment due to its excellent photocatalytic properties. However, despite extensive research on titanium dioxide, its practical applications are limited by its bandgap of 3.2 eV, which only allows it to absorb a small portion of ultraviolet light from sunlight, thus restricting its absorption.

[0003] For economic and practical application considerations, it is necessary to find visible light catalysts that can effectively utilize solar energy. To date, several promising visible light catalysts have been tried and have achieved some excellent results. They are mainly classified as: oxynitrides, sulfides, titanates, niobates, tantalates, etc.

[0004] SnS2, an n-type semiconductor material, is inexpensive, stable, and non-toxic. It belongs to the layered metal sulfide family and has a hexagonal CdI2-type crystal structure. Due to its wide band gap (approximately 2.35 eV) and strong anisotropic optical properties, SnS2 can be widely used in various fields. To further enhance the photocatalytic performance of SnS2, researchers have developed many new methods, including the creation of heterojunctions, noble metal deposition, semiconductor photosensitization, and ion doping. Among these, the design and synthesis of heterojunctions is an effective way to improve the photocatalytic performance of semiconductors. This structure can not only broaden the light absorption range but also reduce the carrier recombination rate and accelerate the electron transfer speed.

[0005] Zhang et al. synthesized SnS2 / SnO2 heterojunctions by in-situ oxidation of SnS2 nanoparticles with H2O2. The SnS2 / SnO2 nanocomposite material prepared after optimizing the mass ratio exhibited better photocatalytic activity and stability than pure SnS2 nanoparticles. Yao et al. prepared SnS2 / SnO2 heterojunctions via hydrothermal oxidation and found that the coupled bandgap structure of the SnS2 / SnO2 heterojunction promoted interfacial electron transfer and reduced charge self-radiative recombination.

[0006] Since the photocatalytic performance of SnS2 / SnO2 composite materials largely depends on their preparation method, the exploration of a novel preparation method for SnS2 / SnO2 composite materials has significant scientific and practical implications. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a SnS2 / SnO2 planar heterojunction photocatalyst, its preparation method, and its applications. In the technical solution described in this invention, oxygen is introduced both inside and outside the layered structure of the SnS2 material, providing a novel nanomaterial catalyst for the photocatalytic oxidation of organic pollutants and the reduction of heavy metal ions. This enhances catalytic activity and stability, while reducing costs, simplifying the process, and facilitating production scale-up.

[0008] To achieve the above objectives, the present invention proposes a SnS2 / SnO2 planar heterojunction photocatalyst, wherein the SnS2 / SnO2 planar heterojunction photocatalyst has a two-dimensional layered structure, wherein oxygen is uniformly distributed on the layered surface of the SnS2 / SnO2 planar heterojunction photocatalyst and in the interior of the layer-to-layer connections.

[0009] In the technical solution described in this invention, the inventors actually generate localized oxidation through the calcination of SnS2. Due to the special hexagonal hollow structure of SnS2, the oxygen introduced during the calcination process exists not only on the layered surface but also inside the layers. The resulting special structure and morphology give the SnS2 / SnO2 planar heterojunction photocatalyst of this invention good optical and catalytic performance.

[0010] It should also be noted that the SnS2 / SnO2 planar heterojunction photocatalyst in this case significantly increases the O content while retaining the S element. Compared to existing semiconductor heterojunction preparation technologies, where O introduced by calcination in air is generally located on the outer surface of the catalyst, the technical solution described in this invention allows oxygen to enter the interior of the catalyst through a simple preparation process, thereby achieving better performance.

[0011] Furthermore, in the SnS2 / SnO2 planar heterojunction photocatalyst described in this invention, an O2-based two-dimensional layered structure of SnS2 is introduced in situ to construct the SnS2 / SnO2 planar heterojunction, promoting the separation of photogenerated charges on the SnS2 surface and improving photocatalytic reduction and oxidation performance. Compared with SnS2 / SnO2 heterojunctions prepared by other methods, the SnS2 / SnO2 planar heterojunction photocatalyst described in this invention introduces O2 at the interface of the original two-dimensional layered SnS2 structure, causing the introduced oxygen to exist not only on the layered surface but also inside the layers, providing more reactive sites. Therefore, the SnS2 / SnO2 planar heterojunction photocatalyst described in this invention is very suitable for use in photocatalytic reactions, especially for the degradation of organic pollutants and the reduction of heavy metal ions, exhibiting high catalytic activity and recyclability.

[0012] Preferably, the diameter of the SnS2 / SnO2 planar heterojunction photocatalyst is 750–1000 μm.

[0013] Furthermore, this invention also proposes a method for preparing the above-mentioned SnS2 / SnO2 planar heterojunction photocatalyst, the preparation method comprising the following steps:

[0014] FJSM-SnS crystals were calcined at 150–550 °C to obtain SnS2 / SnO2 planar heterojunction photocatalysts.

[0015] In some preferred embodiments, the calcination temperature is 350°C.

[0016] Preferably, the heating rate during calcination is 5–10 °C / min.

[0017] Preferably, an air atmosphere is used during calcination.

[0018] Preferably, the calcination time is 1 to 2 hours.

[0019] Preferably, the FJSM-SnS crystal is synthesized by a solvothermal method.

[0020] In addition, this invention also proposes a method for oxidizing organic pollutants and reducing heavy metal ions using SnS2 / SnO2 planar heterojunction photocatalysis, with methyl orange (MO) or hexavalent chromium as the target pollutant, and the above-mentioned SnS2 / SnO2 planar heterojunction photocatalyst as the catalyst to carry out oxidation and reduction reactions.

[0021] Preferably, the pH of the reaction system is 3 to 3.5 when the oxidation and reduction reactions are carried out.

[0022] Furthermore, this invention proposes the application of the aforementioned SnS2 / SnO2 planar heterojunction photocatalyst in the field of photocatalysis.

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

[0024] This invention synthesizes SnS2 / SnO2 planar heterojunction photocatalysts through localized oxidation via calcination. The raw materials are inexpensive and readily available, and the preparation method is simple and controllable. As a photocatalyst for degrading organic pollutants and reducing heavy metal ions, it not only has high activity but also good stability for recycling.

[0025] Furthermore, compared with other SnS2 / SnO2 heterojunctions, the introduced oxygen not only exists on the layered surface, but also inside the layer-to-layer connections, which can better promote the transfer of photogenerated electrons. It is suitable for large-scale applications and has broad application prospects. Attached Figure Description

[0026] Figure 1The image shows a scanning electron microscope (SEM) image of the overall morphology of the SnS2 / SnO2 heterojunction photocatalyst in Example 1.

[0027] Figure 2 The image shows a scanning electron microscope (SEM) image of the cross-section of the SnS2 / SnO2 heterojunction photocatalyst in Example 1.

[0028] Figure 3 This is a diagram showing the oxygen distribution in the SnS2 / SnO2 heterojunction photocatalyst of Example 1;

[0029] Figure 4 The image shows the X-ray photoelectron spectroscopy (XPS) spectrum of the SnS2 / SnO2 heterojunction photocatalyst of this invention, where the horizontal axis represents the binding energy and the vertical axis represents the relative photoelectron flux intensity.

[0030] Figure 5 The image shows the X-ray diffraction (XRD) pattern of the SnS2 / SnO2 heterojunction photocatalyst of this invention, where the horizontal axis represents the diffraction angle and the vertical axis represents the intensity.

[0031] Figure 6 The graphs show the redox activity and the activity after five cycles of photocatalysts. (a) is the activity graph for photocatalytic oxidation of MO, (b) is the activity graph for photocatalytic oxidation of MO after five cycles of photocatalytic recycling, (c) is the activity graph for photocatalytic reduction of hexavalent chromium, and (d) is the activity graph for photocatalytic reduction of hexavalent chromium after five cycles of photocatalytic recycling. Detailed Implementation

[0032] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0033] Experimental methods in the following examples that do not specify specific conditions should be performed according to conventional methods and conditions, or according to the product instructions. All reagents and raw materials used in this invention are commercially available.

[0034] The present invention will be further described below with reference to the embodiments:

[0035] 0.502 g SnCl4·5H2O, 0.131 g elemental S, 3 mL dimethylamine (AR, 40 wt.% In H2O, Macklin), and 1 mL deionized water were thoroughly mixed until homogeneous. The resulting mixture was sealed in a 50 mL stainless steel reactor lined with polytetrafluoroethylene and transferred to an oven. It was heated at 180 °C for 3 days, then cooled to room temperature to obtain yellow hexagonal crystals and fine yellow powder. The yellow crystals were washed with ethanol and dried to obtain the FJSM-SnS sample. 100 mg of FJSM-SnS crystals were placed in a crucible and calcined in a muffle furnace at 350 °C for 1 hour (heating rate 5 °C / min) under air atmosphere to obtain a SnS2 / SnO2 planar heterojunction photocatalyst, designated as the FJSM-SnS-350-air sample.

[0036] The product underwent the following tests:

[0037] Scanning electron microscope (SEM) images such as Figures 1-2 As shown, the testing instrument is a Hitachi S-4800 scanning electron microscope (SEM). Figures 1-2 It can be seen that the prepared SnS2 / SnO2 heterojunction photocatalyst has a two-dimensional layered structure. Furthermore, it combines... Figure 3 It can be observed that O is uniformly dispersed on the catalyst.

[0038] The elemental content in the SnS2 / SnO2 heterojunction photocatalyst was determined using X-ray photoelectron spectroscopy (XPS). The results showed that while sulfur was retained, the oxygen content increased significantly. The results can be found in [reference needed]. Figure 4 , Figure 4 The image shows the X-ray photoelectron spectroscopy (XPS) spectrum of the SnS2 / SnO2 heterojunction photocatalyst of this invention, where the horizontal axis represents the binding energy and the vertical axis represents the relative photoelectron flux intensity.

[0039] X-ray diffraction (XRD) patterns are as follows: Figure 5 As shown, the testing instrument was a Rigaku D / Max-RB X-ray diffractometer from Japan. Figure 5 The curve shown in the figure represents the test results of the FJSM-SnS sample, the curve shown in the figure represents the test results of the SnS2 standard card, the curve shown in the figure represents the test results of the SnO2 standard card, and the other temperatures represent the samples prepared by FJSM-SnS under different calcination temperatures.

[0040] like Figure 5As shown, compared with the standard cards of SnS2 and SnO2, the change in calcination temperature brought about a change in the composition of the FJSM-SnS sample. Comparing the XRD curves (150℃~550℃) of the samples obtained at different calcination temperatures, this indicates that at a calcination temperature of 350℃, the element O was successfully introduced and SnS2 / SnO2 heterojunction was obtained.

[0041] Further reference Figure 5 It can be observed that the FJSM-SnS sample can maintain its original crystal form at 150℃; as the temperature rises, the O content in the catalyst increases significantly at 350℃, transforming into SnS2 / SnO2 heterojunction, resulting in sample FJSM-SnS-350-air; when the temperature reaches 450℃, the S in FJSM-SnS is completely transformed into O, forming SnO2.

[0042] Example 2

[0043] The preparation method of Example 2 is the same as that of Example 1, except that FJSM-SnS crystals are placed in a crucible and placed in a muffle furnace under an argon atmosphere and calcined at 350°C for 1 hour (heating rate 5°C / min) to obtain SnS2 / SnO2 heterojunction photocatalyst.

[0044] Examples 3 to 6

[0045] The preparation methods of Examples 3 to 6 are the same as those of Example 1. The only difference is that, unlike the calcination temperature of 350°C in Example 1, the calcination temperature used in Example 3 is 150°C, the calcination temperature used in Example 4 is 250°C, the calcination temperature used in Example 5 is 450°C, and the calcination temperature used in Example 6 is 550°C.

[0046] Oxidation performance test of photocatalyst

[0047] Visible light performance test: The visible light oxidation activity of the photocatalyst was achieved by the degradation of methyl orange (MO) under monochromatic light at 420 nm. 20 mg of the catalyst (the catalyst was the SnS2 / SnO2 planar heterojunction photocatalyst prepared in Example 1) was added to a 50 mL beaker containing 20 mL of 60 ppm MO solution (the pH was adjusted to 3 with 0.5 mol / L hydrochloric acid). The solution was sonicated for 1 min to uniformly disperse the catalyst. Under dark conditions, the mixture was stirred for a certain time (60 min) to reach adsorption equilibrium. Stirring was continued while the light was turned on. At different time intervals (30 min, 60 min, 90 min, 120 min, 150 min), 1 mL of the mixed solution was taken, centrifuged, and the absorbance of the supernatant was measured at 465 nm using ultraviolet spectrophotometry.

[0048] Performance testing at different wavelengths: The photocatalytic oxidation activity of the photocatalyst at different wavelengths was assessed by measuring the degradation of MO under monochromatic light at different nanometers (365nm, 420nm, 450nm, 500nm, 550nm, 600nm, 650nm, 700nm). 20mg of the catalyst was added to a 50mL beaker containing 20mL of 60ppm MO solution (pH adjusted to 3 with 0.5mol / L hydrochloric acid). The solution was sonicated for 1min to ensure uniform dispersion of the catalyst. Under dark conditions, the solution was stirred for a certain period (60min) to reach adsorption equilibrium. Stirring was continued, and the light was turned on for 1 hour. 1mL of the mixed solution was then removed, centrifuged, and the absorbance of the supernatant was measured at 465nm using ultraviolet spectrophotometry.

[0049] Photocatalyst reduction performance test

[0050] Visible light reduction performance test: The visible light reduction activity of the photocatalyst is achieved by the reduction of Cr(VI) under monochromatic light at 420 nm. 20 mg of catalyst was added to a 50 mL beaker containing 20 mL of 50 ppm Cr(VI) solution (pH adjusted to 3 with 0.5 mol / L hydrochloric acid). The solution was sonicated for 1 min to ensure uniform dispersion of the catalyst. Under dark conditions, the solution was stirred for a certain period (60 min) to reach adsorption equilibrium. Stirring was continued while the light was turned on. At different time intervals (30 min, 60 min, 90 min, 120 min, 150 min), 1 mL of the mixed solution was taken, filtered (using a 0.22 μm filter membrane) or centrifuged. The concentration of Cr(VI) in the resulting solution was determined using the diphenylaminourea (DPCI) complexation method.

[0051] Performance testing at different wavelengths: The photocatalytic reduction activity of the photocatalyst at different wavelengths was determined by the reduction of Cr(VI) under monochromatic light at different nanometers (365nm, 420nm, 450nm, 500nm, 550nm, 600nm, 650nm, 700nm). 20mg of the catalyst was added to a 50mL beaker containing 20mL of 50ppm Cr(VI) solution (pH adjusted to 3 with 0.5mol / L hydrochloric acid). The solution was sonicated for 1min to ensure uniform dispersion of the catalyst. Under dark conditions, the solution was stirred for a certain period (60min) to reach adsorption equilibrium. Stirring was continued, and the light was turned on. After 1 hour of illumination, 1mL of the mixed solution was taken out, filtered (using a 0.22μm filter membrane) or centrifuged. The concentration of Cr(VI) in the resulting solution was determined using the diphenylaminourea (DPCI) complexation method.

[0052] See test results Figure 6 .

[0053] like Figure 6As shown in Figure (a), the FJSM-SnS-350-air sample also exhibited excellent photocatalytic performance in the visible light photocatalytic oxidation of MO experiment. After 150 min of visible light irradiation, the MO removal rate reached over 98%.

[0054] And in Figure 6 As can be seen from (c), in the photocatalytic reduction test of hexavalent chromium at 50 ppm, the FJSM-SnS-350-air sample exhibited the best hexavalent chromium reduction performance, with a removal rate of over 99% after 150 min of visible light irradiation.

[0055] And by Figure 6 As can be seen from (b) and (d), the photocatalytic cycle test shows that the FJSM-SnS-350-air sample obtained in Example 1 has high stability.

[0056] It should be noted that the scope of protection of the prior art in this invention is not limited to the embodiments given in this application. All prior art that does not contradict the solution of this invention, including but not limited to prior patent documents, prior publications, prior public uses, etc., can be included in the scope of protection of this invention.

[0057] Furthermore, the combination of the technical features in this case is not limited to the combination methods described in the claims of this case or the combination methods described in the specific embodiments. All technical features described in this case can be freely combined or combined in any way, unless they contradict each other.

[0058] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A SnS2 / SnO2 planar heterojunction photocatalyst, characterized in that, The SnS2 / SnO2 planar heterojunction photocatalyst, prepared by calcining FJSM-SnS crystals in air at 350°C, has a two-dimensional layered structure in which oxygen is uniformly distributed on the layered surface and inside the layers. By introducing O in situ into SnS2 with a two-dimensional layered structure, the SnS2 / SnO2 planar heterojunction was constructed, increasing the O content while retaining the S element.

2. The SnS2 / SnO2 planar heterojunction photocatalyst according to claim 1, characterized in that, The diameter of the SnS2 / SnO2 planar heterojunction photocatalyst is 750–1000 μm.

3. A method for preparing the SnS2 / SnO2 planar heterojunction photocatalyst as described in claim 1 or 2, characterized in that, The preparation method includes the following steps: FJSM-SnS crystals were calcined in air at 350°C to obtain SnS2 / SnO2 planar heterojunction photocatalysts.

4. The preparation method according to claim 3, characterized in that, During calcination, the heating rate is 5–10 °C / min.

5. The preparation method according to claim 3, characterized in that, During calcination, the calcination time is 1 to 2 hours.

6. The preparation method according to any one of claims 3 to 5, characterized in that, The FJSM-SnS crystal was synthesized using a solvothermal method.

7. A method for photocatalytic oxidation of organic pollutants and reduction of heavy metal ions using a planar heterogeneous SnS2 / SnO2 structure, characterized in that, Using methyl orange or hexavalent chromium as the target pollutant, oxidation and reduction reactions are carried out using the SnS2 / SnO2 planar heterojunction photocatalyst as described in claim 1 or 2.

8. The method according to claim 7, characterized in that, When oxidation and reduction reactions are carried out, the pH of the reaction system is 3 to 3.

5.

9. The application of the SnS2 / SnO2 planar heterojunction photocatalyst as described in claim 1 or 2 in the field of photocatalysis.

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