An oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst, a preparation method and application thereof

Abstract

The application discloses an oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst and a preparation method and application thereof, and relates to the technical field of inorganic photocatalytic materials. The oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst provided by the application is a 1T-2H O-MoS2@S-pCN composite photocatalyst in terms of chemical composition, and the mass ratio of the oxygen-doped molybdenum disulfide and the sulfur-doped carbon nitride in the composite photocatalyst is 10%-18%. The oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst with 1T crystal faces and 2H crystal faces is in-situ synthesized by using N,N-dimethylformamide as a solvent, and has high catalytic efficiency and good stability. The application provides a preparation method of the oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst, and the process is simple, the structure is stable, and the product has high purity. The composite photocatalyst can simultaneously catalyze the reduction of hexavalent chromium and the oxidation of ciprofloxacin.

Description

Technical Field

[0001] This invention relates to the field of inorganic photocatalytic materials technology, and in particular, to an oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst, its preparation method, and its application. Background Technology

[0002] Heavy metals and antibiotics, among other recalcitrant organic pollutants, are significant environmental pollutants that seriously threaten ecological security. Therefore, the degradation of pollutants such as hexavalent chromium and antibiotics in wastewater is a crucial issue. Photocatalysis, an advanced oxidation technology, offers advantages such as being green and highly efficient, making it an important technology for wastewater treatment. However, the low light absorption capacity of photocatalysts and the recombination of photogenerated electrons and holes limit their use. Therefore, developing a highly efficient catalyst that maximizes photoreaction efficiency and inhibits the recombination of photogenerated electrons and holes is essential.

[0003] Molybdenum disulfide (MoD) possesses excellent photoresponsiveness and electron transport capabilities, showing great potential, particularly in photocatalytic redox reactions, which has attracted the research interest of scientists. However, the photocatalytic reduction efficiency of MoD is not high, and it is difficult to achieve simultaneous degradation of pollutants such as hexavalent chromium and antibiotics in wastewater. Furthermore, stepwise degradation processes are large-scale, time-consuming, and costly.

[0004] Therefore, the industry urgently needs a new type of photocatalyst to simultaneously achieve the oxidation and reduction of pollutants. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides an oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst and its preparation method. Carbon nitride possesses a unique electronic structure and excellent visible light absorption capability, while sulfur doping can effectively improve the structure of carbon nitride and its response in the visible light range. This invention uses N,N-dimethylformamide (DMF) as a solvent to synthesize an oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst with 1T and 2H crystal planes in situ. This novel molybdenum disulfide-carbon nitride photocatalyst not only has high catalytic efficiency and good stability, but also exhibits strong photoresponse capability, enabling simultaneous oxidation and reduction treatment of pollutants.

[0006] To achieve the above objectives, the present invention provides an oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst. Chemically, the oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst is a 1T-2H₂O-MoS₂@S-pCN composite photocatalyst, wherein the mass ratio of oxygen-doped molybdenum disulfide 1T-2H₂O-MoS₂ to sulfur-doped carbon nitride S-pCN in the composite photocatalyst is 10%-18%.

[0007] This invention also provides a method for preparing an oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst, comprising the following steps:

[0008] A nitrogen-containing compound was dissolved in water, then thioacetamide was added and dissolved, followed by calcination to obtain sulfur-doped carbon nitride; then the prepared sulfur-doped carbon nitride was mixed with N,N-dimethylformamide to obtain solution A;

[0009] Solution B is obtained by mixing ammonium molybdate tetrahydrate, thiourea, and N,N-dimethylformamide.

[0010] Solution B was slowly added dropwise to solution A, and a hydrothermal reaction was carried out in an autoclave to obtain the oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst.

[0011] Furthermore, the mass ratio of nitrogen-containing compound to thioacetamide is 150-170:1; the mass ratio of sulfur-doped carbon nitride to N,N-dimethylformamide is 1:60-100; and the mass ratio of sulfur-doped carbon nitride, ammonium molybdate tetrahydrate, and thiourea is 1:0.3-1.6:0.7-2.9.

[0012] Furthermore, the nitrogen-containing compound is urea or dicyandiamide.

[0013] Furthermore, the heating rate of the calcination treatment is 3-5℃ / min, and the calcination temperature is 400-500℃.

[0014] Furthermore, the temperature is raised to the hydrothermal reaction temperature of 160-200℃ for 18-24 hours.

[0015] Furthermore, the heating rate to the hydrothermal reaction temperature is 1-3℃ / min.

[0016] The present invention also provides the application of the above-mentioned oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst or the oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst prepared by the above method in the reduction of hexavalent chromium and simultaneous oxidation of ciprofloxacin.

[0017] Furthermore, the application includes the following steps: adding the oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite material to wastewater, and performing a photocatalytic reaction under visible light to complete the reduction of hexavalent chromium and the oxidation of ciprofloxacin. The amount of the oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite material added to the wastewater is 0.2 g / L-1.2 g / L.

[0018] Furthermore, in the aforementioned application, the visible light source is a 300W-500W xenon lamp, the distance between the xenon lamp and the surface of the wastewater is 14cm-16cm, the photocatalytic reaction time is 8min-15min, the concentration of hexavalent chromium in the wastewater is 5mg / L-40mg / L, and the concentration of ciprofloxacin is 5mg / L-40mg / L.

[0019] The present invention has the following beneficial effects:

[0020] 1. The oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst provided by this invention is chemically composed of a 1T-2H₂O-MoS₂@S-pCN composite photocatalyst, wherein the mass ratio of 1T-2H₂O-MoS₂ to S-pCN in the composite photocatalyst is 10%-18%. Compared to the 2.74 eV band gap of sulfur-doped nitrogen nitride (S-pCN), the photocatalyst material of this invention has a minimum band gap of 2.0 eV, exhibiting better light response, shorter reaction time, and higher efficiency. Furthermore, the oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst provided by this invention can effectively catalytically reduce hexavalent chromium to trivalent chromium while simultaneously oxidizing ciprofloxacin under visible light irradiation, demonstrating extremely high catalytic efficiency and good stability.

[0021] 2. The preparation method of the oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst provided by the present invention firstly uses thioacetamide (TAA) to pyrolyze at high temperature to produce sulfur-doped carbon nitride, and disperses it in DMF to obtain solution A; then, ammonium molybdate tetrahydrate, thiourea and N,N-dimethylformamide are mixed to obtain mixed solution B; by stirring, mixed solution B is well dispersed in A, and the ammonium molybdate tetrahydrate and thiourea in solution B generate oxygen-doped molybdenum disulfide through hydrothermal reaction in DMF and condense on sulfur-doped carbon nitride.

[0022] First, the sulfur-doped carbon nitride produced by the high-temperature pyrolysis of thioacetamide (TAA) in this invention has a large specific surface area, providing a good support for the in-situ synthesis of oxygen-doped molybdenum disulfide. Sulfur-doped carbon nitride is also a photocatalyst with photocatalytic effects, but its photocatalytic reduction ability is weak due to its low conduction band and rapid recombination of photogenerated electrons and holes. This invention employs an in-situ synthesis method to form a composite material, specifically, oxygen-doped molybdenum disulfide is directly generated on the surface of sulfur-doped carbon nitride to form a composite material. During photocatalysis, the heterojunction formed by the two materials achieves the separation of holes and electrons, thereby improving the photocatalytic effect.

[0023] Secondly, the method of this invention uses N,N-dimethylformamide (DMF) as a solvent during in-situ synthesis, utilizing the oxygen in the solvent to synthesize oxygen-doped molybdenum disulfide, which can delay the recombination of photogenerated electrons and holes; at the same time, it improves the crystal structure of molybdenum disulfide and enhances the catalytic active sites. Therefore, the photocatalytic material provided by this invention has high catalytic efficiency and good stability. This is because DMF is beneficial for promoting the chemical synthesis of molybdenum disulfide (MoS2), which has two phases, 1T and 2H, corresponding to the octahedral metallic phase and the triangular prism semiconductor phase, respectively. Among these two phases, the 1T phase has superior electrocatalytic performance, while the 2H phase has high chemical stability and reduction ability, thanks to its stable chemical structure and low conduction band. Furthermore, the heterogeneous structure resulting from the different crystal planes also increases the carrier density of the material and suppresses charge recombination.

[0024] Furthermore, this invention provides a method for preparing an oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst, which is simple in process, structurally stable, and produces a product with high purity.

[0025] 3. The oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst provided by this invention can simultaneously reduce hexavalent chromium and oxidize ciprofloxacin under visible light. This is because the photocatalytic material prepared by this invention has a low band gap, enabling it to respond under visible light and excite electron-hole pairs. The heterojunction of the composite material promotes the separation of electrons and holes; electrons reduce hexavalent chromium, and holes oxidize ciprofloxacin. The oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst provided by this invention achieves a hexavalent chromium reduction rate of 99.4% and a ciprofloxacin oxidation rate of 98.5% after 10 minutes of reaction. This represents a 5.86-fold increase in hexavalent chromium reduction rate and a 0.57-fold increase in ciprofloxacin oxidation rate compared to the sulfur-doped carbon nitride photocatalyst used for the same reaction. Furthermore, the oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst provided by this invention exhibits good stability; after three cycles, the hexavalent chromium reduction rate still reaches 94.7%, and the ciprofloxacin oxidation rate reaches 91.6%.

[0026] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0027] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0028] Figure 1 A diagram illustrating the chemical reaction process of the oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst prepared by the method of this invention.

[0029] Figure 2 X-ray diffraction patterns of the composite photocatalysts prepared in Examples 1-2 and Comparative Examples 1-3;

[0030] Figure 3 The images shown are scanning electron microscope (SEM) images of the composite photocatalysts prepared in Examples 1-2 and Comparative Examples 2-3; wherein, Figure 3 Image (a) is a SEM image of the composite photocatalyst prepared in Example 2. Figure 3 (b) is a SEM image of the composite photocatalyst prepared in Comparative Example 3. Figure 3 Image (c) shows the SEM image of the composite photocatalyst prepared in Comparative Example 2. Figure 3 Image d is a SEM image of the composite photocatalyst prepared in Example 1;

[0031] Figure 4 The images show the UV-Vis diffuse reflectance spectra of the composite photocatalysts in Examples 1-2 and Comparative Examples 1-3.

[0032] Figure 5 Tauc curves of the composite photocatalysts of Examples 1-2 and Comparative Examples 1-3;

[0033] Figure 6 Photocatalytic performance curves of the composite photocatalysts prepared for Examples 1-2 and Comparative Examples 1-3 under visible light irradiation with λ>420nm for the reduction of hexavalent chromium;

[0034] Figure 7 Photocatalytic performance curves of the composite photocatalysts prepared for Examples 1-2 and Comparative Examples 1-3 under visible light irradiation with λ>420nm for oxidizing ciprofloxacin;

[0035] Figure 8 XPS spectrum of oxygen in the composite photocatalyst prepared in Example 1;

[0036] Figure 9 The diagram shows the cyclic effect of the composite photocatalyst prepared in Example 1 reducing hexavalent chromium.

[0037] Figure 10 The image shows the cyclic effect of the composite photocatalyst prepared in Example 1 oxidizing ciprofloxacin. Detailed Implementation

[0038] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many different ways as defined and covered by the claims.

[0039] This invention provides an oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst. Chemically, the oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst is a 1T-2H₂O-MoS₂@S-pCN composite photocatalyst.

[0040] In this invention, the mass ratio of 1T-2H₂O-MoS₂ to S-pCN in the composite photocatalyst is 10%-18%, preferably 15%. The oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst provided by this invention has extremely high catalytic efficiency and good stability.

[0041] This invention provides a method for preparing the oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst, comprising the following steps:

[0042] (1) Dissolve a nitrogen-containing compound in water, add thioacetamide (TAA) and dissolve it, then calcine it in a muffle furnace to obtain sulfur-doped carbon nitride (S-pCN);

[0043] (2) Mix S-pCN and N,N-dimethylformamide (DMF) to obtain solution A;

[0044] (3) Ammonium molybdate tetrahydrate ((NH4)6Mo7O 24 Solution B is obtained by mixing *4H2O), thiourea (CH4N2S), and DMF;

[0045] (4) Slowly add solution B to solution A, stir and then put it into a high pressure vessel for hydrothermal reaction to obtain oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst.

[0046] This invention involves dissolving a nitrogen-containing compound in water, adding thioacetamide (TAA) and dissolving it, then calcining the solution in a muffle furnace to obtain S-pCN. In this invention, the nitrogen-containing compound is preferably urea or dicyandiamide. This invention does not have specific requirements regarding the source of the nitrogen-containing compound or thioacetamide; commercially available products well-known in the art can be used. In a specific embodiment of this invention, the mixing operation is as follows: the nitrogen-containing compound is dissolved in deionized water at 50°C under vigorous stirring, and then thioacetamide is added and mixed under stirring; the stirring rate is preferably 500-1000 rpm, more preferably 800 rpm, and the time is 50-80 min, more preferably 60 min. In this invention, the above mixture is placed in a muffle furnace for calcination. The muffle furnace heating rate is preferably 3-5°C / min, more preferably 5°C / min, and the calcination temperature is preferably 400-500°C, more preferably 500°C, to obtain sulfur-doped carbon nitride.

[0047] In this invention, after calcination, the obtained solid is preferably cooled, washed, and dried. The cooling method is not particularly important; methods well-known in the art can be used to cool to room temperature, such as natural cooling. The washing process involves sequentially using deionized water and ethanol. The number of washing cycles is not particularly important; it is sufficient to ensure that the filter cake obtained from filtration is thoroughly cleaned. The drying temperature is preferably 50-70°C, more preferably 60°C, and the drying time is preferably 8-12 hours, more preferably 10 hours. The drying method is not particularly important; methods well-known in the art can be used to ensure the required temperature and time. After drying, sulfur-doped carbon nitride is obtained.

[0048] After obtaining sulfur-doped carbon nitride, the present invention mixes the sulfur-doped carbon nitride and DMF under ultrasound to obtain solution A. In the present invention, the mass ratio of sulfur-doped carbon nitride to DMF is preferably 1:60-100, more preferably 1:70-90, and most preferably 1:80. The present invention does not have special requirements regarding the source of the DMF; commercially available products well-known in the art can be used. The present invention preferably adds DMF to solution A for ultrasonic mixing; the ultrasonic power is preferably 200-500W, more preferably 300W. The present invention uses ultrasound to promote the mixing of sulfur-doped carbon nitride in DMF, which is beneficial to the subsequent reaction.

[0049] This invention mixes ammonium molybdate tetrahydrate, thiourea, and DMF to obtain solution B. This invention does not have specific requirements regarding the source of ammonium molybdate tetrahydrate, thiourea, and DMF; commercially available products well-known in the art can be used. In a specific embodiment of this invention, the mixing operation is as follows: ammonium molybdate tetrahydrate and thiourea are dispersed into DMF under ultrasonication to obtain solution B. In this invention, the mass ratio of ammonium molybdate tetrahydrate, thiourea, and N,N-dimethylformamide is 1:1.5-3.0:20-30. The ultrasonic power is preferably 200-500W, more preferably 300W. Vigorous stirring in this invention promotes the mixing of ammonium molybdate tetrahydrate and thiourea in DMF, which is beneficial for subsequent reactions. Furthermore, the mass ratio of sulfur-doped carbon nitride, ammonium molybdate tetrahydrate, and thiourea is 1:0.3-1.6:0.7-2.9. The volume ratio of solution A to solution B is 5:2.

[0050] Solution B is slowly added dropwise to solution A, stirred, and then placed in an autoclave for a hydrothermal reaction to obtain an oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst. In this invention, solution B is slowly added dropwise to solution A, preferably at a rate of 6-12 drops / min, more preferably 8-10 drops / min; the stirring rate is preferably 500-1000 rpm, more preferably 800 rpm, and the time is 20-50 min, more preferably 30 min. The hydrothermal reaction temperature is preferably 160-200℃, more preferably 170-190℃, and most preferably 180℃; the time is preferably 18-24 h, more preferably 20-24℃, and most preferably 24 h. In this invention, the hydrothermal reaction is preferably carried out in a polytetrafluoroethylene (PTFE) reactor; the temperature of the hydrothermal reaction is preferably controlled by a drying oven; that is, the mixed solution is placed in the PTFE reactor, and then the PTFE reactor containing the mixed solution is placed in a drying oven for heating. In this invention, the heating rate (and the heating rate of the drying oven) to the hydrothermal reaction temperature is preferably 1-3 °C / min, more preferably 2 °C / min; the hydrothermal reaction time is calculated from the time required for the hydrothermal reaction. Using N,N-dimethylformamide as a solvent, oxygen-doped molybdenum disulfide is generated in situ via hydrothermal reaction, and further forms a heterojunction with S-pCN to obtain the oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst. The chemical reaction process of the oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst prepared by the method of this invention is as follows: Figure 1 As shown. Furthermore, the slow dropwise addition of solution B to solution A in this invention is primarily to ensure thorough mixing and to guarantee that ammonium molybdate tetrahydrate and thiourea are uniformly dispersed in the solution. Adding solution A dropwise would make it difficult to ensure thorough mixing, and the amount of solution A is relatively large because sulfur-doped nitrogen carbide is the main component, accounting for over 80% of the synthesized material.

[0051] In this invention, after the hydrothermal reaction, the resulting hydrothermal reaction solution is preferably subjected to sequential cooling, filtration, washing, and drying. The cooling method is not particularly important; methods well-known in the art, such as natural cooling, can be used. Similarly, the filtration method is not particularly important; methods well-known in the art can be used. The washing process involves sequentially using deionized water and ethanol. The number of washing cycles is not particularly important, as long as the filter cake is thoroughly cleaned. The drying temperature is preferably 50-70°C, more preferably 60°C, and the drying time is preferably 8-12 hours, more preferably 10 hours. The drying method is not particularly important; methods well-known in the art can be used to ensure the required temperature and time. After drying, an oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst is obtained.

[0052] This invention provides a method for preparing the oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst described above. The preparation method provided by this invention is simple, and the prepared oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst has high purity.

[0053] This invention provides the application of the oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst described in the above-described schemes, or the oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst prepared by the methods described in the above-described schemes, in the catalytic reduction of hexavalent chromium and the oxidation of ciprofloxacin. The oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst provided by this invention can effectively catalytically reduce hexavalent chromium to trivalent chromium and simultaneously oxidize ciprofloxacin under visible light irradiation, exhibiting extremely high catalytic efficiency and good stability.

[0054] The following detailed description, in conjunction with embodiments, illustrates the oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst, its preparation method, and its applications. However, these descriptions should not be construed as limiting the scope of protection of this invention.

[0055] Example 1

[0056] (1) Dissolve 30g of urea in 40mL of deionized water under vigorous stirring. Heat the solution to 50℃ in a water bath, add 0.5% thioacetamide (TAA), and stir for 1h to obtain a transparent solution. Transfer the above solution into a semi-enclosed crucible and calcine it in a muffle furnace at a heating rate of 5℃ / min to 400℃ for 1h, and then calcine it at 500℃ for 2h at a heating rate of 5℃ / min to obtain a solid powder. The solid powder is washed with water and ethanol, and after cleaning, it is placed in an oven at 60℃ for 12h to obtain sulfur-doped carbon nitride solid powder.

[0057] (2) First, 400 mg S-pCN is dissolved in 50 mL DMF solution by ultrasound to obtain a homogeneous solution, which is solution A.

[0058] (3) Ammonium molybdate tetrahydrate ((NH4)6Mo7O 24 *4H2O (0.4632g) and thiourea (CH4N2S (0.8559g) were dispersed in 20ml of DMF under vigorous magnetic stirring to form solution B.

[0059] (4) Add solution B slowly to solution A at a rate of 10 drops / min and stir for 30 minutes to mix thoroughly. Then transfer the solution to a 100 mL autoclave and maintain it at 180°C for 24 hours, allowing it to cool naturally to room temperature.

[0060] (5) A solid sample was obtained by filtering with filter paper; the sample was washed with anhydrous ethanol and deionized water, and dried at 60°C to obtain a solid powder, which is the oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst. The mass ratio of oxygen-doped molybdenum disulfide 1T-2H O-MoS2 to sulfur-doped carbon nitride S-pCN is 15%, denoted as 15% 1T-2H O-MoS2@S-pCN composite photocatalyst. In this embodiment, the mass ratio of sulfur-doped carbon nitride, ammonium molybdate tetrahydrate, and thiourea is 1:1.158:2.13975.

[0061] Example 2

[0062] The ammonium molybdate tetrahydrate ((NH4)6Mo7O) from Example 1 was used. 24 The amount of *4H2O* was reduced to 0.3088 g, and the amount of thiourea (CH4N2S) was reduced to 0.5706 g, with other parameters the same as in Example 1. The resulting oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst had a mass ratio of 10% for oxygen-doped molybdenum disulfide (1T-2H2O-MoS2) and sulfur-doped carbon nitride (S-pCN), denoted as 10% 1T-2H2O-MoS2@S-pCN composite photocatalyst. In this example, the mass ratio of sulfur-doped carbon nitride, ammonium molybdate tetrahydrate, and thiourea was 1:0.772:1.4265.

[0063] Example 3

[0064] The ammonium molybdate tetrahydrate ((NH4)6Mo7O) from Example 1 was used. 24 The amount of *4H2O* was increased to 0.55584 g, and the amount of thiourea (CH4N2S) was increased to 1.02708 g, with other parameters the same as in Example 1. The resulting oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst had a mass ratio of 18% for oxygen-doped molybdenum disulfide (1T-2H2O-MoS2) and sulfur-doped carbon nitride (S-pCN), and was designated as the 18% 1T-2H2O-MoS2@S-pCN composite photocatalyst. In this example, the mass ratio of sulfur-doped carbon nitride, ammonium molybdate tetrahydrate, and thiourea was 1:1.3896:2.5677.

[0065] Comparative Example 1:

[0066] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 only includes the same step (1) as in Example 1 to obtain sulfur-doped carbon nitride solid powder, without any other steps.

[0067] Comparative Example 2:

[0068] The difference between Comparative Example 2 and Example 1 is that: the ammonium molybdate tetrahydrate ((NH4)6Mo7O) from Example 1 was replaced with ammonium molybdate tetrahydrate ((NH4)6Mo7O) 24The amount of *4H2O* was reduced to 0.1544 g, and the amount of thiourea (CH4N2S) was reduced to 0.2853 g, with other parameters the same as in Example 1. The resulting oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst had a mass ratio of 5% for oxygen-doped molybdenum disulfide (1T-2H2O-MoS2) and sulfur-doped carbon nitride (S-pCN), and was designated as a 5% 1T-2H2O-MoS2@S-pCN composite photocatalyst.

[0069] Comparative Example 3:

[0070] The difference between Comparative Example 3 and Example 1 is that the ammonium molybdate tetrahydrate ((NH4)6Mo7O) in Example 1 was replaced with a different one. 24 The amount of *4H2O* was increased to 0.6176 g, and the amount of thiourea (CH4N2S) was increased to 1.1412 g, with other parameters the same as in Example 1. The resulting oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst had a mass ratio of 20% for oxygen-doped molybdenum disulfide (1T-2H2O-MoS2) and sulfur-doped carbon nitride (S-pCN), and was designated as a 20% 1T-2H2O-MoS2@S-pCN composite photocatalyst.

[0071] The composite photocatalysts prepared in Examples 1-2 and Comparative Examples 1-3 were characterized by X-ray powder diffraction. Figure 2 As shown. By Figure 2 It can be seen that as the amount of oxygen-doped molybdenum disulfide added increases, the characteristic peak of carbon nitride becomes weaker and weaker, while the characteristic peak of oxygen-doped molybdenum disulfide becomes more and more obvious. The oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalysts obtained in Examples 1-2 have a better structure than those in Comparative Examples 1-3.

[0072] The morphology of the composite photocatalysts prepared in Examples 1-2 and Comparative Examples 2-3 was characterized by scanning electron microscopy, such as... Figure 3 As shown, where, Figure 3 Image (a) is a SEM image of the composite photocatalyst prepared in Example 2. Figure 3 (b) is a SEM image of the composite photocatalyst prepared in Comparative Example 3. Figure 3 Image (c) shows the SEM image of the composite photocatalyst prepared in Comparative Example 2. Figure 3 Image (d) is a SEM image of the composite photocatalyst prepared in Example 1. Figure 3 It can be seen that the oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalysts obtained in Examples 1-2 have a loose structure, consisting of irregular flocculent and irregular granular forms. In contrast, the oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst obtained in Comparative Example 3 exhibits significant catalyst agglomeration due to the increased content of oxygen-doped molybdenum disulfide. Figure 3 As shown in (b).

[0073] The light absorption properties of the composite photocatalysts prepared in Examples 1-2 and Comparative Examples 1-3 were characterized by ultraviolet-visible diffuse reflectance spectroscopy, and the results are as follows: Figure 4 As shown. Figure 5 The images show the Tauc curves of the composite photocatalysts from Examples 1-2 and Comparative Examples 1-3. Figure 5 It is known that the band gap of sulfur-doped carbon nitride is 2.74 eV; the band gap of the 15% oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst is 2.0 eV, the band gap of the 10% oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst is 2.05 eV, the band gap of the 5% oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst is 2.22 eV, and the band gap of the 20% oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst is 1.94 eV. In this invention, the oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst has a moderate band gap, ensuring sufficient response to visible light while reducing the recombination of photogenerated electrons and holes, thereby significantly improving the catalytic efficiency of the photocatalyst. Sulfur-doped nitrogen carbide is also a photocatalyst with photocatalytic effects, but its photocatalytic reduction ability is weak due to its low conduction band and rapid recombination of photogenerated electrons and holes. Compared to the 2.74 eV band gap of sulfur-doped nitrogen nitride (S-pCN), the photocatalytic material of this invention has a minimum band gap of 2.0 eV. Therefore, the photocatalytic material of this invention exhibits better photoresponse, shorter reaction time, and higher efficiency. This is because the sulfur-doped carbon nitride produced by high-temperature pyrolysis of thioacetamide (TAA) in this invention has a large specific surface area, providing a better support for the in-situ synthesis of oxygen-doped molybdenum disulfide. This invention employs an in-situ synthesis method to form a composite material, specifically, oxygen-doped molybdenum disulfide is directly generated on the surface of sulfur-doped nitrogen carbide to form a composite material. During photocatalysis, the heterojunction formed by the two materials achieves the separation of holes and electrons, thereby improving the photocatalytic effect.

[0074] The photocatalytic performance of the composite photocatalysts prepared in Examples 1-2 and Comparative Examples 1-3 was evaluated under visible light irradiation with wavelengths greater than 420 nm. The experimental results are as follows: Figure 6 and Figure 7 As shown in the figure. In the experiment, the initial concentration of hexavalent chromium was 10 mg / L, the initial concentration of ciprofloxacin was 10 mg / L, and the amount of photocatalyst was 0.04 g. Figure 6 Photocatalytic performance curves of the composite photocatalysts prepared for Examples 1-2 and Comparative Examples 1-3 under visible light irradiation with λ>420nm for the reduction of hexavalent chromium; Figure 7 The photocatalytic performance curves of the composite photocatalysts prepared for Examples 1-2 and Comparative Examples 1-3 under visible light irradiation with λ>420nm for the oxidation of ciprofloxacin. Figure 6 The vertical axis represents the ratio of the concentration of unreduced hexavalent chromium to the initial concentration of hexavalent chromium. Figure 7The vertical axis represents the ratio of the concentration of unoxidized ciprofloxacin to the initial concentration of ciprofloxacin.

[0075] Depend on Figure 6 and Figure 7 It can be seen that the 15% 1T-2H₂O-MoS₂@S-pCN composite photocatalyst prepared in Example 1 achieved a hexavalent chromium reduction rate of 99.4% and a ciprofloxacin oxidation rate of 98.5% after reacting under visible light for 10 min. In contrast, the photocatalyst prepared in Comparative Example 1 achieved a hexavalent chromium reduction rate of 14.5% and a ciprofloxacin oxidation rate of 63.7% after reacting under visible light for 10 min. This represents a 5.86-fold increase in hexavalent chromium reduction rate and a 0.57-fold increase in ciprofloxacin oxidation rate compared to the sulfur-doped carbon nitride photocatalyst used in Example 2. The 10% 1T-2H₂O-MoS₂@S-pCN composite photocatalyst prepared in Example 2 achieved a hexavalent chromium reduction rate of 62.1% and a ciprofloxacin oxidation rate of 81.3% after reacting under visible light for 10 min. The 5% 1T-2H₂O-MoS₂@S-pCN composite photocatalyst prepared in Comparative Example 2 achieved a 57.6% reduction rate of hexavalent chromium and a 69.2% oxidation rate of ciprofloxacin under visible light for 10 min. The 20% 1T-2H₂O-MoS₂@S-pCN composite photocatalyst prepared in Comparative Example 3 achieved a 42.4% reduction rate of hexavalent chromium and a 63.5% oxidation rate of ciprofloxacin under visible light for 10 min. This is because the photocatalytic material prepared in this invention has a low band gap, enabling it to respond under visible light and excite electron-hole pairs. Due to the heterojunction of the composite material, electron-hole separation is promoted, with electrons reducing hexavalent chromium and holes oxidizing ciprofloxacin. In contrast, in Comparative Example 2, due to the low content of oxygen-doped molybdenum disulfide, the composite material has a larger band gap and relatively weaker photoresponse capability. In Comparative Example 3, although the band gap of the composite material decreases with increasing molybdenum disulfide content, the significant agglomeration of the material leads to a decrease in its catalytic efficiency. This is related to... Figure 3 and Figure 5 The results are also consistent. Furthermore, the results obtained in Example 3 are similar to those in Example 2, and will not be repeated here.

[0076] Figure 8 The XPS spectrum of oxygen in the composite photocatalyst prepared in Example 1 is shown below. Figure 8As can be seen from the above, the composite photocatalyst prepared by this invention has an O-Mo structure, meaning that the prepared composite photocatalyst contains oxygen-doped molybdenum disulfide. In the in-situ synthesis of this invention, N,N-dimethylformamide (DMF) is used as a solvent. The oxygen in the solvent is used to synthesize oxygen-doped molybdenum disulfide, which can delay the recombination of photogenerated electrons and holes; at the same time, it can improve the crystal structure of molybdenum disulfide and enhance the catalytic active sites. Therefore, the photocatalytic material provided by this invention has high catalytic efficiency and good stability. This is because DMF is beneficial for promoting the chemical synthesis of molybdenum disulfide (MoS2), which has two phases, 1T and 2H, corresponding to the octahedral metallic phase and the triangular prism semiconductor phase, respectively. Among these two phases, the 1T phase has superior electrocatalytic performance, while the 2H phase has higher chemical stability and reduction ability, thanks to its stable chemical structure and low conduction band. Furthermore, the heterogeneous structure resulting from the different crystal planes also increases the carrier density and suppresses charge loading.

[0077] The composite photocatalyst prepared in Example 1 was subjected to cycle stability testing, and the specific method is as follows:

[0078] (1) Weigh 40 mg of oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride material from Example 1 and add it to 50 mL of wastewater containing hexavalent chromium and ciprofloxacin. The initial concentration of hexavalent chromium is 10 mg / L and the initial concentration of ciprofloxacin is 10 mg / L.

[0079] (2) The reaction system (wastewater containing oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride material) was subjected to photocatalytic reaction under a 300W xenon lamp with a visible light source, and the timer was started. The distance between the light source and the screen was 15cm. Every 2 minutes, 2mL of solution was taken from the reaction system, filtered through a 0.45µm filter in aqueous phase, and the concentration of hexavalent chromium was measured using a UV-Vis spectrophotometer, and the concentration of ciprofloxacin was measured using a gas chromatograph. After 10 minutes of photocatalytic reaction, the xenon lamp was turned off.

[0080] (3) The material and wastewater were separated by a centrifuge at a speed of 8000 rpm. The oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite material after the reaction was collected and cleaned and dried using the method in Example 1 (5), and then added back into 50 mL of wastewater containing hexavalent chromium and ciprofloxacin.

[0081] Repeat steps (2)-(3) twice.

[0082] Figure 9 The image shows the photocatalytic performance of the composite photocatalyst prepared in Example 1, which undergoes a three-stage reduction of hexavalent chromium in a cyclic reaction. Figure 10 The image shows the photocatalytic performance of the composite photocatalyst prepared in Example 1 for the tertiary oxidation of ciprofloxacin in a cyclic reaction.

[0083] Figure 9The vertical axis represents the percentage of hexavalent chromium concentration, and the horizontal axis represents time. Figure 10 The concentration percentage of cycloprofloxacin is plotted on the ordinate, and time on the x-axis. Figure 9 and Figure 10 As can be seen, after three cycles, the molybdenum disulfide-sulfur-doped carbon nitride material still exhibits highly efficient photocatalytic performance. The removal efficiencies of hexavalent chromium after three cycles are 99.4%, 97.2%, and 94.7%, respectively, and the removal efficiencies of ciprofloxacin after three cycles are 98.6%, 94.9%, and 91.5%, respectively. The molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst exhibits good stability and has good prospects for practical applications. Therefore, the oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst provided by this invention not only has extremely high catalytic efficiency and good stability, but also has a simple preparation method and high purity.

[0084] In summary, the sulfur-doped carbon nitride prepared by high-temperature pyrolysis of thioacetamide (TAA) in this invention has a large specific surface area, providing a good support for the in-situ synthesis of oxygen-doped molybdenum disulfide. Sulfur-doped nitrogen carbide is also a photocatalyst with photocatalytic effects, but its photocatalytic reduction ability is weak due to its low conduction band and rapid recombination of photogenerated electrons and holes. This invention employs an in-situ synthesis method to form a composite material, specifically, oxygen-doped molybdenum disulfide is directly generated on the surface of sulfur-doped nitrogen carbide to form a composite material. During photocatalysis, the heterojunction formed by the two materials achieves the separation of holes and electrons, improving the photocatalytic effect. Simultaneously, the method of this invention uses N,N-dimethylformamide (DMF) as a solvent during in-situ synthesis, utilizing the oxygen in the solvent to synthesize oxygen-doped molybdenum disulfide, which can delay the recombination of photogenerated electrons and holes; at the same time, it improves the crystal structure of molybdenum disulfide and enhances the catalytic active sites. Therefore, the photocatalytic material provided by this invention has high catalytic efficiency and good stability. This is because DMF facilitates the chemical synthesis of molybdenum disulfide (MoS2), which has two phases, 1T and 2H, corresponding to the octahedral metallic phase and the triangular prism semiconductor phase, respectively. Among these two phases, the 1T phase exhibits superior electrocatalytic performance, while the 2H phase possesses higher chemical stability and reduction capability. This is due to its stable chemical structure and low conduction band. Furthermore, the heterogeneous structure resulting from the different crystal planes also improves the material's carrier density and suppresses charge loading.

[0085] Furthermore, the oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst prepared by the method of this invention is chemically a 1T-2H₂O-MoS₂@S-pCN composite photocatalyst, wherein the mass ratio of 1T-2H₂O-MoS₂ to S-pCN in the composite photocatalyst is 10%-18%. Compared to the 2.74 eV band gap of sulfur-doped nitrogen nitride (S-pCN), the photocatalyst material of this invention has a minimum band gap of 2.0 eV, exhibiting better light response, shorter reaction time, and higher efficiency. The oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst provided by this invention can effectively catalytically reduce hexavalent chromium to trivalent chromium and simultaneously oxidize ciprofloxacin under visible light irradiation. This is because the photocatalyst material prepared by this invention has a low band gap, can respond under visible light, and can excite electron-hole pairs. Due to the heterojunction of the composite material promoting the separation of electrons and holes, electrons reduce hexavalent chromium, and holes oxidize ciprofloxacin. Therefore, the material prepared by this invention not only has extremely high catalytic efficiency but also good stability.

[0086] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. The application of an oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst in the reduction of hexavalent chromium and simultaneous oxidation of ciprofloxacin, characterized in that, Chemically, the oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst is a 1T-2H₂O-MoS₂@S-pCN composite photocatalyst, wherein the mass ratio of oxygen-doped molybdenum disulfide 1T-2H₂O-MoS₂ to sulfur-doped carbon nitride S-pCN in the composite photocatalyst is 10%-18%. The preparation method of the oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst includes: A nitrogen-containing compound is dissolved in water, then thioacetamide is added and dissolved, followed by calcination to obtain sulfur-doped carbon nitride; the mass ratio of the nitrogen-containing compound to thioacetamide is 150-170:1; the nitrogen-containing compound is urea or dicyandiamide; The sulfur-doped carbon nitride and N,N-dimethylformamide were then mixed to obtain solution A; the mass ratio of sulfur-doped carbon nitride to N,N-dimethylformamide was 1:60-100. Solution B is obtained by mixing ammonium molybdate tetrahydrate, thiourea, and N,N-dimethylformamide; the mass ratio of sulfur-doped carbon nitride, ammonium molybdate tetrahydrate, and thiourea is 1:0.3-1.6:0.7-2.

9. Solution B was slowly added dropwise to solution A, and a hydrothermal reaction was carried out in an autoclave to obtain the oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite photocatalyst; the hydrothermal reaction temperature was 160-200℃, and the time was 18-24h.

2. The application according to claim 1, characterized in that, The application The process includes the following steps: adding the oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite material to wastewater and performing a photocatalytic reaction under visible light to complete the reduction of hexavalent chromium and the oxidation of ciprofloxacin. The amount of the oxygen-doped molybdenum disulfide-sulfur-doped carbon nitride composite material added to the wastewater is 0.2 g / L-1.2 g / L.

3. The application according to claim 2, characterized in that, In the application, the visible light source is a 300W-500W xenon lamp, the distance between the xenon lamp and the surface of the wastewater is 14cm-16cm, the photocatalytic reaction time is 8min-15min, the concentration of hexavalent chromium in the wastewater is 5mg / L-40mg / L, and the concentration of ciprofloxacin is 5mg / L-40mg / L.

4. The application according to claim 1, characterized in that, The heating rate of the calcination treatment is 3-5℃ / min, and the calcination temperature is 400-500℃.

5. The application according to any one of claims 1 to 4, characterized in that, The heating rate of the hydrothermal reaction is 1-3℃ / min.

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