An antimony sulfide (pipH2) Sb4S7 nanosheet and a preparation method and application thereof

Abstract

The application relates to preparation of antimony sulfide (pipH2) Sb4S7 nanosheets and photocatalytic reduction Cr(VI) performance thereof, and belongs to the field of nanometer material preparation and catalysis. The obtained antimony sulfide nanosheets are uniform in thickness and have regular sheet-like morphology. The (pipH2) Sb4S7 nanosheets exhibit high photocatalytic activity in neutral and alkaline environments, and still have high photocatalytic reduction Cr(VI) activity for high-concentration Cr(VI) alkaline solution. The main path of photocatalytic reduction Cr(VI) of the material is that oxygen is first reduced to a superoxide radical, and the superoxide radical diffuses into the solution to reduce Cr(VI) into Cr(III). This effectively avoids the generation of Cr(OH)3 to block the active sites due to the direct reduction of Cr(VI) on the catalyst surface. The application makes up for the defects that existing photocatalysts are difficult to catalyze reduction of Cr(VI) under alkaline conditions.

Description

TECHNICAL FIELD

[0001] The present application relates to the development of a antimony sulfide (pipH2) Sb4S7 nanosheet and its preparation method and application, belonging to the field of nanomaterial preparation and catalysis. BACKGROUND

[0002] Chromium salts are widely used in leather tanning, metallurgy, electroplating, paint pigments, textile production and other fields, and play a huge industrial value. However, Cr(VI) in industrial wastewater is considered one of the most toxic pollutants, listed by the International Agency for Research on Cancer as a carcinogen and mutagen, with a half lethal dose (LD50) of 50-150 mg / kg. At the same time, Cr(VI) has high mobility and is easily absorbed by the human body through the skin, which can cause serious threats to the ecological environment and human health. Efficiently treating Cr(VI) in industrial wastewater and polluted water bodies is of great significance for creating a green ecology and sustainable development. Cr(III) is less toxic than Cr(VI) and is easy to form Cr(OH)3 precipitate for easy collection and treatment. Therefore, reducing Cr(VI) to Cr(III) in water bodies is an effective way to treat Cr(VI). In recent years, the use of photocatalytic technology to reduce Cr(VI) has received widespread attention due to its green environmental protection, strong sustainability, and simple operation process. A series of photocatalysts have been proven to be useful for Cr(VI) reduction and exhibit considerable catalytic efficiency, such as oxides, sulfides, metal-organic framework materials and their composites. However, most of the above materials can only photocatalytically reduce Cr(VI) under acidic conditions, while in neutral and especially alkaline environments, the efficiency of existing materials for catalytic reduction of Cr(VI) is very low, or even cannot achieve effective reduction of Cr(VI). If the problem of low catalytic efficiency of catalysts in alkaline conditions cannot be solved, a large amount of acid needs to be added to adapt to the working conditions of the catalyst when treating alkaline wastewater. In addition, the Cr(III) obtained by reduction in acidic environment often needs to be further precipitated and recovered under the addition of alkaline solution. This will cause resource waste and secondary pollution, limiting the further development of photocatalytic reduction of Cr(VI) technology. The main reasons why existing catalysts are difficult to reduce Cr(VI) in alkaline environments are as follows: (1) Cr(VI) exists in the form of Cr2O7 2- and HCrO4 - in acidic conditions, with an Nernst reduction potential of 1.36 V vs NHE; while in alkaline conditions, it exists in the form of CrO4 2-, which has a Nernst reduction potential of -0.13 V vs NHE. Therefore, the reduction of Cr(VI) under alkaline conditions requires a catalyst with a more negative conduction band potential. (2) The existing catalysts for reducing Cr(VI) are mainly dominated by photo-generated electron reduction, that is, Cr(VI) adsorbed on the surface of the catalyst is directly reduced to Cr(III) by obtaining electrons. In an alkaline environment, Cr(III) will be deposited on the surface of the catalyst in the form of Cr(OH)3, which will block the active sites of the catalyst and inhibit the occurrence of further reduction reactions. In combination with the complex environment of actual industrial wastewater, solving the above problems and developing a photocatalyst that can efficiently reduce Cr(VI) under alkaline conditions has important industrial value. SUMMARY

[0003] The technical problem solved by the present application is that the present application solves the problem of poor performance of existing photocatalysts in catalyzing the reduction of Cr(VI) under neutral and alkaline conditions. A preparation method of antimony sulfide (pipH2) Sb4S7 nanosheet, which is prepared by solvothermal method using antimony trichloride, thioacetamide and piperazine as raw materials, and acetone and isopropanol as solvents. The material can efficiently catalyze the reduction of high-concentration Cr(VI) in an alkaline environment as a photocatalyst. The problem of existing photocatalysts that cannot effectively catalyze the reduction of Cr(VI) in an alkaline environment or are easily blocked by the generated Cr(OH)3 active sites is solved.

[0004] To solve the above technical problems, the technical solution proposed by the present application is: a preparation method of antimony sulfide (pipH2) Sb4S7 nanosheet: at room temperature, dissolve antimony trichloride and thioacetamide in acetone to form solution A. Dissolve anhydrous piperazine in isopropanol under ultrasonic conditions to form solution B. Slowly pour solution B into solution A while stirring to form a white suspension. Then, the obtained white suspension is transferred to a reaction kettle for heating reaction. After natural cooling to room temperature, the generated orange-yellow solid is taken out by centrifugation. Wash with ethanol and water repeatedly and dry to obtain (pipH2) Sb4S7 nanosheet.

[0005] Preferably, acetone and isopropanol are selected as solvents. Thioacetamide is selected as a sulfur source. The preparation process is a step-by-step reaction, that is, antimony trichloride and thioacetamide are dissolved in acetone in advance, and anhydrous piperazine is dissolved in isopropanol.

[0006] Preferably, the anhydrous piperazine is dissolved in isopropanol under ultrasonic conditions for 20 minutes.

[0007] Preferably, the obtained white suspension is transferred to a reaction kettle for heating reaction, the heating temperature is 190℃, and the heating time is 3 days.

[0008] Preferably, the specific steps of the experiment are as follows:

[0009] (1) At room temperature, weigh antimony trichloride (1 mmol, 228 mg) and thioacetamide (4 mmol, 300 mg) into 4 mL of acetone, stir for 2 minutes to dissolve, and form solution A.

[0010] (2) Weigh 1 g of anhydrous piperazine into 4 mL of isopropanol, and ultrasonically dissolve for 20 minutes to form solution B.

[0011] (3) Under stirring, slowly pour solution B obtained in step (2) into solution A obtained in step (1) to form a white suspension.

[0012] (4) Transfer the white suspension obtained in step (3) into a 50 mL PTFE reaction kettle liner and package in a stainless steel reaction kettle, and place in a common oven at 190℃ for 3 days.

[0013] Preferably, the (pipH2)Sb4S7 nanosheet has a regular morphology, a lateral size of 100-500 nm, and a thickness of about 40 nm. If the sulfur source is replaced by elemental sulfur, if the solvent is replaced by deionized water, and if the step-by-step reaction is not used, the product is (pipH2)Sb4S7 polycrystal, which has a thickness of more than 5 μm, a lateral size of more than 50 μm, and grows in a twin crystal manner rather than a dispersed uniform nanosheet.

[0014] Preferably, the (pipH2)Sb4S7 crystal is in an orthorhombic system, and the space group is Ama2. The compound is composed of one-dimensional [Sb4S7] 2- anion chains and protonated piperazine cations (pipH2). In which Sb adopts a trigonal pyramid coordination configuration, each Sb is coordinated with 3 S atoms to form a [SbS3] structural unit. 3 [SbS3] are connected to each other in pairs by sharing a vertex S to form a [Sb3S6] six-membered ring. [Sb3S6] and [SbS3] are alternately connected to form a one-dimensional [Sb4S7] 2- anion chain.

[0015] To solve the above technical problems, another technical scheme of the present application is that the obtained antimony sulfide (pipH2)Sb4S7 nanosheet can be used as a photocatalyst to photocatalytically reduce Cr(VI) in an alkaline solution environment.

[0016] Preferably, the antimony sulfide (pipH2)Sb4S7 nanosheet catalytically reduces K2Cr2O7 solution under alkaline conditions of pH = 9 or pH = 10, and the concentration of K2Cr2O7 is 50-500 mg / L.

[0017] Beneficial effects

[0018] Inorganic reactants (antimony trichloride and thioacetamide) and organic reactants (piperazine) were pre-dissolved in acetone and isopropanol, respectively, and then the two solutions were thoroughly mixed and reacted. This provided a uniform solution reaction environment for the nucleation and growth of the material, which was beneficial for the micro- and nano-scale preparation of the product and promoted the uniformity of the product morphology. The formed antimony sulfide (pipH2)Sb4S7 nanosheets had regular morphology, with a lateral size of 100-500 nm and a thickness of approximately 40 nm.

[0019] This product exhibits highly efficient photocatalytic activity in alkaline environments. At pH 9, it can completely reduce 100 mg / L of Cr(VI) within 14 minutes; at pH 10, it can completely reduce 100 mg / L of Cr(VI) within 20 minutes. Furthermore, (pipH2)Sb4S7 nanosheets maintain high photocatalytic reduction efficiency for high-concentration alkaline Cr(VI) solutions. In an alkaline environment at pH 9, it can completely reduce 300 mg / L of Cr(VI) within 30 minutes, 400 mg / L within 45 minutes, and 500 mg / L within 60 minutes. Moreover, this material retains high catalytic activity in tap water and natural light environments. It demonstrated high cycling stability in 5-cycle tests.

[0020] The high catalytic activity of this product for Cr(VI) in an alkaline environment can be attributed to the following two points:

[0021] 1. The conduction band position of (pipH2)Sb4S7 nanosheets is -0.71V, which is more negative than O2 / ·O2. - The potential (-0.33V vs. NHE) and CrO4 2- Its reduction potential is -0.13V. Therefore, it exhibits photocatalytic reduction of O2 and CrO4. 2- The ability.

[0022] 2. The process of catalytic reduction of Cr(VI) by (pipH2)Sb4S7 nanosheets is carried out by O2. - As the dominant factor, the generated O2 - It can diffuse into the solution to reduce Cr(VI). This effectively avoids the direct reduction of Cr(VI) on the catalyst surface, which would otherwise cause the generated Cr(OH)3 to block the active sites. Attached Figure Description

[0023] Figure 1 The image shows the SEM image of (pipH2)Sb4S7 nanosheets obtained in Example 1.

[0024] Figure 2 The image shows the SEM image of the (pipH2)Sb4S7 polycrystalline material obtained in Example 2.

[0025] Figure 3 Powder X-ray diffraction patterns of the products obtained in Example 1 and Example 2.

[0026] Figure 4 Crystal structure diagrams of the products obtained in Example 1 and Example 2. a is the structure diagram observed along the b axis; b is the structure diagram observed along the c axis. 2- Chain-like structure; b is the structure diagram observed along the c axis.

[0027] Figure 5 Band structure test results of the product obtained in Example 1. a is the band gap width of the product according to the ultraviolet-visible absorption spectrum and Kubelka-Munk equation fitting; b is the Mott-Schottky curve of the working electrode prepared in Example 3.

[0028] Figure 6 A graph of the photocatalytic reduction of Cr(VI) in a basic environment (pH = 9) by (pipH2)Sb4S7 nanosheets and polycrystals obtained by different preparation processes in Example 5.

[0029] Figure 7 A graph of the photocatalytic reduction of Cr(VI) in different acidic and basic environments (pH = 5, 7, 9, 10) in Example 6.

[0030] Figure 8 A graph of the photocatalytic reduction of Cr(VI) in a basic environment (pH = 9) by the product at different concentrations (50, 100, 200, 300, 400, 500 mg / L) in Example 7.

[0031] Figure 9 A graph of the photocatalytic reduction of Cr(VI) in an acidic environment (pH = 5) by the product at different concentrations (50, 100, 200, 250 mg / L) in Example 8.

[0032] Figure 10 A graph of the photocatalytic reduction of Cr(VI) by different product doses (20, 50, 80, 100 mg) in a basic environment (pH = 9) in Example 9.

[0033] Figure 11 A bar graph of the reduction efficiency of Cr(VI) by the product in 5 cycle tests in Example 10.

[0034] Figure 12 A graph of the photocatalytic reduction of Cr(VI) by the product in a basic environment (pH = 9) (100 mg / L) under natural light conditions in Example 11.

[0035] Figure 13Photocatalytic reduction curve of the product on Cr(VI) solution (100 mg / L) in alkaline (pH = 9) environment for Example 12.

[0036] Figure 14 Photocatalytic reduction curve of the product on Cr(VI) solution (100 mg / L) in alkaline (pH = 9) environment for Example 13 under the condition of adding different radical scavengers.

[0037] Figure 15 Photocatalytic reduction curve of the product on Cr(VI) solution (100 mg / L) in alkaline (pH = 9) environment for Example 14 under the condition of passing different gases (nitrogen, air and oxygen). DETAILED DESCRIPTION

[0038] The application is further explained and described below:

[0039] 1. The influence of different preparation processes on the product morphology and photocatalytic reduction Cr(VI) performance is investigated, see Examples 1, 2 and 5.

[0040] 2. The photocatalytic reduction Cr(VI) performance of (pipH2)Sb4S7 nanosheets under different pH conditions is investigated, see Examples 6, 7 and 8.

[0041] 3. The influence of different conditions on the photocatalytic reduction Cr(VI) performance of (pipH2)Sb4S7 nanosheets under alkaline conditions is investigated, see Examples 6, 7 and 9.

[0042] 4. The cycle performance of (pipH2)Sb4S7 nanosheets in photocatalytic reduction Cr(VI) under alkaline conditions is investigated, see Example 10.

[0043] 4. The photocatalytic performance of (pipH2)Sb4S7 nanosheets on alkaline Cr(VI) solution in natural environment is investigated, see Examples 11 and 12.

[0044] 5. The mechanism of (pipH2)Sb4S7 nanosheets in maintaining high efficiency in catalyzing Cr(VI) under alkaline environment is investigated, see Examples 13 and 14.

[0045] Example 1:

[0046] Preparation of (pipH2)Sb4S7nanosheets: At room temperature, antimony trichloride (1 mmol, 228 mg) and thioacetamide (4 mmol, 300 mg) were added into 4 mL of acetone, stirred for 2 min to dissolve, forming solution A. 1 g of anhydrous piperazine was weighed into 4 mL of isopropanol, and ultrasonically dissolved for 20 min, forming solution B. Under stirring, solution B was slowly poured into solution A, forming a white suspension. Subsequently, the obtained white suspension was transferred into a 50 mL PTFE inner liner of a stainless steel autoclave and placed in a common oven at 190 °C for 3 days. And dried in a constant temperature drying oven at 60 °C for 12 h to obtain an orange-yellow powder. Figure 1 The morphology of the product was shown to be nanosheets, with a lateral size of 100-500 nm and a thickness of about 40 nm.

[0047] Example 2:

[0048] Preparation of (pipH2)Sb4S7polycrystals: At room temperature, antimony trichloride (1 mmol, 228 mg), sulfur (4 mmol, 96 mg) and 1 g of anhydrous piperazine were added into 4 mL of deionized water, stirred to mix uniformly, transferred into a 25 mL PTFE inner liner of a stainless steel autoclave and placed in a common oven at 190 °C for 3 days. After cooling to room temperature, washed repeatedly with ethanol and water by ultrasonication to obtain orange microcrystals. Figure 2 The morphology of the product was shown to be microcrystals grown in a twin crystal manner, with a thickness of more than 5 μm and a lateral size of more than 50 μm.

[0049] If the sulfur source is replaced by elemental sulfur, if the solvent is replaced by deionized water, and if the step-by-step reaction is not used, the product is (pipH2)Sb4S7polycrystals, with a thickness of more than 5 μm and a lateral size of more than 50 μm, and grown in a twin crystal manner rather than dispersed uniform nanosheets.

[0050] Figure 3 The powder X-ray diffraction spectra of the products obtained in Example 1 and Example 2 were compared with the powder X-ray diffraction spectrum of (pipH2)Sb4S7simulated based on single crystal X-ray diffraction data, confirming that both were (pipH2)Sb4S7.

[0051] Figure 4 The crystal structure diagrams of the products obtained in Example 1 and Example 2. a is the [Sb4S7] chain structure observed along the b axis; b is the structure diagram observed along the c axis, with protonated piperazine distributed between the chains. 2-

[0052] Example 3:

[0053] ​Take 5 mg of (pIpH2)Sb4S7 nanosheets prepared in Example 1, disperse it in a mixed solution composed of 200 μL of ethanol, 40 μL of distilled water, and 10 μL of Nafion solution, and ultrasonic for 2 hours to form a uniform colloid. Take 40 μL of the colloid and drop it on an ITO glass plate to form a 1 x 1 cm square, and then place it in a vacuum drying oven to dry for 2 hours to obtain a working electrode for photoelectrochemical test. The working electrode, together with a counter electrode (Pt wire) and a reference electrode (Ag / AgCl), forms a standard three-electrode system, and an electrochemical workstation is used to test the Mott-Schottky curve of the material.

[0054] and 10 μL of Nafion solution, and ultrasonic for 2 hours to form a uniform colloid. Take 40 μL of the colloid and drop it on an ITO glass plate to form a 1 x 1 cm square, and then place it in a vacuum drying oven to dry for 2 hours to obtain a working electrode for photoelectrochemical test. The working electrode, together with a counter electrode (Pt wire) and a reference electrode (Ag / AgCl), forms a standard three-electrode system, and an electrochemical workstation is used to test the Mott-Schottky curve of the material. 2

[0055] Figure 5 The band structure test results of the product obtained in Example 1 are shown. a is the band gap of the product fitted according to the ultraviolet-visible absorption spectrum and the Kubelka-Munk equation, and the value is 1.91 eV; b is the Mott-Schottky curve of the working electrode prepared in Example 3.

[0056] Figure 5 b shows the flat band potential of the product obtained by fitting the curves at different frequencies, and the value is -0.81 V vs. Ag / AgCl. And the slope of the curve is positive, indicating that the product is an n-type semiconductor. Since the conduction band edge of the n-type semiconductor is 0.1 V lower than its flat band potential, the conduction band potential of the product is -0.71 V vs. NHE.

[0057] Example 4:

[0058] At room temperature, take 500 mg of diphenylcarbazide and dissolve it in 125 mL of acetone, and use deionized water to dilute the above solution to 250 mL to obtain a diphenylcarbazide solution. Take 1 mL of the diphenylcarbazide solution and add it to a mixed solution composed of 200 μL of concentrated sulfuric acid, 200 μL of phosphoric acid, and 3 mL of deionized water to prepare a color developing agent for determining the concentration of Cr(VI) by diphenylcarbazide spectrophotometry.

[0059] Example 5:

[0060] ​Take 2 portions of 50 mL K2Cr2O7 solution (100 mg / L, deionized water as solvent) at room temperature, and adjust the pH to 9 using sodium hydroxide solution. Take 50 mg of (pipH2)Sb4S7 nanosheets prepared in Example 1 and 50 mg of (pipH2)Sb4S7 polycrystal prepared in Example 2, respectively, and add them to the above solution, and ultrasonically disperse them. After 30 minutes of reaction in the dark room to reach adsorption-desorption equilibrium, perform the photocatalytic reduction of Cr(VI) under visible light irradiation using a 300 W xenon lamp with a 420 nm filter. Take 100 μL of the reacted solution and add it to the color developing agent prepared in Example 4, and analyze the Cr(VI) concentration using a UV-visible spectrophotometer.

[0061] Figure 6 The performance of the (pipH2)Sb4S7 nanosheets prepared in Example 1 is shown to be much better than that of the (pipH2)Sb4S7 polycrystal prepared in Example 2, proving the necessity of the nanosheet morphology and the necessity of the step-by-step preparation and raw material selection.

[0062] Example 6:

[0063] Take 4 portions of 50 mL K2Cr2O7 solution (100 mg / L, deionized water as solvent) at room temperature, and adjust the pH to 5, 7, 9, and 10, respectively, using dilute hydrochloric acid or sodium hydroxide solution. Take 50 mg of (pipH2)Sb4S7 nanosheets prepared in Example 1, respectively, and add them to the above solution, and ultrasonically disperse them. After 30 minutes of reaction in the dark room to reach adsorption-desorption equilibrium, perform the photocatalytic reduction of Cr(VI) under visible light irradiation using a 300 W xenon lamp with a 420 nm filter. Take 100 μL of the reacted solution and add it to the color developing agent prepared in Example 4, and analyze the Cr(VI) concentration using a UV-visible spectrophotometer.

[0064] Figure 7 It is shown that the product still maintains high catalytic activity under neutral and alkaline conditions. At pH = 9, 100 mg / L of Cr(VI) can be completely reduced in 14 minutes; at pH = 10, 100 mg / L of Cr(VI) can be completely reduced in 20 minutes.

[0065] Example 7:

[0066] At room temperature, 50 mL of K2Cr207 solution (solvent is deionized water) with different concentrations (50, 100, 200, 300, 400, 500 mg / L) was taken, and the pH was adjusted to 9 using sodium hydroxide solution. Subsequently, 50 mg of (pH2)Sb4S7 nanosheets prepared in Example 1 was added to the above solution, and ultrasonic was used to make it fully dispersed. After 30 minutes of adsorption-desorption balance in the dark room, the photocatalytic reduction of Cr(VI) was carried out under visible light irradiation using a 300 W xenon lamp with a 420 nm filter. A certain amount of the reacted solution was added to the color developing agent prepared in Example 4, and the concentration of Cr(VI) was analyzed using a UV-visible spectrophotometer. In the catalytic experiment of 50 mg / L K2Cr207, the amount of the reacted solution taken was 200 μL; in the catalytic experiment of 100 mg / L K2Cr207, the amount of the reacted solution taken was 100 μL; in the catalytic experiment of 200 mg / L K2Cr207, the amount of the reacted solution taken was 50 μL; in the catalytic experiment of 300 mg / L K2Cr207, the amount of the reacted solution taken was 40 μL; in the catalytic experiment of 400 mg / L K2Cr207, the amount of the reacted solution taken was 30 μL; in the catalytic experiment of 500 mg / L K2Cr207, the amount of the reacted solution taken was 20 μL.

[0067] Figure 8 It is shown that the product maintains high catalytic activity for high concentration of Cr(VI) in alkaline environment. 300 mg / L of Cr(VI) can be completely reduced within 30 minutes; 400 mg / L of Cr(VI) can be completely reduced within 45 minutes; 500 mg / L of Cr(VI) can be completely reduced within 60 minutes.

[0068] Example 8:

[0069] At room temperature, 50 mL of K2Cr207 solution (solvent is deionized water) with different concentrations (50, 100, 200, 250 mg / L) was taken, and the pH was adjusted to 5 using dilute hydrochloric acid solution. Subsequently, 50 mg of (pipH2)Sb4S7 nanosheets prepared in Example 1 was added to the above solution, and ultrasonic dispersion was performed. After 30 minutes of reaction in the dark room to reach adsorption-desorption equilibrium, the photocatalytic reduction of Cr(VI) was carried out under visible light irradiation using a 300 W xenon lamp with a 420 nm filter. A certain amount of the reacted solution was added to the color developing agent prepared in Example 4, and the concentration of Cr(VI) was analyzed by ultraviolet-visible light spectrophotometer. In the catalytic experiment of 50 mg / L K2Cr207, the amount of the reacted solution taken was 200 μL; in the catalytic experiment of 100 mg / L K2Cr207, the amount of the reacted solution taken was 100 μL; in the catalytic experiment of 200 mg / L K2Cr207, the amount of the reacted solution taken was 50 μL; in the catalytic experiment of 250 mg / L K2Cr207, the amount of the reacted solution taken was 40 μL;

[0070] Example 9:

[0071] At room temperature, 3 portions of 50 mL of K2Cr207 solution (solvent is deionized water) with a concentration of 100 mg / L were taken, and the pH was adjusted to 9 using sodium hydroxide solution. Different doses (20, 50, 80, 100 mg) of (pipH2)Sb4S7 nanosheets prepared in Example 1 were weighed and added to the above solution, and ultrasonic dispersion was performed. After 30 minutes of reaction in the dark room to reach adsorption-desorption equilibrium, the photocatalytic reduction of Cr(VI) was carried out under visible light irradiation using a 300 W xenon lamp with a 420 nm filter. 100 μL of the reacted solution was added to the color developing agent prepared in Example 4, and the concentration of Cr(VI) was analyzed by ultraviolet-visible light spectrophotometer.

[0072] Example 10:

[0073] At room temperature, 50 mL of K2Cr2O7 solution (100 mg / L, deionized water as solvent) was prepared. The pH of the solution was adjusted to 9 using NaOH solution. 50 mg of (pipH2)Sb4S7 nanosheets prepared in Example 1 was added to the solution and ultrasonically dispersed. After 30 minutes of reaction in the dark room to reach adsorption-desorption equilibrium, the photocatalytic reduction of Cr(VI) was carried out under visible light irradiation using a 300 W xenon lamp with a 420 nm filter. 100 μL of the reacted solution was added to the color reagent prepared in Example 4, and the concentration of Cr(VI) was analyzed using a UV-visible spectrophotometer. The (pipH2)Sb4S7 nanosheets after reaction were washed once with deionized water and ethanol and dried. The dried product was used to repeat the above process, which was the second cycle test. In this way, a total of 5 cycle tests were carried out to verify the repeatability of the product performance. Figure 11 The product was shown to have cycle stability.

[0074] Example 11:

[0075] At room temperature, 50 mL of K2Cr2O7 solution (100 mg / L, deionized water as solvent) was prepared. The pH of the solution was adjusted to 9 using NaOH solution. 50 mg of (pipH2)Sb4S7 nanosheets prepared in Example 1 was added to the solution and ultrasonically dispersed. After 30 minutes of reaction in the dark room to reach adsorption-desorption equilibrium, the photocatalytic reduction of Cr(VI) was carried out under visible light irradiation using a 300 W xenon lamp with a 420 nm filter. 100 μL of the reacted solution was added to the color reagent prepared in Example 4, and the concentration of Cr(VI) was analyzed using a UV-visible spectrophotometer. The (pipH2)Sb4S7 nanosheets after reaction were washed once with deionized water and ethanol and dried. The dried product was used to repeat the above process, which was the second cycle test. In this way, a total of 5 cycle tests were carried out to verify the repeatability of the product performance. Figure 12 The product was shown to have high catalytic activity under natural light.

[0076] Example 12:

[0077] At room temperature, 50 mL of K2Cr2O7 solution (100 mg / L, deionized water as solvent) was prepared. The pH of the solution was adjusted to 9 using NaOH solution. 50 mg of (pipH2)Sb4S7 nanosheets prepared in Example 1 was added to the solution and ultrasonically dispersed. After 30 minutes of reaction in the dark room to reach adsorption-desorption equilibrium, the photocatalytic reduction of Cr(VI) was carried out under visible light irradiation using a 300 W xenon lamp with a 420 nm filter. 100 μL of the reacted solution was added to the color reagent prepared in Example 4, and the concentration of Cr(VI) was analyzed using a UV-visible spectrophotometer. The (pipH2)Sb4S7 nanosheets after reaction were washed once with deionized water and ethanol and dried. The dried product was used to repeat the above process, which was the second cycle test. In this way, a total of 5 cycle tests were carried out to verify the repeatability of the product performance.

[0078] Figure 13 The product was shown to have high catalytic activity in the presence of various unrelated ions in tap water.

[0079] Example 13

[0080] Take 4 portions of 50 mL concentration of 100 mg / L K2Cr2O7 solution (solvent is deionized water), respectively add 1 mM of p-benzoquinone (superoxide radical scavenger), 5 mM of potassium bromate (electron scavenger), 5 mM of isopropanol (hydroxyl radical scavenger), 1 mL of ethanol (hole scavenger). Using sodium hydroxide solution to adjust its pH to 9. To the above solution, respectively add 50 mg of (pipH2) Sb4S7 nanosheets prepared in Example 1, ultrasonic to make it fully dispersed. In the dark for 30 minutes to reach adsorption-desorption balance, with a 300 W xenon lamp with a 420 nm filter as the light source, under visible light irradiation to carry out photocatalytic reduction of Cr(VI) experiment. Take 100 μL of the reaction solution into the color reagent prepared in Example 4, and use UV-visible spectrophotometer to analyze the concentration of Cr(VI).

[0081] Figure 14 It is shown that the addition of p-benzoquinone inhibits the reduction rate of Cr(VI), the addition of potassium bromate and isopropanol has no obvious effect on the reduction rate of Cr(VI), and the addition of ethanol increases the reduction rate of Cr(VI). It is shown that the main way of photocatalytic reduction of product to Cr(VI) is to reduce oxygen to superoxide radical first, and then superoxide radical reduces Cr(VI).

[0082] Example 14

[0083] Take 3 portions of 50 mL concentration of 100 mg / L K2Cr2O7 solution (solvent is deionized water), use sodium hydroxide solution to adjust its pH to 9. To the above solution, respectively add 50 mg of (pipH2) Sb4S7 nanosheets prepared in Example 1, ultrasonic to make it fully dispersed. Respectively, nitrogen, air and oxygen are introduced, and the time for gas introduction is from the beginning of the dark reaction to the end of the photocatalytic reaction. In the dark for 30 minutes to reach adsorption-desorption balance, with a 300 W xenon lamp with a 420 nm filter as the light source, under visible light irradiation to carry out photocatalytic reduction of Cr(VI) experiment. Take 100 μL of the reaction solution into the color reagent prepared in Example 4, and use UV-visible spectrophotometer to analyze the concentration of Cr(VI). Figure 15 It is shown that the introduction of oxygen can significantly improve the reduction efficiency of Cr(VI), further indicating that the main way of photocatalytic reduction of product to Cr(VI) is to reduce oxygen to superoxide radical first, and then superoxide radical reduces Cr(VI).

Claims

1. A method for preparing antimony sulfide (pipH2) Sb4S7 nanosheets, characterized in that: (1) at room temperature, dissolve antimony trichloride and thioacetamide in acetone to form solution A; (2) dissolve anhydrous piperazine in isopropyl alcohol under ultrasonic conditions to form solution B; (3) slowly pour solution B into solution A under stirring to form a white suspension; (4) then, transfer the obtained white suspension into a reaction kettle for heating reaction; (5) after natural cooling to room temperature, centrifuge to take out the generated orange-yellow solid; repeatedly ultrasonic washing with ethanol and water and drying to obtain (pipH2) Sb4S7 nanosheets. Acetone and isopropyl alcohol are selected as solvents; thioacetamide is selected as a sulfur source; the preparation process is a step-by-step reaction, that is, antimony trichloride and thioacetamide are dissolved in acetone in advance, and anhydrous piperazine is dissolved in isopropyl alcohol. In step (2), the anhydrous piperazine is dissolved in isopropyl alcohol under ultrasonic conditions, and the ultrasonic time is 20 minutes. In step (4), the obtained white suspension is transferred into a reaction kettle for heating reaction, the heating temperature is 190 °C, and the heating time is 3 days. The specific steps are as follows: (1) at room temperature, weigh 1 mmol of antimony trichloride, 228 mg, and 4 mmol of thioacetamide, 300 mg, and add them into 4 mL of acetone, stir for 2 minutes to dissolve them to form solution A; 2. The method for preparing antimony sulfide (pipH2)Sb4S7 nanosheets according to claim 1, characterized in that: (2) weigh 1 g of anhydrous piperazine and add it into 4 mL of isopropyl alcohol, ultrasonic for 20 minutes to dissolve it to form solution B; 3. The method for preparing antimony sulfide (pipH2)Sb4S7 nanosheets according to claim 1, characterized in that: (3) under the action of stirring, slowly pour solution B obtained in step (2) into solution A obtained in step (1) to form a white suspension; 4. The method for preparing antimony sulfide (pipH2)Sb4S7 nanosheets according to claim 1, characterized in that: (4) transfer the white suspension obtained in step (3) into a 50 mL polytetrafluoroethylene inner container of a reaction kettle and package it in a stainless steel reaction kettle, and place it in a normal oven at 190 °C for reaction for 3 days.

5. The method for preparing antimony sulfide (pipH2)Sb4S7 nanosheets according to claim 1, characterized in that: The (pipH2) Sb4S7 nanosheets have regular morphology, a horizontal size of 100-500 nm, and a thickness of 40 nm. Ama 8. The antimony sulfide (pipH2) Sb4S7 nanosheets prepared by the method according to any one of claims 1-7. The antimony sulfide (pipH2) Sb4S7 nanosheets act as a photocatalyst to catalyze the reduction of Cr(VI) under alkaline conditions. The antimony sulfide (pipH2) Sb4S7 nanosheets catalyze the reduction of K2Cr2O7 solution under alkaline conditions of pH = 9 or pH = 10, and the concentration of K2Cr2O7 is 50-500 mg / L.

6. The method for preparing antimony sulfide (pipH2)Sb4S7 nanosheets according to claim 1, characterized in that: ​ 7. The method for preparing antimony sulfide (pipH2)Sb4S7 nanosheets according to claim 1, characterized in that: The (pipH2)Sb4S7crystallizes in the orthorhombic system with space group ​ 2; the compound consists of one-dimensional [Sb4S7] 2- anionic chains and protonated piperazine cations pipH2; wherein Sb adopts a trigonal pyramidal coordination geometry, each Sb is coordinated with 3 S atoms to form [SbS3] building units; 3 [SbS3] are connected to each other by sharing a vertex S to form a [Sb3S6] six-membered ring; [Sb3S6] and [SbS3] are connected alternately to form a [Sb4S7] 2- one-dimensional anionic chains. ​ 9. Use of antimony sulfide (pipH2) Sb4S7 nanoplatelets according to claim 8, characterized in that: ​ 10. Use of antimony sulfide (pipH2) Sb4S7 nanoplatelets according to claim 8, characterized in that: ​

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