Preparation method of three-phase Ag / Ag2S / h-RGO photocatalyst

Abstract

The invention discloses a preparation method of a three-phase Ag / Ag2S / h-RGO photocatalyst, comprising the following steps: functionalized SiO2 nanospheres are added to ultrapure water and dissolved to obtain a mixed solution; graphene oxide is dispersed in ultrapure water, ultrasonicated, and then placed in the mixed solution and vigorously stirred to generate SiO2@GO; NaBH4 is then added and stirred, followed by sodium hydroxide, the mixture is stirred, and the resulting product is washed to obtain h-RGO; h-RGO is dissolved in water, thioglycolic acid is added, and vigorously stirred; AgNO3 is then added and stirred, followed by Na2S·9H2O and stirred, followed by centrifugation to obtain a product dissolved in water, and silver sulfide is in situ reduced with a sodium borohydride solution; the product is washed and dried to obtain a three-phase Ag / Ag2S / h-RGO photocatalyst. The present invention adopts a layer-by-layer (LBL) self-assembly method to synthesize nanosheets RGO with a hollow structure, and a simple in situ growth method is used to prepare a three-phase Ag / Ag2S / h-RGO photocatalyst.

Description

Technical Field

[0001] The present invention relates to the technical field of photocatalytic materials, and in particular to a method for preparing a three-phase Ag / Ag2S / h-RGO photocatalyst. Background Art

[0002] Reduced graphene oxide (RGO) has been shown to be an effective structure for photocatalytic supports due to its high specific surface area, high electron collection and transfer capacity, and electrochemical stability. During photodegradation, two-dimensional RGO often plays a crucial role in reducing the recombination of photogenerated electrons and holes, allowing electrons to be rapidly transferred from the photocatalytic material to the 2D RGO surface. Song et al. reported that the photocatalytic activity of Ag / Ag2CO3 / RGO photocatalyst was much higher than that of Ag / Ag2CO3, which was attributed to the enhanced separation rate of photogenerated electrons and holes by the 2D RGO. Huo et al. prepared Ag / Ag2S / RGO using a hydrothermal method and UV-assisted reduction, which exhibited good photocatalytic degradation efficiency for ciprofloxacin under visible light. RGO made a significant contribution to long-range interfacial charge transfer and acted as an electron transfer medium to reduce electron-hole recombination. Notably, there are few reports on the structural manipulation of 2D RGO nanosheets in plasmonic photocatalyst modification to further enhance activity. If the structure of nanosheets can be rolled into hollow nanospheres, the structure of the material hollow nanospheres may have unique morphology with chemical and physical properties: thermal and chemical stability, higher specific surface area, higher utilization rate and better permeability.

[0003] Composites of one-dimensional plasmonic nanoparticles of Ag / nanorodal Ag2S with two-dimensional hollow nanosheets of RGO are an ideal approach to prepare visible-light-induced catalysts with high photocatalytic performance for naphthalene and 1-naphthol. To date, there have been no reports on plasmonic nanoparticles of Ag / nanorodal Ag2S / hollow nanosheets of RGO. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a preparation method of a three-phase Ag / Ag2S / h-RGO photocatalyst.

[0005] The technical solution of the present invention is: a method for preparing a three-phase Ag / Ag2S / h-RGO photocatalyst, comprising the following steps:

[0006] S1. Preparation of h-RGO

[0007] Functionalized SiO2 nanospheres were added to one portion of ultrapure water and dissolved by ultrasonic vibration for 0.5 hours to obtain a mixed solution. Graphene oxide was dispersed in another portion of ultrapure water, ultrasonically treated for 30 minutes, and then placed in the mixed solution and vigorously stirred for 5 hours to produce SiO2@GO. NaBH4 was then added and stirred for 1 hour to reduce the graphene oxide to RGO. Sodium hydroxide was then added and the mixture was stirred for 24 hours to remove the SiO2 template. The resulting product was then washed several times with ultrapure water to remove excess sodium hydroxide to obtain h-RGO.

[0008] Preparation of S2, three-phase Ag / Ag2S / h-RGO photocatalyst

[0009] The prepared h-RGO was dissolved in water, and thioglycolic acid was added and stirred vigorously for 2 hours. Then, AgNO3 was added and stirred for 2 hours to obtain a homogeneous mixture. Subsequently, Na2S·9H2O was added and stirred for 1 hour to obtain a gray solution. The gray solution was centrifuged to obtain the product, which was dissolved in water and then in situ reduced with sodium borohydride solution. Finally, the prepared product was washed several times with ultrapure water and ethanol, and then dried at 60°C to obtain a three-phase Ag / Ag2S / h-RGO photocatalyst.

[0010] Furthermore, the preparation method of the functionalized SiO2 nanospheres is as follows:

[0011] 1) Add 1g of SiO2 nanospheres to 0.12L of 0.5M sodium chloride solution and further disperse by ultrasonic vibration for 1h; then, add 1.5g of PDDA and stir for 1h; then wash the product and centrifuge it several times to obtain a primary product;

[0012] 2) The primary product was further added to 0.12 L of 0.5 M sodium chloride solution and further dispersed by ultrasonic vibration for 1 hour. Subsequently, 0.3 g of PSS was added and stirred for 1 hour. The product was then washed and centrifuged several times to obtain a secondary product.

[0013] 3) The secondary product was further added to 0.12 L of 0.5 M sodium chloride solution and further dispersed by ultrasonic vibration for 1 hour. Subsequently, 1.5 g of PDDA was added and stirred for 1 hour. The product was then washed and centrifuged multiple times to obtain functionalized SiO2 nanospheres that had completed LBL assembly.

[0014] Description: The specific surface area of ​​the photocatalyst depends on the porosity and geometry of the material. A larger surface area can provide more active sites for reactions with reactant molecules, and a higher adsorption capacity can make the photocatalytic degradation process easier and faster. Through the preparation method of the above-mentioned functionalized SiO2 nanospheres, a layer-by-layer (LBL) self-assembly method can be used to synthesize nanosheets of RGO with a hollow structure.

[0015] Furthermore, the preparation method of the SiO2 nanospheres includes the following steps: uniformly mixing 1L of ethanol, 60mL of H2O and 60mL of ammonia solution to form an alkaline condition to obtain a mixed solution; wherein the ammonia solution is 0.91g / cm 3 , 25% ammonia solution; then 30 mL of ethyl silicate was added to the resulting mixed solution and stirred at room temperature for 5 hours; after the reaction was completed, the white suspension was centrifuged at 8000 rpm for 4 minutes, washed with water several times, and dried in a vacuum dryer at 60°C to obtain SiO2 nanospheres.

[0016] Description: The above preparation method can be used to obtain the SiO2 nanospheres required for the present invention. Through the alkaline conditions composed of ethanol, water, and ammonia solution, and with the addition of ethyl silicate, SiO2 nanospheres can be effectively obtained, thereby providing raw materials for the subsequent preparation of functionalized SiO2 nanospheres.

[0017] Furthermore, in step S1, 1 g of functionalized SiO2 nanospheres is used as a base amount, and the functionalized SiO2 nanospheres are added to a portion of 0.5 L of ultrapure water; 0.4 to 0.6 g of graphene oxide is dispersed in another portion of 0.5 L of ultrapure water; 0.2 to 0.3 g of NaBH4 is added; and 0.2 to 0.3 L of 2 M sodium hydroxide is added.

[0018] Description: By controlling the addition amount of the above-mentioned functionalized SiO2 nanospheres, graphene oxide, NaBH4 and other raw materials, h-RGO can be effectively produced, and the raw materials can be fully utilized to avoid excessive consumption of raw materials caused by improper ratio of raw materials, thereby saving manufacturing costs.

[0019] Furthermore, in step S2, 1 g of h-RGO obtained from functionalized SiO2 nanospheres was used as a reference amount, the functionalized SiO2 nanospheres were dissolved in 2 L of water and 1 mL of thioglycolic acid was added; 1 g of AgNO3 and 1.25 g of Na2S·9H2O were added; the gray solution was centrifuged to obtain a product, which was dissolved in 806 mL of water, and then silver sulfide was in situ reduced with 0.806 mL of 0.075 mM sodium borohydride solution.

[0020] Description: By controlling the addition amounts of the above raw materials such as h-RGO, thioglycolic acid, AgNO3, and Na2S·9H2O, a three-phase Ag / Ag2S / h-RGO photocatalyst can be effectively prepared, and the raw materials can be fully utilized to avoid excessive consumption of raw materials caused by improper ratios of raw materials, thereby saving manufacturing costs.

[0021] Furthermore, the vigorous stirring is 400-600 rpm, and the stirring is 200-300 rpm.

[0022] Note: The above-mentioned vigorous stirring and stirring parameters can promote the formation of SiO2@GO and promote the formation of nucleation Ag by the silver ion source introduced by MAA and AgNO3. + / MAA, thereby preparing a three-phase Ag / Ag2S / h-RGO photocatalyst with high catalytic performance.

[0023] Furthermore, in step S1, sodium borohydride is added in the form of gas powder, and the stirring speed is adjusted during the addition. The gas used is nitrogen, and the gas powder concentrations of sodium borohydride and nitrogen are 5 to 15 mg / L.

[0024] Description: By introducing sodium borohydride into the mixed solution by gas powder addition and adjusting the stirring speed and gas powder injection flow rate during the process, the SiO2@GO in the mixed solution can be further reduced to RGO, further strengthening its hollow structure, thereby enhancing the performance of the obtained three-phase Ag / Ag2S / h-RGO photocatalyst.

[0025] Furthermore, the method of adding gas powder includes the following steps:

[0026] 1) Sodium borohydride powder and nitrogen are placed in an injection cylinder. A blower embedded in the piston of the injection cylinder continuously mixes the sodium borohydride powder and nitrogen. When the gas-powder concentration is 5 to 15 mg / L, injection into the mixed solution in step S1 can begin.

[0027] 2) The gas powder is stirred at an initial flow rate of 0.2 L / min, starting from an initial speed of 200-300 rpm and decreasing at a rate of 5-20 rpm / min. When the speed drops to 120 rpm, the gas powder is increased at a rate of 0.03-0.08 L / min. When the gas powder injection volume reaches 100%, use a small amount of ultrapure water to rinse the gas injection cylinder and pour it back into the mixed solution.

[0028] Description: By adopting the above-mentioned dynamic gas powder injection flow rate and stirring speed changes, and regulating according to the correlation between the gas powder injection flow rate and the stirring speed, gas powder injection is used to effectively promote the reduction of SiO2@GO in the mixed solution to RGO, thereby further enhancing the performance of the obtained three-phase Ag / Ag2S / h-RGO photocatalyst.

[0029] Furthermore, the gas powder also contains hydroxymethyl cellulose, and 0.02 to 0.04 g of hydroxymethyl cellulose is added based on 1 g of functionalized SiO2 nanospheres.

[0030] Description: Using the above-mentioned gas-powder composition, by introducing a certain amount of hydroxymethyl cellulose on the basis of sodium borohydride, the reduced RGO in the mixed solution is further strengthened during the gas-powder injection process, thereby enhancing the performance of the three-phase Ag / Ag2S / h-RGO photocatalyst.

[0031] The beneficial effects of the present invention are:

[0032] (1) The three-phase Ag / Ag2S / h-RGO photocatalyst prepared by the present invention has a higher photocatalytic degradation rate for naphthalene than single Ag2S and composite Ag / Ag2S photocatalysts, and the naphthalene degradation efficiency can reach 98.65% within 120 minutes.

[0033] (2) The present invention adopts the layer-by-layer (LBL) self-assembly method to synthesize nanosheets RGO with a hollow structure, and innovatively uses a simple in situ growth method at room temperature to prepare a three-phase composite photocatalyst of plasma nanoparticles Ag / nanorods Ag2S / hollow nanospheres RGO. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of the synthesis of h-RGO and Ag / Ag2S / h-RGO.

[0035] Figure 2 is the XRD spectrum of the sample.

[0036] Figure 3 (a) SEM spectrum of Ag2S; (b) Ag / Ag2S; (c) GO wrapped SiO2; (d) hollow structure GO; (e) TEM spectrum of Ag / Ag2S / h-RGO; (f) HRTEM spectrum of Ag / Ag2S / h-RGO.

[0037] Figure 4 This is the EDS-mapping spectrum of Ag / Ag2S / h-RGO.

[0038] Figure 5 (a) XPS overall spectrum; (b)-(d): XPS peak distribution diagrams of each element.

[0039] Figure 6 (a) DRS spectrum of the sample; (b) PL spectrum; (c) fluorescence lifetime spectrum; (d) photocurrent spectrum.

[0040] Figure 7 (a) Degradation activity curve of the sample for the target pollutant naphthalene; (b) Reaction kinetics curve.

[0041] Figure 8 (a) Repeated experiment of the sample; (b) TEM spectrum and (c) XRD spectrum of the sample after reaction.

[0042] Figure 9 (a) Free radical quenching experiment; (b) EPR spectrum of hydroxyl radicals in the sample captured by DMPO; (c) EPR spectrum of superoxide radicals in the sample captured by DMPO.

[0043] Figure 10 This is the mechanism diagram of the sample's photocatalytic degradation of naphthalene. DETAILED DESCRIPTION

[0044] The present invention will be further described in detail below in conjunction with specific implementation methods to better demonstrate the advantages of the present invention.

[0045] In certain embodiments, a method for preparing a three-phase Ag / Ag2S / h-RGO photocatalyst comprises the following steps: adding 1 g of functionalized SiO2 nanospheres to 0.5 L of ultrapure water, dissolving them by ultrasonic vibration for 0.5 h to obtain a mixed solution; dispersing 0.4 to 0.6 g of graphene oxide in 0.5 L of ultrapure water, for example, 0.4, 0.5, 0.6 g, etc., ultrasonically treating for 30 min, and then placing it in the mixed solution, vigorously stirring at 400 to 600 rpm for 5 h, for example, 400 rpm, 500 rpm, 600 rpm, etc., to generate SiO2@GO; then adding 0.2 to 0.3 g of NaBH4 and stirring at 200 to 300 rpm. m stirred for 1h, for example: 0.2g, 0.25g, 0.3g, etc., 200rpm, 250rpm, 300rpm, etc., then added 0.2~0.3L, 2M sodium hydroxide, for example: 0.2L, 0.25L, 0.3L, etc., stirred the mixture at 200~300rpm for 24h, for example: 200rpm, 250rpm, 300rpm, etc., and washed the resulting product with ultrapure water several times to obtain h-RGO; the prepared h-RGO was dissolved in 2L of water, 1mL of thioglycolic acid was added, and vigorously stirred at 400~600rpm for 2h; for example: 400rpm, 500rpm, 600rpm, etc., and then 1g AgNO₃ was added and stirred at 200-300 rpm for 2 h, e.g., 200 rpm, 250 rpm, 300 rpm, etc., to obtain a homogeneous mixture. Subsequently, 1.25 g of Na₂S·9H₂O was added and stirred at 200-300 rpm for 1 h, e.g., 200 rpm, 250 rpm, 300 rpm, etc., to obtain a gray solution. The gray solution was centrifuged to obtain a product, which was dissolved in 806 mL of water. The silver sulfide was then reduced in situ with 806 mL of 0.075 mM sodium borohydride solution. Finally, the prepared product was washed several times with ultrapure water and ethanol, and then dried at 60°C to obtain a three-phase Ag / Ag₂S / h-RGO photocatalyst. This method synthesized hollow nanosheets of RGO using a layer-by-layer (LBL) self-assembly method and innovatively prepared a three-phase composite photocatalyst of plasmonic nanoparticles Ag / nanorods Ag₂S / hollow nanospheres of RGO using a simple in situ growth method at room temperature.

[0046] In certain embodiments, the preparation method of the functionalized SiO2 nanospheres is as follows: 1g of SiO2 nanospheres is added to 0.12L, 0.5M sodium chloride solution and further dispersed by ultrasonic vibration for 1h; then, 1.5g of PDDA is added and stirred at 200-300rpm for 1h, for example: 200rpm, 250rpm, 300rpm, etc.; then the product is washed and centrifuged several times to remove excess PDDA; similarly, 0.3g of PSS and 1.5g of PDDA are subsequently treated with the sodium chloride solution in the same manner as above to complete the LBL assembly and obtain functionalized SiO2 nanospheres. Through the preparation method of the functionalized SiO2 nanospheres described above, a layer-by-layer (LBL) self-assembly method can be used to synthesize nanosheets of RGO with a hollow structure.

[0047] In certain embodiments, the method for preparing SiO2 nanospheres comprises the following steps: uniformly mixing 1L of ethanol, 60mL of H2O and 60mL of ammonia solution to form an alkaline condition to obtain a mixed solution; wherein the ammonia solution is 0.91g / cm 3 , 25% ammonia solution; then 30mL of ethyl silicate was added to the resulting mixed solution and stirred at room temperature at 200-300rpm for 5 hours, for example: 200rpm, 250rpm, 300rpm, etc.; after the reaction, the white suspension was centrifuged at 8000rpm for 4 minutes, washed multiple times with water, and dried in a vacuum dryer at 60°C to obtain SiO2 nanospheres. Under the alkaline conditions composed of ethanol, water, and ammonia solution, with the addition of ethyl silicate, SiO2 nanospheres were effectively obtained, providing raw materials for the subsequent preparation of functionalized SiO2 nanospheres.

[0048] In certain embodiments, sodium borohydride is added in the form of gas powder, and the stirring speed is adjusted during the addition. The gas used is nitrogen, and the gas powder concentrations of sodium borohydride and nitrogen are between 5 and 15 mg / L. The process comprises the following steps: placing sodium borohydride powder and nitrogen in an injection cylinder, continuously mixing the sodium borohydride powder and nitrogen with a blower embedded in the piston of the injection cylinder, and injecting the mixed solution in step S1 after measuring that the gas powder concentration is between 5 and 15 mg / L; stirring the gas powder at an initial flow rate of 0.2 L / min, starting from an initial speed of 200 to 300 rpm and decreasing at a rate of 5 to 20 rpm / min, and when the speed drops to 120 rpm, increasing the gas powder at a rate of 0.03 to 0.08 L / min, and when the gas powder injection reaches 100%, flushing the injection cylinder with a small amount of ultrapure water and pouring it back into the mixed solution. By introducing sodium borohydride into the mixed solution by gas powder addition and adjusting the stirring speed and gas powder injection flow rate during the process, the SiO2@GO in the mixed solution can be further reduced to RGO, further strengthening its hollow structure.

[0049] In certain embodiments, the gas powder further contains hydroxymethyl cellulose, with 0.02-0.04 g of hydroxymethyl cellulose added to 1 g of functionalized SiO2 nanospheres. By introducing a certain amount of hydroxymethyl cellulose into the sodium borohydride solution, the reduced RGO in the mixed solution is further enhanced during the gas powder injection process.

[0050] Example 1

[0051] A method for preparing a three-phase Ag / Ag2S / h-RGO photocatalyst comprises the following steps:

[0052] S1. Preparation of h-RGO

[0053] 200 mL of ethanol, 12 mL of H2O and 12 mL of ammonia solution were uniformly mixed to form alkaline conditions to obtain a mixed solution; wherein the ammonia solution was 0.91 g / cm 3 , 25% ammonia solution; then 6 mL of ethyl silicate was added to the resulting mixed solution, and stirred at room temperature and 300 rpm for 5 hours; after the reaction, the white suspension was centrifuged at 8000 rpm for 4 minutes, washed with water three times, and dried in a vacuum dryer at 60°C to obtain SiO2 nanospheres;

[0054] 1 g of SiO2 nanospheres was added to a 0.12 L, 0.5 M sodium chloride solution and further dispersed by ultrasonic vibration for 1 h; then, 1.5 g of PDDA was added and stirred for 1 h; the product was then washed and centrifuged several times to obtain a primary product; the primary product was further added to a 0.12 L, 0.5 M sodium chloride solution and further dispersed by ultrasonic vibration for 1 h, followed by the addition of 0.3 g of PSS and stirring for 1 h; the product was then washed and centrifuged several times to obtain a secondary product; the secondary product was further added to a 0.12 L, 0.5 M sodium chloride solution and further dispersed by ultrasonic vibration for 1 h, followed by the addition of 1.5 g of PDDA and stirring for 1 h; the product was then washed and centrifuged several times to obtain functionalized SiO2 nanospheres that had completed LBL assembly;

[0055] 0.1 g of functionalized SiO2 nanospheres was added to 50 mL of ultrapure water and dissolved by ultrasonic vibration for 0.5 h to obtain a mixed solution; 0.05 g of graphene oxide was dispersed in another 50 mL of ultrapure water, ultrasonically treated for 30 min, and then placed in the mixed solution and vigorously stirred at 600 rpm for 5 h to generate SiO2@GO; 25 mg of NaBH4 was then added and stirred at 300 rpm for 1 h to reduce the graphene oxide to RGO; 25 mL of 2 M sodium hydroxide was then added and the mixture was stirred at 300 rpm for 24 h to remove the SiO2 template. The resulting product (hollow structure RGO) was then washed three times with ultrapure water to remove excess sodium hydroxide to obtain h-RGO;

[0056] Preparation of S2, three-phase Ag / Ag2S / h-RGO photocatalyst

[0057] The prepared h-RGO was dissolved in 200 mL of water, 100 μL of thioglycolic acid was added, and the mixture was vigorously stirred at 600 rpm for 2 h; then 0.1 g of AgNO3 was added and stirred at 300 rpm for 2 h to obtain a homogeneous mixture, followed by the addition of 0.125 g of Na2S·9H2O and stirring at 300 rpm for 1 h to obtain a gray solution; the gray solution was centrifuged to obtain the product, which was dissolved in 80.6 mL of water, and then silver sulfide was in situ reduced with 80.6 mL of 0.075 mM sodium borohydride solution; finally, the prepared product was washed with ultrapure water and ethanol three times each, and then dried at 60°C to obtain a three-phase Ag / Ag2S / h-RGO photocatalyst.

[0058] The three-phase Ag / Ag2S / h-RGO photocatalyst prepared by the method of Example 1 was used to photodegrade difficult-to-degrade naphthalene and 1-naphthol to evaluate its photocatalytic performance.

[0059] Sodium sulfide (Na2S·9H2O), ethanol (CH3ch2OH) and ammonia solution (NH3·H2O) were purchased from Nanjing Chemical Reagent Co., Ltd. (Nanjing, China). Ethyl silicate (TEOS, TEOS, C8H 20 O4Si), silver nitrate (AgNO3), sodium hydroxide (NaOH), and sodium borohydride (NaBH4) were provided by Sinopharm Chemical Co., Ltd. (Shanghai, China). Poly(diallyldimethylammonium chloride) solution (PDDA, (C8H 16 ClN) n , MW = 100,000-200,000) was provided by Shanghai Macklin Biochemical Co., Ltd. Poly (styrene sulfonic acid) sodium salt (PSS, [-CH2CH(C6H4)SO3Na-] n,MW=70,000Da) was provided by AlfaAesar Co., Ltd. (Shanghai, China). Graphene oxide (GO) was purchased from Nanjing Pioneer Materials Technology Co., Ltd. (Nanjing, China). Thioglycolic acid (C2H4O2S) was provided by TCI Co., Ltd. (Shanghai, China). In addition, naphthalene (C 10 H8) and 1-naphthol (C 10 HO) was provided by Chengdu Kelong Chemical Co., Ltd. All reagents were of analytical grade and were not further purified. Ultrapure water was used throughout the experiments.

[0060] The synthesis process of h-RGO and Ag / Ag2S / h-RGO is as follows Figure 1 As shown. Single-phase nanorod-like Ag2S, non-phase nanoparticles Ag / nanorod-like Ag2S and multi-phase nanoparticles Ag / nanorod Ag2S / 3d hollow nanospheres RGO can be prepared by a simple in situ growth method at room temperature. First, the three-dimensional hollow nanospheres GO were successfully synthesized by the LBL assembly method using sacrificial template SiO2, and finally removed by sodium hydroxide etching. In particular, after the addition of NaBH4, the color of the solution changed from dark yellow to gray, indicating that graphene oxide was reduced to h-RGO ( Figure 1 a) To produce a stable suspension in water, the three-dimensional hollow nanospheres h-RGO were dissolved in water by ultrasonic vibration for a sufficient time, and then MAA was added under vigorous stirring for a reaction time of 2 h. Then AgNO3 was added as a silver ion source to form nuclei Ag. + / MAA. MAA plays a key role in the entire reaction. It not only acts as a capping agent but also controls the preferential growth of Ag2S nanorods. In addition, there are more oxygen-containing functional groups on the surface of Ag2S precursor, which can be used for Ag + Then, Na2S was dissolved in the prepared solution as a sulfur ion source, and Ag + The precursor is converted into nanorod-shaped Ag2S. In addition, an aqueous solution of NaBH4 is introduced to convert Ag + Reduced to Ag nanoparticles anchored on the surface of Ag2S. Finally, a three-phase Ag / Ag2S / h-RGO photocatalytic material was obtained by a simple in situ growth method at room temperature;

[0061] At the same time, the same preparation method was used to synthesize 0.075-Ag / Ag2S / RGO, and the hollow structure h-RGO prepared was replaced by two-dimensional nanosheet RGO; among them, the preparation of two-dimensional nanosheet RGO: 0.05g graphene oxide was dispersed in 50mL ultrapure water, ultrasonically treated for 30min, vigorously stirred for 5h, and then 25mg NaBH4 was added and stirred for 1h to reduce the graphene oxide to RGO.

[0062] 1) Analytical methods

[0063] The concentration of the target compound was accurately determined using an Agilent 1200 high-performance liquid chromatography (HPLC) with a DAD detector and a C18 reversed-phase column (5 μm, 4.6 × 150 mm). The activity of the photocatalyst can be directly reflected in the degradation efficiency of the target compound. The photocatalytic degradation efficiency is calculated as follows:

[0064]

[0065] Where η represents the photocatalytic efficiency; C0 and C t Represent the concentrations of the pollutant solution before and after the reaction, respectively.

[0066] For naphthalene, methanol-water (4:1, v / v) was used as the mobile phase at 1 ml / min, the detection wavelength was 254 nm, and the injection volume of each sample was 20 μL.

[0067] 2) Evaluation of photocatalytic activity

[0068] The photocatalytic activity of the prepared samples was systematically evaluated for the degradation of naphthalene and 1-naphthol under visible light irradiation. The simulated illumination system (XPA-7, Nanjing, China) consisted of a 1000 W xenon lamp, a 420 nm cutoff filter, a 50 mL quartz reaction tube, and a cooling water circulation system (to prevent thermal catalytic effects). During the experiment, 25 mg of each catalyst was dispersed into 50 mL of the target pollutant solution. The initial concentrations of naphthalene and 1-naphthol were both 10 mg / L. Acetonitrile was used as the solubilizer (acetonitrile:water volume ratio of 1:1000). Before illumination, the suspension was magnetically stirred in the dark for 1 hour to ensure adsorption-desorption equilibrium of the pollutants on the photocatalyst surface. Under visible light irradiation, approximately 3 mL of the suspension was sampled from the reaction tube at specified time intervals, centrifuged, and filtered through a 0.22 μm microporous filter to remove suspended particles. To verify the stability and reproducibility of the photocatalytic reaction, the photocatalyst was collected and the experiment was repeated multiple times under the same conditions.

[0069] 3) Characterization methods

[0070] The crystallinity of the samples was determined by X-ray diffraction at room temperature using an XRD-6000 X-ray powder diffractometer (Shimadzu) at 40 kV and 30 mA. Field emission scanning electron microscopy (FESEM) images were acquired on a FEI-quanta 250 scanning electron microscope at an accelerating voltage of 10 kV. Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) were performed on a JEM-200CX instrument. The surface chemical composition and chemical state of the photocatalysts were analyzed using X-ray photoelectron spectroscopy (XPS) on a PHI5000 Versa Probe electron spectrometer (ULVAC-PHI, Japan). The specific surface area and pore size were analyzed using the Brunauer-Emmett-Teller (BET) method and the Barrett-Joyner-Halenda (BJH) method (ASAP 2020, Micromeritics, USA) under a nitrogen adsorption-desorption isotherm at 77 K. UV-visible absorption spectroscopy was performed on a Lambda 750 (PerkinElmer) spectrophotometer in the wavelength range of 200–800 nm. Fluorescence emission spectra were recorded from 200 to 800 nm using a fluorescence spectrophotometer and a time-resolved fluorescence spectrophotometer with an excitation wavelength of 365 nm. Photoelectrochemical characterization was performed on an electrochemical workstation (CHI760E, Shanghai, China) using a standard three-electrode system. The prepared samples were uniformly coated on an ITO electrode as the working electrode. A Pt electrode and an Ag / AgCl electrode were used as the counter electrode and reference electrode, respectively. The electrolyte was 0.2 M NaSO. A 1000 W xenon lamp provided the light source.

[0071] 4) Morphology and microstructure

[0072] XRD can provide detailed information about the crystal structure and phase purity. Figure 2As shown. The diffraction peaks of Ag2S at 22.43°, 24.91°, 26.32°, 28.96°, 33.61°, 36.81°, 43.40°, 44.20° and 50.73° correspond to the characteristic peaks of the standard card (JCPDS No.14-0072) (-101), (110), (012), (111), (120), (121), (200), (103) and (-221) of orthorhombic Ag2S, respectively. For the Ag / Ag2S sample, in addition to the diffraction peak of Ag2S, a diffraction peak corresponding to face-centered cubic Ag(200) appears at 44.28°. As the concentration of NaBH4 increases during the preparation process, the intensity of the Ag diffraction peak becomes stronger. However, it may also be due to the overlap of the (103) plane of Ag2S (JCPDS No.04-0783, 2θ=44.20), resulting in the peak being not sharp and not obvious. Regarding the composite material 0.075-Ag / Ag2S / h-RGO, after adding RGO to the composite material 0.075-Ag / Ag2S, the diffraction peak did not change significantly, except that the intensity of all peaks became weaker. Due to the low percentage and high dispersion of the RGO component, the corresponding peak cannot be observed in this spectrum. In order to verify that GO was successfully reduced to RGO, the results of XPS analysis are shown below. Compared with the diffraction peak of a single Ag2S photocatalyst, the diffraction peak of the composite sample is slightly broadened. In addition, no obvious diffraction peaks of other phases were detected in the composite material, which shows that the introduction of Ag and RGO substances does not affect the crystal structure of the Ag2S photocatalyst.

[0073] FESEM, TEM and HRTEM images of Ag2S, Ag / Ag2S and 0.075-Ag / Ag2S / h-RGO are shown in Figure 4. Figure 3 As shown. SEM of nanorod-shaped Ag2S catalyst is shown Figure 3 As shown in (a), it is formed by irregular stacking of nanorods. Figure 3 In (a), it can be observed that the surface of the single nanorod-shaped Ag2S sample is smooth and the width is about 80-110nm. After Ag deposition, the microstructure of Ag2S remains almost unchanged (Fig. 3(b)). Figure 3 (d) is the morphology of hollow nanosphere GO after removing the template SiO2. Figure 3 (c) Compared with the above, it is confirmed that the SiO2 template has been successfully removed, and the nanosheet GO with hollow nanosphere structure is obtained. The nanospheres of uniform size are arranged in an orderly manner in the nanosheet structure. The microstructure of the ternary plasma photocatalytic material Ag / Ag2S / h-RGO is shown in Figure 2. Figure 3(e) It is obvious that the bulk structure of the material does not change after the synthesis of the three-phase material. However, when RGO is composited with Ag / Ag2S, the width of the nanorods Ag / Ag2S is reduced to about 50-60nm. This may be due to the presence of h-RGO as a dispersant or stabilizer, which hinders the growth of nanoparticles. In order to obtain the crystal structure of the sample, we further performed HRTEM characterization ( Figure 3 (f) In the prepared composite material Ag / Ag2S / h-RGO, a close interface exists between Ag and Ag2S, and between Ag2S and RGO, successfully forming a heterojunction. In addition, HRTEM images show that the lattice fringes of Ag2S and surface-loaded Ag are approximately 0.244nm and 0.282nm, respectively, corresponding to the (121) plane of the nanorod Ag2S and the (200) plane of Ag. The HRTEM analysis results are consistent with the XRD analysis results.

[0074] To further confirm the elemental composition of Ag / Ag2S / h-RGO, the EDS-mapping results are as follows Figure 4 The three-phase material is mainly composed of Ag, C and O elements, among which C and O elements are evenly distributed, which proves that RGO is well distributed in the nanocomposite material, which is conducive to the carrier transfer between Ag2S, Ag and RGO.

[0075] 5) Surface structure and properties

[0076] X-ray photoelectron spectroscopy (XPS) is an effective tool for elucidating the surface chemical state and composition of heterostructures. XPS data further confirmed the reduction of GO to RGO and the successful preparation of Ag / Ag2S / h-RGO. Figure 5 (a) is the total XPS spectrum of single RGO, single Ag2S, composite 0.075-Ag / Ag2S and Ag / Ag2S / h-RGO. For the single Ag2S sample, composite 0.075-Ag / Ag2S and 0.075-Ag / Ag2S / h-RGO, all three samples showed characteristic peaks of Ag 3d and S 2p, which were attributed to the deposition of Ag2S and Ag nanoparticles on the surface of the composite material. In addition, compared with single Ag2S and 0.075-Ag / Ag2S, a new XPS peak C1s was found in the 0.075-Ag / Ag2S / h-RGO sample, indicating that RGO was formed in the 0.075-Ag / Ag2S / h-RGO three-phase plasma photocatalyst. In order to further observe the chemical information of various elements in the samples, we Figure 5 Their corresponding high-resolution XPS spectra are analyzed in (bd). Figure 5In (b), 0.075-Ag / Ag2S / h-RGO has two characteristic peaks, S 2p3 / 2 and S2 p1 / 2, with binding energies of 161.3 eV and 162.4 eV, respectively. These peaks are obviously shifted to higher binding energies than those of single Ag2S. On the contrary, the binding energy of the peaks of 0.075-Ag / Ag2S is slightly lower than that of single Ag2S. Figure 5 (c) shows the high-resolution XPS spectra of Ag 3d of samples Ag2S, 0.075-Ag / Ag2S and 0.075-Ag / Ag2S / h-RGO. There are two independent peaks at 366.8 eV and 372.7 eV of Ag2S, corresponding to Ag 3d, respectively. + The characteristic peaks of Ag 3d5 / 2 and Ag 3d3 / 2 can be seen from the XPS spectra of 0.075-Ag / Ag2S and 0.075-Ag / Ag2S / h-RGO. These two peaks can be divided into four peaks, indicating the existence of different Ag valence states. Compared with 0.075-Ag / Ag2S, these two strong peaks correspond to Ag 3d5 / 2 and Ag 3d3 / 2. + 3d5 / 2 and 3d 3 / 2, whose binding energies are 367.3eV and 373.2eV respectively, and the other two relatively weak peaks are closely related to metallic Ag. 0 It matches 3d5 / 2 and 3d3 / 2 very well, with binding energies of 368.1eV and 374.2eV. In the XPS spectrum of 0.075-Ag / Ag2S / h-RGO, the Ag 3d binding energy also shifts toward the high binding energy direction to higher binding energy. The shift of the Ag 3d peak indicates that when hybridized with RGO hollow nanospheres, electrons are transferred from Ag to Ag2S and Ag / Ag2S can indeed act as electron donors after being composited with RGO hollow nanospheres. These results confirm the presence of metallic Ag in the three-phase plasma photocatalyst Ag / Ag2S / h-RGO, and confirm the formation of a heterojunction interface between RGO and Ag / Ag2S. High-resolution C1s spectra such as Figure 5 As shown in (d), the C1s spectra of nanosheet RGO and hollow structure RGO clearly display four characteristic peaks. It is clear that the peak intensities of oxygen-containing species such as CO, C=O, and O=C-OH in the RGO hollow nanospheres are significantly reduced after graphene oxide treatment. The peak area ratios of carbon-oxygen species to total area for graphene oxide and RGO were calculated and are detailed in Table 1. In terms of the carbon-oxygen species to total carbon species ratio, the content of oxygen-containing groups in the RGO hollow nanospheres and 0.075-Ag / Ag2S / h-RGO is much lower than that in graphene oxide, providing concrete evidence for the reduction of graphene oxide during the preparation of Ag / Ag2S / h-RGO. Furthermore, compared with graphene oxide, the peaks of the composite 0.075-Ag / Ag2S / h-RGO slightly shift to lower binding energies, indicating the construction of a heterogeneous interface between Ag / Ag2S and RGO.

[0077] Table 1 XPS C1s peak area analysis

[0078]

[0079]

[0080] The specific surface area of ​​a photocatalyst, which depends on the porosity and geometry of the material, plays a significant role in its photocatalytic activity. It is well known that photocatalytic reactions in nanocomposites are generally surface-controlled processes. The larger surface area of ​​the nanocomposite provides more active sites for reactions with reactant molecules. Furthermore, the higher adsorption capacity can facilitate and accelerate the photocatalytic degradation process. The information provided in Table 2 shows that the surface area of ​​RGO hollow nanospheres is greater than that of RGO nanosheets. This means that the larger specific surface area of ​​RGO hollow nanospheres provides more active sites for pollutant degradation, enhancing the photoreactivity of the composite. Table 2 compares the pore sizes of the samples. The majority of pores in the samples are primarily distributed in the 1nm-8nm size range. The 0.075-Ag / Ag2S / h-RGO composite exhibits a wider pore size distribution, which is attributed to the presence of aggregated pores, hollow structures, and uneven surface structures of the nanocrystals between the Ag / Ag2S nanorods and the RGO hollow nanospheres. The BET specific surface areas of single Ag2S, RGO hollow nanospheres, 0.075-Ag / Ag2S and Ag / Ag2S / h-RGO pores (Table 2) were calculated to be 26.727, 68.590, 31.711 and 88.849 m 2 Compared with other samples, the specific surface area and pore volume of the Ag / Ag2S / h-RGO composite material are significantly increased, which is beneficial to the adsorption of reactants and the diffusion of reaction products, thereby improving the photocatalytic performance.

[0081] Table 2 Specific surface area, pore diameter and pore volume of samples

[0082] sample Specific surface area (m2 / g) Pore ​​diameter (nm) Pore ​​volume (cm3 / g) n-RGO 42.275 3.950 0.090 h-RGO 68.590 3.981 0.127 <![CDATA[Ag2S]]> 26.727 1.362 0.074 <![CDATA[0.075-Ag / Ag2S]]> 31.711 1.539 0.083 <![CDATA[Ag / Ag2S / h-RGO]]> 88.849 4.009 0.127

[0083] 6) Optical and electrochemical properties

[0084] The photocatalytic performance of semiconductors is significantly correlated with their optical properties. To verify the changes in optical properties caused by the doping of nanoparticles of Ag and hollow nanospheres of RGO, samples Ag2S, Ag / Ag2S, Ag / Ag2S / RGO, and Ag / Ag2S / h-RGO were studied using UV-visible diffuse reflectance spectroscopy, fluorescence emission, and photocurrent measurements. Figure 6(a) shows the UV-visible absorption spectrum of the sample in the range of 200-700nm, which clearly shows the absorption of Ag2S and Ag / Ag2S from the ultraviolet to the visible light region. In addition, the UV-visible spectrum of the Ag / Ag2S composite material clearly shows a red shift between 200 and 700nm. This may be due to the plasma resonance caused by the in-situ deposition of Ag nanoparticles on the surface of Ag2S nanorods. Obviously, Ag nanoparticles significantly improve the absorption capacity of light, which may increase the formation rate of electron-hole pairs at the interface of Ag and Ag2S, thereby improving the photocatalytic performance. Figure 6 In (b), the single RGO sample shows strong absorption in both the UV and visible light regions. RGO of different shapes has a certain effect on the absorption intensity. Hollow nanosphere RGO has higher light absorption capacity than nanosheet-shaped RGO. The enhancement of visible light absorption is mainly due to the hollow structure, which can indeed induce multiple light reflections, which is beneficial to improving light utilization efficiency. Compared with single Ag2S, 0.075-Ag / Ag2S and Ag / Ag2S / RGO, the absorption intensity of Ag / Ag2S / h-RGO is significantly increased, showing strong and broad absorption in the entire visible region. This shows that RGO added to Ag / Ag2S, especially in the shape of hollow nanospheres, has a positive effect on the light absorption of the sample.

[0085] During the photocatalytic reaction, the recombination of electrons and holes greatly affects the photocatalytic performance of the photocatalyst. Therefore, fluorescence spectroscopy and photocurrent measurement were used to study the charge separation and transfer characteristics of the samples.

[0086] Photoluminescence (PL) emission spectroscopy reveals the migration, separation, and recombination of photogenerated electrons and holes. Photocatalysts with lower PL intensities have slower recombination rates. Since photocatalysts generate electrons and holes upon photoactivation, some of these electrons and holes recombine, releasing energy in the form of fluorescence emission. Figure 6 (b) shows the PL spectra of different samples excited at 365 nm. Compared with single Ag2S, the PL intensity of the composite photocatalyst is significantly reduced. In addition, the addition of RGO hollow nanospheres to the Ag / Ag2S sample significantly reduces the PL intensity of the Ag / Ag2S. This indicates that the hollow nanospheres RGO in the composite Ag / Ag2S / h-RGO can better utilize visible light and a larger specific surface area to transfer electrons, thereby effectively achieving the separation of electron-hole pairs.

[0087] In order to further understand the lifetime of photogenerated electron-hole pairs in photocatalysts, the lifetime decay of photogenerated electron-hole pairs of single Ag2S, 0.075-Ag / Ag2S, Ag / Ag2S / RGO and Ag / Ag2S / h-RGO was analyzed by curve fitting.avg ) is determined by the following equation:

[0088] f(t)=B+A1×exp(-t / τ1)+A2×exp(-t / τ2)

[0089] Where A1, A2 are amplitudes, τ1, τ2 are radiation lifetimes. The kinetic parameters are summarized in Table 3. Figure 6 As shown in (c), the Ag2S sample with Ag nanoparticles deposited on the surface has a longer carrier lifetime than the single Ag2S sample. In addition, the decay time of the composite Ag / Ag2S / h-RGO is relatively longer compared with the single Ag2S sample, the dual-phase composite 0.075-Ag / Ag2S, and the three-phase Ag / Ag2S / RGO curves. The improvement in the carrier life expectancy indicates that the electron transfer process exists on the surface of the Ag2S nanorods. In addition, the hollow nanospheres of RGO in the sample have a higher ability to improve carrier mobility than the nanosheets of RGO, and the transfer of photoexcited electrons and holes between Ag / Ag2S and RGO can better achieve carrier separation, thereby improving the photocatalytic performance.

[0090] Transient photocurrent analysis provides additional evidence supporting the efficiency of photoinduced electron-hole separation. Generally speaking, photocurrent is related to the lifetime of photogenerated carriers, which are generated by electrons transferring from the valence band to the conduction band of the sample. Higher photocurrent intensities indicate longer lifetimes of photocatalyst electron-hole pairs. Figure 6 (d) is the it curve of the sample. Under visible light, the photocurrent intensity of single Ag2S is very low, and there is almost no obvious photocurrent response. In contrast, the photocurrent intensity of the 0.075-Ag / Ag2S sample is higher than that of single Ag2S. In addition, the maximum photocurrent intensity of Ag / Ag2S / h-RGO is 4 times that of the 0.075-Ag / Ag2S composite material, and is also much higher than the photocurrent intensity of 0.075-Ag / Ag2S / RGO. This is attributed to the faster electron transfer between Ag, Ag2S and hollow nanospheres RGO and the strong separation ability of photogenerated carriers after the addition of hollow nanospheres RGO.

[0091] 7) Photocatalytic performance evaluation

[0092] In order to characterize the photocatalytic performance of the prepared samples, the photocatalytic degradation effects of Ag2S, 0.075-Ag / Ag2S, Ag / Ag2S / RGO and Ag / Ag2S / h-RGO samples on naphthalene in aqueous solution were determined ( Figure 7). In the blank experiment, in the absence of a catalyst, there was no obvious photodegradation of naphthalene, indicating that the natural photolysis of naphthalene can be ignored. At the same time, before illumination, a dark reaction was carried out for 60 minutes, and an adsorption-desorption equilibrium was reached between the photocatalyst and the pollutants. Compared with single Ag2S and 0.075-Ag / Ag2S, Ag / Ag2S / h-RGO had a better degradation effect on naphthalene. The removal efficiency of naphthalene by 0.075-Ag / Ag2S / h-RGO was 98.65% ( Figure 7 (a)). It is worth noting that the photocatalytic performance of the composite of nanosheet RGO and Ag / Ag2S is lower than that of 0.075-Ag / Ag2S / h-RGO. In addition, the degradation reaction conforms to the pseudo-first-order kinetic curve, and the reaction kinetic constant k value of the three-phase 0.075-Ag / Ag2S / h-RGO is significantly higher than that of the single sample. The above results show that the introduction of Ag plays a key role in the photodegradation process. The appropriate amount of Ag deposited on the surface of Ag2S will help to improve the photocatalytic performance. In addition, the hollow nanosphere RGO, as an electron acceptor, has better charge transfer ability in the sample than the nanosheet RGO, which effectively improves the separation and transfer efficiency of the carriers, thereby improving the photocatalytic performance.

[0093] The stability and reusability of the 0.075-Ag / Ag2S / h-RGO three-phase photocatalyst for naphthalene photodegradation were studied through repeated experiments. Obviously, after 4 cycles, the photocatalytic efficiency of the 0.075-Ag / Ag2S / h-RGO plasma photocatalyst decreased slightly. Figure 8 As shown. In addition, characterization of the sample after the reaction revealed no significant changes in its morphology and structural composition. Therefore, the 0.075-Ag / Ag2S / h-RGO sample has good photocatalytic stability and recyclability during the photodegradation process.

[0094] 8) Photocatalytic mechanism

[0095] Through characterization and photocatalytic results, it was found that 0.075-Ag / Ag2S / h-RGO photocatalyst can successfully degrade naphthalene under visible light. However, in order to better understand the significant improvement in photocatalytic performance, the underlying degradation mechanism needs to be proposed and discussed.

[0096] 9) Role of active species

[0097] Conducting active species quenching experiments is crucial for capturing active species produced during photodegradation. In the photocatalytic degradation process, the main active species involved in the reaction are ·OH, ·O2 - and h +In the degradation process, one or more active substances may play a role in the photocatalytic oxidation process. In this study, the hydroxyl radical (·OH) inhibitor isopropyl alcohol (IPA), superoxide radical (·O2 - ) inhibitors of nitroxide free radicals piperidinol (TEMPOL) and holes (h + ) inhibitor ammonium oxalate (AO). Figure 9 As shown in (a), the degradation efficiency of naphthalene and 1-naphthol did not change significantly after adding TEMPOL and AO. Similarly, the photodegradation of naphthalene and 1-naphthol was also partially inhibited after adding IPA. The effects of quenchers on photocatalytic activity are arranged in the following order: TEMPOL (·O2 - )>AO(h + )>IPA(·OH). In the quenching experiment, the worse the photocatalytic performance of the photocatalyst is after adding the scavenger, the more significant the role of the corresponding free radicals in the photodegradation process. Therefore, the conclusion is that all O2 - ,h + and OH radicals are involved in the photodegradation process, especially O2 - and h + The effect on the degradation effect is greater. In order to further observe the role of active species intuitively, we conducted EPR experiments on free radicals captured by DMPO on the photocatalyst samples. Under dark conditions and without catalyst, all samples had no characteristic peaks ( Figure 9 (b) and (c)). It can be seen that O2 was detected in both Ag / Ag2S / h-RGO and 0.075-Ag / Ag2S samples. - The characteristic peaks of ·O2 and ·OH are present, and the signal intensities of the two samples are slightly different. The peak intensity of 0.075-Ag / Ag2S / h-RGO is slightly stronger than that of 0.075-Ag / Ag2S. In addition, there is almost no ·O2 in the Ag2S degradation system. - and ·OH, which reflects that the addition of Ag and RGO to single Ag2S is beneficial to improve the photocatalytic activity. As mentioned above, it can be concluded that ·O2 - ,h + and ·OH both play a role in enhancing the photodegradation performance.

[0098] 10) Potential photodegradation mechanisms

[0099] The potential mechanism of photodegradation of Ag / Ag2S / h-RGO is as follows Figure 10As shown. Since the electronic vibration of electrons on the Ag surface produces LSPR, Ag nanoparticles can be excited under visible light, and visible light can also excite nanorods Ag2S to generate holes and electron pairs. At the same time, the strong absorption of LSPR by Ag2S nanoparticles will significantly increase the absorption capacity of the sample in the visible light region, thereby increasing the generation rate of electron-hole pairs. Since the work function of Ag is lower than that of Ag2S, electrons are more likely to transfer from Ag to Ag2S. At the same time, RGO has high conductivity, which promotes interfacial charge transfer along the π-π graphitic carbon network. The electrons in the conduction band of Ag2S are more willing to transfer to the surface of RGO. Obviously, there is a possible pathway for interfacial electron transfer: Ag→Ag2S→RGO. The excess electrons on Ag2S can be taken away by RGO to ensure the stability of the photocatalyst. In addition, the position of the conduction band of Ag2S (E CB ) and valence band position (E vb ) can be calculated using the following two equations:

[0100] E CB =XE e -0.5E g

[0101] E VB =E CB +E g

[0102] X represents the potential of the semiconductor, E e Equal to 4.5eV, E g is the band gap of the photocatalyst. According to the UV-visible data, the energy band of silver sulfide is 1.68eV, the conduction band potential of Ag2S is -0.38eV, and its valence band potential is 1.30eV. Obviously, compared with O2 / ·O2 - Compared with the standard reduction potential of Ag2S (-0.33eV), the conduction band potential of Ag2S is negative enough. The results show that there are a large number of electrons on the conduction band surface of Ag2S that can capture O2 in aqueous solution and reduce it to O2 - Participate in the degradation reaction, and the abundant photogenerated electrons can further react with O2 - The reaction generates ·OH and reacts with pollutants; however, the valence band position of Ag2S is significantly lower than that of ·OH / H2O (2.27 eV) and ·OH / OH - (2.38eV) potential, indicating that most of the h + There is not enough oxidizing power to convert H2O or OH - Oxidized to ·OH. The holes in the valence band can directly react with the target pollutants. ·O2 - ,

[0103] OH and h + Working together, naphthalene will eventually be degraded.

[0104] As mentioned above, the multiphase nanoparticle Ag / nanorodal Ag2S / hollow structure RGO photocatalyst can make the Ag / Ag2S bandgap narrower, better utilize visible light, rapidly form and transfer carriers, and more efficient separation of electron-hole pairs. These factors all improve the visible light degradation efficiency of the three-phase plasmonic photocatalyst.

[0105] In summary, a new type of Ag / Ag2S / h-RGO photocatalyst was successfully synthesized at room temperature for the first time using a simple method. The morphology, structure and photoelectrochemical properties of the prepared photocatalyst were comprehensively characterized by XRD, SEM, TEM, HRTEM, SEM-EDS, XPS, BET, UV-Vis and PL methods. Compared with single Ag2S, composite Ag / Ag2S and Ag / Ag2S / h-RGO photocatalysts, Ag / Ag2S / h-RGO has a higher photocatalytic degradation rate for naphthalene, and the degradation efficiency of naphthalene reaches 98.65% within 120 minutes. This may be due to the LSPR effect of Ag nanoparticles. The hollow nanospheres RGO and nanoparticles Ag inhibit the recombination of photogenerated carriers. ·OH, ·O2 - and h + It is the key active species in the photodegradation system. Free radical capture experiments have determined that ·OH and ·O2 - Free radicals have a greater impact on the photodegradation system. This paper will be a reasonable strategy for developing new visible light driven plasmonic nanocomposites with unique structures, providing a possibility for the future treatment of difficult-to-treat environments.

[0106] Example 2

[0107] This embodiment differs from embodiment 1 in that 0.04 g of graphene oxide is dispersed in 0.5 L of ultrapure water.

[0108] Example 3

[0109] This embodiment differs from embodiment 1 in that 0.06 g of graphene oxide is dispersed in 0.5 L of ultrapure water.

[0110] Example 4

[0111] The difference between this embodiment and embodiment 1 is that 20 mg of NaBH4 is added.

[0112] Example 5

[0113] This embodiment differs from embodiment 1 in that 30 mg of NaBH4 is added.

[0114] Example 6

[0115] This embodiment differs from embodiment 1 in that 20 mL of 2 M sodium hydroxide is added.

[0116] Example 7

[0117] This embodiment differs from embodiment 1 in that 30 mL of 2 M sodium hydroxide is added.

[0118] Example 8

[0119] The difference between this embodiment and embodiment 1 is that the vigorous stirring is 400 rpm and the stirring is 200 rpm.

[0120] Example 9

[0121] The difference between this embodiment and embodiment 1 is that the vigorous stirring is 500 rpm and the stirring is 250 rpm.

[0122] To further verify the effects of the above parameters on the prepared three-phase Ag / Ag2S / h-RGO photocatalyst, the following experiment is briefly described to determine the degradation rate of naphthalene within 120 min of the three-phase Ag / Ag2S / h-RGO photocatalyst prepared in Examples 2-9, as shown in Table 3 below:

[0123] Table 3 Naphthalene degradation rate of three-phase Ag / Ag2S / h-RGO photocatalyst

[0124] Group Example 2 Example 3 Example 4 Example 5 Example 6 Naphthalene degradation rate 97.81％ 98.67％ 97.54％ 98.66％ 97.75％ Group Example 7 Example 8 Example 9 / / Naphthalene degradation rate 98.65％ 97.17％ 98.32％ / /

[0125] By measuring the naphthalene degradation rate of the three-phase Ag / Ag2S / h-RGO photocatalyst prepared in different embodiments within 120 minutes, the preparation parameter range of the three-phase Ag / Ag2S / h-RGO photocatalyst was systematically determined; in comparison with Example 1, Example 2 and 3, the introduction of different addition amounts of graphene oxide had a certain effect on the catalytic activity of the prepared three-phase Ag / Ag2S / h-RGO photocatalyst, which may be related to the generation amount of SiO2@GO, but as the addition amount of graphene oxide continued to increase, the three-phase Ag / Ag2S / h-RGO photocatalyst had no obvious improvement; in comparison with Example 1, Example 4 and 5, the introduction of different addition amounts of NaBH4 (sodium borohydride) had a certain effect on the catalytic activity of the prepared three-phase Ag / Ag2S / h-RGO photocatalyst, but as the addition amount of NaBH4 (sodium borohydride) increased, the catalytic activity of the prepared three-phase Ag / Ag2S / h-RGO photocatalyst increased. As the amount of sodium hydroxide added continues to increase, the use effect of the three-phase Ag / Ag2S / h-RGO photocatalyst is basically not improved; in Example 6 and 7 compared with Example 1, sodium hydroxide has a certain effect on the catalytic activity of the prepared three-phase Ag / Ag2S / h-RGO photocatalyst at different addition amounts, but as the amount of sodium hydroxide added continues to increase, the use effect of the three-phase Ag / Ag2S / h-RGO photocatalyst is not improved; in Example 8 and 9 compared with Example 1, different vigorous stirring and stirring rates have a certain effect on the synthesis of h-RGO and three-phase Ag / Ag2S / h-RGO photocatalysts, and by observing the effect of improving the naphthalene degradation rate in each interval, it can be found that the improvement rate in the interval of Example 8-Example 9 is greater than the improvement rate in the interval of Example 9-Example 1, which can be selected as needed according to actual production costs and other requirements.

[0126] Example 10

[0127] This embodiment differs from embodiment 1 in that, in step S1, sodium borohydride is added in the form of gas powder, and the stirring speed is adjusted during the addition. The gas used is nitrogen, and the gas powder concentrations of sodium borohydride and nitrogen are 10 mg / L. The process specifically includes the following steps:

[0128] 1) Sodium borohydride powder and nitrogen are placed in an injection cylinder. A blower embedded in the piston of the injection cylinder continuously mixes the sodium borohydride powder and nitrogen. When the gas-powder concentration reaches 10 mg / L, injection into the mixed solution in step S1 can begin.

[0129] 2) The gas powder was stirred at an initial flow rate of 0.2 L / min, and the stirring speed was decreased from an initial speed of 300 rpm to a rate of 10 rpm / min. When the speed dropped to 120 rpm, the gas powder was increased at a rate of 0.05 L / min. When the gas powder injection volume reached 100%, a small amount of ultrapure water (10 mL) was used to rinse the gas injection cylinder and poured back into the mixed solution.

[0130] Example 11

[0131] The difference between this embodiment and embodiment 10 is that the gas powder concentrations of sodium borohydride and nitrogen are 5 mg / L.

[0132] Example 12

[0133] The difference between this embodiment and embodiment 10 is that the gas powder concentrations of sodium borohydride and nitrogen are 15 mg / L.

[0134] Example 13

[0135] The difference between this embodiment and embodiment 10 is that the gas powder has an initial flow rate of 0.2 L / min, and the stirring starts from an initial rotation speed of 300 rpm and decreases at a rate of 5 rpm / min. When the rotation speed drops to 120 rpm, the gas powder increases at a rate of 0.03 L / min.

[0136] Example 14

[0137] The difference between this embodiment and embodiment 10 is that the gas powder has an initial flow rate of 0.2 L / min, and the stirring starts from an initial rotation speed of 300 rpm and decreases at a rate of 20 rpm / min. When the rotation speed drops to 120 rpm, the gas powder increases at a rate of 0.08 L / min.

[0138] In order to further verify the influence of the above method and parameters on the prepared three-phase Ag / Ag2S / h-RGO photocatalyst, the following experiment is briefly described to measure the degradation rate of naphthalene of the three-phase Ag / Ag2S / h-RGO photocatalyst prepared in Examples 10-14 within 120 minutes. At the same time, based on Example 10, a group of control examples 1 in which the gas powder was treated at a constant flow rate of 0.2 L / min and stirred at a constant speed of 300 rpm were set, as shown in Table 4 below:

[0139] Table 4 Naphthalene degradation rate of three-phase Ag / Ag2S / h-RGO photocatalyst

[0140] Group Example 10 Example 11 Example 12 Example 13 Example 14 Naphthalene degradation rate 99.53％ 99.31％ 99.45％ 99.11％ 99.28％ Group Comparative Example 1 / / / / Naphthalene degradation rate 98.97％ / / / /

[0141] By measuring the naphthalene degradation rate of the three-phase Ag / Ag2S / h-RGO photocatalyst prepared in different embodiments within 120 minutes, the effects of different process methods and related parameter settings of the three-phase Ag / Ag2S / h-RGO photocatalyst were systematically determined;

[0142] In comparison with Example 1, by adopting the method of adding sodium borohydride + nitrogen gas powder, the performance of the prepared three-phase Ag / Ag2S / h-RGO photocatalyst is further improved; in comparison with Example 10, Examples 11 and 12 have a certain influence on the catalytic activity of the prepared three-phase Ag / Ag2S / h-RGO photocatalyst under different gas powder concentrations, among which the catalytic performance of Example 10 is relatively better; in comparison with Example 10, Examples 13 and 14 have a certain influence on the catalytic activity of the prepared three-phase Ag / Ag2S / h-RGO photocatalyst under different gas powder flow rates and stirring speeds, among which the catalytic performance of Example 10 is relatively better; by comparing Control Example 1 with Example 10, when the stirring speed is not adjusted, the performance of the three-phase Ag / Ag2S / h-RGO photocatalyst decreases to a certain extent;

[0143] Therefore, by further improving the introduction method of sodium borohydride and utilizing nitrogen gas as well as dynamic adjustment of injection flow rate and stirring speed, the performance of the obtained three-phase Ag / Ag2S / h-RGO photocatalyst can be further effectively enhanced.

[0144] Example 15

[0145] The difference between this embodiment and embodiment 10 is that the gas powder further contains hydroxymethyl cellulose, and 3 mg of hydroxymethyl cellulose is added.

[0146] Example 16

[0147] The difference between this embodiment and embodiment 15 is that 2 mg of hydroxymethyl cellulose is added to the gas powder.

[0148] Example 17

[0149] This embodiment differs from embodiment 15 in that 4 mg of hydroxymethyl cellulose is added to the gas powder.

[0150] To further verify the effects of the above parameters on the prepared three-phase Ag / Ag2S / h-RGO photocatalyst, the following experiment is briefly described to measure the degradation rate of naphthalene within 120 min of the three-phase Ag / Ag2S / h-RGO photocatalyst prepared in Examples 15-17, as shown in Table 5 below:

[0151] Table 5 Naphthalene degradation rate of three-phase Ag / Ag2S / h-RGO photocatalyst

[0152] Group Example 15 Example 16 Example 17 Naphthalene degradation rate 99.81％ 99.67％ 99.61％

[0153] By measuring the naphthalene degradation rate of the three-phase Ag / Ag2S / h-RGO photocatalyst prepared in different embodiments within 120 minutes, the effects of different gas powders and related parameter settings of the three-phase Ag / Ag2S / h-RGO photocatalyst were systematically determined;

[0154] In comparison with Example 10, the performance of the prepared three-phase Ag / Ag2S / h-RGO photocatalyst was further improved by adding sodium borohydride + hydroxymethyl cellulose + nitrogen gas powder. In comparison with Example 15, different hydroxymethyl cellulose contents had a certain influence on the catalytic activity of the prepared three-phase Ag / Ag2S / h-RGO photocatalyst, among which the catalytic performance of Example 10 was relatively better.

[0155] Therefore, by further improving the composition of the gas powder and adding sodium borohydride + hydroxymethyl cellulose + nitrogen into the mixed solution, the performance of the obtained three-phase Ag / Ag2S / h-RGO photocatalyst can be further effectively enhanced.

Claims

1. A method for preparing a three-phase Ag / Ag2S / h-RGO photocatalyst, characterized in that: The following steps are involved: S1. Preparation of h-RGO Functionalized SiO2 nanospheres were added to one portion of ultrapure water and dissolved by ultrasonic vibration for 0.5 hours to obtain a mixed solution. Graphene oxide was dispersed in another portion of ultrapure water, ultrasonically treated for 30 minutes, and then placed in the mixed solution and vigorously stirred for 5 hours to produce SiO2@GO. NaBH4 was then added and stirred for 1 hour, followed by sodium hydroxide and the mixture stirred for 24 hours. The resulting product was washed several times with ultrapure water to obtain h-RGO. Preparation of S2, three-phase Ag / Ag2S / h-RGO photocatalyst The prepared h-RGO was dissolved in water, and thioglycolic acid was added and stirred vigorously for 2 hours. Then, AgNO3 was added and stirred for 2 hours to obtain a homogeneous mixture. Subsequently, Na2S·9H2O was added and stirred for 1 hour to obtain a gray solution. The gray solution was centrifuged to obtain a product, which was dissolved in water and then in situ reduced with sodium borohydride solution. Finally, the prepared product was washed several times with ultrapure water and ethanol, and then dried at 60°C to obtain a three-phase Ag / Ag2S / h-RGO photocatalyst. In step S1, sodium borohydride is added in the form of gas powder, and the stirring speed is adjusted during the addition. The gas used is nitrogen, and the gas powder concentrations of sodium borohydride and nitrogen are 5 to 15 mg / L. The method for adding gas powder comprises the following steps: 1) Sodium borohydride powder and nitrogen are placed in an injection cylinder. A blower embedded in the piston of the injection cylinder continuously mixes the sodium borohydride powder and nitrogen. When the gas-powder concentration is 5 to 15 mg / L, injection into the mixed solution in step S1 can begin. 2) The gas powder is stirred at an initial flow rate of 0.2 L / min, starting from an initial speed of 200-300 rpm and decreasing at a rate of 5-20 rpm / min. When the speed drops to 120 rpm, the gas powder is increased at a rate of 0.03-0.08 L / min. When the gas powder injection volume reaches 100%, a small amount of ultrapure water is used to flush the gas injection cylinder and pour it back into the mixed solution; The gas powder also contains hydroxymethyl cellulose, and 0.02-0.04g of hydroxymethyl cellulose is added based on 1g of functionalized SiO2 nanospheres.

2. The method for preparing a three-phase Ag / Ag2S / h-RGO photocatalyst according to claim 1, characterized in that: The preparation method of the functionalized SiO2 nanospheres is as follows: 1) Add 1g of SiO2 nanospheres to 0.12L of 0.5M sodium chloride solution and further disperse by ultrasonic vibration for 1h; then, add 1.5g of PDDA and stir for 1h; then wash the product and centrifuge it several times to obtain a primary product; 2) The primary product was further added to 0.12 L of 0.5 M sodium chloride solution and further dispersed by ultrasonic vibration for 1 hour. Subsequently, 0.3 g of PSS was added and stirred for 1 hour. The product was then washed and centrifuged several times to obtain a secondary product. 3) The secondary product was further added to 0.12 L of 0.5 M sodium chloride solution and further dispersed by ultrasonic vibration for 1 hour. Subsequently, 1.5 g of PDDA was added and stirred for 1 hour. The product was then washed and centrifuged multiple times to obtain functionalized SiO2 nanospheres that had completed LBL assembly.

3. The method for preparing a three-phase Ag / Ag2S / h-RGO photocatalyst according to claim 2, characterized in that: The preparation method of the SiO2 nanospheres comprises the following steps: uniformly mixing 1L of ethanol, 60mL of H2O and 60mL of ammonia solution to form an alkaline condition to obtain a mixed solution; wherein the ammonia solution is 0.91g / cm 3 , 25% ammonia solution; then 30 mL of ethyl silicate was added to the resulting mixed solution and stirred at room temperature for 5 hours; after the reaction was completed, the white suspension was centrifuged at 8000 rpm for 4 minutes, washed with water several times, and dried in a vacuum dryer at 60°C to obtain SiO2 nanospheres.

4. The method for preparing a three-phase Ag / Ag2S / h-RGO photocatalyst according to claim 1, characterized in that: In step S1, 1 g of functionalized SiO2 nanospheres is used as a base amount, and the functionalized SiO2 nanospheres are added to 0.5 L of ultrapure water; Disperse 0.4-0.6 g of graphene oxide in another 0.5 L of ultrapure water; add 0.2-0.3 g of NaBH4; and add 0.2-0.3 L of 2 M sodium hydroxide.

5. The method for preparing a three-phase Ag / Ag2S / h-RGO photocatalyst according to claim 1, characterized in that: In step S2, 1 g of h-RGO obtained from functionalized SiO2 nanospheres is used as a reference amount, the functionalized SiO2 nanospheres are dissolved in 2 L of water and 1 mL of thioglycolic acid is added; 1 g of AgNO3 and 1.25 g of Na2S·9H2O are added; the gray solution is centrifuged to obtain a product, which is dissolved in 806 mL of water, and then silver sulfide is reduced in situ with 0.806 mL of 0.075 mM sodium borohydride solution.

6. The method for preparing a three-phase Ag / Ag2S / h-RGO photocatalyst according to claim 1, characterized in that: The vigorous stirring is 400-600 rpm, the stirring is 200-300 rpm, and the drying temperature is 60°C.

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