α-NiS / CdS photocatalyst, preparation method and application

Abstract

The present invention relates to the field of photocatalysts, and more particularly to a CdS-based photocatalyst, preparation method, and application thereof. The CdS-based photocatalyst comprises CdS nanosheets and NiS supported on the surface of the CdS nanosheets, wherein the mass fraction of the NiS is 5-15 wt%, and the NiS is preferably α-NiS. The CdS-based photocatalyst of the present invention effectively reduces the recombination rate of photogenerated electron-hole pairs, promoting the progress of the photocatalytic reaction. The use of NiS instead of traditional precious metal-supported catalysts reduces production costs and can maintain a high catalytic efficiency in seawater.

Description

Technical Field

[0001] The present invention relates to the field of photocatalysts, and in particular to an α-NiS / CdS photocatalyst, a preparation method and applications thereof. Background Art

[0002] Human survival and development are inseparable from energy consumption. With the massive consumption of fossil energy and the increasing attention paid to environmental protection, the development and utilization of clean renewable energy has become a top priority. Hydrogen, due to its carbon-free emission characteristics, can be used as a good potential substitute for fossil energy. In addition, the calorific value of hydrogen is as high as 14.3×10 7 J / Kg (4.5 times that of coke, 3.9 times that of alcohol, and 3 times that of gasoline), but the current cost of industrial hydrogen production is too high, which limits the development of hydrogen energy. Solar energy is a free resource that exists in large quantities in nature. Using sunlight as the driving force and clean water as the raw material, photocatalytic water splitting to produce hydrogen is a green and efficient energy conversion method that has received widespread attention.

[0003] The ideal way to convert solar energy into chemical energy is to use solar photocatalysis to decompose water to obtain clean hydrogen energy. However, the most critical problem with this method is to find a photocatalyst with high efficiency and stable properties. The ideal photocatalyst not only needs to have a wide spectral response range and be able to maximize and most effectively utilize sunlight, but also needs to effectively separate photogenerated electron-hole pairs, inhibit and reduce the recombination phenomenon of carriers, and allow as many photogenerated electrons as possible to participate in the photocatalytic hydrogen production half-reaction.

[0004] CdS material has an ideal energy band structure and a suitable conduction band position, but single CdS has the problem of easy recombination of photogenerated electron-hole pairs and prone to photocorrosion, which greatly limits the energy conversion efficiency of CdS photocatalysts. Currently, precious metals such as Pt, Au and Ag are often used to load the CdS surface to enhance the catalytic hydrogen production rate, but precious metals are expensive and the production cost is high.

[0005] Currently, photocatalytic water decomposition to produce hydrogen usually requires use in pure water, has low catalytic efficiency in seawater, and has poor corrosion resistance. Summary of the Invention

[0006] The purpose of the present invention is to solve the problems mentioned in the above background technology that single CdS has the problem of easy recombination of photogenerated electron-hole pairs, easy photocorrosion, expensive precious metal loading materials and high production costs, and low catalytic efficiency in seawater. To this end, the present invention proposes an α-NiS / CdS photocatalyst, which can greatly improve the hydrogen production rate, has low cost and can still maintain a high hydrogen production rate in seawater.

[0007] The technical solution adopted by the present invention to solve its technical problem is:

[0008] An α-NiS / CdS photocatalyst comprises CdS nanosheets and α-NiS supported on the surfaces of the CdS nanosheets, wherein the mass fraction of the α-NiS is 5-15 wt%. Preferably, the mass fraction of the α-NiS in the α-NiS / CdS photocatalyst is 10 wt%. The present invention forms a composite material by supporting α-NiS on the surfaces of the CdS nanosheets, using NiS instead of traditional precious metal supporting materials. This achieves effective separation of photogenerated charge carriers in the photocatalyst in a low-cost and efficient manner, accelerating charge utilization and mitigating photocorrosion.

[0009] A method for preparing the α-NiS / CdS photocatalyst as described above, comprising the following steps: S1, mixing Cd(CH3COO)2·2H2O, (NH2)2CS and 60 mL of ethylenediamine solvent, pouring the mixture into a polytetrafluoroethylene-lined hydrothermal autoclave, reacting at 100°C for 8 hours, cooling to room temperature, washing, and vacuum drying to constant weight to obtain CdS nanosheets;

[0010] S2. Dissolve Ni(CH3COO)2·4H2O, (NH2)2CS and sodium dodecyl sulfate in anhydrous ethanol and stir for 60±5 min to obtain a mixed solution. Pour the mixed solution into a polytetrafluoroethylene-lined hydrothermal autoclave and react at 190±1°C for 10 h. Cool to room temperature, centrifuge, wash, and vacuum dry at 70±1°C to constant weight to obtain α-NiS;

[0011] S3. Mix the CdS nanosheets, NiS and 15-20 mL of anhydrous ethanol and stir for 5 h, keep warm at 70±1° C. and continue stirring until all the ethanol evaporates, and vacuum dry at 60±1° C. to constant weight to obtain an α-NiS / CdS photocatalyst.

[0012] The preparation method synthesizes CdS nanosheets and α-NiS separately through a two-step solvothermal method, and then mixes and stirs them to prepare α-NiS nanosheet-modified CdS nanoheterojunctions. The steps are simple, and the prepared composite material has good photocatalytic stability and anti-photocorrosion ability.

[0013] Furthermore, in step S1, the molar ratio of Cd(CH3COO)2·2H2O to (NH2)2CS is 1:1.2-1:3.5. As a preferred technical solution, the molar ratio of Cd(CH3COO)2·2H2O to (NH2)2CS is 1:3.

[0014] Furthermore, in step S2, the molar ratio of Ni(CH3COO)2·4H2O, (NH2)2CS and sodium lauryl sulfate is 1:2.5:0.05.

[0015] Furthermore, in step S3, the mass ratio of the CdS nanosheets to NiS is 9:1.

[0016] Furthermore, in steps S1 and S2, the washing is performed using anhydrous ethanol and water three times each.

[0017] An application of the NiS / CdS photocatalyst described above to catalyze water decomposition and produce hydrogen under light is described in the following manner: when visible light λ≥400nm, 0.150-0.550g of catalyst is added per kg of seawater, and 2-5vol% of lactic acid is used as a sacrificial agent.

[0018] The beneficial effects of the present invention are:

[0019] 1. By loading α-NiS onto CdS nanosheets to form a composite material, the photogenerated electrons on the surface of the CdS material are transferred to the co-catalyst NiS under light, effectively reducing the recombination rate of photogenerated electron-hole pairs and facilitating the photocatalytic reaction. The hydrogen production rate of the α-NiS / CdS nanocomposite in water containing 3 vol% lactic acid as a sacrificial agent can reach 5501.9 μmol·g -1 ·h -1 , which is 6.2 times that of pure CdS and 1.4 times that of β-NiS / CdS. The hydrogen production in simulated seawater is 1.6 times that of β-NiS / CdS, and α-NiS / CdS has good photocatalytic hydrogen production stability.

[0020] 2. Compared with the currently commonly used precious metal co-catalysts such as Pt, Au and Ag loaded on the CdS surface, the present invention uses NiS, which greatly reduces the production cost.

[0021] 3. The α-NiS / CdS photocatalyst of the present invention has a higher efficiency in photocatalytic decomposition of seawater to produce hydrogen than pure water, and has good corrosion resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 XRD spectra of α-NiS, β-NiS, α-NiS / CdS and β-NiS / CdS;

[0023] Figure 2 These are SEM images of CdS (a, b), α-NiS (c), β-NiS (d), α-NiS / CdS (e), β-NiS / CdS (f);

[0024] Figure 3TEM images of CdS (a), α-NiS (b), β-NiS (d), α-NiS / CdS (c), and β-NiS / CdS (e) composite materials, and EDS spectra of α-NiS / CdS (f) and β-NiS / CdS (g);

[0025] Figure 4 Using lactic acid as a sacrificial agent, the photocatalytic hydrogen production activity of different samples in pure water under visible light irradiation is shown in the line graph (a), bar graph (b), cyclic stability graph (c), and hydrogen production rate of different samples in simulated seawater.

[0026] Figure 5 Transient photocurrent response diagram (a), electrochemical impedance spectroscopy (b), and time-resolved fluorescence spectra (c) of different samples;

[0027] Figure 6 UPS spectra of CdS (a) and UPS spectra of α-NiS (b), energy band diagram of CdS and α-NiS (c), and photocatalytic enhancement mechanism diagram of α-NiS / CdS (d); DETAILED DESCRIPTION

[0028] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present application belongs.

[0029] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0030] The present invention will now be further described in conjunction with specific examples. The following examples are only intended to explain the present invention but do not constitute a limitation of the present invention. The test samples and test procedures used in the following examples include the following (if the specific experimental conditions are not specified in the examples, they are usually based on conventional conditions or the conditions recommended by the reagent company; the reagents, consumables, etc. used in the following examples, unless otherwise specified, can be obtained from commercial sources).

[0031] The reagents used in the following examples are cadmium acetate (Cd(CH3COO)2·2H2O), nickel acetate tetrahydrate (Ni(CH3COO)2·4H2O), thiourea ((NH2)2CS), sodium lauryl sulfate (CH3(CH2) 11OSO3Na) was purchased from Aladdin Reagent Company, ethanol (C2H5OH) and ethylenediamine (NH2CH2CH2NH2) were purchased from Sinopharm Chemical Reagent Co., Ltd., and deionized water was used.

[0032] Example 1: Preparation of α-NiS / CdS photocatalyst:

[0033] S1. Add 0.533 g of cadmium acetate (2 mmol) and 0.457 g of thiourea (6 mmol) to 60 mL of ethylenediamine solvent and stir evenly. Pour the mixture into a 100 mL polytetrafluoroethylene reactor and react at 100 °C for 8 h. The reactor is naturally cooled to room temperature, washed with water and anhydrous ethanol three times each, and dried in a vacuum drying oven at 70 °C to constant weight to obtain CdS nanosheets;

[0034] S2, 4.0mmol Ni(CH3COO)2·4H2O, 750mg thiourea (NH2)2CS and 57mg NaC 12 H 25 SO4 was dissolved in 60 mL of anhydrous ethanol and stirred continuously for 60 min. The mixed solution was then poured into a 100 mL polytetrafluoroethylene-lined hydrothermal autoclave and reacted at 190°C for 10 h. The autoclave was naturally cooled to room temperature and centrifuged to obtain a solid precipitate. The solid precipitate was washed three times with water and three times with anhydrous ethanol, and dried in a vacuum drying oven at 70°C to constant weight to obtain α-NiS.

[0035] S3. Weigh 90 mg of CdS nanosheets and 10 mg of α-NiS into a 50 mL centrifuge tube, add 20 mL of ethanol, and stir at room temperature for 5 h. After stirring, seal the mouth of the centrifuge tube with a perforated plastic wrap, place it in a water bath, continue stirring, and heat to 70°C for constant temperature reaction until the sample ethanol in the centrifuge tube is basically evaporated. Vacuum dry at 60±1°C to constant weight to obtain α-NiS / CdS photocatalyst.

[0036] Example 2: Preparation of α-NiS / CdS photocatalyst:

[0037] S1. Add 0.533 g of cadmium acetate (2 mmol) and 0.228 g of thiourea (3 mmol) to 60 mL of ethylenediamine solvent and stir evenly. Pour the mixture into a 100 mL polytetrafluoroethylene reactor and react at 100 °C for 8 h. The reactor is naturally cooled to room temperature, washed with water and anhydrous ethanol three times each, and dried in a vacuum drying oven at 70 °C to constant weight to obtain CdS nanosheets;

[0038] S2, 4.0mmol Ni(CH3COO)2·4H2O, 750mg thiourea (NH2)2CS and 57mg NaC 12 H 25SO4 was dissolved in 60 mL of anhydrous ethanol and stirred continuously for 60 min. The mixed solution was then poured into a 100 mL polytetrafluoroethylene-lined hydrothermal autoclave and reacted at 190°C for 10 h. The autoclave was naturally cooled to room temperature and centrifuged to obtain a solid precipitate. The solid precipitate was washed three times with water and three times with anhydrous ethanol, and dried in a vacuum drying oven at 70°C to constant weight to obtain α-NiS.

[0039] S3. Weigh 115 mg of CdS nanosheets and 10 mg of α-NiS into a 50 mL centrifuge tube, add 20 mL of ethanol, and stir at room temperature for 5 h. After stirring, seal the mouth of the centrifuge tube with a perforated plastic wrap, place it in a water bath, continue stirring, and heat to 70°C for constant temperature reaction until the sample ethanol in the centrifuge tube is basically evaporated. Vacuum dry at 60±1°C to constant weight to obtain α-NiS / CdS photocatalyst.

[0040] Example 3: Preparation of α-NiS / CdS photocatalyst:

[0041] S1. Add 0.533 g of cadmium acetate (2 mmol) and 0.372 g of thiourea (7 mmol) to 60 mL of ethylenediamine solvent and stir evenly. Pour the mixture into a 100 mL polytetrafluoroethylene reactor and react at 100 °C for 8 h. The reactor is naturally cooled to room temperature, washed with water and anhydrous ethanol three times each, and dried in a vacuum drying oven at 70 °C to constant weight to obtain CdS nanosheets;

[0042] S2, 4.0mmol Ni(CH3COO)2·4H2O, 750mg thiourea (NH2)2CS and 57mg NaC 12 H 25 SO4 was dissolved in 60 mL of anhydrous ethanol and stirred continuously for 60 min. The mixed solution was then poured into a 100 mL polytetrafluoroethylene-lined hydrothermal autoclave and reacted at 190°C for 10 h. The autoclave was naturally cooled to room temperature and centrifuged to obtain a solid precipitate. The solid precipitate was washed three times with water and three times with anhydrous ethanol, and dried in a vacuum drying oven at 70°C to constant weight to obtain α-NiS.

[0043] S3. Weigh 70 mg of CdS nanosheets and 10 mg of α-NiS into a 50 mL centrifuge tube, add 20 mL of ethanol, and stir at room temperature for 5 h. After stirring, seal the mouth of the centrifuge tube with a perforated plastic wrap, place it in a water bath, continue stirring, and heat to 70°C for constant temperature reaction until the sample ethanol in the centrifuge tube is basically evaporated. Vacuum dry at 60±1°C to constant weight to obtain α-NiS / CdS photocatalyst.

[0044] Comparative Example 1: Preparation of β-NiS / CdS photocatalyst:

[0045] S1. Add 0.533 g of cadmium acetate (2 mmol) and 0.457 g of thiourea (6 mmol) to 60 mL of ethylenediamine solvent and stir evenly. Pour the mixture into a 100 mL polytetrafluoroethylene reactor and react at 100 °C for 8 h. The reactor is naturally cooled to room temperature, washed with water and anhydrous ethanol three times each, and dried in a vacuum drying oven at 70 °C to constant weight to obtain CdS nanosheets;

[0046] S2, 4.0mmol Ni(CH3COO)2·4H2O, 750mg thiourea and 57mg NaC 12 H 25 SO4 was dissolved in 60 mL of ethanol-water solution (ethanol: deionized water volume ratio of 1:2) and stirred continuously for 60 min. The mixed solution was then poured into a 100 mL polytetrafluoroethylene-lined hydrothermal autoclave and reacted at 190 °C for 10 h. The autoclave was naturally cooled to room temperature and centrifuged to obtain a solid precipitate. The solid precipitate was washed three times with water and three times with anhydrous ethanol, and dried in a vacuum drying oven at 70 °C to constant weight to obtain β-NiS.

[0047] S3. Weigh 90 mg of CdS nanosheets and 10 mg of β-NiS into a 50 mL centrifuge tube, add 20 mL of ethanol, and stir at room temperature for 5 h. After stirring, seal the mouth of the centrifuge tube with a perforated plastic wrap, place it in a water bath, continue stirring, and heat to 70°C for constant temperature reaction until the sample ethanol in the centrifuge tube is basically evaporated. Vacuum dry at 60±1°C to constant weight to obtain β-NiS / CdS photocatalyst.

[0048] The α-NiS, β-NiS, α-NiS / CdS and β-NiS / CdS photocatalysts were characterized below, wherein an X-ray diffractometer (XRD-7000) was used to characterize the crystal structure of the samples. A Fourier transform infrared spectrometer (Thermofisher IS50) was used to collect infrared spectra (FT-IR) of the samples. A field emission scanning electron microscope (S-4800) and a high-resolution transmission electron microscope (Talos F200X) were used to observe their morphology and microstructure. An X-ray photoelectron spectrometer (ThermoFisher Scientific ESCALAB 250Xi) was used to determine the surface composition and chemical state of the samples. Ultraviolet-visible diffuse reflectance spectra (UV-vis DRS) were obtained on a UV-visible near-infrared spectrometer (Cary 5000). Time-resolved PL spectra (TRPL) were obtained using an Edinburgh FLS980 time-resolved spectrometer. Structure and morphology of the catalyst:

[0049] like Figure 1As shown in the figure, the crystal structure of the sample was characterized by X-ray diffractometer (XRD-7000). The obvious diffraction peaks of α-NiS are located at 2θ = 30.1, 34.6, 45.8 and 53.5°, corresponding to the (100), (101), (102) and (110) crystal planes of α-NiS, respectively. The more obvious diffraction peaks of β-NiS are located at 2θ = 32.4 and 48.9°, corresponding to the (300) and (131) crystal planes of β-NiS, respectively. The XRD pattern of CdS can be indexed as the hexagonal phase of CdS, and its peak with a 2θ value of 27.0° is attributed to the (002) crystal plane. After loading α-NiS and β-NiS on the CdS surface, there is no obvious change in the position of the CdS diffraction peak, indicating that the loading of α-NiS and β-NiS does not change the crystal structure of CdS. Comparing the XRD patterns of α-NiS, β-NiS, α-NiS / CdS and β-NiS / CdS, no weak peaks were observed for α-NiS / CdS and β-NiS / CdS, indicating that α-NiS and β-NiS have good dispersion on the CdS surface.

[0050] like Figure 2 As shown in Figure 2, the micromorphology of CdS, α-NiS, β-NiS, α-NiS / CdS and β-NiS / CdS photocatalysts was observed using field emission scanning electron microscopy (FESEM). Figure 2 (a) and (b) are SEM images of CdS, (c) is a SEM image of α-NiS, (d) is a SEM image of β-NiS, (e) is a SEM image of α-NiS / CdS, and (f) is a SEM image of β-NiS / CdS. Figure 2 (a) Figure 2 (b) It can be seen that the CdS sample has a flower-like lamellar structure. Figure 2 (c) It can be seen that the α-NiS sample is a flower-shaped flake cluster. Figure 2 (d) It can be seen that β-NiS is an irregular nanosheet. Figure 2 (e) Figure 2 (f) It can be seen that α-NiS and β-NiS in the α-NiS / CdS and β-NiS / CdS photocatalysts respectively formed binary composite materials with CdS.

[0051] like Figure 3 As shown, transmission electron microscopy (TEM) was used to further study the microstructure of the samples. In the figure, (a) is the TEM image of CdS, (b) is the TEM image of α-NiS, (c) is the TEM image of α-NiS / CdS, (d) is the TEM image of β-NiS, (e) is the TEM image of β-NiS / CdS, (f) is the EDS energy spectrum of α-NiS / CdS, and (g) is the EDS energy spectrum of β-NiS / CdS. Figure 3(a) It can be seen that CdS has a highly uniform lamellar structure, which is consistent with the SEM results. Figure 3 (b) It can be seen that α-NiS is an irregularly overlapped layer structure. Figure 3 (c) It can be seen that small α-NiS nanosheets are deposited on the surface of the CdS layer. Figure 3 (d) It can be seen that β-NiS is an irregular large-layer structure. Figure 3 (e) β-NiS nanosheets and CdS sheets are combined together. Figure 3 (f) and (g) show that Cd, Ni, and S exist and are densely distributed in the composite material, which also indicates the formation of α-NiS / CdS and β-NiS / CdS, which promote the separation and transfer of photogenerated carriers, thereby improving the photocatalytic activity.

[0052] Photoelectrochemical performance evaluation:

[0053] The FTO glass coated with the prepared sample was used as the working electrode, the Ag / AgCl standard electrode was used as the reference electrode, and the platinum electrode was used as the counter electrode to construct a three-electrode system. The electrolyte was 0.10 M Na2SO4 solution. The photoelectrochemical performance of the sample was evaluated on an electrochemical workstation (CHI-660E, Shanghai Chenhua).

[0054] Evaluation of photocatalyst hydrogen production performance:

[0055] 1. Photocatalytic water hydrogen production

[0056] The photocatalytic performance of the prepared samples was evaluated by photocatalytic hydrogen production. In the hydrogen production experiment, 30 mg of photocatalyst was ultrasonically dispersed in 70 mL of water with lactic acid (3 vol%) as a sacrificial agent, the reactor was sealed, and nitrogen was pumped and purged for 40 minutes to drive out the oxygen in the reactor. A 300 W xenon lamp (λ ≥ 400 nm) was placed on the top of the photoreactor, and the light source was turned on to start the photocatalytic reaction. During the entire reaction process, cooling water was passed through the reactor jacket to maintain a constant reaction temperature (15 ° C). The reaction lasted for 3 hours and samples were taken once every hour. The generated H2 was analyzed by gas chromatograph ( The detector was a thermal conductivity detector (TCD) and the carrier gas was high-purity nitrogen.

[0057] 2. Photocatalytic hydrogen production from seawater

[0058] The experimental steps for hydrogen production were the same as those for photocatalytic water hydrogen production. Only 70 mL of water was replaced with 70 mL of simulated seawater solution. The simulated seawater was a 7 wt% NaCl aqueous solution.

[0059] like Figure 4As shown, (a) is a line graph of the photocatalytic hydrogen evolution performance of different samples in pure water, (b) is a bar graph of the photocatalytic hydrogen evolution performance of different samples in pure water, (c) is a cyclic stability graph of different samples, and (d) is a bar graph of the photocatalytic hydrogen evolution performance of different samples in simulated seawater. Figure 4 (a) and (b) show that CdS exhibits relatively low photocatalytic activity during the reaction, with a hydrogen production rate of 879.7 μmol·h -1 ·g -1 The hydrogen production performance of α-NiS was basically undetectable during the reaction, indicating that α-NiS exhibited a metallic state. The hydrogen production rate of α-NiS / CdS nanocomposite in water with 3 vol% lactic acid as the sacrificial agent could reach 5501.9 μmol·g -1 ·h -1 The hydrogen production rate of β-NiS / CdS nanocomposite is 3793.1 μmol·g -1 ·h -1 , which are 6.2 and 4.3 times that of pure CdS, respectively, which are significantly higher than the hydrogen production rate of pure CdS in water. In addition, the hydrogen production performance of α-NiS / CdS is higher than that of β-NiS / CdS, indicating that α-NiS is more effective in improving the hydrogen production performance of CdS. The cyclic stability of α-NiS / CdS nanocomposites was tested every 3 hours. Figure 4 (c) It can be seen that the photocatalytic hydrogen production activity of α-NiS / CdS nanocomposite materials did not decrease significantly after four cycles, indicating that the α-NiS / CdS photocatalyst has good photocatalytic stability and anti-photocorrosion ability. Figure 4 (d) It can be seen that the hydrogen production rates of CdS and β-NiS / CdS in simulated seawater are slightly lower than those in pure water, and the change trend is basically the same as that in pure water. However, compared with pure water, the hydrogen production rate of α-NiS / CdS in seawater is slightly higher, reaching 5638.7 μmol·g -1 ·h -1 The results show that the α-NiS / CdS photocatalyst has higher catalytic performance both in seawater and pure water, and loading α-NiS on the CdS surface is more conducive to improving the photogenerated electron and hole transfer efficiency of the catalyst.

[0060] like Figure 5 As shown, (a) is the transient photocurrent response diagram of samples prepared differently, (b) is the electrochemical impedance curve diagram of samples prepared differently, and (c) is the time-resolved fluorescence spectrum diagram of samples prepared differently; Figure 5(a) and (b) show that compared with CdS, the photocurrent response of α-NiS / CdS and β-NiS / CdS photocatalysts is higher and the AC impedance radius is smaller; the photocurrent response of α-NiS / CdS is higher than that of β-NiS / CdS, and the AC impedance radius is smaller than that of β-NiS / CdS, indicating that α-NiS / CdS and β-NiS / CdS photocatalysts have better electron transport conductivity than pure CdS, and the electron transport ability of α-NiS / CdS is better than that of β-NiS / CdS, indicating that the synergistic effect of α-NiS or β-NiS and CdS leads to a decrease in the recombination rate of photoinduced carriers. Figure 5 (c) It can be seen that the average lifetimes of α-NiS / CdS and β-NiS / CdS nanocomposites are 1.36 ns and 1.48 ns, respectively, which are 2.29 ns longer than the average lifetime of the CdS sample. This is attributed to the electron injection of CdS into NiS. Since α-NiS or β-NiS cannot be excited at 380 nm, electrons and holes can only be generated in CdS, thereby improving the photocatalytic hydrogen activity.

[0061] like Figure 6 As shown, (a) is the UPS spectrum of CdS, (b) is the UPS spectrum of α-NiS, (c) is the energy band diagram of CdS and α-NiS, and (d) is the photocatalytic enhancement mechanism diagram of α-NiS / CdS; combined with Table 1, Table 1 is the band gap width (E g ), work function (W f ), valence band (E VBM ), conduction band (E CBM ).

[0062] Table 1

[0063] sample <![CDATA[E g ]]> <![CDATA[W f ]]> <![CDATA[E VBM (AVS)]]> <![CDATA[E VBM (NHE)]]> <![CDATA[E VBM (AVS)]]> <![CDATA[E CBM (NHE)]]> CdS 2.38 4.62 -6.15 1.65 -3.77 -0.73 α-NiS 3.73

[0064] Combine Figure 6 (a), (b), W f (work function), E VBM and E CBM It can be estimated according to the following formula:

[0065] W f =21.22-E1 (3-1)

[0066] E V =W f +E2 (3-2)

[0067] E C =E V -E q (3-3)

[0068] E NHE -E AVS-4.5 (3-4)

[0069] E1 is the upper limit of the emission starting energy, E2 is the lower limit of the emission starting energy, and E NHE is the standard hydrogen electrode potential, E AVS is the energy level of absolute vacuum. V and E C The values ​​are shown in Table 1. Figure 6 (a) and (b) UPS diagrams and UV-vis DRS spectra. The energy levels of CdS and α-NiS are shown in Figure 2. Figure 6 As shown in (c), pure α-NiS shows metallic properties. CdS (W f ) and α-NiS(W f ) are 4.62eV and 3.73eV, respectively, indicating that the Fermi level (E f ) is higher than CdS. CdS and α-NiS can form an ohmic junction when in close contact. When α-NiS is loaded on the surface of CdS, electrons are transferred from α-NiS to CdS until the Fermi levels of the two components are equal. Figure 6 As shown in (d), after thermal equilibrium is established between α-NiS and CdS, the photogenerated electrons generated by CdS are transferred to α-NiS, thereby preventing the electron-hole recombination in photocatalysis and improving the photocatalytic performance. Under visible light irradiation, the electrons accumulated on α-NiS can transfer H + It is reduced to hydrogen atoms to produce hydrogen, and the holes accumulated in the valence band of CdS can oxidize lactic acid into oxidation products, thereby realizing the photocatalytic cracking of H2O to produce H2 under visible light.

[0070] Application example: α-NiS / CdS photocatalyst for the catalytic decomposition of water to produce hydrogen under light

[0071] In the hydrogen production experiment, 30 mg of photocatalyst was ultrasonically dispersed into 70 ml of simulated seawater solution (7 wt% NaCl solution) with lactic acid (3 vol%) as a sacrificial agent. The reactor was sealed and purged with nitrogen for 40 minutes to drive out the oxygen in the reactor. A 300 W xenon lamp (λ ≥ 400 nm) was placed on the top of the photoreactor and the light source was turned on to start the photocatalytic reaction. During the entire reaction process, cooling water was passed through the reactor jacket to maintain a constant reaction temperature (15 ° C). The reaction lasted for 3 hours and samples were taken once every hour. The generated H2 was analyzed by gas chromatograph ( The detector was a thermal conductivity detector (TCD) and the carrier gas was high-purity nitrogen.

[0072] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from the other embodiments. Reference can be made to the descriptions of the identical or similar parts between the various embodiments. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple, and the relevant parts can be referred to the descriptions of the methods.

[0073] The above is a detailed introduction to the α-NiS / CdS photocatalyst, preparation method, and application provided by the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only intended to help understand the method and core concept of the present invention. It should be noted that for ordinary technicians in this technical field, without departing from the principles of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. An α-NiS / CdS photocatalyst, characterized by: The α-NiS / CdS photocatalyst includes CdS nanosheets and α-NiS supported on the surface of the CdS nanosheets, wherein the mass fraction of the α-NiS is 5-15 wt%. The preparation method of the α-NiS / CdS photocatalyst includes the following steps: S1. Pour Cd(CH3COO)2·2H2O, (NH2)2CS and 60 mL of ethylenediamine solvent into a polytetrafluoroethylene-lined hydrothermal reactor and react at 100 °C for 8 h. Then cool to room temperature, wash, and vacuum dry at 70 °C to constant weight to obtain CdS nanosheets. S2. Dissolve Ni(CH3COO)2·4H2O, (NH2)2CS and sodium dodecyl sulfate in anhydrous ethanol and stir for 60±5 min to obtain a mixed solution. Pour the mixed solution into a polytetrafluoroethylene-lined hydrothermal autoclave and react at 190±1°C for 10 h. Cool to room temperature, centrifuge, wash, and vacuum dry at 70±1°C to constant weight to obtain α-NiS; S3. Mix the CdS nanosheets, α-NiS and 15-20 mL of anhydrous ethanol and stir for 5 h, keep warm at 70±1° C. and continue stirring until all the ethanol evaporates, and vacuum dry at 60±1° C. to constant weight to obtain an α-NiS / CdS photocatalyst.

2. The α-NiS / CdS photocatalyst according to claim 1, wherein: The mass fraction of the α-NiS is 10 wt%.

3. A method for preparing the α-NiS / CdS photocatalyst according to claim 1, characterized in that The preparation method comprises the following steps: S1. Pour Cd(CH3COO)2·2H2O, (NH2)2CS and 60 mL of ethylenediamine solvent into a polytetrafluoroethylene-lined hydrothermal reactor and react at 100 °C for 8 h. Then cool to room temperature, wash, and vacuum dry at 70 °C to constant weight to obtain CdS nanosheets. S2. Dissolve Ni(CH3COO)2·4H2O, (NH2)2CS and sodium dodecyl sulfate in anhydrous ethanol and stir for 60±5 min to obtain a mixed solution. Pour the mixed solution into a polytetrafluoroethylene-lined hydrothermal autoclave and react at 190±1°C for 10 h. Cool to room temperature, centrifuge, wash, and vacuum dry at 70±1°C to constant weight to obtain α-NiS; S3. Mix the CdS nanosheets, α-NiS and 15-20 mL of anhydrous ethanol and stir for 5 h, keep warm at 70±1° C. and continue stirring until all the ethanol evaporates, and vacuum dry at 60±1° C. to constant weight to obtain an α-NiS / CdS photocatalyst.

4. The preparation method according to claim 3, wherein: In step S1, the molar ratio of Cd(CH3COO)2·2H2O and (NH2)2CS is 1:1.2-1:3.

5.

5. The preparation method according to claim 3, wherein: The molar ratio of Cd(CH3COO)2·2H2O and (NH2)2CS is 1:

3.

6. The preparation method according to claim 3, wherein: In step S2, the molar ratio of Ni(CH3COO)2·4H2O, (NH2)2CS and sodium lauryl sulfate is 1:2.5:0.

05.

7. The preparation method according to claim 3, wherein: In step S3 , the mass ratio of the CdS nanosheets to α-NiS is 9:

1.

8. The preparation method according to claim 3, wherein: In steps S1 and S2, the washing was performed using anhydrous ethanol and water three times each.

9. Use of the α-NiS / CdS photocatalyst according to claim 1 to catalytically decompose water to produce hydrogen under light.

10. The use according to claim 9, characterized in that: The application is to add 0.150-0.550 g of catalyst per kg of seawater when visible light λ ≥ 400 nm, and 2-5 vol% of lactic acid as a sacrificial agent.

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