Preparation method and application of NiPc monomolecular layer modified ZnIn2S4 nanosheet photocatalyst

Abstract

The invention provides a preparation method and application of a ZnIn2S4 nanosheet photocatalyst modified by a NiPc monomolecular layer. According to the preparation method disclosed by the invention, the Z-type p-n heterojunction with strong interaction is constructed by utilizing NiPc with a wide conjugated system and the ultrathin ZnIn2S4 nanosheet. Controllable assembly of highly dispersed NiPc and ZnIn2S4 is achieved through phosphate functionalization, the separation and transmission efficiency of photogenerated carriers and carriers is improved, meanwhile, the mild oxidation capacity and the strong reduction capacity of the two components are reserved, and the photocatalytic hydrogen production activity of the catalyst and the selectivity and conversion rate of benzyl alcohol oxidation can be obviously improved. According to the catalyst, products with high added values are generated while photocatalytic hydrogen production is realized, and the economic value of the whole catalytic process is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of photocatalytic materials and their applications in the fields of energy and environmental protection. Specifically, it relates to a photocatalyst of ZnIn2S4 nanosheets modified by a single layer of NiPc, a preparation method thereof, and an application in photocatalytic water splitting for hydrogen production coupled with the selective oxidation of benzyl alcohol. Background Art

[0002] Hydrogen energy is an ideal environmentally friendly energy source with high calorific value and the characteristics of being clean and pollution-free. Its green production technology has been widely concerned. The photocatalytic water splitting for hydrogen production technology is considered to be one of the effective ways to solve the two global problems of energy crisis and environmental pollution. However, a large amount of research on photocatalytic hydrogen production focuses on the reduction half-reaction of using photo-generated electrons, and there is less research on the utilization of photo-generated holes. The coupled reaction of selective organic oxidation of semiconductor photocatalysis and water splitting for hydrogen production is one of the effective strategies to realize the effective utilization of photo-generated holes and the carbon-free characteristics of photocatalytic hydrogen production. In particular, the traditional oxidation of alcohol to aldehyde requires a large amount of toxic oxidants and expensive noble metal catalysts, which is not conducive to green and sustainable development. Therefore, developing a suitable photocatalyst to realize the coupled reaction of water splitting for hydrogen production and the selective oxidation of benzyl alcohol with water as the reaction medium without the need for oxygen and sacrificial agents is a reasonable and feasible catalytic strategy. While achieving efficient water splitting for hydrogen production, it provides an efficient green synthesis route for the synthesis of industrial-related chemicals.

[0003] The present invention uses a solvothermal method to prepare a ZnIn2S4 / NiPc Z-type p-n heterojunction photocatalyst. The phosphate functionalization realizes the controllable assembly of highly dispersed NiPc and ZnIn2S4, enhances the effective transfer of Z-type charges while retaining the mild oxidation ability and strong reduction ability of the two components, accelerates the separation and transmission of photo-generated carriers, and can significantly improve the photocatalytic hydrogen production activity of ZnIn2S4 and the selectivity and conversion rate of benzyl alcohol oxidation. At the same time, the synthesis steps of this catalyst are simple, the cost is low, and the reaction conditions are mild. It is a novel and efficient photocatalytic hydrogen production coupled with organic conversion material. Summary of the Invention The purpose of the present invention is to provide a preparation method and an application of a photocatalyst of ZnIn2S4 nanosheets modified by a single layer of NiPc. Through phosphate functionalization, the controllable assembly of highly dispersed NiPc and ZnIn2S is realized, and a Z-type p-n heterojunction with strong surface interaction is formed between the two, accelerating the separation and transmission of photo-generated carriers, and then improving the photocatalytic hydrogen production activity of ZnIn2S4 and the selectivity and conversion rate of benzyl alcohol oxidation. The present invention is realized through the following technical solutions.

[0004] The XRD data of the ZnIn2S4 / NiPc composite material shows that the diffraction peaks at 2-Theta of 21.60°, 27.61°, 30.45° and 47.33° correspond to the (006), (102), (104) and (110) planes of hexagonal ZnIn2S4 (PDF#65-2023), respectively. Since the content of NiPc in the composite material is relatively low, no obvious peak intensity is shown.

[0005] The present invention provides a method for preparing a NiPc monolayer-modified ZnIn2S4 nanosheet photocatalyst. The method includes the following steps: (1) Preparation of phosphate-functionalized ZnIn2S4 nanosheets: The ZnIn2S4 nanosheets are uniformly dispersed in an aqueous solution containing phosphate, and the solvent is evaporated to dryness under a fixed temperature condition. The obtained yellow solid powder is the phosphate-functionalized ZnIn2S4 nanosheets.

[0006] In step (1), the mass ratio of ZnIn2S4 nanosheets to phosphate is 1-4:0.1-0.4; the drying temperature is 60-90 °C, and the time is 4-24 h. The mass concentration of the phosphate aqueous solution is 0.1-2 g / L. After the reaction, a yellow solid powder is obtained.

[0007] The phosphate is selected from any one or a combination of monohydrogen phosphates, dihydrogen phosphates, phosphates, metaphosphates, pyrophosphates, and polyphosphates. The phosphate can be any one of ammonium salts, sodium salts, and potassium salts. The phosphate is selected from any one of sodium monohydrogen phosphate, sodium dihydrogen phosphate, trisodium phosphate, sodium metaphosphate, sodium pyrophosphate, sodium polyphosphate, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, ammonium metaphosphate, ammonium pyrophosphate, ammonium polyphosphate, potassium monohydrogen phosphate, potassium dihydrogen phosphate, potassium phosphate, potassium metaphosphate, potassium pyrophosphate, and potassium polyphosphate. In some preferred embodiments, the final phosphate is sodium dihydrogen phosphate.

[0008] (2) Preparation of NiPc monolayer-modified ZnIn2S4 nanosheet photocatalyst: First, the phosphate-functionalized ZnIn2S4 nanosheets are uniformly dispersed in a methanol solution, then nickel chloride, 4-nitrophthalonitrile, and ammonium molybdate are added, and the mixture is ultrasonicated until dissolved and then stirred until uniformly dispersed. Finally, a NiPc monolayer-modified ZnIn2S4 nanosheet photocatalyst, abbreviated as ZnIn2S4 / NiPc composite material, is obtained through a solvothermal reaction.

[0009] In step (2), the mass ratio of nickel chloride, 4-nitrophthalonitrile, and ammonium molybdate is (6-15):(1-10):(2-20).

[0010] The volume of anhydrous methanol used as the reagent is 20 - 60 mL (suitable for small-scale reaction kettles in laboratories). The solvothermal temperature is 60 - 180 °C, and the solvothermal time is 5 - 14 h. In the preferred embodiment, the solvothermal reaction time is 5 - 10 h at a temperature of 90 - 150 °C. After the solvothermal reaction in this experiment, it is washed alternately with deionized water and ethanol, with the number of washing times being 3 times for deionized water and 3 times for ethanol, and then dried in a vacuum drying oven at 40 - 80 °C to obtain a yellowish-green powder product.

[0011] The metal phthalocyanine described above is selected from any one of nickel phthalocyanine, cobalt phthalocyanine, and copper phthalocyanine. In some preferred embodiments, nickel phthalocyanine is finally used as the metal phthalocyanine.

[0012] The ZnIn2S4 nanosheets in step (1) can be prepared according to the existing publicly disclosed patents or can be prepared by the following method of the present invention. Among them, the preparation of ZnIn2S4 nanosheets: Zinc chloride, indium tetrachloride, and thioacetamide are added to an anhydrous methanol solution, stirred evenly, and a yellow solid powder ZnIn2S4 is obtained after solvothermal reaction.

[0013] The mass ratio of zinc chloride, indium chloride tetrahydrate, and thioacetamide is 12 - 15:4 - 68:30 - 33.

[0014] The solvothermal temperature is 70 - 210 °C, and the solvothermal time is 20 - 200 min. After the reaction ends, it is washed alternately with deionized water and ethanol, with the number of washing times being 3 times for deionized water and 3 times for ethanol, and then dried in a vacuum drying oven at 40 - 80 °C to obtain a yellow powder product.

[0015] The present invention also provides a NiPc monolayer-modified ZnIn2S4 nanosheet photocatalyst prepared by the method described above. The XRD data of the ZnIn2S4 / NiPc composite material has characteristic diffraction peaks at 2-Theta of 21° ± 1°, 27° ± 1°, 30° ± 1°, and 47° ± 1°.

[0016] The present invention also provides a photocatalyst having light absorption in the visible and near-infrared regions. The photocatalyst is the NiPc monolayer-modified ZnIn2S4 nanosheet photocatalyst described above.

[0017] Another technical solution of the present invention is the application of a NiPc monolayer-modified ZnIn2S4 nanosheet photocatalyst prepared by the method described above in a photocatalytic reaction.

[0018] Another technical solution of the present invention is to provide a photocatalyst for photocatalytic oxidation of benzyl alcohol to produce benzaldehyde and coupled hydrogen production. The photocatalyst is the NiPc monolayer-modified ZnIn2S4 nanosheet photocatalyst described above.

[0019] Another technical solution of the present invention is the application of NiPc monolayer-modified ZnIn2S4 nanosheets in the performance of photocatalytic water splitting for hydrogen production coupled with selective oxidation of benzyl alcohol.

[0020] Disperse the prepared ZnIn2S4 / NiPc photocatalyst in a quartz reactor containing deionized water and benzyl alcohol. Use a xenon lamp as the light source. Before illumination, degas the mixture to ensure that the reactor is in a negative pressure state.

[0021] Ultrasonically disperse the photocatalyst in an aqueous solution containing benzyl alcohol. The amount of catalyst used is 5 - 100 mg, the content of benzyl alcohol is 0.1 - 10 mL, and the deionized water is 80 mL. In the preferred scheme, the amount of catalyst used is 50 mg and the content of benzyl alcohol is 7 mL.

[0022] The performance of photocatalytic water splitting for hydrogen production coupled with selective oxidation of benzyl alcohol is carried out on a fully automatic online analysis nanomaterial testing system. Use a xenon lamp with a power of 300 W and equipped with an AM1.5G filter as the light source. Before the reaction, remove the air in the reactor mixed solution and the test glass system through a vacuum pump to make the system in a negative pressure state. Keep the temperature of the reactor at 298 K through a circulating condensation system. Measure the amount of hydrogen produced per hour by gas chromatography (GC7920-TF2A, Au light, China) and monitor and quantify it through a thermal conductivity detector (TCD). After the reaction, the reaction solution is detected by high performance liquid chromatography (LC5090PLUS, Fuli Instrument). The results are compared with the standard peak emergence time and the amount of benzaldehyde generated is analyzed with a calibration curve.

[0023] The embodiments of the present invention provide a NiPc monolayer-modified ZnIn2S4 nanosheet and its preparation method and application, having the following beneficial effects: (1) Under mild reaction conditions, the present invention significantly improves the yields of benzaldehyde and hydrogen. The hydrogen production efficiency in the presence of benzyl alcohol is 8.1 times that of pure ZnIn2S4, and the selectivity of benzaldehyde is as high as 98% and the conversion rate is as high as 90%. This method is simple to operate and has broad application prospects.

[0024] (2) The NiPc monolayer-modified ZnIn2S4 nanosheet material prepared by the present invention has a simple preparation process, low cost, high reaction activity, and is suitable for large-scale industrial applications.

[0025] In the present invention, the surface hydroxyl groups of ZnIn2S4 nanosheets are modified by phosphate functionalization, and then a strongly interacting ZnIn2S4 / NiPc ultrathin Z-type p-n heterojunction is constructed through hydroxyl-induced assembly. Benefiting from the light absorption characteristics of NiPc, the ZnIn2S4 / NiPc heterojunction has obvious light absorption in the visible and near-infrared regions, improving the utilization rate of sunlight. The H of the surface hydroxyl groups of ZnIn2S4 is connected to the N of the NiPc ligand through hydrogen bonds. This tightly interacting interface is conducive to the transfer and separation of photo-generated charges, thereby improving its photocatalytic hydrogen production and selective oxidation activity of benzyl alcohol. Brief Description of the Drawings

[0026] Figure 1 : XRD pattern of ZnIn2S4 nanosheets modified with a monolayer of NiPc.

[0027] Figure 2 : TEM and HRTEM images of ZnIn2S4 nanosheets modified with a monolayer of NiPc, where a: TEM image of ZnIn2S4 nanosheets modified with a monolayer of NiPc; b: HRTEM image of ZnIn2S4 nanosheets modified with a monolayer of NiPc.

[0028] Figure 3 : UV-Vis diffuse reflectance absorption spectrum of ZnIn2S4 nanosheets modified with a monolayer of NiPc.

[0029] Figure 4 : Photocatalytic hydrogen evolution and benzaldehyde conversion performance of ZnIn2S4 nanosheets modified with a monolayer of NiPc.

[0030] Figure 5 : Benzyl alcohol conversion rate and selectivity of ZnIn2S4 nanosheets modified with a monolayer of NiPc.

[0031] Figure 6 Hydrogen evolution rate and benzyl alcohol rate of ZnIn2S4 nanosheet materials modified with a monolayer of NiPc, CuPc or CoPc.

[0032] Figure 7 : Photocatalytic cycle effect diagram of ZnIn2S4 nanosheets modified with a monolayer of NiPc. Detailed Description of the Embodiments

[0033] The following describes in detail the embodiments of the present invention. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions from beginning to end. The examples described below by referring to the drawings are exemplary and are only used to explain the present invention and should not be construed as a limitation of the present invention.

[0034] Referring to the following description and drawings, the experimental methods and detection methods described in the embodiments of the present invention will be clear. Unless otherwise specified, they are all conventional methods; the reagents and materials, unless otherwise specified, can be obtained in the market.

[0035] Example 1 (1) Preparation of ZnIn2S4 nanosheets Weigh 140 mg of zinc chloride and 590 mg of indium chloride tetrahydrate and add them to 35 mL of anhydrous methanol solution. After stirring evenly, add 310 mg of thioacetamide and continue to mix and stir for half an hour; then transfer the above mixture to a 50 mL stainless steel autoclave with a polytetrafluoroethylene liner, transfer it to an oil bath and stir and heat at 120 °C for 2 hours; cool to room temperature, wash alternately with deionized water and absolute ethanol 3 times, and dry in vacuum at 60 °C to obtain ZnIn2S4 nanosheet material.

[0036] (2) Preparation of phosphate-functionalized ZnIn2S4 nanosheets Weigh 24 mg of sodium dihydrogen phosphate, 24 mg of potassium metaphosphate, 12 mg of ammonium hydrogen phosphate and 12 mg of ammonium pyrophosphate respectively and add them to 25 mL of deionized water. Stir for 20 min until completely dissolved, then add 300 mg of ZnIn2S4 to the above solution respectively. Ultrasonicate the mixed suspension for 30 min, then continue to stir for 1 h, and put the obtained solution into an oven at 80 °C and heat for 10 h until completely dry to obtain different phosphate-functionalized ZnIn2S4 nanosheets.

[0037] (3) Preparation of NiPc monolayer-modified ZnIn2S4 nanosheet material Weigh 220 mg of different phosphate-functionalized ZnIn2S4 nanosheets respectively, add them to 35 mL of anhydrous methanol, stir for 30 min, then add 11 mg of nickel chloride, 5 mg of 4-nitrophthalonitrile and 2 mg of ammonium molybdate respectively, ultrasonicate for 10 min, and then stir for 30 min until evenly dispersed. Finally, put it into an oven at 150 °C and heat for 10 h, cool to room temperature, wash alternately with deionized water and absolute ethanol 3 times, and dry in vacuum at 60 °C for 8 h to finally obtain NiPc monolayer-modified ZnIn2S4 nanosheet photocatalyst.

[0038] The method is the same as the above steps. Only in step (3), cobalt chloride or copper chloride is used to replace nickel chloride respectively, then CuPc-modified ZnIn2S4 nanosheets or CoPc-modified ZnIn2S4 nanosheets are obtained respectively.

[0039] In these preferred embodiments, performance comparison is carried out. Finally, sodium dihydrogen phosphate is used for phosphate, and nickel phthalocyanine is used for metal phthalocyanine.

[0040] As shown in Figure 1

[0040] , the XRD data of the ZnIn2S4 / NiPc composite material show that the diffraction peaks at 2-Theta of 21.60°, 27.61°, 30.45° and 47.33° correspond to the (006), (102), (104) and (110) planes of hexagonal ZnIn2S4 (PDF#65-2023), respectively. Since the content of NiPc in the composite material is relatively low, no obvious peak intensity is shown. As shown in Figure 2 -a is the TEM image of the ZnIn2S4 / NiPc composite material, and it can be seen that the composite material is still ultrathin nanosheets. And Figure 2 -b shows that the lattice fringe with an interplanar spacing of 0.32 nm belongs to the (102) plane of ZnIn2S4, which proves that the crystal phase does not change after the combination of ZnIn2S4 and NiPc. However, due to the high dispersion of NiPc, it is difficult to directly observe the lattice fringe of NiPc from the figure. But in Figure 3 it can be observed that the loading of NiPc increases the light absorption of the ZnIn2S4 / NiPc heterojunction in the visible and near-infrared regions, improving the light absorption efficiency of the catalyst for sunlight.

[0041] Mix 50 mg of the ZnIn2S4 / NiPc photocatalyst prepared in Example 1, 73 mL of deionized water and 7 mL of benzyl alcohol evenly, and then place it in a photocatalytic reactor. Evacuate and pass cooling water to maintain 298 K. Use a 300 W xenon lamp equipped with an AM1.5G filter as the light source and conduct the experiment on a fully automatic online analysis nanomaterial testing system.

[0042] As shown in Figure 4 、 5 the hydrogen evolution rate and benzyl alcohol rate diagram of the ZnIn2S4 nanosheet material modified with a monolayer of NiPc. It can be seen from the figure that the hydrogen production rate of the ZnIn2S4 / NiPc heterojunction photocatalyst is 15.88 mmol g -1 h -1 -1, which is 8.1 times that of ZnIn2S4, and the selectivity is as high as 98%, which is about 4.7 times that of ZnIn2S4. The improvement multiples and selectivity of the present invention are higher than those of most ZnIn2S4-based composite materials. And as shown in Figure 6 5 , the hydrogen evolution rate and benzyl alcohol rate of the ZnIn2S4 nanosheet material modified with a monolayer of NiPc are much higher than those of the ZnIn2S4 nanosheet modified with CuPc or the ZnIn2S4 nanosheet modified with CoPc.

[0043] As shown in Figure 7As shown, the prepared ZnIn2S4 / NiPc composite material was subjected to a cyclic stability test. After 5 cycles of testing, with each cycle lasting 4 hours, the hydrogen production rate could still reach 15.12 mmol g -1 h -1 . At the same time, the selectivity and conversion rate of benzyl alcohol were as high as 95% and 89% respectively, indicating that the composite material has good photocatalytic stability and is conducive to large-scale application.

[0044] The above-mentioned embodiments are only preferred embodiments cited to fully illustrate the present invention. Those skilled in the art can make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Equivalent substitutions or transformations made by those skilled in the art on the basis of the present invention are all within the protection scope of the present invention. The protection scope of the present invention is subject to the claims.

Claims

1. A preparation method of a NiPc monolayer-modified ZnIn2S4 nanosheet photocatalyst, characterized in that, It includes the following steps: Step 1. Preparation of phosphate-functionalized ZnIn2S4 nanosheets: Uniformly disperse ZnIn2S4 nanosheets into a phosphate-containing solution, and dry it to obtain phosphate-functionalized ZnIn2S4 nanosheets; Step 2. Preparation of a photocatalyst of ZnIn2S4 nanosheets modified with a nickel phthalocyanine monolayer: First, uniformly disperse the phosphate-functionalized ZnIn2S4 nanosheets in a methanol solution, then add nickel chloride, 4-nitrophthalonitrile, and ammonium molybdate, ultrasonicate until dissolved, then stir until evenly dispersed, and finally obtain a ZnIn2S4 nanosheet photocatalyst modified with a NiPc monolayer through a solvothermal reaction, abbreviated as ZnIn2S4 / NiPc composite material.

2. The preparation method of a NiPc monolayer-modified ZnIn2S4 nanosheet photocatalyst according to claim 1, wherein In the above Step 1, the mass ratio of ZnIn2S4 nanosheets to phosphate is 1 - 4:0.1 - 0.4; the drying temperature is 60~90 °C, and the time is 4~24 h.

3. The preparation method of a NiPc monolayer-modified ZnIn2S4 nanosheet photocatalyst according to claim 2, characterized in that, The phosphate mentioned above is selected from any one or a combination of monohydrogen phosphates, dihydrogen phosphates, phosphates, metaphosphates, pyrophosphates, and polyphosphates.

4. The preparation method of a NiPc monolayer-modified ZnIn2S4 nanosheet photocatalyst according to claim 1, characterized in that, In the above Step 2, the mass ratio of nickel chloride, 4-nitrophthalonitrile, and ammonium molybdate is 6 - 15:1 - 10:2 - 20, and the metal phthalocyanine is selected from any one of nickel phthalocyanine, cobalt phthalocyanine, and copper phthalocyanine.

5. The preparation method of a NiPc monolayer modified ZnIn2S4 nanosheet photocatalyst according to claim 1, characterized in that In the above Step 2, the ultrasonic power is 200~500 W, and the ultrasonic time is 20~40 min; the solvothermal reaction time is 5~14 h at a temperature of 90~150 °C.

6. A NiPc monolayer-modified ZnIn2S4 nanosheet photocatalyst prepared by the method according to any one of claims 1-5, characterized in that, The XRD data of the ZnIn2S4 / NiPc composite material has characteristic diffraction peaks at 2-Theta of 21°±1°, 27°±1°, 30°±1°, and 47°±1°.

7. A photocatalyst having light absorption in the visible and near-infrared regions, characterized in that, The photocatalyst mentioned above is the ZnIn2S4 nanosheet photocatalyst modified with a NiPc monolayer as described in Claim 6.

8. Application of a ZnIn2S4 nanosheet photocatalyst modified with a NiPc monolayer prepared by the method described in Claim 6 in a photocatalytic reaction.

9. A photocatalyst for photocatalytic oxidation of benzyl alcohol to produce benzaldehyde and coupled hydrogen production, characterized in that, The photocatalyst mentioned above is the ZnIn2S4 nanosheet photocatalyst modified with a NiPc monolayer as described in Claim 6.

10. The photocatalyst according to claim 9, characterized in that, The steps of photocatalytic oxidation of benzyl alcohol to produce benzaldehyde and coupled hydrogen production include the following: Step 1. Add a certain amount of deionized water into a photocatalytic reactor, then add the ZnIn2S4 nanosheet photocatalyst modified with a NiPc monolayer, and then add benzyl alcohol, and disperse evenly; Step 2. Seal and degas the reactor to ensure that the reactor is in a negative pressure state; Step 3. Use a xenon lamp equipped with an AM1.5 filter to irradiate the reactor, and additionally apply a stirrer and cooling water to prepare benzaldehyde and hydrogen.

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