Preparation method of S-mechanism In (OH) 3-xSx quantum dot / (Zn, In) S nanosheet assembly heterojunction

Abstract

The invention discloses a preparation method of an S-mechanism In (OH) 3-xSx quantum dot / (Zn, In) S nanosheet assembly heterojunction, which comprises the following steps: taking Zn (NO3) 2, In (NO3) 3, thiosemicarbazide and urea as raw materials, transferring a mixed aqueous solution of the raw materials into a high-pressure kettle, carrying out one-step hydrothermal reaction to generate S-doped In (OH) 3-quantum dots which grow in situ and are interwoven with In-doped ZnS nanosheets, and preparing the S-mechanism In (OH) 3-xSx quantum dot / (Zn, In) S nanosheet assembly heterojunction. And forming a 0D / 2D heterostructure and carrying out self-assembly to obtain the S-mechanism In (OH) 3-xSx quantum dot / (Zn, In) S nanosheet assembly heterojunction. The self-assembly body with the hierarchical structure endows the nanosheet with more exposed active sites, S mechanism charge transfer is realized, and the nanosheet has higher charge transfer efficiency and strong oxidation-reduction capability. The preparation method of the heterojunction assembly is low in cost and simple in process. The photocatalyst shows excellent photocatalytic activity and stability when being used in the aspects of photocatalytic decomposition of water to produce hydrogen, photocatalytic formaldehyde degradation, environment purification and the like.

Description

Technical Field

[0001] The present invention belongs to the fields of new energy and environmental purification, and relates to a photocatalyst for the preparation of new hydrogen energy and environmental purification, and in particular to a photocatalyst assembled by heterojunction nanosheets and a preparation method thereof. Specifically, it relates to a preparation method of an S-scheme In(OH) 3-x S x quantum dot / (Zn,In)S nanosheet assembly heterojunction. Background Art

[0002] Using visible light to decompose water to produce hydrogen by photocatalysis at room temperature is one of the ideal methods to solve global environmental pollution and current energy demand. However, most photocatalysts face challenges in matching the solar spectrum. Narrow-bandgap semiconductor photocatalysts, which can be directly excited to generate photo-generated carriers in the visible light range, have attracted much attention in recent years. However, semiconductor photocatalysts are usually only responsive to photons of specific wavelengths due to their inherent band characteristics, making it difficult for many semiconductor photocatalysts to be excited by visible light to generate photo-generated electrons and holes. At the same time, there are also defects such as a high recombination rate of photo-generated electron-hole pairs.

[0003] Among various photocatalysts, ZnS is inexpensive, non-toxic, and has unique electron transport characteristics. Since ZnS can rapidly generate charges under light excitation and the excited electrons have good reducing ability, this material is still an attractive candidate for photocatalysts. However, the bandgap of ZnS is relatively wide and its response to visible light is weak, which limits its application. Element doping is an effective strategy to further improve the photocatalytic efficiency of ZnS, and forming a heterojunction is another effective strategy to further improve the photocatalytic efficiency of ZnS

[0004] In recent years, indium hydroxide (In(OH)3) has become a promising catalyst due to its good reduction potential and excellent chemical stability in photocatalytic hydrogen production. Doping and compounding In(OH)3 with ZnS to prepare a heterojunction can effectively improve the visible light photocatalytic efficiency. However, the currently prepared In(OH)3 / ZnS heterojunction photocatalyst either has low utilization of visible light, or ZnS is prone to photocorrosion, or it is difficult to construct an S-scheme heterojunction, resulting in low separation efficiency of photo-generated electrons and holes and inability to obtain high redox ability. Summary of the Invention

[0005] In view of the disadvantages of the In(OH)3 / ZnS heterojunction photocatalyst prepared in the prior art, such as easy recombination of photo-generated carriers, low visible light utilization rate, easy photocorrosion, insufficient stability, the need for multi-step reactions for preparation, difficulty in preparing heterojunctions by one-step method, and inability to obtain high redox ability, etc., a heterojunction photocatalyst with an S mechanism is proposed. Indium hydroxide quantum dots doped with sulfur are embedded in indium-doped ZnS nanosheets to obtain In(OH) 3-x S x / (Zn,In)S heterojunction. This heterojunction nanosheet photocatalyst can be directly prepared by one-step reaction and assembled into a hierarchical structure assembly. The present invention is realized by the following technical solutions:

[0006] A preparation method of an S-mechanism In(OH) 3-x S x quantum dot / (Zn,In)S nanosheet assembly heterojunction, characterized in that the assembly heterojunction is formed by embedding In(OH) 3-x S x quantum dots on (Zn,In)S nanosheets to form a tightly coupled heterojunction, and in-situ assembled into a hierarchical structure assembly. The migration of photo-generated carriers in the heterojunction follows the S mechanism; the S-mechanism In(OH) 3-x S x quantum dot / (Zn,In)S nanosheet assembly heterojunction is obtained by synchronous doping and coupling, and is formed by S-doped In(OH) 3- quantum dots growing in-situ and intertwining with indium-doped ZnS nanosheets to form a 0D / 2D heterostructure. The assembly heterojunction has higher charge migration efficiency and strong redox ability. The specific preparation method includes the following steps: (1) Dissolve 0.2 - 2.0 mmol of Zn(NO3)2, 0.01 - 0.5 mmol of In(NO3)3, 0.2 - 4.0 mmol of thiosemicarbazide, and 0.01 - 0.15 g of urea in 30 mL of water, and stir for 10 - 45 min;

[0007] (2) Transfer the solution obtained in step (1) to an autoclave and heat it in an oven at 100 - 220 °C for 6 - 24 h. After the reaction is completed, cool it to room temperature, and wash the precipitate with deionized water and absolute ethanol respectively to obtain In(OH) 3-x S x quantum dot / (Zn,In)S nanosheet assembly heterojunction.

[0008] The advantages of the present invention are as follows: The preparation method has low cost and simple process; the sulfur-doped In(OH)3 quantum dots constructed by one-step method are embedded on the surface of indium-doped ZnS nanosheets to form In(OH) 3-x S x / (Zn,In)S heterojunction nanosheets. S-doped In(OH) 3- Quantum dots grow in-situ and intertwine with In-doped ZnS nanosheets to form a 0D / 2D heterostructure. The S-scheme heterojunction constructed based on quantum dots has close interfacial contact, efficient charge separation, exhibits high redox ability, abundant active sites, and visible light response. At the same time, the bandgap width is adjusted by introducing doped atoms to enable it to absorb visible light. The prepared In-doped ZnS has a two-dimensional nanosheet assembly structure, increasing the reaction area. S-doped In(OH)3 modifies In-doped ZnS in the form of quantum dots to form a heterojunction. The migration of photo-generated carriers in the heterojunction follows the S mechanism, endowing the photocatalyst with higher charge migration efficiency and strong redox ability. It shows good photocatalytic activity and stability in aspects such as photocatalytic water splitting for hydrogen production, photocatalytic degradation of formaldehyde and harmful gases, environmental purification, inhibition of the generation of bacteria and molds, and photocatalytic degradation of organic wastewater. Description of the Drawings

[0009] Figure 1 S-scheme In(OH) prepared by the method described in Example 1 3-x S x XRD spectra and PDF standard spectra of the S-scheme In(OH) quantum dot / (Zn,In)S nanosheet assembly heterojunction and the sample of the comparative example.

[0010] Figure 2 S-scheme In(OH) prepared by the method described in Example 1 3-x S x SEM photograph of the S-scheme In(OH) quantum dot / (Zn,In)S nanosheet assembly heterojunction

[0011] Figure 3 S-scheme In(OH) prepared by the method described in Example 1 3-x S x TEM photograph of the S-scheme In(OH) quantum dot / (Zn,In)S nanosheet assembly heterojunction.

[0012] Figure 4 S-scheme In(OH) prepared by the method described in Example 1 3-x S x HRTEM photograph of the S-scheme In(OH) quantum dot / (Zn,In)S nanosheet assembly heterojunction.

[0013] Figure 5 S-scheme In(OH) prepared by the method described in Example 1 3-x S x STEM ADF photograph and EDS element distribution map of the S-scheme In(OH) quantum dot / (Zn,In)S nanosheet assembly heterojunction.

[0014] Figure 6S-scheme In(OH) prepared by the method described in Example 1 3-x S x Calculation diagram of the band gap width of the quantum dot / (Zn,In)S nanosheet assembly heterojunction and the comparative sample

[0015] Figure 7 S-scheme In(OH) prepared by the method described in Example 1 3-x S x Relationship diagram of the photocatalytic hydrogen production amount (a) and hydrogen production rate (b) of the quantum dot / (Zn,In)S nanosheet assembly heterojunction and the comparative sample with the reaction time

[0016] Figure 8 S-scheme In(OH) prepared by the method described in Example 1 3-x S x Cyclic stability test diagram of photocatalytic hydrogen production of the quantum dot / (Zn,In)S nanosheet assembly heterojunction

[0017] Figure 9 S-scheme In(OH) prepared by the method described in Example 1 3-x S x Relationship diagram of the fluorescence intensity of the hydroxyl radical capture test of the quantum dot / (Zn,In)S nanosheet assembly heterojunction and the comparative sample with the irradiation time

[0018] Figure 10 S-scheme In(OH) prepared by the method described in Example 1 3-x S x Schematic diagram of the photocatalytic S-scheme of the quantum dot / (Zn,In)S nanosheet assembly heterojunction

[0019] Figure 11 S-scheme In(OH) prepared by the method described in Example 1 3-x S x Relationship diagram of the photocatalytic degradation rate of formaldehyde of the quantum dot / (Zn,In)S nanosheet assembly heterojunction and the comparative sample with time Detailed implementation mode

[0020] The present invention will be further described in detail below through examples

[0021] Example 1

[0022] (1) Dissolve 0.8 mmol of Zn(NO3)2, 0.2 mmol of In(NO3)3, 1.6 mmol of thiosemicarbazide and 0.05 g of urea in 30 mL of water and stir for 30 min

[0023] (2) Transfer the solution obtained in step (1) to an autoclave and heat it in an oven at 180 °C for 12 h. After the reaction is completed, cool it to room temperature and wash the precipitate with deionized water and absolute ethanol respectively to obtain In(OH) 3-x S x Quantum dot / (Zn,In)S nanosheet assembly heterojunction.

[0024] Example 2:

[0025] (1) Dissolve 0.8 mmol of Zn(NO3)2, 0.1 mmol of In(NO3)3, 1.6 mmol of thiosemicarbazide and 0.04 g of urea in 30 mL of water and stir for 30 min;

[0026] (2) Transfer the solution obtained in step (1) to an autoclave and heat it in an oven at 150 °C for 16 h. After the reaction is completed, cool it to room temperature and wash the precipitate with deionized water and absolute ethanol respectively to obtain In(OH) 3-x S x Quantum dot / (Zn,In)S nanosheet assembly heterojunction.

[0027] Example 3:

[0028] (1) Dissolve 0.4 mmol of Zn(NO3)2, 0.01 mmol of In(NO3)3, 1.6 mmol of thiosemicarbazide and 0.02 g of urea in 30 mL of water and stir for 30 min;

[0029] (2) Transfer the solution obtained in step (1) to an autoclave and heat it in an oven at 200 °C for 10 h. After the reaction is completed, cool it to room temperature and wash the precipitate with deionized water and absolute ethanol respectively to obtain In(OH) 3-x S x Quantum dot / (Zn,In)S nanosheet assembly heterojunction.

[0030] Example 4:

[0031] (1) Dissolve 1.2 mmol of Zn(NO3)2, 0.02 mmol of In(NO3)3, 1.6 mmol of thiosemicarbazide and 0.05 g of urea in 30 mL of water and stir for 30 min;

[0032] (2) Transfer the solution obtained in step (1) to an autoclave and heat it in an oven at 160 °C for 16 h. After the reaction is completed, cool it to room temperature and wash the precipitate with deionized water and absolute ethanol respectively to obtain In(OH) 3-x S x Quantum dot / (Zn,In)S nanosheet assembly heterojunction.

[0033] Example 5:

[0034] (1) Dissolve 0.2 mmol of Zn(NO3)2, 0.01 mmol of In(NO3)3, 0.2 mmol of thiosemicarbazide and 0.01 g of urea in 30 mL of water and stir for 45 min;

[0035] (2) Transfer the solution obtained in step (1) to an autoclave and heat it in an oven at 100 °C for 24 h. After the reaction is completed, cool it to room temperature and wash the precipitate with deionized water and absolute ethanol respectively to obtain In(OH) 3-x S x Quantum dots / (Zn,In)S nanosheet assembly heterojunction.

[0036] Example 6:

[0037] (1) Dissolve 1.0 mmol of Zn(NO3)2, 0.1 mmol of In(NO3)3, 2.0 mmol of thiosemicarbazide and 0.12 g of urea in 30 mL of water and stir for 10 min;

[0038] (2) Transfer the solution obtained in step (1) to an autoclave and heat it in an oven at 160 °C for 10 h. After the reaction is completed, cool it to room temperature and wash the precipitate with deionized water and absolute ethanol respectively to obtain In(OH) 3-x S x Quantum dots / (Zn,In)S nanosheet assembly heterojunction.

[0039] Example 7:

[0040] (1) Dissolve 1.6 mmol of Zn(NO3)2, 0.3 mmol of In(NO3)3, 3.2 mmol of thiosemicarbazide and 0.10 g of urea in 30 mL of water and stir for 45 min;

[0041] (2) Transfer the solution obtained in step (1) to an autoclave and heat it in an oven at 220 °C for 6 h. After the reaction is completed, cool it to room temperature and wash the precipitate with deionized water and absolute ethanol respectively to obtain In(OH) 3-x S x Quantum dots / (Zn,In)S nanosheet assembly heterojunction.

[0042] Comparative Example 1:

[0043] (1) Dissolve 0.8 mmol of In(OH)3, 0.2 mmol of thiosemicarbazide and 0.05 g of urea in 30 mL of water and stir for 30 min;

[0044] (2) Transfer the solution obtained in step (1) to an autoclave and heat it in an oven at 180 °C for 12 h. After the reaction is completed, cool it to room temperature and wash the precipitate with deionized water and absolute ethanol respectively to obtain In(OH) 3-x S x .

[0045] Comparative Example 2:

[0046] (1) Dissolve 0.8 mmol of Zn(NO3)2, 0.02 mmol of In(NO3)3 and 1.6 mmol of thiosemicarbazide in 30 ml of water and stir for 30 min;

[0047] (2) Transfer the solution obtained in step (1) to an autoclave and heat it in an oven at 180 °C for 12 h. After the reaction is completed, cool it to room temperature and wash the precipitate with deionized water and absolute ethanol respectively to obtain (Zn,In)S.

[0048] Comparative Example 3:

[0049] (1) Dissolve 0.8 mmol of Zn(NO3)2 and 1.6 mmol of thiosemicarbazide in 30 ml of water and stir for 30 min;

[0050] (2) Transfer the solution obtained in step (1) to an autoclave and heat it in an oven at 180 °C for 12 h. After the reaction is completed, cool it to room temperature and wash the precipitate with deionized water and absolute ethanol respectively to obtain ZnS.

[0051] Comparative Example 4

[0052] (1) Dissolve 0.8 mmol of In(OH)3 and 0.05 g of urea in 30 mL of water and stir for 30 min,

[0053] (2) Transfer the solution obtained in step (1) to an autoclave and heat it in an oven at 180 °C for 12 h. After the reaction is completed, cool it to room temperature and wash the precipitate with deionized water and absolute ethanol respectively to obtain the white product In(OH)3.

[0054] Figure 1 For the S-based In(OH) prepared by the method described in Example 1 3-x S x XRD spectra and PDF standard spectra of the S mechanism In(OH) 3-x S xThe diffraction peaks at 22.3°, 31.7°, 35.7°, 39.4°, 45.6°, 51.3°, and 56.8° correspond to the (200), (220), (310), (222), (400), (420), and (422) crystal planes of In(OH)3, respectively. Compared with the standard diffraction PDF#76-1464 of In(OH)3, the positions of the diffraction peaks shift slightly to the left, and the interplanar spacing becomes larger, indicating that larger sulfur atoms are incorporated between the crystal planes of In(OH)3. The peak positions of ZnS at 28.6°, 47.6°, and 56.4° correspond to the (111), (220), and (311) crystal planes in the standard card PDF#05-0566 of zinc blende structure ZnS. After doping with In, due to the difference in atomic radii between Zn and In, a peak shift to a lower angle is observed in the (111) crystal plane.

[0055] Figure 2 For the S-scheme In(OH) prepared in Example 1 3-x S x SEM image of the S-scheme In(OH) Figure 2 It can be seen that In(OH) 3-x S x / (Zn,In)S is a hierarchical structure assembly composed of ultrathin nanosheets.

[0056] Figure 3 For the S-scheme In(OH) prepared in Example 1 3-x S x TEM image of the S-scheme In(OH) Figure 3 It can be seen that the nanosheets are semi-transparent, indicating their ultrathin structure. In(OH)3 is embedded on the surface of ZnS ultrathin nanosheets in the form of quantum dots. Due to their unique quantum size effect, the quantum dots can effectively promote the rapid migration of electrons. This unique hierarchical structure can, on the one hand, provide a larger contact area with the electrolyte, enabling the material to come into more sufficient contact with the reactants during the photocatalytic reaction process and improving the reaction efficiency. On the other hand, this structure is conducive to capturing light, enhancing the material's ability to absorb photons, promoting the separation and migration of carriers, and improving the photocatalytic activity.

[0057] Figure 4 For the S-scheme In(OH) prepared in Example 1 3-x S x HRTEM image of the S-scheme In(OH) 3-x Sx Quantum dots, the crystal plane spacing of 0.398 nm corresponds to the (200) crystal plane of In(OH)3, and the crystal plane spacing of 0.281 nm corresponds to the (220) crystal plane of In(OH)3. In addition, it can be seen from the figure that there is a tight interfacial contact between the ZnS nanosheets and the In(OH)3 quantum dots, which is beneficial to the rapid transfer of photo-generated electrons and holes, thereby improving the photocatalytic activity.

[0058] Figure 5 The S-mechanism In(OH) prepared in Example 1 3-x S x STEM ADF photograph and elemental distribution photograph of the quantum dot / (Zn,In)S nanosheet assembly heterojunction. The ADF photograph more clearly shows In(OH) 3-x S x Ultra-thin nanosheet structure of the quantum dot / (Zn,In)S. The elemental distribution map can clearly show the presence of Zn, S, In, and O elements, and it can be seen that In(OH)3, as a form of surface modification of ZnS nanosheets, is uniformly distributed on the surface of ZnS.

[0059] Figure 6 The S-mechanism In(OH) prepared in Example 1 3-x S x Calculation diagram of the band gap width of the quantum dot / (Zn,In)S nanosheet assembly heterojunction and the sample of the comparative example. It can be seen from the figure that for Comparative Example 1 In(OH) 3-x S x 、Comparative Example 2 (Zn,In)S, Comparative Example 3 ZnS, and In(OH)3 have band gaps of 3.24 eV, 2.99 eV, 3.38 eV, and 3.64 eV, respectively. By comparison, after doping, In(OH) 3-x S x and (Zn,In)S have significantly narrower band gap widths than In(OH)3 and ZnS, which can improve the absorption of visible light.

[0060] Figure 7 The S-mechanism In(OH) prepared by the method described in Example 1 3-x S x Relationship diagram between the photocatalytic water splitting hydrogen production amount and time of the quantum dot / (Zn,In)S nanosheet assembly heterojunction and the sample of the comparative example. It can be seen that using the Na2SO3-Na2S solution as a sacrificial agent for the hydrogen production experiment, the S-mechanism In(OH) obtained in Example 1 3-x S x The hydrogen production rate of the quantum dot / (Zn,In)S nanosheet assembly heterojunction reaches 353.35 μmol g -1 h -1, nearly 5 times that of Comparative Example 3. This significant performance improvement indicates that In(OH) 3-x S x plays a crucial role in (Zn,In)S in the composite system.

[0061] Figure 8 For the S-scheme In(OH) 3-x S x quantum dots / (Zn,In)S nanosheet assembly heterojunction photocatalytic water splitting hydrogen production cyclic stability experimental results. The experimental results show that during the 5-cycle test for 30 hours, the hydrogen evolution activity did not decrease significantly, indicating that the heterojunction photocatalyst achieved good cyclic stability while maintaining high catalytic activity.

[0062] Figure 9 For the S-scheme In(OH) 3-x S x Relationship between the fluorescence intensity and irradiation time of the hydroxyl capture test for the quantum dots / (Zn,In)S nanosheet assembly heterojunction and the comparative sample. Using terephthalic acid as a molecular probe, it can specifically react with the ·OH radicals generated on the catalyst surface to form products with fluorescence characteristics. Since the standard redox reaction potential for ·OH generation is 1.99 V (vs NHE), it can be seen that In(OH) 3-x S x and Zn(In,S) also showed fluorescence peaks, but the intensity was significantly lower than that of In(OH) 3-x S x / Zn(In,S), indicating that the composite is more conducive to the generation of ·OH radicals.

[0063] Figure 10 For the S-scheme In(OH) 3-x S x Schematic diagram of the photocatalytic S-scheme for the quantum dots / (Zn,In)S nanosheet assembly heterojunction. According to the band gap width and hydroxyl capture test, In(OH) 3-x S x quantum dots / (Zn,In)S nanosheet heterojunction photocatalytic process follows the S-scheme.. Under light illumination, the photogenerated electrons at the S heterojunction interface transfer from In(OH)3-xSx to Zn(In,S) and accumulate on the surface of Zn(In,S), and the H + rapidly reduces to generate H2 on the surface of the catalyst, and at In(OH) 3-x S xPhotogenerated holes are left on the surface, and the sacrificial agent Na2SO3-Na2S is oxidized to form Na2SO4. The S-scheme heterostructure promotes the directional transport of photo-generated electrons in the composite material, realizing the effective separation of photo-generated carriers.

[0064] Figure 11 S-scheme In(OH) prepared by the method described in Example 1 3-x S x Relationship diagram of the degradation rate of formaldehyde by the S-scheme In(OH) 3-x S x Quantum dot / (Zn,In)S nanosheet assembly heterojunction photocatalyst has a formaldehyde purification rate of 90.6% in the degraded gas at 90 min, indicating that the S-scheme In(OH) 3-x S x Quantum dot / (Zn,In)S nanosheet assembly heterojunction photocatalyst can effectively remove harmful formaldehyde gas in the air.

[0065] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, substitutions, simplifications, etc. made without departing from the principle and process of the present invention are equivalent replacements and should be included in the protection scope of the present invention.

Claims

1. A S mechanism In(OH) 3-x S x A method for preparing a quantum dot / (Zn, In)S nanosheet assembly heterojunction, characterized in that: The assembled heterojunction is composed of In(OH) 3-x S x Quantum dots are embedded on (Zn, In)S nanosheets to form a tightly coupled heterojunction, and are in situ assembled into a hierarchical structure assembly. The migration of photogenerated carriers in the heterojunction follows the S mechanism; the S mechanism In(OH) 3-x S x The quantum dot / (Zn,In)S nanosheet assembly heterojunction is obtained by simultaneous doping and coupling. 3- The quantum dots are grown in situ and intertwined with In-doped ZnS nanosheets to form a 0D / 2D heterostructure. The assembled heterojunction has higher charge transfer efficiency and strong redox ability. The preparation method specifically includes the following steps: (1) Dissolve 0.2-2.0 mmol Zn(NO3)2, 0.01-0.5 mmol In(NO3)3, 0.2-4.0 mmol thiosemicarbazide and 0.01-0.15 g urea in 30 mL water and stir for 10-45 min; (2) The solution obtained in step (1) is transferred to an autoclave and heated in an oven at 100-220° C. for 6-24 h. After the reaction is completed, the solution is cooled to room temperature and the precipitate is washed with deionized water and anhydrous ethanol, respectively, to obtain a S-doped In(OH)3 quantum dot / In-doped ZnS nanosheet assembly heterojunction.

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