A MoC quantum dot / zinc indium sulfide composite photocatalyst with lattice strain, its preparation method and application

Abstract

The present invention relates to the technical field of photocatalytic materials, and particularly relates to a MoC quantum dot / zinc indium sulfide composite photocatalyst with lattice strain, and a preparation method and application thereof. The preparation method comprises the following steps: Step 1, preparation of MoC quantum dots with lattice strain: Melamine and ammonium heptamolybdate are dissolved in methanol and deionized water; the ammonium heptamolybdate solution is added dropwise to the vigorously stirred melamine suspension, and the mixture is evaporated to dryness by water bath; the white precipitate is reacted at 700 °C for 1-3 hours; Step 2, in-situ growth and compounding of the MoC quantum dots and zinc indium sulfide to obtain the composite photocatalyst. The present invention realizes the controllable preparation of MoC quantum dots with different lattice strains, which helps to improve the energy level structure of the nanomaterials, thereby affecting the charge transfer efficiency. Moreover, the preparation process does not involve dangerous chemicals, the preparation is safe, the raw materials are cheap and easily available, and the cost is low. Under simulated sunlight, the composite photocatalyst can stably and continuously produce hydrogen for 144 hours.

Description

Technical Field

[0001] The present invention relates to the technical field of photocatalytic materials, and particularly relates to a MoC quantum dot / zinc indium sulfide composite photocatalyst with lattice strain, a preparation method thereof, and an application thereof. Background Art

[0002] Photocatalytic water splitting is considered to be one of the important ways to obtain green hydrogen, and has great application potential in the future field of replacing non-renewable energy. Zinc indium sulfide (ZnIn₂S₄) has attracted wide attention due to its suitable energy band structure and good visible light absorption. However, zinc indium sulfide has a relatively serious carrier recombination phenomenon in photocatalysis, reducing the utilization rate of carriers and resulting in a decline in the photocatalytic hydrogen evolution performance of zinc indium sulfide. In addition, the serious photocorrosion phenomenon will also lead to a decline in the stability of zinc indium sulfide.

[0003] MoC (molybdenum carbide) is a type of transition metal carbide with noble metal-like properties. Due to its low price, high electronic conductivity, and good chemical stability, it has been applied to many photo / electrocatalytic reactions. However, due to the large surface energy of quantum dot MoC, it is extremely easy to cause agglomeration phenomena in catalytic reactions, reducing the catalytic performance and long-cycle stability. Therefore, it is often necessary to load it on a substrate to construct a composite photocatalyst. The document of Chinese Patent "CN112591754A" discloses "a preparation method of a carbon nanocage-coupled molybdenum carbide quantum dot nanocomposite", the reaction conditions are harsh, requiring a high temperature of over 850 °C, with large energy consumption, and most of the obtained MoC is in the form of large-sized bulk morphology, which is not conducive to the separation of charges on nanoscale photocatalysts (such as zinc indium sulfide). The document of Chinese Patent "CN109621998A" discloses "a three-dimensional mesoporous carbon supported molybdenum carbide, a preparation method thereof, and an application thereof", the preparation method is relatively cumbersome, time-consuming, the calcination process uses reducing gas hydrogen, which has certain risks, and in addition, the final acid soaking process uses highly corrosive hydrofluoric acid. At the same time, the synthesized low-dimensional MoC materials are often accompanied by surface carbon coating, which will affect the entry of water molecules and the escape of hydrogen molecules during the reaction process, and further affect the performance of photocatalytic water splitting for hydrogen evolution.

[0004] The document of Chinese patent "CN115608389A" discloses "a MoC@3D graphite carbon@zinc indium sulfide photocatalytic hydrogen production material, its preparation method and application". MoC is used as a carrier to be compounded with zinc indium sulfide. The preparation steps of MoC are complex and time-consuming. The relatively high solvothermal temperature is not conducive to the dispersion of quantum dot MoC, and a higher temperature will cause stress release on MoC. Moreover, the obtained molybdenum carbide still has carbon present. Therefore, using it as a carrier for zinc indium sulfide will affect the transmission of molecules in the reaction, reducing the long-cycle stability of the photocatalytic water splitting hydrogen evolution performance and failing to maximize the hydrogen evolution performance of the composite photocatalyst. The photocatalyst obtained by combining the two does not achieve the expected improvement effect. Additionally, carcinogenic organic substances are used in the preparation, and the safety of the preparation process is poor. Summary of the Invention

[0005] The object of the present invention is to provide a composite photocatalyst of MoC quantum dots / zinc indium sulfide with lattice strain, its preparation method and application, so as to solve the problems existing in the prior art that using MoC as a carrier for zinc indium sulfide will affect the transmission of molecules in the reaction, reduce the long-cycle stability of the photocatalytic water splitting hydrogen evolution performance, the photocatalyst obtained by combining the two does not achieve the expected improvement effect, and the safety of the preparation process is poor.

[0006] To achieve the above object, the object of the present invention is realized through the following technical solutions: A preparation method of a composite photocatalyst of MoC quantum dots / zinc indium sulfide with lattice strain, comprising the following steps:

[0007] Step 1: Preparation of MoC quantum dots with lattice strain: Dissolve melamine and ammonium heptamolybdate in methanol and deionized water solutions respectively according to a certain mass ratio; then gradually add the ammonium heptamolybdate solution dropwise to the vigorously stirred melamine suspension, evaporate the mixed solution to dryness in a water bath to obtain a white precipitate; place the white precipitate in a tubular furnace, introduce an inert gas, and react at 700 °C for 1 - 3 hours to obtain molybdenum carbide MoC quantum dots with different lattice strain magnitudes.

[0008] Step 2: In-situ growth compounding of MoC quantum dots and zinc indium sulfide to prepare a composite photocatalyst.

[0009] Further, in the above Step 1, the mass ratio of melamine to ammonium heptamolybdate is (1 - 4):1.

[0010] Further, in the above Step 1, the water bath temperature is 60 - 80 °C.

[0011] Further, in the above Step 1, the inert gas is argon, nitrogen or helium, and the flow rate is 80 - 120 cm 3 / min.

[0012] Further, the specific steps of Step 2 are as follows:

[0013] First, disperse the MoC quantum dots in absolute ethanol by ultrasonic treatment, and then add zinc nitrate and indium nitrate pentahydrate; after complete dissolution, add thioacetamide, and prepare a suspension after stirring and dispersing.

[0014] Then, perform a solvothermal reaction on the suspension, react at 120 - 160 °C for 12 - 16 hours, and obtain a MoC quantum dot / zinc thiogallate composite photocatalyst with lattice strain after centrifugal washing and vacuum drying.

[0015] Further, in Step 2, in the suspension, the molar ratio of zinc nitrate, indium nitrate pentahydrate, and thioacetamide is 1:2:8.

[0016] Further, in Step 2, the mass ratio of the MoC quantum dots to the obtained zinc thiogallate is 1% - 5%, and the ultrasonic dispersion time is 5 - 10 minutes.

[0017] Further, a MoC quantum dot / zinc thiogallate composite photocatalyst with lattice strain prepared by the above preparation method.

[0018] Further, the above MoC quantum dot / zinc thiogallate composite photocatalyst with lattice strain is applied to the photocatalytic water splitting hydrogen production reaction under simulated sunlight.

[0019] Compared with the prior art, the significant advantages of the present invention are as follows:

[0020] (1) Under relatively mild conditions, the present invention prepares MoC in the form of quantum dots (3 - 10 nm), realizing the synthesis of MoC quantum dots with controllable lattice strain. The synthesis method is simple, operationally safe, green and efficient. By changing the dosage of the precursor and the reaction time, the controllable preparation of MoC quantum dots with different lattice strains can be achieved, which helps to improve the energy level structure of the nanomaterial, thereby affecting the charge transfer efficiency. Moreover, the preparation process does not involve dangerous chemicals, is safe to prepare, the raw materials are cheap and easily available, and the cost is low.

[0021] (2) The present invention first combines MoC quantum dots with lattice strain and zinc thiogallate to obtain a novel photocatalyst. In the obtained MoC quantum dot / zinc thiogallate composite photocatalyst with lattice strain, by optimizing different lattice strains, the charge transfer mode at the interface can be optimized, effectively suppressing the recombination of carriers, thereby greatly improving the long-cycle water splitting hydrogen production performance of the composite photocatalyst. Under simulated sunlight, the composite photocatalyst can stably and continuously produce hydrogen for 144 hours. The present invention regulates the energy level structure of MoC quantum dots through lattice strain, optimizes the interface electric field and the interface charge transfer mode between MoC and zinc thiogallate, reduces the recombination of carriers, and greatly improves the long-cycle stability of photocatalytic water splitting for hydrogen evolution.

[0022] (3) The present invention obtains a MoC quantum dot / zinc indium sulfide composite photocatalyst with lattice strain through an in-situ growth method. The preparation method is simple, which is beneficial to the dispersion of quantum dots. The short pretreatment time helps to maintain the lattice strain in the composite, thereby maximizing the performance of photocatalytic water splitting for hydrogen production.

[0023] (4) The product of the present invention can be applied to the photocatalytic water splitting hydrogen production reaction under simulated sunlight, realizing the efficient separation of carriers and long-term corrosion resistance. The prepared MoC quantum dot / zinc indium sulfide composite photocatalyst with lattice strain provides an idea for the construction of long-life photocatalytic hydrogen production catalysts, and at the same time opens up a new way for the design of other functional long-life photocatalysts containing quantum dots, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is the X-ray diffraction pattern (XRD) of three kinds of MoC quantum dots obtained in Example 1, Example 2 and Comparative Example 1 of the present invention;

[0025] Figure 2 It is the transmission electron microscope image (TEM) of three kinds of MoC quantum dots obtained in Example 1, Example 2 and Comparative Example 1 of the present invention;

[0026] Figure 3 It is the X-ray diffraction pattern (XRD) of four kinds of catalysts ZIS, L-MoC / ZIS, S-MoC / ZIS, and N-MoC / ZIS in Example 1, Example 2, Comparative Example 1 and Comparative Example 2 of the present invention;

[0027] Figure 4 It is the transmission electron microscope image (TEM) of four kinds of catalysts ZIS, L-MoC / ZIS, S-MoC / ZIS, and N-MoC / ZIS in Example 1, Example 2, Comparative Example 1 and Comparative Example 2 of the present invention;

[0028] Figure 5 It is the long-term cycling performance of photocatalytic water splitting hydrogen evolution of four kinds of catalysts ZIS, L-MoC / ZIS, S-MoC / ZIS, and N-MoC / ZIS in Example 1, Example 2, Comparative Example 1 and Comparative Example 2 of the present invention under simulated sunlight (100 mW / cm 2 )

[0029] Figure 6 It is the surface photovoltage spectrum (SPV) of three kinds of MoC quantum dot / zinc indium sulfide composite photocatalysts with different lattice strains in Example 1, Example 2 and Comparative Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] The present invention will be further described in detail below with reference to specific examples, but the embodiments of the present invention are not limited thereto. For process parameters not particularly noted, conventional techniques may be used.

[0031] One of the core ideas of the present invention is to prepare MoC quantum dots with lattice strain. The design idea is: add ammonium heptamolybdate solution dropwise to melamine suspension, evaporate the solution in a 60°C water bath, and then calcine the product under an inert gas atmosphere to obtain MoC quantum dots with lattice strain.

[0032] The second core of the present invention is to prepare and then ultrasonically disperse MoC quantum dots in anhydrous ethanol, add zinc nitrate, indium nitrate tetrahydrate and thioacetamide respectively, and then synthesize MoC quantum dots / sulfur indium zinc composite photocatalytic materials with lattice strain by solvent thermal method.

[0033] Example 1, a method for preparing a MoC quantum dot / sulfur indium zinc composite photocatalyst with lattice strain, comprising the following steps:

[0034] Step 1: Preparation of MoC quantum dots with lattice strain:

[0035] Dissolve 0.516g of melamine in 100mL of methanol and 0.516g of ammonium heptamolybdate in 50mL of deionized water. Then add the ammonium heptamolybdate solution dropwise to the vigorously stirred melamine suspension and evaporate the solvent in a water bath at 80°C. Pour the obtained white precipitate into a mortar and grind it thoroughly. Then, fill a tube furnace with a flow rate of 80cm 3 / min of argon and treated at 700℃ for 3 hours to obtain MoC quantum dots (L-MoC) with large lattice strain.

[0036] Step 2: In situ growth of MoC quantum dots and indium zinc sulfide to prepare a composite photocatalyst:

[0037] 21.12 mg of MoC quantum dots were placed in 60 mL of ethanol and dispersed thoroughly by ultrasonication for 5 minutes. 0.189 g of zinc nitrate, 0.746 g of indium nitrate tetra-point pentahydrate, and 0.601 g of thioacetamide were added during stirring and stirred to obtain a suspension.

[0038] The suspension was transferred to a polytetrafluoroethylene-lined reactor and subjected to a solvothermal reaction at 160°C for 16 hours. After cooling to room temperature, the suspension was washed with deionized water and ethanol, and finally dried in vacuo to obtain a large lattice strain MoC quantum dot / indium zinc sulfur composite photocatalyst (L-MoC / ZIS).

[0039] Example 2, a method for preparing a MoC quantum dot / sulfur indium zinc composite photocatalyst with lattice strain, comprising the following steps:

[0040] Step 1: Preparation of MoC quantum dots with lattice strain:

[0041] Dissolve 2.064g of melamine in 100mL of methanol and 0.516g of ammonium heptamolybdate in 50mL of deionized water. Then add the ammonium heptamolybdate solution dropwise to the vigorously stirred melamine suspension and evaporate the solvent in a water bath at 60°C. Pour the obtained white precipitate into a mortar and grind it thoroughly. Then, fill it with a flow rate of 120cm 3 / min of helium and treated at 700℃ for 1 hour to obtain MoC quantum dots (S-MoC) with large lattice strain.

[0042] Step 2: In situ growth of MoC quantum dots and indium zinc sulfide to prepare a composite photocatalyst:

[0043] 21.12 mg of MoC quantum dots were placed in 60 mL of ethanol and dispersed thoroughly by ultrasonication for 30 minutes. 0.189 g of zinc nitrate, 0.746 g of indium nitrate tetra-point pentahydrate, and 0.601 g of thioacetamide were added during the stirring process. After stirring evenly,

[0044] The suspension was transferred to a polytetrafluoroethylene-lined reactor and subjected to a solvothermal reaction at 120°C for 12 hours. After cooling to room temperature, the suspension was washed with deionized water and ethanol, and finally dried in vacuo to obtain a MoC quantum dot / sulfur indium zinc composite photocatalyst (S-MoC / ZIS) with a large lattice strain.

[0045] Comparative Example 1

[0046] Step 1: Dissolve 2.064 g of melamine in 100 mL of methanol and 0.516 g of ammonium heptamolybdate in 50 mL of deionized water. Add the ammonium heptamolybdate solution dropwise to the vigorously stirred melamine suspension, and evaporate the solvent in a water bath at 60°C. The resulting white precipitate is thoroughly ground in a mortar and then treated in a tube furnace at 500°C under argon for 2 hours to obtain strain-free MoC quantum dots (N-MoC).

[0047] Step 2: 21.12 mg of MoC quantum dots were placed in 60 mL of ethanol and fully dispersed by ultrasonication for 30 minutes. 0.189 g of zinc nitrate, 0.746 g of indium nitrate tetra-point pentahydrate and 0.601 g of thioacetamide were added during stirring and stirred evenly.

[0048] The above mixture was transferred to a reactor equipped with a polytetrafluoroethylene liner, reacted at 160°C for 12 hours, cooled to room temperature, washed with deionized water and ethanol, and finally vacuum dried to obtain a MoC quantum dot / indium zinc sulfur composite photocatalyst (N-MoC / ZIS) without lattice strain.

[0049] Comparative Example 2

[0050] During the stirring process, 0.189 g of zinc nitrate, 0.746 g of indium nitrate tetrahydrate, and 0.601 g of thioacetamide were respectively added to 60 mL of anhydrous ethanol solution. After stirring evenly, the above mixture was transferred to a reaction kettle equipped with a polytetrafluoroethylene liner and reacted at 160 °C for 12 hours. After cooling to room temperature, it was washed with deionized water and ethanol, and finally dried under vacuum to obtain a pure zinc indium sulfide (ZIS) photocatalyst.

[0051] Application Example:

[0052] The obtained ZIS, L-MoC / ZIS, S-MoC / ZIS, and N-MoC / ZIS catalysts were successively used for the photocatalytic water splitting hydrogen production reaction under simulated sunlight. All photocatalytic water splitting tests were carried out under simulated sunlight with a 300 W xenon lamp equipped with an AM1.5G filter and a light intensity of 100 mW / cm 2 The solution for all tests was 100 mL of 10 vol% lactic acid solution, and the mass of the catalyst was 20 mg.

[0053] Figure 1 This is the X-ray diffraction pattern (XRD) of the three kinds of MoC quantum dots with different lattice strains obtained in Example 1, Example 2, and Comparative Example 1 of the present invention. Among them, the MoC with large lattice strain L-MoC and the MoC with relatively large lattice strain S-MoC have similar XRD diffraction peaks, which can both be attributed to cubic phase MoC (PDF#89-2868). Compared with the standard card, the MoC quantum dots obtained in Example 1 show a relatively large high-angle shift, while the MoC quantum dots obtained in Example 2 show a relatively small high-angle shift, indicating that there is compressive strain inside both materials. In addition, the MoC peak intensity obtained in Comparative Example 1 is weak, but it still belongs to cubic phase MoC. It can be seen from the left figure that there is no obvious shift in the (111) crystal plane, so it is a MoC quantum dot without lattice strain (N-MoC).

[0054] Figure 2 This is the transmission electron microscope image (TEM) of the three different MoC quantum dots obtained in Example 1, Example 2, and Comparative Example 1 of the present invention. It can be seen from the high-resolution transmission electron microscope image (the upper right figure) that the main exposed crystal plane of this series of MoC quantum dots is the (111) crystal plane, and the L-MoC with large lattice strain shows the smallest (111) crystal plane spacing, followed by S-MoC, and N-MoC shows a (111) crystal plane spacing of 0.2465 nm, which corresponds to the (111) crystal plane spacing in the standard card. This proves that N-MoC is a MoC quantum dot without lattice strain.

[0055] Figure 3 XRD patterns of four catalysts, namely zinc indium sulfide (ZIS), L-MoC / ZIS, S-MoC / ZIS, and N-MoC / ZIS, in Example 1, Example 2, Comparative Example 1, and Comparative Example 2 of the present invention. All four samples showed similar diffraction peaks, which could be attributed to hexagonal phase ZnIn2S4 (PDF#65-2023). In addition, the peaks of MoC were not detected in the three MoC-containing composite photocatalysts, indicating that MoC could be uniformly dispersed into the layered structure of ZnIn2S4 using the solvothermal method.

[0056] Figure 4 Transmission electron microscope images (TEM) of four catalysts, namely zinc indium sulfide (ZIS), L-MoC / ZIS, S-MoC / ZIS, and N-MoC / ZIS, in Example 1, Example 2, Comparative Example 1, and Comparative Example 2 of the present invention. All four samples showed nanoflowers composed of sheet-like structures, indicating that the introduction of MoC did not change the microscopic morphology of ZnIn2S4 itself.

[0057] Figure 5 Long-cycle performance of photocatalytic water splitting for hydrogen evolution under simulated sunlight of four catalysts, namely zinc indium sulfide (ZIS), L-MoC / ZIS, S-MoC / ZIS, and N-MoC / ZIS, in Example 1, Example  2, Comparative Example 1, and Comparative Example 2 of the present invention. It can be found from the figure that under simulated sunlight irradiation, the performance of zinc indium sulfide showed a significant decline after 4 hours, indicating the occurrence of photocorrosion. The introduction of MoC could significantly increase the cycle time of photocatalytic hydrogen production, and it was found from the right figure that the introduction of MoC quantum dots with larger lattice strain (i.e., Example 2) could extend the long-cycle time of photocatalytic water splitting for hydrogen evolution to 144 hours.

[0058] Figure 6 Surface photovoltage spectra (SPV) of three MoC quantum dot / zinc indium sulfide composite photocatalysts with different lattice strains in Example 1, Example 2, and Comparative Example 1 of the present invention. It can be seen from the figure that among the three composite photocatalysts, MoC quantum dot / zinc indium sulfide with larger lattice strain showed the largest surface photovoltage, indicating the highest carrier separation efficiency. Example 2 was the best example. Followed by MoC quantum dot / zinc indium sulfide composite with large lattice strain, and the smallest was MoC / zinc indium sulfide composite photocatalyst without lattice strain. This trend was consistent with the performance trend of photocatalytic water splitting for hydrogen evolution under simulated sunlight. Benefiting from the efficient charge separation efficiency in the MoC quantum dot / zinc indium sulfide composite with lattice strain, both L-MoC / ZIS with large lattice strain and S-MoC / ZIS with larger lattice strain showed persistent photocatalytic water splitting for hydrogen evolution performance.

[0059] The photocatalyst prepared by the present invention, under the conditions of lactic acid with a volume fraction of 10 vol% as a sacrificial agent and simulated sunlight (light intensity: 100 mW / cm 2 ), compared with the performance reported in the Chinese patent "CN115608389A", both the performance and stability of photocatalytic water splitting for hydrogen evolution have been significantly improved. The hydrogen evolution performance has increased from 1012 μmol g -1 h -1 to 3850 μmol g - 1 h -1 , and the stability has increased from 60 hours to 144 hours.

[0060] The above embodiments are only preferred technical solutions of the present invention and are not regarded as limitations on the present invention. The protection scope of the present invention shall be the technical solutions recorded in the claims, including equivalent replacement solutions of the technical features in the technical solutions recorded in the claims, that is, equivalent replacement improvements within this scope are also within the protection scope of the present invention.

Claims

1. A method for preparing a MoC quantum dot / sulfur indium zinc composite photocatalyst with lattice strain, characterized by: The following steps are involved: Step 1: Preparation of MoC quantum dots with lattice strain: Melamine and ammonium heptamolybdate in a certain mass ratio are dissolved in methanol and deionized water, respectively. The ammonium heptamolybdate solution is then added dropwise to the vigorously stirred melamine suspension, and the mixed solution is evaporated to dryness in a water bath to obtain a white precipitate. The white precipitate is placed in a tube furnace, introduced with inert gas, and reacted at 700°C for 1-3 hours to obtain molybdenum carbide (MoC) quantum dots with different lattice strains. Step 2: In situ growth of MoC quantum dots and indium zinc sulfide to prepare a composite photocatalyst; In the step 1, the mass ratio of melamine to ammonium heptamolybdate is 1-4:1; The specific steps of step 2 are: First, MoC quantum dots were ultrasonically dispersed in anhydrous ethanol, followed by the addition of zinc nitrate and indium nitrate tetrapentahydrate. After complete dissolution, thioacetamide was added and stirred to obtain a suspension. The suspension is then subjected to a solvent thermal reaction at 120-160° C. for 12-16 hours, and is centrifugally washed and vacuum dried to obtain a MoC quantum dot / sulfur indium zinc composite photocatalyst with lattice strain.

2. The method for preparing a MoC quantum dot / sulfur indium zinc composite photocatalyst with lattice strain according to claim 1, characterized in that: In the step 1, the water bath temperature is 60-80°C.

3. The method for preparing a MoC quantum dot / sulfur indium zinc composite photocatalyst with lattice strain according to claim 2, characterized in that: In step 1, the inert gas is argon, nitrogen or helium with a flow rate of 80-120 cm 3 / min.

4. The method for preparing a MoC quantum dot / sulfur indium zinc composite photocatalyst with lattice strain according to claim 3, characterized in that: In the step 2, the molar ratio of zinc nitrate, indium nitrate tetrapentahydrate and thioacetamide in the suspension is 1:2:

8.

5. The method for preparing a MoC quantum dot / sulfur indium zinc composite photocatalyst with lattice strain according to claim 4, characterized in that: In the step 2, the mass ratio of the MoC quantum dots to the obtained sulfur indium zinc is 1% to 5%, and the ultrasonic dispersion time is 5 to 10 minutes.

6. The MoC quantum dot / sulfur indium zinc composite photocatalyst with lattice strain obtained by the preparation method according to claim 1.

7. The MoC quantum dot / sulfur indium zinc composite photocatalyst with lattice strain according to claim 6 is used for the photocatalytic water splitting hydrogen production reaction under simulated sunlight.

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