A fluorine-modified ZnS photocatalyst and its preparation method and application

Abstract

The present invention belongs to the field of photocatalyst technology, and specifically relates to a fluorine-modified ZnS photocatalyst method, its preparation method and application. The method is to dissolve zinc chloride, thioacetamide and NaF in water, stir to obtain a mixed solution, and then subject the mixed solution to a hydrothermal reaction. After the reaction is completed, the solution is cooled to room temperature, washed with water, centrifuged, dried, and ground to finally obtain a fluorine-modified ZnS photocatalyst. The present invention performs a one-pot hydrothermal method on a precursor solution of doping ions and ZnS, so that F ions are uniformly doped with ZnS. The doping of F ions is beneficial to the conduction of electrons, effectively reduces the recombination rate of electron holes, and at the same time changes the energy band position of ZnS, significantly improves the charge separation efficiency, improves the carrier migration efficiency, and thus improves the photocatalytic efficiency. The preparation method of the fluorine-modified ZnS photocatalyst of the present invention is simple, low in cost and has good photocatalytic activity, and is a new type of photocatalyst that can be practically applied.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalysts, and in particular relates to a fluorine-modified ZnS photocatalyst, a preparation method thereof and an application thereof. Background Art

[0002] Semiconductor photocatalytic technology has been widely used in various photocatalytic applications, such as photocatalytic carbon dioxide reduction and photocatalytic water splitting to produce hydrogen. ZnS, a typical transition metal sulfide, has been widely studied in the field of photocatalysis due to its low cost and availability, its ability to meet the band gap requirements of semiconductor photocatalysts for photocatalytic reactions, and its rapid charge carrier transfer. ZnS offers many unique advantages, including excellent electron transport properties, good thermal stability, high electron mobility, non-toxicity, and relatively low cost.

[0003] However, due to the defects of ZnS such as high recombination rate of photogenerated electrons and holes, low photocatalytic efficiency, photoinstability, and imperfect positions of conduction band and valence band, the development and application of ZnS are limited. Therefore, it is of great significance to prepare visible light-driven ZnS-based photocatalysts with high photocatalytic performance. Summary of the Invention

[0004] The purpose of the present invention is to solve the deficiencies of the prior art and provide a method for preparing a fluorine-modified ZnS photocatalyst and its preparation method and application, specifically adopting the following technical solutions:

[0005] A method for preparing a fluorine-modified ZnS photocatalyst comprises the following steps:

[0006] Zinc chloride, thioacetamide and NaF are dissolved in water and stirred to obtain a mixed solution, and then the mixed solution is subjected to a hydrothermal reaction. After the reaction is completed, the solution is cooled to room temperature, washed with water, centrifuged, dried, and ground to finally obtain a fluorine-modified ZnS photocatalyst.

[0007] The present invention performs a one-pot hydrothermal process on the precursor solution of doped ions and photocatalysts to achieve uniform doping modification of the elements of the photocatalyst, and can develop a photocatalyst that is efficient, stable, and has high photogenerated carrier separation efficiency. Among them, surface fluorine modification or fluorine doping can produce electron capture sites, increase the interfacial electron-hole transfer rate of the photocatalyst, improve crystallinity and visible light absorption, and fluorine-modified semiconductors help reduce the recombination rate of electron-hole pairs, adjust the position of the conduction band and valence band of the semiconductor photocatalyst, and improve photocatalytic activity. In addition, the preparation method of the present invention is simple, fast, green and environmentally friendly, and highly operable, making it a new type of photocatalyst that can be practically applied.

[0008] In a further preferred embodiment, the molar ratio of NaF to zinc chloride is 0.01-0.2:1. More preferably, the molar ratio of NaF to zinc chloride is 0.01:1, 0.03:1, 0.05:1, 0.1:1, or 0.2:1. Excessive fluorine doping may cause the doped ions to become recombination centers for electrons and holes, thereby reducing photocatalytic efficiency. Most preferably, the molar ratio of NaF to zinc chloride is 0.05:1.

[0009] As a further preferred embodiment, the molar ratio of zinc chloride to thioacetamide is 1:1.

[0010] As a further preferred embodiment, the hydrothermal reaction temperature is 120°C-180°C and the reaction time is 12 hours-24 hours. More preferably, the hydrothermal reaction temperature is 160°C and the reaction time is 24 hours. Too low a temperature or too short a reaction time will result in incomplete doping of fluoride ions into the ZnS, while too high a temperature or too long a reaction time will result in excessive energy loss.

[0011] As a further preferred embodiment, the drying temperature is 80° C. and the drying time is 12 h.

[0012] The beneficial effects of the present invention are as follows: (1) the precursor solution of doping ions and ZnS is subjected to a one-pot hydrothermal method to uniformly dope F ions into ZnS. The doping of F ions is beneficial to the conduction of electrons, effectively reduces the recombination rate of electrons and holes, and at the same time changes the energy band position of ZnS, thereby promoting the progress of the photocatalytic reaction.

[0013] (2) Compared with pure ZnS, the F-doped ZnS photocatalyst prepared by the present invention not only enhances the electron enrichment effect, reduces the recombination rate of photogenerated carriers, but also improves the migration and separation efficiency of photogenerated carriers, thereby improving the photocatalytic performance.

[0014] (3) The F-ion-doped ZnS photocatalyst prepared by the present invention has better thermal stability, chemical stability and charge transfer efficiency than traditional metal sulfide semiconductor photocatalysts. The preparation method of the present invention is simple, fast and environmentally friendly, and can be used in photocatalytic carbon dioxide reduction and photocatalytic water decomposition to produce hydrogen. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0016] Figure 1Shown are the X-ray diffraction patterns of F-ion-doped ZnS and pure ZnS photocatalysts;

[0017] Figure 2 Shown are the SEM images of the photocatalysts: (a) ZnS; (b) FZnS-5%;

[0018] Figure 3 Shown are the full XPS spectra of ZnS and FZnS-5% photocatalysts;

[0019] Figure 4 Shown is the carbon dioxide reduction performance of different photocatalysts under simulated sunlight;

[0020] Figure 5 Shown is the hydrogen production performance of different photocatalysts under simulated sunlight;

[0021] Figure 6 Shown is a graph of the carbon dioxide reduction rate of FZnS-5% under simulated sunlight. DETAILED DESCRIPTION

[0022] The following will provide a clear and complete description of the concept, specific structure and technical effects of the present invention in conjunction with the embodiments and drawings to fully understand the purpose, scheme and effects of the present invention.

[0023] Example 1

[0024] A fluorine-modified ZnS photocatalyst, the specific preparation method is as follows:

[0025] 0.8178 g zinc chloride, 0.4508 g thioacetamide, and 0.0025 g sodium fluoride were dissolved in 30 mL deionized water to obtain a reaction solution. The molar ratio of zinc chloride to thioacetamide in the reaction solution was 1:1, and the molar ratio of sodium fluoride to zinc chloride in the reaction solution was 0.01:1. The mixture was magnetically stirred at room temperature for 30 min to obtain a mixed solution after dissolution. The mixed solution was then poured into a polytetrafluoroethylene-lined reactor. The reactor was tightened and placed in an oven for hydrothermal treatment at 160 °C for 24 h. After the reaction was completed, the reaction was cooled to room temperature. The product was centrifuged, washed with deionized water three times, and dried at 80 °C for 12 h. After grinding, a fluorine-modified ZnS photocatalyst (FZnS-1%) was obtained.

[0026] Example 2

[0027] The molar ratio of sodium fluoride to zinc chloride in the reaction solution of Example 1 was changed to 0.03:1, while other conditions remained unchanged, to obtain a fluorine-modified ZnS photocatalyst (FZnS-3%).

[0028] Example 3

[0029] The molar ratio of sodium fluoride to zinc chloride in the reaction solution of Example 1 was changed to 0.05:1, while other conditions remained unchanged, to obtain a fluorine-modified ZnS photocatalyst (FZnS-5%).

[0030] Example 4

[0031] The molar ratio of sodium fluoride to zinc chloride in the reaction solution of Example 1 was changed to 0.1:1, while other conditions remained unchanged, to obtain a fluorine-modified ZnS photocatalyst (FZnS-10%).

[0032] Example 5

[0033] The molar ratio of sodium fluoride to zinc chloride in the reaction solution of Example 1 was changed to 0.2:1, while other conditions remained unchanged, to obtain a fluorine-modified ZnS photocatalyst (FZnS-20%).

[0034] Comparative Example 1

[0035] A ZnS photocatalyst, the specific preparation method is as follows:

[0036] 0.8178 g zinc chloride and 0.4508 g thioacetamide were dissolved in 30 mL deionized water to obtain a reaction solution. The molar ratio of zinc chloride to thioacetamide in the reaction solution was 1:1. The mixture was magnetically stirred at room temperature for 30 min. After complete dissolution, the mixed solution was poured into a polytetrafluoroethylene-lined reactor. The reactor was tightened and placed in an oven for hydrothermal treatment. The reaction was carried out at 160 ° C for 24 h. After the reaction was completed, the mixture was cooled to room temperature. The product was centrifuged, washed with deionized water, and dried at 80 ° C for 12 h. Then, ZnS was ground. Its SEM image is shown in FIG. Figure 2 In (a), it can be seen that the average particle size of ZnS is about 45 nm-50 nm.

[0037] The XRD patterns of the F-doped ZnS photocatalysts obtained in Comparative Example 1 and Examples 1-5 are shown in FIG. Figure 1 , SEM images are shown in Figure 2 The XRD patterns of the samples were obtained ( Figure 1 ) It can be seen that all the diffraction peak positions of the F-doped ZnS photocatalyst correspond to the diffraction peaks of ZnS, and there are no impurity peaks, indicating that the prepared F-doped ZnS photocatalyst has high purity and good crystallinity. Figure 2 From the SEM images of (a) ZnS and (b) FZnS-5%, it can be seen that the ZnS photocatalyst and F-doped ZnS photocatalyst prepared by the above method are both spherical. Figure 3 The XPS full spectra of ZnS and FZnS-5% photocatalysts show the presence of F element in FZnS-5% photocatalyst, that is, F element is successfully doped into ZnS.

[0038] Example 6

[0039] The ZnS photocatalyst obtained in Comparative Example 1 was used in the photocatalytic reduction of CO2 experiment, and the specific steps were as follows:

[0040] The photocatalytic performance of ZnS was evaluated by reducing CO₂ under simulated sunlight. First, 20 mg of the catalyst was dispersed in ultrapure water by sonication, and then evenly dropped onto a small watch glass. The watch glass was then placed in an oven to dry, ensuring uniform adhesion of the catalyst. The watch glass was then placed in a reactor, sealed with vacuum ester, and aerated with CO₂ for 15 minutes. Once fully aerated, the reactor was illuminated with simulated sunlight using a 300 W xenon lamp. Every hour, 1 mL of the sample was sampled using a gas-tight needle and injected into a chromatograph for analysis.

[0041] The formula for photocatalytic carbon dioxide reduction rate is: a=v / 22.4 / m / t = v / (22.4mt)

[0042] Where a is the yield of CO or CH4, v is the volume of CO or CH4 produced, m is the mass of the catalyst, and t is the time.

[0043] Example 7

[0044] Fluorine-modified ZnS photocatalysts were prepared according to the method steps in Examples 1-5, wherein the molar proportions of F were 1%, 3%, 5%, 10%, and 20%, respectively, to obtain FZnS-1%, FZnS-3%, FZnS-5%, FZnS-10%, and FZnS-20%, respectively, and then used in the experiment of photocatalytic carbon dioxide reduction. First, 20 mg of the catalyst was added to ultrapure water and ultrasonically dispersed, and the dispersion was evenly dropped on a small watch glass. The watch glass was then placed in an oven for drying to allow the catalyst to be evenly attached to the small watch glass. The watch glass was then placed in a reactor, sealed with vacuum ester, and passed with CO2 for 15 min. After being filled with CO2, it was irradiated with a 300 W xenon lamp to simulate sunlight. 1 mL of the sample was taken with an airtight needle every 1 h and injected into the chromatograph for analysis.

[0045] The formula for the photocatalytic carbon dioxide reduction rate is: a=v / 22.4 / m / t = v / (22.4 mt)

[0046] Where a is the yield of CO or CH4, v is the volume of CO or CH4 produced, m is the mass of the catalyst, and t is the time.

[0047] Six photocatalysts, namely ZnS, FZnS-1%, FZnS-3%, FZnS-5%, FZnS-10% and FZnS-20% obtained in Comparative Example 1 and Examples 1-5, were used for photocatalytic carbon dioxide reduction. The yields of CO and CH4 were as follows: Figure 4 As shown. Figure 4 The CO yields of the six photocatalysts were 2.56 µmol / g / h, 6.88 µmol / g / h, 8.10 µmol / g / h, 15.34 µmol / g / h, 10.17 µmol / g / h, and 4.70 µmol / g / h, respectively. The CH4 yields of the six photocatalysts were 0.96 µmol / g / h, 0.98 µmol / g / h, 0.94 µmol / g / h, 1.44 µmol / g / h, 1.33 µmol / g / h, and 0.89 µmol / g / h, respectively. Among them, the FZnS-5% photocatalyst had the highest CO and CH4 yields, reaching 15.34 and 1.44 µmol / g / h, respectively. These results indicate that the fluorine-modified ZnS photocatalyst has superior catalytic performance to the ZnS photocatalyst.

[0048] After the FZnS-5% photocatalyst obtained in Example 3 was used to reduce carbon dioxide, CO2 was introduced again and the carbon dioxide reduction experiment was carried out again. This cycle was repeated 5 times. Figure 5 As shown in the figure, after five cycles of experiments, the CO yield is 87.7% of that in the first experiment, indicating that the FZnS-5% photocatalyst has good stability.

[0049] Example 8

[0050] The photocatalysts obtained in Comparative Example 1 and Examples 2-4 were used in the experiment of photocatalytic decomposition of water to produce hydrogen. The specific steps were as follows:

[0051] 50 mg of catalyst was added to 50 mL of sacrificial agent (0.35M Na2S-0.25M Na2SO3) to deposit 1 wt% Pt metal. The solution was then transferred to the reactor of an online hydrogen production pipeline device. After sealing, the system was evacuated for half an hour to remove the air from the pipeline and solution. A 300 W xenon lamp was then used to simulate sunlight irradiation. The system automatically sampled every hour for chromatographic analysis.

[0052] Comparative Example 1 and the four photocatalysts of ZnS, FZnS-3%, FZnS-5%, and FZnS-10% obtained in Examples 2-4 were used for photocatalytic decomposition of water to produce hydrogen. The rates were as follows: Figure 6 As shown in the figure, the hydrogen production rates of the four catalysts are 3.19 µmol / g / h, 5.69 µmol / g / h, 16.52 µmol / g / h, and 4.69 mmol / g / h, respectively. The hydrogen production rate of FZnS-5% is the highest, reaching 16.52 mmol / g / h.

[0053] In summary, the method for preparing the catalyst of the present invention is simple to operate, low in cost, fast and green and environmentally friendly. Compared with pure ZnS, the obtained F ion-doped ZnS photocatalyst not only enhances the electron enrichment effect and reduces the recombination rate of photogenerated carriers, but also improves the migration and separation efficiency of photogenerated carriers, thereby improving the photocatalytic performance. It can be used in photocatalytic carbon dioxide reduction and photocatalytic water decomposition to produce hydrogen, and is a new type of photocatalyst that can be practically applied.

[0054] Obviously, the described embodiments are only some of the embodiments of the present application, rather than all of the embodiments. Mentioning "embodiments" in this article means that the specific features, structures or characteristics described in conjunction with the embodiments may be included in at least one embodiment of the present embodiment application. The appearance of this phrase in various places in the specification does not necessarily mean the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It can be understood explicitly and implicitly by those skilled in the art that the embodiments described herein can be combined with other embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of this application. Although embodiments of the present invention have been shown and described, those of ordinary skill in the art will understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and purpose of the present invention, and the scope of the present invention is defined by the claims and their equivalents.

Claims

1. Application of a fluorine-modified ZnS photocatalyst in photocatalytic carbon dioxide reduction or photocatalytic water decomposition to produce hydrogen, characterized in that: The preparation method of the fluorine-modified ZnS photocatalyst comprises the following steps: Dissolve zinc chloride, thioacetamide, and NaF in water, stir, and obtain a mixed solution. Then, subject the mixed solution to a hydrothermal reaction. After the reaction is completed, cool the solution to room temperature, wash with water, centrifuge, dry, and grind to obtain a fluorine-modified ZnS photocatalyst. The molar ratio of NaF to zinc chloride is 0.01-0.1:

1.

2. The use according to claim 1, characterized in that The molar ratio of NaF to zinc chloride is 0.05:

1.

3. The use according to claim 1, characterized in that The molar ratio of zinc chloride to thioacetamide is 1:

1.

4. The use according to claim 1, characterized in that The temperature of the hydrothermal reaction is 120 ℃-180 ℃, and the time is 12 h-24 h.

5. The use according to claim 4, characterized in that The hydrothermal reaction temperature was 160 °C and the reaction time was 24 h.

6. The use according to claim 1, characterized in that The drying temperature was 80 °C and the drying time was 12 h.

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