Composite material for removing Cr(vi) from water body and preparation method thereof

Abstract

The application discloses a composite material for removing Cr(VI) in water bodies and a preparation method thereof, and belongs to the technical field of environmental functional composite nanomaterials. The composite material is a type II heterojunction AgIn5S8 / ZnIn2S4. The preparation method is as follows: first, a high-purity AgIn5S8 is prepared by using a solvothermal method, then, AgIn5S8 particles are added in the process of preparing ZnIn2S4 by using a hydrothermal method, and a yellow suspension liquid is obtained; after centrifugation, the yellow suspension liquid is washed with water and alcohol for several times, so that the AgIn5S8 / ZnIn2S4 composite material is obtained. The material is synthesized by using a hydrothermal method, the preparation process is simple, the raw material cost is low, and the problems of fast electron-hole pair recombination, serious photo corrosion and low reactivity of ZnIn2S4 are improved. Compared with ZnIn2S4, the composite material enlarges the visible light absorption range of the photocatalyst, improves the separation efficiency of the photo-generated electron-hole pairs, inhibits the recombination of the photo-generated carriers, and significantly enhances the removal effect on the Cr(VI) in water bodies.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of environmental functional composite nanomaterials, and particularly relates to an AgIn5S8 / ZnIn2S4 composite material for removing Cr(VI) in water bodies and a preparation method thereof, and is mainly applied to chromium-containing wastewater treatment. BACKGROUND

[0002] In environmental pollution control, heavy metal pollution is a long-standing problem. Among them, water pollution contaminated by heavy metals poses a serious threat to human health and the ecological environment, and has attracted widespread public attention. Among toxic metal pollution, Cr(VI) poses a serious threat to human health and the ecological system due to its persistence, high toxicity, carcinogenicity and strong biofilm penetration. The World Health Organization (WHO) stipulates that the concentration of Cr(VI) in drinking water should not exceed 0.05 mg / L. Reducing Cr(VI) to Cr(III) is a common method for removing Cr(VI) from water bodies, including adsorption, membrane separation, electrochemical treatment and photocatalytic reduction technology. Among them, photocatalytic reduction as a convenient and environmentally friendly environmental restoration method has attracted more and more attention due to its simplicity and no secondary pollution.

[0003] The process of photocatalytic reaction is that the semiconductor photocatalyst absorbs light energy under light conditions to produce electron-hole pairs, which are used for redox reactions on target pollutants. ZnIn2S4 is a transition metal ternary sulfide, which is widely used for removing pollutants in wastewater due to its excellent chemical stability, non-toxicity and good photoelectric conversion performance. It can be activated under visible light irradiation and has an adjustable band gap of 2.06-2.85 eV. Due to its suitable conduction band (CB) and valence band (VB) positions, it shows strong redox ability. However, the application of pure ZnIn2S4 in the field of photocatalysis is very limited, which is mainly due to its uncontrollable electron-hole recombination, high electron migration resistance and serious photo-corrosion. Therefore, prolonging the service life of photo-generated carriers and improving their utilization rate have become the focus of current research.

[0004] Studies have shown that the recombination of photo-generated carriers can be effectively suppressed by combining two semiconductors with appropriate band structures to form a heterojunction. As a representative ternary chalcogenide material, AgIn5S8 has a direct band gap of 1.70-1.80 eV. Due to its low-toxicity elements, wide light absorption range, high carrier mobility through composition control, and other advantages, AgIn5S8 has been widely used in photovoltaic, photoelectric, and photocatalytic fields. However, for single-component AgIn5S8, its rapid charge recombination, low quantum efficiency, and inevitable photo-corrosion make it difficult for practical large-scale application. Theoretically, the band structures of AgIn5S8 and ZnIn2S4 can be well matched, which makes it possible to directly construct a type-II AgIn5S8 / ZnIn2S4 heterojunction. Therefore, the development of type-II heterojunction AgIn5S8 / ZnIn2S4 for removing Cr(VI) from water not only enriches the application of ZnIn2S4, but also provides a technical reference for the removal of heavy metal pollution in water.

[0005] In the prior art, there are some achievements in the preparation method of ZnIn2S4 composite materials. For example, Chinese Patent No. 201910373039.0, published on July 19, 2019, discloses a patent document entitled "CaTiO3@ZnIn2S4 Nanocomposite Material and Its Preparation Method and Application". This patent uses hollow CaTiO3 cuboids as a substrate and uniformly coats ZnIn2S4 nanosheets on the outer layer of the cuboids for photocatalytic hydrogen production. The preparation method is relatively complex, and photocatalytic hydrogen production and photocatalytic reduction of Cr(VI) are two different reaction processes, so it is not known whether it is feasible to use it for Cr(VI) reduction. Chinese Patent Application No. 201610855552.X, published on April 3, 2018, discloses a patent document entitled "High-activity ZnIn2S4 / TiO2 Z System Catalyst Material and Its Preparation Method". This patent first obtains rough-surfaced TiO2 nanobands through step-by-step processing, and then grows ZnIn2S4 on the TiO2 nanobands through a solvothermal method to obtain a composite material for photocatalytic reduction of CO2. The removal of CO2 and Cr(VI) is a photocatalytic reduction process, so the composite material has the potential to photocatalytically reduce Cr(VI). However, the different reaction conditions and different reduction processes of gas and liquid phases result in different mechanisms for removing pollutants. Chinese Patent Application No. 201910753360.1, published on December 17, 2019, discloses a patent document entitled "InVO4 / ZnIn2S4 Photocatalyst, Preparation Method and Application". This patent obtains cubic monomer composite materials by adding ZnIn2S4 particles during the hydrothermal synthesis of InVO4, and degrades tetracycline hydrochloride under visible light. However, the photocatalytic performance of this material is general, and it does not have an advantage in practical applications.

[0006] In the research technology of AgIn5S8 material, there are also related patents. For example, Chinese patent application No. 202110728709.3, published on September 10, 2021, discloses a patent document entitled "Preparation method of carbon dot assisted Zn-AgIn5S8 / Co9S8 quantum dots and application in photohydrolysis hydrogen production"; Chinese patent application No. 201710823546.0, published on April 10, 2018, discloses a patent document entitled "AgIn5S8-ZnS quantum dots, preparation method and use thereof"; Chinese patent application No. 201710374433.7, published on October 20, 2017, discloses a patent document entitled "PDA / Bi-AgIn5S8 / TiO2 heterojunction photoelectrode, preparation method and use thereof". The composite materials in the above patent documents are used for preparing electrodes and are applied in the field of photocatalytic hydrogen production. The reduction mechanism of water Cr(VI) is not clear.

[0007] In the research technology of water Cr(VI) removal, there are some patent documents, for example, Chinese patent application No. 201610098213.1, published on May 25, 2016, discloses a patent document entitled "Preparation method of nanofiber filter material for removing Cr(VI) in sewage"; Chinese patent application No. 202010454504.6, published on August 25, 2020, discloses a patent document entitled "Preparation method of Cr(VI) adsorbent Cu-Al2O3@diatomite"; Chinese patent application No. 201910379569.6, published on July 30, 2019, discloses a patent document entitled "SiO2 / γ-AlOOH composite film for adsorbing toxic Cr(VI), its preparation method and application". The above patents remove water Cr(VI) mainly by adsorption and membrane filtration method, which has the problems of high maintenance cost and secondary pollution. SUMMARY

[0008] In view of the defects and deficiencies of the prior art in removing water Cr(VI) and the problems of uncontrollable electron-hole recombination, high electron migration resistance and serious photo corrosion of ZnIn2S4, the purpose of the present application is to provide a preparation method of composite material for removing water Cr(VI), so as to improve the photocatalytic activity of the composite material and provide a technical reference for the actual removal of water Cr(VI).

[0009] To solve the above problems, the technical scheme adopted by the present application is as follows.

[0010] The application provides a composite material for removing Cr(VI) in water, which is AgIn5S8 / ZnIn2S4, and the AgIn5S8 and ZnIn2S4 form a type II heterojunction.

[0011] The application also provides a preparation method of the composite material, which comprises the following steps:

[0012] (1) silver salt and InCl3·4H2O are added into ethanol and stirred for 30 min; then, thioacetamide (TAA) is slowly added into the ethanol solution and continuously stirred; the two solutions are uniformly mixed and transferred into a 50 mL high-pressure reaction kettle, and reacted at 160 ℃ for 24 h; after cooling to room temperature, a red-brown precipitate is obtained by centrifugation; then, the precipitate is repeatedly washed with distilled water and ethanol and dried at 60 ℃ to obtain AgIn5S8.

[0013] The molar ratio of the silver salt, InCl3·4H2O and TAA is 1:5:8.

[0014] (2) zinc salt, InCl3·4H2O and TAA are dissolved in deionized water, and the mixture is stirred until each component is dissolved; then, the prepared AgIn5S8 is added into the mixed solution, and each mixture is subjected to ultrasonic treatment and stirring for 30 min; then, the suspension is transferred into a 100 mL high-pressure reaction kettle and heat-treated at 160 ℃ for 16 h; the obtained product is repeatedly washed and dried at 80 ℃ to obtain the AgIn5S8 / ZnIn2S4 composite material.

[0015] The molar ratio of the zinc salt, InCl3·4H2O and TAA is 1:2:8; and the mass fraction of the added AgIn5S8 is 5-20%.

[0016] Further in step (1), the silver salt is AgNO3.

[0017] Further in step (2), the zinc salt is ZnSO4·7H2O.

[0018] Further in step (2), the mass fraction of the added AgIn5S8 is 10%.

[0019] The type II heterojunction AgIn5S8 / ZnIn2S4 composite material prepared by the above preparation method can be applied to removing Cr(VI) in water.

[0020] The AgIn5S8 / ZnIn2S4 photocatalyst forms a type II heterojunction, expands the visible light absorption range of the material, effectively improves the separation efficiency of photo-generated electron-hole pairs and inhibits the recombination of photo-generated carriers, and has higher efficiency and faster reaction rate for the photocatalytic reduction of Cr(VI).

[0021] The specific principle is speculated as follows:

[0022] The specific reaction process is as shown in Figure 1 Under light conditions, the semiconductor is excited to produce electron-hole pairs, the electrons in the valence band can absorb light energy and transfer to the conduction band, and the holes remain in the valence band (equations 1-2). Since the E CB of AgIn5S8 is more negative than that of ZnIn2S4, the photo-generated electrons in the conduction band are easily transferred from AgIn5S8 to ZnIn2S4. The photo-generated electrons accumulated on the conduction band of ZnIn2S4 can effectively photocatalytically reduce Cr(VI) (formula 3). At the same time, the value of the conduction band of ZnIn2S4 (-0.49 eV vs. NHE) is more negative than the standard redox potential of O2 / ·O2 - (-0.33 eV vs. NHE), and can produce ·O2 - to participate in the photocatalytic reduction process (formula 4-5). In addition, since the E VB of AgIn5S8 is more negative than that of ZnIn2S4, VB the photo-generated electrons in the conduction band are easily transferred from ZnIn2S4 to AgIn5S8. The E VB of AgIn5S8 (+1.01 eV vs. NHE) is lower than the standard redox potential of OH - / ·OH (+1.99 eV vs. NHE), so the weak oxidation potential of h + is not enough to transfer the hydroxyl radical to ·OH free radicals. The analysis result further proves that the formation of type II heterojunction between AgIn5S8 and ZnIn2S4 plays an important role in inhibiting carrier recombination and improving photocatalytic performance. The main process of AIS / ZIS composite material for Cr(VI) photoreduction is as follows:

[0023] AgIn5S8 + hν → AgIn5S8 (h + +e – ) (1)

[0024] ZnIn2S4 + hν → ZnIn2S4 (h + +e – ) (2)

[0025] Cr(VI) + e –→ Cr(III) (3)

[0026] O2 + e – → ·O2 - (4)

[0027] Cr(VI) + ·O2 - → Cr(III) + O2 (5)

[0028] Compared with the prior art, the present application has the beneficial effects that:

[0029] (1) The preparation process is simple, the composite material is synthesized by a hydrothermal method and a solvothermal method, the production cost is low, the removal efficiency is high, and the applicable condition range is wide. In the preparation process, AgIn5S8 and ZnIn2S4 form a heterojunction, which improves the problems of rapid electron-hole pair recombination, serious photo corrosion and low reactivity of ZnIn2S4, and improves the practical application ability of ZnIn2S4 nanoparticles.

[0030] (2) The composite material can effectively remove Cr(VI) in water, when the initial concentration of Cr(VI) is 20 mg / L and the initial solution pH is 4.0, the removal rate of 10% AgIn5S8 / ZnIn2S4 on Cr(VI) (88.5% or more) is much higher than that of ZnIn2S4 (60%). And the material still maintains high removal efficiency after three cycles.

[0031] (3) The composite material is a type II heterojunction formed by AgIn5S8 and ZnIn2S4, and no related reports have been found. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 is a schematic diagram of photocatalytic reduction of Cr(VI) in water by type II heterojunction AgIn5S8 / ZnIn2S4.

[0033] Figure 2 is a scanning electron microscope image of 10% AgIn5S8 / ZnIn2S4 composite material obtained according to Example 2 of the present application.

[0034] Figure 3 is an energy spectrum analysis diagram of 10% AgIn5S8 / ZnIn2S4 composite material obtained according to Example 2 of the present application.

[0035] Figure 4 is a removal kinetics process diagram of Cr(VI) in water by AgIn5S8 / ZnIn2S4 composite materials with different mass fractions (mass fractions are 5%, 10%, 15%, and 20%) prepared according to the preparation methods shown in Examples 1-4 and AgIn5S8 and ZnIn2S4 prepared in the comparative example. DETAILED DESCRIPTION

[0036] The technical solutions of the present application are described in further detail below in connection with specific examples, but are not limited to the specific examples.

[0037] Example 1

[0038] The present example provides a preparation method of type II heterojunction AgIn5S8 / ZnIn2S4 (mass ratio of silver indium sulfide to zinc indium sulfide is 1:20), which comprises the following steps:

[0039] (1) Preparation of AgIn5S8: 1 mmol of AgNO3 and 5 mmol of InCl3·4H2O were added to 15 mL of ethanol and stirred for 30 min until all components were dissolved, ready for use; 8 mmol of thioacetamide (TAA) was slowly added to 15 mL of ethanol solution and continuously stirred for 30 min until all were dissolved, ready for use; then the two solutions were uniformly mixed and transferred to a 50 mL high-pressure reaction kettle, and reacted at 160°C for 24 h. After cooling to room temperature, a red-brown precipitate was obtained by centrifugation. Then washed repeatedly with distilled water and ethanol and dried at 60°C to obtain AgIn5S8.

[0040] (2) Preparation of AgIn5S8 / ZnIn2S4 composite material: ZnSO4·7H2O (1 mmol), InCl3·4H2O (2 mmol) and TAA (8 mmol) were dissolved in 60 mL of deionized water, and the mixture was stirred until each component was dissolved. Subsequently, 10.56 mg of prepared AgIn5S8 was added to the mixed solution, and the mixed solution was subjected to ultrasonic treatment and stirring for 30 min each. Then the suspension was transferred to a 100 mL high-pressure reaction kettle and heat-treated at 160°C for 16 hours.

[0041] (3) Washing process: the high-pressure reaction kettle was allowed to stand for 24 h, and the obtained suspension was washed repeatedly by centrifugation with deionized water and ethanol and dried at 80°C to obtain AgIn5S8 / ZnIn2S4 composite material (theoretical AgIn5S8 mass fraction is 5%).

[0042] Example 2

[0043] The present example provides a preparation method of type II heterojunction AgIn5S8 / ZnIn2S4 (mass ratio of silver indium sulfide to zinc indium sulfide is 1:10), which comprises the following steps:

[0044] (1) The preparation of silver indium sulfide is the same as described in step (1) of Example 1.

[0045] (2) The preparation of AgIn5S8 / ZnIn2S4 composite material is the same as described in step (2) of Example 1. The difference is that 21.15 mg of silver indium sulfide is added.

[0046] (3) The rinsing process is the same as described in step (3) of Example 1 (the theoretical mass fraction of AgIn5S8 is 10%).

[0047] From the SEM image, it can be seen that the AgIn5S8 / ZnIn2S4 composite material obtained in this example has stable morphology and large specific surface area. Figure 2

[0048] From the EDS analysis image, it can be seen that the main elements of the composite material obtained in this example are Ag, Zn, In and S, indicating that the modified adsorbent has successfully loaded AgIn5S8. Figure 3

[0049] Example 3

[0050] The present example provides a preparation method of type II heterojunction AgIn5S8 / ZnIn2S4 (the mass ratio of silver indium sulfide to zinc indium sulfide is 3:20), which comprises the following steps:

[0051] (1) The preparation of silver indium sulfide is the same as described in step (1) of Example 1.

[0052] (2) The preparation of AgIn5S8 / ZnIn2S4 composite material is the same as described in step (2) of Example 1. The difference is that 31.68 mg of silver indium sulfide is added.

[0053] (3) The rinsing process is the same as described in step (3) of Example 1 (the theoretical mass fraction of AgIn5S8 is 15%).

[0054] Example 4

[0055] The present example provides a preparation method of type II heterojunction AgIn5S8 / ZnIn2S4 (the mass ratio of silver indium sulfide to zinc indium sulfide is 1:5), which comprises the following steps:

[0056] (1) The preparation of silver indium sulfide is the same as described in step (1) of Example 1.

[0057] (2) The preparation of AgIn5S8 / ZnIn2S4 composite material is the same as described in step (2) of Example 1. The difference is that 42.30 mg of silver indium sulfide is added.

[0058] (3) The rinsing process is the same as described in step (3) of Example 1 (the theoretical mass fraction of AgIn5S8 is 20%).

[0059] The present example provides a preparation method of AgIn5S8, which comprises the following steps:​​

[0060] The preparation of silver indium sulfide is the same as described in step (1) of Example 1.

[0061] Comparative Example 2:

[0062] This comparative example provides a method for preparing ZnIn2S4, which comprises the following steps:

[0063] (1) Preparation of zinc indium sulfide material: ZnSO4·7H2O (1 mmol), InCl3·4H2O (2 mmol) and TAA (8 mmol) were dissolved in 60 mL of deionized water, and the mixture was stirred until each component was dissolved. Then the suspension was transferred to a 100 mL high-pressure reaction kettle and heat-treated at 160°C for 16 hours.

[0064] (2) Washing: The high-pressure reaction kettle was allowed to stand for 24 h, and the obtained suspension was washed by centrifugation with deionized water and ethanol several times, and then dried at 80°C to obtain the ZnIn2S4 material.

[0065] The AgIn5S8 / ZnIn2S4 composite materials with different mass fractions (5%, 10%, 15%, and 20%) prepared by the preparation methods shown in Examples 1-4 above and AgIn5S8 and ZnIn2S4 prepared in the comparative example were subjected to photocatalytic reduction of Cr(VI) experiments, and a 350W filter (λ>420nm) with a xenon lamp was used to filter ultraviolet light. The dosage of the photocatalyst was 0.2g / L, and K2Cr2O7 was used to prepare the chromium-containing wastewater for the experiment, and the concentration of Cr(VI) was 20mg / L. First, adsorption was carried out in the dark for 60min. Then, the Xe lamp was turned on, and samples (3 parallel samples) were taken every 60min to measure the concentration of Cr(VI). The experimental results are shown in Figure 4 As shown in the table, after 300min of irradiation, the total content of Cr(VI) in each material group showed a downward trend, and the removal rates of pure AgIn5S8 and ZnIn2S4 on Cr(VI) were 52.5% and 60.0%, respectively. After loading AgIn5S8 onto the surface of ZnIn2S4, the photocatalytic reduction ability of Cr(VI) was significantly improved. Among them, when the loading rate of AgIn5S8 reached 10%, the reduction rate of Cr(VI) reached a maximum value, and within 300min, the removal rate of Cr(VI) reached 88.5%.

[0066] The test data show that the AgIn5S8 / ZnIn2S4 obtained in Examples 1-4 of the present application has very significant removal efficiency on Cr(VI) in water (as shown in Table 1).

[0067] Table 1 Experimental results of different examples for removing Cr(VI) in water

[0068]

Claims

1. A composite material for removing Cr(VI) from water, the composite material being AgIn5S8 / ZnIn2S4, the AgIn5S8 and ZnIn2S4 forming a type II heterojunction; a preparation method of the composite material comprising the following steps: (1) stirring silver salt and indium chloride in ethanol for 30 min, then slowly adding thioacetamide into the ethanol solution and continuously stirring, uniformly mixing the two solutions, transferring into a 50 mL high-pressure reactor, reacting at 160℃ for 24 h, after cooling to room temperature, centrifuging to obtain a red-brown precipitate, then repeatedly washing with distilled water and ethanol, and drying at 60℃ to obtain AgIn5S8; the molar ratio of the silver salt, indium chloride and TAA being 1:5:8; (2) dissolving zinc salt, indium chloride and thioacetamide in nano water, stirring the mixture until each component is dissolved, then adding the prepared AgIn5S8 into the mixed solution, ultrasonically treating and stirring each mixture for 30 min, then transferring the suspension into a 100 mL high-pressure reactor, heat treating at 160℃ for 16 h, repeatedly washing the obtained product, and drying at 80℃ to obtain the AgIn5S8 / ZnIn2S4 composite material; the molar ratio of the zinc salt, InCl3·4H2O and TAA being 1:2:8; the mass ratio of the added AgIn5S8 being 5-20%.

2. The composite material for removing Cr(VI) from water bodies according to claim 1, characterized in that, In step (1), the silver salt is AgNO3.

3. The composite material for removing Cr(VI) from water bodies according to claim 1, wherein In step (2), the zinc salt is ZnSO4·7H2O.

4. The composite material for removing Cr(VI) from water bodies according to claim 1, wherein In step (2), the mass fraction of the added AgIn5S8 is 10%. 5.The composite material according to any one of claims 1-4 for use in removing Cr(VI) from water.

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