A bifunctional Zn-SnS nanosheet and its preparation method and application

Abstract

The present invention belongs to the field of photocatalysis-ion exchange technology, and specifically relates to a bifunctional Zn-SnS nanosheet and a preparation method and application thereof. The nanosheet has a two-dimensional layered structure, wherein Zn 2+ is filled and distributed between the layers of the two-dimensional [Sn3S7] n 2n‑ skeleton; the preparation method is: performing ion exchange on a tin-containing layered metal sulfide and a zinc source, and then ultrasonically exfoliating in deionized water to obtain the nanosheet; the nanosheet is used as a photocatalysis-ion exchanger to break the complex of an organic rhodium complex, degrade the organic ligand, and recover free rhodium. Compared with the prior art, the present invention solves the problem that Rh cannot be recovered from organic rhodium wastewater in the form of a rhodium-organic ligand complex by the ion exchange technology in the prior art. This solution combines photocatalysis technology and ion exchange technology to achieve the recovery of trace Rh from organic rhodium wastewater.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalysis-ion exchange, and particularly relates to a bifunctional Zn-SnS nanosheet and a preparation method and application thereof. Background Art

[0002] Rhodium has stable resistance, good electrical conductivity and thermal conductivity, high catalytic activity, good resistance to acid and alkali corrosion, and good resistance to high-temperature oxidation. Therefore, rhodium has wide applications in high-tech, aerospace, military, petrochemical, fine chemical, environmental protection and other fields and plays an irreplaceable role. In particular, in chemical synthesis reactions, in homogeneous catalytic reaction processes, such as chemical synthesis processes such as catalytic hydrogenation, hydroformylation, and carbonylation, rhodium homogeneous catalysts are required. With the continuous expansion of chemical synthesis capabilities, the consumption of rhodium catalysts has also been increasing; however, during the preparation of organic rhodium homogeneous catalysts, a certain amount of organic rhodium wastewater will also be generated, and a large amount of organic rhodium wastewater will also be generated after the organic rhodium homogeneous catalyst fails.

[0003] The content of rhodium in the earth's crust is very low and the resources are very scarce. Therefore, it is necessary to recover rhodium from organic waste / wastewater to realize the resource utilization of rhodium. However, the raw materials, products and rhodium homogeneous catalysts used in the chemical catalytic process all exist in the same organic system. The types of rhodium-containing organic waste obtained after the reaction are numerous, the system is complex, and the rhodium content in the wastewater is low, making the recovery difficult. At present, the methods for recovering rhodium from waste organic catalysts include incineration method, extraction method, electrochemical method, membrane separation method, biosorption method, etc. However, these methods all have problems to varying degrees, such as serious rhodium volatilization loss, serious pollution, complex operation, high operating cost, low recovery rate, etc. Therefore, developing a simple, safe, high-recovery, wide-adaptability and green environmental protection large-scale and industrialized process to realize the recycling of rhodium, reduce environmental pollution and improve the recovery rate of rhodium is the future development trend.

[0004] Ion exchange technology has been widely used in the recovery of metal ions. Experimental results show that [Me2NH2]2[Ga2Sb2S7]·H2O, [Et2NH2]2[Ga2Sb2S7]·H2O and [Me2NH2] 4 / 3 [Me3NH] 2 / 3Open-framework sulfide complexes such as Sn3S7·1.25H2O have high ion-exchange capacity and excellent stability. For example, "Efficient Removal and Recovery of Uranium by a Layered Organic–Inorganic Hybrid Thiostannate", J. Am. Chem. Soc. 2016, 138, 38, 12578–12585; "A two-dimensionally microporous thiostannate with superior Cs + and Sr 2+ ion-exchange property", J. Mater. Chem. A, 2015, 3, 5665-5673; etc. Unfortunately, they cannot effectively recover Rh from organic rhodium wastewater in the form of rhodium-organic ligand complexes. Therefore, a new type of rhodium recovery method with high recovery rate and low pollution needs to be studied. Summary of the Invention

[0005] The purpose of the present invention is to provide a bifunctional Zn-SnS nanosheet, its preparation method and application to solve at least one of the above problems, so as to solve the problem that Rh cannot be recovered from organic rhodium wastewater in the form of rhodium-organic ligand complexes by ion exchange technology in the prior art. This solution combines photocatalytic technology and ion exchange technology to realize the recovery of trace Rh from organic rhodium wastewater.

[0006] The purpose of the present invention is achieved by the following technical solutions:

[0007] The first aspect of the present invention discloses a bifunctional Zn-SnS nanosheet. The nanosheet has a two-dimensional layered structure. Among them, Zn 2+ is filled and distributed between the layers of the two-dimensional [Sn3S7] n 2n- framework.

[0008] Photocatalytic technology has received extensive attention due to its mild reaction conditions, simple operation, and direct utilization of sunlight. This Zn-SnS nanosheet has both ion-exchange and photocatalytic bifunctions. It can achieve the breaking of the complex of organic rhodium complexes and the degradation of organic ligands through the strong oxidizing property of the photocatalyst, providing the possibility for the ion-exchange recovery of Rh ions, and at the same time recovering free rhodium ions based on ion exchange.

[0009] Preferably, the diameter of the nanosheet is 1-10 μm, and the thickness is 10-100 nm.

[0010] The second aspect of the present invention discloses a preparation method of the bifunctional Zn-SnS nanosheets as described above. The tin-containing layered metal sulfide is subjected to ion exchange with a zinc source, and then ultrasonically exfoliated in deionized water to obtain the nanosheets.

[0011] Preferably, the tin-containing layered metal sulfide is FJSM-SnS; the zinc source is zinc sulfate and / or zinc chloride; the dosage ratio of the tin-containing layered metal sulfide to the zinc source is 500 mg: 5-100 mmol.

[0012] Preferably, the FJSM-SnS is synthesized by a solvothermal method using tin chloride and elemental sulfur.

[0013] Preferably, the ion exchange is carried out in a chromatographic column, and the ion exchange time is 0.5-5 h.

[0014] Preferably, the ultrasonic power for the ultrasonic exfoliation is 50-500 W, and the ultrasonic time is 1-30 min.

[0015] The third aspect of the present invention discloses an application of the bifunctional Zn-SnS nanosheets as described above in the treatment of metal-organic complex wastewater.

[0016] Preferably, in the organic rhodium wastewater, the nanosheets are used as a photocatalytic-ion exchanger to break the complex of the organic rhodium complex, degrade the organic ligand, and recover the free rhodium.

[0017] Preferably, the complex breaking is carried out under the condition of pH 3-5.

[0018] Preferably, the nanosheets can also be regenerated and the Rh ions can be recovered by a reversible ion exchange method. Specifically, the used nanosheets (with Rh ions stored in the interlayer) are placed in a 1 mol / L ZnSO4 solution (the pH is adjusted to 2 with hydrochloric acid) for washing, so that the Rh ions stored in the interlayer of the nanosheets are exchanged with Zn ions, and then concentrated high-concentration rhodium can be obtained, and at the same time, the nanosheets are regenerated.

[0019] The working principle of the present invention is:

[0020] Through ion exchange, the filling of Zn 2+ in the [Sn3S7] n 2n- skeleton layer is realized; then through ultrasonic exfoliation, highly dispersed Zn-SnS nanosheets are obtained, so that the photocatalytic active sites and ion exchange sites are fully exposed, and the Zn-SnS nanosheet photocatalytic-ion exchanger of this solution has good catalytic performance and ion exchange performance.

[0021] The prepared two-dimensional Zn-SnS nanosheets can directly break down complex organic rhodium molecules and, under visible light irradiation, obtain free Rh ions through photocatalytic degradation of organic ligands. Meanwhile, the obtained free Rh ions are continuously enriched and stored in [Sn3S7] through ion exchange. n 2n- Inside the framework, the recycling of Rh ions is achieved. After the Rh ions are saturated in storage, the Rh ions are recycled through reversible ion exchange, realizing the recycling of Rh resources and the recycling of the catalyst.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The invention prepared a Zn-SnS nanosheet photocatalyst-ion exchanger through ion exchange and ultrasonic treatment. The raw materials are cheap and easily available, and the preparation method is simple and controllable. As a photocatalyst-ion exchanger for the recovery of rhodium in organic rhodium wastewater, it not only has high activity but also good recycling stability.

[0024] Under visible light irradiation, the two-dimensional Zn-SnS nanosheets can recover more than 92% of Rh from the [(COD)RhCl]2 solution, and the removal rate of the organic ligand COD can reach more than 86%; the trace Rh in the organic rhodium wastewater is effectively recovered, effectively reducing the harm to the environment. In addition, in the cycle test, the two-dimensional Zn-SnS nanosheets also show high stability, providing the possibility for the efficient recovery of Rh in organic rhodium wastewater and the continuous removal of pollutants.

[0025] The present scheme proposes a synergistic strategy of photocatalysis and ion exchange, providing an effective way for the recovery of Rh from organic rhodium wastewater. The two-dimensional Zn-SnS nanosheet photocatalyst-ion exchanger provided by the present invention can be recycled multiple times, and has low cost and simple process, and has the prospect of large-scale application. Description of the Drawings

[0026] Figure 1 It is a transmission electron microscope (TEM) image of the overall morphology of the Zn-SnS nanosheet photocatalyst-ion exchanger in Example 1;

[0027] Figure 2 It is an energy-dispersive X-ray spectroscopy (EDS) mapping image of the Zn-SnS nanosheet photocatalyst-ion exchanger in Example 1;

[0028] Figure 3 It is the activity test result of the Zn-SnS nanosheet photocatalyst-ion exchanger for recovering Rh in the [(COD)RhCl]2 solution. (a) is the concentration change of Rh ions, and (b) is the concentration change of Zn ions;

[0029] Figure 4Concentration change of COD during the photocatalytic-ion exchange recovery of Rh in [(COD)RhCl]2 solution by Zn-SnS nanosheets;

[0030] Figure 5 Cyclic test results for the photocatalytic-ion exchange recovery of Rh in [(COD)RhCl]2 solution by Zn-SnS nanosheets. (a) is the recovery rate of Rh, and (b) is the removal rate of COD. Specific embodiments

[0031] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that for those of ordinary skill in the art, several changes and improvements can be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0032] The experimental methods without specific conditions in the following embodiments are carried out according to conventional methods and conditions, or selected according to the product specifications. The reagents and raw materials used in the present invention are all commercially available.

[0033] This solution proposes a method combining photocatalytic technology and ion exchange technology to recover trace Rh from organic rhodium wastewater.

[0034] A bifunctional Zn-SnS nanosheet, the nanosheet is a two-dimensional layered structure, wherein Zn 2+ is filled and distributed between the layers of the two-dimensional [Sn3S7] n 2n- skeleton. The diameter of the nanosheet is 1-10 μm, and the thickness is 10-100 nm.

[0035] A preparation method of the bifunctional Zn-SnS nanosheet as described above, wherein the tin-containing layered metal sulfide (FJSM-SnS) is subjected to ion exchange with a zinc source (such as ZnSO4 and / or ZnCl2, etc.), and then ultrasonically exfoliated in deionized water to obtain the nanosheet.

[0036] Among them:

[0037] The zinc source is a solution of 0.1-2 mol / L Zn 2+ The dosage ratio of the tin-containing layered metal sulfide to the zinc source is 500 mg:50 mL.

[0038] The tin-containing layered metal sulfide is synthesized by a solvothermal method using SnCl4•5H2O and elemental S in the presence of dimethylamine: 0.502 g of SnCl4•5H2O, 0.131 g of elemental S, 3 mL of dimethylamine (AR, 40 wt. % in H2O, Macklin), and 1 mL of deionized water are thoroughly mixed until homogeneous. The resulting mixture is sealed in a 50 mL stainless steel autoclave lined with polytetrafluoroethylene, transferred to an oven, heated at 180 °C for 3 days, and then cooled to room temperature to obtain yellow hexagonal crystals and fine yellow powder. The yellow crystals are washed with ethanol and dried to obtain the FJSM-SnS sample.

[0039] Ion exchange is carried out in a chromatographic column, and the ion exchange time is 0.5 - 5 h.

[0040] The ultrasonic power for ultrasonic exfoliation is 50 - 500 W, and the ultrasonic time is 1 - 30 min.

[0041] A bifunctional Zn-SnS nanosheet as described above, used as a photocatalytic-ion exchanger for recovering rhodium in organic rhodium wastewater: during the reaction, the pH of the reaction system is 3 - 5.

[0042] Example 1

[0043] Take 500 mg of FJSM-SnS crystals and fill them in a chromatographic column. Add 50 mL of 1.0 mol / L ZnSO4 solution for ion exchange for 2 hours. Then place the obtained sample in 500 mL of deionized water and ultrasonically exfoliate it at an ultrasonic power of 100 W for 5 min to obtain a Zn-SnS nanosheet photocatalytic-ion exchanger, denoted as the Zn-SnS-1.0-5 sample.

[0044] The product is subjected to the following tests:

[0045] The transmission electron microscope (TEM) image is as Figures 1 - 2 shown, and the test instrument is FEI Talos 200s. It can be seen from Figures 1 - 2 that the prepared Zn-SnS nanosheet photocatalytic-ion exchanger has a two-dimensional layered structure with a diameter of 1 - 10 μm. And in combination with Figure 2 it can be found that Zn is uniformly dispersed on the photocatalytic-ion exchanger.

[0046] Example 2

[0047] The preparation method of Example 2 is the same as that of Example 1, except that 500 mg of FJSM-SnS crystals are taken and filled in a chromatographic column, 50 mL of 1.0 mol / L ZnCl2 solution is added for ion exchange, and then the obtained sample is placed in deionized water and ultrasonically exfoliated for 5 min to obtain a Zn-SnS nanosheet photocatalytic-ion exchanger.

[0048] Examples 3 to 6

[0049] The preparation methods of Examples 3 to 6 are the same as that of Example 1, except that different from the ZnSO4 solution concentration of 1.0 mol / L in Example 1, the ZnSO4 solution concentration used in Example 3 is 0.1 mol / L, the ZnSO4 solution concentration used in Example 4 is 0.5 mol / L, the ZnSO4 solution concentration used in Example 5 is 1.5 mol / L, and the ZnSO4 solution concentration used in Example 6 is 2 mol / L.

[0050] Examples 7 to 10

[0051] The preparation methods of Examples 7 to 10 are the same as that of Example 1, except that different from the ultrasonically exfoliating time of 5 min in Example 1, the ultrasonically exfoliating time of Example 7 is 10 min, the ultrasonically exfoliating time of Example 8 is 30 min, the ultrasonically exfoliating time of Example 9 is 25 min, and the ultrasonically exfoliating time of Example 10 is 1 min.

[0052] Examples 11 to 14

[0053] The preparation methods of Examples 11 to 14 are the same as that of Example 1, except that different from the ultrasonically exfoliating power of 100 W in Example 1, the ultrasonically exfoliating power of Example 11 is 50 W, the ultrasonically exfoliating power of Example 12 is 200 W, the ultrasonically exfoliating power of Example 13 is 350 W, and the ultrasonically exfoliating power of Example 14 is 500 W.

[0054] Examples 15 to 18

[0055] The preparation methods of Examples 15 to 18 are the same as that of Example 1, except that different from the ion exchange time of 2 h in Example 1, the ion exchange time of Example 15 is 4 h, the ion exchange time of Example 16 is 5 h, the ion exchange time of Example 17 is 0.5 h, and the ion exchange time of Example 18 is 1.5 h.

[0056] Activity test of the photocatalytic-ion exchanger

[0057] The recovery activity of the photocatalytic-ion exchanger for rhodium was carried out on a [(COD)RhCl]₂ solution under a 300 W xenon lamp (λ > 420 nm). Take 2 mg of the catalyst (the catalyst is the Zn-SnS nanosheet photocatalytic-ion exchanger prepared in Example 1) and add it to a 100 mL reactor containing 100 mL of [(COD)RhCl]₂ solution (Rh content is 1 ppm, and its pH value is adjusted to 3 with 0.5 mol / L hydrochloric acid). Control the temperature at 25 °C through condensed circulating water, and under dark conditions, stir for a certain time (15 min) to reach the adsorption equilibrium. Continue stirring and turn on the lamp for irradiation. Take out 5 mL of the mixed solution at different intervals (30 min, 60 min, 90 min, 120 min, 150 min), centrifuge to obtain the supernatant, and after filtration, measure the concentrations of Rh and Zn by ICP, and measure the COD concentration by liquid chromatography, which is recorded as the visible light irradiation group.

[0058] Keep the rest of the steps unchanged, but do not turn on the lamp throughout the process (equivalent to only using the ion exchanger, which can only achieve the function of ion exchange). Measure the concentration results of Rh and Zn obtained by testing, and measure the COD concentration by liquid chromatography, which is recorded as the dark group.

[0059] See the test results in Figure 3 and Figure 4 。

[0060] As Figure 3 shown, in the experiment of rhodium recovery, the Zn-SnS nanosheet photocatalytic-ion exchanger demonstrated excellent rhodium recovery performance. After 150 min of visible light irradiation, the rhodium recovery rate reached over 92%. At the same time, the corresponding Zn ion dissolution was detected, proving the occurrence of the ion exchange process. The results of the dark group without light irradiation were significantly inferior to those of the visible light irradiation group with light, indicating that the Zn-SnS nanosheet acts as both a photocatalyst (breaking the complex to obtain free rhodium ions) and an ion exchanger (ion exchange to enrich and recover free rhodium ions) during the rhodium recovery process.

[0061] As Figure 4 shown, in the experiment of rhodium recovery, the Zn-SnS nanosheet photocatalytic-ion exchanger also demonstrated high-efficiency removal performance for the organic ligand COD. After 150 min of visible light irradiation, the COD removal rate reached over 86%.

[0062] Cyclic performance test of the photocatalytic-ion exchanger

[0063] The recovery activity of the photocatalytic-ion exchanger for rhodium was carried out on a [(COD)RhCl]2 solution under a 300 W xenon lamp (λ>420 nm). 2 mg of the catalyst (the catalyst is the Zn-SnS nanosheet photocatalytic-ion exchanger prepared in Example 1) was added to a 100 mL reactor containing 100 mL of [(COD)RhCl]2 solution (Rh content is 1 ppm, and its pH value was adjusted to 3 with 0.5 mol / L hydrochloric acid). The temperature was controlled at 25 °C by condensing circulating water, and under dark conditions, it was stirred for a certain time (15 min) to reach the adsorption equilibrium. Then it continued to be stirred and the lamp was turned on for irradiation. After 150 min of light irradiation, it was centrifuged. The obtained supernatant was filtered and the concentration of Rh was measured by ICP, and the COD concentration was measured by liquid chromatography. The obtained precipitate sample was washed with 1 mol / L ZnSO4 solution (pH was adjusted to 2 with hydrochloric acid) to regenerate the catalyst after ion exchange, centrifuged, and dried, and then the above experiment was repeated to determine the recycling performance of the catalyst.

[0064] The test results are shown in Figure 5 .

[0065] As Figure 5 shown, in the recycling experiment, the Zn-SnS nanosheet photocatalytic-ion exchanger demonstrated excellent recycling stability and could be regenerated and reused after the used Zn-SnS nanosheets.

[0066] The above description of the embodiments is to enable those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative efforts. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. Application of a bifunctional Zn-SnS nanosheet in metal organic complex wastewater treatment, characterized in that: The nanosheet is a two-dimensional layered structure, wherein Zn 2+ Filled and distributed in two dimensions [Sn3S7] n 2n- Between the layers of the skeleton; In organic rhodium wastewater, the nanosheets act as a photocatalyst-ion exchanger to break the organic rhodium complex, degrade the organic ligand, and recover free rhodium.

2. The use according to claim 1, characterized in that: The diameter of the nanosheet is 1-10 μm and the thickness is 10-100 nm.

3. The use according to claim 1, characterized in that: The tin-containing layered metal sulfide is ion-exchanged with a zinc source, and then ultrasonically exfoliated in deionized water to obtain the nanosheet.

4. The use according to claim 3, characterized in that: The tin-containing layered metal sulfide is FJSM-SnS; the zinc source is zinc sulfate and / or zinc chloride; the dosage ratio of the tin-containing layered metal sulfide to the zinc source is 500 mg: 5-100 mmol / L.

5. The use according to claim 4, characterized in that: The FJSM-SnS is synthesized from tin chloride and elemental sulfur through a solvent thermal method.

6. The use according to claim 3, characterized in that: The ion exchange is carried out in a chromatographic column, and the ion exchange time is 0.5 to 5 hours.

7. The use according to claim 3, characterized in that: The ultrasonic power of the ultrasonic peeling is 50-500 W, and the ultrasonic time is 1-30 min.

8. The use according to claim 1, characterized in that: The complex breaking is carried out at a pH of 3 to 5.

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