A preparation method of a cadmium sulfide@metal organic framework heterojunction composite material

Abstract

The application relates to a preparation method of a cadmium sulfide@metal organic framework heterojunction composite material, and belongs to the fields of photochemical energy conversion and photocatalytic degradation. The application aims to solve the technical problems of high-quality preparation of an artificial photosynthesis photocatalytic composite material and how to effectively improve the photochemical energy conversion efficiency. The method comprises the following steps: firstly, zirconium tetrachloride, 2-amino-4,4'-biphenyldicarboxylic acid and acetic acid are dissolved in N,N-dimethylformamide, and then the mixture is transferred into a reaction kettle for heating; after the reaction is completed, the mixture is cooled to room temperature, and then taken out, washed and dried to obtain a UiO-67-NH2 solid powder; secondly, the UiO-67-NH2 powder, cadmium nitrate tetrahydrate and thioacetamide are added into deionized water, and then the mixture is continuously stirred after being heated; after the reaction is completed, the mixture is cooled to room temperature, and then washed and dried for multiple times to obtain a cadmium sulfide@metal organic framework (CdS@UiO-67-NH2) heterojunction composite material.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of photochemical energy conversion and photocatalytic degradation. BACKGROUND

[0002] In recent years, artificial photosynthetic photocatalytic systems have attracted extensive attention from researchers. Artificial photosynthetic photocatalytic systems are a kind of photocatalytic composite material systems based on semiconductor materials inspired by natural photosynthesis, and the electron transfer path thereof presents a Z type, which is also called a Z-scheme photocatalytic system. Direct Z-scheme photocatalysts obtained by directly compounding two semiconductors through in-situ growth have attracted extensive attention due to their simple synthesis process, independence on noble metals as electron mediators, and simple and clear electron transfer path. The specific composition and photo-induced charge transfer mechanism thereof are as follows: based on the reduction photocatalyst PSI (with a relatively high Fermi level) and the oxidation photocatalyst PS II (with a relatively low Fermi level) formed by the adaptation of the Fermi level and the band edge structure of two kinds of semiconductors, an effective interface contact is formed, so that the photo-induced electrons will transfer from the conduction band of PS II to the valence band of PSI under the action of the built-in electric field in the space charge region, promoting the recombination of photo-induced carriers with low redox potential, and retaining photo-induced electrons and photo-induced holes with high reduction and oxidation potentials at the PSI and PS II ends, respectively, so as to realize the efficient spatial separation of photo-induced electrons and holes, and thus achieve the purpose of improving the photocatalytic performance.

[0003] Among various semiconductor photocatalytic materials, transition metal sulfide cadmium sulfide (CdS) is considered to be a promising photocatalyst due to its narrow band gap, high potential, low cost and high activity. Its synthesis method is various, its morphology is controllable and easy to modify, and it is widely used in the construction of efficient heterojunction composite materials. Metal-organic framework (MOF) is a new functional inorganic-organic hybrid material, which is a kind of porous crystalline body constructed by central metal ions or metal oxide clusters and organic ligands in three-dimensional space, has extremely high specific surface area, clear structure and adjustable porosity, and has flexible adjustability in structure, composition and functional properties, and is an excellent photocatalytic carrier. Its high porosity can effectively load other nanoscale photocatalysts, and its stable and ordered structure is conducive to the transfer of photo-induced electrons, so the research on composite photocatalysts constructed by various semiconductors has attracted extensive attention and has excellent performance.

[0004] In summary, the application provides a preparation method of a cadmium sulfide@metal organic framework heterojunction composite material, which adopts a simple and mild co-precipitation method to grow cadmium sulfide nanoparticles on metal organic framework (UiO-67-NH2) nanocrystalline grains in situ, and prepare a cadmium sulfide@metal organic framework (CdS@UiO-67-NH2) heterojunction composite material with high efficient photocatalytic activity. The direct Z-type heterojunction photocatalyst can effectively coordinate the efficiencies of sunlight absorption, photogenerated charge separation and surface chemical reaction. Compared with the preparation strategy of constructing a heterojunction by a conventional two-step hydrothermal method, the co-precipitation synthesis method proposed by the application is under normal pressure, low temperature and fast, and does not need high-temperature and high-pressure hydrothermal reaction. Only under normal pressure, less than 100 DEG C, and less than 5 hours of continuous stirring, the composite material has a complete morphology, excellent heterojunction interface contact, stable combination, and excellent quantity and quality. Meanwhile, the method is convenient, efficient, green and energy-saving, and meets the development strategy of low carbon and low energy consumption. SUMMARY

[0005] The application relates to solving the problems of high-quality low-energy-consumption preparation of a metal organic framework-based artificial photosynthetic heterojunction catalyst and improvement and optimization of catalyst performance, and provides a new strategy for synthesizing a mild, simple and fast heterojunction composite material. In order to solve the above problems, the preparation method of a cadmium sulfide@metal organic framework heterojunction composite material in the application is completed through the following steps.

[0006] Step one: zirconium tetrachloride, 2-amino-4,4'-biphenyldicarboxylic acid and acetic acid are dissolved in N,N-dimethylformamide, and after being fully stirred and dissolved, the solution is transferred to a reaction kettle for a solvothermal reaction; after being cooled to room temperature, the solution is washed and dried to obtain a UiO-67-NH2 solid powder.

[0007] Step two: the UiO-67-NH2 prepared in step one is dispersed in a cadmium nitrate tetrahydrate and a thioacetamide aqueous solution, and heated and stirred; after the reaction is completed, the solution is cooled to room temperature, washed and dried to obtain a CdS@UiO-67-NH2 heterojunction composite material.

[0008] Further limited, in step one, 46.90-87.10 mg of zirconium tetrachloride, 50.40-93.60 mg of 2-amino-4,4'-biphenyldicarboxylic acid and 1.20-1.50 mL of acetic acid are dissolved in 20 mL of N,N-dimethylformamide.

[0009] Further limited, in step one, the stirring and dissolving time is 30 min.

[0010] Further limited, in step one, the solvothermal reaction temperature is 100-140 DEG C, and the reaction time is 20-28 h.

[0011] Further limited, in step one, the vacuum drying box is 60 ℃ for 12 h h.

[0012] Further limit, in step two, 70~130 mg of UiO-67-NH2, 492.70~706.90 mg of cadmium nitrate tetrahydrate, 119.70~171.80 mg of thioacetamide are added into 50 mL of deionized water in turn.

[0013] Further limit, in step two, the stirring dissolution time is 30 min.

[0014] Further limit, in step two, the heating temperature is 60~100 ℃, and the holding time is 2~4 h.

[0015] Further limit, in step two, the vacuum drying box is 60 ℃ for 12 h h.

[0016] The cadmium sulfide@metal organic framework heterojunction catalyst prepared by the method of the application is CdS nanoparticles which are in-situ grown on the surface of UiO-67-NH2nano octahedral crystal grains by coprecipitation, forming a CdS@UiO-67-NH2composite material. The application provides a novel MOF-based composite material preparation technology which is fast, low-temperature and normal-pressure, so as to achieve close contact of the heterojunction interface, effective spatial separation of the photo-generated carriers, and finally achieve the purpose of effectively improving the photocatalytic performance. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is the XRD pattern of UiO-67-NH2, CdS and each component CdS@UiO-67-NH2(CU) composite material; Figure 2 is the scanning electron microscope photo of UiO-67-NH2nano octahedral crystal grains, CdS nanoparticles, 2.7CU, and the transmission electron microscope photo, selected area high-resolution transmission electron microscope photo and energy spectrum analysis diagram of 2.7CU; Figure 3 is the ultraviolet-visible absorption spectrum of UiO-67-NH2, CdS and 2.7CU; Figure 4 is the band gap diagram of UiO-67-NH2, CdS and 2.7CU; Figure 5 is the Mott-Schottky electrochemical test spectrum line of UiO-67-NH2nano octahedral crystal grains, CdS nanoparticles and 2.7CU; Figure 6 is the electrochemical impedance test spectrum line of UiO-67-NH2nano octahedral crystal grains, CdS nanoparticles and 2.7CU; Figure 7 is the photocatalytic reduction degradation curve of each sample with 30 mL of 20 mg / L potassium dichromate indicator with time; Figure 8is the fitting of the chemical reaction kinetics of the photocatalytic reduction degradation of each sample on 30 mL of 20 mg / L potassium dichromate indicator; Figure 9 is the conversion comparison of the degradation rate of each sample on 30 mL of 20 mg / L potassium dichromate indicator. Embodiment

[0018] Example 1: The preparation of UiO-67-NH2 nanooctahedral crystals in this example was carried out according to the following steps: 67 mg of zirconium tetrachloride (ZrCl4), 72 mg of 2-amino-4,4'-biphenyldicarboxylic acid (C 14 H 11 NO4), 1.4 mL of acetic acid (CH3COOH) were dissolved in 20 ml of N,N-dimethylformamide (C3H7NO), stirred for 30 min, and then transferred to a 50 mL reactor, heated at 120 ℃ for 24 h, and then cooled to room temperature. The product was washed with ethanol for 5 times, and dried in a vacuum drying oven at 60 ℃ for 12 h to obtain UiO-67-NH2 powder.

[0019] The preparation method of a kind of cadmium sulfide@metal organic framework heterojunction composite material in this embodiment is completed by the following steps.

[0020] Step one, 67 mg of zirconium tetrachloride, 72 mg of 2-amino-4,4'-biphenyldicarboxylic acid, and 1.4 mL of acetic acid were added to 20 ml of N,N-dimethylformamide solvent, stirred for 30 min, and then transferred to a 50 mL reactor, heated at 120 ℃ for 24 h. The product was washed with ethanol for 5 times, and dried in a vacuum drying oven at 60 ℃ for 12 h to obtain UiO-67-NH2 powder.

[0021] Step two, 100 mg of UiO-67-NH2 powder was dispersed in 6 beakers respectively, each containing 50 mL of deionized water, and then 492.70, 535.60, 578.40, 621.30, 664.10 and 706.90 mg of cadmium nitrate tetrahydrate and 119.73, 130.15, 140.55, 150.98, 161.38 and 171.78 mg of thioacetamide were added in turn. After stirring for 30 min to fully dissolve, the temperature was raised to 80 ℃ and stirring was continued for 3 h. After the reaction was completed and cooled to room temperature, it was washed with anhydrous ethanol and ionized water for 3 times respectively, and dried at 60 ℃ under vacuum for 12 h to obtain CdS@UiO-67-NH2 powder. According to the mass ratio of CdS to UiO-67-NH2, the composite samples were named as 2.3CU, 2.5CU, 2.7CU, 2.9CU, 3.1CU and 3.3CU respectively.

[0022] The photocatalytic reduction degradation of potassium dichromate solution was carried out using a 300 W xenon lamp to simulate sunlight. 10 mg of the catalyst to be tested and 30 mL of potassium dichromate solution with a concentration of 20 mg / L were placed in a 100 mL beaker. The beaker was fixed in front of the light source at a distance of 5 cm, and magnetic stirring was maintained at a constant speed during the degradation reaction. The reaction solution was detected for absorbance at the same time interval, and the concentration of the reaction solution was calculated to draw the degradation rate vs. illumination time curve, thereby analyzing and comparing the photocatalytic activity of the samples. As shown in Figure 6

[0023] As can be seen from Figure 7 , the performance of the 2.3CU ~ 3.3CU composite photocatalysts is higher than that of the reference UiO-67-NH2 and CdS catalysts in the photocatalytic reaction. Among them, the degradation rate of the 2.7CU sample is the fastest, and it can degrade 77% of the potassium dichromate indicator solution in 5 minutes, with a degradation rate of 31.71 μmol·min -1 ·g cat -1 The performance of the CdS@UiO-67-NH2 artificial photosynthetic catalyst shows that the unique photoelectron migration path of the catalyst creates favorable conditions for the separation of space charge, not only prolongs the lifetime of photoelectrons, but also effectively increases the reaction thermodynamic potential energy of photoelectrons, which macroscopically manifests as a significant improvement in the photocatalytic performance of the material.​

Claims

1. A method for preparing a cadmium sulfide@metal-organic framework heterostructure composite material, characterized in that... The preparation method is completed by the following steps: step one, dissolving zirconium tetrachloride, 2-amino-4,4'-biphenyl dicarboxylic acid and acetic acid in N,N-dimethylformamide, stirring sufficiently, then transferring the solution into a polytetrafluoroethylene-lined reaction kettle, heating, cooling to room temperature, washing multiple times and drying in a vacuum drying box to obtain a metal-organic framework UiO-67-NH2 solid powder; step two, adding the UiO-67-NH2 powder obtained in step one into deionized water, stirring sufficiently to disperse, then sequentially adding cadmium nitrate tetrahydrate and thioacetamide into the water dispersion of UiO-67-NH2, continuously stirring after heating, washing multiple times and drying after cooling to room temperature when the reaction is completed, to obtain a cadmium sulfide@metal-organic framework heterojunction composite material. In step two, 70-130 mg of UiO-67-NH2 powder, 492.70-706.90 mg of cadmium nitrate tetrahydrate and 119.70-171.80 mg of thioacetamide are added into 50 mL of deionized water.

2. The method of claim 1, wherein In step one, 46.90-87.10 mg of zirconium tetrachloride, 50.40-93.60 mg of 2-amino-4,4'-biphenyl dicarboxylic acid and 1.20-1.50 mL of acetic acid are dissolved in 20 mL of N,N-dimethylformamide.

3. The method of claim 1, wherein The stirring and dissolving time in step one is 30 min.

4. The method of claim 1, wherein The heating temperature in step one is 100-140 DEG C, and the holding time is 20-28 h.

5. The method of claim 1 wherein In step one, the holding time in a vacuum drying box at 60 DEG C is 12 h.

6. The method of claim 1, wherein In step two, the cadmium nitrate tetrahydrate and thioacetamide are sequentially added into the water dispersion of UiO-67-NH2, and the continuously stirring time after heating is 30 min.

7. The method of claim 1 wherein The heating temperature in step two is 60-100 DEG C, and the holding time is 2-4 h.

8. The method of claim 1, wherein In step two, the holding time in a vacuum drying box at 60 DEG C is 12 h.

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