Copper-doped zinc sulfide nano composite material as well as preparation method and application thereof

Abstract

The invention relates to a copper-doped zinc sulfide nano composite material as well as a preparation method and application thereof, and belongs to the technical field of catalysts. In the copper-doped zinc sulfide nano composite material disclosed by the invention, the doping proportion of Cu is 0.1 wt%-10 wt%. The copper-doped zinc sulfide nano composite material prepared by the preparation method disclosed by the invention can be used for effectively degrading plastics and realizing efficient hydrogen evolution. The visible light absorption range can be effectively expanded by doping a small amount of Cu, and separation and transfer of carriers are promoted. Meanwhile, nuclear magnetic resonance detection analysis shows that the plastic is successfully degraded into small organic molecules such as formate, acetate and glycollate under photocatalysis. The invention provides a new thought for the design of a non-toxic catalyst in a sustainable and sunlight-driven plastic light conversion process, and responds to the aims of environmental protection, low cost and high efficiency.

Description

Technical Field

[0001] The invention belongs to the field of catalysts, and particularly relates to a preparation method and application of a copper-doped zinc sulfide nanocomposite material. Background Art

[0002] Plastics are widely used in daily life because of their durability, low cost and ease of synthesis. However, the thermal stability and chemical inertness of waste plastics make them difficult to decompose, and a large amount of waste plastics have begun to accumulate in landfills or be discarded into the natural environment, causing serious harm to the natural ecosystem. Therefore, exploring environmentally friendly and economical ways to achieve sustainable recycling of plastic waste is a research hotspot in various fields. Compared with physical recycling, chemical recycling is a more promising strategy for plastic value-added. This technology directly uses solar energy to convert waste plastics into organic small molecules, from monomers to hydrocarbons. At the same time, these products can not only be repolymerized into plastics, but also upgraded into high-value-added products and fuels, thereby realizing the closed-loop reuse of materials. Therefore, photocatalytic technology provides a promising way to solve this energy challenge. Summary of the invention

[0003] The present invention provides a copper-doped zinc sulfide nanocomposite material, which is used as a catalyst, in particular as a photocatalyst for various chemical reactions, including the following examples: effectively degrading plastics and achieving efficient hydrogen evolution.

[0004] The photocatalyst-copper-doped zinc sulfide nanocomposite material of the present invention is successfully prepared by a one-step simple reflux method. This catalyst shows high efficiency in the photocatalytic treatment of waste plastics, achieving a hydrogen evolution rate of at least 4.133mmol / g / 4h. The chemical composition, morphology, structure and performance of the catalyst were deeply analyzed through a variety of physical and chemical characterization techniques. The results show that this catalyst not only has a wide visible light absorption capacity, but also can achieve rapid separation and migration of charge carriers. Furthermore, by finely regulating the catalyst components and proportions, the optimization of the structure and interface performance is achieved, thereby promoting a significant improvement in the photocatalytic hydrogen production activity.

[0005] Specifically, the copper-doped zinc sulfide nanocomposite material of the present invention is prepared by a one-pot method, for example, copper acetate is used as a copper source, zinc acetate is used as a zinc source, and thiourea is used as a sulfur source as a precursor, and the desired sample is obtained by reflux at, for example, 100° C. The color of the sample is significantly affected by changing the doping ratio of Cu (0.6wt%, 10wt%), thereby affecting the fluorescence intensity of the sample.

[0006] Among them, 0.6wt% Cu-ZnS shows excellent hydrogen evolution rate under the condition of alkalinity (Alkalinity) such as 5M KOH, and reaches at least 4133.09μmol / g within 4h under the condition of 40°C. Compared with existing reports, it can be said to be the best non-toxic, low-cost, and earth-abundant catalyst for hydrogen production by photoreforming of plastic waste. At the same time, other oxidation products of waste plastic conversion were analyzed by nuclear magnetic resonance spectroscopy, and peroxidation products were detected in the reaction solution mainly in the form of carbonates. The pretreated PET contains complex small molecules such as ethylene glycol (EG) and terephthalic acid (TPA). The organic small molecules after PET photoreforming include acetate, formate and glycolate. After 4 cycles, the catalyst still maintains at least 74% of its catalytic activity, indicating that the catalyst has a certain stability.

[0007] The copper-doped zinc sulfide nanocomposite prepared by the present invention can effectively degrade plastics and realize efficient hydrogen evolution. The doping of a small amount of Cu can effectively expand the visible light absorption range and promote the separation and transfer of carriers. At the same time, nuclear magnetic resonance detection analysis shows that the plastic is successfully degraded into organic small molecules such as formate, acetate and glycolate under photocatalysis. The present invention provides a new idea for the design of non-toxic catalysts in sustainable, sunlight-driven plastic photoconversion processes, responding to the goals of environmental protection, low cost and high efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 The morphology and structure analysis diagrams of 0.6wt% Cu-ZnS and 10wt% Cu-ZnS samples, ab) original sample diagrams, cd) SEM spectra, ef) fluorescence colorimetric photos of the samples;

[0009] Figure 2 Qualitative analysis diagrams of 0.6wt% Cu-ZnS and 10wt% Cu-ZnS samples: a) XRD spectrum, b) EPR spectrum, c) UV-DRS spectrum, d) fluorescence spectrum;

[0010] Figure 3 This is the photocatalytic principle diagram of Cu-ZnS;

[0011] Figure 4 In the figure, a) is the photocatalytic conversion rate diagram of 0.6wt% Cu-ZnS and 10wt% Cu-ZnS samples within 4h; b) is the nuclear magnetic resonance spectrum; c) is the four cyclic test diagrams of the hydrogen evolution performance of 0.6wt% Cu-ZnS. DETAILED DESCRIPTION

[0012] In order to make the technical personnel in the field understand the present invention more clearly and intuitively, the present invention will be further described below in conjunction with the accompanying drawings. The experimental methods without specific conditions in the following examples are selected according to conventional methods and conditions, or according to the product instructions.

[0013] The present invention adopts a simple one-pot method, uses a copper source (such as copper acetate), zinc acetate and a sulfur source (such as thiourea) as precursors, and synthesizes Cu-doped ZnS under mild conditions.

[0014] The specific preparation process is as follows: Cu(CH 3 COO 2 (0.02M) and Zn(CH 3 COO 2 The mixture of (0.5M) was dissolved in 80ml of deionized water, stirred for 5min, and then 40ml of 1.5M thiourea was slowly added. The reacted solution was stirred in the flask for 5 minutes, and then the pH value of the solution was adjusted to 7 (for example, by adding a small amount of NaOH). Then, the total solution was heated to 100°C in a water bath for 6h, washed with deionized water and ethanol, and centrifuged at 10000rpm to obtain 0.6wt% Cu-ZnS. The obtained 0.6wt% Cu-ZnS was dried overnight at 60°C.

[0015] The Cu doping amount was changed accordingly to obtain copper-doped zinc sulfide nanocomposites with different copper contents. For example, when 0.05 M Cu(CH 3 COO 2 , 10wt% Cu-ZnS can be obtained.

[0016] The above describes the one-pot method for preparing ZnS doped with different Cu contents. It uses copper acetate, zinc acetate and thiourea as precursors, and adds an appropriate amount of alkali source, such as NaOH solution, to adjust the pH value of the mixed solution to 7, and finally refluxes under heating at 100°C in a water bath to obtain the desired sample. The amount of the above chemicals and solvents can be adjusted accordingly according to the large-scale production of the catalyst.

[0017] like Figure 1 As shown in Figure 2, changing the Cu doping ratio (0.6wt%, 10wt%) will have a significant effect on the color of the sample, thereby affecting the fluorescence intensity of the sample. The surface morphology and structure of 0.6wt% Cu-ZnS and 10wt% Cu-ZnS samples were analyzed using scanning electron microscopy (SEM), corresponding to Figure 1 cd. It can be observed that the proportion of Cu has a significant effect on the morphology of the sample. When the Cu content is high, the sample consists of evenly distributed nano-scale petal-like small structures. When the Cu content is reduced, the sample structure is more spherical, and the uneven particles on the surface of the sphere are more like Cu doping. Figure 1 In the figure, ab are the original sample images of 0.6wt% Cu-ZnS and 10wt% Cu-ZnS, cd are their SEM spectra, and ef are the fluorescence colorimetric photos of the two samples.

[0018] The crystallinity of the prepared samples was analyzed by X-ray diffraction (XRD) measurement. Figure 2 a shows a cubic crystal structure. The diffraction pattern shows three broad peaks at 29.2°, 48.5° and 57.6°, indicating the formation of pure phase Cu-ZnS polycrystals with cubic sphalerite structure (β-ZnS phase) with good crystal quality. In addition, compared with the PDF cards of ZnS (JCPDS#05-0566) and CuS (JCPDS#06-0464), the peak of the sample has a slight red shift, which may be due to the Cu 2+ The doping of induced lattice phase shift and defects. In addition, the electron paramagnetic resonance (EPR) spectrum ( Figure 2 b) Provides fingerprint evidence for detecting copper vacancies. The sharp signal at 3210mT is attributed to copper vacancies. Obviously, 10wt% Cu-ZnS shows the strongest EPR signal, which may be due to the presence of more unpaired electrons, enhancing delocalization. Therefore, the relative SERS intensity in the resulting Cu-ZnS photocatalyst can be adjusted by changing the content of Cu precursor. As the Cu content decreases, the signal at 3210mT is significantly weakened. This once again proves that Cu has been successfully integrated into the ZnS lattice.

[0019] The optical properties and electronic band structures of the samples were analyzed using UV-visible diffuse reflectance spectroscopy (UV-DRS). Figure 2 As shown in c, with the increase of Cu doping amount, the visible light absorption range is significantly expanded and the color becomes darker. Under zinc-rich growth conditions, the sample is mainly composed of two phases, ZnS phase and non-stoichiometric xCu-ZnS phase, with band gap energies of 3.1~3.4eV and 2.2~2.5eV, respectively. It was found that doping with metal ions will cause a red shift in the photoresponse. The double band gap confirms the alloy nature of the material. The higher band gap can transmit high-energy photons falling on the material, while the lower band gap is conducive to light energy conversion. In order to further explore the separation, migration and recombination of photogenerated carriers, we studied the steady-state photoluminescence (PL). As Figure 2 As shown in Figure d, compared with 10 wt % Cu-ZnS, the fluorescence intensity of 0.6 wt % Cu-ZnS is weaker, which means that the separation / transfer of electron-hole pairs is more effectively accelerated, which is more conducive to the photocatalytic reaction.

[0020] Photocatalytic performance analysis

[0021] The photocatalytic principle Figure 3As shown. Specifically, for example, 20 mg of the photocatalyst is dispersed in 50 ml of a 25 mg / ml plastic, such as PET solution, under ultrasonic treatment, and the photoreforming performance is tested in a 100 ml container. First, the reactor is purged with high-purity argon for 10 minutes to remove residual air. A 300 W xenon lamp is used as the light source, equipped with a 420 nm UV cutoff filter to provide visible light irradiation. When the reactor temperature is 40 ° C, H 2 The yield was analyzed by gas chromatography.

[0022] Generally, in order to quickly break down the durability and inertness of plastics, plastics such as PET particles are first pretreated in an alkaline solution such as KOH at 80°C for 24 hours to depolymerize them into corresponding monomer molecules. Then, the supernatant of the PET solution is collected and filtered with a filter (such as 0.22μm) as the starting material for driving the photoreforming reaction. The amount of hydrogen evolution of the Cu-ZnS photocatalyst was regularly detected by gas chromatography. There are significant differences in the hydrogen evolution performance of Cu-ZnS photocatalysts with different Cu doping ratios.

[0023] like Figure 4 As shown in a, 0.6wt% Cu-ZnS exhibits an excellent hydrogen evolution rate under the condition of 5M KOH alkalinity, reaching 4133.09μmol / g within 4h at 40°C. Compared with existing reports, it can be said to be the best non-toxic, low-cost, and earth-abundant catalyst for hydrogen production from plastic waste photoreforming. At the same time, taking 0.6wt% Cu-ZnS as the best catalyst, nuclear magnetic resonance spectroscopy was further used to analyze other oxidation products of waste plastic conversion. The peroxidation products detected in the reaction solution mainly exist in the form of carbonates. The pretreated PET contains complex small molecules such as ethylene glycol (EG) and terephthalic acid (TPA). As Figure 4 As shown in b, the organic small molecules after PET photoreformation include acetate, formate and glycolate. Figure 4 As shown in c, the catalyst 0.6wt% Cu-ZnS still maintains about 74% of its catalytic activity after 4 consecutive cycles, indicating that the catalyst has a certain stability.

[0024] In general, the present invention successfully synthesized a series of Cu-ZnS with different Cu doping ratios using a one-pot reflux method, which can effectively degrade plastics and achieve efficient hydrogen evolution. A small amount of Cu doping can effectively expand the visible light absorption range and promote the separation and transfer of carriers. At the same time, nuclear magnetic resonance detection analysis shows that plastics are successfully degraded into organic small molecules such as formate, acetate and glycolate under photocatalysis. The present invention provides a new idea for the design of non-toxic catalysts in sustainable, sunlight-driven plastic photoconversion processes, responding to the goals of environmental protection, low cost and high efficiency.

[0025] Therefore, compared with Cd-based catalysts and catalysts with complicated synthesis steps, the catalyst of the present invention is more environmentally friendly and non-toxic, and has high economic benefits. Catalysts with different proportions show different morphologies and structures, such as spherical or nano-flower shapes. 2 and other high-value chemicals exhibit high performance.

[0026] The above description of the embodiments is to facilitate the understanding and application of the present invention by those skilled in the art. 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 work. Therefore, the present invention is not limited to the embodiments herein, and improvements and modifications made to the present invention by those skilled in the art based on the disclosure of the present invention should be within the scope of protection of the present invention.

Claims

1. A copper-doped zinc sulfide nanocomposite material, characterized in that: The doping ratio of Cu is 0.1 wt% to 10 wt%.

2. The copper-doped zinc sulfide nanocomposite material according to claim 1, characterized in that: The doping ratio of Cu is 0.6 wt %.

3. The copper-doped zinc sulfide nanocomposite material according to claim 1, characterized in that: The copper source for preparing the copper-doped zinc sulfide nanocomposite material is copper acetate.

4. The copper-doped zinc sulfide nanocomposite material according to claim 1 or 3, characterized in that: Thiourea is used as a sulfur source for preparing the copper-doped zinc sulfide nanocomposite material.

5. The copper-doped zinc sulfide nanocomposite material according to claim 4, characterized in that: The method is prepared by taking copper acetate, zinc acetate and thiourea as precursors and refluxing at 100°C.

6. The method for preparing the copper-doped zinc sulfide nanocomposite material according to claim 1, characterized in that: The steps include: Dissolve a mixture of copper acetate and zinc acetate in deionized water, keep stirring, and then slowly add thiourea; The reacted solution was stirred continuously in the flask, and then the pH value was adjusted to 7; The total solution is heated to 100° C. in a water bath. After the reaction is completed, it is washed with deionized water and ethanol, and the Cu-ZnS is obtained by centrifugation. The Cu-ZnS is dried.

7. The method for preparing the copper-doped zinc sulfide nanocomposite material according to claim 6, characterized in that: Adjust the pH of the solution using NaOH solution.

8. Use of the copper-doped zinc sulfide nanocomposite material as claimed in claim 1 as a catalyst in photocatalytic treatment of waste plastics.

9. The use according to claim 8, characterized in that At 40°C, the hydrogen evolution rate of copper-doped zinc sulfide nanocomposite with a Cu doping ratio of 0.6wt% in photocatalytic treatment of waste plastics is 4.133mmol / g / 4h.

10. The use according to claim 8, characterized in that After 4 cycles, the catalytic activity of the Cu-doped ZnS nanocomposite was maintained at a level of at least 74%.

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