Synthesis/Modification Of ZnIn₂S₄ Photocatalyst And Its Degradation Characteristics For Dye Wastewater

Photocatalysis can be divided into UV photocatalysis and visible photocatalysis,and UV photocatalysis is the most mature.Up to now,many studies have found that more than 3,000 refractory organic compounds can be rapidly degraded by nanometer TiO₂ or ZnO under ultraviolet irradiation.Nano titanium dioxide has many advantages,including no toxicity,good chemical stability and low price,so it has become a research focus in many photocatalytic materials.However,the absorption band of nanometer TiO₂ is narrow,mainly in ultraviolet light,but the UV ray is less than 5%in the solar spectrum energy distribution.The photogenerated electron-hole generated by UV light is easy to recombine,and the number of electrons and holes are reduce.The light energy is use incompletely.The low efficiency of photoelectric conversion and the reduction of the efficiency of catalyst,so in recent years the research of visible light catalyst has become a new research hotspot.Because of the narrow band gap,strong photocatalytic performance,large specific surface area and good adsorption performance,semiconductor ZnIn₂S₄ has been widely concerned in the degradation of dye wastewater and photocatalytic decomposition of water for hydrogen production.In this paper,ZnIn₂S₄ and TiO₂-ZnIn₂S₄ modified composite photocatalysts were prepared by hydrothermal synthesis method,characterizing the morphology?crystal structure and optical properties of the two catalysts by scanning electron microscopy?SEM?,Energy Dispersive Spectrometer?EDS?,X-ray diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?,UV-Visible absorption spectra?UV-Vis?.Under xenon lamp irradiation,the photodegradation properties of ZnIn₂S₄ and TiO₂-ZnIn₂S₄were investigated and compared with Rhodamine B as the target degradation material.This paper studied the effects of the initial concentration of pollutants,the dosage of catalyst and the initial pH value on the degradation activity of the catalyst.The repeated utilization performance test was carried out to investigate the reutilization performance,and to explore the mechanism of TiO₂-ZnIn₂S₄ adsorption and degradation.The main findings are summarized as follows:?1?ZnIn₂S₄ photocatalyst was prepared by hydrothermal synthesis,and its the main elements of Zn,In,S.Structure of ZnIn₂S₄ photocatalyst is tetragonal structure.By scanning electron microscopy?SEM?,Energy Dispersive Spectrometer?EDS?,X-ray diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?,UV-Visible absorption spectra?UV-Vis?,the samples were characterize.The results showed that the surface of ZnIn₂S₄ spherical particles as skirt structure,and particle size between 1.5?m-3?m.The band gap is 2.385 eV,and the visible light has better response capability.?2?In the process of degradation of Rhodamine B by ZnIn₂S₄,if photocatalyst is added to the contaminant without visible light irradiation,it is found that the photocatalyst can only adsorb some Rhodamine B molecules onto the surface of the photocatalyst.The concentration of Rhodamine B solution will not decrease significantly when the reaction reaches the equilibrium point of adsorption and desorption.If visible light is used to irradiate the solution without adding photocatalyst to the polluted solution,the concentration of Rhodamine B solution does not change.It shows that Rhodamine B can not be degraded by visible light under this condition.?3?The amount of photocatalysis added to the solution should not be excessive and the concentration of simulated pollutants should not be excessive.Because the increase in the amount of photocatalyst and the increase in the concentration of pollutants will change the chroma,concentration and transmittance of the degraded solution,as a result,the number of photogenerated electrons on the surface of photocatalyst was reduced,and the overall efficiency of the reaction was changed.When the amount of catalyst was increased from 20 mg/L to 100 mg/L,the degradation rate of Rhodamine B increased to 97.42%,but the degradation rate increased first and then decreased.?4?pH is an important factor affecting the degradation efficiency in photocatalytic degradation process.Under the conditions of pH=2 and pH=4,the adsorption efficiency is higher.When the adsorption experiment is completed for 30 minutes,the adsorption efficiency is the highest at pH=8,and the adsorption efficiency is 45.12%.The degradation effect of Rhodamine B was the best under the condition of pH=8,reaching 94.75%.It was found that the adsorption efficiency and photocatalytic degradation rate of Rhodamine B in adsorption stage and photocatalytic stage were relatively high at pH=8,so the optimal pH condition for TiO₂-ZnIn₂S₄degradate Rhodamine B was pH=8.?5?TiO₂-ZnIn₂S₄ composite catalysts were prepared by hydrothermal synthesis method.The results of SEM?EDS?XPS?XRD and UV-Vis showed that TiO₂ and ZnIn₂S₄ were successfully compounded together.The structure may be core-shell structure,wrapping in outer layer with TiO₂and ZnIn₂S₄as the core.In the comparison experiment of TiO₂,ZnIn₂S₄ and TiO₂-ZnIn₂S₄,the removal rate of TiO₂-ZnIn₂S₄degradate Rhodamine B by 120min is more than 97.42%.The removal rate was 4.23times of TiO₂ and 1.07 times of pure ZnIn₂S₄.The catalytic performance of pure ZnIn₂S₄ decreased to about 36%after 5 times of repeated degradation experiment.?6?Isopropanol and p-benzoquinone can inhibit photocatalytic degradation efficiency.The inhibition of p-benzoquinone on degradation efficiency was obvious.Adding isopropanol and p-benzoquinone to photocatalytic system,the degradation rates decreased to 88.63%and 73.65.This indicates that the main active substance in photocatalytic degradation is·O_-2,and the secondary one is·OH.