Photocatalytic Degradation Of RhB By ZnIn₂S₄ Under Visible-light Irradiation

Semiconductor photocatalytic oxidation technology has been proved to be a promising approach for environmental pollutant remediation,because it can completely decompose organic pollutant into CO2 and H2 O at room temperature.TiO2 has been considered as an excellent photocatalyst for its nontoxicity,inexpensive and chemical stability.However,due to its wide band gap?3.2 eV?,TiO2 is known to be active only under UV light,which largely restricts its practical applications.As a result,much attention has been focused on designing new photocatalysts active under visible light.In this paper,ZnIn₂S₄ samples were prepared by hydrothermal method and used as photocatalyst,The effects of reaction conditions on the visible-light photocatalytic performances were studied.The as-prepared samples were characterized by XRD?XPS?BET?UV-vis DRS.Active oxygen species generated on as-prepared samples during visible light irradiation were studied by In situ capture experiment.The photodegradation process of RhB was monitored by LCMS–IT–TOF techniques to dentify the intermediates,and a proposed photocatalytic degradation pathway of the pollutions.The main results are summarized as follows:?1?Main components of ZnIn₂S₄ are Zn?In?S,its crystal structure is hexagonal phase,it has a large specific surface area,while the pore size distribution is mostly range from 0⁵0 nm.The band gap energy of ZnIn₂S₄ is 2.046 eV.?2?In the process of adsorption of RhB by ZnIn₂S₄,only part of RhB molecules can be adsorbed onto the surface of the photocatalyst.Photodegradation of RhB under visible light was almost negligible.?3?The concentration of pollutant and catalyst dosage should not be too high.Because with the increase of pollutant concentration and the catalyst dosage,the chroma and light transmittance of the solution will change,so that the amount of photons arrived at the surface of the catalyst will decreases and affected the reaction efficiency.When the initial concentration of RhB solution gradually increased from 5 mg/L to 25 mg/L,the degradation efficiency of RhB also decrease from 97.41% to 88.58%;when the catalyst dosage was increased from 0.05 g/L to 0.20 g/L,the degradation efficiency of RhB was increased to 99.39%.?4?When the initial pH of solution changed from 2 to 12,the adsorption efficiency increased from 42.69% to 44.78% and then decreased to 19.85%.When the initial pH of solution is 4,the adsorption efficiency reached the maximum The Zeta potential of ZnIn₂S₄ and the form of RhB was changed because the initial pH of solution was different,thus the electrostatic force between ZnIn₂S₄ and RhB was different which leaded to the different adsorption efficiency.?5?Compared with the traditional magnetic stirring mixing,Stirring solution with aeration can increase adsorption efficiency about 23%.Bubbling air instead nitrogen,photocatalytic degradation can be promoted to some extent with dissolved oxygen concentration increased,degradation efficiency increased from 96.45% to 97.56%.?6?The stability of pure ZnIn₂S₄ is not so good,After five cycle,the degradation efficiency of two check test reduced from 98.05%,98.08% to 38.45%,37.81% respectively,which is due to the reduction of the number of catalyst because the Zn2+ was reduced to Zn by photogenerated electrons.?7?Capture agent such as isopropyl alcohol?EDTA?benzoquinone have certain influence on the photocatalysis.The adsorption efficiency increased to 46.62%,and the degradation efficiency increased to 98.9% after added EDTA.The degradation efficiency was decreased to 77.77% and 48.64% respectively after added the isopropyl alcohol and benzoquinone.Results showed that ·O₂ is the key active species for degradation of RhB by ZnIn₂S₄ under visible light irradiation,and ·OH played a supplementary role during the photocatalytic process.?8?During the photocatalytic process.RhB was degraded through N-deethylation,under the effects of active substance,Ring-opening reaction is taking on intermediates?rhodamine?,and gradually degraded into small molecules.