Effect of annealing temperature and Mn doping on the structural and optical properties of ZnS thin films for enhanced photocatalytic degradation under visible light irradiation

Abstract

Herein we report a facile and low cost Sol-Gel method was adapted to design and fabricate highly efficient ZnS photocatalyst. The zinc sulfide (ZnS) thin films have been prepared at different annealing temperatures (200, 300 and 400 °C) and annealing temperatures 400 °C was optimized for Manganese (Mn) doped ZnS (Zn1-x Mnx S) (10 wt%) thin films. The effect of annealing temperature and Mn doping on the structural, optical and photocatalytic properties of ZnS thin films were investigated in detail by using XRD, FESEM, EDS, UV–Vis., PL, XPS and N2 adsorption-desorption analysis. XRD pattern exhibited hexagonal crystal structure for prepared samples and average particle size was increased from 25 to 47 nm with increasing annealing temperature and Mn doping. FESEM images revealed that nanoflake like morphology for annealed samples further it’s found to disappear for Mn doped ZnS samples. The presence Mn2+ ions into ZnS lattice was found from EDS and XPS analysis. Optical properties was analyzed by using UV–Vis. and PL studies and it’s found photogenerated recombination process and surface related defects with considerable red shift within the absorption edge and significant narrowing the band gap energy of undoped ZnS by increased annealing temperature with Mn doping. The large surface area with mesopores nature and tuning the optical property in the visible light region could be improve the rapid photo degradation efficiency of methylene blue dye (MB) under stimulated visible light enlightenment. The ZnS:Mn thin films annealed at 400 °C catalyst showed excellent photodegradation efficiency (99%), good stability with better first order kinetic and easy reusability towards MB dye, furthermore the effect of annealing temperature and Mn doping for the enhanced photo catalytic mechanisms by visible light was also discussed.