STUDIES ON SYNTHESIS, CHARACTERIZATION AND DYE-DEGRADATION EFFICIENCY OF ZnO BASED PHOTOCATALYSTS

Abstract

ZnO is a semiconductor having wide band gap energy of 3.37 eV. In the present study, two types of dye degradation studies were performed one with the un-doped ZnO and second with the Sn doped ZnO prepared by combustion synthesis method. The un-doped ZnO samples were synthesized using different types of fuels such as citric acid, dextrose, glycine, oxalyl dihydrazide, oxalic acid and urea. The structural, optical, morphological and textural properties of the ZnO samples will be different for different ZnO samples which were prepared using different types of fuels. In order to study the structural, optical, morphological and textural properties of the synthesized samples, they have been characterized by XRD, UV-vis diffuse reflectance spectroscopy, FE-SEM and by physisorption respectively. All these samples were found to have the standard hexagonal wurtzite structure with the lattice constants a and c having values 3.25 A and 5.21 A, respectively. The diffuse reflectance spectra of the prepared samples have shown the maximum absorption of light in the UV region stating that these catalysts can be used as photocatalysts. The BET surface area measurements of the prepared catalysts were found to vary according to the equivalence ratio. The presence of pronounced hysteresis in N2 adsorption-desorption isotherm curves indicated the three dimensional network arrangement of pores in the ZnO samples prepared using dextrose and urea as fuels. The photodegradation ability of the various synthesized photocatalyts was tested for the photodegradation of an azo dye namely orange G dye solution and the ZnO photocatalyst prepared using oxalic acid as fuel showed highest decolourization and degradation ability under LTV light irradiation. Studies have also been performed to impregnate tin (Sn) into the ZnO matrix using the solution combustion method. Using the factorial method of design of experiments, three variables namely, dopant amount (5-15%), calcination temperature (400-800 °C) and calcination time (1-4 h) have been chosen as factors for checking their effect on various responses such as crystallite size, band gap energy, BET surface area, pore volume (m3/g) and degradation/decolorization efficiencies towards the dye. All the synthesized Sn doped ZnO photocatalysts were characterized with the same techniques as applied for the un-doped ZnO samples in order to find out the responses.