EVALUATION OF THE EFFICIENCY OF EGGSHELL ASH AS PHOTOCATALYST FOR DECOLOURISATION OF AZO DYE USING SOLAR UTRA-VIOLET RADIATION

Abstract

Water pollution is one of the environmental challenges to be surmounted to avoid global public health hazard. Due to the complex chemical structure, azo dyes in industrial effluent have a long shelf life and are toxic to aquatic creatures even at low quantities. In this study, the decolourisation of azo dye, methylene blue (MB) using locally sourced photocatalyst, eggshell ash (ESA) under solar ultra-violet (UV) radiation was investigated. In order to test the photo-activities of ESA, a similar study was performed without sunlight. ESA was characterised using Fourier transform infrared (FTIR) spectroscopy. Maximum decolourisation efficiencies (96% with sunlight and 77% without sunlight) were recorded at contact time of 120 minutes and 1.5 g/dm3 of catalyst. The data obtained were fitted into kinetics models and adsorption isotherms. According to the findings, pseudo-second order kinetics model best described the process with rate constant of 0.1529 g/mg.min and regression value, R2 of 0.9934. Intra-particle diffusion model showed that the uptake of MB was more of film diffusion than the intra-particle diffusion. The adsorption isotherm fitted better into Langmuir isotherm with adsorption capacity of 0.0213 dm3/mg and R2 of 0.9957, while the Temkin isotherm indicates that the process was a physical adsorption as the heat of sorption value (0.0015 Kcal./mol.) was less than 1.0 kcal/mol. Generally, the study revealed that ESA was a suitable photocatalyst for the decolourisation of azo dyes under solar UV rays.