Design of novel zinc oxide nanostructures for photocatalytic degradation of persistent organic pollutants in industrial effluents : case study: methylene blue and phenol

Abstract

Industrial wastewater is a major source of pollutants that must be removed due to their negative impact on health and ecosystem. Conventional treatment techniques are bounded by economic constraints along with poor efficiency due to the persistence and low degradability of some organic molecules . Thereby, the need of alternative methods is a necessity. In this context, Advanced Oxidation Processes (AOPs) particularly photocatalysis has emerged as a promising technology to degrade recalcitrant molecules and particles. In this work a new template free ZnO thin films deposited on glass substrate having high surface area and porosity were synthesized by sol-gel dip coating technique. The operating conditions such as pre-heating and post heating temperatures, as well as the number of layers were optimized in order to control the microstructure of ZnO photocatalyst. For instance, thin films pre-heated at 150 oC and post heated at 450 oC for 1 hour show a wrinkled and porous crystalline structure with a surface porosity of 24%. This ZnO structure registered the highest photocatalytic performance. The photocatalytic activity of thin films was investigated by using UV visible and HPLC techniques on the degradation of methylene blue (MB) as a probe molecule and phenol as a common persistent molecule under UV irradiation (λ =365nm). Optimized catalyst revealed photocatalytic efficiency in removing 84% of MB in 480 minutes and a rate constant of 0.0039 min-1. High efficiency of 98% phenol removal was obtained when increasing radiation time to 24 hours with a degradation rate constant of 0.00225 min-1. Finally, a design of the photocatalytic reactor based on the experimental kinetic data was performed with an overview on the upscaling of reactor to meet the industrial needs.