Ozonation and Carbon-assisted Ozonation of Methylene Blue as Model Compound: Effect of Solution pH

Abstract

This work investigated the pH effect on ozonation and carbon-assisted ozonation processes, where methylene blue (MB) was employed as model compound. Kinetic study and quantitative description on reaction pathway, i.e. molecular ozone attack and hydroxyl radicals (HO) oxidation, were accomplished to evaluate the effect of pH on process control for ozonation. The HO reaction route for MB decolorization intensified with increasing pH and become even comparable to molecular ozonation as pH reached up to 11 (θ=1.14), and this trend can also be reflected by comparative analysis of detected HO species at different pH. Carbon nanotubes (CNTs) were selected as stable carbon material to investigate the pH effect on ozone/carbon systems. The mineralization of MB solution and concentration study of HO both revealed that the performance of CNTs during ozonation depend much on solution pH. At basic environments consequently, CNTs began to perform as an effective ozone catalyst accelerating the generation of HO oxidative species, where the formation of HO2- was thought to be the key promotive intermediate.