Solar photocatalytic degradation of dicamba in aqueous solution and its mechanism

Abstract

The photocatalyzed degradation conditions of dicamba in aqueous titanium dioxide-suspended solution were optimized under sunlight irradiation. The effect of various factors, such as photocatalyst loading, temperature, pH, sunlight intensity and irradiation time on the photocatalytic degradation of dicamba was investigated. The primary photocatalytic decomposition reaction followed a pseudo-first-order kinetic law according to the Langmuir- Hinshelwood model. During photocatalytic degradation, the pseudo-first-order rate constant, kobs, was 0.173 min-1. The half-lives (t1/2) and the activation energy (Ea) were 4.0 min and 10 kJ mol-1, respectively. Chloride ions were detected as a end products. The stoichiometric transformation of organic chlorine to chloride ion was observed at a relatively short irradiation time (15 min), and the complete mineralization of organic carbon atoms took place at around the same irradiation time. Phenol, 3-chloro-6-hydroxy-2-methoxybenzoic acid, and 3,6-hydroxy-2- methoxybenzoic acid were identified as intermediate products. The photocatalytic degradation mechanisms were proposed on the basis of the experimental results with a molecular orbital (MO) simulation of the frontier electron density. The solar photocatalytic degradation treatment for the wastewater including dicamba is simple, easy handling and low cost. Therefore, since artificial lamp devices, for example a Hg-Xe lamp, are particularly expensive in local and poor areas, the proposed technique seems to become a very powerful method for treating wastewater including dicamba in those areas. © 2011 The Japan Society for Analytical Chemistry.