Abstract
The objective of this study was to photocatalytically degrade the pesticide 2.4-dichlorophenoxyacetic acid (2,4-D) by using the integrated UV/TiO2/activated carbon system and to study the degradation kinetics and the role of the chemical and textural properties of activated carbon in this process. Results obtained show that the presence of activated carbon during the catalytic photodegradation (UV/TiO2) of 2,4-D considerably increases its percentage removal. After 60 min of treatment, the highest percentage 2,4-D degradation is obtained in the presence of the activated carbons with the greatest content of carboxyl groups. In order to determine the role of activated carbon in this process, we determined the adsorptive and photocatalytic contribution (UV/TiO2) to the overall 2,4-D removal. The total percentage removal by the UV/TiO2/activated carbon system is much higher than the value obtained by summing the adsorptive and catalytic contributions, mainly when the carbon has an elevated carboxyl group content. No relationship was observed between the textural properties of activated carbons and their synergistic activity; however, the carbons with the greatest carboxyl group content showed the highest synergistic activity. Together with the results of chemical and superficial characterization of the carbon samples after their utilization in the photocatalytic process (UV/TiO2), these findings demonstrate that the reduction of superficial carboxyl groups to alcohol groups is the main pathway by which activated carbon enhances the additional generation of HO center dot radicals in the medium. Experiments conducted in the presence of radical scavengers (carbonate ions, sulfate ions, and t-butanol) revealed that H-center dot, e(aq)(-), and HO center dot species participate in the 2,4-D photodegradation. According to the time course of total organic carbon and toxicity during 2,4-D photodegradation, its complete mineralization is not achieved, and the toxicity of the degradation compounds is lower than that of 2,4-D. (c) 2012 Elsevier B.V. All rights reserved.