Phenylmercury degradation by heterogeneous photocatalysis assisted by UV-A light

Abstract

Photocatalytic degradation of phenylmercury was studied using TiO₂ in aqueous suspension assisted by UV-A irradiation. Reaction conditions, such as pH and amount of TiO₂ were set using a factorial design of experiments resulting in a greater influence of pH on phenylmercury degradation. Hg (II) reduction and simultaneous oxidation of aromatic group was observed. Optimum reaction conditions were obtained under nitrogen atmosphere at pH 10 and 0.35 g/L⁻¹ TiO₂. Under these conditions almost 100% reduction of mercury was reached after 30 min UV irradiation. Total mercury reduction was achieved after 40 min reaction under saturated oxygen. Furthermore, phenol and diphenylmercury were identified as intermediate products of oxidation. It was observed that a major fraction of the reduced mercury was removed as metallic vapor by gas stripping, whereas a minor fraction was adsorbed on the catalyst surface, probably as Hg(OH)₂. Under optimal conditions obtained by multivariable analysis, total mineralization of organic matter was achieved after about 60-min irradiation.

Keywords:

• Mercury reduction
• phenylmercury
• photocatalysis
• TiO₂

Acknowledgments

This work was supported by Fondecyt (grants 1110641 and 1121128); Project Anillo ACT-130 and Project Conicyt/FONDAP/15110019.