Electrochemical and photocatalytic reduction of perchlorate ion

Abstract

The presence of perchlorate in water supplies may have deleterious human health effects. Electrochemical and electrophotocatalytic reduction of the perchlorate ion to the chloride ion were assessed at laboratory scale. Studies were carried out in two-chambered batch reactor systems in which the cathodic and anodic compartments were separated by an ion exchange membrane. Electrodes consisted of titanium coated with a thin film of small TiO 2 particles. Test water systems were buffered to an acid pH and a background electrolyte was added. Applied voltages ranged from −1.75 to −2.0 v. For photolytic systems, ultraviolet light was supplied. Initial perchlorate concentrations ranged from 5×10 −2 M to 5×10 −7 M. Reduction initially proceeded rapidly but slowed with time. The percentage of perchlorate electrochemically reduced after 2 h was found to range from less than 1% at the highest concentration to 30–35% at lower concentrations. The extent of photocatalytic reduction at high perchlorate concentrations was approximately five times greater than for electrochemical reduction at the same concentrations. An additional fourfold improvement in reduction percentage was noted when the electrode was doped with vanadium. A mathematical model suggested that the limiting factor in perchlorate reduction was competition among anions for active sites on the electrode surface. Application of this technology for decontamination of water supplies will require further advances in electrode technology and/or innovations in engineering design.