Synchronous Reduction-Oxidation Process for Efficient Removal of Trichloroacetic Acid: H* Initiates Dechlorination and •OH Is Responsible for Removal Efficiency.
Degradation of chlorinated disinfection by-products using the electro-reduction process has been considered as a promising approach for advanced water treatment, while the removal efficiency is restricted by high barrier for dechlorination of intermediates only by reductive H*, and excessive cost required for reducing atmosphere. In this paper we predict that the dechlorination efficiency for trichloroacetic acid (TCA), a typical chlorinated disinfection by- product, can be accelerated via a synchronous oxidation-reduction process, where dechlorination barrier can be lowered by the oxidation reactions toward the critical intermediates using hydroxyl radicals (•OH). Based on scientific findings, we constructed a synchronous oxidation-reduction platform using a Pd-loaded Cu/Cu2O/CuO array as the core component. According to the combined results of theoretical and experimental analyses, we found that the high dispersion of nano-sized Pd on photocathode was beneficial for the production of a high concentration of H* at low overpotential, a perquisite for initiating dechlorination reaction. Simultaneously, excess H* has the potential to convert O2 to H2O2 in ambient conditions (Air condition), and H2O2 can be further activated by Cu-containing substrate to •OH for attacking the critical intermediates. In this system, ~89.1% of TCA was completely dechlorinated and ~26.8% mineralization achieved in 60 min, which was in contrast to the value of ~65.7% and mineralization efficiency of only ~1.7% achieved through reduction process (Ar condition).