Effective green electro-Fenton process induced by atomic hydrogen for rapid oxidation of organic pollutants over a highly active and reusable carbon based palladium nanocatalyst

Abstract

Heterogeneous electro-Fenton (HEF) reaction is a highly efficient process for the degradation and mineralization of refractory organic pollutants in water. Since atomic hydrogen H*, currently widely used in electrocatalytic hydrogen dechlorination (ECHD) domains, can rapidly transfer one electron to H2O2 to generate OH and H2O, it has been considered as a promising species instead of Fe2+ for HEF reactions. However, H* is extremely unstable as it can be easily combined into hydrogen gas (H2), appropriate electro-catalytic material would be needed in order to speed up the production of H* on the one hand, and stabilize this in-situ formed species on the other. Here we show that house-synthesized Pd nanoparticles dispersed in carbon black (∼8 % Pd on carbon) which were further loaded on carbon felt (Pd/C@CF) exhibited an excellent performance in HEF process for degradation of a variety of organic compounds (with the best of ∼99 % in 75 min). Radical scavenging experiments revealed that hydroxyl radical (OH) was the key reactive species, and cyclic voltammetry tests proved the stabilization of H* by Pd nanoparticles which in turn resulted in a significant increase in the yield of OH via the reduction of H2O2. The superior performance could be attributed to the Pd nanoparticles dispersed uniformly in carbon with a large number of active sites, thereby lowering the over potential to create a suitable microenvironment for H* generation and stabilization. In addition, the Pd/C@CF composite was proved to be a little pH dependent, highly stable, and well recyclable for effective utilization of H* towards a rapid HEF oxidation for potentially many practical applications in wastewater treatment.