New insights into iron/nickel-carbon ternary micro-electrolysis toward 4-nitrochlorobenzene removal: Enhancing reduction and unveiling removal mechanisms

The ternary micro-electrolysis material iron/nickel-carbon (Fe/Ni-AC) with enhanced reducibility was constructed by introducing the trace transition metal Ni based on the iron/carbon (Fe/AC) system and used for the removal of 4-nitrochlorobenzene (4-NCB) in solution. The composition and structures of the Fe/Ni-AC were analyzed by various characterizations to estimate its feasibility as reductants for pollutants. The removal efficiency of 4-NCB by Fe/Ni-AC was considerably greater than that of Fe/AC and iron/nickel (Fe/Ni) binary systems. This was mainly due to the enhanced reducibility of 4-NCB by the synergism between anode and double-cathode in the ternary micro-electrolysis system (MES). In the Fe/Ni-AC ternary MES, zero-iron (Fe0) served as anode involved in the formation of galvanic couples with activated carbon (AC) and zero-nickel (Ni0), respectively, where AC and Ni0 functioned as double-cathode, thereby promoting the electron transfer and the corrosion of Fe0. The cathodic and catalytic effects of Ni0 that existed simultaneously could not only facilitate the corrosion of Fe0 but also catalyze H2 to form active hydrogen (H*), which was responsible for 4-NCB transformation. Besides, AC acted as a supporter which could offer the reaction interface for in-situ reduction, and at the same time provide interconnection space for electrons and H2 to transfer from Fe0 to the surface of Ni0. The results suggest that a double-cathode of Ni0 and AC could drive much more electrons, Fe2+ and H*, thus serving as effective reductants for 4-NCB reduction.