Catalytic Reduction of Bromate Using ZIF-Derived Nanoscale Cobalt/Carbon Cages in the Presence of Sodium Borohydride

Conventional catalytic hydrogenation of bromate involves continuous feeding of H 2 gas, which leads to excessive consumption of H 2 because of limited solubility of H 2 gas in water. Herein, we propose to employ borohydride as a solid-phase H 2 source which releases H 2 with controllability depending on the presence of catalysts. A catalyst, possessing immobilized cobalt, porosity, and magnetic properties, was prepared via a one-step carbonization of a cobalt-based zeolitic imidazole framework. The resultant nanoscale cobalt/carbon cage (NCC) was used to activate NaBH 4 to release H 2 . The presence of H 2 might also allow the variation of oxidative states of cobalt in NCC to act as a reducing agent to reduce bromate. Thus, NCC/NaBH 4 was found to completely convert bromate to bromide in water. Parameters affecting the bromate reduction were also investigated including NCC loading, borohydride dosage, temperature, pH, and competing anions. Hydrogen production of NCC/NaBH 4 was also evaluated, and a mechanism for bromate reduction by NCC/NaBH 4 was proposed. The multiple-cycle usability of the NCC/NaBH 4 system was also demonstrated, and the catalytic activity of NCC remained almost the same even though no regeneration treatments were applied on the used NCC. These features enable NCC as an effective and promising catalyst to activate NaBH 4 for bromate reduction.