Decomposition performance of hypochlorite on bead-type NiO_x(OH)_y catalyst: improving applicability of catalysts

An easy-to-use, pollution-free and reusable beaded NiO_x(OH)_y catalyst for improving hypochlorite oxidation was prepared by impregnating the mixture of persulfate and alkali over alumina and then reduced it with Ni²⁺. The effects of catalyst preparation conditions and reaction parameters on NaClO conversion rate and Ni²⁺ dissolution rate were studied. Impregnating the γ-Al₂O₃ beads in PS/OH^- mixed solution with 0.59 M PS and PS/OH^- molar ratio of 1.1, and then reducing with 0.8 M Ni²⁺ solution is the best condition for preparing catalyst. The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The best catalytic layer is characterized by high content of chemisorbed oxygen which can be converted into atomic oxygen. The hypochlorite conversion rate increased with the catalyst dosage and reuse times, and decreased with available chlorine, while pH of hypochlorite solution had little effect on the conversion rate. After running stably for 120 h in continuous flow test, the chemisorbed oxygen content in the optimal catalytic layer decreased slightly. Atomic oxygen plays an important role in the decolorization of dye solution by NaClO/NiO_x(OH)_y system. The oxidant consumption cost of this process is much cheaper than Fenton reagent. The prepared catalyst has great potential in hypochlorite decomposition and wastewater treatment.