Radical generation via sulfite activation on NiFe2O4 surface for estriol removal: Performance and mechanistic studies

Add time:08/10/2019    Source:sciencedirect.com

We report a process using NiFe2O4 nanocatalyst for the heterogeneous activation of sulfite ions for estriol (E3) oxidation. This NiFe2O4-sulfite system consisted of NiFe2O4 as an catalyst, sulfite as a reductant, O2 as an oxidant, and oxysulfur radicals (SO3−, SO4− and SO5−) and hydroxyl radicals (HO) as generated radicals. The experimental conditions for E3 removal were investigated, including the initial pH values, dissolved oxygen concentration, and NiFe2O4 and sulfite ion dosages. The initial pH has a significant influence on the catalytic performance, and approximately 87.6% of E3 could be removed at pH 9.0. NiFe2O4 nanocatalyst was characterized by high resolution and field emission transmission electron microscopy, X-ray diffractometry, and X-ray photoelectron spectroscopy. The catalytic reactivity and stability of the NiFe2O4 nanocatalyst were investigated by consecutive repeated runs. Radicals generated in this NiFe2O4-sulfite system were identified via radical-scavenging and electron spin resonance experiments. SO5− was identified as major oxidative radicals for E3 removal, which is quite different from the previous studies on sulfite activation. The generation of >SO32−-Ni(II)-OH on NiFe2O4 surface played a critical role in sulfite auto-oxidation. Our results supplemented the mechanism of the sulfate radical generation with sulfite ion as a source.

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