Peroxymonosulfate activation by Ni-Fe (hydr)oxides through radical and nonradical pathways for efficient trichloroethylene degradation

Abstract

Peroxymonosulfate (PMS)-based advanced oxidation processes have become promising water treatment technologies in recent years. The redox cycle between transitional metals in heterogeneous catalysis is essential for continuous activation of PMS and efficient removal of pollutants. In this work, we prepared Fe3O4 using precipitation method and subsequently added Ni aqueous solution to synthesize Ni-Fe (hydr)oxides. Ni-Fe (hydr)oxides show efficient PMS activation ability, causing the degradation of 96.8 % trichloroethylene (TCE) after 40 min with the dosage of Fe, Ni and PMS at 0.2, 0.1 and 0.2 mM, respectively. The catalyst concentration normalized TCE degradation rate constant of Ni-Fe (hydr)oxides/PMS system reaches 1.48 L g−1 min−1. Nonradical pathway is dominant at the initial stage of the reaction which generates high-valent metals, SO5•− and indirectly produces 1O2. 1O2 and dissolved O2 together participate in the O2 cycling, •OH generation, and electron transfer involving the reduction of trivalent metals. Divalent metals react with PMS to generate strong oxidative •OH and SO4•− through radical pathway in later stage. TCE is degraded and dechlorinated by multiple reactive species in Ni-Fe (hydr)oxides/PMS system. The optimum Ni/Fe ratio of catalysts under the studied conditions was 0.50. Ni-Fe (hydr)oxides show high reactivity and stability in real water matrices, demonstrating Ni-Fe (hydr)oxides are promising catalysts for PMS activation to degrade pollutants in contaminated water.