Impact of Crystal Types of AgFeO 2 Nanoparticles on the Peroxymonosulfate Activation in the Water

A simple co-precipitation method was developed to synthesize AgFeO 2 nanoparticles (NPs) with hexagonal 2H and 3R polytypes coexistence. The ratio of 2H and 3R types in AgFeO 2 NPs were regulated by controlling the calcination temperature (300, 400, and 500 °C). Such AgFeO 2 NPs were used as heterogeneous catalysts to activate peroxymonosulfate (PMS) for the removal of Orange I (OI) in the water. External water conditions effects and the stability of AgFeO 2 NPs were investigated. The catalytic performance of AgFeO 2 NPs was found to be significantly enhanced with the increasing content of 2H-AgFeO 2 . 1 O 2, O 2 •–, SO 4 •–, and •OH were identified as the dominating reactive oxygen species (ROSs) participated in the catalytic process. The electron transfer of Ag 0 /Ag + and Fe 2+ /Fe 3+ cycles facilitated the decomposition of PMS to generate ROSs. The surface hydroxyl groups (−OH) were regarded as the catalytic active sites. The higher 2H-AgFeO 2 content in AgFeO 2 NPs promoted the concentration of surface hydroxyl groups ( C –OH ) and the reactivity of AgFeO 2 NPs for PMS activation. Based on theoretical calculations, the 2H-AgFeO 2 (004) plane with more Fe sites was more conducive to binding with the −OH compared to the 3R-AgFeO 2 (012) plane, ascribed to the stronger adsorption energy and shorter Fe–O bond length between 2H-AgFeO 2 and −OH.