The degradation of diethyl phthalate by reduced smectite clays and dissolved oxygen

Abstract

Reduced smectite clay plays an important role in producing hydroxyl radical (OH) and degrading organic contaminants. In this study, the OH formation was examined in the suspension of reduced clay particles (Red-Na-NAu-2) with oxygen; diethyl phthalate (DEP), a widely detected plasticizer in soils, could be degraded in the reaction system. The results show the reactivity of Red-Na-NAu-2 is related to iron content, reduction extents and particle sizes; the oxidation process of Red-Na-NAu-2 may change structural Fe coordination or even destruct clay morphology. There are two stages in the oxidation process, fast oxidation and slow oxidation, which were closely related to active structural Fe(II) entities (e.g. Fe(II)Fe(II)Fe(II)-OH) and less active structural Fe(II) entities (e.g. Fe(II)Fe(II)-OH), respectively. It was hypothesized that dissolved oxygen could accept electrons from Fe(II) in outer surface layers (tetrahedral layers and at broken edges) based on spectra (FTIR, XPS and EELS) analyses, and inner lattice Fe(II) in octahedral layers could donate electrons to outer surface Fe(III) through one-electron pathway. The findings of this study provide a thorough understanding about the degradation of organic pollutants in subsurface environments, an omitted natural attenuating pathway, which should be important in soil remediation.