Photocatalytic oxidation pathways of arsenite on spontaneously forming FeOOH/GO heterostructure

• β-FeOOH phase could enhance the photocatalytic performance of FeGO aggregates. • Fe-O-C bond can serve as a channel to the separation and transfer of carrier. • •OH, H 2 O 2 and photo-generated holes dominated the oxidation of As(III) in liquid and solid phase. • As(III) was oxidized into As(V) on FeGO aggregates under light irradiation. Due to the widespread applications, graphene oxide (GO) possibly interact with natural minerals to form new heteroaggregates in the environment, which will affect the environmental processes of heavy metals as an example of arsenic. In this work, photo-oxidation and sequestration behaviors of As(III) on β-FeOOH/GO (FeGO) heteroaggregates were explored via batch and spectroscopic approaches. The formation of Fe-O-C bonds in FeGO was proved by X-ray photoelectron spectroscopy, which could act as an efficient carrier channel to facilitate the charrier transfer. Compared with pristine GO, the generation of β-FeOOH not only change the band structures of GO, but also improved its photoelectric performance. In the case of GO, only 18% of As(III) was photo-oxidized to less toxic As(V), and both As(III) and As(V) were completely released in the aqueous phase. For FeGO, 74% of As(III) was oxidized, 4 times higher than that in GO system. Due to β-FeOOH phase, 60% of total arsenic species was fixed on FeGO solid. It thus confirmed that β-FeOOH phase could enhance the sorption of As(III) and As(V), as well as promote the photocatalytic oxidation of As(III). The model experiments suggested that the photocatalytic activities of oxygenous groups in the heteroaggregates followed the order of carboxyl ≈ methoxy > hydroxyl > aldehyde > acetyl. Both electron paramagnetic resonance (EPR) spectroscopy and quenching tests revealed the co-existing various pathways for As(III) oxidation. Interestingly, H 2 O 2 and •OH were main oxidation species in liquid phase, whilst photogenerated holes and H 2 O 2 played the important roles during the solid-phase reaction.