Long-acting photocatalytic degradation of crude oil in seawater via combination of TiO2 and N-doped TiO2/reduced graphene oxide

Abstract

ABSTRACT N-doped TiO2/ reduced graphene oxide (N/TiO2/rGO) composite was prepared and used together with the commercial TiO2 for comparative research on photocatalytic degradation of crude oil in seawater. Five test conditions were designed including a combined catalyst of TiO2 and N/TiO2/rGO (4:1) under UV-A light irradiation with a duration of 28 days. The changing trend of the water-soluble fraction (WSF) of crude oil in seawater was monitored by ultraviolet spectroscopy and fluorescence spectroscopy as well as dissolved organic carbon (DOC) measurement. The SARA fractions of oil residues were analysed by column chromatography, and the chemical composition changes of saturates and aromatics were investigated by gas chromatography-mass spectroscopy (GC-MS). The results reveal that although it had high efficiency in the degradation of aromatics, the nano-TiO2 tended to self-agglomerate, which enhanced agglomeration of crude oil, causing its catalytic process actually terminating within seven days. By comparison, the N/TiO2/rGO composite consistently dispersed crude oil in the whole experimental duration, subsequently, it presented a higher photocatalytic degradation rate than TiO2. The combination of TiO2 and N/TiO2/rGO (4:1) shows concerted catalysis on photocatalytic degradation of crude oil, and the oil degradation rate reached to 54.80% while the aromatic degradation rate was 74.83%. The fluorescent components in WSFs were preferentially degraded, and the degradation products of aromatic fraction were CO2 and H2O as well as saturates, mainly C20∼C31 alkanes. Considering its long-acting photocatalysis, the N/TiO2/rGO composite possesses practical utilization potentiality together with TiO2 in spilled oil treatment in the marine environment.