Synthesis of magnetically recoverable Fe0/graphene-TiO2 nanowires composite for both reduction and photocatalytic oxidation of metronidazole

Novel ternary nanocomposite based on nano zero-valent iron (nZVI) and graphene-TiO 2 nanowires (Fe@GNW) was successfully synthesized for both reduction and photocatalytic oxidation of metronidazole (MNZ). Fe@GNW exhibits synergetic effects and significant properties, such as facilitating the photogenerated charges separation, enhancing the surface activity of nZVI, improving the adsorbent ability of catalyst, possessing the magnetic property for facile recycling. Due to the formation of micro-graphene-nZVI batteries and heterogeneous photo-Fenton system, Fe@GNW showed a superior activity in removal of MNZ (99.3%) compared with TiO 2 nanowires (43.0%) and graphene-TiO 2 nanowires (67.6%). Moreover, Fe@GNW retained excellent stability without apparent loss in catalytic activity after five cycles. MNZ removal by Fe@GNW experienced a two-stage process of reduction-adsorption and photocatalytic oxidation, which could be well-described by a revised pseudo-first order kinetics. The decomposition pathways of MNZ were proposed based on the analysis of intermediates. The quenching tests demonstrated that h + and OH are responsible for MNZ decomposition. New insights into the mechanism of the enhanced reduction and photodegradation of MNZ were proposed.