Removal of As(III) via adsorption and photocatalytic oxidation with magnetic Fe–Cu nanocomposites

Abstract

Magnetic Fe–Cu nanocomposites with high adsorption capacity and photocatalytic properties were prepared via the precursor method using soluble substances isolated from urban biowaste (BBS) as carbon sources and different temperatures of the pyrolysis treatment (400, 600, and 800 °C). BBS is used as complexing agent for the Fe3+ and Cu2+ ions in the precursors. The as-prepared magnetic materials were tested in As(III) removal processes from water. Dark experiments performed with the materials obtained at 400 and 600 °C showed excellent adsorption capacities achieving a significant uptake of 911 and 840 mg g−1 for As(III), respectively. Experiments conducted under steady-state irradiation showed a reduction of 50–71% in As(III) levels evidencing the meaningful photocatalytic capacity of Fe–Cu nanocomposites. The best photocatalytic performance was obtained for the nanocomposite synthesized at the highest pyrolysis temperature, in line with the reported trend of HO· radicals production. Transient absorption spectroscopy experiments revealed the occurrence of an alternative oxidation pathway involving the valence band holes and yielded relevant kinetic information related to the early stages of the As(III) photooxidation. The higher absorption of the electron–hole pairs observed for the samples treated at lower temperature means that controlling the pyrolysis temperature during the synthesis of the Fe–Cu nanocomposites allows tuning the photocatalyst activity for oxidation of substrates via valence band holes, or via HO· radicals.