Effect of copper(II) species on the photooxidation of arsenite under UV-C irradiation

•The presence of Cu(II) enhances the photooxidation of As(III) under UV-C irradiation.•The positive effect of Cu(II) on As(III) oxidation is more significant at higher pH.•Cu(II) can directly activate O2 by absorbing UV-C light.•Cu(II) can act as an alternative electron acceptor.•Both Cu(III) and OH are involved in the photooxidation of As(III) to As(V).