Formation of Cu⁰ in Cu₂O under light irradiation and subsequent accelerated decoloration to MO aqueous solution

In the photocatalytically decoloring process of methyl orange (MO) aqueous solution by Cu₂O polycrystalline film, Cu⁺ was reduced to Cu⁰ and oxidized to Cu²⁺ simultaneously. The adsorption of MO molecules onto the Cu₂O film was deduced by complexation reactions between Cu⁰ and the MO molecules, thus enhancing the decoloration rate of the aqueous solution. This research demonstrates that, apart from the photocatalytic activity of Cu₂O, Cu⁰ plays an important role in the bleaching process of MO solution. The results also suggest the application of metallic copper as a candidate for treatment of textile dyeing wastewater.