Enhanced dark adsorption and visible-light-driven photocatalytic properties of narrower-band-gap Cu₂S decorated Cu₂O nanocomposites for efficient removal of organic pollutants

The Cu₂S-decorated Cu₂O nanocomposites were synthesized by a facile co-precipitation and calcination method, and used as adsorbent and photocatalyst to remove organic pollutants from wastewater. Batch adsorption experiments were conducted to investigate the influences of molar ratio of Cu₂O to Cu₂S, initial solution pH, coexisting anion and temperature on the adsorption performances. As-obtained Cu₂O/Cu₂S-9/1 nanocomposite with high specific surface area (45.88 m²/g) exhibited superior adsorption ability towards Congo red, methyl orange and tetracycline in aqueous solution. The adsorption of organics onto the nanocomposite was a spontaneous and exothermic process, and the adsorption processes could be well described by the Freundlich isothermic and Pseudo-second-order kinetic models. The Cu₂O/Cu₂S-9/1 nanocomposite also showed excellent photocatalytic degradation activities for organic pollutants. Optical properties characterization suggested that the decoration of Cu₂S could effectively enhance visible-light absorption and inhibit the recombination of photo-generated electron-hole pairs. ESR tests and trapping experiments of reactive species indicated that both superoxide radicals (O₂^-) and holes (h⁺) were crucial for the photocatalytic degradation of organic pollutants. Moreover, the photocatalytic efficiency of Cu₂O/Cu₂S-9/1 nanocomposite had no significant decrease even after four consecutive runs. The bifunctional nanocomposite as adsorbent and photocatalyst presents a great potential in treating organic-contaminated wastewater.