Facile thermal exfoliation of Cu sheets towards the CuO/CuO heterojunction: a cost-effective photocatalyst with visible-light response for promising sustainable applications.

Unlike semiconductors, metals, especially the Cu element, usually show preeminent ductility and thermal expansivity; accordingly, herein, we report thermal treatment of a commercial copper sheet in air to obtain a black mass, CuO/CuO with a heterojunction, which has been proven to be a photocatalyst. Rapid cooling of the hot sheet detached/knocked off the oxidized layers from the sheet as a powder. The extent of the formation of copper oxides was determined by electrochemical impedance spectroscopy and transient photocurrent responses; in addition, other physical methods for the characterization of the catalyst were performed, and the catalyst exhibited applications in the mineralization of the rhodamine B (RhB) dye, a potential pollutant in water bodies. Moreover, the well-matched band structures of CuO/CuO manifested that CuO and CuO could serve as reduction sites and hole oxygen sites to generate the ·O and ·OH species, respectively, which were subsequently affirmed by the DMPO electron spin resonance technique. In this study, we proposed a novel perspective towards the design of heterogeneous photocatalysts for organic pollutant treatment through a convenient solid-phase synthesis rather than a complicated liquid-phase synthesis. In addition to this, the resultant CuO/CuO photocatalyst proposed herein might inspire the researchers to focus on the preparation of more cost-effective photocatalysts for commercialization rather than complicated nanocomposites for pure theoretical research.