Microwave-assisted hydrothermal synthesis of Cu/Cu₂O hollow spheres with enhanced photocatalytic and gas sensing activities at room temperature

Cu/Cu₂O nano-heterostructure hollow spheres with a submicron diameter (200-500 nm) were prepared by a microwave-assisted hydrothermal method using Cu(OAc)₂·H₂O, PVP and ascorbic acid solution as the precursors. The morphology of the products could evolve with the hydrothermal time from solid spheres to thick-shell hollow spheres, then to thin-shell hollow spheres, and finally to nanoparticles. Moreover, the content of Cu in the products could be controlled by adjusting the hydrothermal time. The spontaneous forming of the hollow structure spheres was found to result from the Ostwald ripening effect during the low temperature (100 °C) hydrothermal reaction process. The photocatalytic degradation activities on MO under visible-light irradiation and the gas sensing activities toward the oxidizing NO₂ gas of different Cu/Cu₂O nano-heterostructure hollow spheres were investigated. As a result, the Cu/Cu₂O nano-heterostructure hollow spheres obtained at the hydrothermal time of 30 min, with a rough/porous thin-shell structure and a Cu content of about 10.5 wt%, exhibited the best photocatalytic and gas sensing performances compared with others.