Morphological Changes in Cu2O Nanoshells During Photocatalysis

Background: Semiconductor nanomaterials are being employed for the degradation of organic compounds under solar light irradiation. Introduction: Cu2O nanomaterial is suitable for visible-light photocatalysis because the narrow band-gap (∼2.17 eV) allows it to absorb visible light. However, the morphological changes of Cu2O during photocatalysis have been rarely investigated. Methods: Porous Cu2O nanoshells (NSs) with a nearly 100% hollow structure were synthesized by a two-step addition of reducer. The synthesized NSs were characterized and employed for the photocatalysis of methyl orange (MO) in a neutral solution at 30 °C in air. Results: The Cu2O NSs exhibited high adsorption and good photocatalysis rates with respect to the degradation of MO. Certain new phenomena were observed upon photocatalysis. Nearly all the chemical bonds in MO were fractured; however, a portion of the sulfur-containing group in MO remained on the NSs. The morphology of the Cu2O NSs changed and a large amount of nano-debris was produced. Further experimental analysis indicated the presence of some nano-debris after adsorption- desorption equilibrium (ADE). A negligible amount of nano-debris appeared during the light irradiation of the Cu2O suspension in the absence of MO. The results obtained via X-ray diffraction (XRD), scanning transmission electron microscopy (STEM) and high-resolution transmission electron microscopy (HRTEM) proved that the nano-debris was composed of Cu2O, and essentially comprised nanosheets that were discarded from the Cu2O NSs. Conclusion: The porous NSs were composed of Cu2O nanosheets with exposed {111} facets, which resulted in their strong adsorption ability and catalysis performance for the degradation of MO. Light irradiation accelerated this interaction and led to the discarding of Cu2O nanosheets from the Cu2O NSs. Because of the strong interaction between Cu⁺ and S, a portion of the sulfur-containing group in MO remained on the NSs after photocatalysis.