Visible-Light Photocatalytic Conversion of Carbon Dioxide into Methane Using Cu2O/TiO2 Hollow Nanospheres

In the past few decades there has been a remarkable rise in the study of visible-light photocatalytic reduction of carbon dioxide (CO2) into value-added chemicals such as methane (CH4) with water as reducing agent in order to prevent global warming and energy crisis. However, so far the conversion efficiency leaves much to be enhanced under sunlight irradiation. In this work, Cu2O hollow nanospheres were synthesized via soft-template method and were combined with TiO2 through in-situ hydrolysis of Ti(OBu)(4) under sonication. The obtained photocatalysts of Cu2O and Cu2O/TiO2 composite were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, X-ray diffraction, UV-visible diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy. Compared to Cu2O hollow nanospheres, the Cu2O/TiO2 composite exhibited higher efficiency in photocatalytic reduction of CO2 into CH4 under visible-light irradiation (lambda >= 420 nm). This is because of the formation of a p-n heterojunction in the composites, resulting in efficient suppression of recombination of the photogenerated electrons and holes as well as an improved stability of the catalyst and, thereby, the improved visible-light photocatalytic activity.