ZnO1-x/carbondots composite hollow spheres: Facile aerosol synthesis and superior CO2 photoreduction under UV, visible and near-infrared irradiation

For the first time, ZnO1-x/carbon dots composite hollow spheres (denoted ZnO1-x/C) have been synthesized via a single-step aerosol process and employed for CO2 photoreduction over the whole UV-vis-NIR spectrum. The effects of the precursor component ratio and synthesis temperature on the physicochemical properties of the composites are systematically investigated to maximize CO2 conversion efficiency. Under UV-vis-NIR light, the best performing sample had an average CO production rate of 60.77 mu mol g(-1) h(-1), which is about 54.7 times higher than that of pristine ZnO, and 11.5 times higher than that of commercial TiO2 (Degussa-P25). More importantly, whereas ZnO and Degussa-P25 are photocatalytically inactive, the photocatalytic response of the ZnO1-x/C composite was successfully achieved under NIR illumination alone, with an average CO production rate of 15.98 mu molg(-1) h(-1). The realization of NIR-driven CO2 photoreduction with enhanced photocatalytic activity benefits from 1) the hollow structure, which allows multiple internal reflections of light for enhanced light absorption; 2) the oxygen deficiency of ZnO1-x and the deposited carbon, which enable efficient charge carrier transfer and improved CO2 adsorption; and 3) the strong NIR absorption of ZnO1-x/C, in which ZnO1-x is excited by absoring the up-converted photoluminescence emissions (410-560 nm) of the carbon dots.