Harnessing Vis-NIR broad spectrum for photocatalytic CO2 reduction over carbon quantum dots-decorated ultrathin Bi2WO6 nanosheets

The photocatalytic reduction of CO2 to energy-rich hydrocarbon fuels is a promising and sustainable method of addressing global warming and the imminent energy crisis concomitantly. However, a vast majority of the existing photocatalysts are only capable of harnessing ultraviolet (UV) or/and visible light (Vis), whereas the near-infrared (NIR) region still remains unexplored. In this study, carbon quantum dots (CQDs)-decorated ultrathin Bi2WO6 nanosheets (UBW) were demonstrated to be an efficient photocatalyst for CO2 photoreduction over the Vis-NIR broad spectrum. It is noteworthy that the synthesis procedure of the CQDs/UBW hybrid nanocomposites was highly facile, involving a one-pot hexadecyltrimethylammonium bromide (CTAB)-assisted hydrothermal process. Under visible light irradiation, the optimized 1CQDs/UBW (1 wt.% CQD content) exhibited a remarkable 9.5-fold and 3.1-fold enhancement of CH4 production over pristine Bi2WO6 nanoplatelets (PBW) and bare UBW, respectively. More importantly, the photocatalytic responsiveness of CQDs/UBW was successfully extended to the NIR region, which was achieved without involving any rare earth or noble metals. The realization of NIR-driven CO2 reduction could be attributed to the synergistic effects of (i) the ultrathin nanostructures and highly exposed {001} active facets of UBW, (ii) the excellent spectral coupling of UBW and CQDs, where UBW could be excited by the up-converted photoluminescence of CQDs, and (iii) the electron-withdrawing nature of the CQDs to trap the photogenerated electrons and retard the recombination of charge carriers.