**4.5 Photocatalytic CO2 reduction**

Liu et al. reported the fabrication of oxygen-deficient blue titania NPs with two exposed (101) (001) facets. The obtained coloured titania showed enhanced photoreduction towards CO2 under visible light illumination. A comparatively higher quantum efficiency (0.31% under full spectrum solar light and 0.134% under visible light region) for CO2 reduction to CO was achieved using water vapour. This quantum yield was almost four times greater than titania having single exposed facets and P25 (**Figure 10b**). The superior performance of titania was attributed to exposure of more active sites, the facilitated electron transfer between (001) and (101) planes, and Ti3+ induced mid-gap states to extend the visible light response (**Figure 10a**) [36].
