Enhanced photocatalytic CO2 reduction to methanol by modulating valence states of copper in CuSrTiO3

Manipulating the oxidation states of transition metals is an ideal solution to achieve selective generation of different products and copper is widely used in CO2 photocatalytic reduction to methanol. However, the understanding on the effects of valence states of copper species in SrTiO3 on its structure and the selectivity of the corresponding product in CO2 photocatalysis are currently still limited. Here, copper-doped SrTiO3 nanofibers with different controllable ratios of Cu+/Cu2+ and Cu+/Cu0 were prepared by the combination of the electrospinning with the in-situ reduction method. The proportion of copper with different valence states (Cu+/Cu2+ and Cu+/Cu0) was changed by rationally adjusting the time of hydrogen reduction. The presence of monovalent copper facilitated the generation of reactive intermediates, thereby enhancing its photocatalytic activity. The copper-doped SrTiO3 nanofibers obtained after 3 h of hydrogen reduction (STCu0.08-H-3 h) had the highest proportion of Cu+/Cu2+ and Cu+/Cu0 with the highest methanol yield (6.96 μmol·g−1·h−1). Methanol generation rate and Cu+/Cu2+ ratio of STCu0.08-H-xh (x = 1, 2, 3, 4,5) with different hydrogen reduction time were proven to be linearly positively correlated. Furthermore, theoretical investigation and in-situ CO2 infrared spectrum deeply understood the difference of CO2 adsorption behavior and CO2 activation over Cu2+ and Cu+ of STCu0.08-H-3 h photocatalyst and the reaction intermediates involved in the photocatalytic CO2 reduction to methanol.