Organic-free synthesis of {001} facet dominated BiOBr nanosheets for selective photoreduction of CO2 to CO

{001} facet dominated BiOBr nanosheets are fabricated via a facile hydrothermal method in the presence of nitric acid without any organic additive and applied for CO2 photoreduction. The concentration of nitric acid easily regulates the thickness of the obtained BiOBr nanosheets. When employing concentrations of 0, 0.1, 0.5, 1 and 4 M nitric acid, the corresponding surface area and percentage of exposed {001} facets of BiOBr-0, BiOBr-0.1, BiOBr-0.5, BiOBr-1 and BiOBr-4 nanosheets significantly increase in sequence. BiOBr-0 nanosheets are incapable of converting CO2 into CO. However, BiOBr-0.1, BiOBr-0.5, BiOBr-1 and BiOBr-4 nanosheets show successively enhanced CO2 photoreduction performance. Surprisingly, they exhibit high selectivity for converting CO2 into CO with negligible generation of CH4. In particular, BiOBr-4 shows the highest CO production rate of 4.45 mu mol g(-1) h(-1) under simulated sunlight irradiation. The electronic structure analysis demonstrates that the conduction band minimum is significantly raised to endow BiOBr-4 with reduction power for CO2/CO conversion, in comparison with the incapability of BiOBr-0. The breakthrough in CO2 reduction of BiOBr-4 nanosheets is ascribed to the larger active surface area, higher electron transfer, more effective charge carrier separation and significantly raised reduction ability.