Photocatalytic reduction of CO2 and protons using water as an electron donor over potassium tantalate nanoflakes.

CO2 photoreduction over KTaO3 photocatalysts in water has been investigated. Both reduction (mainly carbon monoxide and hydrogen) and oxidation products (oxygen) were simultaneously detected in the absence of cocatalysts, sacrificial reagents and electrical bias. KTaO3 (KTO) samples were synthesized by solid-state reaction (SSR-KTO) and solvothermal methods in a hexane-water mixture (Hex-KTO) and pure ethanol (Eth-KTO). The different synthesis methods were used to control particle sizes and morphologies of KTaO3 and their correlation towards photocatalytic activity has been further investigated. Strikingly, KTO prepared in a hexane-water mixture solvent represents a nanoflake-like structure, resulting in a seven fold increase in CO2 reduction and hydrogen evolution activities in comparison to conventional cubic structure KTO under UV light irradiation. CO with trace amounts of CH4 is produced from CO2 photoreduction. Upon addition of a silver cocatalyst on KTO, the reduction selectivity has been controlled to favour CO2 photoreduction, and the CO2 to CO yield has been doubled compared to bare KTaO3.