Photocatalytic conversion of CO2 using various TiO2 modified with Ag and Co dual cocatalysts via an ultrasonic reduction method

The photocatalytic conversion of carbon dioxide (CO2) has attracted considerable attention as a technology for achieving carbon neutrality. To improve the activity for the photocatalytic conversion of CO2, it is important to modify the surface of semiconductor photocatalysts with a suitable cocatalyst using an appropriate method. Although TiO2 offers many advantages for practical use, it is considered unsuitable for the photocatalytic conversion of CO2 to CO because its conduction band potential is close to the CO2/CO redox potential, resulting in a low driving force. In this study, Ag and/or Co cocatalysts are loaded onto various TiO2 catalysts using modification methods, including the ultrasonic reduction method (USR). TiO2 shows the highest catalytic activity for the photocatalytic conversion of CO2 using 2-propanol as a hole scavenger when modified with Ag and Co dual cocatalysts by USR. Furthermore, a TiO2 photocatalyst that possesses a mixed anatase–rutile phase exhibits better photocatalytic activity than those with either anatase or rutile single phases, owing to the more effective separation of charge carriers. Consequently, a high CO formation rate with high selectivity toward CO is achieved using the AgCo/TiO2 photocatalyst, wherein the Ag and Co dual cocatalyst is loaded by USR onto TiO2 with mixed anatase–rutile phases. In conclusion, this study demonstrates that optimizing the cocatalyst composition, loading method, and TiO₂ crystal phase can significantly enhance the efficiency and selectivity of photocatalytic CO₂ conversion, offering a viable pathway for sustainable fuel production.