Solar thermoelectric field plus photocatalysis for efficient organic synthesis exemplified by toluene to benzoic acid

Abstract

The solar thermal electrochemical process synthesis of benzoic acid is an efficient way for organic synthesis based upon solar energy utilization. Graphite and platinum anodes have been developed with high yield and selectivity of benzoic acid. In this article, we present the first demonstration of the solar thermal-electro-photo field for efficient benzoic acid synthesis by using TiO2 nanotubes electrode. By adjusting the three-solar field process, toluene is oxidized at the surface of the photoactive, electrically driven, heat activated TiO2 nanotubes electrode. Results showed that, the synergistic effect of the three fields was found for enhancement of toluene oxidation at TiO2 electrode. The yield of benzoic acid and conversion of toluene is greatly improved with temperature, and arriving to 26.1% and 62.6% at 90°C, respectively. In this process, solar thermal decreases the electrolysis potential of toluene oxidation. Hydroxyl, carboxyl and OOH groups, as well as the emergence of TiOC bond at the surface of the TiO2 nanotubes electrode, lead to an increased UV and visible absorption and a significant enhancement of TiO2 photocatalytic properties to increase the yield of benzoic acid. Simultaneously, an applied solar electric potential promotes the separation of photogenerated electrons and holes. As a result the efficiency of TiO2 photocatalysis enhanced.