Ultrasonically-assisted surface modified TiO2/rGO/CeO2 heterojunction photocatalysts for conversion of CO2 to methanol and ethanol

Abstract

Converting CO₂ to usable fuel may contribute to lowering of global warming, thus this study developed effective heterojunction photocatalysts for the photoreduction of CO₂ with water into methanol and ethanol fuels. The photocatalysts were prepared from combining surface modified titanium dioxide (TiO₂) nanoparticles with reduced graphene oxide (rGO) and cerium oxide (CeO₂). The TiO₂ surfaces were firstly modified via the sono-assisted exfoliation, with high intensity ultrasonic waves (ultrasonic horn, 20 kHz, 150 W/cm²) in 10 M NaOH for 1 h. Highly reactive nanosheets delaminated from outer surfaces of the primary TiO₂ crystals leading to an increase in specific surface active area, light absorption and decrease in electron-hole recombination rate, which enhanced photocatalytic activity. Then, 0.75 wt% rGO and 1 wt% CeO₂ were incorporated into the surface modified TiO₂ to promote photogenerated charge separation, electron mobility and CO₂ absorptivity. The modified TiO₂/rGO/CeO₂ photocatalysts exhibited superior photocatalytic performance by producing methanol at 641 μmol/g_cath and ethanol at 271 μmol/g_cath, almost 7 times higher than rates from pure TiO₂. The significant improvement in CO₂ photoconversion activity was mainly attributed to the high interfacial contact area and strong connection between the reactive delaminated TiO₂ nanosheets, rGO and CeO₂, which, in turn, facilitated the flow of large number of photogenerated charge carriers to react with the absorbed species, and the multi-step charge transportation due to the heterojunction effect that effectively retarded electron-hole recombination.