Visible light active Ce-doped and Cu-Ce co-doped TiO2 nanocrystals and optofluidics for clean alcohol production from CO2

Considering CO2 as an alternative and sustainable resource, rather than as a waste to be treated, this work proposes the combination of doped TiO2 nanocrystals with optofluidics for the continuous photoreduction of CO2 to alcohols under ultraviolet and visible light. This approach aims at overcoming one of the major limitations of this technology, namely, current photoreactor configurations and low activity under visible light of the up-to-date photocatalysts. Ce-doped and Cu–Ce-codoped TiO2 nanocrystals, synthesized by a simple and green hydrothermal method with different Cu and Ce contents, are used in a planar optofluidic microreactor with an enhanced surface-area-to-volume ratio, uniform light distribution, and a larger photon receiving area. The results show promising alcohol production rates when doping the photoactive TiO2 nanocrystals with Ce, which leads to a maximum rate of 116 μmol·g–1·h–1 for ethanol and 106 μmol·g–1·h–1 for methanol, exceeding most of the reported values for visible-light-driven CO2 photoreduction to alcohol systems. It is worth noting that the system remains pseudostable for up to 6 h of continuous operation. Altogether, this work provides novel insights into the development of innovative systems for the transformation of CO2 to alcohols under sunlight irradiation.The authors gratefully acknowledge the financial support from Ministerio de Ciencia e Innovación (MCIN) and Spanish State Research Agency (AEI) through the research projects PID2019-104050RA-I00 and TED2021-129810B-C21 funded by MCIN/AEI/10.13039/501100011033