An optofluidic planar microreactor with photoactive Cu2O/Mo2C/TiO2 heterostructures for enhanced visible light-driven CO2 conversion to methanol

Mixing TiO2 with Mo2C has recently been proposed to improve the photocatalytic conversion of CO2 to methanol under visible light irradiation, although further efforts are still needed to enhance process performance. In this context, the use of p-type semiconductors (i.e., Cu2O) in co-doping strategies can enhance not only the redistribution of electric charges due to its narrowing bandgap, but also the selectivity of the reaction towards methanol. This work focuses on the development of a continuous visible light-driven CO2 photoconversion to methanol process in an optofluidic microreactor using Cu2O/Mo2C/TiO2 heterostructures. A significant improvement in process performance can be seen under visible light with the heterostructures containing 4 wt% of Cu2O. Superior methanol production rates (36.3 µmol∙g−1∙h−1) with an apparent quantum yield = 0.64% and a reaction selectivity = 0.93 are reached, in comparison with the results achieved at Cu2O-free Mo2C/TiO2 photocatalytic surfaces (11.8 µmol∙g−1∙h−1, 0.21% and 0.92, respectively). This can be adscribed to the role of Cu2O in the selectivity of the reaction towards methanol. The synergetic effect between Cu2O, Mo2C, and TiO2 in the heterostructures may also provoke a more efficient charge separation and transfer, while enhancing the visible light absorption properties of the material and its photocatalytic stability. The maximum methanol rate outperforms most of the values previously reported in slurry batch reactors and evidences the possibility of enhancing the continuous visible light-driven CO2-to-methanol photoconversion process with efficient metal co-doping approaches in optofluidic microreactors.