Enhanced visible-light photoreduction of CO2 to methanol over Mo2C/TiO2 surfaces in an optofluidic microreactor

Abstract

Inspired by the photosynthesis process used by plants, the photocatalytic conversion of CO₂ with water to obtain chemical energy can tackle increasing CO₂ emissions and energy demand together. In this work, the performance of Mo₂C/TiO₂ blends in the continuous photocatalytic reduction of CO₂ to methanol is evaluated in a micro-optofluidic reactor illuminated with UV and visible LED lights (5 mW cm⁻²). The photo-responsive Mo₂C/TiO₂ surfaces applied are manufactured by airbrushing a photocatalytic ink containing different weight percent (2–10%) of Mo₂C nanoparticles (synthesized by a carbothermal method) and TiO₂ (P25) onto porous carbon paper. Doping TiO₂ with Mo₂C makes the composite material active in the visible region compared with bare TiO₂, while it does not bring performance enhancement when the photoactive surfaces are illuminated with UV light. A 4% Mo₂C weight percent led to enhanced stable production of methanol under visible light (r = 11.8 μmol g⁻¹ h⁻¹, AQY = 0.21%, S_CH3OH/HCOOH = 12.1), which is ascribed to the presence of Mo₂C, able to extend the spectral response as well as reduce the recombination rate of photogenerated electrons and holes occurring in TiO₂. Higher Mo₂C contents, however, seem to shield the photoexcitation capacity of TiO₂.