Dual-modal Light-harvesting Microfluidic System via Simultaneous Up- and Down-Conversions for Enhanced Flow Photocatalysis

Abstract Microfluidic systems with large surface-to-volume ratios enable photocatalytic reactions to occur, avoiding the limitations of light penetration and allow the efficient transfer/mixing of mass and energy. For enhanced photocatalysis, the utilization of broad-spectrum light, especially over the entire solar spectrum, is highly desirable, but has been less explored in microfluidic systems. Herein, we report a novel microfluidic system with dual-modal light-harvesting capability via simultaneous up- and down-conversions to significantly improve the photocatalytic efficiency of C(sp3)-H functionalization reactions using ultraviolet (UV) to near-infrared (NIR) light. A transparent composite incorporating down-converting (DC) coumarin dye and up-converting (UC) lanthanide-doped nanocrystals (β-NaYF4:Yb/Er/Gd) was coated onto the inner surface of the microchannels, which showed effective dual conversion of UV/NIR to visible light. An improved photocatalytic organic transformation using our single- or double-stacked microfluidic system was achieved utilizing a photocatalytic aza-Henry reaction with rose bengal (RB), which displayed a two-fold increase in reaction conversion.