Solar driven catalytic conversion of cellulose biomass into lactic acid over copper reconstructed natural mineral

Abstract

Development of new technologies for conversion of biomass−based compounds into energy sources and basic chemicals is important for a circular economy. In this study, a unique solar driven catalysis system is developed to convert cellulose into lactic acid (LA) using Cu modified natural palygorskite (Pal) catalyst. Adequate Cu incorporation reframes Pal with a reduced band gap. As the mass ratio of Cu goes beyond 6 wt%, extra Cu2O quantum dots (QDs) assemble in situ on the Cu-Pal surface and form Cu2O/Cu-Pal heterostructure, which effectively promotes the charge transfer and exposes abundant Lewis acid sites for synergistic adsorption and conversion of intermediates. Notably, the colloidal character of the Cu-Pal substrate enables intimate adsorption of catenulate cellulose. The 10 wt% Cu2O QDs/Cu-Pal nanocomposite exhibits remarkable photocatalytic LA selectivity under visible light. Time−resolved in−situ attenuated total reflectance infrared (ATR−IR) spectroscopy and the density functional theory calculation (DFT) are employed to help elucidate the photocatalytic mechanism. Both theoretical and experimental studies demonstrate that such a Cu−modified mineral catalyzes a series of tandem reactions for LA formation, including the precise cleavage of β-1,4-glycosidic bonds of cellulose into glucose, selective cleavage of the C3 −C4 bond of glucose to C3 intermediates via photogenerated holes, and the selective conversion of C3 into LA. Our findings provide a new potential sustainable alternative for biomass valorization.