Insight into F-site enhanced interfacial H-bonding interaction and O₂ activation for selective biomass photo-upgrading to lactic acid

The selectivity modulation is a challenging task for multi-step photo-reforming of biomass sugars into lactic acid (LA). Herein, a fluorine-doped ultrathin porous carbon nitride (F-CN) photocatalyst with frustrated Lewis acid-base pairs (FLPs) was developed, consisting of electron-deficient F and adjacent N as Lewis acid and base site, respectively. The introduction of FLPs not only induced F atoms to form an F–H bond with the –OH of sugar, promoting isomerization (e.g., the conversion of xylose to xylulose), but also modulated the electronic structure of g-C₃N₄ by inhibiting exciton effect. This expedited photogenerated carrier migration and facilitated electron accumulation onto the N atoms, promoting the generation of superoxide radicals for selective C–C bond breaking (e.g., of xylulose), thus enabling the exclusive production of LA. The conversion of xylose over F-CN reached 99 %, achieving an ultrahigh LA yield of 94.8 % within 70 min at 40 °C under visible-light irradiation. Mechanistic investigations validated that the synergistic role of hydrogen bonding and the swift production of •O₂⁻ contributed to the greatly enhanced photocatalyst performance. Moreover, the life-cycle assessment demonstrated that an established photocatalytic system offered significant advantages compared with existing industrial LA production methods in terms of global warming potential (GWP), abiotic resource-fossil fuel (DAR), and ecotoxic potential (ETP). This study provides a paradigm of tailor-made development of non-metallic photocatalysts through regulating the electron transport path enabled by H-bond interaction for oriented conversion of biomass and complex organics.