Modulating structural oxygen/crystallinity enables ambient cascade photo‐upgrading of biomass saccharides to lactic acid

Abstract Photocatalytic transformation of biomass into biofuels and value‐added chemicals is of great significance for carbon neutrality. Metal‐free carbon nitride has extensive applications but with almost no absorption and utilization of near‐infrared light, accounting for 50% of sunlight. Here, a molten salt‐assisted in‐plane “stitching” and interlayer “cutting” protocol is developed for constructing a highly crystalline carbon nitride catalyst containing structural oxygen (HC‐CN). HC‐CN is highly efficient for the photothermal cascade transformation of biomass‐derived glucose into lactic acid (LA) with an unprecedented yield (94.3%) at 25°C under full‐spectrum light irradiation within 50 min, which is also applicable to quantitatively photo‐upgrading various saccharides. Theoretical calculations expound that the light‐induced glucose‐to‐catalyst charge transfer can activate the C _β –H bond to promote the rate‐determining step of intramolecular hydrogen shift in glucose‐to‐fructose isomerization. Meanwhile, the introduced structural oxygen in HC‐CN can not only facilitate the local electric field formation to achieve rapid charge transport/separation and regulate selective •O ₂ ⁻ generation for oriented C3–C4 bond cleavage of fructose but also narrow the energy band gap to broaden the light absorption range of HC‐CN, contributing to enhanced LA production without exogenous heating. Moreover, HC‐CN is highly recyclable and exhibits negligible environmental burden and low energy consumption, as disclosed by the life cycle assessment. Tailored construction of full‐spectrum light adsorption and versatile reaction sites provides a reference for implementing multi‐step biomass and organic conversion processes under mild conditions.