Visible-light-driven prompt and quantitative production of lactic acid from biomass sugars over a N-TiO2 photothermal catalyst

Chemocatalytic production of lactic acid from biomass feedstock is a highly potential alternative route, but with prerequisites of long reaction time, high temperature, and/or a tailored catalyst. In this work, a N-TiO2 photothermal catalyst prepared by a simple sol-gel method using urea as nitrogen and carbon source could catalyse a variety of biomass sugars to quantitatively produce lactic acid (up to 98.9% yield) in water under visible light and a low temperature of 60 °C in a time as short as 30 min. N-TiO2 provides a proper valence band position (2.51 eV) for the photo-oxidation reaction, with more active species being formed on the catalyst surface( e.g., h+, e-, •OH and •O2) and the light-induced heating effect caused by the carbon photothermal layer, which can effectively activate carbohydrates to undergo a cascade reaction process. Theoretical calculations show that the charge of N-TiO2 is highly separated, in which the N element acts as an electron trap and enriches plenty of electrons, leading to effective isolation of holes and electrons. In addition, the N-TiO2 catalyst exhibits good reusability and can be recycled with little loss of activity. The developed N and C-enhanced photothermal synergistic protocol opens an avenue for producing organic acids from renewable biomass resources under mild conditions.