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

Abstract

Chemocatalytic production of lactic acid from biomass feedstock is an alternative route with high potential, but with the prerequisites of long reaction time, high temperature, and/or a tailored catalyst. In this work, an N-TiO₂ photothermal catalyst prepared by a simple sol–gel method using urea as a 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 at a low temperature of 60 °C in a time as short as 30 min. N-TiO₂ provides a suitable 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 a 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 is enriched with 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 up an avenue for producing organic acids from renewable biomass resources under mild conditions.