Nitrogen-doped Titanium Dioxide for Enhanced Photocatalytic Oxidation of Vanillyl Alcohol into Vanillin

Photocatalysis transformation of renewable biomass-derived building blocks into value-added chemicals is an attractive strategy in response to the environmental issues caused by the use of unsustainable petrol-chemical routes. On this basis, photocatalytic selective oxidation of reduced monolignols into aldehydes has emerged as a hotspot to be investigated. Herein, using ammonia solution as nitrogen source, N-TiO2 photocatalysts were prepared through a simple pyrolysis process. Under visible-light irradiation, the N-TiO2 photocatalysts were applied for selective oxidation of vanillyl alcohol into vanillin in acetonitrile. Results suggested that after doping nitrogen into the basic TiO2, the N-TiO2 photocatalysts exhibited a narrow band-gap that could broaden the light absorption range, inhibit the recombination of photogenerated carriers, and enhance the affinity to the substrate molecules. Consequently, the photocatalytic performances of the vanillyl alcohol can be extensively improved by the N-TiO2 (N-400) photocatalyst. A selectivity of 60.37 % of vanillin and a conversion of 60.84 % of vanillyl alcohol can be realized under the optimized conditions. The mechanism for the improved photocatalysis performances of vanillyl alcohol by N-TiO2 was further proposed by combining the experimental and simulated results, which inferred that h(+) was the decisive active species for the effective oxidation of vanillyl alcohol. The N-doped TiO2 photocatalysts are also adequate to selective oxidation of other renewable bio-alcohols into aldehydes.