Enhanced selective photocatalytic oxidation of a bio-derived platform chemical with vacancy-induced core-shell anatase TiO₂ nanoparticles

2,5-Furandicarboxylic acid (FDCA), a biodegradable alternative to fossil fuels, can be obtained via the catalytic oxidation of 2,5-hydroxymethlyfurfural (HMF), which is sourced from biomass. Anatase TiO₂ nanoparticles (NPs) with oxygen vacancies (V_o) effectively promote the oxidation process under ultraviolet/visible-light illumination. The conversion process is accelerated by introducing anatase TiO₂ NPs with a V_o-densified shell and stoichiometric core, which is achieved by a simple base treatment after synthesis. The defective shell acts as an electron-rich catalytic platform to facilitate HMF oxidation. Base-treated NPs measuring less than 20 nm yield ∼40% conversion to FDCA via HMF oxidation at room temperature in water. The photocatalytic activity is achieved at a 580% higher rate than with the corresponding untreated TiO₂. Spectroscopic characterizations clearly visualize the densified layer of V_o enclosing the surface of the high-performance TiO₂ NPs. Our results provide new insights into the optimal defect engineering of oxide-based catalysts for efficient biomass conversions.