Oxygen vacancies modulate reactive oxygen species for high-efficiency photocatalytic synthesis of 2,5-furandicarboxylic acid

Abstract

The selective photocatalytic conversion of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) represents a promising approach to tackle increasing carbon management and climate challenges, but an insurmountable challenge lies in achieving efficient conversion at high substrate concentrations. Herein, Au/TiO₂ catalysts with tunable oxygen vacancy (O_v) concentrations have been successfully prepared through adjusting the calcination atmospheres (air or H₂), and serve as a platform to elucidate the critical role of O_v in selective HMF photo-oxidation. Specifically, thermal treatment under H₂ atmosphere induces the escape of oxygen atoms from the TiO₂ crystal structure, generating beneficial O_v defects that substantially enhance photocatalytic performance. Notably, the O_v-rich Au/TiO_2-H2 catalyst demonstrates remarkably enhanced photocatalytic performance under challenging 500 mM HMF substrate concentration — achieving an exceptional FDCA yield of 97.0 % after 20 h of visible-light irradiation. Combined characterizations and experiments demonstrate the paramount role of ¹O₂ in hydroxyl group oxidation (rate-limiting phase). Besides, it has been conclusively demonstrated that O_v sites fulfill a dual-purpose catalytic function in ¹O₂ generation: facilitating the separation and migration of photo-induced charge carriers by functioning as electron trapping centers, while simultaneously facilitating the conversion of O₂ molecules to generate reactive oxidative intermediates. The significance of this investigation extends beyond merely advancing our mechanistic comprehension of defect-mediated photocatalysis—it presents a viable methodology for the rational construction of high-performance catalytic materials tailored for photochemical selective oxidation transformations.