Selective photooxidation of 5-hydroxymethylfurfural in water enabled by highly dispersed gold nanoparticles on graphitic carbon nitride

Photocatalytic synthesis of chemicals is highly recognized for its eco-friendliness and mild reaction conditions, yet it faces considerable challenges regarding catalytic efficiency, stability and cost. The selective photooxidation of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF) in water is a cost-effective and sustainable route for biomass valorization. The capability of a photocatalyst to capture visible light is paramount for efficiently harnessing solar energy and is the most critical initial step. Therefore, metal nanocatalysts with visible-light response and localized surface plasmon resonance (LSPR) have received widespread attention. In this work, graphitic carbon nitride (g-C₃N₄) with different morphologies was synthesized through high-temperature calcination of various organic precursors. Following that, the photodeposition of Au nanoparticles was used to construct a Schottky junction photocatalyst endowed with the LSPR effect. The optimal Au/CN(I) catalyst achieved 26% yield of DFF and productivity of 72.7 mgDFF gcatal.1 h1 under simulated sunlight in oxygen and water without any additives. This outstanding result outperformed most g-C₃N₄ and metal oxide photocatalysts ever reported in the literature. The interfacial electronic interactions between Au nanoparticles and g-C₃N₄ semiconductor were meticulously elucidated using comprehensive characterizations and computational calculations. The roles of different reactive oxygen species were clarified by a series of controlled experiments. A plausible mechanism explaining the origin of visible-light response and photocatalytic performance was discussed.