Abundant Pd-S interfaces integrate charge shuttling and moderate O₂ adsorption for enhanced photocatalytic 5-hydroxymethylfurfural oxidation

Activation of molecular O ₂ on catalytic surfaces to form reactive oxygen species (ROS) is a pivotal step in catalytic reactions. In this study, we synthesized a bimetallic Zn ₃In ₂S₆ (ZIS) catalyst enriched with Pd-S interfaces via a straightforward cation exchange process between Pd ²⁺ and Zn ²⁺. These interfaces function as electron reservoirs, and Pd incorporation significantly enhances photocatalytic performance by reorganizing the electronic structure of the ZIS matrix, thereby improving charge carrier dynamics and reaction kinetics. Additionally, Pd modification optimizes O ₂ adsorption strength, preventing excessive population of the π* antibonding orbital that can lead to O-O bond cleavage and reduce ROS generation. Theoretical calculations reveal that monodentate adsorption of O ₂ on Pd-ZIS surfaces promotes efficient photo induced electron transfer across all excited states, enabling effective ROS activation. The combination of experimental findings and theoretical analysis identified the mechanisms underlying the improved selectivity of Pd-modified ZIS catalysts. As a result, the optimized Pd-ZIS-5 photocatalyst demonstrates a high photo-oxidation performance for HMF oxidation, achieving 92.4 % conversion, 86.3 % yield, and 93.4 % selectivity–representing a 1.7-fold improvement over prismatic ZIS. Overall, this work demonstrates how Pd doping and tailored O ₂ adsorption strength enhance photocatalytic processes, offering valuable insights for advanced biomass conversion and sustainable chemical production.