Sulfur vacancy engineered FeS2 nanosheets for boosted O2 activation and photocatalytic valorization of 5–Hydroxymethylfurfural

CTAB assisted synthesis of FeS 2 allows precise control over surface sulfur vacancies. • Surface-modified FeS 2 boosts O 2 activation and enhances reactive oxygen species (ROS) population. • Vs-rich FeS 2 lowers HMF conversion barrier, giving 15.73 fold higher DFF yield than pristine FeS 2 . • Synergy of Vs and Fe redox cycling in FeS 2 accelerates charge transfer and surface reactivity. • Tuning defects and redox states in FeS 2 enable sustainable and versatile photocatalysis. The photocatalytic conversion of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF) using molecular oxygen (O 2 ) as the oxidant offers a sustainable route for biomass valorization, yet is limited by inefficient O 2 adsorption and activation on conventional photocatalysts. Herein, we report a Cetrimonium bromide (CTAB) assisted synthesis of iron pyrite (FeS 2 ) with engineered surface sulfur vacancies (Vs) that enable simultaneous activation of O 2 and HMF under solar light. Introduction of Vs increases the catalyst’s specific surface area and modulates the local electronic structure, particularly tuning the Fe 2+ /Fe 3+ redox landscape. These defect sites act synergistically, where Fe 2+ sites act as preferred O 2 adsorption centers, while adjacent Vs promote electron localization and transfer to adsorbed O 2 , thereby facilitating its activation through the oxidation of Fe 2+ to Fe 3+ . Concurrently, the modulated Fe redox states enable efficient HMF adsorption and oxidation through interaction with the activated O 2 species (•O 2 – and 1 O 2 ). This dual activation mechanism, driven by vacancy engineering and Fe redox dynamics, enhances charge transfer kinetics and surface reactivity, leading to a 15.7-fold increase in DFF production compared to prismatic FeS 2 . Our findings emphasize the critical role of Vs and Fe 2+ /Fe 3+ redox interplay in organizing simultaneous O 2 activation and HMF oxidation, advancing the rational design of efficient photocatalysts for biomass-derived chemical production. Download: Download high-res image (117KB) Download: Download full-size image