Role of Structural Features and Heteroatom Functionality in the Photocatalytic Selectivity of Sulfur Dots for Competitive H2 and H2O2 Production

Sulfur dots (S-dots) have emerged as promising elemental semiconducting nanomaterials owing to their distinctive photoluminescence and photocatalytic properties. However, the influence of structural features on their fundamental photophysical and optoelectronic properties remains largely unexplored. Herein, oxygen-rich S-dots (OSDs) and nitrogen-rich S-dots (NSDs) were synthesized by tuning heteroatom functionalities and investigated for selective photocatalytic H2 and H2O2 production. OSDs selectively produce H2O2 through oxygen reduction, whereas NSDs favor H2 evolution via proton reduction. Correlating structural and morphological characteristics with photophysical and optoelectronic properties revealed distinct charge-carrier dynamics governing their photocatalytic selectivity. Ultrafast transient absorption spectroscopy further elucidated the underlying mechanisms. The surface functionalities of NSDs induce photobasicity and promote exciplex formation with H2O, facilitating proton abstraction and H2 evolution. In contrast, the band structure and favorable energy-level alignment of OSDs enable selective H2O2 production. These findings demonstrate heteroatom engineering as an effective strategy for tuning the photocatalytic selectivity of elemental S-dots.