Switching charge transfer direction in heterojunctions: A competition of two driving forces.

The charge transfer pathway and corresponding heterojunction type rely on the combined effects of the material's inherent properties and the interface structure. Herein, we report a crystal facet-dependent switching of charge transfer direction in TiO2/Ni3S4 composites via the competition of two driving forces (work function difference and interfacial bonding). Experimental and theoretical calculations demonstrate that when the dominant contact facet of Ni3S4 transitions from (022) to (113), the density of interfacial Ti-S bonds significantly increases. These Ti-S bonds, polarized by the electronegativity difference between S (2.58) and Ti (1.54), generate a driving force competing with the work function driving force. This competition can determine the charge transfer direction and the heterojunction type, leading to distinct active species generation: TiO2/Ni3S4-3 (S-scheme) produce •O2-, •OH, and •SO4-, while TiO2/Ni3S4-7 (type-II) generates only •OH and •SO4-, and ultimately resulting in different degradation pathways with ofloxacin as the model pollutant. This work highlights the important role of interfacial bonding in determining charge transfer direction, and introduces a "driving force competition" concept for regulating heterojunction types.