Nanoclay-Modulated Interfacial Chemical Bond and Internal Electric Field at the Co₃ O₄ /TiO₂ p-n Junction for Efficient Charge Separation

To achieve a high separation efficiency of photogenerated carriers in semiconductors, constructing high-quality heterogeneous interfaces as charge flow highways is critical and challenging. This study successfully demonstrates an interfacial chemical bond and internal electric field (IEF) simultaneously modulated 0D/0D/1D-Co₃ O₄ /TiO₂ /sepiolite composite catalyst by exploiting sepiolite surface-interfacial interactions to adjust the Co²⁺ /Co³⁺ ratio at the Co₃ O₄ /TiO₂ heterointerface. In situ irradiation X-ray photoelectron spectroscopy and density functional theory (DFT) calculations reveal that the interfacial Co²⁺ OTi bond (compared to the Co³⁺ OTi bond) plays a major role as an atomic-level charge transport channel at the p-n junction. Co²⁺ /Co³⁺ ratio increase also enhances the IEF intensity. Therefore, the enhanced IEF cooperates with the interfacial Co²⁺ OTi bond to enhance the photoelectron separation and migration efficiency. A coupled photocatalysis-peroxymonosulfate activation system is used to evaluate the catalytic activity of Co₃ O₄ /TiO₂ /sepiolite. Furthermore, this work demonstrates how efficiently separated photoelectrons facilitate the synergy between photocatalysis and peroxymonosulfate activation to achieve deep pollutant degradation and reduce its ecotoxicity. This study presents a new strategy for constructing high-quality heterogeneous interfaces by consciously modulating interfacial chemical bonds and IEF, and the strategy is expected to extend to this class of spinel-structured semiconductors.