TiO2-encapsulated CdS heterointerface enables directional charge transfer and suppresses detectable Cd2+ leaching during solar tetracycline degradation

The development of stable semiconductor heterointerfaces that improve charge separation while reducing photocorrosion in visible-light photocatalysis remains challenging. In this work, a buried CdS/TiO₂ heterointerface was created by sequential deposition of a nanocrystalline CdS sensitizing layer followed by full coverage with a rutile TiO₂ overlayer. XRD revealed crystalline phases, whereas SEM, cross-sectional SEM, and AFM supported the continuous layered morphology and interfacial contact. Mott–Schottky, transient photocurrent, and PL/TRPL measurements supported efficient interfacial electron extraction from photoexcited CdS into TiO₂ with reduced charge‒carrier recombination. Tetracycline degradation under simulated solar irradiation reached 96.3% under optimal conditions. Both the pseudo-first-order and pseudo-second-order models described the degradation data well, with a slightly better fit for the latter, whereas the Arrhenius analysis gave an apparent activation energy of 7.56 kJ mol⁻¹. The degradation efficiency of the heterostructure was more than 91% after five consecutive reuse cycles, indicating good short-term operational stability. The dissolved Cd²⁺ concentrations remained below the analytical detection limit throughout the photocatalytic operation, which is consistent with the effective suppression of CdS photocorrosion by TiO₂ encapsulation. These findings show that buried-interface engineering can integrate visible-light sensitization, favorable interfacial charge extraction, photocatalytic activity, and protection of a photocorrosion-prone sensitizer within a single immobilized architecture.