Enhanced Solar Light-Driven Photocatalytic Degradation of Tetracycline Using Fe³⁺-Doped CdO/ZnS Nanocomposite: Mechanistic Insights and Performance Evaluation

In recent years, studies on the efficient spatial charge separation for broad solar light absorption and water remediation have been a major priority. Moreover, the development of transition metal-doped nanocomposites for this purpose is a new endeavor in current research. Here, we constructed an Fe³⁺-doped CdO/ZnS nanocomposite with a low doping level and investigated the effect of doping on the charge transfer and recombination behavior for improved photocatalytic performance. The X-ray diffraction analysis results indicate that both materials, CdO and ZnS, exhibit a cubic phase structure with an average crystallite size of 35 nm. Morphology analysis of the Fe³⁺-doped CdO/ZnS nanocomposite confirms the formation of irregularly shaped particle-like structures. From the optical studies, the bandgap energies of CdO/ZnS and Fe³⁺-doped CdO/ZnS nanocomposites are 3.19 eV and 2.87 eV, respectively, which proved that the iron ions doping reduced the bandgap energy and extended the absorption to the visible range. The efficiency of photodegradation in the tested samples was evaluated using tetracycline under solar light exposure. The experimental results demonstrated that the Fe³⁺-doped CdO/ZnS nanocomposite outperformed the other samples, exhibiting a significantly higher photocatalytic activity. After 80 min, it achieved a remarkable degradation rate of 97.06%. The Fe³⁺-doped CdO/ZnS nanocomposite demonstrated good stability and recyclability after five cycles. Radical trapping experiments showed that hydroxyl (•OH) radicals play a key role in photodegradation.