Precise Tuning of SiO₂ Thickness in SiO₂@Sr_0.4Ti_0.4Mg_0.2Fe₂O_4.4 Core–Shell Nanocomposites for Augmenting Photocatalytic and Antibacterial Activity

Core–shell heterostructures have attracted great concern as promising visible light-driven photocatalysts. Herein, core–shell nanocomposites of SiO₂@Sr_0.4Ti_0.4Mg_0.2Fe₂O_4.4 with varying SiO₂ thickness were rationally designed. Effect of modulating the SiO₂ thickness on the structural and optical properties was studied. Homogenous SiO₂ layer of varying thickness was coated over Sr_0.4Ti_0.4Mg_0.2Fe₂O_4.4 NPs. HRTEM and XRD analyses confirmed the successful formation of core–shell nanocomposites. The photocatalytic performance was evaluated by using tetracycline hydrochloride, azure-B, Staphylococcus aureus, and Escherichia coli as model pollutants. Maximum enhancement in photocatalytic activity was observed in a core–shell nanocomposite having an average shell thickness of 24 nm. The results were supported by its higher porosity and specific surface area, along with a narrowed band gap and fluorescence quenching. The formation of the core–shell heterojunction promoted charge separation. Under the optimized conditions of irradiation time, pH, and dose, its degradation efficiency was 96.5% for tetracycline hydrochloride, 96.3% for azure-B, 97.1% for S. aureus, and 95.4% for E. coli. Hydroxyl radicals and holes played a vital role in the degradation process. The photocatalytic parameters were optimized using Box–Behnken statistical methodology. This work bears broad potential for fabricating an efficient and high-performance photocatalyst of SiO₂ with ferrite having a core–shell heterostructure.