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

Abstract

Core–shell heterostructures have attracted great concern as promising visible light-driven photocatalysts. Herein, core–shell nanocomposites of SiO2@Sr0.4Ti0.4Mg0.2Fe2O4.4 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 Sr0.4Ti0.4Mg0.2Fe2O4.4 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.