Comparative study of silica and silica-decorated ZnO and ag nanocomposites for antimicrobial and photocatalytic applications

The increasing threat of multi-resistant infectious agents and environmental toxins has led to a demand for new therapeutic and catalytic materials. In this study, C-SiO₂ (crystalline silica), Ag-SiO₂ (silver-silica), and ZnO-SiO₂ (zinc oxide-silica) nanocomposites (NCs) were synthesized through green methods and characterized by UV-visible spectroscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). These silica-based nanomaterials were investigated as potential photocatalysts for the degradation of p-nitroanilines and their antibacterial and antioxidant properties. XRD analysis showed crystalline sizes of 14 nm for C-SiO₂ NPs, 18 nm for Ag-SiO₂, and 20 nm for ZnO-SiO₂ NCs. UV-visible spectroscopy revealed energy band gaps of 4.5 eV for C-SiO₂ NPs, 3.23 eV for Ag-SiO₂, and 2.84 eV for ZnO-SiO₂. FTIR analysis confirmed the formation of SiO₂ in all samples through the Si-O-Si absorption peak. SEM revealed distinct morphologies: C-SiO₂ NPs as agglomerated granular particles, Ag-SiO₂ NCs as flattened rods or sheets, and ZnO-SiO₂ as roughly spherical. Antimicrobial testing showed that ZnO-SiO₂ and Ag-SiO₂ NCs exhibited 80% and 88% antimicrobial activity against Escherichia coli and Pseudomonas, with Ag-SiO₂ also demonstrating strong activity against Staphylococcus. The minimum inhibitory concentration (MIC) of Ag-SiO₂ and ZnO-SiO₂ NCs was found to be 80%, outperforming C-SiO₂ NPs. Antioxidant activity assays showed scavenging efficiencies of 45%, 57.8%, and 71% for C-SiO₂, Ag-SiO₂, and ZnO-SiO₂ NCs, respectively, at 30 mg/ml. ZnO-SiO₂ NCs also achieved a 75% degradation rate for p-nitroanilines, while Ag-SiO₂ achieved 45%. This study demonstrates that ZnO-SiO₂ and Ag-SiO₂ NCs are effective materials for disinfection and pollutant degradation, offering an eco-friendly solution for environmental and health challenges.