Sustainable Synthesis of Zn‐Doped Silica Nanocomposites from Waste Silica Gel for Enhanced Methylene Blue Adsorption and Antimicrobial Activity

This study reports the valorization of waste silica gel (60–200 mesh) into silica nanoparticles (SiO 2 NPs) and zinc‐doped silica nanocomposites (Zn–SiO 2 NCs) for wastewater remediation. Comprehensive characterization (SEM, EDX, FTIR, and XRD) confirmed the nanoscale structure and successful incorporation of Zn. Both materials efficiently removed methylene blue (MB), with Zn‐SiO 2 NCs exhibiting slightly higher adsorption capacity (9.59 mg/g) compared to SiO 2 NPs (9.23 mg/g) under optimal conditions (pH 7, 30 min contact time, 10 mg/L MB). Adsorption behavior followed the Temkin isotherm, suggesting uniform active sites and moderate adsorbate–adsorbent interactions. Kinetic data were best described by the pseudo‐second‐order model, indicating surface‐controlled uptake, while thermodynamic analysis (Δ H values within the physisorption range) confirmed that the process is predominantly governed by physical adsorption. This aligns with a mechanism dominated by rapid surface interactions. Both adsorbents retained over 85% efficiency after four regeneration cycles. Furthermore, Zn‐SiO 2 NCs exhibited pronounced antimicrobial activity, producing inhibition zones of 12–14 mm against Escherichia coli , Bacillus sp., Enterococcus ATCC, and Candida albicans . Overall, this work highlights the sustainable transformation of silica waste into multifunctional nanomaterials with dual applications in dye removal and microbial control, contributing to circular economy strategies.