Biosynthesis of cysteine-conjugated zinc oxide nanoparticles using secondary metabolites of Bacillus licheniformis for wastewater purification
Muhammad Naveed, Maida Salah Ud Din, Tariq Aziz, Muhammad Asim, Syeda Izma Makhdoom, Ayaz Ali Khan, Maryam M. Alomran, Ashwag Shami, Fahad Al-Asmari, Abeer M. Alghamdi, Fakhria A. Al‐Joufi, Maymounah A. Alrayyani
Abstract
Urbanization and industrialization have exacerbated water pollution, posing significant environmental and health risks. Conventional wastewater treatment methods often fail to effectively remove persistent contaminants. This study focuses on the green synthesis of cysteine-conjugated zinc oxide nanoparticles (ZnO-Cys NPs) using Bacillus licheniformis to enhance their stability, biocompatibility, and pollutant adsorption efficiency. ZnO-Cys NPs were synthesized through a biogenic approach and characterized using XRD, SEM, FTIR, and UV–Vis spectrophotometry. SEM analysis confirmed the presence of well-dispersed nanoparticles with an average size of 66 nm. Batch adsorption experiments demonstrated superior removal of heavy metals, such as lead and cadmium, with an efficiency exceeding 87%, and degradation of organic pollutants of over 82%. FTIR analysis verified cysteine functionalization, including Zn–O, amino, carboxyl, and thiol groups, which enhance adsorption. Photocatalytic degradation under UV light resulted in over 90% removal of methylene blue within 60 minutes. Adsorption followed a monolayer model. The nanoparticles also exhibited strong biological activity, with 91.9% anti-inflammatory, 95.9% antioxidant, and 85.9% anti-hemolytic effects at a concentration of 500 µg/mL, confirming their low cytotoxicity. Reusability tests showed sustained adsorption efficiency over multiple cycles. Despite their effectiveness, large-scale production, long-term stability, and environmental impact require further evaluation. This study highlights ZnO-Cys NPs as a promising, eco-friendly solution for wastewater treatment, offering multifunctional benefits in the removal of heavy metals, degradation of organic pollutants, and enhancement of biological safety.