Sustainable phytosynthesis of reusable ZnO-NPs for efficient heavy metal ion removal with antibacterial properties

Abstract

In present study, green zinc oxide nanoparticles (ZnO-NPs) were synthesized using Eucalyptus globulus leaf extract, providing an eco-friendly and sustainable approach for nanoparticle production. The synthesised NPs were characterized using various analytical techniques, including XRD, TEM, SAED, FTIR, UV–Vis, FESEM-EDX, TGA, BET and zeta potential analysis. The NPs exhibited a hexagonal structure, good monodispersity, and minuscule morphology as confirmed by TEM and SEM analyses. The results also indicate the formation of spherical nanoparticles with sizes ranging from 44 to 58 nm. XRD pattern confirm the presence of crystalline phase in ZnO-NPs and Brunauer Emmett and Teller’s surface area of synthesized ZnO-NPs was found to be 12.435 m²/g, with an average pore diameter falling within the mesoporous range. ZnO-NPs serve as efficient adsorbents for the removal of heavy metal ions (Ni²⁺ and Cu²⁺) and exhibit promising antibacterial properties due to their higher surface area-to-volume ratio and stronger inherent adsorption capability. The results showed that ZnO-NPs have excellent adsorption efficiency of 95 % and 94 % for Ni²⁺ and Cu²⁺ ions at 8.0 and 7.0 pH, along with 40 mg sorbent dose, 20 mg/L concentration and 90 min of contact time at 30 ºC. The adsorption of both metal ions followed the Langmuir isotherm (R² - 0.99), indicating monolayer adsorption on ZnO-NPs. The kinetic studies further showed that the adsorption followed the pseudo-second-order model, with R² values of 0.99 for Ni²⁺ and 0.97 for Cu²⁺, suggesting that chemisorption was the dominant mechanism. Furthermore, the synthesized ZnO-NPs exhibited higher antibacterial activity, effectively inhibiting growth of Staphylococcus aureus and Pseudomonas aeruginosa, highlighting their potential for environment amelioration and antibacterial applications. These new sustainable solutions advance progress towards Circular Economy and the UN's SDGs.