Low-hazard fabrication of natural zeolite @NiO composite for Pb2+ removal from industrial wastewater: toxicity assessment

The presence of heavy metals in water and industrial wastewater has become a major environmental concern due to their harmful effects on human health and other living organisms. In this study, a Zeolite/NiO composite was employed to investigate its potential for the removal of lead (Pb 2+ ) from aqueous solutions. NiO nanoparticles (∼20 nm) were green-synthesized and loaded onto zeolite to prepare Zeolite@NiO nanocomposites. XRD analysis confirmed that the crystalline structure of zeolite was preserved after NiO incorporation, while uniform dispersion of NiO nanoparticles was achieved. FESEM images demonstrated homogeneous NiO distribution while maintaining the zeolite framework. The Pb 2+ adsorption performance of the composites was evaluated in aqueous solutions. Zeta potentials displayed the highest Pb 2+ removal efficiency, attributed to an optimal balance between zeolite ion-exchange sites and NiO dispersion. The adsorption mechanism involves a synergistic combination of electrostatic interactions, ion exchange, surface complexation with −Ni-OH groups, and Pb 2+ stabilization/precipitation. Cytotoxicity assessment using the MTT assay showed that at a realistic residual catalyst concentration of 0.75 µg/mL, A549 cells maintained ≥90–115% viability. The IC 50 values for NiO, zeolite, and Zeolite: NiO = 1:1 were approximately 1.74, 1.87, and 1.90 µg/mL, indicating negligible biological risk under practical exposure conditions.