Water pollution is a major global challenge due to the fast expansion of industrial activities and the increasing human population. Certain heavy metals can be exceedingly hazardous and contribute significantly to water contamination. In this study, iron oxide nanoparticles (IONPs) were synthesized using cyanobacteria extract to remove heavy metals (Cd and Pb) from the wastewater. To characterize the IONPs, several analytical techniques were employed such as Ultraviolet–visible spectroscopy revealed a SPR (surface plasmon resonance) peak at 348 nm and FTIR (Fourier transform infrared) spectral analysis showed the OH, C–H and S=O functional groups which confirmed the biomolecules responsible for the biogenic synthesis and stability. The surface morphology of the biogenic IONPs was investigated using SEM (scanning electron microscopy) which reveled their nearly spherical or cubic shape. Additionally, XRD (X-ray diffraction) analysis confirmed the crystallinity of IONPs, with a crystalline size measuring 18.21 nm. Effects of contact time, pH, initial metal ions concentrations, and IONPs dosage were studied on the adsorption of Cd and Pb ions. Different adsorption kinetics and isotherm models were applied to the experimental data. Pseudo second-order kinetic and Langmuir isotherm models were well fitted to the adsorption of Cd and Pb onto the IONPs. Higher correlation coefficients (R2) values of Langmuir isotherm (R2: 0.990 for Cd and Pb adsorption) and Pseudo second-order kinetic (R2: 0.998 and 0.999 for Cd and Pb adsorption, respectively) were found, which indicated the favorable interaction between the metal ions and adsorbent. Langmuir isotherm calculated maximal adsorption capacities of 105.932 and 118.764 mg/g for Cd and Pb, respectively. Recyclability of IONPs was conducted and after five adsorption/desorption cycles, IONPs retained their adsorption efficiency with negligible decline. After five cycles, IONPs removal efficiency was up to 80.41 and 88.35 % for Cd and Pb, respectively. Results of this study indicate that cyanobacteria-mediated IONPs were efficient adsorbent for Pb and Cd removal from contaminated aqueous solution.
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