Adsorption mechanism of Pb2+ ions by Fe3O4, SnO2, and TiO2 nanoparticles.

Abstract

Nanosized sorbents for the removal of heavy metal ions are preferred due to high surface area, smaller size, and enhanced reactivity during adsorbate/adsorbent interactions. In the present study, Fe3O4, SnO2, and TiO2 nanoparticles were prepared by microemulsion-assisted precipitation method. The particles were characterized by BET surface area, X-rays diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, transmittance electron microscopy (TEM), and X-ray photoelectron (XPS) spectroscopy. The respective particle sizes calculated from TEM were 7nm (± 2), 10nm (± 2), and 20nm (± 3) for Fe3O4, SnO2, and TiO2. The adsorbents were employed for the adsorption of Pb2+ ions from the aqueous solutions. The respective maximum adsorption capacity for Fe3O4, SnO2, and TiO2 nanoparticles was 53.33, 47.21, and 65.65mg/g at 313K. Based on the exchange reaction taking place on the surfaces of Fe3O4, SnO2, and TiO2, it is concluded that Pb2+ ions are adsorbed in hydrated form. The X-ray photoelectron spectroscopy (XPS) studies also support the exchange mechanism and confirmed the presence of elements like Fe, Sn, Ti, Pb, and O and their oxidation states. Both Langmuir and Freundlich models in non-linear form were applied, however, based on RL values, the Langmuir model fits well to the sorption data. Moreover, adsorption parameters were also determined by using non-linear form of the Langmuir model along with statistical approaches to remove error. The qm and Kb values confirm better adsorption capacity and binding strength for Pb2+ ions as compared to the values reported in the literature.