Combined maghemite - titania nanoparticles embedded in polyvinyl alcohol-alginate beads for heavy metals and radioactive ions removal

Abstract

The presence of heavy metal ions in the environment is of major concern due to their toxicity to many life forms. Their toxicity affects the ecosystem and presents human health risk. Thus, wastes that contain heavy metals ionsmust be well treated so on to protect the people and environment.In this study, potential method for removal of heavy metal ions (such as: lead(II), cadmium(II), cesium(I), barium(II) and iodine(I) ions) from aqueous solution using combined maghemite (γ-Fe2O3) and titania (TiO2) nanoparticles embedded in PVA-alginate beads were investigated. In addition, control experiments that involved the study of TiO2 nanoparticles in polyvinyl alcohol (PVA)-alginate beads and γ-Fe2O3 nanoparticles in PVA-alginate beads were also performed. For this purpose, TiO2 and Fe2O3 nanoparticles were synthesized by hydrothermal and co-precipitation method, respectively. The average size of TiO2 and Fe2O3 nanoparticles was 15 and 9 nm, respectively. The nanoparticles and the beads were characterized by x-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared (FTIR) and transmission electron microscopy (TEM). These beads were used in batch sorption experiments for removal of heavy metal ions and iodine ions from aqueous solution under sunlight. Several operating conditions such as initial ion concentration, pH and contact time were investigated to evaluate their effects on the process. The results showed γ-Fe2O3 and TiO2 PVA-alginate beads could remove Pb(II), Cd(II), Cs(I), Ba(II) and I(I) ions, with efficiency of around 100, 100, 93, 99 and 99%, respectively. Also, the combined γ-Fe2O3 and TiO2 PVA-alginate beads showed best efficiency among three types of beads. After sunlight exposure, the beads were characterized by x-ray photoelectron spectroscopy (XPS) and energy-dispersive x-ray (EDX) system.The results revealed the mechanism for ton removal of photocatalytic process. These beads can be easily recovered from the aqueous solution and they can be recycled for a maximum of seven times before losing their original properties.