Comparative study of Pb(II) ions adsorption on pet fibers and flakes: isotherm, kinetic and mechanism considerations

In this study, the adsorption of Pb(II) ions from aqueous media on polyethylene terephthalate (PET) waste (fibers and flakes) was examined as a function of the most important operating parameters, at room temperature (22 degrees C +/- 1 degrees C), in batch systems. The effect of initial solution pH, adsorbent dosage, contact time and initial metal ions concentration on Pb(II) ions adsorption efficiency on these two adsorbent materials is compared. It was found that for both PET-based materials (fibers and flakes) the adsorption efficiency depends very little on the initial solution pH (in the range 2.0-6.0), and reaches a maximum at 4.0 g/L adsorbent dose and a contact time of 60 min. However, the adsorption of Pb(II) ions on PET fibers is much more efficient than in the case of PET flakes, over the entire range of initial metal ions concentration (20-420 mg Pb(II)/L). To quantitatively evaluate these adsorption processes, the experimental data were modelled using Langmuir, Freundlich and Temkin isotherm models, and pseudo-first order, pseudo-second order and intra-particle diffusion models. The obtained results indicate that the adsorption process of Pb(II) ions on both PET-based materials (fibers and flakes) follow a pseudo-second order kinetic model (R-2 > 0.9998) and Langmuir isotherm model (R-2 > 0.9857). In addition, the maximum adsorption capacity for PET fibers (166.66 mg Pb(II)/g) is 13.6 times higher than for PET flakes (12.27 mg Pb(II)/g). To explain this significant difference of maximum adsorption capacities, the structural characteristics of PET fibers and flakes were highlighted using Fourier-transform infrared spectroscopy, scanning electron microscopy and thermogravimetry methods. The results included in this study will provide a clear image of the possibility of functionalization of these materials to obtain high-performance adsorbents for environmental decontamination.