Chemical modification of waste poly(p-phenylene terephthalamide) fibers and its binding behaviors to metal ions

Abstract

Using waste poly(p-phenylene terephthalamide) fibers (PPTA) as a starting material and novel Schiff base-containing adsorbent for metal ions, PPTA-Sal and its basification product PPTA-Sal(Na) were prepared via a series of chemical modification reactions. The structures of the modified fibers were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and thermogravimetric analysis (TG). Metal ions, such as Pb2+, Cu2+ and Ni2+, were chosen as representatives to determine the adsorption capacities of the modified fibers in aqueous solutions. The experimental results showed that the adsorption capacities for Pb2+ of PPTA-Sal and PPTA-Sal(Na) can reach 15.12 and 19.06mg/g respectively, which are much higher than the 10.56mg/g of the intermediate product amination PPTA (PPTA-NH2). The adsorption of Pb2+ on PPTA-Sal and PPTA-Sa(Na) followed well the pseudo second-order model. Langmuir and Freundlich models were employed to fit the isotherm adsorption of Pb2+ on PPTA-Sal and PPTA-Sal(Na), and the results revealed that both models were able to closely predict the experimental data. The Freundlich isotherm was slightly better than the Langmuir isotherm in describing the Pb2+ adsorption onto PPTA-Sal(Na), while the latter model was more suitable for fitting the data of Pb2+ adsorption onto PPTA-Sal. The adsorption capacities of PPTA-Sal and PPTA-Sal(Na) were compared using various adsorbents.