Modification of PPTA-based polymeric waste and adsorption properties for metal ions

Novel composite adsorbents PPTA-AOx were synthesized by grafting polyacrylonitrile onto poly(p-phenylene terephthalamide) (PPTA) followed by converting the acrylonitrile into the amidoxime (AO) groups. Their structures were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, elemental analysis, transmission electron microscopy, etc. Scanning electron microscopy analysis and pore structure analysis manifested that PPTA-AOx adsorbents are all composed of nanoparticles aggregation. The as-synthesized PPTA-AOx adsorbents showed good adsorption capacity for Hg²⁺ with a maximum adsorption capacity of 2.50 mmol g^?1. The pseudo-second-order model can reasonably describe the adsorption kinetics of the three adsorbents for Hg²⁺. Langmuir model provided better fit for the isothermal adsorption of Hg²⁺ on PPTA-AO₁ and PPTA-AO₂, while the Freundlich model was better for PPTA-AO₃. The adsorption process might involve both chemisorption and physisorption. According to the calculated thermodynamic parameters, it can be concluded that the adsorption is an endothermic, spontaneous and entropy-driven process.