New series of benzene-1,3,5-triamine based cross-linked polyamines and polyamine/CNT composites for lead ion removal from aqueous solutions

For the first time, a new series of polyamines (TRI series) were synthesized by in situ polymerization of benzene-1,3,5-triamine, paraformaldehyde and various alkydiamines. 1% of acylchloride functionalized carbon nanotubes were added to produce a second series of polyamine/CNT composites (CNT TRI series). The synthesized TRI and CNT TRI Series were characterized using various techniques including Fourier transform infrared spectroscopy, powder X-ray diffraction, scanning electron microscope (SEM) equipped with energy-dispersive X-ray spectroscopy (EDX). The functionalized CNTs were characterized by transmission electron microscope (TEM). Both series were evaluated for their efficiency in the removal of lead ions from aqueous solutions. The most efficient adsorbent of both series was evaluated under different controlled conditions, including pH, contact time and initial concentration. The experimental data were subjected to Langmuir, Freundlich, and Temkin isotherm models and found that the adsorption process fit Freundlich isotherm model assuming favorable heterogeneous adsorption process with CNT TRI 1,4 having a higher adsorption capacity toward lead ions than TRI 1,4. Kinetic models including pseudo second-order and intraparticle diffusion model were also employed. The intraparticle diffusion model assumed that the mechanism of the adsorption process is controlled by film diffusion and intraparticle diffusion mechanism. The study provides potential adsorbents for the removal of lead ions from aqueous solutions.