Synthesis,characterization,and heavy metal adsorption properties of sulfonated aromatic polyamides

This work reports on the synthesis of a series of new sulfonated fluorine-containing aromatic polyamides with increasing degree of sulfonation (DS). The chemical structure of the resulting polymers was confirmed by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance (¹H NMR) which evidenced the presence of amide and sulfonic groups in the proposed concentrations. Afterwards, we carried out a comparative study of heavy metal ion adsorption in membranes based on these aromatic polyamides. The main purpose was to determine the adsorption capacity of the prepared polymer membranes toward Pb²⁺ and Hg²⁺ in aqueous media at 30°C and pH neutral. The adsorption kinetics was evaluated with the pseudo-first-order and pseudo-second-order models. The adsorption kinetics in all the polyamide membranes followed the pseudo-second-order rate law for both heavy metal ions. It is observed that the adsorption capacities of all the polyamides toward Pb²⁺ ions are higher than those of the Hg²⁺ ions, and these capacities increase as the DS increases. The equilibrium adsorption amounts, q _e, were 11.87 mg/g for Pb²⁺ and 5.17 mg/g for Hg²⁺ ions for the highest sulfonated polymer.