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

Abstract

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 (1 H 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 Pb 2þ and Hg 2þ 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 Pb 2þ ions are higher than those of the Hg 2þ ions, and these capacities increase as the DS increases. The equilibrium adsorption amounts, q e , were 11.87 mg/g for Pb 2þ and 5.17 mg/g for Hg 2þ ions for the highest sulfonated polymer.

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“…On the other hand, the presence of the −SO 3 H groups causes considerable steric effects to the polymer backbone that hinder the torsional movement of the macromolecules. Other sulfonated polymers have also shown these effects [ 28 , 32 ].…”

“…Polymer films from the novel long-chain polyamides were subjected to X-ray diffraction (XRD) to estimate the degree of crystallinity, DC , as well as the mean intersegmental distance or d -spacing value between polymer chains by applying the Bragg’s equation at the angle of maximum height of the amorphous peak [ 28 ]. In general, the XRD measurements performed on the films revealed amorphous materials with diffraction patterns displaying one broad peak that is characteristic of this kind of polymer and whose maximum reflective intensity was observed at 2θ ≈ 20° ( Figure 6 ).…”

“…The experimental ion exchange capacity of the polymer membrane was assessed as described in the literature [ 28 ] by the titration method using the following mathematical expression: where IEC [meq g −1 ] represents the ion exchange capacity, V [mL] represents the volume of NaOH solution used in the titration, M is the molarity of the solution, and W dry [g] is the mass of the dried membrane.…”

“…The water uptake of the polymer membrane was estimated as described in the literature [ 28 ] by gravimetric measurements employing the expression given below: where W U [%] represents the water uptake, W wet [g] is the mass of the hydrated membrane, and W dry [g] is the mass of the dried membrane.…”

Enhanced heavy metal removal from an aqueous environment using an eco-friendly and sustainable adsorbent

“…The suspensions were centrifuged, and the metal ion concentration in the supernatant from each desorption experiment was tested by the method described in the adsorption experiments. The desorption experiments were conducted thrice in the same manner, and the desorption capacity at equilibrium ( q t,2 ) was calculated using the equation given below 74 : where q t,2 (mg/g) is the amount at desorption time t (min); C t,2 (mg/L) is the concentration of each metal ion in solution at time t (min); V 2 (mL) is the volume of the desorption agent; and m 2 (g) is the final mass of the TLSB after the metal ions were released.…”