Investigation of the removal of lead by adsorption onto 1-(2-thiazolylazo)-2-naphthol (TAN) imbedded polyurethane foam from aqueous solution

A new preconcentration method is presented for lead on TAN-loaded polyurethane foam (PUF) and its measurement by differential pulse anodic stripping voltammetry (DPASV). The optimum sorption conditions of 1.29 × 10^-5 M solution of Pb(II) ions on TAN-loaded PUF were investigated. The maximum sorption was observed at pH 7 with 20 minutes equilibrated time on 7.25 mg mL^-1 of TAN-loaded foam. The kinetic study indicates that the overall sorption process was controlled by the intra-particle diffusion process. The validity of Freundlich, Langmuir and Dubinin - Radushkevich adsorption isotherms were tested. The Freundlich constants 1/n and KF are evaluated to be 0.45 ± 0.04 and (1.03 + 0.61) × 10^-3 mol g^-1, respectively. The monolayer sorption capacity and adsorption constant related to the Langmuir isotherm are (1.38 ± 0.08) × 10^-5 mol g^-1 and (1.46 ± 0.27) × 10 ⁵ L mol^-1, respectively. The mean free energy of Pb(II) ions sorption on-TAN loaded PUF is 11.04 ± 0.28 kJ mol^-1 indicating chemisorption phenomena. The effect of temperature on the sorption yields thermodynamics parameters of ΔH, ΔS and ΔG at 298 K that are 15.0 ± 1.4 kJ mol^-1, 74 ± 5 J mol^-1 K^-1 and -7.37 ± 0.28 kJ mol^-1, respectively. The positive values of enthalpy (ΔH) and entropy (ΔS) indicate the endothermic sorption and stability of the sorbed complexes are entropy driven. However, the negative value of Gibb's free energy (ΔG) indicates the spontaneous nature of sorption. On the basis of these data, the sorption mechanism has been postulated. The effect of different foreign ions on the sorption and desorption studies were also carried out. The method was successfully applied for the determination of lead from different water samples at ng levels.