Removal of Pb(II) ions from aqueous solutions using hybrid organic–inorganic composite material: Zr(IV) iodosulphosalicylate

The present study explored the feasibility of using zirconium(IV) iodosulphosalicylate (ZIS) as adsorbent for the removal of lead(II) under different conditions. Batch studies were performed to evaluate the influence of various experimental parameters such as pH 7.5, adsorbent dose 200 mg or 10 g L−1 of solution and equilibrium time 120 min for the concentration range of 53.87–241.45 ppm at 323 K. A comparison of kinetic models applied to the adsorption of Pb (II) on ZIS was evaluated for the Lagergren pseudo first order, Ho and McKay pseudo second order, Elovich and intraparticle diffusion kinetic models. The experimental data fitted very well in pseudo second order followed by Elovich model. Intraparticle diffusion does not seem to control the Pb (II) removal process. Equilibrium isotherm for the adsorption of Pb (II) on ZIS was analyzed by Freundlich, Langmuir, Dubnin–Radushkevich (D–R) and Temkin isotherm model using linear regression technique. Langmuir and Freundlich isotherms were found to best represent the data for Pb (II) onto ZIS. The maximum adsorption capacity of ZIS is found to be 327.87 mg g−1 Pb (II). The results show that the sorption capacity increases with increase in temperature, concentration, pH but decreased with adsorbent dose. The thermodynamics parameters such as enthalpy change (ΔH° = 6797.23 J mol−1), entropy change (ΔS° = 29.333 J mol−1), Gibb's free energy (ΔG° = −2677.45 J mol−1) and activation energy (Ea = 8198.6 J mol−1) results indicate that adsorption process was spontaneous, endothermic nature, increased randomness and shows feasibility and good affinity of Pb (II) toward the adsorbent.