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Experimental results showed that the adsorption of Pb(2+) ions increased with the increase in solution pH and temperature. Langmuir and Freundlich isotherms models were used to describe the adsorption behavior of Pb(2+) by calix[4]naphthalene. Equilibrium data fitted well with the Langmuir isotherm model and the maximum adsorption capacity of calix[4]naphthalene for Pb(2+) at 30 °C was found to be 29.15 mg g(-1). Kinetic studies indicated that the adsorption followed pseudo-second order model and the thermodynamic studies revealed that the adsorption process was spontaneous and endothermic in nature. The obtained results demonstrated that calix[4]naphthalene can be used as an effective adsorbent for Pb(2+) ions removal from water.

Amberlite XAD-4 resin (AXAD-4) has been functionalized by coupling it through an NN group with 1-(2-pyridylazo)-2-naphthol (PAN). The resulting chelating resin, PAN-AXAD-4, has been characterized by using elemental and thermogravimetric analysis, infrared spectra, water regain value, and hydrogen ion capacity. The sorption capacity was found to be (285, 145, 135, 85, and 76) μmol·g−1 for Zn(II), Co(II), Ni(II), Cu(II), and Pb(II), respectively. The kinetics was studied at different temperatures, and the corresponding rate constants were also determined. All the metals could be eluted with 5 mL of HNO3 resulting in a high preconcentration factor of 300 to 500. The detection limits were found to be (0.65, 0.80, 0.85, 0.95, and 1.40) μg·L−1 for Zn(II), Co(II), Ni(II), Cu(II), and Pb(II), respectively. The validity of the method was checked by analyzing standard reference materials and performing recovery studies. The analytical utility of the PAN-AXAD-4 for preconcentration and determination of metal ions was explored by analyzing river, canal, sewage, tap water, multivitamin formulation, and infant milk substitute by direct as well as the standard addition method.