Removal of Tm(III) ions from aqueous solution using PAN-incorporated sol-gel matrices

The sorption of Tm(III) ions from aqueous solutions by 1-(2-pyridylazo)-2- naphthol (PAN) incorporated sol-gel matrices have been studied extensively using radiotracer and batch techniques. Maximum accumulation (∼98%) of Tm(III) ions (2.55 × 10^-5 M) onto solid surface is achieved from pH 7 buffer solution in 30 min using 50 mg of PAN incorporated sol-gel matrices. The sorption data follow Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherms. The Langmuir constants Q = 123.6 ± 3.6 μmol g^-1 and b = (19.2 ± 2.1) × 10⁴ dm³ mol ^-1 have been computed. Freundlich constants l/n = 0.56 ± 0.04 and C_m = 45.4 ± 6.5 mmol g^-1 have been estimated. Sorption capacity 1.13 ± 0.001 mmol g^-1, β = -0.0035 ± 0.0001 kJ² mol^-2 and energy 11.95 ± 0.2 kJ mol^-1 have been evaluated using D-R isotherm. The variation of sorption with temperature yields ΔH = 31.7 ± 0.8 kJ mol ^-1, ΔS = 128.5 ± 3 J mol^-1 K^-1 and ΔG = -6.5 ± 0.1 kJ mol^-1 at 298 K reflecting the endothermic and spontaneous nature of sorption. Divalent Pb(II), Ba(II) and Mg(II) and monovalent chloride and K(I) increase the sorption while oxalate, citrate, disulfite and tartrate reduce the sorption significantly.