Temperature effected sorption of europium(III) onto 1-(2-pyridylazo)-2- naphthol impregnated polyurethane foam

The sorption of Eu(III) ions onto PAN loaded PUF has been optimized and investigated under the influence of various temperatures, i.e., 303, 313 and 323 K. Maximum retention (>96%) of Eu(III) ions (1.79·10^-5M) onto PAN loaded PUF (7.75 mg·ml^-1) was achieved after 30-minute equilibration time from pH 7 buffer solution. The variation of sorption with temperature yields the thermodynamic parameters ΔH=79±2 kJ·mol^-1, ΔS=276±7 kJ·mol^-1·K^-1 and ΔG = -1.4±0.1 kJ·mol^-1 at 298 K. The positive value of enthalpy and negative free energy show endothermic and spontaneous nature of sorption, respectively. The sorption data followed Freundlich, Dubinin-Radushkevich (D-R) and Langmuir isotherms at all the three given temperatures. The Freundlich constant l/n = 0.70, 0.62 and 0.55 and sorption capacities C_m = 10.8 mmol·g^-1, 6.1 mmol·g^-1 and 4.4 mmol·g^-1, respectively, decreased with increasing temperature. Similarly, the sorption capacities of D-R isotherm X_m = 197.6 μmol·g^-1 201.2 μmol·g^-1 and 137.4 μmol·g^-1, also decreased with temperature. However, the sorption free energy E = 10.2 kJ·mol^-1, 11.2 kJ·mol^-1 and 12.7 kJ·mol^-1, increased with temperature. The monolayer coverage (Q) computed from Langmuir isotherm was 11.1±0.6 μmol·g^-1 and remains constant at all the three temperatures investigated. However, the binding energy constant b increased with temperature. The relationship of b with temperature and differential heat of adsorption (ΔH_diff) have been evaluated and discussed.