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

Summary

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^-1and ΔG=-1.4±0.1 kJ^. mol^-1at 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 1/n=0.70, 0.62 and 0.55 and sorption capacities C _m=10.8 mmol^. g^-1, 6.1 mmol^. g^-1and 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^-1and 137.4 µmol^. g^-1, also decreased with temperature. However, the sorption free energy E=10.2 kJ^. mol^-1, 11.2 kJ^. mol^-1and 12.7 kJ^. mol^-1, increased with temperature. The monolayer coverage (Q) computed from Langmuir isotherm was 11.1±0.6 µmol^. g^-1and remains constant at all the three temperatures investigated. However, the binding energy constant bincreased with temperature. The relationship of bwith temperature and differential heat of adsorption (ΔH _diff) have been evaluated and discussed.