Kinetics, thermodynamics, and sorption profile of Eu(III) and Tm(III) on 4-(2-Pyridylazo) resorcinol (PAR) imbedded polyurethane foam

The adsorption studies of Eu(III) and Tm(III) was investigated on 4-(2-pyridylazo) resorcinol (PAR) loaded polyurethane foam (PUF). The sorption conditions were optimized with respect to pH, shaking time, and loading capacity. Kinetic of sorption of Eu(III) and Tm(III) were evaluated at different intervals of time. The diffusion coefficient of Eu(III) and Tm(III) are found to be 4.48 × 10^-5 cm² sec^-1 and 7.81 × 10^-5 cm² sec^-1. The Freundlich constant (1/n) are estimated to be 0.56 and 0.47 for Eu(III) and Tm(III), respectively, reflects a surface heterogeneity of the PUF. Langmuir isotherm gives a saturated capacity of 1.95 × 10^-5 mol g^-1 for Eu(III) and 1.01 × 10^-4 mol g^-1 for Tm(III), suggest a monolayer coverage of the surface. The Dubinin-Radushkevich (D-R) isotherm is applied and the sorption mean free energy (E) was calculated and was in the range 11-12 kJ mol^-1 suggesting chemisorption involving chemical bonding is responsible for the adsorption process. The thermodynamics parameters such as enthalpy (ΔH), entropy (ΔS) and Gibbs free energy (ΔG) were calculated and interpreted. The large negative values of ΔH indicates that the adsorption of metal ions on PAR-loaded PUF is an exothermic process. A possible explanation of this exothermicity related to bonding has been given. The sorption is greatly affected in the presence of oxalate, citrate, tartrate, and phosphate.