Uptake of Tm(III) ions onto polyurethane foam from H₂O - Ethanol mixture containing 1-(2-pyridylazo)-2-naphthol (PAN)

The sorption of microquantities of Tm(III) ions on washed polyurethane foam (PUF) from a mixture of aqueous solution and ethanol containing PAN was examined. The maximum sorption of 3.18·10^-6M solution of Tm(III) ions was observed at pH 8 with 30-minute equilibration time. The optimum ratio of aqueous-ethanol phase for the sorption of Tm(III) ions was found to be 3:1 v/v, respectively. The sorption rate of metal ions on PUP is followed a first order kinetics and obeyed the equation for an intra particle diffusion process. The equilibrium concentration data of Tm(III) ions could be described satisfactorily by several adsorption isotherms. The Freundlich adsorption isotherm constants l/n and K_F are 0.66±0.02 and (5.7±0.3)·10^-3 mol·g^-1, respectively. The Langmuir isotherm constants for monolayer coverage (Q) and binding strength of sorption (b) are (2.5±0.7)·10^-5 mol·g ^-1 and (1.6±0.1)·10⁴ l·mol ^-1, respectively. The sorption capacity derived from Dubinin-Radushkevich (D-R) isotherm is (1.7±0.2)·10^-4 mol·g^-1 and the sorption free energy (E) is 9.8±0.2 kJ·mol^-1 indicating chemisorption phenomena. The thermodynamic parameters indicate that the sorption of Tm(III) ions onto PUF is endothermic, entropy driven and spontaneous in nature.