Silk fibroin fiber for selective palladium adsorption: Kinetic, isothermal and thermodynamic properties

Abstract

The adsorption of metal ions to silk fibroin (SF) fiber from silkworm, Bombyx mori, was applied for recovering Pd2+ from aqueous solutions. In order to understand adsorption behavior, selectivity for Pd2+, kinetic, isothermal and thermodynamic analysis were carried out. The amount of Pd2+ adsorbed to SF was highest among the metals (Pt2+, Os4+ Ir4+, Rh3+ and Ru4+) used at both single and mixture solutions, which is suggesting high selectivity adsorbent for Pd2+. From dependence of contact time on amount of Pd2+ adsorbed in solutions of PdCl2 at 25 °C, the pseud-second order kinetic model was suitable to this system. From isothermal experiments the Langmuir parameters qm and KL were 46.3 mg g−1 and 3.85 L mg-1, respectively. The Freundlich parameters Kf and 1/n were 30.6 and 0.343, respectively. These imply large adsorption capacity for Pd2+ as nature on the SF adsorbent. According to the Klotz’s treatment, negative values ofΔＧ was obtained, which indicated that the adsorption process was thermodynamically feasible and spontaneous at 298–353 K. Positive value of enthalpy change means the adsorption of Pd2+ to the SF was endothermic. This implies that the change of entropy is dominant to adsorption of Pd2+ to SF.