A Study of the Solubility and Mobility of Silver Ions in Chitosan and Fibroin Membranes

Abstract

Chitosan and fibroin are biopolymers widely applied in wound healing and wastewater treatment with silver ions (Ag+). The solubility and mobility of Ag+ in these polymers are important parameters for designing and optimizing related applications, but they are seldom studied. This study investigates and compares the sorption and transport properties of Ag+ in chitosan and fibroin membranes to reveal the unique interactions between these polymers and ions. The solubility and mobility of NaCl are also studied for comparison. The sorption performance was evaluated through sorption uptake and sorption isotherms at different Ag+ concentrations. The Ag+ equilibrium uptake and solubility in chitosan membranes were higher than those in fibroin membranes. The sorption of Ag+ in fibroin membranes followed the Freundlich isotherms, but neither the Langmuir nor the Freundlich isotherm applied to the sorption of Ag+ in chitosan membranes due to strong Ag+-chitosan complexation interactions. The permeance, permeability and diffusivity were studied through permeation/diffusion tests. The permeance, permeability and diffusivity of Ag+ in chitosan membranes were found to be dependent on the Ag+ concentration, while those values in fibroin membranes were relatively constant lower than those in chitosan, except the transient diffusivity coefficients and steady-state diffusivity coefficients. The transient diffusivity coefficients of Ag+ in chitosan ranged from 0.7 to 7.1 μm/s2, while those values in fibroin were in the range of 42.0 to 48.5 μm/s2. The steady-diffusivity coefficients of Ag+ were 2.7 to 31.7 μm/s2 in chitosan and 32.8 to 49.9 μm/s2 in fibroin. The diffusivity of Ag+ in chitosan was further studied by desorption tests. The diffusivity coefficients obtained from different methods were compared to gain better understanding of the diffusion process. The formation of Ag+-chitosan complexes played an important role and it significantly affected solubility and mobility of Ag+ in chitosan.