Adsorptive removal of copper ions with highly porous chitosan/cellulose acetate blend hollow fiber membranes

In this study, highly porous adsorptive hollow fiber membranes were directly prepared from chitosan (CS) and cellulose acetate (CA) blend solutions and were examined for copper ion removal from aqueous solutions in a batch adsorption mode. Four types of hollow fiber membranes were spun from two CS/CA blends (with a CS/CA/forming acid ratio of 3/12/85 or 2/18/80) in two types of coagulants (water or 3 wt.% NaOH solution). All the CS/CA blend hollow fiber membranes displayed sponge-like and macrovoids-free structures, with specific surface areas in the range of 12.2–15.2 m2/g, porosities of 70.4–79.7%, and pore sizes of 0.05–0.2 μm, depending on the CS/CA ratios and the type of coagulants used. Adsorption experiments showed that the CS/CA blend hollow fiber membranes had good adsorption capacity (up to 35.3–48.2 mg/g), fast adsorption rates and short adsorption equilibrium times (less than 20–70 min) for copper ions, and can work effectively at low copper ion concentrations (<6.5 mg/L) to reduce the residual level to as low as 0.1–0.6 mg/L in the solution. X-ray photoelectron spectroscopic (XPS) study confirmed that the adsorption of copper ions on the CS/CA blend hollow fiber membranes was mainly attributed to the formation of surface complexes with the nitrogen atoms of CS in the hollow fiber membranes, hence higher CS contents in the blend hollow fiber membranes rendering the membranes more adsorptive to copper ions. It was found that the copper ions adsorbed on the hollow fiber membranes can be effectively desorbed in an EDTA solution (up to 99% desorption efficiency) and the hollow fiber membranes can be reused almost without loss of the adsorption capacity for copper ions.