Green synthesis of chitosan-based nanofibers and their applications

We report here a simple and green method for the preparation of chitosan and chitosan-based nanofibers by freeze-drying dilute aqueous solutions, without the use of organic solvent, high concentration of acid solutions, or the need to pre-treat chitosan. Chitosan nanofibers with diameters ranging from 100 to 700 nm were obtained from aqueous chitosan solutions with the concentrations equal to or below 0.1 wt %. Chitosan/poly(vinyl alcohol) blend nanofibers with different mass ratios were produced by freeze-drying the mixture solutions. The effects of solution concentration, chitosan molecular weight, and freezing temperature were examined. The morphology and thermal stability of the nanofibers were analyzed. Pore size and pore volume of the bulk fibrous materials were measured. A uniform coating of calcium phosphate was formed on the chitosan nanofibers in a 5 times concentrated simulated body fluid. The adsorption of copper ions by chitosan nanofibers from aqueous solutions was investigated. It was found that chitosan nanofibers exhibited a high adsorption capacity of Cu(2+) at 2.57 mmol g(-1) of chitosan for aqueous CuSO(4) solution at a concentration of 1000 ppm. Loading and release of small molecules (Rhodamine B) and protein molecules (bovine serum albumin) with chitosan nanofibers as scaffolds were also investigated.