The demineralized shells were treated with 9 wt% NaOH solution at 95 C for 2 h with a weight ratio of 1:1 (w/w), yielding the chitin. Subsequently, 4.0 g of the chitin was refluxed in 140 mL of 40 wt% KOH solution under stirring for 5 h to get chitosan, followed by washing with deionized H2O to remove 48.8 g KOH and freeze-drying.