The crosslinking was conducted by adding CBs to a glass vessel
containing GA, where the molar ratio of the CHO groups of GA and
the amino groups of chitosan was adjusted to 1:2, which was specified
elsewhere [20]. Basically, 70 g of wet CBs was placed in
250 mL of a GA solution (25 wt%) at room temperature for 6 h.
The GA-CBs were washed three times with deionized water to
eliminate the residual GA. Then, they were dried at 65 C for
18 h. The resulting GA-CBs were weighed and used in the following
biosorption experiments and for enzyme immobilization.