Fumed silica (Aerosil 200) was obtained from Evonik Industries,
Japan. All AR-grade reactants were purchased from Aldrich.
NiCl2 × 6 H2O (p.a. grade) was used for the experiments. The molecular
weight of CS and its degree of deacetylation (%DD) are 150 kDa
and 68–75%, respectively. The stock solutions were prepared
freshly for each experiment. The pH of the solutions was adjusted
by addition of aqueous NaOH or HCl solutions at concentrations of
1 M and 0.1 M. All solutions were prepared using deionized water
(DI). Toluene was distilled over sodium/benzophenone.