0.5 g of silica (CO2H-grafted or activated SiO2 by an acid treatment
to augment the number of reactive silanol groups [36]) was
added to 100 ml of 2% chitosan solution (dissolved in acetic acid
solution at 1%) and stirred overnight. Then, this suspension was
poured under stirring into 500 ml of 0.1 M NaOH in order to neutralize
excess acid