The preparation of CG was performed according to the method of Curcio et al. (2009) with slight modifications. Briefly. CS(1 g)was dissolved in 100 mL of 12, acetic acid(vlv) in a 200 mL three-necked round bottom flask. Then, 3 mL of 1.0 M H202 containing 0.27g of Vc was added into the reactor, and a slow stream of oxygen-free nitrogen gas was passed for 30 min with stirring. Afterwards. GA was added to the mixture at different amounts with the follow- ing molar ratios of the repeating unit of CS to GA: 1:0.1. 1:0.5 and 1:1(labeled as CG-1. CG-2 and CG-3. respectively). The reaction was carried out under a continuous flow of oxygen-free nitrogen gas.