After sulfonation, the strong absorption
band at 1032 cm1 and weak absorption band at 1171 cm1
appeared according to O@S@O and ASO3H, respectively
(Suganuma et al., 2012). In the region of 3390 cm1, the absorption
band of a AOH group, which could be in the form of ASO2OH or
ACOOH, also appeared (Fadhil et al., 2016)