Abstract:

The adsorption of low-substituted cationic starch(CS-L) on Mg-Al HTlc was investigated. The following results were obtained:CS-L can be adsorbed on the external surface of positively changed Mg-Al HTlc. The adsorption isotherm followed the typical Langmuir equation and the saturated adsorption amount was 33.92 mg/g. The driving force for adsorption was probably due to two effects:(1)hydrogen bonding between the hydroxyl group or ether group of CS-L and the hydroxyl group of HTlc; (2)entropic effect, where the entropic loss for the CS-L adsorption is less then entropic gain for the released solvent molecules. The adsorption amount of CS-L increased with pH, which may be contributed to the decrease of the zeta potentials of CS-L and the HTlc with pH. The adsorption amount of CS-L increased with the addition of NaCl and CaCl2 because inert electrolytes screened the repulsion between HTlc particles and CS-L and the intramolecular repulsion between the cationic groups of the CS-L. At pH=9, the adsorption of CS-L on HTlc increased dramatically with the concentration of AlCl3 since the hydrolysate of Al3+ might play a role as a linkage between CS-L and HTlc, and. The adsorption amount of CS-L decreased with increasing temperature as a result of hydrogen bonding decrease. The adsorption kinetics of CS-L on Mg-Al HTlc showed that the equilibrium time of adsorption was about 300 min. Furthermore, the comparison of adsorption behaviors between CS-L and CS-H on Mg-Al HTlc was also carried out.

Key words: Adsorption, Hydrotalcite-like compounds, Low degree of substitution, Cationic Starch