Adsorption of Low-substituted Cationic Starch on Aluminum Magnesium Hydrotalcite Analogue

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.