Studies on zero point of charge and intrinsic ionization constant of Zn-Mg-Al hydrotalcite-like compounds

摘要

The zero point of charge (ZPC) and the intrinsic ionization constant (K_a~int) of Zn-Mg-Al hydrotalcite-like compounds (HTlc) with the general formula [(Zn, Mg)_1-x Al_x (OH)_2]~x+ [(OH,Cl)_x]~x- were determined by potentiometric titration (PT). The variation of the ZPC and K_a ~int with x was investigated. For the colloidal particles possessing permanent charges, the ZPC determined by the PT method is the zero point of net charge (ZPNC). The ZPNC (Ph ZPNC) values were 9.63 {[Zn_0.27 Mg_0.36 Al_0.37(OH)_2] Cl_0.13(OH)_0.24}, 9.68{[Zn_0.13 Mg_0.58Al_0.29(OH)_2]Cl_0.12(OH)_0.17}, 9.67 {[Zn_0.17Mg_0.54Al_0.29(OH)_2]Cl_0.16(OH)_0.12}, 10.16{[Zn_0.08Mg_0.67Al_0.25(OH)_2]Cl_0.17(OH)_0.08}, 10.33{[Zn_0.16Mg_0.60Al_0.24(OH)_2]Cl_0.16 (OH)_0.08}and 10.60 {[Zn_0.19Mg_0.60Al_0.21(OH)_2] Cl_0.15 (OH)_0.06}; the intrinsic ionization constants pK~int_as of the same HTlc samples were 10.31, 10.44, 10.44, 11.02, 11.19 and 11.54. With decreasing x, ZPNC and K~int_a2 of HTlc increased, and the acidity of the HTlc samples decreased.