Abstract: Potentiometric titration (PT) method was often used to determine the point of zero net proton charge (pHPZNPC) and intrinsic ionization constant (pKa2int ) of oxide. Extensive studies on the interrelation of and pHPZNPC of various oxides had shown that pKa2int =0.827pHPZNPC＋4.478.From that we can know that different metal had different affinity to H＋ or OH－,however the study on the permanent charged materials such as hydrotalcite-like compounds (HTlc) and clays was rare. The study focused on the influence of permanent charge on the intrinsic ionization constant (pKa2int) had not been reported yet. In our research, potentiometric titration method was used to determine the point of zero net charge (pHPZNC), and potentiometric titration data at pHPZNC was used to calculate pKa2int and the free energy of proton adsorption (G0ads,2) of Zn-Al HTlc samples for the first time. The theoretical permanent charge density (σp) of the HTlc sample was calculated from the crystal structure of Zn-Al HTlc according to the chemical analysis results. The influence of σp on the pKa2int and G0ads,2 was examined. The results showed that pKa2int and G0ads,2 of Zn-Al HTlc decreased with the increase of σp, indicating that protonation decreased with the increase of σp. It was found that pKa2int and pHPZNC had the relationship: pKa2int =1.372 pHPZNC－3.328.

Key words: Hydrotalcite-like compounds, Permanent charge, Intrinsic ionization constant, Potentiometric titration, Point of zero net charge(PZNC)