物理化学学报 >> 2004, Vol. 20 >> Issue (05): 459-462.doi: 10.3866/PKU.WHXB20040503

研究论文 上一篇    下一篇

Zn-Al类水滑石结构正电荷对内禀电离平衡常数的影响

李丽芳;侯万国;焦燕妮;刘春霞   

  1. 山东大学,胶体与界面化学教育部重点实验室,济南　250100;山东农业大学应用化学与材料科学学院,泰安　271018
  • 收稿日期:2003-10-06 修回日期:2003-12-08 发布日期:2004-05-15
  • 通讯作者: 侯万国 E-mail:wghou@sdu.edu.cn

Effect of Permanent Charge on the Intrinsic Ionization Constant of Zn-Al Hydrotalcite-like Compounds

Li Li-Fang;Hou Wan-Guo;Jiao Yan-Ni;Liu Chun-Xia   

  1. Key Laboratory for Colloid and Interface Chemistry of Education Ministry, Shandong University, Jinan　250100;College of Applied Chemistry and Material Science, Shandong Agriculture University, Taian　271018
  • Received:2003-10-06 Revised:2003-12-08 Published:2004-05-15
  • Contact: Hou Wan-Guo E-mail:wghou@sdu.edu.cn

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摘要： 采用电势滴定(potentiometric titration,PT)法测定了Zn-Al类水滑石(HTlc)的零净电荷点(pHPZNC);利用电势滴定数据直接计算得到Zn-Al HTlc的内禀电离平衡常数(pKa2int)和质子吸附自由能(G0ads,2);研究了结构电荷密度(σp)对pKa2int 和G0ads,2的影响.结果表明,随σp增加, pKa2int 和G0ads,2数值均降低,说明σp越大,带正电荷的HTlc与H＋结合力越低,HTlc去质子能力越强,H＋游离出HTlc表面的趋势越大.研究发现，HTlc的pKa2int与pHPZNC之间符合关系式: pKa2int =1.372pHPZNC－3.328.

关键词: 类水滑石, 结构电荷, 内禀电离平衡常数, 电势滴定, 零净电荷点

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)