Zn-Al类水滑石结构正电荷对内禀电离平衡常数的影响  

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

作　　者：李丽芳[1] 侯万国[2] 焦燕妮[2] 刘春霞[2] 

机构地区：[1]山东农业大学应用化学与材料科学学院,泰安271018 [2]山东大学,胶体与界面化学教育部重点实验室,济南250100

出　　处：《物理化学学报》2004年第5期459-462,共4页Acta Physico-Chimica Sinica

基　　金：国家自然科学基金(20273041);教育部跨世纪人才基金资助项目~~

摘　　要：采用电势滴定(potentiometrictitration,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-AlHTlc的内禀电离平衡常数(pKinta2)和质子吸附自由能(ΔG0ads,2);研究了结构电荷密度(σp)对pKinta2和ΔG0ads,2的影响.结果表明,随σp增加,pKinta2和ΔG0ads,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pKinta2与pHPZNC之间符合关系式:pKinta2=1.372pHPZNC-3.328.Potentiometric titration (PT) method was often used to determine the point of zero net proton charge (pH(PZNPC)) and intrinsic ionization constant (pK(a2)(int)) of oxide. Extensive studies on the interrelation of pK(a2)(int) and pH(PZNPC) of various oxides had shown that pK(a2)(int) = 0.827pH(PZNPC) + 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 ( pK(a2)(int)) had not been reported yet. In our research, potentiometric titration method was used to determine the point of zero net charge (pH(PZNC)), and potentiometric titration data at pHPZNC was used to calculate pK(a2)(int) and the free energy of proton adsorption (DeltaG(ads.2)(0))of Zn-Al HTlc samples for the first time. The theoretical permanent charge density (sigma(p)) of the HTlc sample was calculated from the crystal structure of Zn-Al HTlc according to the chemical analysis results. The influence of sigma(p) on the pK(a2)(int) and DeltaG(ads.2)(0) was examined. The results showed that PKa2int and DeltaG(ads.2)(0) of Zn-Al HTlc decreased with the increase of sigma(p), indicating that protonation decreased with the increase of sigma(p). In was found that pK(a2)(int) and pH(PZNC) had the relationship: pK(a2)(int) = 1. 372 PHPZNC - 3.328.

关 键 词：类水滑石 结构电荷 内禀电离平衡常数 正电荷 ZN Al 电势滴定法 零净电荷点 

分 类 号：O648[理学—物理化学]