“中性”粘土矿物对非水溶液中有机碱的吸附

Adsorption of Weak Organic Bases on 1:1 and 2:1 Type Layer Silicates without Layer Charge from Non-polar Organic Solvents

理想品格中无同晶转换，因而不带层电行的中性粘土矿物（即：1：1型的高岭石，板状蛇纹石和2：1型的叶蜡石，滑石）对非极性有机溶剂中有机碱（偶氮苯化合物，pKa＝1.5-5.0）的吸附等温线均属于Langmuir型，且吸附在矿物表面的有机碱均由其碱型变为酸型.偶氮苯化合物的pKa越大，被吸附的量越多在溶剂为正己烷和二硫化碳时粘土的吸附能力比溶剂为苯时高.这些结果说明不带层电行的粘土矿物表面存在着酸位.蒙脱石的酸位数量明显地储存于阳离子种类，但在Na＋、Ca2＋、Mg2＋饱和的条件下高岭石的改位数量几乎相同.随着相对湿度的增加;两矿物对甲基黄的吸附量均减少，但减少的方式明显不同、因此1：1型高岭石和2：1型叶蜡石一样，也具有与蒙脱石不同的表面酸性起源。

Equilibrium adsorption of five substituted azobenzenes with pKa=1.5-5.0 from nonpolar organic solvents on 1:1 and 2:1 type layer silicates without layer charge (kaolinite, lizardite,pyrophyllite, and talc) was studied. It was shown that the shape of each adsorption isotherm belongs to L type, and, the color of the substituted azobenzene molecules adsorbed changed from basic type (yellowish) to acidic type (reddish or purplish). The higher the basicity (pKa) of the substituted azobenzene, the greatcr the adsorptivc capacity. Moreover, the weak orgamc bases were more strongly adsorbed from n-hexane and carbon disulfide solutions than from benzene solution. From these facts, it was concluded that the adsorption mechanism of the weak organic bases on the minerals without layer charge is an acid-base interaction. It was also shown that the amount of acid sites of kaolinite saturated with Na, Ca, and Mg is almost identical, while that of montmorillonite shows strong dcpendence on exchangeable cation species. The decrease of the amount of acid sites due to the increase of RH also has quite different pattern for the nlinerals.These indicate that the origin of the acidity on kaolinite can not attributcd to the hydrolysis of water molecules around exchangeable cations, as in the case of montmorillonite.