Neumann Miguel G, Gessner Fergus, Schmitt Carla C, Sartori Rogerio
Instituto de Química de São Carlos, Universidade de São Paulo, Caixa Postal 780, 13560-970 São Carlos SP, Brazil.
J Colloid Interface Sci. 2002 Nov 15;255(2):254-9. doi: 10.1006/jcis.2002.8654.
The spectroscopic behavior of the dye MB in suspensions of different clays have been used for evaluating layer charge density influence on the adsorption properties of the particles. The clays with higher charge density, like SAz-1 and SCa-3, promote a higher aggregation and do not show deaggregation at longer times, so that practically only the aggregate peak at approximately 570 nm is observed, without any change with time. This is due to, on one side, the larger particle size that decreases the surface area available for adsorption. Additionally, the clay layers will be held together more tightly, avoiding the migration of the dye to the interlamellar region. On the other hand, SWy-1, having a lower charge density, shows a completely different behavior. The dye molecules, initially adsorbed as aggregates on the outer surface of the clay, deaggregate to form monomers that migrate to the interlamellar spaces, giving rise to absorption bands at 670 and 760 nm. Experiments using Ca-exchanged SWy-1, variation of the ionic strength by addition of salt, and the use of different size fractions of the clays confirm the finding that the main factor ruling the adsorption behavior of the probe is the size of the clay particles.
染料亚甲基蓝（MB）在不同黏土悬浮液中的光谱行为已被用于评估层电荷密度对颗粒吸附性能的影响。电荷密度较高的黏土，如SAz - 1和SCa - 3，会促进更高程度的聚集，且在较长时间内不会出现解聚，因此实际上仅能观察到约570 nm处的聚集峰，且随时间无任何变化。一方面，这是由于较大的粒径减小了可用于吸附的表面积。此外，黏土层会更紧密地结合在一起，避免染料迁移到层间区域。另一方面，电荷密度较低的SWy - 1表现出完全不同的行为。最初以聚集体形式吸附在黏土外表面的染料分子会解聚形成单体，这些单体迁移到层间空间，产生670和760 nm处的吸收带。使用钙交换的SWy - 1进行的实验、通过添加盐改变离子强度以及使用不同粒径级分的黏土，均证实了决定探针吸附行为的主要因素是黏土颗粒的大小这一发现。
