Sonication as a tool for preparing nanometric vermiculite particles

We have studied the effect of ultrasound on two different natural macroscopic vermiculite samples from Qjen and Santa Olalla (Spain). We describe the conditions for the preparation of nanometric particles by sonochemistry. Sonication produces not only a delamination effect in the [001] direction, but also a breaking of layers in the other directions, while the crystalline character is retained. Some differences have been observed in the behaviour of both vermiculites. Thus, the Santa Olalla sample suffers an important decrease in crystallite size with up to 30 h treatment time; longer treatment times do not produce any effect on crystallite size. On the other hand, the Ojen sample suffers a decrease in its crystallite size with up to 80 h treatment time, remaining unchanged for longer treatments. The crystallite sizes in the [001] direction are much smaller for the Ojen sample than for the Santa Olalla sample. In addition, the Santa Olalla sample maintains the typical laminar shape after sonication, while the Ojen sample suffers a morphological change. The different behaviours seem to be related to the different compositions and, therefore, the different layer charges of both vermiculite samples.