Preparation and characterization of micron and submicron-sized vermiculite powders by ultrasonic irradiation

Micron and submicron-sized vermiculite lamellar particles with nanometric thickness (< 10 nm) were prepared by ultrasonic treatments (< 12 h) of aqueous and hydrogen peroxide suspensions of thermally exfoliated vermiculite. Laser granulometry characterizations showed that the particles size distribution was dependent on the treatment time and that the use of H2O2 afforded smaller particles than H2O. In both media, an exfoliation and a size reduction were observed after only 1 h of ultrasonic treatment by Scanning Electron Microscopy, X-ray diffraction, and Nitrogen Adsorption Measurements at 77 K. X-ray diffraction studies showed the absence of damage in crystals structure after sonication and also a reduction of crystallites size along the basal direction (00l). The different ultrasonic treatments also induced modifications of the surface properties of the vermiculite particles, brought out by BET surface measurements, infrared spectroscopy, pH modifications of the materials and zeta potential analyses. Sonication of the vermiculites yielded to the formation of carbonate anions from the dissolved CO2 and hydroxide anions released from the clay layers. The long ultrasound irradiation of the vermiculite in hydrogen peroxide (> 5 h) generated the decrease of the surface charge, pointed out by pH and zeta potential modifications, allowing an aggregation of the submicron particles in the suspensions.