Exfoliating kaolin to ultrathin nanosheets with high aspect ratio and pore volume: A comparative study of three kaolin clays in China

A revised intercalation-assisted liquid exfoliation method is proposed to exfoliate three typical kaolin clays (Beihai, Longyan and Suzhou) in China. By combining intercalation, ball milling, ultrasound and freeze-drying technologies, the ultrathin kaolin nanosheets with large lamellar size (1–2 μm), low thickness (∼10 nm), high aspect ratio (∼130) and large pore volume (∼0.3 cm3/g) were obtained. A large number of kaolinite monolayer structures were observed in AFM images, indicating high exfoliation efficiency. The morphology, crystal structure and microstructures of kaolin samples during the intercalation and exfoliation processes are studied in detail by high resolution XRD, SEM, BET and AFM analysis. The mechanism for effective intercalation, exfoliation and stabilization of kaolin clays is clarified. The ultrathin kaolinite nanosheets slightly curved after exfoliation process were found to form some porous structures between the kaolin nanolayers, providing plenty of interlayer spacing for functional loading or interfacial binding. These ultrathin kaolin nanosheets might have the advantages to improve the adhesion ability, loading capacity, and mechanical properties of kaolin-based composite materials.