2D nanosheets of natural vermiculite clay - tuning the aptitude for exfoliation

Vermiculite, which is a nanolayered ionic material, belongs to the family of layered silicates. Negatively charged, 1 nm thin nanosheets are packed into compact crystallites, kept together by positive interlayer cations. The exfoliation ability of this material into the single sheets is low in comparison with smectite clays such as montmorillonite, as the surface charge of natural vermiculite clay is too high in comparison, reaching values between 0.7 – 1.

We present here efficient methods of exfoliation and delamination of vermiculite crystals into single nanosheets, and their physical properties.

More than 15 different types of vermiculite crystals from different places of origin have been tested. Delamination was mediated by selected (in)organic solvents, such as hydrogen peroxide or di-methyl formamide, and can be enhanced by applying mechanical force or increasing temperature during the delamination process. It is demonstrated that exfoliability of vermiculite is mainly driven by the type of interlayer cation, as has been verified by ex-situ and in-situ synchrotron x-ray diffraction and XPS measurements. Moreover, the dynamics of this process has been studied for selected vermiculite samples by the in-situ synchrotron X-ray diffraction. Compactness of delaminated vermiculite sheets was inspected by the AFM, demonstrating that single layer vermiculite sheets can have sizes up to several dozens of micrometers.

Further enhancement of the delamination process and its upscaling is discussed, showing that vermiculite 1 nm single nanosheets are promising material for combination with graphene and other (semi)conductive materials. Moreover, the potential this could allow for large-scale fabrication of novel 2D heterostructures by the self-assembly.