AFM and low-pressure argon adsorption analysis of geometrical properties of phyllosilicates

The distribution of edge and basal surface areas of phyllosilicate particles is an essential parameter for understanding the interaction mechanisms at solid/gas or solid/liquid interfaces. Among the techniques proposed to determine the geometrical heterogeneities of flat solids, low-pressure argon adsorption and AFM analysis are the most promising to derive the weight-averaged values of specific surface areas. A series of publications have recently been dedicated to the combination of both methods showing the correlation between the two approaches. As obtaining a large set of high-resolution AFM images is time-consuming, it is necessary to test the ability of AFM routine analysis to derive surface areas and aspect ratio systematically and statistically, with all possible experimental and instrumental artefacts. In the present study, the expected agreement was found between AFM and argon adsorption determination for total, basal, and edge-specific surface areas of nonswelling clay minerals, except for one kaolinite, which is very heterogeneous in size. In addition, it was observed that for a given sample, individual particles present similar shapes, whatever their size, making it possible to derive a statistical relationship between AFM basal and total surface areas. On the basis of the obtained results, recommendations are given to derive accurate edge, basal, and total specific surface areas of phyllosilicates by combining conventional gas adsorption (nitrogen BET) and routine AFM techniques.