Nanoscale cross-correlated AFM, Kelvin probe, elastic modulus and quantum mechanics investigation of clay mineral surfaces: The case of chlorite

The physical and chemical surface properties of clay minerals have a significant impact on mineral-environment surface interactions. The study of the local surface properties of clay particles at the nanometre and sub-nm scale is of paramount importance to improve our knowledge on a variety of important interaction processes and interfacial phenomena, such as adsorption, coagulation, aggregation, sedimentation, filtration, catalysis, and ionic transport in porous media. In this work we investigated the physico-chemical properties of the (001) surface of chlorite by cross-correlating AFM, Kelvin probe force microscopy and ab initio quantum mechanics studies. Experimental measurements at the nanometre and sub-nm scale by atomic force microscopy and Kelvin probe force microscopy were performed to investigate the nanomorphology, elastic modulus and surface electrostatic potential of chlorite samples presenting Al substitutions in the tetrahedral sheets and in the hydroxylic interlayer. Quantum mechanics simulations were carried out to investigate the effect of the Al substitutions on both the mineral bulk and surface structures, and on the surface electrostatic potential. Experimental measurements and theoretical calculations were found in very good agreement, complementing each other. The approach here presented and the findings of this study can provide a valuable insight into clay mineral surface properties and a variety of interaction phenomena of clay minerals with important environmental, industrial and biotechnological applications.