Identification of montmorillonite particle edge orientations by atomic-force microscopy

Statistical information on the edge surface area and edge crystallographic orientation of clay nanoparticle surfaces is essential for proper accounting of the protonation-deprotonation reactions as a part of mechanistic surface complexation models. A combination of atomic-force microscopy (AFM) measurements and molecular dynamics computer simulations made it possible to quantify the relative contributions of the most frequently occurring montmorillonite edge surfaces to the total edge surface area. Edge surfaces normal to the [110] and [010] crystallographic directions are found to be the most abundant (similar to 60% and similar to 20%, respectively), in agreement with previous estimations.