A computational and experimental investigation of the anchoring of organosilanes on the halloysite silicic surface

In this work, the effect of halloysite nanotubes alkali activation on its grafting efficiency with organosilanes was studied by Density Functional Theory and experimental investigations. In particular, computational analysis allowed to enlight the structural properties of the organic molecules attached to the silanol groups on halloysite outer surface. The energetics of the reactions showed that the pretreatment with a base is crucial for the modification of the surface due to the appearance of a high number of active sites which lead to thermodynamically favored exothermic processes. Experimental evidences are in good agreement with calculation hypothesis. For instance, the coating efficiency is higher after the alkali activation of the inorganic counterpart for both the investigated organosilanes. The findings here reported are important in order to improve any functionalization protocols for aluminosilicates without variations or loss of the hollow nanotubular morphological features and it paves the ground to halloysite based technological applications in many fields, from nanotechnology to catalysis.