Preparation and characterization of montmorillonite–silica nanocomposites: A sol–gel approach to modifying clay surfaces

Montmorillonite–silica nanocomposites were prepared by a sol–gel approach involving hydrolysis reaction of alkoxysilanes (TEOS) and subsequent condensation reaction with hydroxyl groups of the clay, resulting in the formation of the mesoporous silica network and silica nanoparticles covered or attached on the clay surfaces. According to X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and nitrogen adsorption isotherms, the structure and surface properties of the sol–gel-modified clay can be controlled by varying the TEOS/clay mass ratio and/or adding trace amounts of acid as catalyst. In the case of acid-catalyzed procedures, large continuous mesoporous silica was covered on the clay surfaces, resulting in delamination of clay platelets in silica matrix at higher TEOS/clay ratio, and attaching of isolated mesoporous silica on the clay surface at lower TEOS/clay ratio, respectively. In the case of non-catalyzed procedures, silica nanoparticles were attached on the two-dimensional (2D) clay platelets, while the stack order of the clay was maintained regardless of the TEOS/clay ratios. This sol–gel modification approach combines the surface properties of mesoporous silica and nanoparticles with layered clay, while inheriting the structural properties of the pristine clay such as further intercalation with organic compounds and polymers.