Effects of clay activation and amine chain length on silica-palygorskite heterostructure properties

Various approaches have been used for the preparation of heterostructured materials based on clay minerals, with numerous potential applications offered by the resulting functional materials. In this study, a fibrous clay mineral (palygorskite)and a tetraethyl orthosilicate reagent were used to obtain silica-palygorskite heterostructures. The aim was to highlight the influence of two factors during the preparation process: the effect of acid activation pre-treatment of the palygorskite with HCl and the effect of varying the length of the amine chains used - dodecylamine and butylamine - on the formation and development of silica nanoparticles on the surface of the palygorskite fibres. The silica-palygorskite heterostructures were obtained after the removal of the organic templates by calcination at 500°C. The textural and structural properties of the silica-palygorskite heterostructured samples were determined using various experimental characterization techniques, such as X-ray diffraction, transmission electron microscopy, gas adsorption and Fourier-transform infrared spectroscopy. The experimental variables targeted in this study appeared to have a significant effect on the textural properties of the silica-palygorskite heterostructure obtained. The great specific surface area and the mesoporous, microporous and ultramicroporous volumes as determined using nitrogen and/or carbon dioxide gas adsorption confirm the benefit of combining the acid activation pre-treatment of the fibrous clay mineral with the use of a long-chain amine co-surfactant (dodecylamine). The resulting silica-palygorskite heterostucture has a great specific surface area (628 m2 g-1)and a well-developed total pore network (VN2 = 0.24 cm3 g-1; Vultra (CO2)= 0.18 cm3 g-1). This material will be tested for the removal of volatile organic compounds at low concentrations.