Physicochemical properties and morphology of spongolite from Mato Grosso do Sul (Brazil)

The physicochemical properties and morphology of spongolite, a fibrous hollow material from Mato Grosso do Sul State (Brazil) have been studied. The results of thermal analysis, scanning electron microscopy (SEM), X-ray diffraction and NMR spectroscopy indicated that external and internal surfaces of silica spicules are covered by silica gel layers. The water evolved in the range 120–350 °C is the result of silanol groups condensation to siloxane bonds. Total homogenization of the needles is achieved by heating spongolite over 900 °C. This mineral may be considered as a natural composite material containing surface-immobilized reactive species. The presence of active silica gel layers opens the possibilities of attaching functional groups to spongolite surface.