Preparation and Characterization of the Composites Based on Hydridesilylated Nanosilica and Caffeic Acid

Composites of the pristine or hydridesilylated nanosilica with caffeic acid (CA) were obtained either by deposition of CA onto the surface of the corresponding silica from excess ethanol solution, or by sorptive modification of silica with ethanol CA solution under fluidized bed conditions, or by mechanical powder mixing. SEM studies revealed that CA–silica composites are composed of tens-micron-size agglomerates/particles comprising of or covered with the network of nanoparticles. FTIR spectroscopic studies confirmed the presence of ≡SiH groups (2255 cm−1) on the surface of hydride-silica in its composites with caffeic acid, and it was found that at low concentration (23 mg/g) CA is present on the nanosilicas’ surface mainly in the form of monomers and dimers, while at higher concentration (153 mg/g)—mainly in the form of dimers and probably associates; in all cases surface silanols being involved in interaction with CA molecules. The data on thermogravimetric analysis suggest that silica surface affects the mechanism (and in the case of hydridesilylated silica also the kinetics) of CA thermal degradation. It has been shown that hydridesilylation of nanosilica surface and further its sorptive modification with caffeic acid under fluidized bed conditions allows one to obtain redox-active materials without significant impact on the carrier’s structural characteristics (specific surface area). Upon this, caffeic acid deposited onto the nanosilica surface does not loose its antioxidant properties, and hydridesilylated nanosilica has shown the viability of its use as a component of a complex antioxidant.