Interfacial phenomena in natural nanostructured materials based on kaolinite and calcite in blends with nanosilica and neem leaf powder

Abstract

To improve structural characteristics of clays and neem leaf powder (NLP)/clay composites, nanosilica was used as an addition upon mechanical treatment. This results in composites with natural nanostructured materials (NNM) possessing improved structural characteristics and bioactivity. The blends based on NNM with crystalline kaolinite alone and kaolinite/α-quartz or calcite/α-quartz + clay and amorphous admixtures and additions with nanosilica or nanosilica/NLP were treated in a knife mill. The materials were characterized using TEM, SEM, XRD, 1H MAS and 29Si CP/MAS NMR, FTIR spectroscopy, elemental analysis, nitrogen adsorption, quantum chemistry, release of bioactive components and bactericidal effects against various bacteria. There are regularities in the characteristics depending on a type of NNM, particulate morphology and textural features of solids. The morphological and structural characteristics of components slightly changed in the blends because the treatment was performed using relatively low mechanical loading. Release of chlorophyll and anthocyanins is greater for NLP/A―300/NNM composites (especially characterized by minimal confined space effects) than for NLP alone. Some clays and composites demonstrate bactericidal activity tested against four types of bacteria. The morphological, textural, and structural characteristics of the NNM/A―300 and NNM/A―300/NLP systems, as well NLP transformation into a nanostructured state, allow one to expect high activity of the composites as bioactive systems interesting for practical applications in medicine and cosmetics.