Metal oxide nanoparticles emerge via nucleation in sol-gel processes in organic media. Both hydrolytic and non-hydrolytic reactions produce in one step nano-size molecular species, with apparent core-shell structure, resembling oxometallates formed on partial hydrolysis in both aqueous and organic media. The core is always well-ordered and often can be identified as crystalline even by X-ray studies, and more securely by electron diffraction in TEM. It bears generally an imprint of the corresponding solid phase resulting from dense packing of metal cations and oxygen anions. The shell contains residual organic ligands inherited from the precursor molecules and is amorphous. This insight into reaction mechanisms permits to control the size and shape of resulting particles, their hydrophilicity/hydrophobicity and surface reactivity. Hydrolytic approach leaves most often residual hydroxide groups and solvating water molecules on the surface of the particles contributing to the amorphous shell. Higher temperature solvothermal reaction offers generally much better crystallinity than the room temperature hydrolytic one. Elevated temperature helps to improve the diffusion of metal ions and removes the hydroxide and organic residues from the surface. The control of crystallinity and composition and structure of the shell define surface interactions of the produced particles and their both solution and chemical stability in biological systems and in the environment.<br/>Application of these insights open for such new applications as generation of biocompatible colloids for bioencapsulation and drug delivery via both hydrolytic and solvothermal approaches. Exploiting the surface reactivity for grafting of metal oxide colloid particles on carbohydrate and protein structures permit to build up new types of biocompatible nanocomposites for drug delivery and wound healing.

Molecular mechanisms in formation of metal oxide colloids in sol-gel processes

253rd National Meeting (2017)

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