In the last years, nonaqueous sol-gel synthesis techniques to metal oxide nanoparticles have been established as a clear alternative to aqueous methods, allowing the synthesis of many metal oxides as small and uniform nanoparticles. Their main advantage is better control over the particle formation, resulting in highly crystalline products already at comparably low reaction temperatures. Additionally, the organic solvent can function as surface modifier, making the addition of surfactants superfluous, which results in improved purity of the products, but also simplifies the synthesis, as the reaction system then consists of only the precursor and a solvent. Moreover, the precursor may be used in quite high concentration, which makes these approaches highly promising for the large-scale production of high-quality nanoparticles.

We show that the nonaqueous synthesis of nanoparticles can be carried out in multigram scale, allowing the synthesis of more than 20 g nanoparticles per batch. Despite the simple reaction system, the particles are practically monodisperse in size and shape, and are highly crystalline directly after the synthesis at moderate temperatures. Through simple and efficient surface modification treatments, they can be functionalized to ensure high stability and compatibility with solvents. Interestingly, low amounts of organic ligands were sufficient to enable the preparation of stable and transparent nanoparticle dispersions. We have investigated the organic reactions in the system during particle synthesis, which mainly involve ether condensation reactions, and studied the surface chemistry of the obtained nanoparticles to gain insight into the particle formation and functionalization processes. Additionally, to demonstrate the high suitability of the obtained nanoparticles even for elaborate and demanding applications, the fabrication of holographic thin film nanocomposites based on zirconia nanoparticles is presented.

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