Nonaqueous synthesis of metal oxide nanoparticles: Short review and doped titanium dioxide as case study for the preparation of transition metal-doped oxide nanoparticles

The liquid-phase synthesis of metal oxide nanoparticles in organic solvents under exclusion of water is nowadays a well-established alternative to aqueous sol–gel chemistry. In this article, we highlight some of the advantages of these routes based on selected examples. The first part reviews some recent developments in the synthesis of ternary metal oxide nanoparticles by surfactant-free nonaqueous sol–gel routes, followed by the discussion of the morphology-controlled synthesis of lanthanum hydroxide nanoparticles, and the presentation of structural peculiarities of manganese oxide nanoparticles with an ordered Mn vacancy superstructure. These examples show that nonaqueous systems, on the one hand, allow the preparation of compositionally complex oxides, and, on the other hand, make use of the organic components (initially present or formed in situ) in the reaction mixture to tailor the morphology. Furthermore, obviously even the crystal structure can differ from the corresponding bulk material like in the case of MnO nanoparticles. In the second part of the paper we present original results regarding the synthesis of dilute magnetic semiconductor TiO2 nanoparticles doped with cobalt and iron. The structural characterization as well as the magnetic properties with special attention to the doping efficiency is discussed.