Surfactant-Free Nonaqueous Synthesis of Metal Oxide Nanostructures

Graphical Abstract

As few starting materials as possible: Metal oxide nanoparticles and metal-oxide-based organic–inorganic hybrid nanostructures can be prepared in organic solvents under exclusion of water and in the absence of surfactants. Selected chemical formation mechanisms, advantages and limitations of these approaches in comparison to surfactant-directed routes, potential applications and technological aspects are briefly discussed in this Minireview.

Abstract

Surfactant-free nonaqueous (and/or nonhydrolytic) sol–gel routes constitute one of the most versatile and powerful synthesis methodologies for nanocrystalline metal oxides with high compositional homogeneity and purity. Although the synthesis protocols are particularly simple, involving only metal oxide precursors and common organic solvents, the obtained uniform nanocrystals exhibit an immense variety of sizes and shapes. The small number of reactants in these routes enables the study of the chemical mechanisms involved in metal oxide formation. Nonhydrolytic routes to inorganic nanomaterials that used surfactants as size- and shape-controlling agents have been discussed recently. This Minireview supplements this topic by discussing surfactant-free processes, which have become a valuable alternative to surfactant-assisted as well as to traditional aqueous sol–gel chemistry routes.