Colloidal synthesis of organic-capped ZnO nanocrystals via a sequential reduction-oxidation reaction.

A nonhydrolytic route to quantum-sized (d < 9 nm) ZnO nanocrystals in homogeneous organic solutions is presented. Nearly spherical ZnO nanocrystals were grown in a surfactant mixture of hexadecylamine and oleic acid (OLEA) by means of a two-step chemical process, based on the hot reduction (at 180-250 degrees C) of a zinc halide by superhydride (LiBEt3H) followed by oxidation of the resulting product. The experimental results suggested that the controlled growth of ZnO in the nanosized regime depended both on the OLEA-assisted generation of intermediate metallic nanoparticles and on the adjustment of their oxidation conditions by using a mild oxidant, trimethylamine-N-oxide, rather than molecular oxygen. The present synthetic approach demonstrates to be particularly suitable to prepare organic-soluble ultra-small ZnO nanocrystals of low size dispersion and of stable size, which are appealing for optoelectronic, catalytic, and sensing purposes.