Abstract
Here we report two surfactant-free methods for synthesis of small Cu2O octahedra and nanocubes with a large range of size tenability in just 10 min. Cu2O octahedra with corner-to-opposite corner distance varying from 52 nm to 157 nm have been obtained by simply mixing aqueous Cu(NO3)2 solution, N2H4 solution, and different volumes of NaOH solution. Cu2O nanocubes with edge lengths from 9 nm to 87 nm can be synthesized by mixing aqueous CuSO4 solution, different volumes of NaOH solution, and ascorbic acid solution at 35 ºC. The particle size can be controlled systematically. This represents the highest level of size and shape control for ultrasmall Cu2O nanocrystals which have been difficult to make. By comparing cubes and octahedra with similar sizes in terms of particle volume for their optical absorption spectra, nanocubes are consistently more red-shifted than octahedra by approximately 15 nm, proving convincingly that Cu2O nanocrystals possess facet-dependent properties, and that cubes bound by the {100} facets have a more red-shifted absorption band similar to observations made in Au‒Cu2O and Pd‒Cu2O nanocrystals.