Facile synthesis of Cu₂O nanocrystals with systematic shape evolution from cubic to octahedral structures

We report a facile method for the synthesis of cuprous oxide nanocrystals with systematic shape evolution. Monodisperse truncated cubic, cuboctahedral, truncated octahedral, and octahedral nanocrystals can be synthesized directly in an aqueous solution of CuCl₂, sodium dodecyl sulfate (SDS) surfactant, hydroxylamine (NH₂OH-HCl) reductant, and NaOH by simply varying the volume of hydroxylamine added to the reaction mixture. SDS surfactant was found to be necessary for a precise control of the nanocrystal morphology. Adjustment of the volume of NaOH added provides a means to vary the particle size. In the case of octahedral nanocrystals, particles with of 160-460 nm can be prepared. By examining the intermediate products formed, which resemble the final nanocrystal structures, a growth mechanism is proposed. Optical characterization of these Cu₂O nanocrystals showed band gap absorption at 470-490 nm and strong light scattering bands extending from the visible to the near-infrared light region. All four samples displayed activity toward photodegradation of rhodamine B molecules, but truncated octahedral and octahedral nanocrystals exhibited a higher extent of the photodecomposition reaction, suggesting the {111} faces of Cu₂O nanostructures are catalytically more active than the {100} faces. These nanocrystals should allow the examination of their various properties as a function of the particle shape.