Abstract
In most studies describing the preparation of Cu 2 O crystals of various morphologies, the particle sizes are normally hundreds of nanometers to micrometers due to rapid particle growth, so they are not exactly nanocrystals. Here we report surfactant-free formation of sub-100 nm Cu 2 O nanocrystals with systematic shape evolution from cubic to octahedral structures by preparing an aqueous mixture of Cu(OAc) 2 , NaOH, and N 2 H 4 solution. Adjustment of the hydrazine volume enables the particle shape control. Uniform nanocubes and octahedra were synthesized with edge lengths of 37 and 67 nm, respectively. Novel Cu 2 O octapods with an edge length of 135 nm were also produced by mixing CuCl 2 solution, SDS surfactant, NaOH solution, and NH 2 OH·HCl reductant solution. All of them are nearly the smallest Cu 2 O nanocrystals of the same shapes ever reported. These small cubes, octahedra, and octapods were employed as catalysts in the direct synthesis of 1,2,3-triazoles from the reaction of alkynes, organic halides, and NaN 3 at 55 °C. All of them displayed high product yields in short reaction times. The octahedra enclosed by the {111} facets are the best catalysts, and can catalyze this cycloaddition reaction with high yields in just 2 h when different alkynes were used to make diverse triazole products. Hence, the small Cu 2 O particles provide time-saving, energy-efficient, and high product yield benefits to organocatalysis. This journal is © the Partner Organisations 2014.