Direct formation of small Cu2O nanocubes, octahedra, and octapods for efficient synthesis of triazoles

Abstract

In most studies describing the preparation of Cu₂O 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 Cu₂O nanocrystals with systematic shape evolution from cubic to octahedral structures by preparing an aqueous mixture of Cu(OAc)₂, NaOH, and N₂H₄ 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 Cu₂O octapods with an edge length of 135 nm were also produced by mixing CuCl₂ solution, SDS surfactant, NaOH solution, and NH₂OH·HCl reductant solution. All of them are nearly the smallest Cu₂O 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 NaN₃ 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 Cu₂O particles provide time-saving, energy-efficient, and high product yield benefits to organocatalysis.