Scalable Synthesis of Size-Tunable Small Cu₂O Nanocubes and Octahedra for Facet-Dependent Optical Characterization and Pseudomorphic Conversion to Cu Nanocrystals

Abstract

Despite the widespread interest in the examinations of catalytic and facet-dependent properties of Cu2O crystals, it was still difficult to grow ultrasmall Cu2O cubes and octahedra with tunable sizes at a large scale. In this work, CuSO4, NaOH, and sodium ascorbate of varying volumes were added to an aqueous sodium dodecyl sulfate (SDS) solution to generate Cu2O nanocubes with average edge lengths of 16, 25, 29, 36, 51, 63, 72, and 86 nm in just 10 min. Another series of Cu2O cubes with wide size tunability in the range of 27–200 nm is accomplished by simply adjusting the NaOH volume. Similar reaction conditions can also be used to make a large quantity of Cu2O octahedra with opposite corner distances of just 34, 41, and 49 nm. Remarkably, production of these small Cu2O cubes and octahedra is scalable to 500 mL in one reaction. UV–vis absorption and photoluminescence spectra establish their size and facet-dependent optical properties, and a modified band diagram of Cu2O is presented. Recognizing Cu2O nanocrystal shape evolution is possible by changing the cell potential, we have proven this concept to yield cubic to truncated octahedral and octahedral structures by varying the CuSO4 volume. Finally, the tiny Cu2O cubes and octahedra were pseudomorphically converted to Cu cubes and octahedra via the introduction of ammonia borane, so these small copper polyhedra become readily accessible for diverse catalytic and plasmonic applications.