Synthesis of Submicrometer-Sized Cu2O Crystals with Morphological Evolution from Cubic to Hexapod Structures and Their Comparative Photocatalytic Activity

We report a facile method for the synthesis of cuprous oxide nanocrystals with systematic morphological evolution. Cubic, truncated cubic, cuboctahedral, truncated octahedral, octahedral, and short hexapod structures have been synthesized in an aqueous solution of CuCl2, NaOH, sodium dodecyl sulfate (SDS) surfactant, and hydroxylamine (NH2OH·HCl) reductant by simply varying the volume of hydroxylamine added to the reaction mixture. A slight modification in the volume of some reagents produced the extended hexapods. The order of the introduction of the reagents is important to the formation of these crystals with distinct morphologies and sharp faces. The sizes of these particles fall mostly in the range of 400−700 nm. Clear transition in the relative intensities of the (111) and the (200) reflection peaks in their XRD patterns was observed. Scattering bands dominate the UV−vis absorption spectra of these crystals. Crystal model analysis revealed that the 111 face contains surface copper atoms with dangling bonds, and is expected to interact more strongly with negatively charged molecules. Tests of photodegradation of negatively charged methyl orange showed that octahedra and the extended hexapods were catalytically active. The cubes with only the 100 faces were not active. On the contrary, both cubes and octahedra were not effective at photodecomposing positively charged methylene blue molecules. Surprisingly, octahedra and hexapods cannot be well suspended in the methylene blue solution; a significant amount of the crystals gradually moved to the surface of the solution with increasing stirring time. The results clearly demonstrate the dramatic differences in the catalytic activities of the 111 and 100 faces of Cu2O crystals for the first time.