Crystal-Plane-Dependent Etching of Cuprous Oxide Nanoparticles of Varied Shapes and Their Application in Visible Light Photocatalysis

We report a simple, facile, surfactant-free chemical route to fabricate morphologically different Cu₂O nanoparticles such as octahedron, truncated octahedron, hollow octahedron, cube, and sphere by varying the hydrolyzing agents, complexing agent, and reducing agents. Then the componential and morphological evolution of Cu₂O nanoparticles have been studied independently, employing different etching agents such as aqueous NaOH, triethylamine (TEA), and oxalic acid solution. Particles of varied shapes and compositions resulted from the etching, and those particles were characterized by different physical methods. The oxidative dissolution of morphologically different Cu₂O nanoparticles with different etching agents depends on the exposed crystal planes. During oxidative dissolution in aqueous oxalic acid solution, it is realized that the stability of the (100) crystal plane is higher than that of the (111) crystal plane. Among all the etching reagents used, only oxalic acid exhibits shape transformation of the as-prepared Cu₂O nanoparticles. Oxalic acid etching causes the formation of cubes and hollow cubes as etching products with a 50% reduction of edge length compared to that of octahedral, truncated octahedral, and hollow octahedral Cu₂O nanoparticles. But ill-defined cubes are always obtained as the etching products with a 40% reduction of size compared to that of Cu₂O cubes and spheres. As-prepared Cu₂O nanoparticles and chemically etched products exhibit facet-dependent photocatalytic activity under visible light irradiation where mineralization of congo red takes place. Experimentally it has been concluded that photocatalytic activity of different particles bears a close relationship with exposed crystal planes, surface area, and particle size for congo red degradation. Interestingly, NaOH-etched product with hollow octahedral morphology bearing many (111) facets demonstrates the highest photocatalytic activity