Dual-Step Reduction of Copper and Formation Mechanism of Cu Pseudo-Icosahedral Microcrystals

Pseudo-icosahedral Cu microcrystals have been synthesized in a solvothermal system containing CuSO4·5H2O as the precursor, polyvinylpyrrolidone (PVP) reductant/capping agent, and dimethylformamide solvent. The structural morphological evolutions over reaction time are investigated, which enable us to establish novel formation mechanism of pseudo-icosahedral crystals Cu. first crystalline phase that appeared solution is Cu4SO4(OH)6·H2O form microflakes. microflakes reduced decomposed Cu2O nanocrystallites, assemble with PVP into spherulites. further aggregate again spherical particles. An extraordinary phenomenon 20 separated (111) triangular plates on each particle during surface recrystallization Cu, their locations match final facets pseudo-icosahedron. extend cover whole sphere, forming shell, followed by extension from core. This reversed crystal growth process increases thickness until all nanocrystallites core consumed. It found that, polycrystalline spheres, particles preferentially select planes face-centered cubic structure exposed faces because these minimum binding energy. then try keep small possible specific area, shape consisting plates, has about 10% lower than an octahedron, formed eight plates. Accordingly, overall free energy pseudo-icosahedron octahedron. tetrahedra building units icosahedra, predicted previously, not observed. ideal so-called perfect Platonic solid, twin defects between neighboring possible. newly proposed pseudo-icosahedra sheds light understanding many other polyhedral crystals.