Hydrothermal Growth of Centimeter-Scale CuO Plates: Planar Chromium(III) Oligomer as a Facet-Directing Agent

In this work, a simple hydrothermal method was developed to synthesize CuO plates in centimeter scale for the first time. Plates of up to 20 μm thickness and several square millimeters in area have been prepared. The unusual size was obtained under ultrahigh-concentration NaOH and a planar chromium(III) oligomer, which served as a new kind of inorganic facet-directing agent. The obtained CuO plates were glossy black, free-standing, and crack-free. The chromium(III) oligomer offered ideal chemically active sites for adsorbing and confining Cu²⁺ ions. They could be adsorbed on the surface of Cu(OH)₄^2- clusters via hydrogen-bonding interaction, which thus modified the growth orientation. The as-synthesized centimeter-scale CuO plates could possibly serve as substrates and electronic materials with potential applications.