Aqueous synthesis of dark copper oxide selectively reflecting near-infrared rays

Blue copper hydroxide was synthesized by adding aqueous ammonia or sodium hydroxide to copper chloride, copper nitrate, and copper sulfate solutions, and black copper oxide was produced by heat treatment after filtration. When excess sodium hydroxide was added to copper chloride, copper nitrate, and copper sulfate solutions, the precipitated blue copper hydroxide changed to black copper oxide over time. The effects of synthesis temperature, synthesis time, and excess sodium hydroxide on the spectral reflectance of the precipitated copper oxide in the visible and near-infrared regions were determined. Under optimum conditions, it was possible to synthesize black copper oxide (II) with a visible light region reflectance of less than 5 % and a near-infrared region reflectance of more than 70 %. This copper oxide can be applied to high solar reflective paints necessary for heat island measures.