Controlled oxidation of metallic copper nanoparticles by a silica coating

The development of a simple method that perfectly controls the oxidation and aggregation of metallic copper (Cu) nanoparticles has been anticipated. In the present work, silica-coated metallic Cu nanoparticles were used as a control. Metallic Cu nanoparticles were synthesized from Cu(CH3COO)2, hydrazine, citric acid, and cetyltrimethylammonium bromide in water exposed to air. The metallic Cu nanoparticles were silica-coated by adding ethanol, (3-aminopropyl) trimethoxysilane (APMS)/ethanol, tetraethylorthosilicate (TEOS)/ethanol, and NaOH aqueous solution to the metallic Cu nanoparticle colloid solution. The morphology of silica-coated metallic Cu nanoparticles was dependent on the presence or absence of APMS and the TEOS concentration. Oxidation of the metallic Cu nanoparticles even with annealing in air was controlled by the silica shells due to their function as a physical barrier.