Supercritical hydrothermal synthesis of ultra-fine Cu powders

Ultra-fine Cu powders were synthesized using supercritical water as a reaction medium and formic acid as a reducing agent. The effects of reducing agent, reaction temperature, and complexing agent on the phase constituents, particle size distributions and morphology of the synthesized ultra-fine Cu powders were investigated. A complex mixture of Cu2O and Cu powders formed by pure supercritical water while high purity homogeneous ultra-fine Cu powders can be synthesized by supercritical water with formic acid as a reducing agent. Moreover, fine tuning of particle size and morphology can be realized by the addition of Ethylenediamine tetraacetic acid (EDTA). The modification mechanism of EDTA on the surfaces of ultra-fine Cu powders was investigated by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. EDTA adsorbed on the surfaces of nanoparticles by the dehydration reaction of carboxyl groups in the molecule of EDTA and hydroxyl groups on surfaces of copper nanoparticles (CuOH).