Colloidal nanoparticles produced from Cu metal in water by laser ablation and their agglomeration

•Colloidal nanoparticles were prepared from Cu metal in water by laser ablation.•Colloidal nanoparticles were agglomerated as a result of oxidation according to the time elapsed.•Lengthy continuous measurements of colloidal nanoparticle size changes were performed.

Colloidal nanoparticles were prepared from Cu metal in water without any surfactant using a simple one-step laser ablation process with 532 nm Nd-YAG beam irradiation. A surface plasmon band of Cu nanoparticles near 580 nm was not observed; instead, oxidation of the Cu colloidal nanoparticles was noticed. This seems to be due to the partially oxidized copper oxides through the route Cu→Cu2O→CuO. Around 10-nm sized colloidal nanoparticles were agglomerated as a result of oxidation according to the time elapsed, and their sizes were increased to near 200 nm. The agglomeration was confirmed by not only images from transmission electron microscopy but also the long-term observation of the particle size distribution using photon correlation spectroscopy, laser-induced breakdown detection, and field flow fractionation.