Green synthesis of copper nanoparticles using a high-pressure wet-type jet mill

Abstract

In this study, green synthesis of copper nanoparticles (CuNPs) was investigated at low temperatures without the use of harmful reagents. The starting material was a mixture of an aqueous copper nitrate solution and carboxymethyl cellulose (CMC) suspension. Subsequently, the mixture was processed 0–20 times using a high-pressure wet-type jet mill (jet mill) at a discharge pressure of 100 MPa. The number of jet milling cycles affected the shape of the precipitated particles. Transmission electron microscopy images of a sample subjected to five jet milling cycles showed that many CuNPs were precipitated and well-dispersed on the CMC surface. These precipitated CuNPs were spherical with an average particle size of 5.4 ± 1.9 nm. No CuNPs were precipitated by processing the aqueous copper nitrate solution without CMC using the jet mill at a discharge pressure of 100 MPa. This indicates that CMC acted as a reducing and stabilizing agent. In the X-ray diffraction pattern of the sample subjected to five jet milling cycles, only peaks attributed to the cellulose crystalline phase appeared and no other peaks, such as those attributed to metallic copper or copper oxide, appeared, irrespective of the copper content of the sample, which was 3.6 %. This suggests that the synthesized CuNPs were either predominantly amorphous or possessed extremely low crystallinity.