Matching the organic and inorganic counterparts during nucleation and growth of copper-based nanoparticles – in situ spectroscopic studies

Abstract

Although syntheses in organic solvents provide access to a wide range of copper-based nanoparticles, the correlation between organic reactions in solution and nucleation and growth of nanoparticles with defined properties is not well understood. Here, we utilize the Multivariate Curve Resolution-Alternative Least Squares (MCR-ALS) methodology to examine spectroscopic data recorded in situ during the synthesis of copper-based nanoparticles. While earlier studies showed that depending on the temperature copper(II) acetylacetonate reacts with benzyl alcohol and forms either copper oxides or copper nanoparticles, we link the inorganic reaction with their organic counterparts. From X-ray Absorption Near Edge Spectroscopy (XANES) and Ultraviolet-visible spectroscopy (UV-vis) data we learn that copper(I) oxide forms directly from the solution and is the final product at low temperature of 140 °C. We observe in Fourier Transformed Infrared (FTIR) spectra an increasing concentration of benzyl acetate that co-occurs with the formation of a copper enolate and evolution of benzaldehyde, which accompanies the reduction of copper ions. We also record the interaction of organic species at the Cu₂O surface, which inhibits a further reduction to metallic copper. When we raise the synthesis temperature to 170 °C it turns out that the Cu₂O is just an intermediate species. It subsequently transforms by solid-state reduction to metallic copper accompanied by oxidation of benzyl alcohol to benzaldehyde.