Synthesis of Cu Nanoparticles: Stability and Conversion into Cu₂S Nanoparticles by Decomposition of Alkanethiolate

A lean synthesis of copper nanoparticles (Cu NP) from CuCl₂ in dodecane via formation of Cu(I)-dodecanethiolate (Cu(I)-DDT) and their decomposition paths including spontaneous C-S bond cleavage of the alkanethiol on the surface of Cu NP is presented. The reduction of Cu(I)-DDT by the tert-butylamine-borane complex (TBAB) in dodecane under N₂ at elevated temperatures leads to the formation of thiol-protected Cu NP with narrow size distribution in the size range of 3-10 nm depending on the reaction conditions. The Cu NP in the presence of excess dodecanethiol reacts further to Cu₂S NP under decomposition of the ligand on the particle surface. The Cu₂S formation occurs after a short time at T > 175 °C or within ∼12 h at room temperature. If excess thiol is removed immediately after the synthesis, the resulting colloid shows irreversible aggregation within days or hours. Our results suggest that alkanethiols are not long-term stable on nanocopper surfaces and that the formation of copper(I) sulfide under the cleavage of the C-S bond occurs even at room temperature.