Copper nanoparticles synthesized by thermal decomposition in liquid phase: the influence of capping ligands on the synthesis and bactericidal activity

We explored here the synthesis of copper nanoparticles (CuNPs) by thermal decomposition of copper(II) acetate in diphenyl ether in the presence of different capping ligands. To look for any specific role in thermal decomposition, we performed reactions in the presence of oleic acid, oleylamine, and 1,2-octanediol, or in the presence of different combinations of these capping ligands, or in the absence of them. The CuNPs obtained in the presence of oleic acid and oleylamine (in the presence or absence of 1,2-octanediol) were stabilized as Cu(0) NPs, and the naked NPs prepared in solvent only easily oxidized to CuO. Therefore, both oleic acid and oleylamine can act as capping ligands to prepare air-stable Cu(0) NPs. The 1,2-alkyldiol is not necessary for metal reduction during the synthesis, but its presence improves size and morphology control. The presence of capping ligands significantly reduced the bactericidal activity exhibited by the Cu NPs against the gram-negative bacteria Escherichia coli.