Nano-brass colloids: Synthesis by co-hydrogenolysis of [CpCu(PMe ₃)] with [ZnCp*₂] and investigation of the oxidation behaviour of α/β-CuZn nanoparticles

A novel, non-aqueous organometallic access to colloidal copper and copper/zinc (brass) nanoparticles is described. Hydrogenolysis of the precursor [CpCu(PMe₃)] (1) in mesitylene at 150 °C and 3 bar H₂ quantitatively gives elemental Cu. Analogously, a solution of [ZnCp*₂] (2) reacts with H₂ to give elemental Zn in 100% yield. Co-hydrogenolysis of 1 and 2 in exactly equimolar quantities selectively yields the intermetallic phase β-CuZn characterised by powder X-ray diffraction (PXRD). Deep red colloidal solutions of nano-Cu as well as red to violet colloids of nano-brass alloys (α/β-CuZn) are obtained by co-hydrogenolysis of 1 and 2 in the presence of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) as surfactant. All samples of the general formula Cu _1-xZn_x (0.09 ≤ x ≤ 0.50) were characterised by means of elemental analysis, PXRD, transmission electron microscopy (TEM, EDX and SAED) and UV-Vis absorption spectroscopy. The presence and alloying of metallic Cu and Zn in the β-CuZn sample as a representative example of the series was confirmed by extended X-ray absorption fine structure spectroscopy (EXAFS). The oxidation behaviour of the nanoparticles was investigated by EXAFS, PXRD and UV-Vis spectroscopy indicating, that CuO_x@Cu core-shell type particles were formed for pure copper particles, while in the case of brass particles preferential oxidation of the Zn component takes place, which results in core-shell particles of the type (ZnO)_δ@Cu _1-xZn_x-δ.