In situ X-ray absorption spectroscopy investigation during the formation of colloidal copper

The reduction of [N(octyl)(4)](2)[CuCl2Br2] in organic solution (toluene) using Li[BEt3H] leads to colloidal Cu protected by cationic surfactants (NR4+). According to HRTEM (high-resolution transmission electron microscopy) and UV/vis data, the organosol is composed of relatively large Cu particles with diameters of between 5 and 10 nm. An in situ XANES (X-ray absorption near edge structure) investigation was performed for the first time during the colloid synthesis. Our measurements revealed the formation of an intermediate Cu+ state prior to the nucleation of the particles, thus giving direct insight into the mechanism of the colloid formation. The significant differences between the near edge structures of the bulk sample and the colloidal Cu have to be traced back to structural disorder in the lattice of this nanosized material.