Observing the influence of X-rays on aqueous copper solutions by in situ combined video/XAFS/UV-Vis spectroscopy

Abstract

In situ video monitoring and UV-Vis spectroscopy have been used in combination with XAFS spectroscopy to study the effect of synchrotron radiation on a series of copper solutions in a micro-reactor. The samples that were investigated contained initially a mixture of Cu2+ ions and both biologically and non-biologically relevant amine ligands. It was observed that when water was used as the solvent, gas bubbles are formed under the influence of the X-ray beam. At the resultant liquid-gas interface and under certain conditions, colloidal copper nanoparticles were observed to form. This reduction process was influenced primarily by the type of the copper precursor salt (SO42-, NO3- and Cl-), although the ligands surrounding the copper cation and the redox potential of the copper complexes (ranging between +594 and 360 mV) were also observed to have some effect. Critically we show how these results illustrate the benefits of combining methods (and in particular the use of video imaging) to monitor chemical processes and for observing the influence of one technique on the measurement process. Furthermore the results give some insight into the parameters that are important in the redox-processes that occur in biological systems.