Elucidating Chemical and Morphological Changes in Tetrachloroauric Solutions Induced by X-ray Photochemical Reaction

Chemical and morphological changes induced by an X-ray photochemical reaction in tetrachloroauric solutions leading to Au³⁺-to-Au⁰ reduction are monitored in real time by X-ray absorption spectroscopy and X-ray small angle scattering. Prior to metal precipitation, the intermediate state, also observed by other techniques, is unambiguously determined for the first time to be the reduction of Au³⁺ to Au¹⁺, whose kinetics is strictly of the zeroth order. The morphological changes occur simultaneously in the solutions, that is, the gold complexes rearrange and aggregate, as unequivocally observed by the correlated changes in the Au L₃ emission and small angle scattering intensities. The experimental evidence indicates that the eventual metal precipitation is strongly influenced by the changing solution acidity under X-ray irradiation. Detailed local structure changes are also described.