title: Nucleation and growth of gold nanoparticles studied via in situ small angle X-ray scattering at millisecond time resolution.
abstract: Gold nanoparticles (AuNP) were prepared by the homogeneous mixing of continuous flows of an aqueous tetrachloroauric acid solution and a sodium borohydride solution applying a microstructured static mixer. The online characterization and screening of this fast process ( approximately 2 s) was enabled by coupling a micromixer operating in continuous-flow mode with a conventional in-house small angle X-ray scattering (SAXS) setup. This online characterization technique enables the time-resolved investigation of the growth process of the nanoparticles from an average radius of ca. 0.8 nm to about 2 nm. To the best of our knowledge, this is the first demonstration of a continuous-flow SAXS setup for time-resolved studies of nanoparticle formation mechanisms that does not require the use of synchrotron facilities. In combination with X-ray absorption near edge structure microscopy, scanning electron microscopy, and UV-vis spectroscopy the obtained data allow the deduction of a two-step mechanism of gold nanoparticle formation. The first step is a rapid conversion of the ionic gold precursor into metallic gold nuclei, followed by particle growth via coalescence of smaller entities. Consequently it could be shown that the studied synthesis serves as a model system for growth driven only by coalescence processes.
authors.affiliation: BAM Federal Institute of Materials Research and Testing, Richard-Willstatter-Strasse 11, D-12489 Berlin, Germany.
authors.forename: Jörg
authors.initials: J
authors.lastname: Polte
authors.forename: Robert
authors.initials: R
authors.lastname: Erler
authors.forename: Andreas F
authors.initials: AF
authors.lastname: Thünemann
authors.forename: Sergey
authors.initials: S
authors.lastname: Sokolov
authors.forename: T Torsten
authors.initials: TT
authors.lastname: Ahner
authors.forename: Klaus
authors.initials: K
authors.lastname: Rademann
authors.forename: Franziska
authors.initials: F
authors.lastname: Emmerling
authors.forename: Ralph
authors.initials: R
authors.lastname: Kraehnert