Formation of isolated and clustered Au nanoparticles in the presence of polyelectrolyte molecules using a flow-through Si chip reactor

The formation of colloidal gold at room temperature was studied in a micro-reaction system. Ascorbic acid and Fe(II) were used as reducing agents. Besides citric acid, sodium metasilicate and poly( vinyl alcohol) were added as effectors for the formation of nanoparticles. The experimental set-up was based on a 2 + 1 + 1 static micro-mixer in order to test the successive addition of reaction components in a micro-continuous flow process. The residence times for a single mixing step in the chip device were chosen in the range between about 1 second and 1 minute. As a result, single particles of different sizes, simple particle aggregates, core-shell particles as well as complex aggregates and hexagonal nanocrystallites were obtained under different reaction conditions. The reaction mixtures were characterized by UV-Vis spectroscopy as well as by differential centrifugal sedimentation (DCS) and scanning electron microscopy (SEM) reflecting the variety of colloidal gold formed in the microreactor.