Continuous synthesis of ruthenium nanoparticles with tuneable sizes using ruthenium nitrosyl nitrate precursor

Abstract

This paper presents a novel approach for the synthesis of ruthenium nanoparticles via the reduction of ruthenium nitrosyl nitrate with sodium borohydride in flow 3D helical reactors in the absence of capping ligands. Manipulating the pH-speciation of the ruthenium precursor and the fluid dynamics of the flow system allows for the synthesis of small nanoparticles and the tuning of average size with narrow size distributions (2–4 ± 0.5 nm). A mechanism is proposed for the NP synthesis involving the formation of a stable ruthenium nitrite complex from the ruthenium nitrosyl nitrate precursor in the presence of sodium hydroxide, which avoids unwanted metal oxide hydrolysis or precipitation. In contrast, more conventional metal precursors such as chlorides or nitrates easily hydrolyse under basic conditions forming metal oxides or precipitates. We also demonstrate the need of achieving fast mixing of reactants (<50 ms) to enable a homogeneous nucleation under such fast reduction kinetics. This work is a demonstration of the need of combining reaction chemistry and engineering approaches on the synthesis of nanomaterials.