π-stacking intercalation and reductant assisted stabilization of osmium organosol for catalysis and SERS applications

Abstract

Size-selective, mono-dispersed spherical osmium (Os) nanoparticles (NPs) have been synthesized for the first time in a two-phase (water-toluene) extraction procedure in organic medium (in toluene) under ambient conditions. A simple wet chemical synthesis route was employed to prepare the Os organosol from the precursor osmium tetroxide (OsO₄) and tetrabutylammonium borohydride (TBABH₄). Tetraoctylammonium bromide (TOAB) was used as a phase transfer catalyst (PTC) which quantitatively transferred Os precursors to the organic medium from the aqueous medium. Four different spherical Os NP organosols with varying sizes of 1 ± 0.2 nm, 10–30 nm, 22 ± 2 nm and 31 ± 3 nm were synthesized just by changing the concentration ratio of the metal precursor and the amount of reductant added. The role of all the precursor concentrations in the size-selectivity was examined in-detail. The synthesized osmium organosol were stabilized by the extensive π-stacking intercalation effect offered by toluene as well as the interaction of tetrabutylammonium ions (TBA⁺) presented in the organic medium. The synthesized spherical Os NP organosols were utilized in two different applications such as in catalysis and in Surface Enhanced Raman Scattering (SERS) studies. The catalytic activity of osmium organosol was tested for the reduction of hexavalent chromium (Cr⁶⁺) ions under UV light in the presence of sodium thiosulphate. The SERS activity was examined by taking methylene blue (MB) dye as a probe molecule. In the near future, the synthesized Os organosol might be utilized as a potential catalyst in organic catalysis reactions as well as in the field of fuel cells and sensors.