Plasmonic osmium hydrosols: Preparation,characterization, and properties

A simple route for the synthesis of mesoporous and plasmonic chitosan supported osmium hydrosols (Os⁰) has been reported using osmium (III)-sodium borohydride redox reaction at room temperature. The composition and morphology of nanoparticles were determined with XRD, XPS, TEM, EDX, SEM, FTIR and N₂-adsorption desorption techniques. No SPR band of Os⁰ at 485 nm was observed for the same redox reaction with cetyltrimethylammonium bromide (CTAB) for ca. 120 min at room temperature. The surface oxidation of Os⁰ into OsO₂ was detected by XRD and XPS. XRD shows the presence of chitosan onto the surface of nanoparticles. The average pore size, and pore volume were found to be 7.23 nm, and 0.239 cc/g, respectively, for Os⁰. The persulfate activation catalytic activity was tested in situ chemical oxidation of basic red 2 (safranin) under activated and un-activated persulfate. Safranin was adsorbed onto the Os⁰ and complex was formed. The oxidation of dye follows pseudo-first order kinetics (k_app = 14.8 × 10^-3 min⁻¹ at [S₂O₈^2-] = 3.3 mM). The activated system showed a much higher dye oxidation rate compared to either S₂O₈^2- or Os⁰ alone. The activation energy (E_a = 105 kJ/mol) was calculated for the system by using Arrhenius equation. The reaction mechanism of Os⁰ activation of persulfate was elucidated and discussed.