Optical properties of Plasmonic Au-MoO3 colloidal nanoparticles by in situ reduction of HAuCl4 by blue MoOx nanosheets

In this paper defective colloids of blue MoOx nanosheets were prepared by electro-oxidation method in water. This colloidal solution exhibits a plasmonic absorption band in the infrared region at about 760 nm. Here, we report a solution-based approach for the synthesis of colloidal gold nanoparticles (GNPs) by proposing sub-stoichiometric blue MoOx nanosheets as a reducing reagent for HAuCl4. Formation of GNPs of 10 nm in diameter in a molybdenum oxide background emerged two plasmonic peaks at 550-680 nm range. We observed a red-shift in the LSPR spectral peaks that as attributed to change in the local refractive index of gold decorate the molybdenum oxide nanosheets. Crystalline structure and morphology of samples were studied with X-ray diffraction and Transmission electron microscopy. Furthermore, we demonstrate the gasochromic coloration effect in the presence of hydrogen gas in Mo:Au solutions of affecting the LSPR absorptions. It was observed that both gold and Mo oxide plasmonic peaks have a red-shift by insertion of hydrogen gas which is attributed to change in solution refractive index and defect concentration.