Plasmonic Au-MoO3 Colloidal Nanoparticles by Reduction of HAuCl4 by Blue MoOx Nanosheets and Observation of the Gasochromic Property

Abstract

Defective colloids of blue MoOx nanosheets were prepared by anodizing exfoliation method in water. This colloidal solution exhibits an optical plasmonic absorption band in the infrared region at about 760 nm. Merely mixing HAuCl4 solution with the MoOx leads to loss of the blue color, decaying of 760 nm plasmonic peak and simultaneous formation of the gold plasmon absorption peak at 550–570 nm. Some spectral variations in gold plasmonic peak and MoOx optical band gap were observed for Mo:Au ratio of 10:1, 20:1, 30:1, and 40:1. The size of the gold nanoparticles was in the 5–6 nm range with fcc crystalline structure. X-ray photoelectron spectroscopy (XPS) revealed that the initial solution contains Mo5+ states and hydroxyl groups, which after reduction, hydroxyl groups are eliminated and the Mo5+ states converted to Mo6+. The obtained Au-MoO3 colloids have a gasochromic property in which they are colored back to blue in the presence of hydrogen gas and the molybdenum oxide absorption peak recovered again. Furthermore, it was observed that both gold and Mo oxide plasmonic peaks redshift by insertion of hydrogen gas which is attributed to change in solution refractive index and formation of defect concentration.