Molybdenum oxide nanosheets prepared by an anodizing-exfoliation process and observation of photochromic properties

Abstract

Anodizing-exfoliation of molybdenum foil was performed in 0.02M HCl electrolyte at 30V. In this process, the electrolyte rapidly turned into a blue colloidal solution of molybdenum oxide nanosheets with fragmented edges observed on transmission electron microscope (TEM). X-ray Diffraction (XRD) pattern of particles was free of peak while annealing at a temperature range of 100–500°C led to formation of monoclinic (for T<300 °C) and orthorhombic (for T>300°C) phases of MoO3. Moreover, addition of PdCl2 (0.2g/l) salt solution caused a spontaneous bleaching of the initial blue colloid. Annealing of powders extracted from these bleached solutions with different PdCl2 concentrations at 500°C led to a preferential growth of (0k0) orientation. X-ray photoelectron spectroscopy (XPS) revealed that the blue nanosheets solution contains mainly Mo5+ with slightly Mo6+ oxidation states and each of annealing or salt bleaching procedures can entirely convert Mo5+ to Mo6+. When the bleached solutions was exposed to KrF laser beam (λ=248nm) a strong photochromic coloration with a deep blue color was occurred. Regardless of Pd:Mo ratio, the primary and laser irradiated solutions showed analogues optical absorption bands in the 1–3nm photon energy range while the photochromic process led to a broader absorption band.