Oxalic acid induced hydrothermal synthesis of single crystalline tungsten oxide nanorods

Abstract

One-dimensional single-crystalline tungsten oxide nanorods have been synthesized by the hydrothermal technique. The controlled morphology of tungsten oxide was obtained by using sodium tungstate and oxalic acid as an organic inducer. The reaction was carried out at 170°C for 24, 48 and 72h. The obtained tungsten oxides were investigated by using XRD, SEM and HRTEM techniques. In order to understand the role of organic inducer on the shape, size and phase formation of WO3 was prepared with and without organic inducer. On heating of sodium tungstate without organic inducer for 72h at 170°C in the hydrothermal unit we obtain nanoparticles of monoclinic WO3, however, on addition of oxalic acid a single phase hexagonal WO3 with distinct nanorods was formed. On addition of oxalic acid a systematic emergence of nanorod-like morphology was obtained with incrementing reaction times from 24h to 48h. The 72h reaction generates self-assembled 20–30nm diameter and 4–5μm long h-WO3 bundles of nanorods. The XRD studies show hexagonal structure of tungsten oxide, while SAED reveals its single crystalline nature. The photoluminescence (PL) emission spectrum shows a characteristic blue emission peak at 3eV (410nm). Raman spectra provide the evidence of hexagonal structure with stretching vibrations (830cm−1) for 72h of heating at 170°C.