Preparation of hexagonal WO 3 from hexagonal ammonium tungsten bronze for sensing NH 3

Abstract

Hexagonal tungsten oxide (h-WO 3) was prepared by annealing hexagonal ammonium tungsten bronze, (NH 4) 0.07(NH 3) 0.04(H 2O) 0.09WO 2.95. The structure, composition and morphology of h-WO 3 were studied by XRD, XPS, Raman, 1H MAS (magic angle spinning) NMR, scanning electron microscopy (SEM), and BET-N 2 specific surface area measurement, while its thermal stability was investigated by in situ XRD. The h-WO 3 sample was built up by 50–100 nm particles, had an average specific surface area of 8.3 m 2/g and was thermally stable up to 450 °C. Gas sensing tests showed that h-WO 3 was sensitive to various levels (10–50 ppm) of NH 3, with the shortest response and recovery times (1.3 and 3.8 min, respectively) to 50 ppm NH 3. To this NH 3 concentration, the sensor had significantly higher sensitivity than h-WO 3 samples prepared by wet chemical methods.