Preparation Of Hexagonal Wo_3 From Hexagonal Ammonium Tungsten Bronze For Sensing Nh_3

摘要

Hexagonal tungsten oxide (h-WO_3) was prepared by annealing hexagonal ammonium tungsten bronze, (NH_4)_(0.07)(NH_3)_(0.04)(H_2O)_(0.09)WO_(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 ℃. 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.