Synthesis, characterization and formation mechanism of single-crystal WO 3 nanosheets via an intercalation-chemistry-based route

In this work an intercalation-chemistry-based method to synthesize tungstate and tungsten oxide nanosheets was described. A layered bismuth tungstate(Bi2W2O9) was used as the W-containing starting material. After the bismuth oxide layers were leached by a chloride acid, a protonated form, H2W2O7xH2O with sizes of 5—15 μm, was achieved. The intercalation reaction of n-octylamine with H2W2O7xH2O in heptane and the subsequent dissolution-recrystallization process led to the formation of tungstate-based inorganic organic hybrid nanobelts. Orthorhombic WO3H2O nanosheets were obtained by removing the organic species of the as-obtained hybrid nanobelts. After the dehydration of the as-obtained WO3H2O nanosheets at 250—450 ℃, monoclinic WO3 nanosheets were achieved. The results of XRD, TEM and SEM indicate that the obtained WO3H2O and WO3 were single-crystalline nanosheets with areas of (200—500) nm×(200—500) nm and thicknesses of 10—30 nm. The SAED patterns suggest that the WO3H2O and WO3 nanosheets possessed a reduced directions of [010] and [001], respectively. N2 adsorption measurement results indicate that the specific surface areas of the as-obtained WO3H2O and WO3 nanosheets were up to 250 and 180 m2/g, respectively. The formation mechanisms for hybrid nanobelts, WO3H2O and WO3 nanosheets were discussed. The proposed novel route was efficient in producing two-dimensional WO3 nanosheets on a large scale.