Synthesis, characterization and formation mechanism of single-crystal WO₃ 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, H₂W₂O₇·xH₂O with sizes of 5-15μm, was achieved. The intercalation reaction of n-octylamine with H₂W₂O₇·xH₂O in heptane and the subsequent dissolution-recrystallization process led to the formation of tungstate-based inorganic organic hybrid nanobelts. Orthorhombic WO₃·H₂O nanosheets were obtained by removing the organic species of the as-obtained hybrid nanobelts. After the dehydration of the as-obtained WO₃·H₂O nanosheets at 250-450°C, monoclinic WO₃ nanosheets were achieved. The results of XRD, TEM and SEM indicate that the obtained WO₃·H₂O 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 WO₃·H₂O 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 WO₃·H₂O and WO₃ nanosheets were up to 250 and 180 m /g, respectively. The formation mechanisms for hybrid nanobelts, WO₃·H₂O and WO₃ nanosheets were discussed. The proposed novel route was efficient in producing two-dimensional WO₃ nanosheets on a large scale.