用柠檬酸作调控剂水热合成正交相三氧化钨

Hydrothermal Synthesis of Tungsten Trioxides Using Citric Acid as Controlling Agent

用柠檬酸作调控剂,水热合成了正交相纳米尺寸的WO_3矩形片,产物结构与反应温度有很大关系。X射线衍射结果表明,反应产物在393K时为WO_3·H_2O和少量的单斜相WO_3(γ-WO_3);在413K时为γ-WO_3;在433K和453K时为正交相WO_3(β-WO_3)。随反应温度升高,产物发生以下转变:WO_3·H_2O→γ-WO_3→β-WO_3。扫描电镜结果表明反应温度下得到的产物均为矩形片状结构。它们的比表面积相差不大,均在8￣9m2·g^(-1)之间。通过调节柠檬酸与钨酸的物质的量的比(nCit/nTA),可以控制产物的组成、形貌和比表面积。当nCit/nTA=0时,产物为h-WO_3和WO_3·1/3H_2O组成的混合物,形貌为纳米棒;当nCit/nTA=0.5和nCit/nTA=1时,产物为γ-WO_3,形貌为矩形片;当nCit/nTA=2时,产物为β-WO_3,形貌同样为矩形片。在加入柠檬酸的情况下,产物的比表面积随nCit/nTA增加而减小。

Nano-scaled orthorhombic tungsten trioxide rectangular flakes were synthesized by hydrothermal method using citric acid as controlling agent. The phase composition of the products strongly depends on the reaction temperature. XRD results show that the product is tungsten trioxide monohydrate （WO3·H2O） mixed with a small quantity of monoclinic tungsten trioxide （T-WO3） at 393 K, T-WO3 at 413 K, and orthorhombic WO3（β-WO3） at 433 K and 453 K, respectively. SEM images demonstrate that the products obtained at different reaction temperatures are all rectangular flakes with lamellar structure. All the products have almost the same specific surface areas between 8-9 m^2·g^-1. The phase composition, morphology and specific surface area of the products can be controlled by the molar ratio of citric acid to tungstic acid （nCit/nTA）. When nCit/nTA=0, the product is the mixture of h-WO3 （hexagonal system WO3） and WO3·1/3H2O, and have a morphology of nanorods; when nCit/nTA=0.5 or nCit/nTA=1, the product is γ-WO3, and have a morphology of rectangular flakes; when nCit/nTA=2, the product is β-WO3, with the same morphology of rectangular flakes. In the case of adding citric acid, the specific surface area of the products decreases with the increase of nCit/nTA.