Hydrothermal Synthesis of Nano-sized Cupric Tungstate (Ⅵ) Dihydrate and Its Synthesis Mechanism

摘要:

选用Cu(NO3)2·3H2O和Na2WO4·2H2O分析纯作为反应原材料，通过水热合成法制备了纳米级的CuWO4·2H2O粉体。讨论了前驱体Cu2WO4(OH)2的生成过程，并且建立了在水热合成过程中前驱体Cu2WO4(OH)2向CuWO4·2H2O转变的机理。利用HRTEM以及XRD分析了前驱体和水热反应产物的物相及微观结构和形貌。结果表明：水热反应产物CuWO4·2H2O粉体呈球形，粒径分布范围为20~30 nm。CuWO4·2H2O粉体的生成过程符合原位结晶机制。在长时间的高热高压的水热环境中，WO42-离子在前驱体Cu2WO4(OH)2表面吸附扩散，通过脱水和原子重排，CuWO4·2H2O在Cu2WO4(OH)2表面异相形核。WO42-离子通过CuWO4·2H2O层与Cu2WO4(OH)2发生反应，直到WO42-离子被耗尽。

Abstract:

Copper nitrate and sodium tungstate were employed to prepare nano-sized cupric tungstate (Ⅵ) dihydrate (CuWO4·2H2O) by hydrothermal method. Formation processes of Cu2WO4(OH)2 precursors were discussed, and the synthesis mechanism of CuWO4·2H2O precipitates from Cu2WO4(OH)2 precursors during the process of hydrothermal reaction was established. Morphological and microstructural investigations of precursors and precipitates were carried out using high resolution transmission electron microscopy (HRTEM) and X-ray diffractometer (XRD). Results show that the synthetic products CuWO4·2H2O particles are mostly spherical in the size range from 20 to 30 nm. Transmission electron microscopy (TEM) observations indicate that the formation of CuWO4·2H2O follows in situ crystallization mechanism in the process of hydrothermal reaction. In the long term hydrothermal environment of high pressure and temperature, Cu2WO4(OH)2 precursors are surrounded by WO42- ions, which are adsorbed and diffused on the surface of Cu2WO4(OH)2. By dehydrations and molecular rearrangement, CuWO4·2H2O precipitates heterogeneously nucleate here. WO42- ions react with Cu2WO4(OH)2 through CuWO4·2H2O layer until WO42- ions have been depleted.