聚(4-乙烯基吡啶)诱导一步法合成纺锤形钨酸钡晶体

SYNTHESIS OF SPINDLY BaWO_4 CRYSTALS INDUCED BY POLY4-VINYLPYRIDINE

利用高分子量的含氮杂环聚合物聚(4-乙烯基吡啶)(P4VP)作为模板合成了纺锤形钨酸钡晶体,为制备形貌可控的钨酸钡晶体提供了一种简单、条件温和、容易控制的方法.用扫描电镜、透射电镜及X-射线衍射等手段研究了钨酸钡晶体的晶型及形貌.并讨论了P4VP的浓度、溶液离子浓度、pH值等因素对钨酸钡晶体形貌的影响.

Spindly BaWO4 crystals were synthesized by using a high molecular weight N-containing heterocyclic homopolymer, poly4-vinylpyridine （P4VP）, as a template. The well-defined shape of BaWO4 crystals was characterized with scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The size and shape of the spindly BaWO4 crystals can be controlled through adjusting the pH value and the polymer concentration of the solution. The favorite spindly BaWO4 crystals can be obtained at an appropriate polymer concentration. Spindly BaWO4 crystals with various sizes were observed at low concentration of P4VP （ 〈 0.1 g/L）. When the concentration of P4VP was larger than 1 g/L,the dimensions of the spindles were more uniform and smaller. Very uniform BaWO4 crystals with length of 2.5 μm were obtained at P4VP concentration of 10 g/L. The reactant concentration, i. e. the concentration of Ba^2＋ and WO4^2- , played an important role in the morphological control of the BaWO4 crystals. At lower Ba^2＋ concentrations （0.02 mmol/L） ,only clusters without the spindly appearance were found. Spindly BaWO4 crystals were obtained as the concentration of Ba^2＋ was increased to 2 mmol/L. Further increasing Ba^2＋ concentration to 20 mmol/L seriously distorted spindly BaWO4 crystals formed. The pH value also affects the formation of BaWO4 crystals. The increase of pH value promoted the formation of more uniform spindly crystals. Distorted BaWO4 nanoparticles were obtained at lower pH values （ 〈 4）. Spindly crystals were obtained as the pH value increased to 6.5. More uniform small crystals were obtained when the pH value was increased to 8. The formation mechanism of the spindly BaWO4 crystals was suggested according to the experimental results. We suggested that at appropriate conditions （such as pH range, concentration of Ba^2＋ and P4VP）, the Ba^2＋ should react with most suspended pyridyl to form BaWO4 nanoparticles of various sizes at first, and then the residual pyridyl suspended on the main chain should react with the Ba^2＋ in solution further to induce the orderly growth and aggregation of nanosized crystals, and spindly BaWO4 crystals form at last.