聚(4-乙烯基吡啶)诱导一步法合成纺锤形钨酸钡晶体

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.

SYNTHESIS OF SPINDLY BaWO4 CRYSTALS INDUCED BY POLY4-VINYLPYRIDINE

Spindly BaWO_4 crystals were synthesized by using a high molecular weight N-containing heterocyclic homopolymer,poly4-vinylpyridine(P4VP),as a template.The well-defined shape of BaWO_4 crystals was characterized with scanning electron microscopy,transmission electron microscopy and X-ray diffraction.The size and shape of the spindly BaWO_4 crystals can be controlled through adjusting the pH value and the polymer concentration of the solution.The favorite spindly BaWO_4 crystals can be obtained at an appropriate polymer concentration.Spindly BaWO_4 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 BaWO_4 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 WO~(2-)_4,played an important role in the morphological control of the BaWO_4 crystals.At lower Ba~(2+) concentrations(0.02 mmol/L),only clusters without the spindly appearance were found.Spindly BaWO_4 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 BaWO_4 crystals formed.The pH value also affects the formation of BaWO_4 crystals.The increase of pH value promoted the formation of more uniform spindly crystals.Distorted BaWO_4 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 BaWO_4 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 BaWO_4 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 BaWO_4 crystals form at last.