Crystal Splitting And Its Application In The Crystal Engineering Of Zinc Hydroxyfluoride ZnOHF

In recent years,nanocrystalline engineering,that is,manufacturing and utilizing nanocrystals with customized geometry as nanodevices,has become one of the most significant topics in science and technology,because it can provide opportunities to control and manipulate physical,chemical properties of materials and their applications,especially those three-dimensional composite nanosystems constructed from one-dimensional structure.Because of its high porosity and relatively large specific surface area,it can be applied to nanodevices.Therefore,the study of nanocrystalline engineering not only has important theoretical value,but also has broad application prospects.In this paper,the synthesis and characterization of zinc hydroxyfluoride nanomaterials were systematically studied by hydrothermal synthesis.By adjusting the parameters of surfactant,reaction temperature and growth time,the branching degree of zinc hydroxyfluoride hyperbranched structure could be changed.Half-sheaf,double-sheaf and spherical hierarchical nanostructures were synthesized.Therefore,the controlling of its morphology can be achieved by changing of synthetic parameters.Because of the peculiarity of the morphology of the produced zinc hydroxyfluoride,we have studied its growth mechanism in depth,that is,the formation mechanism of hierarchical hyperbranched composite nanostructures of zinc hydroxyfluoride-crystal splitting.The main results are as follows:(1)Zinc hydroxyfluoride nanocrystals were successfully prepared by hydrothermal method.The morphology of the nanocrystalline zinc fluoride was hyperbranched,consisting of single nanowires with a diameter of about 47±5nanometers and a length of about several micrometers.(2)In this paper,a series of morphological evolution process with the reaction time are studied.Nanorods are initially formed via the oriented attachment process.The nanrods begin to split into small nanowires along the growth direction.The individual nanowires continue to grow and split,and finally form the hierarchical structure of hyperbranched zinc hydroxide.Crystal splitting is the mechanism of forming the hyperbranched structure of zinc hydroxide,and its characteristic is that new surface area occurs due to each step of splitting.Thus the process of crystal splitting is the result of the competition between surface energy and defect energy.(3)We studied the properties of the produced zinc hydroxyfluoride with the peculiar hyperbranched structures.The results show that the gas sensing properties of the hyperbranched nanostructures of zinc hydroxyfluoride may vary with the degree of their splitting.In some common harmful volatile compounds(acetone,benzene,methanol,ammonia,ethanol,formaldehyde and toluene)with a concentration of 100 ppm,the gas-sensitive selectivity of hyperbranched nanostructures of zinc hydroxyfluoride with a half-sheaf morphology is the highest for methanol when the working temperature is 200 °C.The thermal properties of the synthesized ZnOHF hyperbranched nanostructures were studied by thermogravimetric analysis(TG)and differential thermal analysis(DTA).The main sharp endothermic peak is located at 349 °C,which can be attributed to the decomposition of ZnOHF and the volatilization of HF gas.