Hydrothermal Synthesis, Structural Characterization And Thermal Stability Of Several Open Framework Vanadium Phosphates

Hydrothermal synthesizing of homo-zeolitie open-framework compounds by using of organic molecules as structure-directing agents becomes one of the most active areas in materials science, solid state chemistry, et al. Vanadium phosphate is one of the most important classes of open-framework transition metal phosphates. In this thesis, the concept of open-framework vanadium phosphates was introduced firstly, then their hydrothermal synthesizing and characterizeation methods and potential application were summarized. Some major problems concerning this kind of open-framework materials are pointed out.Two two-dimensional open-framework vanadium phosphates (pipzH2)0.5[(VO) (PO4)] and (pipzH2)2[(VO)3(HPO4)2(PO4)2]·H2O have been synthesized hydrothermally. Their thermal behaviors were characterized by XRD, TG-DTA, SEM. Results show, the stabilities of two compounds are influenced not only by the decomposed process of organic templates but also by the stability of its inorganic framework. The processes of phase transition are also influenced by the process of the organic templates.A novel three-dimensional open-framework vanadium/titanium phosphate was synthesized and characterized. EPMA study shows that titanium was introduced into the structure and substituted vanadium partly. Its inorganic framework structure can regard as an tetragonal shape cage composed of two 10-number rings and two 8-number rings which are built up from corner-sharing [VO6] octahedron and [PO4] tetrahedrons extends along three dimensions. XRD, TG-DTA, SEM analyses showed that the stability of this compound is lower comparing to other vanadium phosphates. This maybe results from very weak bond between molecular water and inorganic framework. However, its recrystallization temperature is relatively higher and its micro-morphology can be kept to high temperature. This may relate to the high temperature for the organic molecules in the structure to decompose completely and the rigidity of its inorganic framework.