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

Use of organic molecules as structure-directing agents, hydrothermal synthesizing of non-zeolitic novel open-framework materials for potential uses in sorption, ion-exchange, catalysis and material uses are contemporary interest in solid state chemistry. Vanadium phosphate is one of the most important classes of open-framework transition metal phosphates. On the basis of systematic study upon crystal chemistry and crystal structure of vanadium phosphates, a new classification scheme based on non-framework compositions has been proposed. The scheme is-helpful both for revealing the relationships between templates and crystal structure, also directing preparation new compounds. Some major problems about micro-pore open-framework materials are presented. Effects of hydrothermal synthesis parameters on phase products in the V2O5-H3PO4-en-H2O system were systematically investigated. Keeping other factors same, the mole ratio of the reactants is an important factor influencing phase formation. Different addition order of reactants just resulted in different initial reactions, but no relation with final phase products and phase combination. Filling volume has effects on products yields; high filling volume is favorable to the formation of phases of high framework density. There are complicated relationships between factors of hydrothermal synthesis A new lamellar vanadium phosphate [NH3CH2CH2NH2H VOPO4] was prepared and structurally characterized. The structure contains layers built from chains of trans corner-shared [VO5N] octahedron that are interconnected by [PO4] tetrahedron. The ethylenediamonium cation is bonded through the nitrogen to the vanadium site as a monodentate ligand. Strong hydrogen bonds hold the layers together. A three-dimensional open-framework diaminopropane vanadium phosphate [ H3N (CH2)3NH3]2[H3N(CH2)3NH2][H2N(CH2)3NH2][V(H2O)2(VO)8(OH)4(PO4)4(HPO4)4]. 4H2O (dap-VgPg) was synthesized and characterized. Its framework structure is identical to the ethylenediamine-containing compound en-X^Pg. However, the guest molecules have three different conformations based on their crystallographic positions in the structure. It was discovered for the first time that the carbon chain of diaminopropanium in the center of the elliptical cavity is an linear type. Also, these diaminopropane molecules show different order-disorder state. Comparative TG-DTA and FT-IR studies of several typical organic-templated vanadium phosphates shows that framework strength is the key factor affecting the thermal stability of the compounds. The bonding strength between host and guest, and framework type also have important effects on the thermal stability. The decomposition of organic molecules broken the hydrogen bond networks in the structures, leading the structure collapse. The thermal stability of the open framework vanadium aluminumphosphate [NH3CH2CH2NH2][(VO)A1(PO4)2] has been characterized by XRD, TG-DTA, FT-IR and SEM. The reason of its relatively higher thermal stability compared with other vanadium phosphates was attributed to the presence of the rigid corner-shared [AIO4]...