VPO系孔道化合物钒氧化态对结构热稳定性的影响机理

Relationship between vanadium oxidation states and thermal stability of an oxovanadium phosphate with 3-dimensional channels

利用多功能 X 射线光电子能谱(XPS)分析方法,研究了三维孔道结构化合物 (H_3NCH_2CH_2NH_2)_4[V~Ⅲ(H_2O)_2(V~ⅣO)_8(OH)_4(HPO_4)_4(PO_4)_4(H_2O)_2]·3H_2O(简称 V_9P_8-en)在不同气氛下热处理脱除模板过程中的钒氧化态变化规律及其与结构演化的关系．结果表明,380 ℃之前有机模板受热分解形成较强的还原气氛,致使骨架中部分钒被还原(V^(4+)→V^(3+))；随着钒氧化态的改变,原有的配位环境([V~ⅢO_6]八面体、[V~ⅣO_5]四方单锥)随之调整而导致结构重组．因此,热处理过程中控制钒氧化态变化将有助于保持骨架结构的稳定性．

The factors influencing the thermal stability of a vanadium phosphate （H3NCH2CH2NH2）4 [V^Ⅲ （H2O）2（V^ⅣO）8（OH）4 （HPO4）4 （PO4）4 （H2O）2 ]·3H2O （V9P8-en for short） with open-framework were investigated by XPS. The thermal degradation of V9P8-en while heated under Ar and air atmospheres was studied, including the removal of organic templates （en）, phase transition and vanadium oxidation states. It is shown that the structure of the compound collapses with decomposition of the organic template before 380 ℃, and the oxidation states of vanadium atoms become variable, i.e. vanadium atoms in VPO skeleton are reduced from V^4＋ to V^3＋ . As viewed from crystal chemistry, the structure has to be rebuilt because the original coordination environments of V^4＋ （distorted octahedron or trigonal-bipyramid） cannot match ones of V^3＋ （regular octahedron）. It is concluded that the rational control of pretreatment conditions to maintain the original oxidation states of vanadium will be helpful for the thermal stability of open framework vanadium phosphates.