Pica Monica, Vivani Riccardo, Donnadio Anna, Troni Elisabetta, Fop Sacha, Casciola Mario
The Chemistry Department, University of Aberdeen , Meston Building, , AB24 3UE Aberdeen, Scotland, U.K.
Inorg Chem. 2015 Sep 21;54(18):9146-53. doi: 10.1021/acs.inorgchem.5b01573. Epub 2015 Aug 31.
Nanosized α-zirconium phosphate, α-ZrP, undergoes a phase transition at 120 °C, which is not observed with microcrystalline α-ZrP in the same conditions, and which leads to a new 3D phase. The new compound, with formula Zr(HPO4)2 (τ'-ZrP), consists of cubelike nanoparticles and has a tetragonal unit cell (space group P43212, a = 7.955 Å, c = 10.744 Å). The structure of τ'-ZrP is in close relationship with that of the already known τ-ZrP. Both structures are made of packed chains of eight-membered rings, composed of Zr atoms connected to bridging HPO4 groups. The main difference between the two structures concerns the different orientation of the uncoordinated P-OH groups, pointing into the channels. The in situ XRPD analysis on nanosized α-ZrP, performed at 120 °C as a function of time, provided information about the kinetics of the formation of τ'-ZrP, showing that the α-ZrP phase is directly transformed into τ'-ZrP. Moreover, τ'-ZrP is converted into α-ZrP at room temperature in the presence of water vapor. It was proved that the free phosphoric acid, which is originally present in small amounts in nanosized α-ZrP and τ'-ZrP, is necessary for the interconversion between the two phases. As a matter of fact, the removal of phosphoric acid, by washing α-ZrP and τ'-ZrP with anhydrous ethanol, inhibits the above conversion.
纳米尺寸的α-磷酸锆（α-ZrP）在120℃会发生相变，而在相同条件下微晶α-ZrP并未观察到这种相变，且该相变会导致一种新的三维相。这种新化合物的化学式为Zr(HPO4)2（τ'-ZrP），由立方状纳米颗粒组成，具有四方晶胞（空间群P43212，a = 7.955 Å，c = 10.744 Å）。τ'-ZrP的结构与已知的τ-ZrP结构密切相关。两种结构均由八元环堆积链构成，这些八元环由连接到桥连HPO4基团的Zr原子组成。两种结构的主要差异在于未配位的P-OH基团指向通道的方向不同。在纳米尺寸的α-ZrP上于120℃进行的原位XRPD分析，作为时间的函数，提供了有关τ'-ZrP形成动力学的信息，表明α-ZrP相直接转变为τ'-ZrP。此外，在水蒸气存在下，τ'-ZrP在室温下会转化为α-ZrP。已证明，纳米尺寸的α-ZrP和τ'-ZrP中原本少量存在的游离磷酸对于两相之间的相互转化是必需的。事实上，用无水乙醇洗涤α-ZrP和τ'-ZrP以去除磷酸，会抑制上述转化。
