Xu Jun, Chen Lei, Zeng Danlin, Yang Jun, Zhang Minjin, Ye Chaohui, Deng Feng
State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, the Chinese Academy of Sciences, Wuhan 430071, People's Republic of China.
J Phys Chem B. 2007 Jun 28;111(25):7105-13. doi: 10.1021/jp0710133. Epub 2007 May 27.
In the present work, multinuclear solid-state NMR techniques, combined with powder X-ray diffraction (PXRD) and infrared (IR) spectroscopy, are employed to monitor the crystallization of AlPO4-5 aluminophosphate prepared in the presence of HF under hydrothermal condition. The crystallization process is characterized by the evolution of intermediate gels, in which the long-rang ordering arrangement is probed by PXRD, revealing the threshold of the crystallization around 120 min. The appearance of 31P signals at ca. -22 and -29 ppm due to the structural P-O-Al unit and 19F signal at -120 ppm due to the structural F-Alpen-O-P unit in the NMR spectra of the series gels indicates that the crystalline framework is starting to form. The onset of the crystallization is also evidenced by the presence of the pentacoordinated Al in the structural F-Alpen-O-P unit which is considered to be associated with the ordered framework. More information about the local ordering of the gels is obtained from two-dimensional 27Al --> 31P heteronuclear correlation (HETCOR) and 31P/27Al double-resonance experiments. In combination with 1H --> 31P cross-polarization/magic-angle spinning (CP/MAS) experiments, two microdomains can be identified in the 120 min heated gel. A possible evolution mechanism of the gels consisting of three successive stages is proposed for the crystallization process.
在本工作中，采用多核固态核磁共振技术，并结合粉末X射线衍射（PXRD）和红外（IR）光谱，来监测在水热条件下于HF存在时制备的磷酸铝AlPO4-5的结晶过程。结晶过程以中间凝胶的演变为特征，其中通过PXRD探测长程有序排列，揭示了约120分钟时的结晶阈值。系列凝胶的核磁共振谱中，由于结构P-O-Al单元出现约-22和-29 ppm处的31P信号，以及由于结构F-Alpen-O-P单元出现-120 ppm处的19F信号，表明晶体骨架开始形成。结构F-Alpen-O-P单元中五配位Al的存在也证明了结晶的开始，该五配位Al被认为与有序骨架相关。通过二维27Al→31P异核相关（HETCOR）和31P/27Al双共振实验获得了关于凝胶局部有序性的更多信息。结合1H→31P交叉极化/魔角旋转（CP/MAS）实验，在加热120分钟的凝胶中可识别出两个微区。针对结晶过程，提出了由三个连续阶段组成的凝胶可能的演化机制。
