Paskin Alice, Couasnon Thaïs, Perez Jeffrey Paulo H, Lobanov Sergey S, Blukis Roberts, Reinsch Stefan, Benning Liane G
GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany.
Department of Earth Sciences, Freie Universität Berlin, Malteserstr. 74-100, 12249 Berlin, Germany.
J Am Chem Soc. 2023 Jul 19;145(28):15137-15151. doi: 10.1021/jacs.3c01494. Epub 2023 Jul 6.
The fundamental processes of nucleation and crystallization are widely observed in systems relevant to material synthesis and biomineralization; yet most often, their mechanism remains unclear. In this study, we unravel the discrete stages of nucleation and crystallization of Fe(PO)·8HO (vivianite). We experimentally monitored the formation and transformation from ions to solid products by employing correlated, time-resolved and approaches. We show that vivianite crystallization occurs in distinct stages via a transient amorphous precursor phase. The metastable amorphous ferrous phosphate (AFEP) intermediate could be isolated and stabilized. We resolved the differences in bonding environments, structure, and symmetric changes of the Fe site during the transformation of AFEP to crystalline vivianite through synchrotron X-ray absorption spectroscopy at the Fe K-edge. This intermediate AFEP phase has a lower water content and less distorted local symmetry, compared to the crystalline end product vivianite. Our combined results indicate that a nonclassical, hydration-induced nucleation and transformation driven by the incorporation and rearrangement of water molecules and ions (Fe and PO) within the AFEP is the dominating mechanism of vivianite formation at moderately high to low vivianite supersaturations (saturation index ≤ 10.19). We offer fundamental insights into the aqueous, amorphous-to-crystalline transformations in the Fe-PO system and highlight the different attributes of the AFEP, compared to its crystalline counterpart.
成核和结晶的基本过程在与材料合成和生物矿化相关的体系中广泛存在；然而，其机制大多仍不明确。在本研究中，我们揭示了Fe(PO)·8H₂O（蓝铁矿）成核和结晶的离散阶段。我们通过采用相关的、时间分辨的方法，实验监测了从离子到固体产物的形成和转变过程。我们表明，蓝铁矿结晶通过一个瞬态无定形前驱体相分阶段发生。亚稳态的无定形磷酸亚铁（AFEP）中间体可以被分离并稳定下来。我们通过在Fe K边的同步辐射X射线吸收光谱，解析了AFEP向结晶蓝铁矿转变过程中Fe位点的键合环境、结构和对称性变化的差异。与结晶终产物蓝铁矿相比，这种中间的AFEP相含水量较低，局部对称性扭曲较小。我们的综合结果表明，在中等至高到低的蓝铁矿过饱和度（饱和指数≤10.19）下，由AFEP内水分子和离子（Fe和PO）的掺入和重排驱动的非经典的、水合诱导的成核和转变是蓝铁矿形成的主导机制。我们为Fe-PO体系中的水相无定形到结晶转变提供了基本见解，并突出了AFEP与其结晶对应物相比的不同特性。
