Structural Approach to Understanding the Solubility of Metal Hydroxides
Structural Approach to Understanding the Solubility of Metal Hydroxides
复制标题
了解金属氢氧化物溶解度的结构方法
DOI：
10.1021/acs.langmuir.9b01132
复制
发表时间：
2019
期刊：
影响因子：
3.9
通讯作者：
T. Sasaki
中科院分区：
文献类型：
--
作者：
T. Kobayashi;S. Nakajima;R. Motokawa;D. Matsumura;T. Saito;T. Sasaki
我们报道了氢氧化锆在不同温度下老化后的分级结构，以阐明锆在水溶液中溶解度的影响因素。采用扩展X射线吸收精细结构（EXAFS）、广角和小角X射线散射（WAXS和SAXS）以及透射电子显微镜（TEM）技术研究了氢氧化锆固相在25、40、60和90 °C下在酸性至碱性条件下老化后的体相和表面结构，以揭示从纳米级到亚微米级的固相的体相和表面结构。在25 °C下老化后，固相的基本结构单元被认为是四聚和二聚氢氧化物物质。这些多核物质形成尺寸约为3 nm的无定形初级颗粒，其进而形成尺寸为数百纳米的聚集体。发现这种分级结构在酸性和中性条件下高达60 °C是稳定的，在碱性条件下高达40 °C是稳定的。在酸性条件下在90 °C下以及在碱性条件下在60和90 °C下老化后，WAXS和EXAFS测量表明固相结晶。小角X射线衍射（SAXS）和透射电子显微镜（TEM）的观察结果表明，样品中存在尺寸约为60 nm的结晶大颗粒，并且在SAXS中出现了Guinier区，这表明无定形初级颗粒的结晶导致了大聚集体尺寸的减小。讨论了固相结构随温度的变化与溶度积的关系，以了解限制溶解度的固相。氢氧化锆在不同温度下老化后的溶解度不仅取决于无定形初级颗粒或结晶大颗粒的尺寸，而且还取决于它们的表面构型。
We report the hierarchical structure of zirconium hydroxide after aging at different temperatures to elucidate the factors governing zirconium solubility in aqueous solutions. Zirconium hydroxide solid phases after aging at 25, 40, 60, and 90 °C under acidic to alkaline conditions were investigated using extended X-ray absorption fine structure (EXAFS), wide- and small-angle X-ray scattering (WAXS and SAXS), and transmission electron microscopy (TEM) techniques to reveal the bulk and surface structures of the solid phases from the nanoscale to sub-microscale. After aging at 25 °C, the fundamental building unit of the solid phase was considered to be tetrameric and dimeric hydroxide species. These polynuclear species formed amorphous primary particles that are approximately 3 nm in size, which in turn formed aggregates that are hundreds of nanometers in size. This hierarchical structure was found to be stable up to 60 °C under acidic and neutral conditions and up to 40 °C under alkaline conditions. After aging at 90 °C under acidic conditions and at 60 and 90 °C under alkaline conditions, the WAXS and EXAFS measurements suggested the crystallization of the solid phase. The SAXS profiles and TEM observations supported the existence of crystallized large particles about 60 nm in size, and the appearance of the Guinier region in the SAXS profiles indicated that the crystallization of the amorphous primary particles leads to the reduction of the size of the large aggregates. The transformation of the solid-phase structure by temperature was discussed in relation to the solubility product to understand the solubility-limiting solid phase. The solubility of zirconium hydroxide after aging at different temperatures was governed not only by the size of the amorphous primary particles or crystallized large particles but also by their surface configuration.