New Structural Model of Hydrous Sodium Aluminosilicate Gels and the Role of Charge-Balancing Extra-Framework Al
New Structural Model of Hydrous Sodium Aluminosilicate Gels and the Role of Charge-Balancing Extra-Framework Al
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DOI：
10.1021/acs.jpcc.8b00259
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发表时间：
2018-02
影响因子：
3.7
通讯作者：
B. Walkley;Gregory J Rees;R. S. Nicolas;J. Deventer;J. Hanna;J. Provis
中科院分区：
文献类型：
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作者：
B. Walkley;Gregory J Rees;R. S. Nicolas;J. Deventer;J. Hanna;J. Provis
提出了一种新的水合碱铝硅酸盐凝胶（N-A-S-H）骨架结构模型，其中首次在N-A-S-H凝胶中观察到电荷平衡的骨架外铝物种。该模型描述了这些凝胶的关键纳米结构特征，这些特征通过应用17 O，23 Na和27 Al三重量子魔角自旋固态核磁共振光谱来确定合成的富含17 O的不同Si/Al比的凝胶。碱性铝硅酸盐凝胶主要包含通过Na+离子电荷平衡的Q4（4Al）、Q4（3Al）、Q4（2Al）和Q4（1Al）Si单元，所述Na+离子通过3个或4个骨架氧原子配位。一个显着比例的铝3+四面体配位存在于较低的对称性，其中一些电荷平衡能力的网站提供的框架外铝物种，以前没有观察到在这些材料。每种类型的AlIV环境的平均SiIV-O-AlIV键角是高度一致的，与组成的变化决定个别AlIV物种的相对比例，但不改变每个单独的AlIV网站的局部结构。该模型提供了碱性铝硅酸盐凝胶的化学和结构的更先进的描述，是至关重要的理解和控制的分子相互作用，凝胶形成，机械性能和耐久性。
A new structural model of hydrous alkali aluminosilicate gel (N-A-S-H) frameworks is proposed, in which charge-balancing extra-framework Al species are observed in N-A-S-H gels for the first time. This model describes the key nanostructural features of these gels, which are identified through the application of 17O, 23Na, and 27Al triple quantum magic angle spinning solid-state nuclear magnetic resonance spectroscopy to synthetic 17O-enriched gels of differing Si/Al ratios. The alkali aluminosilicate gel predominantly comprises Q4(4Al), Q4(3Al), Q4(2Al), and Q4(1Al) Si units charge-balanced by Na+ ions that are coordinated by either 3 or 4 framework oxygen atoms. A significant proportion of Al3+ in tetrahedral coordination exist in sites of lower symmetry, where some of the charge-balancing capacity is provided by extra-framework Al species which have not previously been observed in these materials. The mean SiIV–O–AlIV bond angles for each type of AlIV environments are highly consistent, with compositional changes dictating the relative proportions of individual AlIV species but not altering the local structure of each individual AlIV site. This model provides a more advanced description of the chemistry and structure of alkali aluminosilicate gels and is crucial in understanding and controlling the molecular interactions governing gel formation, mechanical properties, and durability.