Mergelsberg Sebastian T, Dembowski Mateusz, Bowden Mark E, Graham Trent R, Prange Micah, Wang Hsiu-Wen, Zhang Xin, Qafoku Odeta, Rosso Kevin M, Pearce Carolyn I
Pacific Northwest national Laboratory, Richland, Washington 99352, USA.
Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
Nanoscale. 2021 Oct 28;13(41):17373-17385. doi: 10.1039/d1nr01615f.
Gibbsite [α-Al(OH)] is the solubility limiting phase for aluminum across a wide pH range, and it is a common mineral phase with many industrial applications. The growth mechanism of this layered-structure material, however, remains incompletely understood. Synthesis of gibbsite at low to circumneutral pH yields nanoplates with substantial interlayer disorder. Here we examine defects in this material in detail, and the effects of recrystallization in highly alkaline sodium hydroxide solution at 80 °C. We employed a multimodal approach, including scanning electron microscopy, magic-angle spinning nuclear magnetic resonance (MAS-NMR), Raman and infrared spectroscopies, X-ray diffraction (XRD), and X-ray total scattering pair distribution function (XPDF) analysis to characterize the ageing of the nanoplates over several days. XRD and XPDF indicate that gibbsite nanoplates precipitated at circumneutral pH contain dense, truncated sheets imparting a local difference in interlayer distance. These interlayer defects appear well described by flat Al aluminum hydroxide nanoclusters nearly isostructural with gibbsite sheets present under synthesis conditions and trapped as interlayer inclusions during growth. Ageing at elevated temperature in alkaline solutions gradually improves crystallinity, showing a gradual increase in H-bonding between interlayer OH groups. Between 7 to 8 vol% of the initial gibbsite nanoparticles exhibit this defect, with the majority of differences disappearing after 2-4 hours of recrystallization in alkaline solution. The results not only identify the source of disorder in gibbsite formed under acidic/neutral conditions but also point to a possible cluster-mediated growth mechanism evident through inclusion of relict oligomers with gibbsite-like topology trapped in the interlayer spaces.
三水铝石[α -Al(OH)]是铝在很宽pH范围内的溶解度限制相，并且它是一种具有许多工业应用的常见矿物相。然而，这种层状结构材料的生长机制仍未完全被理解。在低至中性pH条件下合成三水铝石会产生具有大量层间无序的纳米片。在这里，我们详细研究了这种材料中的缺陷，以及在80°C的高碱性氢氧化钠溶液中重结晶的影响。我们采用了多模态方法，包括扫描电子显微镜、魔角旋转核磁共振（MAS-NMR）、拉曼光谱和红外光谱、X射线衍射（XRD）以及X射线全散射对分布函数（XPDF）分析，来表征纳米片在几天内的老化情况。XRD和XPDF表明，在中性pH条件下沉淀的三水铝石纳米片包含致密的、截顶的片层，这导致层间距离存在局部差异。这些层间缺陷似乎可以很好地用扁平的氢氧化铝铝纳米簇来描述，这些纳米簇与合成条件下存在的三水铝石片层几乎同构，并在生长过程中作为层间夹杂物被困住。在碱性溶液中高温老化会逐渐提高结晶度，表明层间OH基团之间的氢键逐渐增加。最初的三水铝石纳米颗粒中有7%至8%表现出这种缺陷，在碱性溶液中重结晶2 - 4小时后，大部分差异消失。这些结果不仅确定了在酸性/中性条件下形成的三水铝石中无序的来源,还指出了一种可能的簇介导生长机制，这种机制通过层间空间中捕获的具有三水铝石样拓扑结构的残留低聚物得以体现。
