The aluminum oxyhydroxide boehmite is an important crystalline phase in nature and industry. We report development of a flexible additive-free hydrothermal synthesis method to prepare high quality boehmite nanoplates with sizes ranging from under 20 nm to 5 μm via using hydrated alumina gels and aluminum hydroxide amorphous powders as precursors. The size and morphology of the boehmite nanoplates was systematically varied between hexagonal and rhombic by adjusting precursor concentrations, pH, and the synthesis temperature, due to face-specific effects. The transformation mechanism is consistent with dissolution and reprecipitation, and involves transitory initial appearance of metastable gibbsite that is later consumed upon nucleation of boehmite. Detailed X-ray pair distribution characterization of the solids over time showed similarities in short-range order that suggest linkages in local chemistry and bonding topology between the precursors and product boehmite, yet also that precursor-specific differences in long-range order appear to manifest subtle changes in resulting boehmite characteristics, suggesting that the rate and extent of water release or differences in the resulting solubilized aluminate speciation lead to slightly different polymerization and condensation pathways. The findings suggest that, during dissolution of the precursor, precursor-specific dehydration or solution speciation could be important aspects of the transformation impacting the molecular-level details of boehmite nucleation and growth.

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勃姆石纳米板的尺寸和形貌控制合成及其晶体生长机理

氢氧化铝氢氧化铝勃姆石是自然界和工业中重要的结晶相。我们报告了一种灵活的无添加剂水热合成方法的开发，该方法通过使用水合氧化铝凝胶和氢氧化铝无定形粉末作为前体来制备尺寸范围从20 nm至5μm的高质量勃姆石纳米板。通过调整前体浓度，pH和合成温度，由于表面特定的影响，勃姆石纳米板的尺寸和形态在六角形和菱形之间系统地变化。该转变机制与溶解和再沉淀相一致，并且涉及亚稳态三水铝石的短暂初始外观，随后在勃姆石成核时被消耗。固体随时间变化的详细X射线对分布特征显示了短程顺序的相似性，这表明前驱物与勃姆石之间的局部化学键合和键合拓扑结构存在联系，但长程顺序的前体特异性差异似乎也很明显生成的勃姆石特性发生细微变化，表明水释放的速率和程度或生成的可溶铝酸盐形态的差异导致聚合和缩合途径略有不同。这些发现表明，在前体溶解期间，前体特异性脱水或溶液形态可能是影响勃姆石成核和生长的分子水平细节的重要转变方面。