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首页> 外文期刊>Chemistry: A European journal >Growth behavior and kinetics of self-assembled silica-carbonate biomorphs
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Growth behavior and kinetics of self-assembled silica-carbonate biomorphs

机译：自组装碳酸硅酸盐生物形态的生长行为和动力学

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Upon slow crystallization from silica-containing solutions or gels at elevated pH, alkaline-earth carbonates spontaneously self-assemble into remarkable nanocrystalline ultrastructures. These so-called silica biomorphs exhibit curved morphologies beyond crystallographic symmetry and ordered textures reminiscent of the hierarchical design found in many biominerals. The formation of these fascinating materials is thought to be driven by a dynamic coupling of the components' speciations in solution, which causes concerted autocatalytic mineralization of silica-stabilized nanocrystals over hours. In the present work, we have studied the precipitation kinetics of this unique system by determining growth rates of individual aggregates using video microscopy, and correlated the results with time-dependent data on the concentration of metal ions and pH acquired online during crystallization. In this manner, insight to the evolution of chemical conditions during growth was gained. It is shown that crystallization proceeds linearly with time and is essentially reaction controlled, which fits well in the proposed morphogenetic scenario, and thus, indirectly supports it. Measurements of the silica concentration in solution, combined with analyses of crystal aggregates isolated at distinct stages of morphogenesis, further demonstrate that the fraction of silica coprecipitated with carbonate during active growth is rather small. We discuss our findings with respect to the role of silica in the formation of biomorphs, and moreover, prove that the external silica skins that occasionally sheath the aggregates-previously supposed to be involved in the growth mechanism- originate from secondary precipitation after growth is already terminated. Even spread: Precipitation of barium carbonate in silica-rich media at high pH yields hierarchically structured polycrystalline materials, termed silica-carbonate biomorphs, which exhibit complex curved shapes. Determination of microscopic growth rates and reagent concentration profiles (see figure) helped to elucidate the chemistry underlying the formation of these materials and provided insight into growth kinetics and morphogenetic aspects.
机译：在pH升高的情况下，从含二氧化硅的溶液或凝胶中缓慢结晶后，碱土金属碳酸盐会自发自组装成显着的纳米晶体超结构。这些所谓的二氧化硅生物形态表现出超出晶体学对称性的弯曲形态，并且有序的纹理使人联想到许多生物矿物中发现的分级设计。这些引人入胜的材料的形成被认为是由溶液中组分形态的动态耦合驱动的，这导致二氧化硅稳定的纳米晶体在数小时内发生一致的自催化矿化作用。在目前的工作中，我们通过使用视频显微镜确定单个聚集体的生长速率，研究了该独特系统的沉淀动力学，并将结果与​​时间相关的数据关联，这些数据与时间有关，在结晶过程中在线获取金属离子的浓度和pH值。以这种方式，获得了对生长期间化学条件演变的见解。结果表明，结晶随时间线性增长，并且基本上受反应控制，这非常适合所提出的形态发生场景，因此间接支持了结晶。溶液中二氧化硅浓度的测量，结合在形态发生不同阶段分离出的晶体聚集体的分析，进一步表明，在活性生长过程中与碳酸盐共沉淀的二氧化硅比例很小。我们讨论了关于二氧化硅在生物形态形成中的作用的发现，此外，证明了偶尔包裹着聚集体的外部二氧化硅表皮（以前被认为与生长机制有关）源自生长后的二次沉淀。终止。均匀扩散：碳酸钡在高pH值的富二氧化硅介质中的沉淀会产生分级结构的多晶材料，称​​为二氧化硅-碳酸酯生物形态，呈现复杂的弯曲形状。微观生长速率和试剂浓度曲线的确定（见图）有助于阐明这些物质形成的化学基础，并有助于洞悉生长动力学和形态发生方面。

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