Crystallization of Mixed Alkaline-Earth Carbonates in Silica Solutions at High pH
Crystallization of Mixed Alkaline-Earth Carbonates in Silica Solutions at High pH
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DOI：
10.1021/cg5004116
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发表时间：
2014-12-01
影响因子：
3.8
通讯作者：
Kellermeier, Matthias
中科院分区：
文献类型：
--
作者：
Eiblmeier, Josef;Dankesreiter, Stephan;Kellermeier, Matthias
二氧化硅影响碱土碳酸盐矿化的能力是在没有任何有机物质的情况下形成仿生结构的一个突出例子。在合适的条件下，二氧化硅稳定的碳酸盐纳米晶体可以自发地自组装成具有复杂形貌的分级材料，通常被称为二氧化硅生物形态。然而，这些晶体聚集体的生长主要限于碱土系列中的高级同系物，即，SrCO 3和BaCO 3，而更相关的碳酸钙的相应结构相当难以实现。为了系统地解决这个问题，我们在高pH值下，在二氧化硅的存在下，使用钡和氯化锶溶液，其中含有增加的摩尔分数的Ca 2+结晶的金属碳酸盐。对所得材料的组成、结构和晶体学进行了分析。所获得的数据表明，生长过程已经受到少量钙的强烈影响。事实上，通常观察到的SrCO 3和BaCO 3的形态仍然不存在高于一定阈值的添加的Ca 2+。相反，球状和半球形结构的生成，由于分形分支的碳酸盐晶体作为一个后果，中毒的二氧化硅。生长行为的这些改变归因于硬钙离子与溶液中的硅酸盐物种的相对较强的相互作用，使其形态向更高的低聚物转变，甚至诱导部分凝固。这一概念通过在增加的离子强度下的额外实验得到证实。我们的研究结果进一步表明，所观察到的半球形颗粒表现出明显的多态性，与斜方晶系的固溶体（文石型（Sr，Ca）CO 3和（Ba，Ca）CO 3）形成在较低的Ca 2+含量，而Sr 2 +/Ba 2 +-取代方解石占主导地位，在较高的Ca 2+分数。在Ba 2 +/Ca 2+混合物的情况下，此外还有一个中间范围，其中几乎相同的形态被证实是Ba 2+掺杂的球霰石。这些发现扩展了在这些简单系统中可获得的结构和组合物的多样性，并且可以解释以前在标准条件下制备碳酸钙生物形态的尝试中遇到的困难。
The ability of silica to influence the mineralization of alkaline-earth carbonates is an outstanding example for the formation of biomimetic structures in the absence of any organic matter. Under suitable conditions, silica-stabilized carbonate nanocrystals can spontaneously self-assemble into hierarchical materials with complex morphologies, commonly referred to as silica biomorphs. However, growth of these crystal aggregates has largely been restricted to the higher homologues in the alkaline-earth series, i.e., SrCO3 and BaCO3, while corresponding architectures of the much more relevant calcium carbonate are quite difficult to realize. To systematically address this problem, we have crystallized metal carbonates in the presence of silica at high pH, using barium and strontium chloride solutions that contained increasing molar fractions of Ca2+. The resulting materials were analyzed with respect to their composition, structure, and crystallography. The obtained data demonstrate that the growth process is already strongly affected by small amounts of calcium. Indeed, morphologies typically observed for SrCO3 and BaCO3 remained absent above certain thresholds of added Ca2+. Instead, globular and hemispherical structures were generated, owing to fractal branching of carbonate crystals as a consequence of poisoning by silica. These alterations in the growth behavior are ascribed to relatively strong interactions of hard calcium ions with silicate species in solution, shifting their speciation toward higher oligomers and even inducing partial coagulation. This notion is confirmed by additional experiments at increased ionic strength. Our results further demonstrate that the observed hemispherical particles exhibit distinct polymorphism, with orthorhombic solid solutions (aragonite-type (Sr,Ca)CO3 and (Ba,Ca)CO3) being formed at lower Ca2+ contents, whereas Sr2+/Ba2+-substituted calcite prevails at higher Ca2+ fractions. In the case of Ba2+/Ca2+ mixtures, there is moreover an intermediate range where virtually identical morphologies were confirmed to be Ba2+-doped vaterite. These findings extend the variety of structures and compositions accessible in these simple systems, and may explain difficulties previously encountered in attempts to prepare CaCO3 biomorphs at standard conditions.