Hayashi Hisashi, Aoki Saya, Suzuki Tomoko
Department of Chemical and Biological Sciences, Faculty of Science, Japan Women's University 2-8-1 Mejirodai, Bunkyo-ku Tokyo 112-8681 Japan
RSC Adv. 2019 Nov 7;9(62):36240-36247. doi: 10.1039/c9ra07960b. eCollection 2019 Nov 4.
Precipitation patterns spontaneously formed by Mn-Fe-based Prussian blue analogues (Mn-Fe PBAs) in agarose gel were investigated over wide concentration ranges for the outer (0.10 ≤ [Mn] ≤ 0.70 M) and inner electrolytes (0.01 ≤ [[Fe(CN)]] ≤ 0.35 M). The precipitation patterns were classified into five types: continuous in the inner electrolyte gel, continuous in the outer electrolyte gel, a very short band close to the gel boundary, periodic bands in the inner electrolyte gel, and filament-like patterns in the inner electrolyte gel. The concentrations found to be suitable for applications as pulsatile Cs adsorbent delivery materials, for which the periodic patterns were most distinct and frequently occurring, were [Mn] ≈ 0.55 M and [[Fe(CN)]] ≈ 0.10 M. The filament-like pattern, reported here for the first time, was generated near the cylindrical gel surface in a local, stochastic, and two-dimensional manner. Scanning electron microscopy (SEM) images of the periodic band patterns indicate that the Mn-Fe PBA precipitates in periodic patterns consist of cubic crystallites (3-10 μm, each side), suggesting significant contributions from Ostwald ripening to the precipitation process. In contrast, precipitates in the filament-like pattern consist of relatively smaller cubic crystallites (≲1 μm, each side), implying an important role of rapid nucleation in the formation of this structure. SEM observations also suggest that, overall, agarose gels support crystallite ripening more effectively, and hence also better suppress the formation of definite periodic bands, than water-glass gels. These findings provide useful information for future applications of self-assembled Mn-Fe PBA patterns in gels.
研究了基于锰铁的普鲁士蓝类似物（Mn-Fe PBAs）在琼脂糖凝胶中在较宽浓度范围内（外部电解质0.10≤[Mn]≤0.70 M，内部电解质0.01≤[[Fe(CN)]]≤0.35 M）自发形成的沉淀模式。沉淀模式分为五种类型：内部电解质凝胶中连续、外部电解质凝胶中连续、靠近凝胶边界的非常短的条带、内部电解质凝胶中的周期性条带以及内部电解质凝胶中的丝状模式。发现适用于作为脉动性铯吸附剂递送材料的浓度，即周期性模式最明显且频繁出现的浓度为[Mn]≈0.55 M和[[Fe(CN)]]≈0.10 M。此处首次报道的丝状模式是以局部、随机和二维方式在圆柱形凝胶表面附近产生的。周期性条带模式的扫描电子显微镜（SEM）图像表明，以周期性模式沉淀的Mn-Fe PBA由立方微晶（每边长3 - 10μm）组成，这表明奥斯特瓦尔德熟化对沉淀过程有显著贡献。相比之下，丝状模式中的沉淀物由相对较小的立方微晶（每边长≲1μm）组成，这意味着快速成核在这种结构形成中起重要作用。SEM观察还表明，总体而言，琼脂糖凝胶比水玻璃凝胶更有效地支持微晶熟化，因此也能更好地抑制确定的周期性条带的形成。这些发现为凝胶中自组装Mn-Fe PBA模式的未来应用提供了有用信息。
