Growth Mechanism of Dendritic Hematite via Hydrolysis of Ferricyanide
Growth Mechanism of Dendritic Hematite via Hydrolysis of Ferricyanide
复制标题
DOI：
10.1021/acs.cgd.6b01655
复制
发表时间：
2017-02-01
影响因子：
3.8
通讯作者：
Zhou, Wuzong
中科院分区：
文献类型：
--
作者：
Green, Alice E.;Chiang, Chang-Yang;Zhou, Wuzong
研究了铁氰化物水解成具有雪花状、羽毛状和叶状形态的树枝状α-Fe2O3（赤铁矿）晶体的详细过程。人们发现[Fe(CN)(6)](3-)阴离子在早期聚合成大的、无序的软物质聚集体。通过进一步水解，赤铁矿晶体的成核发生在这些聚集体的表面附近。当晶体生长到一定尺寸后，开始出现分支。当铁氰化物浓度较低（即2 mM至3.8 mM）时，优先沿六个等效（11（2）超过bar0）方向生长，形成扁平雪花状形状，而高浓度（即9 mM至500 mIvI）铁氰化物导致沿（10（1）超过bar1）区轴选择性方向生长，形成羽毛状或叶状形态。人们发现α-Fe2O3晶体上[Fe(CN)(6)](3-)阴离子的高选择性吸附和表面水解是这些新形貌形成的关键过程。结果发现，铁氰化物的聚合导致pH值降低，而Fe2O3的形成则导致pH值升高。分支开始生长时溶液的 pH 值会显着影响路易斯酸性位点在不同表面上的分布，从而改变生长方向。新建立的机制是对经典晶体生长理论的补充。
The detailed process of the hydrolysis of ferricyanide into dendritic alpha-Fe2O3 (hematite) crystals with snowflake-like, feather-like, and leaf-like morphologies has been investigated. [Fe(CN)(6)](3-) anions were found to polymerize into large, disordered soft matter aggregates at an early stage. The nucleation of hematite crystals took place near the surface of these aggregates via further hydrolysis. After the crystals grew to a certain size, branches started to appear. When the concentration of ferricyanide was low (i.e. 2 mM to 3.8 mM), growth was preferentially along the six equivalent (11 (2) over bar0) directions, resulting in a flat snowflake-like shape, while high concentrations (i.e. 9 mM to 500 mIvI) of ferricyanide led to the growth of selective directions along the (10 (1) over bar1) zone axes, forming a feather-like or leaf-like morphology. Highly selective adsorption and surface hydrolysis of [Fe(CN)(6)](3-) anions on alpha-Fe2O3 crystals was found to be a crucial process in the formation of these novel morphologies. It was found that the polymerization of ferricyanide led to a reduction of pH value and that the formation of Fe2O3 increased the pH value. The pH value of the solution at the point when the branches start to grow can significantly affect the distribution of Lewis acidic sites on different surfaces and, therefore, change the growth direction. The newly established mechanism is complementary to the classical theories of crystal growth.