The role of surface hydrolysis of ferricyanide anions in crystal growth of snowflake-shaped α-Fe2O3.

Zhong Liu,Chang-Yang Chiang,Wuzong Zhou,Wu Li

doi:10.1039/c5cc02011e

Abstract

Selective adsorption and surface hydrolysis of [Fe(CN)6](3-) anions on α-Fe2O3 crystals was found to be a crucial process in the formation of a snowflake-like morphology, and the established mechanism is complementary to the classical theories of crystal growth.

Highlights

Selective adsorption and surface hydrolysis of [Fe(CN)6]3À anions on a-Fe2O3 crystals was found to be a crucial process in the formation of a snowflake-like morphology, and the established mechanism is complementary to the classical theories of crystal growth
Another theory gives a thermodynamic approach: the equilibrium shape of a free crystal is the shape that minimizes its surface free energy. Both of these classical theories deal with the bonding energy of crystal structures without considering external effects, and cannot explain the formation mechanisms of many unusual crystal morphologies, e.g. polyhedra of polycrystalline particles of calcite and MOFs,[1] complicated snowflake-shaped hematite (a-Fe2O3).[2]
The constructed hyperbranched microstructure of the particle looks quite complicated, the corresponding selected area electron diffraction (SAED) pattern (Fig. 1b) indicates that the whole particle can be regarded as a single crystal, and the viewing direction perpendicular to the face of the ‘snowflake’ is along the [0001] zone axis of a-Fe2O3

Summary

Introduction

Selective adsorption and surface hydrolysis of [Fe(CN)6]3À anions on a-Fe2O3 crystals was found to be a crucial process in the formation of a snowflake-like morphology, and the established mechanism is complementary to the classical theories of crystal growth. Both of these classical theories deal with the bonding energy of crystal structures without considering external effects, and cannot explain the formation mechanisms of many unusual crystal morphologies, e.g. polyhedra of polycrystalline particles of calcite and MOFs,[1] complicated snowflake-shaped hematite (a-Fe2O3).[2] The anisotropy of the crystal structure of hematite cannot justify the only active crystal growth directions of six equivalent zone axes, parallel to the (ab) plane of the hexagonal unit cell.

Results

Conclusion