Cooperative effect of pH value and anions on single-crystalline hexagonal and circular α-Fe2O3 nanorings

Ring-like materials have attracted intense research interests because of their intriguing structural features and promising applications. In this work, we report an effective solvothermal method to prepare single-crystalline α-Fe2O3 nanorings with different morphologies without using any templates. Hexagonal nanorings and circular nanorings have been obtained just by varying the pH of initial solution with HCl or NaOH. On the basis of a series of experiments and characterizations, the growth mechanism of these kinds of nanorings is explained by the influence of the pH values and different anionic ligands. Here the cooperative action of the VO43− and SO42−, involving adsorption and coordination, is a crucial factor in bringing about the formation of the ring-like structures.