Synthesis and anion exchange of tunnel structure akaganeite

Akaganeite (β-FeOOH) has been prepared by the hydrolysis of FeCl₃ solutions. The effects of microwave heating, pH of the solution, and addition of manganese with different valence states have been studied for the optimization of its synthesis. The nucleation and growth of akaganeite crystallites are accelerated by microwave heating. A low pH favors the crystallization of akaganeite, and a high pH favors the crystallization of hematite. Addition of manganese appears to impede crystallization at low pH but improves it at high pH. The anion exchange of Cl-akaganeite with F^-, Br^-, and OH^- and some properties of different anion-exchanged akaganeites has been investigated. The exchange rate and capacity depend on the nature of the anions. Anion exchange significantly changes the loss of chloride and affects the decomposition of akaganeite upon being heated.