Competitive ligand exchange on akaganéite surfaces enriches bulk chloride loadings

Akaganéite (β-FeOOH) is a nanosized iron oxyhydroxide mineral with a hollandite structure containing chloride ions in 0.4 × 0.4 nm wide channels. Proton and chloride co-sorption into these channels induces variations in bulk O-H stretching vibrations, crystallographic lattice size, and thermal stability, as a result of hydrogen bond formation with chloride ions. In this work, we show that chloride ions bound to akaganéite surfaces can be dislodged into aqueous solutions by competitive adsorption of foreign ions and then transferred alongside co-sorbed protons into the akaganéite bulk. Fourier transform infrared and X-ray photoelectron spectroscopic measurements show that HClO(4), H(2)SO(4), and benzoic acid, and thereby, many other anions of various charge-to-size ratios can all effectively contribute to this phenomenon. This linked surface-bulk reactivity should be accounted for in mixed anion systems containing akaganéite-like materials.