Review of the structural properties and interfacial reactions of Al-substituted goethite, hematite and ferrihydrite

Isomorphic substitution of ferric ion (Fe³⁺) by aluminum ion (Al³⁺) in iron (hydro)oxides is ubiquitous in natural environments. Aluminum substitution inevitably leads to changes in the microstructures, physicochemical properties, and surface reactions of iron (hydro)oxides, which may have great impacts on the sequestration of nutrients and contaminants in soils and aquatic environments. Over the past decades, the structural properties and surface reactivity of Al-substituted iron (hydro)oxides have been intensively studied. Iron (hydro)oxides in various structural forms and with different Al substitution amounts present high application potentials in addressing environmental issues. A timely summary of the structural properties and interfacial reactions of the most common and representative Al-substituted iron (hydro)oxides is of significance. Herein, the effects of Al substitution on the structural properties and surface activities of iron (hydro)oxides were clarified according to the microstructure, crystal facets, surface site type and density, interfacial reaction mechanisms, and modeling parameters of iron (hydro)oxides. This review systematically elucidates how Al substitution affects the structural properties and surface reactions of iron (hydro)oxides, including the well crystallized goethite and hematite and the poorly crystallized ferrihydrite, providing theoretical guidance for further exploration of the mineralogical characteristics and environmental geochemical behaviors of iron (hydro)oxides.