The first examples of a new mesoporous form of crystalline beta-FeOOH (akaganeite) were prepared by the surfactant-assisted method of nanoparticle assembly using FeCl3 as the precursor and a surfactant of either cationic cetylpyridinium or anionic dodecylsulfonate or nonionic Brij 56 as a hierarchical structure mediator. TEM images indicated the presence of a scaffold-like structure formed through the aggregation and intergrowth of rod-like akaganeite nanoparticles. The synthesized mesoporous akaganeite has a unimodal and very narrow pore size distribution with high surface area, which can be converted to mesostructured alpha-Fe2O3 (hematite) after degassing at 300degreesC. Bimodal pore size distributions could be obtained by increasing the synthetic temperature from 40 to 80degreesC. Mesoporous iron oxides with bicrystalline structure of akaganeite and hydronium jarosite were prepared when using dodecylsulfonate surfactant at 80degreesC. The surfactants were believed to play an important role in the formation of the hierarchical scaffold-like mesostructure. (C) 2004 Elsevier B.V. All rights reserved.