Surfactant mediated nanoparticle assembly of catalytic mesoporous crystalline iron oxide materials

The first examples of a new mesoporous form of crystalline β-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 α-Fe₂O₃ (hematite) after degassing at 300°C. Bimodal pore size distributions could be obtained by increasing the synthetic temperature from 40 to 80°C. Mesoporous iron oxides with bicrystalline structure of akaganeite and hydronium jarosite were prepared when using dodecylsulfonate surfactant at 80°C. The surfactants were believed to play an important role in the formation of the hierarchical scaffold-like mesostructure.