A structural study of haematite samples prepared from sulfated goethite precursors: the generation of axial mesoporous voids

A study of the reflection width anisotropy evident in powder X-ray diffract ion patterns of haematite prepared from sulfated goethite precursors calcin ed at low temperatures has been made. HRTEM has shown that the sulfation pr ocedure is responsible for the generation of mesoporous voidage regions whi ch run axially along acicular alpha-Fe2O3 crystals, producing the effects o bserved in X-ray diffraction. Energy dispersive X-ray elemental mapping has demonstrated the association of such voidage regions with sulfur. Sulfatio n also inhibits sintering of the haematite crystallites and is associated w ith an increase in local disorder as evidenced by Mossbauer spectroscopic s tudies. At higher calcination temperatures the reflection width anisotropy, acicular morphology and porosity is lost. This study indicates that sulfat ion of goethite may prove a successful and simple route to the synthesis of nanoporous haematite.