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 diffraction patterns of haematite prepared from sulfated goethite precursors calcined at low temperatures has been made. HRTEM has shown that the sulfation procedure is responsible for the generation of mesoporous voidage regions which run axially along acicular alpha-Fe(2)O(3) crystals, producing the effects observed in X-ray diffraction. Energy dispersive X-ray elemental mapping has demonstrated the association of such voidage regions with sulfur. Sulfation also inhibits sintering of the haematite crystallites and is associated with an increase in local disorder as evidenced by Mossbauer spectroscopic studies. At higher calcination temperatures the reflection width anisotropy, acicular morphology and porosity is lost. This study indicates that sulfation of goethite may prove a successful and simple route to the synthesis of nanoporous haematite.