BET Sample Pretreatment of Synthetic Ferrihydrite and its Influence on the Determination of Surface Area and Porosity

Ferrihydrite is a poorly-ordered iron oxyhydroxide which possesses a high specific surface area (>200 m(2)/g). This makes it an important constituent for surface related processes in nature and catalysis. This study focuses on the precautions that have to be taken in the sample preparation prior to BET measurements in order to avoid essential structural transformations. The experiments showed that temperatures between 90 and 120 degrees C are necessary to remove surface contaminations and simultaneously prevent structural transformation of the ferrihydrite during the outgassing procedure. Furthermore, care has to be taken to keep the humidity low in the immediate proximity of the sample, due to the strong impact of this parameter on the structural stability of ferrihydrite.