The effect of sintering temperature(150-900 degrees C)on the photocatalytic activities of ferric oxide and silica-supported ferric oxide for Orange II degradation in water has been examined under UV light irradiation in the absence and presence of H2O2. The solids are characterized by X-ray powder diffraction, nitrogen adsorption, UV/vis diffuse reflectance spectroscopy, FTIR, and Raman spectroscopy. It was observed that the amount of dye adsorbed and the rate of dye photodegradation oil these catalysts were a function of sintering temperature and the suspension pH. Evidence appears to correlate with the crystallinity, particle size, and flat-band potential of hematite, in agreement with the model of semiconductor photocatalysis. The recycling experiment showed that bare hematite was relatively stable, whereas silica-supported ferric oxide experienced a progressive degradation, due to preferential deposition of the dissolved ferric species onto silica, possibly with formation of amorphous and low photoactive ferric (hydr)oxide.