Catalytic combustion of Orange II on hematite: Surface species responsible for the dye degradation

The low temperature adsorption and subsequent catalytic combustion of the azo-dye Orange II on hematite suggests a novel use of iron oxide as an inexpensive catalytic ecomaterial. Orange II was adsorbed on hematite and the products of the catalytic oxidation in air atmosphere were analyzed. The Ea for the desorption of CO2 and other PAHs from the hematite surface was determined at 9.9 Kcal/mol. By temperature programmed GC-MS analysis, the gaseous products of Orange II adsorbed on hematite were observed to be different and with a simpler structure than when the dye was combusted in the absence of hematite at the same temperatures. The catalytic oxidation of the dye on hematite was able to be sustained in a cyclic repetitive fashion. XPS analysis of the hematite surface did not vary practically during dye oxidation revealing the stable nature of the iron oxide during this process. Electron microscopy gives evidence for a low degree of particle aggregation at the working temperature. A higher degree of hematite crystallization was observed with increasing temperature. This observation was confirmed by X-ray analysis. The modeling of the Orange II species in solution and the surface hematite surface were carried according to the two-layer diffuse model (Diffuse/GTL) fitting the experimental data within 5%. The considerations used during this calculation allowed to calculate the electrostatic interaction of the oxide and the dye as function of the solution pH.