Photoinduced Formation of Fe(III)-Sulfato Complexes on the Surface of α-Fe2O3 and Their Photochemical Performance

Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) has been used to examine the in situ photochemical formation of sulfate complexes from the adsorption of SO2 on the alpha-Fe2O3 surface. The SO2 adsorption on the oxide surface under irradiation was more pronounced than the adsorption in the dark at 220 K in the presence of O-2, whereas the presence of light did not show as significant of an increase in the amount of adsorption compared to the dark experiment at 297 K. The uptake of SO2 was mainly transformed to bidentate complexes in the presence of oxygen both under the irradiation and in the dark. In contrast, the sulfate complex existed mainly in a monodentate coordination on the oxide surface in the absence of O-2. The surface complexes were not stable and could be involved in interfacial photochemical reactions. These complexes also affected the oxide properties, including optical properties, electrochemistry, and surface wettability. The photochemical mechanism has been discussed in terms of photoassisted charge-transfer reactions associated with the formed surface complexes.