Control of bandgap of iron oxide through its encapsulation into SiO2-basedmesoporous materials

Nanoparticles of iron oxide were encapsulated into the pores of Si-MCM-41 a nd porous vycor glass (PVG) with pore diameters 2.1-4.5 nm. Transmission el ectron micrographs (TEM) observation has revealed the formation of iron oxi de particles in the pores after an adequate preparation including a suspens ion treatment in water. Ultraviolet-visible absorption spectra (UV-VIS) of iron oxide loaded on the respective supports were greatly changed with the pore diameters. The bandgaps of iron oxide, evaluated from the absorption e dges of the UV-VIS spectra, were significantly widened with decrease in the pore diameters. The dependence of the bandgap on the pore diameter could w ell be explained by the Brus' equation when the effective mass of an electr on and a hole in iron oxide was assumed to be 0.27. It follows that the ban dgap was changed by the quantum size effect and could be controlled by the pore size of support. (C) 2000 Elsevier Science B.V. All rights reserved.