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

Nanoparticles of iron oxide were encapsulated into the pores of Si-MCM-41 and porous vycor glass (PVG) with pore diameters 2.1-4.5 nm. Transmission electron micrographs (TEM) observation has revealed the formation of iron oxide particles in the pores after an adequate preparation including a suspension 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 edges of the UV-VIS spectra, were significantly widened with decrease in the pore diameters. The dependence of the bandgap on the pore diameter could well be explained by the Brus' equation when the effective mass of an electron and a hole in iron oxide was assumed to be 0.27. It follows that the bandgap 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.