Proceedings of the 4 th International Conference on Nanostructures (ICNS4) 12-14 March, 2012, Kish Island, I.R. Iran The effect of different Fe 2 O 3 /ZnO nanocomposites on optical properties Azam Anaraki Firooz a, *, Rasol Abdullah Mirzaie a , Firouzeh Kamrani a , Abbas Ali Khodadadi b a Dep. of chemistry –Faculty of science – Shahid Rajaee Teacher Training University- P.O.Box 167855-163 Tehran – Iran, Tel.: +98 2122970060 (2347), Fax: +98 2122970011 b School of Chemical Engineering, University of Tehran, P.O.Box 11155-4563 Tehran, Iran *azam_a_f@yahoo.com Abstract: Different Fe 2 O 3 /ZnO nanocomposites were prepared by a simple solid-state reaction method, using zinc acetate, α-Fe 2 O 3 and sodium hydroxide at room temperature. The characterization results showed that the morphology, crystallite size, BET surface area and optical absorption of the samples varied significantly with the Fe +3 to Zn +2 ratios. The nanocomposites show two absorption edges at ultraviolet and visible region. The optical band gap values of these nanocomposites were calculated to be about 3.98-3.81eV and 2.75-2.98eV, which show a red shift from that of pure ZnO. These red shifts are related to the formation of Fe s-levels below the conductive band edge of ZnO and effectively extend the absorption edge into the visible region. The growth mechanisms of the samples are proposed. Keywords: Fe 2 O 3 /ZnO; optical properties; PL. Introduction In recent years, metal oxide semiconductor materials have been developed due to their photocatalytic ability in the degradation of various environmental pollutants under UV-light irradiation [1-3]. Among various oxide semiconductor photocatalysts, ZnO has been paid much attention in the degradation and complete mineralization of environmental pollutants because of its high photosensitivity and wide band gap [4]. Many efforts were concentrated on the modification of ZnO-based visible-light photocatalysts such as ZnO by doping with an appropriate element or coupling with metal oxide [5]. These coupled semiconductor photocatalysts not only increase the photocatalytic efficiency by increasing the charge separation, but also modified the optical and physical properties due to the quantum confinement effects. Experimental Fe 2 O 3 /ZnO nanocomposites were prepared by a simple solid-state reaction method, using zinc acetate, α-Fe 2 O 3 and sodium hydroxide at room temperature. The Fe 2 O 3 /ZnO photocatalysts with the Fe +3 /Zn +2 molar ratios of 0, 0.5/100, 1/100, 5/100 and 10/100 were labeled by Z, ZF0.5, ZF1, ZF5 and ZF10, respectively. Results and Discussion Figure 1a–e shows the XRD pattern of pure ZnO and Fe 2 O 3 /ZnO nanocomposites prepared by the solid- state reaction. Major ZnO hexagonal wurtzite structure (JCPDS 36-1451) is observed in all XRD patterns. The marked peaks are attributed to formation of α-Fe 2 O 3 phase (JCPDS No 33-0664). The absorption of UV–Vis light is an important factor in evolution of photocatalyst property. Figure 3 shows the comparison of UV–Vis absorption spectra of pure ZnO and Fe 2 O 3 /ZnO nanocomposites at room temperature. The wavelengths of absorption edges are determined by extrapolating the horizontal and sharply rising portions of the curve and defining the edge as the wavelength of the intersection. The band gap energies can be estimated on the basis of the corresponding absorption edges according to Eq. (1). E bg (eV) =1240/λ (1) Where, E bg is the photocatalyst band-gap energy in eV and λ is the wavelength in nanometer. The band gap values of Fe 2 O 3 /ZnO photocatalysts are smaller than that of ZnO and decrease with increasing the concentration of α-Fe 2 O 3 . Z and ZF0.5 samples show one-edge absorption at 310 and 315 nm, respectively, which was blue -shifted from the band gap of bulk ZnO (3.2eV), due to size decrease of the particles and reaching to the quantum confinement limit of nanoparticles. The other samples show two- edge absorption. Figure 2 shows that the absorptions at lower wavelengths can be ascribed to ZnO. The absorptions at higher wavelength (visible range) are attributed to the α-Fe 2 O 3 . It is known that the band gap energy of bulk Fe 2 O 3 is 2.2eV and can be activated by the light below 563 nm. With increasing the concentration of α-Fe 2 O 3 , the intensity of this peak increases. The red-shift in the optical absorption can be explained in terms of the ionic bond strength between metal ions and oxygen ions. The electro-negativity values of Zn, Fe and O are 1.6, 1.8, and 3.4 respectively. Thus, the order of ionic nature is ZnO > Fe 2 O 3 . Hence, the difference in 203