Optical band gap modification of Ce/ZnO for visible light photocatalytic H2 production from aqueous methanol solution

Abstract

Ce (0.5, 1, 2 and 3 mol%) incorporated ZnO crystallites along with bare ZnO were prepared by solution free mechanochemical method and characterized with powder XRD, HR-TEM, SEM, EDX, XPS, UV–visible and Photoluminescence (PL) spectra. The visible light photocatalytic performance of these materials was investigated for H2 evolution with the aqueous 10 vol% methanol solution under one sun conditions using solar simulator. X-ray diffraction data suggests the hexagonal wurtzite structure for Ce incorporated ZnO crystallites and due to incorporation of Ce4+ ion there is expansion in the lattice constants of ZnO, which is attributed to decreases in crystallite size. UV–visible spectra propose the decrease in optical band gap of Ce incorporated ZnO with the increase of Ce content up to 3 mol%. The XPS analysis supports the incorporation of Ce4+ in Ce/ZnO. The PL spectra suggest that, with the insertion of Ce ions into ZnO, intensity of green emission band increases, which reflects the low recombination rate of photogenerated charge carriers which is responsible for higher photocatalytic H2 production. Extent of hydrogen production is affected by calcination temperature of Ce/ZnO. 2 mol% Ce incorporated ZnO calcined at 600 °C produces 43μmolh−1g−1 of hydrogen.