Photocatalytic water splitting over CeO2/Fe2O3/Ver photocatalysts

Abstract

The study is focused on the photocatalytic ability of nanocrystalline oxides Fe2O3 and CeO2 (marked as Fe and Ce) and their 8:2, 5:5 and 2:8 M ratio mixtures (marked as Fe8Ce2, Fe5Ce5 and Fe2Ce8) for the hydrogen production via water splitting. The photocatalysts were prepared using a precipitation procedure both in a "standalone" powder form and in form of the Fe2O3/CeO2 nanoparticles precipitated on vermiculite (Ver). The phase composition and the specific surface area of the samples, the size and morphology of nanocrystallites of individual phases, and the optical and electronic properties of the photocatalysts were characterized in detail by Xray powder diffraction, nitrogen physisorption, transmission electron microscopy, diffuse reflectance UV-Vis spectroscopy and work function measurements. Photocatalytic water splitting over the photocatalysts was performed during 8 h in annular batch photoreactor illuminated with 8 W Hg lamp (lambda = 254 nm). The most active photocatalysts were Fe8Ce2 both in "stand-alone" powder form and in form of the photocatalyst attached on vermiculite. The photocatalytic generation of hydrogen in the presence of the Fe2O3/CeO2 photocatalysts is controlled by the intrinsic photocatalytic properties of the oxides and by the specific surface of the composite. It is enhanced, when heterojunctions between Fe2O3 and CeO2 form. The work function measurements confirmed the formation of heterojunction Type I with bent bands, which effectively inhibits the recombination of photogenerated charge carriers. In addition, it was confirmed that the anchoring of the photocatalyst on vermiculite does not significantly degrade the photocatalytic activity of the composite. In contrast, even if the amount of the photocatalytically active component was three-times smaller as compared with the photocatalysts without vermiculite, just a slight decrease of the photocatalytic activity was observed.