Anatase titania activated by Cu(II) or Zn(II) nanoparticles for the photooxidation of methanol assisted by Rhodamine-B

Abstract

This paper deals with the photocatalytic reactivity of anatase titania particles, modified by surface deposition of Cu2+ and Zn2+ oxide/hydroxide nanoparticles which are detected by EDS and FX techniques. The objective of the preparation steps was chosen to avoid the formation of larges Cu and Zn oxide particles, which could be identified by XRD and other techniques. Their activity for methanol photocatalytic oxidation in water was studied and Rhodamine-B was added as photo-sensibilizer. To obtain a-TiO2 support, a thermal activation of commercial Millennium-PC500 nanosized powder was achieved. 3Cu/a-TiO2 and 3Zn/a-TiO2 catalysts (3 wt% of Cu or Zn) were prepared under simple, easy and reproducible experimental conditions, namely by impregnation with nitrate salts. Catalysts and titania support were characterized by: X-rays diffraction, fluorescence spectroscopy, FEG-SEM equipped with EDS accessory, N2-sorption and UV–Vis Diffuse Reflectance spectroscopy. Only crystalline anatase TiO2was identified by XRD and large Cu and Zn oxide/hydroxide nanoparticles were easily evidenced by EDS and other techniques. Electronic band-gap was measured by UV–Vis spectroscopy using Kubelka-Munkand Tauc's methods, results varied in the order: 3Cu/a-TiO2<a-TiO2 <3Zn/a-TiO2; also, the presence of reduced Ti3+cations have been demonstrated by this technique. Two photo-activated reactions take place in parallel, on the one hand the photooxidation of methanol with titania holes, on the other hand photo-generated electrons are formed in the titania conduction band. They can react rapidly with diluted oxygen to generate superoxide radicals or with RhB molecules to generate RhB° radicals. RhB molecules are mainly mono-deethylated. After 150 min of reaction, RhB was 98% degraded with 3Cu/a-TiO2 best catalyst.