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BACKGROUND: Photoreduction of 4-nitrophenol (4-NP) photocatalytically to 4-aminophenol (4-AP) is considered a promising treatment of this recalcitrant pollutant. 4-aminophenol is widely applied as an intermediate in the pharmaceutical and agricultural industries. In this work, iridium/cerium dioxide (Ir/CeO 2 ) photocatalysts with different Ir contents (0.5, 1.0 and 2.0 wt%) were studied in the photoreduction of 4-NP using Na 2 SO 3 as hole scavengers under UV irradiation. In order to identify their physicochemical properties, the materials were studied by several techniques and photoactivity was monitored by UV-visible spectroscopy. RESULTS:The characterization results provided evidence that the modification of CeO 2 by impregnation of Ir causes a decrease in CeO 2 textural properties and its band gap energy. The photocatalytic reduction of 4-nitrophenol was enhanced by 26.1% using Ir/CeO 2 1.0 wt% in comparison with CeO 2 support. The phrase is related with the comparison between the photocatalytic behavior of Ir/CeO 2 1.0 wt% photocatalyst in regard the results evidenced with CeO 2 unmodified. An effect of the metal loading over photoactivity was observed and the optimal Ir content was 1.0 wt%. A reduction of 84% was obtained using 1.0 wt%Ir/CeO 2 , whereas for higher metal loading (2.0 wt%) 4-NP reduction decreased by 72%. CONCLUSION:The enhancement in the photocatalytic behavior of the Ir/CeO 2 series could be related to the presence of Ir + and Ir 0 species evidenced by X-ray photoelectron spectroscopy (XPS), thus, Ir + species could favor the adsorption of the pollutant and Ir 0 particles could act as trap of the photogenerated electrons that are responsible for reduction of the nitrocompound. The decrease in photoactivity when 2.0 wt% Ir/CeO 2 was used as photocatalyst could be associated with partial blockage of the surface active sites by increasing amounts of metal.

In this study, commercial and lab-prepared TiO2 were modified by fluorination and platinum photodeposition; and the effect of these modifications over the physicochemical and photocatalytic properties of TiO2 was evaluated. It was found that F and Pt addition leads to the modification of the optical and textural properties of TiO2. The materials prepared were tested in the photocatalytic degradation of different organic dyestuffs such as methylene blue (MB) and methyl orange (MO); the degradation of commercial anilines employed in the staining of natural fibers was also evaluated. Photocatalysis was also studied in this work as an eco-friendly treatment of wastewater coming from handicrafts factories. In general it was observed that the effectiveness of the photocatalytic treatment strongly depends on the substrate to be degraded, thus, fluorinated and platinized commercial Titania (Pt-F-P25) showed the best photocatalytic performance in the MB and MO photodegradation and in contrast, in the case of the anilines the highest degradation was obtained over commercial TiO2 fluorinated (F-P25). These results can be explained by differences observed in the structure and in the adsorption of these dyestuffs over the photocatalysts surfaces. F-P25 photocatalyst also demonstrated to be the best material for the treatment of real wastewater coming from handicrafts factories.