Enhanced photocatalytic reduction of 4‐nitrophenol over Ir/CeO2 photocatalysts under UV irradiation

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/CeO2) photocatalysts with different Ir contents (0.5, 1.0 and 2.0 wt%) were studied in the photoreduction of 4‐NP using Na2SO3 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 CeO2 by impregnation of Ir causes a decrease in CeO2 textural properties and its band gap energy. The photocatalytic reduction of 4‐nitrophenol was enhanced by 26.1% using Ir/CeO2 1.0 wt% in comparison with CeO2 support. The phrase is related with the comparison between the photocatalytic behavior of Ir/CeO2 1.0 wt% photocatalyst in regard the results evidenced with CeO2 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/CeO2, whereas for higher metal loading (2.0 wt%) 4‐NP reduction decreased by 72%. CONCLUSION The enhancement in the photocatalytic behavior of the Ir/CeO2 series could be related to the presence of Irδ+ and Ir0 species evidenced by X‐ray photoelectron spectroscopy (XPS), thus, Irδ+ species could favor the adsorption of the pollutant and Ir0 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/CeO2 was used as photocatalyst could be associated with partial blockage of the surface active sites by increasing amounts of metal.