Reverse Micelle Strategy for Effective Substitutional Fe-Doping in Small-Sized Ceo2 Nanocrystals: Assessment of Adsorption and Photodegradation Efficiency of Ibuprofen Under Visible Light

Abstract

Behind the beneficial effect of iron doping in ceria photocatalysts there is a complex interplay of several parameters, mostly arising from the amount of iron content related to its effective inclusion and distribution in the ceria lattice and the type of doping sites. These factors play a crucial role in determining both the adsorption of a specific molecule and the related photodegradation efficiency when used as a photocatalyst. Reverse micelle nanoreactors were successfully designed to synthesize small-sized ceria nanocrystals (3.5-4.2 nm) with a sizeable amount of substitutional iron. Undoped and doped CeO2 catalysts with an iron content (0.50-10 mol %) compliant with the nominal value were prepared and tested for the first time for the removal of ibuprofen both in the dark and under UV or visible light irradiation.The experimental evidence was verified and supported by in-depth physicochemical characterization and density functional theory calculations, and the results are critically discussed. Although the preferential adsorption sites for ibuprofen are identified in the surface substitutional iron and oxygen vacancies, adsorption capacity does not monotonically increase with iron content, revealing contrasting roles of surface characteristics. Substitutional iron is responsible for the decrease in band gap and causes an increase in Ce3+ content and relative defects with a maximum content at 2.5 mol % Fe (Fe2.5). Indeed, catalytic experiments have identified a trade-off between adsorption and photodegradation, finding that Fe2.5 is the most performing catalyst for ibuprofen removal under visible light irradiation. The best catalyst was tested through reuse experiments that proved its stability over 4 cycles. Finally, an attempt was made to identify the photodegradation by-products, allowing the detection of 4-(2-methylpropyl)benzene as the main by-product.

Keywords: Substitutional Fe doped CeO2, Reverse micelle, Ibuprofen, photodegradation, DFT, adsorption