Open Ceramics (Mar 2023)
Adsorption and photocatalytic degradation of Congo red and malachite green by nanostructured Y2O3 synthesized by the coprecipitation method
Abstract
Yttrium oxide is a wide bandgap semiconductor material, with a bandgap energy (Eg) between 4.86 and 5.68 eV, which may anticipate its limitations in photocatalysis. However, its ability to adsorb water and form hydroxyl radicals (•OH) suggests its possible application in the degradation of organic pollutant compounds. Therefore, Y2O3 was prepared by the coprecipitation method, with subsequent calcination at 500 °C. A unique morphology consisting of nanostructured semispheres, with sizes between 1.7 and 2.5 μm, was observed by electron microscopy. This material was used to degrade diluted aqueous solutions of Congo red (CR) and malachite green (MG). For CR, UV–vis spectra revealed a photodegradation percent of ∼24% after 60 min of exposure to UV (λ = 365 nm); meanwhile, the dissociative adsorption accounts for ∼22%, in the same period. Therefore, most of the degradation of this compound can be ascribed to this phenomenon. For MG, an average photodegradation of ∼94% was achieved in the same period, however, dissociative adsorption was estimated as ∼71%. The mechanism of degradation can be explained by the adsorption of dye molecules on Y2O3 and their degradation by reactive oxygen species (ROS). ROS are free hydroxyl radicals such as •OH and • O2− ions that have high oxidizing capacity. XPS analyses performed on samples used in dye degradation provide evidence of the role of ROS, as a significant peak increase associated with OH− groups was observed.
