Photocatalytic activity of the new NiAl2O4/CeO2 heterojunction for the elimination of Rose Bengal under solar irradiation

Abstract

In the pursuit of developing effective catalysts for degradation of organic dyes, this study focuses on synthesizing spinel NiAl₂O₄ and NiAl₂O₄/CeO₂ nanocomposites via co-precipitation and junction methods, respectively, for the photocatalytic degradation of Rose Bengal (RB) dye under sunlight irradiation. The structural analysis performed using X-ray diffraction and Fourier transform Infrared spectroscopy confirmed the successful synthesis of the NiAl₂O₄/CeO₂ heterojunction. The nano-size nature of particles was evaluated by Scanning electronic microscopy and a value of 33.45 nm of particle size was obtained using Scherrer equation. The band gap of the heterojunction (2.94 eV) was found between band gap values of NiAl₂O₄ (1.75 eV) and CeO₂ (3.28 eV) pure materials. Moreover, electrochemical impedance spectroscopy (EIS) confirmed the semiconductor character of the nanoparticles. XPS study confirmed the existence of both Ce⁴⁺ and Ce³⁺ in the prepared heterojunction. A high relative concentration of Ce³⁺ and chemisorbed oxygen (31.6 %) was obtained from the deconvolution of the O1s region of the heterojunction, compared to 3.2 % obtained for pure ceria, which improved the photocatalytic activity of NiAl₂O₄/CeO₂.

The adsorption of RB dye on both catalysts was also investigated. At free pH and with 1 g of the catalyst, the adsorption capacities reached 15 mg/g for NiAl₂O₄ and 8.5 mg/g for the NiAl₂O₄/CeO₂ nanocomposite. The adsorption mechanism was further analyzed using three adsorption isotherm models, with the Freundlich model showing the best fit for RB dye adsorption onto both catalysts. Under sunlight irradiation, the photocatalytic efficiency for RB dye degradation was remarkably high, achieving 99.9 % with the NiAl₂O₄/CeO₂ nanocomposite and 80.36 % with spinel NiAl₂O₄. These results highlight the excellent photocatalytic activity of the NiAl₂O₄/CeO₂ nanocomposite.