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

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 photo- catalytic 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.