Facile sol-gel synthesis of ZnAl2O4 spinel nanoceramics for photocatalytic applications: H2 production and MB dye degradation

ZnAl2O4 spinel nanoceramic was successfully synthesized by a sol-gel combustion method and subsequent annealing at temperatures as low as 500 degrees C. The photocatalytic activity of the synthesized spinels was evaluated for the H-2 photocatalytic production and photodegradation of methylene blue dye (MB) under UV light irradiation. ZnAl2O4 spinels were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FTIR), UV-vis spectroscopy, and Photoluminescence (PL). XRD revealed that the low-temperature calcination ZnAl2O4 spinel nanoceramics have a cubic crystalline structure and nanocrystallites sizes between 10-21 nm. The presence of carbon dot (CDs) nanoparticles is suggested by FTIR, UV-vis, and EDS characterization. Band gap values, estimated from diffuse reflectance spectra, are between 2.00 eV and 4.26 eV, for ZnAl2O4 calcined between 500 degrees C and 900 degrees C. The best H-2 evolution was achieved with ZnAl2O4 treated at 500 degrees C reaching a 145 mu mol g(-1) production after 2 h. The highest percentage of MB dye degradation of 84%, after 120 min of UV irradiation, was achieved with ZnAl2O4 spinel treated at 900 degrees C.