Facile synthesis and characterization of novel Gd2O3-CdO binary mixed oxide nanocomposites of highly photocatalytic activity for wastewater remediation under solar illumination

In this study, pure cadmium oxide (CdO) nanoparticles and mixed gadolinium oxide (Gd2O3)-CdO nanocomposites with different Gd2O3 contents (0-15%) were synthesized by a facile precipitation technique followed by calcined treatment. The X-ray diffraction analysis illustrated that all samples had high cubic-phase purity and a good crystallinity. Further support for the formation of highly pure CdO and Gd2O3 phases was obtained via infrared spectroscopy. The morphologies of pure CdO and mixed Gd2O3-CdO nanoparticles were probed by scanning electron and transmission electron microscopy, which demonstrated that the collected samples consisted of individual semi-spherical shaped entities of different particle sizes (23-31 nm). The optical band gap of the developed samples was computed based on the Tauc equation and showed a decrease from 3.41 to 2.75 eV upon increasing the Gd2O3 content. The 3D fluorescence analysis showed that the quenching in the emission peak intensity with increasing Gd2O3 content was due to the high separation efficiency of photogenerated electron-hole pairs. Moreover, the Gd2O3 (15%)-CdO nanocomposite showed superior photodegradation efficiency (89.1%) of methylene blue compared to 44.4% for pure CdO. At pH 11.5, >3-fold enhancement in degradation rate (0.044 min(-1)) was obtained compared to natural pH 9.6. Reusability study showed stability of the Gd2O3-CdO photocatalyst in four cycles of methylene blue degradation. Trapping experiment of holes and electrons revealed extensive contribution of holes rather than electrons in producing active oxidizing species.