Photocatalytic degradation efficiencies of ZnO nanoparticles and CeO2 nanosheets synthesized via combustion method

In this study, a simple, inexpensive, scalable solution combustion process devoid of toxic chemicals is suggested for the synthesis of ZnO and CeO₂ nanostructures. Different techniques were used to characterize the morphologies, crystal phases, purity and composition of as-synthesized nanostructures. For ZnO nanoparticles, field emission scanning electron microscopy examination revealed spheroidal, elongated hexagonal rods, triangular and pentagonal morphologies, whereas for CeO₂, sheet-like morphologies with various thicknesses were observed. X-ray diffraction investigation indicated wurtzite hexagonal and cubic fluorite phases for ZnO nanoparticles and CeO₂ nanosheets with crystallite sizes of 49.50 and 11.04 nm, respectively. Energy dispersive X-ray spectrometry, electron mapping and elemental distribution images confirmed the purity of the synthesized nanostructures. The optical bandgap of ZnO nanoparticles and CeO₂ nanosheets were found to be 3.28 and 3.55 eV, respectively. ZnO nanoparticles and CeO₂ nanosheets demonstrated outstanding photocatalytic efficiencies for the degradation of model dyes like Congo red (CR), rhodamine (RhB) and methylene blue (MB). However, ZnO nanoparticles outperformed CeO₂ nanosheets in photodegradation. Under UV-light irradiation, the degradation rate of the dyes was reduced in the following sequence for both photocatalysts: CR > MB > RhB. The low degradation efficiency of CeO₂ nanosheets can be attributed to their higher bandgap energy as compared to ZnO nanoparticles. Further, photocatalytic degradation of different dyes followed Langmuir–Hinshelwood pseudo-first-order kinetic model. The exceptional dye-degrading abilities of the as-synthesized nanostructures, synthesized using the combustion process, show that they are suited for photocatalysis applications.