Effect of annealing temperature on structural, optical, and photocatalytic properties of modified sol-gel-driven ZnO nanoparticles

ZnO nanoparticles (NPs) were synthesized in this study using a modified sol-gel route. Synthesized NPs were annealed at various temperatures, namely, 400, 500, 600, and 700 degrees C, to optimize annealing temperature to make the NPs suitable for photocatalytic application. The hexagonal wurtzite structure was revealed by XRD analysis for all NPs, and the crystallinity showed an increase when the annealing temperature was increased. Rietveld analysis was conducted to measure the lattice parameters, crystallite size, and microstrain of the NPs. Micro-strain showed a decrease with increasing annealing temperature. The size of particles showed an increase with increasing annealing temperature, which was evident from the morphological analysis by SEM. Later, activation energy calculated from Scott's equation also revealed differential crystal growth rates with increasing annealing temperatures. Bandgap was found to decrease with increasing annealing temperature as well. XPS confirms the phase purity and the charge states of NPs. Rhodamine B (RhB) was used to measure photocatalytic degradation efficiency and superior photocatalytic degradation was found for 500 degrees C.