Enhancing photodegradation of methylene blue and reusability using CoO/ZnO composite nanoparticles

This study investigates photocatalytic activity performance of CoO/ZnO nanoparticles (NPs). CoO NPs was synthesized under the hydrothermal method, followed by calcination, while CoO/ZnO NPs were successfully synthesized using the precipitation method with various molar ratios of ZnO. X-ray diffraction and selected area electron diffraction showed that CoO and ZnO have a hexagonal structure; another phase appeared as a Co3O4 spinel cubic structure. The crystallite size was decreased as the ZnO concentration increased. The transmission electron microscopy image of CoO/ZnO showed almost spherical, non-uniform, and slightly dispersed under agglomerated conditions with the particle size of 17.4 ± 3.5 and 18.1 ± 4.1 nm for molar ratio of 1:2 and 1:3, respectively. Besides, the corresponding chemical elements are confirmed by energy-dispersive X-ray spectroscopy. Fourier-transform infrared spectra showed metallic functional groups, such as Ctet2+-O, Coct3+-O, and Zn–O at 586.36, 671.23, and 410–429 cm−1 also suggests the formation of NPs. A vibrating sample magnetometer showed that the CoO/ZnO NPs exhibited antiferromagnetic properties. However, redshift absorption and band gap narrowing were observed only with the ZnO addition. The removal efficiency of photodegradation methylene blue was optimal for CoO/ZnO at a concentration of 1:2, reached 67.5% degradation within 3 h for uptake every 30 min. The photodegradation was also analyzed using a Langmuir-Hinshelwood kinetic model, resulting a rate constant (Kapp) of 6.428 × 10−3 min−1 and a half-life time (t1/2) of 107.84 ± 0.01 min at the optimum concentration. The NPs could be reused up to three times without significant change of activity. Therefore, CoO/ZnO NPs is promising photocatalyst to be developed in removal of organic pollutants in various environments.