Efficient removal of anionic and cationic dyes from waste water using green ZnO/NiO/graphene quantum dots nano photocatalyst

Abstract

For its detrimental environmental and health impact, water pollution with organic contaminants has found more attention. In this research, a series of nanostructures were prepared and applied as catalysts for the photodegradation of methylene blue and methyl orange as organic pollutants. In this regard, ZnO nanoparticles (NPs), NiO NPs, ZnO/NiO nanocomposites (NCs), and ZnO/NiO/Graphene quantum dots NCs (ZnO/NiO/GQDs NCs) were prepared by a novel and green co-precipitation and hydrothermal route. The crystallinity and morphological properties of samples were studied via X-ray diffraction pattern (XRD), transmittance electron microscope (TEM), scanning electron microscope (SEM), and energy dispersive spectroscopy (EDS) analysis. The results showed that the applied synthesis routes successfully produced pure nanostructures with uniform shapes and sizes. The optical properties studied with diffuse reflectance measurement-ultraviolet (DRS-UV) analysis revealed that the synthesized green GQDs have an important effect on the optical band gap of the prepared nanostructures. In this regard, the optical band gaps were determined 3.04, 3.07, 2.98, and 2.88 eV for prepared ZnO NPs, NiO NPs, ZnO/NiO NCs, and ZnO/NiO/GQDs NCs, respectively. Photocatalytic tests showed that prepared ZnO/NiO/GQDs NCs is a better catalyst than ZnO NPs, NiO NPs, ZnO/NiO NCs, and photodegraded methylene blue (93.42 %) better than methyl orange (75.68 %) after 90 min. It was also found that the increase in solution acidity reduces photocatalytic performance. As a result, the optimum photocatalytic activity was recorded on pH = 9. Also, the impact of irradiation light on the photocatalytic efficiency was studied.