Synergistic Adsorption-Photocatalysis Under Sunlight Irradiation of NiO/Graphitic Carbon Nitride Nanocomposite for the Removal of Ciprofloxacin from Wastewater

Abstract

A study on the simple synthesis of materials having a synergistic role as photocatalysts when exposed to sunlight irradiation and super-adsorbents in the dark is provided in the present article. NiO@g-C₃N₄ nanocomposite was prepared by mixing and ultrasonicating graphitic carbon nitride (g-C₃N₄) with NiO nanoparticles at a ratio of 1:1. XRD, XPS, BET, DR/UV-Vis spectroscopy, SEM, EDX, and zeta potential analysis were used for the samples’ analysis. XRD pattern of NiO@g-C₃N₄ conforms to the NiO pattern, with diminished peak strength at the main peak of g-C₃N₄, suggesting partial exfoliation of the lamellar g-C₃N₄ layers during the ultrasonication with NiO. In NiO@g-C₃N₄, the g-C₃N₄ sheets were irregularly covered with NiO nanoplatelets as confirmed by SEM images. Employing ciprofloxacin (CIP) as a pollutant model drug, the adsorption efficiency and various parameters influencing the adsorption process without light irradiation were investigated. The synergistic role of the NiO@g-C₃N₄ nanocomposite was studied, where it showed a CIP removal of 80% when exposed to sunlight irradiation versus 10% by adsorption in the dark after 60 min. The rate constant values indicated that NiO@g-C₃N₄ nanocomposite showed a faster photocatalytic degradation rate than bare NiO or bare g-C₃N₄. The band gap measurements and the band alignment of NiO and g-C₃N₄ suggest S-scheme heterojunction’s mechanism, which suppresses the e⁻-h⁺ recombination and increases the photocatalytic efficiency. NiO@g-C₃N₄ nanocomposite could be successfully recycled, where it showed removal of more than 50% of CIP after 4 photocatalysis runs. Moreover, the NiO@g-C₃N₄ was employed for CIP degradation in real water samples.

Graphical Abstract