Graphene nanoplatelets with low defect density as a synergetic adsorbent and electron sink for ZnO in the photocatalytic degradation of Methylene Blue under UV–vis irradiation

[Display omitted] •F-GNP/ZnO was successfully synthesized via a one-step solvothermal method using THF.•Enhanced removal of MB was achieved via synergetic adsorption-photodegradation.•Kinetic models for adsorption and photocatalytic were determined.•Process parameters studies for photocatalytic activity were conducted. Functionalized Graphene Nanoplatelets with ZnO (F-GNP/ZnO) composites has been successfully synthesized and decorated on GNP via one-step solvothermal method. The results showed that the best composite (45 % F-GNP/ZnO) possessed high adsorption and photocatalytic activity of up to 70 % and 87 %, respectively. Photoluminescence (PL) and UV–vis Diffuse Reflectance Spectroscopy (UV–vis DRS) has successfully provided the evidence on the reduction of electron-hole pairs recombination and wider light absorption compared to bare ZnO, respectively. In addition, process parameters studies concluded that the best photocatalytic activity of 45 % F-GNP/ZnO composite was achieved by using 1 g/L photocatalyst loading, MB concentration of 10 mg/L and solution pH of 5. Pseudo-second order for adsorption and pseudo-first order for photocatalytic activity were revealed from kinetic studies with rate constant of 0.2250 g/mg.min and 0.034 min−1, respectively. Based on the scavenger test, hydroxyl radical was found to be the most active species responsible for the MB degradation.