Effective mitigation of azithromycin by hierarchically structured L-cysteine stabilized ZnO-GO nanostructures: fabrication, characterization, thermodynamic and kinetic studies

In this study, zinc oxide nanoparticles (ZnO NPs) decorated with L-cysteine (Cys)-modified graphene oxide (GO) were prepared and characterised by Fourier transform infrared spectroscopy (FT-IR), powder X-ray diffraction (PXRD), ultraviolet-visible (UV-Vis) spectroscopy, scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) techniques. The newly engineered GO/Cys@ZnO nano composite was utilised to eliminate azithromycin (AZT) from an aqueous solution in a batch process. The study evaluated the influence of multiple factors, i.e., pH, temperature, catalyst concentration, contact time and ionic concentration, on the removal process. The optimal conditions for AZT removal were at 25 °C, a pH of 7, 60 mg of catalyst, 90 minutes of contact duration, 0.5 M ionic concentration, and 5 mg/mL of drug concentration. Adsorption isotherm for AZT on GO/Cys@ZnO follows the Langmuir isotherm, while kinetic data are fitted with pseudo-first order. The thermodynamics demonstrated endothermic, non-spontaneous adsorption of AZT on the catalyst with a removal efficiency of 98%.