Performance assessment of graphene oxide decorated with silver nanoparticles as adsorbent for removal of metformin from water: Equilibrium modeling, kinetic and thermodynamic studies

In the present study, graphene oxide decorated with silver nanoparticles (GO@AgNPs) was synthesized for the effective removal of metformin from water. The prepared GO@AgNPs was characterized by using Fourier transform Infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric-differential thermal analyses (TGA-DTA), scanning electron microscopy (SEM) coupled with electron dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM). Response surface methodology via Box-Behnken design was adopted for optimizing the variables of adsorption of metformin on GO@AgNPs. Under the optimized conditions (contact time = 50 min; pH = 6.5; adsorbent dose = 0.015 g; initial concentration = 50 mg/L) the adsorption capacity and removal efficiency for metformin were 131.7 ±.0.30 mg/g and 99.34% ±.0.33, respectively. The adsorption data obtained at 305, 310, 315 and 320 K were assessed by non-linear adsorption isotherm and kinetic models. Freundlich isotherm model fits best to the measured data. The pseudo second order kinetic equation fits well to the measured kinetic data. The study of impact of temperature on the adsorption demonstrated that the sorption process was endothermic (∆H° = 31.335 kJ/mol; Ea = 32.009 kJ/mol) and spontaneous in nature (∆G° = −11.162, −11.876, −12.537 and −13.268 kJ/mol at 305, 310, 315 and 320 K, respectively). Moreover, the value of sticking probability (S* = 0.00082) illustrated high probability for metformin sticking on the surface of GO@AgNPs. The adsorption/desorption study shows that there was no loss in adsorption capacities upto 6 cycles which demonstrated the effectiveness of GO@AgNPs as a potential adsorbent for remediation of metformin from aqueous system.