Effective adsorption of antidiabetic pharmaceutical (metformin) from aqueous medium using graphene oxide nanoparticles: Equilibrium and statistical modelling

Abstract

Micro-pollutants such as pharmaceuticals are one of the emerging contaminates found in water resources and pose potential threat to the living beings. Due to ineffective wastewater management, we require an effective method to remove the micro-pollutant for safe living. In this study, graphene oxide (GO) was examined for the adsorptive removal of metformin (a model micro-pollutant) from aqueous medium. The graphene oxide was synthesized using Hummers method and characterized using Fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray analysis, Raman spectroscopy analysis, scanning electron microscope analysis (SEM), and transmission electron microscope (TEM). The prepared GO was mesoporous and had large surface area (187.2 m2/g), pore volume (0.12 cm3/g) and pore width 17.33 nm. The batch adsorption parameters were varied such as pH (4.5–8.5), temperature (15–45 °C), time (1−3 h), adsorbent dose (50–150 mg) and metformin concentration (300–700 mg/L) and were investigated with the Box-Behnken statistical design. The maximum removal was evaluated using genetic algorithm at 6.26 pH, 126.02 mg/L, 521 mg/L and 20.53 °C. The adsorption data was assessed using different isotherms and kinetic models; the optimal parameters were evaluated using sum of normalized errors methodology. The maximum adsorption capacity of metformin was found to be 122.61 mg/g. The kinetics showed that pseudo-first-order model fit well to the data. The thermodynamic study indicated that the metformin adsorption was spontaneous (ΔG○ < 0) and exothermic (ΔH○ < 0). Desorption studies indicated that 1 N sodium hydroxide solution regenerated the GO for six cycles.