Design of experiment for optimization of adsorptive removal of galantamine onto the thermally reduced graphene oxide nanosheet (rGONS)

The drugs appeared as emerging contaminants in aquatic environment needs proper treatment to safeguard the ecosystem. The present report deals with synthesis of reduced graphene oxide nanosheet (rGONS) from graphite powder by modification of Hummer's method and subsequent thermal treatment and has been tested for the potential removal of Galantamine (Alzheimer's drug). The immobilization of the drug on the adsorbent was confirmed from characterization of the material done by UV–Vis, FTIR, Raman spectroscopy, XRD, SEM, FESEM, TEM and EDS analysis before and after the adsorption of drug. Adsorption was dependent on the operational variables viz. adsorbent dose, initial concentration of drug, contact time, temperature and pH. The interactive influence of the variables was investigated following response surface methodology (RSM) with built up a mathematical model and mapped in design space by response surface and contour plots. The percentage contribution of the variables to the response is found to be temperature (D: 33.13%) > initial concentration (B: 32.88%) > adsorbent dose (A: 16.11%) > contact time (C: 1.38%) > pH (E: 0.22%) obtained from FFD study. The optimized adsorption condition is: adsorbent dose: 10 mg, initial concentration: 40 mg L⁻¹, temperature: 313 K obtained from CCD. The rGONS-drug adsorption process follows a pseudo second-order rate law, Langmuir isotherm and is thermodynamically feasible (−ΔG₀ = 11.35 kJ mol⁻¹). The higher specific surface area, abundant sorption sites, one pot synthesis, short equilibrium time (30 min), high adsorption capacity (81.96 mg g⁻¹), regeneration capacity, and reusability properties makes it a promising nano adsorbent for water remediation.