Synthesis and characterization of carbon xerogel/graphene hybrids as adsorbents for metronidazole pharmaceutical removal: Effect of operating parameters

Abstract

In this work, a series of carbon xerogel/graphene hybrids were synthesized from resorcinol and formaldehyde by adding increasing loadings of graphene oxide (GO) solution. Resulting samples were functionalized with urea and characterized by SEM, adsorption-desorption isotherms of N2 at 77 K, X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Carbon xerogel/graphene hybrids were assessed as adsorbents for metronidazole (MNZ) removal in aqueous solutions under different operational conditions (solution pH, temperature, ionic strength, and type of water) to determine its adsorption mechanism. The maximum adsorption capacities (qm) of carbon xerogel/graphene hybrids towards MNZ were in the range of 110–166 mg g−1 at pH = 5 and 298 K. Moreover, the results showed almost a linear relationship between SBET and qm. The adsorption capacity of MNZ decreased at ionic strength lower than 0.01 N NaCl and remained constant at higher ionic strength. MNZ adsorption is not inhibited by the presence of ions in treated water and the process exhibited endothermic nature. Based on the obtained results from the adsorption equilibrium, the MNZ removal might occurred by different mechanism such as π-π dispersive interactions, attractive electrostatic interactions (at pH = 8), and hydrogen bonds.