Effect of surface area and physical–chemical properties of graphite and graphene-based materials on their adsorption capacity towards metronidazole and trimethoprim antibiotics in aqueous solution

The adsorption of metronidazole (MNZ) and trimethoprim (TMP) antibiotics from water on nanomaterials synthesized from graphene oxide and graphite, was examined thoroughly. The effect of the physicochemical properties and surface area onto the adsorption capacity of the nanomaterials was studied in detail. The nanocarbon materials used were graphene oxide (GO), and GO reduced in inert medium (rGO) or ammonia (N-rGO), and four high surface area graphites (HSAG100, HSAG300, HSAG400, HSAG500). The nanomaterials characterization was performed by transmission and scanning electron microscopy, N2 physisorption, TG-profiles and X-ray diffraction. The increasing order of the nanomaterial adsorption capacity toward MNZ was: HSAG100 < HSAG300 < N-rGO < HSAG400 < HSAG500 < GO < rGO and toward TMP was: HSAG100 < N-rGO ≈ HSAG300 < HSAG400 < HSAG500 ≈ rGO < GO; and except for GO, the adsorption capacity of the nanomaterials increased almost linearly with the surface area. At T = 25 °C, the maximum mass adsorbed of MNZ and TMP on GO were 190 and 218 mg/g, at pH 7 and pH 10, respectively. The adsorption of TMP and MNZ on GO corroborated the presence of different adsorption mechanisms dependent on antibiotic speciation and pH. The adsorption of both antibiotics on the materials based on graphite and reduced graphene oxide was predominantly due to π-π dispersive interactions.