Biomass-derived porous aminated graphitic nanosheets for removal of the pharmaceutical metronidazole: Optimization of physicochemical features and exploration of process mechanisms

The presence of trace levels of pharmaceutically active compounds (PhACs) in the aquatic environment threatens human health and the environment. Metronidazole (MNZ) is a soluble PhAC with low biodegradability, a possible human mutant and carcinogen. This study aimed the synthesis, physicochemical characterizations, and employment of porous amine-modified green-graphene (AMGG) for MNZ removal from aqueous solutions. Response-surface methodology (RSM) based on Box-Benken design (BBD) was used to assess the MNZ adsorption efficiency of AMGG as a function of pH (4–12), contact time (5–60 min), AMGG dose (0.1–1 g/L) and MNZ concentration (10–100 mg/L). From the model optimization, the highest MNZ removal was predicted at a pH of 5.9, a contact time of 27 min, an AMGG dose of 0.86 g /L, and an MNZ concentration of 100 mg /L. The experimental data were in agreement with the pseudo-second order kinetic model and the Langmuir isotherm model. The maximum adsorption capacity of AMGG for MNZ was 416.7 mg/g. The MNZ concentration at equilibrium increased about 4.8 mg/L when the solution temperature increased by 20 oC (from 30 to 50 °C), indicative of an exothermic process. AMGG showed an efficiency decrement from 84 % to 57 %, after five consecutive saturation-regeneration cycles. Moreover, AMGG showed a removal efficiency of 74 % when it was employed for real hospital wastewater treatment.