Treatment of Wastewater Containing Pharmaceutical Micropollutants by Adsorption under Flow in Highly Porous Carbon Monoliths

Flow-through reactors made of highly porous hierarchical micro/meso/macroporous carbon monoliths (CM) were developed to decontaminate water containing pharmaceutical micropollutants (antibiotics). CM were prepared from hierarchical meso/macroporous silica monoliths as sacrificial templates after impregnation with sucrose as a carbon precursor, hydrothermal carbonization, and subsequent pyrolysis and dissolution of silica by NaOH. CM were fully characterized by nitrogen sorption at 77 K, Hg porosimetry, scanning electron microscopy, transmission electron microscopy, microtomography, permeability measurements, X-ray photoelectron spectroscopy, and chemical analysis. CM exhibit a large surface area (1058 m 2 g –1 ), a large pore volume (6.5 mL g –1 ), high permeability, a homogeneous interconnected macropore network (22 μm), bimodal mesopores (6 and 15 nm), micropores (0.85 nm), and a large number of C═O and COO – groups. They are basic in water (pH 9) and negatively charged. First, adsorption of a single pharmaceutical molecule, tetracycline (TC), was studied. Isotherms of adsorption, kinetics, and diffusion were used to study the mechanism of adsorption on CM, and the process was found to be governed by electrostatic interactions. Then, a mixture of several antibiotics (ciprofloxacin, amoxicillin, sulfamethoxazole, and TC, 20 mg L –1 each) was used. The sorption capacity for antibiotics peaked at 815 mg g –1 . In a recirculation flow configuration, with a flow rate of 1 mL min –1, CM could remove 93% of the antibiotics. These CM could represent a highly efficient solution for the purification of real wastewater containing pharmaceutical molecules, which are generally found at much lower concentrations (from a few nanograms per liter to micrograms per liter). Regeneration of CM was successfully achieved by washing with HCl (0.1 M).