Abstract

The next generation of photocatalysts for removing pollutants from water must exhibit UV- and visible-light absorption, strong pollutant adsorption, and the ability to generate high concentrations of reactive oxygen species (ROS). In this context, activated carbons derived from agroindustrial wastes and polymeric carbon nitride (PCN), a metal-free, visible-light-absorbing photocatalyst, exhibit interesting features. The main aim of this study was to successfully incorporate PCN (using urea as a precursor) into porous activated carbons (ACs) derived from sunflower seed shells (Helianthus annuus) activated with phosphoric acid. The composite material (AC@PCN) not only exhibited high pollutant adsorption but also the ability to photogenerate ROS that successfully oxidized adsorbed ibuprofen and diclofenac in water. A multi-technique characterization scheme verified the incorporation of PCN into AC. In addition, continuous-wave electron paramagnetic resonance (CW-EPR) measurements determined the presence of semiquinone persistent free radicals (SQ-PFR) in the AC and pi-electrons from PCN. EPR-spin trapping measurements revealed that AC@PCN photo-generated hydroxyl radicals ((OH)-O-center dot), whereas H2O2 photogeneration was also detected in the presence of sacrificial electron donors (SEDs). The results suggest that photocatalytic formation of H2O2 by irradiated PCN and AC and its further dark (on SQ-PFRs of AC) or photocatalytic (by PCN) decomposition into (OH)-O-center dot could play a prominent role in the photodegradation of both adsorbed pollutants in the AC@PCN hybrid material.