The duet of surface and radical-based carbocatalysis for oxidative destructions of aqueous contaminants over built-in nanotubes of graphite

Abstract

Metal-free mesoporous graphitic frameworks with built-in nanotubes (CPGs) were synthesized via facile co-pyrolysis of cyclodextrin and a cobalt salt with subsequent acid pickling to remove the embedded metal species. Due to the high graphitic degree and built-in few-layer nanotubes, the as-synthesized carbonaceous materials possess a higher catalytic ozonation activity than that of the state-of-the-art carbon nanotubes (CNTs) and LaMnO₃ perovskite catalysts for the destruction of different aqueous contaminants. For recalcitrant oxalic acid removal, 50 mg L⁻¹ oxalic acid was completely degraded in 20 min. Compared with other nanocarbons, the as-synthesized materials also demonstrated robust structural stability and reusability. The electron paramagnetic resonance (EPR) and selective radical quenching tests revealed that the destruction of the aqueous organics predominantly relied on surface-adsorbed complexes (O*(ad) and O₂*) from activated ozone molecules. Owing to the occurrence of this surface oxidation pathway, the compatibility of the CPGs/O₃ system was significantly enhanced for treatment of real wastewater, where the inorganic anions and organic natural organic matter would inhibit radical oxidation as radical scavengers. Furthermore, by employing organics with different ionization potentials (IPs) as the target pollutants, the CPGs/O₃ system was discovered to obtain a high oxidation potential.