Cu nanoparticle-tipped carbon nanofibers stabilized over pelletized biochars for catalytic wet air oxidation of tetracycline under mild operating conditions

Abstract

Tetracycline (TC), a commonly used antibiotic, poses serious risks to environmental safety and public health, even if present in trace amounts in aqueous systems including rivers and groundwater. This study introduced catalytic wet air oxidation (cWAO) as an efficient technique for treating TC-laden water using pelletized biochar-supported Cu nanoparticle (NP)-tipped graphitic carbon nanofibers (CNFs) as a catalyst. The proposed material configuration integrated the favourable redox potential and multiple oxidation states of Cu NPs with the high electron conductivity of CNFs. Micron-sized biochars were derived by the pyrolysis of naturally resourced bamboo (Bambusa vulgaris) shoots and served as a stabilizing matrix for Cu NPs without leaching. Physicochemical characterization revealed the formation of a meso–macroporous structure with a Cu loading of ∼10.8 mg g⁻¹ and an abundance of oxygen functional groups. The cWAO activity tests confirmed ∼99% removal of aqueous TC using 1 g L⁻¹ dose of the pelletized catalyst at 100 °C and 2 bar, with the simultaneous reduction of the chemical oxygen demand (∼78%) and total organic carbon (∼80%). The radical scavenging test and electron paramagnetic resonance analysis confirmed the degradation of TC via the radical (˙OH and ˙O₂⁻) and non-radical (¹O₂) pathways. Liquid chromatography-mass spectroscopy analysis confirmed the transformation of the TC molecule to reaction intermediates, eventually degrading to CO₂ and H₂O. The reusability test showed the stability of the catalyst over five oxidation cycles, while the toxicity test confirmed the treated cWAO samples to be harmless. The findings clearly underscore the need for further study on the Cu-CNF/biochar pellets for treating the recalcitrant pharmaceutical compound-laden wastewater by cWAO in a packed bed reactor under flow conditions.