Sustainable Green Production of a Novel Hierarchical <i>g</i>C₃N₄-Supported CuO–rGO Nanohybrid: Antibiotic-Contaminated Wastewater Remediation through Efficient Photocatalysis

In the quest to develop an eco-friendly, efficient photocatalyst using earth-abundant materials for wastewater remediation, a sustainable green synthesis of a novel CuO–rGO-decorated gC3N4 nanohybrid using an aqueous extract of a high-altitude lichen, Acroscyphus sphaerophoroides, has been devised. The mesoporous nanocomposite material CuO–rGO–gC3N4 demonstrated a high photocatalytic activity of 92% degradation of the tetracycline (TC) antibiotic using H2O2 under optimum conditions of pH (7), catalyst dose (5 mg), and antibiotic concentration (40 mg/L) when irradiated for 25 min. The Brunauer–Emmett–Teller (BET) analysis revealed the nanohybrid material to possess a relatively high surface area (119.37 m2/g) and pore size (9.34 nm). Both CuO–rGO and CuO–rGO–gC3N4 nanohybrid materials showed excellent performance with the ternary system CuO–rGO–gC3N4 showing promising results. This is ascribed to the synergistic effect of CuO–rGO and the exfoliated tubular-shaped gC3N4 sheet, forming heterojunctions. The degradation pathways for the tetracycline antibiotic were confirmed by the liquid chromatography–mass spectrometry (LC–MS) study, indicating that the synthesized catalyst can very effectively degrade the antibiotic into much smaller, comparably less toxic intermediates. Being easily retrievable, showing ∼84% catalytic efficiency with no change in the structure even after four catalytic cycles, is the redeeming feature of the degradation process. The work encompasses developing an easy, cost-effective, green protocol for accessing CuO–rGO–gC3N4 with excellent potential for the viable treatment of antibiotic-contaminated wastewater under scattered sunlight.