Highly efficient treatment of pharmaceutical contaminants: A comprehensive study on the performance and mechanism of sustainable yolk-in-double-shelled CuCo2S4@Bi-doped TiO2 photocatalyst

The photocatalytic potential of TiO₂ is notable, with promising physiochemical properties and oxidation capabilities. Nevertheles, addressing the limited light-harvesting spectrum of TiO₂ is crucial for practical applications. Herein, we propose a novel approach combining electronic enhancement through elemental doping and a hierarchical multi-level configuration under Z-scheme heterojunction to achieve remarkable photocatalytic activity. Using the alcohol-assisted sol-gel method, we incorporated bismuth atoms into the TiO₂ lattice to form (3)Bi-TO nanoparticles. While the hierarchical mesoporous texture provided (3)Bi-TO with a large S_BET (83 m²/g), the Bi incorporation conferred various defects and mid-gaps to improve light-harvesting and promote charge carrier separation. These were then encapsulated onto the exterior shell of alkoxide-based CuCo₂S₄ (YS-CCS) yolk-shell structures using a facile isoelectric point-mediated annealing technique, creating a Z-scheme YS-CCS@(3)Bi-TO yolk-in-double-shell architecture. The yolk-in-double-shelled YS-CCS@(3)Bi-TO heterojunction simultaneously enhanced light-harvesting, improved photon utilization, prolonged charge carrier lifetime, and advanced conductivity, as indicated by the UV–vis diffuse reflectance spectra (UV–Vis DRS), photoluminescence (PL), electrochemical impedance spectroscopy (EIS), and transient photocurrent. Upon optimizing the mass-loading of YS-CCS (40 wt%) and operational parameters (pH: 5, catalyst dosage: 1.0 g/L, and levofloxacin (LFC) concentration: 50 mg/L), the YS-CCS@(3)Bi-TO exhibited remarkable photocatalytic performance in total LFC photodegradation, which was 29.9, 4.7, and 11.3 folds kinetically higher than that of the YS-CCS and (3)Bi-TO, and Bi-free TO, respectively. The robustness of YS-CCS@(3)Bi-TO was demonstrated by sustained efficiency over six consecutive cycles, negligible metal leaching, and confirmed stability through XRD analysis. Additionally, its outstanding performance in long-time LFC mineralization over 5 h and real wastewater treatment over 6 h demonstrated a successful catalyst design with potential industrial applications. Finally, this design and strategy hold promises for developing nanomaterials with geometrical configuration and electronic properties in synergy for enhanced photocatalytic activity.