Nitrogen Vacancy Rich Tubular g-C3N4 Modified with FePc for Efficient and Reusable Photo-Fenton Degradation of Oxytetracycline.

Efficient and reusable photo-Fenton catalysts require the rational integration of photocatalytic platforms, effective H2O2 activation sites, and practical immobilization strategies. Herein, nitrogen-vacancy-rich tubular g-C3N4 (HCNT) was prepared as the photocatalytic platform. Iron (II) phthalocyanine (FePc) was then loaded onto HCNT to form the FePc/HCNT composite for antibiotic degradation. The FePc/HCNT composite was further immobilized in a poly (vinylidene fluoride) (PVDF) membrane, denoted as FePc/HCNT-PVDF, to facilitate catalyst recovery and reuse. Benefiting from the micrometer-scale tubular morphology, the FePc/HCNT remained exposed on the membrane surface, preserving accessible catalytic interfaces and reducing encapsulation within the polymer matrix. The tubular architecture facilitated reactant transport, while surface nitrogen vacancies enhanced photogenerated-carrier separation and utilization. Component-dependent experiments revealed that FePc served as the primary center for H2O2 activation, whereas HCNT functioned as a defect-engineered tubular photocatalytic platform that promoted photogenerated-carrier separation and reactive oxygen species formation. The optimized FePc/HCNT achieved 94% oxytetracycline degradation within 60 min, with an apparent rate constant of 0.04462 min-1, approximately 11 times higher than bulk g-C3N4, and exhibited broad-spectrum degradation capability toward various organic pollutants, including rhodamine B, tetracycline, amoxicillin, and ciprofloxacin. The FePc/HCNT-PVDF membrane removed 90% of oxytetracycline within 60 min and maintained stable performance over ten cycles. This work provides insights into the integrated roles of nitrogen vacancy regulation, FePc-mediated H2O2 activation, and morphology-assisted membrane immobilization in the development of reusable g-C3N4-based photo-Fenton catalysts.