Photocatalytic Degradation of Polycyclic Aromatic Hydrocarbons in Simulated Offshore Oil Spill Wastewater by Magnesium Phthalocyanine Derivatives Supported on Coconut Shell Activated Carbon

Polycyclic aromatic hydrocarbons (PAHs) are highly toxic pollutants in marine ecosystems, necessitating efficient remediation. This study synthesized magnesium phthalocyanine (MgPc) and its modified derivatives, magnesium azaphthalocyanine (NMgPc) and methyl-substituted magnesium azaphthalocyanine (MeNMgPc), as visible-light-driven photocatalysts for PAH degradation. To enhance efficiency and recoverability, these photosensitizers were immobilized onto coconut shell activated carbon (AC) via multiple ultrasonic impregnation. Characterizations (UV-Vis, SEM, EDAX, BET) confirmed successful active component deposition; nitrogen substitution and peripheral methyl groups synergistically tuned the electronic structure and suppressed aggregation. Under xenon lamp irradiation, the MeNMgPc/C composite exhibited superior activity, degrading 90.55% of naphthalene. Box-Behnken response surface optimization identified optimal conditions (13.18 g/L dosage, 20 A, 2.28 h), yielding 96.67% experimental removal and adhering to pseudo-first-order kinetics. Mechanistic studies via electron spin resonance identified hydroxyl (•OH) and superoxide radicals (O2•−) as primary reactive species. GC-MS analysis elucidated a sequential phenanthrene ring-opening pathway, progressing to ultimate mineralization into CO2. Consequently, MeNMgPc/C presents a highly efficient, recoverable photocatalytic platform for marine PAH remediation.