Defect–Engineered Photonic Coupling in Nanostructured WO ₃ Inverse Opals for Enhanced Photoelectrocatalytic Removal of Pharmaceuticals

The increasing presence of pharmaceutical residues in aquatic environments poses a major challenge for sustainable water treatment and prompts the development of advanced photoactive nanomaterials for solar-driven remediation. Photoelectrocatalysis (PEC) offers a promising solar-driven strategy by coupling photocatalysis with bias-assisted charge separation. Herein, we report defect-engineered tungsten trioxide inverse opal (WO3–x IO) photoanodes designed for enhanced PEC removal of pharmaceuticals through the synergistic combination of oxygen vacancy engineering and photonic light management. Ordered WO3–x IOs were prepared via acid-induced metal reduction followed by mild N2 annealing, enabling stabilization of oxygen vacancies while preserving the periodic architecture. The optimized WO3–x photoanodes exhibited a volcano-type PEC response with increasing vacancy concentration, achieving a 3-fold photocurrent enhancement compared with pristine WO3 IOs and significantly improved degradation rates for tetracycline, ciprofloxacin, and ibuprofen pharmaceuticals at an intermediate oxygen deficiency (∼2%). Mechanistic analysis revealed substrate-dependent reactive oxygen species pathways associated with vacancy-mediated O2 activation and hole accumulation. These findings demonstrate that defect–photonic engineering is an effective strategy for developing photonic oxide photoanodes for solar-driven PEC water treatment and pharmaceutical contaminant removal.