Synergistic Charge Modulation in Tb 3 + /Eu 3 + Co‐Doped ZnO–WO 3 Heterojunctions for Enhanced Visible‐Light Photocatalysis

ABSTRACT Rare‐earth co‐doping offers a promising route for enhancing charge separation in semiconductor photocatalysts for sustainable wastewater treatment applications. Herein, Tb 3 + /Eu 3 + co‐doped ZnO‐WO 3 heterostructured nanocomposites (0.5, 1.0, and 2.0 at.%) were synthesized and systematically investigated. X‐ray diffraction (XRD) confirmed crystalline heterojunction formation, while SEM/TEM revealed well‐defined nanostructures. Elemental composition and dopant distribution were verified by energy‐dispersive x‐ray spectroscopy (EDS), and x‐ray photoelectron spectroscopy confirmed chemical states and successful incorporation of Tb 3 + /Eu 3 + . AFM indicated increased surface roughness, while Brunauer–Emmett–Teller (BET) analysis showed enhanced surface area (∼100.17 m 2 g − 1 ), providing abundant active sites. Optical and photoluminescence (PL) studies, supported by electrochemical impedance spectroscopy (EIS), demonstrated that improved visible‐light absorption suppressed charge recombination and enhanced charge transfer. UV–vis analysis revealed a band gap of 2.00 eV. The photocatalytic performance toward methylene blue (MB) degradation under visible light showed ∼93% removal within 120 min for the 1.0 at.% sample. It retained ∼87% efficiency after four cycles, indicating excellent recyclability. The reaction followed pseudo‐first‐order kinetics and Langmuir monolayer adsorption behavior. Radical trapping experiments identified •OH and •O 2 − as dominant reactive species. Thermodynamic parameters (Δ G = −4.16 kJ mol − 1 , Δ H = 18.62 kJ mol − 1 , Δ S = 76.44 J mol − 1 K − 1 ) confirmed spontaneous reaction behavior. Total organic carbon (TOC) analysis indicated 71% mineralization, confirming effective degradation.