Bio‐Engineered Chitosan–ZnO–ZnFe ₂ O ₄ Heterojunction with Tunable Bandgap and Boosted Charge Dynamics for UV‐Driven Photocatalytic Mineralization

A ternary chitosan‐ZnO‐ZnFe 2 O 4 (Cs‐ZnO‐ZnFe 2 O 4 ) nanocomposite was designed to integrate dye adsorption, UV‐light harvesting, and interfacial charge transfer within a single photocatalyst for sustainable wastewater treatment. In this system, ZnO functions as the UV‐active semiconductor, ZnFe 2 O 4 acts as an electron mediator, and chitosan serves as a biopolymeric matrix providing abundant ─OH and ─NH 2 groups that enhance dye binding and nanoparticle dispersion. The composite achieved rapid degradation of rhodamine B (92%) and methylene blue (79%) under UV/H 2 O 2 conditions, with pseudo‐first‐order rate constants of 19.3 × 10 −3 and 11.3 × 10 −3 min −1 , respectively. Optical analysis revealed a progressive reduction in the bandgap from 1.90 eV (ZnFe 2 O 4 ) to 1.56 eV (ZnO‐ZnFe 2 O 4 ) and 1.29 eV (Cs‐ZnO‐ZnFe 2 O 4 ), thereby enhancing photon utilization and carrier generation under UV illumination. Electrochemical analyses confirmed lower charge‐transfer resistance (4.14 → 4.12 Ω from dark to light) and increased photocurrent density, verifying efficient electron‐hole separation. Scavenger studies identified •OH radicals as dominant in the degradation pathway. The composite maintained 88% (Rh‐B) and 77% (MB) activity over five cycles with negligible mass loss, demonstrating excellent reusability. This study establishes Cs‐ZnO‐ZnFe 2 O 4 as a UV‐active, recyclable heterojunction photocatalyst for efficient dye degradation and sustainable wastewater purification.