Controlled CuO-to-Cu₂O Phase Transformation in Electrospun Fibers for Enhanced Photocatalytic Performance

Abstract

Electrospun copper oxide fibers with tunable phase compositions were fabricated using ascorbic acid as a green reducing agent. By varying the treatment time, calcined CuO fibers were progressively transformed into CuO/Cu₂O heterostructures and Cu₂O without compromising their original fibrous architecture. Structural, chemical, and optical analyses confirmed that the reduction process modified the copper oxidation states and electronic structure, resulting in systematic changes in the bandgap and interfacial properties. Photocatalytic performance was evaluated through methylene blue degradation under simulated solar irradiation using an immobilized photocatalyst configuration. Among the studied materials, the CuO/Cu₂O heterojunction exhibited superior activity compared with the individual CuO and Cu₂O phases, highlighting the key role of interfacial charge-transfer processes. Scavenger experiments using hydroxyl-radical (•OH), superoxide-radical (O₂•⁻), and hole (h⁺) quenchers confirmed the participation of multiple reactive species in the photocatalytic mechanism. The addition of a low H₂O₂ concentration further enhanced dye degradation through a synergistic effect, resulting in an efficiency of 94.1%. Kinetic analysis suggested that the improved performance was associated with efficient charge separation and enhanced generation of reactive oxygen species at the CuO/Cu₂O interface. The stability of the CuO/Cu₂O–H₂O₂ system was assessed over three consecutive reuse cycles. Subsequent SEM analysis confirmed preservation of the fibrous morphology. These findings demonstrate that controlled phase engineering combined with a green reduction route provides a promising strategy for designing immobilized copper oxide photocatalysts for water treatment under simulated solar irradiation.

Keywords: Copper oxide; Electrospun; Dye