Optical and dielectric properties of Al2O3/V2O5/Co3O4-chitosan composite films for potential dielectric applications

Abstract

Chitosan (CS)-based composite films containing Al₂O₃, Co₃O₄, and V₂O₅ were prepared to investigate the combined influence of metal oxide incorporation on the structural, thermal, optical, and dielectric properties of CS. Unlike studies that mainly examine the effect of individual oxide fillers, the present work comparatively evaluates the sequential CS, CS/Al₂O₃, CS/Al₂O₃/V₂O₅, and CS/Al₂O₃/V₂O₅/Co₃O₄ systems. Structural and compositional analyses confirmed the incorporation of the metal oxides into the CS matrix, while FESEM observations indicated a broadly distributed filler phase. Thermogravimetric analysis showed that all films remained thermally stable below approximately 300 °C, while the residual fraction increased from 1.7% for pure CS to 36.6% for CS/Al₂O₃/V₂O₅/Co₃O₄. The indirect optical band gap increased from 3.90 eV for pure CS to 5.35 eV after Al₂O₃ incorporation, then decreased to 3.40 and 3.00 eV after the subsequent addition of V₂O₅ and Co₃O₄, respectively. The corresponding refractive indices were 1.87, 1.58, 2.02, and 2.17. Dielectric measurements revealed a pronounced enhancement in the low-frequency permittivity, from approximately 200 for pure CS to approximately 1600 and 1200 for CS/Al₂O₃/V₂O₅ and CS/Al₂O₃/V₂O₅/Co₃O₄, respectively, followed by a decrease with increasing frequency. Impedance analysis further indicated enhanced charge-carrier transport and reduced interfacial resistance after V₂O₅ and Co₃O₄ incorporation. These findings demonstrate that sequential metal oxide incorporation provides an effective route for tuning the optical and dielectric/electrical response of chitosan-based composite films.