Adsorptive performance of TiO₂/chitosan/PVA nanofibers: characterization, kinetic pathways, and equilibrium isotherms for dye removal

Abstract

Methyl orange (MO) is a persistent and toxic azo dye whose removal from wastewater remains challenging. Nanocomposite adsorbents combining titanium dioxide (TiO₂) with biopolymers offer enhanced surface functionality for dye uptake. In this system, chitosan (CS) provides protonable amino groups for electrostatic interaction, while poly(vinyl alcohol) (PVA) improves hydrophilicity and structural stability. Electrospinning enables the fabrication of uniform TiO₂/CS/PVA nanofibers membranes. TiO₂/CS/PVA nanofibers were successfully fabricated by electrospinning, exhibiting homogeneous TiO₂ dispersion and stable fiber morphology. A maximum adsorption capacity of 297.9 mg g⁻ 1 was achieved, and equilibrium data were best described by the Freundlich model (R 2  > 0.99), indicating heterogeneous multilayer adsorption. Kinetic analysis showed that adsorption followed a pseudo-second-order model, suggesting that adsorption was primarily driven by surface interactions, with intraparticle diffusion as a secondary mechanism. Under UV-A irradiation at pH 3.0, nanofibers containing 5 wt% TiO₂ achieved up to 98.7% MO removal. The membranes retained high removal efficiency over five regeneration cycles, demonstrating good reusability. The electrospun TiO₂/CS/PVA nanofibers enabled efficient MO removal through a sequential process involving rapid adsorption in the dark followed by photocatalytic degradation under UV-A irradiation. The hybrid nanofibrous architecture facilitated effective surface interactions and TiO₂ accessibility, enhancing dye capture and subsequent degradation. Overall, this approach offers a cost-effective, biodegradable, and scalable platform, highlighting TiO₂/CS/PVA nanofibers as a promising material for the treatment of dye-contaminated wastewater.