Removal of dyes from wastewater using polyvinyl alcohol/sodium alginate/Fe3O4/TiO2 composite membranes

Purpose This study aims to develop a durable and recyclable bio-based polymer membrane for efficient dye removal from wastewater, overcoming the limitation of excessive hydrophilicity in traditional materials such as polyvinyl alcohol (PVA). Design/methodology/approach A PVA/sodium alginate (SA) composite membrane, incorporating Fe3O4 and TiO2 nanoparticles, was fabricated via solution casting. The membrane was cross-linked using a CaCl2 and citric acid (CA) ethanol solution to enhance its structural stability in aqueous environments. The membrane was characterized using SEM, FT-IR, XRD and thermogravimetric analyzer. Its adsorption performance was evaluated for Congo Red (CR) and Methylene Blue (MB), with a focus on adsorption kinetics, isotherms and reusability. Findings The PVA/SA/Fe3O4/TiO2 membrane demonstrated significantly enhanced adsorption capacity compared to pure PVA. For CR, the maximum removal efficiency and adsorption capacity reached 95.55% and 47.78 mg/g, respectively. For MB, these values were 80.59% and 53.75 mg/g. The adsorption processes for both dyes followed the pseudo-second-order (PSO) model and the Langmuir isotherm model. The membrane exhibited good reusability, maintaining reasonable removal rates (53.76% for CR, 67.21% for MB) after four consecutive cycles. Research limitations/implications For wastewater treatment applications. Practical implications This method realizes low-energy and green adsorption, providing a new route for dye wastewater treatment. Social implications Reduce environmental pollution pressure. Originality/value This work presents a simple and effective strategy to engineer a robust, high-performance, and reusable bio-composite membrane. It offers a practical and sustainable solution for treating dye-contaminated wastewater, addressing a critical environmental challenge.