Highly efficient and reusable polymeric nanofibers for cationic dye removal: isotherm, kinetics and thermodynamic study

Abstract

Electrospun membrane-based adsorbents are gaining widespread use in water treatment due to their ease of handling and effectiveness in removing a variety of pollutants from polluted aqueous media. However, the preparation of some nanofibrous membranes often requires the use of organic solvents, which can pollute the environment. In this study, an environmentally friendly nanofibrous adsorbent without using any organic solvent based on polyvinyl alcohol/poly sodium acrylate (PVA/PANa NFs) was fabricated using an electrospinning and thermal crosslinking process. The fabricated PVA/PANa NFs were characterized using various techniques, including FE-SEM, ATR-FTIR, XRD, DSC and the drift method measurement method. The addition of PANa to PVA NFs led to a decrease in the average diameter of nanofibers and played a prominent role in improving their adsorption performance for methylene blue (MB) dye removal. In alkaline media (pH 9.0) and temperatures of 25 °C, 35 °C, and 40 °C, the calculated maximum adsorption capacity of MB dye was found to be 544.28, 538.98 and 530.25 mg g⁻¹, respectively. The pseudo-second-order model provided a good fit to the kinetic data, whereas the Temkin model was found to be well-suited for describing the isotherm data. The negative free Gibbs energy values, which range between 39.6 and 41.5 kJ mol⁻¹, and the negative enthalpy value (−2.41 kJ mol⁻¹), indicate that the adsorption process was feasible, spontaneous, and exothermic. Desorption studies also revealed that the PVA/PANa NFs retained their adsorption capacity even after six consecutive adsorption/desorption cycles, showing their effective reusability.