Role of Polyvinyl Alcohol in Enhancing Chitosan Membranes for Desalination: An Experimental and Theoretical Study

Abstract

Chitosan is a promising biopolymer for desalination membranes, but its brittleness and poor mechanical strength hinder practical application. Blending with polyvinyl alcohol (PVA) is a common strategy to enhance flexibility, hydrophilicity, and salt rejection. However, the specific role of PVA in improving membrane performance remains insufficiently understood. This study combines experimental characterization with density functional theory (DFT) calculations to elucidate the molecular interactions between chitosan–Na⁺ and PVA–Na⁺ systems. FTIR analysis confirms hydrogen bonding between chitosan and PVA, indicated by a shift in ─OH stretching from 3271 to 3290 cm⁻¹. Increasing PVA content significantly enhances membrane swelling, hydrophilicity, ion rejection, and water flux. The CP3 membrane exhibits optimal performance, with a surface roughness of 0.122 nm, swelling degree of 142.06%, contact angle of 42.96°, water flux of 6.762 L m⁻² h⁻¹, and salt rejection of 98.8%. DFT results reveal stronger Na⁺ binding with PVA than with chitosan, supporting its key role in ion separation. Moreover, CP3 maintains stable performance at 75 °C during pervaporation. These findings offer molecular-level insight into the synergistic function of chitosan and PVA, providing a rational basis for the development of efficient, sustainable desalination membranes.