PFAS adsorption and desorption on functionalized surfaces: A QCM and kinetic modeling approach

The efficient removal of both long- and short-chain per- and polyfluoroalkyl substances (PFAS) remains a critical challenge in advanced water treatment. This study investigates the adsorption and desorption kinetics of two representative PFAS compounds, perfluorooctanoic acid (PFOA) and perfluorobutanoic acid (PFBA), on model surfaces simulating materials commonly used in water purification systems. Quartz crystal microbalance (QCM) was employed under continuous flow for 50 h to monitor real-time mass changes and evaluate the influence of surface hydrophobicity, charge, roughness, and area on PFAS–surface interactions. A key novelty of this work is the integration of QCM with kinetic modeling of adsorption and desorption using the Avrami equation, combined with multivariate statistical analysis. This framework enables a direct comparison of kinetic complexity and interaction strength across surfaces. PFOA exhibited strong adsorption and limited desorption (23–37 %) on hydrophobic, high-surface-area materials, with diffusion-limited kinetics. In contrast, PFBA showed lower adsorption overall but stronger retention on positively charged surfaces (e.g., APTES), with desorption kinetics reflecting surface-dependent release. Pearson correlation and principal component analysis confirmed that hydrophobic interactions dominate PFOA behavior, while PFBA retention and release are more sensitive to electrostatics and surface accessibility. Importantly, this study demonstrates QCM's potential as a rapid, high-resolution screening tool for evaluating material–PFAS interactions under realistic flow conditions. Combining real-time QCM, kinetic modeling, and PCA provides valuable insight for the rational design of tailored adsorbents: hydrophobic porous media for long-chain PFAS and positively charged or structured surfaces for short-chain PFAS in advanced water treatment systems.