A Monolithic Carbon Nanotube-Reinforced Cellulose Benzoate Hydrogel for Simultaneous Removal of Microplastics and Per- and Polyfluoroalkyl Substances from Water

Abstract

Simultaneously removing particulate microplastics and dissolved per- and polyfluoroalkyl substances (PFAS), which differ greatly in physical nature, with a single, easily recoverable material remains challenging. Here, we developed a carbon nanotube (CNT)-modified cellulose benzoate (CB) hydrogel as a reusable cellulose-based adsorbent for the removal of polystyrene (PS) microplastics and perfluorooctanoic acid (PFOA), selected as representative microplastic and PFAS contaminants, respectively. Benzoyl functionalization of the cellulose backbone created aromatic, hydrophobic domains that raised the hydrogel’s affinity toward both contaminants, while CNT incorporation opened up the pore structure of the polymer network and improved the mechanical strength. The hydrogel achieved removal efficiencies above 97% for both contaminants, could be readily retrieved from water after treatment, and retained this performance over five adsorption–desorption cycles. Adsorption kinetics showed rapid uptake of both PS and PFOA, and equilibrium isotherms pointed to a high capacity for PS (estimated at ∼700–800 mg/g) and heterogeneous binding for PFOA over the concentration range studied. High removal efficiencies were also maintained in river water and in a cocontaminant system containing both PS microplastics and PFOA. Density functional theory (DFT) calculations and X-ray photoelectron spectroscopy (XPS) analysis indicated that PS binding is governed mainly by dispersion (van der Waals) interactions, whereas PFOA combines dispersion along its fluorinated chain with stronger, localized polar interactions between its carboxylate headgroup and hydroxyl groups of CB. These findings link the benzoate functionalization and CNT-tuned porous network to the uptake of contaminants with distinct physical nature, providing clear structure–property–performance relationships for the hydrogel. Overall, this work offers an effective strategy for designing reusable cellulose-based hydrogels capable of removing both particulate microplastics and dissolved PFAS, thereby broadening the application potential of biobased hydrogel adsorbents in water treatment.