Amine- and Fluoroalkyl-Functionalized MXene for Dual-Mode PFOS and PFBS Adsorption

Abstract

Despite several years of intensive research, the development of adsorbents that can achieve rapid, selective, and high-capacity removal of per- and polyfluoroalkyl substances (PFAS) remains a critical challenge, particularly for the simultaneous removal of both long- and short-chain PFAS under complex water-matrix conditions. Addressing this challenge requires sorbent platforms with tunable structures capable of integrating multiple adsorption mechanisms. In this study, MXenea two-dimensional material (2D) with robust structural integrity, aqueous stability, and high chemical tunabilitywas selected as a versatile adsorption platform and surface-functionalized via aminosilane grafting (NH2−MXene) and fluoroalkylsilane grafting (F−MXene). These modifications were designed to enhance PFAS affinity through complementary electrostatic, hydrophobic, and fluorophilic interactions toward both long-chain perfluorooctane sulfonate (PFOS) and short-chain perfluorobutane sulfonate (PFBS). Surface functionalization markedly enhanced PFAS uptake within 1 h; at pH 5.5, NH2−MXene and F−MXene achieved PFOS removal of 95.0 ± 2.2% and 86.0 ± 0.9%, respectively, while PFBS removal reached 65.5 ± 2.4% and 72.0 ± 0.7%. To evaluate synergistic effects, a mixed-functionalized MXene (NH2/F−MXene) was systematically synthesized with controlled amine-to-fluoroalkyl ratios. This mixed-functionalized system achieved near-quantitative (∼100%) removal of both PFOS and PFBS at an optimized 75:25 NH2/F ratio in a mixed 100 ppb PFOS−PFBS solution. This work provides a systematic comparison of PFOS and PFBS adsorption on NH2−MXene and F−MXene, elucidating how distinct surface functionalities govern adsorption kinetics, capacity, and selectivity. Furthermore, the performance of functionalized MXene was evaluated in mixed-PFOS and PFBS systems, in the presence of natural organic matter, in tap water, across a broad pH range, and over multiple regeneration cycles, demonstrating their robustness and practical potential for PFOS and PFBS remediation.