Accessibility Matters: Demonstrating the Critical Role of Mesoporous Pore Dimension on PFAS Adsorption Removal by Amine-Functionalized Surfaces

Per- and polyfluoroalkyl substance (PFAS) contamination presents a critical challenge for both industrial and environmental management and drives the need for advanced, high-performance sorbents as a key component of the treatment toolbox. Toward this need, we advance the design of amine-functionalized mesoporous silica nanoparticles (MSNs) by systematically tuning pore entrance diameter and, thereby, internal surface accessibility. MSNs with controlled architectures were synthesized via a modified Stöber method and surface-functionalized with either (3-aminopropyl)triethoxysilane (APTES) or branched polyethylenimine (bPEI10K), yielding a rational library of sorbent materials. Sorption behavior was evaluated as a function of pore dimension, surface chemistry, solution pH, and PFAS structure, including both long- and short-chain carboxylates and sulfonates. Results indicate that pore entrance size influences both amine grafting density and PFAS sorption behavior, suggesting a threshold diameter corresponding to increased access to internal binding sites. Nitrogen-normalized adsorption capacities reflect contributions from both steric accessibility and chemical (surface)-binding affinity. These findings demonstrate that pore architecture, beyond total surface area or surface chemistry, is a critical design element for the development of tunable, high-capacity PFAS sorbents. This structure-function framework connects pore architecture to adsorption performance, directly informing sorbent design for PFAS management.