This proof-of-concept project aimed to advance the development of an improved passive sampling technology for quantitative capture of per- and polyfluoroalkyl substances (PFAS) in water. The passive sampling technology featured two core components: (1) efficient sorbent receiving phase that can quantitatively uptake a range of PFAS under various water matrices, and (2) ceramic membrane barrier with improved stability and controlled PFAS mass transfer rate. The specific objectives were to (1) develop tailored periodic mesoporous organosilica (PMO) materials with enhanced adsorption of PFAS, (2) develop robust ceramic membranes with tunable PFAS mass transfer, and (3) design a prototype integrative passive sampler for PFAS capture.

Three research tasks were performed corresponding to the specific research objectives. Eight representative PFAS with varied charge properties were investigated, including five anionic, one cationic, one zwitterionic, and one neutral/weakly-charged PFAS.

• In Task 1, a range of functionalized PMO materials for PFAS adsorption were synthesized, characterized, and evaluated. The sorbent-water partition coefficients for PFAS were determined based on batch isotherm studies.
• In Task 2, a series of ceramic membranes with controlled structure and pore properties were prepared through a combination of ceramic processing and sol-gel method. The PFAS diffusivity and mass transfer rates through ceramic membranes were measured in a homemade diffusion cell consisting of two compartments (source and receptor).
• In Task 3, a prototype integrative passive sampler was developed consisting of a sorbent phase for PFAS capture sandwiched between two membranes controlling PFAS mass transfer. The integrative passive sampler was evaluated for PFAS uptake through calibration studies in batch mode.

Functional groups of PMO materials can be tuned to tailor the adsorption of PFAS with different charge properties. PMO materials with amine and hydrophobic groups were efficient for adsorption of anionic and neutral/weakly-charged PFAS, and PMOs with hydroxyl and hydrophobic groups enhanced the adsorption of cationic and zwitterionic PFAS. PFAS mass transfer through ceramic membranes was strongly affected by membrane structure and properties, especially membrane porosity. The fibrous ZrO₂ membrane had PFAS mass transfer rates over one order of magnitude higher than porous the Al₂O₃ membrane. An increase of the Al₂O₃ membrane sintering temperature could further decrease its PFAS mass transfer rates. The prototype integrative passive sampler showed linear uptake of PFAS up to ~four weeks. PFAS sampling rates were dependent on both the type of ceramic membranes and PFAS properties (e.g., octanol-water distribution coefficients).

This project has obtained fundamental information on material design for PFAS adsorption and membrane design to control PFAS mass transfer. Future research is needed to calibrate the passive sampler for a wider range of PFAS, investigate the impact of complex environmental factors, elucidate PFAS transport and uptake behavior within the passive sampler, and evaluate the performance of the passive sampler in the field. Deployment of an improved and robust passive sampling technology can provide a significant advancement for PFAS monitoring and analysis, which would facilitate the development of improved and cost-effective PFAS management practices for such sites. (Project Completion - 2023)

Min, X. 2021. Silica-Based Materials for Water Treatment Applications: Adsorption and Supported Noble Metal-Based Catalysis (Ph.D. Dissertation). University of Wisconsin, Milwaukee. dc.uwm.edu/etd/2816.