Chemically Tuned MOF Adsorbent Simultaneously Strips PFAS, Arsenic, and Lead from Water

Water rarely carries just one poison. In industrial plumes, landfill leachate, and agricultural runoff, the notorious “forever chemicals” known as PFAS often coexist with arsenic and lead, three contaminants with wildly different chemistries that have historically demanded separate treatment trains. Now, a team of environmental engineers at the University of Pittsburgh has reported a single adsorbent capable of capturing all three at once: a lanthanum-modified metal-organic framework, La@MOF-808, described in the journal Frontiers in Materials. The work tackles one of the most stubborn problems in water treatment, where conventional adsorbents like granular activated carbon and ion-exchange resins falter against highly mobile short-chain PFAS and lose efficiency when co-occurring contaminants compete for the same binding sites.

The material belongs to a class of crystalline solids called metal-organic frameworks, or MOFs, in which metal ions are stitched together by organic linkers into porous lattices with enormous internal surface areas. MOF-808 is built from zirconium clusters and trimesic acid, and its pores can be chemically decorated after synthesis. In this case, the researchers incorporated lanthanum oxide during the solvothermal synthesis, dissolving zirconium oxychloride and trimesic acid in a mixture of dimethylformamide and formic acid, adding lanthanum oxide, and heating the sealed reactor at 120 degrees Celsius for 24 hours. The result is a bulk batch of La@MOF-808 whose structure and morphology were verified in earlier work by the same group using powder X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, and electron microscopy. Lanthanum incorporation is known to enhance the uptake of oxyanions such as arsenate and to alter the surface charge of the framework, a property that turns out to matter greatly for PFAS capture.

To probe how the adsorbent behaves when contaminants coexist, the team designed an elegant experimental matrix of eight solutions, run in triplicate, containing every combination of a 15-compound PFAS suite, arsenate [As(V)], and lead ions (Pb2+). The PFAS panel spanned the full structural diversity of the contaminant family: four ultra-short-chain compounds such as PFBA and PFBS, seven short-chain species including the GenX replacement chemicals ADONA and HFPO-DA, and four long-chain compounds including PFOA, PFNA, PFDA, and PFOS. Each PFAS was initially present at 0.08 micrograms per liter, while arsenic and lead were each introduced at 10 milligrams per liter. After 24 hours of shaking at 25 degrees Celsius, the suspensions were centrifuged, filtered through 0.22-micrometer membranes, and analyzed: PFAS by triple-quadrupole mass spectrometry with chromatographic separation on a C18 column, and the metals by inductively coupled plasma optical emission spectrometry.

The headline numbers come from Langmuir isotherm fits across a broad concentration range. The fitted maximum adsorption capacities reached 307.7 milligrams per gram for As(V), 223.2 milligrams per gram for Pb2+, and 254.4 to 267.7 milligrams per gram for the grouped short- and long-chain PFAS mixtures, respectively. The researchers are careful to note that the PFAS values represent grouped capacities derived from mixtures of multiple compounds at equal initial concentrations, not compound-specific capacities, and that the Langmuir equation serves here as an empirical description of the equilibrium data rather than proof of monolayer adsorption. For the long-chain PFAS mixture, the Langmuir fit was comparatively weaker, with a correlation coefficient of 0.879 close to the Freundlich value of 0.857, hinting at heterogeneity in the adsorption environment arising from differences in molecular structure and functional groups among the long-chain compounds.

Perhaps the most intriguing finding is that co-contaminants did not uniformly sabotage PFAS removal, as conventional wisdom might predict. Instead, the effects were PFAS-specific. Arsenate enhanced the removal of 4:2FTS, PFHxS, and PFDA, while lead boosted the removal of a longer list including 6:2FTS, PFOA, ADONA, HFPO-DA, PFHxS, and PFDA. When both metals were present simultaneously, removal increased for 6:2FTS, ADONA, HFPO-DA, PFNA, PFHxS, PFPeS, and PFDA, whereas several ultra-short-chain compounds, including PFBA, 4:2FTS, PFHxA, PFHpA, and PFBS, showed reduced uptake. The authors propose that lead ions could act as cation bridges between the adsorbent surface and anionic PFAS functional groups, creating additional localized interactions that partially offset the competitive pressure from arsenate, which vies for overlapping adsorption sites within the framework. They are appropriately cautious: because post-adsorption characterization and direct measurements of lead speciation were not performed, the cation-bridging mechanism remains a hypothesis grounded in the observed removal trends rather than a confirmed molecular pathway.

Chain length emerged as a decisive variable. Longer-chain PFAS generally showed higher removal than their shorter counterparts, consistent with stronger hydrophobic interactions and greater affinity for the porous framework. PFOS concentrations after adsorption fell consistently below the method detection limit of 0.01 micrograms per liter under all conditions, indicating substantial but unquantifiable removal. PFDA, remarkably, improved in every co-contaminant scenario tested. Ultra-short-chain compounds proved the hardest to capture, echoing previous reports that these highly mobile species, prevalent in German drinking water sources and largely unregulated, are notoriously difficult to strip by adsorption.

Solution pH proved equally critical. PFAS removal peaked at pH 4.0, with removal rates exceeding 87 percent for most compounds, while maximum As(V) and Pb2+ removal occurred near pH 5.0, defining a favorable acidic operating window of roughly pH 4 to 5 for simultaneous treatment. The chemistry is straightforward: MOF-808 carries a point of zero charge near pH 4, so below this threshold the surface is positively charged and electrostatically attracts the predominantly anionic PFAS species, which remain deprotonated across the entire tested range because they are strong acids. Above pH 5, hydroxide ions increasingly compete with anionic contaminants for available sites, and very alkaline conditions may even compromise the structural stability of the framework itself.

Kinetic and thermodynamic analyses rounded out the picture. Both pseudo-first-order and pseudo-second-order models described the adsorption data reasonably well, with the pseudo-second-order model providing a marginally better overall fit, particularly noticeable for lead. The authors interpret the kinetics as describing rate behavior rather than as direct evidence of chemisorption, and they note that intraparticle diffusion may contribute, especially for larger PFAS molecules navigating the porous structure. Temperature experiments at 25, 40, and 55 degrees Celsius showed adsorption capacity rising with temperature for all contaminants. Negative Gibbs free energy values confirmed the process is spontaneous, positive enthalpy values revealed it is endothermic, and positive entropy values indicated increased molecular randomness at the solid-liquid interface during uptake.

The reverse perspective also held: the presence of PFAS and co-occurring metals reduced the adsorption capacities of arsenic and lead. Under fixed-concentration multicomponent conditions with all 15 PFAS at 50 milligrams per liter total and each metal at 50 milligrams per liter, the highest As(V) capacity of 281.7 milligrams per gram and Pb2+ capacity of 217.3 milligrams per gram occurred when each metal was present alone, while PFAS decreased the lead capacity to 180.6 milligrams per gram. These trade-offs underscore the authors’ central argument that adsorbent performance must be evaluated under multicomponent conditions rather than relying solely on single-contaminant experiments, a practice that has dominated the MOF adsorption literature to date.

The study arrives amid sobering context. Arsenic contamination alone is estimated to affect roughly 140 million people across 70 nations, PFAS have been detected everywhere from drinking water systems to remote Arctic regions, and toxicological studies associate PFAS exposure with neurological, liver, and pulmonary effects, hormonal imbalances, and elevated risks of kidney and testicular cancers, prompting restrictions on PFOA and PFOS under the Stockholm Convention. The Pittsburgh team, whose work was supported by the university’s Rust 2 Resilience Center, is candid about limitations: the experiments used controlled aqueous matrices rather than real water, the effects of chloride, sulfate, carbonate, phosphate, hardness ions, and natural organic matter remain untested, lanthanum leaching was not measured, and regeneration and reuse of the adsorbent were not evaluated. Future work, they write, should test the material in complex water matrices, characterize it before and after adsorption with techniques such as X-ray photoelectron spectroscopy, and verify trace-level contaminant concentrations in treated water. Until then, La@MOF-808 stands as a promising laboratory-scale demonstration that a single chemically tuned framework can, in principle, confront the full chemical chaos of co-contaminated water in one pass.

Subject of Research: Environmental Chemistry

Article Title: A chemically tuned La@MOF-808 adsorbent for simultaneous removal of Per- and polyfluoroalkyl substances (PFAS), arsenic, and lead from aqueous solutions

Article References: Nawaz, H., Kotchey, G. P., & Sanchez, D. V. P. (2026). A chemically tuned La@MOF-808 adsorbent for simultaneous removal of Per- and polyfluoroalkyl substances (PFAS), arsenic, and lead from aqueous solutions. Frontiers in Materials, 13, Article 1804165. https://doi.org/10.3389/fmats.2026.1804165

Image Credits: AI Generated

DOI: 10.3389/fmats.2026.1804165

Keywords: PFAS, water treatment, metal-organic frameworks, adsorption, arsenic, lead, La@MOF-808, environmental remediation, chemically, tuned, MOF-808, adsorbent