Designing Smarter Adsorbents: Matching Materials to PFAS Molecular Structure

A review by researchers at Tohoku University’s Institute of Multidisciplinary Research for Advanced Materials identifies key molecular design principles for more effective adsorbents to remove PFAS (“forever chemicals”) from water.

Led by Associate Professor Kouki Oka (with Takahiro Ami, Aki Shibata, and Hitoshi Kasai), the work was published in ACS Materials Au (DOI: 10.1021/acsmaterialsau.6c00168) around mid- September 2026, with university press releases in early- to -mid October 2026.

Background on PFAS and the need for better removal

Per- and polyfluoroalkyl substances (PFAS) feature strong carbon- fluorine bonds that give them high chemical stability plus water- and oil- repelling properties. They are widely used in semiconductors, firefighting foams, textiles, food packaging, and coatings. Concerns over health effects of certain “specific PFAS” (e.g., PFOS and PFOA) have driven expanding regulations.⁠

Examples of regulatory limits include:

• EU drinking water: 100 ng/L combined for 20 PFAS.
• EU surface waters: 4.4 ng/L (PFOA- equivalents annual average) for 25 PFAS.
• Canada: 30 ng/L objective for 25 PFAS combined.
• Japan (from April 2026): 50 ng/L combined for PFOS and PFOA in drinking water.⁠

Adsorption (PFAS molecules attaching to a solid adsorbent surface) is a practical removal method because equipment can be relatively simple and materials can be tailored. Conventional options like activated carbon often fall short on capacity, speed, or performance across diverse PFAS structures.

Key insight from the review

Effective design requires treating PFAS molecules as having distinct structural components rather than as single targets. Representative compounds like PFOS and PFOA consist of:

• A fluorinated carbon chain (hydrophobic and fluorophilic character).
• A typically charged terminal (head) group in water (enabling electrostatic or other polar interactions).⁠

These parts have different chemical properties and interact differently with materials. Designing adsorbents that strongly engage both (or the relevant features of a given PFAS class) improves performance.

The review surveys research on PFOS, PFOA, and other regulated and monitored PFAS under EU and Canadian frameworks, summarizing trends, high-performing adsorbent features, and design principles for broader coverage as regulations expand.⁠

As Oka notes: “As the range of PFAS subject to regulation continues to expand, we need adsorbents that can effectively target a wider variety of these compounds. By understanding how different parts of PFAS molecules interact with adsorbent materials, we can establish clearer design principles for developing more effective removal technologies.”

Outlook

The principles aim to guide higher- performance, tailored adsorbents for specific PFAS classes, supporting both water treatment and environmental protection and the fluorochemical industry.

The team’s next steps involve applying these ideas to develop improved materials. The work received support from JST CREST and NEDO programs focused on PFAS detection, concentration, decomposition, and related technologies.

Full English press release: tohoku.ac.jp/en/press/designing_better_adsorbents_to_remove_pfas_from_water.html.

Japanese version and PDF details are also available on the university site.

Summary of adsorption mechanisms by PFAS class (from the 2026 ACS Materials Au review by Ami, Shibata, Kasai & Oka).

The review classifies specific PFASs into four categories and shows that adsorption is governed by a balance of hydrophobic, fluorous, electrostatic, and host, guest interactions.

The relative importance of each mechanism shifts with molecular structure (especially chain length and functional groups). Interactions are grouped by whether they primarily target the perfluoroalkyl chain or the terminal functional (head) group.

1. Long- chain PFASs

(Perfluorinated carbon chain length ≥ 6, excluding the functional- group carbon; e.g., PFOS, PFOA, PFHxS, PFNA, PFDA)

• Dominant mechanisms: Hydrophobic and fluorous interactions with the long perfluoroalkyl chain, often combined with electrostatic attraction or ion exchange involving the anionic head group.
• Pore confinement and host– guest inclusion can further enhance uptake in materials with suitable pore sizes.
• Affinity generally increases with chain length.
• Preferred adsorbents: Activated carbons, ion- exchange resins, cationic porous materials (certain MOFs and COFs), hydrophobized surfaces.
• Practical notes: High capacities and relatively rapid kinetics are achievable, but competitive adsorption from other organics and challenges with regeneration and secondary waste remain common.⁠

2. Short- chain PFASs

(Shorter homologues of conventional PFCAs/PFSAs, typically C3- C5)

• Dominant mechanisms: Electrostatic attraction and ion exchange with the anionic head groups become increasingly important because the shorter fluorocarbon chains produce weaker hydrophobic interactions.
• Hydrophobic contributions are reduced but still present; molecular confinement in tailored pores can help compensate.
• Preferred adsorbents: Ion- exchange resins, cationic adsorbents, and molecularly confined porous materials.
• Practical notes: Lower overall adsorption affinity and earlier breakthrough compared with long- chain species; performance is more sensitive to competing ions.⁠

3. Emerging alternative PFASs

(Structurally modified substitutes featuring ether linkages, branching, chlorine substitution, partially fluorinated chains, fluorotelomer moieties, or neutral precursors)

• Dominant mechanisms: Highly structure- dependent. Can involve electrostatic interactions, hydrophobic and fluorous interactions, hydrogen bonding, host-guest inclusion, or combinations thereof.
• Simple chain- length trends are less reliable; specific chemical features (e.g., ether oxygen, Cl atoms, conformation) dictate preferred binding modes.
• Preferred adsorbents: Materials with chemically tailored binding sites matched to the distinctive structural motifs.
• Practical notes: High structural diversity makes adsorption behavior harder to predict from chain length alone; rational design of complementary binding sites is especially valuable.⁠

4. Ultrashort- chain PFASs

(Very short chains, typically C1- C2, e.g., trifluoroacetic acid and related species)

• Dominant mechanisms: Almost exclusively functional- group- targeted interactions (strong electrostatic attraction and ion exchange, possible hydrogen bonding or coordination). Hydrophobic contributions are minimal or negligible because of the extremely short fluorocarbon moiety.
• Preferred adsorbents: Strongly cationic or ion- exchange materials with high density of complementary charged sites (fluorous modifications can sometimes provide secondary benefits).
• Practical notes: Lowest affinities among the classes; highly mobile, easily outcompeted by inorganic anions, and among the most challenging to remove effectively with conventional hydrophobic adsorbents.⁠

Overall design principle

As chain length decreases, the central design focus shifts from hydrophobic retention of the perfluoroalkyl chain toward functional- group- selective capture.

Multiple interactions often operate simultaneously in real systems, but the primary targeted moiety largely determines which PFAS class a given adsorbent will handle effectively.

Adsorption of Per- and Polyfluoroalkyl Substances across Molecular Classes: Understanding Adsorption Behavior and Adsorbent Performance

This is the open- access review article published in ACS Materials Au (2026) by Takahiro Ami, Aki Shibata, Hitoshi Kasai, and Kouki Oka (Tohoku University).

Abstract summary

Per- and polyfluoroalkyl substances (PFASs) are widely used industrially and commercially due to the exceptional stability of their C– F bonds and their water- and oil-repellent properties. Some “specific PFASs” raise concerns because of persistence, bioaccumulation potential, and possible effects on human health and ecosystems.

Adsorption is a promising water- purification approach, and substantial effort has gone into developing adsorbents for specific-PFAS removal.

Specific-PFAS adsorption is governed by a balance of hydrophobic, electrostatic, and host- guest interactions. Adsorption behavior therefore varies substantially with molecular structure, so adsorbents that work well for one class are not necessarily optimal for others.

The review takes a PFAS- centered perspective and classifies significant specific PFASs into four categories:

1. Long- chain PFASs
2. Short- chain PFASs
3. Emerging alternative PFASs
4. Ultrashort- chain PFASs

It organizes effective adsorbents for each class according to their adsorption mechanisms. This clarifies the relationships between PFAS molecular characteristics and the requirements for adsorption, providing practical guidance for adsorbent selection and design.

Key points from available content

• Interactions that target the perfluoroalkyl chain (hydrophobic and fluorous interactions, host- guest inclusion, pore confinement) are especially important for long- chain PFASs.
• Interactions that target the functional (head) groups (electrostatic attraction, ion exchange, hydrogen bonding, Lewis acid- base, coordination) become increasingly critical for shorter- chain species.
• Representative adsorbent types and practical limitations differ by class (e.g., activated carbons and hydrophobic porous materials perform strongly for long-chain species; electrostatic and ion- exchange materials gain importance for short- chain species).

Cross- class comparison tables and figures in the paper map molecular characteristics → dominant interactions → preferred adsorbent types → main practical limitations (competitive adsorption, regeneration, secondary waste, etc.).

This review underpins the Tohoku University press releases on “Designing Better Adsorbents to Remove PFAS from Water”, emphasizing that treating PFAS molecules as assemblies of distinct structural components (fluorinated chain and charged terminal group) enables more rational, high- performance material design as regulations expand to cover a broader range of PFAS structures.

You can access the full open- access article (including figures, tables, and the complete reference list of ~181 citations) directly at the ACS link you provided.

Title: Adsorption of Per- and Polyfluoroalkyl Substances across Molecular Classes: Understanding Adsorption Behavior and Adsorbent Performance

DOI: 10.1021/acsmaterialsau.6c00168

Journal: ACS Materials Au (2026)

Published online: 16 September 2026

Provided: Tohoku University

Corresponding authors: Takahiro Ami (takahiro.ami.c3@tohoku.ac.jp) and Kouki Oka (oka@tohoku.ac.jp)

Online ISSN: 2694-2461

Authors: Takahiro Ami*; Aki Shibata; Hitoshi Kasai;Kouki Oka*

The article is open access under the indicated license; a PDF is available on the ACS site.