Household activated-carbon water filters must be replaced wholesale and disposed of as hazardous waste once saturated. What they lock inside is PFAS—nicknamed 'forever chemicals'—a family of more than 15,000 compounds found in cookware coatings, outdoor apparel, and firefighting foam. They are so persistent because of a single bond: the carbon-fluorine bond, the strongest single bond in organic chemistry. Incinerators must exceed 1000°C to barely pull it apart, and incomplete combustion at those temperatures can release even more problematic fluorinated byproducts.
A paper published October 19 in *PNAS* offers a new answer: a palladium-coated hollow fiber membrane that fishes PFAS out of water while delivering hydrogen atoms right to them. Over 58 continuous days, it removed more than 90% of each of six regulated PFAS compounds and about 83% of total fluorine.
Capture Is Not Destruction
PFAS can be caught. Activated carbon, ion-exchange resins, and reverse osmosis all separate it from water. The trouble is what comes after: concentrated waste streams, spent filter cartridges, and high-saline brine still contain the original molecules, destined for landfill or high-temperature incineration—options several regulators now restrict because incineration is unreliable.
Traditional solutions are hunters: they bind the prey and haul it away. The killer has always been missing. No microbe can break the carbon-fluorine bond, and ordinary chemical reagents cannot reach it. Fluorine atoms act like a ring of interlocking armor plates shielding the carbon backbone.
Hydrogen from the Inside Out
The device's cleverness lies entirely in the hydrogen delivery route: hydrogen is pressurized into the fiber's inner lumen and diffuses outward, reaching the base of the palladium nanolayer coated on the fiber's exterior. Palladium splits hydrogen molecules into individual hydrogen atoms with greatly heightened reactivity; simultaneously, PFAS from the water adsorb onto the same palladium surface.
> Note: This process is called hydrodefluorination. Palladium is the matchmaker—it holds onto the PFAS with one hand, places the split hydrogen atoms on the same table with the other, and on that table the carbon-fluorine bond is cleaved. Rittmann summarized it plainly: palladium attracts PFAS, palladium attracts hydrogen, and then it brings them together.
Both reactants meeting on the same surface is the core of the design. Bubble hydrogen directly into water, and most atoms escape before finding their target. Delivering it through the membrane lumen gives every palladium site a dedicated hydrogen supply line.
The 58-Day Report Card
The paper's first author is Jie Cheng, with Bruce Rittmann leading the research. The team is from Arizona State University, with collaborators ranging from Rice University (USA) to Tongji University (China), and the National University of Singapore and Nanjing University. The experiment ran continuously for 58 days with six regulated priority PFAS in the water.
| Metric | Reading | Notes | |---|---|---| | Per-compound removal | >90% each | All six regulated PFAS covered | | Total fluorine removal | ~83% | Fluorine truly stripped; molecules dismantled | | Continuous operation | 58 days | Long-term stability demonstration | | Palladium cost | ~$50,000/kg | The biggest current engineering hurdle |
Total fluorine removal is the key figure. Removal rates can be inflated by 'relocation': moving molecules from water onto the membrane keeps measured water concentrations low. Elemental fluorine conservation doesn't cooperate with that trick. Only when the carbon-fluorine bond actually breaks does fluorine leave the molecule and enter the water phase, where it can be measured. The 83% figure is proof of destruction—transfer alone cannot produce such a reading.
Likely Destination
The Rittmann team is clear-eyed about placement. Municipal water plants are unlikely to put reactors directly at intake points. The realistic route is as a second-stage player: first use activated carbon to concentrate PFAS from large water volumes into a small waste stream, then use the catalytic membrane to destroy that stream completely. A palladium-saving alternative is already being tested—combining palladium nanoparticles with pollutant-degrading bacteria in a single membrane, running metal and microbial attack routes in parallel; the team says early results hold.
A long stretch of engineering still lies between the lab and municipal networks: stability at scaled flow rates, re-tuning for fluctuating water quality, and palladium recovery all need to be worked out. But the narrative has flipped: PFAS treatment has moved from 'capture and store' to 'capture and destroy.'
Sources and caveats: Cheng, J. et al., *Catalytic reactive-hydrogen membranes for rapid capture and hydrodefluorination of six PFAS of regulatory concern*, PNAS (2026), DOI 10.1073/pnas.2613985123, published October 19; quotes and background from contemporaneous Phys.org and Interesting Engineering coverage. The 58-day data are from laboratory continuous-flow experiments, not field pilots; palladium price is a market reference at reporting time; author affiliations are based on the paper byline and press coverage—the full paper was not directly verified.