New materials could snatch harmful “forever chemicals” out of water in a faster, more sustainable way than previous ones.

So-called forever chemicals are a group of more than 10,000 infamous compounds. Their official name is per- and polyfluoroalkyl substances, or PFAS for short. And they’re used to make cookware, food packaging, makeup and many other products.  

PFAS are like “the Avengers” of chemicals, in that they’re super hard to destroy, says Soumya Mukherjee. He’s a materials chemist at the University of Limerick in Ireland. But in many ways, PFAS are more like villains than heroes. Because they’re so tough, PFAS that get into the environment stick around for a long time. They pollute soils, food and drinking water. Exposure to those chemicals has been linked to health problems.

Some existing materials, such as activated carbon, can filter PFAS out of water. But it takes hours for activated carbon to suck up all the PFAS it can fit. Pumping water through activated carbon filters is also costly and uses a lot of energy. What’s more, activated carbon isn’t easy to recycle. Once filled with PFAS, it’s typically burned.

Mukherjee’s team wanted to design a faster, reusable alternative. So they turned to metal-organic frameworks, or MOFs. This group of materials is known for their ability to stash molecules. A MOF’s metals and organic molecules form a huge network with a lot of open space inside. PFAS molecules can line the surfaces of all these nooks and crannies.

The researchers created four types of MOFs. All contained the metal zirconium. But they had differences in their organic molecules. These differences changed how PFAS interacted with the MOFs. The researchers also took each of these four MOFs and added a layer of organosilicone (OS). Changing the surface this way can change how PFAS sticks. That gave the team a total of eight materials to test — the original and OS-coated version of each MOF.

Some of the MOFs grabbed more PFAS than activated carbon did. (Activated carbon took up only 40 percent of one forever chemical called PFOA. It took up 71 percent of another called PFOS.) The new materials also trapped forever chemicals in less than 30 minutes. That was much faster than activated carbon worked. Washing the MOFs in acetone or other common lab chemicals removed the PFAS they’d collected. The MOFs could be used to filter drinking water, washed and then used again.

The researchers shared their results February 12 in Advanced Materials.

None of their materials did a great job snagging one type of forever chemical. “There is hardly anything that really works well yet for GenX,” Mukherjee says. GenX was the smallest of the PFAS tested. Smaller molecules can more easily run away from the MOFs, he says. Scientists are still looking for materials with the right chemistry to capture those evasive pollutants.

PFAS collectors

Mukherjee’s team made eight types of MOFs. All types contain the same metal and have the same structure. But they have differences in their organic molecules that change their properties. Each pair of materials shown in this graph has the same MOF. The second in each pair is coated with organosilicone (OS). The data show how well different materials picked up three different types of PFAS chemicals (PFOA, PFOS and GenX). In each test, researchers exposed one type of MOF to a known amount of one type of PFAS. They measured how much of that PFAS was left after 24 hours, then calculated the percentage the MOF had removed.

Data Dive:

1. Look at the first of each pair of MOFs (MOF 1, MOF 2, MOF 3 and MOF 4). Which of these performs best at removing PFAS?
2. Now compare the MOF in each pair with their corresponding MOF-OS. Which performs better at removing PFAS — the one with or without OS?
3. Overall, which MOF or MOF-OS removes the most PFOA and PFOS? How much more PFOS does it remove than GenX?
4. In water, PFAS is usually a mixture of different molecules. What strategy could researchers use to capture different kinds of PFAS in the same solution?