The key to the new filters is a class of material called covalent organic frameworks (COFs). These structures are extremely porous, giving them a massive surface area contained within a small space, which means they're effective at grabbing onto large amounts of molecules. Related materials known as metal-organic frameworks (MOFs) are being investigated for use in carbon capture, desalination or pulling drinking water from thin air, and COFs could have a similar set of functions.
For the new study, the researchers focused on using a COF to remove organic dyes from water. These chemicals are a common pollutant of industrial wastewater, and can be toxic and carcinogenic – not to mention difficult to remove.
The team tweaked the COF to make it selectively grab hold of organic dye molecules. That involves making the pores the right shape and size – between 0.8 and 1.6 nanometers – and giving the surface a negative charge, to attract the positively charged dye molecules.