Nano sponge on graphene helps effectively filter industrial wastewater

The system uses super-porous "nano sponges" embedded on a sheet of graphene.

The key to the new filters is a class of materials known as covalent organic frameworks (COFs). These structures are extremely porous, giving them a large surface area contained in a small space, which means they are effective at attaching large numbers of molecules. Related materials called 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. .

Researchers have developed nano sponges made of a covalent organic framework (COF) on graphene that can effectively filter industrial pollutants out of water.

For the new study, the researchers focused on using COF to remove organic dyes from water. These chemicals are common pollutants of industrial wastewater, which can be toxic and carcinogenic.

The team tweaked COF to make it selectively retain organic dye molecules. That involves making holes of the right shape and size between 0.8 and 1.6 nanometers and giving the surface a negative charge to attract positively charged dye molecules.

But there is another hurdle to overcome when the material is used in powder form, the voids on the outer edge will fill the molecule first, leaving the central voids empty and essentially void. use. So the team developed a way to disperse COF by growing it on a sheet of graphene.

The end result is to create a layer of COF two nanometers thick on top of a monoatomic layer of graphene, increasing the material's maximum ability to hold organic dye molecules. Graphene itself has rather large pores, allowing water to flow through quickly while the COF is active.

'The large pores of the graphene lattice combined with the ultrathin COF layer and its large number of adsorption sites enable exceptionally fast and efficient wastewater treatment,' the researchers said. According to the team, the technique is quite cheap. There is no need to use a lot of graphene and the COF can be cleaned and reused.