A light foam was created from two-dimensional sheets of hexagonal-boron nitride (h-BN) that absorbs carbon dioxide. Freeze-drying h-BN turned it into a macro-scale foam that disintegrates in liquids. Adding a bit of polyvinyl alcohol (PVA) into the mix transformed it into a far more robust and useful material.
The polyvinyl alcohol serves as a glue. Mixed into a solution with flakes of h-BN, it binds the junctions as the microscopic sheets arrange themselves into a lattice when freeze-dried. The one-step process is scalable. Even a small amount of PVA works; it helps make the foam stiff by gluing the interconnects between the h-BN sheets. At the same time, it barely changes the surface area.
In molecular dynamics simulations, the foam adsorbed 340% of its own weight in carbon dioxide. The greenhouse gas can be evaporated out of the material, which can be reused repeatedly. Compression tests showed the foam got stiffer through 2,000 cycles.
When coated with polydimethylsiloxane (PDMS) — another polymer — the foam becomes an effective shield from lasers that could be used in biomedical, electronics, and other applications. Ultimately, the researchers want to gain control over the size of the material’s pores for specific applications like separating oil from water.