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Fabricating hexagonal boron nitride foam for CO2 absorption

(Nanowerk News) In ACS Nano ("Lightweight Hexagonal Boron Nitride Foam for CO2 Absorption"), scientists report a technique to fabricate lightweight 3D macroscopic porous structures formed from hexagonal boron nitride (h-BN) nanosheets.
With its naturally occurring layered structure, hexagonal boron nitride (h-BN) has emerged as an important 2D material, possessing excellent properties such as high temperature stability, high thermal conductivity, as well as mechanical strength.
The fabrication of three-dimensional porous nanostructures from interconnected two-dimensional (2D) materials such as graphene, clays, metal dichalcogenides, etc. has proven to be a promising technique to exploit their properties for several applications including catalysis, energy storage, biological and environmental applications, mechanical damping, and gas sequestration.
Characterization and morphology of h-BN/PVA foams
Characterization and morphology of h-BN/PVA foams. (a) Schematic representation depicting the h-BN nanosheets connected by poly(vinyl alcohol) (PVA) molecules. Typical chains contain 30 monomers (∼6.2 nm chain length). The PVA molecules act like a glue to link the nanosheets through van der Waals interactions between the hydroxyl groups in the PVA and boron/nitrogen atoms in the nanosheets. (b) Structural stability of the h-BN/PVA foam. (c) Mechanical stability of the lightweight foam carrying a vial without any visible degradation. (d) Stable structure of the foam when subjected to liquids. (e) Pristine foam disintegrates in the presence of water, whereas h-BN/PVA maintains its stable interconnected morphology (Rice University owns the copyright for the logo displayed and is used with permission). (f,g) Lowmagnification and high-magnification image of the foam. (© ACS) (click on image to enlarge)
In this new work, the researchers first liquid-phase-exfoliated h-BN in water to separate the layers, and then poly(vinyl alcohol) (PVA) was added (1-1.5 wt %), followed by in situ freeze-drying.
The hybrid structure exhibits enhanced mechanical properties, large surface area, and increased porosity.
According to the team, their fabrication method allows for the creation of intermolecular bonding between h-BN layers, where PVA acts like a bridge to link the individual layers, thus forming a network structure at the nanoscale.
Unlike pristine h-BN foams, which normally disintegrate immediately once removed from a freeze-drier, h-BN/PVA foams show a robust freestanding structure with favorable mechanical stability.
A detailed molecular dynamics study further verified and provided insights on the origins of such interconnections in improving the mechanical integrity.
The foam also exhibits excellent CO2 absorption of 340% and storage under varying pressure values, mainly due to nitrogen functional groups and an increased surface area.
Furthermore, when coated with polydimethylsiloxane (PDMS), the foam shows superior laser shielding properties by withstanding a varied amount of laser energy with minimal structural degradation.
Michael Berger By – Michael is author of three books by the Royal Society of Chemistry:
Nano-Society: Pushing the Boundaries of Technology,
Nanotechnology: The Future is Tiny, and
Nanoengineering: The Skills and Tools Making Technology Invisible
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