Rice University chemists have found a way to make the two-dimensional hexagonal-boron nitride (h-BN) – also known as White Graphene – more amenable to other elements.
Hexagonal-boron nitride is four times stiffer than steel and an excellent conductor of heat. These qualities also make h-BN hard to modify.
According to scientists, the material’s tight hexagonal lattice of alternating boron and nitrogen atoms is highly resistant to change – unlike graphene which can be easily functionalized with other elements.
The Rice lab of chemist Angel Martí has now published a new protocol that enhances h-BN with carbon chains, making it more amenable to bonding with polymers or other materials in composites.
According to Marti, h-BN can be made more dispersible in organic solvents as well.
In order to validate this, Martí and his team modified the ‘Billups-Birch’ reaction process to attack the defenses of h-BN and covalently attach carbons.
Birch reduction – enhanced in 2004 by Rice emeritus chemistry professor Edward Billups to functionalize carbon nanotubes – frees electrons to bind with other atoms.
In the new Rice process, Martí and his team controlled the amount of h-BN functionalization by varying the amount of lithium in the reaction.
Lithium, an alkali metal, sheds free electrons when combined with liquefied ammonia.
When mixed with h-BN flakes and a carbon source (1-Bromododecane in this case), the reaction produces an alkyl radical, a chemical species that reacts with h-BN and makes a bond.
According to Martí, this is the best method found so far to modify h-BN, which resists change even under high temperatures.
“You take a little bit of graphite and put it in a furnace at 800 degrees Celsius, and it will be gone,” he said. “You take hexagonal-boron nitride and do the same, and it will still be there smiling at you.”
A 20-to-1 molar ratio of lithium to h-BN optimized the process of grafting carbon chains to the surface and edges.
And because the base h-BN remains stable under high temperatures, it can be returned to its pristine state by simply burning off the functional chains.
Image and content: Angel Martí Group/Rice University