Aug 26, 2014
Understanding the strength of carbyne
Carbyne structures can be employed in efficient water purification applications. Usually this is within graphyne, which – with optimal permeability, high mechanical robustness and a uniform distribution of pores in the membrane – is more effective than other materials. Yet the impact of environmental factors on this structure is largely unknown. This study, in Nanotechnology, provides a fundamental understanding of the mechanical strength of carbyne chains with different lengths, at different temperatures and varied solvent conditions. This paves the way to realizing efficient purification devices for separating specific contaminants from water.
The rupture of a carbyne chain in a basic solution, and the steps of healing the broken chain via an oxygen atom from the hydroxide group
Graphyne is a family of single-atom-thick two-dimensional membranes composed of carbon atoms. They have a similar nanostructure to graphene, but can comprise various pore sizes and a portion of carbon-carbon bonds are replaced with carbyne chains. Graphyne structures can be used in a range of filtration and purification applications, such as water purification.
The successful application of graphyne nanoweb membranes for selective purification purposes relies on the design and directed fabrication of graphyne membranes with different pore sizes. This is achievable through adjusting the length of carbyne chains that link the benzene rings within the graphyne structure.
Here, molecular dynamics (MD) simulations shed light on the mechanics of carbyne chains with different lengths. In order to facilitate the design and optimization procedure a theoretical framework is also developed. This provides an analytical explanation of the carbyne strength at any temperature and chain length.
In carbyne-based water purification structures, the carbyne chains are in direct interaction with water molecules. However, it is largely unknown how the mechanical properties of this structure are affected by the environmental factors. It is found that the interaction with water molecules improves the bond stability, which is reflected by higher values of their bond order.
For the chains in water, a residual covalent bonding is observed at higher strain values, which leads to larger deformations of the carbyne chain before breaking. As a result of improving the bond stability, both the tensile strength and rupture strain are slightly improved by the water interaction. This renders these structures promising candidates for fabricating nanoweb membranes for the purpose of water purification.
Carbyne-based structures may operate in either acidic or basic solutions. Here, the effect of these chemical environments on the mechanical properties of carbyne chains is studied. It is found that a basic environment decreases the chain strength, while the strength in an acidic solution is slightly increased. A unique self-healing phenomenon is observed in the basic solution, which strongly improves the toughness of the carbyne chains before breaking.
This computational and theoretical study advances the fundamental understanding of the promising role of graphyne in water purification. However, the true potential of graphyne in applications has yet to be reached. This may be achievable once this material, and related structures, can be synthesized in large quantities. Graphyne has tremendous potential in filtering and is reliable in various conditions. Therefore, it is hoped that this work will inspire broad experimental efforts to improve the synthesis method with both improved quality and quantity.
More information about this Fast Track Communication can be found in the journal Nanotechnology 25 371001.
About the author
This study was completed by Reza Mirzaeifar, Zhao Qin and Markus J Buehler, based at the Laboratory for Atomistic and Molecular Mechanics at Massachusetts Institute of Technology.