London Center for the Theory and Simulation of Materials

London, United Kingdom

London Center for the Theory and Simulation of Materials

London, United Kingdom

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Cazorla C.,University College London | Cazorla C.,London Center for the Theory and Simulation of Materials | Shevlin S.A.,University College London | Shevlin S.A.,London Center for the Theory and Simulation of Materials | And 2 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

In view of the interest in calcium-decorated carbon nanostructures motivated by potential biotechnological and nanotechnological applications, we have carried out a systematic and thorough first-principles computational study of the energetic and structural properties of these systems. We use density-functional theory (DFT) and ab initio molecular dynamic simulations to determine minimum energy configurations, binding energy profiles and the thermodynamic stability of Ca-decorated graphene and carbon nanotubes (CNT) as function of doping concentration. In graphene, we predict the existence of an equilibrium (√3×√3) R30° commensurate CaC6 monolayer that remains stable without clustering at low and room temperatures. For carbon nanotubes, we demonstrate that uniformly Ca-decorated zigzag (n≤10,0) CNT become stable against clustering at moderately large doping concentrations while Ca-coated armchair (n,n) CNT exhibit a clear thermodynamic tendency for Ca aggregation. In both Ca-doped graphene and CNT systems, we estimate large energy barriers (∼1 eV) for atomic aggregation processes, which indicates that Ca clustering in carbon nanosurfaces may be kinematically hindered. Finally, we demonstrate via comparison of DFT and Møller- Plesset second-order perturbation calculations that DFT underestimates significantly the weak interaction between a Ca dopant and a coronene molecule, and also that the Ca-coronene system is not physically comparable to Ca-doped graphene due to lack of electronic π-d orbitals hybridization near the Fermi energy level. © 2010 The American Physical Society.


Cazorla C.,CSIC - Institute of Materials Science | Cazorla C.,University College London | Cazorla C.,London Center for the Theory and Simulation of Materials | Shevlin S.A.,University College London | And 3 more authors.
Journal of Physical Chemistry C | Year: 2011

We report a first-principles study of a CO2 gas-sorbent material consisting of calcium atoms and carbon-based nanostructures. In the low gas pressure regime, we find that Ca decoration of nanotubes and graphene possess unusually large CO2 uptake capacities (∼0.4-0.6 g CO 2/g sorbent) as a result of their topology and a strong interaction between the metal dopants and CO2 molecules. Decomposition of the gas-loaded nanomaterials into CO gas and calcium oxide (CaO) is shown to be thermodynamically favorable; thus performance of the carbon capture process is further enhanced via formation of calcium carbonate (CaCO3). Gas adsorption CO2/N2 selectivity issues have been also addressed with the finding that N2 molecules bind to the metal-doped surfaces more weakly than CO2 molecules. The predicted molecular binding and accompanying gas selectivity features strongly suggest the potential of Ca-doped carbon materials for CO2 capture applications. © 2011 American Chemical Society.

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