scholarly journals Exfoliation Energy as a Descriptor of MXenes Synthesizability and Surface Chemical Activity

Nanomaterials ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 127
Author(s):  
Daniel Dolz ◽  
Ángel Morales-García ◽  
Francesc Viñes ◽  
Francesc Illas
Keyword(s):  
Density Functional ◽  
Co2 Adsorption ◽  
Selective Extraction ◽  
Chemical Activity ◽  
Surface Chemical ◽  
Block Element ◽  
Max Phases ◽  
Functional Theory ◽  
Element Group ◽  
Chemical Descriptor

MXenes are two-dimensional nanomaterials isolated from MAX phases by selective extraction of the A component—a p-block element. The MAX exfoliation energy, Eexf, is considered a chemical descriptor of the MXene synthesizability. Here, we show, by density functional theory (DFT) estimations of Eexf values for 486 different MAX phases, that Eexf decreases (i) when MAX is a nitride, (ii) when going along a metal M component d series, (iii) when going down a p-block A element group, and (iv) when having thicker MXenes. Furthermore, Eexf is found to bias, even to govern, the surface chemical activity, evaluated here on the CO2 adsorption strength, so that more unstable MXenes, displaying larger Eexf values, display a stronger attachment of species upon.

scholarly journals Exfoliation Energy as a Descriptor of MXenes Synthesizability and Surface Chemical Activity

2020 ◽  
Author(s):  
Daniel Dolz ◽  
Ángel Morales-García ◽  
Francesc Viñes ◽  
Francesc Illas
Keyword(s):  
Density Functional ◽  
Co2 Adsorption ◽  
Selective Extraction ◽  
Chemical Activity ◽  
Max Phase ◽  
Surface Chemical ◽  
Block Element ◽  
Max Phases ◽  
Functional Theory ◽  
Chemical Descriptor

MXenes are two-dimensional nanomaterials isolated from MAX phases by the selective extraction of the A component —a p-block element. The MAX phase exfoliation energy, Eexf, is regarded as a chemical descriptor of the MXene synthesizability. Here we show, by density functional theory estimations of the Eexf values for 486 different MAX phases, that Eexf decreases i) when MAX is a nitride, ii) when going along a d series of the metal M component, iii) when going down a group of the p-block A element, as well as iv) when having thicker MXene phases. Furthermore, Eexf is found to bias, even to govern, the surface chemical activity, as evaluated here on the CO2 adsorption strength, so that more unstable MXenes, displaying larger Eexf values, display a stronger attachment of species upon.

scholarly journals DFT insights into the electronic structure, mechanical behaviour, lattice dynamics and defect processes in the first Sc-based MAX phase Sc2SnC

2021 ◽  
Author(s):  
M. A. Hadi ◽  
S.-R. G. Christopoulos ◽  
A. Chroneos ◽  
S. H. Naqib ◽  
A. K.M.A. Islam
Keyword(s):  
Density Functional ◽  
Elastic Anisotropy ◽  
Max Phase ◽  
Ionic Character ◽  
Max Phases ◽  
Functional Theory ◽  
Barrier Coating ◽  
Important Addition ◽  
Effective Valence ◽  
Experimental Values

Abstract The ceramic and metallic properties of the MAX phases make them attractive for numerous technological applications. The very recent experimental synthesis of the first scandium (Sc) based MAX phase Sc2SnC is an important addition to the MAX phase family as it further expands the diversity of physical characteristics of this family. Here we employ density functional theory (DFT) calculations to investigate the structural, electronic, mechanical, lattice dynamical properties of Sc2SnC including defect processes to compare with those of existing M2SnC phases. The calculated structural properties are in good agreement with the experimental values. The new phase Sc2SnC is structurally, mechanically and dynamically stable. Sc2SnC is metallic with a mixture of covalent and ionic character. The covalency of Sc2SnC including M2SnC is mostly controlled by the effective valence. Sc2SnC in M2SnC family ranks second in the scale of deformability, softness and machinability. The elastic anisotropy level in Sc2SnC is moderate compared to the other M2SnC phases. Like other members of the M2SnC family, Sc2SnC has the potential to be etched into 2D MXenes and has the potential to be a thermal barrier coating (TBC) material. The hardness and melting point of Sc2SnC, including M2SnC, follows the trend of bulk modulus.

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