Quantum Chemical Simulations of CO₂ and N₂ Capture in Reline, a Prototypical Deep Eutectic Solvent

Deep eutectic solvents such as reline are an emerging class of low-cost, environmentally friendly solvents with tunable properties that are potentially applicable for the capture and separation of CO2. Experimental measurements showed that a reline-based membrane contactor can capture and separate CO2 via physisorption through a dissolution process with 96.7% purity from a mixed gas containing CO2 and N2 (50:50% molar ratio). We examine the nature of the interaction of CO2 and N2 with reline employing quantum chemical methods. We focus on explaining the mechanism by which CO2 and N2 bind to reline and the reason for the high selectivity for absorption of CO2 compared to N2. We analyze the dynamics, energetics, and binding motifs for CO2 and N2 in reline employing density functional theory, density functional tight binding, and ab initio molecular dynamics. We also investigate the effect of reline on the vibrational spectra of CO2 and reline. Our simulations indicate that the selective capture of CO2 from the mixture of CO2 and N2 is due to the interplay between attractive electrostatic and charge polarization forces with opposing entropic effects, which shift the energetic balance and make the N2 absorption unfavorable in reline

Electro-Induced Dewetting and Concomitant Ionic Current Avalanche in Nanopores

Electrically driven ionic transport of room-temperature ionic liquids (RTILs) through nanopores is studied using atomistic simulations. The results show that in nanopores wetted by RTILs a gradual <i>dewetting</i> transition occurs upon increasing the applied voltage, which is accompanied by a sharp <i>increase</i> in ionic current. These phenomena originate from the solvent-free nature of RTILs and are in stark contrast with the transport of conventional electrolytes through nanopores. Amplification is possible by controlling the properties of the nanopore and RTILs, and we show that it is especially pronounced in charged nanopores. The results highlight the unique physics of nonequilibrium transport of RTILs in confined geometries and point to potential experimental approaches for manipulating ionic transport in nanopores, which can benefit diverse techniques including nanofluidic circuitry and nanopore analytics

Correction to Boron Nitride Nanoribbons Become Metallic

Correction to Boron Nitride Nanoribbons Become Metalli

A Novel and Functional Single-Layer Sheet of ZnSe

The recently synthesized freestanding four-atom-thick double-layer sheet of ZnSe holds great promise as an ultraflexible and transparent photoelectrode material for solar water splitting. In this work, we report theoretical studies on a novel three-atom-thick single-layer sheet of ZnSe that demonstrates a strong quantum confinement effect by exhibiting a large enhancement of the band gap (2.0 eV) relative to the zinc blende (ZB) bulk phase. Theoretical optical absorbance shows that the largest absorption of this ultrathin single-layer sheet of ZnSe occurs at a wavelength similar to its four-atom-thick double-layer counterpart, suggesting a comparable behavior on incident photon-to-current conversion efficiency for solar water splitting, among a wealth of potential applications. The results presented herein for ZnSe may be generalized to other group II-VI analogues

Multicomponent Gas Storage in Organic Cage Molecules

Porous liquids are a promising new class of materials featuring nanoscale cavity units dispersed in liquids that are suitable for applications such as gas storage and separation. In this work, we use molecular dynamics simulations to examine the multicomponent gas storage in a porous liquid consisting of crown-ether-substituted cage molecules dissolved in a 15-crown-5 solvent. We compute the storage of three prototypical small molecules including CO₂, CH₄, and N₂ and their binary mixtures in individual cage molecules. For porous liquids in equilibrium with a binary 1:1 gas mixture bath with partial gas pressure of 27.5 bar, a cage molecule shows a selectivity of 4.3 and 13.1 for the CO₂/CH₄ and CO₂/N₂ pairs, respectively. We provide a molecular perspective of how gas molecules are stored in the cage molecule and how the storage of one type of gas molecule is affected by other types of gas molecules. Our results clarify the molecular mechanisms behind the selectivity of such cage molecules toward different gases

Tuning from Half-Metallic to Semiconducting Behavior in SiC Nanoribbons

Half-metallic nanoscale conductors, highly sought after for spintronic applications, are usually realized through metal elements, chemical doping, or external electric fields. By means of local and hybrid density functional theory calculations, we identify pristine zigzag silicon carbide nanoribbons (zSiC-NRs) with bare edges as a metal-free monolayered material that exhibits intrinsic half-metallic behavior without chemical doping or an external electric field. Ab initio molecular dynamics simulations indicate that the half-metallicity is robust at room temperature. We also demonstrate that edge termination with O and S atoms transforms the zSiC-NRs into a full metal or a semiconducting material, respectively, due to the presence of O dimerization only on the Si edge and of S trimerization on both Si and C edges, the latter being driven by an unusual Peierls-like distortion along the functionalizing S atoms. The rich electronic properties displayed by zSiC-NRs may open new perspectives for spintronic applications using layered, metal-free, and light atom material

Ab Initio Predictions of Strong Interfaces in Transition-Metal Carbides and Nitrides for Superhard Nanocomposite Coating Applications

Conceiving strong interfaces represents an effective direction in the development of superhard nanocomposite materials for practical applications in protective coatings. In the pursuit of engineering strong nanoscale interfaces between cubic rock-salt (B1) domains, we investigate using density functional theory (DFT) coherent interface models designed based on hexagonal (HX) NiAs and WC structures, as well as experiment. The DFT screening of a collection of transition-metal (M = Zr, Hf, Nb, Ta) carbides and nitrides indicates that the interface models provided by the HX polymorphs store little coherency strain and develop an energetic advantage as the valence-electron concentration increases. Our result suggests that harnessing the polymorphism encountered in transition-metal (M = Zr, Hf, Nb, Ta) carbides and nitrides for interface design represents a promising strategy for advancing superhard nanomaterials

Ab Initio Predictions of Hexagonal Zr(B,C,N) Polymorphs for Coherent Interface Design

Density functional theory calculations are used herein to explore the hexagonal (HX) NiAs-like polymorphs of Zr­(B,C,N) and compare them with the corresponding Zr­(B,C,N) Hagg-like face-centered-cubic rocksalt (B1) phases. Although all predicted compounds are mechanically stable according to the Born–Huang criteria, only HX Zr­(C,N) are dynamically stable according to ab initio molecular dynamics simulations and lattice dynamics calculations. HX ZrN emerges as a candidate structure with a ground-state energy, elastic constants, and extrinsic mechanical parameters comparable with those of B1 ZrN. Ab initio band structure and semiclassical Boltzmann transport calculations predict a metallic character and a monotonic increase in electrical conductivity with the number of valence electrons. Electronic structure calculations indicate that the HX phases gain their stability and mechanical attributes through Zr d–nonmetal p hybridization and broadening of the Zr d bands. Furthermore, it is shown that the HX ZrN phase provides a low-energy coherent interface model for connecting B1 ZrN domains, with significant energetic advantage over an atomistic interface model derived from high-resolution transmission electron microscopy (HRTEM) images. The ab initio characterizations provided herein should aid the experimental identification of non-Hagg-like hard phases. The results can also enrich the variety of crystalline phases potentially available for designing coherent interfaces in superhard nanostructured materials and in materials with multilayer characteristics