Ideal two-dimensional molecular sieves for gas separation: Metal trihalides MX3 with precise atomic pores

Two-Dimensional CrCl3-Layered Trihalide Nanoflake Sensor for the Detection of Humidity, NO2, and H2

“…To formulate a possible humidity-/gas-sensing response mechanism describing the interaction of H 2 O, NO 2 , H 2 , and NH 3 molecules with the 2D-CrCl 3 surface, Figure a shows a tentative schematic of the structure of monolayered 2D-CrCl 3 . Like zeolites and metal–organic frameworks (MOFs), monolayered TMTHs such as CrCl 3 can be classified as 2D microporous materials ( D pore < 2 nm) because of the presence of intrinsic atomic pores in a size range of 1.53–1.94 Å, as indicated by the dotted-black squares in Figure a . These empty cages, located at the center of the honeycomb lattice formed by Cr atoms (Figure a), similar to the model of Li adsorption over CrI 3 , can be spontaneously filled by ambient oxygen (red spheres in Figure a), resulting in the formation of an ordered semioxidized O–CrCl 3 surface phase, with oxygen impurities intercalated in the Cr atomic layer under ambient conditions, as recently demonstrated by theoretical and experimental observations. ,, Moreover, the presence of Cl vacancies in 2D-CrCl 3 flakes must be also considered, as indicated by the dotted-black circles in Figure a, which are energetically favorable, as proven in refs , .…”

“…Among the various vdW-layered semiconductors, transition-metal trihalides (TMTHs; MX 3 , where M = Ti, V, Cr, Mo, Fe, Ru, and X = Cl, Br, or I) have recently attracted scientific attention because of their layered nature and consequent potential as ultrathin magnetic layers in spintronic devices, batteries, improved catalysts, and molecular sieves with high surface-to-volume ratios. − While few-layer MX 3 TMTHs are used as cleavable 2D ferromagnetic semiconductors, their humidity- and gas-sensing responses are still unknown, probably because of the assumption that their environmental instability in dry/wet air prevents their utilization as reproducible gas sensor interfaces. , Indeed, most TMTHs, such as VI 3 and CrI 3 , immediately degrade or evaporate after being exposed to an oxidizing atmosphere or light, even in their bulk phase. , Conversely, CrCl 3 is only relatively stable under ambient laboratory conditions even after its isolation in reduced dimensionality via mechanical exfoliation, as reported in refs , Specifically, few-layer CrCl 3 does not undergo dramatic oxidation or evaporation up to 200 °C. , This is because CrCl 3 has a semioxidized stable O–CrCl 3 surface phase that is stable up to 400 °C with charge imbalance, and this phase protects the inner pristine material. This means that the surface of CrCl 3 has native polar atomic sites that prefer the adsorption of molecules, which is very helpful for gas-sensing applications where the detection mechanism is mainly based on charge transfer.…”

First-Principles Investigation of Two-Dimensional CuPP-Grid Molecular Sieves for C4 Hydrocarbon Purification by a Double-Bond Effect

“…To evaluate the feasibility of CuPP-Grid as a separation membrane, the adsorption energies are calculated by the following formula: E ads = E normalA + normalB − E normalA − E normalB where E A + B is the total energy of the adsorption system and E A and E B are the energies of the CuPP-Grid membrane and molecules . In Table , the adsorption energies are in the range of −0.10 to −0.15 eV and the calculated equilibrium distance between the molecules and substrate ranges from 2.02 to 2.15 Å, meaning that the interactions between the CuPP-Grid membrane and molecules belong to physical adsorption and the pore would not be blocked with molecules during the penetration processes. − …”

Strain engineering on electronic structure, effective mass and charge carrier mobility in monolayer YBr3

“…Due to the carrier doping effect, the monolayer YBr 3 can also manipulate monolayer MoS 2 as an n-type or p-type semiconductor and improve system stability by constructing heterostructure [33]. Liu et al investigated that monolayer YBr 3 is expected to be used as a 2D molecular sieve for gas separation applications [34].…”