Ti2C is one of the thinnest layers in MXene family with high potential for applications. In the present study, the adsorption of NH3, H2, CH4, CO, CO2, N2, NO2, and O2 on monolayer Ti2CO2 was investigated by using first-principles simulations to exploit its potential applications as gas sensor or capturer. Among all the gas molecules, only NH3 could be chemisorbed on Ti2CO2 with apparent charge transfer of 0.174 e. We further calculated the current-voltage (I-V) relation using the nonequilibrium Green's function (NEGF) method. The transport feature exhibits distinct responses with a dramatic change of I-V relation before and after NH3 adsorption on Ti2CO2. Thus, we predict that Ti2CO2 could be a promising candidate for the NH3 sensor with high selectivity and sensitivity. On the other hand, the adsorption of NH3 on Ti2CO2 could be further strengthened with the increase of applied strain on Ti2CO2, while the adsorption of other gases on Ti2CO2 is still weak under the same strain, indicating that the capture of NH3 on Ti2CO2 under the strain is highly preferred over other gas molecules. Moreover, the adsorbed NH3 on Ti2CO2 could be escapable by releasing the applied strain, which indicates the capture process is reversible. Our study widens the application of monolayer Ti2CO2 not only as the battery material, but also as the potential gas sensor or capturer of NH3 with high sensitivity and selectivity.

Ultralight and compressible carbon materials have promising applications in strain and pressure detection. However, it is still difficult to prepare carbon materials with supercompressibility, elasticity, stable strain-electrical signal response, and ultrasensitive detection limits, due to the challenge in structural regulation. Herein, a new strategy to prepare a reduced graphene oxide (rGO)-based lamellar carbon aerogels with unexpected and integrated performances by designing wave-shape rGO layers and enhancing the interaction among the rGO layers is demonstrated. Addition of cellulose nanocrystalline and low-molecular-weight carbon precursors enhances the interaction among rGO layers and thus produces an ultralight, flexible, and superstable structure. The as-prepared carbon aerogel displays a supercompressibility (undergoing an extreme strain of 99%) and elasticity (100% height retention after 10 000 cycles at a strain of 30%), as well as stable strain-current response (at least 10 000 cycles). Particularly, the carbon aerogel is ultrasensitive for detecting tiny change in strain (0.012%) and pressure (0.25 Pa), which are the lowest detection limits for compressible carbon materials reported in the literature. Moreover, the carbon aerogel exhibits excellent bendable performance and can detect an ultralow bending angle of 0.052°. Additionally, the carbon aerogel also demonstrates its promising application as wearable devices.

When examining the formation energetics of a hydrogen-bonded complex R-X-H...Y-R', focus has been almost always on the atoms directly involved, namely the atoms X, Y, and H. Little attention has been paid to the effects of the secondary alkyl groups R and R'. Taking dimethyl sulfoxide (DMSO)-methanol binary system as an example, we have studied the roles of the alkyl groups in stabilizing the hydrogen bonds by employing FTIR and NMR techniques and quantum chemical calculations. We found that methyl groups play different roles in response to the hydrogen-bonding interactions. The methyl groups of DMSO are electron-donating, whereas that of methanol is electron-withdrawing, both making positive contributions. The findings reveal non-negligible effects of secondary alkyl groups in hydrogen bonding interaction and may shed light on the understanding of other more complicated hydrogen-bonded systems in chemical and biological systems.

MXenes represent a burgeoning family of two-dimensional (2D) functional materials with a variety of applications that highly rely on terminationmediated surface functionalization, but the understanding of termination is limited. Here, we take Ti 3 C 2 T 2 (T = O, F, OH, and H) as an example of MXenes, to demonstrate how termination stabilizes the Ti 3 C 2 monolayer matrix by saturating the nonbonding valence electrons of the surface Ti atom by the low-energy orbitals of the termination. This is achieved by orbitally resolved density of states analysis by simply yet efficiently manipulating the internal coordination of the octahedral crystal field to match exactly the Cartesian coordination. Highly degenerate 3d orbitals of surface Ti split in such a way that it exhibits pseudogaps whose widths predict a stability order Ti 3 C 2 O 2 > Ti 3 C 2 F 2 > Ti 3 C 2 (OH) 2 > Ti 3 C 2 H 2 > Ti 3 C 2 , consistent with Bader charge analysis, thermodynamic calculations, and experimental results. This new criterion could have implications in the general context of ubiquitous termination phenomena of MXenes and other relevant termination-functionalized 2D materials.

All stellar mass black holes have hitherto been identified by X-rays emitted by gas that is accreting onto the black hole from a companion star. These systems are all binaries with black holes below 30 M ⊙ 1-4. Theory predicts, however, that X-ray emitting systems form a minority of the total population of star-black hole binaries 5, 6. When the black hole is not accreting gas, it can be found through radial velocity measurements of the motion of the companion star. Here we report radial velocity measurements of a Galactic star, LB-1, which is a B-type star, taken over two years. We find that the motion of the B-star and an accompanying Hα emission line require the presence of a dark companion with a mass of