Search

A mechanistic understanding of interactions between atomically thin two-dimensional (2D) transition-metal dichalcogenides (TMDs) and their growth substrates is important for achieving the unidirectional alignment of nuclei and seamless stitching of 2D TMD domains and thus 2D wafers. In this work, we conduct a cross-sectional scanning transmission electron microscopy (STEM) study to investigate the atomic-scale nucleation and early stage growth behaviors of chemical vapor deposited monolayer (ML-) MoS

Epidermal electronic systems that simultaneously provide physiological information acquisition, processing, and storage are in high demand for health care/clinical applications. However, these system-level demonstrations using flexible devices are still challenging because of obstacles in device performance, functional module construction, or integration scale. Here, on the basis of carbon nanotubes, we present an epidermal system that incorporates flexible sensors, sensor interface circuits, and an integrated flash memory array to collect physiological information from the human body surface; amplify weak biosignals by high-performance differential amplifiers (voltage gain of 27 decibels, common-mode rejection ratio of >43 decibels, and gain bandwidth product of >22 kilohertz); and store the processed information in the memory array with performance on par with industrial standards (retention time of 10 8 seconds, program/erase voltages of ±2 volts, and endurance of 10 6 cycles). The results shed light on the great application potential of epidermal electronic systems in personalized diagnostic and physiological monitoring.

Vanadium diselenide (VSe2), a member of the transition metal dichalcogenides (TMDs) family, is emerging as a promising two-dimensional (2D) candidate for the electronic and spintronic device with e...

Vanadium diselenide (VSe

Investigating the inherent wettability of rock surfaces at nanoscale is of great importance in ore floatation and oil recovery field. Using molecular dynamics simulations, we systematically study the wetting behavior of water on different rock surfaces (silica, calcite, gypsum, halite and graphite) at nanoscale. It is demonstrated that the inherent rock wettability follows the order of gypsum > calcite > halite > silica > graphite. Remarkably, we also manifest that the polarity of oil molecules can affect the water contact angles on silica surface. For example, the water contact angles on silica surface in hexane, dodecane, thiophene and toluene are 58 ± 2°, 63 ± 3°, 90 ± 1°, 118 ± 1°, respectively. Furthermore, we investigate the wetting behavior of water on heterogeneous rock surfaces and find that water molecules can move from hydrophobic surface to hydrophilic surface.

It is necessary to explore advanced materials with high CO2 selectivity and simple CO2 regeneration to weaken the greenhouse effect. Therefore, in this study, we report a comprehensive investigation of CO2, CH4, H2, C2H2, C2H4 and C2H6 on different Me–N–C nanosheets with different charge densities via density functional theory calculations. Our results demonstrate that CO2 is weakly absorbed on neutral and positively charged Me–N–C monolayer, whereas CO2 adsorption strength can be dramatically strengthened on a negatively charged Me–N–C monolayer, especially the Fe–N–C nanosheet. The adsorption energy of CO2 on the negatively charged Fe–N–C nanosheet with a negative charge density of 15.27 × 1013 e− cm−2 is −3.07 eV, which is about 10 times larger than that (−0.283 eV) on neutral one; in addition, it also shows high CO2 selectivity from mixtures containing CH4, H2, C2H2, C2H4 and C2H6. This investigation can provide valuable information for designing feasible adsorbent materials having high CO2 adsorption capacity and selectivity.

As an ultrathin, high-flux, and energy-efficient membrane, graphene oxide (GO) has shown great potential for gas separation. Using molecular dynamics (MD) simulations, we studied the H2/CH4 separation performance of GO membrane. It is found that the size of gas molecule and its interaction with GO sheet are two key factors in determining the diffusivity in interlayer gallery of GO, which results in significant difference of selectivity and permeability for H2 and CH4. The influences of two interlayer configuration parameters, the interlayer spacing and oxidation degree, on the separation of H2/CH4 are firstly studied. Then the effects of gas thermal behaviors, simulation temperature and initial gas pressure are also examined. Our studies uncover the underlying mechanism of H2/CH4 separation in GO membrane, and these understandings could promote efficient two-dimensional layered gas separation membrane materials development by engineering assemblies.

As sustainable and clean energy, hydrogen is the most attractive and promising energy source in the future. Membrane separation is attractive due to its high hydrogen separation performance and low energy consumption. Van-der-Waals-corrected density functional theory (DFT) calculations are performed to investigate the hydrogen separation performance of 585 divacancy-defective germanene (585 germanene). It is found that the 585 germanene presents a surmountable energy barrier (0.34 eV) for hydrogen molecule passing through the membrane, and that membrane exhibits extremely high selectivity for H 2 molecules over CO, CO 2 , N 2 , CH 4 and H 2 S molecules in a wide range of temperatures. Meanwhile, the hydrogen permeance of 585 germanene can reach 1.94 × 10 −7 mol s −1 m −2 Pa −1 at the low limit temperature of methane reforming (at 450 K), which is higher than the industrially acceptable gas permeance. With high selectivity and permeance, the 585 germanene is a promising candidate for hydrogen separation.

Using Grand Canonical Monte Carlo calculations, sulfur and nitrogen codoped (S/N-) graphite slit-pores with different defects (Divacancy 5-8-5, NS-1, NS-2, Stone–Wales (SW) 5577) are constructed to study their selective CO2 adsorption from CO2/H2, CO2/N2, CO2/CH4 and CO2/H2O mixtures. Among all the defective S/N-graphite slit-pores, it is found that the doped sites of S and N atoms affect slightly on CO2 uptake of graphite slit-pore. More importantly, the increasing ratio of S/N enhances the selective CO2 adsorption. For example, at 300 K and 1 bar, the full N-graphite slit-pore with SW 5577 has a CO2 uptake of 79.77 mmol/mol with good CO2/H2 selectivity (∼356) whereas full S-graphite slit-pore with SW 5577 possesses a considerable CO2 uptake of 104.66 mmol/mol with excellent CO2/H2 selectivity (∼526). Furthermore, density functional theory calculations indicate this defective S/N-graphite slit-pore with higher ratio of S/N interacts more strongly with CO2 molecules compared with other gases, which demons...

Polyacrylonitrile/graphene oxide (PAN/GO) composite fibers with spindle-knot structure have been fabricated by facile electrospinning and then hydrolyzed (H-PAN/GO) for tailoring their chemical features, and their separation performance for oil-water is evaluated. Herein, bio-inspired spindle-knot structures are induced by the GO sheets, which may be attributed to the mismatch between GO size and fiber diameter and the strong interaction between PAN and GO. It is found that H-PAN/GO membrane with GO concentration at 7% (H-PAN/GO7%) is superhydrophilic in air and ultralow-oil-adhesion under water. As a result, the H-PAN/GO7% membrane exhibits ultra-high flux (~3500 LMH), satisfied rejection ration (~99%) and outstanding flux recovery ratio (~99%) for separating oil-water emulsion. These outstanding separation performances mainly are attributed to the combination of chemical features of hydrolyzed PAN and spindle-knotted structure induced by GO. Moreover, self-transport of oil along spindle-knotted fiber under water is demonstrated by Lattice Boltzmann method (LBM) and the anti-fouling mechanism of this structure was also explained in this paper. The H-PAN/GO fibrous membrane offers a novel insight into fabricating next generation membrane to separate oil-water emulsion.

Membrane technology has been widely used for H2 separation. In this paper, we theoretically explored the H2 separation performance of graphitic carbon oxide (g-C2O) monolayer. The van-der-Waals-corrected density functional theory (DFT) calculations demonstrate that g-C2O monolayer is chemically inert to the studied gas molecules (H2, CO2, CO, N2, and CH4), and with a suitable pore size, the g-C2O monolayer shows an exceptionally high selectivity for H2/CO2 (CO, N2, and CH4) in a wide range of temperatures. In addition, the molecular dynamics (MD) simulations yield a high H2 permeance for the g-C2O monolayer at room temperature. With excellent selectivity and ultrahigh permeance, the g-C2O monolayer has great potential application in H2 separation.

Development of low energy cost membranes for separating helium from natural gas is highly desired. Using van der Waals-corrected first-principles density functional theory (DFT) calculations, we theoretically investigate the helium separation performance of divacancy-defective germanene. The 555 777 divacancy-defective germanene presents a 0.53 eV energy barrier for helium, which is slightly larger than the energy threshold value of gas molecule penetration of a membrane (0.5 eV). Thus, the 555 777 divacancy-defective germanene is difficult for helium to permeate, except under high temperature or pressure. However, the 585 divacancy-defective germanene presents a surmountable energy barrier (0.27 eV) for helium, and it shows extremely high helium selectivities relative to other studied gas molecules. Especially, the He/Ne selectivity can be as high as 1 × 104 at room temperature. Together with the acceptable permeance for helium, the 585 divacancy-defective germanene can be used for helium separation with remarkably good performance.