No abstract

Permeation through membrane with pores is important in the choice of materials for filtration and separation techniques. Here, we report by the molecular dynamics simulations that a single-layer graphyne membrane can be impermeable to salt ions, while it allows the permeation of water molecules. The salt rejection and water permeability of graphyne are closely related to the hydrostatic pressure, type of graphyne membrane, and the salt concentration of solution, respectively. By analyzing hydration shell structure, we found that the average coordination number of ions plays a key role in water purification. Our calculation showed that the salt rejection of the graphyne-3 membrane is the best and it can keep an ideal rate of 100% in consideration cases. In comprehensive evaluation of both salt rejection and permeability, the graphyne-4 is a perfect purification membrane. To sum up, our results indicated that the graphynes (graphyne-3 and -4) not only have higher salt rejection but also possess higher water permeability which is several orders of magnitude higher than conventional reverse osmosis membranes. The single-layer graphyne membrane may have a great potential application as a membrane for water purification.

Ca decorated carbon allotropes have a potential for high density hydrogen storage, except that the CaÀgraphene and CaÀfullerenes binding is not strong enough to prevent the formation of a Ca cluster. Using first-principles calculations, we show that Ca can bind strongly to sÀp and sÀp 2 bonded graphyne without the formation of a Ca cluster. This enhanced binding energy is due to the additional in-plane π states which do not exist in the sÀp 2 bonded graphene and fullerenes. The H 2 binding to the CaÀgraphyne system is similar to the CaÀfullerenes system with a maximum of six H 2 molecules per Ca atom and a 0.2 eV per H 2 binding energy which is optimal as hydrogen storage materials. With two Ca atoms per unit cell, this leads to 9.6 wt % hydrogen storage capacity in theory.

Ordered intermetallic nanomaterials are of considerable interest for fuel cell applications because of their unique electronic and structural properties. The synthesis of intermetallic compounds generally requires the use of high temperatures and multiple-step processes. The development of techniques for rapid phase- and size-controlled synthesis remains a formidable challenge. The intermetallic compound Pt1Bi2 is a promising candidate catalyst for direct methanol fuel cells because of its high catalytic activity and excellent methanol tolerance. In this work, we explored a one-step, facile and ultrafast phase- and size-controlled process for synthesizing ordered Pt-Bi intermetallic nanoparticles (NPs) within seconds in microfluidic reactors. Single-phase Pt1Bi1 and Pt1Bi2 intermetallic NPs were prepared by tuning the reaction temperature, and size control was achieved by modifying the solvents and the length of the reaction channel. The as-prepared Pt-Bi intermetallic NPs exhibited excellent methanol tolerance capacity and high electrocatalytic activity. Other intermetallic nanomaterials, such as Pt3Fe intermetallic nanowires with a diameter of 8.6 nm and Pt1Sn1 intermetallic nanowires with a diameter of 6.3 nm, were also successfully synthesized using this method, thus demonstrating its feasibility and generality.

First principles calculations are performed to study the transport properties of zigzag silicene nanoribbons (ZSiNRs). ZSiNRs show symmetry-dependent transport properties similar to those of zigzag graphene nanoribbons, although the σ mirror plane is absent. Even-N and odd-N ZSiNRs have very different current-voltage relationships, which can be attributed to the different parity of their π and π* bands under c2 symmetry operation with respect to the center axis. Moreover, magnetoresistance effect is observed in even-N ZSiNRs, and the order can reach 1 000 000%. On the basis of these interesting transport properties, ZSiNR-based logic devices, such as not, and, and or gates, are proposed.

Most of the photodetectors can measure all of the light illumination with a wavelength below the absorption edge of the detector materials, while they cannot distinguish the different waveband. Herein, a self-powered spectrum-distinguishable photoelectrochemical (PEC) type photodetector based on an α-Ga2O3 nanorod array (NA)/Cu2O microsphere (MS) p–n junction was reported. Under the combined action of the built-in electric field of the p–n junction and the semiconductor/electrolyte junction, the photodetector exhibits an opposite direction of the photocurrent to the illumination of 254 and 365 nm UV light under the applied bias of 0 V, which can be used to distinguish the different wavelengths of light. The photodetector shows a responsivity of 0.42 mA/W under 254 nm UV light and 0.57 mA/W upon 365 nm, respectively. Our results provide an idea for distinguishing the different illumination wavebands through a photodetector constructed by the heterojunction with two different band gap materials.

Recently, Ga2O3-based self-powered ultraviolet photodetectors have aroused great interest due to their potential applications in civil, medical, and environmental monitoring fields. So far, most p–n junction photodetectors are fabricated with p-type semiconductors like GaN and SiC, which are usually nonoxide materials. As a result, the p-type semiconductors are oxidized and the conductive properties degenerated when constructing a p–n junction with the Ga2O3 thin film at a high growth temperature. In this work, we chose the oxide NiO as the p-type material and used radio-frequency reactive magnetron sputtering system to fabricate the all-oxide NiO/Ga2O3 p–n junction at room temperature and manufacture the self-powered UV photodetector. Thanks to the type II band alignment, the photodetector exhibits a responsivity (R) of 57 μA/W, a detectivity (D*) of 5.45 × 109 jones, and an I light/I dark ratio of 122 when exposed to a 254 nm light irradiation at 0 V. In addition, the photodetector based on the all-oxide NiO/Ga2O3 p–n junction shows good stability and reproducibility in air, oxygen, and vacuum. Our results provide an inexpensive and suitable pathway for the mass production of self-powered UV photodetectors.

Finding a membrane with both high permeability and high salt rejection is very important for saline solution purification. Here, we report the performance of molybdenum disulfide (MoS2) membranes with nanoscale pores for saline solution purification via all-atom molecular dynamics simulations. It was found that the nanoporous two-dimensional MoS2 membrane can impede salt ions, while allowing highly efficient permeation of water molecules. By engineering the appropriate sizes of the nanopores within two-dimensional MoS2 membranes, their water permeability can be tens of times as high as that of conventional reverse osmosis membranes, while still maintaining a high salt rejection rate. These remarkable water permeability and salt rejection properties of the nanoporous monolayer MoS2 membranes are attributed to the formation of single chain hydrogen bonds, which link the water molecules within the nanopores and those at the immediate exteriors of the nanopores, causing significant reduction in the resistance of water molecules passing through the nanopores, which are small enough for any salt ions to pass through. Therefore such nanoporous monolayer MoS2 membranes have great potential for saline solution purification.