Latest ArticlesHere, the selective adsorption behaviors of guest molecule COR in two hexamer host grids were investigated by means of scanning tunnelling microscope (STM). The assembled structures of small functional organic molecules TTBTA and TATBA were thermodynamically stable. Interestingly, the introduction of the guest molecule COR destroyed the original hexamer structure of TTBTA and combined with it to form a new triangular host-guest system. Different from TTBTA, the introduction of the guest molecule COR did not affect the six-membered ring structure of TATBA. Furthermore, the co-assembly structure of TTBTA/TATBA/COR was established and the guest molecule COR showed preferential adsorption to the TATBA host grid. Density functional theory (DFT) calculations had been performed to disclose the mechanism of the involved assemblies.
Using the global particle-swarm optimization method and density functional theory, we predict a new stable two-dimensional layered material: MgSiP2 with a low-buckled honeycomb lattice. Our HSE06 calculation shows that MgSiP2 is an indirect-gap semiconductor with a band-gap of 1.20 eV, closed to that of bulk silicon. More remarkably, MgSiP2 exhibits worthwhile anisotropy along with electron and hole carrier mobility. A ultrahigh electron mobility is even up to 1.29×104 cm2 V-1 s-1, while the hole mobility is nearly zero along the a direction. The large difference of the mobility between electron and hole together with the suitable band-gap suggest that MgSiP2 may be a good candidate for solar cell or photochemical catalysis material. Furthermore, we explore MgSiP2 as an anode for sodium-ion batteries. Upon Na adsorption, the semiconducting MgSiP2 transforms to a metallic state, ensuring good electrical conductivity. A maximum theoretical capacity of 1406 mAh/g, a small volume change (within 9.5%), a small diffusion barrier (~0.16 eV) and low average open-circuit voltages (~0.15 V) were found for MgSiP2 as an anode for sodium-ion batteries. These results are helpful to deepen the understanding of MgSiP2 as a nanoelectronic device and a potential anode for Na-ion batteries.
A facile preparation strategy was proposed for preparation of compact zeolite LTA membranes on polyethyleneimine (PEI) modified substrates without seeding. Through the functionalization of substrates by using PEI, compact LTA membranes can be formed on various kinds of substrates. A well-intergrown and phase-pure LTA membrane with a thickness of about 3.0 μm is successfully prepared on the α-Al2O3 disk after crystallization for 24 h at 60 ℃. Besides LTA membrane, well-intergrown zeolite FAU membranes can also be formed on PEI-modified α-Al2O3 substrates, suggesting the universality of this strategy. The zeolite LTA membranes synthesized on PEI-modified α-Al2O3 tubes were evaluated for the separation of alcohols/water mixture through pervaporation. The as-synthesized zeolite LTA membranes display high pervaporation performances. For the separation of 10 wt% iso-propanol/water solution at 90 ℃, a high separation factor of 44991 and a water flux of 1.73 kg m-2 h-1 are achieved.
Using particle swarm optimization (PSO) methodology for crystal structure prediction, we predicted a novel two-dimensional (2D) monolayer of silicide diphosphorus compound: SiP2, which exhibits good stability as examined via cohesive energy, mechanical criteria, molecular dynamics simulation and all positive phonon spectrum, respectively. The SiP2 monolayer is an indirect semiconductor with the band gap as 1.8484 eV (PBE) or 2.681 eV (HSE06), which makes it more advantageous for high-frequency-response optoelectronic materials. Moreover, the monolayer is a relatively hard auxetic material with negative Possion's ratios, and also possesses a ultrahigh carrier mobility (1.069×105 cm2 V-1 s-1) which is approximately four times the maximum value in phosphorene and comparable to the value of graphene and CP monolayers. Furthermore, the effects of strains on band structures and optical properties of SiP2 monolayer have been studied, as well as CO2 molecules can be strongly chemically adsorbed on the SiP2 monolayer. A semiconductor-to-metal transition for -9.5% strain ratio case and a huge optical absorption capacity on the order of 106 cm-1 in visible region present. These theoretical findings endow SiP2 Monolayer to be a novel 2D material holding great promises for applications in high-performance electronics, optoelectronics, mechanics and CO2 capturing material.
Metallic zinc is attractive anode material of rechargeable aqueous Zn-based batteries due to its ambient stability, high volumetric capacity, and abundant reserves. Nonetheless, Zn anodes suffer from issues such as low coulombic efficiency (CE), large polarization and dendrite formation. Herein, uniform Zn electrodeposition is reported on carbon substrates by selective nitrogen doping. Combined experimental and theoretical investigations demonstrate that pyrrolic and pyridinic nitrogen doped in carbon play beneficial effect as zinc-philic sites to direct nucleation and growth of metallic Zn, while negligible effect is observed for graphite nitrogen in Zn plating. The carbon cloth with modified amount of doped pyrrolic and pyridinic nitrogen stabilizes Zn plating/stripping with 99.3% CE after 300 cycles and significantly increases the deliverable capacity at high depth of charge and discharge compared to undoped carbon substrate and Zn foil. This work provides a better understanding of heteroatom doping effect in design and preparation of stable 3D carbon-supported zinc anode.
Multishelled hollow structures have drawn increasing interest because of their peculiar compartmentation environments and physicochemical properties. In this work, deformable double-shelled hollow mesoporous organosilica nanocapsules (DDHMONs) were successfully synthesized by a multi-interfacial etching strategy. The obtained DDHMONs have a double-shelled structure with aninorganic-organic hybrid framework, a uniform outer layer (~320 nm) and inner layer (~180 nm), ordered mesochannels (~2.21 nm), and a large specific surface area (~1233 m2/g). In vitro toxicity tests show that the DDHMONs have excellent biocompatibility when coincubated with human breast cancer cells. In addition, the anticancer substance doxorubicin (DOX) can be highly loaded in DDHMONs (~335 μg/mg). The results from flow cytometry together with confocal laser scanning microscopy show that DOX can be efficiently delivered into MCF-7 cells by DDHMONs, thus improving chemotherapeutic efficiency and demonstrating that DDHMONs have potential nanomedicine applications as anticancer agents.
Constructing 3D multifunctional conductive framework as stable sulfur cathode contributes to develop advanced lithium-sulfur (Li-S) batteries. Herein, a freestanding electrode with nickel foam framework and nitrogen doped porous carbon (PC) network is presented to encapsulate active sulfur for Li-S batteries. In such a mutually embedded architecture with high stability, the interconnected carbon network and nickel foam matrix can expedite ionic/electronic transport and sustain volume variations of sulfur. Furthermore, rationally designed porous structures provide sufficient internal space and large surface area for high active sulfur loading and polar polysulfides anchoring. Benefiting from the synergistic superiority, the Ni/PC-S cathode exhibits a high initial capacity of around 1200 mAh/g at 0.2 C, excellent rate performance, and high cycling stability with a low decay rate of 0.059% per cycle after 500 cycles. This work provides a useful strategy to exploit freestanding porous framework for diverse applications.
A template-free carbonization-activation route is developed to fabricate sub-nanopore-containing porous carbon by using a novel polypyrrole (PPy) hydrogel as a precursor. This design of PPy hydrogel precursor containing molecular-scale grids (diameter ~2.0 nm) allows for homogeneous N, O-codoping into the porous carbon scaffold during the pyrolysis process. A subsequent activation step produces activated porous carbons (APCs) with tailored pore structures, which renders the APCs abundant sub-nanopores on their surface to increase the specific capacitance as extra capacitance sites. Coupled with large specific surface area and abundant heteroatoms, the optimized APC4/1 displays excellent specific capacitance of 379 F/g for liquid-state supercapacitor and 230 F/g for solid-state supercapacitor. The solid-state supercapacitor shows a high energy density of 22.99 Wh/kg at power density of 420 W/kg, which is higher than most reported porous carbon materials and satisfy the urgent requirements of elementary power source for electric vehicles. Moreover, this method can be easily modified to fabricate sub-nanopore-containing porous carbons with preferred structures and compositions for many applications.
The potassium-ion batteries (PIBs) have become the promising energy storage devices due to their relatively moderate cost and plenteous potassium resources. Whereas, the main drawback of PIBs is unsatisfactory electrochemical performance induced by the larger ionic radius of potassium ion. Herein, we report a well-designed, uniform-dispersed, and morphology-controllable zinc sulfide (ZnS) quantum dots loading on graphene as an anode in the PIBs. The directed uniform dispersion of the in-situ growing ZnS quantum dots (~2.8 nm in size) on graphene can mitigate the volume effect during the insertion-extraction process and shorten the migration path of potassium ions. As a result, the battery exhibits superior cycling stability (350.4 mAh/g over 200 cycles at 0.1 A/g) and rate performance (98.8 mAh/g at 2.0 A/g). We believe the design of active material with quantum dot-minimized size provides a novel route into PIBs and contributes to eliminating the major electrode failure issues of the system.
Catalytic oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) have garnered great attention as the key character in metal-air batteries. Herein, we developed a superior nonprecious bifunctional oxygen electrocatalyst, fabricated through spatial confinement of Fe/Fe3C nanocrystals in pyridinic N and Fe-Nx rich carbon nanotubes (Fe/Fe3C-N-CNTs). During ORR, the resultant electrocatalyst exhibits positive onset potential of 1.0 V (vs. RHE), large half-wave potentials of 0.88 V (vs. RHE), which is more positive than Pt/C (0.98 V and 0.83 V, respectively). Remarkably, Fe/Fe3C-N-CNTs exhibits outstanding durability and great methanol tolerance, exceeding Pt/C and most reported nonprecious metal-based oxygen reduction electrocatalysts. Moreover, Fe/Fe3C-N-CNTs show a markedly low potential at j =10 mA/cm2, small Tafel slopes and extremely high stability for OER. Impressively, the Fe/Fe3C-N-CNTs-based Zn-air batteries demonstrate high power density of 183 mW/cm2 and robust charge/discharge stability. It is revealed that the spatial confinement effect can impede the aggregation and corrosion of Fe/Fe3C nanocrystals. Meanwhile, Fe/Fe3C and Fe-Nx play synergistic effect on boosting the ORR/OER activity, which provides an important guideline for construction of inexpensive nonprecious metal-carbon hybrid nanomaterials.
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