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In this paper, NiMoO4@CoWO4 core–shell nanostructures have been synthesized by a hydrothermal process and annealing. Structural characterization and compositional analysis of the as-prepared NiMoO4@CoWO4 nanocomposites were performed using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, cyclic voltammetry, galvanostatic charge–discharge cycling, and electrochemical impedance spectroscopy. Here, NiMoO4@CoWO4 nanostructures were designed and synthesized on Ni foam. NiMoO4 nanorods would provide electron "superhighways" for charge storage and delivery, which could provide an effective electrical connection to the CoWO4 electrode material. In addition, the open space between these nanosheets can increase the active sites and the contribution of capacitive effects. Finally, NiMoO4@CoWO4 directly grown on Ni foam could avoid the "dead" volume caused by the tedious process of mixing active materials with polymer binders/conductive additives. As expected, NiMoO4@CoWO4 exhibited high specific capacity, good rate performance and excellent electrochemical stability. The results show that NiMoO4@CoWO4 exhibited a high specific capacity at a current density of 5 mA cm−2 and splendid electrochemical stability (88.5% retention after 4000 cycles). The great electrochemical performance could be ascribed to the unique core–shell architecture and the synergistic effect from the NiMoO4 nanorods and CoWO4. [ABSTRACT FROM AUTHOR]

The ground and first singlet excited state absorption in distyrylbenzene (DSB) is simulated based on linear-response time dependent density functional theory (LR-TDDFT). It is found that distyrylbenzene shows a strong reverse saturable absorption effect around the near-infrared range. Combining the calculations of cubic response functions to simulate the three-photon absorption in distyrylbenzene, we are able to show that distyrylbenzene is a promising ultrafast optical limiter for the light with wavelengths around 775 nm. The primary mechanism for the optical limiting behavior can be well understood by the three-photon induced excited state absorption (3PA-ESA). This result in that DSB has high transmittance for low-intensity ambient light levels and the ultrafast response of optical-limiting. In addition, the limited optical window can be tuned by changing the length of the π-electron conjugated structure. It was also discovered that the molecular aggregation has an inhibitory effect on the optical limiting efficiency of distyrylbenzene. The present results may serve as a theoretical guideline for the design of distyrylbenzene-based optical limiting materials. [ABSTRACT FROM AUTHOR]

Here we report for the first time a van der Waals (vdW) heterostructure formed from an individual single crystal SbSI whisker and individual PbI2 flake for photodetection. Benefiting from the millimeter-sized whisker and flake, we take advantage of the flexibility of operation and vdW junction interface between SbSI and PbI2. This mixed-dimensional heterostructure is used as an optoelectronics platform due to the larger light-harvesting cross section than the individual material. It generates photocurrent to broaden the spectral response range. The two-dimensional (2D) material acts as a current collector, while the single crystal whisker material acts as a current channel. Compared with the individual SbSI device, the vdW heterojunction device can achieve a lower dark current. As a result, our SbSI–PbI2 photodetector exhibits a responsivity of up to 26.3 mA W−1 and shows a fast response speed of ∼12 ms. Large-area growth and scalable approaches lead to an efficient transfer strategy and heterostructure assembly. These investigations will broaden our fundamental knowledge of vdW heterostructures. This mixed-dimensional vdW heterostructure opens new opportunities for basic research of micro/nano-optoelectronics. [ABSTRACT FROM AUTHOR]

In this paper, K-doped δ-MnO2 nanoflowers decorated with Au nanoparticles (MnO2–Au) were synthesized by a hydrothermal method. To probe the effect of the band gaps in the MnO2 support over the surface plasmon resonance (SPR)-mediated catalytic conversions on Au nanoparticles (NPs), the oxidation of p-aminothiophenol (PATP) to p,p′-dimercaptoazobenzene (DMAB) was used as a model reaction. We found that the PATP conversion was significantly higher for the MnO2–Au hybrid compared with its individual Au NPs under excitation at 633 nm. Furthermore, the activities of the MnO2–Au materials increased as the MnO2 support displayed higher K-doped levels, which led to narrower band gaps. These results could be explained based on the transfer of photogenerated electrons from MnO2 to Au, increasing the electron density in Au NPs and thus contributing to improved SPR-mediated activity. In this case, our observations show that tuning the band gaps can have a significant impact on SPR-mediated conversions, in which narrower band gaps should facilitate the charge transfer of SPR-excited charge carriers and thus lead to better performances. Our findings presented may provide important insights into the role of the support materials in plasmonic catalysis, indicating that, in addition to the control over several physical and chemical parameters (such as shape, surface area, defects, among others), the proper tuning of the band gap can serve as an effective strategy for the optimization of activities. [ABSTRACT FROM AUTHOR]

Large-area and high-quality 2D layered materials with good electrical performance are necessary although active 2D materials for devices are usually limited to micrometer-sizes. Herein, large-size layered-crystalline lead(ii) iodide (PbI2) flakes with sizes of up to 5 mm were synthesized via a hydrothermal method. Thiourea facilitated their large-area growth. Photocurrent measurements of a PbI2 flake photodetector (PD) constructed on flexible polyimide (PI) substrates exhibit a responsivity at 510 nm of up to 5 mA W−1. Additionally, the fast response speed of the device is less than 30 ms. Low dark currents are lower than 10 pA at a bias of 5 V. The spectral selectivity of our PbI2 flakes may potentially be used for narrowband photodetection. The process can also be converted to produce Pb5S2I6 nanowires (NWs) with a broadened spectral response range by changing the ratio of reactants. Our results on the freestanding growth of large area PbI2 flakes and Pb5S2I6 NWs may lead to facile flexible device fabrication possibilities. These findings will broaden our fundamental knowledge of van der Waals layered halide semiconductors. Meanwhile, such a hydrothermal synthetic approach paves a practical route towards large-area promising organic–inorganic perovskite, which is hosted by PbI2. [ABSTRACT FROM AUTHOR]

A series of epitaxial V1−xWxO2 (0 ≤x≤ 0.76%) nanocrystalline films on c-plane sapphire substrates have been successfully synthesized. Orbital structures of V1−xWxO2 films with monoclinic and rutile states have been investigated by ultraviolet-infrared spectroscopy combined with first principles calculations. Experimental and calculated results show that the overlap of π* and d orbitals increases with increasing W doping content for the rutile state. Meanwhile, in the monoclinic state, the optical band gap decreases from 0.65 to 0.54 eV with increasing W doping concentration. Clear evidence is found that the V1−xWxO2 thin film phase transition temperature change comes from orbital structure variations. This shows that, with increasing W doping concentration, the decrease of rutile d orbital occupancy can reduce the strength of V–V interactions, which finally results in phase transition temperature decrease. The experimental results reveal that the d orbital is very important for the VO2 phase transition process. Our findings open a possibility to tune VO2 phase transition temperature through orbital engineering. [ABSTRACT FROM AUTHOR]

Cu(bipy)2(SiF6) is a highly porous metal–organic framework (MOF) and represents a prototypal “pillared sheet” platform offering opportunities to control the pore sizes. Its structural features, low cost and facile synthesis make it a great candidate to fabricate membranes for gas separation. The key to obtaining thin, continuous Cu(bipy)2(SiF6) membranes is to control the Cu(bipy)2(SiF6) crystal growth and enhance the binding between membrane and substrate. Here we explored a new route by direct synthesis and successfully obtained a continuous thin Cu(bipy)2(SiF6) membrane on a macroporous glass-frit disk with high robustness. It is speculated that the SiF62− used to construct the Cu(bipy)2(SiF6) membrane came from the fluorinated substrate. The Cu(bipy)2(SiF6) membrane shows the separation factors of H2–CO2, H2–CH4 and H2–N2 are 8.0, 7.5, and 6.8 respectively at 293 K and 1 bar with H2 permeance of 2.7 × 10−7 mol m−2 s−1 Pa−1 as well as high thermal stability. We expect to explore more membranes of Cu(bipy)2(SiF6) analogues with tuneable pore sizes using this route and to obtain membranes with higher gas separation performance. [ABSTRACT FROM AUTHOR]

A one-step route to the synthesis of Ge nanocrystals on a large-scale from GeO2powders in aqueous solution at 60 °C under an ambient atmosphere is reported, which avoids toxic precursors and by-products, high temperature, and inert atmospheres. [ABSTRACT FROM AUTHOR]

Recent research and development of energy storage devices has focused on new electrode materials because of the critical effects on the electrochemical properties of supercapacitors. In particular, MnO 2 and Fe 2 O 3 have drawn extensive attention because of their low cost, high theoretical specific capacity, environmental friendliness, and natural abundance. In this study, MnO 2 ultrathin nanosheet arrays and Fe 2 O 3 nanoparticles are fabricated on TiN nanowires to produce binder-free core-shell positive and negative electrodes for a flexible and ultra-fast hybrid supercapacitor. The MnO 2 /TiN/CC electrode shows larger pseudocapacitance contributions than MnO 2 /CC. For example, at a scanning rate of 2 mV s -1 , the pseudocapacitance contribution of MnO 2 /TiN/CC is 87.81% which is nearly 25% bigger than that of MnO 2 /CC (71.26%). The supercapacitor can withstand a high scanning rate of 5000 mV s -1 in the 2 V window and exhibits a maximum energy density of 71.19 W h kg -1 at a power density of 499.79 W kg -1 . Even at 5999.99 W kg -1 , it still shows an energy density of 31.3 W h kg -1 and after 10 000 cycles, the device retains 81.16% of the initial specific capacitance. The activation mechanism is explored and explained., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

A series of epitaxial V1-xWxO2 (0 ≤ x ≤ 0.76%) nanocrystalline films on c-plane sapphire substrates have been successfully synthesized. Orbital structures of V1-xWxO2 films with monoclinic and rutile states have been investigated by ultraviolet-infrared spectroscopy combined with first principles calculations. Experimental and calculated results show that the overlap of π* and d∥ orbitals increases with increasing W doping content for the rutile state. Meanwhile, in the monoclinic state, the optical band gap decreases from 0.65 to 0.54 eV with increasing W doping concentration. Clear evidence is found that the V1-xWxO2 thin film phase transition temperature change comes from orbital structure variations. This shows that, with increasing W doping concentration, the decrease of rutile d∥ orbital occupancy can reduce the strength of V-V interactions, which finally results in phase transition temperature decrease. The experimental results reveal that the d∥ orbital is very important for the VO2 phase transition process. Our findings open a possibility to tune VO2 phase transition temperature through orbital engineering.