Dual-polarized nanocrescent antenna designed using efficient optimization techniques.

A novel nanocrescent antenna with polarization diversity is introduced. It is formed from a crescent-shaped patch fed with a coupled strip transmission line. The antenna is located on top of a SiO2 thin film with a shielding ground layer underneath. The structure is supported by an arbitrary substrate. Polarization of the radiated field can be adjusted to be along either one of the two orthogonal polarizations based on which one of the two crescent patch modes is going to be excited. The excitation of either one of these two modes of the patch is achieved by switching between the two propagating modes of the feeding coupled strip transmission line. Using a dual-polarized antenna allows doubling the optical communication system's capacity via frequency reuse. The new crescent antenna dimensions are optimized to satisfy several goals, such as minimizing the losses, the deviation of the main beam direction away from broadside, and maximizing the radiation efficiency and axial ratio. Through the optimization process, simple surrogate kriging models replace the detailed electromagnetic simulation. The optimal response is achieved by applying two different optimizers. The first optimizer employs the design-centering technique using normed distances. The multiobjective particle swarm with the preference ranking organization method for enrichment evaluations is used by the second optimizer. In order to identify the critical dimensions to which the nanoantenna is most sensitive, a sensitivity analysis is used. The optimized antenna is capable of switching its radiation between two orthogonal pure linear polarizations with maximum radiation along the broadside direction. The size of the proposed antenna is about 500nm×500nm. Its impedance-matching bandwidth is higher than 30 THz centered around 193 THz (1550 nm). Its gain and radiation efficiency are higher than 5.2 dBi and 85%, respectively, all over the working frequency band.

Flexible Free-Standing MoO3/Ti3C2T z MXene Composite Films with High Gravimetric and Volumetric Capacities.

Enhancing both the energy storage and power capabilities of electrochemical capacitors remains a challenge. Herein, Ti3C2T z MXene is mixed with MoO3 nanobelts in various mass ratios and the mixture is used to vacuum filter binder free, open, flexible, and free-standing films. The conductive Ti3C2T z flakes bridge the nanobelts, facilitating electron transfer; the randomly oriented, and interconnected, MoO3 nanobelts, in turn, prevent the restacking of the Ti3C2T z nanosheets. Benefitting from these advantages, a MoO3/Ti3C2T z film with a 8:2 mass ratio exhibits high gravimetric/volumetric capacities with good cyclability, namely, 837 C g-1 and 1836 C cm-3 at 1 A g-1 for an ≈ 10 µm thick film; and 767 C g-1 and 1664 C cm-3 at 1 A g-1 for ≈ 50 µm thick film. To further increase the energy density, hybrid capacitors are fabricated with MoO3/Ti3C2T z films as the negative electrodes and nitrogen-doped activated carbon as the positive electrodes. This device delivers maximum gravimetric/volumetric energy densities of 31.2 Wh kg-1 and 39.2 Wh L-1, respectively. The cycling stability of 94.2% retention ratio after 10 000 continuous charge/discharge cycles is also noteworthy. The high energy density achieved in this work can pave the way for practical applications of MXene-containing materials in energy storage devices.

Tailored synthesis approach of (Mo2/3Y1/3)2AlC i-MAX and its two-dimensional derivative Mo1.33CTz MXene: enhancing the yield, quality, and performance in supercapacitor applications.

A vacancy-ordered MXene, Mo1.33CTz, obtained from the selective etching of Al and Sc from the parent i-MAX phase (Mo2/3Sc1/3)2AlC has previously shown excellent properties for supercapacitor applications. Attempts to synthesize the same MXene from another precursor, (Mo2/3Y1/3)2AlC, have not been able to match its forerunner. Herein, we show that the use of an AlY2.3 alloy instead of elemental Al and Y for the synthesis of (Mo2/3Y1/3)2AlC i-MAX, results in a close to 70% increase in sample purity due to the suppression of the main secondary phase, Mo3Al2C. Furthermore, through a modified etching procedure, we obtain a Mo1.33CTz MXene of high structural quality and improve the yield by a factor of 6 compared to our previous efforts. Free-standing films show high volumetric (1308 F cm-3) and gravimetric (436 F g-1) capacitances and a high stability (98% retention) at the level of, or even beyond, those reported for the Mo1.33CTz MXene produced from the Sc-based i-MAX. These results are of importance for the realization of high quality MXenes through use of more abundant elements (Y vs. Sc), while also reducing waste (impurity) material and facilitating the synthesis of a high-performance material for applications.

Pressure-induced semiconductor-to-metal phase transition of a charge-ordered indium halide perovskite.

Phase transitions in halide perovskites triggered by external stimuli generate significantly different material properties, providing a great opportunity for broad applications. Here, we demonstrate an In-based, charge-ordered (In+/In3+) inorganic halide perovskite with the composition of Cs2In(I)In(III)Cl6 in which a pressure-driven semiconductor-to-metal phase transition exists. The single crystals, synthesized via a solid-state reaction method, crystallize in a distorted perovskite structure with space group I4/m with a = 17.2604(12) Å, c = 11.0113(16) Å if both the strong reflections and superstructures are considered. The supercell was further confirmed by rotation electron diffraction measurement. The pressure-induced semiconductor-to-metal phase transition was demonstrated by high-pressure Raman and absorbance spectroscopies and was consistent with theoretical modeling. This type of charge-ordered inorganic halide perovskite with a pressure-induced semiconductor-to-metal phase transition may inspire a range of potential applications.

Flexible Freestanding MoO3-x -Carbon Nanotubes-Nanocellulose Paper Electrodes for Charge-Storage Applications.

Herein, a one-step synthesis protocol was developed for synthesizing freestanding/flexible paper electrodes composed of nanostructured molybdenum oxide (MoO3-x ) embedded in a carbon nanotube (CNT) and Cladophora cellulose (CC) matrix. The preparation method involved sonication of the precursors, nanostructured MoO3-x , CNTs, and CC with weight ratios of 7:2:1, in a water/ethanol mixture, followed by vacuum filtration. The electrodes were straightforward to handle and possessed a thickness of approximately 12 µm and a mass loading of MoO3-x -CNTs of approximately 0.9 mg cm-2 . The elemental mapping showed that the nanostructured MoO3-x was uniformly embedded inside the CNTs-CC matrix. The MoO3-x -CNTs-CC paper electrodes featured a capacity of 30 C g-1 , normalized to the mass of MoO3-x -CNTs, at a current density of 78 A g-1 (corresponding to a rate of approximately 210 C based on the MoO3 content, assuming a theoretical capacity of 1339 C g-1 ), and exhibited a capacity retention of 91 % over 30 000 cycles. This study paves the way for the manufacturing of flexible/freestanding nanostructured MoO3-x -based electrodes for use in charge-storage devices at high charge/discharge rates.

Insights into the Exfoliation Process of V2O5·nH2O Nanosheet Formation Using Real-Time 51V NMR.

Nanostructured hydrated vanadium oxides (V2O5·nH2O) are actively being researched for applications in energy storage, catalysis, and gas sensors. Recently, a one-step exfoliation technique for fabricating V2O5·nH2O nanosheets in aqueous media was reported; however, the underlying mechanism of exfoliation has been challenging to study. Herein, we followed the synthesis of V2O5·nH2O nanosheets from the V2O5 and VO2 precursors in real time using solution- and solid-state 51V NMR. Solution-state 51V NMR showed that the aqueous solution contained mostly the decavanadate anion [H2V10O28]4- and the hydrated dioxovanadate cation [VO2·4H2O]+, and during the exfoliation process, decavanadate was formed, while the amount of [VO2·4H2O]+ remained constant. The conversion of the solid precursor V2O5, which was monitored with solid-state 51V NMR, was initiated when VO2 was in its monoclinic forms. The dried V2O5·nH2O nanosheets were weakly paramagnetic because of a minor content of isolated V4+. Its solid-state 51V signal was less than 20% of V2O5 and arose from diamagnetic V4+ or V5+.This study demonstrates the use of real-time NMR techniques as a powerful analysis tool for the exfoliation of bulk materials into nanosheets. A deeper understanding of this process will pave the way to tailor these important materials.

A heavy metal-free CuInS2 quantum dot sensitized NiO photocathode with a Re molecular catalyst for photoelectrochemical CO2 reduction.

Heavy metal-free CuInS2 quantum dots (QDs) were employed as a photosensitizer on a NiO photocathode to drive an immobilized molecular Re catalyst for photoelectrochemical CO2 reduction for the first time. A photocurrent of 25 µA cm-2 at -0.87 V vs. NHE was obtained, providing a faradaic efficiency of 32% for CO production.

Covalently linking CuInS2 quantum dots with a Re catalyst by click reaction for photocatalytic CO2 reduction.

Covalently linking photosensitizers and catalysts in an inorganic-organic hybrid photocatalytic system is beneficial for efficient electron transfer between these components. However, general and straightforward methods to covalently attach molecular catalysts on the surface of inorganic semiconductors are rare. In this work, a classic rhenium bipyridine complex (Re catalyst) has been successfully covalently linked to the low toxicity CuInS2 quantum dots (QDs) by click reaction for photocatalytic CO2 reduction. Covalent bonding between the CuInS2 QDs and the Re catalyst in the QD-Re hybrid system is confirmed by UV-visible absorption spectroscopy, Fourier-transform infrared spectroscopy and energy-dispersive X-ray measurements. Time-correlated single photon counting and ultrafast time-resolved infrared spectroscopy provide evidence for rapid photo-induced electron transfer from the QDs to the Re catalyst. Upon photo-excitation of the QDs, the singly reduced Re catalyst is formed within 300 fs. Notably, the amount of reduced Re in the linked hybrid system is more than that in a sample where the QDs and the Re catalyst are simply mixed, suggesting that the covalent linkage between the CuInS2 QDs and the Re catalyst indeed facilitates electron transfer from the QDs to the Re catalyst. Such an ultrafast electron transfer in the covalently linked CuInS2 QD-Re hybrid system leads to enhanced photocatalytic activity for CO2 reduction, as compared to the conventional mixture of the QDs and the Re catalyst.

Observation of Interpenetration Isomerism in Covalent Organic Frameworks.

We report herein the first example of interpenetration isomerism in covalent organic frameworks (COFs). As a well-known three-dimensional (3D) COF, COF-300 was synthesized and characterized by the Yaghi group in 2009 as a 5-fold interpenetrated diamond structure ( dia-c5 topology). We found that adding an aging process prior to the reported synthetic procedure afforded the formation of an interpenetration isomer, dia-c7 COF-300. The 7-fold interpenetrated diamond structure of this new isomer was identified by powder X-ray diffraction and rotation electron diffraction analyses. Furthermore, we proposed a universal formula to accurately determine the number of interpenetration degrees of dia-based COFs from only the unit cell parameters and the length of the organic linker. This work not only provides a novel example to the category of interpenetration isomerism but also provides new insights for the further development of 3D COFs.

Facile Water-Based Strategy for Synthesizing MoO3-x Nanosheets: Efficient Visible Light Photocatalysts for Dye Degradation.

Nanostructured molybdenum oxides are promising materials for energy storage, catalysis, and electronic-based applications. Herein, we report the synthesis of MoO3-x nanosheets (x stands for oxygen vacancy) via an environmentally friendly liquid exfoliation approach. The process involves the reflux of the bulk α-MoO3 precursor in water at 80 °C for 7 days. Electron microscopy and atomic force microscopy show that the MoO3-x nanosheets are a few nanometer thick. MoO3-x nanosheets exhibit near infrared plasmonic property that can be enhanced by visible light irradiation for a short time (10 min). Photocatalytic activity of MoO3-x nanosheets for organic dye decolorization is examined using two different dyes (rhodamine B and methylene blue). Under visible light irradiation, MoO3-x nanosheets make a rapid decolorization for the dye molecules in less than 10 min. The simple synthesis procedure of MoO3-x nanosheets combined with their remarkable photochemical properties reflect the high potential for using the nanosheets in a variety of applications.

Synthesis and Structure Determination of Large-Pore Zeolite SCM-14.

SCM-14 (Sinopec Composite Material No. 14), a new stable germanosilicate zeolite with a 12×8×8-ring channel system, was synthesized using commercially available 4-pyrrolidinopyridine as organic structure-directing agents (OSDAs) in fluoride medium. The framework structure of SCM-14 was determined using rotation electron diffraction (RED), and refined against synchrotron X-ray powder diffraction (SXPD) data for both as-made and calcined materials. The framework structure of SCM-14 is closely related to that of three known zeolites: mordenite (MOR), GUS-1 (GON), and IM-16 (UOS). SCM-14 has the same projection as that of mordenite and GUS-1 when viewed along the 12-ring channels, and possesses two more straight 8-ring channels running perpendicular to the 12-ring channels. The structure of SCM-14 can be constructed by either the same layers as that of GUS-1 or the same columns as that of IM-16. Based on their structural relationship, three topologically reasonable hypothetical zeolites were predicted.