Hexagonal Framework Research Articles

Understanding the electronic pi-system of 2D covalent organic frameworks with Wannier functions

We investigate a family of hexagonal 2D covalent organic frameworks (COFs) with phenyl and biphenyl spacer units and different chemical linker species. Chemical trends are elucidated and attributed to microscopic properties of the pi-electron-system spanned by atomic p_z-orbitals. We systematically investigate the electronic structure, delocalization of electronic states, effects of disorder, bond torsion, and doping, and correlate these with variable pi-conjugation and nucleus-independent chemical shift (NICS) aromaticity. Molecular orbitals are obtained from maximally localized Wannier functions that have sigma- and pi-character, forming distinct sigma- and pi-bands for all valence states. The Wannier-orbital description goes beyond simple tight-binding models and enables a detailed understanding of the electronic topology, effective electronic coupling and delocalization. It is shown that a meaningful comparison between COFs with different chemical elements can only be made by examining the entire pi-electron system, while a comparison of individual bands (e.g., bands near the Fermi energy) can be a insufficient to derive general design rules for linker and spacer monomer selection. We further identify delocalized states that are spread across tens or hundreds of pores of the 2D COFs and analyze their robustness against structural and energetic disorders like out-of-plane rotations of molecular fragments, different strength of energetic disorder and energetic shifts due to chemical doping.

Enhancing Trajectory-Based Operations for UAVs through Hexagonal Grid Indexing: A Step towards 4D Integration of UTM and ATM

Aviation is expected to face a surge in the number of manned aircraft and drones in the coming years, making it necessary to integrate Unmanned Aircraft System Traffic Management (UTM) into Air Traffic Management (ATM) to ensure safe and efficient operations. This research proposes a novel hexagonal grid-based 4D trajectory representation framework for unmanned aerial vehicle (UAV) traffic management that overcomes the limitations of existing square/cubic trajectory representation methods. The proposed model employs a hierarchical indexing structure using hexagonal cells, enabling efficient ground based strategic conflict detection and conflict free 4D trajectory planning. Additionally, the use of Hexagonal Discrete Global Grid Systems provides a more accurate representation of UAV trajectories, improved sampling efficiency and higher angular resolution. The proposed approach can be used for predeparture conflict free 4D trajectory planning, reducing computational complexity and memory requirements while improving the accuracy of strategic trajectory conflict detection. The proposed framework can also be extended for air traffic flow management trajectory planning, Air Traffic Control (ATC) workload measurement, sector capacity estimation, dynamics airspace sectorization using hexagonal sectors and traffic density calculation, contributing to the development of an efficient UTM system, and facilitating the integration of UAVs into the national airspace system with ATM

A Novel Hexagonal Psuedo framework for Edge Detection Operators on Hexagonal Framework

Edge detection using a gradient-based detector is a gold-standard method for identifying and analyzing different edge points in an image. A hexagonal grid structure is a powerful architecture dominant for intelligent human-computer vision. This structure provides the best angle resolution, good packing density, high sampling efficiency, equidistant pixels, and consistent connectivity. Edge detection application on hexagonal framework provides more accurate and efficient computations. All the real-time hardware devices available capture and display images in rectangular-shaped pixels. So, an alternative approach to mimic hexagonal pixels using software approaches is modeled in this paper. In this research work, an innovative method to create a pseudo hexagonal lattice has been simulated and the performance is compared with various edge detection operators on the hexagonal framework by comparing the quantitative and qualitative metrics of the grayscale image in both square and hexagonal lattice. The quantitative performance of the edge detection on the hexagonal framework is compared based on the experimental facts. The pseudo-hexagonal lattice structure assures to be aligned toward the human vision.

TEM study of ∼PbCr2S4 columnar misfit phases

The disordered structure of the columnar misfit ​∼ ​PbCr2S4 phase (∼ character indicates that it is close to the stoichiometric composition but slightly away) has been revealed by means of transmission electron microscopy (TEM) varied techniques such as selected area electron diffraction (SAED), high-resolution TEM (HRTEM), dark-field TEM and high-angle annular dark field (HAADF) in scanning-transmision (STEM) mode. The structure consists of a hexagonal framework (Cr21S36), with unit cell parameters a0 ​= ​b0 ​= ​21.407 (1) Å and c0 ​= ​3.476 (1), and with hexagonal (Pb6Cr2S6) and trigonal columns (Pb3S) with the same a and b parameters and different c: c3 ​= ​3.98 Å; c6 ​= ​5.62 ​Å, measured by electron diffraction. While the framework exhibit no crystalline disorder, the arrangement of the two types of columns is disordered. This disorder is shown by electron diffraction as diffuse scattering planes which are perpendicular to the framework c axis and parallel to the a∗b∗ plane. While the disorder between hexagonal columns is due to the lack of correlation between different columns, we observe in the trigonal columns also the presence of intra-columnar atomic disorder. X-ray wavelength dispersive spectroscopy (XWDS) analyses produce Pb0.81(1)Cr2S3.97(6) composition. TEM imaging techniques suggest lack of correlation between trigonal columns as the cause for the observed disorder as well as inside-the-column structural disorder in Pb3S trigonal columns.

Atomic Ruthenium-Riveted Metal-Organic Framework with Tunable d-Band Modulates Oxygen Redox for Lithium-Oxygen Batteries.

Non-aqueous Li-O2 batteries have aroused considerable attention because of their ultrahigh theoretical energy density, but they are severely hindered by slow cathode reaction kinetics and large overvoltages, which are closely associated with the discharge product of Li2O2. Herein, hexagonal conductive metal-organic framework nanowire arrays of nickel-hexaiminotriphenylene (Ni-HTP) with quadrilateral Ni-N4 units are synthesized to incorporate Ru atoms into its skeleton for NiRu-HTP. The atomically dispersed Ru-N4 sites manifest strong adsorption for the LiO2 intermediate owing to its tunable d-band center, leading to its high local concentration around NiRu-HTP. This favors the formation of film-like Li2O2 on NiRu-HTP with promoted electron transfer and ion diffusion across the cathode-electrolyte interface, facilitating its reversible decomposition during charge. These allow the Li-O2 battery with NiRu-HTP to deliver a remarkably reduced charge/discharge polarization of 0.76 V and excellent cyclability. This work will enrich the design philosophy of electrocatalysts for regulation of kinetic behaviors of oxygen redox.

Zinc-Silver Doped Mesoporous Hydroxyapatite Synthesized via Ultrasonic in Combination with Sol-Gel Method for Increased Antibacterial Activity

Bone materials are mainly composed of an inorganic constituent called hydroxyapatite (HA). In the current study, mesoporous Zn2+/Ag+ doped hydroxyapatite nanoparticles (Zn-Ag doped HA) with high antibacterial activity were synthesized through ultrasonic coupled sol-gel techniques under calcination temperatures of 600 °C for 4 h and 1100 °C for 1 h. The variance in the molar ratio of Zn2+/Ag+ in Ca9.0Zn1.0−xAgx(PO4)6(OH)2 (x = 0.0, 0.25 to 1.0) and its effects on the chemical and physical properties of the powdered samples were investigated. The results show that the hexagonal framework of HA incorporated both the Zn2+ and Ag+ ions and the rhombohedral structure of β-TCP. The main functional groups of HA and Zn-Ag doped HA samples were hydroxyl and phosphate. All samples have mesoporous characteristics with a Type IV isotherm. The agar well diffusion process was used to examine antibacterial activity against E. coli, P. aeruginosa, S. aureus, B. cereus and B. subtilis. Effective antibacterial activity was displayed by Zn-Ag doped HA. Excellent antibacterial performance was shown by Ca9.0Zn0.75Ag0.25(PO4)6(OH)2 against all tested bacterial strains, except P. aeruginosa. This material showed inhibition zones ranging from 7 to 11 mm, implying that it is a suitable material with an antibacterial action for environmental applications, specifically for water purification.

Localized Spin Dimers and Structural Distortions in the Hexagonal Perovskite Ba3CaMo2O9.

Extended solid-state materials based on the hexagonal perovskite framework are typified by close competition between localized magnetic interactions and quasi-molecular electronic states. Here, we report the structural and magnetic properties of the new six-layer hexagonal perovskite Ba3CaMo2O9. Neutron diffraction experiments, combined with magnetic susceptibility measurements, show that the Mo2O9 dimers retain localized character down to 5 K and adopt nonmagnetic spin-singlet ground states. This is in contrast to the recently reported Ba3SrMo2O9 analogue, in which the Mo2O9 dimers spontaneously separate into a mixture of localized and quasi-molecular ground states. Structural distortions in both Ba3CaMo2O9 and Ba3SrMo2O9 have been studied with the aid of distortion mode analyses to elucidate the coupling between the crystal lattice and electronic interactions in 6H Mo5+ hexagonal perovskites.

HEXAGON FRAUD IN FRAUDULENT FINANCIAL STATEMENTS: THE MODERATING ROLE OF AUDIT COMMITTEE

This paper aims to examine the effect of the fraud hexagon on fraudulent financial statements (FFS), and the audit committee (AC)'s role in moderating this relation. The research model uses logit regression with data on all non-financial companies in Indonesia ranging from 2016 to 2020, which were obtained from annual reports and Thomson Reuters. The sensitivity test uses a coefficient difference test based on the Overall Manipulation Index. This study shows that the probability of FFS is higher when the manager has the stimulus, opportunity, and capability. On the other hand, rationalization and collusion do not affect the probability of FFS. Interestingly, managers with high ego do not commit fraudulent financial reporting. The AC can minimize the stimulus, opportunity, and capability of the manager to make FFS. On the other hand, the AC cannot minimize the rationalization, ego, and collusion network of the manager. Theoretically, this study contributes to developing the situational action theory literature related to FFS and the fraud hexagon framework. This study provides academic implications that the arguments and empirical research findings that examine the behavior of managers in committing fraudulent financial reporting can be built not only based on the proxies used, but also by referring to the fraud theoretical framework.

Ultralow‐k Amorphous Boron Nitride Based on Hexagonal Ring Stacking Framework for 300 mm Silicon Technology Platform

AbstractThe implementation of ultralow dielectric constant (k value ≈ 2) materials to reduce signal propagation delay in advanced electronic devices represents a critical challenge in next generations of microelectronics technologies. The introduction of well‐stacked and low polarity molecules that do not compromise film density may lead to improvements and desirable material engineering, as conventional porous SiOx derivatives exhibit detrimental degradation of thermo‐mechanical properties when their k values are further scaled down. This work presents a systematic engineering approach for controlling ultralow‐k amorphous boron nitride (aBN) deposition on 300 mm Si platforms. The results indicate that aBN grown from borazine precursor exhibits ultralow dielectric constant ≈2, high density, excellent mechanical strength, and extended thermodynamic stability. Unintentional boron ion doping during plasma dissociation that may induce artificial reductions of k value on n‐type substrates is alleviated by employing a remote microwave plasma process. Moreover, the adoption of low growth rate processes for ultralow‐k aBN deposition is found to be critical to provide for the superior mechanical strength and high density, and is attributed to the formation of hexagonal ring stacking frameworks. These results pave the way and offer engineering solutions for new ultralow‐k material introduction into future semiconductor manufacturing applications.

Preparation and Photocatalytic Properties of Anatase TiO2 with Hollow Hexagonal Frame Structure

Titanium dioxide (TiO2) has been widely used to solve energy and environmental pollution problems due to its excellent properties. In this study, the precursor (HTiOF3) with a spherical structure composed of hexagonal prisms was prepared via a simple solvothermal method using tetrabutyl titanate, hydrofluoric acid, glacial acetic acid and isopropanol as raw materials. Then, the calcination time and temperature of the precursor were controlled to prepare anatase TiO2 with different morphologies, and the photocatalytic performance of the prepared catalysts was studied. When the precursor was calcined at 600 °C for 7 h, the prepared TiO2 had a unique hexagonal framework structure and exhibited excellent photocatalytic performance. The degradation rate of the RhB solution was 98.58% at 40 min and the rate of hydrogen evolution was 2508.12 μmol g−1 h−1.

Mechanically interlocked networks cross-linked by a molecular necklace

Molecular necklaces have attracted much research attention due to their unique topological structures. Although numerous molecular necklaces with exquisite structures have been constructed, it remains a major challenge to exploit the functions and applications associated with their fascinating architectural and dynamic characteristics. Herein, we report a class of mechanically interlocked networks (MINs) cross-linked by a molecular necklace, in which multiple crown ethers are threaded on a hexagonal metallacyclic framework to furnish a cross-linker with delicate interlocked structures. The molecular necklace cross-linker possesses multiple peculiar advantages: multivalent interactions and rigid metallacycle framework guarantee robust features of MINs while the motion and dissociation of the interlocked structures bring in notable mechanical adaptivity. Moreover, the MINs could respond to the stimuli of K+ and Br−, which lead to the dethreading of crown ether and even the complete decomposition of molecular necklace, respectively, showing abundant active properties. These findings demonstrate the untapped potential of molecular necklaces as cross-linkers and open the door to extend their advanced applications in intelligent supramolecular materials.

An efficient hexagonal image framework using pseudo hexagonal pixel for computer vision applications

Nature-inspired computing has been a real source of motivation for the development of many meta-heuristic algorithms. The biological optic system can be patterned as a cascade of sub-filters from the photoreceptors over the ganglion cells in the fovea to some simple cells in the visual cortex. This spark has inspired many researchers to examine the biological retina in order to learn more about information processing capabilities. The photoreceptor cones and rods in the human fovea resemble hexagon more than a rectangular structure. However, the hexagonal meshes provide higher packing density, consistent neighborhood connectivity, and better angular correction compared to the rectilinear square mesh. In this paper, a novel 2-D interpolation hexagonal lattice conversion algorithm has been proposed to develop an efficient hexagonal mesh framework for computer vision applications. The proposed algorithm comprises effective pseudo-hexagonal structures which guarantee to keep align with our human visual system. It provides the hexagonal simulated images to visually verify without using any hexagonal capture or display device. The simulation results manifest that the proposed algorithm achieves a higher Peak Signal-to-Noise Ratio of 98.45 and offers a high-resolution image with a lesser mean square error of 0.59.

Design and optimization of 3D-bioprinted scaffold framework based on a new natural polymeric bioink.

This aimed at the design and production of engineered 3D scaffold prototypes using a natural polymeric bioink made of chitosan and poly-γ-glutamic acid with a specific focus on 3D-bioprinting process and on 3D framework geometry. Prototypes were produced using a 3D bioprinter exploiting layer-by-layer deposition technology. The 3D scaffold prototypes were fully characterized concerning pore size and size distribution, stability in different experimental conditions, swelling capability, and human dermal fibroblasts viability. Hexagonal framework combined with biopaper allowed stabilizing the 3-layers structure during process manufacturing and during incubation in cell culture conditions. The stability of 3-layers structure was well preserved for 48 h. Crosslinking percentages of 2-layers and 3-layers prototype were 88.2 and 68.39, respectively. The swelling study showed a controlled swelling capability for 2-layers and 3-layers prototype, ∼5%. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay results showed good biocompatibility of 3-layers prototype and their suitability for preserving 48 h cell viability in 3D cultures. Moreover, a significant increment of absorbance value was measured after 48 h, demonstrating cell growth. Bioink obtained combining chitosan and poly-γ-glutamic acid represents a good option for 3D bioprinting. A stable 3D structure was realized by layer-by-layer deposition technology; compared with other papers, the present study succeeded in using medical healthcare-grade polymers, no-toxic crosslinker, and solvents according to ICH Topic Q3C (R4).

Versatile Post-Doping toward Two-Dimensional Semiconductors.

We have developed a simple and straightforward way to realize controlled postdoping toward 2D transition metal dichalcogenides (TMDs). The key idea is to use low-kinetic-energy dopant beams and a high-flux chalcogen beam simultaneously, leading to substitutional doping with controlled dopant densities. Atomic-resolution transmission electron microscopy has revealed that dopant atoms injected toward TMDs are incorporated substitutionally into the hexagonal framework of TMDs. The electronic properties of doped TMDs (Nb-doped WSe2) have shown drastic change and p-type action with more than 2 orders of magnitude increase in current. Position-selective doping has also been demonstrated by the postdoping toward TMDs with a patterned mask on the surface. The postdoping method developed in this work can be a versatile tool for 2D-based next-generation electronics in the future.

Reaction-diffusion model to describe biodiesel production using lipase encapsulated in ZIF-8

Lipase has successfully been encapsulated into hexagonal zeolitic imidazolate frameworks (ZIF-8) for use in biodiesel production. It was shown that the lipase encapsulation did not have a significant effect on the morphology, surface properties and crystallinity. The effects of methanol ratio, temperature, oil concentration and water content, on the biodiesel production yield and rate of reaction, were tested. The highest yield was obtained at a methanol ratio and temperature of 6:1 and 40 °C, respectively, and a drop was observed by increasing both. It was also shown that the yield decreased with the increase in water content. The activity and stability of the immobilized lipase in ZIF-8 by encapsulation was compared to that immobilized by surface adsorption. Although the adsorbed lipase on ZIF-8 showed higher activity, the stability of the encapsulated one was higher. At methanol ratio of 12:1, the encapsulated lipase in ZIF-8 maintained 83% residual activity after 5 cycles, compared to only 34% attained by the adsorbed lipase at the same conditions. The experimental results were used to determine the kinetics parameters of modified Ping Pong Bi Bi model, and the accuracy of the prediction were compared to those obtained by the Michaelis Menten model. To gain a better insight into how the reaction occurs inside the ZIF-8 crystal with encapsulated lipase, a diffusion–reaction model was developed and numerically solved. The results clearly show that the substrate did not diffuse deeply into the crystal, which further confirmed the mass transfer limitation that resulted in the lower activity of the encapsulated lipase as compared to the adsorbed one. The developed numerical model can be applied to any diffusion–reaction systems.

Hexagonal Mesoporous Silica for carbon capture: Unrevealing CO2 microscopic dynamics by Nuclear Magnetic Resonance

Global warming and environmental concerns have triggered global efforts to reduce anthropogenic carbon emission. Against this background, mesoporous silica materials have experienced a great expansion in the latest years due to their interesting carbon capture properties. Despite the very vast literature currently available in synthetic strategies and adsorption behaviour of MSs, the internal arrangement and diffusion properties of carbon dioxide (CO2) inside silica mesopores, to date, have been barely clarified. Here, mesoporous silica material with hexagonal framework (MCM-41) has been synthesized by a modified Stöber process, and its CO2 capture properties were assessed yielding a maximum amount of CO2 adsorbed of 18 wt% at 15 bar and RT. Fort the first time, microscopic distribution of CO2 and its mobility in the MCM-41 mesopores have been investigated by 13C NMR techniques. Peak fitting analysis of the 13C NMR spectra and T1-relaxometry data revealed a multiple component configuration for CO2 adsorbed in the silica mesopores with at least two physisorbed species coexisting. 13C PFG NMR self-diffusion study showed anisotropic long-range mobility for carbon dioxide adsorbed in MCM-41. The fastest self-diffusion coefficient, ascribed CO2 molecules diffusing parallel to the axis of the MCM-41 channels, was in the order of 10−5 cm2 s-1, i.e., two order of magnitude higher that of gas diffusing perpendicular to the mesopore. This study is crucial to properly address the future design and preparation of mesoporous silica materials with improved CO2 capture performances.

Hexagonal Grid-Based Framework for Mobile Robot Navigation

The paper addresses the problem of mobile robots’ navigation using a hexagonal lattice. We carried out experiments in which we used a vehicle equipped with a set of sensors. Based on the data, a traversable map was created. The experimental results proved that hexagonal maps of an environment can be easily built based on sensor readings. The path planning method has many advantages: the situation in which obstacles surround the position of the robot or the target is easily detected, and we can influence the properties of the path, e.g., the distance from obstacles or the type of surface can be taken into account. A path can be smoothed more easily than with a rectangular grid.

Exceptional electron conduction in two-dimensional covalent organic frameworks

<h2>Summary</h2> Most organic/polymeric semiconductors are <i>p</i>-type semiconductors, whereas their <i>n</i>-type versions are limited in both availability and carrier mobility. How to develop high-rate <i>n</i>-type organic/polymeric semiconductors remains challenging. Here, we report an approach to high-rate <i>n</i>-type semiconductors via topology-directed polycondensation of conventional <i>p</i>-type knots with <i>n</i>-type isoindigo linkers to form non-conjugated tetragonal and hexagonal two-dimensional polymeric frameworks. The polymers are planar in conformation and show flattened frontier levels, which enable electrons to move along the non-conjugated polymeric backbones. The eclipsed face-to-face stack reduces reorganization energy and greatly strengthens electronic coupling, thus enabling band-like electron conduction perpendicular to polymer layers. A device recording electron mobility as high as 8.2 cm² V⁻¹ s⁻¹ was achieved with Hall effect measurements, whereas time- and frequency-resolved terahertz spectroscopy revealed a benchmark mobility of 13.3 cm² V⁻¹ s⁻¹. These new mechanistic insights with exceptional mobility open the way to high-rate <i>n</i>-type organic/polymeric semiconductors.

Alkali Metallosilicates: Synthesis, Structure and Evaluation in the ROP of ϵ‐Caprolactone

AbstractA series of metallosilicate complexes (tBuO)2(RO)SiOM (R=tBu, iPr, Et, Me; M=Li, Na, K) were prepared from tailor‐made silanols. The complexes show different degree of association and feature heterocubane, double‐heterocubane or hexagonal prism framework in solid state while ESI‐MS shows fragmentation of the oligomers. The steric hindrance around the silicon atom has a direct influence over the association of the alkali derivatives, and the size of the alkali metal influences the shape of the MxOx core. These compounds were studied as initiators in the ROP of ϵ‐caprolactone, varying temperature, reaction‐time, monomer/initiator ratio, metal center variation and association degree. The best results were achieved with [{(tBuO)3SiO}4Li4] (1) producing an almost quantitive yield of polycaprolactone (97 %, Mn=35 kg mol−1, Mw/Mn=1.72).

Selective oxidation of propylene to acrolein over silver-promoted hexagonal molybdates and derivative Ag/Ag2Mo4O13/α-MoO3 composites

Hexagonal molybdates (h-MoO3) include abundant Mo vacancies that are charge-compensated by cations residing within one-dimensional channels. Hence, they present an intriguing structural motif for Mo catalysis which has been hardly explored for selective oxidation of olefins. We discovered that NH4+ and Ag+-exchanged h-MoO3 display surprisingly varied behavior during propylene oxidation. Acrolein and acrylonitrile are the main partial oxidation products with the latter forming due to NH4+ consumption. The catalytic activity more than doubles upon introduction of Ag+ which also enhances selectivity for the main products up to ∼60 %. Unexpectedly, the hexagonal frameworks transform into orthorhombic α-MoO3 40−60 °C below their reported stability limits already. In addition, Ag2Mo4O13 and Ag nanoparticles segregate in case of Ag+-containing h-MoO3 frameworks. The resulting Ag/Ag2Mo4O13/α-MoO3 composites catalyze propylene conversion into acrolein with even higher selectivity (∼80 %). Detailed analyses indicate that Ag2Mo4O13 drives formation of this oxygenate over these composites.