Direct Synthesis Approach Research Articles

A Quantitative Approach for Direct Synthesis of Bandpass Filters Composed of Transversal Resonators

This brief aims to propose a quantitative approach for direct synthesis of bandpass filters (BPFs) composed of a few transversal resonators. In conventional synthesis of these BPFs, coupling coefficients between input/output port and resonators are converted to external quality factor ( Qe ), ignoring inherent characteristics of resonators, such as impedance or reactance/susceptance slopes. As a result, the physical dimensions of resonators could only be determined qualitatively. In this brief, a transversal lowpass prototype derived from coupling matrix is transformed into a bandpass circuit at first, then the coupling coefficients between input/output port and resonators in these BPFs are quantitatively derived as an accurate relationship between ${J}$ inverter and susceptance slope of resonators instead. Hence, the physical dimensions of an entire BPF could be directly synthesized by solving the values of ${J}$ inverters and susceptance slope in addition to the resonant frequency of resonators. In order to verify the theory, a proof-of-concept example using cross-shaped resonator is designed and fabricated. The measured results are found in good agreement between the synthesized and simulated ones.

Catalytic Performance of NiMoS Supported on (Zr)SBA-15 for Hydrodesulfurization of Diesel: Insight into a One-Step Calcination and Reduction Strategy during Sulfidation

We report, herein, the catalytic efficiency and activity of a facilely synthesized sulfided NiMo hydrodesulfurization (HDS) catalyst supported on (Zr)-SBA-15 by one-step calcination and reduction heat treatment prior to sulfidation. Zr-SBA-15-Mo is prepared by a direct synthesis approach, followed by the confinement of Ni into the as-synthesized Zr-SBA-15-Mo without calcination, to generate more dispersion and active sites of metal oxides for an efficient sulfidation process. The HDS performance of these catalysts was evaluated and compared to that of the catalysts prepared by the sequential calcination and reduction approach prior to sulfidation for HDS of dibenzothiophene (DBT) and dimethyldibenzothiophene (DMDBT) in commercial diesel at 350 °C in batch reactor mode. Structural and morphological properties related to catalytic activity have been obtained by means of spectroscopy (X-ray diffraction (XRD), Raman, pyridine-Fourier transform infrared (FTIR), temperature-programmed desorption (TPD), microsco...

Advanced Direct Synthesis Approach for High Selectivity In-Line Topology Filters Comprising $N$ - 1 Adjacent Frequency-Variant Couplings

In this paper, a direct synthesis approach is presented to realize high selectivity in-line topology filters with adjacent frequency-variant couplings (FVCs). By considering the annihilation of frequency-variant elements during admittance matrix transformation for the first time, this paper provides a deterministic mechanism (no optimization is involved) that can generate FVCs between every two cascaded resonators. In consequence, a high selectivity filtering response where N-1 transmission zeros are implemented and independently controllable can be achieved for an Nth-order in-line network. As the foundation, a novel matrix process is detailed to obtain two adjacent FVCs inside of a 4th-order in-line network. The Nth-order prototype is then realized based on the process in an iterative manner. A synthesis example is illustrated in terms of the proposed approach step by step to show validity. Eventually, a 6th-order in-line band-pass filter, which contains adjacent FVCs in two pairs has been designed and fabricated via coaxial cavity structures. The synthesis results, EM simulation results, and tested results are well matched with each other, which reveals the effectiveness of the presented method during physical implementation.

A Scalings Approach to H2-Gain-Scheduling Synthesis without Elimination

We present a direct synthesis approach to H2-gain-scheduling for time-varying parametric scheduling blocks with D- and positive real scalings based on a convexifying transformation for the controller parameters. In particular, finiteness of the H2-norm for the closed-loop system is achieved by solving a specific design problem with structured linear fractional representations of the plant and the controller. To enlarge the field of applications, we extend the framework to networks consisting of gain-scheduling systems with a delayed coupling.

Direct synthesis of tetrazine functionalities on polymer backbones

ABSTRACTTetrazine mediated inverse Electron Demand Diels–Alder Reaction (IEDDA) is an important modification technique due to its high selectivity and super‐fast kinetics. Incorporation of tetrazine moieties on polymer chains requires multistep synthetic pathways and a post‐polymerization step leading to functional polymeric materials. Such approaches involve separate syntheses of polymer and the molecule which will be employed in modification. Herein, we introduce a straightforward synthetic approach for direct synthesis of tetrazine groups on polymers as side chains. As model systems, tetrazine functional poly(N‐isopropylacrylamide)‐and poly(ethylene glycol)‐based polymers from corresponding precursor polymers with nitrile moieties as pendant groups are prepared and IEDDA Click Reaction is achieved with trans‐cyclooctene derivatives. The click reaction is monitored by both NMR and UV–vis spectroscopies. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 673–680

Rhodium‐Catalyzed Cascade Annulation Reaction via C−H Activation of Azobenzenes with Terminal Alkynes: A Synthesis of Indolo[1,2‐b]cinnolines

AbstractThe approach for direct synthesis of Indolo[1,2‐b]cinnolines was first developed from azobenzenes and terminal alkynes by rhodium‐catalyzed cascade annulation reaction. In this reaction, the C−C and C−N bonds can be simultaneously constructed via C−H activation to afford the desired products in moderate to good yields.magnified image

Direct synthesis of compact wideband differential bandpass filter on composite triple-mode resonator

In this paper, a direct synthesis approach is proposed for design of a compact wideband differential-mode (DM) bandpass filter (BPF) on a composite triple-mode resonator. By virtue of intrinsic common-mode (CM) suppression in slotline portion, only the DM transmission performances need to be focused on in our design, so as to facilitate the design process. Consequently, a synthesis approach based on an equivalent simplified network is established to design this DM BPF, resulting to directly determine all the circuit element values. A wideband DM BPF is then designed to validate effectiveness of proposed synthesis method. Finally, two circuit prototypes have been designed, fabricated, and measured. The synthesized, simulated and measured results agree well with each other over a wide operating band, which has demonstrated the proposed DM BPFs' attractive performances, such as wide bandwidth of operation, sharpened frequency selectivity, and good CM suppression.

A Multifunctional Dual-Luminescent Polyoxometalate@Metal-Organic Framework EuW10@UiO-67 Composite as Chemical Probe and Temperature Sensor.

The luminescent [EuW10O36]9− polyoxometalate has been introduced into the cavities of the highly porous zirconium luminescent metal-organic framework UiO-67 via a direct synthesis approach, affording the EuW10@UiO-67 hybrid. Using a combination of techniques (TGA, BET, elemental analysis, EDX mapping,…) this new material has been fully characterized, evidencing that it contains only 0.25% in europium and that the polyoxometalate units are located inside the octahedral cavities and not at the surface of the UiO-67 crystallites. Despite the low amount of europium, it is shown that EuW10@UiO-67 acts as a solid-state luminescent sensor for the detection of amino-acids, the growth of the emission intensity globally following the growth of the amino-acid pKa. In addition, EuW10@UiO-67 acts as a sensor for the detection of metallic cations, with a high sensitivity for Fe3+. Noticeably, the recyclability of the reported material has been established. Finally, it is shown that the dual-luminescent EuW10@UiO-67 material behave as a self-calibrated-ratiometric thermometer in the physiological range.

Ligand Structure Determines Nanoparticles' Atomic Structure, Metal-Ligand Interface and Properties.

The nature of the ligands dictates the composition, molecular formulae, atomic structure and the physical properties of thiolate protected gold nanomolecules, Aun(SR)m. In this review, we describe the ligand effect for three classes of thiols namely, aliphatic, AL or aliphatic-like, aromatic, AR, or bulky, BU thiol ligands. The ligand effect is demonstrated using three experimental setups namely: (1) The nanomolecule series obtained by direct synthesis using AL, AR, and BU ligands; (2) Molecular conversion and interconversion between Au38(S-AL)24, Au36(S-AR)24, and Au30(S-BU)18 nanomolecules; and (3) Synthesis of Au38, Au36, and Au30 nanomolecules from one precursor Aun(S-glutathione)m upon reacting with AL, AR, and BU ligands. These nanomolecules possess unique geometric core structure, metal-ligand staple interface, optical and electrochemical properties. The results unequivocally demonstrate that the ligand structure determines the nanomolecules' atomic structure, metal-ligand interface and properties. The direct synthesis approach reveals that AL, AR, and BU ligands form nanomolecules with unique atomic structure and composition. Similarly, the nature of the ligand plays a pivotal role and has a significant impact on the passivated systems such as metal nanoparticles, quantum dots, magnetic nanoparticles and self-assembled monolayers (SAMs). Computational analysis demonstrates and predicts the thermodynamic stability of gold nanomolecules and the importance of ligand-ligand interactions that clearly stands out as a determining factor, especially for species with AL ligands such as Au38(S-AL)24.

Anisotropic 2D Cu2-x Se Nanocrystals from Dodecaneselenol and Their Conversion to CdSe and CuInSe2 Nanoparticles.

We present the synthesis of colloidal anisotropic Cu2–xSe nanocrystals (NCs) with excellent size and shape control, using the unexplored phosphine-free selenium precursor 1-dodecaneselenol (DDSe). This precursor forms lamellar complexes with Cu(I) that enable tailoring the NC morphology from 0D polyhedral to highly anisotropic 2D shapes. The Cu2–xSe NCs are subsequently used as templates in postsynthetic cation exchange reactions, through which they are successfully converted to CdSe and CuInSe2 quantum dots, nanoplatelets, and ultrathin nanosheets. The shape of the template hexagonal nanoplatelets is preserved during the cation exchange reaction, despite a substantial reorganization of the anionic sublattice, which leads to conversion of the tetragonal umangite crystal structure of the parent Cu2–xSe NCs into hexagonal wurtzite CdSe and CuInSe2, accompanied by a change of both the thickness and the lateral dimensions of the nanoplatelets. The crystallographic transformation and reconstruction of the product NCs are attributed to a combination of the unit cell dimensionalities of the parent and product crystal phases and an internal ripening process. This work provides novel tools for the rational design of shape-controlled colloidal anisotropic Cu2–xSe NCs, which, besides their promising optoelectronic properties, also constitute a new family of cation exchange templates for the synthesis of shape-controlled NCs of wurtzite CdSe, CuInSe2, and other metal selenides that cannot be attained through direct synthesis approaches. Moreover, the insights provided here are likely applicable also to the direct synthesis of shape-controlled NCs of other metal selenides, since DDSe may be able to form lamellar complexes with several other metals.

The remarkable activity of template‐containing Mg/MCM‐41 and Ni/MCM‐41 in CO2 sequestration

AbstractMagnesium and nickel incorporated MCM‐41 were prepared by two approaches: direct synthesis (DS) and wet impregnation (WI). The ionic template was removed by calcination. In some experiments, the ionic template was removed by calcination process and in the others it was preserved to investigate the template effect. For comparison, MgO and NiO nanoparticles were also synthesized. The catalysts were characterized by XRD, EDX‐SEM, and FT‐IR. The catalysts obtained were evaluated for hydration of CO2 and its precipitation as CaCO3 at room temperature. The results showed that template‐containing Mg/MCM‐41 and Ni/MCM‐41 prepared by the DS approach have high CO2 hydration activity. This high activity is due to the presence of strong basic sites. Nano MgO and NiO also exhibited a high yield of CaCO3. It was also found that template‐containing MCM‐41 can be recovered easily from the reaction mixture and reused without deactivation. © 2017 Society of Chemical Industry and John Wiley & Sons, Ltd.

A Direct Approach for Coupling Matrix Synthesis for Coupled Resonator Diplexers

Diplexers are used to separate or combine two bands of frequencies and they are designed by combining channel filters using distribution circuit or alternatively designed based on coupled resonator circuits. Design parameters of coupled resonator circuits such as coupling coefficients, self-resonant frequencies and external couplings are done using optimization techniques. However, optimization techniques are not always efficient particularly for large set of parameters and hence more efficient approaches are required. In this paper, numerical solution instead of optimization is proposed to synthesize coupled resonator diplexers and obtain coupling coefficients directly from equations. The proposed direct approach achieves the desired characteristics for any given number of resonators and some numerical examples are given to demonstrate the validity of the proposed approach. One of the given examples is compared to a diplexer in literature synthesized using optimization technique and implemented using cavity resonators.

Tailoring band gap and thermal diffusivity of nanostructured phase-pure ZnAl2O4 by direct spark plasma sintering synthesis

A rapid, one-step synthesis of pristine ZnAl2O4 by spark plasma sintering has been developed in this work. Using inexpensive reagents (ZnO and Al2O3) and the direct synthesis approach, a total synthesis time of five minutes was achieved. Varying the sintering parameters allows for tailoring of the density, crystallite size, and band gap. An extensive parameter study was performed to understand the formation of impurities at different conditions, and also to investigate the effect of using either γ– or α-Al2O3 as the aluminum source. The experimental results reveal that a heating ramp of 200°C/min up to 1000°C, and immediate cooling thereafter, produces pristine ZnAl2O4. The thermal diffusivity and band gap were found to be dependent on the synthesis conditions employed. The synthesis approach in this work provides a protocol for controlled preparation of bulk ZnAl2O4 with tunable properties.

Decoding Nucleation and Growth of Zeolitic Imidazolate Framework Thin Films with Atomic Force Microscopy and Vibrational Spectroscopy.

The synthesis of metal‐organic framework (MOF) thin films has garnered significant attention during the past decade. By better understanding the parameters governing the nucleation and growth of such thin films, their properties can be rationally tuned, empowering their application as (reactive) membranes. Here, a combined AFM‐vibrational spectroscopy research strategy is employed to detail the chemistries governing the nucleation and growth of zeolitic imidazolate framework (ZIF) thin films, in particular isostructural Co‐ZIF‐67 and Zn‐ZIF‐8. First, a single step direct synthesis approach is used to investigate the influence of different synthesis parameters –metal/linker ratio, temperature, and metal type– on the thin film nucleation and growth behaviour. While the metal/linker ratio has a pronounced effect on the thin film nucleation rate, the temperature mainly influences the growth kinetics of nuclei forming the thin film. In addition, the nucleation and growth of ZIF thin films is shown to be highly dependent on the electronegativity of the metal type. Thin‐film thickness control can be achieved by using a multistep synthesis strategy, implying repetitive applications of single step deposition under identical synthesis conditions, for which a growth mechanism is proposed. This study provides insight into the influence of synthesis parameters on the ZIF thin film properties, using tools at hand to rationally tune MOF thin film properties.

Solvothermal synthesis, nanostructural characterization and gas cryo-adsorption studies in a metal–organic framework (IRMOF-1) material

A nanoporous metal–organic framework material, exhibiting an IRMOF-1 type crystalline structure, was prepared by following a direct solvothermal synthesis approach, using zinc nitrate and terephthalic acid as precursors and dimethylformamide as solvent, combined with supercritical CO2 activation and vacuum outgassing procedures. A series of advanced characterization methods were employed, including scanning electron microscopy, Fourier-transform infrared radiation spectroscopy and X-ray diffraction, in order to study the morphology, surface chemistry and structure of the IRMOF-1 material directly upon its synthesis. Porosity properties, such as Brunauer–Emmet–Teller (BET) specific area (∼520 m2/g) and micropore volume (∼0.2 cm3/g), were calculated for the activated sample based on N2 gas sorption data collected at 77 K. The H2 storage performance was preliminary assessed by low-pressure (0–1 bar) H2 gas adsorption and desorption measurements at 77 K. The activated IRMOF-1 material of this study demonstrated a fully reversible H2 sorption behavior combined with an adequate gravimetric H2 uptake relative to its BET specific area, thus achieving a value of ∼1 wt.% under close-to-atmospheric pressure conditions.

Direct synthesis of thickness-tunable MoS2 quantum dot thin layers: Optical, structural and electrical properties and their application to hydrogen evolution

We report a layer thickness-tunable direct synthesis growth method for bi- to few-layer crystalline molybdenum disulfide (MoS2) thin layers. For the first time, a facile, cost effective, and mass-scalable direct synthesis approach, based on a chemical bath deposition, is designed for quantum dot(QD)-based MoS2 layers using (NH4)6Mo7O24 and thiourea (CH4N2S) as precursors. Using this process, the uniformity of large area thin layer can be retained, and the applicability to various substrates can provide great opportunities in the fabrication of various atomically thin layered structures. The structural and optical properties of the MoS2 QD layers are systematically investigated. Raman, AFM and TEM analyses confirm the formation of continuous and crystalline bi-, tri- and few-layered MoS2. Their electrical properties are evaluated by bottom-gate FETs, and a field-effect mobility value of ~1.06cm2V−1s−1 and a current on/off ratio in the order of ~ 105 are obtained. Particularly, MoS2 prepared as a thin film consisting QD structures of grains shows novel electrocatalytic property. MoS2 QDs on Au/Si are proven to be excellent electrocatalysts for hydrogen evolution reaction, featured by Tafel slope (94mVdecade−1), exchange current density (1.91×10-1mAcm−2) and long-term durability for 20h. Our approach opens new avenues for the design and synthesis of functional MoS2 layers for energy harvesting.

Controlled Synthesis of Composition Tunable Formamidinium Cesium Double Cation Lead Halide Perovskite Nanowires and Nanosheets with Improved Stability

Lead halide perovskites with well-defined morphology have attracted attention for their unique properties as a promising new class of semiconductor materials in photovoltaics and optoelectronics. However, controlling morphologies and compositions of perovskite nanostructures with improved stability, especially for double cation lead halide perovskite, still remains a challenge. Here, we demonstrate a colloidal synthetic approach for direct synthesis of stable single-crystal formamidinium (FA) cesium double cation lead halide FA0.33Cs0.67PbBr3–xIx (0 ≤ x ≤ 3) perovskite nanostructures with controllable morphology over a wide range of halide compositions, without using a previous anion-exchange process. The presence of FA alloyed in the A site for the pure cesium lead halide perovskite structure can stabilize the nanocrystals while delivering a better balance between structure and composition. On the basis of the FA0.33Cs0.67PbBr3–xIx alloy perovskite system, we achieved nanowires and nanosheets with high y...

Analytical design of modified Smith predictor for unstable second-order processes with time delay

ABSTRACTIn this paper, a modified Smith predictor using three controllers, namely, stabilising (Gc), set-point tracking (Gc1), and load disturbance rejection (Gc2) controllers is proposed for second-order unstable processes with time delay. Controllers of the proposed structure are tuned using direct synthesis approach as this method enables the user to achieve a trade-off between the performance and robustness by adjusting a single design parameter. Furthermore, suitable values of the tuning parameters are recommended after studying their effect on the closed-loop performance and robustness. This is the main advantage of the proposed work over other recently published manuscripts, where authors provide only suitable ranges for the tuning parameters in spite of giving their suitable values. Simulation studies show that the proposed method results in satisfactory performance and improved robustness as compared to the recently reported control schemes. It is observed that the proposed scheme is able to work in the noisy environment also.

Chirality-Controlled Synthesis and Applications of Single-Wall Carbon Nanotubes

Preparation of chirality-defined single-wall carbon nanotubes (SWCNTs) is the top challenge in the nanotube field. In recent years, great progress has been made toward preparing single-chirality SWCNTs through both direct controlled synthesis and postsynthesis separation approaches. Accordingly, the uses of single-chirality-dominated SWCNTs for various applications have emerged as a new front in nanotube research. In this Review, we review recent progress made in the chirality-controlled synthesis of SWCNTs, including metal-catalyst-free SWCNT cloning by vapor-phase epitaxy elongation of purified single-chirality nanotube seeds, chirality-specific growth of SWCNTs on bimetallic solid alloy catalysts, chirality-controlled synthesis of SWCNTs using bottom-up synthetic strategy from carbonaceous molecular end-cap precursors, etc. Recent major progresses in postsynthesis separation of single-chirality SWCNT species, as well as methods for chirality characterization of SWCNTs, are also highlighted. Moreover, we discuss some examples where single-chirality SWCNTs have shown clear advantages over SWCNTs with broad chirality distributions. We hope this review could inspire more research on the chirality-controlled preparation of SWCNTs and equally important inspire the use of single-chirality SWCNT samples for more fundamental studies and practical applications.

Synthesis design of a wideband impedance transformer consisting of two‐section coupled lines

An impedance transformer employing two-section coupled lines is presented in this study, which can achieve a wide operating band or passband with three reflection zeros. A direct synthesis approach is proposed and applied to the design of this transformer with the prescribed Chebyshev-function frequency response. If the impedance–transformation ratio, passband return loss (RL), and operating bandwidth are properly specified, all the required design parameters of this transformer can be explicitly gained. Furthermore, a special region for realisable impedance–transformation ratio and operating bandwidth with respect to the passband equal-ripple RL is extensively investigated. As such, various sets of design curves are numerically derived and graphically demonstrated for synthesis design of authors’ proposed impedance transformer. As an example, a 50–25 Ω impedance transformer with the 50% fractional bandwidth and 20 dB passband RL is designed, fabricated, and measured to confirm the theoretical predictions in the experiment.