Synthesis Window Research Articles

Ultrafast and Reproducible Synthesis of Tailor-Made Octacalcium Phosphate.

Octacalcium phosphate (OCP) has excellent bone formation ability and a good resorption rate as compared to the commercial bone substitutes [e.g., Bio-Oss (Geistlich Pharma AG) and MBCP+ (Biomatlante)], as well as synthesized biomaterials (hydroxyapatite and tricalcium phosphate). The synthesis approach to obtain phase-pure OCP possesses a great challenge due to its complex reaction mechanism and narrow synthesis window. Thus, the current study aimed to overcome the synthesis challenges and to define the precise reaction conditions required for controllable and reproducible synthesis of OCP. Using the principles of the coprecipitation method, novel synthesis protocols were developed ensuring ultrafast synthesis of OCP within minutes. XRD analysis confirmed that phase-pure OCP was obtained. These processing schemes enabled the synthesis of tailor-made OCP with specific surface areas ranging from 16 to 91 m2/g. The synthesized OCPs exhibited plate-like morphology. The interaction of the synthesized OCPs with MC3T3-E1 cells was found to be nontoxic, confirming their cytocompatibility. The synthesis approach developed in this study indicates that challenges such as the reaction volume, stirring rate, and flow rate need to be addressed in the future to upscale the technology.

Fast Synthesis of CHA-type Zeolite Using Dealuminated Amorphous Aluminosilicates with High Reactivity

Abstract Use of dealuminated amorphous aluminosilicates (deAl-Amor) achieved faster synthesis of CHA-type zeolites compared with using conventional amorphous aluminosilicates (Amor). The deAl-Amor also expanded the synthesis window of reactant compositions. Moreover, there was a large difference in morphologies of solid products obtained during the crystallization process between deAl-Amor and Amor, suggesting the time gap in supplying aluminosilicate species contributing to the CHA crystal growth. These results indicate the high potential of deAl-Amor as starting materials for zeolite synthesis.

Machine-Learning-Assisted Optimization of a Single-Atom Coordination Environment for Accelerated Fenton Catalysis.

Machine learning (ML) algorithms will be enablers in revolutionizing traditional methods of materials optimization. Here, we broaden the use of ML to assist the construction of Fenton-like single-atom catalysts (SACs) by developing a methodology including model building, training, and prediction. Our approach can efficiently extract synthesis parameters that exert a substantial influence on Fenton activity and accurately predict the phenol degradation rate k of SACs with a mean error of ±0.018 min-1. The extended synthesis window with accelerated learning enables the realization that the heating temperatures during SAC synthesis significantly influence the Fe-N coordination number, which ultimately dictates their performance. Through ML-guided optimization, a highly efficient SAC dominated by Fe-N5 sites with exceptional Fenton activity (k = 0.158 min-1) is identified. Our work provides an example for ML-assisted optimization of single-atom coordination environments and illuminates the feasibility of ML in accelerating the development of high-performance catalysts.

Epitaxial growth, magnetoresistance, and electronic band structure of GdSb magnetic semimetal films

Motivated by observations of extreme magnetoresistance (XMR) in bulk crystals of rare-earth monopnictide (RE-V) compounds and emerging applications in novel spintronic and plasmonic devices based on thin-film semimetals, we have investigated the electronic band structure and transport behavior of epitaxial GdSb thin films grown on III-V semiconductor surfaces. The ${\mathrm{Gd}}^{3+}$ ion in GdSb has a high spin $S=7/2$ and no orbital angular momentum, serving as a model system for studying the effects of antiferromagnetic order and strong exchange coupling on the resulting Fermi surface and magnetotransport properties of RE-Vs. We present a surface and structural characterization study mapping the optimal synthesis window of thin epitaxial GdSb films grown on III-V lattice-matched buffer layers via molecular-beam epitaxy. To determine the factors limiting XMR in RE-V thin films and provide a benchmark for band-structure predictions of topological phases of RE-Vs, the electronic band structure of GdSb thin films is studied, comparing carrier densities extracted from magnetotransport, angle-resolved photoemission spectroscopy (ARPES), and density-functional theory (DFT) calculations. ARPES shows a hole-carrier rich, topologically trivial, semimetallic band structure close to complete electron-hole compensation, with quantum confinement effects in the thin films observed through the presence of quantum-well states. DFT-predicted Fermi wave vectors are in excellent agreement with values obtained from quantum oscillations observed in magnetic field-dependent resistivity measurements. An electron-rich Hall coefficient is measured despite the higher hole-carrier density, attributed to the higher electron Hall mobility. The carrier mobilities are limited by surface and interface scattering, resulting in lower magnetoresistance than that measured for bulk crystals.

Konjac glucomannan reduced-stabilized silver nanoparticles for mono-azo and di-azo contained wastewater treatment

Silver nanoparticles (AgNPs) possess fascinating catalytic, optical, and electrical properties, but their broader application is hindered by their instability and agglomeration tendency. This report presents eco-friendly green synthesis using Konjac glucomannan (KGM) for the synthesis of AgNPs. Here, KGM functions as both reducing and stabilizing agent for AgNPs colloid without the assistance of any toxic reagents. To achieve an optimum synthesis window, reaction parameters such as precursor concentration, media pH, reduction time, and temperature were explored by the factorial design of experiments (FDE). AgNPs synthesized at optimum conditions revealed that the particles are primarily in spherical shapes, smaller in size (14.25 ± 3.42 nm) with a narrow distribution, highly crystalline (d-spacing = 0.258–0.236 nm), well stabilized (zeta potential = −13.1 mV), and coated by thin KGM-carbohydrate layer. The synthesized AgNPs reveal excellent catalytic performance in the degradation of mono-azo (acid orange 74) and di-azo (naphthol blue-black) dyes. The insights on the reaction kinetics revealed in this study could be extended to the practical application for wastewater treatment.

High-quality synthesis of a nanosized CHA zeolite by a combination of a starting FAU zeolite and aluminum sources.

A chabazite (CHA zeolite) was synthesized using high-silica faujasite (FAU) zeolites with a Si/Al ratio of 93, an additional alumina source (aluminum hydroxide) combined with seed crystals, and N,N,N-trimethyl-1-adamantammonium hydroxide. We compared the crystallization behavior of the starting material (HSY + Al) with that of other combinations of silica/alumina sources (high-silica and low-silica FAU, fumed silica, and aluminum hydroxide). HSY + Al rapidly yielded nanosized CHA zeolites with a crystal size of approximately 70 nm, exhibited high product crystallinity and high yield and offered a wide synthesis window. A combination of analytic experiments using electrospray-ionization mass spectrometry and nuclear magnetic resonance (NMR) suggested that in the early stage, the pre-introduced CHA seeds provide a crystal nucleus and the FAU zeolites decompose to form oligomer species in the liquid phase. Meanwhile, aluminum hydroxide retains its solid phase. Subsequent crystallization of the zeolites is accelerated by the liquid silicate oligomer and solid aluminate sources, resulting in a high yield and rapid synthesis of nanosized CHA zeolites. We observed that phosphorus-modified CHA zeolites synthesized using HSY + Al perform well as a catalyst for ethanol conversion reactions. Controlled Si/Al ratios and additional phosphorus modifications improve catalytic durability, thereby exhibiting a higher propylene yield from the reaction within the zeolite pore system.

The critical role of the forest morphology for dry drawability of few-walled carbon nanotubes

Carbon nanotube (CNT) yarns comprise few-walled CNTs (FWCNTs), mainly consisting of double- and triple-walled CNTs, and have several properties which are beneficial for practical bulk-scale carbon devices. These features include high tensile strength, electrical conductivity, thermal conductivity, chemical stability, and environmental tolerance. However, the synthesis window for fabricating CNT yarns with FWCNTs by the dry-spinning method is quite narrow and optimal conditions have yet to be determined. In this study, we fabricated CNT forests mainly comprised of FWCNTs at various synthesis conditions (temperature and time). The drawability of the CNT forests was characterized depending on the synthesis conditions. Our results show that optimum values exist for continuously drawable CNT forests in terms of both their height (>130 μm) and bulk density (>90 mg/cm3) for satisfying enough entanglement force between the CNT bundles. The diameter and number of walls of the CNTs are controlled by the temperature during the formation of catalyst particles because the sizes of catalyst particles are approximately equal to the outer diameter of CNTs. All temperature conditions in the range 350–500 °C, used to form catalyst particles, resulted in a drawable FWCNT forest. These insights will be useful for developing devices based on FWCNT yarns.

Accelerated Development of Perovskite-Inspired Materials via High-Throughput Synthesis and Machine-Learning Diagnosis

Accelerating the experimental cycle for new materials development is vital for addressing the grand energy challenges of the 21st century. We fabricate and characterize 75 unique halide perovskite-inspired solution-based thin-film materials within a two-month period, with 87% exhibiting band gaps between 1.2 eV and 2.4 eV that are of interest for energy-harvesting applications. This increased throughput is enabled by streamlining experimental workflows, developing a set of precursors amenable to high-throughput synthesis, and developing machine-learning assisted diagnosis. We utilize a deep neural network to classify compounds based on experimental X-ray diffraction data into 0D, 2D, and 3D structures more than 10 times faster than human analysis and with 90% accuracy. We validate our methods using lead-halide perovskites and extend the application to novel lead-free compositions. The wider synthesis window and faster cycle of learning enables three noteworthy scientific findings: (1) we realize four inorganic layered perovskites, A3B2Br9 (A = Cs, Rb; B = Bi, Sb) in thin-film form via one-step liquid deposition; (2) we report a multi-site lead-free alloy series that was not previously described in literature, Cs3(Bi1-xSbx)2(I1-xBrx)9; and (3) we reveal the effect on bandgap (reduction to <2 eV) and structure upon simultaneous alloying on the B-site and X-site of Cs3Bi2I9 with Sb and Br. This study demonstrates that combining an accelerated experimental cycle of learning and machine-learning based diagnosis represents an important step toward realizing fully-automated laboratories for materials discovery and development.

Epitaxial stabilization of Sr3Ir2O7 thin films

Ruddlesden-Popper type Srn+1IrnO3n+1 compounds are a major focus of condensed matter physics, where the subtle balance between electron-electron correlation, spin–orbit interaction, and crystal field effect brings a host of emergent phenomena. While it is understandable that a canted antiferromagnetic insulating state with an easy-plane anisotropy is developed in Sr2IrO4 as the two-dimensional limit of the series, it is intriguing that bilayer Sr3Ir2O7, with slightly higher effective dimensionality, stabilizes c-axis collinear antiferromagnetism. This also renders Sr3Ir2O7 a unique playground to study exotic physics near a critical spin transition point. However, the epitaxial growth of Sr3Ir2O7 is still a challenging task because of the narrow growth window. In our research, we have studied the thermodynamic process during the synthesis of Sr3Ir2O7 thin films. We expanded the synthesis window by mapping out the relationship between the thin film crystal structure and the gas pressure. Our work thus provides a more accessible avenue to stabilize metastable materials.

Synthesis of novel aluminosilicate YNU-5 and enhancement of the framework thermal stability by post-synthesis treatment

Abstract An unconventional hydrothermal synthesis of high-silica zeolite starting from a highly concentrated silicate solution was examined. As a result, the novel zeolite YNU-5 (YFI), which contains a 12−12−8-ring pore system and isolated 8-ring straight channels, was synthesized using dimethyldipropylammonium, one of the simplest tetraalkylammonium compounds, as the organic structure-directing agent. Although several competing phases such as MCM-68 (MSE), ZSM-5 (MFI) and beta (*BEA) were observed during investigation, YNU-5 (YFI) was obtained as a pure phase within a narrow synthesis window. The dealumination behavior by post-synthesis treatment using nitric acid was investigated and the Si/Al molar ratios of YNU-5 were controlled in the range from 9 to >200 by tuning acid concentration and/or temperature. Thermal stability of the framework was enhanced under severer acid-treatment conditions, and the stabilized material exhibited better catalytic performance.

Influence of Dip-Coating Temperature Upon Film Thickness in Chemical Solution Deposition

Chemical solution deposition (CSD) is widely used to fabricate YBCO superconducting and oxide buffer layers for high-temperature coated conductors. Controlling film thickness is important in the CSD technology and can be conducted through several methods. This study proposes a new method of adjusting the temperature of dip-coating. A precursor solution was prepared for fabrication of a YBCO layer. The temperatures of the precursor solution and substrate were fixed at 0 °C, 10 °C, 20 °C, or 30 °C during dip-coating by using a water bath system. Film thickness was measured by scanning electron microscopy after pyrolysis. The average thickness of the pyrolyzed films decreased from 265 to 158 nm when the dip-coating temperature increased from 0 °C to 30 °C, therefore verifying the feasibility of the new method for thickness control. The nonuniformity of thickness distribution along the withdrawal direction was detected and discussed. The influence of temperature on solution viscosity and film thickness was analyzed based on the equation of thickness dependence in dip-coating. The proposed method for thickness control could contribute to increasing the synthesis window in thin-film fabrication through CSD.

Facile synthesis of Cd-substituted zeolitic-imidazolate framework Cd-ZIF-8 and mixed-metal CdZn-ZIF-8

Zeolitic-imidazole framework ZIF-8 has attracted tremendous interests for the high-resolution kinetic separation of propylene/propane mixture due to its effective aperture size in between the sizes of propylene and propane molecules. It is of great interest to fine-tune the effective aperture size of ZIF-8 either to improve its propylene/propane separation performances or to extend its use to the separation of other gas mixtures. It has been shown that substituting Zn with other metal nodes (e.g. Co) is a potential means to fine-tune the effective aperture size of ZIF-8. Here, we attempt to introduce another metal center, Cd, into ZIF-8 in a facile and scalable manner. Phase-pure Cd-ZIF-8 was successfully synthesized in methanol using a conventional solvothermal method, although it showed a narrow synthesis window. The presence of an organic base (triethylamine, TEA) was found critical not only for the facile synthesis of phase-pure Cd-ZIF-8 but also for the suppression of its phase transformation. A battery of characterizations including single-crystal X-ray structure solutions confirmed that the effective aperture size of Cd-ZIF-8 is the largest among its iso-structures (Zn-ZIF-8 and Co-ZIF-8). Finally, for the first time, mixed-metal CdZn-ZIF-8 crystals with various Cd/Zn ratios were solvothermally synthesized, demonstrating a further opportunity for varying the effective aperture sizes of ZIF-8 and its iso-structures.

Fast Approach for Analysis Windows Computation of Multiwindow Discrete Gabor Transform

By using the biorthogonal analysis approach, an effective algorithm based on factorization for solving the analysis/dual windows in multiwindow discrete Gabor transform (M-DGT) is presented for arbitrary given synthesis windows. The constraint condition matrix of the M-DGT between analysis/dual windows and synthesis windows is proved to be equivalent to a fixed number of independent orthogonal relationship matrixes of discrete Gabor transform (DGT), which can be quickly and efficiently solved by using sub-equation sets. The analysis and comparison of computational complexity of related algorithms have indicated that the proposed algorithm provided a faster computational approach for computing analysis/dual windows as compared with that of the existing algorithms, which can save amount of computation and memory.

Effective Approach to Calculate Analysis Window in Infinite Discrete Gabor Transform

The long-periodic/infinite discrete Gabor transform (DGT) is more effective than the periodic/finite one in many applications. In this paper, a fast and effective approach is presented to efficiently compute the Gabor analysis window for arbitrary given synthesis window in DGT of long-periodic/infinite sequences, in which the new orthogonality constraint between analysis window and synthesis window in DGT for long-periodic/infinite sequences is derived and proved to be equivalent to the completeness condition of the long-periodic/infinite DGT. By using the property of delta function, the original orthogonality can be expressed as a certain number of linear equation sets in both the critical sampling case and the oversampling case, which can be fast and efficiently calculated by fast discrete Fourier transform (FFT). The computational complexity of the proposed approach is analyzed and compared with that of the existing canonical algorithms. The numerical results indicate that the proposed approach is efficient and fast for computing Gabor analysis window in both the critical sampling case and the oversampling case in comparison to existing algorithms.

A Sparse Analysis Window for Discrete Gabor Transform

Here, we analyze sparse analysis windows for complex-valued and real-valued discrete Gabor transforms. A number of theories presented in this study indicate that the existence and uniqueness of a sparse analysis window for a given synthesis window depend to a great extent on the sparsity of the synthesis window. Specifically, the upper and lower bounds on the analysis window sparsity are obtained for synthesis windows of different sparsities and analyzed in detail. Particularly, if the sparsity of a given synthesis window with connected support is equal to the discrete Gabor transform time-shift parameter, the sparsest analysis window is unique. In addition, we propose an algorithm that searches for a sparse analysis window. Compared with existing algorithms, a sparse analysis window with fewer nonzero elements and/or smaller reconstruction errors can be obtained with the proposed algorithm. A sequence of experimental results reveals its superior effectiveness. In addition, a better Gabor representation with high concentration and time–frequency resolution is obtained with the sparse analysis window.

Reduction of Persistent Organic Pollutant Emissions during Incinerator Start-up by Using Crude Waste Cooking Oil as an Alternative Fuel

Illegal harvesting and recycling of waste cooking oil, also referred to as “gutter oil” in many countries, poses a great food safety threat. Thus, in this study the feasibility of using waste cooking oil as an auxiliary fuel in the furnace of laboratory waste incinerator was evaluated in terms of toxic pollutant emissions. Two fuel blends (W20D80 and W40D60) were blended from varying proportions of diesel fuel (D100), and waste cooking oil (W100) and their physio-chemical characteristics were subsequently determined and compared. Thermogravimetry analysis (TGA) and derivative thermogravimetry (DTG) of D100, W100, W20D80 and W40D60 showed that diesel fuel consist of more volatile short aliphatic hydrocarbons, while the waste cooking oil and its blends had more thermal stable unsaturated long chain molecules. After the de novo synthesis window of 200–400°C, 40% of waste cooking oil and 60% of diesel (W40D60) was injected at around 500–700°C, and reduced the toxicity concentrations of PCDD/Fs and PCBs by an average of 86% and 94%, respectively. This study demonstrated that, by using waste cooking oil as a fuel blend, not only can reduce the possibility of “gutter oil” being put in the food to damage the health of human beings, but also can be recycled as a kind of green fuel to reduce the emissions of persistent organic pollutants (POPs).

Using GIS-based digital raster analysis for improving harmonic models-derived geoidal heights

In this study, the GIS-based raster analysis principle was applied as a trial to enhance the local performance of geopotential models. Specifically, harmonic models-derived geoidal height raster layers, with respect to the WGS-84 reference ellipsoid, were investigated. As an illustrative case study, the Egyptian Territory was used as a test region. A set of geoidal height grids was synthesized from five geopotential harmonic models. The synthesis window was organized so as to avoid any subsequent edge effects during the analysis process. After importing such raster layers into a GIS-platform, an iterative series of linear high-frequency filters was applied. The progress of the spatial quality of the filtered layers, at independent GPS/Leveling points, was interactively monitored. Then, the optimal filtering radius and the relevant best attained spatial quality were picked out for each of the five raster data. The results revealed that the applied GIS-based sharpening algorithm works well, even for a satellite-only model. In general, large spatial quality enhancements were achieved. The maximal attained improvement was 21 and 29 %, in terms of standard deviation and range of differences, respectively, at the control points. So, it is recommended to try the GIS-based raster analysis scheme over other geographical windows. Also, linear and non-linear forms of high-frequency filters may be applied and tested, regarding the improvement of other types of synthesized gravitational signals.

Multiwindow Real-Valued Discrete Gabor Transform and Its Fast Algorithms

Based on the biorthogonal analysis approach, a multiwindow real-valued discrete Gabor transform (M-RDGT) for periodic sequences is presented to efficiently analyze the dynamic time-frequency content of a signal containing components with multiple and/or time-varying frequencies. The M-RDGT offers a computationally efficient implementation as well as a real-valued formulation of the multiwindow complex-valued discrete Gabor transform (M-CDGT). The completeness condition of the M-RDGT is proved to be equivalent to its biorthogonality constraint between analysis windows and synthesis windows. The M-RDGT can utilize the fast discrete Hartley transform algorithms for fast computation and has a simple relationship with the M-CDGT such that its coefficients can be directly computed from the M-RDGT coefficients. Therefore, the M-RDGT offers an efficient method to compute the M-CDGT. Since the analyzed sequence, analysis and synthesis windows in the existing M-CDGT must have an equal period, if the period of a sequence is very long, solving its windows requires a huge amount of computation and memory and could lead to numerical instability. To overcome this problem, a modified M-RDGT for long-periodic (or even infinite) sequences is presented and its corresponding biorthogonality constraint between analysis windows and synthesis windows is modified, in which the period of the analysis and synthesis windows is independent of the period of a analyzed sequence so that one can apply short windows to process any long-periodic (or even in finite) sequence. Finally, the multirate-based parallel implementation of the M-RDGT is presented, which has shown to be effective and fast for time-frequency analysis.

Finite real-valued discrete Gabor transform with multi-windows

To efficiently analyze the dynamic time-frequency contents of signals that contain a wide range of time and frequency components, a new real-valued discrete Gabor transform with multi-windows M-RDGT based on the bi-orthogonal analysis approach is presented in this paper, which permits a computationally faster implementation as an alternate formulation of the complex-valued discrete Gabor transform with multi-windows M-CDGT. The completeness condition of the M-RDGT is proved to be equivalent to its bi-orthogonality constraint between analysis windows and synthesis windows. The M-RDGT is defined by replacing the complex-valued Gabor basis functions of the M-CDGT with real-valued Gabor basis functions. The real-valued Gabor basis functions of the M-RDGT contain the Hartley's cas function which allows the M-RDGT to utilize the fast discrete Hartley transform algorithms for fast computation. In addition, the M-RDGT has a simple relationship with the M-CDGT such that the M-CDGT coefficients can be directly computed from the M-RDGT coefficients. Therefore, the M-RDGT also offers a faster and more efficient method to compute the M-CDGT.

Role of crystal growth modifiers in the synthesis of ZSM-12 zeolite

The effects of crystallization time, temperature and aging time on the synthesis of pure ZSM-12 in the presence of polyethylene glycol (PEG) and polyoxyethylene Brij-35 surfactant with fixed ratios of Si/Al (160) and Na/SiO2 (0.144) were systematically investigated. Larger synthesis window and high purity of ZSM-12 were expected. Pure phase of ZSM-12 was obtained when PEG was added to the synthesis mixture with PEG/Al2O3 ratio in the range of 0.4–2. Furthermore, the addition of both Brij-35 and PEG in the synthesis was found to play a significant role in controlling the crystallization rate. The Brij-35/Al2O3 ratio was varied from 0 to 4.9. Conventional ZSM-12 was typically synthesized at 145°C for 120h. Shorter crystallization time of 60h was achieved when PEG/Al2O3 ratio of 1.22 and a Brij-35/Al2O3 ratio of 1.61 was used in the synthesis.