Precursor Route Research Articles

Comparison of microwave absorption characteristics of Co-Zr substituted Ni-Zn ferrites and Mg-Zr substituted Ni-Zn ferrites in Ka band (26.5 – 40 GHz)

In the present work, microwave absorption characteristics of cobalt-zirconium (Co-Zr) doped and magnesium-zirconium (Mg-Zr) doped nickel zinc (Ni-Zn) ferrites in Ka band, have been compared. The samples with chemical composition, Ni0.6Zn0.4(CoZr)xFe2-2xO4 (x = 0.05, 0.10, 0.15, 0.20 and 0.25) and Ni0.6Zn0.4(MgZr)xFe2-2xO4 (x = 0.05, 0.10, 0.15 and 0.20) have been prepared by sol–gel citrate precursor route and then, sintered at 1000 °C. The absorption characterization has been done by using vector network analyser (VNA) for both the series. Enhancement of dielectric and magnetic properties is observed with the addition of Co-Zr & Mg-Zr in simple Ni-Zn spinel ferrites, which make these ferrites suitable to work as microwave absorber materials (MAMs) in high frequency shielding applications. The minimum values of reflection loss (RL) obtained in both the series have been compared and it has been found that Mg-Zr substituted Ni-Zn ferrites (with lowest RL equal to −53.19 dB) perform better in terms of absorption than their counterpart Co-Zr doped Ni-Zn ferrites (with lowest RL equal to –33.06 dB). The prepared compositions of both the series, can be effectively used as high-performance microwave absorbers.

Preparation of zeolite A by inorganic complex precursor route for efficient elimination of heavy metal cations from aqueous solutions

In the present study, zeolite A was synthesized via inorganic complex precursor as an efficient novel route by using tris(acetylacetonato)aluminum(III), [Al(C5H7O2)3], and tris(acetylacetonato)silicon(IV) chloride hydrochloride, [Si(C5H7O2)3]Cl.HCl. The physicochemical properties of the zeolite A were characterized by FT-IR, XRD, SEM/EDX, BJH, and BET techniques. The performance of the synthesized zeolite A was evaluated for the elimination of heavy metal cations (Co2+, Cu2+, Zn2+, Cr3+ and Pb2+) from aqueous solutions. The results revealed that removal efficiencies of the synthesized zeolite A toward all investigated heavy metal cations were obtained to be more than 95% and the maximum removal efficiency was observed for Pb2+. The influence of parameters such as pH, contact time and adsorbent amount was surveyed on the removal efficiency of Pb2+ by the zeolite A. The most desirable conditions for Pb2+ removal was attained at pH 6.5, the zeolite amount of 0.5 g, 400 mgL−1 initial concentration of Pb2+ and the contact time of 30 min. The adsorption process followed second- order kinetics model and the pseudo-second-order adsorption rate constant (k 2) was obtained to be 4.32 × 10−4 g mg−1min−1.

Microwave absorption analysis of Mg–Zr-substituted Ni–Zn spinel ferrites in the X-band

Due to the incessant increase in harmful electromagnetic pollution, microwave-absorbing materials (MAMs) are in great demand, and the present work is dedicated to meeting these requirements. Mg–Zr-doped Ni–Zn spinel ferrites Ni0.6Zn0.4(MgZr)xFe2-2xO4 (x = 0.05–0.20, Δx = 0.05) have been successfully synthesized by a sol-gel citrate precursor route. The synthesized ferrites have been structurally characterized by X-ray diffraction (XRD) analysis, and their morphological structure has been confirmed by scanning electron microscopy (SEM). The complex electromagnetic parameters, determined by employing a vector network analyzer (VNA), are found to be enhanced with the addition of Mg and Zr. High dielectric and magnetic losses are observed for all of the samples. Among the various samples prepared in the series of Mg–Zr-doped Ni–Zn spinel ferrites, reflection loss (RL) as low as −35.10 dB has been obtained at a matching frequency of 10.552 GHz for the composition with x = 0.10 at a matching thickness of 4 mm.

Construction of rGO-Encapsulated Co3 O4 -CoFe2 O4 Composites with a Double-Buffer Structure for High-Performance Lithium Storage.

Transition metal oxides (TMOs) are promising anode materials for next-generation lithium-ion batteries (LIBs). Nevertheless, their poor electronic and ionic conductivity as well as huge volume change leads to low capacity release and rapid capacity decay. Herein, a reduced graphene oxide (rGO)-encapsulated TMOs strategy is developed to address the above problems. The Co3 O4 -CoFe2 O4 @rGO composites with rGO sheets-encapsulated Co3 O4 -CoFe2 O4 microcubes are successfully constructed through a simple metal-organic frameworks precursor route, in which Co[Fe(CN)5 NO] microcubes are in situ coated by graphene oxide sheets, followed by a two-step calcination process. As anode material of LIBs, Co3 O4 -CoFe2 O4 @rGO exhibits remarkable reversible capacity (1393 mAh g-1 at 0.2 A g-1 after 300 cycles), outstanding long-term cycling stability (701 mAh g-1 at 2.0 A g-1 after 500 cycles), and excellent rate capability (420 mAh g-1 at 4.0 A g-1 ). The superior lithium storage performance can be attributed to the unique double-buffer structure, in which the outer flexible rGO shells can prevent the structure collapse of the electrode and improve its conductivity, while the hierarchical porous cores of Co3 O4 -CoFe2 O4 microcubes can buffer the volume expansion. This work provides a general and straightforward strategy for the construction of novel rGO-encapsulated bimetal oxides for energy storage and conversion application.

Unveiling the roles of Fe-Co interactions over ternary spinel-type ZnCoxFe2-xO4 catalysts for highly efficient CO2 hydrogenation to produce light olefins

Currently, the CO2 conversion to light olefins is attractive in clean energy research. Despite numerous works on Co-Fe bimetallic catalysts, the lack of well-defined bulk structures with identical crystalline phase and similar textural property hinders the in-depth understanding of the roles of Fe and Co species. Herein, series of uniform K-containing spinel-type ZnCoxFe2-xO4 nanoparticles (x = 0, 0.5, 1.0, 1.5, 2.0) were successfully synthesized via a single source layered double hydroxide precursor route. Compared to ZnFe2O4 and ZnCo2O4, as-fabricated ternary ZnCo0.5Fe1.5O4 spinel nanoparticles as the catalyst exhibited an outstanding performance toward CO2 hydrogenation to produce light olefins, with a 36.1% selectivity toward C2=-C4= products at a 49.6% conversion and an unprecedentedly high iron time yield for CO2 conversion to light olefins (∼29.1 μmolCO2·gFe−1·s−1) at the gaseous hourly space velocity of 24000 mL·gcat−1·h−1. In combination with structural characterizations and reaction results, it was unveiled that during the CO2 hydrogenation over ternary ZnCoxFe2-xO4 catalysts, the formation of electron-rich Fe0 atoms in the CoFe alloy phase significantly promoted in situ the generation of active iron-cobalt carbide, Co2C, and θ-Fe3C phases, thereby improving the reactivity of catalysts for the production of hydrocarbons and simultaneously inhibiting both the CO2 methanation and the secondary hydrogenation of olefins. The present findings provide a clear understanding of the roles of Fe-Co interactions over ternary ZnCoxFe2-xO4 catalysts for the highly efficient hydrogenation of CO2 to produce light olefins.

Preparation of Titanium-Aluminum-Carbon MAX Phase via a Simple Precursor Route for High-Temperature Coating Applications

Abstract MAX phase materials are gaining increased research interest because of the unique combination of metallic and ceramic properties. For high-temperature applications, titanium-aluminum-carbon (MAX) phases are extensively investigated. In order to utilize these MAX phase materials as coatings for high-temperature space applications, a pressureless preparation route employing a polymer-based precursor would be advantageous. A cost-effective, pressureless synthetic route using a carbonaceous polymer-based slurry was explored to obtain titanium-alumnium-carbon MAX phase. In continuation of our earlier report on the preliminary investigations on a precursor system, in the present study, an investigation on the effect of (i) heat treatment duration and (ii) nucleating filler on the formation of titanium-aluminum-carbon MAX phase from the precursor was carried out.

Dominating the structural, microstructural, and magnetic features of Li+-substituted strontium hexaferrite (Sr1−xLi2xFe12O19)

Lithium ion-substituted hexagonal strontium ferrite (Sr1−xLi2xFe12O19, where x = 0.1, 0.2, and 0.3) powders have been successfully fabricated using tartrate precursor route. The impact of Li+ content, as well as annealing temperature on the phase evolution, microstructure, and magnetic performance, was monitored by X-ray diffraction profile, scanning electron microscopy, and vibrating sample magnetometer. Single-phase hexagonal ferrite was attained at a Li+ ratio of 0.2 under a range of annealing temperatures, from 1000 to 1200 °C, for 2 h. An α-Fe2O3 impurity phase was observed at high Li+ ratios of 0.4 and 0.6 for all studied temperatures. The crystallo-aspect characteristics were altered with Li+ content and annealing temperature. The microstructure of pure hexagonal ferrite sample visualized platelet-like structure. A fine spherical with platelet shapes were displayed by increasing the Li+ ratios up to 0.4 and 0.6. Energy dispersive X-ray analysis emphasized that the Fe, Sr, O, and Li atoms spread between the plate and spherical shapes. A good saturation magnetization (Ms = 60.88 emu/g) was realized at 0.2 Li+ ratio as the result of increasing the thickness of the nanoplatelet structure.

TiNb2O7-Keratin derived carbon nanocomposites as novel anode materials for high-capacity lithium-ion batteries

TiNb2O7/carbon nanocomposites synthesized through a simple, surfactant assisted precursor route is reported as a promising alternative anode material for lithium-ion batteries (LIBs). The carbon component of the nanocomposites is derived from an inexpensive and sustainable keratin rich biological source. The reinforcement of carbon in TiNb2O7 facilitated the formation of non-stoichiometric (Ti0.712Nb0.288)O2 crystalline phase, in addition to the stoichiometric TiNb2O7 phase. It also yielded a high specific surface area (~90 ​m2 ​g−1) and reduced crystallite size (~4 ​nm). Electrochemical results exemplified high reversible capacity of 356 mAh g−1 at 0.1 ​C and remarkable rate capability of ~26 mAh g−1 at ultra-high current rate of 32C. TiNb2O7/carbon nanocomposites also demonstrated remarkable cyclic stability with large capacity retention of 85% even after 50 cycles at 1 ​C. The experimental data attests the potential of TiNb2O7/keratin derived carbon nanocomposites as economically and environmentally viable promising anode material for LIBs.

Preparation of high-temperature active zirconium boride powders via precursor route and microwave sintering

ABSTRACT ZrB2 powders were synthesised by microwave heating using the sol–gel method for precursor with eight C6H14O6 (ZrOCl2·8H2O), boric acid (H3BO3), citric acid (I), and mannitol (as raw materials). The results show that the temperature at which the ZrB2 powder is completely synthesised by microwave heating is 1400°C, which is 300°C lower than the traditional way. XRD and SEM were used to characterise the phase composition and morphology of the powders. In addition, the effects of raw material ratios and synthesis temperature on the synthesis of powder were investigated. The effect of temperature on the purity of the synthesised zirconium boride was considerable. The nearly spherical ZrB2 ultra-fine powders of high purity were synthesised successfully at 1400°C by microwave, with the ratios of C:Zr is 7.44:1, and B:Zr is 2.77:1.

Low-loss characteristics and sustained magneto-dielectric behaviour of cobalt ferrite nanoparticles over 1–6 GHz frequency range

Cobalt ferrite (CoFe2O4) nanoparticles were synthesized through the citrate precursor route. The XRD pattern confirmed the formation of a homogeneous single-phase spinel structure with an Fd3m space group. No impurities or unreacted constituents in the sample were observed. Analysis of the most prominent (311) peak of the XRD pattern revealed the crystallite size to be ~39 nm with lattice constant and interplanar spacing as ~8.374 Å and ~2.525 Å, respectively. Other key structural parameters, such as dislocation density, strain, X-ray density, and hopping lengths, were also obtained from XRD data. Structural parameters were refined by applying the full pattern fitting of the Rietveld method using the Pseudo-Voigt function. High-resolution images obtained from SEM and TEM confirmed the morphological characteristics and crystallite size of the CoFe2O4 nanoparticles. The hysteresis loop recorded over the applied external magnetizing field of −10 kOe to +10 kOe revealed a specific saturation magnetization, specific remanent magnetization, and coercivity value of ~64 emu/g, ~24 emu/g, and ~565 Oe, respectively. A remanence ratio ~0.374 signified magnetostatic interaction between CoFe2O4 nanoparticles and confirmed their multi-domain structure and soft magnetic nature. Investigations were carried out to obtain the variations in complex dielectric permittivity, complex magnetic permeability, dielectric and magnetic loss tangents, AC conductivity, and quality factor in 1–6 GHz frequency range. The CoFe2O4 nanoparticles exhibited low dielectric and magnetic loss tangents of 10−2 and 10−3 order, along with moderate values of relative permittivity and refractive index, i.e., 4.801 and 2.3, respectively. The sustained magneto-dielectric behaviour and low-loss characteristics suggest that CoFe2O4 nanoparticles can be suitably dispersed in a dielectric matrix and used to develop efficient substrate material for improved telemetry, telecommunications and radar systems of aerospace systems operating over the 1–6 GHz frequency range.

Molecular Precursor Route to CuCo2S4 Nanosheets: A High-Performance Pre-Catalyst for Oxygen Evolution and Its Application in Zn-Air Batteries.

Development of high-efficiency non-precious metal-based electrocatalysts to drive the complex four-electron process of the oxygen evolution reaction (OER) is crucial for production of hydrogen and energy storage components. Herein, bimetallic CuCo2S4 nanosheets were created by a new molecular precursor route. The optimal CuCo2S4 catalyst demonstrates superior performance to catalyze the OER with excellent stability, which was confirmed by the low overpotential of 290 mV at 10 mA cm-2 in 1 M KOH. The catalytic activity can be maintained for at least 40 h. The catalyst after the OER was then detected. The results indicate that S-doped CoOOH/CuO nanosheets formed on the catalyst surface during the OER may act as the catalytic active substance. Furthermore, when employed as an air cathode in a Zn-air battery, it reveals a high open-cycle potential of 1.38 V and a peak power density of 123.9 mW cm-2. The performance of the rechargeable Zn-air battery is close to that fabricated with commercial precious metal-based electrocatalysts. These findings would furnish some guidelines for the design, development, and applications of bimetallic sulfide electrocatalysts for the OER.

Enantiomeric 4′-truncated 6′-fluoro-3-deazaneplanocin and its 3-bromo derivative: Synthesis and antiviral properties, including Ebola and Marburg

In seeking to increase the library of fluorine containing adenine-derived carbocyclic nucleoside antiviral candidates, d-like and l-like 6′-fluoro-3-deazaneplanocin and its 3-bromo derivative lacking the 4′-hydroxylmethylene substituent (2/3 and 4/5, respectively) are presented. Their synthesis was accomplished from d-ribose by developing a more facile precursor route than suggested by the literature. The 2/4d-like pair displayed significant anti-filo virial properties while the enantiomeric l-like congeners 3/5 were inactive. Target compounds 2/4 also were active towards measles and norovirus. The effect of 2/4 is further evidence of the role fluoro-derived adenine carbocyclic nucleoside can play in antiviral drug discovery. Furthermore, the simplicity of their synthesis lends them to more efficacious analogs and to scale-up optimization. There were no other relevant antiviral properties for 2/3 and 4/5 (except BK polyomavirus for 3/5).

Enhanced thermal stability and red-ox activity of PrBaMn2-xFexO6–δ oxides

The design of new oxygen storage materials remains the key factor for intensive progress in technologies of air-free hydrocarbons combustion. The influence of the iron concentration on the oxygen storage characteristics of solid solutions PrBaMn2–xFexO6–δ is discussed. The complex oxides are synthesized via combined glycine-glycerol-nitrate precursor route. Dependence of unit cell parameters on iron content is estimated by X-ray powder diffraction at heating and an extended solid solution is shown to be formed up to x = 1.00. The temperature increase, as well as iron doping, is shown to be favorable factors for the crystallization of highly symmetric perovskites. Thermogravimetry with differential scanning calorimetry is used to demonstrate a phase stability of iron doped materials at elevated temperatures in air. Solid solutions exhibit large oxygen storage capacity and excellent reversibility of exchange under switching gas phase between air ↔ 5% H2 in Ar. With the increase of iron concentration, the kinetics of redox processes are shown to decline which caused by suppression in anisotropy of thermal expansion under doping.

A novel precursor route for Y2Mo4O15:Yb3+,Ho3+ phosphor and investigation of up-conversion luminescence

Hydrothermal reaction of Y(NO3)3·6H2O and (NH4)6Mo7O24·4H2O at 180 °C for 24 h was performed in this work via systematically varying the solution pH (4–10) and Mo/Y molar ratio (R, 2–5), which produced a NH4Y(MoO4)2·0.19H2O new compound that yielded phase-pure Y2Mo4O15 upon calcination at 500–700 °C. The pH/R window for the compound to crystallize was determined to be 6–7/3 and 6–9/4–5. The products were characterized in detail by XRD, FTIR, elemental analysis, SEM, TEM, STEM and TG to understand chemical composition and the courses of phase/morphology evolution. Applying the above synthesis strategy successfully produced Y2Mo4O15:xYb3+,yHo3+ phosphors that exhibit strong deep-red (630–670 nm, 5F5 → 5I8 transition) and weak green (530–560 nm, 5F4/5S2 → 5I8) emissions under 978 nm laser pumping, where the optimal Yb3+ and Ho3+ contents were determined to be x = 0.20 for y = 0.01 and y = 0.03 for x = 0.10, respectively. Spectral analysis indicated that the up-conversion luminescence occurred via a two-photon process, with the red/green intensity ratio and also the emission color dependent on Yb3+ and Ho3+ contents, which were explained by considering ground state excitation, energy transfer, non-radiative relaxation and cross relaxation.

Engineering hard carbon with high initial coulomb efficiency for practical sodium-ion batteries

Although hard carbons holds the most promise as anodes for practical sodium-ion batteries, high cost and low initial coulomb efficiency (ICE) limit their commercial application. In the present work, we develop an efficient solvothermal stabilization method to fabricate hard carbon spheres with high carbon yield from the wheat starch precursor. As anode for sodium-ion batteries, the obtained samples deliver not only a high capacity above 300 mAh g−1, but also an enhanced initial coulombic efficiency up to 90% and long cycle stability. Furthermore, when coupled with Na0.9[Cu0.22Fe0.30Mn0.48]O2 as cathode electrode, the full cell exhibited a high ICE of 85%, an average voltage of 3.2V and excellent stability during 300 cycles charging and discharging. These desirable electrochemical performances, combined with the renewable precursor and efficient synthesis route, make the obtained hard carbon sphere a promising anode for practical material for sodium-ion batteries.

Highly luminescent CdS nanoparticles synthesized using microwave irradiation of Dithiocarbazate ligand as a single molecular precursor source

In this paper, we have reported microwave-assisted synthesis of highly luminescent cadmium sulfide nanocrystals using dithiocarbazate Cd (II) chloride complex single-molecule precursor route. The precursors were heated using microwave irradiation to obtain CdS nanocrystals. The irradiation of precursor in DMSO environment played an important role in reducing reaction time, minimizing possibility of side reactions, and resulted in obtaining good quality particles. The obtained samples were analyzed using structural, morphological, and optical characterizations. X-ray diffraction studies confirm the hexagonal crystalline phase. High-resolution electron microscopy and transmission electron microscopy exhibit rod-shape structures with an average particle size of 80 nm. Sharp absorption edge at 320 nm indicates good quality of the particles. Strong luminescence peaks in the visible wavelength range 450–490 nm is observed in PL spectra. Another luminescence peak at 680 nm for excitation at 320 nm ensured the involvement of deep donor and acceptor levels in the crystals. The luminescence spectra show strong dependence on excitation wavelength which makes these particles suitable for various optoelectronic applications. The method reported here is a good candidate for obtaining large-scale high-quality CdS nanoparticles for optoelectronic applications.

Photoluminescence characteristics and white light generation in borohydride derived co-doped (Eu3+, Tb3+) YBO3 phosphors

The prime theme of this work is to explore the excitation wavelength dependent photoluminescence characteristics and white light generation in activators [europium (Eu) and terbium (Tb)] doped yttrium borate (YBO3) phosphors. In order to study the influence of excitation wavelength on photoluminescence emission intensity, a fixed amount (5 mol%) of Tb and different concentration of Eu (1, 2, 3, 5 and 7 mol%) were co-doped into yttrium borate (YBO3) host matrix via a solution precursor route using sodium borohydride as a precipitating agent. The ratio of Tb and Eu emission peaks suggests that it is possible to produce multi-color emissions including white light. The excitation dependence of emission comes from the combined contribution of host, activator and energy transfer between host to activator as well as among individual activators, which gives rise to change in output emission color. Moreover, the optimum composition i.e. 3 mol% Eu, 5 mol% Tb co-doped YBO3 was found to be appropriate for white light emitting phosphor.

A simplified model for the vapor – Solid distribution of Silicon Germanium Chemical Vapor Deposition

A simplified model of Silicon Germanium Chemical Vapor Deposition is proposed for the determination of Vapor – Solid distributions via any precursor route. The incorporation of the atomic element into the crystal lattice imposes to the chemical precursor the loss of all the ligands. Thus, dichlorosilane, silane, and disilane are discriminated on the basis of the amount of the atomic element brought into the equilibrium, instead of being different chemicals. Experimental trends show the ratio relative to silane is 2 for disilane and about ½ for dichlorosilane. The ratio relative to Si{100} is 0.59 for Si{110} and 0.82 for Si{111} for a growth via dichlorosilane and germane. Furthermore, Silicon Germanium alloy content is controlled by a thermodynamic equilibrium and the theoretical VS distribution is demonstrated for a growth via silane and germane. VS distribution of any chemistry onto any substrate orientation can therefore be estimated with the application of a straightforward corrective coefficient to a reference silane and germane chemistry.

Beyond p-Hexaphenylenes: Synthesis of Unsubstituted p-Nonaphenylene by a Precursor Protocol.

The synthesis of unsubstituted oligo‐para‐phenylenes (OPP) exceeding para‐hexaphenylene—in the literature often referred to as p‐sexiphenyl—has long remained elusive due to their insolubility. We report the first preparation of unsubstituted para‐nonaphenylenes (9PPs) by extending our precursor route to poly‐para‐phenylenes (PPP) to a discrete oligomer. Two geometric isomers of methoxylated syn‐ and anti‐cyclohexadienylenes were synthesized, from which 9PP was obtained via thermal aromatization in thin films. 9PP was characterized via optical, infrared and solid‐state 13C NMR spectroscopy as well as atomic force microscopy and mass spectrometry, and compared to polymeric analogues. Due to the lack of substitution, para‐nonaphenylene, irrespective of the precursor isomer employed, displays pronounced aggregation in the solid state. Intermolecular excitonic coupling leads to formation of H‐type aggregates, red‐shifting emission of the films to greenish. 9PP allows to study the structure–property relationship of para‐phenylene oligomers and polymers, especially since the optical properties of PPP depend on the molecular shape of the precursor.

Effects of Ca doping on structural and optical properties of PZT nanopowders

The influence of the addition of calcium ions (Ca2+) in the Pb(1-x)CaxZr0.52Ti0.48O3 system (PCZT) for x = 0.05, 0.10, 0.15, 0.20, and 0.25 on the structural and optical properties was systematically studied. The compositions were synthesized through a polymerized-complex approach based on the Pechini polymeric precursor route. The solubility limit of calcium ions within the PCZT lattice is in between x = 0.10 and x = 0.15, at which a CaTiO3 secondary phase is detected. The Goldschmidt tolerance factors, modified tolerance factors, and the effective vacancy sizes were all estimated for the synthesized nanopowders. While the Goldschmidt tolerance factors suggest the formation of a distorted perovskite structure, the values of the modified tolerance factor were extremely close to unity, indicating a strong stable ferroelectric perovskite structure. The optical band gap was found to decrease with calcium concentration to a minimum at x = 0.20 and then slightly increase at x = 0.25.