Solid-state Preparation Research Articles

Facile Preparation of BaClxFy for the Catalytic Dehydrochlorination of 1-Chloro-1,1-Difluoroethane to Vinylidene Fluoride

BaClxFy as well as BaF2 and BaClF catalysts were prepared by solid-state reaction at room temperature with Ba(OH)2 as the precursor and NH4F/NH4Cl as the F and Cl sources. The catalysts were applied for the dehydrochlorination of 1-chloro-1,1-difluoroethane to vinylidene fluoride at 350 °C. The industrial manufacture of vinylidene fluoride (VDF) is carried out at 600–700 °C, whereas the BaClxFy catalysts provided a promising pathway to produce VDF at much lower temperatures. Unfortunately, the selectivity of VDF over BaF2 decreased from 94% to 84% along with the deactivation of the BaF2 catalyst monotonically. In the presence of small amounts of Cl in BaF2, stabilized selectivity was achieved. Over BaCl0.05F0.95, BaCl0.1F0.9 and BaCl0.25F0.75, no decrease in VDF selectivity was observed. Clearly, the presence of small amounts Cl during solid-state preparation inhibited the growth of BaF2 crystalline significantly. Far smaller particles were achieved. The particle size, or more precisely, the crystal size of the barium catalyst played a major role in the catalytic performance. In addition to the crystal growth, the presence of small amounts of Cl during catalyst preparation changed the chemical state of Ba, and therefore the adsorption and activation of the C–Cl bond for HCFC-142b were altered.

Structural and electrochemical investigation of binary Na2Fe1-xZnxP2O7 (0 ≤ x ≤ 1) pyrophosphate cathodes for sodium-ion batteries

Transition metal pyrophosphate material forms a robust polyanionic cathode family for sodium-ion batteries. Here, binary Na2(Fe1-yMny)P2O7 (0 ≤ y ≤ 1) system has been recently investigated by different groups, as Na2FeP2O7 is reported as a low-cost cathode with promising electrochemical performance and thermal stability. While the isostructural Na2FeP2O7 and Na2MnP2O7 assume triclinic P1‾ (#2) framework, pyrophosphate system shows structural diversity/polymorphism. Considering this, we have investigated the binary Na2(Fe1-xZnx)P2O7 (0 ≤ x ≤ 1) pyrophosphate family with anisostructural end members Na2FeP2O7 (P1‾, #2) and Na2ZnP2O7 (P42/n, #86). The current study reports solution combustion as well as solid-state preparation of novel Na2(Fe1-xZnx)P2O7 (0 ≤ x ≤ 1) family of materials, their structural and electrochemical characterizations. The degree of solid-solution formation and effect of Zn on Fe-redox activity in Na2(Fe1-xZnx)P2O7 (x = 0, 0.25) cathodes has been examined using electrochemical titration techniques such as galvanostatic intermittent titration (GITT) and potentiostatic intermittent titration (PITT) mode.

Photocatalytic Overall Water Splitting: Observing H2 and O2 Transients with Ni/NiOx-Modified Mg:SrTiO3

SrTiO3 is a promising semiconductor driving photocatalytic overall water splitting (POWS) under UV light illumination. Improving the performance of SrTiO3 in decomposing water into H2 and O2 can be achieved by introducing feasible co-catalyst, such as Pt or Ni/NiOx. Though co-catalysts are employed in heterogeneous photocatalysis engineering of semiconductor/co-catalysts interfaces is rarely reported in literature [1]. In addition, limited attention has been paid to structural/electronic changes of co-catalysts during illumination/reaction and transients occurring in hydrogen and/or oxygen evolution are barely discussed. In this contribution the photocatalytic performance of SrTiO3-based systems will be analyzed using a Continuously Stirred Tank Reactor (CSTR) connected to a micro GC-PDD (Pulsed Discharge Detector). Due to the favorable time-resolution of the GC-PDD transients in the evolution of H2 and O2, especially in the initial stages of testing, can be easily revealed. We will highlight the following recent observations: For Ni/NiOx-modified SrTiO3, severe changes in the oxidation state of NiOx assigned to the transformation of Ni(OH)2 to NiOOH leading to an active photocatalyst/co-catalyst material in agreement with transient H2 evolution will be discussed [2];Electronic modification of SrTiO3 by Mg incorporation into the perovskite structure can be obtained by a simple solid-state preparation [3]. While significant improvements in the steady state photocatalytic efficiency are obtained (Fig. 1), we also observed drastic changes in the initial transients caused by the interaction of Mg and Ni/NiOx;Finally, it will be highlighted that stabilization of the Ni/NiOx-modified Mg:SrTiO3 photocatalyst is obtained by photodeposition of CrOx from Cr(VI) containing solutions [4]. Enhanced stability is probably caused by electronic modification of Ni/NiOx as a severe influence of the back reaction of H2 and O2 was not observed for the process conditions used.Finally, the general stability of SrTiO3 in aqueous environment will be discussed. Thus, using state-of-the-art micro-GC analysis we were able to design a stable composite photocatalyst and improve the efficiency of the system (AQE) from 0.6% to >40%.

The effect of Sm and Nb on impedance spectroscopy and high frequency modulus, complex modulus, conductivity studies of BaTiO3-Li0.5Fe2.5O4 ceramics

The Sm and Nb substituted 90% of BaTiO3-10% of Li0.5Fe2.5O4 are synthesized using solid state preparation method. The X-ray diffraction, the frequency dependent of impedance, complex impedance at different temperatures, Nyquist plots at different temperatures, the variation of modulus and conductivity with high frequency region between 1 MHz and 3.2 GHz at 30 °C of composites were studied. The impedance of composites decreases steeply beyond 100 kHz and impedance value of 90BLF increases with increase in the concentration of Sm and Nb in BLF. The real and complex impedance changes with frequency. As temperature increases the real part of impedance of composites decreases and beyond certain frequencies, the impedance decreases sharply and merge at 10 MHz. As temperature increases the complex impedance Z″ max peaks shifted towards higher frequency i.e peak frequency fmax increases with increase in temperature. The impedance curve of composites identified by exhibits single semi circle represents type of relaxation described by Debye model. The relaxation time (τ) of composites decreases with the increase in temperature. Beyond frequency 3 GHz, the modulus of composites exhibits complex behavior and the complex modulus (M″) peaks exhibits jumping behavior could be explained by Debye-type relaxation. The conductivity peak of 90BLF composites are shifted towards higher frequency with the increase in concentration of Sm and Nb in it due to the substitution of Nb and Sm in 90BLF.

Solid-State Preparation, Structural Characterization, Physical Properties, and Theoretical Studies of a Series of Novel Rare-Earth Metal Chalcogenides with Unprecedented Closed-Cavities

Multinary rare-earth metal chalcogenides have aroused great concern owing to their special structure characteristics and diverse physical functions. In this work, five novel rare-earth chalcogenides adopt the formula Cs2[RE8InS14] (where RE = Ho–Lu), obtained by the elemental mixture in CsCl flux at 1273 K. They are isotype and belong to orthorhombic Cmca (no. 64) [a = 15.711(7)–15.385(2) A, b = 22.232(2)–21.786(2) A, c = 15.483(5)–15.244(2) A, V = 5408.4(4)–5130.1(7) A3 and Z = 8], exhibiting a dense 3D [RE8InS14] framework consisting of RES6 octahedron and discrete InS4 tetrahedron. The large closed-cavities of Cs4@S26 are far apart and embedded within the network along bc-plane, which was discovered for the first time. The band gaps from 2.45 to 2.72 eV for Cs2[RE8InS14] were deduced from the UV–Vis–NIR spectroscopy based on the Kubelka–Munk function. A magnetic test indicates that the Cs2[RE8InS14] (RE = Ho–Yb) compounds possess paramagnetism above 50 K. In addition, the solid-state preparation, struc...

Solid-state preparation of mixed metal-oxides nanostructure from anionic metal-organic framework via cation exchange process

An anionic Metal-Organic Framework, [HDMA]2[Zn2(BDC)3(DMA)2].6DMF (TMU-3) (HDMA+: dimethylamonnium, BDC2−: 1,4-benzenedicarboxilate, DMA: dimethylamine, DMF: N,N′-dimethylformamide) with 3D channels has been synthesized. The NH2Me2+ ions within the 3D channel are easily exchanged with Fe2+ ions and characterized by X-ray powder diffraction (XRPD), Fourier transform infrared spectroscopy (FT-IR) and inductively coupled plasma (ICP) analyses. Fe2O3/ZnFe2O4 nanostructure were synthesized by direct heating of the cation exchanged MOF in air at 550 °C and determined by scanning electronic microscope (SEM). This strategy shows that the cationic exchange process in anionic MOF can create a good route for preparation of easy and high yield different inorganic nanocomposites.

Structural, surface and magnetic properties of chalcogenide Co9S8 nanoparticles prepared by mechanochemical synthesis

In this study, the mechanochemical synthesis of Co9S8 nanoparticles from cobalt and sulphur by high-energy milling in a planetary mill in an argon atmosphere is reported. Structural characterization of the synthesized nanoparticles by XRD was performed. Co9S8 nanoparticles crystallize in the cubic structure with the crystallite size of about 16 nm. The microstructure of the Co9S8 nanoparticles was further studied using TEM, HRTEM and EDS-HAADF-STEM techniques. Co9S8 nanoparticles consist of nanocrystals exhibiting size in the range of 10–30 nm that are densely aggregated into spherical-like objects. The highest specific surface area value observed was 4 m2g-1 and the pore properties of this sample are quite poor. The magnetic properties of mechanochemically synthesized nanoparticles were investigated using SQUID magnetometer. The room temperature magnetic data supported the paramagnetic spin structure of Co9S8 nanoparticles. The transition from paramagnetic to weak ferromagnetic or ferrimagnetic behaviour was indicated from temperature dependence of magnetization at cryogenic temperatures. It is demonstrated that mechanochemical synthesis can be successfully employed in the one-step solid-state preparation of Co9S8 nanoparticles.

Promoting Photocatalytic Overall Water Splitting by Controlled Magnesium Incorporation in SrTiO3 Photocatalysts.

SrTiO3 is a well-known photocatalyst inducing overall water splitting when exposed to UV irradiation of wavelengths <370 nm. However, the apparent quantum efficiency of SrTiO3 is typically low, even when functionalized with nanoparticles of Pt or Ni@NiO. Here, we introduce a simple solid-state preparation method to control the incorporation of magnesium into the perovskite structure of SrTiO3 . After deposition of Pt or Ni@NiO, the photocatalytic water-splitting efficiency of the Mg:SrTiOx composites is up to 20 times higher compared to SrTiO3 containing similar catalytic nanoparticles, and an apparent quantum yield (AQY) of 10 % can be obtained in the wavelength range of 300-400 nm. Detailed characterization of the Mg:SrTiOx composites revealed that Mg is likely substituting the tetravalent Ti ion, leading to a favorable surface-space-charge layer. This originates from tuning of the donor density in the cubic SrTiO3 structure by Mg incorporation and enables high oxygen-evolution rates. Nevertheless, interfacing with an appropriate hydrogen evolution catalyst is mandatory and non-trivial to obtain high-performance in water splitting.

Solid-state preparation of CuO/ZnO nanocomposites for functional supercapacitor electrodes and photocatalysts with enhanced photocatalytic properties

In this paper, hybrid CuO/ZnO nanocomposites are synthesized by a simple and cost-effective solid-state grinding method for multifunctional applications as supercapacitor electrodes and photocatalysts for the degradation of dye pollutants. In the synthesis process, ZnCO3-SLS used as a reactant that not only provides Zn source but also serves as a template to induce the nanoparticles to arrange orderly. The resultant CuO/ZnO (ZnCO3-SLS, 1.00 g) nanocomposites exhibit a maximum degradation efficiency of 91.5% for Rhodamine B and 74.3% for Congo Red under visible light irradiation for 240 min, respectively. Besides, it also demonstrates high specific capacitance of 579.5 F g−1 and excellent cyclic performance with nearly 83.0% capacity retention after 2000 cycles at a current density of 5 A g−1, seemed to be superior to other nanocomposites. The excellent electrochemical performance can be attributed to a rational combination of two electrochemical active materials. The hybrid nanocomposites design opens up new opportunities to use in wastewater treatment and energy storage applications.

Comparative Photocatalytic Performance on the Degradation of 2-Naphthol Under Simulated Solar Light Using α-Bi4V2O11 Synthesized by Solid-State and Co-precipitation Methods

In this investigation, the photocatalytic activity of α-Bi4V2O11 in the degradation of 2-naphthol under simulated solar light was evaluated. Bismuth vanadate α-Bi4V2O11 was synthesized by the solid-state reaction method and by co-precipitation in aqueous media, with the aim of comparing their performance in the photodegradation of the aromatic pollutant. The latter method (co-precipitation) has not been previously reported for the synthesis of α-Bi4V2O11. Structural evolution of the oxides precursors was determined by X-ray diffraction. Morphology and optical properties of the solids were analyzed by scanning electron microscopy (SEM) and UV-vis diffuse reflectance spectroscopy (UV-vis), respectively. The results showed that at 800 °C, only α-Bi4V2O11 was formed in both preparations. The SEM micrographs revealed that the powders were composed of agglomerates with sizes between 0.8–2 μm for those synthesized by co-precipitation and 2–10 μm for those obtained by solid-state reaction. The optical properties indicated that α-Bi4V2O11 was activated with visible light during the photocatalytic process. The photocatalytic degradation of 2-naphthol was largely influenced at basic pH, degrading 79% of the contaminant in 240 min, with the powder obtained by co-precipitation; meanwhile, for the solid-state preparation, the degradation reached only 55%.

Robust, Transformable, and Crystalline Single-Node Organometallic Networks Constructed from Ditopic m-Terphenyl Isocyanides.

The preparation of 3D and 2D Cu(I) coordination networks using ditopic m-terphenyl isocyanides is described. The incorporation of sterically encumbering substituents enables the controlled, solid-state preparation of Cu(I) tris-isocyanide nodes with a labile solvent ligand in a manner mirroring solution-phase chemistry of monomeric complexes. The protection afforded by the m-terphenyl groups is also shown to engender significant stability towards heat as well as acidic or basic conditions, resulting in robust single-metal-node networks that can transition from 3D to 2D extended structures.

Structure and ion dynamics of mechanosynthesized oxides and fluorides

AbstractIn many cases, limitations in conventional synthesis routes hamper the accessibility to materials with properties that have been predicted by theory. For instance, metastable compounds with local non-equilibrium structures can hardly be accessed by solid-state preparation techniques often requiring high synthesis temperatures. Also other ways of preparation lead to the thermodynamically stable rather than metastable products. Fortunately, such hurdles can be overcome by mechanochemical synthesis. Mechanical treatment of two or three starting materials in high-energy ball mills enables the synthesis of not only new, metastable compounds but also of nanocrystalline materials with unusual or enhanced properties such as ion transport. In this short review we report about local structures and ion transport of oxides and fluorides mechanochemically prepared by high-energy ball-milling.

Melt Synthesis of LiFePO4: Fundamentals, Versatility and Application

With its good thermal stability, abundance in nature and benign environmental impact, LiFePO4 (LFP) cathode material is seen as one of the most promising candidate for the next generation of Li-ion batteries. Many synthetic routes have already been used for preparing LFP material, best known being solid state, sol-gel, hydrothermal, co-precipitation and microwave preparations. All of them are performed at moderate temperature and/or in a wide range of pressures. Melt process of LFP, advanced by Gauthier et al. in 2003[1], operates in the liquid phase above 1000⁰C and then benefits from increased reaction kinetics and from the thermodynamic stability of LFP in a mild reducing atmosphere. The melt synthesis allows the use of a wide range of simple raw materials as well as a possible purification strategy during the melt step or upon solidification, potentially enabling for usage of less pure non-expensive raw materials. In this work, thermodynamic considerations are first addressed for deep understanding of the Li-Fe-P-O systems. A model has recently been developed and is supported by experimental data. On this basis, recent experimental observations and progress on raw material selection (including direct use of iron ore concentrates) and systems will be reported. Eventually, melt-synthesis conditions and the latest results in controlling the purification of LiFePO4 from major phase impurities will also be covered. All these considerations allow the selection of the best conditions to prepare a high purity LiFePO4 by melt-process. This work is part of an Automotive Partnership of Canada supported program to develop and pilot the molten-synthesis process to make high purity C-LiFePO4with excellent electrochemical properties for using as a cathode material in Li-ion batteries for EVs and PHEVs application. [1] M. Gauthier, L. Gauthier, D. Lavoie, C. Michot, N. Ravet, US Patent 7,534,408 B2. (2003).

Low-temperature solid-state preparation of ternary CdS/g-C3N4/CuS nanocomposites for enhanced visible-light photocatalytic H2-production activity

Low-temperature solid-state method were gradually demonstrated as a high efficiency, energy saving and environmental protection strategy to fabricate composite semiconductor materials. CdS-based multiple composite photocatalytic materials have attracted increasing concern owning to the heterostructure constituents with tunable band gaps. In this study, the ternary CdS/g-C3N4/CuS composite photocatalysts were prepared by a facile and novel low-temperature solid-state strategy. The optimal ternary CdS/g-C3N4/CuS composite exhibits a high visible-light photocatalytic H2-production rate of 57.56μmolh−1 with the corresponding apparent quantum efficiency reaches 16.5% at 420nm with Na2S/Na2SO3 mixed aqueous solution as sacrificial agent. The ternary CdS/g-C3N4/CuS composites show the enhanced visible-light photocatalytic H2-evolution activity comparing with the binary CdS-based composites or simplex CdS. The enhanced photocatalytic activity is ascribed to the heterojunctions and the synergistic effect of CuS and g-C3N4 in promotion of the charge separation and charge mobility. This work shows that the low-temperature solid-state method is efficient and environmentally benign for the preparation of CdS-based multiple composite photocatalytic materials with enhanced visible-light photocatalytic H2-production activity.

On the Versatility of Melt-Synthesis of LiFePO4 cathode Material

LiFePO4 (LFP) has attracted much attention as a promising candidate for cathode materials in new generation of Li-ion batteries due to its good thermal stability, being environmentally friendly and abundance in nature. Many synthetic routes, such as solid state, sol-gel, hydrothermal, co-precipitation, and microwave preparations, have been used for preparing LFP. In 2003, Gauthier et al. advanced the concept of melt synthesis. The process operating above 1000°C in the liquid phase, benefits from fast reaction kinetics and the thermodynamic stability of LiFePO4 in a reducing atmosphere. This approach allows the use of a wide range of simple raw materials as well as a possible purification strategy in the melt or upon solidification, potentially enabling for usage of less pure non-expensive raw materials. Fundamental aspects will be addressed as this work is only feasible with a good understanding of the thermodynamics of the Li-Fe-P-O system. A model has been developed and it is supported by our experimental data. On this basis, recent experimental observations and progress on raw material selection and systems will be then reported. Melt-synthesis conditions and the latest result in controlling the purification of LiFePO4 from major phase impurities will also be covered. All these considerations allow the selection of the best conditions to prepare a high purity LiFePO4 by melt-process. This work is part of an Automotive Partnership of Canada supported program to develop and pilot the molten-synthesis process to make high purity C-LiFePO4 with excellent electrochemical properties for using as a cathode material in Li-ion batteries for EVs and PHEVs application.

Solid state preparation of NiO-CeO2 catalyst for NO reduction

The development of efficient method for preparation of well-performed catalyst is an attractive topic in heterogeneous catalysis. Conventional route to obtaining mixed oxide catalysts is based on wet chemical methods. In the present study, a novel solid state method was proposed to fabricate NiO-CeO2 catalyst by directly mixing metal precursors (nickel nitrate hydrate and cerium nitrate hydrate) and the subsequent calcination, omitting the common drying procedure in wet preparations. The preparation process was tracked by thermogravimetry-differential thermal analysis (TG-DTA) and obtained catalyst was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 physisorption, powder X-ray diffraction (XRD), Raman spectroscopy, H2 temperature programmed reduction (H2-TPR) and tested in the model reaction of NO reduction by CO. Results showed that simultaneous decomposition of the mixed nitrates was occurred, suggesting cooperative interaction between the precursors. Moreover, in comparison with wet impregnation method, the catalyst from solid state preparation displayed not only improved textual properties (larger surface area and enriched porous structure), but also enhanced interfacial interactions between nickel and ceria, which promoted the bulk doping, surface dispersion of nickel species and the reduction of surface oxygen species. As a result, the catalytic performance in NO+CO reaction was significantly upgraded. Based on the preliminary results of this study, it is supposed the solid state preparation may open a convenient and versatile pathway to fabricate mixed oxide catalysts.

Octafluorodirhenate(III) Revisited: Solid-State Preparation, Characterization, and Multiconfigurational Quantum Chemical Calculations.

A simple method for the high-yield preparation of (NH4)2[Re2F8]·2H2O has been developed that involves the reaction of (n-Bu4N)2[Re2Cl8] with molten ammonium bifluoride (NH4HF2). Using this method, the new salt [NH4]2[Re2F8]·2H2O was prepared in ∼90% yield. The product was characterized in solution by ultraviolet-visible light (UV-vis) and (19)F nuclear magnetic resonance ((19)F NMR) spectroscopies and in the solid-state by elemental analysis, powder X-ray diffraction (XRD), and infrared (IR) spectroscopy. Multiconfigurational CASSCF/CASPT2 quantum chemical calculations were performed to investigate the molecular and electronic structure, as well as the electronic absorption spectrum of the [Re2F8](2-) anion. The metal-metal bonding in the Re2(6+) unit was quantified in terms of effective bond order (EBO) and compared to that of its [Re2Cl8](2-) and [Re2Br8](2-) analogues.

Microwave dielectric properties of LBBS glass added (Zn0.95Co0.05)2SiO4 for LTCC technology

The effects of Li2O–B2O3–Bi2O3–SiO2 (LBBS) glass on the sintering characteristics and microwave dielectric properties of (Zn0.95Co0.05)2SiO4 were investigated in this study. (Zn0.95Co0.05)2SiO4 powders were fabricated by traditional solid-state preparation, and LBBS glass was synthesised by quenching method. The LBBS glass can effectively reduce the sintering temperature of (Zn0.95Co0.05)2SiO4 from 1300°C to 900°C and thus promote the densification and uniformity of the specimens. XRD patterns indicated that no other secondary phases existed in our doping range (0–2wt%). To obtain the highest sintering density and a uniform microstructure when the samples were sintered at 900°C, the optimal doping content was set to be 1.5wt%. The sample also demonstrated the following excellent microwave dielectric properties: ɛr=6.16, Qf=33,000GHz and τf=−59ppm/°C.

Structural, vibrational and photoluminescence properties of Sr(1-x)PbxMoO4 solid solution synthesized by solid state reaction

In this paper, strontium lead molybdate Sr1-xPbxMoO4 polycrystalline samples with 0≤x≤1 were prepared by solid state preparation method at 1000°C. These materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and micro-Raman spectroscopy. Their photoluminescence responses were analyzed under X-ray excitation. Rietveld refinements indicate that all the materials present a scheelite-type tetragonal structure. Micro-Raman spectra confirmed the formation of the solid solution with a specific effect due to Sr-O-Mo and Pb-O-Mo links in the scheelite structure. SEM images showed modifications in the shapes and grain sizes as x increased. Broad photoluminescent emission bands were observed in the energy range 2.1–2.9eV. The emission bands were decomposed into four gaussian components. The intensities of all components presented a strong maximum in the composition range 0.1<x<0.4.

固相法制备Ce,Cr∶YAG透明陶瓷及其荧光性能研究

固相法制备Ce,Cr∶YAG透明陶瓷及其荧光性能研究