Molten Zinc Chloride Research Articles

Ultrastable Covalent Triazine Organic Framework Based on Anthracene Moiety as Platform for High-Performance Carbon Dioxide Adsorption and Supercapacitors.

Conductive and porous nitrogen-rich materials have great potential as supercapacitor electrode materials. The exceptional efficiency of such compounds, however, is dependent on their larger surface area and the level of nitrogen doping. To address these issues, we synthesized a porous covalent triazine framework (An-CTFs) based on 9,10-dicyanoanthracene (An-CN) units through an ionothermal reaction in the presence of different molar ratios of molten zinc chloride (ZnCl2) at 400 and 500 °C, yielding An-CTF-10-400, An-CTF-20-400, An-CTF-10-500, and An-CTF-20-500 microporous materials. According to N2 adsorption–desorption analyses (BET), these An-CTFs produced exceptionally high specific surface areas ranging from 406–751 m2·g−1. Furthermore, An-CTF-10-500 had a capacitance of 589 F·g−1, remarkable cycle stability up to 5000 cycles, up to 95% capacity retention, and strong CO2 adsorption capacity up to 5.65 mmol·g−1 at 273 K. As a result, our An-CTFs are a good alternative for both electrochemical energy storage and CO2 uptake.

Why the Brillouin Light Scattering Relaxation Times of Molten Zinc Chloride Are Shorter and Weaker in Temperature Dependence than the Structural Relaxation Times from Depolarized Light and Neutron Spin Echo Spectroscopy

A longstanding problem in the Brillouin light scattering (BLS) study of polymers is the relaxation times τBLS(T) being more than an order of magnitude shorter than the α-relaxation times τα(T) determined by dielectric, depolarized light scattering (DLS), and molecular dynamics simulations. In tackling the problem, τBLS(T) was identified with the relaxation time τ0(T) of the primitive relaxation in the coupling model, which can be calculated from τα(T) and the stretch exponent βK of the Kohlrausch correlation function for the α-relaxation.. The problem was solved by finding that indeed τ0(T) is in good agreement with τBLS(T). A recent work performed the neutron spin echo study of the structural α-relaxation of the network ionic liquid ZnCl2 and found the same anomaly as polymers. The α-relaxation time τNSE(T) from neutron spin echo (NSE) as well as the α-relaxation time τDLS(T) from DLS of ZnCl2 are much longer than τBLS(T) from BLS obtained before by several research groups. The finding of the same anomaly in ZnCl2 and polymers with very different chemical and physical structures offers an opportunity to critically test the explanation given before. The test was carried out by calculating the primitive relaxation times τ0,DLS(T) and τ0,NSE(T) from τDLS(T) and τNSE(T), respectively, in zinc chloride. Good agreements of τBLS(T) from BLS with τ0,DLS(T) and τ0,NSE(T) were found and thus the explanation given for polymers remains valid for ZnCl2. The test was extended to glycerol by comparing τBLS(T) with τ0,ICNS(T) and τ0,CNS(T) calculated from the α-relaxation time τICNS(T) and τCNS(T) from incoherent and coherent neutron scattering, respectively. There is good agreement between τBLS(T) and τ0,ICNS(T) in glycerol. There is also semiquantitative agreement of τBLS(T) with τ0,DS(T) from dielectric spectroscopy as well as τ0,CNS(T). Thus, the explanation for polymers is verified in the two very different glass formers, ZnCl2 and glycerol, and it is an advancement in the application of BLS to study the dynamics of glass formers.

Ultrastable conductive microporous covalent triazine frameworks based on pyrene moieties provide high-performance CO2 uptake and supercapacitance

Two pyrene-functionalized CTFs through ionothermal treatment TCNPy in the presence of molten zinc chloride at 500 °C, which displayed high-performance CO2 uptake and supercapacitance.

Direct Synthesis of Microporous Bicarbazole-Based Covalent Triazine Frameworks for High-Performance Energy Storage and Carbon Dioxide Uptake.

In this study a series of bicarbazole-based covalent triazine frameworks (Car-CTFs) were synthesized under ionothermal conditions from [9,9'-bicarbazole]-3,3',6,6'-tetracarbonitrile (Car-4CN) in the presence of molten zinc chloride. Thermogravimetric and Brunauer-Emmett-Teller analyses revealed that these Car-CTFs possessed excellent thermal stabilities and high specific surface areas (ca. 1400 m2 /g). The electrochemical performances of this Car-CTF series, investigated by using cyclic voltammetry, showed a highest capacitance of (545 F/g at 5 mV/s), which also exhibited excellent columbic efficiencies of 96.1 % after 8000 cycles at 100 μA/0.5 cm2 . The other Car-CTF samples displayed similar efficiencies. Furthermore, based on CO2 uptake measurements, one of the series showed the highest CO2 uptake capacities: 3.91 and 7.60 mmol/g at 298 and 273 K, respectively. These results suggest a simple method for the preparation of CTF materials that provide excellent electrochemical and CO2 uptake performance.

Mesoporous germanium nanoparticles synthesized in molten zinc chloride at low temperature as a high-performance anode for lithium-ion batteries.

In a simple and convenient way, mesoporous germanium nanoparticles (mp-Ge NPs) are prepared by a "metathesis" reaction of magnesium germanide (Mg2Ge) and zinc chloride (ZnCl2) in an autoclave at 300 °C. Investigated as anode materials for lithium-ion batteries, the prepared mp-Ge NPs exhibit a high capacity retention of 1048 mA h g-1 at 1 C after 1000 cycles and a high rate capacity of 727.1 mA h g-1 at 10 C in Li-Ge half cells. Additionally, a 3.4 V lithium-ion full cell (Ge-LiCoO2) with an energy retention of 85% (∼268.8 W h kg-1) over 100 cycles is achieved.

Effect of water of crystallization on the dissolution efficiency of molten zinc chloride hydrate salts during the pre‐treatment of corncob biomass

AbstractBACKGROUNDAgro‐wastes albeit abundant and cheap, require pre‐treatment steps tailored to overcome the characteristic recalcitrance of lignocellulosic biomass. In this study, zinc chloride hydrate salts were studied for their biomass deconstruction potential. The role of salts' hydration and to what degree it affects the dissolution efficiency was evaluated. Milled corn cobs from local farmlands were dissolved in the following solvent systems; ZnCl2.3H2O, ZnCl2 .4H2O, ZnCl2 .5H2O and ZnCl2 .7H2O at 70 °C for 60 mins at a biomass to solvent ratio of 1:12.RESULTSThe difference between the least and most hydrated solvent systems in terms of total released sugars as a percentage of recoverable sugar is 70.1%. The ZnCl2.4H2O solvent system extracted up to 49.1% of glucose and 95% of xylose. There were significant differences in the crystallinity indices and surface morphologies between the untreated and treated biomass.CONCLUSIONThe findings as documented contribute to current insights on the mechanisms of disintegration of lignocellulosic biomass in molten hydrate salts. The extraction of sugar components of biomass by ZnCl2.4H2O solvation was about 43% glucan and 99% xylan. © 2017 Society of Chemical Industry

Environmentally benign and economic synthesis of covalent triazine-based frameworks

Covalent triazine-based frameworks (CTFs) are important microporous materials with a wide range of applications. Here, we demonstrate an environmentally benign and economic synthetic pathway to CTFs. The monomers used for CTFs, aromatic nitriles, were obtained by cyanation using nontoxic potassium hexacyanoferrate(II) in place of commonly used toxic cyanides. Then, the CTFs were synthesized by trimerization of the corresponding cyano monomers in molten zinc chloride. A series of CTFs was synthesized, and the highest Brunauer-Emmett-Teller surface area measured in this series was 2404 m2/g. Among the synthesized CTFs, CTFDCP exhibited excellent CO2 adsorption properties, with a CO2 uptake of 225 mg/g at 0 °C.

Synthesis of Two-dimensional Microporous Carbonaceous Polymer Nanosheets and Their Application as High-performance CO2 Capture Sorbent.

The synthesis of two-dimensional (2D) polymer nanosheets with a well-defined microporous structure remains challenging in materials science. Here, a new kind of 2D microporous carbonaceous polymer nanosheets was synthesized through polymerization of a very low concentration of 1,4-dicyanobenzene in molten zinc chloride at 400-500 °C. This type of nanosheets has a thickness in the range of 3-20 nm, well-defined microporosity, a high surface area (∼537 m(2) g(-1) ), and a large micropore volume (∼0.45 cm(3) g(-1) ). The microporous carbonaceous polymer nanosheets exhibit superior CO2 sorption capability (8.14 wt % at 298 K and 1 bar) and a relatively high CO2 selectivity toward N2 (25.6). Starting from different aromatic nitrile monomers, a variety of 2D carbonaceous polymer nanosheets can be obtained showing a certain universality of the ionothermal method reported herein.

N-containing covalent organic frameworks as supports for rhodium as transition-metal catalysts in hydroformylation reactions

Porous cross-linked polymers containing nitrogen donor functionalities are a promising class of materials for the immobilization of transition metal catalysts. These highly porous materials are built from ligand-containing building blocks using a bottom-up approach. Utilizing dinitrile containing monomers, highly porous covalent triazine frameworks (CTFs) are formed at elevated temperatures in molten zinc chloride. Containing a large number of accessible nitrogen coordination sites, metal species can be stabilized within these materials. The materials' porosity can be tuned, depending on the monomeric building block used and synthesis conditions. By immobilizing rhodium species within the framework followed by pre-activation, Rh@CTF materials are suitable as catalysts in the solvent-free hydroformylation of 1-octene. These Rh@CTF catalysts are not as active as conventional homogeneous benchmark catalysts; however, their activity and selectivity clearly outperform comparable carbon-based catalysts. A correlation between porosity and polarity of the support material and the observed catalytic activity could be established. Furthermore, CTF-based catalysts could be recycled easily with no further treatment for up to five runs with just a gradual deactivation. The leaching of active species has been studied intensively to elucidate the strength of the metal-support-interactions in this rather challenging reaction for an immobilized catalyst.

A Simple Pyrolysis Route To Synthesize Carbon Nanofibers in Molten Zinc Chloride as an Anode Material for Li Ion Batteries

In this study, carbon nanofibers (CNFs) have been synthesized by a simple pyrolysis of tetrahydrofuran using molten zinc chloride as a liquid environment at 600 °C for 10 h. Scanning electron microscope images reveal that the obtained CNFs have diameters of about 50 nm and lengths up to tens of micrometers. As an anode material for Li ion batteries, the obtained CNFs can deliver a reversible capacity of 310 mA h/g after 200 cycles at a current density of 100 mA/g. When tetrahydrofuran is substituted by other carbon sources (ferrocene or lactic acid), CNFs can also be synthesized through this similar process; therefore, the pyrolysis method is a general way to prepare CNFs in molten zinc chloride.

Hydrogenolysis of lignin in ZnCl2 and KCl as an inorganic molten salt medium

Abstract Lignin can be converted into monomeric products with the aid of molten salt media. Molten zinc chloride (ZnCl2)/potassium chloride (KCl) mixtures are suitable for this purpose. The application of an eutectic mixture with low melting points leads to similar main products as are obtained by pyrolysis. The hydrogenolysis of an organosolv lignin in molten salts of ZnCl2/KCl was investigated as a function of reaction temperature, residence time, and lignin concentration, and the composition of liquid products and monophenols was analyzed by gas chromatography-mass spectrometry (GC-MS). The yields can be optimized by the proper selection of the reaction temperature. A longer residence time and higher lignin concentrations lead to increased formation of solid residues and gaseous products. The liquid products mainly consist of substituted phenols derived from lignins. Polymeric products are the result of condensation reactions (i.e., the formation of new C-C linkages in the course of secondary reactions).

Straightforward synthesis of a triazine-based porous carbon with high gas-uptake capacities

A triazine-based porous carbon material (TPC-1) was prepared directly from a fluorinated aromatic nitrile in molten zinc chloride. Trimerization of the nitrile and subsequent defluorination carbonization of the polymeric network result in the formation of TPC-1. The defluorination process is reversible and can etch the polymeric network to release CFn, thereby generating additional porosity and rendering TPC-1 a nitrogen-rich porous material. TPC-1 shows a high BET surface area of 1940 m2 g−1 and contains both micropores and mesopores, which facilitate the diffusion and adsorption of gas molecules. Gas adsorption experiments demonstrate outstanding uptake capacities of TPC-1 for CO2 (4.9 mmol g−1, 273 K and 1.0 bar), CH4 (3.9 mmol g−1, 273 K and 1.0 bar), and H2 (10.1 mmol g−1, 77 K and 1.0 bar). This straightforward synthesis procedure provides an alternative pathway to prepare high-performance porous carbon materials.

Polyamorphism and the evolution of intermediate-range order in moltenZnCl2

The pressure- and temperature-dependent properties of molten zinc chloride areinvestigated by means of molecular dynamics computer simulation. The potential modelused is based on a pair potential augmented with a description of the (many-body) anionpolarization. The static experimental and simulated structural properties arebriefly reviewed. The structural properties obtained from the simulation modelare compared with those obtained from experimental investigations and trendswith the change in system pressure and temperature are discussed. Preliminarystudies of the pressure behaviour of the simulated glassy states show the existenceof low-and high-density amorphous states (LDA and HDA). The LDA/HDAcoexistence line is established and its relationship to the underlying phase diagram isdiscussed.

Solidification of molten zinc chloride

Solidification of molten zinc chloride was studied both experimentally and theoretically. By isothermal thermal analysis the time needed for the melt to crystallize at a given temperature ranging between 453 and 553 K was determined and the data obtained were compared with those of a calculated TTT curve. The extremum coordinates (temperature TN, time tN) of the curve, critical cooling rate vCR, interfacial energy σ, and an additional parameter of kinetics barrier for nucleation ɛ were determined as TN=508 K, tN=7.29 s, vCR=11.38 K s−1, σ=0.11956 J m−2 and ɛ=0.5712. By non-isothermal method the critical cooling rate of glass formation was determined as 1.25 K s−1.

A convenient one-pot synthesis of 7-hydroxy-isoflavones from resorcinol with substituted phenylacetic acids

A mild and highly efficient one-pot synthesis of 7-hydroxy-isoflavones is reported. The acylation of resorcinol with various phenyl acetic acids in molten zinc chloride affords an intermediate deoxybenzoin which without isolation is subjected to cyclization with N, N-dimethylformamide in the presence of boron trifluoride diethyl etherate and methanesulfonyl chloride to afford the 7-hydroxy-isoflavone without the formation of any by-product.

Partial structure factors from disordered materials diffraction data: An approach using empirical potential structure refinement

Neutron and x-ray diffraction are widely used to measure the structure of liquids and disordered solids. Using techniques such as isotope substitution or anomalous dispersion or combining neutron and x-ray data, it is sometimes possible to invert the total diffraction patterns from these materials into a set of partial structure factors, which describe the correlations between specific atom types in the material. However, even in situations where the matrix for performing this inversion appears well determined, there are significant uncertainties in the process and it is rarely possible to achieve a unique set of partial structure factors in practice. Based on the much earlier method of F. G. Edwards and J. E. Enderby [J. Phys. C 8, 3483 (1975)] and extending the reverse Monte Carlo method of McGreevy [J. Phys.: Condens. Matter 13, R877 (2001)] and others, a modified approach is developed here that allows possible atomic distribution functions, which are consistent with the measured data to be explored. The basis of the present approach is that any solution to the inversion process must be derivable from a distribution of nonoverlapping atoms or molecules as in the physical system under investigation. Solutions to the problem of inverting the measured differential cross sections to partial structure factors are then extracted assuming different levels of confidence in the data, confidence being represented by a feedback factor on a scale of 0--1. These different solutions serve to identify where ambiguities exist in the derived partial structure factors, particularly when a particular partial structure factor contributes only weakly to the total diffraction pattern. The method is illustrated using some old diffraction data on molten zinc chloride that have significant uncertainties associated with them, but that have been used extensively as the basis for a number of computer simulations of this material.

The structure of molten ZnCl2: A new analysis of some old data

Using a recently derived method, based on empirical potential structure refinement (EPSR), the structure of molten zinc chloride (ZnCl2) is re-analysed. Contrary to the picture given in some early analyses, the results indicate that there are significant uncertainties in the extracted site-site radial distribution functions, particularly the Zn-Zn distribution. These are derived from the small weighting of this partial structure factor in the measured diffraction data and from systematic uncertainties in the original data. The simulated atom distributions are used to discuss the three-dimensional structure of this molten salt.

High temperature–high pressure apparatus for neutron diffraction on molten salts: Structure factors of molten zinc chloride

An apparatus for neutron diffraction experiments on corrosive liquids at high temperatures and high pressures is presented. The cell is constructed for temperatures up to 900 K and pressures up to 5000 bar and tested on molten zinc chloride at five different thermodynamic states at 723 K up to pressures of 4000 bar. The distinct terms and the total atom pair correlation functions of all five thermodynamic states are determined and their density dependences are discussed.

High Pressure Studies on Molten Zinc Chloride.

AbstractFor Abstract see ChemInform Abstract in Full Text.

High pressure studies on molten zinc chloride

The structure of molten zinc chloride was investigated at pressures up to 3000 bar and temperatures up to 500°C with a new high pressure cell. The distinct terms and the total atom pair correlation functions were determined with high energy photons. The distinct terms show systematic change in the low κ-range between 0 and 3 A−1 as a function of the applied pressure. A reduction of the first sharp diffraction peak (prepeak) intensity of the distinct part is observed with increasing pressure. It is concluded, that this behaviour indicates a network breaking tendency of the corner shared [ZnCl4]2− tetrahedra with increasing pressure, while the tetrahedra themselves remain unchanged over the whole applied pressure and temperature range.