Thermal Stability Range Research Articles

Use of Electrochemical Etching to Produce Doped Phenylacetylene Functionalized Particles and Their Thermal Stability

Silicon is an attractive material for the fabrication of thermoelectric materials. Previously, it was reported that phenylacetylene capped silicon nanoparticles (PA-SiNPs), which were synthesized from micelle reduction, displayed a ZT of up to 0.6 at ambient temperature. The major contributing factor to this result was the material’s low thermal conductivity. However, this material also displayed a low electrical conductivity compared to other thermoelectric materials. This is contributed to, in part, by low charge carrier concentration, which is difficult to control in micelle reduction-based methods. Top–down methods allow control of the carrier concentration as the material is doped prior to the breaking down of the material. PA-SiNPs were synthesized using electrochemical etching followed by functionalization. These particles were then analyzed with transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, thermo-gravimetric analysis (TGA), and differential scanning calorimetry (DSC). The DSC and TGA trace were compared to those of PA-SiNPs synthesized by micelle reduction to show that the thermal stability range is much higher in the particles synthesized from the top–down method giving them a wider range of potential thermoelectric applications.

The incorporation of calix[6]arene and cyclodextrin derivatives into sol–gels for the preparation of stationary phases for gas chromatography

New polyethylene-glycol-based sol–gels containing cyclodextrin or calix[6]arene derivatives have been synthesized. An original method for sol–gel preparation and capillary column coating, which consumes smaller quantities of selectors and allows for control of their amounts in the stationary phase, is reported herein. The new stationary phases exhibited excellent column efficiencies over a large range of temperatures and thermal stability up to 280°C. The cyclodextrin derivative generally showed the best separation factors for aromatic positional isomers. The calix[6]arene derivative exhibited the best selectivity for the polychlorobiphenyl congeners and some polycyclic aromatic hydrocarbon isomers. The relationship between the structure and the chromatographic properties of the selectors is discussed. The tert-butyl groups on the upper rim of the calix[6]arene were found to possibly play an important role in the recognition of solutes. The incorporation of the cyclodextrin derivative into the sol–gel matrix did not affect its enantioselective recognition capabilities.

Production and application of amylases of Rhizopus oryzae and Rhizopus microsporus var. oligosporus from industrial waste in acquisition of glucose

AbstractAmylases from Rhizopus oryzae and Rhizopus microsporus var. oligosporus were obtained using agro-industrial wastes as substrates in submerged batch cultures. The enzymatic complex was partially characterised for use in the production of glucose syrup. Type II wheat flour proved better than cassava bagasse as sole carbon source for amylase production. The optimum fermentation condition for both microorganisms was 96 hours at 30°C and the amylase thus produced was used for starch hydrolysis. The product of the enzymatic hydrolysis indicated that the enzyme obtained was glucoamylase, only glucose as final product was attained for both microorganisms. R. oligosporus was of greater interest than R. oryzae for amylase production, taking into account enzyme activity, cultivation time, thermal stability and pH range. Glucose syrup was produced using concentrated enzyme and 100 g L−1 starch in a 4 hours reaction at 50°C. The bioprocess studied can contribute to fungus glucoamylase production and application.

Hexadecylpyridinium surfactant modified zeolite A as an active component of a polymeric membrane sulfite selective electrode

Zeolite A was synthesized from waste porcelain and modified by hexadecylpyridinium surfactant to change the cation exchanger property of the raw zeolite to anion exchanger property in the obtained surfactant modified zeolite (SMZ). The SMZ was used as an active ingredient component of a membrane selective sulfite electrode. The electrode was fully characterized in terms of composition, response time, thermal stability and usable pH range. The sensor showed suitable response to sulfite in the concentration range of 8.0×10−7 to 1.0×10−1molL−1, with a detection limit of 5.0×10−7molL−1 and a slope of −29.5±0.8mV per decade of sulfite concentration.

The effect of Si alloying on the thermal stability of Al2O3 films deposited by filtered cathodic arc

The effect of Si alloying on the phase transformation sequence and phase formation temperatures of Al2O3 thin films deposited by filtered cathodic arc was investigated by annealing experiments in air. By addition of Si the transformation of γ- to δ- and θ-Al2O3 is restrained by 100°C. The thermal stability range of the δ- and θ-phase is also increased by ≥200°C with respect to the unalloyed Al2O3 thin film and the formation of α-Al2O3 is restrained by 200°C upon addition of Si. Based on the observed Si addition induced changes in phase formation, crystallite size and bonding it appears reasonable that the presence of SiO2 at the grain boundaries impeding mass transport governs the Si induced stability enhancement of the metastable γ-/δ- and θ-Al2O3 phases and the restrained α-Al2O3 formation. The competing proposal assuming a random substitution of Al by Si on the lattice sites is not consistent with the XPS data.

A Step toward the Development of High-Temperature Stable Ionic Liquid-in-Oil Microemulsions Containing Double-Chain Anionic Surface Active Ionic Liquid

Owing to their fascinating properties and wide range of potential applications, interest in nonaqueous microemulsions has escalated in the past decade. In the recent past, nonaqueous microemulsions containing ionic liquids (ILs) have been utilized in performing chemical reactions, preparation of nanomaterials, synthesis of nanostructured polymers, and drug delivery systems. The most promising fact about IL-in-oil microemulsions is their high thermal stability compared to that of aqueous microemulsions. Recently, surfactant-like properties of surface active ionic liquids (SAILs) have been used for preparation of microemulsions with high-temperature stability and temperature insensitivity. However, previously described methods present a limited possibility of developing IL-in-oil microemulsions with a wide range of thermal stability. With our previous work, we introduced a novel method of creating a huge number of IL-in-oil microemulsions (Rao, V. G.; Ghosh, S.; Ghatak, C.; Mandal, S.; Brahmachari, U.; Sarkar, N. J. Phys. Chem. B2012, 116, 2850-2855), composed of a SAIL as a surfactant, room-temperature ionic liquids as a polar phase, and benzene as a nonpolar phase. The use of benzene as a nonpolar solvent limits the application of the microemulsions to temperatures below 353 K. To overcome this limitation, we have synthesized N,N-dimethylethanolammonium 1,4-bis(2-ethylhexyl) sulfosuccinate (DAAOT), which was used as a surfactant. DAAOT in combination with isopropyl myristate (IPM, as an oil phase) and ILs (as a polar phase) produces a huge number of high-temperature stable IL-in-oil microemulsions. By far, this is the first report of a huge number of high-temperature stable IL-in-oil microemulsions. In particular, we demonstrate the wide range of thermal stability of [C6mim][TF2N]/DAAOT/IPM microemulsions by performing a phase behavior study, dynamic light scattering measurements, and (1)H NMR measurements and by using coumarin-480 (C-480) as a fluorescent probe molecule.

Control of Gold Nanoparticle Superlattice Properties via Mesogenic Ligand Architecture

Hybrid structures made of metal nanoparticles with liquid crystalline coating attract considerable attention due to their conspicuous self-assembly and potential synergistic properties. Here we report on a new structural parameter that can be used to control the formation of hybrid gold nanoparticles superlattice. A series of Au nanoclusters covered with mixed monolayers of alkyl and liquid-crystalline ligands were obtained. For the first time in such systems the lengths of both alkyl ligands and mercapto-functionalized alkyl spacers of the promesogenic molecules were varied. The physicochemical properties of the obtained materials were investigated by different instrumental techniques, such as X-ray photoelectron spectroscopy (XPS), small-angle X-ray diffraction (SAXRD), and transmission electron microscopy (TEM). Interestingly, the applied variations of the grafting layer composition enabled the formation of 1D (lamellar) and 3D long-range ordered structures with systematically changing thermal stability range. Such behavior is explained based on the structural parameters of the hybrid nanoparticles, namely the separation of the cores and ligand flexibility. This work gives some new insights into the nanoparticle self-assembly subject and points out the critical parameters controlling the degree of order within the self-assembled superstructures.

A simple criterion for gas chromatography/mass spectrometric analysis of thermally unstable compounds, and reassessment of the by‐products of alkyl diazoacetate synthesis

A principal limitation of gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS) is the thermal instability of analytes. We propose that the injector and column temperatures should not exceed the atmospheric pressure boiling point, without decomposition, of the highest homologue of the series being analyzed, instead of the time-consuming procedure of obtaining chromatograms using different temperatures. A series of thermally unstable diazocarbonyl compounds, alkyl diazoacetates (predicted limit of stability approx. 140 °C, the boiling point of ethyl diazoacetate), was selected for GC/MS analysis using standard equipment. Different GC separation conditions were selected so that the retention temperatures of target compounds were both below and above 140 °C. Analyzing alkyl diazoacetates within their thermal stability range permitted reanalysis of their typical synthesis by-products. No dialkyl fumarate or maleate impurities, principal decomposition products which have often been reported previously, were found. Instead, alkyl esters of glycolic acid nitrate, O(2)NOCH(2)CO(2)R, and 'pseudo-dimeric' products, ROCO[C(2)H(3)NO]CO(2)R, were discovered for the first time. Avoiding the decomposition of thermally unstable organic compounds during GC and/or GC/MS analysis requires estimating their degradation temperature limits. This limit can be estimated as being equal to the atmospheric pressure boiling point of the highest homologue in the homologous series under consideration that does not decompose on boiling.

Electro-enzymatic degradation of carbofuran with the graphene oxide–Fe3O4–hemoglobin composite in an electrochemical reactor

In this paper, the degradation of carbofuran with graphene oxide–ferroferric oxide–hemoglobin (GO–Fe3O4–Hb) composite in an electrochemical–enzyme system was reported. The graphene oxide–Fe3O4–hemoglobin composite was fabricated by a two-step process. First, graphene oxide–Fe3O4 (GO–Fe3O4) composite was prepared via a simple and effective chemical precipitation method. Then, hemoglobin was covalently immobilized onto the graphene oxide–Fe3O4 by glutaraldehyde (GA). The GO–Fe3O4–Hb composite showed improved enzyme thermal stability and wider active pH range compared with Fe3O4–Hb and soluble Hb. Furthermore, the GO–Fe3O4–Hb composite can be easily separated under a magnetic field from the reaction solution and reused. To evaluate the electro-enzymatic degradation of carbofuran, electrolytic experiments were carried out with 1U/mL GO–Fe3O4–Hb composite at 0.007A, and oxygen flow rate 25mL/min. Under the optimum conditions by the electrogeneration of hydrogen peroxide (H2O2), the removal efficiency of carbofuran reached 94.6%. Compared with electrochemical and biochemical methods, the removal of carbofuran through electroenzymatic method was comparatively favorable.

Spectroscopic, optical, thermal and AC conductivity studies on semi-organic nonlinear optical crystal: AMCTC

Good quality needle shaped (14 × 3 × 3 mm3) single crystals of ammonium mercury chloride thiocyanate (NH4[HgCl2(SCN)]; AMCTC) were grown using slow solvent evaporation method for the first time. The incorporation of thiocyanate ligand is confirmed by the strong and highly intense FT-IR band observed at 2112.0 cm−1, which corresponds to the stretching frequency vibration of CN. The signal at about 120 ppm of FT-NMR spectrum is a strong evidence, which in turn supports the binding of thiocyanate in the resulting compound of AMCTC. Further, the sample was also subjected to UV–Vis–NIR and TG–DTA and DSC studies to understand the range of optical transparency and thermal stability of the sample, respectively. The melting point of AMCTC is found to be 151.7 °C. The powder second harmonic generation efficiency of the sample is superior to potassium dihydrogen phosphate.

Cold-active hydrolases producing bacteria from two different sub-glacial Himalayan lakes

Microorganisms, native to the cold environments have successfully acclimatized their physiological, metabolic, and biological features, exhibiting uniqueness in their enzymes, proteins, and membrane structures. These cold-active enzymes have immense biotechnological potential. The diversity of culturable bacteria in two different water lakes (the sub-glacial freshwater and the brackish) of Himalayas was analyzed using SYBR green staining and cultural methods. A total of 140 bacteria were isolated and were grouped as psychrophiles, psychrotrophs, and psychrotolerant organisms, based on their optimal temperature for growth. The amplified ribosomal DNA restriction analysis using three restriction enzymes facilitated the grouping of these isolates into 96 genotypes at ≥85% polymorphism. Phylogenetic analysis using 16S rRNA gene sequences revealed that the bacterial strains from both lakes belonged to Firmicutes, Proteobacteria (α, β, and γ) or Actinobacteria. Screening of the germplasm for the activity of different cold-active hydrolases such as protease, amylase, xylanase, and cellulase, revealed that about 16 isolates were positive, and exhibiting a wide range of stability at various temperature and pH. Our results suggest that the distinctly different ecosystems of sub-glacial freshwater and brackish water lakes have diverse groups of bacteria, which can be an excellent source of extracellular hydrolases with a wide range of thermal stability.

이미다졸계 이온성 액체의 물성

Ionic liquids (ILs) existing as liquid state at room temperature are composed of a immense heterocyclic cation and inorganic anion which is smaller than cation`s size. Thus, the species of cation and anion as well as the length of alkyl group on the cation have influence on their physical properties. Their outstanding properties such as non-volatility, thermal stability and wide range of electrochemical stability make these materials excellent candidates for green solvent which can substitute the conventional organic solvents. In this study, ILs based on imidazolium cation have been synthesized such as 1-butyl-3-methylimidazolium bromide ([BMIM][Br]), 1-butyl-3-methylimidazolium chloride ([BMIM] [Cl]), 1-butyl-3-methylimidazolium iodide ([BMIM][I]), and 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][]). The density, viscosity, refractive index, heat capacity and ionic conductivity of [BMIM][Br], [BMIM][I], and [BMIM] [] were measured over range of temperature of 293.2 to 323.2 K. The density and refractive index values of [BMIM][I] were the highest among three ILs and the viscosity values of [BMIM][Br] were the highest among three ILs. The heat capacities [BMIM][] were higher than those of [BMIM][Br]. The ionic conductivities of [BMIM][] were higher than those of [BMIM][I].

Mesoporous and Macroporous Brookite Thin Films Having a Large Thermal Stability Range

A sol-gel chemistry approach is employed to generate mesoporous and macroporous brookite thin films using Ag ions as dopant species whose thermal stability is well above previously reported literature values for thin films. The Ag ions not only induce the formation of brookite but also participate in its enhanced thermal stability. Despite brookite being metastable in nature, which renders it a challenge to synthesize, it has been prescribed as a potential competitor to anatase. We have used a layer-by-layer approach to generate a mesoporous Ag-doped brookite structure at 500 °C with 95% composition by XRD. This tightly packed mesoporous structure can be described as striated grains of brookite protruding from the surface to form an interlocked network whose thermal stability spans up to 800 °C. The open structure of brookite makes it an apt host for the intercalant Ag species, whose inclusion within the brookite framework is improved by the presence of a stabilizing agent. Both the morphology of the surface and the presence of a stabilization agent for Ag contribute to enhancing its thermal stability. This is in contrast to the thermal stability of the macroporous brookite thin film, which was found to be lower (<700 °C) than that of the mesoporous brookite thin film. The reagents are deliberately chosen to produce a macroporous film in the absence of a stabilizing agent. Ag nodules are observed to be formed at 700 °C, which implies their limited intercalation into the brookite structure, thus rendering them relatively less stable. Moreover, the macroporous film being relatively more relaxed is more susceptible to phase transformation at a higher calcination temperature. Our results provide a platform that paves the way toward better control, thereby leading to a broader technological application of brookite.

Zirconia-Based Stationary Phases for Chiral Separation: Mini Review

Separation of enantiomers is one of the most interesting and challenging tasks in the field of separation science. High-performance liquid chromatography (HPLC) and recently capillary electrochromatography (CEC) using chiral stationary phases (CSP) are two of the most useful techniques for both enantioseparation and determination of enantiomeric composition. Although silica has been extensively used as the base material for the stationary phases due to attractive properties including desirable mechanical strength, surface characteristics, catalytic inertness, and surface derivatization possibilities, it has some inherent shortcomings including the narrow range of pH and thermal stability. The zirconia-based stationary phases have shown excellent performance in the separation of wide range of compounds and have been considered as an alternative to silica-based stationary phases due to desirable chemical and physical properties such as resistance to thermal conditions, resistance to extreme pHs, and mechanical stability. Recently, zirconia-based CSPs in either particle-packed or monolithic columns have received considerable attention. This mini-review reports the development and applications of zirconia based stationary phases for chiral separations by HPLC and CEC.

TiAlNb-alloy with a modulated B19 containing constituent produced by powder metallurgy

ABSTRACTIntermetallic TiAl alloys are of interest to the aero engine industry because of their light weight, corrosion resistance and excellent high temperature strength. This justifies the continued effort to improve properties and processing of these alloys.A critical parameter that limits the practical implementation of Ti aluminides is their low ductility at room temperature. Recently, a new class of TiAl alloys based on a modulated lath structure has been introduced that exhibit an excellent combination of ductility and strength. A key component in this alloy is the orthorhombic phase B19 that is attributed to alloying with high amounts of niobium. The driving forces and mechanisms that lead to the observed modulated structures involving the B19 phase are not fully understood yet. As a first step to a better understanding we present a study of the thermal stability range of the phases involved.

Surfactant modified zeolite carbon paste electrode (SMZ-CPE) as a nitrate selective electrode

A nitrate-selective electrode based on surfactant-modified zeolite (SMZ) particles into carbon paste was proposed (SMZ-CPE). The electrode was fully characterized in terms of composition, response time, ionic strength, thermal stability and usable pH range. The electrode containing 10% SMZ exhibited linear response range to nitrate species in the range of 1.00 × 10 −6 to 1.00 × 10 −3 M with a detection limit of 1.00 × 10 −6 M and a Nernstian slope of 59.4 ± 0.7 mV per decade of nitrate concentration. The response of the electrode to nitrate remains constant in the pH ranges of 3.5–9.8 and 1.7–10.5 for 1.00 × 10 −4 and 1.00 × 10 −2 M nitrate, respectively, and in presence of 1 × 10 −4 to 1 × 10 −3 M NaCl. The response of the electrode reaches to its equilibrium value within several seconds (10 s) after immersing the electrode in nitrate solution. Selectivity coefficients showed multivalent anions (such as arsenate, dichromate and sulfate) have higher interferences than monovalent anions (such as iodide, fluoride, bromide, chloride and thiocyanate). The electrode was used for determination of nitrate in an ammonium nitrate fertilizer sample, using direct potentiometry, and the satisfactory results were obtained. The electrode was also used for the potentiometric titration of nitrate. The validation of the obtained results in each case was proved by statistical “ t” and “ g” tests.

Application of surfactant modified zeolite carbon paste electrode (SMZ-CPE) towards potentiometric determination of sulfate

A sulfate-selective electrode based on surfactant modified zeolite (SMZ) particles into carbon paste has been proposed (SMZ-CPE). The electrode was fully characterized in terms of composition, response time, ionic strength range, thermal stability and usable pH range. The electrode containing 10% of the SMZ was exhibited linear response range to sulfate species in the range of 2.0 × 10 −6–3.1 × 10 −3 M with detection limit of 2.0 × 10 −6 M and Nernstian slope of 29.8 ± 0.8 mV per decade of sulfate concentration. The electrode response remains constant in the pH range of 4–10 and in the presence of 1 × 10 −4–2 × 10 −3 M NaNO 3. The response of the electrode reaches equilibrium within several second after immersing the electrode in sulfate solution. A successful application of sulfate determination sulfate in real sample of a pharmaceutical zinc sulfate capsule, using direct potentiometry, is presented. The electrode was also used for potentiometric titration of sulfate. The validation of the obtained results in each case was proved by statistical methods.

Proton mobility in complex [RhL 4Cl2]HSO4 · nH2SO4 · mH2O salts (L = Py, γ-picoline)

The method of deposition from solutions was used to synthesize [RhL4Cl2]HSO4 · nH2SO4 · mH2O complex salts (L = Py, γ-picoline), n ≈ 0.5−0.6, m ≈ 5−6. According to the data of X-ray phase analysis, the crystal structure of these salts is formed by layers of cations separated by layers consisting of anions molecules of sulfuric acid and water connected through a system of hydrogen bonds. Calorimetric methods were used to study phase transitions and the range of thermal stability of salts. The method of 1H NMR spectroscopy discovered that protons within the {HSO4− · nH2SO4 · mH2O} subsystem featured enhanced conductivity. Conductivity studies showed that trans-[RhL4Cl2]HSO4 · nH2SO4 · mH2O samples had high proton conductivity.

Effect of the nature of chiral fragment on mesomorphic properties of triphenylene ethers

A number of new 2,3,6,7,10,11-hexakis(heptyloxy)triphenylenes possessing a chiral substituent in position 1 of the triphenylene ring system and characterized by predictable mesomorphism were synthesized. The effect of the nature of the chiral fragment (dehydrocholic, lipoic, and d-tartaric acid residues) on the mesomorphic properties of triphenlylene ethers was studied. N-[2,3,6,7,10,11-hexakis(heptylozy)triphenylen-1-yl]amides derived from the above acids, unlike initial monomesomorphic amine, exhibit enantiotropic columnar polymorphism and give rise to helical columnar structure at reduced temperature. The newly synthesized amides are characterized by lower thermal stability and broader temperature range of the mesophase. Introduction of two chiral dehydrocholic acid fragments into the triphenylene core favors columnar (including chiral) mesomorphism.

Elucidating the Time Scale and Geometry of Phosphate and Phosphonate Rotation in Solid Acid Electrolytes Using Multinuclear NMR

The dynamics of the anions in a series of solid acid electrolyte materials have been determined using solid-state 31P CODEX NMR. The time scale and activation energy of the phosphate reorientation were quantified; however, the characterization proved to be nontrivial due to interactions with the quadrupolar 133Cs nuclei. The series of compounds studied included other known proton conductors, where the alkali cation was replaced systematically with Rb+, Tl+, or K+. The nuclear properties of the cations, together with the relative proton conductivities of these electrolyte analogues, allowed for a complete analysis of the interactions (both structure reorientations and spin dynamics) giving rise to the observed CODEX buildup curves. The high-temperature super-protonic transition, and the narrow range of thermal stability, limits the usefulness of cesium dihydrogen phosphate (CDP) in fuel cell applications. With the goal of achieving a broader range of thermal stability and enhanced proton dynamics, the phos...