Construction,calibration and testing of a micro-combustion calorimeter

An isoperibolic micro-combustion calorimeter was designed, built and set up in our laboratory, taking as base a 1107 Parr combustion bomb of 22 cm³ of volume. Taken into account the geometrical form of the bomb, it was designed and constructed a vessel and a submarine chamber in brass. All of the pieces of the calorimeter were chromium-plated to reduce heat loss by radiation. The calorimeter was calibrated by using pellets of standard benzoic acid (mass approximate of 40 mg) leading to the energy equivalent of ε(calor) = (1283.8 ± 0.6) J · K⁻¹. In order to test the calorimeter, combustion experiments of salicylic acid were performed leading to a value of combustion energy of Δ_cu^∘ = −(21,888.8 ± 10.9) J · g⁻¹, which agrees with the reported literature values. The combustion of piperonylic acid was carried out as a further test leading to a value of combustion energy of Δ_cu^∘ = −(20,215.9 ± 10.4) J · g⁻¹ in accordance with the reported literature value. The uncertainty of the calibration and the combustion of salicylic acid and piperonylic acid was 0.05%.     

Stress-induced ligand field distribution and consequent multi-mode spin crossover in FeII(phen)2(NCS)2 and FeII[HB(pz)3]2

Changes in the nature of spin crossover caused by mechanical stressing exerted on the crystalline powders were studied for Fe^II(phen)₂(NCS)₂ (phen = 1,10-phenanthroline) and Fe^II[HB(pz)₃]₂ (pz = pyrazol-1-yl) by means of a multi-component fitting of the temperature dependence of magnetic susceptibility. The analysis revealed the development and broadening of the ligand field distribution as a consequence of mechanical stressing. This was confirmed by the broadening of Mössbauer and far-infrared spectra.     

1,2,4-Triazole as a reference material for combustion calorimetry of N-containing compounds

A micro-bomb combustion calorimeter recently designed for samples of mass  ≈ 80 mg has been improved and tested with m -methoxybenzoic acid in order to verify the chemistry of the combustion process and the accuracy of the energy corrections involved in the analysis of results. From measurements in this calorimeter, the standard massic energy of combustion of 1,2,4-triazole was determined to beΔ_cu^o =  − (19200.3  ±  3.4)J · g ^− 1. Some new measurements with our macro combustion calorimeter confirm an earlier result from this laboratory of  − (19203.1  ±  1.2)J · g ^− 1. Determination of the purity by d.s.c. of 1,2,4-triazole purified some 10 years ago reveals that samples of this compound remained unchanged and suggest that 1,2,4-triazole be used as a possible reference material for organic compounds with a high content of nitrogen. From the experimental results with the micro-bomb combustion calorimeter, the actual and earlier results from macro-bomb combustion calorimetry, and those obtained in other laboratories, the standard massic energy of combustion of 1,2,4-triazole was deduced to beΔ_cu^o =  − (19202.5  ±  1.7)J · g ^− 1.     

Doping effect of nonmagnetic impurity on the spin-Peierls-like transition in the quasi-one-dimensional (quasi-1D) spin system of 1-(4′-nitrobenzyl)pyridinium bis(maleonitriledithiolato)nickelate

A nonmagnetic compound, [NO₂BzPy][Cu(mnt)₂] (mnt^2? = maleonitriledithiolate; NO₂BzPy⁺ = 1-(4′-nitrobenzyl)pyridinium), is isostructural with [NO₂BzPy][Ni(mnt)₂], which is a quasi-1D spin system and exhibits a spin-Peierls-like transition with J = 192 K in the gapless state and spin energy gap = 738 K in the dimerization state, respectively. Further, five nonmagnetic impurity doped compounds [NO₂BzPy][Cu_xNi_1?x(mnt)₂] (x = 0.04–0.74) were prepared, and their crystal structures as well as magnetic properties were investigated. The nonmagnetic doping causes the suppression of the spin transition with an average rate of 139(13) K/percentage of dopant concentration, and the transition collapse is estimated at around x > 0.5.     

Iron(II) spin transition 1,2,4-triazole chain compounds with novel inorganic fluorinated counteranions

New one-dimensional spin transition coordination polymers of formula [Fe(NH₂trz)₃](AF₆) · nH₂O (A = Ti, Zr, Sn; NH₂trz = 4-amino-1,2,4-triazole) have been synthesized in MeOH and EtOH media. These materials display an abrupt and hysteretic spin transition around 200 K as well as a reversible thermochromic effect on cooling. A preliminary evaluation of the lattice dynamics in the high-spin and low-spin states is presented.     

Nanoscale heterogeneities in radiation-cured diacrylate networks: Weakness or asset?

The crosslinking polymerization of multifunctional monomers is known to yield brittle matrices, therefore limiting the development of this technique for the production of high performance composite materials. Among the various possible causes of the brittleness, the spontaneous formation of nanoheterogeneities during radiation-initiated polymerization is supported by atomic force microscopy imaging and by calorimetric analyses. The controlled polymerization-induced phase separation of nanosized clusters of polyethersulfone was evaluated as a means for alleviating the inherent tendency of the diacrylate materials to fragile failure. Various homogeneous formulations including the aromatic diacrylate monomers, and polyethersulfone together with a compatible reactive diluent were prepared and polymerized by electron beam irradiation. The resulting toughened materials show optimized critical stress intensity factor (K_Ic) over 2 MPa m^0.5, whereas the K_Ic value is about 1 MPa m^0.5 for the unmodified reference resin.     

Spin crossover FeII complexes as templates for bimetallic oxalate-based 3D magnets

We present the synthesis and structural characterization of the salt [Fe(bpp)₂][MnCr(ox)₃]₂ · bpp · CH₃OH. It crystallizes in the monoclinic space group. This material contains an anionic [MnCr(ox)₃]⁻ 3D 10-gon ferromagnetic network, that orders below 3.0 K. The channels created by this architecture are filled by the spin crossover cations [Fe(bpp)₂]²⁺ (bpp = 2,6(bispyrazol-3-yl)pyridine), free ligand and solvent molecules. No spin transition has been observed at ambient pressure.     

Disparity in properties of 20-mol% Eu-doped ceria synthesized by different routes

Ce_0.8Eu_0.2O_2?δ was synthesized by conventional solid state route as well as wet chemical route (i.e. cation complexation, combustion method). The crystallite size obtained for cation complexation and combustion samples is 14 and 19 nm while their surface area is 11.70 and 29.63 m²g^?1 respectively. Cation complexation synthesized product lead to formation of agglomerates and hence the sintered sample showed porosity compared to combustion synthesized sample. However, despite high packing density the combustion synthesized sample showed lower grain boundary, total conductivity than cation complexation synthesized product due to the formation of siliceous film at the grain boundary.     

Determination of As in tobacco by using electrochemical hydride generation at a Nafion® solid polymer electrolyte cell hyphenated with atomic fluorescence spectrometry

In the present work, a novel solid polymer electrolyte hydride generation (SPE-HG) cell was developed. The home-made SPE-HG cell, mainly composed of three components (Nafion®117 membrane for separating and H⁺ exchanging, a soft graphite felt cathode and a Ti mesh modified by Ir anode), was employed for detecting As by coupling to atomic fluorescence spectrometry (AFS). The H⁺ generated by electrolysis of pure water in anode chamber transferred to cathode chamber through SPE, and immediately reacted with As^3 + to generate AsH₃. The relative mechanisms and operation conditions for hydride generation of As were investigated in detail. The developed cell employed water as an alternative of acid anolyte, with virtues of low-cost, more than 6 months lifetime and environment friendly compared with the conventional cell. Under the optimized conditions, the limit of determination of As^3 + for sample blank solution was 0.12 μg L^? 1, the RSD was 2.9% for 10 consecutive measurements of 5 μg L^? 1 As^3 + standard solution. The accuracy of the method was verified by the determination of As in the reference Tea (GBW07605) and the developed method was successfully applied to determine trace amounts of As in tobacco samples with recovery from 97% to 103%.     

Electrochemical performances of LaBaCuFeO5+x and LaBaCuCoO5+x as potential cathode materials for intermediate-temperature solid oxide fuel cells

Layered perovskite-structure oxides LaBaCuFeO_5+x (LBCFO) and LaBaCuCoO_5+x (LBCCO) were prepared and the electrical conductivity and electrochemical performance were investigated as potential cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The electrical conductivity of LBCCO is much higher than that of LBCFO. Area specific resistances of LBCFO and LBCCO cathode materials on Ce_0.8Sm_0.2O_1.9 (SDC) electrolyte are as low as 0.21 Ω cm² and 0.11 Ω cm² at 700 °C, respectively. The maximum power density of the LBCFO/SDC/Ni-SDC and LBCCO/SDC/Ni-SDC cells with 300 μm thick electrolytes attains 557 mW cm^?2 and 603 mW cm^?2 at 800 ^oC, respectively. Preliminary results demonstrated that the layered perovskite-structure oxides LBCFO and LBCCO are very promising cathode materials for application in IT-SOFCs.     

A feasibility study on oxidation state of arsenic in cut tobacco,mainstream cigarette smoke and cigarette ash by X-ray absorption spectroscopy

This work describes the application of synchrotron-based X-ray Absorption Near-Edge Structure spectroscopy to study the oxidation state of arsenic in cigarette mainstream smoke, cut tobacco and cigarette ash. The level of arsenic in the total particulate matter of the smoke is approximately 1 ppm for the standard research reference cigarette 2R4F and its replacement 3R4F. Smoke particulate samples collected by a conventional glass-fiber membrane (commercially known as Cambridge filter pad) and a jet-impaction method were analyzed and compared. In addition smoke particulate samples were aged either at ambient temperature or at 195 K. X-ray Absorption Near-Edge Structure spectroscopy results revealed that the cut tobacco powder and cigarette ash contained almost exclusively As^V. The smoke particulate samples however contained a mixture of As^III and As^V. The As^V in the smoke particulate was reduced to As^III upon aging. Stabilizing the smoke particulate matter at 195 K by solid CO₂ slowed down this aging reaction and revealed a higher percentage of As^V. This behavior is consistent with the redox properties of the arsenic species and the smoke particulate matrix.     

Spin density distribution in oxamato-type transition metal complexes

The spin density distribution of the paramagnetic [ⁿBu₄N]₂[Cu(dana)] dana = N,N′-(naphthalene-2,3-diyl)-bis(oxamato) has been derived from angular dependent electron paramagnetic resonance measurements at room temperature. The results indicate a noticeable spin density transfer from the central metal to the coordinated N and O atoms. Quantum chemical studies using density functional theory reinforce the results.     

Bi2O3 deposited on highly ordered mesoporous carbon for supercapacitors

A simple route has been employed to prepare nanosized Bi₂O₃ deposited on highly ordered mesoporous carbon. The electrochemical measurements reveal that, by loading only 10% Bi₂O₃ on the mesoporous carbon, the specific capacitance of the composite is improved by 62%, with the maximum value reaching 232 F g^?1 at a sweep rate of 5 mV s^?1. The specific capacitance of Bi₂O₃ is calculated and reaches 1305 F g^?1 at 1 mV s^?1. It is found that the mass transfer in the framework of the crystalline oxide is still difficult in spite of its nanosize, as evidenced by the decline of the specific capacitance of the Bi₂O₃ with the increase of the sweep rate. The cyclic life of composite materials is also measured and the capacitance only declines 21% after 1000 cycles.     

Ab initio and XPS studies of pyrite (1 0 0) surface states

Ab initio quantum chemical modelling (GGA, CASTEP and B3LYP, CRYSTAL03) is used to predict differences in electronic structure between the (1 0 0) surface and bulk of pyrite. Experimental X-ray photoelectron spectroscopic (XPS) data for the S 2p core lines show the presence of two types of S surface states: surface S²⁻ monomers at a S 2p_3/2 binding energy (BE) of 161.2 eV, and (S–S)²⁻ surface dimer states at a S 2p_3/2 BE of 162.0 eV, compared to the S 2p_3/2 BE of bulk pyrite at 162.7 eV. The Fe 2p surface XPS displays several multiplets (implying high spin configuration) at higher BE than the bulk Fe 2p signal, which can be ascribed to surface state contributions. The quantum chemical simulation predicts an S 2p core level shift of 0.69 eV between the S bulk and S surface dimers, in good agreement with the 0.6 eV found in XPS measurements. A Mulliken population analysis confirms the conjectured charge distribution on the surface, which leads to the two different S surface states, as well as the surface high spin configuration responsible for the high BE Fe multiplets. Evidence for surface Fe²⁺ and Fe³⁺ surface states can be seen in the Fe projected valence band density of states, confirming the interpretation of the photoemission spectra.     

Electrochemical characterization of vertical arrays of tin nanowires grown on silicon substrates as anode materials for lithium rechargeable microbatteries

Vertical arrays of one-dimensional tin nanowires on silicon dioxide (SiO₂)/silicon (Si) substrates have been developed as anode materials for lithium rechargeable microbatteries. The process is complementary metal-oxide-semiconductor (CMOS) compatible for fabricating on-chip microbatteries. Nanoporous anodized aluminum oxide (AAO) templates integrated on SiO₂/Si substrates were employed for fabrication of tin nanowires resulting in high surface area of anodes. The microstructure of these nanowire arrays was investigated by scanning electron microscopy and X-ray diffraction. The electrochemical tests showed that the discharge capacity of about 400 mA h g⁻¹ could be maintained after 15 cycles at the high discharge/charge rate of 4200 mA g⁻¹.     

Na4Co2.4Mn0.3Ni0.3(PO4)2P2O7: High potential and high capacity electrode material for sodium-ion batteries

Na₄Co_2.4Mn_0.3Ni_0.3(PO₄)₂P₂O₇ has been evaluated as a positive electrode for sodium-ion batteries. The novel material has two redox couples around 4.2 V and 4.6 V and can deliver the high capacity of ca. 103 mAh g^− 1 at the high current density of 850 mA g^− 1 (5 C). X-ray absorption spectroscopy (XAS) results show that the redox reactions of Co, Mn and Ni ions proceed simultaneously in the charge process and it is indicated the novel material provide high mixed potential by the redox reactions of Co, Mn and Ni ions. These findings suggest that the derivatives of Na₄Co₃(PO₄)₂P₂O₇ should be employed as high potential and high capacity electrode materials.     

Preparation of monodisperse carbon nanospheres for electrochemical capacitors

The efficiently hydrothermal route using sucrose without any catalysts is employed to prepare the uniform carbon spheres. The monodisperse 100–150 nm carbon spheres are obtained with the activation treatment in molten KOH. The carbon spheres are characterized by transmission electron microscope, X-ray diffraction, N₂ adsorption, Raman spectroscopy and electrochemical techniques. The relationships of specific capacitance and surface properties of carbon spheres are investigated. A single electrode of carbon nanosphere materials performs excellent specific capacitance (328 F g⁻¹), area capacitance (19.2 μF cm⁻²) and volumetric capacitance (383 F cm⁻³).     

Anisotropic exchange in a tetranuclear CoII complex

Very high-frequency (50–715 GHz) electron paramagnetic resonance (EPR) studies of the tetranuclear Co^II complex [Co(hmp)(dmb)Cl]₄ (1), where dmb is 3,3-dimethyl-1-butanol and hmp^? is the monoanion of 2-hydroxy-methylpyridine, reveal the presence of significant zero-field-splitting (ZFS) within the ground state spin multiplet. Meanwhile, low-temperature hysteresis measurements of 1 (and related Co^II₄ complexes) provide evidence for slow magnetization relaxation, suggesting that it could be a single-molecule magnet (SMM). However, EPR studies of a Zn analog of 1, doped with a small quantity of Co^II, show the ground state of the Co^II ions to be an effective spin S′ = 1/2 Kramers doublet with a highly anisotropic g-tensor. The question then arises as to the origin of the ZFS within the ground state spin multiplet of 1, as well as the slow magnetization relaxation. Here, we consider the effect of anisotropic exchange interactions between the effective spin S′ = 1/2 Kramers ions within the tetranuclear complex. Such exchange anisotropy arises naturally when one treats the ground state of high-spin Co^II as a Kramers doublet. Our model provides an explanation for the ZFS in the ground state observed via EPR, and can also account for qualitative features observed through magnetic measurements.     

Low-temperature heat capacity and standard molar enthalpy of formation of 9-fluorenemethanol (C14H12O)

Low-temperature heat capacities of the 9-fluorenemethanol (C₁₄H₁₂O) have been precisely measured with a small sample automatic adiabatic calorimeter over the temperature range between T=78 K and T=390 K. The solid–liquid phase transition of the compound has been observed to be T_fus=(376.567±0.012) K from the heat-capacity measurements. The molar enthalpy and entropy of the melting of the substance were determined to be Δ_fusH_m=(26.273±0.013) kJ · mol⁻¹ and Δ_fusS_m=(69.770±0.035) J · K⁻¹ · mol⁻¹. The experimental values of molar heat capacities in solid and liquid regions have been fitted to two polynomial equations by the least squares method. The constant-volume energy and standard molar enthalpy of combustion of the compound have been determined, Δ_cU(C₁₄H₁₂O, s)=−(7125.56 ± 4.62) kJ · mol⁻¹ and Δ_cH_m^∘(C₁₄H₁₂O, s)=−(7131.76 ± 4.62) kJ · mol⁻¹, by means of a homemade precision oxygen-bomb combustion calorimeter at T=(298.15±0.001) K. The standard molar enthalpy of formation of the compound has been derived, Δ_fH_m^∘(C₁₄H₁₂O,s)=−(92.36 ± 0.97) kJ · mol⁻¹, from the standard molar enthalpy of combustion of the compound in combination with other auxiliary thermodynamic quantities through a Hess thermochemical cycle.