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1.
Highly crystalline one-dimensional (1D) α-MnO2 nanostructures were synthesized by a hydrothermal method. All samples were characterized by X-ray diffraction, transmission electron microscope, thermogravimetric and differential scanning calorimeter, and infrared spectroscopy. During the formation reactions, the tunnel structure of 1D α-MnO2 was simultaneously modified by NH4+ species and water molecules. The amount of NH4+ species that were trapped in the tunnels is almost independent on the reaction temperature, while the total water content increased with the reaction temperature. The average diameter of α-MnO2 nanorods increased from 9.2 to 16.5 nm when the reaction temperature increased from 140 to 220 °C. 1D α-MnO2 was destabilized by a subsequent high-temperature treatment in air, which is accompanied by a structural transformation to 1D Mn2O3 of a cubic structure. At low temperatures, all 1D α-MnO2 nanorods showed two magnetic transitions that were characterized by a decreased Néel temperature with rod diameter reduction. According to the effective magnetic moments experimentally measured, Mn ions presented in the nanorods were determined to be in a mixed valency of high spin state Mn4+/Mn3+.  相似文献   

2.
Two pure strontium borates SrB2O4·4H2O and SrB2O4 have been synthesized and characterized by means of chemical analysis and XRD, FT-IR, DTA-TG techniques. The molar enthalpies of solution of SrB2O4·4H2O and SrB2O4 in 1 mol dm−3 HCl(aq) were measured to be −(9.92 ± 0.20) kJ mol−1 and −(81.27 ± 0.30) kJ mol−1, respectively. The molar enthalpy of solution of Sr(OH)2·8H2O in (HCl + H3BO3)(aq) were determined to be −(51.69 ± 0.15) kJ mol−1. With the use of the enthalpy of solution of H3BO3 in 1 mol dm−3 HCl(aq), and the standard molar enthalpies of formation for Sr(OH)2·8H2O(s), H3BO3(s), and H2O(l), the standard molar enthalpies of formation of −(3253.1 ± 1.7) kJ mol−1 for SrB2O4·4H2O, and of −(2038.4 ± 1.7) kJ mol−1 for SrB2O4 were obtained.  相似文献   

3.
The enthalpies of solution of NaRb[B4O5(OH)4]·4H2O in approximately 1 mol dm−3 aqueous hydrochloric acid and of RbCl in aqueous (hydrochloric acid + boric acid + sodium chloride) were determined. From these results and the enthalpy of solution of H3BO3 in approximately 1 mol dm−3 HCl(aq) and of sodium chloride in aqueous (hydrochloric acid + boric acid), the standard molar enthalpy of formation of −(5128.02 ± 1.94) kJ mol−1 for NaRb[B4O5(OH)4]·4H2O was obtained from the standard molar enthalpies of formation of NaCl(s), RbCl(s), H3BO3(s) and H2O(l). The standard molar entropy of formation of NaRb[B4O5(OH)4]·4H2O was calculated from the Gibbs free energy of formation of NaRb[B4O5(OH)4]·4H2O computed from a group contribution method.  相似文献   

4.
A comprehensive thermodynamic model based on the electrolyte NRTL (eNRTL) activity coefficient equation is developed for the NaCl + H2O binary, the Na2SO4 + H2O binary and the NaCl + Na2SO4 + H2O ternary. The NRTL binary parameters for pairs H2O-(Na+, Cl) and H2O-(Na+, SO42−), and the aqueous phase infinite dilution heat capacity parameters for ions Cl and SO42− are regressed from fitting experimental data on mean ionic activity coefficient, heat capacity, liquid enthalpy and dissolution enthalpy for the NaCl + H2O binary and the Na2SO4 + H2O binary with electrolyte concentrations up to saturation and temperature up to 473.15 K. The Gibbs energy of formation, enthalpy of formation and heat capacity parameters for solids NaCl(s), NaCl·2H2O(s), Na2SO4(s) and Na2SO4·10H2O(s) are obtained by fitting experimental data on solubilities of NaCl and Na2SO4 in water. The NRTL binary parameters for the (Na+, Cl)-(Na+, SO42−) pair are regressed from fitting experimental data on dissolution enthalpies and solubilities for the NaCl + Na2SO4 + H2O ternary.  相似文献   

5.
Single-crystalline nanorods of γ-MnOOH (manganite) phase with diameters of 120 nm and lengths of 1100 nm have been prepared using a new cluster growth route under low-temperature hydrothermal conditions starting from [Mn12O12(CH3COO)16(H2O)4]·2CH3COOH·4H2O or [Mn12O12(C2H5COO)16(H2O)3]·4H2O without any catalyst or template agents. The so-obtained nanorods were studied by X-ray diffraction (XRD), infrared (IR) spectroscopy, Raman spectroscopy and high resolution transmission electron microscopy (HRTEM). Their thermal conversion opens an access to Mn3O4 (hausmannite) and β-MnO2 (pyrolusite) nanorods, respectively, under argon or air atmosphere. A coercive field of 12.4 kOe was obtained for the Mn3O4 nanorods.  相似文献   

6.
A pure calcium borate Ca2[B2O4(OH)2]·0.5H2O has been synthesized under hydrothermal condition and characterized by XRD, FT-IR and TG as well as by chemical analysis. The molar enthalpy of solution of Ca2[B2O4(OH)2]·0.5H2O in HC1·54.582H2O was determined. From a combination of this result with measured enthalpies of solution of H3BO3 in HC1·54.561H2O and of CaO in (HCl + H3BO3) solution, together with the standard molar enthalpies of formation of CaO(s), H3BO3(s) and H2O(l), the standard molar enthalpy of formation of −(3172.5 ± 2.5) kJ mol−1 of Ca2[B2O4(OH)2]·0.5H2O was obtained.  相似文献   

7.
Subsolidus phase relations have been determined for the Bi-Mn-Nb-O system in air (750-900 °C). Phases containing Mn2+, Mn3+, and Mn4+ were all observed. Ternary compound formation was limited to pyrochlore (A2B2O6O′), which formed a substantial solid solution region at Bi-deficient stoichiometries (relative to Bi2(Mn,Nb)2O7) suggesting that ≈14-30% of the A-sites are occupied by Mn (likely Mn2+). X-ray powder diffraction data confirmed that all Bi-Mn-Nb-O pyrochlores form with structural displacements, as found for the analogous pyrochlores with Mn replaced by Zn, Fe, or Co. A structural refinement of the pyrochlore 0.4000:0.3000:0.3000 Bi2O3:Mn2Ox:Nb2O5 using neutron powder diffraction data is reported with the A and O′ atoms displaced (0.36 and 0.33 Å, respectively) from ideal positions to 96g sites, and with Mn2+ on A-sites and Mn3+ on B-sites (Bi1.6Mn2+0.4(Mn3+0.8Nb1.2)O7, (?227), a=10.478(1) Å); evidence of A or O′ vacancies was not found. The displacive disorder is crystallographically analogous to that reported for Bi1.5Zn0.92Nb1.5O6.92, which has a similar concentration of small B-type ions on the A-sites. EELS spectra for this pyrochlore were consistent with an Mn oxidation between 2+ and 3+. Bi-Mn-Nb-O pyrochlores exhibited overall paramagnetic behavior with negative Curie-Weiss temperature intercepts, slight superparamagnetic effects, and depressed observed moments compared to high-spin, spin-only values. At 300 K and 1 MHz the relative dielectric permittivity of Bi1.600Mn1.200Nb1.200O7 was ≈128 with tan δ=0.05; however, at lower frequencies the sample was conductive which is consistent with the presence of mixed-valent Mn. Low-temperature dielectric relaxation such as that observed for Bi1.5Zn0.92Nb1.5O6.92 and other bismuth-based pyrochlores was not observed. Bi-Mn-Nb-O pyrochlores were readily obtained as single crystals and also as textured thin films using pulsed laser deposition.  相似文献   

8.
Precipitated γ-alumina support was decorated with Mn(acac)3 by incipient wetness impregnation with toluene solutions containing Mn(acac)3 in amount equivalent to loading of 0.35, 0.74, 1.38, 2.38 and 3.50 Mn(acac)3 moleculs per nm2 of the support. In order to evaluate the mechanism of Mn(acac)3 interaction with the surface of γ-alumina support and subsequent transformations of the supported Mn(acac)3 species, oxidative thermolysis of Mn(acac)3/Al2O3 samples in air was studied by diffuse reflectance FTIR, thermogravimetric analysis (TG/DTG), differential thermal analysis (DTA) and XRD. It has been found out that decoration of γ-Al2O3 support with Mn(acac)3 results in the formation of surface bound Mn(acac)3−x species when Mn(acac)3 loading does not exceed 1.38 Mn(acac)3/nm2. At higher Mn(acac)3 loading the formation of the supported bulk-like Mn(acac)3 species also occurs. The interaction of Mn(acac)3 molecules with the support surface occurs via substitution of acetylacetonate ligand(s) with the oxygen atom of surface hydroxyl group(s) accompanied by elimination of acetylacetone molecules. The evolved acetylacetone reacts with the alumina surface that results in the formation of surface Al(acac)3−x species. The oxidative thermolysis of Mn(acac)3−x species on the surface of γ-alumina proceeds via partial elimination of acetylacetonate ligands and partial oxidation of the remaining ligands without destruction of their cyclic structure within 425-550 K. The complete oxidative destruction of acetylacetonate ligands takes place within 600-700 K and results in the formation of manganese oxide species on the alumina surface. The dispersed surface manganese oxide species originate upon the oxidative thermolysis of the surface bound Mn(acac)3−x species while crystalline Mn2O3 phase results from the supported bulk-like Mn(acac)3 species.  相似文献   

9.
Yongjin Zou  Lixian Sun  Fen Xu 《Talanta》2007,72(2):437-442
A Prussian Blue (PB)/polyaniline (PANI)/multi-walled carbon nanotubes (MWNTs) composite film was fabricated by step-by-step electrodeposition on glassy carbon electrode (GCE). The electrode prepared exhibits enhanced electrocatalytic behavior and good stability for detection of H2O2 at an applied potential of 0.0 V. The effects of MWNTs thickness, electrodeposition time of PANI and rotating rate on the current response of the composite modified electrode toward H2O2 were optimized to obtain the maximal sensitivity. A linear range from 8 × 10−9 to 5 × 10−6 M for H2O2 detection has been observed at the PB/PANI/MWNTs modified GCE with a correlation coefficient of 0.997. The detection limit is 5 × 10−9 M on signal-to-noise ratio of 3. To the best of our knowledge, this is the lowest detection limit for H2O2 detection. The electrode also shows high sensitivity (526.43 μA μM−1 cm−2) for H2O2 detection which is more than three orders of magnitude higher than the reported.  相似文献   

10.
The Mn5−xCox(HPO4)2(PO4)2(H2O)4 (x=1.25, 2, 2.5, 3) finite solid solution has been synthesized by mild hydrothermal conditions under autogeneous pressure. The phases crystallize in the C2/c space group with Z=4, belonging to the monoclinic system. The unit-cell parameters obtained from single crystal X-ray diffraction are: a=17.525(1), b=9.0535(6), c=9.4517(7) Å, β=96.633(5) ° being R1=0.0436, wR2=0.0454 for Mn75Co25; a=17.444(2), b=9.0093(9), c=9.400(1) Å, β=96.76(1) ° being R1=0.0381, wR2=0.0490 for Mn60Co40; a=17.433(2), b=8.9989(9), c=9.405(1) Å, β=96.662(9) ° being R1=0.0438, wR2=0.0515 for Mn50Co50 and a=17.4257(9), b=8.9869(5), c=9.3935(5) Å, β=96.685(4) ° being R1=0.0296, wR2=0.0460 for Mn40Co60. The structure consists of a three dimensional network formed by octahedral pentameric entities (Mn,Co)5O16(H2O)6 sharing vertices with the (PO4)3− and (HPO4)2− tetrahedra. The limit of thermal stability of these compounds is, approximately, 165 °C, near to this mean temperature the phases loose their water content in two successive steps. IR spectra show the characteristic bands of the water molecules and the phosphate and hydrogen-phosphate oxoanions. The diffuse reflectance spectra are consistent with the presence of MO6 octahedra environments in slightly distorted octahedral geometry, except for the M(3)O6 octahedron which presents a remarkable distortion and so a higher Dq parameter. The mean value for the Dq and B-Racah parameter for the M(1),(2)O6 octahedra is 685 and 850 cm−1, respectively. These parameters for the most distorted M(3)O6 polyhedron are 825 and 880 cm−1, respectively. The four phases exhibit antiferromagnetic couplings as the major magnetic interactions. However, a small spin canting phenomenon is observed at low temperatures for the two phases with major content in the anisotropic-Co(II) cation.  相似文献   

11.
Cathode materials Li[CoxMn1−x]O2 for lithium secondary batteries have been prepared by a new route—precursor method of layered double hydroxides (LDHs). In situ high-temperature X-ray diffraction (HT-XRD) and thermogravimetric analysis coupled with mass spectrometry (TG-MS) were used to monitor the structural transformation during the reaction of CoMn LDHs and LiOH·H2O: firstly the layered structure of LDHs transformed to an intermediate phase with spinel structure; then the distortion of the structure occurred with the intercalation of Li+ into the lattice, resulting in the formation of layered Li[CoxMn1−x]O2 with α-NaFeO2 structure. Extended X-ray absorption fine structure (EXAFS) data showed that the Co-O bonding length and the coordination number of Co were close to those of Mn in Li[CoxMn1−x]O2, which indicates that the local environments of the transitional metals are rather similar. X-ray photoelectron spectroscopy (XPS) was used to measure the oxidation state of Co and Mn. The influences of Co/Mn ratio on both the structure and electrochemical property of Li[CoxMn1−x]O2 have been investigated by XRD and electrochemical tests. It has been found that the products synthesized by the precursor method demonstrated a rather stable cycling behavior, with a reversible capacity of 122.5 mAh g−1 for the layered material Li[Co0.80Mn0.20]O2.  相似文献   

12.
Traditionally the monitoring of atmospheric pollutants is aimed at managing accidents and short-term actions for the protection of human health on local and regional scales. These monitoring networks required continuous measurements with high time resolution, involving costly equipment, operation and maintenance. More recent simulations with mathematical models and scenario-building on regional, continental and global scales, as well as studies of environmental personal exposure are demanding three main types of monitoring design, where need for special resolution surpasses the one of temporal resolution: remote places, where no electric power nor trained human resources are available; validation of dispersion simulation by mathematical modeling on regional to larger scales; indoor measurements where people are acting under noise restriction such as residences, school and hospitals. To meet these demands environmental passive samplers for atmospheric gaseous pollutants have been developed and applied for different situations and environments of Brazil. Passive samplers were developed based on molecular diffusion of gas through a static layer of air with fixed filters impregnated with a specific solution for SO2, NO2, O3 and H2S and used in the following situations: in remote forest area, urban areas with different characteristics - near the sea, with clean ocean air masses coming in and in areas under direct industrial influence. The passive samplers showed good performance when exposed to different types of areas and during different periods: accuracy of measurements, based on standard deviation, were within the recommended limit by the European Union of ± 25% for this type of device and precision below the maximum of 20% cited in the literature, with variation of 2.0 to 16% in the case of these work. The passive devices were able of measuring concentrations very low as those found in the Amazon region (0.58 ± 0.05 µg m− 3 SO2 and 1.10 ± 0.07 µg m− 3 NO2) and higher concentrations in industrial areas (20.0 ± 1.3 µg m− 3 SO2 e 21.0 ± 1.3 µg m− 3 NO2).  相似文献   

13.
The layered LiNi1/3Co1/3Mn1/3O2−zFz (0 ≤ z ≤ 0.12) cathode materials were synthesized from oxalate precursors by a simple self-propagating solid-state metathesis method with the help of the ball milling and the following calcination. Li(Ac)·2H2O, Ni(Ac)2·4H2O, Co(Ac)2·4H2O, Mn(Ac)2·4H2O(Ac = acetate), LiF and excess H2C2O4·2H2O were used as starting materials without any solvent. The structural and electrochemical properties of the prepared LiNi1/3Co1/3Mn1/3O2−zFz were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and electrochemical measurements, respectively. The XRD patterns indicate that all samples have a typical hexagonal structure with a space group of . The FESEM images show that the primary particle size of LiNi1/3Co1/3Mn1/3O2−zFz gradually increases with increasing fluorine content. Though the fluorine-substituted LiNi1/3Co1/3Mn1/3O2−zFz have lower initial discharge capacities, a small amount of fluorine-substituted LiNi1/3Co1/3Mn1/3O2−zFz (z = 0.04 and 0.08) exhibit excellent cycling stability and rate capability compared to fluorine-free LiNi1/3Co1/3Mn1/3O2.  相似文献   

14.
A suberato-pillared Mn(II) coordination polymer Mn2(H2O)(C8H12O4)2 was hydrothermally synthesized at 170°C for 3 days and characterized by single-crystal X-ray diffraction. Crystal data: monoclinic, C2/c, Z=4, a=26.544(5), b=7.617(2), c=9.187(2) Å, β=105.38(2)°, V=1791.0(7) Å3, R1=0.064 and wR2=0.162. The compound shows a layered structure consisting of inorganic Mn oxygen polyhedral layers and organic regions. The inorganic Mn oxygen layers are generated from Mn2O10 bioctahedral units, which share corners with neighbors to form zigzag chains along the [001] direction and are, along the [010] direction, further connected by carboxylate groups of the suberato ligands and hydrogen bonds. The magnetic studies indicated that the compound becomes antiferromagnetic at low temperatures with TNéel=12 K and follows Curie-Weiss law χm(T+22.429)= 4.48 cm3 mol−1 K between 25 and 300 K. Upon heating in Ar stream, Mn2(H2O)(C8H12O4)2 decomposes in three steps.  相似文献   

15.
A pure hydrated potassium borate K2B5O8(OH)·2H2O has been synthesized under mild hydrothermal conditions and characterized by single-crystal X-ray diffraction, XRD, FT-IR, Raman spectra and DTA-TG. The crystal structure consists of two K-O polyhedra and [B5O8(OH)]2− polyborate anion. The enthalpy of formation was determined to be −4772.6 ± 4.0 kJ mol−1 by solution calorimetry.  相似文献   

16.
A new magnesium borate MgO·3B2O3·3.5H2O has been synthesized by the method of phase transformation of double salt and characterized by XRD, IR and Raman spectroscopy as well as by TG. The structural formula of this compound was Mg[B6O9(OH)2]·2.5H2O. The enthalpy of solution of MgO·3B2O3·3.5H2O in approximately 1 mol dm−3 HCl was determined. With the incorporation of the standard molar enthalpies of formation of MgO(s), H3BO3(s), and H2O(l), the standard molar enthalpy of formation of −(5595.02±4.85) kJ mol−1 of MgO·3B2O33.5H2O was obtained. Thermodynamic properties of this compound was also calculated by group contribution method.  相似文献   

17.
Using an on-line solution-reaction isoperibol calorimeter, the standard molar enthalpies of reaction for the general thermochemical reaction: LnCl3·6H2O(s) + 2C9H7NO(s) + CH3COONa(s) = Ln(C9H6NO)2(C2H3O2)(s) + NaCl(s) + 2HCl(g) + 6H2O(l) (Ln: Nd, Sm), were determined at T=298.15 K, as  kJ mol−l, respectively. From the mentioned standard molar enthalpies of reaction and other auxiliary thermodynamic quantities, the standard molar enthalpies of formation of Ln(C9H6NO)2(C2H3O2)(s) (Ln: Nd, Sm), at T=298.15 K, have been derived to be: −(1494.7±3.3) and −(1501.5±3.4) kJ mol−l, respectively.  相似文献   

18.
The present work evaluates the influence of vessel cooling simultaneously to microwave-assisted digestion performed in a closed system with diluted HNO3 under O2 pressure. The effect of outside air flow-rates (60–190 m3 h−1) used for cooling of digestion vessels was evaluated. An improvement in digestion efficiency caused by the reduction of HNO3 partial pressure was observed when using higher air flow-rate (190 m3 h−1), decreasing the residual carbon content for whole milk powder from 21.7 to 9.3% (lowest and highest air flow-rate, respectively). The use of high air flow-rate outside the digestion vessel resulted in a higher temperature gradient between liquid and gas phases inside the digestion vessel and improved the efficiency of sample digestion. Since a more pronounced temperature gradient was obtained, it contributed for increasing the condensation rate and thus allowed a reduction in the HNO3 partial pressure of the digestion vessel, which improved the regeneration of HNO3. An air flow-rate of 190 m3 h−1 was selected for digestion of animal fat, bovine liver, ground soybean, non fat milk powder, oregano leaves, potato starch and whole milk powder samples, and a standard reference material of apple leaves (NIST 1515), bovine liver (NIST 1577) and whole milk powder (NIST 8435) for further metals determination by inductively coupled plasma atomic emission spectroscopy (ICP-OES). Results were in agreement with certified values and no interferences caused by matrix effects during the determination step were observed.  相似文献   

19.
Three mixed-metal single-molecule magnets containing [Mn8Fe4O12]16+ cores are synthesized and characterized. The reaction of FeCl2·4H2O with KMnO4 and RCOOH (R = CH2Cl, CH2Br) in H2O gives [Mn8Fe4O12(O2CR)16(H2O)4] (R = CH2Cl (1), CH2Br (2)) in yields of 43% and 40%, respectively. Treatment of complex 1 with an excess of CHCl2COOH in CH2Cl2 gives [Mn8Fe4O12(O2CCHCl2)16(H2O)4]·CH2Cl2·10H2O (3·CH2Cl2·10H2O) in a yield of 83%. The X-ray structure analysis reveals that all three complexes consist of a trapped-valence dodecanuclear core comprising 4MnIII, 4FeIII, and 4MnIV ions. DC magnetic susceptibility and magnetization measurements indicate that all three complexes exhibit intramolecular antiferromagnetic interaction, resulting in an S = 4 ground state. In addition, frequency-dependent out-of-phase AC magnetic susceptibility signals at low temperature for complexes 1, 2, and 3 are indicative of their single-molecule magnetism behavior.  相似文献   

20.
The thermal conductivity and heat capacity of high-purity single crystals of yttrium titanate, Y2Ti2O7, have been determined over the temperature range 2 K?T?300 K. The experimental heat capacity is in very good agreement with an analysis based on three acoustic modes per unit cell (with the Debye characteristic temperature, θD, of ca. 970 K) and an assignment of the remaining 63 optic modes, as well as a correction for CpCv. From the integrated heat capacity data, the enthalpy and entropy relative to absolute zero, are, respectively, H(T=298.15 K)−H0=34.69 kJ mol−1 and S(T=298.15 K)−S0=211.2 J K−1 mol−1. The thermal conductivity shows a peak at ca. θD/50, characteristic of a highly purified crystal in which the phonon mean free path is about 10 μm in the defect/boundary low-temperature limit. The room-temperature thermal conductivity of Y2Ti2O7 is 2.8 W m−1 K−1, close to the calculated theoretical thermal conductivity, κmin, for fully coupled phonons at high temperatures.  相似文献   

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