共查询到20条相似文献,搜索用时 15 毫秒
1.
Quanlong Li Xiaoxia Ma Dongxing Yuan Jinsheng Chen 《Journal of chromatography. A》2010,1217(15):2191-2196
A solid-phase microextraction (SPME) fiber coated with single walled carbon nanotubes (SWCNTs) was prepared by electrophoretic deposition and treated at 500 °C in H2 stream. In order to evaluate the characteristics of the obtained fiber, it was applied in the headspace solid-phase microextraction (HS-SPME) of benzene, toluene, ethylbenzene and xylenes (BTEX) from water sample and quantification by gas chromatography with flame ionization detection (GC-FID). The results indicated that the thermal treatment with H2 enhanced the extraction of the SWCNTs fiber for BTEX significantly. Thermal stability and durability of the fiber were also investigated, showing excellent stability up to 350 °C and life time over 120 times. In the comparison with the commercial CAR–PDMS fiber, the SWCNTs fiber showed similar and higher extraction efficiencies for BTEX. Under the optimized conditions, the linearity, LODs (S/N = 3) and LOQs (S/N = 10) of the method based on the SWCNTs fiber were 0.5–50.0, 0.005–0.026 and 0.017–0.088 μg/L, respectively. Repeatability for one fiber (n = 3) was in the range of 1.5–5.6% and fiber-to-fiber reproducibility (n = 3) was in the range of 4.2–8.3%. The proposed method was successfully applied in the analysis of BTEX compounds in seawater, tap water and wastewater from a paint plant. 相似文献
2.
Antonio Gerson Bernardo da Cruz 《Thermochimica Acta》2006,443(2):217-224
Thermal properties and thermal decompositions of [NEt4]2[M(dmit)2] (M = Ni(II), Pd(II), dmit = 1,3-dithiole-2-thione-4,5-dithiolate) have been studied by thermogravimetry (TG). The TG analysis has shown that the complexes are thermally stable up to 460 K and the decomposition of the complexes occurs in three consecutive stages up to 873 K. A thermal stability scale for [M(dmit)2]n− anions was based on the thermal properties. Kinetics parameters, such as activation energy, Ea, and kinetic apparent pre-exponential factor, ln Aapp, have been calculated from the thermogravimetric data at heating rates of 10, 15, 20 and 25 K/min involving differential (Friedman's equation) and integral (Flynn-Wall-Ozawa's equation) methods. 相似文献
3.
Cezar A. Bizzi Juliano S. BarinEdivaldo E. Garcia Joaquim A. NóbregaValderi L. Dressler Erico M.M. Flores 《Spectrochimica Acta Part B: Atomic Spectroscopy》2011,66(5):394-398
The feasibility of using diluted HNO3 solutions under oxygen pressure for decomposition of whole and non-fat milk powders and whey powder samples has been evaluated. Digestion efficiency was evaluated by determining the carbon content in solution (digests) and the determination of Ca, Cd, Cu, Fe, K, Mg, Mn, Mo, Na, Pb and Zn was performed by inductively coupled plasma optical emission spectrometry and Hg by chemical vapor generation coupled to inductively coupled plasma mass spectrometry. Samples (up to 500 mg) were digested using HNO3 solutions (1 to 14 mol L− 1) and the effect of oxygen pressure was evaluated between 2.5 and 20 bar. It was possible to perform the digestion of 500 mg of milk powder using 2 mol L− 1 HNO3 with oxygen pressure ranging from 7.5 to 20 bar with resultant carbon content in digests lower than 1700 mg L− 1. Using optimized conditions, less than 0.86 mL of concentrated nitric acid (14 mol L− 1) was enough to digest 500 mg of sample. The accuracy was evaluated by determination of metal concentrations in certified reference materials, which presented an agreement better than 95% (Student's t test, P < 0.05) for all the analytes. 相似文献
4.
A novel macroporous silica-based chelating polymeric composite, DtDo/SiO2-P, was synthesized by molecular modification of 4,4′,(5′)-di-(tert-butylcyclohexano)-18-crown-6 (DtBuCH18C6) with a long carbon chain organic compound 1-dodecanol. It was performed through impregnation and immobilization of DtBuCH18C6 and 1-dodecanol molecules into the pores of the SiO2-P particles. The adsorption of a few fission and non-fission product elements Sr(II), Ba(II), Cs(I), Ru(III), Mo(VI), Na(I), K(I), Pd(II), La(III), and Y(III) onto DtDo/SiO2-P was investigated at 323 K. The effects of contact time and the HNO3 concentration in a range of 0.1-4.0 M were investigated. It was found that at the optimum concentration of 2.0 M HNO3, DtDo/SiO2-P exhibited strong adsorption ability and excellent selectivity for Sr(II) over all of the tested elements, which showed very weak or almost no adsorption except Ba(II). The bleeding of total organic carbon (TOC) from DtDo/SiO2-P was evaluated. The quantity of TOC in aqueous phase increased with an increase in HNO3 concentration in terms of a linear equation [TOC] = 35.82[HNO3] + 115.5 with a correlation coefficient of 0.9751. The TOC content leaked from DtDo/SiO2-P modified by 1-dodecanol, 119.0-269.3 ppm, in the range of 1.0-4.0 M HNO3 was significantly lower than that of 424.8-634.6 ppm in the case without modification. It resulted from the intermolecular interaction force of DtBuCH18C6 and 1-dodecanol through hydrogen bonding. The reduction of DtBuCH18C6 leakage by molecular modification was achieved. It is of great benefit to application of DtDo/SiO2-P in partitioning of Sr(II), one of the main heat generators, from high level liquid waste (HLLW) in reprocessing process of nuclear spent fuel in MAREC (Minor Actinides Recovery from HLLW by Extraction Chromatography) process developed. 相似文献
5.
Single-walled carbon nanotubes (SWCNTs) were treated with sulfuric acid at 300 °C to synthesize sulfonated SWCNTs (s-SWCNTs), which were characterized by electron microscopy, infrared, Raman and X-ray photoelectron spectroscopy, and thermo analysis. Compared with activated carbon, more sulfonic acid groups can be introduced onto the surfaces of SWCNTs. The high degree (∼20 wt%) of surface sulfonation led to hydrophilic sidewalls that allows the SWCNTs to be uniformly dispersed in water and organic solvents. The high surface acidity of s-SWCNTs was demonstrated by NH3 temperature-programmed desorption technique and tested by an acetic acid esterification reaction catalyzed by s-SWCNTs. The results show that the water-dispersive s-SWCNTs are an excellent solid acid catalyst and demonstrate the potential of SWCNTs in catalysis applications. 相似文献
6.
Reaction steps and mechanisms of the thermal dehydration of lithium metaborate dihydrate were investigated by means of thermoanalytical measurements, high temperature powder X-ray diffractometry, FT-IR spectroscopy, and microscopic observations. The first half of thermal dehydration was characterized by the melting of the sample producing viscous surface layer, the formation of bubbles on the particle surfaces, and the sudden mass-loss taking place by an opportunity of cracking and/or bursting of the bubble surface layer. The second half of the dehydration with a long-tailed mass-loss process in a wide temperature region was divided further into three distinguished reaction steps by the measurements of controlled rate thermal analysis. During the course of the thermal dehydration, four different poorly crystalline phases of intermediate hydrates were observed, in addition to an amorphous phase produced by an isothermal annealing. Just after completing the thermal dehydration, an exothermic DTA peak of the crystallization of β-LiBO2 was appeared at around 750 K. The phase transition from β-LiBO2 to α-LiBO2 was observed in the temperature range of 800-900 K, which subsequently melted by indicating a sharp endothermic DTA peak with the onset temperature at 1101.4 ± 0.6 K. 相似文献
7.
A kind of non-conjugated blue luminescent polymer based on fluorene and benzoxazole was synthesized via solution condensation polymerization from 2,2-bis(3-amino-4-hydroxyphenyl)-propane and 2,7-dicarboxyl-9,9-dioctyl-fluorene and was characterized with H NMR, FT-IR, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), UV-vis absorption and photoluminescence (PL) spectroscopy. The polymer displayed the maximum photoluminescence emission peak at 415 nm and showed high PL spectroscopic stability. The green-to-blue emission intensity ratio IGreen/IBlue is only 0.073 even after thermal annealing at 150 °C for 30 h. After being exposed to UV light for 30 min, no bathochromic emission or obvious crosslink is observed. The common phenomenon of greenish blue emission of fluorene-based polymer around 525 nm has been effectively restrained in this polymer by introducing the isopropylidene group into the backbone of polymer. 相似文献
8.
The ash properties of Pinus halepensis (Aleppo pine) needles before and after treatment with diammonium phosphate (NH4)2HPO4 (DAP) have been investigated, using thermogravimetric analysis (TG), differential thermal analysis (DTA), titrimetry, inductively coupled plasma-emission spectrometry (ICP-ES), X-ray diffraction (XRD) and scanning electron microscopy (SEM). DAP is extensively used as active component in wildland fire retardants.The following crystalline compounds have been identified in ashes prepared at 600 °C before treatment with DAP: KCl, Ca(OH)2, MgO, (CaMg)CO3, K2CO3·CaCO3, K2CO3, K2SO4, CaO and CaCO3, whereas CaO, MgO, K2SO4, K2CO3, CaCO3, KCl and CaO, MgO, K2SO4 and K2CO3 at 800 and 1000 °C, respectively. The presence of DAP alters the composition of ashes converting, almost completely at high temperatures, the metallic oxides into phosphate salts. Thus, decreasing their alkalinity. The micrographs obtained by SEM indicate that pine needles ashes contain large porous particles of carbon compounds and several inorganic particles of irregular shape <1.0 mm, whereas after treating the needles with DAP an amorphous rigid structure was formed.To facilitate our investigation model mixtures of CaCO3 + DAP, MgCO3 + DAP, K2CO3 + DAP were heat treated under the same conditions used for preparing the ashes. The chemical transformations taken place during heating were studied by analysing the reaction products using thermal analysis and XRD.The physical, mineralogical and chemical forest ash properties determined could be used to evaluate the environmental risk of the use of fire retardants on soils, plants and aquatic systems as well as to investigate the mechanism of combustion of forest fuels in the presence of DAP. 相似文献
9.
Selected properties of commercial iron powders, standardised in the atmosphere of hydrogen, have been studied. The reactivity of iron oxides in the thermal decomposition of KClO4 in the solid-state mechanical mixture of Fe and KClO4 containing 9, 13, 17, 21 and 25 wt.% of KClO4, respectively, has been tested by the differential thermal analysis (DTA) and thermogravimetric analysis (TG). It has been established that the Fe3O4 phase on the surface of the iron powder act as an effective catalysts in the thermal decomposition of KClO4. 相似文献
10.
In the present work, the activated carbon (AC) support was treated with HCl, HNO3 and HF solution. The order of catalyst dispersion was as follows: Rb-K/AC-HNO3 > Rb-K/AC-HF > Rb-K/AC-HCl > Rb-K/AC. The same sequence was also observed for the amount of the acid surface oxygen groups on AC, but not for the basicity of the catalyst. The key role of acid treatment on AC surface chemistry and the basic sites, which are closely related to catalyst dispersion and basicity, is examined to rationalize these findings. On the other hand, a consideration of the reaction mechanism suggests that the reaction proceeds via CF2 carbenes formed on the catalyst surface as intermediates, followed by carbine disproportionation to CF3 radicals and CF3CF2 radicals, followed by reaction with I2 to produce CF3CF2I, and it was also found that the Rb-K/AC-HCl catalyst with a high dispersion and moderate basicity was helpful for the enhancement of catalytic activity for C2F5I synthesis. 相似文献
11.
Zohreh Rashidi RanjbarAli Morsali 《Polyhedron》2011,30(6):929-934
A nano-sized mixed-ligand Cd(II) coordination polymer, {[Cd(bpa)(4,4′-bipy)2(H2O)2](ClO4)2}n (1); bpa = trans-1,2-bis(4-pyridyl)ethane and 4,4′-bipy = 4,4′-bipyridine, has been synthesized by a sonochemical method and characterized by IR and 1H NMR spectroscopy. Compound 1 grows in one dimension by two different bridging ligands, 4,4′-bipy and bpa. The thermal stability of compound 1 in the bulk form and nano-sized was studied by thermogravimetric (TG) and differential thermal analysis (DTA). The crystallinity of this compound was studied by X-ray powder diffraction and compared with an XRD simulation of the single crystal data. CdO nanoparticles were obtained by direct calcination at 500 °C and decomposition in oleic acid at 200 °C of the nano-sized compound 1. The obtained cadmium(II) oxide nano-particles were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). 相似文献
12.
A series of new HgI2 organic polymeric complexes, [Hg2(L1)I4]n (1), [Hg(L2)I2]n (2), [Hg(L3)I2]n (3), [Hg2(L4)I4]n (4), [Hg(L5)I2]n (5), [Hg(L6)I3](HL6) (6) {L1 = 1,4-bis(2-pyridyl)-2,3-diaza-1,3-butadiene, L2 = 1,4-bis(3-pyridyl)-2,3-diaza-1,3-butadiene, L3 = 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene, L4 = 2,5-bis(2-pyridyl)-3,4-diaza-2,4-hexadiene, L5 = 2,5-bis(3-pyridyl)-3,4-diaza-2,4-hexadiene and L6 = 2,5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene} was prepared from reactions of mercury(II) iodide with six organic nitrogen donor-based ligands under thermal gradient conditions using the branched tube method. All these compounds were structurally characterized by single-crystal X-ray diffraction. The HgI2 coordination polymers obtained with the ligands L2, L3 and L5 show one-dimensional zig-zag motifs and in these compounds the HgI2 units are connected to each other by the ligands L2, L3 and L5 through the pyridyl nitrogen atoms. The L1 and L4 ligands in the compounds 1 and 4 act as both a chelating and bridging group. In the compound 6 the ligand L6 acts as a monodentate ligand, resulting form a discrete compound. The thermal stabilities of compounds 1–6 were studied by thermal gravimetric (TG) and differential thermal analyses (DTA). 相似文献
13.
L. Vasylechko V. Vashook A. Senyshyn M. Knapp M. Berkowski U. Bismayer 《Journal of solid state chemistry》2003,172(2):396-411
Crystal structure and anisotropy of the thermal expansion of single crystals of La1−xSrxGa1−2xMg2xO3−y (x=0.05 and 0.1) were measured in the temperature range 300-1270 K. High-resolution X-ray powder diffraction data obtained by synchrotron experiments have been used to determine the crystal structure and thermal expansion. The room temperature structure of the crystal with x=0.05 was found to be orthorhombic (Imma, Z=4, a=7.79423(3) Å, b=5.49896(2) Å, c=5.53806(2) Å), whereas the symmetry of the x=0.1 crystal is monoclinic (I2/a, Z=4, a=7.82129(5) Å, b=5.54361(3) Å, c=5.51654(4) Å, β=90.040(1)°). The conductivity in two orthogonal directions of the crystals has been studied. Both, the conductivity and the structural data indicate three phase transitions in La0.95Sr0.05Ga0.9Mg0.1O2.92 at 520-570 K (Imma-I2/a), 770 K (I2/a-R3c) and at 870 K (R3c-R-3c), respectively. Two transitions at 770 K (I2/a-R3c) and in the range 870-970 K (R3c-R-3c) occur in La0.9Sr0.1Ga0.8Mg0.2O2.85. 相似文献
14.
Tessy López Roberto Alexander-Katz Alexander Balankin 《Journal of solid state chemistry》2004,177(6):1873-1885
Sol-gel TiO2-CeO2 materials were synthesized at pH=3 employing HNO3 as hydrolysis agent. Gels were thermally treated at 473, 673, 873, and 1073 K, respectively. Morphologies of the final substrates were studied via N2 sorption, XRD and TEM. N2 isotherms indicated a steady porosity in TiO2-CeO2 samples treated up to 873 K. Adsorption-desorption isotherms and TEM micrographs were used to perform fractal analyses of annealed samples. A dominant anatase phase was detected by XRD between 473 and 873 K while a rutile phase was evident at 1073 K. The presence of cerium conferred an increased thermal stability to the TiO2 materials against particle sintering and pore collapse. The structure of cerium-doped anatase lattice was visualized through crystal simulation to investigate the possible substitution of Ti4+ by Ce+4 ions. This effect and the progressive segregation of CeO2 crystals with temperature on the surface of TiO2 grains lead to substrates of assorted morphologies. 相似文献
15.
A. Gomathi 《Journal of solid state chemistry》2007,180(1):291-295
We have been able to prepare nanoparticles (∼4 nm diameter) of cubic γ-Mo2N by a simple procedure involving the reaction of MoCl5 with urea at 873 K. The nanoparticles show a superconducting transition around 6.5 K. The γ-Mo2N nanoparticles are readily transformed to nanoparticles of δ-MoN with a slightly larger diameter on heating in a NH3 atmosphere at 573 K. Phase-pure δ-MoN obtained by this means shows a superconducting transition around 5 K. 相似文献
16.
The decomposition pattern of tetraalkyl-tetrathiomolybdates with general formula (R4N)2MoS4 (with R increasing from methyl to heptyl) was determined by means of differential thermal analysis (DTA), thermogravimetric analysis (TGA) and mass spectroscopy (MS) techniques. The complexity of thermal decomposition reactions increases with the size of the R4N group. Prior to decomposition at least one phase transition seems to occur in all complexes. The onset of thermal reactions was also a function of the tetra-alkylammonium precursor. All compounds decompose without forming sulfur rich MoS2+x intermediates. For R = methyl to pentyl precursors the MoS2 produced was nearly stoichiometric, however for R = hexyl and heptyl the S content was significantly reduced with a Mo:S ratio of about 1.5. The carbon and hydrogen residual contents in the product increased with the number of C atoms in R4N; for N contamination no clear trend was obvious. SEM images show that the formation of macro-pores was also a function of the alkyl group in R4N. The MoS2 materials obtained show a sponge-like morphology. Results of DSC experiments in combination with in situ X-ray diffraction also revealed the complex thermal behavior of (R4N)2MoS4 materials; reversible and irreversible phase transitions and glass-like transformations were identified in the low temperature range (35-140 °C), before the onset of decomposition. 相似文献
17.
Sr2CrSbO6 was synthesized by the conventional solid-state reaction process. X-ray powder diffraction (XRPD) and neutron powder diffraction (NPD) has been used to reinvestigate the structure at room temperature and to study the phase transitions at high- and low-temperature. Rietveld analysis revealed that Sr2CrSbO6 crystallizes at room temperature in a monoclinic system having a space group I2/m, with a=5.5574(1) Å; b=5.5782(1) Å; c=7.8506(2) Å and β=90.06(2), no P21/n space group as was previously reported. The high-temperature study (300-870 K) has shown that the compound presents the following temperature induced phase-transition sequence: I2/m-I4/m-Fm-3m. The low-temperature study (100-300 K) demonstrated that the room-temperature I2/m monoclinic symmetry seems to be stable down to 100 K. 相似文献
18.
The phase transitions in Sr2SnO4 at high temperature have been studied using high resolution time-of-flight powder neutron diffraction. The room temperature structure of Sr2SnO4 is orthorhombic (Pccn), which can be derived from the tetragonal K2NiF4 structure by tilting the SnO6 octahedra along the tetragonal [100]T- and [010]T-axes with non-equal tilts. At the temperature of about 423 K, it transforms to another orthorhombic structure (Bmab) characterized by the SnO6 octahedral tilt around the [110]T-axis. At still higher temperatures (∼573 K) the structure was found to be tetragonal K2NiF4-type (I4/mmm). 相似文献
19.
Manel Jammali 《Journal of solid state chemistry》2010,183(5):1194-1199
The phases NdSrNi1−xCrxO4+δ (0.1≤x≤0.9) have been synthesized by modified sol-gel method and subsequent annealing at 1250 °C in 1 atm of flowing argon. X-ray diffraction (XRD) analysis and electrical resistivity have been measured at room temperature. Rietveld refinement shows that all compositions with x>0.1 were found to crystallize in the tetragonal K2NiF4 type structure in the space group I4/mmm, while for x=0.1, a mixture of two phases with the tetragonal space group I4/mmm and the orthorhombic space group Fmmm. Variations of a and c parameters show a complex behavior with increasing chromium content. It was established that compounds with chromium content less then x≤0.5 are oxygen-deficient, while for x>0.5 the sample are oxygen-overstoichiometric. The NdSrNi0.5Cr0.5O4+δ compound exhibits semiconductive behavior and the electrical transport mechanism agrees with the non-adiabatic small polaron hopping model in the temperature ranges 298-493, 493-573 and 573-703 K separately. 相似文献
20.
M. NasuiT. Petrisor Jr. M.S. GaborR.A. Varga L. CionteaT. Petrisor 《Journal of Analytical and Applied Pyrolysis》2011,92(2):439-444
A new copper propionate complex was synthesised and characterized for application as precursor for CuO based oxide thin films deposition. The FT-IR and X-ray diffraction analyses have revealed the formation of a cooper propionate complex [Cu(CH3CH2COO)2]·2H2O. The crystal and molecular structure of a new copper propionate complex was determined by XRD on the copper propionate single crystal. The copper propionate complex has a binuclear structure, connected by bridging bidentate carboxylates groups and a Cu?Cu bond of 2.6 Å. The thermal decomposition of copper propionate has been investigated by thermal analysis using thermogravimetric (TG) and differential thermal analysis (DTA), differential thermal analysis coupled with quadrupole mass spectrometry-QMS, X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FT-IR) techniques. TG and XRD data indicate the reduction of Cu(II)-Cu(I,0) during the decomposition of copper propionate. 相似文献