Evaluation of the solid-phase microextraction fiber coated with single walled carbon nanotubes for the determination of benzene,toluene, ethylbenzene,xylenes in aqueous samples

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.     

The decomposition kinetics of [Et4N]2[M(dmit)2] (M = Ni, Pd) in a nitrogen atmosphere using thermogravimetry

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, E_a, and kinetic apparent pre-exponential factor, ln A_app, 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.     

Improvement of microwave-assisted digestion of milk powder with diluted nitric acid using oxygen as auxiliary reagent

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.     

Modification of a novel macroporous silica-based crown ether impregnated polymeric composite with 1-dodecanol and its adsorption for some fission and non-fission products contained in high level liquid waste

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.     

Synthesis and characterization of sulfonated single-walled carbon nanotubes and their performance as solid acid catalyst

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.     

Thermal dehydration of lithium metaborate dihydrate and phase transitions of anhydrous product

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.     

Synthesis and photoluminescence stability of non-conjugated polymers based on fluorene and benzoxazole

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 I_Green/I_Blue 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.     

Ash properties of Pinus halepensis needles treated with diammonium phosphate

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.     

Textural and catalytic properties of the FexOy/Fe-KClO4 system

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.     

Effects of acid treatment on activated carbon used as a support for Rb and K catalyst for C2F5I synthesis and its mechanism

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.     

Ultrasound assisted syntheses of a nano-structured two-dimensional mixed-ligand cadmium(II) coordination polymer and direct thermolyses for the preparation of cadmium(II) oxide nanoparticles

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).     

Mercury(II) iodide coordination polymers generated from polyimine ligands

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).     

Crystal structure, thermal expansion and conductivity of anisotropic La1−xSrxGa1−2xMg2xO3−y (x=0.05, 0.1) single crystals

Crystal structure and anisotropy of the thermal expansion of single crystals of La_1−xSr_xGa_1−2xMg_2xO_3−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 La_0.95Sr_0.05Ga_0.9Mg_0.1O_2.92 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 La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85.     

Porosity, structural and fractal study of sol-gel TiO2-CeO2 mixed oxides

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.     

Nanoparticles of superconducting γ-Mo2N and δ-MoN

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.     

Decomposition of tetra-alkylammonium thiomolybdates characterised by thermoanalysis and mass spectrometry

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 MoS_2+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.     

Crystal structures and phase transitions of Sr2CrSbO6

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.     

Neutron powder diffraction study of phase transitions in Sr2SnO4

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).     

Investigation on the structural and electrical properties of NdSrNi1−xCrxO4+δ (0.1≤x≤0.9) system

The phases NdSrNi_1−xCr_xO_4+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 NdSrNi_0.5Cr_0.5O_4+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.     

Synthesis, crystal structure and thermal decomposition of a new copper propionate [Cu(CH3CH2COO)2]·2H2O

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.