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1.
Diana L.D. Lima 《Talanta》2007,72(4):1404-1409
Operational parameters like migration time, temperature, voltage, composition of background electrolyte and content of organic modifier were optimized in CZE for the determination of lignin-like phenolic compounds.The applied background electrolyte buffer consisted of a Na2B4O7, KH2PO4 aqueous solution, pH 9.15 using acetonitrile as organic modifier with UV-detection. Compounds, such as acetosyringone, acetovanillone, syringealdehyde, p-hydroxyacetophenone, vanillin, syringic acid, ferulic acid, p-hydroxybenzaldehyde, p-coumaric acid, vanillic acid and p-hydroxybenzoic acid were applied as reference compounds.The quality and quantity of different phenolic compounds obtained upon alkaline CuO oxidation of a commercial humic acid were determined with CZE using ethylvanillin as internal standard.The optimized CZE revealed has being an appropriate method since it is quick, sensitive and quantitative and does not require a time-consuming sample preparation. 相似文献
2.
This study presents the determination of the pseudo-total and available element contents in suspended matter in leachate using stripping voltammetry (DPASV) on a hanging mercury drop electrode and an inductively coupled plasma mass spectrometer (ICP-MS). The following elements were studied: Zn, Pb, As, Sb, Co, Cu, Ni, Cr, Sn, Mo and Cd. To determine the pseudo-total metal contents, we applied microwave digestion using a mixture of HNO3 and HClO4 with a small quantity of HF. To assess the metal availability from suspended matter in leachate, the single extraction procedure with 0.1mol·L–1 acetic acid and 0.01mol·L–1 ammonium acetate was applied. Metal bioavailability based on single extraction with 15% H2O2 was determined. We also estimated the association with particular phases of suspended matter in leachate. 相似文献
3.
The corrosion and anodic dissolution behaviors of pure aluminum in Na2SnO3-containing 4 mol·L−1 KOH methanol-water mixed solutions with a methanol/water volume ratio of 4:1 were investigated. This was carried out by means of hydrogen collection, polarization curve, galvanostatic discharge, scanning electron microscopy (SEM), and energy dispersive analysis of X-ray (EDAX). The experimental results indicated that the addition of stannate inhibited the corrosion of aluminum in the 4 mol·L−1 KOH methanol-water solutions by the deposition of tin with a higher hydrogen evolution overpotential on the electrode surface. In the electrolytes with higher stannate contents the inhibiting effect decreased because of the occurrence of some cracks on the tin deposition film. The results of galvanostatic discharge showed that the discharge of aluminum in the Na2SnO3-containing 4 mol·L−1 KOH methanol-water solutions were obviously improved. In addition, the improvement effect enhanced with the increase of stannate content. It was noted that the aluminum anode showed a very flat discharge plateau at relatively low potentials in the electrolyte with 10.0 mmol·L−1 Na2SnO3 at 20 mA·cm−2 discharge current density. 相似文献
4.
The aim of this work was to characterize the fulvic acids (FA) extracted from peat by use of capillary electrophoresis (CE). Two FA extracts have been obtained using two different extractants (0.1 M NaOH and 0.1 M NaOH plus 0.1 M Na4P2O7, Na+PP). The CE runs wre performed using a coated silica capillary, and several buffer solutions at different PH values. The results obtained show that the Fa extracts may be well characterized by CE even if the isolelectric point of the fulvic compounds is very low. The best fractionation has been obtained using a buffer borate at PH 8.9 as funning buffer. The charcterization of the two extracts also showed some important differences between the NaOH extract and the Na+PP extract. 相似文献
5.
用循环伏安、交流伏安和交流阻抗法对Dawson型磷钨杂多阴离子P2W18O626-的电化学性质进行了详细研究, 循环伏安结果显示, P2W18O626-在pH 2.52的0.1 mol·L-1 Na2SO4+NaHSO4溶液中有两对可逆的单电子还原-氧化波和两对可逆的双电子还原-氧化波. 单电子波的峰电位和电流与溶液的pH无关, 双电子波的峰电位则随溶液pH的增加而负移, 峰电流降低, 表明双电子电极过程有H+参与, 其数目为2. 交流阻抗谱表明P2W18O626-的电极过程完全受扩散控制, 实验测定其扩散系数(DO)为2.5×10-6 cm2·s-1. 循环伏安结果表明P2W18O626-的第III对波对O2还原为H2O2具有显著的电催化作用, 催化效率约达300%. 将P2W18O626-应用于PW11O39Fe(III)(H2O)4-构成的类电-芬顿过程, 使该过程对硝基苯的降解效率显著提高. 相似文献
6.
Structural models for stabilized O– in -irradiated alkaline ices are evaluated. INDO calculations on hydrated O– indicate octahedral coordination and hydrogen bond orientations for the water molecules are preferred. INDO results for hydrated OH– are compared with crystallographic data for NaOH hydrates: a scaling factor for calculated hydrogen bond lengths is developed and applied to hydrogen bonded O– models. The hydrated O– model is closely similar to the hydrated anions in KF · 4H2O, NaOH · 4H2O, and NaOH · 7H2O. A second model is developed, involving H3O+ along with H2O, in the O– stabilization shell. Both models are discussed in terms of alkaline ice radiation chemistry. 相似文献
7.
R. Celis L. Cox M. C. Hermosin J. Cornejo 《International journal of environmental analytical chemistry》2013,93(1-4):245-260
Abstract Adsorption isotherms of metamitron on model soil colloidal components: kaolinite, illite, montmorillonite, iron oxide and humic acid, and their binary associations were obtained using a batch equilibration procedure. Sorption parameters, Kf and nf, were calculated by fitting the sorption data to the Freundlich equation and results obtained for binary associations were compared with those obtained for the individual model components. The sorption efficiency of the humic acids and their binary associations was measured as Koc. The adsorption behaviour of the < 2 μm fraction of two soils from Southern Spain was also studied as natural particulate matter. Montmorillonite and humic acids were found to be the most important components responsible for metamitron retention by the model adsorbents studied. On the contrary, metamitron showed little interaction with kaolinite, illite or iron oxide. These individual adsorption behaviours were reproduced in the montmorillonite-iron oxide-humic acid binary systems, but with differences suggesting changes on the surface properties upon association. Differences in Koc values of isolated humic acids and their associations indicate that the interaction transforms the humic acid surfaces and suggest different types of bonding between colloids and metamitron. The results obtained with model adsorbents and their associations were in agreement with the highest adsorption of metamitron found for the natural clay fraction of two soils which displayed the largest adsorption in that with the highest content in montmorillonite and organic carbon. The importance of organic matter and montmorillonite in metamitron adsorption by colloidal components was also shown by the decrease in Kf and the increase in Koc observed after removal of organic matter from the soil clay fraction with the highest organic carbon content. 相似文献
8.
Dr. Shiwen Wang Dr. Lijiang Wang Dr. Zhiqiang Zhu Zhe Hu Dr. Qing Zhao Prof. Dr. Jun Chen 《Angewandte Chemie (International ed. in English)》2014,53(23):5892-5896
Developing organic compounds with multifunctional groups to be used as electrode materials for rechargeable sodium‐ion batteries is very important. The organic tetrasodium salt of 2,5‐dihydroxyterephthalic acid (Na4DHTPA; Na4C8H2O6), which was prepared through a green one‐pot method, was investigated at potential windows of 1.6–2.8 V as the positive electrode or 0.1–1.8 V as the negative electrode (vs. Na+/Na), each delivering compatible and stable capacities of ca. 180 mAh g?1 with excellent cycling. A combination of electrochemical, spectroscopic and computational studies revealed that reversible uptake/removal of two Na+ ions is associated with the enolate groups at 1.6–2.8 V (Na2C8H2O6/Na4C8H2O6) and the carboxylate groups at 0.1–1.8 V (Na4C8H2O6/Na6C8H2O6). The use of Na4C8H2O6 as the initial active materials for both electrodes provided the first example of all‐organic rocking‐chair SIBs with an average operation voltage of 1.8 V and a practical energy density of about 65 Wh kg?1. 相似文献
9.
The assessment of physico-chemical properties in forest soils affected by fires was evaluated using near infrared reflectance (NIR) spectroscopy coupled with chemometric methods. In order to describe the soil properties, measurements were taken of the total organic carbon on solid phase, the total nitrogen content, the organic carbon and the specific absorbences at 254 and 280 nm of humic substances, organic carbon in humic and fulvic acids, concentrations of NH4+, Ca2+, Mg2+, K+ and phosphorus in addition to NIR spectra. Then, a fire recurrence index was defined and calculated according to the different fires extents affecting soils. This calculation includes the occurrence of fires as well as the time elapsed since the last fire. This study shows that NIR spectroscopy could be considered as a tool for soil monitoring, particularly for the quantitative prediction of the total organic carbon, total nitrogen content, organic carbon in humic substances, concentrations of phosphorus, Mg2+, Ca2+ and NH4+ and humic substances UVSA254. Further validation in this field is necessary however, to try and make successful predictions of K+, organic carbon in humic and fulvic acids and the humic substances UVSA280. Moreover, NIR coupled with PLS can also be useful to predict the fire recurrence index in order to determine the spatial variability. Also this method can be used to map more or less burned areas and possibly to apply adequate rehabilitation techniques, like soil litter reconstitution with organic enrichments (industrial composts) or reforestation. Finally, the proposed recurrence index can be considered representative of the state of the soils. 相似文献
10.
Summary A simple method has been developed to determine the concentration of organic chlorine in waste oil. The determination is based on the conversion of organic chlorine to inorganic chloride by reaction with sodium biphenyl followed by extraction with nitric acid and a mixture of nitric acid and water. The concentration of chloride is determined by direct potentiometry with an ion-selective electrode. The limit of determination amounts to 3·10–5 mol·l–1 chloride ions with a standard deviation of 3.5%. Different samples of waste oil have been analyzed and the results have been compared to those obtained by combustion in a H2/O2 flame followed by potentiometric titration with silver nitrate. 相似文献
11.
A. Rahmel 《Journal of Electroanalytical Chemistry》1975,61(3):333-341
Using the Pt-(O2) electrode as an indicator electrode for the O2? concentration of a sulphate melt, potentiometric acid-base titrations have been carried out at 625°C in the eutectic Li2SO4-K2SO4-Na2SO4 melt. Na2CO3 has been used as an O2? donor, and MoO3, K2Cr2O7, NaPO3, Na4P2O7 and V2O5 were used as acid species. While the equivalence point is at an acid/Na2CO3 molar ratio of 1:1 with MoO3, K2Cr2O7, NaPO3 and Na4P2O7, it is situated at about 0.3:1 in the system V2O5/Na2CO3. 相似文献
12.
The crystal structure of Na7Mg4.5(P2O7)4 has been solved by direct methods from the three-dimensional X-ray data. The space group is . The crystal structure consists of Mg2+, Na+, and P2O4?7 ions. One magnesium atom at symmetry center (0,0,0) and two sodium atoms at ±(?0.0421, ?0.0596, 0.2230) display occupation factors 0.5 each. A short interatomic distance between these Na+ and Mg2+ ions (1.80 ± 0.01 Å) excludes the occupation of both sites in the same unit cell. The crystal structure of Na7Mg4.5(P2O7)4 consists of unit cells containing Na8Mg4(P2O7)4 or Na6Mg5(P2O7)4 with a statistical occurrence 1:1.Each Mg2+ ion is octahedrally coordinated by six O2? ions at distances 1.979 – 2.270 Å. The coordination polyhedra around the Na+ ions are ill-defined. The bond angles POP in the P2O4?7 groups are 126.6 and 133.6° (±0.3°). The final reliability factor R is 7.1%. 相似文献
13.
Shurdumov B. K. Trunin A. S. Kuchukova M. A. 《Russian Journal of General Chemistry》2002,72(5):675-677
Thermal analysis of the pseudoternary systems Na4P2O7-WO3-NaCl and K4P2O7-WO3-KCl was performed, and the crystallization fields were revealed of sodium and potassium pyrophosphates, incongruently melting compounds Na4P2O7·3WO3 and K4P2O7·3WO3, and of products formed by reactions of WO3 with NaCl and KCl. Low-melting compositions were revealed, which are of interest for preparing Na(K)-W oxide bronzes. 相似文献
14.
Mechanochemical modification of the structure of brown coal humic acids for preparing a sorbent for heavy metals 总被引:2,自引:0,他引:2
T. S. Urazova A. L. Bychkov O. I. Lomovskii 《Russian Journal of Applied Chemistry》2014,87(5):651-655
Mechanochemical modification of the structure of brown coal humic acids with classical base (NaOH) and oxidizing base (Na2CO3·1.5H2O2) reagents was studied. Treatment of brown coal under these conditions leads to an increase in the degree of recovery of humic acids without breaking the macrostructure of the molecules. The reaction with the base reagent leads to an increase in the content of carboxy groups at hydrocarbon chains, whereas the action of the oxidizing base reagent leads to an increase in the content of phenolic and carboxy groups at aromatic rings, with the formation of chelating structures. The samples obtained show high performance as sorbents for heavy metals. 相似文献
15.
T. Nishida 《Journal of Radioanalytical and Nuclear Chemistry》1995,190(2):381-390
57Fe-Mössbauer spectra of 38Na2O·61WO3·57Fe2O3 glasses, heat treated at 355°C for 5–150 min, show a change of the coordination number of Fe3+ from 6 (FeO6 octahedra) to 4 (FeO4 tetrahedra), as a result of the formation of Na2W2O7 (Na2O/WO3=1/2), Na2WO4 (Na2O/WO3=1.0), FeWO4, and Fe2WO6 phases.57Fe-Mössbauer spectra of 25K2O·65V2O3·10Fe2O3 glasses show a drastic decrease of and after the heat treatment at 340°C for 10–2100 min, since a homogeneous crystallization took place without a phase separation. A KV3O8 phase with the K2O/V2O5 ratio of 1/3 was precipitated, and the ratio was equal to the K2O/(V2O5+Fe2O3) ratio of the original 25K2O·65V2O3·10Fe2O3 glass. 相似文献
16.
利用水热法制备 NiS 负载的 Cd1-xZnxS 光催化剂.结果表明:在0.35 mol?L-1 Na2SO3和0.25 mol?L-1 Na2S牺牲剂下,0.5%(摩尔分数, y) NiS/Cd0.3Zn0.7S (1840μmol?h-1)获得最好活性,是Cd0.3Zn0.7S (884μmol?h-1)的2.1倍,高于0.5%(质量分数, w) Pt (1390μmol?h-1)的产氢活性.测得其在λ=420 nm附近的表观量子效率为36.8%. X射线衍射(XRD)、紫外-可见漫反射光谱(UV-Vis DRS)、透射电子显微镜(TEM)以及X射线光电子能谱(XPS)的表征结果表明, NiS作为产氢活性位,转移光生电子,因此提高了光催化产氢活性. 相似文献
17.
分别以LiMn_2O_4,NaTi_2(PO_4)_3为正负极,1 mol·L~(-1) Li_2SO_4和0.5 mol·L~(-1) Na_2SO_4的混合水溶液为电解液组装成一种水系混合离子全电池。分别将正负极材料在3种不同水相电解液(1 mol·L~(-1) Li_2SO_4、0.5 mol·L~(-1)Na_2SO_4以及1 mol·L~(-1) Li_2SO_4+0.5 mol·L~(-1)Na_2SO_4混合电解液)中进行循环伏安和恒流充放电测试,结果发现,LiMn_2O_4在上述电解液中仅有Li~+的脱出/嵌入而Na~+由于半径较大而不参与该过程,NaTi_2(PO_4)_3在3种电解液中Li+、Na+均参与嵌入/脱嵌过程,且Li~+和Na~+的嵌入/脱出峰电位相差不大,分别为-0.82和-0.64 V,-0.95和-0.75 V;全电池在265 mA·g~(-1)电流密度下平均放电电压为1.55 V,充放电比容量分别为100.1和74.9 m Ah·g~(-1)。 相似文献
18.
The following extraction systems have been studied: (Ce3++Eu3+) (NO3)-(EDTA, DCTA, DTPA)/TBP in n-alkane and (Ce3++Eu3+)(NO3)/DEHPA in n-alkane at concentration ratios as follows: [Ce3+]=trace –1 mol·dm–3, [Eu3+]=trace –0.1 mol·dm–3. [TBP]=(0.183–1.83) mol·dm–3, [DEHPA]=(5·10–3–0.1) mol·dm–3, [(H, Na)NO3]=(0.1–6) mol·dm–3, [Eu3+]: [EDTA, DCTA, DTPA]=11–110. The initial concentration of Eu3+ in aqueous phase in the extraction system containing a mixture of Ce3+ and Eu3+ was trace, 1% and 10% compared with the Ce3+ concentration. The distribution of the elements between the phases was observed radiometrically using141Ce,152Eu and154Eu. The results are documented by the distribution ratios DCe, DEu and separation factor =DEu/DCe as functions of variable parameters of the systems. 相似文献
19.
Xing-Zhi Liu Da-Wei Fang Jia-Zhen Yang Jun Li Shu-Liang Zang 《The Journal of chemical thermodynamics》2004,36(12):1061-1065
The equilibrium molalities In3+ in {In2(SO4)3 + Na2SO4 + HDEHMTPCA + n-C8H18 + water} were measured at ionic strength from (0.1 to 2.0) mol · kg−1 containing Na2SO4 as supporting electrolyte in aqueous phase and at constant molality extractant at temperatures from (278.15 to 303.15) K in organic phase. The standard extraction constants K0 at various temperatures were obtained by methods of extrapolation and polynomial approximation. Thermodynamic quantities for the extraction process were calculated. 相似文献
20.
Annenkov V.V. Filina E.A. Danilovtseva E.N. Zinchenko S.V. Mikhaleva A.I. 《Journal of Sol-Gel Science and Technology》2003,27(2):163-166
The formation of alumina particles from aluminum salts in the presence of poly(1-vinylimidazole) was investigated by quantitative 27Al NMR, potentiometry and FTIR spectra. The interaction of poly(1-vinylimidazole) with aluminum chloride and nitrate in an aqueous medium stabilizes [AlO4Al12(OH)24]7+ and less ordered polymeric particles. The addition of NaOH (NaOH: Al 2) results in water-insoluble organic/inorganic hydrogen-bonded composites. Stabilization of the complexes is realized by cooperative hydrogen N···H—O—Al bonds, without N Al donor-acceptor interactions. 相似文献