首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到10条相似文献,搜索用时 140 毫秒
1.
Summary Chromium can be present in aqueous solution as Cr(VI) or in monomeric, dimeric, trimeric and higher polymeric forms of Cr(III). Many monomeric forms of Cr(III) are possible, with the water molecules of Cr(H2O) 6 3+ substituted by anionic or neutral species. This proliferation of Cr(III) species makes the complete speciation of chromium a continuing challenge to the analyst. A simple and effective cation exchange procedure for the separation of various of these species uses a small glass column containing 1 mL of pre-treated cation exchange resin (Na+ form). Stepwise elution with solutions of perchloric acid, Ca2+ (pH=2) and La3+ (pH=2) separates Cr(VI) and seven Cr(III) species from CrX3 to tetramer. Radiometric (Cr-51), spectrophotometric and other detection methods can be employed; the use of radiochromium gives the lowest detection limit.  相似文献   

2.
We report an in-situ harvesting technique of electron-hole (e-h+) carriers (e.g., the defect electrons in the O2 − matrix and the self-trapped holes, Si–O–Si) generated during sol-gel processing. In the absence of redox species, the e-h+ centers created during room temperature sol-gel polycondensation steps are quickly annihilated and deactivated. However, when Cr(VI) ions are pre-dispersed in sol-gel solutions, the ejected electrons can be effectively harvested for the reduction of Cr(VI) to Cr(III) ions which are encapsulated in the silica gel matrix. The Cr(VI) ions, the possible intermediate oxidation states of chromium ions such as Cr(V) and/or Cr(IV), and the stable Cr(III)-hole complexes in the sol-gel matrix are investigated using uv-visible spectroscopy, electron paramagnetic resonance spectroscopy, and cyclic voltammetry. The chemical stability of Cr(VI) and Cr(III) in sol-gel networks is compared to that in aqueous solutions. The results indicate that the utilization of e-h+ carriers generated in the sol-gel can be an effective and selective means for investigating the redox process of Cr(VI) and encapsulating the stable Cr(III) ions in the confined sol-gel environments.  相似文献   

3.
The bacterial reduction of Cr(VI) from industrial wastewater was evaluated using a 2.0-m3 bioreactor. Liquid pineapple waste was used as a nutrient for the biofilm community formed inside the bioreactor. The use of rubber wood sawdust as packing material was able to immobilize more than 106?CFU?mL?1 of Acinetobacter haemolyticus cells after 3?days of contact time. Complete reduction of 15?C240?mg?L?1 of Cr(VI) was achieved even after 3?months of bioreactor operation. Cr(VI) was not detected in the final effluent fraction indicating complete removal of Cr from solution from the flocculation/coagulation step and the unlikely re-oxidation of Cr(III) into Cr(VI). Impatiens balsamina L. and Gomphrena globosa L. showed better growth in the presence of soil?Csludge mixture compared to Coleus scutellarioides (L.) Benth. Significant amounts of Cr accumulated at different sections of the plants indicate its potential application in Cr phytoremediation effort. The bacterial-based system was also determined not to be detrimental to human health based on the low levels of Cr detected in the hair and nail samples of the plant operators. Thus, it can be said that bacterial-based Cr(VI) treatment system is a feasible alternative to the conventional system especially for lower Cr(VI) concentrations, where sludge generated can be used as growth supplement for ornamental plant as well as not detrimental to the health of the workers.  相似文献   

4.
The structure of copper(I,II) penta­chromium(III) germanate, Cu(Cu0.44Cr4.56)Ge2O12, contains one Cu position (m2m), one Ge position (m) and three Cr positions (2/m, m and 2). The close‐packed structure is described in terms of slabs of edge‐sharing Cr3+O6 octa­hedra and isolated CuO4 and GeO4 tetra­hedra. These slabs are aligned parallel to the bc plane and are separated from each other by GeO4 tetra­hedra along a. The tetra­hedral coordination observed for the Cu+/Cu2+ ions represents an unusual feature of the structure. The Cr—O and Cu—O bond lengths are compared with literature data.  相似文献   

5.
Ions of Ti(III), V(III) and Cr(III) seem to be converted to the following azido complexes in acetonitrile, propanediol-1,2-carbonate and trimethylphosphate: [Ti(N3)2]+ (inTMP), Ti(N3)3 (probably distorted octahedral inAN, PDC andTMP, low solubility inTMP), [Ti(N3)4]? (probably tetragonal inAN, probably octahedral inTMP), [Ti(N3)6 3? (probably distorted octahedral inAN andPDC); [V(N3)]2+ (inAN, PDC andTMP), V(N3)3 (octahedral inAN, PDC andTMP, low solubility inTMP), [V(N3)4]? (inPDC), [V(N3)6]3? (octahedral inAN andPDC); [Cr(N3)]2+ (inTMP), [Cr(N3)2]+ (octahedral inAN andPDC), Cr(N3)3 (octahedral inAN, PDC andTMP), [Cr(N3)6]3? (octahedral inAN andPDC).  相似文献   

6.
Cr (III) sorption on microporous strong cation exchanger Amberlite.120 (Na+) is studied as a function of time and temperature. The pH changes show the co-sorption of H+ ions along with the chromium. The rate constant values for Cr (III) sorption are calculated for both film and particle diffusion processes. However, the particle diffusion is found to be more dominant than the film diffusion. The temperature is found to have a positive effect on both the diffusional processes. The low values of energy of activation also confirm the diffusional nature of the process. Equilibrium data are explained with the help of Langmuir equation. Various thermodynamic parameters (??H, ??S and ??G) for Cr (III) exchange on the resin are calculated. The ??G values are found to be negative, while both the ??H and ??S values obtained are positive.  相似文献   

7.
Ultrafine heavy metal aerosols can have severe toxic and carcinogenic effects when inhaled in higher concentrations. The objective of this work was to develop a mobile continuous emission monitor (CEM) based on laser-induced plasma spectroscopy (LIPS) for an on-line analysis of chromium aerosols. The LIPS emission sensor was installed in an electroplating facility for a fast monitoring of particulate emissions to provide instantaneous feedback for process control. The prototype was tested in cooperation with an independent laboratory, which determined the total chromium content and the Cr(VI)/Cr(III) ratio in the exhaust stream by conventional filter analysis. The system provided both the necessary time-resolution and detection limits (14 μg m–3) for emission monitoring below the legal threshold (1 mg m–3) values. A good correlation was found between the on-line LIPS measurement and the independent reference analysis. Received: 22 March 1999 / Revised: 5 May 1999 / Accepted: 11 May 1999  相似文献   

8.
Conclusion A study was carried out on the35Cl NQR spectra of bis(chlorobenzene)chromium(O) and bis(chlorobenzene)chromium(I) iodide. The coordination of chlorobenzene with the charged ClC6H6Cr+ fragment leads to a sharp decrease in electron density. This effect is significantly greater than that resulting from the coordination of chlorobenzene with the ClC6H5Cr group in neutral bis(chlorobenzene)chromium.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2801–2803, December, 1986.  相似文献   

9.
A novel potentiometric sensor, based on carbon paste electrode (CPE), modified with ion-imprinted polymer (IIP) and multi-walled carbon nanotubes (MWCNTs), is introduced for detection of chromium (III). The IIP nanomaterial was synthesised and characterised by using scanning electron microscopy and Fourier Transform Infrared. The modification of the CPE with the IIP (as a ionophore) resulted in an all-solid-state Cr(III)-selective sensor. However, the presence of appropriate amount of MWCNTs in the electrode composition was found to be necessary to observe Nernstian response. The optimised electrode composition was 76.7% graphite, 14.3% binder, 5% IIP, and 4% CNT. The proposed sensor exhibited Nernstian slope of 20.2 ± 0.2 mV decade?1 in the working concentration range of 1.0 × 10?6?1.0 × 10?1 mol L?1 (52 µg L?1–5.2 g L?1), with a detection limit of 5.9 × 10?7 mol L?1 (30.68 µg L?1) and a fast response time of less than 40 s. It displayed a stable potential response in the pH range of 2–5. It exhibited also high selectivity over some interfering ions. The proposed sensor was successfully applied for the determination of Cr(III) in real samples (sea, river water and soil).  相似文献   

10.
The compounds investigated were: [Cr(en)3]3+, [Cr(ur)6]3+, [Cr(DMSO)6]3+, [Cr(dien)2]3+, [Cr(en)2(acac)]2+, [Cr(en) (acac)2]+ and Cr(acac)3.A distinctly different behaviour is caused by the introduction of one or moreacac ligands into the molecule. The first step is much more cathodic and quite irreversible, while it is reversible or quasi reversible for the first group of ions. This is due to a -type interaction between theacac ligand and the central ion. This interaction is responsible for a third peak occurring for the second group of compounds and may be attributed to the reduction of the Cr(I) ion.Some correlations were found e.g. between the extinction of thed-d band of the first group of ions and the potential of the first peak, and the number ofacac groups introduced in the second group of compounds and the shift of the potential of the first peak.The determined electrochemical data are tabulated.
Untersuchungen zur elektrochemischen Reduktion einiger Cr(III)-Komplexe in DMSO mittels zyklischer Voltammetrie
Zusammenfassung Die elektrochemischen Daten einer Reihe von Cr(III)-Komplexen miten-, ur-, DMSO-, dien- undacac-Liganden werden präsentiert und einige Möglichkeiten der Korrelation der physikalischen Eigenschaften der Komplexe werden aufgezeigt.Die erste Stufe bei der Einführung vonacac-Liganden ist auf Grund einer -Wechselwirkung zwischen Ligand und Zentralion irreversibel.
  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号