Chromate Anions Research Articles

Aromatic 3,5-Di(2′,4′-dicarboxylphenyl)benozoic acid based coordination polymers as luminescent sensor for the sensitive detection of chromate anions in aqueous solution

Based on the mixed ligands of aromatic pentacarboxylate of 3,5-di(2′,4′-dicarboxylphenyl)benozoic acid (H5L) and 1,4-bis(imidazol-1-yl) benzene (bib), two novel coordination polymers, namely, [Ni1.5(H2L)(bib)1.5(H2O)2]n (1), and {[Pb2(HL)(bib)1.5(H2O)]·H2O}n (2) have been synthesized and characterized by EA, IR, TG, PXRD. Structure analyses reveal that complexes 1 and 2 are both (3,4,4)-connected structures with the same stoichiometry of (3-c)2(4-c)2(4-c), the 2D {63}2{64.8.10}{64.82}2 trilayer for 1, and 3D {6.82}2{64.82}2{8.104.12} network for 2. Complexes 1 and 2 exhibit excellent recyclable, selective, and sensitive detection of Cr(VI) anions in aqueous solution. The possible mechanism for selective luminescence quenching responses toward Cr(VI) anions is also discussed in detail.

Adsorption of Chromate from Aqueous Solution by Polyethylenimine Modified Multi-Walled Carbon Nanotubes.

In this paper, multiwall carbon nanotubes (MWCNTs) were modified by Polyethylenimine of different molecular weight of 1800 (MWCNTs-18) and 7000 (MWCNTs-70). The structure and morphology of the functionalized MWCNTs were characterized by thermogravimetric analysis (TGA), X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The curve of TGA showed that the mass loss of MWCNTs-18 and MWCNTs-70 were 46.5% and 51.9% respectively, which was remarkably different with pristine MWCNTs. The XRD demonstrated that the structure of the pristine MWCNTs and functionalized MWCNTs were similar. In addition, the experiment of the removal of chromate from water solution using functionalized MWCNTs was also conducted. The experimental conditions such as concentration of chromate, temperature, pH were studied. The maximum uptake capacities for chromate anions were obtained at the concentration of 0.4 mmol·L-1. The solution pH showed a significant effect on chromate removal over a pH range from 4.0 to 9.0. Besides, the uptake capacities for chromate anions on MWCNTs-18 and MWCNTs-70 increased as the temperature increase within the range from 30 to 60 °C. Under the experimental conditions, the maximum uptake capacities of MWCNTs-18 and MWCNTs-70 for chromate anions were 0.27 and 0.33 mmol·g-1 respectively. The thermodynamic parameters of the uptake process were calculated, and the results showed that the process of uptake chromate was spontaneous.

Structural diversity and luminescent sensing of three coordination polymers based on the hydrolysates of N,N′-bis(3,5-dicarboxylatophenyl)pyromelliticdi-imide)

Based on the hydrolysates of N,N′-bis(3,5-dicarboxylatophenyl)pyromelliticdi-imide) (H4L) and 1,3-bis(imidazol-1-ylmethyl)benzene (bimb), three coordination polymers, namely, {[Zn(BTC)0.5(bimb)]·4H2O}n (1), [Cu(BTC)0.5(bimb)]n (2), and {[Cd(AIP)(H2O)]·H2O}n (3), have been obtained under solvothermal conditions. The possible hydrolysis mechanism of H4L was investigated here. Structural analyses reveal that complex 1 is a 3D (4,4)-c {64.82}{66}2-bbf net. Complex 2 displays a 2D 4-c {32.62.72}-kgm sheet. While complex 3 exhibits a 3D (3,6)-c {4.62}2{42.610.83}-rtl net based on binuclear {Cd2(COO)4} SBUs. Besides, luminescent sensing investigation indicated that 1 and 3 exhibit highly sensitive and selective sensing of chromate anions in aqueous solution.

Jahn–Teller Effect in the [CuEn3]CrO4 Structure

A change in the coordination of the copper atom in the crystal structure of [CuEn3]CrO4 (En is ethylenediamine) in studied in the range 150–300 K. According to the single crystal X-ray diffraction (XRD) data at 150 K, the single crystal has a complicated twining character based on the triclinic cell (a = 9.027(2) A, b = 13.335(3) A, c = 13.339(3) A, α = 71.77(3)°, β = 70.53(3)°, γ = 70.42(3)°) composed of two crystallographically independent [CuEn3]2+ complex cations. The coordination of copper atoms is a distorted square bipyramid; four short Cu–N distances lie in the range 2.049-2.082 A; two long ones are 2.415 A and 2.470 A. According to the differential scanning calorimetry (DSC) data, near 218 K there is a phase transition. The single crystal XRD experiment performed at 250 K (a = 15.6992(19) A, c = 9.7573(13) A, V = 2082.6(6) A3, space group P\(\bar 3\)c1 (No. 165), Z = 6) shows that chromate anions are disordered over three positions about the с axis, and Cu–N distances are 2.120-2.177 A. According to the DSC data, on further heating the structure undergoes yet another two alterations (260 K and 270 K) due to the disordering of oxygen atoms of chromate anions and the subsequent equalization of Cu–N distances. At 300 K in the structure (a = 9.0778(6) A, c = 9.7715(5) A, V = 697.4 A3, space group P\(\bar 3\)c (No. 163), Z = 2) all Cu–N distances are 2.155 A, and chromate anions are disordered over six positions about the с axis. A comparative crystal chemical analysis of the packing of the studied structures is carried out.

Determination and speciation of ultratrace arsenic and chromium species using aluminium oxide supported on graphene oxide

Alumina supported on graphene oxide (Al2O3/GO) nanocomposite as new nanosorbent in dispersive micro-solid phase extraction (DMSPE) for As(V) and Cr(III) preconcentration is described. The crucial issue of the study is synthesis of novel nanocomposite suitable for sorption of selected species of arsenic and chromium. Al2O3/GO demonstrates selectivity toward arsenates in the presence of arsenites at pH 5 and chromium(III) ions in the presence of chromate anions at pH 6. The Al2O3/GO nanocomposite was characterized by scanning electron microscopy (SEM) transmission electron microscopy (TEM), powder X-ray diffraction (XRD) and the Raman spectroscopy. The maximum adsorption capacity calculated based on the Langmuir adsorption model were 43.9 mg g−1 and 53.9 mg g−1 for As(V) and Cr(III), respectively. The nanocomposite was used as solid sorbent in preconcentration of As(V) and Cr(III)_ions from water samples and their determination using energy dispersive X-ray fluorescence spectrometry (EDXRF). The As(V) and Cr(III) ions can be quantitatively preconcentrated from 25 to 100 mL aqueous samples within 5 min using DMSPE procedure and 1 mg of Al2O3/GO. The nanocomposite was also used for preparation of Al2O3/GO membrane. Then, As(V) and Cr(III)_ions can be retained under flow condition by passing analyzed solution through Al2O3/GO membrane. Under the optimized conditions, As(V) and Cr(III) ions can be determined with very good recovery (92–108%), precision (RSD 2.7–4.0%) and excellent limit of detection (0.02 ng mL−1 As and 0.11 ng mL−1 Cr). The accuracy of the method was studied by analyzing certified reference materials (NIST 1640a) and spiked real water samples.

Structure of A Coordination Polymer [Cu(En)2CrO4

The crystal structure of [Cu(En)2CrO4]n (En is ethylenediamine) is determined: a = 14.7359(4) A, b = 9.8083(3) A, c = 14.2664(4) A, V = 2061.98(10) A3, space group Cmce, Z = 8, dx = 1.931 g/cm3. It is demonstrated that the studied phase is isostructural with [Сu(Еn)2SO4]n. A pseudotetragonal copper atom coordination (Cu–N 2.0204 A and 2.0244 A, ∠N–Cu–N 84.73°) is completed to distorted octahedral by two oxygen atoms of chromate anions (Cu–O 2.433 A and 2.380 A).

Ultrasound-assisted synthesis of zinc molybdate nanocrystals and molybdate-doped epoxy/PDMS nanocomposite coatings for Mg alloy protection

Zinc molybdate (ZM) is a safer anticorrosive additive for cooling systems when compared with chromates and lead salts, due to its insolubility in aqueous media. For most molybdate pigments, their molybdate anion (MoO4-2) acts as an anionic inhibitor and its passivation capacity is comparable with chromate anion (CrO4-2). To alleviate the environmental concerns involving chromates-based industrial protective coatings, we have proposed new alternative in this work. We have synthesized ZM nanocrystals via ultrasound-assisted process and encapsulated them within an epoxy/PDMS coating towards corrosion protection. The surface morphology and mechanical properties of these ZM doped epoxy/PDMS nanocomposite coatings is exhaustively discussed to show the effect of ZM content on protective properties. The presence of ZM nanocrystals significantly contributed to the corrosion barrier performance of the coating while the amount of ZM nanocrystals needed to prepare an epoxy coating with optimum barrier performance was established. Beyond 2 wt% ZM concentration, the siloxane-structured epoxy coating network became saturated with ZM pigments. This further broadened inherent pores channels, leading to the percolation of corrosion chloride ions through the coating. SEM evidence has revealed proof of surface delamination on ZM3 coating. A model mechanism of corrosion resistance has been proposed for ZM doped epoxy/PDMS nanocomposite coatings from exhaustive surface morphological investigations and evidence. This coating matrix may have emerging applications in cooling systems as anticorrosive surface paints as well as create an avenue for environmental corrosion remediation.

Mesoporous Iron-Manganese Magnetic Bimetal Oxide for Efficient Removal of Cr(VI) from Synthetic Aqueous Solution

A facile co-precipitation method was established for synthesis of mesoporous iron-manganese magnetic bimetal oxide (MIMO) and its adsorption property was studied for removal of toxic metal ion hexavalent chromium from aqueous solution. XRD pattern of MIMO confirms the existence of Fe2O3 and Mn3O4 particle, out of which Mn3O4 is ferrimagnetic in nature. Synthesized MIMO has shown high saturation magnetization (23.08 emu/g), high BET surface area (178.27 m2/g) and high pore volume (0.484 cm3/g), which makes it a potential adsorbent. Adsorption process followed second order kinetic and Langmuir isotherm model. Involvement of intra-particle diffusion is also confirmed from kinetic data, which can be attributed to the mesoporous nature of the MIMO. Cr(VI) adsorption shows high pH dependency and maximum adsorption capacity of 116.25 mg/g is reported at pH 2.0. Electrostatic attraction between anionic chromium species and protonated MIMO surface is the predominant mechanism in this adsorption process.

Terphenyltetracarboxylate acid based 3D modular cobalt(II) coordination polymer with highly sensitive luminescent sensing of chromate anions

Based on the mixed ligands synthesis strategy, a 3D cobalt (II) coordination polymer, [Co(tptc)0.5(bib)]n (1), has been assembled from p-terphenyl-2,2″,5″,5″'-tetracarboxylate acid (H4tptc) and 1,3-bis((imidazol-1-yl) benzene (bib). Structural analysis revealed that complex 1 is a 3D framework, which can be simplified into a (4,4)-connected {64.82}{66}2bbf net. And the modular analysis reveals the tiling of 1 is [6.82] + [63.8] = [6c.8a.8b] + [6a.6b.6c.8a] with the transitivity is 2352. And the luminescent sensing investigation indicating complex 1 exhibits highly sensitive sensing of CrO42−/Cr2O72− anions in aqueous solution through strong luminescence quenching effects.

Simultaneous determination of chromate and common inorganic anions using suppressed ion chromatography

Simultaneous determination of chromate and common inorganic anions using suppressed ion chromatography

Experimental and Theoretical Studies on the Adsorption and Desorption Mechanisms of Chromate Ions on Cross-Linked Chitosan.

In this work, chitosan bead materials were modified by cross-linking with epichlorohydrin (EP) and glutaraldehyde (GA) for the removal of heavy metals in wastewater. Using these cross-linked chitosan materials, the dependence of adsorption of chromate anions on pH was investigated experimentally and theoretically. The experimental results show that the adsorption process of the chromate (Cr) ions greatly depends on the pH of the solution, with the chitosan modified by cross-linking being an efficient adsorbent for chromate. On the other hand, quantum chemistry calculations were conducted to find out the factor determining the pH dependence of the adsorption efficiency of chromate ions on the dimer chitosan molecule, and show results similar to those found in the experiment. Both the experimental and numerical results show that the total charge numbers of the adsorbent and the adsorbate species and their relative molecular geometries are crucial in determining the adsorption efficiency.

Influence of catalyst amount on properties of resorcinol-formaldehyde xerogels

The effect of catalyst amount on properties of resorcinol-formaldehyde xerogels was investigated. The samples were prepared by sol-gel polycondensation of resorcinol with formaldehyde at three different levels of catalyst (Na2CO3, molar ratios of resorcinol/catalyst R/C = 1000, 2000, 3000). The influence on mechanical, thermal and thermomechanical properties of organic xerogels and on properties of carbon xerogels (surface, adsorption and oxyreactivity) was evaluated. The higher R/C ratio leads to increased particle size of the materials, which affects mechanical strength, residual humidity and shrinkage during heating (all parameters decrease). The R/C ratio does not affect significantly pyrolysis process and microporosity of the materials, the effect on oxyreactivity was negligible. Contrary, higher catalyst content (R/C = 1000) lead to relative high volume of ink-bottle shaped mesopores, but this pores are practically unavailable for adsorption of large molecules of methylene blue or hydrated chromate anions, which negatively influenced adsorption of both adsorbates from aqueous solution on the carbon xerogels.

Interactions of low-energy electrons with the FEBID precursor chromium hexacarbonyl (Cr(CO)6).

Interactions of low-energy electrons with the FEBID precursor Cr(CO)6 have been investigated in a crossed electron–molecular beam setup coupled with a double focusing mass spectrometer with reverse geometry. Dissociative electron attachment leads to the formation of a series of anions by the loss of CO ligand units. The bare chromium anion is formed by electron capture at an electron energy of about 9 eV. Metastable decays of Cr(CO)5− into Cr(CO)4−, Cr(CO)4− into Cr(CO)3− and Cr(CO)3− into Cr(CO)2− are discussed. Electron-induced dissociation at 70 eV impact energy was found to be in agreement with previous studies. A series of Cr(CO)nC+ (0 ≤ n ≤ 3) cations formed by C–O cleavage is described for the first time. The metastable decay of Cr(CO)6+ into Cr(CO)5+ and collision-induced dissociation leading to bare Cr+, are discussed. In addition, doubly charged cations were identified and the ration between doubly and singly charged fragments was determined and compared with previous studies, showing considerable differences.

Minerals with Brackebuschite-Like Structures: A Novel Solid Solution System Involving Cr6+ and V5+

A novel complex continuous system of solid solutions involving vauquelinite Pb2Cu(CrO4)(PO4)(OH), bushmakinite Pb2Al(VO4)(PO4)(OH), ferribushmakinite Pb2Fe3+(VO4)(PO4)(OH), and a phase with the endmember formula Pb2Cu(VO4)(PO4)(H2O) or Pb2Cu(VO4)(РО3ОН)(ОН) is studied based on samples from the oxidation zone of the Berezovskoe, Trebiat, and Pervomaisko-Zverevsky deposits in the Urals, Russia. This is the first natural system in which chromate and vanadate anions show a wide range of substitutions and the most extensive solid solution system involving (CrO4)2– found in nature. The major couple substitution is Cr6+ + Cu2+ ↔ V5+ + M3+, where M = Fe, Al. The correlation coefficients calculated from 125 point analyses are: 0.96 between V and (Fe + Al), 0.96 between Cr and (Cu + Zn),–0.96 between V and (Cu + Zn),–0.97 between Cr and (Fe + Al), and–0.97 between (Fe + Al) and (Cu + Zn). The substitutions V5+ ↔ Cr6+ (correlation coefficient–0.98) and to a lesser extent P5+ ↔ As5+ (correlation coefficient–0.86) occur at two types of tetrahedral sites, whereas the metal–nonmetal/metalloid substitutions, i.e., V or Cr for P or As, are minor. The substitution Fe3+ ↔ Al3+ is also negligible in this solid solution system.

ZnEn3]CrO4 as a precursor of zinc chromite spinel

The structure of [ZnEn3]CrO4 (En is ethylendiamine) complex salt is determined. It is demonstrated that at room temperature the crystallographic characteristics are as follows: а = 9.0942(4) A, с = 9.7673(4) A, space group Р-31с (No. 163). Contrary to [ZnEn3]SO4, disordered chromate anions participate in its formation. When [ZnEn3]CrO4 is heated in a hydrogen atmosphere up to 700 °C, zinc chromite spinel is formed (а = 8.328 A, space group Fd-3m), which has a complex nanocrystalline structure.

A bifunctional chemosensor for detection of volatile ketone or hexavalent chromate anions in aqueous solution based on a Cd(II) metal–organic framework

Abstract A new porous metal–organic framework with chemical formula of [Cd3(cpota)2(phen)3]n·5nH2O (MOF-1) (H3cpota = 2-(4-carboxyphenoxy)terephthalic acid & phen = 1,10-phenanthroline) has been synthesized and characterized by infrared spectroscopy, elemental analysis, thermogravimetry and X-ray single crystal and powder diffracting methods. MOF-1, as a potential material of the sensing applications, has an uncommon 3D microporous structure in which the trinuclear [Cd3(phen)3(μ2-COO)4]2+ SBUs are interconnected by the V-shaped cpota3− ligands. MOF-1 has good stabilities not only in aqueous solution in the range of pH = 1.0 ∼ 14.0 but also in solid from room temperature (RT) to 330 °C. Fluorescence titration, cyclic and anti-interference experiments demonstrate that MOF-1 is an excellent probe for volatile organic ketones (acetone/2-butanone) and hexavalent chromate (CrO42−/Cr2O72−) in aqueous solution. The luminescence investigations in the aqueous solution of pH = 9 reveal that the MOF-1 can efficiently and selectively detect Cr(VI) ions without the interference of other metal cations. Quenching mechanisms are also studied in detail.

Electrospun Nanofibrous Polyacrylonitrile/calixarene Mats: an Excellent Adsorbent for the Removal of Chromate Ions from Aqueous Solutions.

Herein, calixarene molecules containing piperidine units at lower rim or upper rim of calix skeleton was turned into a water resistant composite nanofiber adsorbent using polyacrylonitrile (PAN) polymeric support via electrospinning process. The PAN based calixarene nanofibrous adsorbents showed an excellent adsorption capacity toward the toxic chromate anions in aqueous solution. Furthermore, this new nanofiber mats would be promising filter materials for drinking water purification.

Mixed-Ligand LMOF Fluorosensors for Detection of Cr(VI) Oxyanions and Fe3+/Pd2+ Cations in Aqueous Media.

Zn(II)/Cd(II)-based dual ligand Luminescent Metal-Organic Frameworks (LMOFs) {[M(ATA)(L)]}n·xH2O (1) and (2) were synthesized by versatile synthetic routes, viz., diffusion of precursor solutions, conventional reflux, and green mechanochemical (grinding) reactions from bipyridyl-based Schiff base, (E)-N'-(pyridin-4-ylmethylene)isonicotinohydrazide (L) and amino functionalized 2-aminoterephthalic acid (H2ATA) as linkers. Chemical and thermal stability, phase purity, and characterization of both LMOFs were established by various analytical methods. SXRD analysis revealed the 3D framework is composed of two-dimensional [M(ATA)]n nets doubly pillared by L through the terminal nitrogen atom. Selective and sensitive detection of chromate anions (CrO42-/Cr2O72-) and Fe3+/Pd2+ cations in the aqueous phase by fluorescent quenching of the LMOFs 1 and 2 has been established. Competitive experiments in the presence of interfering anions/cations with 1 and 2 revealed no major change in the quenching efficiency. The observed limits of detection (LOD) values by 1 for CrO42-/Cr2O72- were 0.25 μM (48 ppb)/0.43 μM (126 ppb) and for Fe3+/Pd2+ were 3.76 μM (0.61 ppm)/0.20 μM (35 ppb), whereas LOD values by 2 were 0.18 μM (35 ppb)/0.19 μM (55 ppb) and 1.77 μM (0.29 ppm)/0.10 μM (18 ppb), respectively. Simple fluorescent-based test paper strips have been developed for reliable and visual detection of the mentioned analytes in practical applications. The present investigation clearly demonstrates selective detection of CrO42-/Cr2O72- and Fe3+/Pd2+ in aqueous media, and the probable mechanism for the quenching phenomena based on structural aspects has also been discussed.

Variation in Extracellular Detoxification Is a Link to Different Carcinogenicity among Chromates in Rodent and Human Lungs.

Inhalation of soluble chromium(VI) is firmly linked with higher risks of lung cancer in humans. However, comparative studies in rats have found a high lung tumorigenicity for moderately soluble chromates but no tumors for highly soluble chromates. These major species differences remain unexplained. We investigated the impact of extracellular reducers on responses of human and rat lung epithelial cells to different Cr(VI) forms. Extracellular reduction of Cr(VI) is a detoxification process, and rat and human lung lining fluids contain different concentrations of ascorbate and glutathione. We found that reduction of chromate anions in simulated lung fluids was principally driven by ascorbate with only minimal contribution from glutathione. The addition of 500 μM ascorbate (∼rat lung fluid concentration) to culture media strongly inhibited cellular uptake of chromate anions and completely prevented their cytotoxicity even at otherwise lethal doses. While proportionally less effective, 50 μM extracellular ascorbate (∼human lung fluid concentration) also decreased uptake of chromate anions and their cytotoxicity. In comparison to chromate anions, uptake and cytotoxicity of respirable particles of moderately soluble CaCrO4 and SrCrO4 were much less sensitive to suppression by extracellular ascorbate, especially during early exposure times and in primary bronchial cells. In the absence of extracellular ascorbate, chromate anions and CaCrO4/SrCrO4 particles produced overall similar levels of DNA double-stranded breaks, with less soluble particles exhibiting a slower rate of breakage. Our results indicate that a gradual extracellular dissolution and a rapid internalization of calcium chromate and strontium chromate particles makes them resistant to detoxification outside the cells, which is extremely effective for chromate anions in the rat lung fluid. The detoxification potential of the human lung fluid is significant but much lower and insufficient to provide a threshold-type dose dependence for soluble chromates.

Comparative sorption studies of chromate by nano-and-micro sized Fe2O3 particles

AbstractThe comparative adsorption studies of Cr (VI) on nano and micro-powder Fe2O3 were investigated using kinetics and batch adsorption techniques. The uptake of chromate onto both the oxides of iron was observed to be dependent on the pH, contact time, temperature, media dosage and concentration of chromate anions. The values of sorption maxima were higher in the case of Fe2O3 nanopowder than the micro-powder which can be ascribed to the high surface area and point of zero charge (PZC) of the former oxide. The Dubinin-Radushkivech and Langmuir models were found well fitted for the description of the batch adsorption data. The FTIR studies confirmed that the hexavalent chromium was adsorbed onto both the iron oxides in the form of the Cr2O72−.