CrVI Ions Research Articles

Synthesis, Characterization, and Application of a Polyoxometalates‐Based CuII Complex for Efficient Catalytic Oxidation and Electrochemical Detection

AbstractThe development of eco‐friendly, high‐efficiency polyoxometalates (POMs) catalysts is vital for advancing catalytic oxidation and electrochemical detection in environmental protection. Herein, a POM‐based CuII‐containing complex with the molecular formula [H(4‐AP)]8[Cu2(H2O)4(P2Mo5O23)2]·8H2O (1) (4‐AP = 4‐aminopyridine) is synthesized using the hydrothermal method, and the crystal structure is determined by single X‐ray diffraction (SXRD), infrared (IR) spectroscopy, and powder X‐ray diffraction (PXRD). Structurally, complex 1 exhibits a one dimension (1D) chain arrangement, composed of CuII ions and Strandberg‐type (P2Mo5O23)6− anionic clusters. These 1D chains are further interconnected through [H(4‐AP)]+ ligands, resulting in the formation of a two dimension (2D) supramolecular network. Complex 1 serves as an outstanding heterogeneous catalyst for the oxidation of methyl phenyl sulfide (MPS), demonstrating a remarkable conversion rate of 99% for MPS and a selectivity of 98% toward methyl phenyl sulfoxide (MPSO). In addition to its catalytic capabilities, complex 1 is also employed in the electrochemical detection of FeIII and CrVI ions, with low limits of detection (LODs) at 4.92 µm for FeIII and 7.82 µM for CrVI.

PH-Stable Luminescent Metal-Organic Frameworks for the Selective Detection of Aqueous-Phase FeIII and CrVI Ions.

The development of chemically stable metal-organic framework (MOF)-based luminescent platforms for toxic ion detection in an aqueous medium is highly challenging because most of the classical MOFs are prone to water degradation, and that is the reason why most of the MOF-based luminescent sensors use a nonaqueous medium for sensing. In this contribution, we report two new water-stable luminescent MOFs (Zn-MOF-1 and Zn-MOF-2), assembled from a mixed-ligand synthesis approach. Because of the presence of a hydrophobic trifluoromethyl group to the backbone and stronger metal-N coordination, these MOFs exhibit excellent stability not only in water but also in acidic/alkaline aqueous solutions (pH = 3-10). Here, we report a green sensing approach by exploiting the significant reduction in photoluminescence of these MOFs in the presence of toxic ions. Fe3+ and CrO42-/Cr2O72- ions could be traced with a detection limit (LOD) in the micromolar range (0.045 and 0.745/0.33 μM for Zn-MOF-1; 125.2 and 114.2/83.5 μM for Zn-MOF-2). The mechanistic study reveals that competitive absorption of the excitation energy coupled with fluorescent resonance energy transfer are responsible for the turn-off quenching. The anti-interference ability and recyclability along with the pH stability gave these MOFs high potential to be used as practical sensors toward FeIII and CrVI ions in water as a greenest medium.

Multivariate Functionalization of UiO‐66 for Photocatalytic Water Remediation

AbstractThe fast‐increasing interest in multivariate metal–organic frameworks (MTV‐MOFs) has burgeoned due to the possibility to create synergetic functions and achieve performance significantly better than their simple sum. In this work, the opportunities and the effects of multivariate functionalization of UiO‐66 on diverse properties important for photocatalytic water remediation: hydrolytic stability, bandgap energy, photoconduction, CrVI and CrIII adsorption capacity and kinetics, and CrVI to CrIII photoreduction efficiency, are explored. By developing a (Zr)UiO‐66‐NH2‐(OH)2‐NO2 multivariate material based on the combination of 2‐aminoterephthalate, 2,5‐dihydroxyterephthalate, and 2‐nitroterephthalate organic linkers in the same framework, a dual sorbent/photocatalyst is developed for water remediation with excellent properties: 1) enhanced adsorption efficiency of CrVI and CrIII ions, 2) improved photocatalytic conversion of CrVI to CrIII, and 3) with suitable chemical stability under acidic conditions for catalytic applications. This work represents a milestone for an emerging class of reticular materials that can synergistically use the properties of individual functionalities to solve complex problems beyond just the water remediation application discussed in this paper.

The Potential of Cellulose from the Sugar Palm (Arenga Pinnata) Seed Shell for Removal of Cr(Vi) Ions

Cr (VI) is persistent, bio-accumulative, toxic metal, unable to decompose in the environment, and accumulates in the human body through the food chain. The Cr(VI) ions can remove in aqueous solution by adsorption technique with cellulose extracted. Extract of cellulose were prepare from palm (Arenga pinnata) seed shell using acidified H2SO4 and bleaching methods. The cellulose have contained the hydroxyl (–OH) functional groups in structure, it can be an adsorbent for heavy metal ions. Cellulose was obtained with delignification and bleaching methods to break the bond between lignin and cellulose. The cellulose extracted were characterized by Fourier Transformation Infra-Red (FT-IR) and Scanning Electron Microscopy - Energy Dispersive X-Ray (SEM)-EDX. The adsorption process was conducted using pH, contact time, and concentration of Cr(VI) ions. The results showed that the optimum pH was obtained at pH 3 with an adsorption capacity is 0.88 mg/g. The optimum contact time was obtained at 120 minutes with an adsorption capacity is 0.89 mg/g. The optimum concentration was obtained at a concentration of 200 ppm with an adsorption capacity is 20.34 mg/g

Efficiency of humic acid from various organic sources for reducing hexavalent chromium in aqueous solutions

In this study, efficiency of humic acids (HAs) derived from various sources to reduce CrVI in aqueous solutions was compared. HAs were extracted from leonardite, peat moss, peat, cocopeat, coal, common char, biochar, vermicompost and sewage sludge. Some chemical and spectral characteristics of the extracted HAs were measured. Then, the reducing efficiency of HAs was measured and its relationship with the determined properties was investigated. To measure the reducing efficiency of HAs, a concentration of 0.1 mM CrVI (as potassium dichromate) in a sodium nitrate solution (0.03M) with a pH of 2 and in the presence of 100 mg of HA per liter was used. The experiment was conducted in three ways (symbolized by E1, E2 and E3). They differ from each other with respect to the method of phosphate buffer addition to release CrVI ions adsorbed by HA. This buffer was added to an aliquot of final extract, to the whole volume of final suspension and to initial solution containing CrVI in experiments E1, E2 and E3, respectively. According to the results, the CrVI reducing efficiency depends not only on the nature of HA but on the method of experiment. The minimum reducing efficiency was observed for common char using experiment E2 and the maximum value was for biochar and cocopeat in all three experiments. The results showed that the two factors of ΔlogK and maximum reducing efficiency in the format of a multiple regression had a significant relationship with CrVI reducing efficiency of HAs.

Selective sensing of CrVI and FeIII ions in aqueous solution by an exceptionally stable TbIII-organic framework with an AIE-active ligand

We herein report a new lanthanide metal-organic framework (MOF) that exhibits excellent chemical stability, especially in the aqueous solution over a wide pH range from 1 to 14. In contrast to many reported lanthanide MOFs, this Tb-based MOF emits cyan fluorescence inherited from the integrated AIE-active ligand, rather than Ln3+ ions. More remarkably, its fluorescence signal features a highly selective and sensitive “turn-off” response toward CrO42−, Cr2O72− and Fe3+ ions, highlighted with the low detection limits down to 68.18, 69.85 and 138.8 ppm, respectively. Thus, the exceptional structural stability and sensing performance render this material able to be a superior luminescent sensor for heavy metal ions in wastewater.

Assembly of CeO2–MoO3–SiO2(CH2)3-(Alginate)2 As A novel nanocomposite for removal of MnII/CrVI and 56Mn/51Cr radionuclides from water

A new nanocomposite, CeO2–MoO3–SiO2(CH2)3-(Alg)2, has been synthesized via a simple synthesis method using a microwave irradiation technique. The morphological characterization indicated that the average particle size of the nanocomposite is 94.26–141.54 nm.The adsorptive remediation was established for MnII and CrVI ions by the nanocomposite under the influence of the microwave sorption process. Additionally, remediation of 51Cr and 56Mn radioactive nuclides was established using column technique. In this study, all the adsorption controlling parameters were explored like, solutions pH, contact time, amount of nanocomposite, and ionic concentration of the target metals. The maximum metal up-take capacities were estimated as 122.06 mg/g for MnII and 151.96 mg/g for CrVI by utilizing 5.0 mg of the nanocomposite at pH values 7.0 for MnII, and 2.0 for CrVI, while the equilibrium time at 25, and 20 s for MnII, and CrVI ions, respectively. The adsorption kinetics of MnII, and CrVI ions onto the CeO2–MoO3–SiO2(CH2)3-(Alg)2 nanocomposite proved to fit with the pseudo-second-order kinetics model and the adsorption mechanism fitted to the Langmuir and Freundlich isotherm models compared to the other models.

Yellow Mombin (Spondias mombin L.) Seeds from Agro-Industrial Waste as a Novel Adsorbent for Removal of Hexavalent Chromium from Aqueous Solutions

The objective of this study was to develop a low-cost and eco-friendly adsorbent from agro-industrial waste for the removal of hexavalent chromium in the aqueous medium. The adsorbent (BMC) produced from yellow mombin (Spondias mombin L.) seeds was characterized by the determination of the chemical composition, thermal analysis (thermogravimetric (TG) analysis and differential thermal analysis (DTA)), Fourier transform infrared spectroscopy (FTIR), pH in suspension and determination of the point of zero charge (PZC). The presence of proteins, fats and carbohydrates (15.690, 1.004, and 73.706%, respectively) suggests that the material can be a promising adsorbent, given the availability of functional groups. The following conditions were set: pH 2.0, adsorbent mass 450 mg, and equilibrium was reached after 80 min. The maximum adsorption capacity was approximately 98%. Kinetic studies showed that the pseudo-second-order kinetic equation was the one that best adjusted to the experimental data. Under the conditions investigated, the Langmuir isotherm model described the best balance data, signaling the adsorption in monolayer. According to the results, it was found that the BMC showed an outstanding performance for the removal of CrVI ions and may become a viable and efficient alternative for the treatment of industrial effluents containing trace elements.

Two Cd(II)-organic frameworks for the highly luminescence sensitive detection of CrVI ions in an aqueous medium

Two novel cadmium-based luminescent metal-organic framework (LMOFs), {[Cd(PIAD)(H2O)]·H2O}n (1) and [Cd(PIAD)]n (2), has been successfully assembled by H2PIAD a solvothermal method. Complex 1 possesses a 2D layered structure with a binodal 4,4-connected net. Complex 2 presents a 3D dense-packing structure with a binodal 5,5-connected net. Meanwhile, complex 1 exhibits highly efficient luminescent sensing towards CrO42− and Cr2O72− ions with the detection limits of 2.12 ​× ​10−4 and 2.02 ​× ​10−5 ​M, respectively, and the mechanisms of the quenching effect are studied in detail.

Chitin-based magnetic composite for the removal of contaminating substances from aqueous media

A method of obtaining multipurpose magnetic chitin, which combines the magnetic properties of magnetite and the adsorption properties of polysaccharide, was proposed. The possibility of using chitin-(CT) and chitosan (CS)-containing magnetic composites for the adsorption of inorganic ions CoII and CrVI and organic substances (2- and 4-nitrophenols) from aqueous media was analyzed. It was shown that the adsorption capacity of magnetic chitin with respect to CoII and CrVI ions reached 41 mg g−1 and 15 mg g−1, respectively. The maximum adsorption capacity for 4-nitrophenol (19 mg g−1 per CT-containing magnetic composite or 56 mg g−1 per chitin component) was about three times higher than for 2-nitrophenol. The obtained adsorbent Fe3O4/CT is environmentally friendly and reusable.

Facile photocatalytic reduction of carcinogenic Cr(vi) on Fe-doped copper sulfide nanostructures.

In this study, Fe-doped copper sulfide nanoparticles (NPs) were investigated for the solar-assisted reduction of CrVI ions in raw water. The Fe-doped NPs were synthesized by decomposing copper(ii) N,N-diphenylmethylpiperazinecarbamodithioate via a facile single-step, one-pot solvothermal method in the presence of iron salt. The CrVI photoreduction data were fit to a pseudo-first-order kinetic model and a Langmuir model. The CuS/Cu2S NP reduction ability for CrVI increases with an increase in dopant percentage. The best catalyst (9% Fe-doped) was able to reduce CrVI (10−4 M K2Cr2O7) to CrIII in raw water using an initial amount of 10 mg in 6 min with a reduction efficiency of up to 100%. The photocatalytic activity was examined while varying five different parameters: sunlight, diffused light, change in pH, and changes in the concentration of the catalyst and the temperature. This new approach presents an active, simple, and cost-effective means for wastewater treatment.

Four Zn(II)–organic frameworks as luminescent probe for highly selectivity detection of CrVI ions and antibiotics

Four new luminescent metal–organic frameworks (LMOFs), {[Zn(L)]·CH3CN}n (1), [Zn2(L)2]n (2), [Zn(L) (H2O)]n (3) and {[Zn(L) (H2O)]·DMA}n (4), were assembled employing 6-(3-pyridyl)isophthalic acid (H2L) with Zn(II) ions, revealing versatile frameworks as well as various types of coordination modes of H2L. Single-crystal X-ray diffraction analyses reveal that complexes 1 and 4 exhibit a 3D dense-packing structure with a bi-nodal 3,6-connected net and an uninodal 3-connected net, respectively; while complexes 2 and 3 show 2D layered structures with a bi-nodal 3,6-connected net and an uninodal 3-connected net, respectively. Further, the solid-state luminescence properties of the complexes were measured at room temperature. The results manifest that 1 shows high selectivity and sensitivity for Cr(VI)-containing anions with detection limits of 43.77 ppm for CrO42− and 64.77 ppm for Cr2O72−. In addition, the luminescence of 1 can be quenched efficiently by trace amounts of antibiotics (dimetridazole, DTZ; sulfadiazine, SDZ; nitrofurazone, NZF; nitrofurantoin, NFT; furazolidone, FZD; chloramphenicols, INN). Complex 1 is responsive to antibiotics with detection limits of 1.35 ppm for DTZ, 1892.27 ppm for SDZ, 0.62 ppm for NZF, 0.78 ppm for NTF, FZD for 6.87 ppm.

A pillar-layer strategy to construct 2D polycatenated coordination polymers for luminescence detection of Cr2O72− and CrO42− in aqueous solution

Six polycatenated coordination polymers 1–6 based on the pillar-layer strategy have been designed and synthesized. Compound 6 exhibited strong fluorescence that was selectively quenched by CrVI ions in aqueous solution at low concentrations.

Crystal structures of hybrid completely reduced phosphomolybdates and catalytic performance applied as molecular catalysts for the reduction of chromium(VI).

The exploration of highly efficient and low-cost catalysts for the treatment of hexavalent chromium CrVI in environmental remediation is currently one of the most challenging topics. Here, three phosphomolybdate hybrid compounds have been successfully isolated by the hydrothermal method and been applied as supramolecular catalysts for the reduction of CrVI. Single-crystal X-ray diffraction revealed their formulae as (H2bpp)2[Fe(H2O)][Sr(H2O)4]2{Fe[Mo6O12(OH)3(H2PO4)(HPO4)(PO4)2]2}·5H2O (1), (H2bpp)2[Na(H2O)(OC2H5)][Fe(H2O)2][Ca(H2O)2]2{Fe[Mo6O12(OH)3(H2PO4)(HPO4)(PO4)2]2}·4H2O (2) and (H2bpe)3{Fe[Mo6O12(OH)3(HPO4)3(H2PO4)]2}·8H2O (3) [bpp is 1,3-bis(pyridin-4-yl)propane (C13H14N2) and bpe is trans-1,2-bis(pyridin-4-yl)ethylene (C12H10N2)]. The three hybrids consist of supramolecular networks built up by noncovalent interactions between {Fe[P4Mo6VO31]2}22- polyanions and protonated organic cations. This kind of hybrid polyoxometalate could be applied as heterogeneous molecular catalysts for the reduction of CrVI. It was found that the organic moiety plays a vital role in influencing the catalytic activity of the polyanions. Organic bpp-containing hybrids 1 and 2 are highly active in the catalytic reduction of heavy metal CrVI ions using HCOOH as reductant, while bpe-containing hybrid 3 is inactive to this reaction. This work is significant for the design of new catalysts, as well as the exploration of reaction mechanisms at a molecular level.

Fe-based multi-phase nanocrystalline ribbons with hierarchically flowerlike structured metal oxides after modified by Orange II for CrVI absorption

Three-dimensional flowerlike nanostructured metal oxides attached on the surfaces of Fe-based multi-phase nanocrystalline ribbons (Fe-MNRs) were prepared by a simple way (through immersing the Fe-MNRs in Orange II solution). It has been found that the as-prepared Fe-MNRs with 3D flowerlike nanostructures (Fe-MNRs + FNs) exhibit good absorption property for a typical heavy metal ion (CrVI) in wastewater, while Fe-MNRs do not possess such properties. The Fe-MNRs + FNs could remove 99% CrVI ions from the solution in 40 min, and this adsorption property can be attributed to the ion exchange between CrVI and surface hydroxyl groups (O–H) of 3D flowerlike nanostructures. The present result suggests that the Fe-MNRs + FNs, prepared by facile way, possess great potentials in removing heavy metallic ions in wastewater.

Stable ZnI -Containing MOFs with Large [Zn70 ] Nanocages from Assembly of ZnII Ions and Aromatic [ZnI8 ] Clusters.

Two unique ZnI -containing MOFs {[ZnI8 ZnII3 (H2 O)x (HL)12 ](OH)2 ⋅13 H2 O}n (x=6, 1; x=2, 2) (HL=tetrazole monoanion) with high-nuclearity Zn-cages were prepared successfully. These Zn-cages are constructed from [ZnI8 ] clusters with multi-centered ZnI -ZnI bonds and ZnII ions. [ZnI8 ] clusters in 1 and 2 display Oh and D4h symmetry, respectively. Importantly, eight [ZnI8 ] clusters and six ZnII ions form a large [Zn70 ] nanocage in 1. To our knowledge, this is the first MOF based on polynuclear Zn-cages consisting of ZnI and ZnII ions. Compared with reported ZnI -species, 1 and 2 display high thermal and solvent stabilities. Theoretical investigations based on DFT calculations uncover that effective 4s-4s orbital overlap and electron delocalization through these a1g +t1u molecular orbitals on [ZnI8 ] clusters lead to considerable aromatic stabilization, which can explain well the intrinsic stability of 1 and 2. Interestingly, 1 can behave as a luminescent probe to detect the toxic CrVI ions in aqueous.

Isotherm Studies of Adsorption of Cr (Vi) Ions onto Coconut Husk

In this study, the application of ground coconut husk GCH for removal of Cr (VI) from its aqueous solution was investigated. Several batch experiments were carried out with different values of test conditions including sorbent concentration, contact time, temperature and pH. The results obtained showed that adsorption of Cr (VI) followed Freundlich isotherm model. Dubinin-Radushkevich isotherm revealed that adsorption of the three metal ions principally followed chemical adsorption process. Adsorption kinetics was best described by pseudo-second order. Thermodynamic studies revealed that adsorption of Cr (VI) were endothermic process since ∆H was positive. Adsorption of Cr (VI) was spontaneous as evident from the negative value ∆G. Uptake of metal ion from their aqueous solution increases with increase in pH but decreases slightly at pH of 8.

Tuning the adsorption behaviour of β-structure chitosan by metal binding

Environmental contextChitosan is an abundant natural component of marine life with potential applications as an adsorbant material for pollutants. We investigate the binding behaviour of chitosan, and show that the β-type structure readily chelates metal ions leading to enhanced adsorption of anionic pollutants in the chitosan-metal complex. The results are highly relevant to the removal of anionic organic pollutants from water. AbstractChitosan, which is commonly extracted from squid pens of the Loligo genus, has a β-type structure. Chitosan has potential application to the adsorption of pollutants but has received little study. We investigate the adsorption ability of β-structure chitosan as well as FeIII and AlIII chitosan-metal complexes. Pristine β-chitosan shows lower adsorption abilities for dye, CrVI and fluoride ions compared with those for α-chitosan, mainly owing to having fewer –NH3+ groups on its surface. However, the anionic pollutant adsorption efficiency of β-chitosan is clearly enhanced when chelated with metal ions. A β-structure chitosan-Fe-Al complex displayed adsorption capacities of 621.45 mg g−1 and 144.53 mg g−1 for Acid Red 73 dye and fluoride ions, respectively, according to the fitted Langmuir–Freundlich model; and of more than 173.03 mg g−1 for CrVI, according to the Freundlich model. These values are much higher than those observed for α-structure chitosan-metal complexes. This enhancement effect on the sorptive behaviour of β-chitosan can be attributed to its loose structure. The polymer chains of β-chitosan are arranged in parallel with relatively weak intermolecular forces, which allows them to easily chelate metal ions. Anionic pollutants can then be efficiently adsorbed by the chelated metal ions in the chitosan-metal complex if the electrostatic attraction of the –NH3+ groups is weak. This investigation provides a better understanding of β-chitosan-based adsorbents for application to anionic pollutant adsorption and removal.

Mechanism of Initiation in the Phillips Ethylene Polymerization Catalyst: Ethylene Activation by Cr(II) and the Structure of the Resulting Active Site

The structure and mechanism of the formation of sites which initiate ethylene polymerization in the atomically dispersed Phillips catalyst (Cr/SiO2) are two of the great unsolved mysteries of heterogeneous catalysis. After CO or C2H4 reduction of silica-supported CrVI ions to CrII ions in the precatalyst, exposure to ethylene results in the formation of organoCrIII sites that are capable of initiating polymerization without recourse to an external alkylating cocatalyst. In this work, a Phillips catalyst prepared, via sol–gel chemistry, as a mesoporous, optically transparent monolith was reduced with CO to the spectroscopically determined CrII end point. Ethylene causes rapid reoxidation of these CrII sites to CrIII, even at low temperatures. Solid-state 13C CP-MAS NMR, IR, and Raman spectroscopies reveal that the resulting sites contain a vinyl ligand, described as (≡SiO)2CrIII–CH═CH2 although likely with a higher coordination number, which are capable of initiating polymerization. The formation of these ...

A novel adsorbent based on magnetic Fe3O4 contained polyvinyl alcohol/chitosan composite nanofibers for chromium (Ⅵ) removal

The magnetic Fe3O4 contained polyvinyl alcohol/chitosan (Fe3O4@PVA/CS) composite nanofibers were successfully synthesized via the electrospinning method and characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), vibrating sample magnetometer (VSM) and Fourier transform infrared (FT-IR). The composite nanofibers were used as a novel adsorbent for removing toxic chromium (Ⅵ) (CrⅥ) in aqueous solution. The doping of Fe3O4 nanoparticles (NPs) into the fibers had a positive effect on the absorption for CrⅥ ions both under neutral and acidic conditions, and the saturated adsorption reached the highest when pH was 3.0. The results of the kinetics of CrⅥ removal on the as-prepared Fe3O4@PVA/CS composite nanofibers suggested a rapid initial loading and a subsequent stable stage, and the adsorption was well described by the pseudo-first-order model. The possible CrⅥ removal mechanism of the magnetic Fe3O4@PVA/CS composite nanofibers was also proposed.