Anionic Metal Ions Research Articles

Preliminary studies on ion-pair extractions of Zr, Hf, Nb, and Ta using extractants having tertiary N atom from H2SO4 and HF

Abstract Ion-pair extraction enables the recovery of anionic metal ions, such as pertechnetate and chlorinated rhodium ions, by protonated extractants with tertiary amino N atom in their structures. We expand this technique for other anionic species dissolved in different mineral acids. Extractions of Zr, Hf, Nb, and Ta, metal anions present in sulfuric and hydrofluoric acids (H2SO4 and HF), are examined. Zr and Hf in H2SO4, and Zr, Hf, Nb, and Ta in HF can be extracted by ion-pair extraction using NTAamide (nitrilotriacetamide), methylimino-N, N’-dioctylacetamide (MIDOA), and trioctylamine (TOA). Basic information about their extraction behavior was obtained through this study.

Yeast Inhibitive Assay for Anionic Heavy Metals: A review

One of the most common types of pollution that has a negative impact on the biotic community in aquatic habitats is heavy metal poisoning of the water. Both essential and non-essential heavy metals can be toxic to living things if their concentrations are too high for their bioavailability. Although the toxicity of heavy metals, and especially anionic metal ions, is better known than that of cationic metal ions, it is just as toxic, if not more so. The focus of this review is on the usefulness of eukaryotic organisms like yeast, Saccharomyces cerevisiae, for toxicity assessment because they can be easily maintained and developed in controlled circumstances, thereby avoiding variability issues that arise when employing more complex organisms. Recent research has shown that the majority of cellular MTT reduction occurs outside of the mitochondrial inner membrane, and that this reduction is dependent on NADH and NADPH but is resistant to respiratory chain inhibitors.

Synthesis of MnFe2O4 and Mn3O4 magnetic nano-composites with enhanced properties for adsorption of Cr(VI): artificial neural network modeling.

This study reports adsorptive removal of Cr(VI) by magnetic manganese ferrite and manganese oxide nano-particles (MnF-MO-NPs) composite from aqueous media. The X-ray diffraction pattern of MnF-MO-NPs revealed a polycrystalline nature with nanoscale crystallite size. The prepared adsorbent with high Brunauer-Emmett-Teller specific surface area of 100.62 m2/g and saturation magnetization of 30.12 emu/g exhibited maximum Cr(VI) removal at solution pH 2.0 and was easily separated from water under an external magnetic field. Adsorption capacity as much as 91.24 mg/g is reported and electrostatic interaction between positively charged adsorbent surface and anionic metal ion species is the main driving force in this adsorption. Adsorption experimental data followed Langmuir isotherm and second order kinetics. Partial involvement of intra-particle diffusion was also observed due to the mesoporous nature of MnF-MO-NPs. The thermodynamic studies revealed that the process was favorable, spontaneous and exothermic in nature. An artificial neural network model was developed for accurate prediction of Cr(VI) ions removal with minimum mean squared error (MSE) of 15.4 × 10-4 and maximum R2 of 0.98. Owing to large surface to volume ratio, advantage of easy magnetic separation, and high adsorption capacity towards Cr(VI), the reported MnF-MO-NPs appear to be a potential candidate in Cr(VI) contaminated wastewater remediation.

A Generalized Method for the Synthesis of Ligand-Free M@SiO2 (M = Ag, Au, Pd, Pt) Yolk-Shell Nanoparticles.

A universal method is reported for the synthesis of ligand free noble metal M@SiO2 (M = Ag, Au, Pd, Pt) yolk-shell nanoparticles (YSNs). Mesoporous hollow silica shells (mHSS) are used as smart nanoreactors for the synthesis of noble metal yolk-shell nanoparticles. The nanocavity of a mHSS and anionic metal ions play a critical role in the formation of yolk-shell nanoparticles. The synthesis mechanism can be tuned by simply varying the pH of the noble metal precursor aqueous solution. A critical pH ≥ 4 is required for the formation of YSNs. The anionic metal ions can pass freely through the mesopores of mHSS and eventually lead to the formation of YSNs, whereas the cationic metal ions can show strong interaction with the surface of mHSS which hinders the formation of YSNs. The syntheses of YSNs are achieved without using any external capping ligands and reducing agents in the reaction.

Diethylenetriamine-assisted synthesis of amino-rich hydrothermal carbon-coated electrospun polyacrylonitrile fiber adsorbents for the removal of Cr(VI) and 2,4-dichlorophenoxyacetic acid

An environmentally benign and efficient hydrothermal carbonization method is widely applied for the preparation of carbon-based adsorbents. However, the adsorption capacity toward anionic species would be influenced due to the negatively charged surface of the traditional hydrothermal carbonaceous materials; moreover most of the carbonaceous materials were in the form of powder which restricted the practical applications. Herein, amino-rich hydrothermal carbon-coated electrospun polyacrylonitrile fiber (PAN@NC) adsorbents were obtained through one-step hydrothermal carbonization approach assisted by diethylenetriamine using polyacrylonitrile (PAN) fibers as the templates, which showed highly efficient adsorption for anionic pollutants. The PAN@NC fibers were characterized in detail to confirm their structures and composition. The flexible and robust PAN@NC fiber membrane exhibited high adsorption capacity and good regeneration and recycling ability toward the anionic metal ion Cr(VI) and herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). According to the Langmuir model, the adsorption behaviors showed monolayer adsorption capacities of 290.70mg/g and 164.47mg/g for Cr(VI) and 2,4-D, respectively, which were higher than that of many other adsorbents. Recycling study indicated that the removal efficiencies for both pollutants retained above 90% after five cycles. These findings demonstrate that PAN@NC fibers are promising adsorbents for the removal of anionic pollutants from wastewater solutions.

Cooperative Anion Recognition in Copper(II) and Zinc(II) Complexes with a Ditopic Tripodal Ligand Containing a Urea Group

The ability of Cu(II) and Zn(II) complexes of the ditopic receptor H2L [1-(2-((bis(pyridin-2-ylmethyl)amino)methyl)phenyl)-3-(3-nitrophenyl)urea] for anion recognition is reported. In the presence of weakly coordinating anions such as ClO4(-), the urea group binds to the metal ion (Cu(II) or Zn(II)) through one of its nitrogen atoms. The study of the interaction of the metal complexes with a variety of anions in DMSO shows that SO4(2-) and Cl(-) bind to the complexes through a cooperative binding involving simultaneous coordination to the metal ion and different hydrogen-bonding interactions with the urea moiety, depending on the shape and size of the anion. On the contrary, single crystal X-ray diffraction studies show that anions such as NO3(-) and PhCO2(-) form 1:2 complexes (metal/anion) where one of the anions coordinates to the metal center and the second one is involved in hydrogen-bonding interaction with the urea group, which is projected away from the metal ion. Spectrophotometric titrations performed for the Cu(II) complex indicate that this system is able to bind a wide range of anions with an affinity sequence: MeCO2(-) ∼ Cl(-) (log K11 > 7) > NO2(-) > H2PO4(-) ∼ Br(-) > HSO4(-) > NO3(-) (log K11 < 2). In contrast to this, the free ligand gives much weaker interactions with these anions. In the presence of basic anions such as MeCO2(-) or F(-), competitive processes associated with the deprotonation of the coordinated N-H group of the urea moiety take place. Thus, N-coordination of the urea unit to the metal ion increases the acidity of one of its N-H groups. DFT calculations performed in DMSO solution are in agreement with both an anion-hydrogen bonding interaction and an anion-metal ion coordination collaborating in the stabilization of the metal salt complexes with tetrahedral anions.

Reverse Micelle Mediated Bulk Liquid Membrane Separation of Platinum Gold and Silver From Real Samples

Simple and selective reverse micelle mediated bulk liquid membrane extraction procedure is developed for the separation and simultaneous pre-concentration of precious metals from valuable wastes like spent auto mobile catalytic converters and gold jewelry washings. Quantification has been carried out using inductively coupled plasma optical emission spectrometry (ICP-OES). Tri octyl methyl ammonium chloride (TOAC), a cationic hydrophobic surfactant, forms reverse micelles after dissolution in trichloroethylene facilitating the extraction of platinum, gold and silver ions into the bulk liquid membrane. The procedure is based on the formation of extractable hydrophobic ion-associates between TOAC cationic reverse micelles and anionic metal ions. These hydrophobic ion-associates which are transported into the bulk organic membrane from an aqueous feed phase are subsequently stripped into a receiving solution in a unitary process. Optimum conditions for the overall transport efficiency of precious metals have been evaluated. The accuracy of the procedure was validated by analyzing GBWAu-18 ore from faulted zone and PTM-1a nickel-copper sulphide matte certified reference materials. The procedure has been applied to spent catalytic converters and jewellery washings. Supplemental materials are available for this article. Go to the publisher's online edition of Separation Science & Technology to view the supplemental file.

Adsorption characteristics of both cationic and oxyanionic metal ions on hexadecyltrimethylammonium bromide-modified NaY zeolite

In this study, we investigated the adsorption capacities and the mechanisms of adsorption of cationic [copper(II), zinc(II), nickel(II), lead(II), cadmium(II)] and oxyanionic [dichromate(-II), permanganate(-I)] metal ions onto hexadecyltrimethylammonium (HDTMA)-modified and unmodified NaY zeolites. To understand the surface characteristics of the modified adsorbents, we analyzed the NaY zeolite and the HDTMA-modified zeolite (HMZ) in terms of their surface areas, zeta potentials, Fourier transform infrared (FTIR), elemental composites and cation exchange capacities. The results reveal that HMZ behaved as a dual-electronic adsorbent. Because cationic heavy metals cannot replace the HDTMA forming admicelles on the external surface, the obtained adsorbent could simultaneously adsorb both cationic and anionic metal ions. We propose that ion exchange is the primary mechanism through which cationic metal ions adsorb onto the NaY zeolite—with adsorption capacities, dependent on the ion radius, following the order Pb>Cd>Cu>Zn>Ni. The mechanisms for the adsorption of the cationic and anionic metal ions onto HMZ include ion exchange and complexation reactions and/or surface precipitation, with the adsorption capacities of the cationic metal ions following the order Pb>Cu>Cd>Zn>Ni and those of anionic metal ions following the order MnO4->Cr2O72-.

Synthesis and Characterization of Water-Operative Cationic and Anionic Metal-Ion Activated Molecular Receptors for Aromatic Anions

Two new, octadentate, water-soluble, macrocyclic ligands, 1,4,7,10-tetrakis((2S)-(-)-2-hydroxy-3-[3'-(N,N,N-trimethylammonium)-phenoxy]-propyl)-1,4,7,10-tetraazacyclododecane tetratriflate, ((S)-tmappc12 triflate, L1 triflate) and 1,4,7,10-tetrakis((2S)-(-)-2-hydroxy-3-[2'-sulfo-4'-methylphenoxy]-propyl)-1,4,7,10-tetraazacyclododecane, ((S)-sthmppc12, L2H4) have been prepared with a view to using them to study anion sequestration in aqueous solution. Their pKa and metal-ion binding constant values with a range of alkaline earth, transition, and post-transition metals are reported. The eight-coordinate, water-soluble Cd(II) complexes of (L1)4+ and (L2)4-, [CdL1](CF3SO3)6 and (NH4)2-[CdL2], the former cationic and the latter anionic, have both been shown to be capable of acting as anion receptors in aqueous solution. The binding constant values (log(K/M-1) given in parentheses) for binding by the cationic receptor to a range of aromatic anions in water are p-nitrophenolate (1.7), p-formylphenolate (2.1), p-nitrobenzoate (3.0), p-aminobenzoate (4.5), p-dimethylaminobenzoate (>4.5), D- and L-tryptophanate (1.6, 2.2), phenoxyacetate (2.1), and acetate (2.3). With the anionic receptor, nonzero binding constants were only measurable for p-nitrobenzoate (approximately 0.4), p-aminobenzoate (2.0), and p-dimethylaminobenzoate (1.8). By reference to the X-ray determined structures of related, but water-insoluble inclusion complexes, anion retention is thought to occur within a hydrophobic cavity, with four convergent hydroxy groups at its base, which develops in (L1)4+ and (L2)4- through the juxtapositioning of aromatic rings that occurs as a consequence of octadentate coordination.

Synthesis of chitosan-based polymeric surfactants and their adsorption properties for heavy metals and fatty acids

Chitosan-based polymeric surfactants (CBPSs) were prepared by N-acylation of chitosans (chitosan 10 and 500) with several acid anhydrides such as hexanoic (C 6), lauric (C 12), and palmitic (C 16) anhydrides. Among the CBPS samples, CBPSs having a good solubility at pH 4.0 were selected and observed for viscosity, surface tension, and adsorption of heavy metals (Cd 2+, Co 2+, Cr 2O 7 2−, and Pb 2+) as well as the fatty acid ( n-octanoic acid). The 1H NMR spectrum of chitosan 10 modified with C 16 at the substitution ratio of 0.4 (CBPS 10–C 16, 0.4 ) showed 85% of acylation in 1% DCl/D 2O solutions. CBPS 10 with the substitution ratio less than 0.4 showed a good solubility because of shorter repeating units and lesser amounts of hydrophobic substituents. The intrinsic viscosity of CBPS 10 was slightly increased, while that of CBPS 500 was decreased. As the substitution ratio and length of the carbon chain increased, the surface tension of CBPS 10 tended to decrease. CBPS 10–C 16, 0.2 had high adsorption ability for cationic metal ions such as Cd 2+, Co 2+, and Pb 2+ comparable to chitosan. Interestingly, CBPS 10–C 16, 0.2 showed a unique pH optimum for the anionic metal ion such as Cr 2O 7 2−. In addition, CBPS 10–C 16, 0.2 exhibited the highest adsorption ability for n-octanoic acid among the tested CBPS 10 with different carbon chains.

Characterizing the Metal Adsorption Capability of a Class F Coal Fly Ash

The surface physical-chemical characteristics of a class F coal fly ash were studied in an effort to establish a quantitative understanding of metal adsorption. The ash surface acidity (acid site density and acidity constant), surface electrical characteristics, and adsorption constants for selected heavy metal ions were determined using a batch titration method, an electrophoretic method, and a batch equilibrium metal adsorption method, respectively. Results showed that the fly ash has a pHzpc value of 6.2. Its surface contains three types of acid sites. The densities of these acid sites are 2.1 x 10(-4), 1.8 x 10(-5), and 5.3 x 10(-5) mol/g, with acidity constants (pK(H)) of 2.7, 7.8, and 11.0, respectively. Metal adsorption results indicated that, of the three types of acid sites on surface, only the acid site with 7.8 pK(H) is responsible for metal adsorption. The adsorption constants (log K(S)) of Cd(II), Cr(III), Cu(II), Ni(II), and Pb(II) are 4.8, 7.0, 6.4, 4.9, and 8.6, respectively. Adsorption results indicated that the metal adsorption is in the linear range of the Langmuir isotherm if the total metal in the system is less than 10% of the total metal binding site. Results also showed that the presence of anionic metal ions does not affect the adsorption of cationic metal ions by the fly ash.