Aqueous Perchlorate Research Articles

Investigations into the Extraction of Copper (II) using Methyl Isobutyl ketone solvent

AbstractThis work concerns the study of the extraction of copper (II) in the perchlorate medium by Bis‐2‐ethylhexyl phosphoric acid (D2EHPA) in methyl isobutyl ketone (MIBK) at 25 °C at different ionic strength (1, 1/6, 1/10 mol kg−1). The stoichiometry of the reaction of extracted complexations was determined by the slope method. The organometallic complexes extracted in the organic phase are of the type CuL2 in methyl isobutyl ketone has unit ionic strength. The organometallic complexes extracted in the organic phase are of the type CuL2ClO4(H2O) or CuL2ClO4 (MIBK)x in methyl isobutyl ketone has different ionic strength Efficiency of the extraction of copper (II) depends on the ionic strength of the aqueous medium. Hence when the ionic strength of the aqueous perchlorate medium increases the extraction of copper (II) increases.

Biological Reduction of Perchlorate from Spent Modified Reed Mediated by an Enriched Microbial Culture

Disposal of untreated perchlorate-laden modified reed (MR) generated in the treatment of contaminated water risks further contamination issues. The primary aim of this study was to assess the enriched microbial culture (EMC)-mediated biodegradation of perchlorate bound to spent quaternary amine-MR adsorbent. The culture was enriched to utilize perchlorate as an electron acceptor and brewer’s yeast as an electron donor. Kinetics experiments were performed to determine biodegradation rates and the total time for complete removal. The secondary aim of this research was the development and testing of a microwave-assisted extraction (MAE)-facilitated accurate perchlorate quantitation method. Extraction efficiency was optimized by adjusting the nitric acid concentration, resulting in 90 ± 5% recovery. Results show that EMC can degrade aqueous perchlorate effectively and consistently. EMC can also effectively degrade adsorbed perchlorate from spent MR. In conclusion, anaerobic biodegradation of perchlorate from spent MR can be used as an efficient, cost-effective, and environmentally friendly alternative or supplement to other treatment options, such as ion exchange and incineration. This approach can also be an effective solution to the waste generated by using MR to remove perchlorate from contaminated water.

Powdered MnySb1–yOx Catalysts for Cerium-Mediated Oxygen Evolution in Acidic Environments

MnySb1–yOx powders with a series of compositions were evaluated as catalysts for chemical water oxidation in aqueous perchloric, sulfuric, or methanesulfonic acid. O2(g) evolved spontaneously over MnySb1–yOx catalyst powders that had been suspended in solutions that were pre-loaded with Ce4+ ions. The rate of O2 evolution depended on the amount, as well as the oxidation state, of the Mn in the powder. The highest O2 evolution rate was observed from the most Mn-rich catalyst, which had an effective surface oxidation state of Mn2.9+ in its rest state. The facile synthetic accessibility of such catalysts in powder form constitutes a step toward replacing Ir or Ru in Ce-mediated oxygen evolution in decoupled water splitting systems, as well as toward developing inks of earth-abundant catalysts for preparation of catalyst-coated membranes used in conventional proton-exchange membrane electrolyzers.

Differences in perchlorate adsorption to azobenzene monolayers on gold formed from thioacetate and thiol precursors

Abstract Modification of metal surfaces with complex molecules opens interesting opportunities to build additional functionality into these surfaces. In this work, self assembled monolayers (SAMs) based on the same photoswitchable azobenzene motif but with different head groups have been synthesized and their SAMs on Au(111)/Si substrates have been characterized. 3-[(4-phenylazo)phenoxy]propyl thiol (PAPT) and its acetyl group protected analog, 3-[(4-phenylazo)phenoxy]propyl thioacetate (PAPA), have been synthesized. SAMs from PAPT and PAPA have been characterized by infrared (IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), ellipsometry and cyclic voltammetry (CV). The SAM-forming units of both SAMs are the same, as confirmed by IR and XPS, and the SAMs have similar surface coverage, as evidenced by analysis of the reductive desorption peaks in CVs. The tilt angle of the azobenzene moiety was ca. 75° with respect to the surface normal as determined by IR spectroscopy, i.e., the molecules are lying quite flat on the gold surface. Despite similar surface coverages, the CVs for PAPT in aqueous perchlorate solution show a typical perchlorate adsorption peak to gold, whereas the corresponding experiments with PAPA show no perchlorate adsorption at all. In conclusion, SAM formation can lead to an increase in the number of electrochemically accessible surface sites on the final, SAM covered surface. Whether the amount of such sites increases or decreases, depends on the precursor. The precursor most likely affects the adsorption mechanism and thus the atomic surface structure of the metal at the metal/SAM interface. Thus, details of the SAM formation mechanism, which is affected by the precursor used, can have quite strong effects on the electrochemical properties, and likely also electrocatalytic properties, of the resulting modified surface.

Bioinspired Catalytic Reduction of Aqueous Perchlorate by One Single-Metal Site with High Stability against Oxidative Deactivation

Reduction of perchlorate (ClO4–) with an active and stable catalyst is of great importance for environmental, energy, and space technologies. However, after the rate-limiting oxygen atom transfer (OAT) from inert ClO4–, the much more reactive ClOx– (x ≤ 3) intermediates can cause catalyst deactivation. The previous Re–Pd/C catalyst contained a [ReV(O)(hoz)2]+ site (Hhoz = 2-(2′-hydroxyphenyl)-2-oxazoline) and readily reduced ClO4–, but ClOx– intermediates led to rapid formation and hydrolysis of [ReVII(O)2(hoz)2]+. While microbes use delicate enzymatic machinery to survive the oxidative stress during ClO4– reduction, a synthetic catalyst needs a straightforward self-protective design. In this work, we introduced a methyl group on the ligand oxazoline moiety and achieved a substantial enhancement of catalyst stability without sacrificing the performance of ClO4– reduction. A suite of kinetics measurement, X-ray photoelectron spectroscopy characterization, reaction modeling, stopped-flow photospectrometry, and 1H NMR monitoring revealed the underlying mechanism. The most critical and unexpected effect of the methyl group is the deceleration (for 2 orders of magnitude) of OAT from ClO3– to [ReV(O)(Mehoz)2]+. However, the rate of OAT with ClO4– was not affected. The methyl group also slowed down the hydrolysis of [ReVII(O)2(Mehoz)2]+ and allowed the introduction of methoxy onto the phenolate moiety to further accelerate ClO4– reduction. With 1 atm H2 at 20 °C, the Re–Pd/C catalyst used [ReV(O)(MehozOMe)2]+ as the only reaction site to reduce multiple spikes of 10 mM ClO4– into Cl– without decomposition. This work showcases the significant effect of simple ligand modification in improving catalyst stability for high-performance ClO4– reduction.

A Bioinspired Molybdenum Catalyst for Aqueous Perchlorate Reduction.

Perchlorate (ClO4-) is a pervasive, harmful, and inert anion on both Earth and Mars. Current technologies for ClO4- reduction entail either harsh conditions or multicomponent enzymatic processes. Herein, we report a heterogeneous (L)Mo-Pd/C catalyst directly prepared from Na2MoO4, a bidentate nitrogen ligand (L), and Pd/C to reduce aqueous ClO4- into Cl- with 1 atm of H2 at room temperature. A suite of instrument characterizations and probing reactions suggest that the MoVI precursor and L at the optimal 1:1 ratio are transformed in situ into oligomeric MoIV active sites at the carbon-water interface. For each Mo site, the initial turnover frequency (TOF0) for oxygen atom transfer from ClOx- substrates reached 165 h-1. The turnover number (TON) reached 3840 after a single batch reduction of 100 mM ClO4-. This study provides a water-compatible, efficient, and robust catalyst to degrade and utilize ClO4- for water purification and space exploration.

On the Hydration of the Rare Earth Ions in Aqueous Solution

The totally symmetric stretching mode nu_{1} Ln–(OH2) of the first hydration shells of all the rare earth (RE) ions across the series from lanthanum to lutetium has been measured on dilute aqueous perchlorate solutions at room temperature. An S-shaped relationship has been found between the nu_{1} Ln–(OH2) peak positions and the Ln–(OH2) bond distances of the lanthanide(III) aqua ions. While the light rare earth ions form nona-hydrates, the heavy ones form octa-hydrates and the rare earth ions in the middle of the series show non integer hydration numbers between 9 and 8. A relationship between wavenumber positions nu_{1} Ln–(OH2) and the Ln–(OH2) bond distances of the RE hydrates has been given. Recent quantum mechanical calculations support the given interpretation.

Promising Biocompatible, Biodegradable, and Inert Polymers for Purification of Wastewater by Simultaneous Removal of Carcinogenic Cr(VI) and Present Toxic Heavy Metal Cations: Reduction of Chromium(VI) by Poly(ethylene glycol) in Aqueous Perchlorate Solutions.

A spectrophotometric technique has been applied for studying the reduction of chromium(VI) by poly(ethylene glycol) (PEG) as water-soluble and nontoxic synthetic polymer at a constant ionic strength of 4.0 mol dm–3 in the absence and presence of the ruthenium(III) catalyst. In the absence of the catalyst, the reaction orders in [Cr(VI)] and [PEG] were found to be unity and fractional first orders, respectively. The oxidation process was found to be acid-catalyzed with fractional second order in [H+]. The addition of Ru(III) was found to catalyze the oxidation rates with observation of zero-order reaction in [CrO42–] and fractional orders in both [PEG] and [Ru(III)], respectively. The PEG reduces the soluble toxic hexavalent Cr(VI) as a model pollutant to the insoluble nontoxic Cr(III) complex, which is known to be eco-friendly and more safer from the environmental points of view. The acid derivative of PEG was found to possess high affinity for the removal of poisonous heavy metal ions from contaminant matters by chelation. Formation of the 1:1 intermediate complex has been kinetically revealed. A consistent reaction mechanism of oxidation was postulated and discussed.

Orientation on the Mechanistics of Electron-Transfer on Oxidation of Chondroitin-4-Sulfate as Sustainable Sulfated Polysaccharide by Permanganate Ion in Aqueous Perchlorate Solutions

A spectrophotometric investigation of oxidation of chondroitin-4-sulfate (CS) as a sustainable and biodegradable sulfated macromolecule by oxyanion permanganate ion as multi-equivalent oxidant in acid perchlorate solutions a... | Find, read and cite all the research you need on Tech Science Press

Double Layer at the Pt(111)-Aqueous Electrolyte Interface: Potential of Zero Charge and Anomalous Gouy-Chapman Screening.

We report, for the first time, the observation of a Gouy–Chapman capacitance minimum at the potential of zero charge of the Pt(111)‐aqueous perchlorate electrolyte interface. The potential of zero charge of 0.3 V vs. NHE agrees very well with earlier values obtained by different methods. The observation of the potential of zero charge of this interface requires a specific pH (pH 4) and anomalously low electrolyte concentrations (<10−3 m). By comparison to gold and mercury double‐layer data, we conclude that the diffuse double layer structure at the Pt(111)‐electrolyte interface deviates significantly from the Gouy–Chapman theory in the sense that the electrostatic screening is much better than predicted by purely electrostatic mean‐field Poisson–Boltzmann theory.

Double Layer at the Pt(111)–Aqueous Electrolyte Interface: Potential of Zero Charge and Anomalous Gouy–Chapman Screening

AbstractWe report, for the first time, the observation of a Gouy–Chapman capacitance minimum at the potential of zero charge of the Pt(111)‐aqueous perchlorate electrolyte interface. The potential of zero charge of 0.3 V vs. NHE agrees very well with earlier values obtained by different methods. The observation of the potential of zero charge of this interface requires a specific pH (pH 4) and anomalously low electrolyte concentrations (&lt;10−3 m). By comparison to gold and mercury double‐layer data, we conclude that the diffuse double layer structure at the Pt(111)‐electrolyte interface deviates significantly from the Gouy–Chapman theory in the sense that the electrostatic screening is much better than predicted by purely electrostatic mean‐field Poisson–Boltzmann theory.

Integrating cationic metal-organic frameworks with ultrafiltration membrane for selective removal of perchlorate from Water

We design a novel cationic metal-organic framework hybrid ultrafiltration polyvinylidene fluoride membrane (PVA/Cu-iMOFs/PVDF-0.05) and report its unique capture of aqueous perchlorate (ClO4−) at ppm-level. This membrane outperformed traditional adsorption materials and exhibited a specific affinity toward ClO4− in the presence of various competing anions at greater levels (up to a concentration ratio of 20). In the batch experiment, the ClO4− removal ratio reached 99.6% over a wide pH range (3˜10). Membrane filtration by using a 12.56 cm2 PVA/Cu-iMOFs/PVDF-0.05 membrane could effectively treat 4.71 L of ClO4−-contaminated water before breakthrough occurred, while maintaining a satisfactory permeability (˜627.32 L/(m2 h bar)) and antifouling property. The exhausted membrane could easily be regenerated in aminoethanesulfonic acid solution for repeated use with a negligible decrease in capacity. Moreover, the membrane showed excellent long-term stability in a cross-flow filtration process due to the amido bond between the Cu-iMOFs and membrane surface as well as the "protection" of polyvinyl alcohol. Selective and reversible ion-exchange between the sulfonic acid (R-SO3) ligands of Cu-iMOFs and tetrahedral oxo-anionic species was verified to be the pathway for ClO4− trapping. Thus, other problematic elements that also occur in tetrahedral form in water can be removed by this method.

Kinetics and Mechanism of Permanganate Oxidation of ADA in Aqueous Perchlorate Solutions

Background: ADA as N-(2-Acetemido) iminodiacetic acid has been widely used in preparation of organic buffers and protein-free media for fibroblasts as chelating agent chicken embryo fibroblasts as tridentate chelating agent ligand. However, a little attention has been focused to the behavior of its oxidation in aqueous acidic solutions. Accordingly, a lack of information on the aqueous chemistry of oxidation of ADA in acidic solutions was recognized. Therefore, we have prompted to undertake the present work with the aims at shedding more light on the behavior of oxidation and the nature of oxidation products. Again, it aims to compensate the lack of information about the aqueous chemistry of ADA and the nature of electron-transfer for redox reactions involving permanganate ion as a multi-equivalent oxidant. Method: A spectrophotometric investigation of oxidation of ADA by permanganate ion in aqueous perchlorate solutions has been investigated. Results: Absorbance-time curves indicated the presence of two distinct stages for the oxidation process. The experimental results indicated a decrease in the reaction rates with increasing the [H+], ionic strength and F- ions. Again, the reaction rates were found to increase with increasing the added Mn2+ and temperature. Conclusion: These results indicated that the oxidation process was of acid-inhibition nature and proceeding by free-radical intervention mechanism. Again, the reactive species in the fast second stage was the Mn4+ species formed in the initial stage. The activation parameters have been evaluated from the temperature dependence of the rate constants. A tentative reaction mechanism was suggested for such redox reaction.

Orientation on Electron-Transfer Nature for Oxidation of Some Water-Soluble Carbohydrates: Kinetics and Mechanism of Hexacholroiridate (IV) Oxidation of Methyl Cellulose in Aqueous Perchlorate Solutions

The kinetics and mechanism of oxidation of methyl cellulose (MC) polysaccharide by hexacholroiridate (IV) in aqueous perchlorate solutions at a constant ionic strength of 0.1 mole dm-3 has been investigated, spectrophotometrically. The experimental results showed first-order dependence in [IrCl6]2- and fractional first-order kinetics with respect to the MC concentration. The reaction rate was found to increase with decreasing the [H+]. A kinetic evidence for formation of 1:1 intermediate complex was revealed. The reaction kinetics seems to be of considerable complexity where one chloride ion from hexacholoiridate (IV) oxidant may act as a bridging ligand between the oxidant and the substrate within the formed intermediate complex. However the added chloride ions and oxidation products were found to have negligible effects on the reaction rate, the added acrylonitrile indicated the intervention of free-radical mechanism during the oxidation process. The kinetic parameters have been evaluated and a tentative reaction mechanism consistent with the kinetic results is discussed.

Kinetics and mechanistic aspects on electron‐transfer process for permanganate oxidation of poly(ethylene glycol) in aqueous acidic solutions in the presence and absence of Ru(III) catalyst

AbstractThe kinetics and mechanism of oxidation of poly(ethylene glycol) (PEG) by the permanganate ion as a multiequivalent oxidant in aqueous perchlorate solutions at an ionic strength of 2.0 mol dm−3 has been investigated spectrophotometrically. The reaction kinetics was found to be of complex in nature. The pseudo–first‐order plots showed curves of inverted S‐shape, consisting of two distinct stages throughout the entire course of reaction. The first stage was relatively slow, followed by a fast reaction rate at longer time periods. The first‐order dependence in [MnO4−], fractional first‐order dependence in [H+], and fractional first‐order kinetics in the PEG concentration for the first stage have been revealed in the absence of the Ru(III) catalyst. The influence of the Ru(III) catalyst on the oxidation kinetics has been examined. The oxidation was found to be catalyzed by the added Ru(III) catalyst. The First‐order dependence on the catalyst and zero order with respect to the oxidant concentrations have been observed. The kinetic parameters have been evaluated, and a tentative reaction mechanism consistent with the kinetic results is suggested and discussed.

Kinetics and mechanism of oxidation of pyruvate by permanganate ion in aqueous perchlorate solution

The kinetics and mechanism of permanganate oxidation of pyruvic acid in aqueous perchlorate at a constant ionic strength of 2.0 mol dm−3 have been investigated spectrophotometrically. The pseudo-first-order plots showed two distinct phases for the reaction, characterized as induction and auto-acceleration periods. The induction phase is relatively slow at the early stages of reaction and is followed by a faster process. The rate law for the oxidation was described by the sum of two exponential terms. The oxidation showed overall second-order kinetics with respect to the reactants in the initial slow phase. However, second-order kinetics was not maintained throughout the faster second stage. The effects of added salts lead to the conclusion that Mn(III) and/or Mn(IV) play the main role in the reaction kinetics of the second stage. A reaction mechanism consistent with the kinetic results is suggested and discussed.

Vibrational spectroscopic study of pH dependent solvation at a Ge(100)-water interface during an electrode potential triggered surface termination transition

The charge-dependent structure of interfacial water at the n-Ge(100)-aqueous perchlorate interface was studied by controlling the electrode potential. Specifically, a joint attenuated total reflection infrared spectroscopy and electrochemical experiment was used in 0.1M NaClO4 at pH ≈ 1-10. The germanium surface transformation to an H-terminated surface followed the thermodynamic Nernstian pH dependence and was observed throughout the entire pH range. A singular value decomposition-based spectra deconvolution technique coupled to a sigmoidal transition model for the potential dependence of the main components in the spectra shows the surface transformation to be a two-stage process. The first stage was observed together with the first appearance of Ge-H stretching modes in the spectra and is attributed to the formation of a mixed surface termination. This transition was reversible. The second stage occurs at potentials ≈0.1-0.3 V negative of the first one, shows a hysteresis in potential, and is attributed to the formation of a surface with maximum Ge-H coverage. During the surface transformation, the surface becomes hydrophobic, and an effective desolvation layer, a "hydrophobic gap," developed with a thickness ≈1-3 Å. The largest thickness was observed near neutral pH. Interfacial water IR spectra show a loss of strongly hydrogen-bound water molecules compared to bulk water after the surface transformation, and the appearance of "free," non-hydrogen bound OH groups, throughout the entire pH range. Near neutral pH at negative electrode potentials, large changes at wavenumbers below 1000 cm-1 were observed. Librational modes of water contribute to the observed changes, indicating large changes in the water structure.

Electrochemical Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy: Bonding, Structure, and Ion-Pairing of the Positive Charge Bearing Pyridinium Ring Terminated Monolayer at Smooth Gold Electrode

Electrode potential effect on the molecular structure of adsorbed species at an interface is one of the most important issues in physical electrochemistry. In this study, shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) was used to probe the electrochemical potential effect on bonding with surface, ion-pairing, and molecular structure of a positive charge bearing self-assembled monolayer formed from N-(6-mercapto)hexylpyridinium (MHP) at a smooth gold electrode in aqueous perchlorate solutions. In situ electrochemical SHINERS results show that the Au–S stretching frequency exhibits near linear blue-shift as the electrode potential was tuned to more positive values. The frequency tuning rate was found to be as high as 18.6 ± 0.9 cm–1/V. Analysis of ion-pairing at the interface revealed a decrease in intensity of the vibrational spectrum of electrostatically attracted perchlorate anions as the electrode potential shifts progressively to more negative values. Spectroscopic evidence for poten...

Structural Inhomogeneity in Electrolyte Solutions: The Calcium Perchlorate–Water System

A new approach has been proposed to study the structure of aqueous electrolyte solutions. NIR, Raman and attenuated total reflectance, Fourier transform infra-red (ATR FTIR) spectra have been measured for aqueous calcium perchlorate solutions in the 0.22–4.3 mol·L−1 (0.22–7.46 mol·kg−1) concentration range at 25 °C. By the methods of principal component analysis (PCA) and multivariate curve resolution—alternating least squares (MCR-ALS) the number, spectra and concentration profiles have been determined for spectroscopically distinguishable forms of water and ClO 4 − ion in solutions. The results have been analyzed using a phenomenological model, establishing thereby: concentration ranges for structural rearrangements of the solution, the nature of structural microirregularities and different states of the ClO 4 − ion in the areas of domination of the natural water structure, and of cybotactic groups of calcium perchlorate hexa and tetra hydrates.

Nonwoven materials based on polyethylene oxide for use as a polymer electrolyte in memristive devices

Nonwoven materials were prepared by electrospinning from solutions of polyethylene oxide in water and in a 0.1 M aqueous lithium perchlorate solution. Addition of lithium perchlorate increases the conductivity of the solutions but does not alter their viscosity. The mean diameter of the fibers obtained was 100–500 nm. The supramolecular structure of the polymer underwent no significant changes in the course of electrospinning. The materials obtained can be applied directly onto organic memristive devices and used as a polymer electrolyte.