Correction to: Peculiarities of chromium electrodeposition from water − dimethylformamide solutions

Journal of Solid State Electrochemistry - This original article contained a mistake. The page numbers of reference Kuznetsov et al. 2000 are incorrect, “853–858” should be...     

Removal of chromium from water using pea waste – a green approach

Abstract

Agro-waste materials have carboxylic and phenolic groups that play the main role in metal adsorption. The advantages of these materials include easy availability, low cost, and reasonable metal removal capacity. One of the materials (usually considered as waste) is pea waste (pods). Present work comprises adsorption of chromium from aqueous solution using powder of pods of garden peas (Pisum sativum) in batch. Important parameters like adsorbent dose, pH, contact time, and agitation speed were studied. Adsorption equilibrium was explained by Langmuir, Freundlich, and Temkin isotherms. Maximum chromium uptake (q _m) was 3.56 mg/g of adsorbent. Heat of adsorption, as evaluated by Temkin isotherm was 1.96 kJ/mol. It is proposed that pea pods can be an effective and environmentally benign (green) adsorbents for removal of chromium from industrial effluents and waste waters.     

Silver electrodeposition from water–acetonitrile mixed solvents in the presence of tetrabutylammonium perchlorate

In this paper, surface-enhanced Raman spectroscopy has been used to investigate the electrode/electrolyte interface during Ag electrodeposition from water–acetonitrile mixed solvents. The reactivity of acetonitrile during Ag electrodeposition has been monitored, promoted by the electrocatalytic activity of silver clusters electrodeposited onto the electrode surface. The effect of the addition of tetrabutylammonium cations to the mixed solvents has been investigated and its adsorption and tilting on the silver surface has been followed as a function of the cathodic overpotential.     

Morphology of cellulose objects regenerated from cellulose–N-methylmorpholine N-oxide–water solutions

The precipitation in aqueous media of cellulose from solutions in N-methylmorpholine N-oxide (NMMO) hydrates is an important stage in the process of manufacturing of fibres, films and other cellulose objects. It is responsible for the formation of the structure of the regenerated object and their morphological characteristics significantly influence the properties of the final products. Regeneration of rather large cellulose objects was observed in situ by optical microscopy. It was found that all regenerated objects present an asymmetric structure composed of a dense skin surrounding a sub-layer characterised by the presence of finger-like voids. The porous texture of the cellulose parts between these voids is typical of the one obtained by spinodal decomposition. The morphologies of regenerated cellulose samples are described as a function of various parameters, initial cellulose solutions and composition and temperature of the aqueous regeneration bath. A mechanism of the structure formation during regeneration is proposed. P. Navard is a Member of the European Polysaccharide Network of Excellence (EPNOE), .     

Electrodeposition of corrosion-resistant Cr–P and Cr–P–W coatings from solutions based on compounds of trivalent chromium

Journal of Solid State Electrochemistry - Corrosion-resistant Cr–P and Cr–P–W coatings were obtained by electrodeposition from aqueous and aqueous–organic (DMF/water)...     

Influence of processing parameters on regeneration kinetics and morphology of porous cellulose from cellulose–NaOH–water solutions

The kinetics of cellulose regeneration in acetic acid bath from cellulose–8% NaOH–water solutions and gels is studied as a function of gelation conditions, acid concentration and bath temperature. The diffusion coefficient of NaOH from cellulose solution or gel into regenerating bath was calculated. It does not depend either on gelation mode or on acid concentration. On the contrary, cellulose regeneration from non-gelled solutions is slower than from a gel. The increase in bath temperature induces diffusion coefficient increase obeying Arrhenius law. Scanning electron microscopy images of regenerated swollen-in-water freeze-dried cellulose and of the same samples dried in supercritical CO₂ show highly porous morphology. CEMEF is a Member of the European Polysaccharide Network of Excellence (EPNOE), .     

Thermalization lengths of “subexcitation electrons” in water determined by photoinjection from metals into electrolyte solutions

Ranges of 0–4 eV electrons in aqueous electrolyte solutions have been measured using the technique of photoinjection. Variations of the method based on investigation of the dependence of the photoinduced charges on scavenger concentration, the intensity of incident light and time (in nanosecond scale) are used. The values of electron ranges in H₂O are found to amount to 80 Å and in D₂O—110 Å. The mechanism of thermalization of slow electrons in water is discussed. It is caused, mainly, by non-local losses associated with the excitation of the vibration-rotation matter spectrum. During thermalization the slow electrons are subject to numerous elastic scatterings whose cross-section is close to a gas-phase one.     

Hydrothermal processing and characterization of Ce1−xPbxO2−δ solid solutions

Nanocrystals of Ce_1?xPb_xO_2?δ (x = 0.00, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, and 0.35) were prepared by a hydrothermal reaction route. During the formation reaction, buffer solutions were explored as an effective additive to retain the initial molar ratio. With increasing the Pb²⁺ content, the average crystallite size was slightly retarded. Morphologies observed by transmission electron microscope indicated that the particles were spherical-like and highly uniformed. Pb²⁺ ions are homogenously distributed in the solid solutions. Analyses using X-ray diffraction, Raman and UV spectroscopies showed that the solid solubility limit of Pb²⁺ in CeO₂ was about x = 0.20. For x < 0.20, with increasing the Pb²⁺ content, the bulk conductivity increased, and the oxygen storage capacity was enhanced as followed by a decrease in reduction temperature.     

X-ray absorption signatures of hydrogen-bond structure in water–alcohol solutions

Despite fundamental importance, the experimental characterization of the hydrogen bond network, particularly in multicomponent protic solutions, remains a challenge. Although recent work has experimentally validated that the oxygen K-edge X-ray absorption spectra is sensitive to local hydrogen bond patterns in pure water and aqueous alcohol solutions, the generality of this observation is unknown—as is the sensitivity to the electronic structure of the alcohol cosolvent. In this work, we investigate the electronic structure of water solvated alcohol model geometries using energy specific time-dependent density functional theory to calculate oxygen K-edge X-ray excitations. We find that the geometry of dangling hydrogen bonds in pure water is the main contributor to the pre-edge feature seen in the X-ray absorption spectra, agreeing with previous experimental and theoretical work. We then extend this result to solvated alcohol systems and observe a similar phenomenon, yet importantly, the increase of electron donation from alkyl chains to the alcohol OH group directly correlates to the strength of the core excitation on the dangling hydrogen bond model geometry. This trend arises from a stronger transition dipole moment due to electron localization on the OH group.     

Thermodynamic characteristics of the adsorption of 1,3,4-oxadiazoles and 1,2,4,5-tetrazines from methanol and water–methanol solutions onto hypercrosslinked polystyrene

Russian Journal of Physical Chemistry A - The thermodynamic characteristics of the adsorption of several 1,3,4-oxadiazoles and 1,2,4,5- tetrazines from methanol and water-methanol solutions onto...     

Ion-molecule reactions of gas-phase chromium oxyanions: CrxOyH z − + O2

Chromium oxyanions, Cr(x)O(y)H(z)(-), were generated in the gas-phase using a quadrupole ion trap secondary ion mass spectrometer (IT-SIMS), where they were reacted with O(2). Only CrO(2)(-) of the Cr(1)O(y)H(z)(-) envelope was observed to react with oxygen, producing primarily CrO(3)(-). The rate constant for the reaction of CrO(2)(-) with O(2) was approximately 38% of the Langevin collision constant at 310 K. CrO(3)(-), CrO(4)(-), and CrO(4)H(-) were unreactive with O(2) in the ion trap. In contrast, Cr(2)O(4)(-) was observed to react with O(2) producing CrO(3)(-) + CrO(3) via oxidative degradation at a rate that was approximately 15% efficient. The presence of background water facilitated the reaction of Cr(2)O(4)(-) + H(2)O to form Cr(2)O(5)H(2)(-); the hydrated product ion Cr(2)O(5)H(2)(-) reacted with O(2) to form Cr(2)O(6)(-) (with concurrent elimination of H(2)O) at a rate that was 6% efficient. Cr(2)O(5)(-) also reacted with O(2) to form Cr(2)O(7)(-) (4% efficient) and Cr(2)O(6)(-) + O (2% efficient); these reactions proceeded in parallel. By comparison, Cr(2)O(6)(-) was unreactive with O(2), and in fact, no further O(2) addition could be observed for any of the Cr(2)O(6)H(z)(-) anions. Generalizing, Cr(x)O(y)H(z)(-) species that have low coordinate, low oxidation state metal centers are susceptible to O(2) oxidation. However, when the metal coordination is >3, or when the formal oxidation state is > or =5, reactivity stops.     

Synthesis and characterization of γ-Fe2O3/carbon hybrids and their application in removal of hexavalent chromium ions from aqueous solutions

Magnetic Fe(2)O(3)/carbon hybrids were prepared in a two-step process. First, acetic acid vapor interacted with iron cations dispersed on the surface of a nanocasted ordered mesoporous carbon (CMK-3). In the second step, the primarily created iron acetate species underwent pyrolysis and transformed to magnetic iron oxide nanoparticles. X-ray diffraction, Fourier-transform infrared, and Raman spectroscopies were used for the chemical and structural characterization of the hybrids, while surface area measurements, thermal analysis, and transmission electron microscopy were employed to determine their physical, surface, and textural properties. These results revealed the preservation of the host carbon structure, which was homogenously and controllably loaded (up to 27 wt %) with nanosized (ca. 20 nm) iron oxides inside the mesoporous system. M?ssbauer spectroscopy and magnetic measurements at low temperatures confirmed the formation of γ-Fe(2)O(3) nanoparticles exhibiting superparamagnetic behavior. The kinetic studies showed a rapid removal of Cr(VI) ions from the aqueous solutions in the presence of these magnetic mesoporous hybrids and a considerably increased adsorption capacity per unit mass of sorbent in comparison to that of pristine CMK-3 carbon. The results also indicate highly pH-dependent sorption efficiency of the hybrids, whereas their kinetics was described by a pseudo-second-order kinetic model. Taking into account the simplicity of the synthetic procedure and possibility of magnetic separation of hybrids with immobilized pollutant, the developed mesoporous nanomaterials have quite real potential for applications in water treatment technologies.     

Determination of cadmium, chromium and copper in high salt samples by LA-ICP-OES after electrodeposition—preliminary study

A novel method is presented for determination of heavy metal ions in a high-saline matrix. It is based on the electrodeposition of the ions and subsequent laser ablation coupled to inductively coupled plasma optical emission spectrometry (LA-ICP-OES). Three arrangements for electrodeposition were worked out, two of them with stationary working electrodes. Materials for use in the working electrodes, and conditions for electrodeposition of Cd, Cr and Cu (pH, deposition current, time of electrolysis) were studied. Nickel was found to be the best electrode material. The metals accumulate on the surface of electrode and were then evaporated/ablated with a Nd:YAG laser focused into the ICP-OES spectrometer. The detection limits are 0.13 mg?L^?1 for Cd, 0.15 mg?L^?1 for Cu, and 1.9 mg?L^?1 for Cr in case of a stationary bottom working electrode, and 0.25 mg?L^?1 for Cd, 0.05 mg?L^?1 for Cu, 0.8 mg?L^?1 for Cr when using a rotating electrode. The relative standard deviation is in range from 3.8 to 10.3%. Waste water was analyzed in this way by the standard addition method.     

Electrochemical reduction process of bilirubin in dimethylformamide

The electrochemical reduction behavior of bilirubin (BR) at platinum electrode in DMF was investigated by cyclic voltammetry, in situ electron spin resonance spectroscopy and in situ rapid scanning thin layer spectroelectrochemistry. Experimental results revealed that thereduction of BR firstly undergoes an ECE process: BR-+e BR-dimerize (BR)22- +e(BR)23-. The generated (BR)23- can be re-oxidized to BR and then to purpurin (Pu) by a series of oxidation processes:(BR)23- -e (BR)22- -2e 2BR, BR --2e BV --2e Pu. However, the re-reduction reactions of Pu are not the reverse processes. The different reduction mechanisms are discussed in detail.     

Study of the behavior of chromium(III) in potassium nitrate solutions at 25°C

Solubility in the KNO₃-Cr(NO₃)₃-H₂O system at 25°C was studied by an isothermal method. The existence of solid phases of potassium nitrate and chromium(III) nitrate nonahydrate was confirmed by constructing a phase diagram, chemical analysis, and IR spectroscopy. Crystallization of potassium nitrate from aqueous solutions was studied. Potassium nitrate does not interact with chromium(III) nitrate within the range of micro and macro concentrations. The capture of chromium(III) by KNO₃ crystals is due to adsorption and occlusion of a mother solution.     

The ionization of sulfurous acid in Na−Mg−Cl solutions at 25°C

The stoichiometric pK ₁ ^* and pK ₂ ^* for the ionization of sulfurous acid has been determined from emf measurements in NaCl solutions with varying concentrations of added MgCl₂ (m=0.1, 0.2 and 0.3) from I=0.5 to 6.0 molal at 25°C. These experimental results have been treated using both the ion pairing and Pitzer's specific ion-interaction models. The Pitzer parameters for the interaction of Mg²⁺ with SO₂ and HSO ₃ ^– yielded =0.085±0.004, ⁽⁰⁾ = 0.35±0.02, ⁽¹⁾ = 1.2±0.04, and C = –0.072±0.007. The Pitzer parameters ⁽⁰) = –2.8±0.4, ⁽¹⁾ = 12.9±2.9 and ⁽²⁾ = –2071±57 have been determined for the interactions of Mg²⁺ with SO ₃ ^2– . The calculated values of pK ₁ ^* and pK ₂ ^* using Pitzer's equations reproduce the measured values to within ±0.04 pK units. The ion pairing model with log K_MgSO3=2.36±0.02 and log_MgSO3 = 0.1021, reproduces the experimental values of pK ₂ ^* to ±0.01. These results demonstrate that treating the data by considering the formation of MgSO₃ yields a better fit of the experimental measurements with fewer adjustable parameters. With these derived coefficients obtained from the Pitzer equations and the ion pairing model, it is possible to make reliable estimates of the activity coefficients of HSO ₃ ^– and SO ₃ ^2– in seawater, brines and marine aerosols containing Mg²⁺ ions.     

Determination of enthalpy of ionization of water from 250 to 350° C

The enthalpy changes at zero ionic strength (H°) for the ionization of water (H₂O=H⁺+OH^–) were determined by flow calorimetry from the heats of mixing of aqueous NaOH and HCl solutions in the temperature range 250 to 350°C. Pitzer ion-interaction models developed by other workers were used to calculate enthalpies of dilution of aqueous NaOH, HCl, and NaCl solutions for the extrapolation of H values from the conditions of the experiment to infinite dilution. Equations are derived for thermodynamic quantities (log K, H°, S°, C _p ^° and V°) for the ionization of water using the H° values determined in this study from 250 to 350°C and literature log K and H° values from 0 to 225°C. Smoothed values of log K, H°, S°, C _p ^° , and V° are presented at rounded temperatures from 0 to 350°C and at the saturation pressure of water for each temperature. The equations in the present study provide a better representation of experimental thermodynamic data from 0 to 350°C than the Marshall-Franck equation.     

Solvent extraction of uranium from aqueous solutions by α-benzoinoxime

Solvent extraction of uranium with α-benzoinoxime from aqueous solutions has been systematically investigated. The extraction equilibration was very fast and achieved at 60 s for uranium. The extraction of uranium was pH-dependent using α-benzoinoxime as extractant. The effect concentration of uranium and α-benzoinoxime was studied. The uranium loaded in the organic phase can be stripped efficiently with 93 % yield using 0.1 M HCl as the stripping agent in a single stripping step. A good selectivity for uranium was observed through α-benzoinoxime as extractant from aqueous solution with other interfering cation ions. Present study suggested that α-benzoinoxime can be used as a potential extractant for separation of uranium from aqueous solution using centrifugal extractor in industrial application.