Showing papers on "Chromium published in 2015"
TL;DR: The Fe3O4@PmPDs have great potential in treating Cr( VI)-contaminated water and the coating of PmPD significantly enhanced Cr(VI) adsorption capacity from 46.79 (bare MNPs) to 246.09 mg g(-1) (71.55% Pm PD loading proportion), much higher than many reported composite adsorbents.
Abstract: Magnetic Fe3O4@poly(m-phenylenediamine) particles (Fe3O4@PmPDs) with well-defined core–shell structure were first designed for high performance Cr(VI) removal by taking advantages of the easy separation property of magnetic nanoparticles (MNPs) and the satisfactory adsorption property of polymers. Through controlling the polymerization on MNPs, directly coating was realized without the complicated premodification procedures. The particle property and adsorption mechanism were analyzed in details. Fe3O4@PmPDs exhibited tunable PmPD shell thickness from 10 to 100 nm, high magnetic (∼150 to ∼73 emu g–1) and facile separation property by magnet. The coating of PmPD significantly enhanced Cr(VI) adsorption capacity from 46.79 (bare MNPs) to 246.09 mg g–1 (71.55% PmPD loading proportion), much higher than many reported composite adsorbents. The high Cr(VI) removal performance was attributed to the adsorption of Cr(VI) on protonated imino groups and the efficient reduction of Cr(VI) to Cr(III) by amine, followed...
331 citations
TL;DR: In this paper, static equilibrium experiments were conducted to distinguish the adsorption performance between the two valence states of chromium on biochar derived from municipal sludge, showing that Cr(III) is much easier to be stabilized than Cr(VI).
253 citations
TL;DR: Using graphitic carbon nitride (g-C3N4) nanosheets, an effective and facile fluorescence sensing approach for the label-free and selective determination of chromium (VI) (Cr(VI), which has the potential application for detection of Cr(VI) in lake waters and AA in biological fluids.
236 citations
TL;DR: In this paper, a series of Fe-Cr-Al alloys with 10 −18 ¼ % Cr and 2.9 −4.9 % Al were irradiated at 382 −C to 1.8 dpa to investigate the irradiation-induced microstructural and mechanical property evolution as a function of alloy composition.
198 citations
TL;DR: Choosing an appropriate bioremediation strategy for Cr is extremely important and must involve investigating and understanding the key mechanisms that are involved in microbial resistance to and removal of Cr(VI).
Abstract: Chromium is a naturally occurring element found in rocks, animals, plants, soil and in volcanic dust and gases. It exists in different oxidation states that range from +2 to +6. The most stable forms are Cr(VI) and Cr(III), although they significantly differ in biological, geochemical and toxicological properties. Cr(III) occurs naturally in the environment at a narrow concentration range and is considered to be less toxic than Cr(VI). Hexavalent chromium is used extensively in industrial processes such as electroplating, tanning, textile dyeing, corrosion inhibition and wood treatment, all of which produce discharge of chromium-containing effluents (Lauwerys et al. 2007). The high solubility of Cr(VI) makes it a hazardous contaminant of water and soil when discharged by industries that produce or utilize chromium. When it is released to the environment, Cr(VI) is a potential contaminant of groundwater that can participate in trophic transfer in food chains. The United States Environmental Protection Agency has identified Cr(VI) as one of the 17 chemicals posing the greatest threat to humans (Marsh and McInerney 2001). The permissible limit for total chromium in drinking water is 0.05 mg/L (WHO 2004).
192 citations
TL;DR: In this paper, an interesting interaction between oxidized multiwalled carbon nanotubes (oxi-MWCNTs), tetra n-heptylammonium bromide (ionic liquid) and total chromium ((Cr(VI)/Cr(III)) was reported.
Abstract: We report an interesting interaction between oxidized multiwalled carbon nanotubes (oxi-MWCNTs), tetra n-heptylammonium bromide (ionic liquid) and total chromium ((Cr(VI)/Cr(III)) in this study. The interaction between the IL and oxidized MWCNTs primarily involves electrostatic affinity between the quaternary ammonium cation, and surface carboxyl and hydroxyl groups in oxi-MWCNTs. The IL-oxi-MWCNT adsorbent acts as a host in welcoming the incoming guest hydrochromate anions and several interesting interactions such as cation–π interactions, electrostatic interactions as well as anion–π interactions could be conceptualized in this process. The abundant oxygen-containing functional groups on the surfaces of oxi-MWCNTs play an important role in Cr(VI)/Cr(III) sorption. Characterization of the adsorbent was performed using various characterization techniques such as cross polarization magic angle spinning nuclear magnetic resonance (13CPMAS-NMR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), powder-X-ray diffraction (Powder-XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy analysis (TEM), Brunauer–Emmett–Teller (BET) isotherm studies, scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). The capability of inductively coupled plasma mass spectrometry (ICP-MS) for Cr(VI) adsorption was extensively studied under different optimal parameters and the maximum adsorption capacity was found to be 85.83 mg g−1 from a nonlinear Langmuir isotherm model. A kinetic study confirms a pseudo second order model and the process could be upgraded by column studies to a sample volume of 2000 mL. Effective regeneration of the adsorbent could be accomplished with sodium hydroxide and the potential of this novel adsorbent has been examined in the removal of Cr(VI)/Cr(III) from aqueous solutions.
190 citations
TL;DR: In this article, the effects of chromium amount in anodizing solution on the morphologies, structure, photoabsorption and photoelectrochemical water splitting of the TiO 2 nanotube array film were investigated.
188 citations
TL;DR: In this article, a novel approach based on stepwise roasting has been proposed to extract vanadium and chromium separately from vanadium slag with high chromium content (V-Cr slag), which consists of two stages of sodium roasting and water leaching.
184 citations
TL;DR: Iron sulphate (FeSO4) and colloidal nano zero-valent iron (nZVI) as reducing agents were compared, with the aim of assessing their effectiveness in hexavalent chromium [Cr(VI)] removal from a contaminated industrial soil, and Cr(VI) reduction by colloidal nZVI proved to be faster and more effective.
177 citations
TL;DR: In this paper, a combined two-step EC-EF process was designed to simultaneously remove Cr(VI) and fluoride from pretreated acidic semiconductor effluents, where a hybrid Fe-Al was used as sacrificial anode and stainless steel as cathode.
174 citations
TL;DR: 3-(2-aminoethylamino) propyltrimethoxysilane (AAPTS) functionalized multi-wall carbon nanotubes (MWCNTs) were synthesized and employed as the adsorbent for simultaneous speciation analysis of inorganic arsenic, chromium and selenium in environmental waters by microcolumn solid-phase extraction (SPE)-inductively coupled plasma mass spectrometry (ICP-MS).
TL;DR: The experimental results revealed that chromium speciation played a key role in the adsorption process, also for the occurrence of Cr(VI)-to-Cr(III) reduction reactions.
15 Jul 2015
TL;DR: In this article, the effect of low-level chromium substitution in Na3V2-xCrx(PO4)3 (0≤x≤0.4), a potential cathode material in Na-ion cells, has been examined.
Abstract: The effect of low-level chromium substitution in Na3V2-xCrx(PO4)3 (0≤x≤0.4), a potential cathode material in Na-ion cells, has been examined. A suitable synthesis procedure is developed to obtain composites of crystalline NASICON phosphate and an amorphous carbon phase to enhance the electrical conductivity of the electrode. The optimized cathode materials were characterized by using X-ray diffraction and spectroscopic techniques. The electrochemical evaluation was carried out by using galvanostatic and potentiostatic methods. The activity of the V5+/V4+ redox couple at approximately 4 V is remarkable for the samples containing chromium. A reversible capacity of 107 mAh g−1 with a coulombic efficiency of 99 % was determined for Na3V1.9Cr0.1(PO4)3 after 40 cycles. The observed performance correlates with a good kinetic response, resulting from low charge-transfer resistance and high diffusion coefficient.
TL;DR: The reduction of toxic Cr(VI) to the less or nontoxic Cr(III) by the reticulated chitosan micro/nanoparticles can be considered a very efficient detoxification technique for the treatment of Cr( VI) contaminated water.
TL;DR: In this article, the authors used a sequential extraction procedure (acid soluble, reducible, oxidizable, and residual) as proposed by the Community Bureau of Reference (BCR) of the European Commission.
Abstract: The present research was conducted to determine heavy metals in agricultural soils from Canakkale, Turkey, using a sequential extraction procedure (acid soluble, reducible, oxidizable, and residual) as proposed by the Community Bureau of Reference (BCR) of the European Commission. Soil samples were taken from 12 different cultivated sites and analyzed for Cd, Co, Cr, Cu, Mn, Ni, Pb, and Zn concentrations. The results revealed an order of Mn > Cd > Pb > Co > Ni > Cu > Zn > Cr for the heavy metals based on the sum of the first three fractions (acid soluble + reducible + oxidizable). The relationships between soil properties and each metal fraction were identified through Pearsons's correlation analysis. Hierarchical cluster analysis was performed to determine the behaviors and similarities of metals in each fraction. While Mn, Pb, and Zn exhibited subjective behaviors in the acid-soluble fraction, Cd, Co, Cu, Cr, and Ni exhibited similar behaviors with each other.
TL;DR: Stacked chitosan nanofibers with an average diameter of 75 nm were successfully produced by electrospinning and it was found that the adsorption correlated well with pseudo-second order kinetic model, and followed a mixed isotherm of Freundlich and Langmuir.
TL;DR: This review assembles articles published since 2000 regarding chromium speciation in water samples with the use of HPLC/ICP-MS and addresses the following issues: chromium chemistry, the possibilities of dealing with interferences, metrological aspects, analytical performance and speciated isotope dilution mass spectrometry (SIDMS) which is a definitive measurement method.
TL;DR: In this paper, the authors investigated feasibility of using waste eggshells for the removal of Cr(VI) ions from its aqueous solutions and found that the maximum removal (about 93%) of chromium ion onto egg shells can be achieved at 25°C and pH 5 in 90 min.
Abstract: Chromium is one of the hazardous pollutants in industrial effluents. The aim of this research is to investigate feasibility of using waste eggshells for the removal of Cr(VI) ions from its aqueous solutions. Characterization of crushed and sieved eggshell have been carried out using scanning electron microscope, Fourier transform infrared spectroscopy, X-ray diffraction, X-ray fluorescence, etc. analysis. The effect of pH, Cr(VI) ions concentration, amount of eggshell, contact time, temperature, etc. parameters have been investigated on the adsorption and it has been found that the maximum removal (about 93%) of Cr(VI) onto eggshells can be achieved at 25°C and pH 5 in 90 min. Freundlich and Langmuir adsorption isotherm models e have been verified using experimental data. Results also include calculation of thermodynamic parameters like, change in enthalpy (ΔH0), change in entropy (ΔS0), and change in free energy (ΔG0) of the ongoing adsorption process. Chromium sorption kinetics is also found to ...
TL;DR: In this paper, the authors examined the influence of temperature on oxide scale growth and vaporization in Solid Oxide Fuel Cells (SOFCs) when Cr 2 O 3 -forming alloys are used as the interconnect material.
TL;DR: In this article, the authors reported that GQDs are viable fluorescent probes for the determination of chromium(VI) and ascorbic acid in an on-off-on mode.
Abstract: We report that graphene quantum dots (GQDs) are viable fluorescent probes for the determination of chromium(VI) and ascorbic acid in an on-off-on mode. The fluorescence of GQDs is strongly quenched by Cr(VI) mainly due to an inner filter effect and static quenching. This shifts the system to the “off” status. The quenching mechanism of this fluorescent system was investigated in some detail. Fluorescence intensity is inversely proportional to the concentration of Cr(VI) in the 0.05 to 500 μM concentration range with a 3.7 nM detection limit. The fluorescence of GQDs-Cr(VI) system is converted back to “on” by adding ascorbic acid which will reduce yellow Cr(VI) ion, thereby eliminating the inner filter effect and static quenching. The relative intensity of restored fluorescence is directly proportional to the concentration of ascorbic acid in the 1.0 to 500 μM range, and the limit of detection is 0.51 μM. There are almost no interferences to commonly encountered other substances. The methods were applied to the determination of Cr(VI) in spiked tape, lake and river waters, and of ascorbic acid in a tablet and human urine. Both gave satisfactory results.
TL;DR: Application of multifunctional plant-growth-promoting bacteria (PGPB) exhibiting chromium resistance and reducing traits when used as bioinoculants with phytoremediating plants, has resulted in a better plant growth and chromium remediating efficiency in a short time span.
TL;DR: In this article, Pterocladia capillacea, a red marine macroalgae, was tested for its ability to remove toxic hexavalent chromium from aqueous solution.
TL;DR: An enzyme-mediated chromate reduction process has therefore been developed for bioremediation of toxic chromium sp.
TL;DR: The reactivity of well-defined chromium silicates toward ethylene and propane is described and it is found that these materials, slightly contaminated with a minor amount of Cr(II) sites, have poor polymerization activity and few active sites, in contrast, chromium(III) silicates have 1 order of magnitude higher activity.
Abstract: We describe the reactivity of well-defined chromium silicates toward ethylene and propane. The initial motivation for this study was to obtain a molecular understanding of the Phillips polymerization catalyst. The Phillips catalyst contains reduced chromium sites on silica and catalyzes the polymerization of ethylene without activators or a preformed Cr–C bond. CrII sites are commonly proposed active sites in this catalyst. We synthesized and characterized well-defined chromium(II) silicates and found that these materials, slightly contaminated with a minor amount of CrIII sites, have poor polymerization activity and few active sites. In contrast, chromium(III) silicates have 1 order of magnitude higher activity. The chromium(III) silicates initiate polymerization by the activation of a C–H bond of ethylene. Density functional theory analysis of this process showed that the C–H bond activation step is heterolytic and corresponds to a σ-bond metathesis type process. The same well-defined chromium(III) sili...
TL;DR: In this paper, the formation of a trivalent conversion coating on aluminium has been investigated using analytical electron microscopy, atomic force microscopy and ion beam analysis, glow discharge optical emission spectroscopy.
Abstract: The formation of a trivalent conversion coating on aluminium has been investigated using analytical electron microscopy, atomic force microscopy, ion beam analysis, glow discharge optical emission spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. The coating is shown to comprise a chromium- and zirconium-rich outer layer and an aluminium-rich inner layer. Zirconium and chromium are present in chemical states consistent with ZrO 2 , ZrF 4 , Cr(OH) 3 , Cr 2 (SO 4 ) 3 , CrF 3 and CrO 3 or CrO 4 2 − . However, negligible amounts of Cr(VI) species occurred in coatings formed in de-aerated solution. Electrochemical impedance spectroscopy revealed that the inner layer provides the main corrosion protection during short-term tests in 0.1 M sodium sulphate solution at room temperature.
TL;DR: The calculated thermodynamic parameters indicate the nature of chromium sorption is spontaneous and endothermic.
22 Sep 2015
TL;DR: Learn about chromium regulation in public drinking water systems and the potential that the regulation may be amended in the future to better address chromium-6.
Abstract: Learn about chromium regulation in public drinking water systems and the potential that the regulation may be amended in the future to better address chromium-6.
TL;DR: The potential applicability of AuPd/CNTs was revealed by their stability in electrocatalytic conversion over 10 cycles, and the crucial intermediates of Cr(V) and As(IV) and active free radicals HO(•) and O2(•-) were found for the first time, whose roles in the control ofCr(VI)/As(III) redox conversion were proposed.
Abstract: Simultaneous reduction of Cr(VI) to Cr(III) and oxidation of As(III) to As(V) is a promising pretreatment process for the removal of chromium and arsenic from acid aqueous solution. In this work, the synergistic redox conversion of Cr(VI) and As(III) was efficiently achieved in a three-dimensional electrocatalytic reactor with synthesized AuPd/CNTs particles as electrocatalysts. The AuPd/CNTs facilitated the exposure of active Pd{111} facets and possessed an approximate two-electron-transfer pathway of oxygen reduction with the highly efficient formation of H2O2 as end product, resulting in the electrocatalytic reduction of 97.2 ± 2.4% of Cr(VI) and oxidation of 95.7 ± 4% of As(III). The electrocatalytic reduction of Cr(VI) was significantly accelerated prior to the electrocatalytic oxidation of As(III), and the effectiveness of Cr(VI)/As(III) conversion was favored at increased currents from 20 to 150 mA, decreased initial pH from 7 to 1 and concentrations of Cr(VI) and As(III) ranging from 50 to 1 mg/L. The crucial intermediates of Cr(V) and As(IV) and active free radicals HO(•) and O2(•-) were found for the first time, whose roles in the control of Cr(VI)/As(III) redox conversion were proposed. Finally, the potential applicability of AuPd/CNTs was revealed by their stability in electrocatalytic conversion over 10 cycles.
TL;DR: Geochemical and mineralogical analyses showed that chromium concentrations in soils and sediments range from 115 to 959 mg/kg and that serpentine prevails among the phyllosilicates and, therefore, in groundwater, and the high correlation between chromium and serpentine, amphibole and pyroxene minerals verifies the geogenic origin of chromium in soils.
TL;DR: In this paper, the authors used an electrochemical reactor using iron sacrificial electrode to remove hexavalent chromium and COD from wastewater by electrocoagulation and showed that this process of removal can reduce chromium (VI) into chromium(III) with an output of 100% and 95.95% of COD in a relatively short reaction time and at low cost.
Abstract: The purpose of this study is to remove hexavalent chromium and COD from wastewater by electrocoagulation. The experiments were carried out in an electrochemical reactor using iron sacrificial electrode. Operating parameters such as current density (100, 150, 200 A/m 2 ), pH of the effluent, number of electrodes and their materials were studied. The optimal operating conditions were determined and applied to the process. The results show that this process of removal can reduce chromium (VI) into chromium (III) with an output of 100% and 95.95% of COD in a relatively short reaction time and at low cost.