Redox Reaction Of Cr Research Articles

Mechanism of Removal of Hexavalent Chromium from Aqueous Solution by Fe-Modified Biochar and Its Application

This study discussed the mechanism of Fe-modified biochar (FeBC) derived from rice straw biochar (BC) as an adsorbent for removing Cr(VI) from aqueous solution and assessed its applicability in actual industrial wastewater. The Cr(VI) removal percentage increased with the FeBC dose, which achieved a removal of 99.5% at 8.0 g/L FeBC. Increasing the solution pH from 2 to 10 slightly reduced Cr(VI) adsorption by 6.6%. Coexisting ions such as Ca2+, Na+ and Cl− inhibited the removal of Cr(VI); the removal rate decreased to 60% at their concentration of 0.25 mol/L. The adsorption isotherm and kinetics were better described by the Langmuir isotherm and pseudo-second-order kinetic models, respectively. Through scanning electron microscopy with energy dispersive X-ray, the Brunauer–Emmett–Teller method, Fourier transform infrared, X-ray diffraction and X-ray photoelectron spectroscopy, the analysis revealed that FeBC with iron oxides loaded onto its surface had more active sites than BC; the surface functional groups changed; the removal of Cr(VI) by FeBC was mainly attributed to electrostatic adsorption; the redox reaction of Cr, and Fe loaded onto BC enhanced Cr(VI) reduction process. FeBC showed a good removal performance on actual industrial wastewater with the concentration of both total Cr and Cr(VI) meeting the integrated wastewater discharge standard of China.

Iron-Loaded Carbon Aerogels Derived from Bamboo Cellulose Fibers as Efficient Adsorbents for Cr(VI) Removal.

A unique iron/carbon aerogel (Fe/CA) was prepared via pyrolysis using ferric nitrate and bamboo cellulose fibers as the precursors, which could be used for high-efficiency removal of toxic Cr(VI) from wastewaters. Its composition and crystalline structures were characterized by FTIR, XPS, and XRD. In SEM images, the aerogel was highly porous with abundant interconnected pores, and its carbon-fiber skeleton was evenly covered by iron particles. Such structures greatly promoted both adsorption and redox reaction of Cr(VI) and endowed Fe/CA with a superb adsorption capacity of Cr(VI) (182 mg/g) with a fast adsorption rate (only 8 min to reach adsorption equilibrium), which outperformed many other adsorbents. Furthermore, the adsorption kinetics and isotherms were also investigated. The experiment data could be much better fitted by the pseudo-second-order kinetics model with a high correlating coefficient, suggesting that the Cr(VI) adsorption of Fe/CA was a chemical adsorption process. Meanwhile, the Langmuir model was found to better describe the isotherm curves, which implied the possible monolayer adsorption mechanism. It is noteworthy that the aerogel adsorbent as a bulk material could be easily separated from the water after adsorption, showing high potential in real-world water treatment.

Spectroelectrochemical Behavior of Cr, Fe, Co, and Ni in LiCl-KCl Molten Salt for Decontaminating Radioactive Metallic Wastes

This study examines the thermodynamic, kinetic, and spectroscopic behaviors of Cr, Fe, Co, and Ni to lay the foundation to develop an electrochemical decontamination process for radioactive metallic wastes. Cyclic voltammetry combined with numerical fitting was used to obtain the formal potentials, standard rate constants, and diffusion coefficients of redox reactions, Cr(II)/Cr, Fe(II)/Fe(0), Co(II)/Co(0), and Ni(II)/Ni(0), in LiCl-KCl at 773 K. The order of the diffusion coefficients was 10–5 cm2 s−1, which agrees with the existing data and the standard rate constants showed similar values with the order of 10–3 cm s−1 between experimental correlations and numerical fitting. UV–vis-NIR absorption spectroscopy of the metallic constituents was performed to derive molar absorption coefficients and molecular structures in molten salt media. In particular, the redox reaction of Cr(III)/Cr(II) was investigated by chronoabsorptometry to obtain its formal potential, the number of electrons, and the diffusion coefficient of Cr(II). The obtained reaction properties were used in the numerical modeling of the ECE reaction in a Ni and Co binary system to reproduce the experimental results of CV, revealing the presence of chemical reaction. The findings of this study will be directly used for designing a decontamination process to produce acceptable waste forms and reduce waste volume.

Ultra-trace determination of hexavalent chromium by novel two dimensional biphenol-biphenoquinone nanoribbons/silver nanoparticles

In this study, decorated silver nanoparticles on two dimensional (2D) -biphenol-biphenoquinone nanoribbons (AgNPs-BP-BPQ NRs) were prepared for the first time by a novel, fast and simple method. The mentioned compound was then used as modifier for preparation of modified graphite paste electrode (GPE/AgNPs-BP-BPQ NRs) for indirect voltammetric determination of carcinogen hexavalent chromium (Cr (VI). Peak current of BP/BPQ redox system was decreased in the presence of Cr (VI), hence, this decrease in peak current was used as the electroanalytical signal for quantitative determination of Cr (VI). Moreover, the redox reaction of Cr (VI) and BP was investigated in this study for the first time and the product was characterized. Different techniques such as field emission electron microscopy, Energy-dispersive X-ray spectroscopy, transmission electron microscopy, atomic force microscopy and fourier transform infrared spectroscopy were performed for characterization of the AgNPs-BP-BPQ NRs. Different electrochemical methods, such as cyclic voltammetry, electrochemical impedance spectroscopy and differential pulse voltammetry, were employed to study the behavior of Cr (VI) on the proposed modified electrode. Under the optimum conditions, the calibration curve was liner in the ranges of 8.0 × 10−11 to 1.0 × 10-8, 1.0 × 10-8 to 1.0 × 10-6 and 1.0 × 10-6 to 1.0 × 10-4 M with a detection limit of 2.0 × 10-12 M. Finally, this sensor was successfully used for determination of Cr (VI) in tap water, river water and electroplating waste water samples.

Investigation of adsorption/desorption behavior of Cr(VI) at the presence of inorganic and organic substance in membrane capacitive deionization (MCDI)

The adsorption and desorption behavior of Cr(VI) in membrane capacitive deionization (MCDI) was investigated systematically in the presence of bovine serum albumin (BSA) and KCl with different concentrations, respectively. Results revealed that Cr(VI) absorption was enhanced and the adsorption amount for Cr(VI) increased from 155.7 to 190.8 mg/g when KCl concentration increased from 100 to 200 mg/L in the adsorption process, which was attributed to the stronger driving force. However, the adsorption amount sharply decreased to 90.2 mg/g when KCl concentration reached up to 1000 mg/L suggesting the negative effect for Cr(VI) removal that high KCl concentration had. As for the effect of BSA on ion adsorption, the amount for Cr (VI) significantly declined to 78.3 mg/g and pH was found to be an important factor contributing to this significant reduction. Then, the desorption performance was also conducted and it was obtained that the presence of KCl had negligible effect on Cr(VI) desorption, while promoted by the addition of BSA. The incomplete desorption was obtained and the residual chromium ions onto the electrode after desorption was detected via energy-dispersive X-ray spectroscopy (EDS). Based on above analysis, the enhanced removal mechanism for Cr(VI) in MCDI was found to be consisted of ion adsorption onto electrode surface, the redox reaction of Cr(VI) into Cr(III) and precipitation, which was demonstrated by X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM).

Insight into efficient co-removal of Se(IV) and Cr(VI) by magnetic mesoporous carbon microspheres: Performance and mechanism

In this study, carbon microspheres (CMSs) and magnetic carbon microspheres (MCMSs) were synthesized and applied to remove Se(IV) and Cr(VI) in Se(IV), Cr(VI), and Se(IV)-Cr(VI) coexisting systems, respectively. Transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), Vibrating-sample magnetometry (VSM), and X-ray diffraction (XRD) were employed to investigate the physical properties, compositions, and structures of CMSs and MCMSs. X-ray photoelectron spectroscopy (XPS) was employed to reveal the removal mechanism of Se(IV) and Cr(VI) with MCMSs. Under optimum conditions, 100% Se(IV) and 100% Cr(VI) can be removed by MCMSs in 120 min from Se(IV)-Cr(VI) coexisting system containing initial concentration of 10.0 mg/L Se(IV) and 10.0 mg/L Cr(VI). Cr(VI) was removed due to the hydrogen bonding interaction between Cr(VI) and carboxylate groups and redox reaction of Cr(VI) with alcoholic hydroxyl groups on CMSs. Besides, the Fe3O4 nanoscale particles on the surface of CMSs can form outer-sphere complexes with Cr(VI) and reduce Cr(VI) to Cr(III). Se(IV) can form precipitates with the generated Cr(III). Moreover, the Fe3O4 nanoscale particles can form inner-sphere complexes with Se(IV) and reduce Se(IV) to elemental selenium (Se0) by Fe(II).

In-situ functionalization of poly(m-phenylenediamine) nanoparticles on bacterial cellulose for chromium removal

A novel efficient adsorbent of bacterial cellulose/poly(m-phenylenediamine (BC/PmPD) was prepared for Cr(VI) removal by combining the advantages of high adsorption capacity of PmPD and easy reclamation of BC. Through monomer (mPD) pre-adsorption on BC, the stable hybrid structure of PmPD nanoparticles functionalization on BC fibril was successfully realized by in-situ oxidative polymerization of adsorbed mPD. The morphology and structure of the adsorbents were analyzed by SEM, TEM, XRD, FTIR, and XPS techniques. The interaction between BC and PmPD and adsorption mechanism were also analyzed. The optimized BC/PmPD has Langmuir Cr(VI) adsorption capacity of 434.78 mg/g, much higher than many reported adsorbents. The Cr(VI) adsorption on BC/PmPD was ascribed to the Cr(VI) adsorption on protonated NH and NH2 groups and the redox reaction of Cr(VI) to Cr(III) by the reduction of amine, followed by Cr(III) chelation on imino groups of PmPD. The recycling test indicated that the BC/PmPD has good regeneration and reusability capacity with its fast-reversible macroscopic assembly and disassembly features, and high stabilization of PmPD on BC. Findings in the present study demonstrated that the BC/PmPD can be considered as a promising adsorbent for Cr(VI) removal due to its high adsorption capacity, efficient reclamation, good regeneration performance.

Interaction of Pyridine-2,6-dicarboxylic Acid with Cr(VI) in the Oxidative Decarboxylation of Phenylsulfinyl Acetic Acid and Linear Free Energy Relationship

Aims: To investigate the catalytic activity of pyridine-2,6-dicarboxylic acid in the redox reaction of Cr(VI) and phenylsulfinyl acetic acid. Study Design: The mechanism of the reaction was designed on the basis of the observed results of kinetic, spectral and substituent effect studies. Place and Duration of Study: Laboratory of the Research Department of Chemistry, Aditanar College of Arts and Science, Tiruchendur, Tamil Nadu, India. September 2013 – January 2014. Methodology: Phenylsulfinyl acetic acid and ten metaand para-substituted phenylsulfinyl acetic acids essential for the present kinetic study were synthesized. The kinetic study was performed in 40% acetonitrile-60% H2O medium under pseudo-first-order conditions by maintaining [PSAA] >> Original Research Article Subramaniam and Thamil Selvi; ACSj, 6(2): 105-114, 2015; Article no.ACSj.2015.042 106 [Cr(VI)] throughout the experiment. The progress of the reaction was monitored by following the rate of disappearance of Cr(VI) spectrophotometrically at 351 nm. The effect of pyridine-2,6dicarboxylic acid on the rate of the reaction and the applicability of linear free energy relationship with different phenylsulfinyl acetic acids were tested. Results: The reaction shows unit order dependence on Cr(VI) but follows Michalis-Menten kinetics with respect to substrate as well as catalyst. The order with respect to [H] is between one and two. The thermodynamic parameters ∆ ‡ S (-93.2 JK -1 mol -1 ) and ∆ ‡ H (57.7 kJ mol -1 ) are evaluated respectively from the intercept and slope of the Eyring’s plot. The Hammett’s correlation affords a negative ρ value (-1.05). Conclusion: Pyridine-2,6-dicarboxylic acid catalyzes the reaction and Cr(VI)-PDA complex is assumed to be the oxidizing species of the reaction. The sulfur of PSAA undergoes nucleophilic attack on Cr(VI)-PDA complex forming a ternary complex, Cr(VI)-PDA-PSAA which experiences decarboxylation, ligand coupling and further decomposition giving methylphenyl sulfone as the product. The mechanism with the associated reaction kinetics is assigned in support of substituent effect.

Adsorption and Reduction of Chromium(VI) from Aqueous Solution by Multiwalled Carbon Nanotubes

The adsorption of Cr(VI) on the raw multiwalled carbon nanotubes (MWCNTs) as a function of initial Cr(VI) concentration, pH, temperature, and MWCNT dosage were studied. The removal of Cr(VI) from aqueous solution was dominated by adsorption of Cr(VI) and redox reaction of Cr(VI) to Cr(III). The adsorption of Cr(VI) decreased with in- creasing pH and increased with the rise in temperature and MWCNT dosage. The adsorption data of Cr(VI) on MWCNTs could be described well by Langmuir isotherm model. The thermodynamic values of Gibbs free energy ( G o ), enthalpy ( H o ), and entropy ( S o ) were calculated from temperature-dependent adsorption data, and the results indicated that the adsorption of Cr(VI) on the raw MWCNTs was a spontaneous process. The results suggest that MWCNTs are suitable materials in the preconcentration and solidification of Cr(VI) from large volume of solutions.

Oxygen nonstoichiometry and defect structure analysis of B-site mixed perovskite-type oxide (La, Sr)(Cr, M)O 3−δ ( M=Ti, Mn and Fe)

The defect chemical relationships in various B-site mixed LaCrO 3-based ceramics were investigated by means of high-temperature gravimetry. The nonstoichiometric deviation, δ, in (La 0.7Sr 0.3)(Cr 1− y Ti y )O 3− δ ( y=0.1, 0.2 and 0.3) (LSCT) , (La 0.75Sr 0.25)(Cr 0.5Mn 0.5)O 3− δ (LSCM) and (La 0.75Sr 0.25)(Cr 0.5Fe 0.5)O 3− δ (LSCF) were measured as a function of oxygen partial pressure, P O 2 , at temperatures between 973 and 1373 K. The effects of partial replacement of the donor on Cr-sites were examined in LSCT. In LSCM and LSCF, effects of the partial substitution of isovalent transition metals on Cr-sites are discussed. Oxygen nonstoichiometries of various B-site mixed LaCrO 3-based ceramics were compared with those of A-site substituted perovskite-type oxides, (La 1− x Sr x ) MO 3− δ (where x=0–0.3, M=Cr, Mn and Fe). The partial substitution of the different elements on Cr-sites drastically changed the P O 2 and temperature dependence of oxygen vacancy formation in LaCrO 3-based ceramics. The defect equilibrium relationships of the localized electron well explained the oxygen vacancy formation in B-site mixed LaCrO 3-based ceramics. Oxygen vacancy formation in (La 0.7Sr 0.3)(Cr 1− y Ti y )O 3− δ ( y=0.1 and 0.2) and (La 0.7Sr 0.3)(Cr 0.7Ti 0.3)O 3− δ was explained by redox reaction of Cr and Ti ions, respectively. The defect equilibrium relationships of LSCM and LSCF were interpreted by redox reaction of Mn ions and Fe ions, respectively. No significant change in valence state of Cr 3+ ions in LSCM and LSCF was confirmed under the experimental conditions.

Kinetics and mechanism of oxidation of Cr(II) ions by tetrachloromethane

Kinetics of the redox reaction of Cr(II) ions with tetrachloromethane has been studied in H2O-CH3OH-HClO4 and H2O-CH3COOH-HClO4. In the redox reaction 2 moles of Cr(II) are consumed per one mol of CCl4, and CrCl2+ and CrCCL2+3 ions are formed in the same amounts. Second order rate constants (k293 = 2.31 mol-1 s -1 in 50% CH3OH, k293 = 1.66 l . mol-1 s-1 in 50% CH3COOH) are independent of H+ ions concentration.The rate determining step is an inner sphere transfer of the halogen from CCl4 to Cr(II), the Cr-Cl-C bridge structure being retained in both media.

An inner sphere redox reaction of Cr(II) ions with halogenoacetic acids. Stoichiometry, kinetics, and mechanism

An inner sphere redox reaction of Cr(II) ions with halogenoacetic acids. Stoichiometry, kinetics, and mechanism