Comparison of Cr(VI) Adsorption Using Synthetic Schwertmannite Obtained by Fe3+ Hydrolysis and Fe2+ Oxidation: Kinetics, Isotherms and Adsorption Mechanism.

Good sorption properties and simple synthesis route make schwertmannite an increasingly popular adsorbent. In this work, the adsorption properties of synthetic schwertmannite towards Cr(VI) were investigated. This study aimed to compare the properties and sorption performance of adsorbents obtained by two methods: Fe3+ hydrolysis (SCHA) and Fe2+ oxidation (SCHB). To characterise the sorbents before and after Cr(VI) adsorption, specific surface area, particle size distribution, density, and zeta potential were determined. Additionally, optical micrographs, SEM, and FTIR analyses were performed. Adsorption experiments were performed in varying process conditions: pH, adsorbent dosage, contact time, and initial concentration. Adsorption isotherms were fitted by Freundlich, Langmuir, and Temkin models. Pseudo-first-order, pseudo-second-order, intraparticle diffusion, and liquid film diffusion models were used to fit the kinetics data. Linear regression was used to estimate the parameters of isotherm and kinetic models. The maximum adsorption capacity resulting from the fitted Langmuir isotherm is 42.97 and 17.54 mg·g-1 for SCHA and SCHB. Results show that the adsorption kinetics follows the pseudo-second-order kinetic model. Both iron-based adsorbents are suitable for removing Cr(VI) ions from aqueous solutions. Characterisation of the adsorbents after adsorption suggests that Cr(VI) adsorption can be mainly attributed to ion exchange with SO42- groups.

Synthesis of a chitosan/polyvinyl alcohol/activate carbon biocomposite for removal of hexavalent chromium from aqueous solution.

In this study, a biocomposite of chitosan/poly vinyl alcohol/activated carbon was synthesized and used for hexavalent chrome removal from aqueous solution. The synthesized adsorbent was characterized by Scanning Electron Microscopy (SEM) and Fourier Transform Infrared (FTIR) analysis. The effect of important variables such as pH, concentration, contact time, temperature, and adsorbent dosage was investigated. The value of pHPZC for the adsorbent was evaluated at 4.9. Results showed that adsorption of chrome onto the adsorbent follows the Langmuir isotherm model and has a pseudo-second-order kinetic model. The maximum capacity of chrome adsorption was determined 109.89 (mg/g) according to the Langmuir isotherm model. According to adsorption results, the removal percentage of chrome increases with increasing the activated carbon content in the biocomposite, the adsorbent dosage, and decreasing the initial chrome concentration, pH, and temperature. The results showed that the synthesized adsorbent can be used as an effective adsorbent for chrome removal from aqueous solutions.

Oxidación de etanol por dicromato y bromación de fenol: historia de dos reacciones / Dichromate oxidation of ethanol and phenol bromination: a tale of two reactions

Un breve informe de la importancia e historia de dos reacciones relevantes, la oxidación de etanol con dicromato y la bromación de fenol se describe en este trabajo, en el que se perfilan las valoraciones volumétricas de etanol y fenol (AU)

A brief account of the worth and history of two relevant reactions, the dichromatometric oxidation of ethanol and phenol bromination is attempted in this paper. Titrimetric analyses of ethanol and phenol are outlined (AU)

La aportación húngara a los métodos iodométricos, Karoly Than y Lajos Winkler, la determinación de oxígeno disuelto y el índice de iodo / The Hungarian contribution to iodometric methods, Karoly Than and Winkler Lajos, the determination of dissolved oxygen and the iodo index

Tras el trasfondo de los métodos iodométricos se procede a analizar la vida y la obra de dos grandes científicos húngaros, Than y Winkler, maestro y discípulo, responsables de la introducción de la química científica y de la educación farmacéutica en su país, que se movía en la órbita del imperio austro-húngaro, generando una escuela de excelencia en el ámbito académico. Than contribuye entre otros muchos descubrimientos a la utilización del bi-iodato potásico para la estandarización de tiosulfato de sodio. Winkler pone a punto un método iodométrico de determinación del oxígeno disuelto en aguas, un clásico de la química analítica, todavía en uso hoy día. El uso del dicromato de potasio por Zulkovsky abre la posibilidad a las aplicaciones analíticas de las oxidaciones con dicromato en iodometría. Las determinaciones de ioduro y bromuro y la del índice de yodo, entre otras, hace que la química analítica de los halógenos pueda considerarse una rama distintiva de la ciencia húngara. Schulek, discípulo de Winkler, abre las puertas al desarrollo del análisis y de la industria farmacéutica en Hungría (AU)

Under the background of the iodometric methods we analyze the life and work of two great Hungarian scientists, Than and Winkler, teacher and disciple. They were responsible for the introduction of scientific chemistry and pharmaceutical education in his country, which moved in the orbit of the Austro-Hungarian Empire. Both generated a school of excellence in the academic field. Than contributes among many other discoveries to the use of potassium biiodate for the standardization of sodium thiosulfate and Winkler develops an iodometric method for the determination of dissolved oxygen in waters, a classic of chemical analysis, the use of which continues today. The use of potassium dichromate by Zulkovsky opened the possibility to the analytical applications of the oxidations with dichromate in iodometry. The iodide, bromide and iodine index determinations, make the analytical chemistry of halogens a distinctive branch of Hungarian science. Schulek, a disciple of Winkler, opens the door to the development of pharmaceutical analysis and the pharmaceutical industry in Hungary (AU)

Effect of pre-analytical treatments on bovine milk acute phase proteins.

BACKGROUND: Samples for diagnostic procedures often require some form of pre-analytical preparation for preservation or safe handling during transportation prior to analysis in the laboratory. This is particularly important for milk samples which frequently need preservatives to retain milk composition as close to that found in freshly collected samples as possible. METHODS: Milk samples were treated by heating at 56 °C for 30 min or preserved by addition of either potassium dichromate or bronopol respectively. Haptoglobin (Hp), mammary associated serum amyloid A3 (M-SAA3) and C-reactive protein (CRP) were measured in the various treatment groups and in control samples which were not treated, using enzyme linked immunoassays. The concentrations of each APP were compared between treated and non-treated groups using the Wilcoxon signed ranks tests. RESULTS: Heat treatment of samples was found to have a significant lowering effect on milk M-SAA3 and CRP but not Hp. The use of potassium dichromate and bronopol as preservatives in milk had no significant effects on milk Hp and M-SAA3 concentration but lowered milk CRP values compared to controls. CONCLUSIONS: The observed effects of heating and preservative use on milk APP should be taken into consideration when assaying samples which have undergone heat treatment as a result of international transfer regulations involving biological samples or samples needing chemical preservation prior to transport to laboratory.

EPR and DFT analysis of biologically relevant chromium(V) complexes with d-glucitol and d-glucose.

1,2-diolato ligands, such as carbohydrates and glycoproteins, tend to stabilize chromium(V), thus forming important intermediates that have been implicated in the genotoxicity of Cr(VI). Since many years, room-temperature continuous-wave electron paramagnetic resonance (EPR) at X-band microwave frequencies has been used as a standard characterization tool to study chromium(V) intermediates formed during the reduction of Cr(VI) in the presence of biomolecules. In this work, the added value is tested of using a combination of pulsed and high-field EPR techniques with density functional theory computations to unravel the nature of Cr(V) complexes with biologically relevant chelators, such as carbohydrates. The study focuses on the oxidochromium(V) complexes formed during reduction of potassium dichromate with glutathione in the presence of the monosaccharide d-glucose or the polyalcohol d-glucitol. It is shown that although the presence of a multitude of Cr(V) intermediates may hamper a complete structural determination, the combined EPR and DFT approach reveals unambiguously the effect of freezing on the location of the counterions, the gradual replacement of water ligands by the diols, and the preference of Cr(V) to bind certain conformers.

Removal of As(V), Cr(III) and Cr(VI) from aqueous environments by poly(acrylonitril-co-acrylamidopropyl-trimethyl ammonium chloride)-based hydrogels.

Cationic poly(Acrylonitril-co-Acrylamidopropyl-trimethyl Ammonium Chloride) (p(AN-co-APTMACl)) hydrogels in bulk were synthesized by using acrylonitrile (AN) and 3-acrylamidopropyl-trimethyl ammonium chloride (APTMACl) as monomers. The prepared hydrogels were exposed to amidoximation reaction to replace hydrophobic nitrile groups with hydrophilic amidoxime groups that have metal ion binding ability. Those replacements were increased the hydrogels absorption capacity for As(V) and Cr(VI). Langmuir and Freundlich isotherms equations were utilized to obtain the best-fitted isotherm model for the absorption of the ions at different metal ion concentrations. The absorption data of As(V) ion were fitted well to Freundlich isotherm while those of Cr(VI) and Cr(III) ions were fitted well to Langmuir isotherm. The maximum absorption of poly(3-acrylamidopropyl-trimethyl ammonium chloride (p(APTMACl)) and amid-p(AN-co-APTMACl) macro gels were 22.39 mg and 21.83 mg for As(V), and 30.65 mg and 18.16 mg for Cr(VI) ion per unit gram dried gel, respectively. Kinetically, the absorption behaviors of Cr(III) and Cr(VI) ions were fitted well to a pseudo 2nd-order kinetic model and those of As(V) ions were fitted well to a pseudo 1st order kinetic model.

Graphene oxide coated coordination polymer nanobelt composite material: a new type of visible light active and highly efficient photocatalyst for Cr(VI) reduction.

A visible light active photocatalyst was synthesized successfully by coating graphene oxide (GO) on a coordination polymer nanobelt (CPNB) using a simple colloidal blending process. Compared with neat CPNB, the resulting graphene oxide coated coordination polymer nanobelt composite material (GO/CPNB) exhibits excellent photocatalytic efficiency in the reduction of K2Cr2O7 under visible light irradiation. In the composite material, GO performs two functions. Firstly, it cuts down the band gap (E(g)) of the photocatalyst and extends its photoresponse region from the ultraviolet to visible light region. Secondly, GO exhibits excellent electron transportation ability that impedes its recombination with holes, and this can enhance photocatalytic efficiency. For GO, on its surface, the number of functional groups has a great influence on the photocatalytic performance of the resulting GO/CPNB composite material and an ideal GO"coater" to obtain a highly efficient GO/CPNB photocatalyst has been obtained. As a photocatalyst that may be used in the treatment of Cr(VI) in wastewater, GO/CPNB exhibited outstanding stability during the reduction of this pollutant.

Preparation of water-dispersible porous g-C3N4 with improved photocatalytic activity by chemical oxidation.

Hydrophilic treatment of bulk graphene-like carbon nitride (g-C3N4) for future applications has aroused extensive interest, due to its enhanced specific surface area and unusual electronic properties. Herein, water-dispersible g-C3N4 with a porous structure can be obtained by chemical oxidation of bulk g-C3N4 with K2Cr2O7-H2SO4. Acid oxidation results in the production of hydroxyl and carboxyl groups on its basal plane and the formation of a porous structure of g-C3N4 at the same time. The porous g-C3N4 appears as networks with tens of micrometers in width and possesses a high specific surface area of 235.2 m(2) g(-1). The final concentration of porous g-C3N4 can be up to 3 mg mL(-1). Compared with bulk g-C3N4, the as-obtained porous g-C3N4 exhibits excellent water dispersion stability and shows great superiority in photoinduced charge carrier separation and transfer. The photocatalytic activities of porous g-C3N4 towards degradation of organic pollutants are much higher than those of the bulk due to the larger band gap (by 0.2 eV) and specific surface areas.

Observation of a physical matrix effect during cold vapour generation measurement of mercury in emissions samples.

The observation of a physical matrix effect during the cold vapour generation-atomic fluorescence measurement of mercury in emissions samples is reported. The effect is as a result of the different efficiencies of liberation of reduced mercury from solution as the matrix of the solution under test varies. The result of this is that peak area to peak height ratios decease as matrix concentration increases, passing through a minimum, before the ratio then increases as matrix concentration further increases. In the test matrices examined - acidified potassium dichromate and sodium chloride solutions - the possible biases caused by differences between the calibration standard matrix and the test sample matrix were as large as 2.8% (relative) representing peak area to peak height ratios for calibration standards and matrix samples of 45 and 43.75, respectively. For the system considered there is a good correlation between the density of the matrix and point of optimum liberation of dissolved mercury for both matrix types. Several methods employing matrix matching and mathematical correction to overcome the bias are presented and their relative merits discussed; the most promising being the use of peak area, rather than peak height, for quantification.

Prenatal exposure to chromium induces early reproductive senescence by increasing germ cell apoptosis and advancing germ cell cyst breakdown in the F1 offspring.

Hexavalent chromium (CrVI), one of the more toxic heavy metals, is widely used in more than 50 industries such as chrome plating, welding, wood processing and tanneries. As one of the world's leading producers of chromium compounds, the U.S. is facing growing challenges in protecting human health against multiple adverse effects of CrVI. CrVI is rapidly converted to CrIII intracellularly, and can induce apoptosis through different mechanisms. Our previous studies demonstrated postnatal exposure to CrVI results in a delay or arrest in follicle development and puberty. Pregnant rats were treated with 25 ppm potassium dichromate (CrVI) from gestational day (GD) 9.5 to 14.5 through drinking water, placentae were removed on GD 20, and total Cr was estimated in the placentae; ovaries were removed from the F1 offspring on postnatal day (PND)-1 and various analyses were performed. Our results show that gestational exposure to CrVI resulted in (i) increased Cr concentration in the placenta, (ii) increased germ cell apoptosis by up-regulating p53/p27-Bax-caspase-3 proteins and by increasing p53-SOD-2 co-localization; (iii) accelerated germ cell cyst (GCC) breakdown; (iv) advanced primordial follicle assembly and primary follicle transition and (v) down regulation of p-AKT, p-ERK and XIAP. As a result of the above events, CrVI induced early reproductive senescence and decrease in litter size in F1 female progeny.

Adsorption of Cr(VI) using synthetic poly(m-phenylenediamine).

Poly(m-phenylenediamine) (PmPD) with different oxidation state was successfully synthesized by the improved chemically oxidative polymerization. The function of oxidation state on Cr(VI) adsorption was systematically examined through adsorption experiments. Results showed that the Cr(VI) adsorptivity of all PmPD increased with decreasing the initial pH. When the oxidation state of PmPD was dropped, the equilibrium time for Cr(VI) adsorption was obviously shortened and its Cr(VI) removal and adsorption selectivity were profoundly obviously increased. Typically, PmPD with the lowest oxidation state in this research possesses the highest Cr(VI) removal of 500 mg g(-1). Moreover, PmPD with lower oxidation state displays a potentially superior prospect in Cr(VI) treatment through preliminary experiments on 5 cycles of adsorption, column adsorption and practical wastewater treatment. The possible adsorption mechanism was discussed mainly according to characterizations (FTIR, XPS) and experiments, which together suggests that the Cr(VI) adsorption most possibly involve redox reaction, chelation and doping adsorption.

Modelling of biological Cr(VI) removal in draw-fill reactors using microorganisms in suspended and attached growth systems.

The kinetics of hexavalent chromium bio-reduction in draw-fill suspended and attached growth reactors was examined using sugar as substrate and indigenous microorganisms from the industrial sludge of the Hellenic Aerospace Industry. Initially, experiments in suspended growth batch reactors for Cr (VI) concentrations of 1.4-110 mg/l were carried out, to extensively study the behaviour of a mixed culture. The maximum Cr(VI) reduction rate of 2 mg/l h was achieved for initial concentration 12.85 mg/l with biomass production rate 4.1 mg biomass/l h. Analysis of the microbial structure in the batch reactor culture indicated that the dominant bacterial communities were constituted by bacterial members of Raoultella sp., Citrobacter sp., Klebsiella sp., Salmonella sp., Achromobacter sp. and Kerstersia sp. while the dominant fungal strain was that of Pichia jadinii. Experiments using the same mixed culture were also carried out in packed-bed reactors with plastic support media. High removal rates were achieved (2.0 mg/l h) even in high initial concentrations (109 mg/l). A combination of the model of Tsao and Hanson for growth enhancement and that of Aiba and Shoda for growth inhibition was used in order to describe and predict the process of Cr(VI) bio-reduction in suspended growth and packed-bed reactors. Kinetic constants of the equation obtained from both batch (or draw-fill) culture experiments. In the draw-fill experiments at the packed-bed reactor, hexavalent chromium inhibitory effects were minimized increasing the inhibitory constant value K(i)' at 148.5 mg/l, compared to suspended growth experiments which was K(i) = 8.219 mg/l. The model adequately predicts hexavalent chromium reduction in both batch reactors for all initial concentrations tested.

Zinc PVA versus potassium dichromate for preservation of microsporidian spores of human origin.

Microsporidia are emerging opportunistic parasites. Preservation of the biological properties of microsporidian spores is often required in research work. The present study compared two preservatives; zinc polyvinyl alcohol (zinc PVA) and potassium dichromate solutions for preservation of microsporidian spores separated from human faecal samples. After 0, 1, 2 and 4 months of storage, morphological features and staining characters of the spores were assessed by light microscopy in modified trichrome-stained smears and their viability percentages were calculated using acridine orange/ethidium bromide mixture. Also, spore infectivity was evaluated by faecal spore shedding and intestinal spore load in mice orally inoculated with the preserved spores. Results revealed that morphological features, staining characters and viability of the spores were maintained in both solutions throughout the study period. Spore infectivity was completely preserved in zinc PVA solution but showed significant reduction in potassium dichromate solution at the fourth month of the preservation duration.

Spectroscopic investigation on the interaction of Cr(VI) with bovine serum albumin.

The interaction of potassium dichromate (Cr(VI)) with bovine serum albumin (BSA) was investigated by fluorescence, synchronous fluorescence, resonance light scattering (RLS), ultraviolet-visible absorption, and circular dichroism (CD) spectroscopies under simulated physiological conditions. The experimental results showed that Cr(VI) could quench the intrinsic fluorescence of BSA following a static quenching process, which indicates the formation of a Cr(VI)-BSA complex. The binding constant (KA) and binding site (n) were measured at different temperatures. The spectroscopic results also revealed that the binding of Cr(VI) to BSA can lead to the loosening of the protein conformation and can change the microenvironment and skeleton of BSA.

Microdiffusion-based UV-LED spectrometric setup for determining low levels of ethanol in fruit juice.

A novel setup is described in which we combined the separation of a volatile substance from a sample with a complex matrix on the basis of a microdiffusion process with a kinetic on-line spectrometric monitoring of the reaction in the receptive medium at 365 nm. The fruit juice was selected as a model for testing the performance of the setup in real-life applications. The ethanol content in fruit juice can be considered as an indicator of the fruit-juice quality and should not exceed the regulatory limiting values. After optimising the microdiffusion process, blackcurrant, orange and two varieties of apple juice were analysed. The sample analysis lasted 15 min at 35°C. The ethanol concentrations were found to be between 0.9 and 4.0 mmol/L, and were comparable to the results obtained using the SIST:ISO 2448:1998 standard method, which is time consuming, labour intensive and requires high sample volumes. The setup can easily be adapted for determining other volatile substances in low concentrations in complicated samples of different types by introducing different chemistry and replacing the light source if the light of a different wavelength is required. The measuring characteristics of the setup were critically assessed, the main sources of uncertainty recognised and the possibilities for further improvements of the setup and the procedure considered.

The "single-section" Golgi method adapted for formalin-fixed human brain and light microscopy.

The Golgi method has been used for over a century to describe the general morphology of neurons in the nervous system of different species. The "single-section" Golgi method of Gabbott and Somogyi (1984) and the modifications made by Izzo et al. (1987) are able to produce consistent results. Here, we describe procedures to show cortical and subcortical neurons of human brains immersed in formalin for months or even years. The tissue was sliced with a vibratome, post-fixed in a combination of paraformaldehyde and picric acid in phosphate buffer, followed by osmium tetroxide and potassium dicromate, "sandwiched" between cover slips, and immersed in silver nitrate. The whole procedure takes between 5 and 11 days to achieve good results. The Golgi method has its characteristic pitfalls but, with this procedure, neurons and glia appear well-impregnated, allowing qualitative and quantitative studies under light microscopy. This contribution adds to the basic techniques for the study of human nervous tissue with the same advantages described for the "single-section" Golgi method in other species; it is easy and fast, requires minimal equipment, and provides consistent results.

Hexavalent chromium adsorption on impregnated palm shell activated carbon with polyethyleneimine.

Removal of Cr(VI) ions from aqueous solution was investigated using modified palm shell activated carbon. Low Molecular Weight Polyethyleneimine (LMW PEI) was used for impregnation purpose. The maximum amount of LMW PEI adsorbed on activated carbon was determined to be approximately 228.2mg/g carbon. The adsorption experiments were carried out in a batch system using potassium dichromate K(2)Cr(2)O(7) as the source of Cr(VI) in the synthetic waste water and modified palm shell activated carbon as the adsorbent. The effects of pH, concentration of Cr(VI) and PEI loaded on activated carbon were studied. The adsorption data were found to fit well with the Freundlich isotherm model. This modified Palm shell activated carbon showed high adsorption capacity for chromium ions.

Proposing a pH stabilised nutrient medium for algal growth bioassays.

Ecotoxicological assessment of chemicals and contaminated sites relies on bioassays using apical endpoints such as detection of growth inhibition using suspension cultures of green algae. For valid effect assessment observable responses should be causally linked to chemical exposure and thus confounding factors should be minimised. In this study we report that concentration response relationships for substances in current standardised protocols for unicellular algal growth assays are prone to variation from ill-defined assay conditions. The currently used growth media are not optimised to provide a stable pH regime for an exposure period of 72h, resulting in undefined speciation for charged or ionising molecules. We therefore propose a modified pH-stabilised growth medium for algal bioassays and demonstrate that this can substantially reduce variation in effect determination for reference compounds.

The structural properties of poly(aniline)--analysis via FTIR spectroscopy.

Aniline was polymerized under different experimental conditions like variation in time, temperature, monomer and concentration of initiators. Relative intensity of the benzenoid and quinonoid forms were estimated and correlated with poly(aniline) (PANI) structure. TGA counseled the thermal stability of poly(aniline). Through FTIR study, the structure of poly(aniline) was recognized. Comparison of polymerized aniline with two different initiators was done.