Fluoride removal by calcite: evidence for fluorite precipitation and surface adsorption

Fluoride contamination of groundwater, both anthropogenic and natural, is a major problem worldwide. In this study, fluoride removal by crushed limestone (99% pure calcite) was investigated by batch studies and surface-sensitive techniques from solutions with fluoride concentrations from 150 micromol/L (3 mg/L) to 110 mM (approximately 2100 mg/L). Surface-sensitive techniques, including atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) as well as zeta potential measurements, confirm that, in addition to precipitation reactions, adsorption of fluoride also occurs. Results indicate that fluoride adsorption occurs immediately over the entire calcite surface with fluorite precipitating at step edges and kinks, where dissolved Ca2+ concentration is highest. The PHREEQ geochemical model was applied to the observed data and indicates that existing models, especially at low fluoride concentrations and high pH (>7.5) are not equipped to describe this complex system, largely because the PHREEQ model includes only precipitation reactions, whereas a combination of adsorption and precipitation parameters are required.     

P NMR spectroscopic investigations of caseins treated with microbial transglutaminase

Caseins - the main constituents of bovine milk proteins - self-assemble into large supramolecular aggregates, so-called casein micelles. The enhancement of the stability of casein micelles is advantageous with respect to technological milk processing. A promising approach to accomplish this goal is the cross-linking of caseins using microbial transglutaminase (mTG). The present paper describes the combined use of liquid- and solid-state ³¹P NMR spectroscopy as well as dynamic light scattering in order to characterize the influence of an mTG treatment upon the structure of micelles in ultrahigh temperature (UHT)-treated skim milk at a molecular level. Liquid-state ³¹P NMR spectroscopy was applied to characterize milk, milk serum and casein dispersions. A narrow SerP signal in the liquid-state ³¹P NMR spectra of UHT-treated milk is shown to be due to casein molecules in the milk serum whereas the casein molecules bound in the micelles give rise to broad signals. Most of the caseins contribute to a 3 kHz broad background signal which can be visualized in the spectrum of suspensions of re-dispersed micellar material derived from UHT-treated milk. Treatment with mTG results in a cross-linking of caseins, which could be followed by liquid-state ³¹P NMR spectroscopy. Especially, the cross-linking of β-casein was demonstrated by quantitative liquid-state ³¹P NMR experiments. Furthermore, the stability of cross-linked micellar aggregates against EDTA could be investigated by liquid-state ³¹P HR NMR in combination with dynamic light scattering (DLS). Solid-state ³¹P NMR was used to show that the motional state of the κ-caseins located at the outer surface of the micelles derived from UHT-treated milk is not significantly changed by the applied mTG treatment.     

13C NMR spectroscopic determination of diethyleneglycol in wine

A procedure for the structure specific determination of diethylene glycol from wine is described. The analysis can be performed without pretreatment of the samples. The detection limit is 10 mg/l.     

Neptunium(V) coprecipitation with calcite

Coprecipitation experiments of Np(V) and U(VI) with calcite were performed in mixed-flow reactors under steady state conditions at room temperature for up to 400 h at precipitation rates of 1.0 x 10(-8) to 6.8 x 10(-8) mol/(m2 s). The saturation index with respect to calcite varied between 0.04 and 0.95. Initial Np(V) or U(VI) concentrations were 1 micromol/L, 0.01 mol/L NaCl was used as background electrolyte, and pH ranged from 7.8 to 12.8. Partition coefficients for Np(V) were in the range of 0.5-10.3, compared to 0.02 for U(VI). Np L(III) and U L(III) EXAFS were used to characterize the local structural environment of the incorporated actinides. In the case of U(VI), the structural environment is not unambiguously characterized. Our data suggest that Np(V) ions occupy calcium lattice sites. The two axial oxygen atoms of the linear neptunyl moiety substitute two calcite carbonate groups in the first coordination sphere. Thus, four carbonate groups coordinate the neptunyl-ion in a monodentate fashion with four equatorial oxygen atoms (Oeq) at 2.4 A and associated carbon atoms (C) at 3.2 A. The interatomic distances indicate slight structural relaxation of the carbonate groups from their ideal sites. A similar structural model has been reported for U(VI) incorporated into natural calcite.     

Infrared spectroscopic evidence supporting heterogeneous site binding models for humic substances

Infrared spectroscopy was used to corroborate predictions made by newly developed heterogeneous site binding models for humic substances. Experimental conditions to acquire the spectra of soil humic substances (humic and fulvic acid and a polysaccharide fraction) in an aqueous state using horizontal attenuated total reflectance Fourier transform infrared spectroscopy (HATR-FTIR) were established. Elimination of the water spectrum from that of the sample was achieved by spectral subtraction of the water peak at 2020 cm(-1). A KSCN internal standard with an absorption band at 2067 cm(-1) was used to verify the efficacy of the subtraction procedure. Spectral artifacts produced by the water spectrum subtraction and from contaminants within the humic materials have been identified. Three fulvic and one humic acid solution were examined in solutions of varying pH. Results show that the observed proportion of ionized carboxylate in relation to pH is consistent with models that assume electrostatic effects and a continuous distribution of proton association constants (log KH). The spectroscopic data were in accordance with calculations made using the generic humic and fulvic acid NICA-Donnan model parameters.     

Interaction of uranyl with calcite in the presence of EDTA

Adsorption of uranyl at the surface of calcite was investigated by using batch sorption experiments and synchrotron X-ray standing wave (XSW) measurements. Aqueous solutions containing 236U(VI) (4.5 x 10(-7) to 1.0 x 10(-4) M) and EDTA (5.0 x 10(-7) to 1.1 x 10(-4) M) were reacted for 90 s to 60 min with freshly cleaved calcite (104) surfaces and calcite powders. Surface exchange coefficients, sorption kinetics, and influence of powder surface area/solution volume (SA/V) ratio were investigated by alpha-counting of 236U. Powder sorption results at SA/V = 870 cm2/mL fit a Freundlich isotherm [log [U]surface (in monolayers) = log K + n log [U]aq (in moles/L)], where K = 1.9+/-0.5 and n = 0.9+/-0.1, consistent with uptake of U(VI) by a specific surface reaction where the availability of sorption sites is nonlimiting in the U concentration range measured. Measured U(VI) coverages along this isotherm, based on the calcite (104) surface Ca site density, ranged from 0.04% to 5.4% of a monolayer. Steady state surface coverages were obtained within 90 s. Sorption of U(VI) on calcite (104) single-crystal cleavage surfaces using identical solutions yielded higher coverages, because of increased step density induced by dissolution at the relatively low SA/V ratio (approximately 1) of these measurements. The crystallographic location of the sorbed U(VI) was examined with the synchrotron XSW technique. Measurements were performed at the Advanced Photon Source on fresh calcite (104) cleavage surfaces reacted for 90 s with U(VI) solutions. Coherent fractions for sorbed U ranged from 0.14 to 0.62, and the mean value of the U coherent position was 0.84+/-0.02. This position was independent of dissolved U(VI) concentration and corresponds to a distance between the U atom and the calcite (104) plane of 2.55+/-0.06 A. These results are consistent with U(VI) adsorption atthe calcite surface as an inner-sphere uranyl-carbonate surface complex bonded with the outer oxygen atom(s) of a single surface carbonate group. Steric considerations allow this observed U(VI) surface complex to occur both at step sites ((441)_ and (481)_) and on terrace areas adjacent to Ca vacancies.     

Characterization of wines from grape varieties through multivariate statistical analysis of H NMR spectroscopic data

¹H NMR spectroscopic analysis coupled with multivariate statistical data was used to characterize wines vinified from four grape varieties: Muscat Bailey A (Vitis labrusca), Campbell Early (V. labrusca B.), Kyoho (V. labrusca L.) and Meoru (Vitis coignetiae). Pattern recognition methods, such as principal component analysis (PCA) and orthogonal projection to latent structure discriminant analysis (OPLS-DA), showed clear differentiation between wines made from these grape varieties. Metabolites responsible for the differentiation were identified as 2,3-butanediol, glycerol, malate, citrate, tartrate, succinate, lactate, proline, alanine, choline and trigonelline. The PCA score plot of quantitative analysis of targeted profiling data also showed clear separation between the wines. The highest levels of glycerol, 2,3-butanediol, succinate and alcohol were found in Kyoho wines, suggesting higher sugar content in the Kyoho grape berry compared to other grape varieties. Higher contents of citrate and trigonelline in Muscat Bailey A wines, alanine in Campbell Early wines and proline, malate and choline in Meoru wines demonstrated that the metabolites of the wines vary with the grape variety. This study provides insight into the relationship between grape variety and its wine through global and targeted analysis of ¹H NMR spectral data.     

Effect of steric hindrance on carbon dioxide absorption into new amine solutions: thermodynamic and spectroscopic verification through solubility and NMR analysis

Acid gas absorption technology is of great importance in these days for the prevention of global warming and the resulting worldwide climate change. More efficient process design and development for the removal of acid gases has become important, together with the development of new absorbents as one of urgent areas of research in addressing global-warming problems. In the present work, aqueous solutions of 2-amino-2-hydroxymethyl-1,3-propanediol (AHPD), a sterically hindered amine, has been examined as a potential CO2 absorbent and compared with the most commonly used absorbent, monoethanolamine (MEA) solution, through equilibrium solubility measurements and 13C NMR spectroscopic analyses. The solubilities of CO2 in aqueous 10 mass % AHPD solutions were higher than those in aqueous 10 mass % MEA solutions above 4 kPa at 298.15 K, but below 4 kPa, the solubility behavior appeared to be the opposite. The solubility difference between these two solutions increased with the CO2 partial pressures above the crossover pressure. Equilibrated CO2-MEA-H2O and CO2-AHPD-H2O solutions at various CO2 partal pressures ranging from 0.01 to 3000 kPa were analyzed by 13C NMR spectroscopy to provide a more microscopic understanding of the reaction mechanisms in the two solutions. In the CO2-amine-H2O solutions, amine reacted with CO2 to form mainly the protonated amine (AMH+), bicarbonate ion (HCO3-), and carbamate anion (AMCO2-), where the quantitative ratio of bicarbonate ion to carbamate anion strongly influenced the CO2 loading in the amine solutions. A profusion of bicarbonate ions, but a very small amount of carbamate anions, was identified in the CO2-AHPD-H2O solution, whereas a considerable amount of carbamate anions was formed in the CO2-MEA-H2O solution. AHPD contains more hydroxyl groups than nonhindered MEA, and hence, the chemical shifts in its 13C NMR spectra were strongly influenced by the solution pH values. In contrast, MEA appeared to be insensitive to pH. The strong interrelations among CO2 solubility, CO2 partial pressure, bulkiness of the amine structure, and pH identified through the present experimental investigations can provide basic guidelines for finding new potential organic absorbents, including specifically designed amine chemicals.     

Positron annihilation spectroscopic evidence to demonstrate the flux-enhancement mechanism in morphology-controlled thin-film-composite (TFC) membrane

In this study, positron annihilation lifetime spectroscopy (PALS) is applied to explain the flux-enhancement mechanism in thin-film-composite (TFC) membranes prepared by using dimethyl sulfoxide (DMSO) as an additive in the interfacial polymerization. The TFC membranes show a large increase in water flux, up to 5-fold, compared to nonadditive membrane. Atomic force microscopy (AFM) shows that surface roughness and surface area increase when DMSO in the aqueous phase solution phase works to increase miscibility of the aqueous and the organic phase by reducing the solubility difference of two immiscible solutions. X-ray photoelectron spectroscopy (XPS) reveals the variation of the chemical compositions to the extent that there is a considerable increase in the cross-linked amide linkages of the flux-enhanced TFC membranes. The effects of these structural changes on the molecular-size free volume properties are evaluated by PALS studies. The PALS results are the first to experimentally show that the thin films of cross-linked aromatic polyamide RO membranes are composed of two types of pores having radii of about 2.1-2.4 A from tau3, network pore, and 3.5-4.5 A from tau4, aggregate pore. The increase in the size and number of network pores by means of DMSO addition during interfacial polymerization enhances the water flux notably. The size of aggregate pores also increases and may contribute to enhance water flux, although their number inevitably decreases as the number of network pores becomes increased. Details on the correlations between RO performances and o-Ps lifetime parameters are clearly described based on the pore-flow model of reverse osmosis developed by Sourirajan et al.     

Research Watch: Organic contaminants

Sediments.     

Research Watch: Organic chemicals

Analysis.     

穿着简单与理性：天然染料与有机衣服

无人愿意吃下一碗充满杀虫剂的食物,那么为什么要穿充满化学药物的衣服呢？数个世纪前,人们与自然和谐相处,获得了丰厚的回报。如今,人类贪婪地追求金钱、奢华与享受,他们正在超越自然难以承受的底线。     

Inhibition of calcite precipitation by natural organic material: kinetics, mechanism, and thermodynamics

The inhibition of calcite precipitation by natural organic material (NOM) in solutions seeded with calcite was investigated using a pH-stat system. Experiments were carried out using three NOMs with different physical/chemical properties. For each of the materials, inhibition was found to be more effective at lower carbonate/calcium ratios and lower pH values. The reduction in the precipitation rate could be explained by a Langmuir adsorption model using a conditional equilibrium constant. By identification of the type of site on the NOM molecules that is involved in the adsorption reaction, the "conditional" equilibrium constants obtained at different solution compositions converged to a single "nonconditional" value. The thermodynamic data determined at 25 degrees C and 1 atm suggest that the interaction between NOM molecules and the calcite surface is chemisorptive in nature and that adsorption is an endothermic reaction driven by the entropy change. The greatest degree of inhibition was observed for the NOM with the highest molecular weight and aromatic carbon content. For a given type of NOM, the degree of inhibition of calcite precipitation was dictated bythe balance between the enthalpy change and the entropy change of the adsorption reaction.     

Research Watch: Organic pollutants

Modeling.     

有机化合物交联改性明胶的研究进展

综述了有机化合物对明胶的化学交联改性方法,包括醛类、烷烯类、糖类、植物单宁等对明胶的交联改性。     

有机化合物交联改性明胶的研究进展(续)

综述了有机化合物对明胶的化学交联改性方法,包括醛类、烷烯类、糖类、植物单宁等对明胶的交联改性。     

Reactions of the flavonoid hesperetin with chlorine: a spectroscopic study of the reaction pathways

The flavonoid hesperetin (Hsp) contains aromatic rings substituted with hydroxyl and methoxyl groups, which activate it toward electrophilic attack and hence make it a potential surrogate for natural organic matter with respect to reactions with chlorine. This paper describes the chlorination pathway of Hsp, based on a combination of electrospray tandem mass spectrometry (MS/MS) and absorbance spectroscopy. When a solution containing Hsp is dosed with NaOCl at pH 7, chlorine substitution into Hsp occurs exclusively into the meta-dihydroxy substituted ring. The first two Cl atoms to enter the ring do so at the highly activated carbons that are each ortho to two oxygenated carbon atoms. These substitutions make the molecule more acidic, but do not change its primary structure or aromaticity. The third Cl atom that substitutes into the molecule does so at one of the previously chlorinated sites, destroying the aromaticity of the ring and altering the molecular properties more dramatically than do the first two. The absorbance spectra of Hsp and mono- and di-chlorinated Hsp are all very similar and are very distinct from that of trichlorinated Hsp. In particular, the latter is the only one of those species that absorbs visible light (in a characteristic band centered at approximately 422nm). Di- and trichloroHsp form even at low molar Cl/Hsp ratios, and can coexist with Hsp and monochloroHsp in neutral, aqueous solutions for at least 24 h in the absence of free chlorine. If free chlorine is present, the less-chlorinated species continue to acquire Cl, and trichloroHsp undergoes further reaction, until either the free chlorine or the trichloroHsp is fully depleted. The appearance of di- and trichloroHsp while substantial amounts of Hsp remain unreacted indicates that substitution of one or two Cl atoms into the ring facilitates the incorporation of yet more Cl into the ring. This autoacceleration of the chlorination process is hypothesized to be induced by the increase in acidity that accompanies Cl incorporation. Specifically, the increase in the acidity of the phenolic groups shifts the equilibrium toward the enolate anion, which is considered to be much more amenable to electrophilic attack than the enol.     

In situ spectroscopic evidence for neptunium(V)-carbonate inner-sphere and outer-sphere ternary surface complexes on hematite surfaces

Np(V) surface speciation on hematite surfaces at pH 7-9 under pC2 = 10(-3.45) atm was investigated using X-ray absorption spectroscopy (XAS). In situ XAS analyses suggest that bis-carbonato inner-sphere and tris-carbonato outer-sphere ternary surface species coexist at the hematite-water interface at pH 7-8.8, and the fraction of outer-sphere species gradually increases from 27 to 54% with increasing pH from 7 to 8.8. The results suggest that the heretofore unknown Np(V)-carbonato ternary surface species may be important in predicting the fate and transport of Np(V) in the subsurface environment down gradient of high-level nuclear waste respositories.     

Fingering carcinogens with genetic evidence

Predictable mutation patterns in DNA give researchers another tool to identify potential environmental carcinogens.