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ABSTRACT: HKUST-1 is one of the popular metal–organic frameworks (MOFs). The formation of this MOF is significantly accelerated by adding Keggin polyoxometalate anions to the synthesis solution. In this paper the chemistry behind this observation was investigated. Upon addition of Keggin type H3PW12O40 heteropolyacid the speciation of Cu2+ cations in ethanol:H2O mixture drastically changes. Combining EPR and XANES measurements with accurate pH measurements and prediction of Cu2+ hydrolysis provides strong evidence for surface induced hydrolysis and consequent dimerisation of monomeric Cu2+ species on Keggin ions in acidic conditions. This enables paddle wheel formation, hence explaining the instantaneous precipitation of Cu3(BTC)2 at room temperature and the systematic encapsulation of Keggin ions in its pores.
Journal of Materials Chemistry 01/2011; 21:9768-9771. · 5.97 Impact Factor
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ABSTRACT: The geochemical fate of selenium is of key importance for today's society due to its role as a highly toxic essential micronutrient and as a significant component of high level radioactive waste (HLRW) originating from the operation of nuclear reactors. Understanding and prediction of the long-term behavior of Se in natural environments requires identification of the in situ speciation of selenium. This article describes an XAS-based investigation into the solid phase speciation of Se upon interaction of Se(IV) with Boom Clay, a reducing, complex sediment selected as model host rock for clay-based deep geological disposal of HLRW in Belgium and Europe. Using a combination of long-term batch sorption experiments, linear combination XANES analysis and ITFA-based EXAFS analysis allowed for the first time to identify Se0 as the dominant solid phase speciation of Se in Boom Clay systems equilibrated with Se(IV).
Environmental Science & Technology 09/2010; 44(17):6649-55. · 4.80 Impact Factor
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ABSTRACT: A structure elucidation strategy combining X-ray Absorption Spectroscopy (XAS) and Density Functional Theory (DFT) is demonstrated and reveals the existence of the [Tc=O](2+) moiety.
Dalton Transactions 11/2009; · 3.84 Impact Factor
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ABSTRACT: The adsorption of humic and fulvic acids onto nitrate, chloride and carbonate intercalated layered double hydroxides with Mg/Al ratios ranging from 85/15 to 60/40 was studied by adsorption isotherms at different ionic strengths and the characterization of the preferentially adsorbed humic substance size fractions. The adsorption of humic and fulvic acids onto LDHs occurred by ion exchange with both the intercalated and surface anions of the LDH and ligand exchange reactions with surface groups. The contribution of both mechanisms to the total HA and FA adsorption was estimated. Lower molecular weight humic and fulvic acids were preferentially adsorbed because these fractions can more easily enter the mesoporous LDHs and contain more carboxylic groups, which are known to be involved in ligand exchange reactions with e.g. surface Al-OH groups. Intercalation of the entire HA or FA molecules in-between the LDH sheets is unlikely to occur.
Applied Clay Science 02/2008; 38(3-4):237-249. · 2.47 Impact Factor
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ABSTRACT: In this contribution, the formation and immobilisation of chromium(iii) hydroxyoxide colloids is investigated. Nano-sized Cr(iii) colloids are generated in situ upon reduction of Cr(vi), dosed to a stirred reactor. The growth of the elementary colloids by the consumption of solved Cr is kinetically unfavorable compared to their aggregation to larger secondary particles, the size of which depends on the concentration of the building block colloids. This aggregation process can be steered by simple process parameters such as dosing rate and concentration of the Cr(vi). The Cr(iii) colloids are immobilised in situ on a support material via precipitation chromatography. Upon drying, the initially amorphose hydroxyoxides are gradually transformed into crystalline Cr(2)O(3) nanoparticles, mainly located at the external surface of the support. This approach opens new opportunities for the synthesis of supported metal oxide catalysts.
Physical Chemistry Chemical Physics 11/2007; 9(39):5382-6. · 3.57 Impact Factor
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Angewandte Chemie International Edition 12/2006; 45(45):7584-8. · 13.45 Impact Factor
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ABSTRACT: The solid phase partitioning of metals (Zn, Cu and Pb) was determined in four anoxic, metal polluted sediments by investigating at pH 8 the 1 day oxidation kinetics of the metal sulphide phases present in the sediments in a background solution containing excess EDTA. A mathematical model consisting of a combination of two pseudo-first order reactions was used to fit the metal release data as a function of oxidation time. The model permitted to fractionate the trace metals in a 'quickly-oxidizable' and a 'slowly-oxidizable' fraction, which could be assigned to two different trace metal pools, respectively (1) FeS minerals (e.g. amorphous FeS, mackinawite) and (2) discrete trace metal sulphide phases. The sum of the fractions associated with these sulphide pools was taken as an approximation for the sulphide-associated fraction of the trace metals and coincided (for the case of Zn and Pb) with the sulphide-associated fraction derived from the analysis of acid volatile sulphide (AVS) and simultaneously extracted metals (SEM). Oxidation kinetics modelling allowed also determining the sulphide-associated fraction of a broad range of trace metals (as demonstrated for Cu) more accurately than the AVS/SEM method, which suffers from non-efficient extraction of a number of trace metal sulphides. A correction was made for the determination of the sulphide-associated fraction by subtracting the trace metal fraction dissolved after 1 day under anoxic conditions in the background EDTA solution. The combination of (1) one day oxidation kinetics modelling and (2) correction for the 1 day anoxic EDTA-soluble fraction is a suitable method to determine accurately the true sulphide speciation of trace metals in anoxic sediments.
Science of The Total Environment 09/2006; 367(1):405-17. · 3.29 Impact Factor
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ABSTRACT: Two freeze-dried poly(hydroxo aluminum) intercalated Wyoming bentonites were prepared starting from two different aluminum pillaring solutions. Their charge versus pH properties were studied by zeta potential measurements, potentiometric titrations and calcium sorption measurements in order to determine the speciation of the intercalated Al-species as a function of pH. The structural changes of the intercalated bentonite induced by the pH increase were studied by XRD analysis and N2 adsorption/desorption measurements. At pH 5 the permanent charge (0.75 meq/g) of the original Wyoming bentonite is completely neutralized by positively charged Al-hydroxo species. With increasing pH the Al-species deprotonate and aggregate until their complete neutralization at pH 9.4. Above this pH the Al-polymers start to dissolve from the clay as Al(OH)4−.
Applied Clay Science 08/2006; 33(3-4):260-286. · 2.47 Impact Factor
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ABSTRACT: The purpose of this study was to investigate the potential use of both Al-hydroxy intercalated clays and ‘pillared clays’ (calcinated Al-hydroxy intercalated clays) for the removal of fulvic acids (FA) from water. Different preparation procedures of the Al-hydroxy intercalated clays were tested and the products were characterised (XRD and N2 sorption) and tested for their FA sorption capacity. It was observed that the drying method (oven or freeze-drying) and the calcination step were the most important parameters influencing the FA sorption capacity of the Al-hydroxy intercalated clays. The noncalcined freeze-dried Al-hydroxy intercalated clays showed the largest sorption capacity for FA. Comparison with freeze-dried Wyoming bentonite and granular activated carbon showed that this freeze-dried Al-hydroxy intercalated clays are potential good sorbents for the removal of fulvic acids from water.
Applied Clay Science 05/2006; 32(3-4):283-290. · 2.47 Impact Factor
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Journal of Soils and Sediments 04/2005; · 1.86 Impact Factor
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ABSTRACT: A sorbent (Organosorb) is used in the wastewater purification from organic contaminants, here simulated by tetradecane. A short hydrodynamic treatment in a rather intense hydrodynamic field (G>10(3)) (called ultraflocculation) is applied to the sorbent suspension to which a flocculant is added. The efficiency of removal of the sorbent is studied. The sorbent concentration, the flocculant concentration, the treatment time, the organic pollutant (which has to be sorbed by the sorbent), the detergent (used for the emulsification of the pollutant), the pH and the calcium concentration of the water all influence the flocculation efficiency (E) of the sorbent particles. For each set of these parameters there exists an optimum intensity of the hydrodynamic treatment at which maximum flocculation efficiency is reached. An increase in the optimum intensity of the hydrodynamic field corresponds to an increased floc break-up, and consequently a lower maximum flocculation efficiency.
Water Research 05/2003; 37(9):2090-6. · 4.86 Impact Factor
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ABSTRACT: The possibility of removing cadmium, copper, lead and zinc from Belgian loamy soil by a combination of sulfidisation pre-treatment and Denver flotation was investigated. The potentially available--sulfide convertible--metal content of the metal polluted soil was estimated by EDTA (0.1 M, pH 4.65) extraction and BCR sequential extraction. EDTA extraction is better at approximating the metal percentage that is expected to be convertible into a metal sulfide phase, in contrast to the sequential extraction procedure of 'Int. J. Environ. Anal. Chem. 51 (1993) pp. 135-151' in which transition metals present as iron oxide co-precipitates are dissolved by hydroxylammoniumchloride in the second extraction step. To compare the surface characteristics of metal sulfides formed by sulfidisation with those of crystalline metal sulfides, two types of synthetic sediments were prepared and extracted with 0.1 M EDTA (pH 4.65) in anoxic conditions. Separate metal sulfides or co-precipitates with iron sulfide were formed by sulfide conditioning. The Denver flotation of both types of synthetic sediments (kerosene as collector at high background electrolyte concentrations) resulted in similar concentrating factors for freshly formed metal sulfides as for fine-grained crystalline metal sulfides. The selective flotation of metal sulfides after sulfide conditioning of a polluted soil, using kerosene or potassium ethyl xanthate as collectors and MIBC as frother, was studied at high background electrolyte concentrations. The sulfidisations were made in ambient air and inside an anoxic glove box. The concentrating factors corrected by the potentially available metal percentage, determined by 0.1 M EDTA extraction, lie between 2 and 3. The selective flotation of these finely dispersed, amorphous, metal sulfides can possibly be improved by optimising the bubble-particle interaction.
Science of The Total Environment 06/2002; 290(1-3):69-80. · 3.29 Impact Factor
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ABSTRACT: 79Se is considered as a key mobile fission product for nuclear waste disposal in the Boom Clay, the reference host formation presently studied in Belgium. Therefore, a good understanding of selenium migration behaviour through the clay barrier is essential to underpin its transport parameters selected for the performance assessment of a deep repository for spent fuel and high-level waste. Under the reducing conditions prevailing in Boom Clay, selenide, [Se(-II)], is the predominant thermodynamically stable chemical form of selenium. However, selenium may suffer of severe redox disequilibrium and selenate is very reluctant to reduction while a kinetically controlled sorption-reduction-precipitation behaviour is observed for selenite. Due to the large uncertainty on the speciation of selenium in the waste form, and taking the stability of selenate versus reduction into account, it is necessary to consider the non-solubility limited SeO42– as a possible migrating species. However, when a lower oxidation state [Se(IV), Se(0), and Se( II)] is present in the waste form, a solubility limit may also contribute to delay and attenuate the 79Se release. Therefore, two sets of transport parameters are proposed to PA: a first set for selenate (without solubility limit) and a second set for selenide (with solubility limit).
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ABSTRACT: Two poly(hydroxo aluminum) intercalated Wyoming bentonites were prepared starting from two different aluminum pillaring solutions. The sorption mechanism of Laurentian fulvic acid (FA) onto these poly(hydroxo aluminum) intercalated bentonites was investigated at different pH values and at different ionic strengths (NaCl or CaCl2). Three mechanisms contribute to the FA adsorption, depending on the pH and the nature (NaCl or CaCl2) and ionic strength of the background electrolyte. In the presence of NaCl the FA sorption onto poly(hydroxo aluminum) intercalated bentonites can be mainly ascribed to ligand exchange between the amphoteric poly(hydroxo aluminum) hydroxyl groups and the deprotonated carboxylic groups of the FA. The FA adsorption due to ligand exchange reactions decreases with increasing pH. In presence of Ca2+ ions the FA adsorption is enhanced, compared to the presence of Na+, due to Ca2+ bridging between negatively charged groups on the FA molecules and the poly(hydroxo aluminum) intercalated bentonite. The FA adsorption due to Ca2+ bridging increases with increasing pH. A third mechanism is enhanced FA adsorption ascribed to FA-Ca-FA bridging and was detected from the FA adsorption in presence of Ca2+ at the zero point of charge of the poly(hydroxo aluminum) bentonite (pH 5).
Applied Clay Science.
