Oxidation-assisted alkaline precipitation : the effect of H2O2 on the size of CuO and FeOOH nanoparticles

H2O2 was demonstrated to narrow the size distribution and decrease the size of CuO and hydrous FeOOH (2-line ferrihydrite) nanoparticles under conditions of high supersaturation. We introduce oxidation-assisted alkaline precipitation (Ox-AP) and compare it to traditional alkaline precipitation (AP). While for AP, a metal salt solution (e.g., CuCl2) is mixed with an alkali (e.g., NaOH), for Ox-AP, the more reduced form of that metal salt solution (e.g., CuCl) is simultaneously mixed with that alkali and an oxidant (e.g., H2O2). The resulting precipitates were characterized with SEM, XRD, DLS and single particle ICP-MS and shown to be nanoparticles (NPs). Ox-AP CuO NPs were up to 3 times smaller than AP NPs. Ox-AP FeOOH NPs were up to 22.5% smaller than AP NPs. We discuss and propose a possible mechanism of Ox-AP through careful consideration of the known reaction chemistry of iron and copper. We propose that an increased monomer formation rate enhances the nucleation rate, which ultimately results in smaller particles with a more narrow distribution. The more distinct effect of Ox-AP on copper, was attributed to the fast formation of the stable CuO monomer, compared to AP, where the Cu(OH)(2) and/or Cu-2(OH)(3)Cl monomers are more likely formed. Although, the exact mechanism of Ox-AP needs experimental confirmation, our results nicely demonstrate the potential of using Ox-AP to produce smaller NPs with a more narrow distribution in comparison to using AP

Boron isotope ratio (delta B-11) measurements in water framework directive monitoring programs: comparison between double focusing sector field ICP and thermal ionization mass spectrometry

International audienceThe aim of our research was to compare delta B-11 measurements performed with thermal ionization mass spectrometry (TIMS) and sector field-inductively coupled plasma-mass spectrometry (SF-ICP-MS) and evaluate the feasibility of implementing stable isotope methods in European water framework directive (WFD) monitoring programs. The comparison was based on delta B-11 measurements of 192 ground-and surface water samples and 15 leachates of nitrate pollution source materials (organic and mineral fertilisers). The precision of delta B-11 measurements attainable with SF-ICP-MS, 2 sigma= +/- 2.6 parts per thousand; (n = 192), is as expected lower than the precision achieved by TIMS, 2 sigma= +/- 0.3 parts per thousand (n=183). However the ease of use, rapidity and availability of SF-ICP-MS on one hand and the observed variability in delta B-11 in ground-and surface water on the other (from -3.4 to +37 parts per thousand), demonstrates that using SF-ICP-MS as an isotopic screening method would promote the use of isotopic methodology for WFD monitoring. Based on the results of the different case studies it is shown that retrieving precise information on the identification of pollution sources from delta B-11 values requires reaching the best analytical precision and accuracy possible. Hence, the superior precision of TIMS advantages tracing of nitrate pollution sources. However for some cases, e. g. trying to decipher contributions between sources with really distinct delta B-11 signatures (e.g. manure and sewage effluent), SF-ICP-MS results lead to the same conclusions and can therefore be used as a first approachable screening method for the determination of delta B-11 in WFD monitoring programs

Development of methods based on ICP-mass spectrometry for the determination, speciation and isotopic analysis of metals and oxy-anions in an environmental context

Since its introduction in 1980, ICP-MS evolved from a lab-built instrument to a family of commercially available analytical techniques, ranging from single-collector quadrupole mass filter units (ICP-QMS) to single-collector and multi-collector sector-field based ICP-MS instruments with high mass resolution capabilities. The versatility of ICP-MS units as (i) environmental regulatory monitoring tool for the determination of major and trace elements, (ii) elemental-specific detector in the context of hyphenation with different separation techniques and (iii) mass spectrometer for the determination of isotope ratios is endorsed in this dissertation. As an introduction, the synchronicity in the emergence of (Flemish) environmental legislation on the one hand and that of ICP-MS in environmental analysis since 1980 on the other hand is discussed. Subsequently, ranges of background concentrations of heavy metals are summarised for all environmental compartments in Flanders based on European Standard ICP-MS methods and on a selection of non-polluted background locations (derived from regulatory monitoring studies). Thereafter, the scientific papers covering the development of methods based on ICP-MS for the determination, speciation and isotopic analysis of metals and oxy-anions in an environmental context are presented (see timeline) with emphasis on the connecting thread of the PhD dissertation, i.e., the relation between the ICP-MS measurement, the environmental issue and the regulatory context

Characterization of gold nanorods conjugated with synthetic glycopolymers using an analytical approach based on spICP-SFMS and EAF4-MALS

A new comprehensive analytical approach based on single-particle inductively coupled plasma-sector field mass spectrometry (spICP-SFMS) and electrical asymmetric-flow field-flow-fractionation combined with multi-angle light scattering detection (EAF4-MALS) has been examined for the characterization of galactosamine-terminated poly(N-hydroxyethyl acrylamide)-coated gold nanorods (GNRs) in two different degrees of polymerization (DP) by tuning the feed ratio (short: DP 35; long: DP 60). spICP-SFMS provided information on the particle number concentration, size and size distribution of the GNRs, and was found to be useful as an orthogonal method for fast characterization of GNRs. Glycoconjugated GNRs were separated and characterized via EAF4-MALS in terms of their size and charge and compared to the bare GNRs. In contrast to spICP-SFMS, EAF4-MALS was also able of providing an estimate of the thickness of the glycopolymer coating on the GNRs surface

A discrete mutualism model: analysis and exploration of a financial application

We perform a stability analysis on a discrete analogue of a known, continuous model of mutualism. We illustrate how the introduction of delays affects the asymptotic stability of the system’s positive nontrivial equilibrium point. In the second part of the paper we explore the insights that the model can provide when it is used in relation to interacting financial markets. We also note the limitations of such an approach

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