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In situ trace metal speciation monitoring

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Investigating the binding heterogeneity of trace metal cations with SiO2 nanoparticles using full wave analysis of stripping chronopotentiometry at scanned deposition potential
Publication . Rotureau, Elise; Rocha, Luciana S.; Goveia, Danielle; Alves, Nuno G.; Pinheiro, José Paulo
Silica oxides nano- and microparticles, as well as silica-based materials, are very abundant in nature and industrial processes. Trace metal cation binding with these bulk materials is generally not considered significant in speciation studies in environmental systems. Nonetheless, this might change for nanoparticulate systems as observed in a previous study of Pb(II) with a very small SiO2 particle (7.5 nm diameter). Besides, metal binding by those nanoparticles is surprisingly characterized by a heterogeneity that increases with the decrease of metal-to-particle ratio. Therefore, it is interesting to extend this study to investigate different trace metals and the influence of the nanoparticle size on the cation binding heterogeneity. Consequently, the Cd(II), Pb(II), and Zn(II) binding by two different sized SiO2 nanoparticles (Ludox LS30 and TM40) in aqueous dispersion was studied for a range of pH and ionic strength conditions, using the combination of the electroanalytical techniques Scanned Stripping ChronoPotentiometry and Absence of Gradients and Nernstian Equilibrium Stripping. The coupling of these techniques provides the free metal concentration in the bulk (AGNES) and information of the free and complex concentration at the electrode surface for each Stripping Chronopotentiometry at Scanned deposition Potential (SSCP). A recent mathematical treatment allows the reconstruction of a portion of the metal to ligand binding isotherm with the included heterogeneity information using the full SSCP wave analysis. In this work, we observed that the Zn(II) binding is homogeneous, Cd(II) is slightly heterogeneous, and Pb(II) is moderately heterogeneous, whereas the results obtained with the 7.5 nm diameter nanoparticle are slightly more heterogeneous than those obtained with the one of 17 nm. These findings suggest that the Zn(II) binding is electrostatic in nature, and for both Cd(II) and Pb(II), there should be a significant chemical binding contribution.
Effect of monomer organization on the behavior of PSS-PS micelles
Publication . Alves, Nuno G.; Rocha, Luciana S.; Moreira, José; Costa, Ana M. Rosa da; Pinheiro, J. P.
Six copolymers of styrenesulfonate-styrene (SS-S) of varying molecular weights were prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization and proven to give rise to micelles in aqueous solution. Three are diblock copolymers (PSS-b-PS), while the other three have a random distribution of the two monomers, probably forming a gradient (PSS-co-PS). The latter ones form micelles of smaller sizes and present lower critical micellar concentrations (CMC) than the former. The morphologic and dimensional features of the micelles were obtained by TEM analysis and their CMC were determined by fluorescence spectroscopy.The trace metal ion removal ability of these micelles was tested. Thus the complexation capacity of PSS-b-PS and PSS-co-PS micelles towards Cd and Pb was evaluated using an electro-analytical stripping technique (AGNES). Both micelles performed similarly yielding percentages of metal removal that varied between 85 and 97% and 95-99%, for Cd(II) and Pb(II) respectively. Both copolymers demonstrate a good potential for future application in metal removal from water, namely on Micellar Enhanced Ultrafiltration techniques. (C) 2016 Elsevier B.V. All rights reserved.
Ligand size polydispersity effect on SSCP signal interpretation
Publication . Rocha, Luciana S.; Botero, Wander G.; Alves, Nuno G.; Moreira, José; Costa, Ana M. Rosa da; Pinheiro, J. P.
The present study aims to establish unambiguously the conditions required for the validity of the average diffusion (D) approximation in fully labile systems with significant ligand size polydispersity. The average diffusion coefficient is a key parameter in mass transfer that affects signal interpretation in dynamic electroanalytical techniques. To achieve this goal, the binding of Cd(II) and Pb(II) to binary and ternary mixtures containing chemically homogenous (PSS)n-COOH polymers (ligand excess conditions were required) of different sizes (4, 10 and 30 KDa) was evaluated. It was experimentally evidenced that the average diffusion coefficient (D), can indeed be computed as the weighted average of several metal-polymer complexes of diverse sizes.
Sustainable approach for recycling seafood wastes for the removal of priority hazardous substances (Hg and Cd) from water
Publication . Monteiro, Rui J. R.; Lopes, Cláudia B.; Rocha, Luciana S.; Coelho, João P.; Duarte, Armando C.; Pereira, E.
Mercury and cadmium are considered by the water framework directive priority hazardous substances. In this work, the capacity of crab carapace and clam shell wastes to remove mercury and cadmium from water was evaluated under batch conditions, for realistic contamination scenarios in monometallic and binary solutions. The results evidenced that in monometallic solutions and under studied operational conditions, both biosorbents can achieve Hg2+ removal efficiencies higher than 80% and the kinetic process is well described by two of the most widely used equations, the pseudo-second order and the Elovich model. In terms of biosorption equilibrium, crab carapace and clam shell wastes displayed very distinct behaviours. While clam shells achieve the complete monolayer coverage and the isotherm is well described by the Langmuir model, crab carapace powder display a more unusual behaviour, that is well described by the BET isotherm, and is characterized by an almost convex shape to the concentration axis, with an infinite slope for an Hg2+ concentration in solution around 25 mu g/L. In binary solutions, both wastes are able to uptake simultaneously Hg2+ and Cd2+, however the uptake of Hg2+ was inhibited in some extent, attributed to the high kinetic and equilibrium selectivities of the bio-wastes for cadmium. (C) 2016 Elsevier Ltd. All rights reserved.
Isolation and purification treatments change the metal-binding properties of humic acids: effect of HF/HCl treatment
Publication . Botero, Wander G.; Pineau, Michael; Janot, Noemie; Domingos, Rute F.; Mariano, José; Rocha, Luciana S.; Groenenberg, Jan E.; Benedetti, Marc F.; Pinheiro, Jose P.
Environmental contextStudying the mechanism of binding between metals and natural organic matter is fundamental to understanding the transport and availability of these contaminants in the environment. The influence of sample treatment on the purification of organic matter showed significant differences in the interaction with metals. The results will contribute to improved modelling of metal binding to organic matter in soils, thereby providing a basis for a more realistic risk assessment. AbstractWe studied the changes in metal binding characteristics of extracted humic acids induced by HF/HCl treatment followed by dialysis, i.e. the last step of the International Humic Substances Society (IHSS) extraction protocol. We performed metal binding experiments with both the alkaline-extracted material (AE) and the fully purified (FP) humic acid using the electrochemical stripping technique (AGNES) and modelled the results using the NICA-Donnan model. The results showed an increase of free Zn, Cd and Pb concentrations of similar to 1 order of magnitude for the AE compared with the FP. These differences may be mostly explained by the different carbon content (51.3% FP and 36.5% AE) associated with an AE/FP carboxyl ratio of 0.5. Simulations using the NICA-Donnan model showed that halving the amount of carboxylic groups (Q(max,1)) for the FP reduced this difference to 0.25 log units for Cd and Zn and to 0.15 log unit for Pb. There is a clear need for further research on the differences between purified v. less-disturbed natural organic material, which will contribute to improved modelling of metal binding to organic matter in soils, hence providing a basis for a more realistic risk assessment.

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Funding agency

Fundação para a Ciência e a Tecnologia

Funding programme

3599-PPCDT

Funding Award Number

FCT-ANR/AAG-MAA/0065/2012

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