Ifsttar PhD subject

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Title : Impact of physicochemical heterogeneities on the transport and retention of nanoparticles in soils

Main host Laboratory - Referent Advisor GERS - EE  -  PEYNEAU Pierre-Emmanuel      tél. : +33 240845736

Director of the main host Laboratory PEYNEAU Pierre-Emmanuel  -

PhD Speciality Hydrodynamique physico-chimique, transport réactif en milieu poreux

Axis of the performance contract 3 - COP2017 - Planning and protecting regions

Main location Nantes

Doctoral affiliation Université Bretagne Loire

PhD school EGAAL - Ecologie, Géosciences, Agronomie et Alimentation

Planned PhD supervisor BECHET Béatrice  -  Université Gustave Eiffel  -  GERS - EE

Planned financing Contrat doctoral  - Ifsttar

Abstract

Context
Understanding the different factors influencing the retention and release of colloids (microbes, clays, nanoparticles, etc.) in porous media (soils, membranes, filters) is very important in many contexts, both industrial and environmental (contaminant transport facilitated by the presence of colloids [1], pollution control or trace pollutant detection techniques based on the injection of nanoparticles [2], etc.). This is an extremely rich and complex subject given the diversity of processes in which these particles can be involved [3,4]: hydrodynamic forces, osmotic forces, Brownian motion due to thermal agitation, electrostatic interactions with solid surfaces, chemical reactivity...

The theoretical approaches used to predict colloidal retention in porous media give results that in some cases differ markedly from what is observed experimentally [5]. This poor match between theory and experience is often attributed to the physical (small-scale grain roughness) and/or chemical (inhomogeneity of the electrical charge carried by solid surfaces) heterogeneity of the porous medium considered [6,7]. However, the quantitative consequences of this hypothesis on the transport and retention of colloids in porous media have never been studied in detail, even though these properties are of considerable practical importance.

Goal
In this work, we plan to study the impact of physicochemical heterogeneities (irregularity of the surfaces of the solid matrix, inhomogeneity of the surface charge) on the transport of colloids in porous media differing by their geometry and the physicochemical heterogeneities they display.

We will focus on the influence of colloid size (from a few nanometers to a few hundred nanometers), shape (spheres, rods, cubes...) and surface chemistry. We will also vary the flow rate (which influences hydrodynamic interactions), pH and ionic strength (quantities likely to modify electrostatic interactions) of the injected colloidal suspension. Finally, we will look at the influence of the possible presence of a clay fraction (clays are indeed colloids naturally present in soils, likely to affect the transport of other colloidal substances [8]).

Methods
This work will be based on a dual approach, experimental and numerical. The experimental part will be based on the determination of the physicochemical properties of the porous media and suspensions used as well as on measurements of colloid breakthrough curves in a cylindrical tube (smooth or rough [9]), then in homogeneous columns filled with different porous media having several levels of local heterogeneities: smooth or rough glass beads, Ottawa sand (moderately angular), Hostun sand (very angular and with cracks). The colloids used will be gold nanoparticles: there is indeed a wide variety of colloidal gold suspensions and these nanoparticles can be detected by many methods. Different analytical techniques will potentially be used: detection of individual nanoparticles by mass spectrometry, dynamic light scattering, zetametry, UV-visible spectroscopy, fluorimetry.

In the computer simulation part of this work, the impact of physical and/or chemical heterogeneities at the pore size scale will be considered. Particular attention will be paid to the modelling of the influence of physicochemical heterogeneities on electrostatic interactions and on hydrodynamics, which are two of the main processes governing the transport of colloids.

Keywords : Soils, pollutants, nanoparticles, transport, retention, breakthrough curves, mass spectrometry, dynamic light scattering, computer simulation.

Main host Laboratory - Referent Advisor	GERS - EE - PEYNEAU Pierre-Emmanuel tél. : +33 240845736
Director of the main host Laboratory	PEYNEAU Pierre-Emmanuel -
PhD Speciality	Hydrodynamique physico-chimique, transport réactif en milieu poreux
Axis of the performance contract	3 - COP2017 - Planning and protecting regions
Main location	Nantes
Doctoral affiliation	Université Bretagne Loire
PhD school	EGAAL - Ecologie, Géosciences, Agronomie et Alimentation
Planned PhD supervisor	BECHET Béatrice - Université Gustave Eiffel - GERS - EE
Planned financing	Contrat doctoral - Ifsttar
Abstract Context Understanding the different factors influencing the retention and release of colloids (microbes, clays, nanoparticles, etc.) in porous media (soils, membranes, filters) is very important in many contexts, both industrial and environmental (contaminant transport facilitated by the presence of colloids [1], pollution control or trace pollutant detection techniques based on the injection of nanoparticles [2], etc.). This is an extremely rich and complex subject given the diversity of processes in which these particles can be involved [3,4]: hydrodynamic forces, osmotic forces, Brownian motion due to thermal agitation, electrostatic interactions with solid surfaces, chemical reactivity... The theoretical approaches used to predict colloidal retention in porous media give results that in some cases differ markedly from what is observed experimentally [5]. This poor match between theory and experience is often attributed to the physical (small-scale grain roughness) and/or chemical (inhomogeneity of the electrical charge carried by solid surfaces) heterogeneity of the porous medium considered [6,7]. However, the quantitative consequences of this hypothesis on the transport and retention of colloids in porous media have never been studied in detail, even though these properties are of considerable practical importance. Goal In this work, we plan to study the impact of physicochemical heterogeneities (irregularity of the surfaces of the solid matrix, inhomogeneity of the surface charge) on the transport of colloids in porous media differing by their geometry and the physicochemical heterogeneities they display. We will focus on the influence of colloid size (from a few nanometers to a few hundred nanometers), shape (spheres, rods, cubes...) and surface chemistry. We will also vary the flow rate (which influences hydrodynamic interactions), pH and ionic strength (quantities likely to modify electrostatic interactions) of the injected colloidal suspension. Finally, we will look at the influence of the possible presence of a clay fraction (clays are indeed colloids naturally present in soils, likely to affect the transport of other colloidal substances [8]). Methods This work will be based on a dual approach, experimental and numerical. The experimental part will be based on the determination of the physicochemical properties of the porous media and suspensions used as well as on measurements of colloid breakthrough curves in a cylindrical tube (smooth or rough [9]), then in homogeneous columns filled with different porous media having several levels of local heterogeneities: smooth or rough glass beads, Ottawa sand (moderately angular), Hostun sand (very angular and with cracks). The colloids used will be gold nanoparticles: there is indeed a wide variety of colloidal gold suspensions and these nanoparticles can be detected by many methods. Different analytical techniques will potentially be used: detection of individual nanoparticles by mass spectrometry, dynamic light scattering, zetametry, UV-visible spectroscopy, fluorimetry. In the computer simulation part of this work, the impact of physical and/or chemical heterogeneities at the pore size scale will be considered. Particular attention will be paid to the modelling of the influence of physicochemical heterogeneities on electrostatic interactions and on hydrodynamics, which are two of the main processes governing the transport of colloids.
Keywords :	Soils, pollutants, nanoparticles, transport, retention, breakthrough curves, mass spectrometry, dynamic light scattering, computer simulation.

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