pollutants from water J. Campos 1 , L. Checa-Fernandez 1,2 , Ch. - - PowerPoint PPT Presentation

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Enhancing magnetic separation of nanoparticles by counter-ion adsorption: towards extraction of micro- pollutants from water

• J. Campos1, L. Checa-Fernandez1,2, Ch. Hurel1, C. Lomenech1,
• A. Bee3, D. Talbot3, P. Kuzhir1

1 Université Côte d’Azur, INPHYNI 2 University of Granada, Dep. Applied Physics 3 Sorbonne Univeristé, PHENIX

Water purification with magnetic nanoparticles

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Advantage of nano before micro  increased specific area Colloidal scale:

charged colloid Pollutant molecule

Molecular scale:

SIROFLOC process

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Magnetic interactions between nanoparticles phase separation

H

N S

How to separate nanoparticles from water desite strong Brownian motion

To get phase separation multicore nanoparticles of d30 nm Ezzaier et al. Nanomaterials (2018) (high cost syntheis with low issue) Nanoclusters of d60 nm Orlandi et al. Phys. Rev. E (2016) (high polydispersity, release of physisorbed surfactant)

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We need to use mono-core magnetic nanoparticles of d=8 nm (cost-effective synthesis, large issue, high specific area) Fe2O3 + + + + counter-ion (micropollutant) Fe2O3 + + + + + repulsion

Basic hypothesis: progressive

counter-ion adsorption decreases colloidal stability In the absence of field: Primary aggregation d In the presence of field:

H

Secondary (field-induced) aggregation  efficient magnetic separation Impossible to separate nanoparticles of d=8 nm by moderate magnetic field gradients If we want to extracte charged micropollutant…

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Objective: how does the surface coverage by counter-ions affect primary/secondary aggregation and magnetic separation

MB Adsorption isotherme

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-Fe2O3 Na -Fe2O3 Na

Citrate ion

water

Methylene blue (MB) pH7

q

No field

_ max

46%

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C C q   

Primary aggregation

• I. Primary aggregation at zero field

micropolluant modèle

x4

• II. Secondary (field-induced) aggregation

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No chains Chains

q

0.5 mm q=32% q=9% q=18% H=2.5 kA/m

q

H=2.5 kA/m j = 0.15%

D0 for q=18% Initial supersaturation

3/7 max 1 exp

t L L                

4/3 2 1 max

a few min

diff

L d D d 



  D    

Aggregate length: Characteristic time:

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• III. Magnetic separation on a micro-pillar

PDMS pillar with iron particles To benefit from field-induced aggregation: Travel time > Aggregation timescale (a few min)

• utlet

inlet PDMS mould glass slide micro-channel micro-pillar magnetic field flow

H=17.5 kA/m

time flow

j=0.16% Q=30 µl/min q=32%

200 µm

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Naked pillars 10 µl/min 30 µl/min

H=18 kA/m

q=9% q=18% q=32% flow

200 µm

/

h m NP

F u d Ma F µ M H   

q

Magnetic separation is strongly enhanced with BM adsorption

Primary aggregation (zero field)

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Summary

Fe2O3 + + + + Fe2O3 + + + + + electrostatic repulsion 

H

Secondary (field-induced) aggregation efficient magnetic separation

flow

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Fe2O3 + + + + + Na Na Na Na Na + BM Why the nanoparticles aggregate at q<50%?

• Debye length ≈ const with q
• Does electrostactic interaction change

with a restructuring of adsorbed layer?

• Does the NP surface partially coated with

MB become less hydrophilic? Constant charge until 50%

• f surface coverage by MB

Fe2O3 + + + + + Progressive desorption of Na+ with MB adsorption

Merci!

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Nanoparticle suspension

• II. Field-induced phase separation

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gas liquid gas liquid

µ µ p p       

Binodal decomposition Dipolar coupling parameter

2

2

p

H V kT   

Volume fraction Hynninen, PRL 2005

H

Lower bound of the phase separation At F=0.1%vol. nanoparticles of d=30 nm aggregate at B>5mT

Adjustable parameters V0 aggregate volume F0 aggregate volume fraction at the end of nucleation stage H0=13,5kA/m 0,177% j 

Two stage kinetics

migration coalescence

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Fabrication de la cellule microfluidique pour la séparation magnétique

Micropillar

( ) 1 exp ut s t sm s L m              F    

[Tien&Ramaro (2007)]

ln

in

• ut

j j  

in

j

• ut

j deposit area micropillar area s 

u

Deposit area S

Dynamics of separation

Sm



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Governing parameter

2

/

h m

F v d Ma F µ H   

Mason number

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Sodium at the NP surface