Assessing the heteroaggregation of manufactured nanoparticles with naturally occurring colloids in a typical surface water

SNO Conference 2013, Santa Barbara

Jérôme Labille1, Antonia Praetorius2, Jean-Yves Bottero1, Martin Scheringer2

1Aix-Marseille Université, CNRS, CEREGE, Aix en Provence, France 2ETH Zurich, Institute for Chemical and Bioengineering, Zurich, Swiss

Email: labille@cerege.fr

ERA-NET SIINN NANOHETER program 2013-2015

Modelling the aggregation mechanism

dn k

d

1

2 ij ij n i n j

i k j 1

k 1

n k ik ik n i n k i 1

According to von Smoluchovski approach,Aggregation consists of two steps: 1. transport to collision

2. sticking reaction

collision frequency

sticking efficiency

k

ij

i + j k k + i bigger

settling

2 key factors:

Experimental determintion of the sticking efficiency

Labille et al., Env. Pollut., 2010

However, the NP concentrationis not relevant!

(10-100 mg/L for easy measurement by DLS)1

10

100

0,001 0,01 0,1 1

Sta

bil

ity

ra

tio

NaCl concentration, M

0

500

1000

1500

2000

2500

3000

0 0,01 0,04 0,1

ave

rag

e s

ize,

nm

NaCl concentration, mol/L

ref TiO2

neutral EPS

EPS/anionic side chains

EPS/anionic backbone

humic acid

tannic acid

0

500

1000

1500

1 10 100

Av

era

ge s

ize

, n

m

Time, min

1M

0.5 M

0.1 M

0.05 M

0.01 M

0.001 M

TiO2 + NaClKinetics of aggregation

CCC

+ NOM

• salt-induced aggregation by coagulation

• electro / steric stabilisation by NOM

DLS

Labille et al. (2012) Encyclopedia of Nano

Effect of the ENP concentration on their kinetics of homo-aggregation

Example for TiO2 NPsrj = 50 nm

f = 3,9Gm = 100 s-1

T = 25°C

NP (10 mg/L) tc≈ 1 h

NP (0.1 mg/L) tc≈ 100 h

At low NPs concentration, collision with natural colloids must be favored.

tc ?

Collision time tc =4

ab jj

1

n j-

1

n j0

æ

èçç

ö

ø÷÷

homo-aggregation

heteroaggregation

Sampling and characterisation of natural surface water

2 sites selected in France:• Rhone river

high mineral, variable NOM• Lake of Ribou

low mineral, TOC = 8 ppm

Heteroaggregation kinetics measurementRhone water + nano-TiO2

Size measurement by laser diffraction: blind regarding ENP (< mg/L)

• Rhone water SPM = 30 mg/L

• + TiO2 20 nmat t = 0 (µg/L)

Pump

Meansize

Measuringcell

Detectors

• ENPs heteroaggregate rapidly with SPM.• This has a major impact on their fate.

vs. time

Praetorius et al. in prep.

SPM ini. size= 25 µm

0

5

10

15

20

25

30

35

40

0 200 400 600 800 1000

volumem

ediansizeDv50(mm)

Time(s)

SiO2+0.5mg/Lnano-TiO2

0

5

10

15

20

25

30

35

40

0 200 400 600 800 1000

volumem

ediansizeDv50(mm)

Time(s)

SiO2+0.8mg/Lnano-TiO2

SiO2+0.5mg/Lnano-TiO2

Fate of ENPs in the water column under natural conditions. Role of the heteroaggregation

with naturally occurring suspended matter

Aggregation kinetics measurementby laser diffraction (blind regarding ENP)

• electrolyte• colloids 0.5 mm

(100 mg/L)

• + TiO2 20 nm (< 1 mg/L) at t = 0

Pump

Meansize

Measuringcell

Detectors

• ENPs heteroaggregate with colloids at concentration > 0.5 mg/L (surf. Ratio = 2.4%)

pH = 5TiO2 (+), (IEPTiO2 = 6.7)SiO2 (-)

NP-C = 1

C-NP-C = ?

Praetorius et al. in prep.

0

20

40

60

80

100

120

0 500 1000 1500 2000

volumem

ediansizeDv50(mm)

Time(s)

0MNaCl

0.01MNaCl

0.05MNaCl

0.1MNaCl

0

20

40

60

80

100

120

0 500 1000 1500 2000

volumem

ediansizeDv50(mm)

Time(s)

10mg/LSRHA

1mg/LSRHA

0.1mg/LSRHA

0mg/LSRHA

SiO2 (100 mg/L) + TiO2 (0.8 mg/L) + NaCl (variable)

Heteroaggration in case of weak interaction between ENPs and colloids

ERA-NET SIINN NANOHETER 2013/2015

• CCCNaCl (SiO2) = 0.5-1 M > CCCNaCl (SiO2 + NP) = 0.05-0.1 M• Salt induces screening of the electrostatic repulsions.• Salt enables heteroaggregation.

Effect of salt

zTiO2 = -40 mV

zTiO2 = -20 mV

SiO2 (100 mg/L) + TiO2 (0.8 mg/L) + NaCl (0.1M)+ SRHA (variable)

• SRHA prevents heteroaggregation despite salt addition.• SRHA induces higher interparticle repulsions.

zTiO2 = -30 mV

Effect of NOM

pH = 8TiO2 (-), (IEPTiO2 = 6.7)SiO2 (-)

Praetorius et al. in prep.

Praetorius et al. ES&T 2012

Rhine River model:(1)

520 boxes (increasing length), 3 environmental media

Cross section

Processes

Modeling the fate of ENPs in surface water at the river scale

emissions: 0.4 kg/day

khet-agg = het-agg x kcoll

ERA-NET SIINN NANOHETER 2013/2015

Conclusion/Perspectives

• Low ENP concentration implies favoured interaction with SPM/NOM, rather thanENP homo-aggregation

• ENP affinity to mineral SPM follows classical interparticle forces (EDL, vdW, sterric)• ENP adsorption to SPM induces heteroggregation if surface coverage

> 2.5%• Laser diffraction is a powerful tool to assess such heteroaggregation with mineral

colloids• Measuring/modeling the overall C-NP-C enables to calculate NP-C on a surface ratio

basis• Experimental and model approaches need complementation from each other for a

wider range of environmental conditions studied• Hollistic and mechanistic parallel approaches enable to validate more realistic fate

scenarios

• Reconduct a similar approach with each type of SPM in Rhone river to getrespective affinities to ENPs

• Develop an optimized approach to asses the affinity of SPM with NOM

Thanks

Merci

CEREGE group working on Nano & Environment:

Research scientists• Dr Bottero Jean-Yves• Dr Masion Armand• Dr Rose Jérôme• Dr Doelsch Emmanuel• Dr Labille Jérôme• Dr Auffan Mélanie• Dr Levard Clément

Engineers• Dr Chaurand Perrine• Dr Borschneck Daniel • Dr Miche Helene• Mr Angeletti Bernard

Postdocs• Dr Slomberg Danielle• Dr Tella Marie

PhD students• Bossa Nathan• Avelan Astrid• Layet Clément• Woohib

Partners and collaborators• ETH Zurich: A. Praetorius, N. Sani-Kast, Dr. M. Scheringer• Univ. Wyoming: C. Harns, Dr. J. Brant• CEA (France): Dr. A. Thill• Duke Univ.: M. Theresien, Prof. M. Wiesner

ERA-NET SIINN NANOHETER program 2013-2015