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

Transcription

1 Assessing the heteroaggregation of manufactured nanoparticles with naturally occurring colloids in a typical surface water Jérôme Labille 1, Antonia Praetorius 2, Jean-Yves Bottero 1, Martin Scheringer 2 1 Aix-Marseille Université, CNRS, CEREGE, Aix en Provence, France 2 ETH Zurich, Institute for Chemical and Bioengineering, Zurich, Swiss labille@cerege.fr ERA-NET SIINN NANOHETER program SNO Conference 2013, Santa Barbara

2 Modelling the aggregation mechanism According to von Smoluchovski approach, Aggregation consists of two steps: 1. transport to collision 2. sticking reaction i j k settling i + j k k + i bigger dn k d 1 2 k 1 ij ij n i n j n k ik ik n i n k i k j 1 i 1 2 key factors: sticking efficiency collision frequency

3 Average size, nm M 0.5 M 0.1 M 0.05 M 0.01 M M DLS Experimental determintion of the sticking efficiency TiO 2 + NaCl + NOM Kinetics of aggregation 3000 ref TiO2 Stability ratio Time, min salt-induced aggregation by coagulation electro / steric stabilisation by NOM CCC average size, nm neutral EPS EPS/anionic side chains EPS/anionic backbone humic acid tannic acid 0 0,01 0,04 0,1 NaCl concentration, mol/l 1 0,001 0,01 0,1 1 Labille NaCl et al., concentration, Env. Pollut., 2010 M However, the NP concentration is not relevant! ( mg/l for easy measurement by DLS) Labille et al. (2012) Encyclopedia of Nano

4 Effect of the ENP concentration on their kinetics of homo-aggregation Collision time t c = 4 æ 1 ab ç - 1 jj è n j n j 0 ö ø homo-aggregation t c? NP (10 mg/l) NP (0.1 mg/l) t c 1 h t c 100 h Example for TiO 2 NPs r j = 50 nm f = 3,9 G m = 100 s -1 T = 25 C heteroaggregation At low NPs concentration, collision with natural colloids must be favored.

5 2 sites selected in France: Rhone river high mineral, variable NOM Lake of Ribou low mineral, TOC = 8 ppm Sampling and characterisation of natural surface water

6 Heteroaggregation kinetics measurement Rhone water + nano-tio2 Size measurement by laser diffraction: blind regarding ENP (< mg/l) Rhone water SPM = 30 mg/l + TiO 2 20 nm at t = 0 (µg/l) Pump Measuring cell Detectors vs. time Mean size SPM ini. size = 25 µm ENPs heteroaggregate rapidly with SPM. This has a major impact on their fate. Praetorius et al. in prep.

7 Fate of ENPs in the water column under natural conditions. Role of the heteroaggregation with naturally occurring suspended matter Aggregation kinetics measurement ENPs heteroaggregate with colloids at concentration > 0.5 mg/l (surf. Ratio = 2.4%) by laser diffraction (blind regarding ENP) volume median size Dv50 (mm) electrolyte colloids 0.5 mm (100 mg/l) + TiO 2 20 nm (< 1 mg/l) at t = 0 Pump Measuring cell Detectors Mean size ph = 5 TiO 2 (+), (IEP TiO2 = 6.7) SiO 2 (-) SiO mg/l nano-tio2 SiO mg/l nano-tio2 SiO mg/l nano-tio2 NP-C = 1 C-NP-C =? Time (s) Praetorius et al. in prep.

8 Heteroaggration in case of weak interaction between ENPs and colloids ph = 8 TiO 2 (-), (IEP TiO2 = 6.7) SiO 2 (-) Effect of salt ERA-NET SIINN NANOHETER 2013/2015 Effect of NOM volume median size Dv50 (mm) SiO 2 (100 mg/l) + TiO 2 (0.8 mg/l) + NaCl (variable) M NaCl z TiO2 = -20 mv M NaCl 0.05 M NaCl M NaCl z TiO2 = -40 mv Time (s) volume median size Dv50 (mm) SiO 2 (100 mg/l) + TiO 2 (0.8 mg/l) + NaCl (0.1M) + SRHA (variable) 10 mg/l SRHA 1 mg/l SRHA 0.1 mg/l SRHA 0 mg/l SRHA z TiO2 = -30 mv Time (s) CCC NaCl (SiO 2 ) = M > CCC NaCl (SiO2 + NP) = M Salt induces screening of the electrostatic repulsions. Salt enables heteroaggregation. SRHA prevents heteroaggregation despite salt addition. SRHA induces higher interparticle repulsions. Praetorius et al. in prep.

9 Rhine River model: (1) 520 boxes (increasing length), 3 environmental media Processes ERA-NET SIINN NANOHETER 2013/2015 Modeling the fate of ENPs in surface water at the river scale k het-agg = het-agg x k coll emissions: 0.4 kg/day Cross section Praetorius et al. ES&T 2012

10 Conclusion/Perspectives Low ENP concentration implies favoured interaction with SPM/NOM, rather than ENP 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 get respective affinities to ENPs Develop an optimized approach to asses the affinity of SPM with NOM

11 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 Thanks Merci