Extracellular polymeric substances stabilize carbon nanotubes in aqueous phase

Transcription

1 Extracellular polymeric substances stabilize carbon nanotubes in aqueous phase Adeyemi Adeleye, Arturo Keller University of California, Santa Barbara 2 nd Sustainable Nanotechnology Organization Conference November 3-5, 2013 Santa Barbara, California

2 Applications of carbon nanotubes (CNTs)

3 Life cycle analysis of CNTs ~3200 tons/yr About 10% of manufactured CNTs may end up in water bodies annually Emission may increase with applications and use Keller et al.(2013). J Nano Res 15,1692

4 Important factors in aquatic systems Prokaryotes Eukaryotes Biological CNT Geological Suspended sediment Temperature Chemical ph Electrolytes Fate of CNTs in natural waters

5 Fate of Engineered Nanomaterials (ENMs) in Aquatic Systems Adeleye and Keller (2013). Water Res, In review

6 Natural Organic Materials (NOM) could be Humic acid Fulvic acid Alginate Natural organic matter mix (e.g. Suwannee River NOM). But also, Extracellular polymeric substances (EPS) 6 Planchon et al. (2013) J Coll Interf 405, 35 Synechocystis PCC6803 wild type Synechocystis PCC6803 mutant

7 Extracellular polymeric substances (EPS) o o o o o Are polymers produced by microorganisms (prokaryotic and eukaryotic) Are composed of polysaccharides, proteins, glycoproteins, glycolipids, nucleic acids, humic substances, uronic acid, etc Are produced when growing under normal conditions or under stress (e.g. toxin) Are either bonded to the microorganism (bound or attached EPS) or freely suspended in media (soluble or unattached EPS) May interact with engineered nanomaterials (ENMs) in aquatic systems via several mechanism Flemming et al. (2007), J Bacteriol 189, 7945 Fang et al. (2012), Water Res 46, 5613

8 Research Questions 1. Do EPS interact with CNTs in aqueous systems 2. How do EPS affect surface properties of CNTs 3. How do EPS influence CNT stability

9 Materials and Methods o SWCNT (Carbon Solutions, CA). TEM, SEM, DLS etc o Unattached EPS were extracted from Isochrysis galbana, a marine phytoplankton: Centrifugation -> 0.2 μm filtration -> Dialysis (3kD) for 96 hr -> 4 o C EPS characterization: Hydrodynamic size, carbohydrate and protein o 100 mg L -1 SWCNT stock was stabilized using either EPS (5 mg-c L -1 ) or SRNOM (3 mg L -1 ). Stable supernatant was removed for analyses o Critical coagulation concentration (CCC) in NaCl via DLS (Eqs. 1 and 2) o Dynamic aggregation via UV-Vis spectrophotometry Saleh et al (2008), ES&T 44, 2412 Zhou et al (2012) ES&T 46, 7520 k 1 N 0 da h dt t t0 Eq. 1 dah ( t) dt dah ( t) dt t0 t0, fav Eq. 2

10 Physicochemical properties of SWCNT Property Value Unit Tube diameter 1.4 nm Bundle diameter 13±3.5 nm Length μm Carbon content % Nickel content 8.83 % Yttrium content 1.08 % Zeta (ζ) potential a -44.1±3.63 mv a Measured after 15 min probe sonication to disperse nanotubes in water Bennett et al. (2013) Water Res 47, 4074 Adeleye and Keller (2013) Water Res, In review

11 A B C (A) SEM, (B) TEM, and (C) EDS of SWCNT Adeleye and Keller (2013). Water Res, In review

12 Physicochemical properties of EPS Hydrodynamic diameter = ±12.50 nm [Carbohydrate] = mg L -1 glucose equivalent [Protein] = 3.63 mg L -1 using a Bovine serum albumin (BSA) standard

13 DI EPS NOM Hydrodynamic diameter (nm) Particle size 10 0 CNT-DI CNT-EPS CNT-NOM 300 Particle concentration 1.0 Particle polydispersity Mean count rate (kcps) Polydispersity index CNT-DI CNT-EPS CNT-NOM 0.0 CNT-DI CNT-EPS CNT-NOM

14 Effect of EPS on ζ potential of SWCNT C 0-10 NaCl concentration 0 mm 0.1 mm 1 mm 10 mm 100 mm Surface charge may originate from surface oxidation, accumulation of OH -, defect and mechanochemistry, or surface electron density distribution Zeta () potential (mv) NOM EPS Neither ζ potential of SWCNT was less negative at higher ionic strength ζ potential was more negative in the presence of EPS as with SRNOM No statistical difference (p < 0.05) between ζ potential in EPS and SRNOM Adeleye and Keller (2013). Water Res, In review Saleh et al. (2010). ES&T 44: 2412

15 Adeleye and Keller (2013). Water Res, In review 1 1 Attachment efficiency, CCC ~ 15 mm A NOM Attachment efficiency, a CCC ~ 60 mm B NOM+EPS 1E [NaCl] (mm) [NaCl] (mm) 1 Attachment efficiency, CCC ~ 100 mm C EPS DI EPS NOM [NaCl] (mm) Aggregation kinetics of SWCNT stabilized with (A) 0.3 mg L -1 SRNOM, (B) 0.3 mg L -1 SRNOM mg-c L -1 EPS, and (C) 0.5 mg-c L -1 EPS 15

16 1.0 With 0.3 mg L -1 SRNOM 1.0 With 0.5 mg-c L -1 EPS Normalized conentration (C/C 0 ) min 60 min 120 min 240 min 354 min 0.1 mm 1 mm 10 mm 100 mm 1000 mm Normalized conentration (C/C 0 ) min 60 min 120 min 240 min 354 min 0.1 mm 1 mm 10 mm 100 mm 1000 mm NaCl Concentration (mm) NaCl Concentration (mm) Sedimentation: SRNOM > EPS Carbon content: SRNOM < EPS Reduced sedimentation at high [salt] may be due to buoyancy: ρ SWCNT ~ 1.4 g cm -3 (Huang & Trentjev 2012) Adeleye and Keller (2013). Water Res, In review

17 Conclusion and Environmental Implications EPS interact with SWCNTs Interaction may affect magnitude of SWCNT surface charge The stability of SWCNT is improved by EPS interaction Coating of SWCNTs by EPS and other NOMs may increase bioavailability Exposure risk of SWCNTs (and possibly other ENMs) to pelagic organisms in natural waters may be higher than expected due to stabilization by EPS

18 Thank you Acknowledgement Sahar El Abbadi Daniel Dunham UCSB MRL Labs Copyright 2013 UC Center for Environmental Implications of Nanotechnology. The Regents of the University of California. All Rights Reserved. Contact to obtain permission to use copyrighted material. This material is based upon work supported by the National Science Foundation and the Environmental Protection Agency under Cooperative Agreement Number DBI and DBI Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation or the Environmental Protection Agency. This work has not been subjected to EPA review and no official endorsement should be inferred.