Controlled Evaluation of Nanoparticle Transformations. Peter Vikesland Ronald Kent

Transcription

1 Controlled Evaluation of Nanoparticle Transformations Peter Vikesland Ronald Kent

2 We often conceptually diagram nanomaterial transformations - unfortunately these diagrams are typically too simple Batley, Kirby, and McLaughlin Acct. Chem. Res., 2012 Alvarez, Colvin, Lead, and Stone ACS Nano,

3 Aggregation confounds nanomaterial dissolution 0 Nanorods Microrods Rubasinghege, G. et al. Langmuir 2010, 26, 1524

4 Aggregation confounds nanomaterial dissolution PbS Dissolution Liu et al. ES&T 2009 α-fe2o3 Dissolution Echigo et al. Geochim. Cosma. Acta 2012 Lanzi, Baltrusaitis & Cwiertny, Langmuir, 2012 AgNP Dissolution Li, Lenhart & Walker, Langmuir, 2010

5 How do we isolate dissolution processes from aggregation? 5

6 Nanosphere lithography (NSL) was used to fabricate arrays of isolated nanoparticles on glass substrates. 1) Deposition of colloidal mask on thiolated glass 2) Deposition of metal vapor through mask 3) Mask removal to reveal particles Kent and Vikesland ES&T, 2012

7 Nanosphere lithography produces uniform nanoparticle arrays Silver nanoparticle arrays 100 nm 1 µm Kent and Vikesland ES&T, 2012

8 TEM imaging of nanoparticles indicates FCC crystal structure 200 nm 100 nm 8

9 Atomic force microscopy (AFM) was used to characterize effects of dissolution on nanoparticle morphology Sample characterization by tapping-mode AFM in air Ag + Ag + Sample dissolution period in sample tubes in the dark

10 Representative AFM Images: 550 mm NaCl 4 Ag 0 + O2 + 4H + 4 Ag + + 2H2O Initial Day 1 Day 7 Day 15 A' B' C D' A B C' D A A' B B' C C' D D' Particle heights are in nm All experiments performed at ph 7.0 ± 0.1 and 25 C in a 2 mm phosphate buffer Kent and Vikesland ES&T, 2012

11 Under our reaction conditions AgCl precipitation is not expected.

12 XPS does not detect AgCl precipitates. 550 mm NaCl 1 mm NaCl Buffer solution No solution

13 Internal redox potential differentials may explain the observed change in height. 100 nm 100 nm Cathode Ag + + e - Ag 0 V ave = 3.5 x 10 5 nm 3 V ave = 3.8 x 10 5 nm 3 Kent and Vikesland ES&T, 2012 Anode Ag 0 Ag + + e -

14 Nanoparticle dissolution is a function of the NaCl concentration Contracting sphere rate law nt and Vikesland ES&T, 2012

15 Comparisons to other studies Present study Data extrapolates to 0.36 nm/d dissolution rate at ph 7, [NaCl] = 0, and room temperature Dissolution rate of 2.2 nm/d in 550 mm NaCl Previous studies Dissolution rate of 0.7 nm/d at neutral ph Dissolution rate of 2 nm/d at ph 4 Chloride generally enhances dissolution, but AgCl precipitation or aggregation may limit dissolution in some cases Liu, J. et al. Environ Sci Technol 2011, 45, 7345; Liu, J. et al. Environ Sci Technol 2010, 44, 2169; Liu, J. et al. ACS Nano 2010, 4, 6903; Li, X. et al. Langmuir 2010, 26, 16690

16 What else can we do? Study how solution chemistry influences silver nanoparticle dissolution (vary ph, use synthetic freshwater, use natural organic matter, compare with real freshwater) Test effects of surface functionalization on dissolution using citrate, bovine serum albumin (BSA), polyethylene glycol (PEG), and polyvinylpyrrolidone (PVP) Test inorganic and organic sulfides over a range of concentrations and compare with chloride Produce nanoparticle arrays with different shapes and sizes to study how particle morphology affects dissolution Dissolution in synthetic freshwater

17 Closing thoughts Nanomaterial transformations affect particle-particle, particle-cell, particlematrix interactions in complex ways. Only by careful isolation of system variables can we truly begin to achieve a fundamental understanding of complex nanoparticle systems.

18 Funding Center for Environmental Implications of Nanotechnology (NSF/EPA) VT Institute for Critical Technology and Applied Science Charles Via fellowship (VT Department of Civil and Environmental Engineering) EPA STAR fellowship Substrate production Dr. Stefan Stoianov Dr. Hans Robinson Erich See Lab support Dr. Jeffrey Parks Jody Smiley Dr. Jerry Hunter Acknowledgments Thank you!