Raman Spectroscopy Nanomaterials Exposure? Three-dimensional Visualization and Quantification of Gold Nanomaterial Deposition and Aggregation in Porous Media via Raman Spectroscopy Matthew Y. Chan, Weinan Leng, Peter J. Vikesland Department of Civil and Environmental Engineering, Virginia Tech
Stable Transport Aggregation/Deposition Sedimentation Other (Chemical) Transformation
AuNP Concentration (mg/l) 35 [CaCl2] = 0.1 mm [CaCl2] = 0.4 mm 30 [CaCl2] = 0.6 mm [CaCl2] = 0.8 mm [CaCl2] = 1.0 mm 25 20 15 10 5 0 0 2 4 6 8 10 V pore Column experiment Column packed with media to simulate the Quartz environment Crystal Microbalance Versatile Sensitive environmental measurement of parameters deposition Breakthrough Compares change curves in quartz from spectroscopy resonance frequency or dynamic before and light after scattering deposition Electron Microscopy Limited Balance to surface macroscopic can be adaptably interpretation modified Clear and detailed observation of nanomaterials Limitation Limited approximation of DLS or spectroscopic of the environment methods in various state Difficult to interpret in situ microscopic Independent of sample preparation interaction Often includes drying process that alters sample Difficult to image nanoparticles with coatings Sample preparation can become difficult Challenging in situ analysis https://upload.wikimedia.org/wikipedia/commons/0/0d/qcm_principle.gif
Raman Spectroscopy Current Methods Difficult/altering sample preparation Difficult and limited in situ analysis Limited visualization Raman Spectroscopy No sample preparation True in situ analysis 2D or 3D chemical imaging Versatile Sensitive
Raman spectroscopy detacts changes in photon frequency due to ineleastic scattering No scattering: Photon is absorbed Rayleigh scattering: Photon is elastically scattered Stokes/Anti-Stokes scattering: Photon s energy is inelastically scattered; the emitted photon has a different frequency than the incident photon.
Raman Incident laser with irradiate sample adjacent to a rough noble metal surface (e.g. Au, Ag) Metal surface plasmon excites and oscillates Sample Laser Surface Plasmon Rough Noble Metal Surface When laser wavelength and surface plasmon frequency matches: Resonance effect greatly enhance Raman shift signal Moskovits, M. Rev. Mod. Phys. 1985, 57, 783 826.
Dissolved species in the environment interacts with released nanomaterials Inducing aggregation Halides such as chloride interact strongly with Au Cl - Cl - Cl - Cl - Cl - The gold nanoparticle aggregate surface doubles as a SERS surface greatly enhancing Raman shift signal intensity Cl - Cl - Au
By convention, low frequency Raman shift (< 300 cm -1 ) is often ignored These Raman shifts can be highly specific and sensitive NaX Gold Raman Substrate SERS Intensity (CCD Counts) Nano-Gold Surfaces Interacting with Adsorped Ions 450 400 350 300 250 200 150 100 50 Au - I - Au - Br - Au - Cl - Au - F - We will utilize these interaction to track gold nanoparticles aggregation in situ 0 0 100 200 300 400 Raman Shift (cm -1 )
Raman Identical amount of AuNP Quartz packed-bed filled with glass beads, AuNP aggregates, and NaCl 0 mm NaCl control AuNP aggregates 3 mm NaCl Intensity / a.u. No AuNP, just Silica AuNP with Silica 500 1000 1500 2000 2500 3000 Raman Shift / cm -1 10 mm NaCl 100 mm NaCl
0 mm NaCl 100 mm NaCl
200 μm The Raman can probe into the interior of the packed bed This is a 300 μm x 300 μm x 200 μm cross section
By stacking all the images, we can interpolate a 3D projection of the packed-bed interior
10 mm NaCl 30 mm NaCl 100 mm NaCl 6 6 6 4 4 4 U/kT 2 U/kT 2 U/kT 2 0 0 0-2 0 20 40 60 80 100-2 0 20 40 60 80 100-2 0 20 40 60 80 100 Distance (nm) Distance (nm) Distance (nm)
Raman Spectroscopy Current Methods Difficult/altering sample preparation Difficult and limited in situ analysis Limited visualization Raman Spectroscopy No sample preparation True in situ analysis 2D or 3D chemical imaging Versatile Sensitive
Sustainable Nanotechnology Organization Funding provider CEINT (NSF & EPA) ICTAS VTSuN The Vikesland Group Dr. Peter Vikesland Dr. Weinan Leng Becky Lahr Talk @ Tuesday 2:10 5C!!! And the rest of the group
mychan@vt.edu
Gold Nanoparticles Surfaces Interacting with Chloride 100 Raman Spectroscopy 785 nm SERS Intensity (CCD Counts) 50 1.00 Time-resolved Evolution of Raman Peak 0 0 100 200 300 400 Raman Shift (cm -1 ) 0.98 Quartz cell filled with gold nanoparticles and NaCl Normalized CCD Counts 0.96 0.94 0.92 0.90 0.88 0.86 0.84 0 20 40 60 80 100 120 Time (minutes)