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Cleaning Water With Silver Nanowires David and Alia Schoen Han-Sun Kim, Liangbing Hu, Sarah Heilshorn, Yi Cui
The Geballe Lab at Stanford University Home to 18 research groups in Materials Science and Applied Physics.
• Nanotechnology • Biomaterials • Solid-State Physics • Advanced Microscopy • Alternative Energy
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2 m
B
David’s Background Alia’s Background
2 µm
Virus Bacteria Silver
Nanowire
My Gizmo
Make Tiny Devices using Single Nanowires
Engineering Materials using Proteins and Biomolecules
20 nm
Schoen, A. P.; Schoen, D. T.; Huggins, K. N.; Arunagirinathan, M. A.; Heilshorn, S. C. J. Am. Chem. Soc. 2011, 133, 18202–18207.
How to do New Science
1. Find Inspiration • Just like any other creative pursuit
2. Figure out your Key Problem • What are the main challenges other people face?
3. Apply what you Already Know • This is the hard part! How can you make a difference?
4. Design a Controlled Experiment • This is where you use the Scientific Method
5. Go look for more Inspiration!
8/27/13
Finding Inspiration
8/27/13 MRS Bulletin, Volume 33, January 2008 S. Kaur, et al. MRS Bull. 33(1) 21-26. 2008
2 µm
My Own Work
Silver Nanowires
20 µm
Nanofilter
Water is a Big Problem!
2.4 billion people without improved sanitation. 1.1 billion people without improved water sources.
8/27/13 Mokolumne River System, CA 10/2008
1 UNESCO World Water Assesment Program 2006, 1.
Dark = Places Where Water is Used Faster than Replenished
Nanofilters
The article was about Nanofilters, which are made of Plastic fibers. They need to be small so they can filter out cells.
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20 µm
Cell Size
The Key Problem: Fouling
When you filter a lot of water, cells can build up on the filter. They form a sticky plaque, called a Biofilm, which cannot be removed. (Its actually the same as the plaque on your teeth the dentist removes) 8/27/13
20 µm
Over Time
A Biofilm
Metal Nanowires?
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Bug Zapper
2 µm
My Own Work
Silver Nanowires
20 µm
Nanofilter
Grows
The most important thing about metal nanowires is that they conduct electricity. Can this Help?
Dies?
How do you make Nanowires?
Recipe for Silver Nanwires: • Dissolve AgCl and Polyvinylepyrolodine (PVP, soap) in Ethelyne
Glycol at 170 °C. Slowly add AgNO3 over the course of 10 minutes.
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Reagents
Heater
Nanowires!
Flask
What Does it Look Like?
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1 mm
200 µm
1 µm
200 nm
Schoen, Schoen, Hu, Kim, Cui. Nano Letters. 10(9) 3628. 2010.
Does It Work?
How to Test It?
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1. Treat water in different conditions.
2. ‘Plate’ Cells 3. Wait 4. Count Cell Colonies
Without Voltage
With Voltage
A Controlled Experiment The combination of Silver Nanowires and Voltage is really effective at killing cells. How to be sure? 1. Do we need all the pieces to
make it work? 2. How much voltage do we
need?
3. Perform the experiments many times to get statistics. (We counted 1000’s of cell colonies by hand!)
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0"
20"
40"
60"
80"
100"
-20" -10" 0" 10" 20"
% R
emov
ed!
Voltage (V)!
Silver Treated" NT Only"
Conclusion
Creative application of what you Already Know to the Key Problems of Inspiring topics helps you knew exciting New Science. You will never know everything yourself, so the best work often comes out of Interdisciplinary Teams
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Acknowledgements: NSF GRFP NDSEG Stanford Bio-X KAUST
How do you make Nanowires?
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The microscopic Picture: • AgCl (unstable) reacts with the solvent to form nanoparticles • Key Trick – PVP has a special interaction with Ag and sticks to it • Slow addition of AgNO3 means new Ag atoms add to the nanowires
Putting it in Context
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Our Filter Nanofibers Pulsed Electric Fields
Electro-chlorination
Flow Rate 100,000 L/hr*m2 130 L/hr*m2 ? 160 l/hr Energy/L 216 J/L 896 J/L High ? 9.75 A Incubation Time
1 s N/A ? 0.5 < t < 60 min
Current/Area .48 mA/cm2 0 mA/cm2 High 50-150 mA/cm2
Batch? ✖ ✖ ✔ ✖ Antifouling ✔ ~ ? ✔ Cheap ~ ✖ ✖ ✖ Scalable ✔ ✖ ✖ ✖ Mechanically Robust
✔ ✖ ✖
Stability ? ✖ ✔ ✔ Secondary Filtration?
✔ ✖ ✔ ✔