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!

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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.

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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

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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

Making Our Device

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1. 2.

3.

Schoen, Schoen, Hu, Kim, Cui. Nano Letters. 10(9) 3628. 2010.

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?

✔ ✖ ✔ ✔