Silver Deposition on Alumina Membranes

Friday, July 01, 2005

Alteration from original chemical polishing procedure
In addition to chemical polishing using FeCl3 many other solutions can be used. Before trying the FeCl3 solution, I tried different molarities of nitric acid solutions. The first trial revealed a 10mM nitric acid solution was not at a high enough concentration to chemically polish the membrane and remove excess silver. Next, I tried a 5:1 dilution of nitric acid in distilled water. This also appeared to not chemically polish the membrane. Finally, a 2:1 dilution of nitric acid in distilled was tried. This resulted in very fast removal of silver particles from the membrane. That is why I chose another solution for chemical polishing. The FeCl3 solution takes a few minutes to take full affect so, there is more time to monitor the removal of the silver particles from the membrane.

Alteration from deposition procedure
Also, there is another solution/process for electroless deposition of silver on alumina membranes. It requires the membrane be placed in two initiator solutions before being immersed in the silver plating solution. The first initiator solution contained 0.9858g tin(II)chloride dissolved in 100mL distilled water. The membrane was immersed in the first initiator solution for five minutes, then it was placed in another containing silver nitrate dissolved in 100mL distilled water. The purpose of this extra initiator solution is to place a seed layer of silver on the membrane to improve electroless silver plating from the silver plating solution. The silver plating solution remained the same from the prior process I used, 0.6749g silver nitrate, 1.55g cobalt sulfate, 9.91g ammonium sulfate, and 16.33mL ammonium hydroxide. Trifluoroacetic acid can be used to stablize the initiator solution with tin(II)chloride.

Tuesday, June 28, 2005

Electroless Silver Plating

Electroless Ag deposition on alumina membranes

Silver and gold nanowires can be made using a process called electroless deposition. Using Whatman commercial alumina membranes containing 200nm pores, silver and gold can be deposited in the pores by immersing an activated membrane in a silver or gold plating solution. Also, it can be done by using either pulsed or ac electrodeposition.
When this experiment was conducted I used the electroless silver plating process. This requires that a membrane be activated by first placing it in an initiator solution. The initiator solution contained 1g tin (II) chloride, 1mL trifluoroacetic acid, 100mL distilled water, and 100mL methanol. Once the membrane had been immersed in 30mL of initiator solution for 5 minutes it was washed three times using 200 proof ethanol.
The membrane was then placed in 50mL of the silver plating solution. This solution contained 0.6749g silver nitrate, 1.55g cobalt sulfate, 9.91g ammonium sulfate, 16.33mL ammonia liquor (ammonium hydroxide), and 50mL distilled water. After making sure all the solids had been dissolved by using sonication, the membrane was placed in the silver plating solution. Then I placed the solution with the membrane on the wrist action shaker.
After doing trials of various times (15, 30, 45, 60, 120 min.), the membranes were washed using distilled water then dried with a kimwipe. The membranes were then prepared for SEM microscope viewing by chemical etching. The chemical etching solution I used contained 2g iron(II)chloride dissolved in 100mL distilled water. After swabbing the membrane with the solution for several minutes chemical polishing was observed. The membranes changed from greenish before polishing to a darker silver color. Upon viewing the membranes using the SEM microscope silver deposition was not uniform throughout the nanopores.

This image shows how the pores (dark areas) are not completely filled with silver particles.

This is a cross section of the membrane; again silver is not continuous thoughout the pores.

This membrane appears not to be chemically polished enough. There is still silver on top of the membrane.

Monday, June 27, 2005

I began as a leader in my high school chemistry lab, now I am leading myself toward as much knowledge as I can endure. I am beginning my sophmore year at Drexel University this September, and I hope to continue my research as an undergraduate chemistry major. I was picked for the Maryanoff Fellowship through Drexel, which has allowed me to feel comfortable in a labratory environment long before my first co-op experience. So far avarything is as new and exciting as one would expect.
As I continue toward fulfilling my degree requirements I hope to be accepted to a B.S./M.S. program at Drexel. If I am accepted, I would complete my Master of Science in the same time I could complete my Bachelor. My work is dealing with silver deposition in nanoporous alumina membranes. I am working in Dr. Bradley's Chemistry Lab.