Procedure modified by J. Whitsett, S. M. Condren, and G. Lisensky from
A. K. Bentley, M. Farhoud, A. B. Ellis, G. C. Lisensky, Anne-Marie Nickel, and W. C. Crone,
"Template Synthesis and Magnetic Manipulation of Nickel Nanowires,"
Journal of Chemical Education, 82,
765-768 (2005).
A simple way to make nanowires is
to use a mold or template. In this experiment nickel nanowires are grown inside
the pores of an alumina filter and then the filter is removed by etching to
yield magnetic nanowires.
Nanoporous membranes were designed for health care applications
including virus filtration, sample preparation, and liposome manufacture (http://www.whatman.com).
These alumina membranes are manufactured by applying a large electrical potential
to a piece of aluminum metal submerged in an acid. Aluminum is oxidized to
alumina (Al2O3) and pores are created. The size of the
pores depends on the applied potential.
This version of the experiment uses uses a syringe holder, clamps, and an o-ring to hold the filter.
It uses more equipment equipment than another version that uses electrical tape but the manipulation is easier.
Procedure
Wear eye protection
Chemical gloves recommended
Fumehood recommended
Avoid contact with or inhalation of nickel and nickel solutions.
Obtain a 0.02 micrometer Anodisc filter. These ceramic discs are
quite brittle and are supported by a polymer ring. Always use tweezers
to hold the membranes by the support ring; the alumina will crack if handled
directly. Remove the disc from the packaging, remembering which side was
up in the box. Fully coat the upper side (the polymer ring looks wider)
with a conducting metal (see options in next steps).
One option is to use a cotton applicator and liquid GaIn alloy to
paint the surface. The coated side will look shiny (and the opposite side
will remain lighter.) While it is important to fully coat the surface
to prevent leaks, it is only necessary to dip the applicator in the GaIn
once. The GaIn can be spread quite thin. Check for gaps in the GaIn coating
by looking at the non-coated face of the membrane. Any areas without GaIn
will appear light blue in color while areas with GaIn will appear white
or opaque.
Another option is to sputter Ag metal onto the surface. Conditions
used were 50 millitorr argon, 45 milliamps current, for three 150 second
depositions. The coated side will look shiny (and the opposite side will
remain lighter.)
Place the copper electrode on the stand.
Place the disc, metal coated side down, on the copper electrode.
Place the o-ring on the disc.
Stand the cut-off syringe barrel on the o-ring.
Firmly hold the barrel in place while securing opposite sides of the
barrel with binder clamps.
Connect the negative lead of a 1.5 V battery to the copper electrode.
Add nickel plating solution to the barrel up to the first markings. Check
for leaks. Connect the positive lead to a coil of nickel wire and insert
into the solution. Electrolyze for 10-45 minutes. Longer times give longer
wires unless the pore length is exceeded.
Disconnect the battery from the copper electrode. Remove the nickel
electrode from solution.
The nickel solution can be reused for this experiment. Why does the concentration
of nickel in solution not change during the electrolysis?
Rinse the disc with water.
Firmly hold the barrel in place and remove the binder clips. Transfer
the disc from the copper electrode and gently tape the disc shiny side
up to a glass slide for removal of the metal coating.
In a fume hood, use concentrated nitric acid and a cotton applicator
to remove the shiny GaIn or the Ag coating. Soak the cotton applicator
in water before disposal.
Rinse with water.
Place the disc in 5 mL of 6 M NaOH for at least 10 minutes. The ceramic
material will dissolve. Discard the polymer support ring.
Place the beaker on a strong magnet. The nickel nanorods will be attracted
towards the magnet. Remove the NaOH solution. Add water to rinse, place
the beaker on a strong magnet, and remove the rinse solution. Repeat several
times. Transfer the final suspension to a vial for storage. Keep the wires
in solution.
Materials
Whatman Anodisc alumina filters with polypropylene support rings and
0.02 micrometer pores (not available directly from Whatman):
Fisher Scientific (#09-926-34) or VWR International (#28138-067)
GaIn Eutectic: Aldrich (49542-5)
Nickel plating solution: 300g/L NiSO4.6H2O, 45g/L each H3BO3
and NiCl2.6H2O. "Watts Ni Pure," (#130859), Technic Inc.,1 Spectacle
St, Cranston, Rhode Island 02910 Tel: 401-781-6100, Fax: 401-781-2890, Email: info@technic.com
Ni wire: VWR International (#AA41361-G6) or Alfa Aesar 1 mm diameter x 10 m long. CAUTION: Avoid physical contact (especially inhalation) with nickel and
nickel solutions as nickel is an irritant and carcinogen.
0.032 inch thick satin finish copper sheet, 12" x 12", McMaster-Carr,
(#9801K11) http://www.mcmaster.com
30 mL plastic syringes, VWR International (66064-760)
1-1/8 x 7/8 x 1/8" o-ring (same diameter as the 1" syringe),
Ace
Hardware (35741B)
Wooden support blocks made from a 1x2: one piece 3" long, one piece
2-1/2" long and cut in half lengthwise. Screw the acrylic square
to the blocks using a 1-1/4" round head screw and washer.
The movie shows using a saw to cut the syringe at the 15 mL mark and the
plunger at the support closest to the end.
Wires with alligator clips: Mouser (#13AC012)
http://www.mouser.com.
The left movie shows assembly of the battery holders. Cut in half a wire with
aligator clips on each end. Strip off the insulation for a short distance.
Use a soldering iron to melt some solder onto each wire and onto the ends
of the battery holder, then use a soldering iron to connect the wires
to the battery holder.
Make a hole in the end of the plunger for the positive lead of the battery holder.
Properties
Nickel nanowires viewed through an optical microscope (20x) while
a magnet is moved back and forth from the front to the side of the microscope.
The nanowires rotate to align with the magnetic field. The scale bar represents
100 micrometers.
Nickel nanowires viewed through an optical microscope (20x) while
a magnet is spun at one side. The nanowires rotate to align with the magnetic
field. The scale bar represents 100 micrometers.
Nickel nanowires suspended in water controlled by a magnetic field.
