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. The size of the pores depends on the applied potential.
This version of the experiment uses electrical tape to hold the filter. It uses less equipment, but taping the filters without breaking them requires careful manipulation.
- Wear eye protection
- Chemical gloves recommended
- Fume hood recommended
- Avoid contact with or inhalation of nickel and nickel solutions.
Step 1. 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
Step 2. 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.
Step 3. Firmly hold the barrel in place while securing opposite sides of the barrel with binder clamps. Look down the barrel of the syringe to make sure it is centered over the o-ring.
What is the measured voltage of your 1.5 V battery?
Step 4. Insert the battery into the battery holder, paying attention to polarity. The positive end should be connected to the nickel electrode. Add nickel plating solution to the barrel up to the first markings. Check for leaks. Connect the negative lead of the battery to a multimeter set to read current and then use a jumper cable to connect the multimeter to the copper stage. Insert the nickel electrode into the nickel solution, start timing, and record the current passing through the circuit. If no current flows, examine the apparatus to fix any bad electrical connections. Electrolyze for 10-45 minutes. What is the average current reading? Longer times give longer wires unless the pore length is exceeded. How many minutes did you use?
Step 5.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?
Step 6.Rinse the disc with water.
Step 7. 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.
Step 8. Tape the disc shiny side up to a glass slide for removal of the metal coating.
Step 9. 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.
Step 10. Rinse with water.
– Option A: Obtain the powder x-ray diffraction spectrum (2θ = 40-100°, step width 0.05, count 1.0s) of the nickel nanowires in the filter. Place the wet filter on a glass microscope slide as a holder. Which side should be up? How similar is the spectrum to that of nickel metal?
Step 11. 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.
Step 12. 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.
- Option A: Obtain the powder x-ray diffraction spectrum (2θ = 40-100°) of the free nickel nanowires. Wrap a piece of tape tightly around a microscope slide with the sticky side out. Puddle a fairly dense solution of the nanowires onto the tape and let dry.
- Option B: Use an SEM to measure the length of the nanowires. Does the length correlate with deposition time?
- Option C: Rinsing with ethanol (and storing the nanowires in ethanol) gives a suspension that leaves less residue and that evaporates more quickly for preparation of SEM samples.
- Based on the electrolysis time and the average current, how many moles of nickel did you make?
- If you obtained an SEM image, how long are your nickel nanowires? You should measure this many times and take an average.
- If you obtained XRD data, do the nanowires show any evidence for a preferred crystal orientation in the filter?
- Is your product magnetic? How do you know?
- Whatman Anodisc alumina filters 25mm 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)
- 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.
- “Watts” Nickel plating solution: 300g/L NiSO4.6H2O, 45g/L H3BO3 and 45g/L NiCl2.6H2O.
- Tweezers, cotton swabs, water wash bottle, beaker
- Nitric acid (conc), 6 M NaOH
- Strong magnet
- 0.032 inch thick satin finish copper sheet, 12″ x 12″, McMaster-Carr, (#9801K11)
- 1-1/8″ OD x 7/8″ ID x 1/8″ W o-ring (same diameter as the 1″ syringe), Ace Hardware or McMaster-Carr, (#9452K32)
- 1-1/4″ binder clips, Staples , (831602)
- 2-1/4″ acrylic square, 0.10″ thick
- Wooden support blocks made from a 1×2: 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.
- 30 mL plastic syringes, VWR International, (66064-760). Use a saw to cut the syringe at the 15 mL mark and cut the plunger at the support closest to the end.
- AA Battery holders: Mouser (#534-139) http://www.mouser.com
- Make a hole in the end of the plunger for the positive lead of the battery holder.
- Wires with alligator clips: Mouser (#13AC012) http://www.mouser.com.
To prepare 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, and then use a soldering iron to connect the wires to the battery holder.
- 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.