The overall goal of this procedure is to grow iridium oxide nanocrystals on a semiconductor substrate by photochemical oxidation. Photochemical oxidation as a synthetic tool expands the methods by which chemists can create new hybrid materials. They can photocatalyze production to unexplored frontiers.
Our work treats the Achilles heel of cadmium sulfide, which is known to be highly active for hydrogen production, but is hampered by photochemical instability. Photochemical oxidation, when applied on nanoscale materials with localized charge carriers can also be exploited from a kinistic styleze of redox reactions by simple examination of the products. To start, first synthesize cadmium sulfide-cadmium selenide seeded rods, and then suspend them in toluene solution indicated in the text protocol.
Transfer about half of the solution to a centrifuge tube, and add up to a one-half volume of methanol to precipitate the rods. Centrifuge the tube at 3, 400 Gs for five minutes, and decant the supernatant. Retain the pellet for later use.
Next, add 250 milligrams of mercaptoundecanoic acid and 400 milligrams of tetramethylammonium hydroxide to 10 milliliters of methanol in a centrifuge tube. Vortex until all the solids are dissolved. Add the methanol mixture to the cadmium sulfide-cadmium selenide seeded rod pellet, and shake the tube by hand to fully dissolve it.
Allow the solution to sit for at least one hour. After one hour, split the solution into two centrifuge tubes, and add 20 milliliters of toluene to each tube. Centrifuge the tubes at 7, 700 Gs for 15 minutes.
Carefully decant the clear supernatant, and invert the centrifuge tubes to dry the samples. Add five milliliters of ultrapure water to the pellets, and then store the rods in foil-wrapped vials. To begin, make solutions of iridium precursor, sodium nitrate, sodium persulfate, and sodium hydroxide as indicated in the text protocol.
Add 0.50 milliliters of the nitrate solution to 0.20 milliliters of the iridium precursor in a standard polystyrene cuvette equipped with a spectroscopic stir bar. Next, add 0.30 milliliters of the seeded rods in water, followed by 0.50 milliliters of the persulfate solution, and 0.50 milliliters of the sodium hydroxide solution. Place the cuvette in a holder, and stir the solution.
Then illuminate the sample at 450 nanometers and 100 milliwatts for up to four hours. The solution should turn green, and then blue. After the desired incubation time, transfer the solution to a tube, and centrifuge for 10 minutes at 7, 700 Gs.Carefully decant the supernatant and retain the pellet.
Disperse by sonicating in polar methanol solvent for further use. The visual appearance of the cadmium sulfide-cadmium selenide rods changes when coated with iridium oxide using irradiation. The uncoated rods begin orange-red in color, which after two hours of illumination turns green, and then blue after four hours of illumination.
Transmission electron micrographs were used to analyze the growth of the iridium oxide particles on the cadmium sulfide-cadmium selenide seeded rods over time. Control samples with no iridium oxide have rods of four to five nanometers in diameter. Samples illuminated for 10 minutes to four hours show the progression from small to larger particles with a full coating of iridium oxide.
Rods that were illuminated for four hours have a total diameter of nine to ten nanometers, with a two to three nanometer thick outer coating of iridium oxide evident after two hours of illumination. Once mastered, this technique can be done in a few hours if it is properly performed. After watching this video, you should have a good understanding of how to photochemically grow iridium oxide on seeded rods.
The methods used in this procedure can be extended towards the photochemical growth of other metal oxides as well. Don't forget that working with cadmium oxide and highly caustic solutions can be extremely hazardous, and precautions such as working in a glove box and wearing protective clothing should always be taken while performing this procedure.
