You Wish You Had My Prof
Apr. 20th, 2010 04:20 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
tanarillSo, I am a senior. At my school, being in your last two semesters means that you have to apply to a professor for an then be accepted to a senior research project. Basically, you lab monkey for a prof and learn all kinds of tricks.
My prof is attempting to make hollow gold nanoparticles. A gold nanoparticle, as we have known since the Renaissance, will absorb light differently than large gold nuggets, and therefore appear red; thus, "ruby gold," a very difficult to make and therefore massively expensive form of glass (at the time).
What we are trying to do is make a gold shell, only 6-10 nanometers thick, but empty on the inside. How do you do it?! you may well ask.
It involves making a cobalt nanoparticle first. Cobalt(II) ions are easily soluble, so we put those in solution, and then add a reducing agent. Reducing agents donate electrons, and therefore the cobalt(II) ions become very, very tiny particles of metallic cobalt. Nanoparticles, even.
Then we add some gold(III) ions. See, cobalt doesn't really like to be metallic; the second you add something which will accept electrons, it will give them up. Therefore, whenever a gold atom hits a cobalt nanoparticle, the cobalt immediately gives up the electrons and the gold becomes metallic. Thus, a gold shell forms around what was the cobalt nanoparticle. At the same time, the cobalt becomes cobalt(II) and floats off into solution.
Of course, it's far more complicated than that. Cobalt, as I have said, really likes giving away electrons, to anything that will accept them. Unfortunately, this includes oxygen out of the air, so before beginning the reaction you have to spend about an hour removing oxygen and replacing it with nitrogen gas (which, on the whole, doesn't react). And then you have to keep oxygen from getting it when you add the gold . . .
Then there is the issue of forming cobalt nanoparticles. Sure, they start off that way, but what is to keep them from sticking together and forming large cobalt particles? The answer is acid (or rather, conjugate bases, but since you're mostly not-chemists . . . ). If you add an acid, it will stick to the outside of the nanoparticles. And, since all the acids have a negative charge, they repel each other, preventing any of the cobalt particles from getting close enough to stick. To make ruby glass, Renaissance glassmakers suspended the gold in a mix of nitric and hydrochloric acids! Fortunately, it's possible to use very a non-toxic acid called citric acid, which is incidentally vital to every cell in your body for getting energy out of food. So we add some citrate and call it good.
And, if we do it right, and keep the oxygen away, and add enough acid to keep the cobalt particles apart but not enough to acid-dissolve them, and everything is perfect . . . then the bright red gold nanoparticles can be turned into purple, blue, or even green nanoparticls.
Of course, that is what happens if we do it right, but when have we ever done that?
Yesterday, we managed to make: solid gold nanoparticles, at low concentration, which made a very pretty pink color; what are quite possibly nanorods, which are a lovely royal purple; and, somehow, gold plate the magnetic stir bar, which is a strange accomplishment all on its own that I blame on the citrate, or lack thereof. We also managed to explode the nitrogen hose (we have more of that, though, so it is okay). And finally, I neutralized the acid (which must be done before it is safe to put down the drain) in the test tube instead of a beaker, which resulted in a few seconds of amusing foamy hiss.
Altogether, a successful day.
My prof is attempting to make hollow gold nanoparticles. A gold nanoparticle, as we have known since the Renaissance, will absorb light differently than large gold nuggets, and therefore appear red; thus, "ruby gold," a very difficult to make and therefore massively expensive form of glass (at the time).
What we are trying to do is make a gold shell, only 6-10 nanometers thick, but empty on the inside. How do you do it?! you may well ask.
It involves making a cobalt nanoparticle first. Cobalt(II) ions are easily soluble, so we put those in solution, and then add a reducing agent. Reducing agents donate electrons, and therefore the cobalt(II) ions become very, very tiny particles of metallic cobalt. Nanoparticles, even.
Then we add some gold(III) ions. See, cobalt doesn't really like to be metallic; the second you add something which will accept electrons, it will give them up. Therefore, whenever a gold atom hits a cobalt nanoparticle, the cobalt immediately gives up the electrons and the gold becomes metallic. Thus, a gold shell forms around what was the cobalt nanoparticle. At the same time, the cobalt becomes cobalt(II) and floats off into solution.
Of course, it's far more complicated than that. Cobalt, as I have said, really likes giving away electrons, to anything that will accept them. Unfortunately, this includes oxygen out of the air, so before beginning the reaction you have to spend about an hour removing oxygen and replacing it with nitrogen gas (which, on the whole, doesn't react). And then you have to keep oxygen from getting it when you add the gold . . .
Then there is the issue of forming cobalt nanoparticles. Sure, they start off that way, but what is to keep them from sticking together and forming large cobalt particles? The answer is acid (or rather, conjugate bases, but since you're mostly not-chemists . . . ). If you add an acid, it will stick to the outside of the nanoparticles. And, since all the acids have a negative charge, they repel each other, preventing any of the cobalt particles from getting close enough to stick. To make ruby glass, Renaissance glassmakers suspended the gold in a mix of nitric and hydrochloric acids! Fortunately, it's possible to use very a non-toxic acid called citric acid, which is incidentally vital to every cell in your body for getting energy out of food. So we add some citrate and call it good.
And, if we do it right, and keep the oxygen away, and add enough acid to keep the cobalt particles apart but not enough to acid-dissolve them, and everything is perfect . . . then the bright red gold nanoparticles can be turned into purple, blue, or even green nanoparticls.
Of course, that is what happens if we do it right, but when have we ever done that?
Yesterday, we managed to make: solid gold nanoparticles, at low concentration, which made a very pretty pink color; what are quite possibly nanorods, which are a lovely royal purple; and, somehow, gold plate the magnetic stir bar, which is a strange accomplishment all on its own that I blame on the citrate, or lack thereof. We also managed to explode the nitrogen hose (we have more of that, though, so it is okay). And finally, I neutralized the acid (which must be done before it is safe to put down the drain) in the test tube instead of a beaker, which resulted in a few seconds of amusing foamy hiss.
Altogether, a successful day.
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Date: 2010-04-25 11:14 pm (UTC)Oh, thank you so much! I will let you know if something comes up.