My Notes
Categories
This is a nanochemistry lab I developed for my Junior and Senior level Inorganic Chemistry course. I am NOT a nano/matertials person, but I know how important nanochemistry is and I wanted to make something where students could get an interesting introduction to the area. The first time I ran this lab was also the first time I made gold nanoparticles ever!
We do not have any surface/nano instrumentation here (AFM, SEM/TEM, DLS, etc... we can access them at other universities off-campus but that takes time and scheduling), so that was a key limitation in making this lab.
While it was made for an upper-division course, I think It could be adapted and implemented at many levels, including gen chem. I do not spend much time on nano in the lecture (none in fact), so this lab was made to have students learn a bit about nanochemistry somewhere in inorganic chemistry. We have one 10-week quarter of inorganic lecture and lab, offered every spring quarter.
This lab takes approximately 2-3 hours if students are well prepared and using their time well, but is usually spread over 2 days. Students are concurrently doing experiments for another lab or two because we have a lab schedule that overlaps multiple labs, and can do these during one day or across two days. The lab space is an organic chemistry laboratory, so we have access to the usual lab synthetic equipment
Students in thelaboratory write lab reports,which are the due the week after the last day of the lab experiment. In the lab report they use their UV-Vis data to calculate information about the AuNP.
The lab has been posted, as well two photos from students' ferrofluids (these were posted with permission on our departmental blog). A rubric has been posted as a faculty-only file. I have also included a student submission that received over 90% on the lab with their identifying information removed. Students write and introduction and need to cite journal articles in their report, so they are expected to do reading on nanochemistry topics outside of the lab period as they write their reports.
I am sure the lab can be improved, this was what i came up with the materials and time I had. I plan on continuing to revise and edit it as time goes on. Any suggestions are very welcome!
| Attachment | Size |
|---|---|
| Lab 3 - Nano 2017 KAG.docx | 28.48 KB |
| ferrofluid.png | 106.7 KB |
| ferrofluid2.png | 68.63 KB |
A student should be able to perform a chemical laboratory experiment safely and follow proper lab notebook protocol.
A student should be able to determine the average size of AuNPs from spectroscopic data and primary literature.
A student should determine atomic and nano-scale information from physical properties.
A student should be able to construct a lab report in the style of an ACS article (Students in my lab wrote lab reports for each experiment).
For this experiment, you need
The chemical materials - HAuCl4, trisodium citrate,
Heating/stirring plates
Glassware
UV-Vis spectrometer (mainly Vis)
A laser pointer
Strong magnets (the stronger and larger the better)
The syntheses are relatively straightforward, although we've had some problems getting "spikes" for the ferrofluid. Anecdotally, adding the reagents and doing the steps faster tends to give better "spiking". Some students just see a blob moving around in response to the magnet, which was fine in terms of their report.
The AuNP synthesis can also be done with an ultrasonicator or by addition of sodium borohydride, among other methods. We don't have them make a calibration curve of chloride addition, but that could be a possibility.
I like having a pre-made solution of a red oroganic dye to shine the laser pointer through to compare versus the laser shining through the AuNP solution.
One year, the AuNP synthesis was going very slow. We realized it was because the Au(III) was diluted in acid, so it was protonating the citrate. Boiling for a while before adding the citrate solution helped fix this problem.
KAuCl3 is also a good source of Au(III) for this lab.
Evaluation
Students are evaluated on their participation in lab, lab safety, lab notebook pages, and a lab report turned in a week after the last day of the experiment.
This lab was first run in spring of 2016, and again in spring of 2017 and 2018 (a different instructor carried out the lab in 2018).
In general, students do well on the lab report and seem to enjoy the experiment.They often need guidance when interpreting the Analytical Chemistry article and selecting the correct equations. Discussing their values with them in office hours ("does that make sense?") helps them understand their calculations.
A sample lab report that scored above 90% is included in the faculty-only files.
Kyle,
We did the Au portion of this lab in my foundations inorganic course this morning. The synthesis part worked really well. The yellow solution of the HAuCl4 (which I assumed was aqueous although the lab doesn't exactly state that) immediately turned colorless upon addition of the sodium citrate (also presumed to be aqueous). After a few seconds it turned to a grey/black color and then finally to a deep red. Then the problems started. Partially due to the crappy old UV-Vis I was using (running Windows older than my students) and part of the issue was with the salt addition. I'm okay with some vagueness in the lab for the students, but the instructor could use a little more guidance (at least this instructor could). Roughly how concentrated is the salt solution? At first I figured it could be extremely dilute. That didn't seem to change much. So we went more aggressive and that seemed to get some change in color to more of a blue-purple. It was a lot of guesswork on my part. I saved the samples and we are going to throw them on a slide and see what XRD tells us in a few weeks. My guess is that we won't get squat out of it but what the heck?
Another comment Kyle. In the student report and the lab instructions I think there is an error in the calculations of the number of atoms in the nanoparticles. You provide the equation N = ((pi)(rho)D3/(6 x M)) x Na. It took me a minute to figure out how you got 6. Essentially this equation is getting you moles of gold which you multiple by Na to get atoms. That's fine.So the top part of the equation is density (rho) times volume. In the bottom of the equation is the mass to mole conversion accounting for the number of atoms in the cell. You say treat the particle as a sphere. That's all well and good. So, you are using the equation V = 4/3 (pi) r3. Diameter is of course 1/2 the radius. So tracking the numbers, you get a 4 up top from the 4/3 and in the denominator your get 3 (from 4/3) x 2 (from the 1/2 diameter) x 4 (from 4 gold atoms in a FCC unit cell). The problem is that you need r3 in the volume formula and thus it needs to be (diameter/2)3. So the real equation here should be N = ((pi)(rho)D3/(24 x M)) x Na or better yet just convert the diameter to radius and get N = ((pi)(rho)r3/(3 x M)) x Na.
Kyle, this is a great LO and I am thinking of using it this year. When you make the HAuCl4 from the KAuCl4 what concentration of acid (HCl, I assume?) do you use to dissolve it?
In reply to Kyle, this is a great LO and… by Hilary Eppley / DePauw University
Hi! I think we just made a neutral solution of KAuCl4 without added acid. Too much acid can protonate your citrate and make it a worse reducing agent so that the reduction doesn't occur (the first time we ran this lab with commercial HAuCl4 in acid we had this problem).
Kyle
In reply to Another comment Kyle. In the by Chip Nataro / Lafayette College
Hi Chip,
Thanks! I'll update the file when I get a chance. I also plan on adding more details to this LO.
Kyle
Hi Kyle,
I am thinking of using this lab in my inorganic chemistry class in the winter term! I have a few questions: first, how long did it take for the gold nanoparticles to form? I am thinking of potentially doing the preparation and analysis of gold nanoparticles in the same 3 hour lab, and I am wondering if that is doable. Also, does any laser pointer work for this lab? Can you just use one that we use in presentations? Or one we use to play with cats? Thanks!
In reply to Hi Kyle, I am thinking of… by Feier Hou / Western Oregon University
Hi Feier,
Yes, it can be easily done in a short time, the reaction is a couple of minutes to do the color change when boiling.
That laser pointer is the same one I use for presentations (its a $20 one from Radioshack from like 2009 or so), so any laser pointer should work.
Kyle
In reply to Hi Feier, Yes, it can be… by Kyle Grice / DePaul University
Thank you!
Hi Kyle, another question: what is the concentration of the NaCl solution added to the Au nanoparticles? I can't seem to find it anywhere in the lab or the faculty only files. Thank you!
In reply to Hi Kyle, another question:… by Feier Hou / Western Oregon University
Hi Feier,
Yeah, sorry... I didn't have a specific number, we just scoop some in lol.
Kyle