2.7 Silver nanoparticles: a case study in cutting edge research  (Page 5/6)

After the ethanol has evaporated, your TA will now have an alkanethiol monolayer with the sulfur atoms bound to the silver and the hydrocarbon tails pointing away. Your TA has effectively coated the surface with hydrocarbons.

How attracted are the water drops to the surface? (Like attracts like.)

Do water drops on the monolayer coated surface spread out or bead up?

Is the contact angle greater or less than before the alkanethiol was added?

Is the water attracted more to the plain glass, to the silver, or to the alkanethiol monolayer-coated silver?

Experimental procedure no1 - ripening of silver nanoparticle

Solutions of silver nitrate (250 mg to 500 mL) and mercaptosuccinic acid (405 mg to 500 mL) have ALL been previously prepared for you. This can be gathered from the glass bottles situated in the lab.

1. Find and open the microlab program. Ensure that the accompanying box has power and is turned on, and that it is connected to the laptop via the USB plug. Once everything is connected and you double clock the microlab.exe file, a box will open in front of you.
2. In the tab labeled “New” you will find the icon for the “Spectrophotometer”, please double click this.
3. This brings up the program that we will use, at which point you should take a reading of a blank sample, this is done by filling a vial with DI water and placing in the appropriate slot, and covering with the film case. When the blank sample is in place, click the button “Read Blank”. This will a generate a series of data points that you can see.
4. Please take note to read from the Absorbance tab, this is the third option on the top right.
5. In a beaker gather 50 mL of silver nitrate solution; use the photo spectrometer to take an absorbance measurement of the silver solution on its own. To do this place twenty drops (approx 1 mL) into the glass vial provided, and dilute to the top with DI water. Shake the vial twice to ensure the solution is homogenous. Record the UV-Vis spectrum.
6. Place the 50 mL silver solution into the Erlenmeyer flask and start stirring, your TA will have the stir bars.
7. Complete the same process as above but this time uses 50 mL of the solution of mercaptosuccinic acid. Please make sure to rinse out the glass vial thoroughly. Take a spectrum using the photo spectrometer of the MSA solution.
8. Now place the 50 mL of MSA solution into the Erlenmeyer with the silver that you are already stirring vigorously – this means stirring at such a rate that you can see a vortex created.
9. Take a spectrum of the solution that is currently stirring, this should include the MSA and silver. You should notice, similar to DI water, and the MSA and silver on their own, that there is no response in absorbance of either of the chemicals when analyzed combined that would indicate that the nanoparticles have not been formed yet, but all the final ingredients are already there. This is why we need to add the sodium borohydride, as this will break the silver nitrate up so the silver can bind with the sulfur atom in the MSA molecule and the silver ions can start bunching up and the nanoparticles can begin to form.
10. Make the sodium borohydride solution by diluting 300 mg with DI water to 100 mL using a volumetric flask. From the equation of the chemical, NaBH ₄ , and upon the addition of water did you notice anything occurring, what happened in the reactions? (Did it change color, consistency, did gas evolve) what could have caused this? Sodium borohydride is highly hygroscopic, that means it reacts very readily with water, and the water in the atmosphere (especially in Houston) could have caused the salt to harden – this means you may have to coax the salt a little with some prodding using the spatula – without breaking the spatula!
11. To the solution of silver nitrate and mercaptosuccinic acid that is stirring place a few drops of the sodium borohydride solution, note the color change, then place some more sodium borohydride and note the color change again. What do you think is happening here, and why is the colors changing? What were the colors of the solution? Stop adding sodium borohydride when the color has reached a steady state and is not changing anymore. If you add too much sodium borohydride the products could come out of solution.
12. When you have a steady dark, black coffee color, you have added sufficient sodium borohydride Immediately take 20 drops of your Ag nanoparticle solution and place into the glass vial; make sure it is diluted down to a slightly sandy color by the addition of DI water. Place the filled vial into the slot and acquire spectroscopic data in the same manner as before, this will be your “time = 0” run – now what is different this time, compared with the last spectra you aquired? And how has this occurred?
13. Continue to repeat this process of taking 20 drops of your Ag nanoparticle solution and dilute in a vial and take spectroscopic data every 5 minutes for a total of 50 minutes,
14. When you are finished completing the experimental runs, then you can export the data so that it can be graphed in Excel.
15. Go to File, then scroll down to ‘Export Data as.’ and then select “Comma separated values’. This generates a file ending in .csv that can be later opened and used in Microsoft Excel; please take note where the file was saved.
16. Use excel to graph each of the data sets on the same graph. Complete an Area graph, with 3D visualization to graph the ripening process. You should notice some of the intensity changing from the first data set until the last – why do you think this is happening?
17. Using Excel again take the data from the first profile and data from the profile with the tallest peak. Graph each one separately. This is to demonstrate how the nanoparticles ripen over time. So you can see there is some movement in the system and it can take several hours before the entire system reaches some equilibrium. Note: You will not see the trough that we showed you in the PowerPoint as MicroLab does not go down to 310 nm, which is why we are posting data so that you can calculate the full width half maximum..
18. You have now successfully made some silver nanoparticles! Congratulations.
19. Finally plot a graph from the data posted online in order to calculate the diameter of the nanoparticels once you have extrapolated the full width half maximum (FWHM), using the equation: