Can anyone help me make sense of my lab results?

[hyddro]

Hello,

I recently did an experiment of nanoparticles (specifically Au Nanoparticles)
We did the Turkievich method and the borohydride method)

for the turkievich method we got good results and this is indicated by the UV spectrum of the sample..

for borohydride though... we got a funny UV spectrum. I will post both pictures and I need people to help me explain the difference. (since I am not too familiar with UV spectra)

The au colloids from the first method are supposed to be of about 20nm in diameter and the ones from borohydride are supposed to be of about 10nm in diameter.

Also the color of the solution from the second method was gray, which was very confusing.

Finally we tried to aggregate the partticles by using NaCl and ethanol separetly.

for the turkievich colloids, the the solution (whcih was initially dark red) became clear when we used NaCl but didnt change when we added ethanol (we added about 30 drops).

for the borohydride colloids, the solution went from gray to clear when we added nacl and ethanol (Separately) .. i don't know what this means... please any help will be appreciated.

 

[Zefram]

Hello,

Thank you for sharing your results and asking for help in understanding the difference in the UV spectra and color of your Au nanoparticles from the two methods. I am happy to provide some insights and help explain these differences.

First, let's start with the UV spectra. The UV spectrum is a graphical representation of the absorbance of light by a sample at different wavelengths. In the case of Au nanoparticles, the UV spectrum can provide information about the size and shape of the nanoparticles. The peak in the spectrum usually corresponds to the surface plasmon resonance, which is the collective oscillation of the electrons in the nanoparticles.

In your experiment, you have observed that the UV spectrum for the Turkievich method shows a clear peak, indicating that the nanoparticles are well-formed and have a narrow size distribution. However, for the borohydride method, you have observed a "funny" UV spectrum. This could be due to several factors such as aggregation of the nanoparticles, a broad size distribution, or impurities in the sample. Without seeing the actual spectra, it is difficult to pinpoint the exact cause of the difference. I would recommend checking the purity of your starting materials and repeating the experiment to ensure consistent results.

Moving on to the color of the solutions, it is important to note that the color of nanoparticles is dependent on their size and shape. In general, smaller nanoparticles tend to appear more red, while larger nanoparticles appear more blue. This is because the surface plasmon resonance shifts to longer wavelengths as the size of the nanoparticles increases. In your experiment, you have observed that the solution from the borohydride method was gray, which could indicate a larger size of the nanoparticles compared to the Turkievich method.

Lastly, your results from aggregating the particles with NaCl and ethanol are interesting. The fact that the solution for the Turkievich method became clear with NaCl but not with ethanol suggests that the nanoparticles were stabilized by the presence of the salt. On the other hand, for the borohydride method, the solution became clear with both NaCl and ethanol, which could indicate that the nanoparticles were not well-formed and easily aggregated.

In conclusion, the differences in the UV spectra and color of the solutions from the two methods could be attributed to various factors such as size distribution, purity of starting materials, and stability of the nanoparticles. I hope this helps in understanding your results and provides some direction for further