I dispersed 0.2mg/milt SWNT 95% purity (1-2nm OD) in 2% SDS and sonicated for 2h using tip type sonicator with 2W power and 70% cycle. I use a sample of it for Uv-Vis spectroscopy. The result is in attachment. While in all reports on Uv-Vis of SWNT there is two or rather three peaks related to metal and semiconductor transitions, I only got one peak. I would wonder what the problem is OR how I can interpret this one peak?
Dear Sai,
between 190nm to 230nm wavelength our cell have a problem. But we calibrate it before we start our work....however, i still not know what would be the problem....
Dear Moises,
Thank you. I will try to use Kubelka-Munk .....
By the way, do you know why i got this absorption spectrum, while others did not?
Another point is that, I read somewhere that Kubelka-Munk function is for solid, while our sample is in aqueous solution. Can I use K-M for this form too?
Thanks again.
I doubt that nanotubes scatter much, their are strongly absorbing and scattering would rather be negligible provided that they don't cluster to some large agglomerates. To rule out the calibration problem, I would re-measure the spectrum of cuvette with pure solven (water?) without CNTs, is it zero? Otherwise, I'd play around with the concentration of CNTs and their dispersion. Are you sure, you have enough SDS? 2W ultrasonic power sound too small for me, why can't you increase it. You also should consider the size of the ultrasonic tip and the volume of your sample, because if the tip is too small, 2W power would produce no dispersing action at all.
Dear Roman,
Thanks.... I checked the water +SDS in absorption and it was zero. 2% SDS is reported to be enough... i should increase time of sonicate from 2h to 5h.... i can not increase the power since any increment in the power would break my CNT and the length of my CNTs are important for me.
i will check the results and let you know.
I really appreciate for your help.
masoud
Masoud, at which wavelenths those transitions are usually reported? Could you please give me a reference for ultrasonic damage to CNTs?
Roman, transitions were reported to be around 300, 500 and 800nm for instance paper entitled as :Simple and Scalable Gel-based sepration of metallic and semiconducting carbon nanotubes shows all type of transitions.
for ultrasonic damage "Ultrasound-Assisted SWNTs Dispersion: Effects of Sonication Parameters and Solvent Properties" is great paper .
http://pubs.acs.org/doi/abs/10.1021/jp101431h
Well, I don't have time to read the paper completely but isn't it correct that in the second one an ultrasonic processor of 750 W at 26% of full power was used? This is more or less 200 W, which is two orders of magnitude higher than you try. If this is really the case, firstly, you can easily increase the power at least tenfold, and second, this is no wonder that your CNTs don't get dispersed.
Strong agglomeration may happen to be the reason why you cannot find transitions described in those papers like "Diameter grouping in bulk samples of single-walled carbon nanotubes from optical absorption spectroscopy" or "Optical Properties of Single-Wall Carbon Nanotubes"
I would also assume that the broad maximum measured is due to a broad range of particle sizes, which can be due to agglomerates, differences in length of the tubes or both.
Would be useful to have an information about size distribution and compare this to the literature you refer to.
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