I am trying to evaluate MWCNT nanofluid (NF) stability by measuring absorbance by UV vis, however since the concentration I am interested in leads to an opaque solution, I get absorbance higher than the max recommended for UV measurements (I get around 5). Is there is any why to come around this without changing concentration? , would decreasing cuvette path length solve the problem?
Dear mohamad,
As you mentioned you have a dilute solution of CNTs, you have to get very low absorbance. some issues to check for your problem:
1: check the wavelength you are measuring, maybe you are considering the wrong wavelength for your study. at some border line wavelengths the absorbance is usually high.
2:if the above point is OK, check your instrument with an standard or other solution that you know to have a definite range of absorbance
about your last question : changing the cuvette path length wouldn't solve your problem, your problem is somewhere else !!
best...
Dear Mohamed,
Do you have the absorption spectrum even saturated to the maximum absorbance of your spectrophotometer, so it can help us to identify the problem?
Reducing the optical path for the same concentration of solution, it could help. However, the way you recorded the spectra, it is very important.
Best
Xuhua
@Behzad Behnam
Thanks for your response
Regarding the first point, I had checked the whole spectrum from 200 to 1000 nm and selected the wave length crosponding to max absorbition which was 320 nm.
For second point, I checked it and the instrument and it showed acceptable results for other samples.
For path length, wouldn't less path of uv ray reduce amount of absorbed and scattered beam leading to less absorbance for the same sample.
Thanks
@Xuhua Wang
Thanks for your response
Regarding saturation, The same problem occured for different sample concentration, the lowest absorbance I got was 2.5 at a concentration 100 less than the max concentration I have tried, does this eleminate saturation possibility? If not please recommend how to check it.
Regarding recording spectra, I record absorbition crosponding to max peak, is there any other method to do the same thing.
Thanks
Dear Muhamad,
The best way to avoid the problem is to record a transmittance spectrum of your sample against air. What I meant is to do the baseline leaving both sample beam path and reference beam path empty (nothing there). Then measure the solvent or liquid which is used to disperse MWCNTs. After that, measure your samples. Please make sure all solvent or samples which are put into the sample beam and leave the reference beam empty. The absorbance can be manually calculated using A=-log (Ts/Tr). The Ts and Tr are transmittance of your sample and transmittance of your solvent, respectively. If you want to monitor the stability of your dispersed CNT solutions, you had better to monitor the transmittance spectra of your samples. Hope it helps.
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