I exfoliate graphite by liquid phase exfoliation method. after synthesis the Dispersion is in liquid form. I normally use filtration method to find the concentration but I read some authors find concentration by using UV-Vis-Spectrometer.
My question is that how to find the molar absorptivity of the mixture of solvent to find the concentration of graphite that is dispersed as graphene in the solvent.
We first draw a Calibration curve as follows:
[I]A PVP[Poly(vinyl pyrrolidone) havingM.W: 10,000 g mol-1 is a linear homopolymer ofN-vinylpyrrolidone (VP) that is soluble in water and a number of other polar solvents.
[ii]A stock solution was prepared by magnetically stirring 10 mg/mL of PVP in the solvent[ used by you in your experiment] for 10 minutes. Stable graphene dispersions were prepared by adding 40 mg/mL of Expanded Graphite (EG) to the PVP solution. The EG was then mixed with PVP solution for the same amount of time. Make up the volume to 100mL in a clean/ dry measuring flask.
[iii]Take eight washed and dried test tubes(20mL capacity) and label them as 1,2,3-----8.
[iii] Add 10 ml of the solution in tube No:1. Assume this concentration to be one.
[iv] Similarly, add 9 ,8 ,7,6,5,4,3 ml* of the colored solution in the remaining seven tubes and make up the volume of each one these 7 tubes to 10ml by adding 1,2,3,4,5,6 and7 ml of deionized water respectively .These tubes have now different concentrations of the solution[0.9,0.8,0.7,.0.6,0.5.0.4.0.3],
[v] Now note the absorbance* of each one of these 8 tubes containing the colored solution at different molar concentrations with the help of the spectrophotometer using 660 nm .
[vi] Plot a graph between molar concentration {along X-axiz} and absorbance {Along Y-axis} to obtain the standard calibration curve.
[vii] Now take 10ml of the your solution( the one you want to know the ε ) in a clean/ dry 20mL capacity test tube and note its absorbance(A) at 660nm.
[viii] This point lies on Y-axis. From this point,draw a straight line which touches the calibration curve at a certain point. Now drop a perpendicular from this point on the X-axis .The point where it touches the X-axis gives the molar concentration(C).
[vii] Calculate the absorbance coefficient by dividing absorbance(A) by the corresponding value of molar concentration(C) as both of them are known from the the calibration curve.
ε= A/C.
*The samples are so diluted so that the measured absorbance is never above 2.
Dear Manohar Sehgal!
Thank you for your answer, My problem is that my dispersion is not very stable. Secondly , Could you plz email me the reference article of the mentioned method.
I am glad full to you.
[I] It is to bring to your kind information that the authors have given a number of methods to quantitatively determine graphite dispersed as graphene in paper[A] .
[II] The method to draw a calibration curve is commom in 90-95% of cases irrespective of their being Inorganic or Organic species such as Cr(III), Zn(II), MB( Methylene Blue etc. Of course, the solvent used to prepare their solutions and λmax( in nm) used to note absorption are different.
[III] The actual paper to be taken into consideration is[B] while paper [A] gives the methods of estimation; both have same authors
[IV] Let me try to answer your other question—“Does anyone have an idea of how to calcula-------” if you want to know the absorbance limits to graphine- it should be at the maximum two.
[A]Polymer-stabilized graphene dispersions at high concentrations in organic solvents for nano composite production.
Ahmed S. Wajid, Sriya Das, Fahmida Irin, H.S. Tanvir Ahmed, John L. Shelburne
, Dorsa Parviz Robert J. Fullerton , Alan F. Jankowski , Ronald C. Hedden , Micah J. Green [Page1-12] For absorption methos- look in page-5(bottom).
[B]Carbon Volume 50, Issue 2, February 2012, Pages 526–534.
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