Attenuation of Electron Transfer and Presence of Dispersant Role When Dispersing Multi-walled Carbon Nanotubes (CNTs)

Note: CNTs in some samples contain many impurities,  such as graphene polyhedral particles, amorphous carbon, and  catalyst particles. The optical absorption of these impurities is related to the spectrum  and is necessary  for quantitative evaluation of  the  background absorption, which is not possible in this case and quantitative analysis will be accompanied by errors  . The third problem is caused by the presence  of dispersant, which is dispersed when dispersing  CNTs, and  its presence causes confusion in the quantitative determination of the amount of  SWCNT in the state.

When  functional groups are covalently  attached to CNTs, the absorption peaks  are significantly weakened or even  disappear because the nanotube structure  changes  from some hexagonal SP2 structures to  parts of the SP3 structure  . NIR-VIS-UV absorption spectroscopy  has two important applications: the extent of covalent reactions  and selectivity towards  different nanosheets.  Non-covalent doping or molecular adsorption  provides valence electrons (P-doping ) or conduction band saturation  (n-doping).

These non-covalent interactions  can affect  the intensity of the absorption peaks  . When doped, electron donors such as (Cs, K) or electron acceptors  (-Br2 )  produce  very similar changes in the NIR-vis-UV spectrum  , both of which attenuate electron transfer.  Absorption spectroscopy  is used  to estimate the abundance of metallic and semiconductor species by comparing  the intensities of the corresponding peaks, since the position of these resonance peaks  depends on chirality and diameter. For  qualitative analysis, absorption spectroscopy is excellent because  it shows the overall composition of the sample;  however, quantitative evaluation depends on (m, n)  for several possible reasons  .

The ratio of extinction coefficients for metallic to semiconductor SWCNTs  has been reported  to be 0.352+, which should be independent of the separation method  or starting materials. However, the values  ​​of extinction coefficients of SWCNTs reported in  the literature are inconsistent and better measurement methods are still  needed to determine the extinction coefficients  of different (m,n) nanotubes. Secondly,  the strong π absorption in the short wavelength region causes  the resonant transitions to be indistinguishable.  In addition, the complexity of  peak overlap is problematic. As a result, the presence of a large number of SWCNTs with  different (m,n) of unknown abundance, together with  various errors associated with data analysis, makes it  difficult  to quantitatively assess the concentration of a specific (m,n) species  in the sample, and only approximate data are obtained.

Conclusion :

Multiwalled carbon nanotubes (CNTs) in some samples contain many impurities,  such as graphene polyhedral particles, amorphous carbon, and  catalyst particles. The optical absorption of these impurities is related to the spectrum  and is necessary  for quantitative evaluation of  background absorption  , which is not possible in this case and quantitative analysis  will be accompanied by errors. The third problem is caused by the presence of  dispersant, which is dispersed when dispersing  multiwalled carbon nanotubes (CNTs), and  its presence causes confusion in the quantitative determination of the amount of  SWCNT in the state.