Dear all,
Greetings. I purchased MWCNTs, which are >98% carbon basis, O.D. × L 6-13 nm × 2.5-20 μm(Sigma, cat no. 698849) and oxidised them using the method described by Thi Mai Hoa, 2018. A total of 100 mg of pristine MWCNTs is added into 20 mL of 4 M of HNO3 and 10 M of H2SO4 (1:3) and left stirring for 18 h at room temperature after which, it is coated with chitosan in 1% and 2% acetic acid as described by Sobh et al., 2019.
Previous papers have emphasised the importance of the oxidation step to prevent the aggregation of MWCNTs thus, I decided to conduct the dispersion assay as described by Singer et al., 2018 (in their paper,). A total of 20 mg of pristine, oxidised and coated MWCNTs were dispersed in 20 mL of water and sonicated in a waterbath for 30 min followed by an hour of sedimentation. The mixtures were observed over a week. Based on my observation, the pristine MWCNTs sank to the bottom after 24 h. However, the oxidised MWCNTs also appeared to be settling after 48 h (as observed in the picture). The MWCNTs coated with chitosan appeared the same from Day 1 (Picture labelled 1 h).
How important would the oxidation step be in this case? Would it be safe to utilised the coated MWCNTs since it shows no signs of settling? I've attached some pictures from the first hour and a week after sonication. I would appreciate your feedbacks or recommendations. Thank you.
Sulin Choo
The settling tells you that the particles are in the micron+ size range - probably tens of microns. Such a system isn't stable probably from a zeta potential aspect after the oxidation process. The non-settling system is obviously stable. In order to stabilize the system that is settling I'd look for a pH change. Take a look at this webinar (registration needed):
Dispersion and nanotechnology
https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W190528DispNanoMat
Pay close attention to slides 27 onward.
oxidation not only will affect settling properties but also others. So you should start thinking from the end. Coated with chitosan might also mean that polymer is left in aqueous phase increasing the viscosity slowing down settling.
Use surfactants such as SLS, CTAB for proper dispersion. Regarding the use of chitosan refer my work Article Effect of Chitosan Surfactant Concentration on the Thermal C...
Hi Dr. Titus Sobisch, Thank you for your reply. As I'm planning to work on the chitosan coated MWCNTs, I was wondering if the initial oxidation step would be considered a problem (since the chitosan coated MWCNTs seems stable based on the nonsettling)? I've checked the chitosan coated MWCNTs with FTIR and TEM, both of which indicate that the MWCNTs are coated.
Hi Abhilash Kumar Tilak, thank you for your reply. I am planning to utilise the MWCNTs as a drug carrier. Previous literatures indicate that chitosan is the most appropriate polymer to load my drug. Utilising other surfactants would be quite tricky as it would probably require a drug that has a functional group, which would enable it to covalently bond to the MWCNTs, if I'm not mistaken, but I can't do that with my compound without inactivating it, unfortunately.
If the effect of MWCNT on rate is assessed, the sample will be abruptly released in the early stages (~ 1 hour), but subsequently the rate will be reduced, showing a sustained release.
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