In functionalizing MWCNTs using HNO3, I used vacuum filtration with a PTFE membrane but in a couple of seconds the solution stopped passing through the membrane and the rate became almost zero. I know that this blockage of membranes with CNTs is common in this sense but would you please help me how to overcome this problem?
let the solution decant and filter the top half then slowly filter the rest. Its is time consuming but its the best way. Let me know how it works
Have you tried high speed centrifugation? Maybe a majority of the carbon nanotubes can be settled down and filtration of the supernatant will be faster.
Thank you Srikanth and Zhiyong for your heelp, I actually did that. after acid treatment the sample was centrifuged 3 to 4 times in 3500 rpm and then the supernatant was decanted. The amount that was filtered at last was about 10 ml of solution containing MWCNTs. As soon as the vacuum pump started working and I poured the solution it passed through very fast at first and then it stopped, forming a paper of black precipitate on top. Is this the end of the experiment? Then how would I be able to rinse it to reach neutral pH. I was thinking to add some more centrifugation, washing cycles to neutralize and then filter the residual solution. Is that logical?
Have you activated the PTFE membranes? I used to add a small amount of con.HNO3 first after switching on the vacuum pump before adding the CNT dispersion. It is anyway a time consuming process but the acid activation has helped me to get it quicker. If you are filtering a small volume, use a pipette and add them slowly in such a manner that the entire filter paper is not covered at any point of time. This procedure needs you to stay there for longer periods but helps in getting it done quicker.
Now to bring it to neutral pH it is tricky. Once filtered dispersing it again is tough. I would centrifuge and disperse it in water or NaOH solution to attain neutral pH and then filter it. Adding NaOH actually worked wonders for me the solution reached neutral pH in 3 - 4 washes. I hope it helps
Thank you very much Ramaiyan Kannan
It is great that I can use your experiences.
in case of PTFE activation, I immersed in ethanol. According to what I have read in membrane user guides, PTFE should be washed with ethanol or methanol to make it hydrophilic. I don't know whether if immersing PTFE in ethanol is efficient or not? Do you have any idea about wetting PTFE? Does Con HNO3 makes it hydrophilic?
Regards
Dear Srikanth Ammu
Thank you very much. I will do the neutralizing process as you mentioned, it is the most convenient way I suppose
Regards
Hi guys,
I am also trying to filter acid treated carbon nanotubes. Once I wash the nanotubes on the membrane with watee, the nanotubes go straight through the membrane into the filtrate. I am using a hydrophobic 0.6 um membrane. What do you think is the problem?
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