What use do you intend the PTFE membrane for? Filtration of carbon nanotubes again? Perhaps you may neutralize the acid with a base and rinse thoroughly and try... recyclability of a membrane is normally a challenging topic and the treatment depends on the application.

Thank you very much Clara Casado Coterillo, it is so kind of you. the solution is neutralized during centrifugation and washing cycles. it is an aqueous solution containing CNTs. after filtration MWCNTs are probably stuck in the pores of the membrane. now I want to use this membrane in another filtration step if possible

Hi! You have better to use them only once! Recycling is not totally succesful, because the pores of the membranes will be closed up by small pieces of CNTs. So it is very difficult to obstruct the whole surface of the membrane. Moreover, there is the possibility to damage it during the obstruction.

Dear Minas M. Styliankis

Thank you very much for your help, actually the "blocking" in membrane due to CNTs is part of my problem cause it leads to lower filtration efficiency.

Regards

if you want to use it for filtration of the same material then you can ultrasonicate  your PTFE membranes in Isopropyl alcohol. It reopens the pores mostly and makes it possible to use the PTFE membrane one more time. but more than that is not advisable. you should do this only if cross contamination is not an issue. 

Dear Ramaiyan Kannan

Thank you very much for your help

Regards