You need to prepare GO solution by dispersion of GO in water using probe sonication beforehand. The concentration of GO must not too low and must be adequate for formation of thick and peel able GO film. Preparation of GO film can be accomplished using vacuum filtration of GO solution on nylon filter membrane with 0.02 micron pore size.

@ Zulhelmi Ismail

Thank you for your response.

We used an ultrasonic cleaner to disperse the GO in de-ionized water. After several days the GO was still dispersed in the solution. Is a probe sonicator really necessary?

We used a concentration of 4mg GO to 1 ml. Is there a better concentration to produce the thick and peelable film?

Our lab currently does not have .02 micron filters. Can the membrane be prepared with spin coating, drop coating, or spray coating? Other posts on this forum have suggested that spin coating can be used to produce free-standing membranes.

In your case, the application of probe sonication is not necessary since the suspended GO solution was stable from dispersing by bath sonication. As for the amount GO, i think that would be enough. However,the size of your film must be small for thick formation of film ( diameter membrane of 40 mm). Regarding the preparation method of membrane,i'm not sure. However, i would to make a correction here as the mentioned pore size should be actually 0.22 micron and not 0.02 ( sorry,my mistake there).

@ Zulhelmi Ismail

Thank you again.

We will try with .22 micron filters.

Zulhelmi Ismail

Thanks for your suggestions. We prepared a new batch of GO powder using Hummer's method, vacuum cleaned the powder with 10% HCl, sonicated the powder in DI water for 1 hour (4mg to 1mL), filtered the solution through a 300 um sieve, and then centrifuged the solution to separate out the unexfoliated graphite. Finally, we vacuum filtered 10 to 30 mL of the solution using .22um filters. We were able to produce good films on the filters using both MCE and nylon filters. (see the attached picture)

Our question is:

How do we now remove the GO films from the membrane filters?

It seems to have adhered too well to the substrate.

I'm afraid the amount of GO (4 mg/ml) may still not be enough for formation of peel-able GO film. Here a reference that might help you in the preparation of free-standing GO film. In this reference, the used concentration of GO is 60 mg in 1 ml.

Article Preparation and characterization of graphene oxide paper

Zulhelmi Ismail,

I read the paper you suggested. From the methods section:

"Graphite oxide was synthesized from purified natural graphite (SP-1, Bay

Carbon) by the Hummers method. Colloidal dispersions of individual graphene

oxide sheets in water at the concentration of 3 mg/ml were prepared

with the aid of ultrasound (Fisher Scientific FS60 ultrasonic cleaning bath) in

20 ml batches. Graphene oxide paper was made by filtration of the resulting

colloid through an Anodisc membrane filter (47mm in diameter, 0.2 mm pore

size; Whatman), followed by air drying and peeling from the filter."

It seems they used a 3mg/ml solution. Other papers I've read used 5 mg/ml, .33 mg/ml, and 1 mg/ml solutions to produce free standing films. Our 4 mg/ml solution should be similar to what has been used before.

Based on another reference, we tried to dissolve the MCE filter in acetone. It worked, but we are having difficulty in removing 100% of the MCE filter material (a thin film of MCE sticks to the GO membrane).

Note: We also prepared a GO membrane on a nylon filter. It has the same issue as the ones prepared on MCE filters--we cannot peel the GO film from the nylon filter.