Hello, I'm really curious about if filter papers are affected or damaged by stronglyl acidic solution.
I'm handling GO usually. In the process of making GO, I usually use a centrifugation to increase pH to attain netural state.
But, there is limiation for me to be able to make it in neural state in a short time.
That's why I was going to dilute it with a bunch of water and then filtered it with an 'advantec filter paper', but the problem is the paper doesn't work even though I find this paper efficient when I filter silica coated graphite made at a base state with the same size of GO mentioned above.
I think the only reason is a filter paper is influenced by pH.
am I right?
Yes. pH can affect the efficiency of the filter paper. Even some filter papers melt in some solutions.
Some filter papers have hydrophilic/hydrophobic property as well. So you should select the right filter paper. In my case when I was filtering CNTs after strong acid treatment, membrane filter work very well. I suggest, 1st you must remove the acid with centrifuge, subsequently wash with water and filter it. You have to do it for several time to make the pH neutral.
You can use rockwool filters or some chemical resistant filters like in the link below (if it is really necessary) in such cases. But in the case of GO preparation it is much easier to follow Muhammad advice (this approach I can recommend from personal experience).
http://www.sigmaaldrich.com/catalog/product/aldrich/z241598?lang=en®ion=CZ
In GO synthesis H2SO4 is usually employed. It dissolves common paper. On the other side yes, pH of the solution to be filtered should influence the efficiency of the filter, think about the electrical charges: more or less affinity with the filtering media and between the particles to be filtered their-selves can occur. It is wise to check the datasheet of manufacturers to select the better media. In the case you only have one type of paper then try previous neutralization as Muhammad suggested. In our case we rinse in the same Erlenmeyer, let settle the material, separate by decantation three times and finally centrifuge or filter in common paper (not whatman-like i mean).
The pH of GO can not be neutral if you do not proceed neutralization. It acts like weak acid. After you will make neutralization you will not obtain GO, but its salt (this is sometimes not mentioned). Functional -COOH groups on GO surface gives this material acidic pH (value depend on oxidation or one can simply say on C/O ratio - the more oxygen you have, the more COOH groups can be expected - theoretically). Even small amount of sulphur can be inconporated to the GO and bonded in groups like SO3H (it is sometimes writen approx. 1 %). But washing and centrifugation (or filtration) remove free acid (in case of using H2SO4 it removes free sulphuric acid which makes even in quite low amount dramatical pH decrease according to it pKa value - concentration of 0.x M has pH around 1, concentration of 0.0x has pH arround 2, concentration about 0.00x has pH 3 - again simplified). But what is important - GO without sulphuric acid can not affect your paper. In case of washing is not important how many times but with how much volume of water you have used for washing (simply calculate the residual concentration of H2SO4 in several dilutions steps and you will see if it is diluted enough).
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