Abstract: Some embodiments of the invention include a method for preparing a carbon-containing membrane. The method includes preparing a carbon-containing solution and then washing and filtering the carbon-containing solution. The method further provides adding a volume of the washed and filtered carbon-containing solution to a receptacle that includes an aqueous solution. After a predetermined amount of time, the carbon-containing solution will equilibrate and form sheets of carbon-containing materials that float on a surface of the aqueous solution. The method further includes defining an aperture through at least a portion of a substrate and then inserting the substrate in the receptacle so that at least a portion of the carbon-containing sheets adhere to the substrate. In addition, the method further includes thermally treating the membrane to improve its molecular impermeability.