My group makes activated carbons, typically using KOH as an activating agent. We employ an extensive washing process following synthesis, involving stirring in 10% HCl, followed by filtration and washing in deionized water until the supernatant is neutral (usually using approx. 4 L for a 0.07 g sample).

Previously this procedure was sufficient to remove inorganic matter from the structure i.e. potassium salts. However, recently members in the group have found that it has become less effective. XRD analysis indicates that the retained material is likely to be the afforementioned potassium salts. Changes in procedure such as increasing HCl concentration, temperature of wash, increasing water volume used in final washing step, and washing with hot EtOH appear to have no significant effect on the cleanliness of the samples. I find it unlikely that this change in results is due to procedural slopiness as it appears to be a problem throughout the group.

Has anyone developed a procedure that reliably removes inorganic material from porous carbons?