Chemical activation by KOH and NaOH of carbon materialswith different crystallinity

摘要

Chemical activation with KOH or NaOH is a promising method to prepare activated carbon materials. Both hydroxidesrnpresent different behaviours as activating compounds when carbon materials with different crystallinity are used. In order torndetermine the effect of the crystallinity, the activation of a graphite, carbon fibres obtained from coal tar pitch andrnpolyacrylonitrile based carbon fibres was studied. XRD patterns show that the graphite has a high crystallinity, the PANrnbased fibres present a certain order of the graphene layers and, finally, the carbon fibres obtained from pitch show the lowestrnstructural order. NaOH develops more porosity in samples with lower crystallinity. KOH gives higher values of porosity inrnmore crystalline because its ease to form intercalation compounds. The strong influence that the crystallinity of the samplernhas on the activation process confirms that it occurs via a solid (carbon)-liquid (hydroxide) reaction and hence the carbonrnmaterials become more difficult to be activated when the crystallinity increases. The graphite can not be activatedrnsuccessfully by chemical activation, the porosity obtained is the same as the raw material. The present work shows that thernnature of the hydroxide is an important variable and that usually, the micropore size distribution obtained with KOH isrnnarrower than for NaOH, specially for high ratios of chemical activating agent to carbon sample.