Activated carbons (ACs) with different amounts of acidic functional groups and similar porous structure were prepared by oxidation with nitric acid, followed by outgassing at 500 degrees C and 900 degrees C. Desorption profiles of nitrobenzene (NB) were examined for NB pre-adsorbed ACs using differential thermogravimetric (DTG) analysis to inspect adsorption sites on ACs. Two peaks were observed in DTG profiles for ACs with acidic functional groups, whereas only one peak appeared for AC without carboxylic and lactonic groups. The DTG peaks observed around 100 degrees C and 160 degrees C could be assigned to desorption of NB adsorbed on pi-electrons of graphene layer via pi-pi interactions, and on acidic functional groups via electro static interactions, respectively. This implies that pi-pi interactions are stronger than electro static interactions for NB adsorption.