results from our previous study.22) The treatment with diluted sulfuric acid did not influence pore struc- ture, because the BET surface area and total pore volume hardly changed by the treatment with diluted sulfuric acid. In the study by Maruyama et al.,21) the BET surface area and pore volume decreased due to the loading of many acidic functional groups by the liquid phase oxidation using (NH4)2S2O8. However, in this study, a few acidic functional groups were loaded and the BET surface area and pore volume hardly changed due to using diluted sulfuric acid as a weak oxidizing agent.