Surface Modification of Activated Carbon and its Effects on Methane Adsorption

In this work, one activated carbon (AC) was modified with H2O2, (NH4)2S2O8 saturated solution and H2SO4/(NH4)2S2O8 mixture respectively. The oxygen groups on ACs surface were characterized by Boehm titration. The textures of the ACs were investigated by N2 adsorption at 77 K. The influence of surface oxygen groups on methane adsorption on ACs has been studied. The results of Boehm titration showed that the concentration of acidic oxygen functional groups on the AC surface increased after modification. N2 adsorption data showed that the specific surface area SBET and the micropore volume Vmic of AC were changed lightly after modification. It was observed that there was, in general, a positive correlation between the methane saturated adsorption capacity and the SBET of ACs while a negative correlation between methane saturated adsorption capacity and the total surface acidic groups. The methane saturated adsorption capacity was determined by the ACs surface chemistry when the microporosity parameters of two samples were similar. AC with a higher amount of oxygen surface groups, and consequently with a less hydrophobic character, had lower methane adsorption capacity.