The interaction potential of an n-nonane molecule was calculated with the wall of slit-shaped graphitic micropores, with a width of 0.83 nm. The reason why n-nonane often blocks further adsorption near the entrance of micropores is discussed on the basis of the above calculation. Modification of the surfaces of activated carbon fibers (ACF) with titanium isopropoxide-triisostearate (TTS) enhanced markedly the low pressure adsorption of n-nonane at 303 K. This enhancement is associated with the quasi-equilibrium adsorption controlled by the micropore diffusion at the entrance of the micropore. A micropore filling mechanism is proposed in which the enrichment of n-nonane molecules near the hydrocarbon branches of TTS at the entrances of the pores accelerates the micropore-diffusion facilitating the attainment of the adsorption equilibrium.