Less adsorption than the parent material was observed at the relative pressure lower than 0.01 indicating the decrease in the external surface area. The mesopore condensation of all silylated samples shifted to the lower relative pressure and the height before the flat steps of condensation was lower than that of the parent RH-MCM-41. It could possibly be that the insertion of silylating agent was the factor not only blocking the pore mouth but also the surface inside the channel. The
concentration and aging time had affects on the external surface area and mesopore volumes. For example, T9-24,
D9-24, and P9-24 had lower amount of adsorption amount than T1-1, D1-1, and P1-1, respectively. The most effect
was observed with the P9-24 sample. Moreover, the hysteresis was absent in some samples explaining the reversible adsorption occurring over the range. The decrease of adsorption volume at low relative pressure region indicated that pore entrances became narrower.