Pore size control of highly ordered mesoporous silica MCM-48

The synthesis of highly ordered cubic mesoporous silica MCM-48 with tunable pore sizes in the range 1.6-3.8 nm is reported. Pore size control has been achieved by using (mixtures of) gemini surfactants, [CH3(CH2)(n)NMe2(CH2)(m)NMe2(CH2)(n)CH3](2+)2Br(-), of different average chain length (m = 12 and n = 15, 21) as a structure-directing agent and by hydrothermal restructuring at pH > 9 and temperatures > 100 degreesC. A mesoporosity index, M, is introduced to describe porosity features of periodic mesoporous silica (PMS) materials. M is shown to provide distinct values for high quality MCM-48 (M 0.34-0.35) and MCM-41 materials (M 0.29-0.31) and to sensitively indicate microporosity in mesoporous and macroporous solids. Surface silylation based on tetramethyldisilazane, HN(SiHMe2)(2), reveals different surface silanol populations in dependency of the pore size, and hence, of the surface curvature.