Mesoporous silica SBA-15 sheet with perpendicular nanochannels

Free-standing thin sheet form of mesoporous silica materials with perpendicular orientation is a much desired materials for its possible applications in catalysis, mask, and separation. A three component amphiphile system of sodium dodecyl sulfate/hexadecyltrimethylammonium bromide/pluronic-123(C₁₆TMAB/SDS/P123) was employed to template the condensation of sodium silicates for the formation of SBA(⊥), a thin sheet of SBA-15 with perpendicular nanochannels. SBA(⊥) can be synthesized at SDS/C₁₆TMAB=1.5 and T≥40°C and shows pH-dependent morphology. It has uniform pore size ~9nm, homogeneous sheet thickness in the range of 60-300nm and dimension of several microns. We studied in details the structure and morphology of the SBA(⊥) with variation of three experimental parameters: the SDS/C₁₆TMAB ratio, the temperature, and the pH condition in the synthetic gel. It is proposed that the mixed surfactants of SDS and C₁₆TMAB form catanionic vesicle in which the P123 and silicates are condensed. The balanced interaction of P123/silicate with the narrow confinement under surfactant bi-layers of C₁₆TMAB/SDS promoted the formation of perpendicular nanochannels. Low temperature and pH conditions favor stronger segregation of the PPO and PEO-oligosilicate segments in the SBA(⊥) structure which gives the basis of thickness control of the sheet. The control of structure and morphology are discussed with modern theory of microphase separation in block copolymers under confinement.