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(C(16)TMAB/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/C(16)TMAB=1.5 and T≥40°C and shows pH-dependent morphology. It has uniform pore size ～9 nm, homogeneous sheet thickness in the range of 60-300 nm and dimension of several microns. We studied in details the structure and morphology of the SBA(⊥) with variation of three experimental parameters: the SDS/C(16)TMAB ratio, the temperature, and the pH condition in the synthetic gel. It is proposed that the mixed surfactants of SDS and C(16)TMAB 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 C(16)TMAB/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.