Control of Pore Size in Mesoporous Silica by Incremental Surface Modification Using Tetramethyl Orthosilicate

Abstract

The pore size of mesoporous silica is precisely controlled by repeated surface treatment with tetramethyl orthosilicate (TMOS) and water. This surface treatment produces a silica monolayer by reaction between surface hydroxy groups and TMOS, and successive water treatment regenerates the surface silanol groups ready for further TMOS modification. This treatment method reduces the pore size of SBA-15 mesoporous silica incrementally by ca. 0.5 nm per treatment step, while preserving the original hexagonal pore structure.

Crystallization of Mesoporous Metal Oxides

“…A portion of the hydroxyl groups are dehydrated to form the silica layer, and some remaining hydroxyl groups reacted with TMOS provided in the next cycle. The optimum conditions for TMOS treatment depend on the amount of surface hydroxyl groups on the mesoporous oxides: a cycle of single supply of TMOS and water forms a silica monolayer on the sufficiently hydrated silica surface in a stepwise manner . However, the hydrophobicity of mesoporous Ta oxide , requires such severe TMOS treatment conditions for the formation of a silica layer.…”

Preparation of Crystallized Mesoporous Ta3N5 Assisted by Chemical Vapor Deposition of Tetramethyl Orthosilicate

“…Second, the CVD treatment enables us to tune the thickness of the silica layer and thus prevent complete filling of the mesopores. 22 As a result, the nitrogen source can continue to reach the Ta 2 O 5 inside the mesopores even after introduction of the "silica scaffold" by CVD. It is therefore expected that the TMOS-CVD method will prove preferable to the conventional silica backfilling method for the development of mesoporous Ta 3 N 5 .…”

“…The TMOS-CVD treatment has two purposes: First, the silica layer deposited homogeneously on the pore wall of the mesoporous Ta 2 O 5 serves as a scaffold against phase transition during nitridation of the mesoporous oxide. Second, the CVD treatment enables us to tune the thickness of the silica layer and thus prevent complete filling of the mesopores . As a result, the nitrogen source can continue to reach the Ta 2 O 5 inside the mesopores even after introduction of the “silica scaffold” by CVD.…”