Pore ordering in mesoporous matrices induced by different directing agents

TL;DR

This study investigates how different structure directing agents and catalysts influence pore ordering and size in mesoporous silica particles, revealing that surfactant type and catalyst choice significantly affect porosity and thermal stability.

Contribution

It provides a comparative analysis of the effects of various surfactants and catalysts on pore structure and stability in mesoporous silica synthesis.

Findings

Surfactant type controls pore size.

NaOH catalyst results in smaller porosity.

Heat treatment destroys ordered structure.

Abstract

Mesoporous silica particles of MCM-41 type were synthesized by sol-gel method from tetraethyl orthosilicate (TEOS) in 2-methoxyethanol and deionized water mixture in base conditions at room temperature. Ammonia or sodium hydroxides were used as catalysts and cetyl-trimethylammonium bromide (CTAB) and n-dodecyl-trimethylammonium bromide (DTAB) as structure directing agents. The porosities and the ordered structure have been analyzed using transmission and scanning electron microscopy, small angle neutron and X-ray diffraction, nitrogen adsorption, thermal analysis and FTIR spectroscopy. The samples consist of spherical particles of sub-micrometer size, with radially arranged pores. The comparison of the effect of the different surfactants and catalysts shows that by varying the surfactant type and their proportion, the pore sizes can be controlled. As compared to the commonly used ammonia catalyst, the use of NaOH as catalyst results in a much smaller porosity of the as-prepared materials. These materials are not resisting to the heat treatment at 700 C used for the template removal, and the ordered porous structure is completely lost.