Review on Template Removal Techniques for Synthesis of Mesoporous Silica Materials

Abstract

The key step in the preparation of mesoporous silica materials is the removal of organic templates occluded inside the pores including nonionic, cationic, anionic surfactants and even ionic liquid (IL). The most common method to remove templates is conventional calcination under air at 550 °C. Although templates can be completely removed from the pores, calcination suffers many serious drawbacks including significant framework shrinkage, the collapse of the ordered structure, reduction of silanol concentrations on the pore wall (which are of high importance for postmodification), generation of large amounts of CO2 and organic amine compounds, the presence of carbon deposits or coke as a contaminant, elimination of organic functionalities (such as organoalkoxysilanes with amino groups), and the inability to recover or reuse expensive organic templates. That is why many attempts have been reported in the literature to develop novel methods for removing organic templates that are favorable from both economic and environmental standpoints for potentially large-scale applications. The current study reviews the recent development methods for template removal from various types of mesoporous silica materials. We have divided the template removal approaches into two categories: physical method and chemical method. The effects of those methods are discussed in detail on the textural and structural properties of mesoporous silica materials along with the template removal mechanism and their pores and coins.