Design strategies for charge reversal and temporally regulated functionalities in porous and non-porous systems

Abstract

In the last few decades, tremendous advances have been made in synthesis of ordered porous solids with controlled pore size, shape and regularity of the pores.1-5 Among them, ordered mesoporous silica stands out due to their high surface area, ease of synthesis and chemical modifications, high thermal stability and bio-compatibility.6- 10 Mesoporous silica is generally synthesized via organic-inorganic assembly of amphiphilic surfactants and silicate species (produced by base or acid catalysed hydrolysis of silane precursors, tetraalkoxysilane). The amphiphilic surfactants act as structure directing agents or templates. After the condensation of silicates species around the superstructures formed by surfactant molecules (template), the solid mesoporous silica can be obtained by removing the template (via calcination or ion exchange or simple washing).11-12 The term surface engineering in the context of mesoporous silica is primarily associated with controlling the parameters like pore structure, pore philicity and surface charge. Since, these parameters define the mass transport through the mesopores, it is necessary to optimise them for their applications in drug delivery10, 13-16, sensing17, catalysis18-19, bio-mimetic channels20-21 etc. This chapter highlights various strategies adopted such as gating, incorporation of receptor molecules, philicity and surface charge modifications to regulate the mass transport in mesoporous silica.