Engineering of hybrid nanoreactors; a promising porous materials for green organic transformations

Engineering of mesoporous silica has emerged as a nanoreactor in various fields, especially in material chemistry, industerials and medicine [1-2]. As our ongoing research interest in the development of catalytic applications of mesoporous silica materials [2], we recently discussed and reviewed organocatalysts which are supported inside the mesopores [3]. Herein, we aimed to review recent advances in the catalytic applications of sulfonic acid-based mesostructures and metal-organic frameworks as nanoreactor (Figure 1) in a comprehensive paper. Fig 1. Reactor and Nanoreactor. Primary reports on sulfonic acid-based precursors go back to 1998 [4], in which the earliest versions of SAPs in mesoporous silicas were prepared by two general routes: 1) post-functionalization of mesoporous silica with 3-mercaptopropyltrimethoxysilane (MPTS) (M1) and 2) co-condensation of MPTS and silica source, specifically tetra-ethyl/methylorthosilicate (TEOS and TMOS, respectively) (M2). Here, the final key step to produce SAPs was to oxidate the thiol groups to sulphonic acid using H2O2. Generally, four methods have been developed for preparation of SAPs and functionalization of mesoporous silica materials which are depicted in scheme 1. So far, many developments had been performed by various research groups [5]. For instance, enhancing the capacity of MPTS loading by coating method [6], co-condensation method by using TMOS rather than TEOS [4], replacing calcination with extraction [7]. Most of the sulfonic acid based silica mesopores (SASM) were primarily employed in biomass production [4-7].