# Silica Mesoporous Structures: Effective Nanocarriers in Drug Delivery and Nanocatalysts
## 3 Factors in the Synthesis of a Mesoporous Material  
### Surfactant  
Generally, surfactants act as templates and have key roles in the syntheses of mesoporous materials. These surfactants can be divided into four groups, including (1) ionic surfactants, which contain sulphonated compounds with the general formula R-SO\({}_{3}\)Na and sulphated compounds with the general formula R-OSO\({}_{3}\)Na [62]; (2) cationic surfactants, which commonly contain alkali hydrophilic and methylammoniums such as CTAB (cethyltrimethylammonium bromide (C\({}_{16}\)H\({}_{33}\)N (CH\({}_{3}\))\({}_{3}\)Br)) and hexadecyltrimethylammonium (HDTMA)) [63]; (3) non-ionic surfactants, which, when dissolved in solvents, do not decompose into ions [64]; and (4) amphoteric surfactants, which exhibit characteristics of ionic and non-ionic surfactants simultaneously, e.g., phospholipids. Different aspects, such as chain length [65], chain structure [66], pH [67], being used as an electrolyte [68], and temperature [69], affect the efficiency of these kinds of surfactants. For instance, in order to prepare mesoporous materials for different purposes having pores of uniform size and with diameters larger than 5 nm, the active surface of Pluronic P123 (EO\({}_{20}\)PO\({}_{70}\)EO\({}_{20}\)) (a non-ionic surfactant), a three-dimensional polymer, can be used as a template in an acidic environment. The sizes of the pores and the wall thicknesses can be changed by enhancing the hydrophilic head of the surfactant [55]. [PERSON] et al. [69] developed a mesoporous core-shell with two modes using amphiphilic copolymers of (polystyrene-b-poly (acrylic acid), PS-b-PAA) and CTAB as co-templates (Figure 1). As can be seen in Figure 1, the PAA copolymer, by attaching to the CTAB micelles, initially creates the micelle composition. Then, the TEOS (tetraethyl ortho-silicate) is placed on the micelle composition. Subsequently, through the self-assembly actions of the CTAB and TEOS, a core-shell mesoporous material with a two-mode structure is obtained. [PERSON] et al. [70] have reported the synthesis of aminated-mesoporous particles with adjusted particle sizes. Contrary to findings in the previous work, the presence of ethyl acetate in an ammonia solution increased the amount of aminosilane connected to the mesoporous material greatly, while its ordered shape remained intact. Recently, gemini surfactants (GSs) have been investigated as versatile templates for the synthesis of silica mesopores. GSs have hydrophobic heads and interconnected spacers between or near the hydrophobic chains, allowing convenient aggregations in solution [70]. [PERSON] et al. used GS with 14-2-14 molecules to prepare hollow mesoporous silica (HMS) [71]. In summary, surfactants have essential roles in the polymerization of silicate species to form their respective mesoporous silicate nanoparticles. Self-assembly in solution produces desirable results for various applications.  
Figure 1: Synthesis of a silica mesopore using cetyltrimethylammonium bromide (C\({}_{16}\)H\({}_{33}\)N (CH\({}_{3}\))\({}_{3}\)Br) (CTAB) and (polystyrene-b-poly (acrylic acid) (Ps-b-PAA) as amphiphilic.