# Silica Mesoporous Structures: Effective Nanocarriers in Drug Delivery and Nanocatalysts
## 4 Catalytic Applications of Mesoporous Silica Materials
### Organic Synthesis  
#### 4.2.1 Oxidation Reaction  
In mesoporous materials, the transition metal is grafted onto the framework to introduce redox properties, which are devoid of oxidant activity. Some transition metals could be introduced to occupy the vacant positions within the mesoporous silica framework.  
[PERSON] et al. synthesized tungsten-containing functionalized MCM-41 and employed it in the desulphurization reaction of dibenzothiophene (DBT). The results established that the mesoporous structures were well-preserved after the introduction of the tungsten species into the mesoporous materials [116]. These materials showed a good dispersion of the W species and formed an efficient and highly recyclable catalyst for the removal of dibenzothiophene (Figure 5). The characterization results showed that the mesoporous structure of MCM-41 was maintained after the introduction of the W species. These catalysts showed homogeneous dispersions of the W species in the mesoporous material and excellent catalytic activity in the removal of sulphur-containing compounds. The sulphur content in model oil can be reduced from 500 to 0 ppm with the low usage of an oxidant in 30 min. In the reaction, no organic solvents were added as extractants, and the mesoporous elements  
Figure 4: The removal of organic acid blue 25 and methylene blue (MB) via the SBA-15/PDA/Ag nano-adsorbent.  
Figure 3: The reduction of 4-nitrophenol (4-NP) and rhodamine B (RhB) using the magnetic Fe\({}_{3}\)O\({}_{4}\)/SiO\({}_{2}\)-Pr-SH-Ag nanocatalyst.  
of W-MCM-41 acted not only as adsorbents to absorb the sulphur-containing compounds but also as active sites to activate H\({}_{2}\)O\({}_{2}\) to oxidize the sulphur compounds and convert them to sulphones. The oxidative reactivity of the sulphur-containing compounds decreased according to the following order: 4,6-DMDBT (4,6-dimethyldibenzothiophene) > DBT > BT (Benzothiophene) > DT (Dithiophene). In addition, it was possible to recycle the oxidation system nine times without a significant decrease in activity. Moreover, according to the GC-MS analysis of the oxidation products, a mechanism was proposed for the investigation of the absorptive oxidation process occurring between W-MCM-41 and sulphur-containing compounds [116].  
Also, [PERSON] et al. reported the solvent-free oxidation of benzyl alcohol to benzaldehyde by iron-chloride immobilized on SBA-15 (SIL-FeCl3) (Figure 6). The SIL-FeCl\({}_{3}\) revealed higher catalytic activity in terms of the effective solvent-free oxidation of benzyl alcohol to benzaldehyde when using the oxidant. This mesoporous catalyst was easily recovered and reused without a significant loss in its activity and selectivity, leading to its potential application in an _eco_-friendly synthesis of chlorine-free benzaldehyde [117].  
Furthermore, [PERSON] et al., reported a novel-sized Pt-decorated SBA-15 rod catalyst functionalized with the tetrakis (hydroxymethyl) phosphonium chloride group (THPC) as both a stabilizer and  
Figure 5: The desulphurization reaction of dibenzothiophene on W- MCM-41 (Mobil Composition of Matter No. 41) mesoporous silica.  
Figure 6: The oxidation of benzyl alcohol to benzaldehyde on Santa Barbara amorphous (SBA)-15 (SIL-FeCl\({}_{3}\)).  
reductant in the mesoporous catalysis of \(n\)-hexane through a facile synthesis method under oxidation, having observed excellent stability and high activity (Figure 7) [118].