# Silica Mesoporous Structures: Effective Nanocarriers in Drug Delivery and Nanocatalysts
## 4 Catalytic Applications of Mesoporous Silica Materials
### Removal of Organic Dyes  
Large amounts of toxic pollutants, including dyes and heavy metals, have considerable environmental consequences, so the removal of even small amounts of these hazardous compounds is crucial [93]. Many methods, such as separation [94], oxidation/reduction [95], ion exchange [96], adsorption [97], membrane [98], and biological [99] methods, have been developed by researchers over the past decade. Among these methods, the adsorption process is of great interest due to its greater efficiency and simplicity [100]. Organic dyes are dangerous sources of industrial wastewater and come from textiles, dyestuffs, papers, plastics, and cosmetics. Their presence in water endangers humans and plants [101]. For example, Sudan Red (RS) and its derivatives have high levels of toxicity and carcinogenicity, even at low concentrations. Considering that most organic dyes have aromatic structures, they are resistant to dye-removal reactions, although their toxicities are reduced during such reactions [102]. A large number of nano-adsorbents, such as active carbon [103], zeolite [104], nanoclay [105], and an imprinted molecular polymer [106], are used to remove organic dyes from aqueous solutions but have a low adsorption capacity. Therefore, it is necessary to find novel nano-adsorbents that will eliminate the effects of these contaminants and control them at maximum adsorption capacity. To date, nanostructures have been shown to be superior at removing toxic and harmful organic dye compared to other adsorbents, which has made them extremely valuable. Mesoporous materials are one of the most extensively investigated silica nanomaterials because they are excellent adsorbents due to their high pore volumes, large surface areas, and adjustable pore sizes [107]. Like any other absorbent materials, silica nanoparticles can serve in the effective removal of organic pollutants, e.g., methylene blue (MB) [108], methyl orange (MO) [109], methyl red (MR) [110], malachite green (MG) [111], and everzol blue (EB) [112].  
Mesoporous materials can be good candidates for this purpose because they have large surface areas, adjustable cavity sizes, and very high adsorption capacities [107]. The modification and functionalization of mesoporous materials via various functional groups, such as--NH\({}_{2}\), COOH,  
Figure 2: The role of acidic and basic catalysts in the sol-gel process used for the preparation of mesoporous materials.  
and SH and their placement on active sites result in the easy removal of dye pollution [113]. [PERSON] et al. reported high catalytic activity on the part of magnetic silica nanoparticles in reducing the organic dyes 4-nitrophenol (4-NP), rhodamine B (RhB), and MB (Figure 3) [114].  
In another study, [PERSON] et al. reported on the synthesis of the SBA-15/polydopamine (PDA)/Ag nanocomposite [115]. They showed that the tested nanocomposite degraded 4-NP and MB without decreasing its catalytic activity (Figure 4). [PERSON] et al., removed acid blue 25 and MB using modified MCM-41 with amine and carboxylic acid groups, respectively. Their results showed that there are base-acid interactions between these dyes and the modified mesopores with absorption capacities of 256 mg g\({}^{-1}\) (acid blue 25) and 113 mg g\({}^{-1}\) (MB) [115].