# Metal-Organic Frameworks as Promising Textile Flame Retardants: Importance and Application Methods
## 4 Metal-Organic Framework
### Metal-Organic Frameworks for Flame Retardants and Their Mechanism  
Concern about the environmental impact of halogenated flame retardants has led to the development of new products to replace them, with a focus on environmental responsibility. In this context, MOF-based flame retardants have emerged as a new class of additives and have been the subject of several studies. Works by [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] [103]; [PERSON] et al. [104]; and [PERSON], [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] [105] review the application of organometallic materials for flame-retardum polymers.  
As mentioned above, flame retardancy is achieved by interfering with combustion at some stage of the process, and metal-organic frameworks comply with this principle. MOFs are capable of creating metal oxides on their surface during the thermal decomposition phase; this layer serves as a protective coating, preventing the associated material from continuing to combust. It is worth noting that the porous configuration of the MOFs is capable of efficiently capturing smoke nuclei and particles, thereby reducing the density of the smoke in the polymer matrix [106; 107]. In addition to providing a physical barrier and capturing particles, these materials can perform the gas-dilution mechanism. When they  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Method** & **MOF** & **Composition** & **Functionality** & **References** \\ \hline Direct synthesis & Cu-BTC & Cotton, Linen and Silk & Insect repellent & [79] \\ Direct synthesis & MIL-68(In)-NH\({}_{2}\) & & Cotton and Silk & UV protection & [80] \\ Direct synthesis & HKUST-1 & Wool & Antibacterial & [83] \\ Dip–pad–dry & ZIF-8 & Polyester & & Odor adsorption and \\ Dip–pad–dry & Uio-66 & Cotton & Fire safety and UV protection & [45] \\ Direct synthesis & UiO-66, UiO-66-NH\({}_{2}\), & & Cotton & Arsenate adsorption & [91] \\ Dip–pad–dry & ZIF-8 e ZIF-67 & Cotton & Adsorption of pollutants & [97] \\ Direct synthesis & Cu(BDC) & Polyester & Antibacterial & [77] \\ Dip–pad–dry & ZnO derivado de MOF & Cotton & Photocatalytic and antibacterial activities & [98] \\ Direct synthesis & Ln-MOF & Viscose & Self-cleaning & [99] \\ Direct synthesis & MOF-derivado Ni3S2@C & Cotton & Electrode potential & [100] \\ Direct synthesis & ZIF-8 & Cotton & Absorption of acid dyes & [101] \\ Direct synthesis & MOF-199, MOF-74, & & Cotton & Antimicrobial & [102] \\  & MOF-5 e MIL-53 & & & \\ Direct synthesis & MOF Zr4+ & Cotton & Removal of toxic oxyanions & [7] \\ \hline \hline \end{tabular}
\end{table}
Table 3: Methodologies used to functionalize textiles.  
combust, they produce non-flammable gases, which reduce the concentration of flammable gases by diluting them. Both mechanisms interfere with the amount of fuel available, whether in physical or gaseous form, thus reducing the release of heat [103; 105; 108; 109].  
The transition metals zirconium and zinc are examples of compounds capable of forming layer of carbon from oxides. Classified within the typical MOFs [110], ZIFs (ZIF for Zeolitic Imidazole Framework) and UiOs (UiO for University of Oslo) are MOFs that feature zinc and zirconium nodes, respectively, and are known for their thermal, hydrothermal and chemical stability, being the target of several studies in the incorporation of flame retardant polymeric matrices. Figure 3 shows the schematic scanning electron microscopy (SEM) images of the structure and junctions of the metal nodes (SBUs) of the ZIF-8 and Uio-66 MOFs.  
Cellulose is a biopolymer found in cotton fibers. Despite its properties such as absorbency, light weight, stability, and chemical simplicity, the use of cotton fiber is limited due to its high flammability. Given the high performance and effectiveness of MOFs in polymeric matrices, the potential benefits of incorporating these compounds into cotton fiber textile substrate are increasing.