# Metal-Organic Frameworks as Promising Textile Flame Retardants: Importance and Application Methods
## 4 Metal-Organic Framework  
By opening up opportunities for product development, the study of materials chemistry has become invaluable. Combined with nanotechnology, this can lead to innovation and the development of composites that add functionality to materials. Metal-organic materials, or metal-organic frameworks (MOFs), are defined as a coordination networks with organic ligands that have potentially empty cavities [61].  
The nomenclatures given to metal-organic frameworks are usually abbreviations that refer to the place or name of the institution where the material was originally synthesized, or even the type of material or the type of structure that is formed after synthesis, and this abbreviation is followed by an integer, which assigns a chronological order of discovery. Examples are MOFs known as MIL-n (MIL--Materiaux de I'Institut Lavoisier), HKUST-n (HKUST--Hong-Kong University of Science and Technology) or UiO-n (UiO--Universitetet i Oslo) [62,63].  
These compounds are formed by coordinating secondary building units (SBUs) with organic ligands. SBUs refer to metal nodes containing metal cations so that the nodes can be directly coordinated with organic ligands to form three-dimensional structures [64].  
Over the last two decades, studies have been conducted on MOFs with different metals and ligands. With this feature of using different metal ions, the structures can form numerous geometric shapes. Figure 1 shows the common formation of metal-organic frameworks from SBUs and ligands.  
These materials have properties that have been described as favorable, such as high porosity, large internal specific area, the presence of coordinately unsaturated sites, the ability to incorporate functionalities and active species, and the flexibility for different processes due to the combination of the metal and the organic networks [65]. Thermal stability, well-ordered structures, very low density, facile synthesis routes, and the ability to control pore size, shape, and functionality due to their structural and chemical diversity [66; 67; 68] are all relevant properties for various applications such as gas separation [69], purification [70], adsorbents [71], catalysts [15], sensors [72], and drug delivery [73].  
Pioneering work on MOF synthesis began in the late 1990s, and conventional methods for MOF synthesis mostly result in crystalline powders with crystallite sizes ranging from nanometers to micrometers [74]. In addition, an increasing number of studies have led to the development of new synthesis routes that aim to reduce the use of reagents or even produce them from waste depolymerization, such as the work of [PERSON] et al. [75], [PERSON] et al. [76], and [PERSON] et al. [77]. MOFs are mostly crystalline, have high porosity and are resistant to structural collapse after evacuation in the presence of adsorbate [78].  
Classified as finishes, MOFs aim to modify the textile surface to achieve a specific assigned functionality. Thus, the incorporation of MOFs into the fabric can provide specific applications in textile articles due to their mechanical stability, chemical stability, selectivity, and other properties mentioned. MOFs such as Ui0-66, ZIF-8, MOF-808, and HKUST-1 can impart specific properties that increase their attractiveness in technical textiles in the areas of gas and liquid waste treatment, gas storage, and even flame retardancy. Table 2 shows some of the functionalities obtained by incorporating organometallic structures into the textile substrate.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Functionality** & **MOF** & **References** \\ \hline Insect repellency & Cu-BTC & [79] \\  & MIL-68(In)-NH\({}_{2}\) & [80] \\   UV protection & MIL-125(Ti)-NH\({}_{2}\) & [81] \\   Pesticle Removal & UiO-66 & [81] \\   Photocatalytic effect & AI-PMOF & [82] \\   Antimicrobial & HKUST-1 & [83] \\ \hline \hline \end{tabular}
\end{table}
Table 2: Textile functionalizations from MOF.  
Figure 1: Formation of metal–organic frameworks from SBUs and ligands.