# Nanomaterials in Photocatalysis: An In-Depth Analysis of Their Role in Enhancing Indoor Air Quality
## 9 Metal-Organic Frameworks  
Metal-organic frameworks (MOFs) represent a unique class of materials composed of metal ions or clusters coordinated to organic ligands, forming a highly porous three-dimensional structure. Their exceptional surface area, tunable pore sizes, and chemical versatility make them highly attractive for various photocatalytic applications. The porous nature of MOFs allows for the efficient adsorption of reactants, while their intrinsic properties can be engineered by altering the metal centers or organic linkers, enabling tailored photocatalytic performance [203]. Research on MOFs started in the 1990s when researchers synthesized highly porous materials like MOF-5, developed by [PERSON] in 1999. The focus during this period was primarily on their gas storage and separation capabilities. However, the highly ordered structures and tunable pore sizes of MOFs hinted at their potential for other catalytic processes, including photocatalysis. A breakthrough occurred when researchers identified the potential of using organic ligands in MOFs as light-harvesting centers. By tailoring the conjugation of the ligands or incorporating metal-organic chromophores, MOFs could be engineered to exhibit strong visible light absorption, expanding their utility in solar-driven processes. Metal-Organic Frameworks (MOFs) can exhibit photocatalytic properties, but their intrinsic efficiency often requires enhancement through functionalization. Certain MOFs, particularly those with metal centers like Ti [204], Zr [205], and Fe [206] and organic linkers capable of absorbing UV or visible light, can act as photocatalysts on their own; however, they are typically limited by the rapid recombination of electron-hole pairs. To improve their photocatalytic performance, MOFs are commonly functionalized or modified. Techniques include doping with metals or non-metals, such as Ti or graphitic carbon nitride [207], to enhance light absorption and facilitate electron transfer, or incorporating semiconductor nanoparticles like TiO\({}_{2}\)[208] or ZnO [209] to utilize their photoactive properties while retaining the high porosity of MOFs. Additionally, modifications to organic linkers can extend light absorption toward the visible range and introduce active sites for desired reactions. In essence, although MOFs have inherent photocatalytic potential, functionalization is frequently necessary to maximize their efficiency and make them more competitive with traditional photocatalysts [210]. The potential applications of MOFs in photocatalysis are diverse and promising. They have been extensively studied for environmental remediation [203], particularly in the degradation of organic pollutants and dyes under visible light [211]. Additionally, MOFs are being explored for hydrogen production [212] through photocatalytic water splitting and for carbon dioxide reduction into useful chemicals, offering a pathway to address global energy and environmental challenges. Recent advancements in the synthesis and functionalization of MOFs have expanded their applicability, making them a compelling choice for future photocatalytic technologies. As research progresses, MOFs are likely to play a significant role in developing sustainable photocatalytic systems for various industrial and environmental applications (Table 4). When compared to competitor photocatalytical materials, MOF possesses a higher surface area (up to 7000 m\({}^{2}\)/g) and porosity, allowing for enhanced adsorption of reactant molecules. Moreover, their modular design allows for better control of bandgap, light adsorption, and overall catalytic activity. This means that, for example, MOFs can be engineered to absorb visible light by incorporating photoactive organic ligands or metal centers, making them highly efficient for solar-driven photocatalytic processes or that they can be tuned to target specific pollutants or be focused on the conversion of CO\({}_{2}\).