# Nanomaterials in Photocatalysis: An In-Depth Analysis of Their Role in Enhancing Indoor Air Quality
## 6 Carbon-Based Nanomaterials
### Graphene  
Recently, graphene has gained significant attention in photocatalytic oxidation for the removal of pollutants. It has been demonstrated that graphene possesses excellent adsorption capacity and can extend the light absorption range, thereby enhancing the photocatalytic activity of TiO\({}_{2}\)[90]. Graphene has a high affinity for pollutants, particularly polar volatile organic compounds (VOCs), along with a large surface area, chemical and thermal stability, and a robust pore structure. Due to its electronically conductive two-dimensional structure, graphene acts as a sink for accepting and transporting photogenerated electrons to the photocatalyst. The conduction band energy of most semiconductors is typically more negative than the low Fermi level of graphene (E = \(-0.08\) V) [164]. Consequently, when graphene is coupled with a semiconductor, photogenerated electrons are rapidly transferred from the conduction band of the photocatalyst to graphene. Additionally, graphene exhibits high charge carrier mobility, allowing electrons to move swiftly [165]. This characteristic makes graphene an effective electron acceptor and mediator, reducing charge carrier recombination and enhancing photocatalytic activity [166].  
Recently, graphene-derived materials such as graphene oxide (GO) [167] and reduced graphene oxide (rGO) [168] have been studied for their advantageous properties. Unlike hydrophobic graphene, GO contains functional groups, including carboxyl (COOH) and hydroxyl (OH), enabling efficient interaction with various compounds through covalent [169] and non-covalent bonding [170]. The band structure of GO is linked to its degree of oxidation and can be altered using different synthesis methods. rGO is prepared by chemically or thermally treating GO to remove surface functional groups, resulting in a material with a high surface area and a significant affinity for non-polar VOCs due to its hydrophobic nature. rGO can also be modified to increase its pore volume, thereby enhancing its adsorption capacity.  
In a study [90] (Figure 20), rGO/TiO\({}_{2}\) exhibited remarkable photocatalytic activity under visible light for the degradation of formaldehyde. The introduction of rGO into the photocatalyst led to better dispersion of TiO\({}_{2}\) nanoparticles, which typically tend to aggregate. Analysis of UV-visible adsorption spectra revealed that the incorporation of rGO into the photocatalyst improved its adsorption properties in the visible light range. The rGO/TiO\({}_{2}\) composite demonstrated higher photocatalytic efficiency for formaldehyde removal under visible light compared to untreated TiO\({}_{2}\) and rGO. This high photocatalytic efficiency can be attributed to the conductive properties of rGO, which facilitate the rapid transfer of photogenerated electrons from the valence band of TiO\({}_{2}\) to electron acceptors within the rGO structure. The enhanced electron transfer leads to an increased lifetime of the photogenerated charge carriers, resulting in improved photocatalytic activity [90].  
Figure 19: (**a**) Photocatalytic activity of TiO\({}_{2}\), TiO\({}_{2}\)/CNT with various molar ratio, P25 and TiO\({}_{2}\)/AC, and (**b**) UV–vis spectra of TiO\({}_{2}\) and TiO\({}_{2}\)/CNT with various molar ratio [163].