**4. Conclusion**

This chapter discusses various methods that can be employed to produce defective TiO2 containing V0. These methods include thermal processing in an oxygen-depleted atmosphere, doping with non-metal or metal ions, bombardment with high-energy particles, and even *in situ* catalytic processes. These processes remove lattice oxygen from the surface or bulk of TiO2, resulting in a vacancy state. The presence of V0 defects provides defective TiO2 with unique chemical and physical characteristics, including enhanced reductive and dissociative adsorption properties and visible light absorption capabilities. Although the function of V0 in photocatalytic processes is still not completely understood, defective TiO2 has been shown to have benefits for a wide range of applications, such as selective charge separation and visible light response for photocatalytic activities. However, there are also conflicting claims about the role of V0 in the photocatalytic performance of semiconductors. Overall, the intentional introduction of V0 defects into TiO2 has great potential for improving the material's properties and enhancing its performance in various applications. Further research is necessary to fully understand the impact of V0 defects on TiO2 and to explore the potential of defective TiO2 materials in emerging fields such as sensing, photoelectrochemical water splitting, and photocatalytic air purification.
