*3.3.2 H2O adsorption*

As an example of a straightforward surface chemical reaction with considerable applications, water dissociation on TiO2 is of basic importance. It has been thoroughly investigated how H2O and TiO2 interact with surfaces, significantly influencing the photocatalytic processes [102]. It is particularly well known that on the imperfect TiO2 surface, H2O molecules that have been chemically dissociated are energetically preferred, whereas H2O molecules are only physically adsorbed on the ideal TiO2 surface [103–105]. H2O dissociation only occurs on defect sites linked to V0 at low coverage, according to research by Besenbacher et al. [106] that combines experimental and theoretical methods. They used scanning tunneling microscopy (STM) to show a direct correlation between V0 before water exposure and surface hydroxyl groups after exposure, and they used DFT to show that only the defect sites are energetically capable of supporting water dissociation. It is shown that V0 in the surface layer dissolves H2O by transferring one proton to an oxygen atom nearby, resulting in the formation of two OH groups for every vacancy.

## *3.3.3 Adsorption of alcohol*

The reactive sites on metal oxides, both in powder form and in single crystal, have been intensively probed using alcohols. Both experimental characterizations and

### *Oxygen Vacancy in TiO2: Production Methods and Properties DOI: http://dx.doi.org/10.5772/intechopen.111545*

theoretical calculations have been used to extensively study the adsorption of alcohols on TiO2 [107]. Using theoretical calculations, Oviedo et al. [108] have shown that methanol dissociation is thermodynamically advantageous on the V0 states. According to Farfan-Arribas and Madix, temperature programmed reaction spectroscopy (TPRS) and X-ray photoelectron spectroscopy (XPS) are used to investigate the function of V0 in the adsorption of aliphatic alcohols on TiO2. They discovered that the existence of V0 on the surface leads to greater alcohol adsorption on the surface. At room temperature, the adsorbed aliphatic alcohols spontaneously dissolve on the TiO2-(110) surfaces containing V0, generating hydroxide and alkoxide groups [109]. Particularly, it is discovered that the alkoxide species is more photocatalytically reactive than the physisorbed species. Additionally, chemically dissociated alcohols may swiftly scavenge the photogenerated h<sup>+</sup> , substantially extending the lifespan of photogenerated e [110].
