**2.4 Chemical vapor deposition method**

Chemical vapor deposition (CVD) is a powerful method for the synthesis of nanomaterials with enhanced performances.

Several works have been reported on the fabrication of TiO2 NPs by CVD. For example, Liu et al. [41] prepared TiO2 NPs by CVD method. They revealed that the gas phase hydrolysis reaction may be decomposed into two processes: (i) hydrolysis of TiCl4 into TiO(OH)2 and (ii) decomposition of TiO(OH)2 to TiO2. The influence

of various concentrations of TiO2 NPs on CVD grown graphene was investigated by electrical charge transport measurements and Raman spectroscopy [42]. The schematic diagram of TiO2 doped CVD grown single layer graphene devices is presented in **Figure 6**. The obtained results showed that TiO2 change the electronic properties besides the structure of the CVD grown graphene.

Similarly, Li et al. [43] synthesized TiO2 NPs, with mean particle size of 22 nm, by CVD method. The TEM image of TiO2 NPs is presented in **Figure 7**. They concluded that the TiO2 NPs with the metal ion dopants possess elevated photocatalytic activities compared to un-doped TiO2 NPS.

Ding et al. [44] synthesized TiO2 NPs via CVD process. The results obtained by XPS and nitrogen ads/desorption revealed that most of TiO2 NPs were distributed on the external surface of the support and the coating was stable. V2O5-TiO2 NPs were prepared from two precursors by CVD [45]. They revealed that the CVD process was a suitable method for the single step synthesis of nanocomposite coatings. Lee et al. [46] prepared TiO2 NPs by CVD method. The results revealed that a 60 min sample coating time gave the most highly photocatalytic activity.

**Figure 6.**

*Schematic diagram of TiO2 doped CVD grown single layer graphene devices [42].*

**Figure 7.** *TEM image of TiO2 NPs prepared by CVD [43].*
