# Titanium Dioxide in Chromogenic Devices: Synthesis, Toxicological Issues, and Fabrication Methods
## 2 Synthetic Routes and Fabrication Techniques for TiO\({}_{2}\)
### The \"Green\" Route
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Synthetic Methods** & **Advantages** & & **Disadvantages** & & **Morphology and Uses** & **References** \\ \hline Sol-gel & – High yield; & & & & – & TiO\({}_{2}\)NPs (anatase and rutile); & \\ – Low temperature; & & & Low purity; & – & amorphous and crystalline & \\ – High control of size and shape & – & Long post treatment synthesis. & & & T\({}_{2}\) thin film EC device; & [36; 37; 38; 42; 43; 45; 46] & \\  & & of nanoparticles. & & & – & \\  & & & & & & solar cells. \\ \hline Chemical Vapor & – & The use of high vacuum is & – & The source materials used are & \\  & – & not required; & & toxic or flammble, requiring & \\  & – & It permits the covering of & careful management in the & & \\  & & rough surfaces uniformly; & design and operation of a CVD & & \\  & & & & process system; & \\ Chemical Vapor & – & The pressures used allow for & – & The process requires & – & T\({}_{2}\) nanorods; \\ Deposition (CVD) & – & The structures have large & high temperatures; & – & Amorphous TiO\({}_{2}\) films. & [24; 48; 54; 55; 102] \\  & & aspect ratios; & & & - The alteration of bond & \\  & – & The reactor can be scaled to fit & & & \\  & & several substrates; & & & \\ \hline Physical Vapor & – & The use of specialized & – & The PVD targets are & \\  & – & precursor materials, as used in & – & A degradation of the substrate & \\  & CVD, is not required; & & can occur after radiation and & \\  & – & A large range of materials & bombardment from & \\  & & (elements, alloys, and & the plasma; & – & Amorphous TiO\({}_{2}\) films; \\ Physical Vapor & & compounds) are available & – & The incident energy on the & \\ Deposition(PVD) & & for deposition; & target turns into heat; & \\  & – & The materials are less toxic & – & In some cases, the flux & \\  & & than those used for CVD. & distribution is not uniform and & \\  & – & The sputtering target shows a & requires other procedures to & \\  & & stable geometry. & & substrates to achieve thin films & \\  & & & & & of uniform thickness. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Synthetic routes, advantages, disadvantages, and morphology of nano TiO\({}_{2}\). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Synthetic Methods** & **Advantages** & **Disadvantages** & **Morphology and Uses** & **References** \\ \hline Sonochemical and & – The sonochemical reactors & – The decline of power & & & \\  & show high mass transfer, & – & It is not easy to obtain a & & \\  & & mining time, and flow pattern; & uniform distribution of & – & \\  & – High rate of heating; & ultrasonic energy with an & & & \\  & – High rate of cooling; & ultrasonic bath; & & \\  & – Generation of shock waves. & – High frequency of irradiation; & & \\  & – & Generation of shock waves. & – High power consumption. & & \\ \hline Hydrothermal method & – & Suitable for creating & & & \\  & – & crystalline phases; & – & Expensive equipment; & \\  & – & Suitable for materials with & – & Impossibility of observing the & \\  & – & high vapor pressure; & crystal grow; & & \\  & – & It provides well crystallized & – & Autoclaves require 300 ”C and & – & \\  & & and pure materials, & & \\  & preventing additional & & & 10 bar. & & \\ \hline Oxidation method & – & TiO\({}_{2}\) nanomaterials are & & & \\  & generated in one-step & & & & \\  & anodization of titanium & – & Use of toxic solvents; & – & \\  & without any & – & Growth and nucleation & – & \\  & particular pretreatment; & & steps instability. & – & \\  & – & The annealing temperature & & & \\  & required is low. & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._