## 3 Results and Discussions
### Growth Mechanism of TiO\({}_{2}\) Nanocrystals
In the case of the ligand-assisted process, ligands, mainly in the form of hot ligand solutions (e.g., trioctylphosphine oxide, oleic acid, and oleylamine), are present in the reaction mixture, either as a solvent or as a coordinating ligand providing control over the growth, size, and shape of the metal oxide NPs [46]. However, in solvent-controlled approaches, the initial reaction mixture mainly consists of two components, metal oxide precursors and common organic solvents. Thus the role of solvents may include acting as a reactant, oxygen donor, structure-directing agent, or reducing factor [28,48]. One should also keep in mind that these nonhydrolytic sol-gel routes, also known as nonaqueous reactions, are not necessarily totally water-free. In fact, even though the initial components of the reaction mixture have been dried and degassed, specific organic reactions are able to produce water in situ (e.g., aldol condensation and esterification reactions), rendering the system in principle hydrolytic. Therefore, even in the (virtual) absence of water, it is possible to have hydroxylation reactions [36]. Figure 1: (**a**) As-synthesized TiO2 NCs including NRs of different aspect ratios and semispherical NCs; (**b**) SAED pattern of anatase NRs presenting reflected rings clearly indexed to typical planes of anatase; (**c**) an individual anatase NR that has a (010) zone axis growing along the (001) direction. (**d–g**) TiO2 NCs after the size-selective process in two main categories, NRs and semispherical NCs, and their corresponding size distributions from a statistical analysis of TEM images. In our experiment, titania NRs were synthesized via a ligand-assisted nonhydrolytic sol-gel method in which the rapid thermal decomposition of a titanium precursor (titanium (IV) isopropoxide or TTIP) occurred in a hot solvent solution (OLAC), at a relatively high temperature (around 250 \({}^{\circ}\)C). It is well-known that titanium alkoxides are relatively reactive (e.g., as compared to silicon alkoxides) and almost instantly react with carboxylic acids (e.g., oleic acid, decanoic acid, linoleic acid, etc.,) even under mild conditions producing mixed alkoxy carboxylates and hydroxyalkoxides [20; 40; 49]. For instance, it was shown that titanium (IV) butoxide (Ti(OBu)\({}_{4}\) where Bu refers to \(-\)C\({}_{4}\)H\({}_{9}\)) can readily react with linoleic acid (C\({}_{17}\)H\({}_{31}\)CO\({}_{2}\)H) yielding a titanium butoxide-carboxylate complex Ti(OBu)\({}_{4\times}\)(C\({}_{17}\)H\({}_{31}\)CO\({}_{2}\))\({}_{\rm x}\) with the release of xBuOH. This BuOH formed, may react with unreacted linoleic acid left in the mixture leading to the formation of water by an esterification reaction [46; 49]. Analogous to the literature, we believe that in our experiment, upon the addition of TTIP (Ti(O\({}^{\rm P}\)P)\({}_{4}\) where Pr refers to \(-\)C\({}_{3}\)H\({}_{7}\)) to the degassed OLAC (C\({}_{17}\)H\({}_{33}\)COOH) solution at room temperature and as indicated by a color change of the mixture to pale yellow, a titanium carboxylate complex ((C\({}_{17}\)H\({}_{33}\)COO)\({}_{\rm x}\)\(-\)Ti(O\({}^{\rm P}\)P)\({}_{4\times}\)) formed with the release of xPrOH. Since the OLAC molecules were present in an excess amount acting as both ligand and solvent, therefore _x_PrOH could react with OLAC molecules and release water molecules via an esterification reaction. The water produced could then react with the titanium carboxylate complex to generate Ti\(-\)OH and subsequently through a hydrolysis-condensation process, Ti\(-\)**O\(-\)Ti** bonds were formed [50]. It has been shown that in synthetic routes where the ligand and solvent are the same, the desorption rate of ligand bound at the surface of the NCs is low giving them higher colloidal stability [47]. It has also been demonstrated that the in situ water generated during the esterification reaction favors the formation of anatase and TiO\({}_{2}\)(B) which is in agreement with our results in Figure 4, as well [51].