## 3 Results and Discussions
### Characterization of Synthesized TiO\({}_{2}\) Nanocrystals  
The crystallinity of the synthesized NCs was analyzed by the XRD technique (next to HRTEM observations and selected area electron diffraction results). Contrary to the results presented in the paper from which we follow the synthesis protocol ([PERSON] et al. [34]) our XRD patterns (Figure 4) confirmed the existence of two titanium oxide polymorphs in the resulting NCs. Both the anatase phase and the titanium dioxide bronze phase (TiO\({}_{2}\)(B)) could be recognized in our data. The XRD data, together with reference data of anatase TiO\({}_{2}\) (JCPDS-01-086-1155) and TiO\({}_{2}\)(B) (JCPDS-00-046-1238), respectively, are shown in Figure 4, as well. In the case of anatase NRs, the relative intensity of the diffraction peak for (004) planes has been reported to become more pronounced as compared to the intensity of (200) planes [31; 62]. This is a well-known phenomenon for anatase crystals if their anisotropic growth occurs along the \(c\) axis of the anatase lattice: the (004) diffraction peaks become stronger and sharper in comparison to (200) diffraction peaks and this is consistent with our TEM observations and the NRs SAED pattern in Figure 1b [26; 34; 49; 63]. Furthermore, the bandgap of the anatase NRs was found to be ca. 3.28 eV by using their light absorption spectrum. The measured bandgap value was indeed analogous to reported optical bandgaps for nanocrystalline anatase NPs [5; 34; 64] (See Figure S1). To confirm that the peak broadening arose from NCs' size and shape effects, the average crystallite sizes of the anatase NCs were calculated by using the Scherrer formula [65] (See Table S1). Scherrer analysis from the (101), (200), and (004) diffraction peaks yields approximately 3.8, 3.5, and 19.9 nm, respectively, for the dimensions of the anatase NRs which are in agreement with the measured width and length from the TEM micrographs. Furthermore, the optical properties of the anatase NRs were characterized using their light absorption spectrum. Even though several diffraction peaks could be matched with the anatase reference signal, some other peaks at 34.4\({}^{\circ}\), 35.4\({}^{\circ}\), 36.2\({}^{\circ}\), and 52.3\({}^{\circ}\) were pointing at the existence of another phase. [PERSON] et al. suggested that these peaks could correspond to crystalline OLAC aggregated present among the TiO\({}_{2}\) NRs due to the fact that these NRs were formed in an excess amount of OLAC [66]. However, in our experiment, TiO\({}_{2}\) NRs were purified via a size-selective aggregation process after the synthesis step, therefore the presence of aggregated OLAC seems less likely to us. Moreover, a possible explanation of these signals could be the formation of brookite titania as an impurity, as it has been reported before during the synthesis of the other polymorphs [25; 63; 67]. Although the diffraction peak located at 36.2\({}^{\circ}\) could be assigned to the (121) plane of the brookite phase, the other three diffraction peaks at 34.4\({}^{\circ}\), 35.4\({}^{\circ}\), and 52.3\({}^{\circ}\) are not compatible with the brookite, anatase, or rutile polymorphs [68]. After careful examination, we concluded that the last four measured reflections could be a fit for the TiO\({}_{2}\)(B) phase of titania, which is given in the reference card (JCPDS-00-046-1238). The (001), (\(-\)111), (003) reflections are typical of TiO\({}_{2}\)(B) titania which were detected in the XRD patterns of both the NRs and the semispherical NCs [17; 69]. These peaks are relatively more prevalent in the semispherical NCs rather than NRs. The reason could be the existence of semispherical NCs left after the size-selective process among anatase NRs since the full separation of the small NCs from bigger NRs is practically difficult. Furthermore, it has been shown that surface hydroxylation during TiO\({}_{2}\)(B) NCs formation will introduce surface relaxation and thereby the TiO\({}_{2}\)(B) NCs may exhibit an ellipsoidal shape in the c direction [17; 69].