## 3 Results and Discussion
### SEM/EDS and TEM Analysis  
The N-TiO\({}_{2}\) nanoparticles were morphologically tested by SEM/EDS. The images and elementary analysis are presented in Figure 5.  
The SEM images reveal a microstructural morphology, with particles of spherical shape. The EDS analysis (Figure 5d) revealed that the N dopant was present at 3.26 wt.%, with the expected Ti percentage being 54.07 wt.%. Oxygen and carbon were also found at 39.99 and 2.68 wt.%, respectively. This was due to the oxygen present in TiO\({}_{2}\), and to carbon residuals from the final annealing step of the powder.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Sample**} & **BET Surf. Area \(\sigma\) (m\({}^{2}\) g\({}^{-1}\))** & \multirow{2}{*}{\(V_{\text{1.7-300 nm}}\) (cm\({}^{3}\) g\({}^{-1}\))} & **Av. Pore Diam. (nm)**. \\  & **(Micropore Surf. Area)** & & \\ \hline N-TiO\({}_{2}\) & 82 (6) & 0.3 & 13 \\ \hline \hline \end{tabular}
\end{table}
Table 1: BET analysis and properties of N-TiO\({}_{2}\) powder.  
Figure 4: N\({}_{2}\)-sorption diagram for the N-TiO\({}_{2}\) nanoparticles. The black line represents adsorption and the red line represents desorption. The inset shows the pore size distribution as determined by the BJH method.  
As the distinctive ability of the SEM apparatus is of a certain level, further examination of the powder via TEM analysis followed. Figure 6 shows the TEM images for the N-TiO\({}_{2}\) NPs.  
The TiO\({}_{2}\)-based particles exhibited a size ranging between 5 and 15 nm, and they had a spherical shape with different crystalline orientations. The color difference in these particles was due to the different shade effects created by the electrons when hitting the surface of the variably oriented particles. These size results differed from those obtained by the DLS technique, as nanoparticles in solution tend to aggregate into larger particles and, therefore, their size in solution is larger than that in the dry powder form [35]. This overestimation of the DLS size compared to the TEM size is commonly found in the literature [42]. Light-scattering techniques provide information regarding the hydrodynamic diameter, whereas TEM measures the particles' dense core [43].  
All of the abovementioned results are in accordance with a recent similar study conducted by our research group, where the N-TiO\({}_{2}\) particles were fully characterized by applying various techniques, including X-ray powder diffraction (XRD) (see Figure 1 in [32]), micro-Raman analysis (see Figure 2 in [32]), X-ray photoelectron spectroscopy (XPS) (see Figure 3 in [32]), ultraviolet-visible (UV-Vis) spectroscopy (see Figures 4 and 5 in [32]), and transmission electron microscopy (TEM) (see Figure 7 in [32]). This research is an extension of the findings of our recent publication, aimed at exploring the capability of such particles to have end-use biomedical applications, along with environmental ones.  
Figure 5: SEM/EDS analysis for the N-TiO\({}_{2}\) NPs: (**a**) \(\times\)100 magnification image of the powder, (**b**) \(\times\)1500 magnification image of the powder, (**c**) EDS spectrum of the powder, and (**d**) EDS analysis results of the powder.  
Figure 7: _Salmonella_ Typhimurium biofilm population (log CFU/cm\({}^{2}\)) with the presence of N-TiO\({}_{2}\) NPs under visible-light irradiation and in the dark for 0, 1, 2, and 3 h of irradiation. Control specimens are included (no N-TiO\({}_{2}\) presence), and the reported data are the mean values of two replicates with three samples each, \(\pm\)standard deviation.  
Figure 6: TEM images at (**a**) \(\times\)58,000, (**b**) \(\times\)190,000, and (**c**) \(\times\)500,000 magnification for the N-TiO\({}_{2}\) NPs.