## 3 Results and Discussion
### Photocatalytic Results  
The photocatalytic behavior of the as-produced N-TiO\({}_{2}\) powder was assessed by testing the photocatalytic degradation of solutions of different pollutants, under different parameters (see Table 1). All the photocatalytic tests were conducted at room temperature and pH = 6. The results are illustrated based on the pollutant used, with Figures 8-10 corresponding to Rhodamine B, Methylene Blue, and Brilliant Green, respectively. In every figure, the photolysis of the pollutant is also included. Figure 7: TEM images of the as prepared N-TiO\({}_{2}\) nanoparticles in (**a**) \(\times\)190,000, (**b**) \(\times\)245,000, and (**c**) \(\times\)500,000 magnification. Figure 8: Degradation curves of Rhodamine B for different amounts of catalyst and irradiation time, under visible light irradiation. Photolysis of the pollutant is also included. Figure 10: Degradation curves of Brilliant Green for different amounts of catalyst and irradiation time, under visible light irradiation. Photolysis of the pollutant is also included. Figure 9: Degradation curves of Methylene Blue for different amounts of catalyst and irradiation time, under visible light irradiation. Photolysis of the pollutant is also included. It is observed that Rhodamine B is a pollutant with high resistance to the catalyst, as its final degradation value reaches only 50% for 200 min irradiation. Even at 10 g/L, a catalyst load that is considered high, the degradation curve is similar to the one for the 1 g/L load. The stability of Rhodamine B is also evident in photolysis (no use of catalyst), as for 150 min of irradiation in visible light, the degradation is up to 10%. The other pollutants, Brilliant Green and Methylene Blue, as shown in Figures 9 and 10, respectively, both approach a degradation of \(\sim\)35% for a total time duration of 150 min. Regarding the Methylene Blue pollutant, which is widely used in photocatalytic tests, the results in Figure 9 prove that it is an unstable pollutant that degrades very easily, even in a small load of catalyst. Therefore, this makes it ineligible for photocatalytic tests and investigation of catalyst activity. The instability of Methylene Blue becomes apparent by its photolysis (no use of a catalyst), where there is a degradation of 35% for 150 min irradiation, a percentage almost equal to when a load of 0.1 g catalyst/L pollutant is tested. Furthermore, it is observed that in both 1 g/L and 10 g/L loads of catalyst, the degradation reaches \(\sim\)80% at 200 min and 150 min of irradiation, respectively, followed by an almost visual complete discoloration of the pollutant. Brilliant Green is also an unstable pollutant and ineligible for photocatalysis, as it is observed in Figure 10 due to the phenomenon of photolysis up to 40% at 150 min of irradiation. In addition, in the presence of a catalyst of 0.1 g/L of pollutant (a relatively small amount), it decomposes to a greater extent, reaching a 60% degradation at 200 min. Another noteworthy observation regarding Brilliant Green is that in the case of a catalyst to a pollutant load of 10 g/L at 10 cm distance of the sample from the radiation source, there is an immediate 70% degradation of the pollutant in the first 10 min. At 50 min, it is 80% and then it plateaus, which occurs due to the absorption of the dye from the catalyst. The preliminary conclusions from these graphs are that, first of all, the chosen pollutant is one of the main factors influencing photocatalytic degradation. Rhodamine B is much more resistant to the catalyst, i.e., it degrades to a lower scale than the other two organic dyes, Brilliant Green and Methylene Blue. This indicates a stability that makes it suitable to be the main pollutant in photocatalytic tests. As for the load of catalyst to pollutant, it was observed that as the amount of catalyst increases, the degradation of the pollutant increases.