# Improvement of Buildings' Air Quality and Energy Consumption Using Air Purifying Paints
## 3 Results  
### Physical and Chemical Properties  
To identify the most efficient and cost-effective synthetic method yielding photoactive powders, we synthesized doped titanium dioxide powders using various synthetic procedures. In order to find the best synthetic procedure, which will be easy, cost-effective, and lead to photoactive powders, we prepared doped titanium dioxide powders with different synthetic procedures. Undoped and metal-doped TiO\({}_{2}\) powders are prepared by a modified sol-gel method according to which the photocatalyst can be obtained by precipitating titanium dioxide with different dopants (such as Mn-, Co-, Cu-, Ni-, Fe-, and Al-). The XRD patterns of undoped titanium dioxide in different synthetic procedures based on ammonia synthesis and alkali-based synthesis are shown in Figure 9a. In the ammonia-based synthesis, the resulting powder exhibits only the anatase phase in comparison with the alkali-based synthesis, which displays a mixed-phase composition. XRD patterns of pure TiO\({}_{2}\) and Mn-, Co-, Cu-, Ni-, Fe-, and Al-doped TiO\({}_{2}\) are displayed in Figure 9b. The anatase phase is shown in pure TiO\({}_{2}\) and metal-doped TiO\({}_{2}\) at an optimum dopant concentration (0.04 %wt) except Ni-doped TiO\({}_{2}\). The characteristic peaks indicating the presence of the anatase phase are observed at 20 values of 25.3\({}^{\circ}\), 37.6\({}^{\circ}\), 48.2\({}^{\circ}\), 53.9\({}^{\circ}\), 54.8\({}^{\circ}\), 62.7\({}^{\circ}\), and 75.2\({}^{\circ}\). These peaks correspond with the crystallographic planes (101), (004), (200), (105), (211), (204), and (215) of anatase, respectively. Moreover, no obvious diffraction peaks attributed to metal or metal oxides (such as MnO\({}_{2}\), Co\({}_{3}\)O\({}_{4}\), CuO,  
Figure 9: XRD patterns of (**a**) undoped TiO\({}_{2}\) synthesized through ammonia-based and alkali-based procedures and (**b**) metal-doped TiO\({}_{2}\) synthesized through ammonia-based procedure. Fe\({}_{2}\)O\({}_{3}\), and Al\({}_{2}\)O\({}_{3}\)) were observed in those samples, confirming the purity of synthetized powders. The metal ions were probably integrated into either the interstitial positions or substitution sites within the crystalline structure of TiO\({}_{2}\). Among these dopants, the Fe-doped TiO\({}_{2}\) demonstrated the most promising photocatalytic behavior. Consequently, we directed our efforts towards optimizing its performance. Then, our subsequent efforts involved attempts to optimize and control the particle size of the iron-doped titanium. In Figure 10a, the XRD patterns before and after the ball milling process are displayed. The peak shown at 25.3\({}^{\circ}\) is related to crystal plane 101 of the anatase phase. From the diagram, the significant decrease in grain size from 29.9 nm to 19.4 nm is clear, alongside a change in the intensity of the main crystal plane. The SEM images of Fe-doped TiO\({}_{2}\) before and after milling are depicted in Figure 10c,d. Figure 10c shows a relatively small number of small agglomerates (1-3 \(\upmu\)m) along with large agglomerates between 10 and 70 \(\upmu\)m. The agglomerates were composed of nanosized particles (below 100 nm). UV-VIS absorption as a function of wavelength for VISION powder is shown in Figure 10b. The incorporation of the Fe into TiO\({}_{2}\) resulted in the shift of the absorption edge to the visible light region (400-800 nm). The extension of the absorption spectra of Fe-doped TiO\({}_{2}\) into the visible light region was achieved by modifying the electronic energy band structure of TiO\({}_{2}\) through the introduction of doped Fe\({}^{+3}\) ions. Despite enhancing the spectral response into the visible region, the introduction of iron may present challenges such as thermal instability affecting the anatase phase, potential blocking of reaction sites, and increased charge recombination at the metal sites.