3. Results and discussion
3.1. Characterization of the photocatalysts
Fig. 1a shows the XRD patterns of iodine, nitrogen and iron doped titanium dioxide samples. The phase composition; particle size; specific surface area and metal/nonmetal dopant concentrations are listed in Table 1. The iron doped titania is shown to consist of 29.4 wt% anatase and 70.6 wt% rutile whilst the iodine and nitrogen doped samples contained mostly anatase (98.0 and 95.3 wt%) particles. This difference could be ascribed to the iron dopant facilitating the formation of rutile phase by lowering the required anatase rutile phase transformation temperature. It should be noted that the optimal calcination temperatures obtaining the highest photocatalytic activity were different for the investigated samples. TiO2-Fe sample was calcinated at 600 °C that was sufficiently high for the formation of rutile. The sol–gel made TiO2-RHSE sample calcinated at the same temperature and time as iron doped titania also contains rutile phase (17.6 wt%). Its particle size was somewhat larger resulting in lower specific surface area (20.1 m2/g). Iodine and nitrogen doped samples were calcinated at lower temperature (400 °C) and this resulted in smaller anatase particle size (D = 9.0 and 6.5 nm) and higher specific surface area values (SBET = 79.5 and 139 m2/g) than those determined for the iron doped sample (DA = 34.8, DR = 31.0 nm, SBET = 27.9 m2/g). Fig. 1b shows the XRD patterns of noble metal deposited P25 TiO2 samples, the flame made titanium dioxide and the reference samples. The TiO2-Ag and TiO2-Au diffraction patterns are virtually identical to the bare P25 TiO2 and the noble metal content is too small to be detected from standard measurements. Fig. 1c shows two low intensity peaks at 32.2° and 38.1° that were found for TiO2-P25-Ag using slower scans in the 30–34° and 36–40° (2Θ) range. The first peak is most probably due to Ag2O particles [61]. The later peak coincides with an anatase peak, is only visualized when the P25 background is subtracted, is due to elemental silver (Ag0) [7] and [62]. Silver-oxide can coat the silver nanoparticles as the surface is oxidized by molecular oxygen. XPS results confirmed that silver(I) oxide is the dominate form of silver present on modified titanium dioxide samples prepared by photodeposition technique [8]. However, XRD patterns for the gold deposited sample do not show any unique patterns.
3. ผลลัพธ์ และสนทนา3.1. คุณสมบัติของ photocatalystsFig. 1a shows the XRD patterns of iodine, nitrogen and iron doped titanium dioxide samples. The phase composition; particle size; specific surface area and metal/nonmetal dopant concentrations are listed in Table 1. The iron doped titania is shown to consist of 29.4 wt% anatase and 70.6 wt% rutile whilst the iodine and nitrogen doped samples contained mostly anatase (98.0 and 95.3 wt%) particles. This difference could be ascribed to the iron dopant facilitating the formation of rutile phase by lowering the required anatase rutile phase transformation temperature. It should be noted that the optimal calcination temperatures obtaining the highest photocatalytic activity were different for the investigated samples. TiO2-Fe sample was calcinated at 600 °C that was sufficiently high for the formation of rutile. The sol–gel made TiO2-RHSE sample calcinated at the same temperature and time as iron doped titania also contains rutile phase (17.6 wt%). Its particle size was somewhat larger resulting in lower specific surface area (20.1 m2/g). Iodine and nitrogen doped samples were calcinated at lower temperature (400 °C) and this resulted in smaller anatase particle size (D = 9.0 and 6.5 nm) and higher specific surface area values (SBET = 79.5 and 139 m2/g) than those determined for the iron doped sample (DA = 34.8, DR = 31.0 nm, SBET = 27.9 m2/g). Fig. 1b shows the XRD patterns of noble metal deposited P25 TiO2 samples, the flame made titanium dioxide and the reference samples. The TiO2-Ag and TiO2-Au diffraction patterns are virtually identical to the bare P25 TiO2 and the noble metal content is too small to be detected from standard measurements. Fig. 1c shows two low intensity peaks at 32.2° and 38.1° that were found for TiO2-P25-Ag using slower scans in the 30–34° and 36–40° (2Θ) range. The first peak is most probably due to Ag2O particles [61]. The later peak coincides with an anatase peak, is only visualized when the P25 background is subtracted, is due to elemental silver (Ag0) [7] and [62]. Silver-oxide can coat the silver nanoparticles as the surface is oxidized by molecular oxygen. XPS results confirmed that silver(I) oxide is the dominate form of silver present on modified titanium dioxide samples prepared by photodeposition technique [8]. However, XRD patterns for the gold deposited sample do not show any unique patterns.
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