Preparation Of Metal Or Nonmetal Doped TiO₂ Nanotubes And Their Characteristics

Two-step hydrothermal method was developed to prepare nonmetal S, B and metal Fe doped TiO2 nanotubes. Their characteristics were investigated by TEM, XRD, XPS, FT-IR, UV-Vis spectroscopy. The photocatalytic activity was evaluated by decomposing methyl orange.S-doped TiO2 nanotubes (S-TNTs-H) were fabricated using H2SO4 as dopant. When the molar ratio of S:Ti was 1:1, H2SO4 aqueous solution and TiO2 nanotubes were hydrothermaly treated at 120℃for 6h, the S-TNTs-H exhibited the optimal quality. The XRD and TEM results indicated that S-TNTs-H had the single-crystalline anatase TiO2 with outer diameter of 10-20 nm and length of approximately 200 nm. FT-IR and XPS results showed that the doped sulfur may be assigned to a SO42? bidentate co-ordinated to TiO2 nanotubes. UV-Vis showed that the absorption edge of S-TNTs-H shifted toward the longer wavelength and its absorbance in the visible region increases obviously. The photocatalytic tests revealed the S-TNTs-H possessed the high photocatalytic activity, the degradation of MO were 95.52% and 84.26 % under UV light irritation for 220 min and sunlight (53.33 klux) irritation for 190 min, respectively. The pseudo-first-order reaction rate constant k was about 0.7992 h-1 under UV-light and 0.5208 h-1 under sunlight irradiation, which are approximately 5 times and 10 times higher than those of undoped TiO2 nanotubes. Moreover, the sulfur-doped TiO2 nanotubes could be easily separated from the reaction solution by sedimentation. Doping of S and large surface area of one -dimensional tubular possessed the synergistic effects on enhancement of S-TNTs-H photocatalytic activity.B-doped TiO2 nanotubes (B-TNTs-H) were prepared using H3BO3 as dopant. When the molar ratio of B:Ti was 0.24:1, H3BO3 aqueous solution and TiO2 nanotubes were hydrothermaly treated at 120℃for 6 h, the B-TNTs-H exhibited the optimal quality. The results from TEM indicated that B-TNTs-H with diameter of 10-20 nm and length of severalμm. The XRD revealed that the B-TNTs-H had crystalline structure of anatase. FT-IR and XPS results showed that doped boron was present as the form of B3+ in B-TNTs-H forming a possible chemical environment like B-Ti-O. Especially, the photocatalytic tests indicated that the B-TNTs-H showed higher photocatalytic activity, the degradation of MO were 99.8% and 90.6% under UV light irritation for 90 min and sunlight (56 klux) irritation for 75 min, respectively. The pseudo-first-order reaction rate constant k about 2.3424 h-1 under UV-light and 1.1394 h-1 under sunlight(53.32 klux)irradiation, are approximately 12 times higher than those of undoped TiO2 nanotubes. Additionally, the B-TNTs-H could be easily separated from the reaction solution by sedimentation and the photocatalytic activities was still high under visible irradiation. Boron atoms can substitute oxygen atoms in the TiO2 lattice, which causes the band gap narrowing and extend its light absorption into the visible region. Moreover, large specific surface area and one–dimensional structure of B-TNTs-H may be contributed to the greater absorption to organic pollutants and lower combination of electron hole pairs. The synergetic effect of B-doped and one-dimensional tubular structure leads to a higher photocatalytic activities of B-TNTs-H. These results showed that B-TNTs-H will provide possibility to future industrial applications in environmental pollutants cleaning up.Fe-doped TiO2 nanotubes (Fe-TNTs) were prepared using FeCl3.6H2O as Fe sources. While FeCl3.6H2O aqueous solution and TiO2 nanotubes were mixed at the molar ratio of Fe:Ti was0.013:1, reacting under the optimal conditions of pH=1, 120℃for 6h, the products Fe-TNTs was mix-crystals phase of antase, brookite and rutile. The Fe-TNTs were about diameter of 50 nm and length of severalμm. UV-Vis showed that the absorption edge of Fe-TNTs shifted toward the longer wavelength and its absorbance in the visible region increases obviously. The photocatalytic tests revealed that the Fe-TNTs showed higher photocatalytic activity, the degradation of MO were 98.7% and 96.4% under UV light irritation for 220 min and sunlight (69.6 klux) irritation for 180 min, respectively. The pseudo-first-order reaction rate constant k of degradation MO were about 1.2096 h-1 under UV-light and 1.0572 h-1 under sunlight irradiation,which are approximately 16 times and 8 times higher than those of undoped TiO2 nanotubes. Furthermore, the reusing catalysts still show high activity under visible irradiation. Fe-TNTs showed obviously higher photocatalytic activity and can be easily separated from the reaction solution by sedimentation, which may be related to the doping of Fe, effect of mix-crystal and one-dimention of TiO2 nanotubes.