Solid-Phase Synthesis And Property Of Novel Aluminum-Doped Titanium Dioxide Mesoporous Materials

With the development of the serious globality environmental pollution, the application of photocatalytic technology for pollution treatment has been attracted a great attention in all countries. The preparation and application of the photocatalysts with high activity and effective under the sunlight have become hot topics in the fields of materials science, chemistry, environmental science and energy science. TiO2photocatalyst is widely regarded as a promising material for photocatalytic application due to its low cost, non-toxicity, chemical stability, and high photocatalytic activity. However, TiO2displays its wide band-gap which responds to narrow range of the light absorbed and high recombination of photogenerated electrons and holes, which decreases its photocatalytic efficiency. Many studies indicate that the modification of TiO2can improve the photocatalytic efficiency, and the different preparation methods result in various properties for the same materials. Therefore, it is of scientific meaning and economic value to adopt the right methods to synthesize the modification of TiO2materials with high photocatalytic efficiency, and to investigate the performances of these materials.In the present dissertation, Al-doped mesoporous TiO2nanomaterials were prepared by a solid-phase synthesis method. The effects of ethanol, template agent, sulfur, nitrogen etc. on the structures and properties of Al-doped mesoporous TiO2 nanomaterials were discussed. The influences of defect concentration, lattice distortion, morphology, particle size, apparent acidity, doping content, and the photocatalytic property were also investigated. The reaction kinetics and thermodynamics of Al-doped TiO2with solid-phase synthesis were researched. The growth mechanism of mesoporous TiO2nanocrystals was not only proposed, the effect of temperature on the structure, and the photoinduction on the photocatalytic activity were also studied. Hence, some new and interesting results were obtained and listed as follows.1. A novel Al-doped mesoporous TiO2nanocrystal with anatase structure was synthesized via a low temperature solid-phase reaction route using CATB as template, A12(SO4)3·18H2O and TBOT as starting reagents for the first time. The reaction mechanism was in accordance with Yangder kinetic equation. The Al-doped TiO2mesoporous material with crystals size about7.0nm, specific surface area of155.7m2/g, pore volume of0.3579mL/g and pore size of4.6nm could be easily gained. The results reveal that the Al3+doped in TiO2crystal structure which can lead to large microdefects and slightly aluminum-oxide produce, and the bending vibration of Ti-O-Al bond on the Al-TiO2materials is found at1134cm-1, their UV-Vis spectra depend on the ratio of Ti/Al and the aluminum-oxide content. The absorption peaks at210-370nm in those UV-Vis diffuse reflection spectra can be assigned to metallic oxide band.2. The effect of ethanol in solid-phase reaction system was researched. The results reveal that the ethanol has significant effects on the morphology of defects, and secondly as microvoid defects. The photodegradation of pyridine is beneficial from the microvoid defects but decreased by the free volume defects, and the increase of the density of microvoid defects enhances the photocatalytic activity. Moreover, higher temperature leads to larger loss of Al3+in the Al-TiO2materials. The loss of Al3+first decreases with the increase of pH and reaches to a minimum value when pH approach to7, then increases as pH value is further increased. The visible light photodegradation of pyridine on the Al-TiO2material’s surfaces follows the first-order reaction kinetics rule, and the phtocatalytic acitivity is7-18times higher than the undoped TiO2.5. The doping of sulfur has the very tremendous influence to the Al-TiO2material’s structure and the performance. In S and Al co-doped TiO2materials, S enters into the crystal lattice of anatase TiO2as the form of S6+, while Al3occupies the position of Ti4+. The growth of TiO2crystalites is effectively depressed due to the codope of S and Al. The unit cell minimum value appears when S:Al=4:6. The crystallinity of S-Al-TiO2-pyridine prepared using pyridine as template is higher than that of S-Al-TiO2-CTAB prepared using CTAB, as well as the crystal size, the cell parameters of a-and c-axis, and the cell volume. The absorbance of S-Al-TiO2-pyridine in ultraviolet range enhances when the ratio of S/Al≤5/5. However, the decrease of absorbance in UV and visible light range is observed when S/Al>5/5, and absorption band tend to blue shift. The uv-visible diffuse reflection absorption spectrum of S-Al-TiO2-CTAB covers the UV and visible light ranges and extends to the near infrared area. It was found that the doping quantity of S and Al and the resulting change of surface acidity of S-Al-TiO2-CTAB play the key roles in the photocatalytic activity of the samples. The apparent acidity (pH value) of S-Al-TiO2shows shows a positive correlation to the photodegradation of paclobutrazol. The photocatalytic of S-Al-TiO2can be enhanced by tailoring the ratio of S/Al. When S/Al=4:6, S-Al-TiO2shows the highest photocatalytic activity, and the photocatalytic activity of S-Al-TiO2(4S-6Al)-pyridine (0.00414mm-1) material is nearly4times higher than that of S-Al-TiO2(4S-6A1)-CTAB material (0.00111min-1).6. As for the thermodynamics metastable anatase S and Al codoped TiO2catalysts, the crystal size D shows a positive correlation to the reaction rate constant k when D<8nm, while a negative correlation is observed when D≥8nm. Grinding temperature, solid-phase reaction temperature, and calcining temperature have significant effects on the phase and surface acidity of S-Al-TiO2-pyridine materials. Higher calcining temperature may result in larger pH value on the material surface when S/Al is fixed.7. Mesoporous N-Al-TiO2(3A1-7N) photocatalysts were obtained when CTAB and pyridine were applied as templates. It was found that the samples from CTAB and pyridine as templates present short rod-like morphology and irregular shape and possess surface area of124.9and138.4m2/g, respectively. The crystal size of catalyst prepared with pyridine as a template is samller than that prepared with CTAB as a template. But the specific surface area, the crystal size and crystal lattice distortion stress don’t significant affect on the degradation of puerarin. N exists in the form of N3-. N and Al enter into the crystal lattice of TiO2and occupy the positions of O and Ti, respectively. It results in the decrease of absorbence of TiO2in the UV and visible light area and the red-shift due to the doping of Al. However, the codope of Al and N gives rise to the enhancement of UV absorbance and the reduce of visible absorbance of TiO2, and there exists Ti-O、Ti-O-Al、 N-Ti-O、Ti-O-N、Ti-N-O bonds in the surface of N and Al codoped TiO2catalyst. Moreover, the results show that the doping quantities of N and Al play a key role in the photocatalytic activity, and the adsorption performance of the materials shows a positive correlation to visible light degradation of puerarin. The N-Al-TiO2(3A1-7N)-Pyridine catalyst presents the highest photocatalytic activity at20℃, which is8.5times higher than Al-N-TiO2-no prepared without template,97.7%of puerarin was degraded within2h when N-Al-TiO2(3Al-7N)-pyridine was applied, which is5%higher than the N-Al-TiO2(3A1-7N)-CTAB catalyst. The response of N-Al-TiO2(3N-7A1)-CTAB to UV and visible light is enhanced under the irradiation of UV, and its photocatalytic activity first decreases then increases.