Research On Preparation And Properties Of Nano-TiO₂-Al₂O₃ Composites

TiO2 is the most widely used good photocatalyst nowadays. It has high activity, high chemical stability and will not cause secondary pollution. Presently the application of TiO2 photocatalyst is mainly for organism degradation, noble metal recycling. It's also used to catalyze, oxidize and degrade hazardous substances, such as organic pollutant and NOx in wastewater and atmosphere, to clean water and air. However, its application is limited by its small specific surface area (comparing toγ-Al2O3) and bad thermal stability. TiO2-γ-Al2O3 composite material can overcome those shortcomings and make it a superior catalyst.It was prepared by liquid phase precipitation method and sol-gel method separately in this thesis. The performances of the composite material were compared through photodegradation experiment of methyl orange. Firstly, TiO2-γ-Al2O3 composite material was prepared by Liquid Phase Precipitation method. Raw materials Al sheet and TiCl4 solution with mass ratio of 1:1 were dissolved in concentrated sulfuric acid separately and then mixed. Ammonia water served as precipitant to make complete precipitation at pH=9, and Then the TiO2-γ-Al2O3 composite material was made after firing at 850℃. The product was characterized by XRD and SEM and the results showed that the TiO2 in composite material made by this method is all anatase TiO2.50mg of nano composite material was added into lOmL 10mg/L methyl orange solution to carry on a photodegradation experiment. The degradation rate was 80.2% after being exposed under UV for 4 hours.TiO2-γ-Al2O3 composite material was also prepared by sol-gel method. Aluminum nitrate was hydrolyzed as source of aluminum. Ammonia water was used to adjust pH until 8. the material was then firied at 950℃after precipitation, rinsing and desiccation to formγ-Al2O3 supporter, tetrabutyl titanate was used as raw material while glacial acetic acid was used as depressor to prepare TiO2 sol. TiO2 andγ-Al2O3 are loaded with a mass ratio of 1:1 and then firied at 550℃to form TiO2-γ-Al2O3 composite material. The composite material was characterized by XRD and SEM and the results showed that this material was homodispersed, had small particle size and the surface ofγ-Al2O3 supporter was covered by TiO2 evenly.50mg of nano composite material was added into 10mL 10mg/L methyl orange solution to carry on a photodegradation experiment. The degradation rate was 98.7% after being exposed under UV for 4 hours. The composite material made by this method improved the availability of TiO2, and its photodegrading capability is twice as much as TiO2 of the same mass. The performances of the composite material were compared through photodegradation experiment of methyl orange, of which the results showed sol-gel method made TiO2-γ-Al2O3 composite material was better. The specific surface area ofγ-Al2O3, which is the supporter, is large. The increased loading capacity of TiO2 improved its availability, so the degradation capability of the composite material was remarkably improved.