Of Tio <sub> 2 </ Sub> Nanotube, Modification And Applications

Titania nanotubes have impressive properties compared with its analogues in other forms for application in photocatalysis,sensing,photoelectrolysis,and photovoltaics.However,the widespread technological use of titania is impaired by its wide band gap(3.2 eV),which requires ultraviolet(UV) irradiation for photocatalytic activation,which accounts for only a small fraction(8%) of the sun's energy compared to visible light(45%).Therefore,how to improve the adsorption in visible light of the TiO₂ is what we need to resolve.Ion doping is considered as an effectual method.Titania nanotubes were prepared by hydrothermal synthesis method using TiO₂ nano-powder.The effect of synthesis parameters to titaina nanotubes performance have been studied,including reaction temperature,reaction time,precursor amount and annealing conditions.It indicated that the higher the reaction temperature may result in a better phase composition and photocatalytic activity.As discussed in this thesis,a reaction time of 24h and a precursor amount of 0.6g is the best synthesis condition for photocatalysis.Annealed samples exhibit improved degree of crystallinity.Titania nanotube arrays were prepared by anode oxidation method.Anodize voltage,reaction time,and the pH value of electrolyte had significant influence on the morphology of samples.Under voltage at 20V,high-ordered nanotubes with diameter of 60-80 nm,wall thickness of 20-30 nm can be abtained by anodic oxidizing Ti plate in electrolyte(pH value 3) for 5 minutes.The as-anodized titania nanotubes are amorphous,while the anatase can be obtained after annealing at 400℃for 2 h,and the mixture of anatase and rutile after annealing at 400-700℃for 2 h.As the temperature raise to 700℃or higher,the crystalline transformed to rutile completely.Nitrogen-doped TiO₂ nanotubes were synthesized by annealing of the anodized titania nanotubes with ammonia.The ordered structure of titania nanotubes maintained after the nitrogen-doping process.The films have been applied in photocatalytic degradation of methyl orange as model of organic pollutant,indicating that nitrogen-doped titania nanotubes had better photocatalytic activity than non-doped ones.The contact angle was measured before and after visible light irridation,indicating that nitrogen doped titania nanotubes had better wetting conversion quality under visible light irradiation.HAP coating was synthesized at anodized titania nanotubes by electrodepositing process,and the effects of voltage,H₂O₂ content and temperature to morphologies and structural properties of samples were studied.The optimistic synthesis condition to prepare TiO₂/HAP coating was determined as electrodeposit in electrolyte containing 2.5ml H₂O₂ for 2 hours at the temperature of 60℃and the voltage of 1V,utilizing as-prepared titania nanotube arrays as deposition substrates.