Synthesis And Properties Of C-axis Preferentially Oriented TiO₂Nanotube Arrays

Titania nanotube arrays has ordered tubular structure, high specific surface area, and otherunique properties is widely used in photocatalytic degradation of pollutants, spitting water intohydrogen, photovoltaic conversion of solar energy, energy storage and many other applications.But as-prepared titania nanotube arrays are amorphous, high-temperature annealingcrystallization is usually lead to disordered structure orientation, poor electrical conductivity,low electrochemical activity, insufficient usage of sunlight, hindering its applications in the fieldof environment and energy. This paper stuyd titania nanotubes formed by secondary anodicoxidation, disscuss the water content and the annealing atmosphere, to obtain a high degree ofc-axis oriented crystallization, high conductivity, and a better response to visible light noveltitania nanotubes array. The nanotube were used in lithium ion batteries, supercapacitors, andphotoelectrocatalytic material. The main contents are as follows:(a) The preparation and the mechanism of highly c-axis orientation titania nanotube arrays.Titania nanotube arrays prepared by anodic oxidation are tens of microns long, clean surface,almost no cracks. We focused on the crystallization orientation of nanotube arrays caused by thewater content of the electrolyte and impact of the annealing atmosphere (oxygen-rich andoxygen-poor environment).We found2wt%of water content and oxygen-poor annealing aretwo key factors in orientation crystallization. We use experimental data to present mechanismsof highly c axis oriented crystallization.(b) The performance of lithium-ion battery of titanium dioxide nanotube array was studied.The vacuum annealed titania nanotube array with a high concentration of oxygen vacancies(about31.7%of tetravalent Ti is reduced to trivalent titanium), which has a high conductivity(the carrier concentration up to1023cm-3, than the air annealing two high magnitude). Thecapacity at1C charge and discharge rate is270mAhg-1(highest of reported) with good cycleperformance. Lithium ion storage mechanism was discussed, the high concentration of oxygenvacancies did not only provides high conductivity,but also contribute to the formation of Li-richphase. (c) The performance of supercapacitor of titanium dioxide nanotube array was studied. Thecapacity of the c-axis orientation of crystallized titanium dioxide nanotube array was measuredby cyclic voltammetry. The capacity of c-axis orientation of crystallized titanium dioxidenanotube array in100mV s-1scanning rate is8.21mF cm-2, capacity fell after the5000cyclewas only16%, indicating the material has good cycle stability.(d) Photoelectriccatalytic properties of titanium dioxide was studied. The vacuum annealedhighly c axis oriented titania nanotube arrays has high conductivity and excellent visible lightresponse characteristics. The visible photoelectrocatalysis degradation of methyl orange wascarried out, the perfermance of c axis oriented nanotube arrays have better catalytic activity thanrandom oriented air annealed nanotube arrays.