Research On TiO₂ Single Crystals Inherited From Amorphous TiO₂ Nanotubes And Their Electrochemical Capacitance Performance

In 1991,Zwilling group uses an electrochemical anodic oxidation method to prepare TiO₂ nanotubes with regular morphology on the surface of metallic titanium for the first time.Since then,TiO₂ nanotubes were studied comprehensively and applied widely in many fields.In this paper,anodized TiO₂ nanotubes were used as basic object to discuss their properties.The main three research works were discussed as following:（1）Well-defined anatase TiO₂ single crystals inherited from solid-state amorphous precursor through the thermal treatment,and their performance of degradation of Rhodamine B was studied;（2）MWNTs-TiO₂ nanotube hybrid electrode was synthetized,and its supercapacitance performance was evaluated;（3）One-dimensional structure of TiO₂ nanorods were synthetized by solvothermal method and the formation mechanism of TiO₂ nanorods was explored.Firstly,TiO₂ single crystals with（001）facet exposed was obtained by annealing amorphous TiO₂ nanotubes.The growth mechanisms of TiO₂ single crystals were explored from the following two perspectives:（1）Nanoindentation test in combination with strength calculation model were used to evaluate and calculate the streagth of TiO₂ nanotubes.We can establish a relationship between the geometries with mechanical performances of anodized TiO₂ nanotubes.The wall thickness of the anodized TiO₂ nanotube determines the fracture strength of the nanotube.Experimental results showed that TiO₂ nanotubes with thin wall were more prone to cystallize.（2）Experimental results,DFT calculation,and Smoluchowski equations were used to analyze the mechanism of single crystal growth.Nanoclusters with active dangling bonds were formed by annealing anodized TiO₂ nanotubes,which can attach to the surface of crystal nucleus through a way of atom rearrangement.The crystal growth was terminated when the adjacent transferrable precursor is depleted resulting to uniform well-defined single crystals.Secondly,a novel method（electrostatic attraction）was used to design and prepare of an effective MWNTs-TiO₂ nanotube electrode for high supercapacitance performance in acid environmental.Experimental results showed that MWNTs-TiO₂ nanotube（10 mg m L-1 APS,pH=5.5）hybrid electrode with a uniform morphology exhibited a high capacitance performance（4.4 mF cm-2）,which is 9 times higher than that of bare TiO₂ nanotubes.This result shows that MWNTs improve the conductivity and reduce the interfacial resistance of hybrid electrode.This synthetic method can be used to apply in other hybrid structures and lead to the development of new structure for applications in energy storage.Thirdly,TiO₂ nanorods were synthetized by solvothermal method and their growth mechanism was investigated.The additional amount of oleic acid and the reaction temperature can afftect the morphology of TiO₂ nanorods.The aspect ratio of TiO₂ nanorods depends on the additional amount of oleic acid and reaction temperatures.When the reaction temperature was 130 oC,TiO₂ nanorods with highly uniform size（length 33 ± 6 nm,diameter 4 nm）were obtained.It is notable that TiO₂ nanorods formed by nanoparticles attachment,which includes contact,rotation,lattice matching,and mass redistribution between the TiO₂ nanoparticles.