Study Of Hydrothermal Synthesis Process And Photocatalytic Properties Of TiO₂ Nanotubes

Titania nanomaterials are widely applied in fields of photocatalytic degradation,sensitive solar cells,hydrogen generation by splitting water and the gas sensor.Compared with the nanoparticle form,one-dimensional titania nanotubes have much higher photocatalytic activity and photoelectric conversion efficiency because of their large specific surface area and adsorption capacity.In this study,titania nanotubes were synthesized by a simple one-step hydrothermal method;the effects of hydrothermal reaction temperature,reaction time,calcination process and Fe-doping on phase formation and morphology of the nanotubes were investigated using high resolution transmission electron microscope with energy spectrum analysis?HRTEM/EDS?,X-ray diffraction?XRD?and scanning electron microscope?SEM?;the photocatalytic performance of nanotubes in methylene blue solution under UV rediation were studied by using a self-prepared devices,the preparation technique for synthesis of titania nanotubes with excellent photocatalytic degradation behavior was obtained.The experimental results are shown as follows.In the one-step process,the titania nanotubes with an anatase structure and an excelent crystallinity can be obtained by a series of operations,hydrolysising tetrabutyl titanate sol in NaOH solution,hydrothermal reaction,acid-washing and calcination.The nanotubes had a diameter of 5 nm and a length of 100 nm,the orientation of section is??01?.The hydrothermal reaction stimulates transformation of amorphous TiO₂ to Na₂Ti₂Ti₆O₁₆ flakes;the acid-washing promotes the transition of Na₂Ti₂Ti₆O₁₆ flakes to H₂Ti₄O₉·H₂O nanotubes and the calcination improves H₂Ti₄O₉·H₂O nanotubes transforming into titania nanotubes with anatase structure.Iron-doping facilitates H₂Ti₄O₉·H₂O nanotubes to transform into titania nanotubes.When the dopant is less than 5 mol%,the doping has less influence on morphology of the nanotubes;however,when the doping concentration is higher than 5 mol%,it leads to a decrease of length of the nanotubes.With an increase of the calcination temperature,titanate nanotubes are easy to be transformed into anatase TiO₂ nanotubes in oxidation and reduction atmospheres.When calcination temperature is less than 500?,the morphology of the nanotubes can not be destroyed;when calcination temperature is higher than 500?,the morphology of the nanotubes begains to collapse.The calcination atmosphere has less influence on morphology of the nanotubes.The photocatalytic experiments show that the titania nanotubes doped with 3 mol% of Fe,hydrothermal reaction in 10 mol/L of Na OH solution at 150? for 16 h,washing in acid solution and calcinated at 400? for 2 h in reducing atmosphere had the best photocatalytic degredation efficiency?over 93%?.The change in thickness of the surface attachments of methylene blue on TiO₂ nanotubes in the reaction process shows the photocatalytic degradation and recycle behaviors of the TiO₂ nanotubes.