Preparation, Photocatalytic Photoelectrochemical Properties Of Nanostructured Titanium Dioxide

In the past decades, the titanium dioxide （Ti02） nanomaterials aredrawing great interest because of their unique photoelectric propertiesand photocatalytic activity. The high surface area brought by nanometersize is beneifcial to many Ti02based devices, because the reactionmainly occurs on the surface or at the interface and strongly depends onthe surface area of the Ti〇2nanomaterial. The structures of Ti〇2nanomaterials could decide different properties. Tremendous efforts havebeen devoted to the preparation of nanostructured titanium dioxidematerials, including nanoparticles，nanorods, nanowires, nanofibers,nanosheets and nanotubes, etc. Recently, much attention has been focusedon the preparation of Ti02nanomaterials with designed nanostructure dueto their attractive potentials in many promising ifelds such as highlyefficient photocatalyst and low cost photovoltaic dye-sensitized solar cell（DSSC）. The nanostructured crystalline Ti02nanomaterials could providedirect electrical pathways to ensure the rapid electron transport rate,which in turn may improve the photocatalytic activity and photon-to-current conversion eiffciency. Nanostructured Ti02with manyexcellent properties has been synthesized by various available processingtechnologies in our studies, and the main contents are described asfollows.1. Titanium dioxide thin iflms with porous structures have beensuccessfully achieved by photopolymerization stimulating the particledispersion combined Ti02colloid with photoinitiator and monomer. Thephotopolymerization monomer Pentaerythritol Triacrylate （PETA） andphotoinitiator2-Hydroxy-2-methyl-propiophenone （HMPP） are added tothe Ti02colloidal solution to form the new colloidal Ti02dispersion.After coating the dispersion on the substrate, the coating is cured withUV light. With the evaporation of solvent and the formation of microgelsinduced by polymerization, a phase separation occurs in the system. Aporous Ti〇2film with various pore sizes from mesoporous tomacroporous could be produced atfer heat treatment. The morphologyand size of pores could be tuned by changing the process of phaseseparation, which is controlled by the composition of colloidal Ti〇2dispersion. The content of photoinitiator and the temperature of heattreatment were decided by UV-vis absorption spectra and thermalanalysis （DTA-TGA）. The as-prepared Ti〇2porous films exhibited higherphotocatalytic activity for degradation methylene blue in comparison withconventional Ti〇2dense film due to its porous structure. 2.It reported a facile, template-free route to directly prepare largeTi02nanopillars arrays. That was, ethylene glycol substituted foralkoxide to form a titanium glycolated precursor, then the precursor canfurther react to generate Ti_0Ti bonds by hydrolysis and condensationprocess after a slow in-situ esterification in the reaction mixtures. Finally,the product was Ti02nanoparticle after a series of reactions andprocessing. The novel structures of nanopillars were prepared by thestacking of Ti02nanoparticles without the need of templates. A "stacking"growth schematic model including three steps of substitution, hydrolysis,and stacking was performed to explain the formation process of Ti02nanopillar structure. We believe that the application of the stackinggrowth method to different substrates for preparation of nanostructuresshould be available, and this new class of Ti〇2nanopillar nanostructuresfabricated on the Ti〇2thin film could ifnd great potential for applicationin various ifelds.3.Two types of hollow crystalline titanium dioxide （Ti〇2）nanofibers were successfully fabricated through a facile coaxialelectrospinning technique, with titanium sol and titanium precursorrespectively as the materials for the shell. The two types of hollow Ti〇2nanofibers possessed a similar tubular feature on the nanometer scale, butdifferent morphology on surface nanostructures and size on shellthickness. Hollow nanofibers prepared by using titanium sol demonstrated that a small amount of water in core could preventefficiently the diifusion of the core and shell solutions. For the titaniumprecursor without spinnability, it could be coated on the poly（vinylpyrrolidone） core nanofibers as shell templates during the coaxialelectrospinning process and properly developed into nanostructured Ti02wall of the hollow nanofibers. Both of hollow Ti02nanofibers exhibitedhigher photocatalytic activity for degradation methylene blue incomparison with the solid Ti02nanofibers prepared by normalelectrospinning due to their unique hollow structure.4. TiO₂nanotube arrays films were prepared by using of anodizationin ethylene glycol electrolyte containing glycolic acid, ammoniumfluoride, and water. The effect of anodization potential, anodization time,and electrolyte on the morphology and structure of Ti〇2nanotube arraywere characterized. Research results show that the addition of glycolicacid in classic ethylene glycol based electrolyte can successfully achievehighly ordered one-dimensional Ti〇2nanotube array under a high voltagewithout anodic breakdown. During the anodization processing, theelectrolyte yielded a fast nanotube growth rate for Ti〇2nanotube, whichwas based on the field enhancement effect of organic acid. The Ti02nanotube array films atfer heat treatment exhibited photocatalytic activityand photoelectric conversion eiffciency.