Preparation Of Anatase Titanium Dioxide Nanorods On The Basis Of "Oriented Attachment" Mechanism

The increasing need for solar energy has driven research towards the goal of safety and abundant renewable sources.Low costs and high efficiency are advantages for dye-sensitized solar cells(DSSCs) to become a potential and promising energy source.Therefore,titanium dioxide nanocrystals in DSSCs have been investigated in various aspects, including new processes,new materials and thin film technology,and have shown the application value for solar cells.To improve photoelectrical performance and commercialization of dye-sensitized solar cells,many researches are foucsing on the key components of DSSCs.In recent years,lots of studies have proved that nanorods or nanowires in the nanonetwork-like structure can enhance photoelectrical conversion efficiency of semiconductor.Thereby,how to control the morphology titanium dioxide have been becoming more crucial.In this paper,The wet titania precipitates were obtained by the thermal-hydrolysis of titanium salt as main raw materials.Then anatase titanium dioxide nanorods were prepared by a peptized-hydrothermal method,and its growth mechanism were discussed.The effects of different peptizing agents and hydrothermal conditions on the crystallite size,shape and optical spectra of TiO₂ nanorods were investigated.The as-prepared TiO₂ nanorods was characterized by X-ray powder diffraction,Raman spectra,UV-vis absorption spectra, photoluminescence spectra,BET specific surface area and transmission electron microscopy.The TiO₂ nanorods were mixed with the blue sol which was prepared by hydrothermal treatment at 150℃for 24h with nitric acid as a peptizing agent.The mixture was then autoclaved at 150℃for 24h once again,and branched nanorods were formed by the two-step hydrothermal treatment.All of the TiO₂ nanorods were in the anatase phase with high aspect ratio and an average diameter of less than 10 nm,and grew along the c-axis.Prolonging the hydrothermal time made TiO₂ nanoparticles aligned and grew to the longer nanorods even formed a complex nanoring-like structure via the oriented attachment mechanism.The specific surface area of TiO₂ with one-step hydrothermal and two-step hydrothermal treatment TiO₂ are of 115 m²/g and 108 m²/g,respectively. During peptization-hydrothermal treatment,forming mechanism of nanorods can be explained via the oriented attachment mechanism.The TiO₂ nanorods sols with good dispersible ability and stability were also obtained by hydrothermal treatment with hydrogen peroxide as a peptizing agent.The as-prepared TiO₂ sols under different hydrothermal conditions were in the anatase phase with the average diameter of less than 10 nm,and high aspect ratio is more than 5.The anatase nanorods with high aspect ratio have larger specific surface area,prolonging the hydrothermal time made TiO₂ nanoparticles grew to the longer nanorods via the oriented attachment mechanism,and much stronger luminescence property was observed at higher hydrothermal temperature.Surface adsorption property of the TiO₂ nanorods under optimization condition were studied by using a typical sensitizer such as the ruthenium dye(N719).The anatase nanorods with high aspect ratio and larger specific surface area have the adsorption capacity of 0.50 molecule/nm² for N719 in a 3.0×10^-4 M dye solution,respectively,which exhibited a higher adsorption capacity.