Synthesis Of TiO₂ Particles And Preparation Of Photonic Crystals

Titanium dioxide is a kind of very important functional materials.Because of its high refractive index and excellent optical properties,it is very likely that high-quality photonic crystals with a near-infrared or visible light bandgap will be prepared using TiO₂ colloidal microspheres in the future.Monodisperse TiO₂ microspheres is the base for us to fabricate colloidal photonic crystals.In this paper,on the basis of sol-gel method,we synthesized monodisperse submicron and narrow dispersed nano TiO₂ particles using tetrabutyl titanate?TBOT?as raw materials,and prepared high-quality colloidal photonic crystals by centrifugal self-assembly.Adding KCl as a stabilizer,monodisperse submicron TiO₂ microspheres with the size range of 100⁴65 nm were successfully synthesized in the ethanol system.We also obtained narrow dispersed nano TiO₂ particles with the polydiseperse index between 0.05 and 0.25.Different effects of reaction time?0⁸ h?,concentration of KCl(4.06×10^-41.74×10^-3 mol/L),molar ration of H2 O to Ti?4.05⁹.45?,and reaction temperature?15⁴0°C?on size and particle size distribution of TiO₂ microspheres were studied.Results showed that particles' agglomeration and sedimentation could be effectively inhibited by adding of KCl.And TiO₂ microspheres with different particle sizes could be obtained under appropriate reation conditions.Using acetone-EtOH or dimethyl sulfoxide?DMSO?-EtOH mixed solvent as the reaction medium,monodisperse TiO₂ regular microspheres with the size range of 100⁴65nm and smooth surface were prepared by adding KCl as a stabilizer.It was found that the particle size decreaseed with the increase of concentration of KCl(4.06×10^-41.45×10^-3 mol/L),and meanwhile monodispersity kept good;higher volume fraction of acetone or DMSO,causing both particle size and PDI bigger,particularly for the effect of DMSO.Mixed solvent method provided a new way for the synthesis of monodisperse submicron TiO₂ regular microspheres.A two-step process was applied to synthesize good water-soluble nano TiO₂ particles.The precipitate formed at room temperature and then was peptized via the reflux method at 80°C.The amount of tetrabutyl titanate?TBOT?and pH value were investigated in the experiments.Results showed that uniformly dispersed smallest TiO₂ particles were obtained at the pH value of 1.5,with 0.5 mol/L TBOT as titanium source.Using pre-synthesized monodisperse TiO₂ microspheres with the diameters of 145 nm,179 nm,200 nm and 230 nm as raw materials respectively,three-dimensional colloidal photonic crystals with large area wree prepared by centrifugation self-assembly under different speed of 2500 rpm,3500 rpm and 4500 rpm.Samples were characterized by scanning electron microscope?SEM?and UV-vis spectrophotometer.Results showed that the centrifugation self-assembly was simple to operate with short preparation cycle.The colloidal photonic crystals had obvious photonic band gaps.As the the particle size increaseed,redshift of forbidden band position occurred.Speed also affected the quality of the colloidal photonic crystals,and the appropriate speed should be choosen according to the size of the microspheres.This provided the experimental basis and effective guidance for the application of photonic crystals in the optical devices.