Development of Continuous Synthesis Process of Nanosize Titania Particles for Dye-Sensitized Solar Cell

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The purpose of this study is to construct the continuous synthesis process of monodispersed nanosize titania (TiO_2) particles in which mean particle size is under 50 nm and geometric standard deviation is under 1.2. To synthesis the nanosize TiO_2 particles, there are a build-up and a breakdown method. In this study, alkoxide method was used as a build-up method, and peptization was used as a breakdown method.First, alkoxide method, the synthesis method of TiO_2 particles by hydrolysis and condensation reaction of tetraethyl orthotitanate (TEOT), was examined. The condition to prepare the nanosize particles was examined by using a batch reactor. The ethanol solution of TEOT and hydroxypropyl cellulose (HPC), a polymer dispersant, was mixed with the water-ethanol solution to progress the reaction. At 0.025 mol/dm^3 of TEOT, 0.025 mol/dm^3 of water, and 2.5 g/dm^3 of HPC, the particle with 38 nm of mean particle size and 1.19 of geometric standard deviation was obtained.Based on the result of the batch experiment, the continuous synthesis was carried out using a slug flow tubular reactor system we have proposed. In this system, a packed bed for the nucleation of particles is connected in series with a slug flow aging tube. Mean particle size and geometric standard deviation of the particles obtained by the continuous system were almost same as that of the batch reactor.The peptization in which large particle was divided by the dissolution of the particle surface was carried out by using the batch reactor. The particle obtained by the alkoxide method was peptized using nitric acid. The optimum value exists for the nitric acid concentration, and the particle with 32 nm was obtained, which was smaller than the particle obtained by the alkoxide method. The geometric standard deviation was 1.22.