Thus, precipitation of pure crystalline titania particles in large quantities with controlled shape and size is of considerable practical interest. In partic-Uniform spindle-type titania (TiO 2 ) particles were prepared by ular, well-defined anatase-type particles may be useful as photocatalysts.
a novel gel-sol method. A mixed solution of titanium(IV) isopro-On the other hand, a novel general method for the preparation of monodispoxide and triethanolamine at molar ratio 1:2 prepared in a drybox perse particles has recently been invented and developed for the synthesis was mixed with doubly distilled water to make the final concentraof uniform hematite (a-Fe 2 O 3 ) particles (5-10). The novel method, named tion of titanium(IV) 0.50 mol dm 03 . The mixture was further the ''gel-sol method,'' for preparation of monodisperse particles in large mixed with an equal volume of 2.0 mol dm 03 ammonia solution, quantities is based on the idea of using a highly condensed precursory metal and the resulting solution was aged for 24 h at 100ЊC. By this hydroxide gel as a protective matrix against the coagulation of the growing aging a highly viscous gel was formed, but there was no sign of particles as well as a reservoir of the metal ions, and it has successfully nucleation of titania at this stage. The gel was then aged at 140ЊC been applied to the synthesis of monodisperse CdS (11-14), ZnS (13), for 3 days to nucleate and grow the titania particles. The gel and basic aluminum sulfate (15) particles.
This paper pertains to the synthesis of pure and uniform spindle-like network formed in the first aging played a decisive role in the anatase-type particles different in size and aspect ratio in alkaline media as second aging to produce the uniform particles of titania, as a an application of the gel-sol method. reservoir of the metal ions to lower the supersaturation for preventing extensive nucleation and as an anticoagulant fixing the growing particles in the matrix. The product was identified by EXPERIMENTAL XRD as anatase particles elongated in the direction of the c-axis. The aspect ratio, as well as the size of the resulting particles, was Preparation of Uniform Spindle-Type Titania Particles reduced as the concentration of ammonia was decreased. ᭧ 1997 The established standard conditions for the preparation of uniform spin-Academic Press dle-like anatase-type titania particles were as follows. First, a stock solution Key Words: synthesis; gel-sol method; titania; anatase; uniform of Ti 4/ was prepared by mixing titanium(IV) isopropoxide (TIPO) with particles; spindle-type particles.
triethanolamine (TEOA) under nitrogen atmosphere at a molar ratio of TIPO:TEOA Å 1:2 to form a stable complex of Ti 4/ for preventing the excessively rapid hydrolysis of Ti 4/ . Doubly distilled water was then added to make the solution 0.50 mol dm 03 in Ti 4/ . Then, 10 cm 3 of the stock solution was mixed with the same volume of 2.0 mol dm 03 ammonia solu-FIG. 1. Scanning electron micrographs of the TiO 2 particles prepared under the standard conditions (a) and by skipping the first aging for gelation 1 Presented in part at the 49th Symposium on Colloid and Interface Chemistry, Hachioji, Japan, September 19-21, 1996. under otherwise the standard conditions (b).