etc., the formation of the other product such as metallic Cu Uniform spherical Cu 2 O particles with an average diameter of 0.27 must be avoided, and thus a moderate reducing activity is mm were prepared in large quantities by aging a 0.5 mol dm 03 CuO required for the reducing agent. McFadyen and Matijevic Εuspension containing 0.5 mol dm 03 N 2 H 4 and 3 wt% deionized gelatin (2) prepared uniform Cu 2 O particles of characteristic shapes for 3 h at 30ΠC. Use of amorphous Cu(OH) 2 as a reservoir of copper by reducing copper(II) tartrate complexes with a mild reducions in place of the crystalline CuO yielded polydispersed particles ing agent, glucose. In this system, the coagulation of the due to the too high solubility of Cu(OH) 2 , causing the renucleation growing particles was avoided by diluting the entire system. of Cu 2 O during its growth. Gelatin played a decisive role as an inhibitor If we can produce the uniform Cu 2 O particles in large quantiof the direct attack of N 2 H 4 to CuO surfaces and coagulation of the ties, we will be able to enjoy in practice the utmost functions growing Cu 2 O particles as well as a pH buffer in producing the uniform particles. The Cu 2 O particles grew through the surface reaction of the proper to general monodispersed particles. Cu / ions and/or their complexes formed by the reduction of Cu 2/
On the other hand, Sugimoto and co-workers (3-6) develions dissolved from the CuO particles. The reducing activity of hydraoped a new method in the preparation of monodisperse hezine was controlled by regulating the initial pH and by the pH buffer matite (a-Fe 2 O 3 ) particles in large quantities starting from action of gelatin. The dissolution process of Cu 2/ ions from the CuO a highly condensed ferric hydroxide gel. It may be one of solid was the rate-determining step in the growth of Cu 2 O particles at the answers to the growing demands for the industrial use pH no less than 9.3, so that the supersaturation was kept low enough of monodispersed particles as the most ideal particulate mato prevent significant renucleation. But, an excessively high pH above terials. Since the process is based on a phase transformation ca. 10 led to the formation of metallic Cu particles of a rather broad from a condensed gel to monodispersed sol, it was named size distribution due to the too high reducing activity of hydrazine.
the ''gel-sol method.'' In the case of a-Fe 2 O 3 particle for-Under standard conditions, 38% of N 2 H 4 was consumed by the reaction mation, the final particles are formed through a two-step N 2 H 4 / CuO r 1/2 Cu 2 O / 1/2 N 2 / NH 3 / 1/2 H 2 O and 15% by N 2 H 4 / 4 CuO r 2 Cu 2 O / N 2 / 2 H 2 O. α§ 1997 Academic Press phase transformation, i.e., Fe(OH) 3 r b-FeOOH r a-Fe 2 O 3 , Key Words: Cu 2 O particles; uniform particles; CuO; gelatin; in which the precursory solid network in each step works N 2 H 4 ; condensed system; formation mechanism. as a protective matrix against the coagulation of the subsequently formed particles as well as a source of metal ions. The precipitation of b-FeOOH as the intermediate contributes to the inhibition of the renucleation of a-Fe 2 O 3 by 1 Presented in part at 47th Symposium on Colloid and Interface Chemistry This is a report on the synthesis of uniform spherical Cu 2 O at Okayama, October 8-10, 1994.
2 To whom correspondence should be addressed.
particles prepared from a condensed CuO suspension, as an 167