S. Sakohara et al., Preparation and optical properties of nano-sized ZnO colloidal particles using NH3 gas as volatile catalyst, J CHEM EN J, 34(1), 2001, pp. 15-21
Nano-sized zinc oxide (ZnO) colloids were prepared by hydrolyzing zinc acet
ate solution with ammonia (NH3) gas as a volatile catalyst, instead of meta
l hydroxides such as NaOH and LiOH, which have been used previously. The pr
ocedure consists of two major steps: (1) preparing the precursor by reactin
g zinc acetate with ethanol, and (2) hydrolyzing the precursor to form the
colloid. Hydrolysis was performed by bubbling the desired composition of NH
3-N-2 gas mixture into the precursor for the desired time in an ultrasonic
bath. The hydrolysis conditions required for forming ZnO colloids such as t
he composition of the NH3-N-2 gas mixture and bubbling Limes are examined.
In addition, optical properties such as luminescence and absorption of thes
e ZnO colloids produced via this basic hydrolysis procedure, and the effect
of the residual NH, in the suspension on colloidal stability are examined.
It is found that a critical amount of dissolved NH, to form nano-sized ZnO
particles is existent, and that the Luminescence intensity largely depends
on the gas composition and the bubbling time. Residual NH, remaining in the
suspension greatly affects colloidal stability, But, it could be easily re
moved by evaporating ethanol of the solvent under reduced pressure. The res
ulting ZnO powder could be re-dispersed quickly and completely into ethanol
, The luminescence and absorption properties of the re-dispersed colloidal
suspension were almost the same as those of the original suspension. Moreov
er, the redispersed ZnO suspension was absolutely transparent for more than
one month at room temperature. In other words, the colloidal stability is
remarkably improved.