from 60 to
180 C (at 30 C intervals) for reaction times of 1, 10, or
60 h to investigate the effect of both reaction temperature
and time on the product yield. To investigate the role of oxygen
several experiments were repeated in an
oxygen-free environment by sealing the pressure vessel under
an argon atmosphere and using oxygen-free water. Upon completion
of the heating profile, the pressure vessel was allowed
to cool naturally to room temperature. The precipitates were
then collected by filtration and washed with distilled water
several times.