The colloidal synthesis of metal oxide nanocrystals (NCs) in oleyl alcohol requires the metal to
catalyze an esterification reaction with oleic acid to produce oleyl oleate ester and M-OH
monomers, which then condense to form MxOy solids. Here we show that the synthesis of Cu2O
NCs by this method is limited by the catalytic ability of copper to drive esterification and thus
produce Cu+
-OH monomers. However, inclusion of 1-15 mol% of a group 13 cation (Al3+, Ga3+
,
or In3+) results in increased yields for the consumption of copper ions toward Cu2O formation and
exhibits size/morphology control based on the nature of M3+
. Using a continuous-injection
procedure where the copper precursor (Cu2+
-oleate) and catalyst (M3+
-oleate) are injected into
oleyl alcohol at a controlled rate, we are able to monitor the reactivity of the precursor and M3+
catalyst using UV-visible and FTIR absorbance spectroscopies. These time-dependent
measurements clearly show that M3+ catalysts drive esterification to produce M3+
-OH species,
which then undergo transmetallation of hydroxide ligands to generate Cu+
-OH monomers required
for Cu2O condensation. Ga3+ is found to be the “goldilocks” catalyst, producing NCs with the
smallest size and a distinct cubic morphology not observed for any other group 13 metal. This is
believed to be due to rapid transmetallation kinetics between Ga3+
-OH and Cu
+
-oleate. These
studies introduce a new mechanism for the synthesis of metal oxides where inherent catalysis by
the parent metal (i.e. copper) can be circumvented with the use of a secondary catalyst to generate
-OH ligands.
Immobilization of enzyme using natural feldspar for use in the synthesis of oleyl oleate
