Fig. 8 shows the dependence of methanol formation
on illumination time. Various yields of methanol
were obtained in a period depending on the catalysts.
In all cases, the concentration of methanol was
too small to be measured by GC for nearly initial
180 min. The formation of methanol was found much
Contact between TiO2 and metal generally involves
a redistribution of electric charge. In the
presence of copper clusters, electrons are enriched
owing to the alignment of Fermi levels of the metal
and the semiconductor, that is the Schottky barrier
[9]. Copper then serves as an electron trapper and
prohibits the recombination of hole and electron. In
addition, the rapid transfer of excited electrons to
the copper cluster enhances the separation of holes
and electrons [4], significantly promoting photoefficiency.
The formation of methanol was more efficient
than that of other hydrocarbons in the presence of
supported Cu+ on TiO2 from the CO2 and H2O
system [14].