The potential redox value for Cu+ and
Cu2+ areBecause Cu2O has the highest positive potential redox
value of Cu+, Cu2O dopant should effectively act as an
electron trapper to prohibit electron–hole recombination.
However, owing to the relatively strong interaction
between TiO2 and the dopant particle implanted in the
vacant sites of TiO2, the dopant with more positive potential
redox exceedingly catches electron from conduction
band edge. Consequently the dopant-trapped
electrons are more difficult to be transformed to the adsorbed
species on catalyst surface and hence it may play
a role as a center of electron–hole recombination.
In this context, Cu2+ with the lower potential redox is
a more promising dopant species especially in the case of
strong implanted dopant in the vacant site of TiO2.
Since a Cu2+ ion has an unfilled 3d shell and the reduction
of Cu2+ is thermodynamically feasible, it is valid to
assume that electrons can be trapped by CuIIO on the
surface of TiO2 [5]. Eq. (5) illustrates the redox cycle
of Cu2+/Cu+ that maybe played by CuO dopant on
the TiO2 matrix. Photoexcited electrons on the conduction
band will be trapped by Cu2+, as a consequence the
species of Cu2+ can be predicted to become Cu+ species.
Trapped electrons could be consumed via the reduction
of H+ and/or O2 forming radicals of H and/or O
2 ,
respectively. In other words, the Cu+ species could be
re-oxidized to Cu2+ by ion of H+ and/or O2 that present
in the system. As a result of these sequential reactions
(Eq. (5)), the electron–hole recombination rate could
be effectively reduced.
The potential redox value for Cu+ and
Cu2+ areBecause Cu2O has the highest positive potential redox
value of Cu+, Cu2O dopant should effectively act as an
electron trapper to prohibit electron–hole recombination.
However, owing to the relatively strong interaction
between TiO2 and the dopant particle implanted in the
vacant sites of TiO2, the dopant with more positive potential
redox exceedingly catches electron from conduction
band edge. Consequently the dopant-trapped
electrons are more difficult to be transformed to the adsorbed
species on catalyst surface and hence it may play
a role as a center of electron–hole recombination.
In this context, Cu2+ with the lower potential redox is
a more promising dopant species especially in the case of
strong implanted dopant in the vacant site of TiO2.
Since a Cu2+ ion has an unfilled 3d shell and the reduction
of Cu2+ is thermodynamically feasible, it is valid to
assume that electrons can be trapped by CuIIO on the
surface of TiO2 [5]. Eq. (5) illustrates the redox cycle
of Cu2+/Cu+ that maybe played by CuO dopant on
the TiO2 matrix. Photoexcited electrons on the conduction
band will be trapped by Cu2+, as a consequence the
species of Cu2+ can be predicted to become Cu+ species.
Trapped electrons could be consumed via the reduction
of H+ and/or O2 forming radicals of H and/or O
2 ,
respectively. In other words, the Cu+ species could be
re-oxidized to Cu2+ by ion of H+ and/or O2 that present
in the system. As a result of these sequential reactions
(Eq. (5)), the electron–hole recombination rate could
be effectively reduced.
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