2h = 25.34 and 2h = 27.42 correspond to the main
peak of anatase and rutile, respectively. It can be seen
that for all copper modified TiO2 samples, only the characteristic
peaks corresponding to P25 were found (which
consisted of 79% anatase and 21% rutile). CuO diffraction
peak appeared near 2h = 35.6 only on the high
CuO loading samples (P3%), and the peak intensities
increase for higher CuO loading. The disappearance of
the CuO peaks in the low CuO loading samples is due
to the high dispersion of the dopant species. In addition,
the disappearance of the CuO peaks after reduction of
the samples (Fig. 2-d0) indicated that CuO has been successfully
reduced to other species. It can also be inferred
from Fig. 2 that the crystalline form of the TiO2 has not
been changed by loading CuO as the shapes and relative
intensity of the characteristic TiO2 peaks remained
unchanged.
To discuss the interactions between the dispersed
ionic species and the support, the surface structure of
the support should be taken into consideration. According
to Xu et al. [7] only the octahedral vacant sites are
available in the preferentially exposed (0 0 1) plane of
anatase, and the dispersion capacity of CuO on TiO2
(anatase) should be equal to the number of the surface
vacant sites available, i.e., 6.98 Cu2+ nm2. When the
CuO loading exceeds its dispersion capacity, all the vacant
sites have been occupied, and then the existence
of crystalline CuO can be detected by XRD.