Noble metal doping can reduce the e/hþ recombination
because the photo-excited electrons tend to migrate to the
noble metals with lower Fermi levels while the holes stay in
TiO2 (Ni et al., 2007). The photocatalytic activity of TiO2 can
also be promoted by creating highly reactive crystallographic
facets. Because high-energy {001} facets diminish quickly
during crystal growth, anatase TiO2 is usually dominated by
the low-energy {101} facets.