Figure 7.

Atomic structure of typical photocatalysts for photodegradation. (a) ZnO wurtzite cell, Zn atoms in yellow, O atoms in grey [51]. (b) The hexagonal representation of unite cell of ferric oxide (hematite) with Fe atoms in blue and O atoms in red [52]; reprinted from [52] with permission from IOP Publishing. Structure of (c) s-triazine and (d) tri-s-triazine as the primary building blocks of graphitic carbon nitride with C atoms in grey and N atoms in blue [50]; reprinted from [50] with permission from Elsevier.