Band gap width of the photocatalyst is an important criterion
in the choice of the photocatalyst.
For instance, TiO2 photo-catalyst has a band gap of 3.0–3.2 eV and it has been subjected
to several treatments including mixing with semiconductors, doping with various metals, and various preparation methods to enhance its catalytic activity and surfacearea, adjust its band gap, and decrease the possibility of charge carriers recombination [13–15].