There have been a
number of attempts aimed at overcoming this drawback.
Among the routes followed are doping TiO2 with transition
metals and/or rare earth elements [24,25] or non-metal
atoms [26,27], making composite TiO2 photocatalysts
[28,29] or heterojunction photocatalysts [30,31]. Recently,
an approach developed in order to absorb visible-light
radiation is the deposition of noble metal nanoparticles
(NP) onto the surface of the semiconductor material.