Nanotechnology in manufacturing paints for eco-efficient buildings - Nanotechnology in Eco-efficient Construction - page 347

methylene blue) (Abe et al. , 2000; Chatterjee and Mahata, 2001, 2002; Mele
et al. , 2003; Moon et al. , 2003; Kaur and Singh, 2007), a polymer (e.g.,
polyfl uorine-co-thiophene) (Song et al. , 2007; Qiu et al. , 2008) or a narrow
band gap semiconductor (e.g., Bi 2 S 3 , CdS, CdSe or V 2 O 5 ) (Bessekhouad
et al. , 2004; Ho and Yu, 2006; Jianhua et al. , 2006; Wu et al. , 2006) to the TiO 2
surface. The sensitizer acts as an intermediary and, by enhancing the absorp-
tion of visible light, it enables the activation of the photocatalyst by electron
transfer between the excited sensitizer and TiO 2 .
TiO 2 sensitized with meso-tetrakis(4-sulfonatephenyl) porphyrin has
been applied successfully to the photo-oxidation of acetaldehyde in indoor
air under visible light irradiation (Ismail and Bahnemann, 2010).
The doping approach involves the modifi cation of the electronic structure
of TiO 2 by adding a dopant that modifi es the band structure either by
increasing the energy of the valence band or by minimizing the energy of
the conduction band. The ultimate effect is a minimization of the band gap,
thus enabling the doped photocatalyst to be activated by means of visible
radiation.
Doped TiO 2 photocatalysts prepared by doping with either non-metals
(e.g., N, C or S) (Ao et al. , 2009; Jo and Kim, 2009; Rockafellow et al. , 2009)
or transition metals (e.g., Fe, Co, Cu, Au or Mn) (Andronic et al. , 2009;
Bengtsson et al. , 2009; Kafi zas et al. , 2009; Song et al. , 2009; Cacho et al. ,
2011) have been applied successfully for the degradation of indoor air pol-
lutants when activated by visible light.

Non-TiO 2 photocatalytic materials activated by visible light
Only a few attempts at the development of non-TiO 2 -based photocatalytic
materials that can be activated directly by visible light have been successful,
due to their narrower band gap. In this sense, metal calcogenides (e.g., CdS,
CdSe) (Reutergardh and Iangphasuk, 1997; Green and Rudham, 2003),
metal oxides ( -Fe 2 O 3 , In 2 O 3 SnO 2 , WO 3 , ZnO) (Faust et al. , 1989; Kormann

et al. , 1989; Pulgarin and Kiwi, 1995; Mazellier and Bolte, 2000; Bandara
et al. , 2001) and mixed metal oxides (SrTiO 3 , CaBi 2 O 4 ) (Rothenberger et al. ,
1985; Tang et al. , 2004) have been evaluated as potential photocatalysts.
However, the formation of short lived metal-to-ligand and ligand-to-metal
charge transfer states, and the narrower band gap, make these materials
considerably less stable towards their own photocorrosion.

α

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15.3.2 Investigation into the effi ciency of photocatalytic
indoor paints at the laboratory scale
Photocatalysis of NO and NO 2

Photocatalytic decomposition of NO and NO 2 has been widely investigated
using pure TiO 2 fi lm surfaces, photocatalytic paints, photocatalytic concrete