411
cleaning applications, titanium oxide (TiO 2 ) nanoparticles that are
in their anatase form (one of the three forms of titanium oxide)
are used due to their photocatalytic properties. Exposure to UV
radiation produces electron-hole pairs in the material. The free
radicals or electrons that result react with foreign substances on the
surface and produce chemical reactions that ultimately decompose
the foreign substances through oxidation. Organic matter can be
quickly decomposed. The loosened and decomposed material can
then be washed away by normal rainfall or other means. Since
bacteria formation is associated with organic matter, the washing
away of this matter also causes the surfaces to have antibacterial
qualities. As we discuss more later, the same photocatalytic effect
can also reduce pollutants in the air.
Most photocatalytic processes are activated by UV wavelengths that
are commonly present in sunlight. Wavelengths in the UV range,
however, constitute only a narrow portion of the sunlight spectrum.
Increased photocatalytic efficiencies can be envisioned if activated
by other wavelengths as well. Considerable research is under way
to find nanosubstances that exhibit photocatalytic properties when
subjected to a broader range of wavelengths.
The three major actions discussed—hydrophobicity, hydrophilicity, and photocatalysis—form the basis of current easy-cleaning,
self-cleaning, and antimicrobial surfaces. The surfaces can form on
glasses, tiles, enameled panels, and other hosts (see the following
discussion). They also can have overlapping actions. Of particular interest here are photocatalytic surfaces made using titanium
dioxide (TiO 2 ). These same surfaces have high surface energies
and hence have been found to exhibit hydrophilic behaviors
where water forms into thin films rather than beading. This
combined behavior is very useful and has been exploited in many
products, including the so-called self-cleaning glasses we’ll discuss
in a moment.
Specific applications in glasses, tiles, paints, textiles, and other
product forms will be discussed shortly. It is important to observe
that the use circumstance can dictate which approach is used.
Photocatalytic processes now based only on UV light are obviously
primarily suitable for exterior, not interior, surfaces where sunlight is present. Products based on the Lotus Effect® are best used
where there is frequent general washing from rain or other sources;
otherwise streaks can develop. Many surfaces are particularly
sensitive to degradation when exposed to the kinds of disinfectants commonly used in cleaning. (This is a particular problem in
Functional Characteristics
cleaning applications, titanium oxide (TiO 2 ) nanoparticles that are
in their anatase form (one of the three forms of titanium oxide)
are used due to their photocatalytic properties. Exposure to UV
radiation produces electron-hole pairs in the material. The free
radicals or electrons that result react with foreign substances on the
surface and produce chemical reactions that ultimately decompose
the foreign substances through oxidation. Organic matter can be
quickly decomposed. The loosened and decomposed material can
then be washed away by normal rainfall or other means. Since
bacteria formation is associated with organic matter, the washing
away of this matter also causes the surfaces to have antibacterial
qualities. As we discuss more later, the same photocatalytic effect
can also reduce pollutants in the air.
Most photocatalytic processes are activated by UV wavelengths that
are commonly present in sunlight. Wavelengths in the UV range,
however, constitute only a narrow portion of the sunlight spectrum.
Increased photocatalytic efficiencies can be envisioned if activated
by other wavelengths as well. Considerable research is under way
to find nanosubstances that exhibit photocatalytic properties when
subjected to a broader range of wavelengths.
The three major actions discussed—hydrophobicity, hydrophilicity, and photocatalysis—form the basis of current easy-cleaning,
self-cleaning, and antimicrobial surfaces. The surfaces can form on
glasses, tiles, enameled panels, and other hosts (see the following
discussion). They also can have overlapping actions. Of particular interest here are photocatalytic surfaces made using titanium
dioxide (TiO 2 ). These same surfaces have high surface energies
and hence have been found to exhibit hydrophilic behaviors
where water forms into thin films rather than beading. This
combined behavior is very useful and has been exploited in many
products, including the so-called self-cleaning glasses we’ll discuss
in a moment.
Specific applications in glasses, tiles, paints, textiles, and other
product forms will be discussed shortly. It is important to observe
that the use circumstance can dictate which approach is used.
Photocatalytic processes now based only on UV light are obviously
primarily suitable for exterior, not interior, surfaces where sunlight is present. Products based on the Lotus Effect® are best used
where there is frequent general washing from rain or other sources;
otherwise streaks can develop. Many surfaces are particularly
sensitive to degradation when exposed to the kinds of disinfectants commonly used in cleaning. (This is a particular problem in
Functional Characteristics