Environmental Engineering Reference
In-Depth Information
The free radicals of OH
∙
and superoxides
O
2
( )
earlier are highly destructive to organic
matter. Research has shown that the TiO
2
/UV combination is highly effective in water
treatment. Photocatalysis can kill animal cells, and its application has been extended to
cancer treatment [19]. By observing an indigo-carmine dye pill color change, the killing of
bacteria was conirmed.
Despite a dramatic progress in the decontamination of water, there are still problems
related to the treatment of wastewater contaminated with dyes from the textile indus-
tries, agricultural wastes, and chemical plants chlorinated by products and chemicals.
The presence of trace metals such as Hg, Cr, Pb, As, and Ni, and inorganic compounds
like bromates, chromates, and halides, in water may further complicate the treatment
processes.
Whereas crumb rubber and the solar distillation process are highly effective in remov-
ing pathogens and impurities, the removal of contaminants originating from industries
and agricultural lands need powerful oxidants for their removal. Photocatalytic treatment,
which produces OH
∙
and
O
2
−
free radicals, has the capability to remove these contami-
nants. Whereas substantial research has been conducted on photocatalytic reactors, it is
limited mainly to the availability of antirelecting transparent strong, thin surfaces, light-
emitting resources, arrangement of lenses, a high ratio of activated immobilized catalysis
to illuminated surface, and rigid control of angle of incidence [20]. In our ongoing research
program on the development of photocatalytic reactors, consideration has been given to
resolve the above issue. If we could succeed in overcoming the above challenges, mainly
the limitations imposed by distribution of uniform light, prolonged contact time between
the catalyst and water, and providing a large surface area for contact, we could succeed in
scaling up reactors for hollow tubes for industrial use [16].
The major issue is that of creation of a surface that does not relect light. In our work on
nanocoatings, we realized these shortcomings. In our work on design, which is in prog-
ress, we have developed nanostructured surface on glasses by shotless cavitation peening
aiming to obtain a grain size of 10 nm on the blasted surface. Nanostructured surfaces can
be obtained by cold deformation. Sand blasting with silica particles gave a grain size of
50 nm. The process of sand blasting is performed to obtain a nanostructured surface. This
process can also be used to obtain small grain sizes on steel. Because of sharp high-density
boundaries, the relection would be minimized, which would allow a uniform distribu-
tion of light. We are examining the effect of grain size and light absorption and relec-
tion. Work on the effect of nanostructured surface on light relection on different types
of glasses, such as Corning, Pyrex, Schott, and Xo glass, is showing promising results.
Current work on coating of nanosilica, hydrophobic SiO
2
coatings with
n
-TiO
2
, and meso-
porous TiO
2
is expected to provide a complete suppression of relection and allow the
scaling up of photocatalytic reactors. The design of the photocatalytic reactor is shown in
Figure 1.2. The use of mesoporous TiO
2
synthesis via a chemical route provides an alter-
native for conventional TiO
2
[21]. It has an optical band gap of 3.75 eV and a diameter of
200-300 nm. Hollow spheres are excellent catalyst carriers. By making the speciied glass
surface nanostructured and applying a coating of mesoporous TiO
2
and
n
-SiO
2
, on hollow
tubes of glass, we expect to achieve antirelecting coatings on the hollow glass surface of
photocatalytic reactors and overcome the existing challenges.
This extension of our work from a crumb rubber/UV radiation bimodal system and
attempts to design large-scale photocatalytic reactors show the attempt that has been
made to decontaminate water from pathogens, dyes, chemicals, agriculture runoff, and
pesticides.
