Environmental Engineering Reference
In-Depth Information
(a)
(b)
(c)
1
1
TiO
2
nanoparticles
(
b
)
(
b
)
Hollow core at tip of CNT
after Ni removal
0.8
0.8
(
a
)
0.6
0.6
(
a
)
0.4
0.4
CNT wall at tip
0.2
0.2
TiO
2
coating
50 nm
0
0
100
120
0
100
120
20
40
60
80
20
40
60
80
Time (min)
Time (min)
FIGURE 12.10
(a) TEM image of a TiO
2
/MWNT heterojunction nanotube at tip of the CNT, after removing the Ni seed from tip
of the CNT. Normalized ratio of the killed bacteria on surface of the TiO
2
/MWNT samples annealed at 100°C
(b) and 400°C (c) (
a
, in dark;
b
, under visible light irradiation). (From Akhavan, O. et al.,
Carbon
, 47, 3280, 2009.
With permission.)
the bacteria increased from MWNTs to TiO
2
to TiO
2
/MWNTs, in which the bacteria could
even slightly breed on the MWNTs (Figure 12.10b,c).
60
This approach can be used to make
a TiO
2
/MWNT composite that can be used as a ilter or membrane in water disinfection.
Photodegradation of bacteria with organic-TiO
2
composites have the potential for use in
water disinfection if the visible light photocatalytic antimicrobial activity can be enhanced.
Overall, the polymer-Ag composites with dual mode of antimicrobial action have tre-
mendous application wherein the polymers are also antibacterial, confer the controlled
release of silver and long-lasting antimicrobial activity. Photocatalytic materials like TiO
2
also have great potential if its visible light antibacterial activity can be enhanced.
12.3 Carbonaceous and Mesoporous Materials
Advanced techniques such as membrane iltration, reverse osmosis, and ion exchange
have been shown to be highly eficient in removing various types of contaminants from
water. However, their high costs limit the use of membrane iltration technology in devel-
oping countries. With adsorption as one of the principal mechanisms, carbonaceous and
mesoporous materials have been identiied for a wide range of point-of-use (POU) and
other water treatment options.
12.3.1 AC-Ag Composites
The most widely used material, AC has the best possible surface area and could be pro-
duced at low cost. A number of other forms of carbon have appeared with very large
adsorption capacities. Carbonaceous materials such as AC, graphene, carbon nanoibers,
fullerenes, and carbon nanotubes (single-walled carbon nanotubes [SWNTs] and MWNTs)
have been used extensively in water puriication and, hence, are affordable adsorbents
in all commercial water technologies. AC, carbon monoliths (CMs), and AC ibers (ACFs)
have been widely used in wastewater treatment to remove organic or inorganic pollut-
ants because of their extended surface area, high adsorption amount and rate, and speciic
