Environmental Engineering Reference
In-Depth Information
interface of nanocrystalline TiO 2. It was found that Arsenite can be oxidized and
removed effectively by TiO 2 (Pena et al., 2006). On a similar study Ferguson et al.
(2005) reported the sorption isotherms for As(III) and As(V) on P25 TiO 2 . The results
show that, in the absence of light, As(V) is adsorbed to a greater extent than As(III) at
pH 6.3. The maximum adsorbed concentrations of As(III) and As(V) observed under
these conditions were 32 and 130 μmol/g TiO 2 , respectively. Synthesis of nanoporous
zirconium oxophosphate and its application for removal of U(VI) has been reported by
Um et al (Um et al., 2007). The study showed that U(VI) adsorption followed a
traditional Langmuir adsorption isotherm, and the distribution coefficient (K d ) calculated
from the linear region of the Langmuir isotherm was 105,000 mL/g. This signifies the
great potential of applying nanoporous TiO 2 for the removal of various contaminants. Li
et al. (2003) studied the degradation of reactive brilliant red X-3B (a reactive dye) and
catechol (a refractory organic compound). The degradation was done by oxidation with
ozone in the presence of UV light in three ways: (a) without catalyst; (b) with TiO2
catalyst; and (c) carbon black coated TiO2 catalyst (CB TiO2). Figure 11.5(II) shows
that the reaction rate is almost double by the use of TiO 2 nanoparticles (Li et al., 2003a).
11.2.1.5 Ag (Bio Active Materials)
A variety of strong oxidants such as chlorine are used as disinfectants for
pathogens (e.g., viruses and bacteria). However these oxidants tend to generate toxic
disinfection byproducts such as trihalomethanes, haloacidic acid and aldehydes. Hence,
alternative disinfectants are critically needed where nanomaterials have strong role to
play due to its unprecedented opportunities. In general, bioactive materials such as silver
nanoparticles are known to develop chlorine free and disinfection byproduct free
biocides. Silver particles are easier and safer than other purifying agents such as chlorine
and do not produce disinfection byproducts. Furthermore, addition of silver in water
during treatment does not change in pH solution, and hence, eliminates the need to add
pH adjustment chemicals. Approximately half of the municipal sewer codes in the
United States limit the silver discharge from 0.05 to 5.0 mg/L (ppm) (USEPA, 1991).
Silver is also used as excellent reducing catalyst and antimicrobial compounds in various
biomedical products including environmental applications (Savage and Diallo, 2005). It
is mostly used in the form of nanoparticles either using its pristine state or in conjunction
with other materials to form porous materials which not only reduces the cost but also
increases the efficiency. Figure 11.6 shows HRTEM images of Ag nanoparticles in a
crystalline state and the rate of degradation of carbaryl as a function of time.
Mahmood et al. (1993) prepared silver coated sand and used for the disinfection
of contaminated water. Highly contaminated water passed through 1:1, 1:2 and 1:3
mixtures of silver treated and untreated sands of 10, 35 and 60 mesh sizes. The sand
mixtures of 35 mesh removed coliform and fecal coliform more effectively. This
indicates that silver has great potential to be used as a water disinfectant (Mahmood et
 
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