Environmental Engineering Reference
In-Depth Information
Silver nanoparticles has also been used as a novel catalyst by combining with
zeolite (Ag-zeolite Y) for the photodecomposition of carbaryl (1-naphthyl, N -
methylcarbamate) (Kanan et al., 2003) (Figure 11.6B). In the absence of the catalyst, (in
the presence of UV light) 30 ppm solution of carbaryl decomposes with a first-order rate
constant of (5.6 ± 0.3) × 10 -5 /s (298 K) and a quantum efficiency of 4.8 × 10 -3
molecules/photon. In the presence of the Ag-zeolite Y catalyst, the photodecomposition
rate becomes 80 times faster. It was observed that the addition of Suwannee River
natural organic matter (NOM) had a minimal effect on this system. In the presence of
three different concentrations of NOM and 30 ppm carbaryl tested, the results indicate
that the NOM increases or decreases the catalytic photodecomposition rate by only a
factor of 3 (Kanan et al., 2003).
Sanchez-Polo et al. (2007) reported high efficiency of silver-doped carbon
aerogels for the removal of bromide (Br ) and iodide (I ) from drinking water (Sanchez-
Polo et al., 2007). Similarly, Hoskins et al. (2002) prepared silver-impregnated activated
carbons (SIACs) (0.05 and 1.05 wt % silver) and investigated their ability to remove and
sequester iodide from aqueous solutions by a series of batch sorption and leaching
experiments. Silver content, total iodide concentration, and pH were the factors for
controlling the removal mechanisms of iodide. Iodide uptake increased with decreasing
pH for both SIACs and their pristine granular activated carbon (GAC). The 0.05% SIAC
behaved similarly to its GAC in all experimental conditions because of its low silver
content. At pH values of 7 and 8 there was a marked increased in iodide removal for the
1.05% SIAC over that of its GAC, while their performances were similar at a pH of 5.
Oxidation of metallic silver was observed in the presence of oxygen, and the carbon
surface appears to catalyze this reaction. When the molar ratio of silver to iodide was
greater than 1 (i.e., M Ag,SIAC > M I,TOTAL ), precipitation of silver iodide was the dominant
process. However, unreacted silver leached into solution with decreasing pH while
iodide leaching did not occur. When M Ag,SIAC < M I,TOTAL , silver iodide precipitation
occurred until all available silver had reacted, and additional iodide was removed from
solution by pH-dependent adsorption to the GAC. Under this condition, silver leaching
did not occur while iodide leaching increased with increasing pH (Hoskins et al., 2002).
In this way, silver nanoparticles and their derivatives have great potential to be used as
an antimicrobial material in drinking water treatment, oxidation of other contaminants in
the presence of UV light, reduction as well as adsorption of a variety of contaminants.
11.2.1.6 Fe-Based Nanoporous Materials
There are different types of Fe such as zero-valent iron, iron oxides and iron
oxyhydroxides. In this review, however, we focused on applications of porous zero-
valent iron nanoparticles (INPs) for water treatment. Because of their small size and
very high reactivity, nano-scale iron materials have been widely studied for treating
contaminated soil, groundwater and wastewater (Li et al., 2006; Tratnyek and Johnson,
 
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