pesticides, detergents, coke plants and oil refineries release phenolic compounds to
the water bodies. Therefore, thorough treatment of water to get rid of these extremely
toxic phenolic compounds is an essential requirement. Among other techniques,
metal oxide-based electrocatalytic oxidative degradation of phenol is a very successful one in terms of phenol decontamination efficiency. Some representative
reports have been discussed below.
Upon using activated carbon impregnated with CuO as the catalyst, Liou and Chen
(2009) achieved >98% removal of phenol and > 90% removal of chemical oxygen
demand upon stepwise addition of H 2 O 2 . In a similar study, Shukla et al. (2010)
found that Co 2 O 3 supported on activated carbon could produce a decomposition of
100% and a total organic carbon removal of 80% in presence of sulfate radicals within
60 min. Again, it was found that phenol can be treated by using catalytic nanoparticles
of Fe 3 O 4 that were superparamagnetic in nature, with a total organic carbon removal
of 42.79% in presence of H 2 O 2 (Zhang et al. 2009b). Using a mixed metal oxide of Ru
as the anode catalyst, Yavuz and Koparal (2006) reported a removal efficiency of
phenol as high as 99.7% from synthetic wastewater. However, when the authors used
real wastewater from petroleum refinery, they could achieve a 94.5% phenol removal
and 70.1% chemical oxygen demand removal efficiencies. Similarly, Yang et al.
(2009) designed a mixed metal oxide-coated Ti electrode, for oxidative removal of
phenol from water. A 78.6% removal was observed at a pH of 7 and a temperature of
20
C, which got increased to 97.2% upon addition of chloride. In this study, the
mixed metal oxide was comprised of PbO 2 , Nb 2 O 5 , Sb 2 O 3 and SnO 2 . Similar studies
have been performed by others, using a number of metal oxides, and have reported
good performance (Feng and Li 2003; Wang et al. 2009b).
1.9 Other Contaminants
Other than the contaminants dealt with above, there are certain other harmful
contaminants present in water and wastewater that need to be treated. Among
them, the most important are nitrates and pathogens. Nitrates general enter the
waterbodies through agricultural wastewater, owing to the use of excessing fertilizers. Consumption of nitrate-containing water at above safety limit can lead to
diseases like methemoglobinemia. Therefore, decontaminating water from nitrates is
essential. In this respect, metal oxides have played a role (Mook et al. 2012). For
example, zero valent iron nanoparticles and its composite with TiO 2 have been used
effectively for this purpose (Huang et al. 2013; Pan et al. 2012).
Pathogens are microorganisms, mainly viruses and bacteria, that can cause
diseases upon entering our bodies through contaminated water. Therefore, their
removal from drinking water is of utmost importance before intake. In this regard,
metal oxide nanoparticles such as TiO 2 doped with silver has been used to inactivate
virus Bacteriophage MS2 (ATCC 15597-B1) (Liga et al. 2011). Increase formation
of hydroxyl radical owing to the presence of silver dopant was found to be the chief
cause behind the virus deactivation process. Similarly, virus MS2 coliphage was
successfully treated via a photo-Fenton process using semiconductor iron oxides
1 Metal Oxides as Decontaminants of Water and Wastewater
17
the water bodies. Therefore, thorough treatment of water to get rid of these extremely
toxic phenolic compounds is an essential requirement. Among other techniques,
metal oxide-based electrocatalytic oxidative degradation of phenol is a very successful one in terms of phenol decontamination efficiency. Some representative
reports have been discussed below.
Upon using activated carbon impregnated with CuO as the catalyst, Liou and Chen
(2009) achieved >98% removal of phenol and > 90% removal of chemical oxygen
demand upon stepwise addition of H 2 O 2 . In a similar study, Shukla et al. (2010)
found that Co 2 O 3 supported on activated carbon could produce a decomposition of
100% and a total organic carbon removal of 80% in presence of sulfate radicals within
60 min. Again, it was found that phenol can be treated by using catalytic nanoparticles
of Fe 3 O 4 that were superparamagnetic in nature, with a total organic carbon removal
of 42.79% in presence of H 2 O 2 (Zhang et al. 2009b). Using a mixed metal oxide of Ru
as the anode catalyst, Yavuz and Koparal (2006) reported a removal efficiency of
phenol as high as 99.7% from synthetic wastewater. However, when the authors used
real wastewater from petroleum refinery, they could achieve a 94.5% phenol removal
and 70.1% chemical oxygen demand removal efficiencies. Similarly, Yang et al.
(2009) designed a mixed metal oxide-coated Ti electrode, for oxidative removal of
phenol from water. A 78.6% removal was observed at a pH of 7 and a temperature of
20
C, which got increased to 97.2% upon addition of chloride. In this study, the
mixed metal oxide was comprised of PbO 2 , Nb 2 O 5 , Sb 2 O 3 and SnO 2 . Similar studies
have been performed by others, using a number of metal oxides, and have reported
good performance (Feng and Li 2003; Wang et al. 2009b).
1.9 Other Contaminants
Other than the contaminants dealt with above, there are certain other harmful
contaminants present in water and wastewater that need to be treated. Among
them, the most important are nitrates and pathogens. Nitrates general enter the
waterbodies through agricultural wastewater, owing to the use of excessing fertilizers. Consumption of nitrate-containing water at above safety limit can lead to
diseases like methemoglobinemia. Therefore, decontaminating water from nitrates is
essential. In this respect, metal oxides have played a role (Mook et al. 2012). For
example, zero valent iron nanoparticles and its composite with TiO 2 have been used
effectively for this purpose (Huang et al. 2013; Pan et al. 2012).
Pathogens are microorganisms, mainly viruses and bacteria, that can cause
diseases upon entering our bodies through contaminated water. Therefore, their
removal from drinking water is of utmost importance before intake. In this regard,
metal oxide nanoparticles such as TiO 2 doped with silver has been used to inactivate
virus Bacteriophage MS2 (ATCC 15597-B1) (Liga et al. 2011). Increase formation
of hydroxyl radical owing to the presence of silver dopant was found to be the chief
cause behind the virus deactivation process. Similarly, virus MS2 coliphage was
successfully treated via a photo-Fenton process using semiconductor iron oxides
1 Metal Oxides as Decontaminants of Water and Wastewater
17