photocatalyst, like magnetite, maghemite and wüstite, in presence of H 2 O 2
(Giannakis et al. 2017). Biosand filters amended with iron oxide have also served
as an effective virus decontaminant (Bradley et al. 2011). On a similar note, sand
coated with iron oxide can effectively adsorb and lead to photoinactivation (Pecson
et al. 2012). Other important works in this area have been reported in Brown and
Sobsey (2009), Yang et al. (2013) and Ahammed and Davra (2011).
1.10 Dual- and Multi-contaminants
Some authors have reported use of metal oxide nanoparticles for removal of more than
one contaminant. This fact shows the real potency of metal oxides in water and
wastewater treatment. For instance, nanosheets of graphene oxide-supported
nanoparticles of TiO 2 was successfully used to degrade azo dyes by photocatalytic
oxidation as well as convert Cr(VI) to Cr(III) by photocatalytic reduction (Jiang et al.
2011). Similarly, hollow spheres of α-FeOOH has been used as an adsorbent to remove
Congo red dye (maximum adsorption capacity: 275 mgg
À1
) and heavy metal ions As
(V) (maximum adsorption capacity: 58 mgg
À1
) and Pb(II) (maximum adsorption
capacity: 80 mgg
À1
) (Wang et al. 2012). On the other hand, manganese oxide- and
iron hydroxide-coated sand filter was used to remove bacteria (removal capacity: 99%)
and zinc (removal capacity: 96%) simultaneously (Ahammed and Meera 2010).
On the other hand, Singh et al. (2011) demonstrated the use of Fe 3 O 4 magnetic
nanoadsorbent as a decontaminant of bacteria Escherichia coli as well as heavy
metals As(III), Pb(II), Cd(II), Cu(II), Ni(II), Co(II) and Cr(III). The inverse spinel
magnetic nanostructures were functionalized with thiol, amine and carboxyl
functionalizations. The mechanism for metal ion adsorption by the functionalized
magnetic nanoparticles has been presented in Fig. 1.11. Other important results
relating to dual-contaminant removal can be found in Gollavelli et al. (2013), Mishra
and Ramaprabhu (2010), Xiong et al. (2011), Yang et al. (2012) and Zhong et al.
(2006). Targeting a multi-contaminant removal approach, Ma et al. (2012) prepared
nanocomposites of Bi 2 WO 6 modified by reduced graphene oxide. This
nanocomposites was found to effectively remove Cr(VI), phenol and Rhodamine B
dye from their respective aqueous solutions under visible and UV light irradiations.
1.11 Conclusion
In summary, we have tried to bring out the wide use of metal oxides and their
composites in various categories of decontaminant removal from water and wastewater. Table 1.3 presents a comparative summary of the different metal oxides that
have been used in water treatment applications. We have seen that metal oxides and
their composites have found high use in treatment and removal of polluting contaminants, such as heavy metals, salts, dyes, oils, phenols, phosphates, nitrates,
18
K. Dutta
(Giannakis et al. 2017). Biosand filters amended with iron oxide have also served
as an effective virus decontaminant (Bradley et al. 2011). On a similar note, sand
coated with iron oxide can effectively adsorb and lead to photoinactivation (Pecson
et al. 2012). Other important works in this area have been reported in Brown and
Sobsey (2009), Yang et al. (2013) and Ahammed and Davra (2011).
1.10 Dual- and Multi-contaminants
Some authors have reported use of metal oxide nanoparticles for removal of more than
one contaminant. This fact shows the real potency of metal oxides in water and
wastewater treatment. For instance, nanosheets of graphene oxide-supported
nanoparticles of TiO 2 was successfully used to degrade azo dyes by photocatalytic
oxidation as well as convert Cr(VI) to Cr(III) by photocatalytic reduction (Jiang et al.
2011). Similarly, hollow spheres of α-FeOOH has been used as an adsorbent to remove
Congo red dye (maximum adsorption capacity: 275 mgg
À1
) and heavy metal ions As
(V) (maximum adsorption capacity: 58 mgg
À1
) and Pb(II) (maximum adsorption
capacity: 80 mgg
À1
) (Wang et al. 2012). On the other hand, manganese oxide- and
iron hydroxide-coated sand filter was used to remove bacteria (removal capacity: 99%)
and zinc (removal capacity: 96%) simultaneously (Ahammed and Meera 2010).
On the other hand, Singh et al. (2011) demonstrated the use of Fe 3 O 4 magnetic
nanoadsorbent as a decontaminant of bacteria Escherichia coli as well as heavy
metals As(III), Pb(II), Cd(II), Cu(II), Ni(II), Co(II) and Cr(III). The inverse spinel
magnetic nanostructures were functionalized with thiol, amine and carboxyl
functionalizations. The mechanism for metal ion adsorption by the functionalized
magnetic nanoparticles has been presented in Fig. 1.11. Other important results
relating to dual-contaminant removal can be found in Gollavelli et al. (2013), Mishra
and Ramaprabhu (2010), Xiong et al. (2011), Yang et al. (2012) and Zhong et al.
(2006). Targeting a multi-contaminant removal approach, Ma et al. (2012) prepared
nanocomposites of Bi 2 WO 6 modified by reduced graphene oxide. This
nanocomposites was found to effectively remove Cr(VI), phenol and Rhodamine B
dye from their respective aqueous solutions under visible and UV light irradiations.
1.11 Conclusion
In summary, we have tried to bring out the wide use of metal oxides and their
composites in various categories of decontaminant removal from water and wastewater. Table 1.3 presents a comparative summary of the different metal oxides that
have been used in water treatment applications. We have seen that metal oxides and
their composites have found high use in treatment and removal of polluting contaminants, such as heavy metals, salts, dyes, oils, phenols, phosphates, nitrates,
18
K. Dutta