and Jahangiri 2014) including the sulphides of iron (Han et al. 2011) and zinc
(Piquette et al. 2012), have been explored for arsenic removal.
2.7
Nanoadsorbents for Arsenic Remediation
2.7.1 Iron-Based Nanomaterials
NZVI is a widely explored phase among the iron-based nanomaterials utilized for
arsenic removal through both ex situ and in situ treatment processes. As compared to
bulk, its nanosize does not only enhance the surface area (Kanel et al. 2006), but the
high intrinsic activity of these nanoparticles delivers the high density of reactive sites
to the contaminant for electrostatic interactions (Morgada et al. 2009; Robalds et al.
2016). Generally, the arsenic removal mechanism of bare nZVI involves the precipitation, co-precipitation, oxidation and reduction reactions.
Magnetite is a predominant constituent of the subsurface environment
(N. Compounds 2001). This phase has been found to be more efficient for the
arsenic removal as compared to extensively explored bare zero-valent iron
nanoparticles (Hunt and Amrhein 2002). Υ -FeOOH is a predominant and highly
reactive phase which occurs as ore deposits, sediments and terrestrial soil (Cornell
and Schwertmann 2003; van der Zee et al. 2003). The vacant sites are located
between the Fe occupied double chain rows and considered as false tunnel-like
structures (Cornell and Schwertmann 2004). The nanostructured β-FeOOH has been
considered as having a true tunnel-like structure along with the single row of anions
missing in the unit cell (Scheck et al. 2015). The presence of tunnel-like formation
has been considered to be responsible for its efficient adsorption capabilities,
providing large surface area and reactive sites. The nanostructured iron oxides
containing iron in trivalent state, such as hematite (α-Fe 2 O 3 ), beta phase
(β-Fe 2 O 3 ), maghemite (Υ -Fe 2 O 3 ), have been investigated for various environmental
applications (Kaloti et al. 2015; Kaloti and Kumar 2016).
2.7.2 Ti-, Al-, Zr-, Ce-, Zn- and Cu-Based Nanomaterials
Anatase, brookite and rutile are common polymorphs of titanium dioxide, which
have been reported to be explored for arsenic. These have been considered as
significant nanomaterials for the environmental applications due to their
non-corrosive, non-toxic and chemically stable properties (Hung et al. 2007). Alumina is an important adsorbent as it acquires excellent physical and textural
properties comparable to those of other transitional metal oxides (Takanashi et al.
2004). It has been found in several industrial wastes, such as blast furnace slag, coal
combustion ash and waterworks sludge. Nanoscale zirconia- and ceria-based
nanomaterials have demonstrated an adequate affinity for As
V due to which it has
been explored for arsenic treatment (Hristovski et al. 2007; Haron et al. 2008). These
have been considered as suitable adsorbents for field-scale applications due to their
44
A. Kumar et al.
(Piquette et al. 2012), have been explored for arsenic removal.
2.7
Nanoadsorbents for Arsenic Remediation
2.7.1 Iron-Based Nanomaterials
NZVI is a widely explored phase among the iron-based nanomaterials utilized for
arsenic removal through both ex situ and in situ treatment processes. As compared to
bulk, its nanosize does not only enhance the surface area (Kanel et al. 2006), but the
high intrinsic activity of these nanoparticles delivers the high density of reactive sites
to the contaminant for electrostatic interactions (Morgada et al. 2009; Robalds et al.
2016). Generally, the arsenic removal mechanism of bare nZVI involves the precipitation, co-precipitation, oxidation and reduction reactions.
Magnetite is a predominant constituent of the subsurface environment
(N. Compounds 2001). This phase has been found to be more efficient for the
arsenic removal as compared to extensively explored bare zero-valent iron
nanoparticles (Hunt and Amrhein 2002). Υ -FeOOH is a predominant and highly
reactive phase which occurs as ore deposits, sediments and terrestrial soil (Cornell
and Schwertmann 2003; van der Zee et al. 2003). The vacant sites are located
between the Fe occupied double chain rows and considered as false tunnel-like
structures (Cornell and Schwertmann 2004). The nanostructured β-FeOOH has been
considered as having a true tunnel-like structure along with the single row of anions
missing in the unit cell (Scheck et al. 2015). The presence of tunnel-like formation
has been considered to be responsible for its efficient adsorption capabilities,
providing large surface area and reactive sites. The nanostructured iron oxides
containing iron in trivalent state, such as hematite (α-Fe 2 O 3 ), beta phase
(β-Fe 2 O 3 ), maghemite (Υ -Fe 2 O 3 ), have been investigated for various environmental
applications (Kaloti et al. 2015; Kaloti and Kumar 2016).
2.7.2 Ti-, Al-, Zr-, Ce-, Zn- and Cu-Based Nanomaterials
Anatase, brookite and rutile are common polymorphs of titanium dioxide, which
have been reported to be explored for arsenic. These have been considered as
significant nanomaterials for the environmental applications due to their
non-corrosive, non-toxic and chemically stable properties (Hung et al. 2007). Alumina is an important adsorbent as it acquires excellent physical and textural
properties comparable to those of other transitional metal oxides (Takanashi et al.
2004). It has been found in several industrial wastes, such as blast furnace slag, coal
combustion ash and waterworks sludge. Nanoscale zirconia- and ceria-based
nanomaterials have demonstrated an adequate affinity for As
V due to which it has
been explored for arsenic treatment (Hristovski et al. 2007; Haron et al. 2008). These
have been considered as suitable adsorbents for field-scale applications due to their
44
A. Kumar et al.