core-shell structure or as a bimetallic oxide. In a typical study, Ociński et al. (2016)
residuals of water treatment with surface area as high as 120 m
2 g
À1 , which get
generated during processing of infiltration water for removal of manganese and iron,
as adsorbents for As(III) and As(V) anions. In the residuals, the oxides of iron and
manganese were present in the ratio of 5:1. The adsorption was found to fit into the
Langmuir isotherm model, and the capacities were found to be 77 mgg
À1 for As
(V) and 132 mgg
À1 for As(III). The presence of manganese oxide was found to be
critical for oxidation of As(III), which led to its high adsorption. In a similar study,
Zhang et al. (2010) used bimetallic oxides MnFe 2 O 4 and CoFe 2 O 4 magnetic
nanoparticles for adsorption of As(III) and As(V) anions. While MnFe 2 O 4 showed
adsorption capacities of 94 mgg
À1 for As(III) and 90 mgg
À1 for As(V), CoFe 2 O 4
exhibited higher values of 100 mgg
À1 and 74 mgg
À1 , respectively. In this study too,
the presence of the second metal, i.e. Mn and Co, was found to be critical behind
exhibition of higher adsorption capacities, because they enabled formation of surface
hydroxyl moieties. This performance-enhancing effect of the second metal is evident
from the fact that Fe 3 O 4 could produce only 50 mgg
À1 for As(III) and 44 mgg
À1 for
As(V). Moreover, the bimetallic nanoadsorbent demonstrated good desorption of
higher than 90% for As(V) and 80% for As(III).
In another study, a graphene oxide/bimetallic MnFe 2 O 4 nanoparticle hybrid
composite was utilized for removing As and Pb contaminants from water (Kumar
et al. 2014). The presence of graphene oxide layers ensured availability for higher
surface area for better dispersion of the magnetic bimetallic particles. This
nanohybrid composite exhibited adsorption capacities of 673 mgg
À1 for Pb(II),
207 mgg
À1 for As(V) and 146 mgg
À1 for As(III), which was much higher than
that obtained for only the bimetallic nanoparticles (without the presence of graphene
oxide) with the respective values of 488 mgg
À1 , 136 mgg
À1 and 97 mgg
À1 . Desorption of the adsorbed contaminants was realized to be 99%, 93% and 99% for As(V),
As(III) and Pb(II), respectively. Most importantly, the nanohybrid could be used for
five cycles of adsorption, without noticeable change in the efficiency. On the other
hand, Kim et al. (2013) designed magnetic Fe 3 O 4 nanoparticles coated with amorphous MnO 2 , which exhibited a hierarchical core-shell nanocomposite threedimension flower-like structure (Fig. 1.4). This nanocomposite showed enhanced
adsorption efficiency towards Cu(II), Zn(II), Pb(II) and Cd(II) ions over bare Fe 3 O 4
nanoparticles. From Langmuir isotherm model, the adsorption capacity of the
nanocomposite towards Cd(II) was found to be 53.2 mgg
À1 , with a recycling
capacity of up to 5 cycles.
Oxides of iron have been the material of choice in heavy metal treatment
application. For example, mesoporous nanocomposites of iron/iron oxide have
been used for removal of chromate anions from solution in water (Kim et al.
2012). From the Langmuir model, the maximum value of adsorption capacity was
found to be 34.1 mgg
À1 . Nalbandian et al. (2016) used nanofibers of Fe 2 O 3 for
adsorptive removal of chromate from aqueous solution. With a specific surface area
of 59.2 m
2 g
À1 , the nanofibers with 23 nm average diameter demonstrated an
adsorption capacity of 90.9 mgg
À1 . This result was better than that obtained for
the commercial Fe 2 O 3 nanoparticles (49.3 mgg
À1 ). Both the specific surface area
8
K. Dutta
residuals of water treatment with surface area as high as 120 m
2 g
À1 , which get
generated during processing of infiltration water for removal of manganese and iron,
as adsorbents for As(III) and As(V) anions. In the residuals, the oxides of iron and
manganese were present in the ratio of 5:1. The adsorption was found to fit into the
Langmuir isotherm model, and the capacities were found to be 77 mgg
À1 for As
(V) and 132 mgg
À1 for As(III). The presence of manganese oxide was found to be
critical for oxidation of As(III), which led to its high adsorption. In a similar study,
Zhang et al. (2010) used bimetallic oxides MnFe 2 O 4 and CoFe 2 O 4 magnetic
nanoparticles for adsorption of As(III) and As(V) anions. While MnFe 2 O 4 showed
adsorption capacities of 94 mgg
À1 for As(III) and 90 mgg
À1 for As(V), CoFe 2 O 4
exhibited higher values of 100 mgg
À1 and 74 mgg
À1 , respectively. In this study too,
the presence of the second metal, i.e. Mn and Co, was found to be critical behind
exhibition of higher adsorption capacities, because they enabled formation of surface
hydroxyl moieties. This performance-enhancing effect of the second metal is evident
from the fact that Fe 3 O 4 could produce only 50 mgg
À1 for As(III) and 44 mgg
À1 for
As(V). Moreover, the bimetallic nanoadsorbent demonstrated good desorption of
higher than 90% for As(V) and 80% for As(III).
In another study, a graphene oxide/bimetallic MnFe 2 O 4 nanoparticle hybrid
composite was utilized for removing As and Pb contaminants from water (Kumar
et al. 2014). The presence of graphene oxide layers ensured availability for higher
surface area for better dispersion of the magnetic bimetallic particles. This
nanohybrid composite exhibited adsorption capacities of 673 mgg
À1 for Pb(II),
207 mgg
À1 for As(V) and 146 mgg
À1 for As(III), which was much higher than
that obtained for only the bimetallic nanoparticles (without the presence of graphene
oxide) with the respective values of 488 mgg
À1 , 136 mgg
À1 and 97 mgg
À1 . Desorption of the adsorbed contaminants was realized to be 99%, 93% and 99% for As(V),
As(III) and Pb(II), respectively. Most importantly, the nanohybrid could be used for
five cycles of adsorption, without noticeable change in the efficiency. On the other
hand, Kim et al. (2013) designed magnetic Fe 3 O 4 nanoparticles coated with amorphous MnO 2 , which exhibited a hierarchical core-shell nanocomposite threedimension flower-like structure (Fig. 1.4). This nanocomposite showed enhanced
adsorption efficiency towards Cu(II), Zn(II), Pb(II) and Cd(II) ions over bare Fe 3 O 4
nanoparticles. From Langmuir isotherm model, the adsorption capacity of the
nanocomposite towards Cd(II) was found to be 53.2 mgg
À1 , with a recycling
capacity of up to 5 cycles.
Oxides of iron have been the material of choice in heavy metal treatment
application. For example, mesoporous nanocomposites of iron/iron oxide have
been used for removal of chromate anions from solution in water (Kim et al.
2012). From the Langmuir model, the maximum value of adsorption capacity was
found to be 34.1 mgg
À1 . Nalbandian et al. (2016) used nanofibers of Fe 2 O 3 for
adsorptive removal of chromate from aqueous solution. With a specific surface area
of 59.2 m
2 g
À1 , the nanofibers with 23 nm average diameter demonstrated an
adsorption capacity of 90.9 mgg
À1 . This result was better than that obtained for
the commercial Fe 2 O 3 nanoparticles (49.3 mgg
À1 ). Both the specific surface area
8
K. Dutta