nanotube surface by both internal and external grooves (Fig. 6.3a). It has been
reported that the external sites are occupied earlier than the internal sites under
equal conditions, as the external sites are more accessible because they come in
direct contact with the adsorbing material. In order to improve their adsorptive
properties, it can be improved by adding certain functional groups like –COOH, –
NH 2 , –OH (Wepasnick et al. 2011). Some oxidants like KMnO 4 , HNO 3 , H 2 SO 4 , and
NaOH can also be employed for the improved adsorption by modifying the surface
properties. Adsorption affinity of carbon nanotube to heavy metal depends upon the
(1) ionic radius of heavy metals and (2) metal electronegativity, which means higher
electronegativity has stronger adsorption. The process by which adsorption takes
place is through π-π interaction, ion exchange, surface complexation, and electrostatic interaction as shown in Fig. 6.3b.
6.4
Graphene Nanomaterials
Graphene is another two-dimensional crystalline atomic structure. It has huge
surface area, exceptional chemical properties and geometry which make it as a
promising adsorbent for remediation of environmental pollutant from wastewater
like toxic organic and inorganic species (Zhao et al. 2011a, b; Peng et al. 2017).
Graphene membrane interacts actively with inorganic and organic contaminants.
These pollutants get easily drawn to the membrane by hydrophobic interaction, Van
der Waals forces, π–π stacking, and hydrogen bonding as depicted in Fig. 6.4. In
order to make them attractive adsorption functional groups are added to graphene
nanomaterials such as oxygen to form GO which increases its hydrophilic nature.
Hence these properties make it more efficient, easy, and flexible for the eradication
Table 6.2 Application of graphene (G), graphene nanosheets (GNs), graphene oxide (GO), rGO,
and modified graphene as adsorbents
Adsorbent
Target
Adsorption capacity
(mg/g)
Reference
Oxidized MWCNT/
SDBS
Pb(II)
66.95
Li et al. (2011)
Diethylenetriamine
Pb(II), Cd(II)
58.26, 31.45
Yukovi et al.
(2011)
MWCNT/Fe 3 O 4
As(III), As(V)
39, 53
Mishra and
Ramaprabhu
(2010)
SWCNTs
Zn(II), Ni(II)
43.66, 9.22
Lu and Lu
(2006)
CNT–OH, CNT–
CONH 2 , CNT–
COO¯
Pb(II), Cu(II), Cd(II),
Hg(II) Pb(II), Cu(II)
428.90, 85.27, 428.90,
395.13, 111.51, 175.68
Kommu et al.
(2015)
CNTs (HNO 3 )
Pb(II)
49.95
Li et al. (2002)
MWCNTs,
MWCNTs (NaClO)
Ni(II), Ni(II)
7.53, 38.46
Lu and Chiu
(2006)
150
N. Dhiman et al.
reported that the external sites are occupied earlier than the internal sites under
equal conditions, as the external sites are more accessible because they come in
direct contact with the adsorbing material. In order to improve their adsorptive
properties, it can be improved by adding certain functional groups like –COOH, –
NH 2 , –OH (Wepasnick et al. 2011). Some oxidants like KMnO 4 , HNO 3 , H 2 SO 4 , and
NaOH can also be employed for the improved adsorption by modifying the surface
properties. Adsorption affinity of carbon nanotube to heavy metal depends upon the
(1) ionic radius of heavy metals and (2) metal electronegativity, which means higher
electronegativity has stronger adsorption. The process by which adsorption takes
place is through π-π interaction, ion exchange, surface complexation, and electrostatic interaction as shown in Fig. 6.3b.
6.4
Graphene Nanomaterials
Graphene is another two-dimensional crystalline atomic structure. It has huge
surface area, exceptional chemical properties and geometry which make it as a
promising adsorbent for remediation of environmental pollutant from wastewater
like toxic organic and inorganic species (Zhao et al. 2011a, b; Peng et al. 2017).
Graphene membrane interacts actively with inorganic and organic contaminants.
These pollutants get easily drawn to the membrane by hydrophobic interaction, Van
der Waals forces, π–π stacking, and hydrogen bonding as depicted in Fig. 6.4. In
order to make them attractive adsorption functional groups are added to graphene
nanomaterials such as oxygen to form GO which increases its hydrophilic nature.
Hence these properties make it more efficient, easy, and flexible for the eradication
Table 6.2 Application of graphene (G), graphene nanosheets (GNs), graphene oxide (GO), rGO,
and modified graphene as adsorbents
Adsorbent
Target
Adsorption capacity
(mg/g)
Reference
Oxidized MWCNT/
SDBS
Pb(II)
66.95
Li et al. (2011)
Diethylenetriamine
Pb(II), Cd(II)
58.26, 31.45
Yukovi et al.
(2011)
MWCNT/Fe 3 O 4
As(III), As(V)
39, 53
Mishra and
Ramaprabhu
(2010)
SWCNTs
Zn(II), Ni(II)
43.66, 9.22
Lu and Lu
(2006)
CNT–OH, CNT–
CONH 2 , CNT–
COO¯
Pb(II), Cu(II), Cd(II),
Hg(II) Pb(II), Cu(II)
428.90, 85.27, 428.90,
395.13, 111.51, 175.68
Kommu et al.
(2015)
CNTs (HNO 3 )
Pb(II)
49.95
Li et al. (2002)
MWCNTs,
MWCNTs (NaClO)
Ni(II), Ni(II)
7.53, 38.46
Lu and Chiu
(2006)
150
N. Dhiman et al.