Remediation for Heavy Metal Contamination 287
10 nm and coated with ascorbic acid were highly efficient in removing As. These nanoadsorbentions
had the maximum adsorption capacity of 16.56 mg g–1 and 46.06 mg g–1 for As(III) and As(V),
respectively (Feng et al. 2012). Further, Fe2O4 MNPs coated with oxide shells of Mn-Co is an
excellent adsorber of Pb (II) (481.2 mg g–1), Cu (II) (386.2 mg g–1) and Cd (II) (345.5 mg g–1)
(Ma et al. 2013). Silica nanoparticles are also considered to be highly efficient in removing heavy
metals. Silica nanoparticles along with graphite oxide were used to remove Zn, Ni, Cr, Pb and Cd
by Sheet et al. (2014). When metal oxides are used as adsorbents without any supporting elements
(viz., clays or zeolites), they may have limited adsorption capacity, smaller surface area and release
hazardous metals into the environment.
16.4.4.3 Clay-polymer Nanocomposites
Describing the removal of metalloids from polluted media and many types of adsorbents (organic
and inorganic materials) have already been addressed. The clay polymer adsorbents include
zeolites (activated and natural), natural clay minerals, modified clay minerals, etc. (Mukhopadhyay
et al. 2020). Available clay minerals are of low cost, readily available and can be exclusively
used. However, their low surface area, less effectiveness for micro pollutants and lack of standard
protocols for regeneration are major limitations. In the recent past, researchers have begun to utilize
Clay-Polymer Nanocomposites (CPNs) obtained by clay minerals and resins conjointly as a single
adsorbent. The nanocomposites have shown immense potential for removal of major pollutants
in water such as Cu, Cr, As, Pb, Ni and Cd (Table 16.6). With the development of nanoscience,
several clay polymer nanocomposites are synthesized, such as, epoxy-clay nanocomposites,
polystyrene-clay nanocomposites, polyurethane-clay nanocomposites, magnetic clay polymer
nanocomposites, polyimide-clay hybrids, etc. Recently, magnetized-CPN was developed using
bentonite clay, iron oxide nanoparticles and monomer methyl methacrylate for the removal of Cr (VI)
(Sundaram et al. 2018). The application of these CPN had an adsorption capacity of 113 mg g–1.
Whereas chitosan-Al-pillared-montmorillonite nanocomposite can adsorb Cr (VI) 15.67 mg g–1
Table 16.6. Efficiency of clay-polymer nanocomposites in metal removal.
Clay-polymer nanocomposites
Metal removed
Efficiency (mg g–1)
References
Alginate–montmorillonite nanocomposite
Pb
238.1
Shawky 2011
Polyacrylic acid/bentonite
Ni
270.27
Mukhopadhyay et al. 2020
Polyacrylic acid/bentonite
Pb
1666.67
Bulut and Tez 2009
Chitosan-Al-pillared-montmorillonite
nanocomposite
Pb
-
Mukhopadhyay et al. 2020
Chitosan immobilized on bentonite
Ni
15.82
Mukhopadhyay et al. 2020
Polyacrylic acid/bentonite
Cd
416.67
Mukhopadhyay et al. 2020
Modifed bentonite clay composits
Zn
-
Mukhopadhyay et al. 2020
Polyetherimide/porous activated bentonite
Cd
-
Chitosan-Al-pillared-montmorillonite
nanocomposite
Cu
-
Pereira et al. 2013
Chitosan:clay (0.45:1)
Cu
-
Pereira et al. 2013
Montmorillonite and chitosan
Se
18.4
Pillared bentonite by MnCl2
Pb
12.6
Mukhopadhyay et al. 2020
Chitosan-bentonite clay
Ni, Cd
-
Mukhopadhyay et al. 2020
Alginate–montmorillonite nanocomposite
Fe
Mukhopadhyay et al. 2020
Bentonite/thiourea-formaldehyde
composite
Mn
4.81
Mukhopadhyay et al. 2020
Na-montmorillonite/cellulose
Cr
22.2
Mukhopadhyay et al. 2020
Chitosan–clay composites and oxides
Se
Bleiman and Mishael 2010