258
cation exchange mechanism. There are a variety of peats such as eutrophic and oligotrophic peat. Eutrophic peat has less cellulose content, but has high humic acid,
and oligotrophic peat such as sphagnum is more acidic than eutrophic peat (Babel
and Kurniawan 2003).
10.3.4 Chitosan
Chitin is readily available natural adsorbent which exists in exoskeletons of arthropods and cell walls of some fungi (Ren et al. 2008). Chitosan is deacetylated chitin
derivative and the second most abundant biopolymer after cellulose. Chitosan is not
only efficient and abundant but also cheap (Kumar 2000). Chitosan has some special characteristics such as hydrophilicity, biocompatibility, biodegradability, and
non-toxicity, and it also offers ease of derivatization (Huo et al. 2009). It can form
chelate complex due to the presence of amino and hydroxyl groups with heavy metals (Hu et al. 2011). In spite of having such advantages, chitosan has its own limitation as because it is mechanically weak, pH sensitive, and soluble in acidic medium
and may remove carbon sources when applied in raw form (Kumar 2000; Hu et al.
2011). Therefore, to improve its stability as well as adsorption performance, various
cross-linkers like formaldehyde, glutaraldehyde, and ethylene glycol diglycidyl
ether have been used (Wang et al. 2011). A group of researchers also developed “ion
imprint technology” for the same purpose which involves the technology to develop
a novel adsorbent like urea-modified magnetic ion embossed chitosan@TiO 2 composite for Cd
+2
removal. The result with this adsorbent at pH 7 showed an adsorption
capacity of 256.41 mg g
−1
. Chitosan also help in coating on ceramic alumina composite through which active binding sites of heavy metal increases. There has been
a wide application of ceramic or chitosan – alumina composites as an adsorbent to
eliminate heavy metals like arsenic, chromium, copper, and nickel. Nano-chitosan
synthesized by ionotropic gelation of tripolyphosphate and chitosan was experimented for lead adsorption with an adsorption capacity of 398.0 mg g
−1
(Qi and Xu
2004). It was reported that metal ion adsorption is relatively high with the order of
Cd
+2
> Cu
+2
> Pb
+2
on chitosan and sulfhydryl-functionalized graphene oxide composites due to the increase in selectivity and specific surface area (Li et al. 2015).
However, recovery of these materials limits its large-scale application as they
require complex separation procedures. To solve this issue, researchers now focused
on chitosan composite which can give magnetic response. Magnetic chitosan composites exhibit high potential ability for removal of toxic metal ions such as Ni
+2
,
Cu
+2
, and Pb
+2
with maximum uptakes of 108.9, 216.8 and 220.9 mg g
−1
, respectively. Recently a very interesting research work was done which is not only economic but also versatile method to remove multiple metal ions from natural or
M. Maharana et al.
cation exchange mechanism. There are a variety of peats such as eutrophic and oligotrophic peat. Eutrophic peat has less cellulose content, but has high humic acid,
and oligotrophic peat such as sphagnum is more acidic than eutrophic peat (Babel
and Kurniawan 2003).
10.3.4 Chitosan
Chitin is readily available natural adsorbent which exists in exoskeletons of arthropods and cell walls of some fungi (Ren et al. 2008). Chitosan is deacetylated chitin
derivative and the second most abundant biopolymer after cellulose. Chitosan is not
only efficient and abundant but also cheap (Kumar 2000). Chitosan has some special characteristics such as hydrophilicity, biocompatibility, biodegradability, and
non-toxicity, and it also offers ease of derivatization (Huo et al. 2009). It can form
chelate complex due to the presence of amino and hydroxyl groups with heavy metals (Hu et al. 2011). In spite of having such advantages, chitosan has its own limitation as because it is mechanically weak, pH sensitive, and soluble in acidic medium
and may remove carbon sources when applied in raw form (Kumar 2000; Hu et al.
2011). Therefore, to improve its stability as well as adsorption performance, various
cross-linkers like formaldehyde, glutaraldehyde, and ethylene glycol diglycidyl
ether have been used (Wang et al. 2011). A group of researchers also developed “ion
imprint technology” for the same purpose which involves the technology to develop
a novel adsorbent like urea-modified magnetic ion embossed chitosan@TiO 2 composite for Cd
+2
removal. The result with this adsorbent at pH 7 showed an adsorption
capacity of 256.41 mg g
−1
. Chitosan also help in coating on ceramic alumina composite through which active binding sites of heavy metal increases. There has been
a wide application of ceramic or chitosan – alumina composites as an adsorbent to
eliminate heavy metals like arsenic, chromium, copper, and nickel. Nano-chitosan
synthesized by ionotropic gelation of tripolyphosphate and chitosan was experimented for lead adsorption with an adsorption capacity of 398.0 mg g
−1
(Qi and Xu
2004). It was reported that metal ion adsorption is relatively high with the order of
Cd
+2
> Cu
+2
> Pb
+2
on chitosan and sulfhydryl-functionalized graphene oxide composites due to the increase in selectivity and specific surface area (Li et al. 2015).
However, recovery of these materials limits its large-scale application as they
require complex separation procedures. To solve this issue, researchers now focused
on chitosan composite which can give magnetic response. Magnetic chitosan composites exhibit high potential ability for removal of toxic metal ions such as Ni
+2
,
Cu
+2
, and Pb
+2
with maximum uptakes of 108.9, 216.8 and 220.9 mg g
−1
, respectively. Recently a very interesting research work was done which is not only economic but also versatile method to remove multiple metal ions from natural or
M. Maharana et al.