132
combined with chitin and chitosan to form nano-hydroxyapatite-chitin and nanohydroxyapatite- chitosan composites, respectively. These materials were useful for
treatment of Cu(II). Sun et al. synthesized magnetic cellulose nanocomposites and
obtained high removal efficiency for Cr(VI) with maximum adsorption capacity of
171.5 mg g
−1
at 25 °C. The reaction was exothermic and very fast, reaching the
equilibrium within 10 mins. The adsorbents showed good reusability (Sun et al.
2014). Researchers (Li et al. 2015) tried by immobilizing TiO 2 nanocrystals on cellulose fibers, and the new composite material had excellent capacity in Pb(II)
removal. The adsorption capacity was 371.0 mg g
−1
which was 18 times more than
the sole material TiO 2 nanocrystal. Novel adsorbents were synthesized (Cao et al.
2017) by cross-linking oxidized microcrystalline cellulose for exclusion of heavy
metals. Oxidized microcrystalline cellulose was combined with tetrafluoroterephthalonitrile at different ratios, and the new materials were named as S 1 , S 2 , and S 3 .
The materials were porous, and the surface area increased to 88.32 m
2
g
−1
from
25.74 m
2
g
−1
for the sample cross-linked with only epichlorohydrin. The adsorbents
had reusability using dilute HCl. Others (Subedi et al. 2019) prepared magnetic
chitosan nanocomposites and modified it with graphene oxide. They tried both the
materials for Cr(VI) eradication and obtained encouraging results with four times
reusability. The q max value of magnetic chitosan nanocomposites and graphenemodified nanocomposite was 142.32 and 100.51 mg g
−1
, respectively. The
grapheme- modified composite surface had more negative charge, and thus adsorption of Cr(VI) complex anion was restricted compared to the magnetic chitosan. The
reaction was endothermic and spontaneous and followed pseudo-second-order
kinetics. The composites were successful in fixed bed column operation also.
Cellulose Chars and Activated Carbon
Due to high carbon content of cellulosic materials (40–44%), all wood parts are
considered as a cheap source for preparation of char and activated carbon.
Carbonization enhances the carbon content to nearly 80% in char and 95% in activated carbon (Gupta et al. 2016, Khezami et al. 2005). Powdered cellulose was
burnt in nitrogen atmosphere at 200–1000 °C to prepare chars and further treated
with steam or in acidic/basic conditions to activate it. The thermal treatment and
activation helped in the improvement of surface characteristics. The pore size was
related with the rate of heating and the temperature (Babel 2004, Shen et al. 2013).
Carbonizing at a slower rate yields four times better surface area and pore volume
compared to rapid heating. Brunner and Roberts suggested controlling the temperature and heating rate to yield better results (Brunner and Roberts 1980). The surface
area of activated carbon prepared from cellulose may be as high as 1317 m
2
g
−1
(Lorenc-Grabowska and Rutkowski 2014).
S. Nag and S. Biswas
combined with chitin and chitosan to form nano-hydroxyapatite-chitin and nanohydroxyapatite- chitosan composites, respectively. These materials were useful for
treatment of Cu(II). Sun et al. synthesized magnetic cellulose nanocomposites and
obtained high removal efficiency for Cr(VI) with maximum adsorption capacity of
171.5 mg g
−1
at 25 °C. The reaction was exothermic and very fast, reaching the
equilibrium within 10 mins. The adsorbents showed good reusability (Sun et al.
2014). Researchers (Li et al. 2015) tried by immobilizing TiO 2 nanocrystals on cellulose fibers, and the new composite material had excellent capacity in Pb(II)
removal. The adsorption capacity was 371.0 mg g
−1
which was 18 times more than
the sole material TiO 2 nanocrystal. Novel adsorbents were synthesized (Cao et al.
2017) by cross-linking oxidized microcrystalline cellulose for exclusion of heavy
metals. Oxidized microcrystalline cellulose was combined with tetrafluoroterephthalonitrile at different ratios, and the new materials were named as S 1 , S 2 , and S 3 .
The materials were porous, and the surface area increased to 88.32 m
2
g
−1
from
25.74 m
2
g
−1
for the sample cross-linked with only epichlorohydrin. The adsorbents
had reusability using dilute HCl. Others (Subedi et al. 2019) prepared magnetic
chitosan nanocomposites and modified it with graphene oxide. They tried both the
materials for Cr(VI) eradication and obtained encouraging results with four times
reusability. The q max value of magnetic chitosan nanocomposites and graphenemodified nanocomposite was 142.32 and 100.51 mg g
−1
, respectively. The
grapheme- modified composite surface had more negative charge, and thus adsorption of Cr(VI) complex anion was restricted compared to the magnetic chitosan. The
reaction was endothermic and spontaneous and followed pseudo-second-order
kinetics. The composites were successful in fixed bed column operation also.
Cellulose Chars and Activated Carbon
Due to high carbon content of cellulosic materials (40–44%), all wood parts are
considered as a cheap source for preparation of char and activated carbon.
Carbonization enhances the carbon content to nearly 80% in char and 95% in activated carbon (Gupta et al. 2016, Khezami et al. 2005). Powdered cellulose was
burnt in nitrogen atmosphere at 200–1000 °C to prepare chars and further treated
with steam or in acidic/basic conditions to activate it. The thermal treatment and
activation helped in the improvement of surface characteristics. The pore size was
related with the rate of heating and the temperature (Babel 2004, Shen et al. 2013).
Carbonizing at a slower rate yields four times better surface area and pore volume
compared to rapid heating. Brunner and Roberts suggested controlling the temperature and heating rate to yield better results (Brunner and Roberts 1980). The surface
area of activated carbon prepared from cellulose may be as high as 1317 m
2
g
−1
(Lorenc-Grabowska and Rutkowski 2014).
S. Nag and S. Biswas