Aerogels, on the other hand, are ultralightweight materials with threedimensional porous networks. They are increasingly valuable in the environmental
remediation of heavy metals and dyes and oil removal from water as well as in water
purification, due to their high porosity, large specific surface area, and ease of
separation from aqueous solutions (Sharma et al. 2020b). The nanocellulosic
aerogels can be produced in three steps: dissolving/dispersing cellulose or cellulose
derivatives, forming cellulose gel according to the sol-gel process, and drying
cellulose gel while maintaining the porous 3D structure. Various methods are
available for drying the cellulose gel, in particular oven-drying, freeze-drying, and
supercritical drying, which are preceded by solvent exchange. The NC-based
aerogels usually have a pore size in the range of 2–50 nm with high porosity
(generally>90%). To improve their function, NC-based aerogels can be cross-linked
with
other
materials,
including
3-mercaptopropyltrimethoxysilane,
trimethylolpropane tris (2-methyl-1-aziridine) propionate (TMPTAP), and others.
Mo et al. (2019) demonstrated the formation of 3D multiwall perforated
nanocellulose-based polyethylenimine aerogels (TO-CNF/TMPTAP/PEI) using
0.6 wt% TEMPO-oxidized CNF. The CNF suspension was untrasonicated for
30 min and cross-linked with trimethylolpropane-tris-(2-methyl-1-aziridine) propionate (TMPTAP) and polyethyleneimine (PEI) under adjusted pH and concentrations of the cross-linking agents. The resulting recyclable aerogels obtained post
freeze-drying were rich in amino-functionalized surfaces and showed an ultrahigh
adsorption capacity for removing heavy metal ions from aqueous environments (Fig
4.4b). Similarly, Xu et al. (2018b) developed an innovative approach for the
production of cellulose nanofibers (CNFs)/multiwalled carbon nanotubes
(MWCNTs) and carbon aerogels, using bamboo powder as the initial bioresource,
through a simple dipping and carbonization process. The pertinent properties of the
synthesized aerogels included low density (0.056 g cm
-3
), high porosity (95%), and
an efficient ability to separate oily droplets from the water beside a high adsorption
efficacy for a wide range of oils and organic solvents. Another porous structure
based on NC are the xerogels, fabricated via evaporative drying of wet gels.
However, their manufacturing process has been a challenge due to the shrinking of
the gels that ultimately reduce porosity. Nevertheless, several approaches, such as
solvent exchange and the use of very fine type CNFs with a width of ~3 nm have
expanded the domains NC as materials for xerogel synthesis (Yamasaki et al. 2019).
Concert of various organic or inorganic materials with nanocellulose yields
products of superior quality. Nanocarbon, nanographene, organic polymer matrices,
as well as various inorganic nanoparticles have been adroitly employed to fabricate
avant-garde NC-based nanocomposites (Jodeh et al. 2018; Tshikovhi et al. 2020;
Lebogang et al. 2019). As an exemplary endeavor, Bossa et al. (2017) reported the
fabrication of cellulose nanocrystal-zero valent iron nanocomposites (CNC-nanoZVI) for prospective in situ groundwater remediation. Their study attested that NC
improved the mobility of nano-ZVI particles. Additional attractive applications of
NC pertain to the preparation of nanocellulose-based composite membranes and
highly porous adsorption composites (Sharma et al. 2020a; Patel et al. 2019). In this
regard, functionalized bacterial nanocellulose (BNC) composites have also fetched a
4 Harnessing the Sustainable Bioresource, Cellulose at the Nanoscale for. . .
77
remediation of heavy metals and dyes and oil removal from water as well as in water
purification, due to their high porosity, large specific surface area, and ease of
separation from aqueous solutions (Sharma et al. 2020b). The nanocellulosic
aerogels can be produced in three steps: dissolving/dispersing cellulose or cellulose
derivatives, forming cellulose gel according to the sol-gel process, and drying
cellulose gel while maintaining the porous 3D structure. Various methods are
available for drying the cellulose gel, in particular oven-drying, freeze-drying, and
supercritical drying, which are preceded by solvent exchange. The NC-based
aerogels usually have a pore size in the range of 2–50 nm with high porosity
(generally>90%). To improve their function, NC-based aerogels can be cross-linked
with
other
materials,
including
3-mercaptopropyltrimethoxysilane,
trimethylolpropane tris (2-methyl-1-aziridine) propionate (TMPTAP), and others.
Mo et al. (2019) demonstrated the formation of 3D multiwall perforated
nanocellulose-based polyethylenimine aerogels (TO-CNF/TMPTAP/PEI) using
0.6 wt% TEMPO-oxidized CNF. The CNF suspension was untrasonicated for
30 min and cross-linked with trimethylolpropane-tris-(2-methyl-1-aziridine) propionate (TMPTAP) and polyethyleneimine (PEI) under adjusted pH and concentrations of the cross-linking agents. The resulting recyclable aerogels obtained post
freeze-drying were rich in amino-functionalized surfaces and showed an ultrahigh
adsorption capacity for removing heavy metal ions from aqueous environments (Fig
4.4b). Similarly, Xu et al. (2018b) developed an innovative approach for the
production of cellulose nanofibers (CNFs)/multiwalled carbon nanotubes
(MWCNTs) and carbon aerogels, using bamboo powder as the initial bioresource,
through a simple dipping and carbonization process. The pertinent properties of the
synthesized aerogels included low density (0.056 g cm
-3
), high porosity (95%), and
an efficient ability to separate oily droplets from the water beside a high adsorption
efficacy for a wide range of oils and organic solvents. Another porous structure
based on NC are the xerogels, fabricated via evaporative drying of wet gels.
However, their manufacturing process has been a challenge due to the shrinking of
the gels that ultimately reduce porosity. Nevertheless, several approaches, such as
solvent exchange and the use of very fine type CNFs with a width of ~3 nm have
expanded the domains NC as materials for xerogel synthesis (Yamasaki et al. 2019).
Concert of various organic or inorganic materials with nanocellulose yields
products of superior quality. Nanocarbon, nanographene, organic polymer matrices,
as well as various inorganic nanoparticles have been adroitly employed to fabricate
avant-garde NC-based nanocomposites (Jodeh et al. 2018; Tshikovhi et al. 2020;
Lebogang et al. 2019). As an exemplary endeavor, Bossa et al. (2017) reported the
fabrication of cellulose nanocrystal-zero valent iron nanocomposites (CNC-nanoZVI) for prospective in situ groundwater remediation. Their study attested that NC
improved the mobility of nano-ZVI particles. Additional attractive applications of
NC pertain to the preparation of nanocellulose-based composite membranes and
highly porous adsorption composites (Sharma et al. 2020a; Patel et al. 2019). In this
regard, functionalized bacterial nanocellulose (BNC) composites have also fetched a
4 Harnessing the Sustainable Bioresource, Cellulose at the Nanoscale for. . .
77