437
Halloysite is a natural kaolinite clay with tubular aluminosilicate structure
(Szczepanik 2017). Halloysite nanotube and its organic- and inorganic-based composites have been extensively utilized in adsorbing the different types of dyes.
Carvalho et al. used cyclodextrin/silica hybrid adsorbent for the adsorption of
methylene blue from aqueous solution (De Carvalho et al. 2014). Cheng et al.
(2016) synthesized and tested hemicellulose/clay hybrid hydrogels for removal of
cationic dyes from aqueous medium.
Chitosan, a natural cationic polysaccharide, and its derivatives have a very high
affinity for the direct, reactive, and disperse dyes. However, chitosan-based hybrids
are not suitable for basic dyes. Sadeghi-Kiakhani et al. (2013) examined the adsorption behavior of chitosan–PPI dendrimer hybrid toward textile dyes.
Zhao et al. (2013) designed and tested acid red 138/CaF 2 as a low-cost adsorbent
for the removing methyl blue and ethyl violet dyes.
Metal–Organic Frameworks
Metal and organic frameworks are a group of high-porosity materials that are synthesized via covalent bonding metal cations and di-, tri-, or tetradendate organic
ligands. The metal–organic frameworks have highly ordered crystalline structures
and large specific surface area. Due to their excellent properties, the metal–organic
frameworks have now found a wide variety of applications in wastewater treatment,
catalyst, sensor, energy, pharmaceuticals, etc. (Lee et al. 2014; Ahmed and Jhung
2014; Férey 2008). These materials have a comparative advantage over other porous
materials due to their large specific surface area, high porosity, tunable porosity,
varying composition, and open metal sites. Such prominent characteristics have
made the metal–organic frameworks as favorable adsorbent (Haque et al. 2010). In
this regard, cationic metal–organic frameworks exhibited an excellent adsorption
capacity toward methyl orange, which is an anionic dye (Haque et al. 2010). Metal–
organic framework-235 and MIL-100 (Fe) have been tested to adsorb cationic methylene blue through electrostatic attraction mechanism (Haque et al. 2011; Zhang
et al. 2013). The hybridization of metal–organic frameworks (Stock and Biswas
2011; Ostermann et al. 2011) with suitable complementary materials has been
reported for the preparation of metal–organic framework-based hybrids (Wee et al.
2011). These metal–organic frameworks hybrids have attracted a great deal of attention for adsorption process (Liu et al. 2016; Ahmed and Jhung 2014).
Yi et al. (2015) used metal–organic frameworks based on hexacarboxylate ligand
and tri-cadmium-ion secondary building units to remove the methylene blue, methyl
orange, and rhodamine B dyes. The results revealed that methylene blue could be
easily adsorbed by the prepared metal–organic frameworks. Rhodamine B could not
penetrate the metal–organic framework pore channels because of the large molecule
size. Zhang et al. (2015) probed the adsorption behavior of Zn–multicarboxylate
ligand metal–organic frameworks toward methylene blue, methyl orange, rhodamine B, and Congo red. It was found out that the MOF could efficiently adsorb
Congo red but exhibited a weak performance toward the other dyes. Du et al. (2015)
16 Hybrid Adsorbents for Dye Removal from Wastewater
Halloysite is a natural kaolinite clay with tubular aluminosilicate structure
(Szczepanik 2017). Halloysite nanotube and its organic- and inorganic-based composites have been extensively utilized in adsorbing the different types of dyes.
Carvalho et al. used cyclodextrin/silica hybrid adsorbent for the adsorption of
methylene blue from aqueous solution (De Carvalho et al. 2014). Cheng et al.
(2016) synthesized and tested hemicellulose/clay hybrid hydrogels for removal of
cationic dyes from aqueous medium.
Chitosan, a natural cationic polysaccharide, and its derivatives have a very high
affinity for the direct, reactive, and disperse dyes. However, chitosan-based hybrids
are not suitable for basic dyes. Sadeghi-Kiakhani et al. (2013) examined the adsorption behavior of chitosan–PPI dendrimer hybrid toward textile dyes.
Zhao et al. (2013) designed and tested acid red 138/CaF 2 as a low-cost adsorbent
for the removing methyl blue and ethyl violet dyes.
Metal–Organic Frameworks
Metal and organic frameworks are a group of high-porosity materials that are synthesized via covalent bonding metal cations and di-, tri-, or tetradendate organic
ligands. The metal–organic frameworks have highly ordered crystalline structures
and large specific surface area. Due to their excellent properties, the metal–organic
frameworks have now found a wide variety of applications in wastewater treatment,
catalyst, sensor, energy, pharmaceuticals, etc. (Lee et al. 2014; Ahmed and Jhung
2014; Férey 2008). These materials have a comparative advantage over other porous
materials due to their large specific surface area, high porosity, tunable porosity,
varying composition, and open metal sites. Such prominent characteristics have
made the metal–organic frameworks as favorable adsorbent (Haque et al. 2010). In
this regard, cationic metal–organic frameworks exhibited an excellent adsorption
capacity toward methyl orange, which is an anionic dye (Haque et al. 2010). Metal–
organic framework-235 and MIL-100 (Fe) have been tested to adsorb cationic methylene blue through electrostatic attraction mechanism (Haque et al. 2011; Zhang
et al. 2013). The hybridization of metal–organic frameworks (Stock and Biswas
2011; Ostermann et al. 2011) with suitable complementary materials has been
reported for the preparation of metal–organic framework-based hybrids (Wee et al.
2011). These metal–organic frameworks hybrids have attracted a great deal of attention for adsorption process (Liu et al. 2016; Ahmed and Jhung 2014).
Yi et al. (2015) used metal–organic frameworks based on hexacarboxylate ligand
and tri-cadmium-ion secondary building units to remove the methylene blue, methyl
orange, and rhodamine B dyes. The results revealed that methylene blue could be
easily adsorbed by the prepared metal–organic frameworks. Rhodamine B could not
penetrate the metal–organic framework pore channels because of the large molecule
size. Zhang et al. (2015) probed the adsorption behavior of Zn–multicarboxylate
ligand metal–organic frameworks toward methylene blue, methyl orange, rhodamine B, and Congo red. It was found out that the MOF could efficiently adsorb
Congo red but exhibited a weak performance toward the other dyes. Du et al. (2015)
16 Hybrid Adsorbents for Dye Removal from Wastewater