quenched by addition to the cyclodextrin-modified graphene oxide layer; however,
introduction of amantadine, a pharmaceutical agent, displaced Rhodamine 6G from
the surface and led to significant fluorescence increases. Furthermore, Mondal et al.
also used a graphene-bound β-cyclodextrin as a cholesterol sensor based on the
competitive host-guest interaction between Rhodamine 6G and cholesterol [26]. The
emission of Rhodamine 6G was quenched by encapsulation in the cavity of the
graphene-bound β-cyclodextrin. Cholesterol selectively displaced the Rhodamine
6G, freeing it from the quenching agent and turning the fluorescence back on. Carbon
dots (CDots) or graphene quantum dots (GQDs), which are quasi one-dimensional
graphene particles, have also been widely used for molecular recognition by luminescent sensors [27–29]. For example, the α-CD-modified CDots have been used in
molecular recognition of derivatives of methyl viologen (MV
2+
), due to the MV
2+
-
induced assembly of CDots via the host-guest approach [28]. The electron transfer
processes between CDots and MV
2+ have been explored carefully by time resolved
fluorescence decay and transient absorption spectroscopy.
15.2.2 Carbon Materials Functionalized with Cyclodextrins as
Adsorbents
The high surface area of the carbon nanomaterials as well as their ability to bind
various organics via π-π stacking not only can be utilized toward the abovediscussed electrochemical and luminescent detection but also can be played in
adsorption. The main examples of such application of CNMs, primarily for
graphene-family nanomaterials and carbon nanotubes, are in water treatment,
which is associated with removing organic pollutants from aqueous solutions.
Moreover, it has been well established that because of the unique properties of
CDs toward the formation of inclusion complexes, these molecules can be employed
to further enhance the sorption capacity of the resultant CNMs adsorbent. Therefore,
a new trend to fabricate CD-decorated CNMs adsorbents can be regarded as the
promising way in the development of applied materials for water treatment.
In general, the chemical energy of the covalent bond is higher in comparison to
non-covalent interactions, and the stabilization of material structure could be ensured
by covalent bonds during the adsorption process. Therefore, in contrast to electrochemical sensors of the conjugates of CDs and CNMs, covalent approaches were
mainly employed for preparing CD-CNMs as the adsorbents. β-Cyclodextrin grafted
on the surface of multi-walled carbon nanotubes exhibits a high adsorption in the
removal of polychlorinated biphenyls (PCBs) from aqueous solution [30]. A crosslinked nanoporous polymer containing CD and carbon nanotube (CNT) has shown
excellent adsorption capacity for p-nitrophenol which can be removed as much as
99% from a 10 mg/L spiked water sample; in contrast, activated carbon removed
only 47% [31].
15 Cyclodextrin Hybrid Inorganic Nanocomposites for Molecular Recognition. . .
431
introduction of amantadine, a pharmaceutical agent, displaced Rhodamine 6G from
the surface and led to significant fluorescence increases. Furthermore, Mondal et al.
also used a graphene-bound β-cyclodextrin as a cholesterol sensor based on the
competitive host-guest interaction between Rhodamine 6G and cholesterol [26]. The
emission of Rhodamine 6G was quenched by encapsulation in the cavity of the
graphene-bound β-cyclodextrin. Cholesterol selectively displaced the Rhodamine
6G, freeing it from the quenching agent and turning the fluorescence back on. Carbon
dots (CDots) or graphene quantum dots (GQDs), which are quasi one-dimensional
graphene particles, have also been widely used for molecular recognition by luminescent sensors [27–29]. For example, the α-CD-modified CDots have been used in
molecular recognition of derivatives of methyl viologen (MV
2+
), due to the MV
2+
-
induced assembly of CDots via the host-guest approach [28]. The electron transfer
processes between CDots and MV
2+ have been explored carefully by time resolved
fluorescence decay and transient absorption spectroscopy.
15.2.2 Carbon Materials Functionalized with Cyclodextrins as
Adsorbents
The high surface area of the carbon nanomaterials as well as their ability to bind
various organics via π-π stacking not only can be utilized toward the abovediscussed electrochemical and luminescent detection but also can be played in
adsorption. The main examples of such application of CNMs, primarily for
graphene-family nanomaterials and carbon nanotubes, are in water treatment,
which is associated with removing organic pollutants from aqueous solutions.
Moreover, it has been well established that because of the unique properties of
CDs toward the formation of inclusion complexes, these molecules can be employed
to further enhance the sorption capacity of the resultant CNMs adsorbent. Therefore,
a new trend to fabricate CD-decorated CNMs adsorbents can be regarded as the
promising way in the development of applied materials for water treatment.
In general, the chemical energy of the covalent bond is higher in comparison to
non-covalent interactions, and the stabilization of material structure could be ensured
by covalent bonds during the adsorption process. Therefore, in contrast to electrochemical sensors of the conjugates of CDs and CNMs, covalent approaches were
mainly employed for preparing CD-CNMs as the adsorbents. β-Cyclodextrin grafted
on the surface of multi-walled carbon nanotubes exhibits a high adsorption in the
removal of polychlorinated biphenyls (PCBs) from aqueous solution [30]. A crosslinked nanoporous polymer containing CD and carbon nanotube (CNT) has shown
excellent adsorption capacity for p-nitrophenol which can be removed as much as
99% from a 10 mg/L spiked water sample; in contrast, activated carbon removed
only 47% [31].
15 Cyclodextrin Hybrid Inorganic Nanocomposites for Molecular Recognition. . .
431