7 Computational and Experimental Analysis of Carbon Functional Nanomaterials
299
Fig. 7.21f. The Zn-induced state was observed in the middle of the band gap which
indicates that the dangling bonds of ionic Zn act as an energy gradient. Due to this
intermediate state, the electrons or holes can efficiently move to the surface of Cdots which enhances the charge transfer, thereby resulting in the higher fluorescence
quantum yield.
7.5.2 Sensing Analysis of Graphene Quantum Dots
and Carbon Dots
The design and fabrication of new fluorescent chemosensors have been developed
enormously since successful synthesis of carbon nanomaterials last decade [149–
153]. There are two fundamental moieties which merged to obtain the fluorescent
chemosensor, composed of the recognition site and the fluorescence signaling
source. It is possible to develop a specific fluorescent sensor by switching these two
moieties, thereby yielding a strong stable fluorescence signal with high specificity
and enhancing the ability for detection of analyte. Generally, the fluorescent
sensor materials should have multiple features such as ease for preparation and
functionalization, high quantum yield with tunable absorption and fluorescence
properties, reliable photostability, non-toxicity, and capability of sensing an analyte
at lower detection limit. The GQDs and C-dots exhibit aforementioned unique
merits and deserve a wide attention for the application of prospective sensors.
To date, the GQDs and C-dots have been extensively utilized as a fluorescence
sensing probes to detect analytes including inorganic metal cations and anions, nitro
explosives, pesticides, drugs, toxic organic molecules, and important biomolecules
based on the fluorescence turn-on and/or turn-off mechanisms. A diverse form of
chemical functionalization of these nanomaterials is required in order that their
functional properties might be involved in the detection of analytes. Indeed, a variety
of analytes could be detected selectively by simply tuning the different functional
groups on the surface of nanomaterial. The process of surface functionalization
is of crucial importance to impart desired properties to nanomaterials for their
applications. The functionalization of nanomaterials can be achieved through either
covalent or noncovalent modification techniques. Rich functional groups including
carboxylic, amine, alcohol, and thiol groups and also functional small molecules
can attach on the surface of nanomaterials to improve their optical properties
by controlling the energy gap and electronic properties. Moreover, formation of
metal/element doping (N, S, transition metals, etc.) and composites/hybrids (with
noble nanoparticles, metal oxides, etc.) with nanomaterials were applied to enhance
their inherent properties to expand the application range.
For instance, the S-doped GQDs show the improved electronic properties and
surface chemical reactivities compared with that of GQDs, and thereby can be
used as an efficient fluorescent probe for highly selective and sensitive detection
of Fe 3+ , reported by Li et al. [153]. The DFT calculations (B3LYP/6-31G*) that the
299
Fig. 7.21f. The Zn-induced state was observed in the middle of the band gap which
indicates that the dangling bonds of ionic Zn act as an energy gradient. Due to this
intermediate state, the electrons or holes can efficiently move to the surface of Cdots which enhances the charge transfer, thereby resulting in the higher fluorescence
quantum yield.
7.5.2 Sensing Analysis of Graphene Quantum Dots
and Carbon Dots
The design and fabrication of new fluorescent chemosensors have been developed
enormously since successful synthesis of carbon nanomaterials last decade [149–
153]. There are two fundamental moieties which merged to obtain the fluorescent
chemosensor, composed of the recognition site and the fluorescence signaling
source. It is possible to develop a specific fluorescent sensor by switching these two
moieties, thereby yielding a strong stable fluorescence signal with high specificity
and enhancing the ability for detection of analyte. Generally, the fluorescent
sensor materials should have multiple features such as ease for preparation and
functionalization, high quantum yield with tunable absorption and fluorescence
properties, reliable photostability, non-toxicity, and capability of sensing an analyte
at lower detection limit. The GQDs and C-dots exhibit aforementioned unique
merits and deserve a wide attention for the application of prospective sensors.
To date, the GQDs and C-dots have been extensively utilized as a fluorescence
sensing probes to detect analytes including inorganic metal cations and anions, nitro
explosives, pesticides, drugs, toxic organic molecules, and important biomolecules
based on the fluorescence turn-on and/or turn-off mechanisms. A diverse form of
chemical functionalization of these nanomaterials is required in order that their
functional properties might be involved in the detection of analytes. Indeed, a variety
of analytes could be detected selectively by simply tuning the different functional
groups on the surface of nanomaterial. The process of surface functionalization
is of crucial importance to impart desired properties to nanomaterials for their
applications. The functionalization of nanomaterials can be achieved through either
covalent or noncovalent modification techniques. Rich functional groups including
carboxylic, amine, alcohol, and thiol groups and also functional small molecules
can attach on the surface of nanomaterials to improve their optical properties
by controlling the energy gap and electronic properties. Moreover, formation of
metal/element doping (N, S, transition metals, etc.) and composites/hybrids (with
noble nanoparticles, metal oxides, etc.) with nanomaterials were applied to enhance
their inherent properties to expand the application range.
For instance, the S-doped GQDs show the improved electronic properties and
surface chemical reactivities compared with that of GQDs, and thereby can be
used as an efficient fluorescent probe for highly selective and sensitive detection
of Fe 3+ , reported by Li et al. [153]. The DFT calculations (B3LYP/6-31G*) that the