(002) plane with d-spacing value 3.45 Å. Interestingly after oxidation to GO, the
XRD pattern depicts a characteristic peak at 2h = 9.9° for the plane (100) having a
d-spacing value of 8.9 Å, which confirms the successful functionalization of graphite to GO [39].
3 Fluorescence (Fluorometry) Detection of Water
Pollutants
The term fluorescence means the emission of light by material, and it is denoted as a
specific type of luminescence phenomenon. When electromagnetic radiation falls
on molecules or substance, the electrons gain the energy and are excited to higher
energy level and produce luminescence. This process of emission is termed as
photoluminescence. Mostly there are two types of photoluminescence, fluorescence
and phosphorescence. In the case of fluorescent, the release of electromagnetic
energy is instantaneous or ceases on the withdrawing of the exciting radiation and
emission occurs between states of same spin multiplicity. But for phosphorescence,
the energy release or emission is continuous or delayed after the existing radiation
has been removed. Among the two techniques, fluorescence is extremely effective
as the detectors on the machine are highly sensitive. Other than these two techniques, other luminescence processes are chemiluminescence, bioluminescence,
electrochemiluminescence, electroluminescence, lyoluminescence, etc.
The fluorescent optical detection methods have also been recognized as powerful
and promising tools over other techniques because of its better sensitivity, high
speed, easy operation, and low cost for quantitative detection of anions and cation.
The sensitivity of the fluorometric technique is approximately 1000 times greater
than the absorption technique [40]. Thus, when working with low quantity or
expensive materials fluorescence method is very useful as using a minute amount of
the compound, can be achieved better sensitivity as well as detection limits. Only
fluorescence active molecules or samples can be detected by this method, show
better selectivity and specificity compared to UV/Vis and other techniques. In
fluorescence, wide concentration range can be detected, e.g., more than three to six
log orders of concentration. Again, in the case of fluorescence, sample preparation
is also very easy and simple, shows accurate and precise reading [33–35].
Graphene and its analogs such as GO, GQDs, rGO have found extensive
applications in fluorescent sensors for detection of water pollutants in recent years.
Main benefits of graphene-based nanomaterials are that they can be employed as in
tunable fluorophore as well as a potent fluorescence quencher. In this section, we
want to focus the origin of fluorescence, its excitation dependent fluorescence, and
strategies for sensor design based on plasmonic nanoparticle-decorated GO and
GQDs.
86
M. J. Deka et al.
XRD pattern depicts a characteristic peak at 2h = 9.9° for the plane (100) having a
d-spacing value of 8.9 Å, which confirms the successful functionalization of graphite to GO [39].
3 Fluorescence (Fluorometry) Detection of Water
Pollutants
The term fluorescence means the emission of light by material, and it is denoted as a
specific type of luminescence phenomenon. When electromagnetic radiation falls
on molecules or substance, the electrons gain the energy and are excited to higher
energy level and produce luminescence. This process of emission is termed as
photoluminescence. Mostly there are two types of photoluminescence, fluorescence
and phosphorescence. In the case of fluorescent, the release of electromagnetic
energy is instantaneous or ceases on the withdrawing of the exciting radiation and
emission occurs between states of same spin multiplicity. But for phosphorescence,
the energy release or emission is continuous or delayed after the existing radiation
has been removed. Among the two techniques, fluorescence is extremely effective
as the detectors on the machine are highly sensitive. Other than these two techniques, other luminescence processes are chemiluminescence, bioluminescence,
electrochemiluminescence, electroluminescence, lyoluminescence, etc.
The fluorescent optical detection methods have also been recognized as powerful
and promising tools over other techniques because of its better sensitivity, high
speed, easy operation, and low cost for quantitative detection of anions and cation.
The sensitivity of the fluorometric technique is approximately 1000 times greater
than the absorption technique [40]. Thus, when working with low quantity or
expensive materials fluorescence method is very useful as using a minute amount of
the compound, can be achieved better sensitivity as well as detection limits. Only
fluorescence active molecules or samples can be detected by this method, show
better selectivity and specificity compared to UV/Vis and other techniques. In
fluorescence, wide concentration range can be detected, e.g., more than three to six
log orders of concentration. Again, in the case of fluorescence, sample preparation
is also very easy and simple, shows accurate and precise reading [33–35].
Graphene and its analogs such as GO, GQDs, rGO have found extensive
applications in fluorescent sensors for detection of water pollutants in recent years.
Main benefits of graphene-based nanomaterials are that they can be employed as in
tunable fluorophore as well as a potent fluorescence quencher. In this section, we
want to focus the origin of fluorescence, its excitation dependent fluorescence, and
strategies for sensor design based on plasmonic nanoparticle-decorated GO and
GQDs.
86
M. J. Deka et al.