Page 140 - Polymer-based Nanocomposites for Energy and Environmental Applications

Energy and environmental applications of graphene and its derivatives 115

reversible capacity of 852.6 mAh g 1 at a current density of 500 mA g 1 and retained
a charge capacity of 594 mAh g 1 even after 150 cycles [53]. Researchers, however,
claimed that practical applications in energy devices and high rate of electrochemical
reaction are not effectively fulfilled by graphene [56]. It can be explained by the fact
that graphene sheets on the electrode show a tendency to restack or form irreversible
agglomerates due to the strong π-π stacking and van der Waals interactions between
the graphene sheets. This affinity dramatically reduces the surface area of electrode
and consequently hinders the rapid electrolyte diffusion affecting the application in
energy devices.

4.5 Environmental and electrochemical sensing

The production of graphene from 3-D graphene (graphite) by oxidation-exfoliation-
reduction creates many defective sites on the graphene and thus offers further
functionalization [23]. The functionalization and flexibility in modification through
covalent and noncovalent of the graphene surface opened up many possibilities to
explore its innumerable application in electrochemical sensing area. Electrochemical
sensing area involves (i) graphene in disease diagnosis and molecule electrochemical
sensing (ascorbic acid, glucose, uric acid, and dopamine), (ii) graphene in drug
molecule electrochemical sensing (artemisinin, codeine, acetaminophen, and rutin),
(iii) graphene in food molecule electrochemical sensing (clenbuterol, tartrazine,
sunset yellow, diethylstilbestrol, sudan, and bisphenol A), and (iv) graphene in
environment molecule electrochemical sensing (chlorpyrifos, phenols, toxic heavy
mental ions, and estriol). Graphene along with its carbonaceous nanomaterials, such
as CNTs and fullerene, is devoted to explore the excellent selective and sensitive
fluorescence probes for fast quantitatively Fe 3+ determination, among many
functionalized organic chromospheres [57], conjugated polymers [58], and
nanomaterials [59], on account of excellent performance and size-tunable optical
properties [60,61]. Graphene quantum dots (GQDs) are graphene sheets smaller
than 100 nm that exhibit unique and superior properties such as better optical,
electronic, blinking, outstanding photostability against photobleaching and good
biocompatibility along with low toxicity due to their edge effects and quantum
confinement [62,63]. Based on photoluminescence (PL) of different GQDs, they
are used for Fe 3+ detection [64]. Recently, amino acid-modified GQDs were
synthesized through acylation and amination reactions [65]. The presence of Fe 3+
selectively and efficiently quenches the fluorescence of GQDs and emits strong
and stable blue fluorescence at a quantum yield of 10.92%–12.67%. Moreover,
research study stated that functionalization of pristine graphene with metal NPs, such
as Pd and/or Pt, has proved to effectively sensitize the material at room temperature
based on CVD [66,67]. Recently, graphene hybrid decorated with Pd-NPs was
characterized as chemiresistive material, owing to its fast and selective detection of
hydrogen operating at environmental conditions [68]. Developed device was also
found suitable to detect hydrogen in the range of flammability showing a 14% relative
conductance variation at 0.2% H 2 concentration at room temperature and 50% of