Photophysical and Electrochemical Studies of Anchored Chromium (III) Complex on Reduced Graphene Oxide via Diazonium Chemistry

Article abstract of DOI:10.1002/aoc.5063

Covalently anchored chromium complex on reduced graphene oxide (rGO-Cr) is successfully synthesised through trimethoxy silyl propanamine (TMSPA) and phenyl azo salicylaldehyde (PAS) coupling. The rGO-Cr is characterised by Fourier transform infrared spect

Full text of DOI:10.1002/aoc.5063

Received: 4 February 2019
DOI: 10.1002/aoc.5063
Revised: 21 May 2019
Accepted: 23 May 2019
F U L L P A P E R
Photophysical and Electrochemical Studies of Anchored
Chromium (III) Complex on Reduced Graphene Oxide
via Diazonium Chemistry
Jemini Jose1 | Athimotlu Raju Rajamani2 | Sreekanth Anandaram3
Sebastian C. Peter2 | Sreeja P B1
| Sujin P. Jose4 |
1 Department of Chemistry, CHRIST
Covalently anchored chromium complex on reduced graphene oxide (rGO‐Cr)
is successfully synthesised through trimethoxy silyl propanamine (TMSPA) and
phenyl azo salicylaldehyde (PAS) coupling. The rGO‐Cr is characterised by
Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD),
X‐ray photoelectron spectroscopy (XPS), electron dispersive analysis of X‐rays
(EDAX), Raman spectroscopy, scanning electron microscopy (SEM) and high
resolution transmission electron microscopy (HRTEM). Absorption and emis-
sion properties of rGO‐TMSPA‐PAS are studied by excitation dependent
photoluminescence emissions at room temperature. Electrochemical sensing
activity of rGO‐Cr is monitored for paracetamol using modified glassy carbon
electrode. Cyclic voltammetry measurements indicated that rGO‐Cr substan-
tially enhance the eletrochemical response of paracetamol. The experimental
factors are investigated and optimized.
(Deemed to be University), Bengaluru
560029, India
2 New Chemistry Unit, School of
Advanced Materials, Jawaharlal Nehru
Centre for Advanced Scientific Research,
Jakkur, Bengaluru 560064, India
3 Department of Chemistry, National
Institute of Technology, Tiruchirappalli
620015, India
4 School of Physics, Madurai Kamaraj
University, Madurai 625021, India
Correspondence
Sreeja P B, Department of Chemistry,
CHRIST (Deemed to be University),
Bengaluru 560029, India.
Email: sreeja.pb@christuniversity.in
KEYWORDS
anchored chromium complex, cis‐trans switch, electrochemical detection of paracetamol,
functionalization of GO/rGO, graphene oxide hybrid material, immobilized compounds,
photoluminescence
1 | INTRODUCTION
carbon atoms. The manipulation of the size, shape and
relative fraction of the sp2 hybridized domains of GO
The framework of graphene, the ‘amazing material’ of
the scientific world has got ample attention due to its
extraordinary optical,[1] electronic[2–4] and elastic prop-
erties.[5] Moreover, graphene oxide (GO) stands for a
new type of solution processable, non‐stoichiometric
macromolecule which can complex with many organic
and inorganic systems with tunable properties.
Graphene oxide has covalently decorated basal planes
and edges with oxygen‐containing functional groups,
so that it contains a mixture of sp2 and sp3 hybridized
by reduction chemistry offers opportunities for tailoring
its optoelectronic properties due to the heterogeneous
chemical and electronic structures.[6,7] Graphene oxide
has a distinct band gap, well treated as a chemically
tunable platform for optical applications by modern
scientific community. Since it has many conductive
electrons and holes, scientists have made many attempts
to advance the dispersibility and compatibility of
graphene framework through covalent and non‐covalent
functionalization.[8–12]
Appl Organometal Chem. 2019;e5063.
wileyonlinelibrary.com/journal/aoc
© 2019 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.5063

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JOSE ET AL.
Modern surface science is focusing on diazonium
2 | EXPERIMENTAL SECTION
2.1 | Materials and methods
chemistry for the modification of materials, particularly
carbon‐based nanostructures. The successful modification
of sp2 carbon materials by diazonium chemistry intro-
duced new strategies for the attachment of aryl layers to
different organic and inorganic moieties, on account of
the applications such as sensing,[13] energy storage sys-
tems[14] and molecular electronic junctions.[15–17] Aryl
diazonium compounds perform as precise coupling
agents for polymers, biomacromolecules and nanoparti-
cles which are extensively used for catalysis.[18–22]
Modification of materials by diazonium chemistry also
provides a well‐defined pathway to design and tune the
optical properties for polymers fillers, polymer nanocom-
posites and polymer sensing layers. This also offers
explicit routes to manipulate the nanorobots for cancer
probes and drug delivery.[19,23–34] Diazonium modifica-
tion on graphene frame work appears promising since it
results in significant increase of room temperature
resistance and optical band gap of ~380 meV based on
angle resolved photoemission electron microscopy
All chemicals used were of analytical grade. Graphite,
potassium permanganate, sulphuric acid (36 M),
HCl (5%), hydrogen peroxide (30%), trimethoxy
silylpropanamine (TMSPA), aniline, salicylaldehyde,
CrCl3.6H2O were purchased from Sigma Aldrich,
Bangalore, India. Dipotassium hydrogen orthophosphate
and potassium dihydrogen orthophosphate were obtained
from Merck. Extra pure paracetamol was obtained from
sd fine chemicals limited, India. All the reactions were
carried out under an argon atmosphere with the use of
standard Schlenk techniques. Toluene was purified and
dried prior to the use. Dimethyl sulphoxide (DMSO) and
ethanol were used without further purification.
2.2 | Synthesis of anchored chromium
complex on reduced graphene oxide
(rGO‐Cr) through diazonium chemistry
measurements which leads graphene oxide as
a
potential material in optoelectronics.[35–37] There
are reports on functionalization of GO with highly
conjugated aromatic molecules, polymers and ionic elec-
trolytes.[38–40] They are highly significant in heteroge-
neous catalysis,[41–44] supercapacitors,[45–47] adsorption
and conversion of polluted gases.[48–51]
2.2.1 | Synthesis of trimethoxysilyl
propanamine functionalized reduced
graphene oxide (rGO‐TMSPA)
Graphene oxide (GO) was synthesized from graphite, by
modified Hummers method[53] and reduced graphene
oxide was obtained by further thermal treatment of
graphene oxide.
Trimethoxysilyl propanamine (TMSPA) functionalised
reduced graphene oxide was prepared from reduced
graphene oxide and TMSPA.[52] Reduced graphene oxide
(1.0 g) was sonicated in toluene for dispersion and
refluxed with 3 mL of TMSPA under argon atmosphere
for 24 hr. The product was washed with ethanol, filtered
and dried at 50 °C.
In this work, we explored the possibility of covalent
interaction through diazonium chemistry, to enhance
the photoluminescence emission of graphene oxide.
Reduced graphene oxide is functionalised by phenyl azo
salicylaldehyde through silane coupling, based on
known procedure.[52] The coordination property of
functionalised azo dye was studied by preparing its
chromium (III) complex. The products isolated were
characterised by Fourier transform infrared spectroscopy
(FTIR), powder X‐ray diffraction (PXRD), X‐ray photo-
electron spectroscopy (XPS), electron dispersive analysis
of X‐rays (EDAX), Raman spectroscopy, Scanning
electron microscopy (SEM) and High resolution transmis-
sion electron microscopy (HRTEM). The absorption and
excitation‐dependent emission properties of PAS and
rGO‐TMSPA‐PAS at room temperature were performed
to understand the geometrical variations caused by an
external stimulus and this can be used in developing a
dynamic molecular devices. We also discuss the electro-
chemical detection of paracetamol by modified glassy
carbon electrode with rGO anchored chromium complex.
The comparative study of electrochemical performance
of rGO/GCE and rGO‐Cr/GCE presented an enhanced
2.2.2 | Synthesis of trimethoxysilyl
propanamine phenyl azo salicylaldehyde
functionalised reduced graphene oxide
(rGO‐TMSPA‐PAS)
The 5‐phenyl azo salicylaldehyde was prepared by the
reported procedure.[54] Aniline (2.26 ml) was mixed with
3 ml HCl (37%) in distilled water, diazotized at 5 °C. The
diazotized aniline compound was coupled with
salicylaldehyde in a mixture of sodium hydroxide and
sodium carbonate at 5 °C at a pH of 7 to 9. Trimethoxy
silyl propanamine functionalized reduced graphene oxide
(500 mg) was dispersed in ethanol and refluxed with
electrochemical
response
for
rGO‐Cr/GCE
for
paracetamol.

JOSE ET AL.
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5‐phenyl azo salicylaldehyde (1.0 g) under argon atmo-
sphere for 6 hr.
by ultra High‐Resolution Scanning Electron Microscopy
(ULTRA 55 FESEM) and High Resolution Transmission
Electron Microscopy (HRTEM JEOL JEM 2100). At room
temperature, Micro‐Raman spectra of the samples were
recorded using HORIBA Jobin Yvon Lab RAM HR 800
equipped with a thermoelectrically cooled CCD detector.
He–Ne laser of wavelength 632.81 nm with 20 mW of
power was used as an excitation source. Chemical compo-
sition and states at the surface of rGO‐Cr was done by
X‐ray Photoelectron Spectroscopy (XPS) (Thermo scien-
tific K‐alpha surface analysis). Shimadzu UV‐2600
UV–Vis spectrophotometer was used to record
UV–visible spectra using quartz cell with 1 cm path
length. Photoluminescence studies were recorded in
RF‐5301 PC Shimadzu spectrofluorometer with slit width
5 nm and in the scan range of 220 nm to 770 nm.
CHI660E electrochemical instrument was used for cyclic
voltammetric studies.
2.2.3 | Synthesis of anchored chromium
complex on reduced graphene oxide (rGO‐
Cr)
Ethanolic dispersed solution of reduced graphene oxide
3‐(trimethoxysilyl)‐1‐propanamine
5‐phenyl
azo
salicylaldehyde (rGO‐TMSPA‐PAS) was mixed in an
ethanolic solution of metal salt CrCl3.6H2O for 6 hr.
The obtained immobilized complex was washed with eth-
anol to remove the unreacted reactants. The route of the
synthesis of rGO anchored chromium complex is shown
in Figure 1.
2.3 | Structural characterisation of
anchored chromium complex on reduced
graphene oxide
3 | RESULTS AND DISCUSSION
The IR spectra of rGO, rGO‐TMSPA, rGO‐TMSPA‐PAS
and rGO‐Cr were recorded in Frontier IR spectrometer
(Perkin Elmer) in the range 400–4000 cm−1 at room tem-
perature. Powder X‐ray Diffraction (PXRD) patterns of
the samples were recorded with a Rigaku, Ultima IV
using Ni‐filtered Cu‐Kα X‐ray source (λ = 1.5406 Ao).
PXRD patterns were obtained in the 2θ range scanning
from 10–90o with a scan speed of 2o min−1. The morphol-
ogy of the functionalized rGO samples was characterized
The IR spectra of rGO, rGO‐TMSPA, rGO‐TMSPA‐PAS,
and rGO‐Cr are shown in Figure 2. The appearance of
the broad peak in pure rGO at 3393 cm−1 is attributed
to the stretching vibration of carboxyl –OH. It is evidence
for the occurrence of a number of hydroxyl groups. The
other distinct peaks are 1710 cm−1 (C=O), 1149 cm−1
(C‐OH) and 1031 cm−1 (C‐O) represent the hydroxyl,
carboxylic and epoxy groups.[55–60] The FTIR spectrum
FIGURE 1 Schematic illustration of the
synthesis of anchored chromium complex
on reduced graphene oxide via silane and
azo coupling

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JOSE ET AL.
FIGURE 2 FTIR spectra of reduced graphene oxide and its functionalization by chromium complex through silane and azo coupling a.
rGO and rGO‐TMSPA b. rGO‐TMSPA‐PAS and rGO‐Cr
of functionalized rGO shows several new peaks as com-
pared to pure rGO. The doublet at 2922 cm−1 and
2859 cm−1 illustrate the asymmetric and symmetric alkyl
chains of TMSPA. The vibrational bands of stretching and
bending –NH2 groups are at 3497 cm−1 and 1564 cm−1
respectively.[32] The peaks at 1106 cm−1 and 1019 cm−1
correspond to the Si‐O‐Si and Si‐O‐C, confirms the silane
coupling of rGO.[53,61] The presence of these peaks reveals
the anchoring of TMSPA onto reduced graphene oxide.
The C=N frequency at 1627 cm−1 confirms the condensa-
tion reaction between the –NH2 of rGO‐TMSPA and –OH
of 5‐phenyl azo salicylaldehyde.[55] The slight shift of the
C=N frequency at 1598 cm−1 (Δυ is 29 cm−1) confirmed
the coordination of chromium (III) metal ion with
azomethine nitrogen atom of functionalized rGO.[34]
The detailed IR spectrum of rGO, rGO‐TMSPA,
rGO‐TMSPA‐PAS and rGO‐Cr are given in supporting
information Figure S2.
In Raman spectra, graphene based materials display
three major bands. The G band refers to the 1st order scat-
tering of the E2g and the D band is related to the out of
plane modes of vibrations.[38,39] The D‐band intensity is
directly related to the amount of disorder in the graphene
sheets. 2D band, combination bands at 2723 cm−1 repre-
sents the graphite exfoliation and the activation of two
phonons with identical momentum.[66] Raman spectra
of rGO and rGO‐Cr are shown in Figure 4. The vibration
Figure 3 displays the XRD pattern of rGO, rGO‐
TMSPA, rGO‐TMSPA‐PAS and rGO‐Cr. The as prepared
rGO shows a broad 2θ peak at 24.29 in (002) diffraction
plane associated with reduced graphene oxide (rGO) of
an interplanar distance 0.36 nm calculated by the Bragg's
equation. This is due to the introduction of oxygenic
functional groups and trapped water molecules between
the graphite layers.[41,62,63] During the anchoring of
TMSPA, PAS and metal complex on the rGO surface,
the diffraction peak of rGO do not disappear, indicating
the structure of rGO is retained during the
functionalization. However, it is clear from the XRD pat-
terns that rGO‐TMSPA, rGO‐TMSPA‐PAS, rGO‐Cr are
multilayered and illustrates a broad diffraction peak with
an interplanar distance of 0.81 nm. This is attributed to
increased layer to layer distance on further functionalisa-
tion of rGO.[41,64,65]
FIGURE 3 Powder XRD patterns of rGO, rGO‐TMSPA, rGO‐
TMSPA‐PAS, rGO‐Cr

JOSE ET AL.
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indicates higher the degree of graphitization during the
functionalisation in rGO‐Cr.[69,70]
Wide range X‐ray photoelectron spectrum of the hybrid
rGO‐Cr complex on graphene oxide and their
deconvoluted peaks are displayed in Figure 5 which reveals
the presence of C1s, N1 s, O1s, Si2p, Cl2p, Cr2p1/2, Cr2p3/2
at 284.6 eV, 401.2 eV, 532.1 eV, 102.6 eV, 195.9 eV, 587.1 eV
and 577.3 eV respectively. The successful synthesis of rGO‐
covalently immobilized chromium (III) complex via diazo-
nium chemistry was substantiated by the following: The
highly resolved C1s spectrum was brought about four com-
ponent peaks positioning at 284.4 eV, 286.4 eV, 285.3 eV,
and 287.7 eV and are ascribed for C=C/C‐C in GO aro-
matic rings, C=N of rGO‐TMSPA‐PAS, C‐O in epoxy and
alkoxy group of rGO and C=O in COOH of rGO
respectively.[71] The oxygen 1 s peak at 533.1 is revealed
the C‐OH in the functionalization of rGO.[72,73] The
distinctive resolution peak of N1 s obtained at 399.0 eV
can be assigned to C=N‐C of nitrogen.[74–78]
To understand more about the morphology, micro-
structure and crystallinity rGO and rGO‐Cr were exam-
ined by SEM and HRTEM. FESEM of rGO‐Cr is shown in
Figure 6. The loose agglomerates of tiny particles with a
rough surface and irregular shapes are distributed in
the extended sheet‐like structures of rGO. For more
clarity high resolution TEM images of rGO and rGO‐Cr
are presented in Figure 7. The white region refers to
layered graphene sheet and the dark spots designate the
anchored chromium complex through azo and silane
coupling on rGO.
FIGURE 4 Measured Raman spectrum of reduced graphene
oxide (rGO) and anchored chromium (III) complex on reduced
graphene oxide (rGO‐Cr)
of sp2 hybridised carbon systems illustrate the G band at
about 1595 cm−1 and D band at 1329 cm−1 corresponds
to the distortions in the edge centred band structure of
carbon framework of rGO.[67] The intensity ratio ID/IG
of rGO and rGO‐Cr are 1.49 and 1.29 respectively. The
broad D band compared to G band is owing to the struc-
ture disorders and defects in the graphene surface
sheets.[68] Here in after the functionalization of rGO, the
G band shift to lower frequency region 1583 cm−1
,
confirming the reduction and increasing number of layers
in hybrid rGO.[67] Decrease in ID/IG intensity ratio
FIGURE 5 Wide‐scan survey XPS spectrum of rGO‐Cr (a) and Deconvoluted XPS peaks of C1s (b), O1s (c), N1 s (d), Si2p (e), Cr2p (f)

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JOSE ET AL.
FIGURE 6 FESEM images of rGO‐Cr
FIGURE 7 HRTEM images (a & b) rGO, (c & d) rGO‐Cr
and C=O absorptions respectively. The peak at 455 nm
in the PAS spectrum is associated with the cis to trans iso-
meric switching of the PAS molecule.[79] The dissolved
form of PAS molecule is known to switch from the cis
to trans at room temperature, in presence of an electric
field or under UV irradiation.[80] Trans isomer of azo
benzene is more stable than cis isomer due to the less
exothermic heat of combustion.[81] It is also predominant
in dark at room temperature and the photoexcited state is
3.1 | Photoluminescence properties of
rGO‐TMSPA‐PAS
The absorption and excitation‐dependent emission prop-
erties of PAS and rGO‐TMSPA‐PAS at room temperature
with the same concentration are shown in Figure 8. The
literature reveals that rGO has a peak at 267 nm is due
to the π → π* transition band and the shoulder at
~320 nm corresponding to the n → π* transition band of
carbonyl group.[55] The π → π* transition band of PAS
is at 274 nm. The other peaks are at 290 nm and
372 nm illustrating the n → π* transition of the N=N
at ~23 kcal mol .
−1 [82] The trans PAS isomerises to cis PAS
with a wavelength of 372 nm and gets back to trans at
455 nm when it absorbs a photon and it is shown in

JOSE ET AL.
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TABLE 1 UV–Visible transitions of rGO, rGO‐TMSPA, PAS and
rGO‐TMSPA‐PAS
Wavelength
π → π* (nm)
n → π* (nm)
rGO
267
249
274
282
320[85]
rGO‐TMSPA
PAS
297[55]
290,372,455
368, 455
rGO‐TMSPA‐PAS
The cis‐trans switch of PAS initiates the change in the
photoluminescence performances of pure and hybrid
PAS. To understand the photoluminescence properties of
the same, excitation dependent photoluminescence mea-
surements were performed at 282 nm, 368 nm, 372 nm
and 455 nm as shown in Figure 10. It is seen that, as the
excitation wavelength of both PAS and rGO‐TMSPA‐PAS
increases, the emission peaks also move towards from
green to red in visible light with differnt intensities. GO
exhibits the emission bands at 438 nm and 500 nm at
the excitation wavelength of 360 nm.[48] The excitation
dependent photoluminescence spectrum of PAS and
rGO‐TMSPA‐PAS at 455 nm shows broad bands with
higher intensity for rGO‐TMSPA‐PAS compared to PAS.
The broad emission peak in the range of 500 nm to
850 nm is due to the π → π* gap created by the structure
distortions which in turn result in the optical transitions
among the localised states.[48] Photoluminescence spectra
also substantiate that the emission emerges from four
differnt regions, viz., green, yellow, orange and red. This
means that the fluorescence colour of both PAS and
rGO‐TMSPA‐PAS could be turned simply by changing
the excitation wavelength. The emission intensity of PAS
at excitation wavelength 455 nm is decreased by ~75%
compared to 372 nm. It is inferred that this change in
photoluminescence is due to the fact that the major part
of the energy at 455 nm excitation is used for isomeric
switching. Thus the resultant emission spectrum is due
to the residual energy present in the excitation radiation.
Such an inference is supported by previous reports
FIGURE 8 Absorption properties of PAS and rGO‐TMSPA‐PAS
showing the excimer at 583 for rGO‐TMSPA‐PAS
Figure 9. Azobenzenes easily undergo isomerisation. In
the wavelength between 320–350 nm, trans isomer
isomerises to cis isomer by irradiation (S1 ← S0 and
S2 ← S0 excitations). It reverts back to trans isomer when
it absorbs light between 400–450 nm by exciting into the
S1 or S2 state.[83] This photoinduced isomerisation of the
azobenzenes leads to a remarkable change in their phys-
ical properties which make them as potential molecular
switches. The UV spectrum of GO‐TMSPA‐PAS in DMSO
gives three peaks at 282 nm, 368 nm and a less intense
peak at 455 nm. The peak at 282 nm indicates the absorp-
tion of rGO in the functionalized PAS because of the π
electron interaction of rGO and TMSPA‐PAS. The peaks
at 368 and 455 nm are designated as the n → π* transi-
tions of the GO‐TMSPA functionalized azo dye.[84] The
wavelengths and intensity shifts in the absorption bands
of PAS and covalently grafted rGO‐TMSPA‐PAS propos-
ing the electronic communication and π‐π interactions
between the electron donor PAS and electron acceptor
rGO‐TMSPA. The excimer peak at 583 nm is attributed
to an eletronically excited dimer of the rGO‐TMSPA‐
PAS. The UV spectral values of rGO, rGO‐TMSPA, PAS,
rGO‐TMSPA‐PAS are represented in Table 1.
FIGURE 9 Cis‐Trans switch of phenyl azo salicylaldehyde at 372 and 455 nm

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JOSE ET AL.
FIGURE 10 Photoluminescence spectra of PAS and GO‐TMSPA‐PAS in dimethyl sulphoxide at an excitation wavelength a) 282 nm b)
368 nm c) 372 nm and d) 455 nm
studying cis‐ trans switch in PAS derivatives.[42,80,86] The
special features of the excitation dependent
photoluminescence spectra signify the capturing of elec-
trons of the rGO‐TMSPA from PAS.[87] This enhances
the electron hole pairs and hence, the photoluminescence
quenching. These studies can lead to a better route for the
solution processable optoelectronics material.
measurements, the sensors were immersed in 30 ml of
0.1 M PBS containing 0.1 mg ml−1 applying the potential
in the range of −0.2 V to 0.6 V. Differential pulse scan-
ning voltammetry was carried out in −0.4 to 0.8 V with
an increment of 0.004 V, an amplitude of 0.05 V along
with a pulse width of 0.05 s using 0.1 M phosphate buffer
as the background electrolyte. The GCE surface was mod-
ified manually by drop casting the synthesised materials
on the working area. A comparative study using a bare
and modified electrode (GCE/rGO, GCE/rGO‐Cr) in the
presence of 1 mM K4Fe(CN)6 in 0.1 M KCl solution was
conducted. Electrochemical studies were further carried
out for the detection of paracetamol in 0.1 M phosphate
buffer solution (pH ‐7).
The electrochemical behavior of paracetamol at
rGO‐Cr modified GCE (rGO‐Cr/GCE) was investigated
by cyclic voltammetry. As shown in Figure 11 (a), the
rGO‐Cr modified/GCE shows the highest peak current
response in comparison to bare and other modified elec-
trodes in the presence of a redox species 1 mM K4Fe(CN)6
in 0.1 M KCl at 100 mVs−1. Figure 11 (b) represents an
increased electrocatalytic current response of bare GCE,
rGO/GCE, rGO‐Cr/GCE individually in the presence of
3.2 | Electrochemical studies of anchored
chromium complex on reduced graphene
oxide (rGO‐Cr)
Cyclic voltammetry and differential pulse voltammetry
(DPV) were used to resolve the electrochemical sensing
properties of rGO anchored chromium complex for para-
cetamol. The electrochemical experiments were carried
out in 0.1 M phosphate buffer solution (PBS), pH 7 in a
three electrode system using the bare and modified GCE
as the working electrode, platinum wire as the counter
electrode and Ag/AgCl electrode as the reference elec-
trode to examine the electrochemical activity of the rGO
anchored chromium complex. For cyclic voltammetry

JOSE ET AL.
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FIGURE 11 (a) Cyclic voltammogram CV) of the bare GCE, rGO/GCE and rGO‐Cr/GCE in the presence of 1 mM ferro/ferricyanide in
0.1 M KCl at 100 mVs‐1. (b) Development of the Electrocatalytic behaviour of rGOCr/GCE compared to bare GCE, rGO/GCE and rGO‐
Cr/GCE in the presence of 0.1 mg ml −1 (0.6 mM) paracetamol in PBS (pH = 7)
0.1 mg ml−1 (0.6 mM) paracetamol (pH ‐7) at the scan
rate of 100 mVs−1.The rGO‐Cr/GCE gives the maximum
current response and also a positive potential shift com-
pared with the bare GCE. The potential shift is due to
the increased electron transfer mechanism between the
modified electron surface and the oxidizable species
(paracetamol). It is evident that the rGO‐Cr/GCE could
be an effective electrocatalyst for the redox reaction of
paracetamol and it is facilitated by the electron transfer
between the electrode and analyte.
0.1 M buffer. Figure 12 (a) shows a series of cyclic voltam-
mograms for rGO‐Cr/GCE with the scan rate range from
50 mVs−1 to 225 mVs−1. The scan rate effect also gives
information about the mechanism which involved in
electrochemical redox process of paracetamol. The redox
peak current at the modified electrode was linearly
increased with increasing in the scan rate and is shown in
Figure 12 (b).
Differential pulse voltammetry (DPV) technique was
performed to understand the association between peak
current and concentration of paracetamol. Differential
pulse voltammetry of rGO‐Cr/GCE in 0.1 M phosphate
buffer in different concentrations of paracetamol is
shown in the Figure 13, which signifies a linear relation-
ship between the peak current and concentration of the
analyte. The peak obtained at 0.4 V is due to the
oxidation of paracetamol to N‐(4‐oxo‐cyclohexa‐2,
3.2.1 | Optimization of scan rate and
concentration of analyte
The effect of scan rate on the electrochemical redox pro-
cess of paracetamol at rGO‐Cr/GCE was studied in
FIGURE 12 (a) Cyclic voltammograms of the rGO‐Cr/GCE in 0.1 M PBS containing 0.1 mg ml‐1 paracetamol at different scan rates
50,60,70,80,90,100,125,150,175,200 mVs‐1, respectively. (b) Variations of anodic peak current (Ipa) and cathodic peak current (Ipc) with
the square root of the scan rate

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JOSE ET AL.
rGO‐Cr complex showed an enhanced electrocatalytic
activity which was utilized for the fabrication of the
sensitive electrode for the quantitative detection of
paracetamol.
ACKNOWLEDGMENTS
The work was financially supported by Centre for
Research, CHRIST (Deemed to be University), Benga-
luru, India. SPB is thankful to Prem Prabhakar, Hannam
University Daejeon, South Korea and Sadasivan Shaji,
Autonomous University of Nuevo Leon, Mexico.
ORCID
Sreekanth Anandaram
https://orcid.org/0000-0002-2942-
8487
FIGURE 13 Differential pulse voltammetry of rGO‐Cr/GCE in
0.1 M phosphate buffer with different concentrations of
paracetamol like 10 ppm, 20 ppm, 30 ppm, 40 ppm, 50 ppm, 60 ppm
and 70 ppm
Sreeja P B https://orcid.org/0000-0002-2106-7867
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In summary, trimethoxysilyl propanamine phenyl azo
salicylaldehyde functionalized rGO (rGO‐TMSPA‐PAS)
and its mononuclear chromium complex are synthesised
through diazonium chemistry. The spectroscopic and
morphological studies supported the successful syntheses
of rGO, rGO‐TMSPA, rGO‐TMSPA‐PAS and rGO‐Cr.
Powder XRD studies and Raman spectra showed the
distortions of the framework of graphene surface due to
the functionalization. The FESEM and HRTEM images
revealed that sheet structure of rGO is retained in a large
extent during the multistep synthesis. Elemental analysis
like XPS is well supported the functionalization of rGO.
Amazing emission properties in the range of 542 nm to
732 nm were observed for functionalized azo dye on
graphene oxide through silane coupling (rGO‐TMSPA‐
PAS) and free azo dye (PAS) with an excitation depen-
dent photoluminescence study at room temperature.
Photoluminescence studies experience a red shift, with a
decrease in intensity when the excitation wavelength
increases. These results demonstrate that both silane
functionalized graphene oxide and azo dye enable an
electronic interaction due to the recombination of sp2
and sp3 states and electron–hole pairs which have exten-
sive importance in developing optoelectronic devices. The
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How to cite this article: Jose J, Rajamani AR,
Anandaram S, Jose SP, Peter SC, P B S.
Photophysical and Electrochemical Studies of
Anchored Chromium (III) Complex on Reduced
Graphene Oxide via Diazonium Chemistry. Appl
Organometal Chem. 2019;e5063. https://doi.org/
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