Sensitive and selective Cu2+ sensor based on 4-(3-(thiophen-2-yl)-9H-carbazol-9-yl)benzaldehyde (TPCBZ) conjugated copper-complex

Article abstract of DOI:10.1016/j.jorganchem.2016.05.013

4-(3-(thiophen-2-yl)-9H-carbazol-9-yl)benzaldehyde (TPCBZ) was synthesized under microwave irradiation with auto generated pressure (at 130.0 °C) and characterized by ¹H NMR, ¹³C NMR, Mass and FTIR spectroscopy, thin-layer chromatogr

Full text of DOI:10.1016/j.jorganchem.2016.05.013

Journal of Organometallic Chemistry 817 (2016) 43e49
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Sensitive and selective Cu2þ sensor based on 4-(3-(thiophen-2-yl)-9H-
carbazol-9-yl)benzaldehyde (TPCBZ) conjugated copper-complex
,
b
,
, b
Mohammed M. Rahman a *, Khalid A. Alamry b, Tamer S. Saleh c, Abdullah M. Asiri a
a Center of Excellence for Advanced Materials Research (CEAMR), King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia
b Chemistry Department, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia
c Chemistry Department, Faculty of Science, University of Jeddah, P.O. Box 80327, Jeddah 21589, Saudi Arabia
a r t i c l e i n f o
a b s t r a c t
Article history:
4-(3-(thiophen-2-yl)-9H-carbazol-9-yl)benzaldehyde (TPCBZ) was synthesized under microwave irra-
diation with auto generated pressure (at 130.0 ꢀC) and characterized by 1H NMR, 13C NMR, Mass and FTIR
spectroscopy, thin-layer chromatography (TLC), and elemental analyses. Here, a thin-layer of TPCBZ onto
glassy carbon electrode (GCE) is fabricated with conducting coating agents (5% nafion) to fabricate a
selective and selective Cu2þ sensor in short response time in phosphate buffer phase. The fabricated
sensor (TPCBZ/Nafion/GCE) is exhibited higher sensitivity, large-dynamic concentration ranges, long-
term stability, and improved electrochemical performances towards TPCBZ-conjugated copper com-
plex for selective Cu2þ sensor. The calibration plot is linear (r2: 0.9979) over the large Cu2þ ions con-
Received 23 March 2016
Received in revised form
16 May 2016
Accepted 17 May 2016
Available online 20 May 2016
Keywords:
4-(3-(thiophen-2-yl)-9H-carbazol-9-yl)
benzaldehyde (TPCBZ)
TPCBZ-Conjugated-copper complex
I-V method
centration ranges (1.0 nMe1.0 mM). The sensitivity and detection limit is ~1.12974 m m
Acmꢁ2 Mꢁ1 and
~0.84 0.02 nM (signal-to-noise ratio, at a SNR of 3) respectively, which is calculated from the slope of
the calibration plot. This novel effort is initiated a well-organize way of efficient cationic sensor
improvement with carbazide for heavy metallic pollutants in environmental and health-care fields in
large scales.
Glassy carbon electrode
Cu2þ sensor
Sensitivity
© 2016 Elsevier B.V. All rights reserved.
1. Introduction
synthetic avenues to carbazole and its well-modified derivatives,
which are well documented [9,10]. Based on the documented facts
A long-standing goal of organic synthesis is the development of
new methods that access many novel derivatives of aromatic ni-
trogen heterocycles for wide applications [1e4] such as carbazoles,
because they are prevalent in important medicinal compounds and
materials [5]. Carbazoles are among exclusive types of N-containing
aromatic heterocycles possessing desirable electronic and charge-
transport properties, as well as large pi-conjugated system [6].
The structurally rigid carbazolyl ring is also found friendly towards
the introduction of various functional groups. Carbazole nucleus
has always stimulated the endeavors to find new pathways for
synthesis of novel derivatives because of extensive photo-physical,
photochemical, and biological properties [7], especially their
amazing pharmacological profile and their role as drug molecule
[8]. To date, numerous researchers make efforts to develop efficient
which highlighted the incredible potential applications of
carbazole-based derivatives in the field of chemistry, the work
undertaken here relates to the synthesis of novel carbazoles and
heavy cationic sensors development.
Heavy toxic metal contamination is a major concern in envi-
ronmental pollution due to their serious toxic effects on plants,
animals and human being [11]. Among various heavy metals, cop-
per (Cu) are the most probable causes for the heavy metal-related
diseases [12]. For example, both inorganic and organic mercury
can be absorbed through the gastrointestinal tract, resulting in the
damage to the nervous system, and the kidneys [13]. Cu(II) is also
an essential and necessary micronutrient for many plants and an-
imals at very low levels [14]. However, it is toxic to aquatic plants at
high levels due to its association with cell membranes, preventing
the transport across the wall cell [15]. Because of various applica-
tions in industrial and agricultural processes, Cu(II) can be released
into the environment from many sources. Drinking water can be a
potential source for an intense Cu(II) exposition because of the
production and industrial use. Copper(II) is highly toxic for drinking
* Corresponding author. Center of Excellence for Advanced Materials Research
(CEAMR), King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia.
E-mail
addresses:
mmrahman@kau.edu.sa,
mmrahmanh@gmail.com
(M.M. Rahman).
http://dx.doi.org/10.1016/j.jorganchem.2016.05.013
0022-328X/© 2016 Elsevier B.V. All rights reserved.

44
M.M. Rahman et al. / Journal of Organometallic Chemistry 817 (2016) 43e49
water, and mercury is the only metal more toxic than copper [16].
The excessive intake of Cu(II) could be damaged in kidney and liver,
increased blood pressure and respiratory rates, and damaged to
central nervous system [17]. Moreover, Menkes and Wilson dis-
eases have been found closely related to the disorder of Cu(II)
metabolism [18]. Therefore, the maximum permissible limit in
drinking water is not to exceed 0.05 mg/L [19]. Then the develop-
ment of novel methods for simultaneous detection and removal of
low levels copper from natural waters has special importance.
Copper is an essential element to human bodies, but the excessive
copper can seriously destroy tissue since it can interact with lipid
hydroxyl-peroxides to produce some DNA damaging agents such as
malondialdehyde and 4-hydroxynonenal [20]. Measurements of
Cu(II) ions with atomic absorption spectrometry, inductively
coupled plasma-atomic emission spectrometry, inductively
coupled plasma-mass spectrometry, potentiometric techniques
and X-ray fluorescence are sensitive and reliable [21,22]. However,
the costly instrumentations, sampling, storage, handling, time-
consuming and complicated pretreatment make them unsuitable
for on-line or field monitoring. Therefore, an effective I-V method
for technological assortment is used as a noble organic compound
adsorbent model for the detection and quantification of toxic heavy
metal ions. Several physical and chemical methods are now
developed to remove Cu(II) from water such as ion exchange,
reverse osmosis, membrane technologies, chemical precipitation,
and electrochemical treatment [23]. However, most of these
methods required sophisticated instruments, controlled condi-
tions, sludge problem, unable to use repeatedly and high costs. In
addition, these are low efficiency, time-consuming, producing un-
expected sludge, making them unattractive for the selective
detection and removal of Cu(II) ions [24]. Adsorption is one of the
few alternatives available to remove low level Cu(II) and widely
accepted in environmental treatment applications throughout the
world [25]. Cu(II)) is micronutrient constituent and carries a sig-
nificant responsibility in the bone-formation collectively with
definite proteins and enzymes [26,27]. Nevertheless, it is consid-
ered an unsafe pollutant when it cannot be controlled at a suitable
physiological concentration. It has been commenced from different
industries wastewater such as mining, metallurgy, plating, steel-
works, chemical manufacturing, petroleum refining and printing
circuits and affect the nature environment [28]. The excess Cu(II)
consumption will cause several diseases such as gastro-intestinal
symptoms and liver toxicity, Wilson, osteoporosis and Alz-
heimer’s diseases [29]. The permissible limits given by the world
health organization for Cu(II) into drinking water is 0.05 mg/L [30].
Therefore, simple, green, reliable, selective and sensitive method
for Cu(II) monitoring and removal are important for environmental
safety and health. Monitoring of Cu(II) ion has attracted due to the
toxicity to organisms [31]. Various techniques have been developed
to detect Cu(II) ions such as UVevis spectroscopy, atomic absorp-
tion spectroscopy/emission spectroscopy, X-ray analysis method,
anodic stripping voltammetry, fluorescence spectroscopy, colori-
metric method and ICP-MS [32,33]. However, UVevis spectroscopy
and anodic stripping voltammetry are insensitive. The X-ray anal-
ysis and ICP-MS test procedures are time-consuming and costly,
requiring sophisticated and expensive instrumentation. Therefore,
simple, sensitive and selective methods are demanded for Cu(II)
ions detection. Compared to these methods, optical methods allow
in-situ visual detection with a naked eye is more suitable because
these are cost-effective and easy-to-use without the need for so-
phisticated instruments [34]. Recently, several ligands impregnated
materials for sensitive Cu(II) detection even in the presence of
diverse competing ion [35]. The complexation mechanism and
optimum condition are the key factors for selective capturing of
target ions [35]. From the stand point, the specific functional group
containing ligand is developed for Cu(II) detection at optimum
condition [36].
Excessive Cu2þ ion is usually serious to health and environment,
therefore it is immediately required the detection by using a reli-
able cationic-sensor method with TPCBZ using GCE. The Cu2þ ion
by thin TPCBZ films on GCE is prepared and studied in details of the
cationic sensors. The easy-coating method for the construction of
TPCBZ thin-film within binding-agents is executed for preparation
of films onto GCE. In this approach, TPCBZ fabricated films with
conducting binders was utilized towards the target copper analytes
using reliable Current-vs-Voltage (I-V) method. It was confirmed
that the fabricated cationic sensor is unique and noble research
work for ultra-sensitive recognition of Cu2þ ions with conjugation
of TPCBZ as copper-complex onto GCE in short response-time.
2. Experimental sections
2.1. Materials and methods
Analytical grade of disodium phosphate (Na2HPO4), silver ni-
trate, auric chloride, calcium nitrate, cadmium sulphate, copper
chloride, cobalt nitrate, nickel chloride, cerium nitrate, mercury
chloride, magnesium chloride, lead nitrate, stannic chloride,
yttrium nitrate, zinc chloride, monosodium phosphate (NaH2PO4)
was used and purchased from Sigma-Aldrich Company, USA. They
were used without further purification. All organic solvents were
purchased from commercial sources and used as received unless
otherwise stated. Stock solution of Cu2þ (0.1 M) was prepared from
the purchased chemical. I-V technique was executed by using
Electrometer (Keithley, 6517A, Electrometer, USA; www.keithley.
nl) for measuring the current responses in two electrode systems
for target Cu2þ sensor based on TPCBZ in buffer phase at room
conditions, where flat-GCE and Pd-wire was used as working and
counter electrode respectively. All organic solvents were purchased
from commercial sources and used as received unless otherwise
stated.
Thin-layer chromatography (TLC) was performed on pre-coated
Merck 60 GF254 (www.merckmillipore.com) silica gel plates with a
fluorescent indicator, and detection by means of UV light at 254 and
360 nm. The melting points were measured on a Stuart melting
point apparatus and are uncorrected. IR spectra were recorded on a
Smart iTR (www.thermofisher.com), which is an ultra-high-
performance, versatile Attenuated Total Reflectance (ATR) sam-
pling accessory on the Nicolet iS10 FT-IR spectrometer (www.
thermofisher.com). The NMR spectra (www.bruker.com) were
recorded on a Bruker Advance III 400 (9.4 T, 400.13 MHz for 1H and
100.62 MHz for 13C with a 5-mm BBFO probe, at 298 K. Chemical
shifts (d in ppm) are given relative to internal solvent, DMSO-d6
2.50 for 1H and 39.50 for 13C. Mass spectra were recorded on a
Thermo ISQ Single Quadrupole GC-MS. Elemental analyses (www.
eurovector.it) were carried out on a EuroVector instrument C, H,
N, S analyzer EA3000 Series. Microwave experiments were per-
formed using CEM Discover & Explorer SP microwave apparatus
(300 W; www.cem.com), utilizing 35.0 mL capped glass reaction
vessels Automated power control based on temperature feedback.
Current-vs-voltage (I-V) method (two electrodes composed onto
fabricated GCE) was measured for toxic copper ions for TPCBZ/GCE
by using Keithley-Electrometer from USA (www.keithley.nl).
2.2. Preparation and fabrication of GCE with TPCBZ
Phosphate buffer solution (PBS, 0.1 M) at pH 7.0 is prepared by
mixing of equi-molar concentration of 0.2 M Na2HPO4 and 0.2 M
NaH2PO4 solution in 100.0 mL de-ionize water at room conditions.
GCE is fabricated with TPCBZ using 5% ethanolic nafion solution as a

M.M. Rahman et al. / Journal of Organometallic Chemistry 817 (2016) 43e49
45
conducting binder. Then it is kept in the oven at 35.0 ꢀC for 2 h until
the film is completely dried, stable, and smooth. A cell is assembled
with TPCBZ/GCE and Pd-wire as a working and counter electrodes
respectively. As received Cu2þ solution (10.0 mM) is diluted to make
various concentrations (1.0 nMe10.0 mM) in DI water and used as a
target analyte. A calibration plot is drawn from the data-point taken
(at þ0.5 V) from each I-V curve on respective concentration of Cu2þ
solution. The ratio of current versus concentration (slope of cali-
bration curve) is used to calculate the Cu2þ sensitivity. Detection
limit is evaluated from the ratio of 3 N/S (ratio of Noise ꢂ 3 vs.
Sensitivity) from the linear dynamic range of calibration curve.
Electrometer is used as a constant voltage sources for I-V mea-
surement in simple two electrode system. Amount of 0.1 M PBS was
kept constant in the beaker as 5.0 mL throughout the chemical
investigation. The TPCBZ is fabricated and employed for the
detection of Cu2þ in liquid phase. I-V response is measured with
TPCBZ/GCE film. The active surface area of TPCBZ/GCE is
0.0316 cm2. The electrode assembly is WE (TPCBZ/Nafion/GCE) and
CE (Pd-wire) for the detection of cations.
and the mixture was extracted with DCM. The organic phase was
dried with MgSO4. After the solvent was evaporated, the product
was processed by column chromatography on silica gel with pe-
troleum ethereacetic ether (20: 1, by volume) to give a yellow
power (68% yield). The melting point was measured (261e263 ꢀC)
and characterized by 1H NMR. The result of 1H NMR was obtained
as below.
1H NMR (400 MHz, DMSO-d6)
d: 6.58 (m, 2H), 7.32 (m, 1H), 7.35
(m, 1H), 7.53 (d, 2H, J ¼ 8.2 Hz), 7.58e7.69 (m, 2H), 7.95 (m, 2H),
8.26 (d, 2H, J ¼ 8.2 Hz), 8.68 (s, 1H), 10.20 (s,1H).
3. Results and discussion
3.1. Detection of Cu2þions with TPCBZ/GCE
The potential application of TPCBZ compound assembled onto
GCE as heavy metallic sensor (especially Cu2þ analyte in buffer
system) has been executed for measuring and detecting target Cu2þ
ions. The TPCBZ/GCE sensors have facile advantages such as sta-
bility in air, non-toxicity, chemical inertness, electro-chemical ac-
tivity, simplicity to assemble, ease in fabrication, and chemo-safe
characteristics. As in the case of Cu2þ ions sensor, the current
response in I-V method of TPCBZ/GCE considerably changes when
aqueous metallic analyte is adsorbed. The TPCBZ/GCE was applied
for fabrication of ionic-sensor, where heavy metallic Cu2þ ion was
measured as target analyte. The fabricated-surface with TPCBZ/GCE
sensor was prepared with conducting coating binders (5% nafion)
on the GCE surface. The fabricated TPCBZ/GCE electrode was put
into the oven at low temperature (45.0 ꢀC) for 2.0 h to make it dry,
stable, and uniform the surface totally. I-V signals of Cu2þ ion
chemical sensor are anticipated having TPCBZ/GCE on thin-film as a
function of current versus potential. The resultant electrical re-
sponses of target Cu2þ ion are investigated by simple and reliable I-
V technique using TPCBZ/GCE. The holding time of electrometer
was set for 1.0 s. A significant amplification in the current response
with applied potential is noticeably confirmed.
2.3. Preparation of 4-(3-(thiophen-2-yl)-9H-carbazol-9-yl)
benzaldehyde (TPCBZ)
It was prepared the target TPCBZ of carbazole derivatives rep-
resented in Scheme 1. According to the Scheme 1, the derivatives of
carbazole (3, 4, & 5) are explained in details of their characteriza-
tion by TLC, 1H NMR, FTIR, Elemental analysis, and 13C NMR.
2.3.1. 4-(9H-carbazol-9yl)benzaldehyde (3)
This compound was prepared with a modified method to the
reported literature [37] in where the synthesis process was per-
formed using microwave irradiation, the reactants 4-
flurobenaldehyde (5.0 mmol) and carbazole (5.0 mmol) were
taken in DMF (15.0 ml) and K2CO3 (20.0 mmol) was added, The total
mixture was placed in a process vial in the microwave, and was
irradiated with a power of 300 W to reach a reaction temperature of
130.0 ꢀC under auto generated pressure. The vial was exposed to
microwaves irradiation for the appropriate time (2 h) until the
starting materials were no longer detectable by TLC (eluent; ethyl
acetate/chloroform). Upon completion of the reaction, the reaction
mixture poured on ice (30.0 g) an organic fraction was extracted
using ethyl acetate (3 ꢂ 20.0 ml), the extract were washed with
water dried with anhydrous sodium sulfate and the organic layers
were concentrated under reduced pressure to afford yellow solid
crystals. The obtained solid product was pure enough and no need
for purification. The results of 1H NMR and 13C NMR are presented
in below.
The TPCBZ/GCE was employed for the detection of Cu2þ ion in
liquid phase. I-V responses were measured with TPCBZ/GCE coated
thin-film (in two electrodes system). The concentration of Cu2þ ion
was varied from 1.0 nM to 10.0 mM by adding de-ionized water at
different proportions. It is studied the control experiment about the
uncoated and nanocomposites-coated electrode using I-V method
and presented in Fig. 1. Here, Fig. 1(a) is represented the I-V re-
sponses for uncoated-GCE (gray-dotted) and TPCBZ/GCE (green-
dotted) electrodes. In PBS system, the TPCBZ/GCE electrode shows
that the reaction is reduced slightly owing to the presence of TPCBZ
on bare-GCE surface. A considerable enhancement of current value
with applied potential is demonstrated with fabricated TPCBZ/GCE
in presence of target Cu2þ ion analyte, which is presented in
Fig. 1(b). The light-blue-dotted and deep-blue-dotted curves were
indicated the response of the fabricated film after and injecting
1H NMR (400 MHz, DMSO-d6):
d 7.31e7.36 (m, 4H), 7.56 (d, 2H,
J ¼ 8.4 Hz), 7.92 (d, 2H, J ¼ 8.4 Hz), 8.12e8.21 (m, 4H), 11.73 (s,
1H).
13C NMR (100 MHz, DMSO-d6): 108.25, 121.06, 121.84, 123.94,
126.47, 126.98, 130.47, 135.62, 141.57, 144.28, 196.04.
25.0 m
L Cu2þ ion in 5.0 mL PBS solution respectively measured by
fabricated TPCBZ/GCE films. Significant increases of current are
measured after injection of target component in regular interval.
I-V responses to varying Cu2þ concentration (1.0 nMe10.0 mM)
on thin TPCBZ/GCE were investigated (time delaying, 1.0 s) and
presented in the Fig. 2(a). Analytical parameters (such as sensitivity,
detection limit, linearity, and linear dynamic range etc) were
calculated from the calibration curve (current vs. concentration),
which was presented in Fig. 2(b). A wide range of Cu2þconcentra-
tion was selected to study the possible detection limit (from cali-
bration curve), which was examined in 1.0 nMe10.0 mM. The
sensitivity was calculated from the calibration curve, which was
2.3.2. 3,6-dibromo derivative (4)
This compound was obtained by direct bromination via bromin
in acetic acid at room temperature [38].
2.3.3. 4-(3-(thiophen-2-yl)-9H-carbazol-9-yl)benzaldehyde (5)
(TPCBZ)
Compound 4 (1.0 mmol) and 2-thienylboronic acid (1.5 mmol),
Pd (PPh3)4 (0.2 mmol), aqueous Na2CO3 (2.0 M, 5.0 ml), THF
(20.0 ml) and toluene (30.0 ml) were mixed in a flask. The mixture
was refluxed for 48 h. After being cooled, a lot of water was added
close to ~1.12974 m M
Acmꢁ2m ꢁ1. The linear dynamic range of the

46
M.M. Rahman et al. / Journal of Organometallic Chemistry 817 (2016) 43e49
Scheme 1. Synthesis of TPCBZ. Preparation of 4-(3-(thiophen-2-yl)-9H-carbazol-9-yl)benzaldehyde (5), (TPCBZ).
TPCBZ/nafion/GCE sensor was employed from 1.0 nM to 1.0 mM
(linearly, r2: 0.9979), where the detection limit was calculated
about ~0.84 0.02 nM (ratio, 3N/S). In presence of TPCBZ/nafion/
GCE layer on electrode, the electrical resistance is decreased under
with the target Cu2þ in PBS phase. The film-resistance was
decreased gradually (increasing the resultant current) upon
increasing the Cu2þ concentration in bulk system.
presented in Fig. 3(a). The concentrations of heavy metallic analytes
are kept constant at 0.1 M level in PBS system. From the current
m
response of each individual analytes, it is calculated the percentile
of responses at þ0.5 V of Agþ (1.3%), Au3þ (2.2%), Ca2þ (1.7%), Cd2þ
(2.1%), Cu2þ (83.8%), Co2þ (2.5%), Ce2þ (1.3%), Hg2þ (2.0%), Mg2þ
(1.8%), Pb2þ (1.6%), Sn2þ (2.6%), Y3þ (1.0%), Ni2þ(1.4%) and Zn2þ
(0.8%) with TPCBZ/GCE sensors. Here, it is clearly demonstrated the
TPCBZ/GCE electrode sensor is most selective toward Cu2þ (83.8%)
compared with other heavy cationic components.
In two-electrode system, I-V characteristic of the TPCBZ/GCE is
activated as a function of Cu2þconcentration at room conditions,
where improved current response is observed. As obtained, the
current response of the TPCBZ-film is increased with the increasing
concentration of Cu2þ; however similar phenomena for cationic
detection have also been reported earlier [39e42]. For a low con-
centration of Cu2þin liquid medium, there is a smaller surface
coverage of Cu2þ ions on TPCBZ/GCE film and hence the surface
reaction proceeds steadily. By increasing the Cu2þconcentration,
the surface reaction is increased significantly (gradually increased
the response as well) owing to large surface area contacted with
Cu2þ molecules. Further increase of Cu2þ concentration on TPCBZ/
GCE surface, it is exhibited a more rapid increased the current re-
sponses, due to larger surface covered by Cu2þ chemical. Usually,
the surface coverage of Cu2þ molecules on TPCBZ/GCE surface is
reached to saturation, based on the regular enhancement of current
responses.
To check the reproducibly and storage stabilities, I-V response
for TPCBZ/GCE sensor was examined and presented in Fig. 3(b).
After each experiment (each runs), the fabricated TPCBZ/GCE sub-
strate was washed thoroughly with the phosphate buffer solution
and observed that the current response was not significantly
decreased. Here it is observed the current loss in each reading is
negligible compared to initial response of sensors using TPCBZ/GCE.
A series of eight successive measurements of 0.1 m
M Cu2þ in 0.1 M
PBS yielded a good reproducible signals at TPCBZ/nafion/GCE
sensor with a relative standard deviation (RSD) of 1.6%. The sensi-
tivity was retained almost same of initial sensitivity up to seven
days, after that the response of the fabricated TPCBZ/nafion/GCE
electrode gradually decreased. The Cu2þ sensor based on TPCBZ/
GCE is displayed good reproducibility and stability for over week
and no major changes in sensor responses are found. After a week,
the cationic Cu2þ sensor response with TPCBZ/GCE was slowly
decreased, which may be due to the weak-interaction between
fabricated TPCBZ/nafion/GCE active surfaces and Cu2þ ions.
Selectivity was studied for Cu2þ sensor in presence other
chemicals like Agþ, Au3þ, Ca2þ, Cd2þ, Cu2þ, Co2þ, Ce2þ, Hg2þ, Mg2þ
,
Pb2þ, Sn2þ, Y3þ, Ni2þ, and Zn2þ using the TPCBZ/GCE, which is

M.M. Rahman et al. / Journal of Organometallic Chemistry 817 (2016) 43e49
47
Fig. 1. Study of control experiment. I-V responses of (a) bare-GCE and TPCBZ/GCE, (b) TPCBZ/GCE (in absence), and TPCBZ/nafion/GCE (in presence) of Cu2þ in the solution system.
Fig. 2. Analysis of Cu2þ cationic responses. I-V responses of (a) concentration variations (1.0 nMe10.0 mM) of Cu2þ ions and (b) calibration plot of TPCBZ fabricated GCE electrode
(at þ0.5 V).
Current-voltage behaviors of the TPCBZ are activated as a
function of Cu2þ ions concentration at room conditions, where the
improved current response is observed. The possible complexation
bonding mechanism between Cu(II) and TPCBZ is explained here in
Fig. 4. As obtained, the current response of the TPCBZ-film is
the TPCBZ [48]. Usually, the surface coverage of Cu2þ ions on TPCBZ/
Nafion/GCE surface is reached to saturation, based on the regular
enhancement of current responses (Fig. 4(c)).
The significant result was achieved by TPCBZ/GCE, which can be
employed as proficient electron mediators for the development of
efficient cationic sensors. Actually the response time was around
10.0 s for the fabricated TPCBZ/GCE to reach the saturated steady-
state level. The higher sensitivity of the fabricated TPCBZ/GCE
could be attributed to the excellent absorption (porous surfaces in
TPCBZ/nafion/GCE), adsorption ability, and high catalytic-
decomposition activity of TPCBZ. The estimated sensitivity of the
fabricated sensor is relatively higher and detection limit is
comparatively lower than previously reported chemical sensors
based on other nano-composites or nano-materials modified
electrodes measured by I-V systems [49e57]. Due to high specific
surface area, TPCBZ provides a favorable nano-environment for the
Cu2þ detection with good quantity. The modified TPCBZ/GCE sensor
has also better reliability and stability. The higher sensitivity of
TPCBZ/GCE provides higher electron communication features
increased (p-p* interaction) with the increasing concentration of
Cu2þ ions in the bulk solution, however similar phenomena for
toxic chemical detection have also been reported earlier [43e47].
For a low concentration of Cu2þ ions in buffer medium, there is a
smaller surface coverage of Cu2þ ions on TPCBZ/nafion/GCE film
(Fig. 4(a)) and hence the surface reaction proceeds steadily. By
increasing the Cu2þ ions concentration, the surface reaction is
increased significantly (gradually increased the response) due to
surface area (assembly of TPCBZ/Nafion/GCE) contacted with bulk
Cu2þ ions molecules (Fig. 4(b)). Further increase of Cu2þ ions con-
centration on TPCBZ/Nafion/GCE surface, it is exhibited a more
rapid increased the current responses, due to larger area covered by
Cu2þ ions and the
interaction could be approaches as inter-molecular interactions of
p-p interaction of the functional groups. The p-p

48
M.M. Rahman et al. / Journal of Organometallic Chemistry 817 (2016) 43e49
Fig. 3. Optimization of TPCBZ/GCE sensors. (a) Selectivity study with various analytes by TPCBZ/GCE electrodes. (b) Reproducibility study with analytes using TPCBZ/GCE elec-
trodes. I-V responses of all reproducible signals (Run-1 to Run-8) with Cu2þ; Analyte concentration was taken at 0.1
M; Potential range: 0 to þ1.5 V; Delay time: 1.0 s.
m
which enhanced the direct electron transfer between the active
sites of TPCBZ and nafion-coated-GCE. The TPCBZ/GCE system is
demonstrated a simple and reliable approach for the detection of
toxic heavy metallic cations. It is also revealed that the significant
access to a large group of cations chemicals for wide-range of
ecological and biomedical applications in environmental and
health-care fields respectively.
binders onto GCE by electrochemical approaches, which displayed
higher sensitivity and selective Cu2þ sensing applications. The
analytical performances of the fabricated Cu2þ sensors are excellent
in terms of sensitivity, detection limit, linear dynamic ranges, and
selectivity in short response time. TPCBZ/GCE assembly is exhibited
higher-sensitivity (1.12974
limit (~0.84 0.02 nM) with good linearity in short response
m mM
Acmꢁ2 ꢁ1) and lower-detection
time, which efficiently utilized as a cationic-sensor for selective
Cu2þ onto TPCBZ/GCE via, conjugated complex formation. This
novel approach is introduced a well-organized route of efficient
heavy metallic cationic sensor development for environmental
pollutants and health-care fields in broad scales.
4. Conclusions
TPCBZ has been prepared using simple adsorption techniques. It
is fabricated a heavy metallic sensor with the conducting coating
Fig. 4. Schematic representation of Cu2þ interaction onto TPCBZ/Nafion/GCE electrode. Mechanism of the probable interaction of Cu2þ with TPCBZ with conducting nafion
binders embedded onto flat-GCE. (a) Fabricated electrode, (b)
fabricated TPCBZ/Nafion/GCE electrode.
P-P
inter-molecular bonding interactions between lone-pair of nitrogen (TPCBZ) and Cu2þ , and (c) I-V responses of

M.M. Rahman et al. / Journal of Organometallic Chemistry 817 (2016) 43e49
49
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