Sensor Colorimétrico para Detecção de Íons de Co2+

Prévia do material em texto

Materials Chemistry and Physics 273 (2021) 125082
Available online 31 July 2021
0254-0584/© 2021 Elsevier B.V. All rights reserved.
Highly selective colorimetric onsite sensor for Co2+ ion detection by 
povidone capped silver nanoparticles 
Kausar Rajar a,b, Esra Alveroglu a,*, Mujdat Caglar c, Yasemin Caglar c 
a Istanbul Technical University, Faculty of Science and Letters, Department of Physics Engineering, 34469, Maslak, Istanbul, Turkey 
b University of Sindh, National Centre of Excellence in Analytical Chemistry, Jamshoro, 76080, Pakistan 
c Eskisehir Technical University, Faculty of Science, Department of Physics, Eskisehir, 26470, Turkey 
H I G H L I G H T S G R A P H I C A L A B S T R A C T 
• PVP functionalized Ag nanoparticles 
(PVP@Ag NPs) grown by chemo- 
reductive methodology at ambient 
conditions. 
• PVP@Ag NPs were employed to develop 
a highly selective and sensitive colori-
metric nanosensor for Co2+ detection. 
• PVP-Ag NPs sensor was applied real 
water samples and the recovery of this 
sensor for cobalt ion was defined. 
A R T I C L E I N F O 
Keywords: 
Silver nanoparticles 
Polyvinylpyrrolidone 
Colorimetric sensor 
Co2+ detection 
A B S T R A C T 
Highly efficient colorimetric povidone (PVP) mediated Ag nanosensing strategy has been adopted for the sen-
sitive and selective quantification of cobalt ion in aqueous system. PVP functionalized Ag nanoparticles grown by 
chemo-reductive methodology at ambient conditions. These efficient nanoparticles were confirmed by UV–Vis 
(UV–Vis) spectroscopic characteristic absorption peak at 390 nm and strong Fourier Transform Infrared (FT-IR) 
stretching bend at 455 cm− 1. The topographical and crystalinity analysis by Field Emission Scanning Electron 
Microscope (FESEM) and X-ray diffractometer (XRD) analysis reveals that the obtained PVP@Ag NPs have rough 
surface and size in range of 30–45 nm respectively. Later PVP@Ag NPs were employed to develop a highly 
selective and sensitive colorimetric nanosensor for Co2+ detection in the concentration from 0.1 to 5 μM in 
aqueous environment. 
1. Introduction 
Various transition elements have vital importance to the chemistry of 
living beings, the greatest intimate varieties are copper (Cu), molybde-
num (Mo), cobalt (Co) and iron (Fe). Though, cobalt is one of the ex-
pected element especially in animal alimentation, it is necessary for 
biochemical reaction of vitamin B12 and related co-enzymes [1]. The Co 
is naturally existing in the soils, rocks, water, plants and animals. 
However even cobalt is crucial nutrients, it may be dangerous if 
consumed in excessive amount. Therefore exposure to extreme amount 
of cobalt in the environment may cause in various adverse health effect 
such as mutagenesis, cardiotoxicity, asthma, lung fibrosis, and even lung 
* Corresponding author. 
E-mail address: alveroglu@itu.edu.tr (E. Alveroglu). 
Contents lists available at ScienceDirect 
Materials Chemistry and Physics 
journal homepage: www.elsevier.com/locate/matchemphys 
https://doi.org/10.1016/j.matchemphys.2021.125082 
Received 15 August 2020; Received in revised form 28 July 2021; Accepted 30 July 2021 
mailto:alveroglu@itu.edu.tr
www.sciencedirect.com/science/journal/02540584
https://www.elsevier.com/locate/matchemphys
https://doi.org/10.1016/j.matchemphys.2021.125082
https://doi.org/10.1016/j.matchemphys.2021.125082
https://doi.org/10.1016/j.matchemphys.2021.125082
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Materials Chemistry and Physics 273 (2021) 125082
2
cancer [2]. Thus an exact numerical detection of the quantity in bio-
logical samples is increasingly required. It is critical to detect the trace 
amounts of cobalt in the environment. The conventional methods such 
as Atomic Absorption Spectrometry (AAS) and High Performance Liquid 
Chromatography (HPLC) are very sensitive and precise for the quanti-
fiable determination of Co (II), but these techniques are highly slow, 
where as the spectrophotometric approaches, even though less sensitive 
but are fast and easy operation, so in contrast to such methods colori-
metric studies are more favored sat on their mode stand cheap opera-
tion, quick investigation and benefit of real time works [3]. 
Nanotechnology is the hottest field of investigation and innovation in 
current sensor studies. There are several metal NPs based colorimetric 
sensors for the detection of cobalt ion, A colorimetric assay has been 
developed for facile, rapid and sensitive detection of Co2+ using 
dopamine dithiocarbamate functionalized silver nanoparticles (DDTC- 
Ag NPs) as a colorimetric sensor based on unique surface plasmon 
resonance properties [4]. The another fluorescent gold nanoclusters (Au 
NCs) by using trypsin as a ligand was developed by Ghosh, Subhadeep, 
et al. [5] The red fluorescence of trypsin-Au NCs was greatly quenched 
by the addition of multiple analytes such as drugs (carbidopa and 
dopamine) and three divalent metal ions (Cu2+, Co2+ and Hg2+ ion). 
Therefore Metal nanoparticles-based optical technologies are based on 
either new class of organic molecular assembly or with 
aggregation-induced optical changes features, which can also improve 
the sensitivity of drug assays in pharmaceutical analysis [6]. The metal 
nanoparticles, especially silver (Ag) nanoparticles (NPs) are of especial 
focus to scientists thanks to the Localized Surface Plasmon Resonance 
(LSPR) properties, which later define its composition, size, shape, 
refractive index and surrounding texture [7]. LSPR produces strong 
spectra of resonance absorbance peak shift in the visible band of light 
with a smallest change in refractive index of the medium [8]. Ag NPs are 
the most commercialized nano-material based products per year. 
Generally metal nanoparticles can be synthesized by chemical reduction 
[9], green [10,11] and microbial methods [12]. Among them chemical 
reduction technique is proved to best for the fabrication of nanoparticles 
with varied sizes and shapes, nano rods, nano wires, nano prisms and 
nano plates [13]. The usage of Ag NPs as a detection device have been 
employed for the colorimetric determination of several small molecules 
and proteins [14–16]. The response of that sensor schemes rely on the 
kind of functional part which brings the replace in the locality of silver 
NPs, which has some significant fluctuations the perceive SPR intensity 
allow in acceptable quantification of selected analyte [17] studied 
L-cysteine functionalized silver (Ag) NPs for selective purpose of mer-
curic ion (Hg2+) wherever cysteine is observed as the surface binder 
with Ag NPs via thiol group by carboxylate group charge pointing outer 
for selective quantification. In the same way, the usage of 4,4-bipyridi-
ne-functionalized silver (Ag) NPs for colorimetric study of toxic tryp-
tophan pesticide was reported in the literature [18]. 
In spite of the wonderful function of Ag NPs as optical sensors, the 
possible ability of functionalized Ag NPs as active probe for pollutants 
need much more investigation. Recently the application of tyrosine 
capped Ag NPs for the colorimetric measurement of cobalt was 
demonstrated [19], this report focused on the a-amino and a-carboxyl 
groups of the surface-confined amino acid can coordinate the entitled 
metal ions which caused aggregation of Ag NPs. In the study [20,21] 
potential ability of ethylene diamine (en) and S2O32 to form (en)2CoS2O3+
modified Ag–Au bimetallic nanoparticles for cobalt determination in 
liquid solution was verified. The above-mentioned detecting system 
utilise non-specific electrostatic forces for ratification of cobalt ion. 
Though are useful but these sensor has lack the selective nature towards 
cobalt which is an important necessity as soon as quantifying cobalt in 
complex systems. 
Herein, we developed and examined PVP capped Ag NPs for the 
sensing of Co2+ ion in aqueous solutions. The PVP-Ag NPs sensor wasalso used for sensing different metals as an optical probe in liquid media. 
2. Experimental 
2.1. Materials and reagents 
Ag (NO3)2⋅5H2O (97%)) was purchased from E. Merck. Poly-
vinylpyrrolidone (PVP) and salts including MgCl2⋅6H2O, Ca 
(NO3)2⋅4H2O, Pb(NO3)2, Zn(NO3)2⋅6H2O, Co(NO3)2⋅6H2O, Ni 
(NO3)2⋅6H2O, Mn(NO3)2⋅4H2O, Cd(NO3)2, AgNO3 and HgSO4⋅H2O were 
obtained from Sigma–Aldrich. To ensure purity of the synthesized Ag 
NPs, all the stock solutions were prepared using deionized water. 
2.2. Synthesis of PVP capped silver nanoparticles (PVP–Ag NPs) 
The silver nano particles were produced by reducing the silver ni-
trate in sodium borohydride (NaBH4) aqueous solution. The 0.1% of PVP 
was used as capping agent and NaBH4 was used to accelerate the reac-
tion. In this procedure, first we prepared the NaBH4 aqueous solution of 
0.001 mol/L concentration in 30 ml of water. This 30 ml solution of 
NaBH4 was kept on stirring for 10 min. The 20 μL of PVP solution was 
added in the aqueous solution of sodium borohydride. Finally, 5 μL of 
AgNO3 with the concentration of 0.01 mol/L was added slowly drop by 
drop. The solution was kept at 450 rpm stirring for the formation of the 
silver nanoparticles till the yellow colour appear. The synthesized 
nanostructure was centrifuged, washed and dried in vacuum oven for 
overnight. 
2.3. Colorimetric response of PVP-Ag NPs to Co2+
Different concentrations of Co2+ in the range of 0.1–10 μL were 
sensed for their colorimetric response in existence of fixed amount of 
PVP-Ag NPs solution. The shift of the colour from yellow to colourless 
was fulfilled within 4–5 min for each addition of the standard. The 
consistent change in the absorbance with each addition were saved 
against the blank solution in the form of SPR spectra during the cali-
bration study. Picture of the colour change were also saved via digital 
camera of all solutions and blank. 
2.4. Instrumentation 
The UV–Vis spectrometer model lambda 35 from PerkinElmer 
(Shelton, USA) was used for the initial characterization of Ag NPs within 
the spectral window of 300–800 nm. Fourier transform infrared (FTIR) 
spectroscopy model Nicolet 5700 of Thermo Madison, USA analysis was 
carried to investigate the interaction between the PVP and Ag NPs. XRD 
model D-8 of Bruker (Germany) was used to verify the crystalline 
properties of PVP capped Ag NPs. High resolution ULTRAPLUS ZEISS 
scanning electron microscope (SEM) which has EDAX model EDX de-
tector was used to morphological study of NPs. 
Fig. 1. UV–Visible spectra of PVP-Ag NPs. 
K. Rajar et al. 
Materials Chemistry and Physics 273 (2021) 125082
3
3. Results and discussion 
3.1. UV–vis spectroscopy and morphologic studies of the PVP-Ag 
NPs 
PVP-Ag NPs show the intense absorption peak around 390–430 nm 
due to the collective absorption of free conduction band electrons of the 
nanoparticles, which is known as surface plasma resonance (SPR) [22, 
23]. Fig. 1 shows the absorption spectra of PVP-Ag NPs as prepared and 
four months later, as seen from the figure the maximum intensity 
decreased slightly and there is no shift seen on the wavelength for 
maximum intensity. These proof that the prepared PVP-Ag NPs are 
highly stable. The stability of the nanoparticles revealed to be few 
months when the sample stored at low temperature. 
Fig. 2 shows the FESEM images of PVP-Ag NPs, the average size of 
NPs was found around 20 nm. Similarly, the EDX study was carried out 
for the further confirmation. Fig. 2 shows an intense peak in the silver 
region and proves the production of Ag NPs. Ag NPs typically show 
characteristic optical absorption peak around at 3 KeV because of sur-
face plasmon resonance [24]. EDX study detected strong peak for Ag and 
weak carbon and oxygen signal which may have resulted from the PVP 
that was used as capping agent to the surface of Ag NPs, specify the 
reduction of Ag ions to elemental Ag. There were no other signal seen 
except the silver compounds which reveals the complete reduction of Ag 
NPs from the silver compounds as shown in the spectrum. 
3.2. X-ray diffractometer (XRD) analysis of the PVP-Ag NPs 
The crystalline nature of the synthesized nanostructure of silver was 
confirmed by X-ray diffraction pattern. The XRD pattern of the 
synthesized PVP-Ag NPs is shown in Fig. 3. Two strong reflections at 38∘ 
and 45∘ corresponds to the planes of (111) and (200) respectively which 
can be indexed according to the face centered cubic crystal structure of 
silver and shows the good crystallinity of the ultrafine silver nano-
particles. That is the agreement of previously literature data, reported 
for silver nanoparticles [25–27]. 
3.3. FT-IR study of the PVP-Ag NPs 
FTIR study was carried out in the frequency range of 4000 to 500 
cm− 1 in order to check the existence of the various functional group 
which responsible for the reduction of the silver nanoparticles as well as 
the capping of silver nanoparticles. The FTIR spectrum of the synthe-
sized PVP-Ag NPs is shown in Fig. 4. It is shown that the sample shows 
strong stretching bonding at 3342 cm− 1 responsible for the N–H 
stretching with amine, which revealed that the Ag binds with amide 
group by strong ionic bonding in polymer chain. The peaks at 1334 cm− 1 
and 1251 cm− 1 are the vibration bonds of N–H–O and NO3 respectively 
[28]. The strong absorption band at 1652 cm− 1 and 1420 cm− 1 resultant 
to symmetric stretching of carboxylate anion and O–H and C–H bending 
from PVP which is used as capping agent for silver nanoparticles and 
prevent the silver nanoparticles for growth and agglomeration [29]. The 
functional unit C–N present in PVP, therefore the peak at 1128 cm− 1 
indicates that the N or O atoms and at 989 cm− 1 is the C–N peak of the 
PVP molecules interact with the surface of Ag nanoparticles by chemical 
absorption [30]. The bond around 815 cm− 1 arises due to the carbonyl 
stretch with strong absorption band. The small peak at 455 cm− 1 cor-
responds to PVP-Ag NPs. 
Fig. 2. FESEM image and EDX Spectrum of PVP-Ag NPs. 
Fig. 3. XRD pattern of the synthesized PVP-Ag NPs. 
Fig. 4. FTIR spectrum of PVP-Ag NPs. 
K. Rajar et al. 
Materials Chemistry and Physics 273 (2021) 125082
4
3.4. Co2+ sensing via PVP-Ag NPs 
PVP-Ag NPs in solution form usually familiar by its yellow colour 
characteristic based on the SPR band between 350 and 450 nm [8]. The 
SPR band of the PVP-Ag NPs at 390 nm is showed in Fig. 5. After adding 
the Co2+ to the solution of PVP-Ag NPs, the colour of PVP-Ag NPs was 
changed from yellow to grey due to the aggregation of PVP capped Ag 
NPs. The colorimetric change of sample from bright yellow to grey or 
colourless is shown inset of Fig. 5. The aggregation of the silver nano-
particles since the interaction of the PVP-Ag with the cobalt ion exhibits 
the change in spectral property of the PVP-Ag NPs, the peak of PVP-Ag 
NPs at 390 nm decreases in the absorbance and newly broad band at 
600 nm arises. The selectivity of the probe towards the Co2+ ions can be 
explained on the basis of the unique character of this metal ion. The 
Co2+ ions have highly flexible bond lengthand geometry with a 
maximum coordination number 6 [31]. Due to these properties, the 
Co2+ ions have a high tendency to coordinate with the polymer PVP to 
form assembly of the AgNPs. Co2+ ion is a borderline acid which can 
bind to different group of ligands. Thus, when the Co2+ ions are added to 
the PVP-capped AgNPs, the metal ions coordinate with the N and O 
group of the PVP as displayedin Fig. 5. Consequently, an assembly of the 
AgNPs was formed. The other metal ionsinteract very less or not at all 
with the ligand due to rigid coordination geometry of these ions. Hence 
upon the addition of these metal ions, there was little or no change on 
the absorption spectrum of the AgNPs. These results were further 
confirmed by FESEM and EDX images as shown in Fig. 6, the particles 
size of the NPs seems increased due to the aggregation. Similarly, very 
low signal of silver can be seen in the EDX spectra along with strong peak 
of C, oxygen and Co after aggregation of Ag NPs by adding Co2+. All can 
be seen in the EDX it may be come from the substrate. 
The decreasing of PVP-Ag NPs absorption is probably related to a 
perturbation effect due to the complexation of the surface bounded PVP 
with the metal ions. PVP-Ag NPs can be incorporated to a core shell 
nanoparticle where the core is constituted by silver and the outer shell 
by the PVP or PVP-Ag complex. In other words, the conduction electrons 
of the nanoparticle, displaced by the incident electromagnetic radiation, 
gives rise to an induced dipole: the larger the electron displacement 
induced by the electromagnetic radiation, the larger the induced dipole 
and consequently the restoring force [32]. The presence of positive 
charges on the external surface of the particle can reduce the restoring 
force of the oscillation and, via a lowering of the polarizability, inducing 
a decrease of the refraction index of the shell. Therefore, the complex-
ation of the surface bounded PVP with the positively charged silver 
metal ions induces a reduction in the refraction index of the shell that, in 
turn, gives rise to a lower absorbance acting on electrons. 
3.5. Calibration of Co2+ via PVP-Ag NPs 
The calibration of sensor was checked by addition of the different 
concentration of cobalt ion from 0.1 to 5 μM. The variation in colori-
metric response of PVP-Ag NPs at 390 nm upon the adding of Co2+ was 
monitored by UV–Vis spectroscopy and the spectra are given in Fig. 7. 
The absorbance of PVP-Ag NPs was notice to decrease with increasing 
the concentration of Co2+ ion, a drastic variation in its optical absor-
bance was also perceived when new absorbance appears at 600 nm. The 
observed decreasing in the absorbance of PVP-Ag NPs was attributed 
after 30 min to the decrease in the Ag NPs concentration. The change in 
absorbance or SPR of PVP-Ag NPs vs concentration of Co2+ was plotted 
as linear calibration plot in the range of 0.1–5.0 μM (Fig. 7). The R2 
Fig. 5. UV–Vis spectra and photos of PVP-Ag NPs before and after adding the 
Co2+ ion. 
Fig. 6. FESEM and EDX Spectrum of PVP-Ag NPs after adding Co2+ ion. 
K. Rajar et al. 
Materials Chemistry and Physics 273 (2021) 125082
5
value and the LOD were calculated as 0.9984 and 0.1 μM respectively. 
Table 1 represents the analytical performance of PVP-Ag NPs sensor for 
the detection of Co2+ with the previous reported methods [3,33–35], 
additionally the limit of detection (LOQ) were found to be 0.3 μM, which 
further confirm the extremely sensitive nature of the sensor. 
3.6. Selectivity of the PVP-Ag NPs sensor 
The selectivity of the sensor was evaluated by different metal ions 
like Na, Zn, Cd, Pb, Ag, Ba, Mn, Fe, K, Ni etc. The different types of 
interference metals ion are given in the bar graph Fig. 8, the concen-
tration of these metals ion are 10 times higher than the Co2+(5.0 μM). 
The graph as shown in Fig. 8 is showing the change in the Co2+ sensor 
against others types of interference. The observed insignificant value in 
the bar graph shows the high selectivity of the synthesized PVP-Ag NPs 
sensor for the Co2+ ions. 
3.7. Co2+ ion detection in real samples analysis 
The analytical ability of the synthesized PVP-Ag NPs sensor was also 
monitored in the real water sample. The samples of water were collected 
from the ITU Ayazağa Campus, Turkey from the different places of the 
campus. The samples were free from the Co2+ ion contamination. Hence 
the standard addition method was applied for the detection of the Co2+
ion in real water sample. The PVP-Ag NPs sensor shows the high 
Fig. 7. UV–Vis-spectra of PVP-Ag NPs with increasing the concentration of Co2+ in range of 0.1–5.0 μM and the calibration plot with linear fit analysis. 
Table 1 
Analytical performance of the PVP-Ag NPs sensor with previous reported sensors 
for the Co2+. 
Detection probe Techniques Linear 
Range 
LOD Ref 
Ag NPs Uv–visible 
spectrophotometer 
05–100 
μM 
7.0 
μM 
[3] 
Au NPs Uv–visible 
spectrophotometr 
02–10 
μM 
2.0 
μM 
[33] 
Carbon dots Fluorescence 0–40 μM 0.45 
μM 
[34] 
chemosensor based on 
1,8-naphthalimide 
appending thiourea 
Fluorescence 0–25 μM 0.26 
μM 
[35] 
PVP-Ag NPs Uv–visible 
spectrophotometr 
0.1–10 
μM 
0.1 
μM 
This 
work 
Fig. 8. The bar graph in the presence of various interferents of metal ion with 
concentration 10 times higher than Co2+. 
Table 2 
Co2+ ion determination in the real samples analysis with PVP-Ag NPs. 
Sample number Co+ Added (μM) Co+ founded (μM) Recovery (100 %) 
Restaurant Sample 
1 2 1.97 98.40 
2 2 2.02 100.00 
3 2 1.99 99.34 
Physics Laboratory 
1 5 4.96 99.14 
2 5 4.97 99.32 
3 5 4.92 98.38 
Dormitory 
1 3 2.98 99.44 
2 3 2.96 98.81 
3 3 2.95 98.50 
K. Rajar et al. 
Materials Chemistry and Physics 273 (2021) 125082
6
recovery in Table 2. 
4. Conclusion 
The PVP-Ag NPs was employed as very cost effective, simple and 
highly sensitive chemical sensor concerning the colorimetric sensing of 
Co2+ by changes in SPR band. The change in absorbance of PVP-Ag NPs 
vs concentration of Co2+ was plotted in the range of 0.1–5.0 μM. The 
sensor was successfully applied for the detection of Co2+ in the real 
samples collected from the different places of ITU Ayazağa Campus 
Turkey and the recovery was found in the range 98.3–100%. The limit of 
detection as LOD was calculated as 0.1 μM, while the limit of quantifi-
cation LOQ was found to be 0.3 μM which further confirm the extremely 
sensitive nature of the sensor. 
CRediT authorship contribution statement 
Kausar Rajar: Conceptualization, and design of study, Acquisition of 
data, Formal analysis, Writing – original draft, Writing – review & 
editing, critically for important intellectual content. Esra Alveroglu: 
Conceptualization, and design of study, Writing – original draft, Writing 
– review & editing, critically for important intellectual content. Mujdat 
Caglar: Acquisition of data, Writing – original draft, Writing – review & 
editing, critically for important intellectual content. Yasemin Caglar: 
Formal analysis, Writing – original draft, Writing – review & editing, 
critically for important intellectual content. 
Declaration of competing interest 
The authors declare that they have no known competing financial 
interests or personal relationships that could have appeared to influence 
the work reported in this paper. 
Acknowledgements 
Kausar Rajar strongly acknowledges the scholarship support from 
the “Scientific and Technological Research Council of Turkey (TUBI-
TAK-2221) Research Fellowship Program for International Citizens”. 
Authors also thank to Prof. Dr. Turan ÖZTÜRK, Chemistry Department, 
ITU for FTIR facilities. 
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	Highly selective colorimetric onsite sensor for Co2+ ion detection by povidone capped silver nanoparticles
	1 Introduction
	2 Experimental
	2.1 Materials and reagents
	2.2 Synthesis of PVP capped silver nanoparticles (PVP–Ag NPs)
	2.3 Colorimetric response of PVP-Ag NPs to Co2+
	2.4 Instrumentation
	3 Results and discussion
	3.1 UV–vis spectroscopy and morphologic studies of the PVP-Ag NPs
	3.2 X-ray diffractometer (XRD) analysis of the PVP-Ag NPs
	3.3 FT-IR study of the PVP-Ag NPs
	3.4 Co2+ sensing via PVP-Ag NPs
	3.5 Calibration of Co2+ via PVP-Ag NPs
	3.6 Selectivity of the PVP-Ag NPs sensor
	3.7 Co2+ ion detection in real samples analysis
	4 Conclusion
	CRediT authorship contribution statement
	Declaration of competing interest
	Acknowledgements
	References