A fluorescence quenching sensor for Fe3+ detection using (C6H5NH3)2Pb3I8·2H2O hybrid perovskite

Article abstract of DOI:10.1016/j.inoche.2019.107562

A new organic-inorganic hybrid perovskite (C₆H₅NH₃)₂Pb₃I₈·2H₂O single crystal has been synthesized through a facile solution method. In this perovskite, there exists a 1D infinite lead iodide chains constituted by Pb₃I₈ groups, which is surrounded by anilines. As an active fluorescence quenching sensor material, this perovskite shows excellent performance for Fe³⁺ detection in N, N-dimethylformamide (DMF) solution with a detection limit of 1.0 × 10^?7 mol/L, including short response time, high sensitivity and high selectivity. The sensitivity and selectivity towards Fe³⁺ is much higher than that towards other metal cations, which provides a facile way for detecting Fe³⁺ cations in solution. Electron paramagnetic resonance (EPR) confirms that the mechanism of fluorescence quenching can be attributed to Fe³⁺ inhibition to the radiative electron-hole recombination via capturing electrons.

Full text of DOI:10.1016/j.inoche.2019.107562

InorganicChemistryCommunications109(2019)107562
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Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Short communication
A fluorescence quenching sensor for Fe3+ detection using
(C6H5NH3)2Pb3I8·2H2O hybrid perovskite
⁎
⁎
Meng-Ya Zhua, Le-Xi Zhanga, , Jing Yinb, Jing-Jing Chena, Li-Jian Biea,
a School of Materials Science and Engineering, Tianjin Key Lab for Photoelectric Materials and Devices, Key Laboratory of Display Materials and Photoelectric Devices
(Ministry of Education), Tianjin University of Technology, Tianjin 300384, China
b School of Environmental Science and Safety Engineering, Tianjin University of Technology, Tianjin 300384, China
G R A P H I C A L A B S T R A C T
Organic-inorganic hybrid 1D perovskite (C6H5NH3)2Pb3I8·2H2O has been synthesized. Employed as a Fe3+ sensing material based on fluorescence quenching, it
shows excellent performance for Fe3+ detection in DMF solution, with a LOD of 7.51 × 10−8 mol/L. The mechanism of fluorescence quenching can be attributed to
Fe3+ inhibited radiative electron-hole recombination via capturing electrons.
A R T I C L E I N F O
A B S T R A C T
Keywords:
A new organic-inorganic hybrid perovskite (C6H5NH3)2Pb3I8·2H2O single crystal has been synthesized through a
facile solution method. In this perovskite, there exists a 1D infinite lead iodide chains constituted by Pb3I8
groups, which is surrounded by anilines. As an active fluorescence quenching sensor material, this perovskite
shows excellent performance for Fe3+ detection in N, N-dimethylformamide (DMF) solution with a detection
limit of 1.0 × 10−7 mol/L, including short response time, high sensitivity and high selectivity. The sensitivity
and selectivity towards Fe3+ is much higher than that towards other metal cations, which provides a facile way
for detecting Fe3+ cations in solution. Electron paramagnetic resonance (EPR) confirms that the mechanism of
fluorescence quenching can be attributed to Fe3+ inhibition to the radiative electron-hole recombination via
capturing electrons.
Hybrid perovskite
(C6H5NH3)2Pb3I8·2H2O
Fluorescence quenching sensor
Ferric cations
Radiative electron-hole recombination
The past several years have witnessed potential advantages of or-
ganic-inorganic hybrid perovskites in optoelectronic applications [1–3].
In this field, especially for solar cells, instability caused by electron-hole
recombination is one of the main problems that need to be addressed
[4,5]. Researches mostly focused on decreasing electron-hole re-
combination in AMX3 and A2MX4 through introducing hole or electron-
transport materials [6,7]. As a matter of fact, organic-inorganic hybrid
perovskites are interesting semiconductor materials [8]. For three-di-
mensional (3D) network AMX3, the charge carrier transports along
2−
corner-sharing MX6 octahedra [9]. The size of cation A is limited by
the structure of 3D network [10], which affects the formability in dif-
ferent perovskites. However, the size of organic cation is no longer
⁎ Corresponding authors.
E-mail addresses: lxzhang@tjut.edu.cn (L.-X. Zhang), ljbie@pku.org.cn, ljbie@tjut.edu.cn (L.-J. Bie).
https://doi.org/10.1016/j.inoche.2019.107562
Received 15 July 2019; Received in revised form 14 August 2019; Accepted 31 August 2019
Availableonline31August2019
1387-7003/©2019ElsevierB.V.Allrightsreserved.

M.-Y. Zhu, et al.
InorganicChemistryCommunications109(2019)107562
Fig. 1. Crystal structure of (C6H5NH3)2Pb3I8·2H2O (a, b); bird view along c-axis (c) and infinite extension lead iodide chains (d).
confined in a two-dimensional (2D) A2MX4 layered perovskite [9]. The
inorganic component provides the opportunity for higher carrier mo-
bility, meanwhile organic component offers the possibility of structural
diversity [11]. 2D materials form repeating multi-quantum well struc-
tures, the carriers are limited in the inorganic component layer formed
All the chemical reagents used in the experiment were in analytical
grade without further purification. Distilled water was employed
throughout the experiment. In a typical synthesis, 6 ml aniline was
dissolved in 30 ml HI (47 wt%) and 30 ml absolute C2H5OH solution in
an ice-water bath. After magnetic stirring for 30 min, the mixed solu-
tion was maintained at 90 °C for 4 h in a water bath, resulting in the
formation of white acicular crystals. The white acicular crystals were
collected, washed several times with absolute C4H10O, and dried in a
vacuum oven for 12 h at 70 °C to obtain C6H5NH3I. After that, 1.1574 g
PbI2 and 1.1065 g C6H5NH3I were mixed in solution composed of 10 ml
HI (47 wt%) and 10 ml absolute C2H5OH. Under strong magnetic stir-
ring for 30 min, the solution was kept at 90 °C for 7 h in a water bath.
Light yellow acicular single crystal (C6H5NH3)2Pb3I8·2H2O can be ob-
tained after crystallization in two weeks, which was collected with
vacuum filtered, washed several times with absolute ether, and dried in
a vacuum oven for 12 h at 70 °C.
2−
by MX6 octahedron, and the organic part acts as a potential barrier,
in which the particular structure characteristic leads to the existence of
excitons with large binding energy [12]. Recently, attentions have been
focused on 1D [13] and 0D [14] perovskites, due to the strong quantum
confinement and site isolation. Among them, 1D perovskites have good
potential for applications involving radiative hole-electron recombina-
tion due to their low exciton dissociation efficiency [13].
It is reported that ionic movement influences recombination in
perovskite solar cells [4]. As fluorescence is an important way to release
energy via radiative electron-hole recombination, view from the sen-
sing point, external metal cations may have influences on radiative
electron-hole recombination in 1D perovskites, so 1D perovskites might
be good fluorescence sensors for detecting metal cations.
The scanning electron microscope (SEM) image of the sample was
examined using a JEOL JSM-6700F field-emission scanning electron
microscope (FE-SEM), with an accelerating voltage of 10 kV. A suitable
crystal with size of 0.220 × 0.210 × 0.180 mm was selected for single
crystal X-ray diffraction analysis. Crystallographic data was collected
on a Bruker Apex II CCD diffractometer with graphite monochromated
Mo Kα radiation (λ = 0.71073 Å) at room temperature. The structure
was determined by the direct method using the SHELXTL-2014 pro-
gram. To refine the structures, anisotropic thermal factors were em-
ployed for the non-H atoms. The hydrogen atoms of water in the crystal
could not be found in the Fourier map because of the disordered ar-
rangement. UV–Vis absorption spectra were recorded on a Shimadzu
UV-2550 spectrometer. Fluorescence spectra were measured with a
Hitachi F-4600 fluorescence spectrophotometer by a 280 nm excitation
from a Xenon lamp as the excitation source at room temperature. The
optical images were conducted on the fluorescent inverted microscope
Nikon Eclipse TE2000U with 20 times magnification under UV lamp.
Electron paramagnetic resonance (EPR) was carried out on Bruker EMX
Plus at room temperature.
As known to all, iron is one of the essential transition metals in
living things, and it is of vital importance to detect iron cation in so-
lution sensitively and selectively. Previously, methods reported for
detecting iron include electrochemical methods [15], atomic absorption
spectrometry (AAS) [16], inductively coupled plasma-atomic emission
spectrometry (ICP-MS) [17], and so on. Despite the good sensitivity and
selectivity, electrochemical method had drawbacks such as toxicity
derived from mercury electrode and the longer chelating reaction time
[15]. Spectrometric analysis required sophisticated apparatus and ex-
pensive cost [15,18]. It is still a challenge to develop a facile way or a
novel material for fast iron detection with high sensitivity, selectivity.
Recently, fluorescence quenching sensor to detect Fe3+ using such as
Bi2S3-TiO2 [19] and metal organic frameworks [20,21] has been re-
ported.
In this work, a novel 1D organic-inorganic hybrid perovskite single
crystal (C6H5NH3)2Pb3I8·2H2O synthesized through a solution method
was reported, which exhibits excellent fluorescence quenching perfor-
mance for Fe3+ cations, including short reaction time, low cost, high
sensitivity and selectivity. And mechanism of the fluorescence
quenching sensor was discussed via EPR as well from the inhibition of
radiative electron-hole recombination.
The crystal structure of (C6H5NH3)2Pb3I8·2H2O was shown in Fig. 1,
determined by single crystal X-ray diffraction. There are three Pb atom
positions (Pb1, Pb2, Pb3) in one unit cell, with slightly distorted octa-
hedral coordination. Each Pb atom is hexa-coordinated by iodine
2

M.-Y. Zhu, et al.
InorganicChemistryCommunications109(2019)107562
Fig. 2. (C6H5NH3)2Pb3I8·2H2O dispersed in DMF: (a) UV–Vis absorption spectra, inset is the absorbance v.s. the concentration ratio of Fe3+ over the sample, (b)
fluorescence titration spectra, (c) the fluorescence intensity, inset is the corresponding calibration between the fluorescence intensity and Fe3+ concentration;
Fluorescence results in blank and presence of various metal cations: (d) emission spectra, (e) fluorescence intensity, (f) selectivity.
atoms. Carbon atoms in aniline vibrate at two symmetric positions, and
water molecules situated between layers (Fig. 1a and b). Obviously, it is
a 1D structure isolated by larger organic aniline. The conduction band
(CB) and valence band (VB) of these perovskites are derived primarily
from the inorganic lead iodine octahedron layer. Viewing along c-axis,
layers are composed of alternate organic aniline groups and inorganic
octahedra (Fig. 1c), which is favorable for electron-hole recombination
between VB and CB. Infinite lead iodide octahedral chains are con-
stituted by the Pb3I8 groups, surrounded by anilines (Fig. 1d), which
might be a good structural characteristic for a fluorescence quenching
sensor. The morphology of the obtained crystal is acicular, with a
length of ~2 mm, width of ~30 μm, and thickness of ~8 μm (Fig. S2),
consistent with the self-regulation principle in crystal growth. Crystal-
lographic data has been deposited as CCDC 1864099, and crystal details
and refinement results for (C6H5NH3)2Pb3I8·2H2O can also be found in
the Supporting Information.
Fig. S3. The sample shows bright fluorescence in Fe3+ blank (Fig. S3a),
fluorescence quenching appears as the Fe3+ concentration is
1.0 × 10−5 mol/L, which is consistent with the result in Fig. 2(b). The
fluorescence intensity at 339 nm was plotted as a function of the Fe3+
concentrations, as shown in Fig. 2(c), the inset illustrates Fe3+ con-
centration v.s. emission intensity, showing a linear relation. Quantita-
tively, the effect can be fitted as the equation If = 475.9–3.303 × 106
CFe(III), with a linear factor of R2 = 0.9965, meaning that Fe3+ has a
strong interaction with the sample. The association constant (Ka) is
3.303 × 106, revealing an extremely strong quenching effect on the
(C6H5NH3)2Pb3I8·2H2O sample [22,23]. The detection limit was mea-
sured to be as low as 1.0 × 10−7 mol/L through the titration method,
which is superior to other methods regarding Fe3+ detection in solu-
tions [24–26]. In addition, all the fluorescence data were recorded di-
rectly in the Fe3+ titration process, implying fast response, good for
rapid detecting Fe3+ quantitatively.
Fluorescence quenching performance of (C6H5NH3)2Pb3I8·2H2O for
detecting metal cation were investigated using a signal transduction
pathway by titration in DMF. Since the as-synthesized sample is stable
under sunlight, it was dispersed directly in DMF to form solution. Fig. 2
(a) illustrated the UV–Vis absorption spectra of the solution with dif-
ferent Fe3+ concentrations at room temperature. According to the
UV–Vis absorption intensity of the solution, optimum excitation wa-
velength for the fluorescence measurement was chosen as 280 nm. At
the excitation wavelength of 280 nm and a slit of 2.5 nm, the sample
exhibits a broad fluorescence peak centered at 339 nm, as can be seen in
Fig. 2(b). Fluorescence titration spectra were carried out in the presence
of different Fe3+ concentrations ranging from 1.0 × 10−7 to
1.0 × 10−3 mol/L. The fluorescence intensity (If) decreases as the Fe3+
concentration (CFe(III)) increase from 1.0 × 10−7 to 1.0 × 10−3 mol/L,
and the fluorescence is almost quenched as the Fe3+ concentration is
1.0 × 10−5 mol/L.
Based on the equation LOD = 3δ/s (where δ is the standard devia-
tion of the signals and s is the slope of the linear calibration plot)
[26,27], the limit of detection (LOD) was calculated to be
7.51 × 10−8 mol/L. The linear range and LOD of fluorescence sensing
materials for Fe3+ detection were summarized in Table 1 [26–31]. The
linear range and LOD of the developed sensing material
(C6H5NH3)2Pb3I8·2H2O are improved over those of most reported
fluorescence sensing materials in Table 1. It is worth noting that the
Table 1
Comparison of fluorescence sensing materials for Fe3+ detection.
Sensing materials
Linear range (μmol·L−1
)
LOD (μmol·L−1
)
Ref.
FNCD
2–25
3.32–32.26
50–250
0–16
0.9
26
N-CQDs
0.7462
0.3
27
[Zn2(oba)2(bpy)]
Cd-MOF
28
0.3
29
In order to observe the fluorescence quenching effect intuitively,
optical images of sample in DMF with Fe3+ concentrations ranging
from 0 to 1.0 × 10−5 mol/L were recorded on a fluorescent inverted
microscope with 20 times magnification under UV lamp, as presented in
CuNCs
1–100
0.3
30
AuNCs-PbS-QDs
(C6H5NH3)2Pb3I8·2H2O
3–40
1.5
31
0.1–100
0.0751
This work
3

M.-Y. Zhu, et al.
InorganicChemistryCommunications109(2019)107562
Fig. 3. EPR spectra of Fe3+ as absence and presence of (C6H5NH3)2Pb3I8·2H2O in DMF with the X-axis using g-factor (a) and magnetic field (b).
Table 2
The standard electrode potential of different metal ions.
Ion pairs
Mn2+/Mn
Ni2+/Ni
Cd2+/Cd
Ca2+/Ca
Mg2+/Mg
−2.372
Zn2+/Zn
−0.762
Cr3+/Cr
−0.744
Co2+/Co
−0.280
Al3+/Al
−1.662
Pb2+/Pb
−0.126
Fe2+/Fe
−0.447
Hg2+/Hg
0.790
Fe3+
Fe2+
/
E°/V
−1.030
−0.257
−0.403
−2.868
0.770
lowest detection concentration for Fe3+ in this work is 0.1 μmol·L−1
,
hole recombination in the sample via capturing electrons. Standard
electrode potential (E°) usually represents the ability of gaining elec-
trons, the higher the electrode potentials, the higher the ability for
getting electrons [40]. As listed in Table 2, standard electrode potential
of Fe3+/Fe2+ and Hg2+/Hg+ cation pairs are high, so they exhibit
stronger fluorescence quenching effect than other cations. Furthermore,
ion diameter (D) might be another factor affecting the fluorescence
quenching effect. The diameter of Fe3+ (D = 1.1 Ǻ) is smaller than that
which is even lower than the LOD of most reported materials [26–31].
Thinking about the interference of other metal cations, selectivity
towards different metal cations was measured under same condition. As
can be seen in Fig. 2(c), the fluorescence intensity was decreased by
97.41% with 4.0 × 10−4 mol/L Fe3+, so this concentration was chosen
to investigate the selectivity of (C6H5NH3)2Pb3I8·2H2O with other 13
metal cations. The fluorescence emission spectra towards various metal
cations are shown in Fig. 2(d). Influences on the fluorescence intensity
at 339 nm are different with various metal cations, as illustrated in
Fig. 2(e). Compared with other metal cations, Fe3+ displays obvious
fluorescence quenching effect.
of Hg2+ (D = 2.0 Ǻ), thus fluorescence quenching effect of Fe3+ is
higher than that of Hg2+ cation [40,41], as more charge with smaller
ion diameter means stronger polarization and electron gaining poten-
tial. The CB and VB of these perovskites semiconductor are derived
primarily from the inorganic lead iodine octahedra layer, so a proper
ion size is needed to penetrate into the anionic chains for efficient
electron transfer. The fluorescence quenching mechanism might be
thought as the organic aniline layer inhibits metal ions with bigger
diameter from approaching inorganic layer of lead iodine octahedra in
the perovskite. On the basis of electron capture, Fe3+ shows the best
fluorescence quenching effect via inhibition of radiative electron-hole
recombination in the perovskite, which provides an effective method to
detect Fe3+ quantitatively.
The selectivity of sample to a certain metal cation (M) is defined as:
SM = (F0 F)/F0 × 100%
where F and F0 are the fluorescence intensity in metal cations presence
and blank.
Detailed selectivity of (C6H5NH3)2Pb3I8·2H2O towards other metal
ions are shown in Fig. 2(f). The selectivity towards Fe3+ is much higher
than other metal cations, with a SFe(III) value of 97.41%, showing very
good selectivity [22,32,33].
Among the tested metal cations, Fe3+ exhibits obvious quenching
effect on the sample. Since Fe3+ has five unpaired electrons in d orbital,
electron paramagnetic resonance (EPR) was taken to investigate the
fluorescence quenching mechanism. As shown in Fig. 3, the EPR spectra
of Fe3+ are measured in blank and presence of (C6H5NH3)2Pb3I8·2H2O
in DMF. The EPR signal at g = 2.16 in Fig. 3(a) can be ascribed to Fe3+
cation [34,35], and the signal observed in Fig. 3(b) can also be attrib-
uted to Fe3+ [36–38]. Furthermore, the concentration of the sample
can be calculated qualitatively by integrating areas of detected peaks
[35,39]. Comparing the EPR signal intensity of Fe3+, the intensity de-
creases obviously as sample presents. This implies that Fe3+ might react
with (C6H5NH3)2Pb3I8·2H2O, leading to decreased Fe3+ concentration.
Similar with light emission and absorption in MAPbI3, the electron-hole
separation in (C6H5NH3)2Pb3I8·2H2O can generate photocurrent under
sunlight radiation (Fig. S5), and the fluorescence is resulted from the
radiative recombination of electrons and holes [5,8,12]. It is reasonable
that Fe3+, as an oxidant, gain electrons from the sample, resulting in
fluorescence quenching. Namely, Fe3+ inhibits the radiative electron-
In summary,
a
novel organic-inorganic hybrid perovskite
(C6H5NH3)2Pb3I8·2H2O single crystal has been synthesized through a
solution method. It has a unique perovskite structure that 1D lead io-
dide octahedron chains is constituted by the Pb3I8 groups, which is
surrounded by anilines. Viewing from c-axis, layers are composed of
alternate organic aniline groups and inorganic octahedra, which is fa-
vorable for radiative electron-hole recombination between the VB and
the CB. This structure characteristic is good for fluorescence quenching
sensor. The obtained organic-inorganic hybrid 1D perovskite
(C6H5NH3)2Pb3I8·2H2O shows excellent fluorescence quenching per-
formance as Fe3+ titration in DMF with
a detection limit of
1.0 × 10−7 mol/L, including short reaction time, high sensitivity and
selectivity. Based on the EPR results, the fluorescence quenching me-
chanism of (C6H5NH3)2Pb3I8·2H2O by Fe3+ can be attributed to the
inhibition of radiative electron-hole recombination via capturing elec-
trons. This work demonstrates the potential of these compounds in
quantitatively detecting oxidizing metal cations.
4

M.-Y. Zhu, et al.
InorganicChemistryCommunications109(2019)107562
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