Layered yttrium hydroxide composite as supersensitive fluorescent sensor on Fe(III) ions

Article abstract of DOI:10.1016/j.materresbull.2020.111135

The synthesized HN/OS-LYH composite (HN: 3-hydroxy-2-naphthoic acid, OS: 1-octane sulfonate, LYH: layered yttrium hydroxide) demonstrates tuned luminescence performance and sensitive recognition capability for Fe³⁺. In solid state, the HN/OS-LYH presents a green emission of 505 nm, with 40 nm blue shift relative to the 545 nm green emission of free HN-Na salt; under delamination in formamide (FM), the HN/OS-LYH displays a blue emission of 480 nm in contrast to a 515 nm emission of HNˉ in FM solution. The delaminated HN/OS-LYH exhibits excellent recognition capability towards Fe³⁺ with distinct fluorescence quenching. For Fe³⁺, a much large quenching constant of 3.85 × 10³ M^?1 and an extremely low detection limit of 1.14 × 10^-8 M are achieved. The HN/OS-LYH is expected to be a “turn-off” type fluorescent sensor for Fe³⁺ detection. This work may provide new ideas for design of novel LRH composites which can be applied on fluorescent sensoring.

Full text of DOI:10.1016/j.materresbull.2020.111135

Materials Research Bulletin 135 (2021) 111135
Contents lists available at ScienceDirect
Materials Research Bulletin
journal homepage: www.elsevier.com/locate/matresbu
Layered yttrium hydroxide composite as supersensitive fluorescent sensor
on Fe(III) ions
,
,
,
Jian Lia, Huiqin Yaob *, Feifei Suc, Zupei Lianga *, Shulan Mac *
a School of Chemistry &Chemical Engineering and Environmental, Weifang University, Weifang, 261061, China
b School of Basic Medical Sciences, Ningxia Medical University, Yinchuan 750004, China
c College of Chemistry, Beijing Normal University, Beijing, 100875, China
A R T I C L E I N F O
A B S T R A C T
Keywords:
The synthesized HN/OS-LYH composite (HN: 3-hydroxy-2-naphthoic acid, OS: 1-octane sulfonate, LYH: layered
yttrium hydroxide) demonstrates tuned luminescence performance and sensitive recognition capability for Fe3+
.
Luminescence
LRH composite
Delamination
Ion recognition
Fluorescence sensing
In solid state, the HN/OS-LYH presents a green emission of 505 nm, with 40 nm blue shift relative to the 545 nm
green emission of free HN-Na salt; under delamination in formamide (FM), the HN/OS-LYH displays a blue
emission of 480 nm in contrast to a 515 nm emission of HNˉ in FM solution. The delaminated HN/OS-LYH
exhibits excellent recognition capability towards Fe3+ with distinct fluorescence quenching. For Fe3+, a much
large quenching constant of 3.85 × 103 Mꢀ 1 and an extremely low detection limit of 1.14 × 10-8 M are achieved.
The HN/OS-LYH is expected to be a "turn-off" type fluorescent sensor for Fe3+ detection. This work may provide
new ideas for design of novel LRH composites which can be applied on fluorescent sensoring.
1. Introduction
an inner filter effect (IFE) which enabled the LYH:xTb (LYH is the
abbreviation of layered yttrium hydroxide) to work as fluorescent
Layered materials have attracted comprehensive attention for rich
interlayer chemistry [1] and multiple applications such as ion ex-
changers, sensors, catalysts, and photochemical materials [2]. Layered
rare-earth hydroxides (LRH) are a new kind of layered compounds that
have recently appeared. When combined with the inorganic LRH layers,
structural stability of the organics is generally enhanced, and fluores-
cence performance can be improved due to the synergetic effect of host
layers and organics [3–5]. So far, there are many reports with regards to
LRH-chromophore hybrids [3–14], however, most of them emphasise on
the luminescence property of individual organic chromophore or inor-
ganic RE3+, rather than the synergetic interactions of the including
components. We have developed a convenient method for delamination
of LRH materials [15–17], for which the readily available colloidal
suspensions would expand the application range of the LRH materials.
In addition, following the extensive applications in environmental
and physiological aspects, chemosensors that can detect metal ions are
of great significance [18–20]. Fluorescent chemosensing has been highly
valued by researchers due to the low cost, rapid response, and desirable
real-time monitoring [21,22]. But there are have been rare reports on
LRH composites acting as chemsensors. Byeon’s group [23] developed
sensor to detect Cr(VI). They also used organic spacer-modified LGdH:
Eu to recognize vanadate anions [24]. These recognition effects are
realized through luminescence change of RE3+ rather than organics.
However, there are few studies on fluorescence sensing performance of
organic-LRH hybrids.
Iron is a key element in most organisms such as plants and animals
and performs an important role in biochemical processes [25,26]. Fe3+
overload or deficiency could induce various disorders, for example
anemia, hemochromatosis, heart failure, liver damage, diabetes and
Parkinson’s disease [27]. Relying on fluorescence ‘turn-on’ [28,29] or
‘turn-off’ [30,31] mechanisms, recognition of Fe3+ from co-existing ions
can be realized, for example, the naphthalimide and coumarin based
‘turn-on’ fluorescence chemosensor for detecting Fe3+ [32]. Fan et al.
[33] presented fluorescent off-on enantiomers utilizing rhodamine de-
rivatives for Fe3+ imaging in living cells. In addition, Dy-Zn MOF
working as turn-off chemosensor for Fe3+ had also been reported [34].
There are few researches on the identification of Fe3+ using intercalation
compounds. Thanks to the protection of the host layers normally
regarded as inorganic macromolecules, the chemical stability of the
organic luminophors in the interlayers can be enhanced. Also, inorganic
* Corresponding authors.
E-mail addresses: huiqin_yao@163.com (H. Yao), zupeiliang@163.com (Z. Liang), mashulan@bnu.edu.cn (S. Ma).
https://doi.org/10.1016/j.materresbull.2020.111135
Received 12 August 2020; Received in revised form 8 November 2020; Accepted 16 November 2020
Available online 21 November 2020
0025-5408/© 2020 Elsevier Ltd. All rights reserved.

J. Li et al.
Materials Research Bulletin 135 (2021) 111135
Fig. 1. XRD patterns of NO3-LYH precursor (a) and composites of OS-LYH (b),
HN/OS-LYH (c). The d-values are given in nanometers.
Fig. 2. FT-IR spectra of HN (a), OS (b), NO3-LYH (c), and HN/OS-LYH com-
nanoscale layers are regularly present in a colloidal state, which could
uniformly contact with the solution systems of metal ions to be identi-
fied, thus improving the recognition effect. We recently demonstrated a
FLN/OS-LRH composite which exhibited fluorescence turn-off chemo-
sensoring for detecting Fe(III) [35]. So far, there is still a lack of research
on the recognition of Fe3+ by LRH composites.
posite (d).
2.2. Synthesis of sodium salt of HN (HN-Na)
For the preparation of sodium salt of HN (HN-Na), equal molar
equivalent of NaOH was mixed with the HN to remove its protons. After
complete dissolution of HN and NaOH, the solvents were evaporated
slowly. During the solvent evaporation process, solid product was
precipitated out gradually. After filtration, the HN-Na salt was collected,
which can be used to test the fluorescence property.
The 3-hydroxy-2-naphthoic acid (HN) is a small fluorescent organic
molecule which has been utilized to detect aluminium [36], copper
[37], and vanadium [38]. We want to figure out if the HN can be used
to identify iron. Moreover, when the HN is combined with certain
inorganic host layers such as LYH, its luminescence performance
may be changed or sometimes improved. Thus we synthesize the
HN/OS-LYH composite to check its luminescence performance and
the capability to recognize iron ions. Contrary to the ‘turn-on’ type
fluorescence chemosensor for Al3+ [39], the HN/OS-LYH shows a
‘turn-off’ recognition character for Fe3+, with a large quenching con-
stant of 3.85 × 103 Mꢀ 1 and an extremely low detection limit of 1.14 ×
10-8 M. This describes a novel example of LRH composites applied in
2.3. Ion recognition experiments of HN/OS-LYH
For recognition experiments, nine metal ions (Mg2+, Co2+, Ni2+
,
Cu2+, Zn2+, Pb2+, Cd2+, Hg2+ and Fe3+) were selected as target ions. The
ion solutions were got from dissolving their corresponding nitrate salts.
To the colloidal suspension (3 ml), the aqueous solution (1 ml) of the
metal ion with certain concentrations were added. Then fluorescence
emission spectrum of the mixtures were tested.
fluorescence sensoring to identify Fe3+
.
2. Experimental sections
3. Results and discussion
2.1. Synthesis of NO3-LYH, OS-LYH and HN/OS-LYH and delamination
3.1. Characterization of the prepared samples
NO3-LYH and OS-LYH were prepared referring to the literatures [5,
40], with the details shown in supplementary materials. Intercalation of
HN/OS into LYH was performed via an ion exchange reaction. The 1:1
stoichiometric NaOH was mixed with HN to make it deprotonated be-
forehand, and then the OS was added. Into the aqueous solution with a
1.29 mmol of HN + OS (HN:OS molar ratio: 1:4), 0.43 mmol of NO3-LYH
XRD patterns of NO3-LYH, OS-LYH and HN/OS-LYH were detected.
As depicted in Fig. 1a, the series of (00l) diffractions at 0.89, 0.45 and
0.29 nm indicate a basal spacing (dbasal) of 0.89 nm, consistent with that
reported for NO3-LYH [41]. For the OS-LYH (Fig. 1b), the (00l) dif-
fractions at 2.01, 1.01, 0.67, 0.51, 0.41 nm shows a 2.01 nm dbasal. The
diffractions of HN/OS-LYH are similar to those of OS-LYH, with a close
dbasal of ~2.0 nm (Fig. 1c). This illustrates the interlayer space of
HN/OS-LYH is mainly supported by the OS, possibly due to the higher
content and longer size of OS. As seen all samples contain a peak located
at 0.31 nm, which belongs to (220) reflection of LRH layers [41,42]. This
means that the layer structure does not change during ion exchange
process.
powders were added. The mixture was transferred into
a
Teflon-autoclave (solution volme is 80 ml) and reacted at 70 ◦C. After
reaction for 24 h, the as-formed HN/OS-LYH precipitates were filtered,
water-washed, and dried at vacuum at 50 ◦C over night.
For the delamination of the HN/OS-LYH, 0.05 g of sample was
dispersed into FM (20 mL) and treated with mechanical shaking (~2 h).
A transparent colloidal suspension was then obtained, indicating that
the HN/OS-LYH was exfoliated.
Fig. 2 depicted FT-IR spectra of the samples. For unprotonated HN
––
(Fig. 2a), the band at 3284 cmꢀ 1 belongs to Oꢀ H vibration
[43],
and those at 1665/1467 cmꢀ 1 correspond to Cꢀ O vibration of ꢀ COOH.
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Materials Research Bulletin 135 (2021) 111135
Fig. 3. SEM images of NO3-LYH precursor (a, a’) and HN/OS-LYH composite (b, b’).
Fig. 4. Emission spectra of (a) HN-Na (λex ¼394 nm) and (b) HN/OS-LYH (λex ¼415 nm) in (A) solid state and (B) delamination state in FM (λex ¼390 nm). (A’)
and (B’) are corresponding CIE1931 chromaticity. Inserts in (A’) and (B’) are corresponding photographs of (a) and (b) under 365 nm UV irradiation.
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J. Li et al.
Materials Research Bulletin 135 (2021) 111135
1
The 1516 cmꢀ
band is ascribed to C C vibration of naphthalene ring
–
–
–
[44]. For OS (Fig. 2b), two bands at 1199/1067 cmꢀ 1 are characteristic
absorptions of SO3ˉ [45]. In Fig. 2c, the 1384 cmꢀ 1 band of NO3ˉ proves
successful synthesis of NO3-LYH [46]. In Fig. 2d, the NO3ˉ band at 1384
cm-1 becomes unobservable, suggesting substitution of NO3‾ by HNˉ and
OS in the HN/OS-LYH. The SO3‾ vibrations observed at 1171/1049 cm-1
signify the presence of OS in the composite. The absorption bands at
1596/1401 cmꢀ 1 can be assigned to ꢀ COOˉ, for which the red shift of
the wavelengths relative to the 1665/1467 cm-1 of ꢀ COOH results
from the deprotonation. The hydrogen bonding interactions of ꢀ COOˉ
with layer ꢀ OH groups also decrease in vibration frequency.
SEM observations were employed for the NO3-LYH and HN/OS-LYH
as shown in Fig. 3. The NO3-LYH precursor (Fig. 3a,a’) exhibits plate-like
morphology with a nearly regular hexagon shape, and some crystals
grow into columnar or flower-like aggregates. The HN/OS-LYH (Fig. 3b,
b’) basically maintains the morphology of NO3-LYH. The coincidence of
morphology of the HN/OS-LYH composite with the NO3-LYH precursor
means a topotactic intercalation process of the organics into the LYH
interlayers.
Fig. 5. Emission spectra of HN/OS-LYH colloid mixed with various metal ions
(λex =355 nm). For measurements, 3 ml of composite colloid mixed with 1 ml of
aqueous solutions containing metal ions in a 1000 ppm concentration. The
‘None’ case is a control experiment, for which 3 ml of composite colloid was
mixed with 1 ml of pure water.
3.2. Luminescence performance of HN/OS-LYH in solid state and
delaminated state
Emission spectra of HN-Na salt and HN/OS-LYH in solid state were
depicted in Fig. 4A. For HN-Na, at the 394 nm excitation (λex ¼394 nm,
with the excitation spectra shown in Fig. S1a), a green emission is
observed at 545 nm (see Fig. 4A-a). For HN/OS-LYH (Fig. 4A-b and
Fig. S1b, λex ¼415 nm), though it is still a green emission, the peak
position appears at 505 nm, with a 40 nm blue-shift, and the lumines-
cence intensity is much enhanced in comparison to HN-Na. It is noted
that in the testing, the solid dosage of HN-Na and HN/OS-LYH composite
is equal, which means a much less HN amount in the HN/OS-LYH. Inter-
molecular aggregation of HN can be prevented by the LYH layers and
interlayered OS [47], thus causing the increased luminescence intensity.
Meanwhile, OS and LYH layers together induce the blue shift of emission
wavelength. The same green color range but different emission position
of the two samples is depicted in the CIE 1931 chromaticity diagram
(Fig. 4A’).
Fig. 6. Fluorescence intensity (525 nm) of HN/OS-LYH colloidal suspension
with the addition of Fe3+ and other metal ions (λex =355 nm). The luminous
intensity of Fe3+ is too low to be displayed.
Luminescence behavior of HN-Na solution and HN/OS-LYH colloid
in FM were investigated. The HN/OS -LYH colloid displays a blue
emission at 480 nm (Fig. 4B-b), forming striking contrast to the green
luminescence (505 nm) of the composite in solid state (Fig. 4A-b) as well
as the green emission (515 nm) of free HNˉ in FM solution (Fig. 4B-a).
This marked blue shift identifies the role of LYH host layers and inter-
layered OS. Moreover, the delamination of the HN/OS-LYH offers much
free space for HNˉ surrounding positively-charged LYH layers (loose
contact), giving the opportunity of OS to play its role in terms of lumi-
nescence regulation. Also, the delamination process may also promote
the appearance of blue emission. The blue shift phenomenon was re-
ported in DDS–AQS/LDH [48]. As we know surfactants may reduce
aggregation of chromophores [49]. Here the OS acts as a diluter for the
luminous organic anions (here is HN) and thus prevents them from ag-
gregation which may reduce the fluorescence [47,50,51]. The CIE 1931
chromaticity diagram and inserted photos in Fig. 4B’ present the
transition from green to blue color of the two samples, coinciding with
the emission spectrum. Here we see the CIE1931 chromaticity dia-
grams enable a clearer view of the emitted color of related samples.
The chromaticity diagram mainly divides three color areas, that is,
red, blue and green. In the present work, in solid state, although
the emissions of HN-Na (545 nm) and the HN/OS-LYH composite
(505 nm) both belong to green luminescence, their emission
wavelengths are different (with 40 nm change), for which the
corresponding position can be displayed in the chromaticity dia-
gram. Moreover, the green emission (515 nm) of the HN-Na solu-
tion and the blue emission (480 nm) of the exfoliated HN/OS-LYH
can be well distinguished and observed in the chromaticity
diagram. Based on integrating sphere technique [52], the PL
quantum yield of the HN/OS-LYH composite was determined to be
23.20 %, which is much larger than that (4.86 %) of the HNA-Na
[39]. The increased quantum yield of the composite demonstrates
the significant function of the LYH layers for improvement of the
luminescence performance of HN.
3.3. Ion recognition of HN/OS-LYH composite
Luminescence performance was studied for HN/OS-LYH mixed with
aqueous solutions containing metal ions at certain concentrations. As
shown in Fig. 5, red shift of emission from 480 nm to 525 nm is found
after addition of aqueous solutions of metal ions, which may be because
of the H2O entrance. To detect the effect of solvents, emission spectra of
HN-Na in H2O, FM and their mixtures were measured (Fig. S2). In pure
FM, water and different proportional FM+H2O, emission wavelengths of
515, 530, and 515ꢀ 530 nm were observed. As shown in Fig. 5, fluo-
rescence intensity varied in the cases with various types of metal ions.
The fluorescence was remarkably quenched by Fe3+, forming sharp
contrast to other metal ions. This may originate from the interactions
between Fe3+ and HN/OS-LYH composite. As known Fe3+ may coordi-
nate with the hydroxyl and carboxylate groups of HN, and radiative
transition can be disrupted, which causes the quenching of fluorescence.
The highly effective recognition capability towards Fe3+ verifies an
admirable fluorescent sensoring. The high selectivity may be due to
strong affinity of Fe3+ with HN. Meanwhile, paramagnetic Fe3+ has
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Materials Research Bulletin 135 (2021) 111135
the mixture has been gradually weakened and finally quenched,
demonstrating a sensitive sensing for Fe3+. As displayed in Fig. 8,
emission intensity exhibits a linear relationship with Fe3+ concentration
(4.5 × 10ꢀ 7-1.79 × 10ꢀ 4 M). At low concentration range of 0-0.2 mmol/
L (0ꢀ 10 ppm), quenching coefficient (Ksv) can be determined from the
slope of titration curve, based on the modified Stern-Vollmer equation
[54]:
I0/I = 1+ Ksv[M]
where I/I0: fluorescence intensity with/without metal ions (here is
Fe3+), Ksv: quenching constant, [M]: Fe3+ concentration. Based on the
above equation, we get the Ksv value of 3.85 × 103 Mꢀ 1. From the linear
relationship, the detection limit is determined to be 1.14 × 10-8 M. This
value is much lower than maximum contaminant level of drinking water
based on the U. S. EPA [55–58]. The Ksv of the present HN/OS-LYH is
larger than those other reported materials for Fe3+ recognition [35,
59–61], for example, Ksv of 2.26 × 102 M-1 by pyrene-doped electrospun
PMMA-PVC fibers [59], and Ksv of 3.96 × 102 M-1 by polyvinyl
chloride-graft-polystyrene copolymers [60]. The detection limit of 1.14
× 10-8 M is extremely lower than the values of other reported materials
[35,62–64] such as 1.2 £ 10-6 M for N-doped carbon quantum dots
[62], 10-7 M for hexahomotrioxacalix [3]arene [63], 7.03 × 10-3 M and
8.76 × 10-3 M for PP and PS, respectively [64], and 2.58 × 10-8 M for
FLN/OS-LRH [35].
Fig. 7. Emission spectra of HN/OS-LYH colloidal suspension with addition of
Fe3+ at various concentrations (0ꢀ 1000 ppm) (3 ml colloid +1 ml
aqueous solution).
Considering that there are many heteroions co-existing in actual
wastewater, interference of other metal ions to Fe3+ sensor is worthy of
careful study. To 3 ml of the HN/OS-LYH colloid, the solution with
mixed ions (1000 ppm for each ion) was added. As shown in Fig. 9, for
the cases containing Fe3+ mixed with other ions, the fluorescence in-
tensity presents a slight enhancement compared with that with only
Fe3+, but the degree of enhancement seems to be small. This demon-
strates that other ions have almost no interference for the Fe3+ recog-
nition. All these results verify the superior recognition capability of the
HN/OS-LYH composite towards Fe3+
.
4. Conclusions
Fig. 8. Linear relationship between fluorescence intensity ratio (I0/I) at 525 nm
of HN/OS-LYH colloid and Fe3+ concentration (mmol/L) in the range of 0.018
¡ 0.18 mmol/L (1-10 ppm). The luminescence intensities used for plotting
I/I0 are the y-coordinate values in Fig. 7.
In conclusion, co-intercalation of HN and OS into LYH via an ion
exchange reaction generates the HN/OS-LYH composite which exhibits
tuned luminescence and ion recognition performance. In solid state,
HN/OS-LYH composite displays a green emission (505 nm) while a blue
emission (480 nm) in delaminated state. The blue shift of HN/OS-LYH
composite in comparison to free HN-Na salt results from the confined
effect of LYH layers, dilution function of OS as well as the intermolecular
interactions between HN and OS. The delaminated colloid of HN/OS-
LYH composite is highly selective to Fe3+ over other metal ions. It is a
good turn-off chemosensor for Fe3+ exhibiting an extremely low detec-
tion limit of 1.14 × 10ꢀ 8 M and a much large quenching constant of 3.85
strong coordination interactions with the oxygen ligand-containing HN,
which may lead to the change of charge distribution of HN [53]. For
clarity, I bar diagram (Fig. 6) was used to show the relative magnitude of
fluorescence intensity for the cases with varied metal ions.
We also measured the emission spectra of HN/OS-LYH contacted
with solutions of Fe3+ at varied concentrations (0ꢀ 1000 ppm). From
Fig. 7, following the increase of Fe3+ concentration, the fluorescence of
Fig. 9. (A) Contrast of luminescence intensity of HN/OS-LYH colloid and its mixtures with single and mixed metal ions (concentration is 1000 ppm), (B) Enlarged
view of luminescence intensity of Fe3+-existing systems after the red bars of (A) are omitted.
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Materials Research Bulletin 135 (2021) 111135
× 103 M-1. The excellent recognition selectivity may be due to the strong
affinity between Fe3+ and HN with oxygen as the ligand. This work
opens a new way for the fabrication of novel LRH materials that can be
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and experimental meaurements. All the authors discussed the results
and participated in writing of the manuscript.
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Appendix A. Supplementary data
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