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Novel dual ligands capped perovskite quantum dots for fluoride detection
Accepted Manuscript Title: Novel dual ligands capped perovskite quantum dots for fluoride detection Authors: Li-Qiang Lu, Meng-Yuan Ma, Tian Tan, Xi-Ke Tian, Zhao-Xin Zhou, Chao Yang, Yong Li PII: DOI: Reference:
S0925-4005(18)30940-7 https://doi.org/10.1016/j.snb.2018.05.038 SNB 24694
To appear in:
Sensors and Actuators B
Received date: Revised date: Accepted date:
11-1-2018 9-5-2018 9-5-2018
Please cite this article as: Li-Qiang Lu, Meng-Yuan Ma, Tian Tan, XiKe Tian, Zhao-Xin Zhou, Chao Yang, Yong Li, Novel dual ligands capped perovskite quantum dots for fluoride detection, Sensors and Actuators B: Chemical https://doi.org/10.1016/j.snb.2018.05.038 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Novel dual ligands capped perovskite quantum dots for fluoride detection
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Li-Qiang Lu, Meng-Yuan Ma, Tian Tan, Xi-Ke Tian*, Zhao-Xin Zhou, Chao Yang , Yong Li
Faculty of Material Science and Chemistry, China University of Geosciences, Wuhan 430074,
*Corresponding
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PR China author. Tel.: +86 027 67884574. Email address: [email protected]
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Graphical abstract:
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Dual ligands capped CH3NH3PbBr3 perovskite quantum dots were applied for visual fluorescence detection of fluoride based on induced growth mechanism with a
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low detection limit of 3.2 μM.
Highlights
A novel dual ligands capped perovskite quantum dots fluorescent sensor for fluoride ions was fabricated by ligand-assisted reprecipitation method. This original fluorescent nanosensor was successfully applied to the detection of fluoride with high sensitivity and excellent selectivity.
The limit of detection is down to 3.2 μM (0.061 mg/L) and quite lower than
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the WHO guideline. The nanosensor can also be used for visual detection of fluoride.
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ABSTRACT Organolead halide perovskite quantum dots (PQDs) have attracted emerging attention due to their high quantum yield and tremendous potential for lighting and display technology. However, monotonous ligands impede their application, especially in analytical chemistry. In this paper, we have developed a novel dual-ligand strategy to facilely synthesize fluoride-responded CH3NH3PbBr3 PQDs which employ n-Octylamine (OA) and 6-amino-1-hexanol (AH) as two capping ligands. The usual ligand, OA, stabilizes the PQDs emitting intense fluorescence; the new introduced ligand, AH, could interact with fluoride through hydrogen bonding between hydroxyl group and fluoride, leading to the growth and fluorescence quenching of the PQDs. This original fluorescent nanosensor was successfully applied to the detection of fluoride with high sensitivity and excellent selectivity. The limit of detection was down to 3.2 μM (0.061 mg/L) and quite lower than the WHO guideline. Spot plate test indicated that the nanosensor could also be used for visual detection of fluoride. 1. Introduction Since Schmidt and co-workers reported the colloidal synthesis of nanosized CH3NH3PbBr3 perovskites, [1] organolead halide perovskite quantum dots (PQDs) have aroused intensive attention very recently. [2-5] These PQDs, emerging as a novel member of the quantum dots family, are prepared by facile synthetic process, and exhibit remarkable optical properties, such as wide wavelength tenability, narrow emission bands and high photoluminescence quantum yields, making them promising materials for lighting and display technology. [6-8] Due to their excellent photoluminescence performance, PQDs would have much potential to develop highly sensitive fluorescent chemosensors. Attempts to use PQDs as probes for detecting picric acid and mercuric ion have been made respectively. [9-10] However, the application of PQDs for sensing purpose is
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still rarely reported up to now. Because most of PQDs in the previous reports use long alkyl chain ammonium or amine as single ligand, the surface of the PQDs is relatively inert. This is in favor of their stability, but is adverse to their surface-functionalization, greatly restricting the analytical application of PQDs. Therefore, how to functionalize the surface of PQDs is very significant for broadening their application. Fluoride contamination in groundwater has been recognized as a severe threat worldwide, though a moderate concentration (0.5-1 mg/L) of fluoride in drinking water is beneficial to bone and dental enamel. [11-13] Long-term ingestion of water with a high concentration of fluoride could cause dental fluorosis, skeletal fluorosis, urolithiasis, osteoporosis, etc. [14] The World Health Organization (WHO) has set a guideline value of 1.5 mg/L for fluoride concentration in drinking water. [11] However, groundwater containing high fluoride concentrations which exceed the WHO guideline occurs throughout the world, especially in China, India, Africa and America, and it is estimated that more than 200 million people worldwide have to drink high fluoride content groundwater. [13-15] Therefore, it is of great importance to develop sensitive and convenient assay methods of fluoride in water for ensuring its concentration at safe level, particularly in remote areas. The main analytical methods for detection of fluoride include ion-selective electrode potentiometry [16-18] and ion chromatography, [19-21] as recommended by WHO [11,14]. But these techniques are not suitable for field detection due to fragile or sophisticated instrumentation and tedious preparation procedures. As a consequence, fluorescence methods have attracted extensive concern because of their high sensitivity and operational simplicity, and numerous fluorescent sensors have been developed for fluoride detection in recent years. [22-31] These fluorescent probes with elaborate molecular structure show fluorescence response toward fluoride through hydrogen bonding or/and Lewis acid–base interaction. Besides the molecule probes, some fluorescent quantum dots modified by diverse ligands were also developed for sensing fluoride, such as CdSe/ZnS, CdTe, CdS, CdS/ZnS and CDs. [32-37] However, they suffered from expensive reagent, complicated preparation, poor quantum yield or low sensitivity. Herein, we present a novel dual-ligand strategy for synthesizing surface-functionalized CH3NH3PbBr3 PQDs to serve as a fluorescent sensor for sensitive and visual detection of fluoride. The surface-functionalized CH3NH3PbBr3 PQDs used n-Octylamine (OA) and 6-amino-1-hexanol (AH) as two capping ligands. Thereinto, OA makes the PQDs stably emit strong fluorescence with high quantum yield, and a small amount of AH introduced hydroxyl groups on the surface of the PQDs, making the PQDs respond to fluoride. When the PQDs were exposed to fluoride, the hydroxyl groups could react with fluoride through hydrogen bonding, inducing the growth of the PQDs, and thus the PQDs’ fluorescence was quenched. Hence, the dual ligands capped CH3NH3PbBr3 PQDs (DL-PQDs) could be employed to effectively detect fluoride. To the best of our knowledge, this multi-ligand surface-functionalizing strategy has not been reported yet. 2. Experimental section 2.1. Materials and instrumentation Hydrobromic acid (HBr, 48%), N,N-dimethylformamide (DMF, 99.9%), oleic acid (99%), n-octylamine (OA, 99%), 6-amino-1-hexanol (AH, 97%), toluene and sodium fluoride (NaF, 98.0%) were purchased from Aladdin. Lead bromide (PbBr2, 99.99%) was purchased from Macklin. Methylamine aqueous solution (CH3NH2, 40.0%) was obtained from Kelong Chemical
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Reagent Co., Ltd. (Chengdu, China). Fluorescein was obtained from Beijing Chemical Reagent Co. (Beijing, China). All reagents and solvents were analytical-reagent grade and used without further purification. Ultrapure water (18.2 MΩ cm) was used throughout all the experiments. Ultrapure water was purified by an Aquapro ultrapure water system (Nanjing Quankun bio-technology Co., Ltd., China). The XRD patterns were obtained on a D8-FOCUS X-ray diffractometer (Bruker AXS, Germany), using a Cu Kα radiation source (λ = 1.5405 Å) at a voltage of 40 kV and current of 30 mA. The FT-IR spectra were recorded with an EQUNOX 55 FT-IR spectrometer (Thermo Fisher Scientific, USA) with KBr pellets, scanning from 4000 to 400 cm−1 at room temperature. Liquid samples in toluene were deposited on amorphous carboncoated copper grids, and the samples were analyzed using a JEOL 2000EX TEM machine (JEOL, Japan) operating at a 200 kV accelerating voltage. XPS determinations were carried out at a VG Multilab 2000 electron spectrometer (Thermo VG Scientific, UK) using 300 W Al Kα radiations. Particle size distribution were recorded by a Zetasizer Nano ZS90 (Malvern, UK). The UV-Vis absorption spectra were measured on a TU1901 UV-Vis spectrophotometer (Beijing Purkinje General Instrument Co., Ltd., China). Fluorescence spectra were taken using a LS55 fluorescence spectrometer (Perkin Elmer, USA). 2.2. Synthesis of CH3NH3Br Powdery methylammonium bromide (CH3NH3Br) was synthesized via the procedure as previously reported with minor modification. [3] Briefly, 15 mL of HBr were slowly added dropwise with a separating funnel to a round bottom flask containing 10 mL of CH3NH2 at 0 ℃. The reaction mixture was stirred for ~2 h until a clear solution was formed. Then, the solution was heated to 70 ℃ for ~12 h until it was evaporated to dryness. Finally, the precipitate was washed 2-3 times with absolute ethanol, and then filtered and dried in vacuo at 50 ℃ for 6 h to obtain powdered CH3NH3Br. 2.3. Synthesis of DL-PQDs DL-PQDs were prepared through a simple ligand-assisted reprecipitation method. [2] In detail, 0.35 mL of oleic acid, 0.04 mmol (7 μL) of OA, 0.01 mmol (0.0012 g) of AH, 0.1 mmol (0.0112 g) of CH3NH3Br, 0.1 mmol (0.0369 g) of PbBr2 were dissolved in 2.5 mL of DMF to form a clear precursor solution. Then, 20 μL of the precursor solution was added dropwise to 20 mL of toluene
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under vigorous stirring. After being stirred for 15 min, the mixture was centrifuged at 15000 g for 10 min. The obtained DL-PQDs were washed twice with toluene, dried in vacuo at 50 ℃ for 24 h, and redispersed in toluene for further use. 2.4. Determination of fluoride For fluoride (F-) detection, 2 mL of DL-PQDs solution (pH≈7.13) was mixed with various concentrations of F- (0−160 μM), then the fluorescence spectrum was collected from 440 nm to 580 nm with 350 nm excitation after 10 min. The selectivity was checked by addition of 450 μM
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of Cr2O72-, SCN-, WO42-, HPO42-, SeO42-, CO32-, H2PO4-, SeO32-, HCO3-, S2-, SO32-, S2O32-, I-, Brand Cl- under the same analytical conditions. The concentration of the DL-PQDs used for detection was expressed as 0.8 mg/L lead. 2.5. Spot plate of the DL-PQDs for F- sensing To test the practicality of the DL-PQDs for visual detection of F-, spot plate test was done. A few drops of F- solution with concentrations of 0, 0.2, 0.4, 0.6, 0.8, 1.0 mM were dripped into the spot plate with 1mL of the pure DL-PQDs in the holes respectively. The fluorescence color responses were observed under an UV lamp with excitation at 365 nm.
3. Results and discussion 3.1. Design of fluoride-responded CH3NH3PbBr3 PQDs The usual ligand used in the synthesis of PQDs is long alkyl chain ammonium or amine, [1-3] like n-octylamine (OA), which makes the PQDs stably emit strong fluorescence with high quantum yield due to its ability to control crystallization kinetics and further to control the size of PQDs, previously reported in the literatures [1-3, 38]. However, OA capped CH3NH3PbBr3 PQDs
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cannot respond to F- (Fig. 1B). We presumed if there are hydroxyl groups on the surface of CH3NH3PbBr3 PQDs, they would respond to F- because F- is the anion with the strongest electronegativity and the smallest ion radius, which is easily to form hydrogen bonds with hydroxyl group [39-41]. So we chose 6-amino-1-hexanol (AH) as the ligand, which has an amino group at one end of the alkyl chain and a hydroxyl group at the other end. The amino group makes AH attach to the PQDs, letting the hydroxyl group exposed on the surface of the PQDs. However, when AH was used alone as the ligand, stable fluorescent CH3NH3PbBr3 PQDs were not obtained (data not shown), probably because hydrogen bonding between hydroxyl groups induced the aggregation of the CH3NH3PbBr3 PQDs. To avoid the aggregation, a strategy of dual ligands capping was proposed. OA and AH were employed as dual ligands to synthesize novel CH3NH3PbBr3 PQDs. As shown in Fig. 1A, the as-prepared DL-PQDs (the molar ratio of AH to OA = 1:4) steadily gave off intense fluorescence
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at 510 nm, and showed significant decrease in fluorescence intensity while exposed to F-. The results demonstrate that fluoride-responded CH3NH3PbBr3 PQDs have been successfully synthesized.
Fig. 1. Fluorescence responses of (A) dual ligands (OA and AH) and (B) single ligand (OA)
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capped CH3NH3PbBr3 PQDs to 60 μM and 90 μM of F-. 3.2. Optimum molar ratio of the two ligands To obtain stable fluoride-responded CH3NH3PbBr3 PQDs, the effect of the molar ratio of AH to OA was investigated. While maintaining the total amount of the two ligands at 0.05 mmol, we adjusted the molar ratio of AH to OA to 1:1, 1:2, 1:3, 1:4 and 1:5. It can be seen from Fig. 2 that the lower the molar ratio is, the more stable the DL-PQDs become and the stronger the fluorescence is. Stable and strongly emitting DL-PQDs were obtained in the molar ratio of 1:4 and 1:5 (Fig. 2D and 2E), while the fluorescence of the DL-PQDs was weaker and decreased with time in the molar ratio of 1:1, 1:2 and 1:3 (Fig. 2A, 2B and 2C). The reason probably is that when the
majority of the ligands is OA, the long alkyl chains of OA sterically hinder hydrogen bonding between hydroxyl groups of AH, increasing the stability of the DL-PQDs. On the other hand, if the amount of AH is too small (the molar ratio of 1:5), the fluorescence response of the DL-PQDs to
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F- is less sensitive (Fig. S1), compared with the molar ratio of 1:4 (Fig. 1A). Thus, the optimum molar ratio of 1:4 was selected for further experiments.
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Fig. 2. Evolution of fluorescence spectra of DL-PQDs in the molar ratio AH/OA of (A) 1:1, (B) 1:2, (C) 1:3, (D) 1:4 and (E) 1:5.
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3.3. Characterization of DL-PQDs As stated above, fluoride-responded DL-PQDs were prepared in the molar ratio AH/OA of 1:4 through a facile ligand-assisted reprecipitation method. The DL-PQDs in toluene solution emitted bright green fluorescence under the 365 nm UV light, and the fluorescence quantum yield was 27.2% (vs fluorescein, 95%, see the Supporting Information). The morphology of the DL-PQDs was determined using HRTEM and the corresponding fast Fourier transformation (FFT) image, as shown in Fig. 3A, 3B and 3C, which indicate their particle size distribution and local crystallinity. The DL-PQDs show spherical nanoparticles with an average diameter of 3.5 nm and relatively uniform dispersion (Fig. 3A). An interlayer spacing of 2.96 Å (Fig. 3B, 3C) was obtained corresponding to the (200) plane of CH3NH3PbBr3 perovskite, which is in accordance with previous reports. [1-3] The XRD patterns of the DL-PQDs were measured to further confirm their crystal structures. As shown in Fig. 3D, the black line (line a) exhibits sharp and intense peaks, which could be assigned to (100), (110), (200), (210), (220) and (300) planes of CH3NH3PbBr3 perovskite with cubic phase structure, confirming the formation of CH3NH3PbBr3 PQDs. [2] Relatively, the red line (line b) shows that all peaks are almost unchanged after exposed to F-, indicating that the interactions between DL-PQDs and F- did not cause phase distortions to the structure of perovskite.
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Fig. 3. (A), (B) HRTEM images of DL-PQDs, (C) the corresponding FFT pattern and (D) XRD
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patterns of DL-PQDs in the absence and presence of 90 μM of F-.
3.4. Optimal time for F- sensing The reaction time is an important factor for F- sensing due to the process of F--induced growth of the DL-PQDs. The effect of time on fluorescence quenching of the DL-PQDs in the presence of
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F- (90 μM) is shown in Fig. S2. As can be seen, the fluorescence quenching efficiency of the DL-PQDs achieves a maximum and keeps stable after 10 min. Thus the quenching reaction time was optimized to 10 min.
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3.5. Sensitive detection of F- by the DL-PQDs To explore the sensitivity of the DL-PQDs for sensing F-, various concentrations of F- (0-160 μM) were added into the DL-PQDs solution, and the corresponding fluorescence responses were recorded. As shown in Fig. 4A, the intrinsic fluorescence emissions of the DL-PQDs decreased
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with sequentially increasing concentrations of F- with slight peak shift, which can be used as a basis for quantitative determination of fluoride ions. The fluorescence quenching was evaluated
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using Stern-Volmer equation: I0 / I = 1 + KSV [F-], where I0 and I are the fluorescence intensities of the DL-PQDs in the absence and presence of F- respectively, [F-] represents the concentration of F-, and KSV is the Stern-Volmer quenching constant. Fig. 4B shows the Stern-Volmer plot describing
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I0/I as a function of F- concentration. A good linear Stern-Volmer equation was obtained in the range of 10-50 μM with a correlation coefficient of 0.997 (R2 = 0.994). The limit of detection (LOD) was 3.2 μM according to three times the standard deviation of blank (3σ/slope). The LOD
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Fig. 4. (A) Fluorescence spectra of DL-PQDs in the assay solution containing various
concentrations of F-. The concentration of F- from the top to the bottom: 0-160 µM. The inset image shows the corresponding fluorescence color change under UV lamp (365 nm). (B) Plot of
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the ratio of I0/I versus concentration of F-.
Table 1 Comparison of LOD of some fluorescence methods for detection of FLOD (μM)
reference
Thiophene and diethylaminophenol moieties
14.36
39
9
40
6
21
600
15
8
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Carbon nanodots (CDs)
110
23
[N1 N3-bis(4-cyanobenzylidene)isophthalahydrazide]
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DL-PQDs
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This work
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Hexametaphosphate-capped CdS QDs
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Active pyridinium fused tetraphenylethene
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3.6. Selectivity of the DL-PQDs for F- detection To assess the selectivity of the detection system, the effect of various anions on the fluorescence emission of DL-PQDs was examined under the same experimental conditions. As shown in Fig. 5A, only 90 μM of F- could respond to the nanosensor evidently and result in an obvious fluorescence quenching, whereas other anions including 450 μM of H2PO4-, HPO42-, HCO3-, CO32-, CH3COO-, SeO42-, SeO32-, Cr2O72-, WO42-, S2-, SO32-, S2O32-, SCN-, I-, Br- and Cl- led to either very slight or even no fluorescence intensity change. The result demonstrated good selectivity of
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the novel fluorescent nanosensor toward F- over other competitive anions. In addition, interfering experiments were carried out by adding 90 μM F- to the nanosensor solution containing 450 μM other anions as mentioned. As shown in Fig. 5B, coexisting anions do not interfere with the detection of F- even the concentration of the interfering substances was 5 times higher than that of F-. Furthermore, interference experiment with some common cations in water was conducted. As can be seen in Fig. S3, the common cations including 450 μM of Na+, K+, Ag+, Cu2+, Fe2+, Fe3+, Ba2+, Mg2+, Ca2+ and Al3+ showed very weak influence on the detection of F-.
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Fig. 5. (A) Fluorescence response of DL-PQDs to different anions and F- (90 µM for F- and 450 µM for other anions). (B) Interference studies of the novel nanosensor toward F-. The black bars represent the fluorescence response of DL-PQDs to F- and other anions (90 µM for F-, 450 µM for other anions). The red bars represent the change of emission occurred after the subsequent addition of 90 µM of F- to the above solutions.
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3.7. Possible mechanism of the fluorescence detection of F- by DL-PQDs The possible sensing mechanism of the novel nanosensor for F- is illustrated in Fig. 6. By using the dual-ligand strategy, the obtained DL-PQDs have two kinds of capping ligand, OA and AH, on their surface. OA, the usual ligand for capping PQDs, provides an inert alkyl chain of eight carbon atoms, allowing the DL-PQDs stably emitting strong fluorescence; [1-2] AH, the new introduced ligand, has a shorter alkyl chain of six carbon atoms with a reactive hydroxyl group at one end, functionalizing the DL-PQDs’ surface. As discussed above, a small amount of AH does not cause the aggregation of the DL-PQDs due to steric hindrance by the long alkyl chains of OA. Because
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of the presence of hydroxyl groups on the surface, the DL-PQDs would respond to F- with the hydroxyl groups through hydrogen bonding, resulting in growth and fluorescence quench of the DL-PQDs. As is well known, the hydrogen bonds formed by the combination of fluorine and protons (H) are the strongest and the bond energy of O−H···F is greater than other hydrogen bonds except F−H···F. [22-23] Therefore, the synthesized DL-PQDs can selectively and sensitively detect fluoride due to their high quantum yield and strong hydrogen bonding.
Fig. 6. Schematic illustration of sensing mechanism of F- by DL-PQDs. The proposed mechanism was investigated by TEM, FT-IR and UV-Vis. The TEM image (Fig.
7A) shows that the initial as-prepared DL-PQDs were nearly spherical and uniformly dispersed with an average diameter of 3.5±0.4 nm (Fig. 7C). When the DL-PQDs were exposed to F- (90 μM), the particles showed some aggregation (Fig. 7B), and had an average diameter of 8.5±0.6 nm (Fig. 7D), indicating the growth of the DL-PQDs induced by F-. As shown in Fig. S4, a broad O−H stretching band from 3300 cm-1 to 3600 cm-1 was found in the DL-PQDs’ spectrum. After reacting with F-, the O−H stretching band was much weaker, indicating the reduction of amount of AH on the surface of the DL-PQDs. It is due to the formation of hydrogen bonding between fluoride ion and hydroxyl group, separating AH from the DL-PQDs. In the UV-Vis spectra (Fig. S5), compared with the initial DL-PQDs, the absorption intensity of DL-PQDs in the presence of
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S6), showing that the fluorescence quenching induced by F- is irreversible.
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F- increases, suggesting an increase in the particles’ size. [43-44] The result is consistent with the TEM analysis. Moreover, the addition of Ca2+ didn’t recover the fluorescence of DL-PQDs (Fig.
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Fig. 7. TEM images of DL-PQDs in the (A)absence and (B) presence of 90 μM of F-, and analysis of size distribution of DL-PQDs in the (C) absence and (D) presence of 90 μM of F-.
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3.8. Spot plate test for visual detection of FThe simple and convenient spot test has been investigated for visual sensing of F- to show the actual application of the as-prepared DL-PQDs for F- detection. As shown in Fig. 8, with the increasing concentration of F-, the fluorescence intensity in the holes under the UV lamp (365 nm) decreases in turn. The color variation could be observed by naked eyes when the concentration of
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F- is greater than 200 μM, exhibiting an ability of this nanosensor for visual sensing of F-.
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Fig. 8. Images of DL-PQDs containing different concentrations of fluoride under UV lamp (365
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nm). The concentration of F- is 0, 0.2, 0.4, 0.6, 0.8 and 1.0 mM, respectively.
4. Conclusions In summary, we have developed a novel fluoride-responded CH3NH3PbBr3 PQDs probe using AH and OA as dual ligands. When the molar ratio of AH to OA is 1:4, the DL-PQDs are stable
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and emit strong fluorescence due to the steric hindrance of OA. In the presence of F-, hydrogen bonding between hydroxyl group of AH and F- induced the growth of the DL-PQDs, resulting in their fluorescence quenching. The proposed DL-PQDs probe exhibits excellent sensitivity and
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selectivity for detection of F- with low LOD down to 3.2 μM, which is quite lower than the WHO guideline. Our multi-ligand strategy presented here may promote the application of PQDs in many fields.
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Acknowledgements The authors acknowledge the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (no. 41521001), the National Natural Science Foundation of China (no. 51371162) and the Fundamental Research Funds for the Central Universities, China University of Geosciences (Wuhan).
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Author Biographies Li-Qiang Lu is an Associate Professor at the Faculty of Material Science and Chemical Engineering, China University of Geosciences (Wuhan). He has obtained his Ph.D. degree from China University of Geosciences (Wuhan).
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And his current research interests include nano-analytical chemistry and
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spectral analysis.
Meng-Yuan Ma is currently pursuing her master degree in Faculty of Material Science and Chemistry, China University of Geosciences (Wuhan). And her
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current research interests focused on the design of nanosensors for chemical
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and biological sensing.
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Tian Tan is currently studying her master degree in Faculty of Material Science and Chemistry, China University of Geosciences (Wuhan). And her current
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biological sensing.
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research interests focused on the design of nanosensors for chemical and
Xi-Ke Tian is a Professor at the Faculty of Material Science and Chemistry,
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China University of Geosciences (Wuhan). He got his Ph.D. degree from Institute of Solid State Physics, Chinese Academy of Sciences. His current
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research interests include optical detection technology and prevention treatment research of hazardous substances in the environment. Zhao-Xin Zhou is an Associate professor at Faculty of Materials Science and Chemistry, China University of Geosciences (Wuhan). His research focused on optical detection technology on pollutant in the environment and oilfield
sewage disposal. Chao Yang is an Associate professor at Faculty of Materials Science and Chemistry, China University of Geosciences (Wuhan). His research focused on optical detection technology on environmental pollutants.
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Yong Li is a Lecturer at Faculty of Materials Science and Chemistry, China University of Geosciences (Wuhan). He has obtained his Ph.D. degree from
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Lanzhou University. And his current research interests mainly focus on the optical detection nanomaterials and processing techniques for environmental
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pollutants.
S0925-4005(18)30940-7 https://doi.org/10.1016/j.snb.2018.05.038 SNB 24694
To appear in:
Sensors and Actuators B
Received date: Revised date: Accepted date:
11-1-2018 9-5-2018 9-5-2018
Please cite this article as: Li-Qiang Lu, Meng-Yuan Ma, Tian Tan, XiKe Tian, Zhao-Xin Zhou, Chao Yang, Yong Li, Novel dual ligands capped perovskite quantum dots for fluoride detection, Sensors and Actuators B: Chemical https://doi.org/10.1016/j.snb.2018.05.038 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Novel dual ligands capped perovskite quantum dots for fluoride detection
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Li-Qiang Lu, Meng-Yuan Ma, Tian Tan, Xi-Ke Tian*, Zhao-Xin Zhou, Chao Yang , Yong Li
Faculty of Material Science and Chemistry, China University of Geosciences, Wuhan 430074,
*Corresponding
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PR China author. Tel.: +86 027 67884574. Email address: [email protected]
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Graphical abstract:
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Dual ligands capped CH3NH3PbBr3 perovskite quantum dots were applied for visual fluorescence detection of fluoride based on induced growth mechanism with a
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low detection limit of 3.2 μM.
Highlights
A novel dual ligands capped perovskite quantum dots fluorescent sensor for fluoride ions was fabricated by ligand-assisted reprecipitation method. This original fluorescent nanosensor was successfully applied to the detection of fluoride with high sensitivity and excellent selectivity.
The limit of detection is down to 3.2 μM (0.061 mg/L) and quite lower than
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the WHO guideline. The nanosensor can also be used for visual detection of fluoride.
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ABSTRACT Organolead halide perovskite quantum dots (PQDs) have attracted emerging attention due to their high quantum yield and tremendous potential for lighting and display technology. However, monotonous ligands impede their application, especially in analytical chemistry. In this paper, we have developed a novel dual-ligand strategy to facilely synthesize fluoride-responded CH3NH3PbBr3 PQDs which employ n-Octylamine (OA) and 6-amino-1-hexanol (AH) as two capping ligands. The usual ligand, OA, stabilizes the PQDs emitting intense fluorescence; the new introduced ligand, AH, could interact with fluoride through hydrogen bonding between hydroxyl group and fluoride, leading to the growth and fluorescence quenching of the PQDs. This original fluorescent nanosensor was successfully applied to the detection of fluoride with high sensitivity and excellent selectivity. The limit of detection was down to 3.2 μM (0.061 mg/L) and quite lower than the WHO guideline. Spot plate test indicated that the nanosensor could also be used for visual detection of fluoride. 1. Introduction Since Schmidt and co-workers reported the colloidal synthesis of nanosized CH3NH3PbBr3 perovskites, [1] organolead halide perovskite quantum dots (PQDs) have aroused intensive attention very recently. [2-5] These PQDs, emerging as a novel member of the quantum dots family, are prepared by facile synthetic process, and exhibit remarkable optical properties, such as wide wavelength tenability, narrow emission bands and high photoluminescence quantum yields, making them promising materials for lighting and display technology. [6-8] Due to their excellent photoluminescence performance, PQDs would have much potential to develop highly sensitive fluorescent chemosensors. Attempts to use PQDs as probes for detecting picric acid and mercuric ion have been made respectively. [9-10] However, the application of PQDs for sensing purpose is
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still rarely reported up to now. Because most of PQDs in the previous reports use long alkyl chain ammonium or amine as single ligand, the surface of the PQDs is relatively inert. This is in favor of their stability, but is adverse to their surface-functionalization, greatly restricting the analytical application of PQDs. Therefore, how to functionalize the surface of PQDs is very significant for broadening their application. Fluoride contamination in groundwater has been recognized as a severe threat worldwide, though a moderate concentration (0.5-1 mg/L) of fluoride in drinking water is beneficial to bone and dental enamel. [11-13] Long-term ingestion of water with a high concentration of fluoride could cause dental fluorosis, skeletal fluorosis, urolithiasis, osteoporosis, etc. [14] The World Health Organization (WHO) has set a guideline value of 1.5 mg/L for fluoride concentration in drinking water. [11] However, groundwater containing high fluoride concentrations which exceed the WHO guideline occurs throughout the world, especially in China, India, Africa and America, and it is estimated that more than 200 million people worldwide have to drink high fluoride content groundwater. [13-15] Therefore, it is of great importance to develop sensitive and convenient assay methods of fluoride in water for ensuring its concentration at safe level, particularly in remote areas. The main analytical methods for detection of fluoride include ion-selective electrode potentiometry [16-18] and ion chromatography, [19-21] as recommended by WHO [11,14]. But these techniques are not suitable for field detection due to fragile or sophisticated instrumentation and tedious preparation procedures. As a consequence, fluorescence methods have attracted extensive concern because of their high sensitivity and operational simplicity, and numerous fluorescent sensors have been developed for fluoride detection in recent years. [22-31] These fluorescent probes with elaborate molecular structure show fluorescence response toward fluoride through hydrogen bonding or/and Lewis acid–base interaction. Besides the molecule probes, some fluorescent quantum dots modified by diverse ligands were also developed for sensing fluoride, such as CdSe/ZnS, CdTe, CdS, CdS/ZnS and CDs. [32-37] However, they suffered from expensive reagent, complicated preparation, poor quantum yield or low sensitivity. Herein, we present a novel dual-ligand strategy for synthesizing surface-functionalized CH3NH3PbBr3 PQDs to serve as a fluorescent sensor for sensitive and visual detection of fluoride. The surface-functionalized CH3NH3PbBr3 PQDs used n-Octylamine (OA) and 6-amino-1-hexanol (AH) as two capping ligands. Thereinto, OA makes the PQDs stably emit strong fluorescence with high quantum yield, and a small amount of AH introduced hydroxyl groups on the surface of the PQDs, making the PQDs respond to fluoride. When the PQDs were exposed to fluoride, the hydroxyl groups could react with fluoride through hydrogen bonding, inducing the growth of the PQDs, and thus the PQDs’ fluorescence was quenched. Hence, the dual ligands capped CH3NH3PbBr3 PQDs (DL-PQDs) could be employed to effectively detect fluoride. To the best of our knowledge, this multi-ligand surface-functionalizing strategy has not been reported yet. 2. Experimental section 2.1. Materials and instrumentation Hydrobromic acid (HBr, 48%), N,N-dimethylformamide (DMF, 99.9%), oleic acid (99%), n-octylamine (OA, 99%), 6-amino-1-hexanol (AH, 97%), toluene and sodium fluoride (NaF, 98.0%) were purchased from Aladdin. Lead bromide (PbBr2, 99.99%) was purchased from Macklin. Methylamine aqueous solution (CH3NH2, 40.0%) was obtained from Kelong Chemical
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Reagent Co., Ltd. (Chengdu, China). Fluorescein was obtained from Beijing Chemical Reagent Co. (Beijing, China). All reagents and solvents were analytical-reagent grade and used without further purification. Ultrapure water (18.2 MΩ cm) was used throughout all the experiments. Ultrapure water was purified by an Aquapro ultrapure water system (Nanjing Quankun bio-technology Co., Ltd., China). The XRD patterns were obtained on a D8-FOCUS X-ray diffractometer (Bruker AXS, Germany), using a Cu Kα radiation source (λ = 1.5405 Å) at a voltage of 40 kV and current of 30 mA. The FT-IR spectra were recorded with an EQUNOX 55 FT-IR spectrometer (Thermo Fisher Scientific, USA) with KBr pellets, scanning from 4000 to 400 cm−1 at room temperature. Liquid samples in toluene were deposited on amorphous carboncoated copper grids, and the samples were analyzed using a JEOL 2000EX TEM machine (JEOL, Japan) operating at a 200 kV accelerating voltage. XPS determinations were carried out at a VG Multilab 2000 electron spectrometer (Thermo VG Scientific, UK) using 300 W Al Kα radiations. Particle size distribution were recorded by a Zetasizer Nano ZS90 (Malvern, UK). The UV-Vis absorption spectra were measured on a TU1901 UV-Vis spectrophotometer (Beijing Purkinje General Instrument Co., Ltd., China). Fluorescence spectra were taken using a LS55 fluorescence spectrometer (Perkin Elmer, USA). 2.2. Synthesis of CH3NH3Br Powdery methylammonium bromide (CH3NH3Br) was synthesized via the procedure as previously reported with minor modification. [3] Briefly, 15 mL of HBr were slowly added dropwise with a separating funnel to a round bottom flask containing 10 mL of CH3NH2 at 0 ℃. The reaction mixture was stirred for ~2 h until a clear solution was formed. Then, the solution was heated to 70 ℃ for ~12 h until it was evaporated to dryness. Finally, the precipitate was washed 2-3 times with absolute ethanol, and then filtered and dried in vacuo at 50 ℃ for 6 h to obtain powdered CH3NH3Br. 2.3. Synthesis of DL-PQDs DL-PQDs were prepared through a simple ligand-assisted reprecipitation method. [2] In detail, 0.35 mL of oleic acid, 0.04 mmol (7 μL) of OA, 0.01 mmol (0.0012 g) of AH, 0.1 mmol (0.0112 g) of CH3NH3Br, 0.1 mmol (0.0369 g) of PbBr2 were dissolved in 2.5 mL of DMF to form a clear precursor solution. Then, 20 μL of the precursor solution was added dropwise to 20 mL of toluene
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under vigorous stirring. After being stirred for 15 min, the mixture was centrifuged at 15000 g for 10 min. The obtained DL-PQDs were washed twice with toluene, dried in vacuo at 50 ℃ for 24 h, and redispersed in toluene for further use. 2.4. Determination of fluoride For fluoride (F-) detection, 2 mL of DL-PQDs solution (pH≈7.13) was mixed with various concentrations of F- (0−160 μM), then the fluorescence spectrum was collected from 440 nm to 580 nm with 350 nm excitation after 10 min. The selectivity was checked by addition of 450 μM
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of Cr2O72-, SCN-, WO42-, HPO42-, SeO42-, CO32-, H2PO4-, SeO32-, HCO3-, S2-, SO32-, S2O32-, I-, Brand Cl- under the same analytical conditions. The concentration of the DL-PQDs used for detection was expressed as 0.8 mg/L lead. 2.5. Spot plate of the DL-PQDs for F- sensing To test the practicality of the DL-PQDs for visual detection of F-, spot plate test was done. A few drops of F- solution with concentrations of 0, 0.2, 0.4, 0.6, 0.8, 1.0 mM were dripped into the spot plate with 1mL of the pure DL-PQDs in the holes respectively. The fluorescence color responses were observed under an UV lamp with excitation at 365 nm.
3. Results and discussion 3.1. Design of fluoride-responded CH3NH3PbBr3 PQDs The usual ligand used in the synthesis of PQDs is long alkyl chain ammonium or amine, [1-3] like n-octylamine (OA), which makes the PQDs stably emit strong fluorescence with high quantum yield due to its ability to control crystallization kinetics and further to control the size of PQDs, previously reported in the literatures [1-3, 38]. However, OA capped CH3NH3PbBr3 PQDs
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cannot respond to F- (Fig. 1B). We presumed if there are hydroxyl groups on the surface of CH3NH3PbBr3 PQDs, they would respond to F- because F- is the anion with the strongest electronegativity and the smallest ion radius, which is easily to form hydrogen bonds with hydroxyl group [39-41]. So we chose 6-amino-1-hexanol (AH) as the ligand, which has an amino group at one end of the alkyl chain and a hydroxyl group at the other end. The amino group makes AH attach to the PQDs, letting the hydroxyl group exposed on the surface of the PQDs. However, when AH was used alone as the ligand, stable fluorescent CH3NH3PbBr3 PQDs were not obtained (data not shown), probably because hydrogen bonding between hydroxyl groups induced the aggregation of the CH3NH3PbBr3 PQDs. To avoid the aggregation, a strategy of dual ligands capping was proposed. OA and AH were employed as dual ligands to synthesize novel CH3NH3PbBr3 PQDs. As shown in Fig. 1A, the as-prepared DL-PQDs (the molar ratio of AH to OA = 1:4) steadily gave off intense fluorescence
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at 510 nm, and showed significant decrease in fluorescence intensity while exposed to F-. The results demonstrate that fluoride-responded CH3NH3PbBr3 PQDs have been successfully synthesized.
Fig. 1. Fluorescence responses of (A) dual ligands (OA and AH) and (B) single ligand (OA)
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capped CH3NH3PbBr3 PQDs to 60 μM and 90 μM of F-. 3.2. Optimum molar ratio of the two ligands To obtain stable fluoride-responded CH3NH3PbBr3 PQDs, the effect of the molar ratio of AH to OA was investigated. While maintaining the total amount of the two ligands at 0.05 mmol, we adjusted the molar ratio of AH to OA to 1:1, 1:2, 1:3, 1:4 and 1:5. It can be seen from Fig. 2 that the lower the molar ratio is, the more stable the DL-PQDs become and the stronger the fluorescence is. Stable and strongly emitting DL-PQDs were obtained in the molar ratio of 1:4 and 1:5 (Fig. 2D and 2E), while the fluorescence of the DL-PQDs was weaker and decreased with time in the molar ratio of 1:1, 1:2 and 1:3 (Fig. 2A, 2B and 2C). The reason probably is that when the
majority of the ligands is OA, the long alkyl chains of OA sterically hinder hydrogen bonding between hydroxyl groups of AH, increasing the stability of the DL-PQDs. On the other hand, if the amount of AH is too small (the molar ratio of 1:5), the fluorescence response of the DL-PQDs to
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F- is less sensitive (Fig. S1), compared with the molar ratio of 1:4 (Fig. 1A). Thus, the optimum molar ratio of 1:4 was selected for further experiments.
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Fig. 2. Evolution of fluorescence spectra of DL-PQDs in the molar ratio AH/OA of (A) 1:1, (B) 1:2, (C) 1:3, (D) 1:4 and (E) 1:5.
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3.3. Characterization of DL-PQDs As stated above, fluoride-responded DL-PQDs were prepared in the molar ratio AH/OA of 1:4 through a facile ligand-assisted reprecipitation method. The DL-PQDs in toluene solution emitted bright green fluorescence under the 365 nm UV light, and the fluorescence quantum yield was 27.2% (vs fluorescein, 95%, see the Supporting Information). The morphology of the DL-PQDs was determined using HRTEM and the corresponding fast Fourier transformation (FFT) image, as shown in Fig. 3A, 3B and 3C, which indicate their particle size distribution and local crystallinity. The DL-PQDs show spherical nanoparticles with an average diameter of 3.5 nm and relatively uniform dispersion (Fig. 3A). An interlayer spacing of 2.96 Å (Fig. 3B, 3C) was obtained corresponding to the (200) plane of CH3NH3PbBr3 perovskite, which is in accordance with previous reports. [1-3] The XRD patterns of the DL-PQDs were measured to further confirm their crystal structures. As shown in Fig. 3D, the black line (line a) exhibits sharp and intense peaks, which could be assigned to (100), (110), (200), (210), (220) and (300) planes of CH3NH3PbBr3 perovskite with cubic phase structure, confirming the formation of CH3NH3PbBr3 PQDs. [2] Relatively, the red line (line b) shows that all peaks are almost unchanged after exposed to F-, indicating that the interactions between DL-PQDs and F- did not cause phase distortions to the structure of perovskite.
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Fig. 3. (A), (B) HRTEM images of DL-PQDs, (C) the corresponding FFT pattern and (D) XRD
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patterns of DL-PQDs in the absence and presence of 90 μM of F-.
3.4. Optimal time for F- sensing The reaction time is an important factor for F- sensing due to the process of F--induced growth of the DL-PQDs. The effect of time on fluorescence quenching of the DL-PQDs in the presence of
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F- (90 μM) is shown in Fig. S2. As can be seen, the fluorescence quenching efficiency of the DL-PQDs achieves a maximum and keeps stable after 10 min. Thus the quenching reaction time was optimized to 10 min.
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3.5. Sensitive detection of F- by the DL-PQDs To explore the sensitivity of the DL-PQDs for sensing F-, various concentrations of F- (0-160 μM) were added into the DL-PQDs solution, and the corresponding fluorescence responses were recorded. As shown in Fig. 4A, the intrinsic fluorescence emissions of the DL-PQDs decreased
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with sequentially increasing concentrations of F- with slight peak shift, which can be used as a basis for quantitative determination of fluoride ions. The fluorescence quenching was evaluated
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using Stern-Volmer equation: I0 / I = 1 + KSV [F-], where I0 and I are the fluorescence intensities of the DL-PQDs in the absence and presence of F- respectively, [F-] represents the concentration of F-, and KSV is the Stern-Volmer quenching constant. Fig. 4B shows the Stern-Volmer plot describing
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I0/I as a function of F- concentration. A good linear Stern-Volmer equation was obtained in the range of 10-50 μM with a correlation coefficient of 0.997 (R2 = 0.994). The limit of detection (LOD) was 3.2 μM according to three times the standard deviation of blank (3σ/slope). The LOD
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Fig. 4. (A) Fluorescence spectra of DL-PQDs in the assay solution containing various
concentrations of F-. The concentration of F- from the top to the bottom: 0-160 µM. The inset image shows the corresponding fluorescence color change under UV lamp (365 nm). (B) Plot of
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the ratio of I0/I versus concentration of F-.
Table 1 Comparison of LOD of some fluorescence methods for detection of FLOD (μM)
reference
Thiophene and diethylaminophenol moieties
14.36
39
9
40
6
21
600
15
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Carbon nanodots (CDs)
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[N1 N3-bis(4-cyanobenzylidene)isophthalahydrazide]
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DL-PQDs
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This work
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Hexametaphosphate-capped CdS QDs
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3.6. Selectivity of the DL-PQDs for F- detection To assess the selectivity of the detection system, the effect of various anions on the fluorescence emission of DL-PQDs was examined under the same experimental conditions. As shown in Fig. 5A, only 90 μM of F- could respond to the nanosensor evidently and result in an obvious fluorescence quenching, whereas other anions including 450 μM of H2PO4-, HPO42-, HCO3-, CO32-, CH3COO-, SeO42-, SeO32-, Cr2O72-, WO42-, S2-, SO32-, S2O32-, SCN-, I-, Br- and Cl- led to either very slight or even no fluorescence intensity change. The result demonstrated good selectivity of
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the novel fluorescent nanosensor toward F- over other competitive anions. In addition, interfering experiments were carried out by adding 90 μM F- to the nanosensor solution containing 450 μM other anions as mentioned. As shown in Fig. 5B, coexisting anions do not interfere with the detection of F- even the concentration of the interfering substances was 5 times higher than that of F-. Furthermore, interference experiment with some common cations in water was conducted. As can be seen in Fig. S3, the common cations including 450 μM of Na+, K+, Ag+, Cu2+, Fe2+, Fe3+, Ba2+, Mg2+, Ca2+ and Al3+ showed very weak influence on the detection of F-.
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Fig. 5. (A) Fluorescence response of DL-PQDs to different anions and F- (90 µM for F- and 450 µM for other anions). (B) Interference studies of the novel nanosensor toward F-. The black bars represent the fluorescence response of DL-PQDs to F- and other anions (90 µM for F-, 450 µM for other anions). The red bars represent the change of emission occurred after the subsequent addition of 90 µM of F- to the above solutions.
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3.7. Possible mechanism of the fluorescence detection of F- by DL-PQDs The possible sensing mechanism of the novel nanosensor for F- is illustrated in Fig. 6. By using the dual-ligand strategy, the obtained DL-PQDs have two kinds of capping ligand, OA and AH, on their surface. OA, the usual ligand for capping PQDs, provides an inert alkyl chain of eight carbon atoms, allowing the DL-PQDs stably emitting strong fluorescence; [1-2] AH, the new introduced ligand, has a shorter alkyl chain of six carbon atoms with a reactive hydroxyl group at one end, functionalizing the DL-PQDs’ surface. As discussed above, a small amount of AH does not cause the aggregation of the DL-PQDs due to steric hindrance by the long alkyl chains of OA. Because
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of the presence of hydroxyl groups on the surface, the DL-PQDs would respond to F- with the hydroxyl groups through hydrogen bonding, resulting in growth and fluorescence quench of the DL-PQDs. As is well known, the hydrogen bonds formed by the combination of fluorine and protons (H) are the strongest and the bond energy of O−H···F is greater than other hydrogen bonds except F−H···F. [22-23] Therefore, the synthesized DL-PQDs can selectively and sensitively detect fluoride due to their high quantum yield and strong hydrogen bonding.
Fig. 6. Schematic illustration of sensing mechanism of F- by DL-PQDs. The proposed mechanism was investigated by TEM, FT-IR and UV-Vis. The TEM image (Fig.
7A) shows that the initial as-prepared DL-PQDs were nearly spherical and uniformly dispersed with an average diameter of 3.5±0.4 nm (Fig. 7C). When the DL-PQDs were exposed to F- (90 μM), the particles showed some aggregation (Fig. 7B), and had an average diameter of 8.5±0.6 nm (Fig. 7D), indicating the growth of the DL-PQDs induced by F-. As shown in Fig. S4, a broad O−H stretching band from 3300 cm-1 to 3600 cm-1 was found in the DL-PQDs’ spectrum. After reacting with F-, the O−H stretching band was much weaker, indicating the reduction of amount of AH on the surface of the DL-PQDs. It is due to the formation of hydrogen bonding between fluoride ion and hydroxyl group, separating AH from the DL-PQDs. In the UV-Vis spectra (Fig. S5), compared with the initial DL-PQDs, the absorption intensity of DL-PQDs in the presence of
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F- increases, suggesting an increase in the particles’ size. [43-44] The result is consistent with the TEM analysis. Moreover, the addition of Ca2+ didn’t recover the fluorescence of DL-PQDs (Fig.
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Fig. 7. TEM images of DL-PQDs in the (A)absence and (B) presence of 90 μM of F-, and analysis of size distribution of DL-PQDs in the (C) absence and (D) presence of 90 μM of F-.
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3.8. Spot plate test for visual detection of FThe simple and convenient spot test has been investigated for visual sensing of F- to show the actual application of the as-prepared DL-PQDs for F- detection. As shown in Fig. 8, with the increasing concentration of F-, the fluorescence intensity in the holes under the UV lamp (365 nm) decreases in turn. The color variation could be observed by naked eyes when the concentration of
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F- is greater than 200 μM, exhibiting an ability of this nanosensor for visual sensing of F-.
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Fig. 8. Images of DL-PQDs containing different concentrations of fluoride under UV lamp (365
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nm). The concentration of F- is 0, 0.2, 0.4, 0.6, 0.8 and 1.0 mM, respectively.
4. Conclusions In summary, we have developed a novel fluoride-responded CH3NH3PbBr3 PQDs probe using AH and OA as dual ligands. When the molar ratio of AH to OA is 1:4, the DL-PQDs are stable
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and emit strong fluorescence due to the steric hindrance of OA. In the presence of F-, hydrogen bonding between hydroxyl group of AH and F- induced the growth of the DL-PQDs, resulting in their fluorescence quenching. The proposed DL-PQDs probe exhibits excellent sensitivity and
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selectivity for detection of F- with low LOD down to 3.2 μM, which is quite lower than the WHO guideline. Our multi-ligand strategy presented here may promote the application of PQDs in many fields.
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Acknowledgements The authors acknowledge the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (no. 41521001), the National Natural Science Foundation of China (no. 51371162) and the Fundamental Research Funds for the Central Universities, China University of Geosciences (Wuhan).
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Author Biographies Li-Qiang Lu is an Associate Professor at the Faculty of Material Science and Chemical Engineering, China University of Geosciences (Wuhan). He has obtained his Ph.D. degree from China University of Geosciences (Wuhan).
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And his current research interests include nano-analytical chemistry and
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spectral analysis.
Meng-Yuan Ma is currently pursuing her master degree in Faculty of Material Science and Chemistry, China University of Geosciences (Wuhan). And her
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current research interests focused on the design of nanosensors for chemical
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and biological sensing.
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Tian Tan is currently studying her master degree in Faculty of Material Science and Chemistry, China University of Geosciences (Wuhan). And her current
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biological sensing.
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research interests focused on the design of nanosensors for chemical and
Xi-Ke Tian is a Professor at the Faculty of Material Science and Chemistry,
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China University of Geosciences (Wuhan). He got his Ph.D. degree from Institute of Solid State Physics, Chinese Academy of Sciences. His current
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research interests include optical detection technology and prevention treatment research of hazardous substances in the environment. Zhao-Xin Zhou is an Associate professor at Faculty of Materials Science and Chemistry, China University of Geosciences (Wuhan). His research focused on optical detection technology on pollutant in the environment and oilfield
sewage disposal. Chao Yang is an Associate professor at Faculty of Materials Science and Chemistry, China University of Geosciences (Wuhan). His research focused on optical detection technology on environmental pollutants.
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Yong Li is a Lecturer at Faculty of Materials Science and Chemistry, China University of Geosciences (Wuhan). He has obtained his Ph.D. degree from
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Lanzhou University. And his current research interests mainly focus on the optical detection nanomaterials and processing techniques for environmental
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pollutants.