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Amino-Functionalized Metal-Organic Frameworks Nanoplates based Energy Transfer Probe for Highly Selective Fluorescence Detection of Free Chlorine Ting Lu, Lichun Zhang, Mingxia Sun, Dongyan Deng, Yingying Su, and Yi Lv Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.6b00253 • Publication Date (Web): 24 Feb 2016 Downloaded from http://pubs.acs.org on February 26, 2016

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Analytical Chemistry

AminoAmino-Functionalized MetalMetal-Organic Frameworks Nanoplates based Energy Transfer Probe for Highly Selective Fluorescence Detection of Free Chlorine

Ting Lu, † Lichun Zhang, † Mingxia Sun, † Dongyan Deng, † Yingying Su, ‡ Yi Lv† *

†

Key Laboratory of Green Chemistry & Technology, Ministry of Education, College of

Chemistry, Sichuan University, Chengdu, Sichuan 610064, China ‡

Analytical & Testing Center, Sichuan University, Chengdu, Sichuan 610064, China

*Corresponding Author. Email: [email protected]; Tel. & Fax +86-28-8541-2798

1

ACS Paragon Plus Environment


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ABSTRACT: Novel highly fluorescent NH2-MIL-53(Al) was controllably synthesized by a facile one-step hydrothermal treatment of AlCl3·6H2O and NH2-H2BDC in water with urea as a modulator. The as-synthesized NH2-MIL-53(Al) nanoplates exhibited excellent water solubility and stability. In the present work, it can be found that strong fluorescence of NH2-MIL-53(Al) nanoplates was significantly suppressed after the addition of free chlorine, and a simple sensing system for fast, highly selective direct detection of free chlorine in water was established. Compared with other fluorescent sensors for free chlorine, the present methodology has a comparable detection limit of 0.04 µM (S/N=3) and a wide detection range of 0.05 to 15 µM. On the other hand, the traditional redox-based fluorescent probes sharply suffered from the interference of MnO4-, Cr2O72-, and other oxidants with stronger oxidation capability than free chlorine while ours overcame this disadvantage. Further research suggests that it is more likely the energy transfer through N-H···O-Cl hydrogen bonding interaction between amino group and ClO- ions plays the key role in our system, providing a new and promising platform for free chlorine determination in the water quality monitoring.

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INTRODUCTION: Chlorine, a powerful oxidizing agent, has been widely used in water disinfection, deodorization, blanching, and other numerous manufacturing processes.1 In water treatment, the concentration of free residual chlorine [the sum of dissolved chlorine (Cl2), hypochlorous acid (HClO), and hypochlorite (ClO−)] must be strictly controlled. According to international regulations, only when the residual free chlorine concentration fall within the specified range can chlorine-treated water be sent from the treatment plant to the distribution system. Because free residual chlorine with too low level cannot kill viruses and pathogenic bacteria in water effectively while too high level may produce a large number of undesirable byproducts, especially trihalomethanes (THMs), which have been reported to be potentially detrimental to health.2-5 As a result, it is imperative to monitor and control the concentration of free residual chlorine in drinking water, swimming pool water and waste water for nonpotable reuse. To date, great progress has been made in the development of free chlorine determination. Pan et al. recently have employed commercial 2B pencil lead to fabricate a modified graphite-based electrode and achieved its repeated use in free chlorine sensing.6 In our preliminary work, carbon nitride quantum dots (g-CNQDs)-based chemiluminescence (CL) method has been successfully developed for detection of free chlorine with high selectivity and outstanding sensitivity.7 Additionally, continuing efforts have been also focused on fluorescent sensors for free chlorine. In 2010, CdSe-ZnS QDs with carboxylate coating layers (QDs-poly-CO2-) has been synthesized as a novel sensing platform for ultrasensitive and selective free chlorine quantification in tap water. Meanwhile, Yan et al. successfully applied it to detect free chlorine in HL60 cells by fluorescent imaging.8 In 2012, Dong et al. described a standard addition method to measure the

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concentration of free chlorine in a local tap water sample via GQDs-based sensing system which exhibit great advantages over the traditional N-N-diethyl-p-phenylenediamine (DPD) colorimetric method, especially for the quantification purposes of low concentration samples.9 In 2015, Hu’s group have demonstrated a H2O2-assisted hydrothermal technique for facile, green and low-cost synthesis of highly fluorescent carbon dots (C-dots) that can serve as multifunctional fluorescence nanosensors to detect pH, temperature, and free chlorine.10 In the same year, nitrogen and sulfur co-doped carbon dots (N,S-CDs) was proposed as a sensitive fluorescent probe for analysis of free chlorine.11 Even though several materials have been designed to establish fluorescent sensing systems of free chlorine, most of them served as the reducer of free chlorine, and there is no way to prevent the hindrance from the oxidants with stronger oxidation capability than free chlorine. Consequently, it still remains great challenging to develop new materials based sensors for highly selective detection of free chlorine. Metal−organic frameworks (MOFs), also called as porous coordination polymers (CPs) or coordination networks, are compounds built from metal ions or metal clusters with organic ligands, have been popular materials since the beginning of this century.12 Owing to their unique structures and fascinating chemical properties, including high surface areas, uniform nanoscale cavities, controlled pore sizes, tailorable molecular structures and catalysis activity, MOFs have demonstrated extensive applications in gas storage,13-15 separation,16 molecular recognition,17 chemical sensing,18 catalysis19 and drug delivery.20,21 In recent years, various of modified MOFs have been synthesized through the introduction of functional groups to organic ligands or the incorporation of lanthanide ions, as a result, potential applications of MOFs are rapidly increasing, especially in luminescence which include photocatalysis,22 nonlinear optics,23

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electroluminescence,24 biomedical imaging25 and fluorescent sensors. MOFs-based fluorescent sensors have attracted tremendous attention due to their remarkable advantages. Up to now, more and more fluorescent MOFs for sensing ions have been reported. Jia et al. developed a rapid and facile microwave-ultrasound assisted synthesis method for preparing nanoscale MIL-53(Fe) and had success in establishing a highly selective sensing system of MeHg+.26 Chen et

al.

presented

a

new

microporous

Tb-MOF,

Tb(BTC)·G

(MOF-76:

BTC=benzene-1,3,5-tricarboxylate, G=guest solvent) which has extraordinary sensitive response to F- ions results from the much stronger binding of F- to the terminal methanol molecules.27 On the basis of donor-acceptor electron transfer mechanism, Xiang et al. explored an amino group functionalized UMCM-1-NH2 as luminescent probe for highly selective recognition of Fe3+.28 Yang et al. reported a fluorescent MOFs MIL-53(Al), in which the center metal ions Al3+ can be exchanged with Fe3+. Building on the cation exchange mechanism, MIL-53(Al) was wisely employed to design a highly selective and sensitive fluorescent sensing platform for Fe3+.29 In addition, other ions such as Ag+, Cu2+, Co2+, Zn2+, Mg2+, Ca2+, Ba2+, PO43- and NO2- have been also investigated.30-37 Here's a brief summary of the prominent superiority of MOFs showing in those sensing systems. On the one hand, its uniform nanoscale cavities could be considered as microreactors which specific size and surface characteristics play crucial roles in the recognition and selective sensing of ions. On the other hand, the perfect combination of metal ions and organic ligands in MOFs offers more active sites which greatly expand its applications in sensing field.38 Here, we have developed a facile one-step hydrothermal approach to prepare highly fluorescent

NH2-MIL-53(Al)

(formed

by

connecting

5


together

Al3+

with


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2-amino-1,4-benzenedicarboxylic acid ) nanoplates with urea as a modulator. In this case, the prepared NH2-MIL-53(Al) nanoplates was explored as a fluorescent probe for highly selective analysis of free chlorine in water. Moreover, we have expounded that the amine group located in the nanoscale cavities of NH2-MIL-53(Al) nanoplates is primarily responsible for the fluorescence quenching phenomenon. The present attempt to fabricate a free chlorine fluorescent sensor with MOFs, would give a window opportunity to open up a new research field of MOFs in optical utilization.

EXPERIMENTAL SECTION Materials. All the reagents were analytical grade and used as received without further purification. 2-amino-1,4-benzenedicarboxylic acid (NH2-H2BDC) was purchased from Aladdin Chemistry Co. Ltd. while Aluminium (III) chloride hexahydrate (AlCl3·6H2O), urea, N,N-dimethylformamide (DMF), methanol (CH3OH) were obtained from Tianjin Kermel purification system (ULUPURE, Chengdu, China). Methods. All fluorescence measurements were carried out on a F-7000 fluorescence spectrophotometer (Hitachi Co., Tokyo, Japan) with experimental parameters as follows: photomultiplier voltage was 400 V, scan speed was 1200 nm min−1, excitation and emission slit widths were all 10 nm. The UV-vis absorption spectra were received by a U-2910 UV/Vis spectrophotometer (Hitachi Co., Tokyo, Japan). Fourier transform infrared (FT-IR) spectra were recorded in the range of 4000-400 cm-1 on a Thermo Nicolet IS10 FT-IR Spectrometer. Powder X-ray diffraction (XRD) patterns were collected using a Philips X'Pert Pro X-ray diffractometer employing Cu Kα radiation (λ=1.5406 Å). The scanning electron microscopy (SEM) images

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were recorded on a JEOL JSM-7500F scanning electron microscope at 5.0 KV. The thermogravimetric (TGA) investigation was performed on TG 209F1, from 30 to 800 ºC. The fluorescence lifetime was measured with a FL-TCSPC fluorescence spectrophotometer (Horiba Jobin Yvon Inc, France), with NanoLED-350 used as excitation source. The surface charge of the products was performed with a Zeta sizer Nano ZS (Malvern Co., UK). Preparation of NH2-MIL-53(Al). The synthesis of NH2-MIL-53(Al) was developed from the previously reported method.39 In brief, AlCl3·6H2O (3 mmol) was dissolved with 15 mL deionized water followed by addition of NH2-H2BDC (3 mmol) to the solution under magnetic stirring. 30 min later, 15 mL deionized water containing an appropriate amount of urea was dropped into the above mixture, continuing to stir for another 30 min. Then the as-obtained mixture was placed in a 50 mL Teflon-lined autoclave and maintained at 150 ºC for 5 hours under static conditions. After slowly cooling to room temperature, the acquired milky yellowish or white precipitates were separated from the reaction mixture by suction filtration and rinsed thoroughly with abundant of deionized water. Thereafter, the products were dispersed in 20 mL DMF and stirred for one day at room temperature. The next day, replaced the DMF with equal volumes of methanol and stirred for another day. Finally, removed the methanol and dried at 70 ºC in vacuum overnight. Fluorescence Assay of Free Chlorine. NH2-MIL-53(Al) nanoplates suspensions (5 mg L-1) were prepared by dispersing 1.0 mg of NH2-MIL-53(Al) nanoplates powder in 200 mL of ultrapure water under ultrasound at 300W and 25 MHz for 5 min. Subsequent fluorescence experiments were carried out in a 1 cm×1 cm quartz cell, where 1850 µL of NH2-MIL-53(Al) nanoplates suspension, 50 µL of phosphate buffered solution (PBS, 0.1 M), and 100 µL of

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different concentrations free chlorine solution were added sequentially and mixed for fluorescence measurements by excitation with 335 nm light. Analysis of Real Sample. The tap water sample obtained from Sichuan University campus and other two swimming pool water samples collected from adult pool and children pool in Sichuan University western swimming pool were analyzed for free chlorine through both the DPD colorimetric procedure and the proposed method without dilution. To ensure the accuracy of the results, the water samples were analyzed as soon as collected in consideration of their poor stability.

RESULTS AND DISCUSSION Synthesis and Characterization of NH2-MIL-53(Al) Nanoplates. As the cheapest, abundant natural resources on earth, water has less negative impact on the environment and is the most commonly used solvent in solvothermal reaction. However, NH2-H2BDC is soluble only in strong polar organic solvent, such as DMF, N,N-diethylformamide (DEF) and dimethyl sulphoxide (DMSO) which are harmful both to the environment and human beings. Though the synthesis of NH2-MIL-53(Al) with water as sole solvent has also been reported, product yield is typically low and most of the precursors are wasted attributed to the low solubility of NH2-H2BDC in water.40 Encouragingly, Sánchez-Sánchez’s group have demonstrated the introduction of organic salts as anionic linker sources or alternatively on the use of protonated linker sources plus a suitable base to deprotonate their groups to coordinate to the metal ions, which remarkably changes the solubility and deprotonation of the linker anion as well as the kinetics of MOF formation.41 Inspired by their successful experience, we attempted to use urea

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as a weak base to prepare NH2-MIL-53(Al) by a modified hydrothermal procedure. On the one hand, urea is stable at low temperature, with the increasing temperature, the decomposition rate of urea become fast and an alkalescence system is simultaneously formed which make sure the nucleation and crystal growth can be finished after deprotonated NH2-H2BDC connecting to Al3+. On the other hand, although hydrothermal temperature is lower than the decomposition temperature of urea, the existence of H+ originates from NH2-H2BDC is facilitate for the decomposition of urea, as a result the coordination reaction between Al3+ and NH2-H2BDC can be accomplished as expected. To our surprise, the participation of urea not only drastically increased product yield, but also harvested NH2-MIL-53(Al) nanoplates with predominant water solubility and stability. According to the XRD patterns (Figure 1A) of the products synthesized with different amounts of urea, it’s easy to find that NH2-MIL-53(Al) with good crystallinity could only be gained with relatively lower content of urea. When further increase the amount of urea, the coordination effect of NH2-H2BDC would be severely disturbed ascribed to the competition from hydroxyl. Therefore, the products crystalline phase transformed from NH2-MIL-53(Al) to AlOOH.42 The size and morphology of the obtained NH2-MIL-53(Al) were observed and the corresponding images are shown in Figure 2B. Interestingly, with the content of urea up to 6 mmol, NH2-MIL-53(Al) nanoplates came out and it’s logical that highly fluorescent NH2-MIL-53(Al) nanoplates become a desired candidate of fluorescent probe with much better dispersibility (Figure 2B). As can be seen from the FT-IR spectra (Figure 1B), there exist great distinctions

between

NH2-MIL-53(Al)

nanoplates

and

NH2-H2BDC.

Obviously,

the

disappearance of a broad band in the region of 2500-3300 cm-1 indicated that NH2-H2BDC

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linked into the framework of NH2-MIL-53(Al) nanoplates with fully deprotonated.43 Another clear change is that two new bands assigned to Al-O are observed at 1000-1100 cm-1, conforming the coordination from Al3+ to O atoms in NH2-H2BDC.42 What is more, the preserved while comparatively weaker and broader characteristic bands at 3390 and 3505 cm-1 corresponding to symmetric and asymmetric stretching modes of N-H bonding suggested the richness of hydroxyl groups contained in NH2-MIL-53(Al) nanoplates,44 which contributed to its remarkable water-solubility. Furthermore, the TGA was carried out to investigate the thermal stability of NH2-MIL-53(Al) nanoplates and the collected TGA data reveals that it is thermally stable up to 280 ºC (Figure S1B of the Supporting Information). Fluorescent Properties of MIL-53(Al) Nanoplates. As we noticed before, NH2-MIL-53(Al) nanoplates possessed higher fluorescence emission at 435 nm with excitation at 335 nm, which might be illustrated by reason that plate-like shape is easier to be dispersed while massive incorporated hydroxyl is helpful to promote its water-solubility (Figure 2). Otherwise, NH2-MIL-53(Al) nanoplates also displays a good day-to-day fluorescence stability and pH-independent fluorescence stability in the pH range of 5-10 (Figure 3), laying the foundation for fluorescent sensing. Establishment of NH2-MIL-53(Al) Nanoplates-Based Sensor for Free Chlorine. Such a highly fluorescent NH2-MIL-53(Al) nanoplates motivated us to explore its promising application in fluorescent sensing. Inspiringly, we found that its strong fluorescence was dramatically suppressed after contacted with free chlorine, thus further efforts have been made towards the establishment of NH2-MIL-53(Al) nanoplates-based free chlorine sensor. The response rate of the fluorescence intensity was first investigated. Just as seen in Figure S2B of

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the Supporting Information, the fluorescence intensity of NH2-MIL-53(Al) nanoplates rapidly reduced by about 80% of the original value as soon as 20 µM free chlorine is incorporated, but there is a little recovery with the growth of time, so the time point of the measurements must be limited in 2-5 min after the involvement of free chlorine. To ensure the consistency of experiment conditions, 3 min is conducted as the collection time of fluorescence data. Additionally, although the proposed sensing system possessed pH-independent fluorescence stability, considering its probably application in vivo we would carry out in the future, pH 7.4 was chosen as the optimized pH throughout subsequent experiment. In order to make sure that the proposed sensing system can be used for quantitatively detection of free chlorine, the fluorescence suppression induced by free chlorine at different concentrations were measured. As shown in Figure 4A, with the increasing of free chlorine concentration, the fluorescence intensity of NH2-MIL-53(Al) nanoplates gradually decreased while the emission peak has nearly no shift. According to the built calibration equation, there is a good linear relationship between the quenched fluorescence intensity (I0-I) of NH2-MIL-53(Al) nanoplates and the concentration (C) of free chlorine in the range from 0.05 to 15 µM, with a correlation coefficient of 0.998 (Figure 4B). NH2-MIL-53(Al) nanoplates probe also promise a low detection limit (S/N=3) of 0.04 µM for free chlorine, which is comparable to those obtained by other fluorescent probe, such as CdSe/ZnS QDs, GQDs, C-dots, and N,S-CDs with detection limits of 0.5 µM, 0.05 µM , 0.08 µM, and 5 nM, respectively.8-11 Selectivity of the Sensing System. Before applied in real sample detection, selectivity also is an important performance which must be taken into account. The fluorescence response of NH2-MIL-53(Al) nanoplates toward various metal ions and common anionic, including K+, Ag+,

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Mg2+, Mn2+, Zn2+, Cu2+, Co2+, Ni2+, Pb2+, Cd2+, Cr3+, Fe3+ , Hg2+, NO3-, SO42-, Ac-, CO32- and Clwere investigated. From Figure 5, we can see that the fluorescence intensity declined to about half with the addition of 10 µM free chlorine, while the forementioned ions (except Fe3+ and Hg2+) with 10-fold concentration of free chlorine had almost no influence on the fluorescence intensities. It should be noted that Fe3+ and Hg2+ with higher concentration do have unneglected impacts on the fluorescence intensities, which might be explained by the following reasons. Similar to the cation exchange mechanism between Fe3+ and the framework metal ion Al3+ in MIL-53(Al) previously reported, here Fe3+ also played the same role.29 As for Hg2+, it’s well known that Hg2+ is a general fluorescence inhibitor mainly attributed to its strong coordination to N atoms or O atoms belonged to the fluorescence materials.45 Fortunately, most nature water samples would not contain such high concentration of Fe3+ and Hg2+, meanwhile we have discovered that only little weakness of the fluorescence intensities happens in the presence of Fe3+ or Hg2+ at the same concentration as free chlorine, implying that the encumbrance derived from Fe3+ and Hg2+ could be ignored. Further experiments were performed to study the effects of coexisting ions in water on the presented sensing system for detection of 10 µM free chlorine. As shown in Figure 5, the fluorescence of NH2-MIL-53(Al) nanoplates response to free chlorine is impervious to these coexisting ions (100 µM or 10 µM). These results confirmed that the presented sensing system exhibits merits of high selectivity for free chlorine against the most potential interfering species existing in nature water samples and is suitable for the analysis of free chlorine in real samples. Application of the Proposed Method in Real Samples Assay. On the basis of the outstanding characteristics of the proposed method, the application of NH2-MIL-53(Al)

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nanoplates as a fluorescent probe for detecting free chlorine in tap water and swimming pool water were put into practice. The results given in Table 1 show that the value obtained with the presented method is extremely consistent with those obtained by the most widely used DPD colorimetric method.46 In addition, recovery tests of standard addition in real samples showed the recoveries for sample determination were in the range of 97%-101%. All the above results strongly revealed the capability of the proposed method in practical free chlorine detection in real samples with high reliability and accuracy. Possible Mechanism of the Sensing System. Great efforts have been concentrated on exploring the mechanism for the fluorescence quenching of NH2-MIL-53(Al) nanoplates caused by free chlorine. The XRD pattern of NH2-MIL-53(Al) nanoplates (Figure S3A of the Supporting Information) remains intact after being in contact with free chlorine, and both are correlate with NH2-MIL-53(Al) reported.41 As shown in the corresponding SEM images (Figure S3B of the Supporting Information), NH2-MIL-53(Al) nanoplates still maintains plate-like structure only with a little smaller size which might be owing to the ultrasonic treatment in water. There are neither disappearance of existing bands, nor appearance of new bands in the FT-IR spectrum (Figure S3C of the Supporting Information), and even no noticeable change of the intensity. Meanwhile, UV-vis response of NH2-MIL-53(Al) nanoplates upon addition of different concentrations of free chlorine was also studied and the absorption spectra are shown in Figure 6A, from which we can see that there is slight blue shift of the absorption peak assigned to the n−π* transition of the C=O band at about 325 nm.47 These results confirmed the existence of the interaction from free chlorine to NH2-MIL-53(Al) nanoplates, but it is too weak to destroy the crystalline structure of NH2-MIL-53(Al) nanoplates.

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It’s well known that free chlorine is a powerful oxidizing agent and in most of the free chlorine sensing systems, fluorescent probes served as reducer of free chlorine.5-8 Hence, these redox-based free chlorine sensing systems sharply suffered from the interference of MnO4-, Cr2O72-, and other oxidants with stronger oxidation capability than free chlorine. In this regard, NH2-MIL-53(Al) nanoplates-based sensor for free chlorine showed complete different result. From Figure 6B, it’s clear that the fluorescence intensity of NH2-MIL-53(Al) nanoplates substantially quenched to about 20% as 20 µM free chlorine is incorporated, whereas the involvement of same concentration of MnO4- or Cr2O72- couldn’t induce marked inhibition of the fluorescence intensity. At the same time, the zeta potential of NH2-MIL-53(Al) nanoplates nearly unchanged (from -40.0 to -40.5 mV) after the exposure to 20 µM free chlorine. One reasonable explanation for these findings is that it isn’t oxidation mechanism that plays the key role in this sensing system. In order to further explain the fluorescence quenching phenomenon, time-resolved fluorescence decay experiments in the absence and presence of free chlorine were performed. The results were given in Figure 7A, from which it can be seen that the fluorescence lifetime of NH2-MIL-53(Al) nanoplates is shortened from 15.6 to 13.2 ns after the addition of 20 µM free chlorine, which turned out that the fluorescence quenching of NH2-MIL-53(Al) nanoplates triggered by free chlorine could be chiefly due to dynamic quenching effect (DQE), rather than static quenching effect (SQE).48 As mentioned in the earlier section, when we investigated the response rate of the fluorescence intensity, we found that the quenching is partially recovered with the growth of time. For a more intuitive result will be displayed, time-dependent fluorescence response of NH2-MIL-53(Al) nanoplates to 10 µM free chlorine is also studied and

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the result is shown in Figure S4A of the Supporting Information. Apparently, the fluorescence intensity recovered dramatically and as we incorporate free chlorine again, the quenching phenomenon recurred. It is not clear what kind of interaction existed between NH2-MIL-53(Al) nanoplates and free chlorine, but we can make sure that the recovery results from the decomposition of free chlorine and it could be further proved through the following study on the effect of illumination. The reaction mixture (a), (b), (c), (d) all contained 10 µM free chlorine, nevertheless the fluorescence signal of (a) was collected immediately after free chlorine incorporation; before measuring, (b) and (c) were placed in darkness and under 365 nm UV lamp for 2 hours, respectively; as for (d), the same amount of free chlorine was exposed under 365 nm UV lamp with an illumination time of 2 hours then added into NH2-MIL-53(Al) nanoplates suspensions and recorded the photoluminescence spectrum immediately. As can be seen in Figure S4B of the Supporting Information, the value of (b) is close to (a) while (c) is close to (d) which is almost the same as that without free chlorine, strongly indicating that free chlorine existed in a stable state without light and favorably induced fluorescence quenching, but once exposed to light, the decomposition of free chlorine lead to the recovery. To gain an insight into the mechanism, we further discussed what kind of interaction existed between NH2-MIL-53(Al) nanoplates and free chlorine. It is generally appreciated that amino group is an important functional group and often be used as a binding site to bind with other ions,28,37,49 thereby it is extremely necessary to be researched by contrast test whether amine group plays the crucial role in this reaction. Besides NH2-MIL-53(Al) nanoplates, the quenching effect of free chlorine on NH2-H2BDC, p-aminobenzoic acid (PABA), and terephthalic acid (H2BDC) were also examined. Fascinating, except H2BDC, others with amine group all have

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response to free chlorine in varying degrees, particularly for NH2-MIL-53(Al) nanoplates (Figure 7B), eloquently pointing out that the amine group connected to ligand molecules is the key component of NH2-MIL-53(Al) nanoplates which works better than individual NH2-H2BDC on the reaction with free chlorine. Because of the special pore system, most amine groups are housed within the nanoscale cavities of NH2-MIL-53(Al) nanoplates where once come into, ClO- ions are immobile and the distance from amine groups to ClO- ions is closed to benefit their interaction. Furthermore, the gap between NH2-MIL-53(Al) nanoplates and NH2-H2BDC also arised from the structure of NH2-H2BDC in which amine group and adjacent carboxyl easily form inner salt complexes, hampering amine groups in responding to ClO- ions. Keeping all these results in mind, a possible mechanism of energy transfer for the fluorescence quenching of NH2-MIL-53(Al) nanoplates induced by free chlorine flashes out. Scheme 1 shows the schematic of the whole process. It is thought that ClO- ionsimmobilized within micropores of NH2-MIL-53(Al) nanoplates shorten the distance between them and amine groups to build N-H···O-Cl hydrogen bonding, which set up a bridge for energy migration from NH2-MIL-53(Al) nanoplates to ClO- ions, ultimately triggering the fluorescence quenching phenomenon.

CONCLUSIONS Highly fluorescent NH2-MIL-53(Al) nanoplates with superior water solubility and stability was successfully synthesized by a facile one-step hydrothermal treatment of AlCl3·6H2O and NH2-H2BDC in water with urea as a modulator. In the current work, the synthesized NH2-MIL-53(Al) nanoplates has been served as a simple sensing platform for free chlorine with

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notable sensitivity and selectivity in a wide detection range of 0.05 to 15 µM and a comparable detection limit as low as 0.04 µM. A possible mechanism of energy transfer through N-H···O-Cl hydrogen bonding constructed between free chlorine and the amine groups attached to NH2-MIL-53(Al) nanoplates has been amply demonstrated. Unlike the traditional redox-based free chlorine fluorescent sensors, ours invalidate the interference from MnO4-, Cr2O72-, and other oxidants with stronger oxidation capability than free chlorine, paving the way for free chlorine detecting in the water quality monitoring.

Acknowledgement The authors gratefully acknowledge financial support from the National Natural Science Foundation of China (Nos. 21375089 & 21505095) and Science & Technology Department of Sichuan Province of China (2015JY0272). Supporting Information Available: This material including Figure S1-S4 are available free of charge via the Internet at http://pubs.acs.org.

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REFERENCES (1) White, G. C. Handbook of Chlorination, 2nd ed.; Van Nostrand Reinhold Co. Inc.: New York, NY, 1986. (2) Rook, J. J. Water Treat. Exam. 1974, 23, 234-243. (3) Report on Carcinogenesis Bioassay of Chloroform; National Cancer Institute: Washington, D. C., 1976. (4) Simpson, K. L.; Hayes, K. P. Water Res. 1998, 32, 1522-1528. (5) Theiss, J. C.; Stoner, G. D.; Skimkin, M. B.; Weisburger, E. K. Cancer Res. 1977, 37, 2717-2720. (6) Pan, S.; Deen, M. J.; Ghosh, R. Anal. Chem. 2015, 87, 10734-10737. (7) Tang, Y. R.; Su, Y. Y.; Yang, N.; Zhang, L. C.; Lv, Y. Anal. Chem. 2014, 86, 4528-4535. (8) Yan, Y.; Wang, S. H.; Liu, Z. W.; Wang, H. Y.; Huang, D. J. Anal. Chem. 2010, 82, 9775-9781. (9) Dong, Y. Q.; Li, G. L.; Zhou, N. N.; Wang, R. X.; Chi, Y. W.; Chen, G. N. Anal. Chem. 2012, 84, 8378-8382. (10) Hu, Y. P.; Yang, J.; Li, J.; Yu, J. S. Carbon. 2015, 93, 999-1007. (11) Xue, M. Y.; Zhang, L. L.; Zou, M. B.; Lan, C. Q.; Zhan, Z. H.; Zhao, S. L. Sens. Actuators B. 2015, 219, 50-56. (12) Zhou, H. C.; Long, J. R.; Yaghi, O. M. Chem. Rev. 2012, 112, 673-674. (13) Eddaoudi, M.; Kim, J.; Rosi, N.; Vodak, D.; Wachter, J.; O’Keeffe, M.; Yaghi, O. M. Science. 2002, 295, 469-472.

18


Page 18 of 27

Page 19 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(14) Yaghi, O. M.; O’Keeffe, M.; Ockwig, N. W.; Chae, H. K.; Eddaoudi, M.; Kim, J. Nature. 2003, 423, 705-714. (15) Hamon, L.; Serre, C.; Devic, T.; Loiseau. T.; Millange, F.; Férey, G.; Weireld, G. D. J. Am. Chem. Soc. 2009, 131, 8775-8777. (16) Li, J. R.; Sculley, J.; Zhou, H. C. Chem. Rev. 2012, 112, 869-932. (17) Harbuzaru, B. V.; Corma, A.; Rey, F.; Atienzar, P.; Jorda, J. L.; García, H.; Ananias, D.; Carlos, L. D.; Rocha, J. Angew. Chem. Int. Ed. 2008, 47, 1080-1083. (18) Lu, Y.; Yan, B.; Liu, J. L.; Chem. Commun. 2014, 50, 9969-9972. (19) Wan, X. Y., Wu, L. Q.; Zhang, L. C.; Song, H. J.; Lv, Y. Sens. Actuators B. 2015, 220, 614-621. (20) Taylor-Pashow, K. M. L.; Rocca, J. D.; Xie, Z. G.; Tran, S.; Lin, W. B. J. Am. Chem. Soc. 2009, 131, 14261-14263. (21) He, C. B.; Lu, K. D.; Liu, D. M.; Lin, W. B. J. Am. Chem. Soc. 2014, 136, 5181-5184. (22) Wang, D. K.; Wang, M. T.; Li, Z. H. ACS Catal. 2015, 5, 6852-6857. (23) Serra-Crespo, P.; van der Veen, M. A.; Gobechiya, E.; Houthoofd, K.; Filinchuk, Y.; Kirschhock, C. E. A.; Martens, J. A.; Sels, B. F.; De Vos, D. E.; Kapteijn, F.; Gascon, J. J. Am. Chem. Soc. 2012, 134, 8314-8317. (24) Xamena, F.; Corma, A.; Garcia, H. J. Phys. Chem. C. 2007, 111, 80-85. (25) Rocca, J. D.; Liu, D. M.; Lin, W. B. Acc. Chem. Res. 2011, 44, 957-968. (26) Jia, J.; Xu, F. J.; Long, Z.; Hou X. D.; Sepaniak, M. J. Chem. Commun. 2013, 49, 4670-4672.

19



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(27) Chen, B. L.; Wang, L. B.; Zapata, F.; Qian, G. D.; Lobkovsky, E. B. J. Am. Chem. Soc. 2008, 130, 6718-6719. (28) Xiang, Z. H.; Fang, C. Q.; Leng, S. H.; Cao, D. P. J. Mater. Chem. A. 2014, 2, 7662-7665. (29) Yang, C. X.; Ren, H. B.; Yan, X. P. Anal. Chem. 2013, 85, 7441-7446. (30) Liu, W. S.; Jiao, T. Q.; Li, Y. Z.; Liu, Q. Z.; Tan, M. Y.; Wang, H.; Wang, L. F. J. Am. Chem. Soc. 2004, 126, 2280-2281. (31) Xiao, Y. Q.; Cui, Y. J.; Zheng, Q.; Xiang, S. C.; Qian, G. D.; Chen, B. L. Chem. Commun. 2010, 46, 5503-5505. (32) Zhao, B.; Chen, X. Y.; Chen, Z.; Shi, W.; Cheng, P.; Yan, S. P.; Liao, D. Z. Chem. Commun. 2009, 3113-3115. (33) Zhao, B.; Chen, X. Y.; Cheng, P.; Liao, D. Z.; Yan, S. P.; Jiang, Z. H. J. Am. Chem. Soc. 2004, 126, 15394-15395. (34) Lu, W. G; Jiang, L.; Feng, X. L.; Lu, T. B. Inorg. Chem. 2009, 48, 6997-6999. (35) Yang, Y.; Jiang, F. L.; Chen, L.; Pang, J. D.; Wu, M. Y.; Wan, X. Y.; Pan, J.; Qian J. J.; Hong, M. C. J. Mater. Chem. A. 2015, 3, 13526-13532. (36) Xu, H.; Xiao, Y. Q.; Rao, X. T.; Dou, Z. S.; Li, W. F.; Cui, Y. J.; Wang, Z. Y.; Qian, G. D. J. Alloys Compd. 2011, 509, 2552-2554. (37) Qiu, Y. C.; Deng, H.; Mou, J. X.; Yang, S. H.; Zeller, M.; Batten, S. R.; Wu H. H.; Li, J. Chem. Commun. 2009, 5415-5417. (38) Ma, Y.; Su, H.; Kuang, X.; Li, X. Y.; Zhang, T. T.; Tang, B. Anal. Chem. 2014, 86, 11459-11463.

20


Page 20 of 27

Page 21 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(39) Ahnfeldt, T.; Gunzelmann, D.; Loiseau, T.; Hirsemann, D.; Senker, J.; Férey, G.; Stock, N. Inorg. Chem. 2009, 48, 3057-3064. (40) Cheng, X. Q.; Zhang, A. F.; Hou, K. K.; Liu, M; Wang, Y. X.; Song, C. S.; Zhang G. L.; Guo, X. W. Dalton Trans. 2013, 42, 13698-13705. (41) Sánchez-Sánchez, M.; Getachew, N.; Díaz, K.; Díaz-García, M.; Chebude, Y.; Díaz, I. Green Chem. 2015, 17, 1500-1509. (42) Liang, H.; Liu, L.; Yang, H. X.; Wei, J. J.; Yang, Z. J.; Yang, Y. Z. CrystEngComm. 2011, 13, 2445-2450. (43) Xu, F. J.; Kou, L.; Jia, J.; Hou, X D.; Long, Z.; Wang, S. L. Anal. Chim. Acta. 2013, 804, 240-245. (44) Lin, K. Y. A.; Liu, Y. T.; Chen, S. Y. J. Colloid Interface Sci. 2016, 461, 79-87. (45) Wang, H. M.; Yang, Y. Y.; Zeng, C. H.; Chu, T. S.; Zhua, Y. M. Ng, S. W. Photochem. Photobiol. Sci. 2013, 12, 1700-1706. (46) Jensen, J. N.; Johnson, J. D. Environ. Sci. Technol. 1990, 24, 985-990. (47) Zhai, W. Y.; Wang, C. X.; Yu, P.; Wang, Y. X.; Mao, L. Q. Anal. Chem. 2014, 86, 12206-12213. (48) Jin, S, Y.; Son, H. J.; Farha, O. K.; Wiederrecht, G. P.; Hupp, J. T. J. Am. Chem. Soc. 2013, 135, 955-958. (49) He, H. M.; Song, Y.; Sun, F. X.; Zhao, N. A.; Zhu, G. S. Cryst. Growth Des. 2015, 15, 2033-2038.

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Table 1. Analytical results for the determination of free chlorine in tap water and swimming pool water samples. proposed samples

tap water

method

a

DPD method

a

[Cl] spiked

founda

recoverya

(µM)

(µM)

(%)

(µM)

(µM)

10.3 ± 0.2

10.4 ± 0.1

10.0

20.3 ± 0.3

100 ± 1

10.3 ± 0.2

10.9 ± 0.1

10.0

20.9 ±0.1

101 ± 1

11.9 ± 0.1

11.9 ± 0.3

10.0

21.6 ± 0.4

97 ± 3

swimming pool water for children swimming pool water for adults a

Mean ± SD, n = 3.

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Figure 1. (A) XRD images of the products synthesized with different amounts of urea. (B) FT-IR spectra of (a). NH2-H2BDC and (b). NH2-MIL-53(Al) nanoplates.

Figure 2. (A) Excitation spectra (dash line), emission spectra (solid line), and (B) SEM images of NH2-MIL-53(Al) synthesized with different amounts of urea: (a). 0 mmol, (b). 3 mmol, (c). 6 mmol. The inset shows the corresponding photographs taken under ambient light and 365nm UV light, respectively.

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Figure 3. (A) Effect of pH (PBS) on the fluorescence intensity of NH2-MIL-53(Al) nanoplates (5 mg L−1). (B) Day-to-day fluorescence stability of NH2-MIL-53(Al) nanoplates (5 mg L−1) in PBS (pH=7.4, 2.5 mM).

Figure 4. (A) Fluorescence emission spectra of NH2-MIL-53(Al) nanoplates (5 mg L-1)-based sensor toward various concentrations of NaClO: 0, 0.05, 0.1, 0.5, 0.8, 1, 2, 3, 5, 7, 10, 15, and 20 µM from top to bottom. The inset shows the corresponding photos of NH2-MIL-53(Al) nanoplates in the absence (left) and presence of 10 µM (middle), 20 µM (right) free chlorine under 365 nm UV light. (B) Standard curve (equation: I0-I=217.15C+54.793; R=0.998) for the determination of free chlorine concentration.

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Figure 5. Fluorescence response of NH2-MIL-53(Al) nanoplates (5 mg L−1) in PBS (pH 7.4, 2.5 mM) toward various ions in the absence (blue bar) and presence (purple bar) of 10 µM free chlorine; concentrations of other ions were all 100 µM (except Fe3+ and Hg2+); concentrations of Fe3+ and Hg2+ were 10 µM.

Figure 6. (A) UV-vis response of NH2-MIL-53(Al) nanoplates (5 mg L−1) in PBS (pH 7.4, 2.5 mM) upon addition of different concentrations of free chlorine. (B) Fluorescence emission spectra of NH2-MIL-53(Al) nanoplates upon addition of deionized water, 20 µM MnO4-, 20 µM Cr2O72-, and 20 µM free chlorine.

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Figure 7. (A) Time-resolved fluorescence decay curves of NH2-MIL-53(Al) nanoplates in the absence (black curve) and presence (red curve) of 20 µM free chlorine. (B) The fluorescence quenching of different species with the addition of 20 µM free chlorine.

Scheme 1. Working principle for free chlorine sensing.

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for TOC only

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Amino-Functionalized Metal-Organic Frameworks ... - ACS Publications

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