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Aug 24, 2016 - then mixed with 4.0 g of Sylgard 184 and 0.75 g of curing agent under fast stirring ..... four guest molecules, H2O, CH3CH2OH, THF, and 1,4-.
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Multifunctional Luminescent Porous Organic Polymer for Selectively Detecting Iron Ions and 1,4-Dioxane via Luminescent Turn-off and Turn-on Sensing Dingxuan Ma,† Baiyan Li,*,† Zhonghua Cui,† Kang Liu,‡ Cailing Chen,† Guanghua Li,† Jia Hua,† Benhua Ma,† Zhan Shi,*,† and Shouhua Feng† †

State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012, China ‡ College of Chemistry and Molecular Engineering, Qingdao University of Science and Technology, Qingdao 266042, China S Supporting Information *

ABSTRACT: The first case of selective Fe3+ ions and 1,4-dioxane luminescent sensor based on a porous organic polymer, POP-HT, was synthesized by reaction of tetra(p-aminophenyl)methane and chromophoric 2,5,8-trichloro-s-heptazine. POP-HT displayed prominent fluorescence quenching or enhancement in the presence of Fe3+ ion or 1,4-dioxane. Moreover, an excellent linear relationship was established between luminescent intensity and the corresponding Fe3+ ion or 1,4-dioxane concentration. The mechanisms of luminescence quenching and enhancement were also studied by both experiment and theoretical calculation. The results of this study suggest that POP-HT can work as an effective luminescent indicator for qualitative and quantitative detection of Fe3+ ions and 1,4-dioxane in aqueous solution over other metal ions and organic solvents. KEYWORDS: luminescent sensor, Fe3+ ions, 1,4-dioxane, porous organic polymer, multifunctional



reported so far exhibit mainly organic explosive detection.27−30 Only rare examples have reported the application of POPs in the luminescent detection of metal ions and pollutional organic molecules.31−34 Iron(III) ion is one of the most important elements for all living systems. It plays a crucial role in a variety of vital cell functions such as hemoglobin formation and brain function.35,36 However, excess amounts of Fe3+ ions, over normal permissible limits, can induce serious disorders. The cellular toxicity of Fe3+ ions has been connected with Alzheimer’s and Parkinson’s diseases.37 The considerable importance of Fe3+ ions in biological and environmental systems has made selective sensing of Fe3+ ions over other metal ions a very important research topic for human health. Although some investigations about use of luminescent MOFs to detect Fe3+ ions were reported,38−40 the reports on POPs as luminescent sensors for detecting Fe3+ ions are rather limited.33 In addition, 1,4dioxane, as an important organic solvent, has been widely used in dyes, textile, cosmetic, and paper industries.41,42 But 1,4dioxane has been categorized as carcinogenic hazardous solvent and the U.S. Environmental Protection Agency has classified 1,4-dioxane in group B2.43 Therefore, the detection of 1,4dioxane has become more significant in industrial production

INTRODUCTION Sensing and detection of hazardous substances plays an important role in life sciences and environmental sciences. Among various analytical techniques, fluorometric methods have gained much attention because of their significant advantages, that is, high sensitivity and facilitated manipulation and detection.1,2 The past decade has witnessed fast growth of several classes of luminescent porous materials. Among them, luminescent metal−organic frameworks (MOFs) have been recognized as a kind of sensing material for guest detection.3−10 However, the higher density compared to pure organic materials due to the presence of metals and the limited physicochemical stability against moisture and other harsh conditions are disadvantages in practical applications. Recently, porous organic polymers (POPs),11−13 as organic analogues of MOFs, have exhibited rapid progress and have been explored as a new class of functional solid materials for applications in gas storage,14−17 separation,18−20 catalysis,21−23 and energy applications.24−26 Compared with MOFs, POPs are assembled via strong covalent bonds between different organic building blocks. Therefore, POPs usually exhibit low framework density due to the use of light elements (C, H, N, O, and B), low toxicity (no heavy metal ions), excellent porosity, and good physicochemical stability. Up to now, the primary focus of most POPs studies has been on gas storage and separation.14−20 The optical properties of POPs and their potential applications in sensing are seldom reported. The luminescent POP sensors © 2016 American Chemical Society

Received: June 20, 2016 Accepted: August 24, 2016 Published: August 24, 2016 24097

DOI: 10.1021/acsami.6b07470 ACS Appl. Mater. Interfaces 2016, 8, 24097−24103

Research Article

ACS Applied Materials & Interfaces and daily life. Only one luminescent MOF material has been reported as a probe for sensing 1,4-dioxane.6 However, no relevant studies on POPs as luminescent sensors for detecting 1,4-dioxane have been reported. In this paper, by selecting the ideal building blocks and conducting the appropriate chemical reaction, we synthesized for the first time a novel multifunctional luminescent porous organic polymer, named POP-HT, which not only exhibits the function of selectively, qualitatively, and quantitatively recognizing Fe3+ ions over other metal ions by significant luminescence quenching but also can detect 1,4-dioxane by prominent luminescence enhancement (Figure 1). To the best

Figure 2. FT-IR spectra of tetra(p-aminophenyl)methane (black), 2,5,8-trichloro-s-heptazine (red), and POP-HT (blue).

by 13C solid-state NMR spectroscopy. POP-HT shows a clear NMR signal at 67.8 ppm, corresponding to the sp3 carbon, and a series of close peaks in the range of 100−200 ppm, which are assigned to the sp2 carbons in the benzene rings and s-heptazine (Figure 3). Powder X-ray diffraction (PXRD) demonstrated

Figure 1. Synthesis of POP-HT.44

of our knowledge, it is the first case of a POP material used as a multifunctional sensor for Fe3+ ions and 1,4-dioxane detection. In addition, the luminescence quenching and enhancement mechanisms were also studied by both experiment and theoretical calculation. The results indicate that these luminescent characteristics are attributed to the interactions between guest molecules and the POP framework.



EXPERIMENTAL SECTION

Synthesis of POP-HT. Tetra(p-aminophenyl)methane (152 mg, 0.3 mmol), dimethylacetamide (DMA; 10 mL), and N,N-diisopropylethylamine (DIPEA; 0.2 mL) were mixed well under nitrogen. After the resulting mixture was cooled to 0 °C, 2 mL of 2,5,8-trichloro-sheptazine (86 mg, 0.4 mmol) solution in DMA was added dropwise into the mixture under vigorous stirring. Then the reaction solution was warmed and heated at 60 °C for 48 h. After removal of the solvent by centrifugation, the product was extracted with tetrahydrofuran (THF) in a Soxhlet apparatus 48 h. Synthesis of Fluorescent Test Film. POP-HT (5 mg) was dispersed in 0.25 mL of glycol by sonication. This glycol solution was then mixed with 4.0 g of Sylgard 184 and 0.75 g of curing agent under fast stirring and cross-linked at 70 °C for 2 h to produce the fluorescent film.



RESULTS AND DISCUSSION Characterization. Successful preparation of POP-HT was verified by Fourier transform infrared (FT-IR) spectroscopy and 13C solid-state NMR. As shown in Figure 2, the disappearance of N−H bond stretching vibration at 3396 cm−1 clearly indicates the substitution of amine groups in tetra(p-aminophenyl)methane. Meanwhile, the absence of the characteristic C−Cl stretching vibration at 942 cm−1 confirms that all chlorine atoms were substituted. The peak at 1650 cm−1 is assigned to the CN bond, proving the existence of s-heptazine in the framework. Further support for the local structures of POP-HT was given

Figure 3. (a) 13C solid-state NMR spectroscopy for POP-HT. (b) Structure of POP-HT.

four diffraction signals, suggesting a low degree of crystalline order of the POP-HT solid (Figure S1). Scanning and transmission electron microscopy (SEM and TEM) were performed to probe the morphology of POP-HT. As shown in Figure S2, POP-HT powders are composed of agglomerates of micro- and nanoparticles. The thermal stability of POP-HT was 24098

DOI: 10.1021/acsami.6b07470 ACS Appl. Mater. Interfaces 2016, 8, 24097−24103

Research Article

ACS Applied Materials & Interfaces assessed by thermogravimetric analysis (TGA), which reveals that it can be stable up to 250 °C (Figure S3). Porosity of POP-HT. To investigate the porosity of POPHT, we performed gas sorption experiments. As shown in Figure 4, a CO2 sorption experiment on POP-HT at 198 K

Figure 5. (a) Relative intensities of POP-HT dispersed in acidic aqueous solutions containing different metal ions (0.01 mol·L−1) upon excitation at 437 nm. (b) Photograph of POP-HT in acidic aqueous solutions containing different metal ions (0.01 mol·L−1) under the UV lamp (Ex at 365 nm).

Figure 4. CO2 sorption isotherms of POP-HT at 198 K.

reveals highly reproducible typical type I gas adsorption isotherms, which confirms the existence of micropores in POP-HT. The Brunauer−Emmett−Teller (BET) surface area of POP-HT is 414.1 m2·g−1. Pore-size distributions based on a density functional theory (DFT) model show that the pore width of this POP material was 0.41 nm (Figures S4 and S5). Luminescence Response of Fe3+ Ions in N,N-Dimethylformamide and Aqueous Solution. The luminescence spectra of POP-HT are shown in Figure S6. A H2O suspension of POP-HT shows emission at 478 nm upon excitation at 437 nm, attributing to the rich π-system of s-heptazine, which could act as the source of luminescence. The luminescence property and the presence of free Lewis base sites within the pores encouraged us to study its potential application as a metal ion sensor. The as-synthesized POP-HT was immersed in an extradry N,N-dimethylformamide (DMF) solution or an acidic aqueous solution of 0.01 mol·L−1 MClx (M = K+, Na+, Mg2+, Ca2+, Mn2+, Al3+, Zn2+, Cd2+, Ni2+, Fe2+, Co2+, Cr3+, Cu2+, or Fe3+) to form metal ion-incorporated M@POP-HT for luminescence studies. POP-HT shows almost the same sensitivity for Fe3+ ions in an extra-dry DMF solution (Figure S7) or an acidic aqueous solution. The photoluminescence properties of M@POP-HT in acidic aqueous solution are recorded and compared in Figure 5. Interestingly, the luminescence intensity of M@POP-HT is heavily dependent on the type of metal ion, providing an opportunity for selective sensing. For example, alkaline metal ions, alkaline-earth metal ions, and transition metal ions with filled d shell (Zn2+ and Cd2+) have negligible effects on the luminescence intensity. But varying degrees of luminescence quenching are observed with transition metal ions like Ni2+, Fe2+, Co2+, Cr3+, Cu2+, and Fe3+. The addition of Ni2+ and Fe2+ ions led to less than 10% reduction of the original luminescence intensity. Co2+ and Cr3+ ions make the luminescence intensity decrease by about 25%. The luminescence intensity is about half the original when Cu2+ ions are involved. Compared with other metal ions, Fe3+ ions exhibit significant luminescence quenching toward POP-HT. There is almost no luminescence emission detected for Fe3+@ POP-HT within a very short period, resulting in a 44-fold decrease in luminescence intensity. Thus, POP-HT shows extra-high selectivity for Fe3+ ions over other metal ions. We

attribute the significant luminescence quenching of POP-HT to the strong bonding of Fe3+ ions toward free heterocyclic nitrogen atoms. To explore the potential of such a highly selective and sensitive POP sensor for practical application in life sciences and environmental sciences, concentration-dependent luminescence tests were carried out in acidic aqueous solution with different concentration of FeCl3. As demonstrated in Figure 6,

Figure 6. Concentration-dependent luminescence intensity of Fe3+@ POP-HT upon addition of different contents of Fe3+ in acidic aqueous solution (Ex at 437 nm).

the luminescence intensity of POP-HT decreased dramatically with increasing Fe3+ ion concentration from 5 to 600 ppm. It is worth noting that the luminescence intensity of POP-HT exhibits excellent linear dependency on Fe3+ ion concentration (correlation coefficient R2 = 0.992 05). Some reported selective Fe3+ ion luminescence MOF sensors, such as Eu-BTPCA,38 UMCM-1-NH2,39 and Eu-BTMIPA,40 show only the ability to qualitatively detect the existence of Fe3+ ions, while quantitative detection of Fe3+ in these luminescence MOF materials has not been obtained. In addition, the sensing experiments based on 24099

DOI: 10.1021/acsami.6b07470 ACS Appl. Mater. Interfaces 2016, 8, 24097−24103

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ACS Applied Materials & Interfaces these MOF materials can only be performed in nonaqueous medium due to possible instability of MOF materials or probable luminescence quenching effect of water on rare-earth ion-based MOFs.38−40 The limit of detection can be down to 5 ppm, suggesting that this luminescent POP sensor can be used for detecting the concentration of Fe3+ ions with a very sensitive optical signal. In order to make the detection simple and portable, we developed a fluorescent test film for detection of Fe3+ in aqueous solution. As shown in Figure 7, under the irradiation of

Figure 7. Photograph of POP-HT test film under natural light and UV lamp (Ex at 365 nm).

UV light at 365 nm, the test film showed bright aquamarine, and it changed to black after the test film was immersed in FeCl3 acidic aqueous solution. The naked eye can distinguish the existence of Fe3+ ions. Mechanism Research on Luminescence Quenching. In order to prove that the luminescence quenching is caused by interactions between Fe3+ ions and POP-HT framework, rather than the Fe3+ ion solution absorbing the emission light of POPHT, we performed a UV−vis absorption study of Fe3+ ions in acidic solution. As shown in Figure S8, the absorption spectrum shows absorption at 250 and 340 nm. The absorption band is inconsistent with the emission light of POP-HT (478 nm). To elucidate the possible mechanism for such heavy luminescence quenching effect by Fe3+ ions, N 1s X-ray photoelectron spectorscopy (XPS) studies and theoretical calculations were carried out on POP-HT and some metal ions incorporated M@ POP-HT. As shown in Figure 8a, the N 1s peak of heterocyclic nitrogen atoms is observed at 399.18 eV in metal ion-free POPHT. Mg2+, Fe2+, Mn2+, and Na+ ions have negligible interaction with the nitrogen atoms, with no shift being observed for their N 1s peaks in XPS spectra. Cu2+ ions make the bonding energy of N 1s shift to 399.41 eV, which may be caused by a weak coordination interaction between Cu2+ ions and POP-HT. This result is also consistent with the luminescent quenching effect of Cu2+ compared with other metal ions. Compared with other M@POP-HT, the XPS spectra of nitrogen atoms in POP-HT have the most obvious shift after the introduction of Fe3+ ions. The bonding energy of N 1s in Fe3+@POP-HT shifted to 400.07 from 399.18 eV, with 0.89 eV of upshift compared with free POP-HT, indicating the existence of very strong interactions between Fe3+ ions and nitrogen atom in POPHT. Therefore, we believe that the mechanism of Fe3+ ionselective luminescent detection may be due to the stronger interactions between Fe3+ ions and Lewis base sites in POP-HT framework compared with other metal ions. In order to further confirm the possible bonding interaction sites between Fe3+ ions and nitrogen atoms in POP-HT, we calculated the bond distance and interaction energy of Fe3+ ions and different nitrogen atoms at B3LYP/def2-TZVPP level by use of the Gaussian03 package. As shown in Figure 8b,c, the Fe···N

Figure 8. (a) N 1s XPS spectra of the original POP-HT and M@POPHT. (b, c) Preferential Fe3+ ion bonding sites and the corresponding bonding energies obtained from theoretical calculations (C, gray; N, blue; H, white; Fe, purple; Cl, green).

distance of s-heptazine groups (2.146 Å) is shorter than the Fe···N distance of NH groups (2.249 Å). The interaction energy of bonding Fe3+ ions with nitrogen atoms of s-heptazine groups was calculated to be approximately −35.1 kcal·mol−1 more favorable than bonding with nitrogen atoms of NH groups (−15.5 kcal·mol−1). The calculation results provide further insight into the observed interaction between Fe3+ ions and nitrogen atoms of POP-HT. The XPS experimental data and theoretical computational results demonstrate that the marked quenching is mostly due to the change in electrons of sheptazine groups after bonding of Fe3+ ions via Lewis acid− base interactions. Luminescence Response of 1,4-Dioxane. In order to study the potential application of POP-HT as a luminescence sensor for detecting 1,4-dioxane, POP-HT was dispersed in some common organic solvents that can be miscible with aqueous solution, such as methanol, ethanol, glycol, methyl cyanide, acetone, THF, DMF, and 1,4-dioxane. Among these solvents, the most explicit luminescence enhancement was observed for 1,4-dioxane, which induced a luminescence intensity of 124% enhancement. With the naked eye, we can see the obvious luminescence intensity change of POP-HT in aqueous solution and 1,4-dioxane (Figure 9). Although 1,4-dioxane is harmful to the environment and human beings, it is still a useful chemical material, which can be widely used as a solvent and precursor in manufacturing production.41,42 One of the most successful and economical preparation routes for synthesizing 1,4-dioxane is the condensation reaction of glycol.45 So sensing the mixture of glycol and 1,4-dioxane is quite useful in practical application. As mentioned above, compared with the other solvents as well as glycol, POP-HT exhibits the most remarkable luminescence enhancement in 1,4-dioxane. This obvious luminescence 24100

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Here, the H atom of the imino group in POP-HT was used as H-bond donor to react with the O atom of guest molecules as a H-bond acceptor. In order to prove our conjecture, we calculated the H-bond distance and interaction energy of POP-HT and four different guest molecules at the M06-2X/631G (d,p) level by use of the G09 package (Figure 11). For the

Figure 9. Emission spectra of POP-HT in different solvents (Ex at 437 nm) and photographs of POP-HT in aqueous solution and 1,4dioxane under the UV lamp (Ex at 365 nm).

change prompts us to consider the potential property of POPHT to monitor the ratio of 1,4-dioxane in glycol as a luminescence sensor. The suspension-state photoluminescence spectra of POP-HT in 1,4-dioxane, glycol, and their mixtures with different volume ratios were recorded. The luminescence intensity of POP-HT gradually increases when the volume ratio (φ) varies from 0 to 1. Excellent linear dependence of luminescence intensities on the volume ratio of 1,4-dioxane in glycol were observed, which indicate that POP-HT is an excellent luminescent sensor for quantitative analysis of mixtures of 1,4-dioxane and glycol over a large volume ratio range (Figure 10).

Figure 11. Preferential H-bond distance and corresponding bonding energies obtained from theoretical calculations: (a) H2O, (b) CH3CH2OH, (c) THF, and (d) 1,4-dioxane (C, gray; N, blue; H, white; O, red).

Figure 10. (a) Schematic diagram of the condensation of glycol to 1,4dioxane. (b) Luminescence intensity of POP-HT recorded in different volume ratios (φ) of 1,4-dioxane in glycol from 0 to 1.

four guest molecules, H2O, CH3CH2OH, THF, and 1,4dioxane, the H-bond distances are similar. Among them, the Hbond distance of 1,4-dioxane is not the shortest, which could be because 1,4-dioxane has a large molecular weight and chair conformation, which limit its molecule mobility compared with other small-mass guest molecules. Nonetheless, for 1,4-dioxane the interaction bonding energy of H-bond was calculated to be −16.5 kcal/mol, significantly larger than the other three guest molecules. On the basis of overall consideration, we believe that the H-bond interaction between the O atom of 1,4-dioxane and the H atom of imino group in POP-HT is stronger than those of other guest molecules. The strong H-bond interaction between 1,4-dioxane and POP-HT framework restricted molecular rotation, which reduced the possibility of nonradiative decay and resulted in luminescence enhancement.46,47 Cyclical Ability of POP-HT. Regeneration is an important issue for a sensor. The luminescence of POP-HT can be recovered by simple centrifugation and then rinsed with H2O and THF, respectively, which almost regained the initial luminescence intensity of the fresh-made sample (Figure 12).

Mechanism Research on Luminescence Enhancement. To understand the origin of POP-HT’s high selectivity toward 1,4-dioxane, the mechanism of luminescence enhancement was investigated. Generally, the change of luminescence intensity is based on the interaction between guest molecules and the framework. From comparison of molecular structures of the different solvents and their effect on luminescence intensity, we speculated that the hydrogen-bond (H-bond) interactions between guest molecules and the framework are the main reasons for guest-dependent luminescence change.21

Figure 12. Cycling tests of POP-HT: (a) Fe3+ ions and (b) 1,4dioxane. 24101

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(6) Zhou, J.; Li, H.; Zhang, H.; Li, H.; Shi, W.; Cheng, P. A Bimetallic Lanthanide Metal−Organic Material as a Self-Calibrating ColorGradient Luminescent Sensor. Adv. Mater. 2015, 27, 7072−7077. (7) Hu, Z.; Deibert, B. J.; Li, J. Luminescent Metal−Organic Frameworks for Chemical Sensing and Explosive Detection. Chem. Soc. Rev. 2014, 43, 5815−5840. (8) Zhao, S.-N.; Song, X.-Z.; Zhu, M.; Meng, X.; Wu, L.-L.; Feng, J.; Song, S.-Y.; Zhang, H.-J. Encapsulation of LnIII Ions/Dyes within a Microporous Anionic MOF by Post-synthetic Ionic Exchange Serving as a LnIII Ion Probe and Two-Color Luminescent Sensors. Chem. - Eur. J. 2015, 21, 9748−9752. (9) Zhao, S.-N.; Li, L.-J.; Song, X.-Z.; Zhu, M.; Hao, Z.-M.; Meng, X.; Wu, L.-L.; Feng, J.; Song, S.-Y; Wang, C.; Zhang, H.-J. Lanthanide Ion Codoped Emitters for Tailoring Emission Trajectory and Temperature Sensing. Adv. Funct. Mater. 2015, 25, 1463−1469. (10) Song, X.-Z.; Song, S.-Y.; Zhao, S.-N.; Hao, Z.-M.; Zhu, M.; Meng, X.; Wu, L.-L.; Zhang, H.-J. Single-Crystal-to-Single-Crystal Transformation of a Europium(III) Metal−Organic Framework Producing a Multi-responsive Luminescent Sensor. Adv. Funct. Mater. 2014, 24, 4034−4041. (11) Zhang, X.; Lu, J.; Zhang, J. Porosity Enhancement of Carbazolic Porous Organic Frameworks Using Dendritic Building Blocks for Gas Storage and Separation. Chem. Mater. 2014, 26, 4023−4029. (12) Thomas, A. Functional Materials: From Hard to Soft Porous Frameworks. Angew. Chem., Int. Ed. 2010, 49, 8328−8344. (13) Zou, X.; Ren, H.; Zhu, G. Topology-Directed Design of Porous Organic Frameworks and Their Advanced Applications. Chem. Commun. 2013, 49, 3925−3936. (14) Zhu, Y.; Long, H.; Zhang, W. Imine-Linked Porous Polymer Frameworks with High Small Gas (H2, CO2, CH4, C2H2) Uptake and CO2/N2 Selectivity. Chem. Mater. 2013, 25, 1630−1635. (15) Lu, W.; Sculley, J. P.; Yuan, D.; Krishna, R.; Wei, Z.; Zhou, H.C. Polyamine-Tethered Porous Polymer Networks for Carbon Dioxide Capture from Flue Gas. Angew. Chem. 2012, 124, 7598−7602. (16) Xie, L.-H.; Suh, M. P. High CO2-Capture Ability of a Porous Organic Polymer Bifunctionalized with Carboxy and Triazole Groups. Chem. - Eur. J. 2013, 19, 11590−11597. (17) Dawson, R.; Adams, D. J.; Cooper, A. I. Chemical Tuning of CO2 Sorption in Robust Nanoporous Organic Polymers. Chem. Sci. 2011, 2, 1173−1177. (18) Lau, C. H.; Konstas, K.; Thornton, A. W.; Liu, A. C. Y.; Mudie, S.; Kennedy, D. F.; Howard, S. C.; Hill, A. J.; Hill, M. R. GasSeparation Membranes Loaded with Porous Aromatic Frameworks that Improve with Age. Angew. Chem., Int. Ed. 2015, 54, 2669−2673. (19) Saleh, M.; Lee, H. M.; Kemp, K. C.; Kim, K. S. Highly Stable CO2/N2 and CO2/CH4 Selectivity in Hyper-Cross-Linked Heterocyclic Porous Polymers. ACS Appl. Mater. Interfaces 2014, 6, 7325− 7333. (20) Meng, L.; Zou, X.; Guo, S.; Ma, H.; Zhao, Y.; Zhu, G. SelfSupported Fibrous Porous Aromatic Membranes for Efficient CO2/N2 Separations. ACS Appl. Mater. Interfaces 2015, 7, 15561−15569. (21) Totten, R. K.; Weston, M. H.; Park, J. K.; Farha, O. K.; Hupp, J. T.; Nguyen, S. T. Catalytic Solvolytic and Hydrolytic Degradation of Toxic Methyl Paraoxon with La(catecholate)-Functionalized Porous Organic Polymers. ACS Catal. 2013, 3, 1454−1459. (22) Zhang, Y.; Riduan, S. N. Functional Porous Organic Polymers for Heterogeneous Catalysis. Chem. Soc. Rev. 2012, 41, 2083−2094. (23) Ding, S.-Y.; Gao, J.; Wang, Q.; Zhang, Y.; Song, W.-G.; Su, C.Y.; Wang, W. Construction of Covalent Organic Framework for Catalysis: Pd/COF-LZU1 in Suzuki-Miyaura Coupling Reaction. J. Am. Chem. Soc. 2011, 133, 19816−19822. (24) Kou, Y.; Xu, Y.; Guo, Z.; Jiang, D. Supercapacitive Energy Storage and Electric Power Supply Using an Aza-Fused π-Conjugated Microporous Framework. Angew. Chem., Int. Ed. 2011, 50, 8753−8757. (25) Hao, L.; Ning, J.; Luo, B.; Wang, B.; Zhang, Y.; Tang, Z.; Yang, J.; Thomas, A.; Zhi, L. Structural Evolution of 2D Microporous Covalent Triazine-Based Framework toward the Study of HighPerformance Supercapacitors. J. Am. Chem. Soc. 2015, 137, 219−225.

Similar decrease or increase in the degree of luminescence intensity was observed during each cycling test. Because of the excellent porosity and good stability, POP-HT can be used repetitively, and a significant deterioration in the sensitivity and response does not occur.



CONCLUSIONS In summary, we have successfully designed and synthesized for the first time a multifunctional luminescent POP sensor, POPHT, which possesses high sensitivity and selectivity for Fe3+ ions and 1,4-dioxane through luminescence quenching and enhancement. In particular, the luminescent POP sensor exhibits the ability to detect the concentration of Fe3+ ions and 1,4-dioxane with excellent linear correlation between luminescence intensity and their concentration. These results indicate that POP-HT can be applied as a potential functional luminescent sensing material for qualitatively and quantitatively detecting Fe 3+ ions and 1,4-dioxane. In addition, the luminescent sensing mechanism was also studied by both experiment and theoretical calculations. Our investigation thus not only develops POP as a new multifunctional material platform for luminescent sensors but also provides a new route and further insights for the design and synthesis of Fe3+ ions and 1,4-dioxane sensing materials.



ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.6b07470. Additional experimental details and eight figures showing X-ray diffraction patterns, SEM and TEM images, TGA data, pore size distribution, BET plots, excitation and emission spectra, luminescence intensity comparison, and UV−vis absorption spectrum (PDF)



AUTHOR INFORMATION

Corresponding Authors

*(B.L.) E-mail [email protected]. *(Z.S.) E-mail [email protected]. Notes

The authors declare no competing financial interest.



ACKNOWLEDGMENTS This work was supported by the Foundation of the National Natural Science Foundation of China (21371069) and the National High Technology Research and Development Program (863 program) of China ( 2013AA031702).



REFERENCES

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DOI: 10.1021/acsami.6b07470 ACS Appl. Mater. Interfaces 2016, 8, 24097−24103