Novel Pyrene-Based Anionic Metal–Organic Framework for Efficient

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Novel Pyrene-Based Anionic Metal−Organic Framework for Efficient Organic Dye Elimination Nian Zhao,† Fuxing Sun,*,† Ning Zhang,† and Guangshan Zhu*,‡,§ †

State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012, China ‡ Key Laboratory of Polyoxometalate Science of the Ministry of Education, Faculty of Chemistry, Northeast Normal University, Changchun 130024, China § Key Laboratory for Micro-Nano Energy Storage and Conversion Materials of Henan Province, Institute of Surface Micro and Nano Materials, Xuchang University, Henan 461000, P. R. China S Supporting Information *

ABSTRACT: A novel anionic metal−organic framework, JUC-138, constructed by In(III) and a pyrene-based linker, H8TIAPy (H8TIAPy = 1,3,6,8tetrakis(3,5-isophthalic acid)pyrene), has been synthesized by solvothermal reaction successfully. In JUC-138, only four carbonyl groups in each ligand connect to In3+ ions, while the others remain uncoordinated. However, each In3+ connects to four carbonyl groups in a bidentate chelate style, resulting in the formation of 2D square sheets in JUC-138. The 2D sheets interact with adjacent layers through the O−H···O hydrogen bonds between the uncoordinated carboxyl groups, thus generating the whole 3D supramolecular structure of JUC-138. UV−vis tests show the energy gap Eg of JUC-138 is 3.34 eV, indicating the semiconductor nature of JUC-138. In addition, JUC-138 shows good photocatalytic activity in Azure B (AB) decolorization and could decompose 90% AB within 4 h. This photocatalytic property makes JUC-138 promising in environment governance.

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INTRODUCTION Nowadays, environment protection has been a consensus of governments and scientists all over the world, and billions of expenditures were cast to treat the pollution every year, such as heavy metal pollution,1−3 organic wastewater pollution,4−7 nuclear radiation pollution,8−10 and so on. Among all these pollutions, organic dyes are one of the major pollutants in water because of their long lifetime and wide distribution. In order to treat the organic dye wastewater, numerous strategies have been proposed, including trapping the organic molecules in the pores of porous materials,11−14 decomposing organic molecules by electrolysis method,15−18 and photocatalytic degradation.19−22 Among these methods, photocatalytic degradation is both an efficient and inexpensive way to decompose organic dyes into harmless and environment friendly products. Metal−organic frameworks (MOFs) are a new class of crystalline materials that are constructed by multifunctional organic ligands as linkers and metal/metal clusters as nodes. Owing to their delicate and various structures, controllable pore size, elegant topologies, high surface area, MOFs have attracted tremendous attentions in the fields of gas storage,23−26 separation,27−29 detection and sensing,30−32 catalysis,33−35 and so on. Recently, many photoactive MOFs behaving as semiconductors have been used to treat organic dye pollutants.36−39 Comparing to other traditional inorganic photocatalysts such as ZnO, WO3, and TiO2, photoactive © 2017 American Chemical Society

MOFs have some incomparable advantages including high BET surface and tunable pore size, which can facilitate the diffusion and enrichment of the pollutants; vast exposed metal sites in favor of contacting with adsorbates; and versatile synthesis strategies that allow to synthesize samples with different particle sizes and morphologies. Herein, we report a novel anionic MOF material, JUC-138, constructed by In(III) and a pyrene-based linker, H8TIAPy (H8TIAPy = 1,3,6,8-tetrakis(3,5-isophthalic acid)pyrene) (Scheme 1). The assembly of ligand H8TIAPy with In3+ forms a 2D square sheet. Among the adjacent sheets, the uncoordinated carbonyl groups interact with each other by O− H···O hydrogen bonds, thus generating the whole 3D supramolecular structure. UV−vis test gives the energy gap of JUC-138 of 3.34 eV, located in the semiconductor interval. In order to test the photoactivity of JUC-138, we choose Azure B (AB) as organic pollutant to conduct photocatalytic degradation experiment. Decolorizing AB about 90% within 4 h confirms the good photocatalytic performance of JUC-138 and makes it promising for organic pollutant treatment. Received: December 20, 2016 Revised: March 21, 2017 Published: April 13, 2017 2453

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hydrogen bonds and each In3+ ion connected to four ligands. So each ligand could be simplified as a 6-connected node and each In3+ as a 4-connected node; thus, the whole framework could be simplified as a (4, 6)-connected tcj net (Figure 1e). The point symbol for net was {44·610·8}{44·62}. Thermogravimetric analyses (TGA) showed that JUC-138 started to decompose around 400 °C and the weight loss before 350 °C could be mainly attributed to the guest molecules in the channels (Figure S4). Phase purity could be confirmed by the similarity between the simulated and experimental X-ray diffraction patterns (Figure S3). The solid-state UV−vis diffuse-reflection spectrum of JUC138 was measured at room temperature. The energy gap Eg obtained by extrapolation of the linear portion of the absorption edges was estimated to be 3.34 eV according to the Kubelka−Munk function (Figure S6), which indicated the semiconductor nature of JUC-138.42 Here, we chose Azure B (AB) for photocatalytic experiments which was a common organic dye. Considering the anionic framework character of JUC-138 and the cationic character of AB, we soaked the JUC138 crystals in DMF solution of AB for 2 h with stirring in darkness prior to photocatalytic tests. The UV−vis absorption kept constant, indicating the equilibration of adsorption of AB (Figure S7). We used a 400 W high pressure mercury lamp as a UV light source and kept the distance between the liquid surface and the lamp 10 cm. The UV−vis adsorption spectra of AB were monitored every 1 h. During the first hour, AB had been degraded about 30%. After UV irradiation for 4 h, AB had been degraded about 90% (Figure 2a) and the solution gradually became colorless (Figure 2c). However, when no catalyst was added, AB could only be decomposed about 30% within 4 h under UV irradiation (Figure 2b, Figure S8). Moreover, we reused JUC-138 for the other four catalytic cycles, and PXRD confirmed JUC-138 could still maintain good crystallinity, indicating good catalytic reproducibility (Figures S9 and S10). Good catalytic performance and great catalytic

Scheme 1. Structure of H8TIAPy Ligand

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RESULTS AND DISCUSSION The synthesis of H8TIAPy is according to our previous work.40,41 The reaction of H8TIAPy with In(NO3)3 in DMF at 120 °C for 3 days gave the yellow rhombic crystals of JUC-138 formulated as [(CH3)2(NH2)+][In(H4TIAPy)]·(DMF)5. Single crystal X-ray diffraction showed that JUC-138 crystallized in the monoclinic space group C2/c with the lattice parameters a = 27.853 Å, b = 11.653 Å, c = 33.523 Å and β = 99.14°. In JUC138, each In3+ connected to four ligands in a bidentate chelate style (Figure 1a). Each ligand connected to four In3+, and of all the eight carbonyl groups in the ligand, only four participated in coordinating, while the others kept uncoordinated (Figure 1b), thus forming a 2D anionic square sheet (Figure 1c). The sheets stacked along the [100] direction. The uncoordinated carbonyl groups in each sheet interacted with each other by the O−H··· O hydrogen bonds (O2−H1O···O7 = 2.45 Å; ∠DHA = 171.8°), generating a 3D supramolecular structure (Figure 1d, Figure S2). The attempts for locating the highly disordered NH2(CH3)2+ ions embedded among the sheets failed and had been squeezed by PLATON. The solvents accessible volume was as high as 72.5%. The topology analysis of JUC-138 was conducted by TOPOS 4.0 program. Each ligand connected to four In3+ ions by coordinate bonds and other two ligands by

Figure 1. (a) Coordination style of In3+ in JUC-138. (b) Coordination style of H8TIAPy in JUC-138. (c) Two-dimensional square sheet from the direction [100] of JUC-138. (d) Hydrogen bonds constructed 3D supramolecular structure. (e) The tcj topology of JUC-138. Gray atoms are C, red are O, and green are In. 2454

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Figure 2. (a) Time-dependent UV−vis spectra of AB solution with JUC-138 as catalyst. (b) Comparison of the degradation rates of AB with and without JUC-138. (c) Photographs of photodegradation of AB solution. isotropic placement parameters set to 1.2 × Ueq of the attached atoms. In the structure, free solvent molecules and NH2(CH3)2+ cations were highly disordered, and attempts to locate and refine the solvent peaks were not successful. Contributions to scattering due to these solvent molecules were removed using the SQUEEZE routine of PLATON, and the structures were then refined again using the data generated. The contents of the solvent region are not represented in the unit cell contents in the crystal data. Crystallographic data and structural refinements for JUC-138 are summarized in Table S1 (Supporting Information).

reproducibility made JUC-138 alternative for organic pollutants treatment.

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CONCLUSIONS In conclusion, a novel anionic In-MOF, JUC-138, constructed by a pyrene-based ligand, H8TIAPy, with a (4,6)-connected tcj net has been investigated. The coordination of the ligand and In3+ forms a 2D square sheet. The uncoordinated carbonyl groups in the ligand in each sheet interact with each other by O−H···O hydrogen bonds, generating a 3D supramolecular structure. UV−vis diffuse-reflection test confirms the semiconductor nature of JUC-138. After 4 h’ UV irradiation, JUC138 can catalytic the photodegradation of AB for about 90%, while AB only decomposes 30% without JUC-138 as catalyst. Good catalytic performance and great catalytic reproducibility make JUC-138 promising for organic pollutants treatment.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.cgd.6b01864. Crystal structure representation of JUC-138, PXRD and UV−vis spectra, crystal structure data, and CIF of JUC138 (PDF)

EXPERIMENTAL SECTION

Materials and Methods. All the reagents and solvents for the syntheses were purchased from commercial sources and used as received, except for H8TIAPy, which was synthesized according to our previous work. Powder X-ray diffraction (PXRD) measurements were performed on a Rigaku DMAX 2550 diffractometer at 50 kV, 20 mA for Cu Kα (λ = 1.5418 Å). Thermogravimetric analysis (TGA) was performed on a Pekin-Elmer thermogravimetric analyzer with a heating rate of 5 °C per minute. UV−vis spectroscopy was performed with a U-4200 spectrophotometer. Synthesis of JUC-138. H8TIAPy (10 mg, 0.0058 mmol), In(NO3)3 (20 mg, 0.0667 mmol), DMF (5 mL), and 3 M HCl (0.3 mL) were mixed in a 15 mL autoclave, and heated to 120 °C for 72 h and then cooled to room temperature. Yellow rhombic crystals were collected and air-dried (yield: 40% based on H8TIAPy). Elemental analysis for [(NH2)(CH3)2+][In(H4TIAPy)] = C50H30NO16In: calculated (%), C, 59.11; H, 2.96; N, 1.38; found (%): C, 60.22; H, 3.23; N, 1.40. Single Crystal X-ray Crystallography. Single crystal X-ray diffraction data were collected using a Bruker-AXS SMART APEX2 CCD diffractometer (Mo Kα, λ = 0.71073 Å). Indexing was performed using APEX2 (Difference Vectors method). Data integration and reduction were performed using SaintPlus. Absorption correction was performed by multiscan method implemented in SADABS. Space groups were determined using XPREP implemented in APEX2. Structures were solved using SHELXL-2014 (direct methods) and refined using SHELXL-2014 (full-matrix least-squares on F2) with anisotropic displacement contained in APEX2 program packages. Hydrogen atoms on carbon were calculated in ideal positions with

Accession Codes

CCDC 1520657 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_ [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Guangshan Zhu: 0000-0001-6841-737X Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank the financial support from National Basic Research Program of China (973 Program, grant no. 2014CB931804) and NSFC (grant no. 21501064 & 21531003). 2455

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