from Aqueous Solution by a Highly Stable Hydrogen-Bonded Metal

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Efficient and Selective Removal of Copper(II) from Aqueous Solution by a Highly Stable H-Bonded Metal-Organic Framework Caixia Yu, ZhiChao Shao, Lei-Lei Liu, and Hongwei Hou Cryst. Growth Des., Just Accepted Manuscript • Publication Date (Web): 19 Apr 2018 Downloaded from http://pubs.acs.org on April 19, 2018

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Crystal Growth & Design

Efficient and Selective Removal of Copper(II) from Aqueous Solution by a Highly Stable H-Bonded Metal-Organic Framework Caixia Yu,†,‡ Zhichao Shao,† Leilei Liu,*,‡ and Hongwei Hou*,†

†

College of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou 450001, P. R.

China ‡

Henan Key Laboratory of New Optoelectronic Functional Materials, College of Chemistry and

Chemical Engineering, Anyang Normal University, Anyang 455000, P. R. China

* To whom correspondence should be addressed. e-mail: [email protected] (H. Hou) †

Zhengzhou University

‡

Anyang Normal University

1

ACS Paragon Plus Environment

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ABSTRACT: Copper(II) is an indispensable element in nature, while exposure to excessive Cu2+ will potentially cause health issues. It is imperative to develop new strategies for the efficient Cu2+ uptake

from

aqueous

solution.

Herein,

a

H-bonded

metal-organic

framework

[(Zn3L3(H2O)6][(Na)(NO3)] (1) with high stability was elaborately constructed. The uncoordinated carboxylate oxygen atoms in the channels of MOF were designed as active sites to recognize Cu2+ and further coordinate with it. Without pre-treatment, MOF 1 demonstrated a relative high adsorption capacity (379.13 mg g−1), exceeding most of Cu2+ adsorbents. Even with the existence of different metal ions and high concentration of interfering ions, highly selective adsorption of Cu2+ can be achieved. Moreover, the excellent water stability together with the high removal efficiency in the presence of coexisting ions offers MOF 1 the possibility in practical application. The mechanism for Cu2+ selective adsorption was systematically investigated by UV-vis, FT-IR and fluorescence lifetime techniques, which may originate from the strong interaction between Cu2+ and the carboxylate oxygen atoms. Our work may open an avenue to develop MOFs into adsorbent materials for water pollutants. INTRODUCTION Copper(II) is an important and essential trace element required for normal metabolism of many living organisms.1 While both deficiency and overload of copper(II) may lead to some copper metabolism disorders such as Parkinson’s, Alzheimer’s and Wilson’s diseases.2,3 With the increasing demand of copper at the fields of electrical equipment, industrial machinery, building construction and renewable energy, more and more Cu2+ effluents were released into the environment.4,5 The U.S. Environmental Protection Agency (EPA) has set the limit of copper(II) concentration in drinking water to be 1.3 ppm.6 Consequently, it is of great significance to remove Cu2+ to a safety level in our drinking water. Considerable efforts have been made to remove heavy metal ions.7-12 Among various methods, adsorption holds considerable promise due to its cost-effectiveness, eco-friendliness and simple operation.13-16 Porous materials are promising candidates in adsorption. For the traditional porous materials, such as activated carbon, aluminosilicates, zeolites, their application are limited to some extent owing to the difficulty in pore modification.17,18 Excellent one inherent structural feature of metal-organic frameworks (MOFs) that distinguishes them from traditional inorganic porous materials, is that they 2


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are hybrid materials with inorganic units and organic moieties.19-21 Based on this characteristic, various active sites can be rationally introduced into the MOFs for related applications22-30 by postfunctionalization or ligand modifications.31-35 Owing to the high surface area, permanent porosity and tunable chemical composition, MOFs are considered to be one of the most promising platforms for the adsorption application.36-39 Extensive MOFs have been explored as adsorbents for the elimination of heavy metal ions in recent years.40-50 Nonetheless, the employment of MOFs for selective removal of Cu2+ from other metal ions in aqueous solution was rarely reported. In this study, the ligand 1,3-benzenedicarboxylic acid (denoted as H2L) and Zn(NO3)2·6H2O were purposefully selected to construct MOF for the removal of Cu2+. The ligand H2L prefers to generate porous and rigid structures for metal ions encapsulation. Moreover, zinc is an environmentally friendly and nontoxic metal, which has more practical interest for environmental remediation. Solvothermal reaction of Zn(NO3)2·6H2O with H2L and NaOH results in a novel 3D H-bonded MOF, [(Zn3L3(H2O)6][(Na)(NO3)] (1). The uncoordinated carboxylate oxygen atoms in the channels of MOF 1 are expected to work as Cu2+ recognition sites and endow Cu2+ with a facile access to be adsorbed. The as-synthesized MOF 1, with high stability and good dispersibility in aqueous solution, showed highly selective and effective adsorption for Cu2+. EXPERIMENTAL SECTION Materials and Physical Measurements. All the chemicals were commercially available reagents of analytical grade unless otherwise specified, and were used without further purification. Fourier transform infrared (FT-IR) spectrum was performed on a Thermo Nicolet iS50 spectrometer. Powder X-ray diffraction (PXRD) were measured on PANalytical X’Pert PRO MPD system (PW3040/60). The energy-dispersive X-ray (EDX) spectroscopy was recorded with a Bruker XFlash 6130 system at 15 KV. Atomic force microscopy (AFM) image was acquired on a dimension edge microscope equipped with a tapping mode. The thermal behavior was studied by a Netzsch STA-449F3 thermogravimetric analyzer. The luminescence excitation/emission spectra was measured at room temperature on a Hitachi F-4600 fluorescence spectrophotometer. The emission lifetime was recorded with a TCSPC laser as the excitation source, and the data was analyzed by exponential curve fitting. Simultaneous inductively coupled plasma optical emission spectrometry (ICP-OES) on a PerkinElmer Optima 8000 instrument was used to determine the metal ion concentration in 3



aqueous solution. Preparation of [(Zn3L3(H2O)6][(Na)(NO3)] (1). Zn(NO3)2·6H2O (89 mg, 0.3 mmol), H2L (27 mg, 0.15 mmol), NaOH (0.25 M, 0.15 mL), 24 mL CH3CN and 1 mL H2O were sealed in a Teflon-lined stainless steel autoclave (50 mL). After heating 48 h at 170 °C, the mixture was cooled to room temperature, and the colorless blocks of 1 were obtained (yield: 39% based on H2L). Elemental analysis (%) calculated: C, 32.69; H, 2.74; N, 1.59. Found: C, 33.21; H, 2.81; N, 1.41. X-ray Crystallography. Single crystal of 1 was gained from the above preparation. The measurement was made on a Bruker smart Apex CCD II diffractometer by using graphite monochromated Mo Kα (λ = 0.071073 nm). Its crystal was mounted on glass fibers at 133 K. The crystal structure of 1 was solved by direct method refined on F2 by full-matrix least-squares technique with the SHELXTL-97 program.51 Crystallographic data of 1 is listed as follows: C24H24NNaO21Zn3, Mr = 881.61, hexagonal, space group P63/mmc, a = 16.971(2) Å, b = 16.971(2) Å, c = 6.9844(14) Å, α = 90°, β = 90°, γ = 120°, V = 1742.1(6) Å3, Z = 2, Dc = 1.681 g cm–3, F(000) = 888 and µ = 2.146 mm-1, 11810 reflections collected, 618 unique (Rint = 0.0278). R1 = 0.0506, wR2 = 0.1933 and S = 0.975. Adsorption Experiments. The experiments for removal of Cu2+ were conducted according to the batch model: 10 mg of the adsorbents were added into 80 mL of Cu2+ solution with constant agitation, and the Cu2+ concentrations were determined by ICP-OES at given time intervals. The adsorption isotherm experiments were performed in a concentration range from 1 ppm to 100 ppm. The removal efficiency and the amount qt (mg g−1) of adsorbed Cu2+ were calculated according to the formulas: Removal efficiency (%) = qt =

C0 − C e × 100 % (1) C0

(C0 − Ct )V m

(2)

where C0 (mg L−1) and Ce (mg L−1) are the initial and equilibrium concentrations of analyte in the solution, respectively. V (L) is the volume of the solution, m (g) is the mass of the adsorbent. RESULTS AND DISCUSSION Characterization of MOF 1. Single-crystal X-ray diffraction studies reveal that 1 is composed of a 3D framework crystallizing in the hexagonal system with space group P63/mmc. There are one-twelfth of [(Zn3L3(H2O)6] unit, one-twelfth of Na+ cation and one-twelfth of NO3− anion in the 4


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asymmetric unit. Each Zn atom is four-coordinated with a tetrahedral geometry by bonding to two O atoms of two carboxylate groups from two L2− ligands and two O atoms from two water molecules (Figure 1a). Each [Zn(H2O)2] subunit is connected by three L2− ligands to give a metallocyclic [(Zn3L3(H2O)6] unit. Such [(Zn3L3(H2O)6] units are interconnected by O−H···O hydrogen bonds (O1W−H1W···O2, 2.126 Å; Figure S2) to construct a 3D H-bonded framework with two kinds of 1D channels (Figure 1b), which was rarely reported in the previous studies. Interestingly, these channels are occupied by Na+ cations and NO3− anions (Figure 1b), which improve the water-dispersion of MOF 1.52,53 The electrostatic interaction generated by the NO3− anions is in favor of Cu2+ adsorption. Moreover, the face-to-face π···π interactions between phenyl rings, with the distances of 4.034 Å (Figure S3), would facilitate the stabilization of the 3D supramolecular architecture.54,55 The uncoordinated carboxylate oxygen atoms in the channels are expected to give Cu2+ a facile access to interact with MOF 1 (Figure 1b), suggesting that MOF 1 would be a potential adsorbent. The chemical composition of MOF 1 was characterized by EDX spectra (Figure S4). The content of Zn given by EDX spectra is 7.70%, almost three times that of Na (2.66%). These results and the elemental analysis further verified the chemical formula of MOF 1. Moreover, the PXRD pattern of MOF 1 is in agreement with the simulated one (Figure S5), which is an indicative of pure sample for MOF 1. (Figure 1 here) As we know, structural stability is a very important factor for the practical applications of MOFs. We investigated the stability by Thermogravimetric analysis and found that MOF 1 was thermally stable up to 180 °C (Figure S6). After immersing in aqueous solution at pH of 3.0 ~ 10.0 for 24 h, the MOF still retained its framework structure (Figure 2), suggesting the good water stability of MOF 1. The good thermal and water stability of MOF 1 could be stem from its unique 3D H-bonded framework structure. In addition, AFM images revealed that the grinded MOF samples were well dispersed in water with relative small particle sizes (Figure 3), which benefits the further application in adsorption. (Figures 2 & 3 here) Cu2+ Sorption Studies. The high stability, good water-dispersion as well as the uncoordinated carboxylate oxygen atoms of MOF 1 prompted us to study the adsorption application in aqueous 5



solution. We first investigated the pH effect on Cu2+ adsorption in the range of 3.0-7.0, as pH value greatly influences the adsorption performance of heavy metal ions. At pH lower than 6.0, the decreasing pH value resulted in a significant reduction of uptake capacity for Cu2+, due to the diminishing sorption sites caused by the protonation effect. At pH of 7.0, higher concentrations of Cu2+ solution are easily subject to precipitation. Consequently, the subsequent adsorption tests were conducted at the optimum pH of 6.0. Without pre-treatment, the freshly prepared MOF samples were added into the dilute Cu2+ solution (10 ppm) and stirred to reach equilibrium. The residual concentration was determined to be 0.304 ppm, which was well below the acceptable limit of copper in drinking water. The adsorbed Cu2+ was observed by XPS spectra (Figure S7). The collected experiment data were well fitted with the pseudo-second-order kinetic model (R2 = 0.999; Figure S8), suggesting that chemisorption is the rate limiting step.56 In order to ascertain the reason for Cu2+ sorption, the content of Zn2+ in the solution was analyzed, and no Zn2+ was released in Cu2+ adsorption. In the previous reported Zn-MOFs,57,58 the central-metal Zn2+ tend to be exchanged by other metal ions, especially by Cu2+. While in this work, no Zn2+ was exchanged during Cu2+ sorption, which could be stem from the strong interaction between Cu2+ and the uncoordinated carboxylate oxygen atoms. Furthermore, we also measured the concentration of Na+ in the solution, as Na+ in the channels could also be exchanged by Cu2+ in the sorption process. After the equilibrium reached, the concentration of Cu2+ was reduced from 10 ppm to 0.304 ppm, while the concentration of exchanged Na+ in the solution was determined to be only 2.56 ppm, indicating that most Cu2+ were adsorbed onto MOF rather than by ion exchange. It is worth noting that the framework remains in its main original structure after Cu2+ sorption, as demonstrated by PXRD analysis (Figure S9). As Cu2+ is essential to living biological systems, which often found in a mixture with the presence of various ions, it is important to study Cu2+ selective adsorption. For this, MOF 1 were added into the mixed solution containing different M(NO3)x (M = Cu2+, Mn2+, Ni2+, Na+, K+, Ca2+, Mg2+, Co2+, Ba2+, Sr2+, Cd2+). Each of metal ions was presented in a same concentration of 10 ppm. After the equilibrium reached, more than 90% Cu2+ were removed. While the removal efficiency for other metal ions were obviously lower than 10% (Figure 4). So MOF 1 shows a high selectivity for Cu2+. (Figure 4 here) 6


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Light metals like Ca2+ and Mg2+, which play a significant role in biological processes, are commonly found in water environment. Therefore, the selectivity over light metals is of paramount importance in decontaminating heavy metals for an adsorbent. Samples of MOF 1 were immersed in a mixed solution of M(NO3)x (M = Cu2+, Ca2+ and Mg2+). As highlighted in Table 1, MOF 1 exhibited a distinct selectivity toward Cu2+ over light metals (Ca2+, Mg2+) and the concentrations were reduced from 10 ppm to 0.526, 9.771 and 9.879 ppm for Cu2+, Ca2+ and Mg2+, respectively. In daily life, the concentrations of Ca2+ and Mg2+ in drinking water were always higher than that of Cu2+. Then a new question arises: if the high level of Ca2+ and Mg2+ are well removed by MOF adsorbents, the adsorption ability for Cu2+ will be decreased drastically and the amount of beneficial light elements in water would obviously reduce. Thus, it is crucial to investigate Cu2+ adsorption behavior with the existence of the highly concentrated Ca2+ and Mg2+. As shown in Table 2, 93.04% Cu2+ could be removed in the presence of ten equivalents of Ca2+ and Mg2+, while only 1.56% Ca2+ and 2.33% Mg2+ were adsorbed. These results suggested the adsorption abilities of MOF 1 for these beneficial light elements of Ca2+ and Mg2+ were negligible. (Tables 1 & 2 here) To further investigate the selectivity for Cu2+ sorption, the distribution coefficient (Kd) and the selectivity coefficient (SCu/M) were measured to evaluate the affinity and the selectivity of adsorbent. As shown in Table 1, the Kd value of MOF 1 for Cu2+ was determined to be 1.44 × 105 mL g−1, which is significantly higher than that of Ca2+ and Mg2+ in the mixed solution with a same concentration. Moreover, even in the presence of ten equivalents of Ca2+ and Mg2+, there is no obvious decrease of Kd value for Cu2+, and a relative high value of 1.07 × 105 was still obtained (Table 2). Generally, the Kd value higher than 104 mL g−1 is regarded as excellent.8,9 Thus MOF 1 has a high affinity for Cu2+. More importantly, the selectivity coefficients of SCu/Ca and SCu/Mg can achieve 844 and 561 in the presence of ten equivalents of Ca2+ and Mg2+ (Table 2). Although the Gibbs free energy of hydration for Cu2+ is not beneficial to its adsorption, a good adsorption performance could still obtained for Cu2+,59,60 which was mainly attributed to its high electronegativity and ionic potential, resulting in a relative high affinity for Cu2+ sorption. Moreover, the interaction with the uncoordinated carboxylate oxygen atoms in MOF 1 could also be responsible for the highly selective adsorption of Cu2+. As Cu2+ is a borderline metal, it has a high preference for 7



oxygen atoms;61,62 the electrostatic interaction generated by NO3− anions in the channels of MOF 1 can be in favor of Cu2+ adsorption; unlike other transition metal ions, the flexible geometry of Cu2+ would help it to be accommodated in diverse coordination environments.63 To evaluate the maximum uptake capacity, a very important parameter in assessing the efficiency and practicability of an adsorbent in economical wastewater disposal system, the adsorption isotherms were investigated. In Figure 5a, with Cu2+ concentration increasing, the uptake capacity increased and then reached a plateau. Langmuir model was employed to fit the equilibrium data, affording a high correlation coefficient (R2 = 0.999; Figure 5b). The calculated maximum uptake capacity of 378.79 mg g−1 is very close to the experimental value (379.13 mg g−1), which is among the second highest of the MOF adsorbents for Cu2+ sorption and exceeded most of other Cu2+ adsorbents (Table S1). Although the uptake capacity of MOF 1 is lower than that of ZIF-8,64 the selectivity for Cu2+ sorption is obviously higher than that of ZIF-8 and other Cu2+ adsorbents (Table S1). For heavy metal ions removal, many adsorbents showed poor or even no selectivity. Recently, a robust MOF incorporated with ethylenediaminetetraacetic acid (MOF-808-EDTA) exhibited excellent removal performance for various heavy metal ions, but without selectivity.49 (Figure 5 here) Interaction between MOF 1 and Cu2+. To investigate the mechanism for Cu2+ selective adsorption, the fluorescence emission of MOF 1 with serial concentrations of Cu2+ were recorded. After addition of Cu2+ into the suspension, the intensity of MOF 1 was quenched to different degrees and a linear relation was obtained (Figure 6). So there is a strong interaction between MOF 1 and Cu2+, which has been verified by the obviously reduced lifetime after Cu2+ encapsulation (Figure S10). The strong interaction could act as a driving force during Cu2+ sorption. As demonstrated in Figure S11, an obvious red shift from 1379 cm−1 to 1369 cm−1 after Cu2+ adsorption can be ascribed to the symmetric stretching vibration of COO−. The absence of 1200 cm−1 (C–O of COOH) and 1720 cm−1 (C=O of COOH) bands give more evidence of the presence of COO−, and the band of COO− usually appears at ca 1385 cm−1.65-68 So there is a strong interaction between Cu2+ and the carboxylate oxygen atoms of MOF 1. In the UV-vis spectra, a new peak appeared at 730 nm after Cu2+ adsorption further confirmed the interaction between Cu2+ and the carboxylate oxygen atoms (Figure S12),18 which could be responsible for the selective adsorption of Cu2+ by MOF 1. It is worth 8


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mentioning that the antisymmetric stretching vibration of NO3− locates at ca 1379 cm−1 (Figure S11). The shift from 1379 cm−1 to 1369 cm−1 after Cu2+ adsorption also indicate that an interaction may exist between Cu2+ and NO3−. (Figure 6 here) CONCLUSIONS In this study, a H-bonded Zn(II)-MOF with uncoordinated carboxylate oxygen atoms was elaborately constructed. The as-synthesized MOF well dispersed in aqueous solution with small particle sizes and could be stable in a wide pH range (3.0 ~ 10.0). It exhibited a high selectivity for Cu2+, which may stem from the strong interaction between the uncoordinated carboxylate oxygen atoms and Cu2+. Without pre-treatment, this MOF material demonstrated a good ability for high-performance Cu2+ adsorption (379.13 mg g−1). The excellent water stability and high removal efficiency with the existence of coexisting ions made MOF 1 a promising candidate for Cu2+ removal. Our work may bring up a new way for exploring MOF materials as an appealing platform in constructing adsorbents for environmental pollutants. Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.xxxxxxx. PXRD patterns, TGA curve, EDX spectra, XPS spectra, UV-vis spectra, FT-IR spectra, additional figures and Tables. (PDF) Crystallographic data for 1 in CIF format (CIF) Accession Code CCDC 1588807 contains the supplementary crystallographic data for this paper. This data can be obtained

free

of

charge

via

www.ccdc.cam.ac.uk/data_request/cif,

or

by

emailing

[email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033. Corresponding Author *E-mail: [email protected] (H. Hou). 9



*E-mail: [email protected] (L. Liu). Notes The authors declare no competing financial interest. Acknowledgments This work was supported by the National Natural Science Foundation (Nos. 21671174 and 21371155) and the Natural Science Foundation of Henan province. References (1) Chen, Y. Z.; Jiang, H. L. Porphyrinic Metal-Organic Framework Catalyzed Heck-Reaction: Fluorescence “Turn-on” Sensing of Cu(II) Ion. Chem. Mater. 2016, 28, 6698–6704. (2) Ye, J.; Zhao, L.; Bogale, R. F.; Gao, Y.; Wang, X.; Qian, X.; Guo, S.; Zhao, J.; Ning, G. Highly Selective Detection of 2,4,6-Trinitrophenol and Cu2+ Ions Based on a Fluorescent Cadmium-Pamoate Metal-Organic Framework. Chem. Eur. J. 2015, 21, 2029–2037. (3) Du, P. Y.; Gu, W.; Liu, X. Multifunctional Three-Dimensional Europium Metal-Organic Framework for Luminescence Sensing of Benzaldehyde and Cu2+ and Selective Capture of Dye Molecules. Inorg. Chem. 2016, 55, 7826–7828. (4) Liu, Z.; He, W.; Pei, M.; Zhang, G. A Fluorescent Sensor with a Detection Level of Pm for Cd2+ and Nm for Cu2+ Based on Different Mechanisms. Chem. Commun. 2015, 51, 14227–14230. (5) Li, L.; Shen, S.; Lin, R.; Bai, Y.; Liu, H. Rapid and Specific Luminescence Sensing of Cu(II) Ions with a Porphyrinic Metal-Organic Framework. Chem. Commun. 2017, 53, 9986–9989. (6) Aragay, G.; Pons, J.; Merkoçi, A. Recent Trends in Macro-, Micro-, and Nanomaterial-Based Tools and Strategies for Heavy-Metal Detection. Chem. Rev. 2011, 111, 3433–3458. (7) Qaiser, S.; Saleemi, A. R.; Umar, M. Biosorption of Lead from Aqueous Solution by Ficus Religiosa Leaves: Batch and Column Study. J. Hazard. Mater. 2009, 166, 998–1005. (8) Ma, L.; Wang, Q.; Islam, S. M.; Liu, Y.; Ma, S.; Kanatzidis, M. G. Highly Selective and Efficient Removal of Heavy Metals by Layered Double Hydroxide Intercalated with the MoS42− Ion. J. Am. Chem. Soc. 2016, 138, 2858–2866. (9) Ma, S.; Huang, L.; Ma, L.; Shim, Y.; Islam, S. M.; Wang, P.; Zhao, L. D.; Wang, S.; Sun, G.; Yang, X.; Kanatzidis, M. G. Efficient Uranium Capture by Polysulfide/Layered Double Hydroxide Composites. J. Am. Chem. 10


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Table 1. Adsorption of MOF 1 toward the Mixed Ions _________________________________________________________________________________ Mixed ions

C0 (ppm)

Ce (ppm)

Removal (%)

Kd (mL g−1)

SCu/M

_________________________________________________________________________________ Cu2+

10

0.526

94.74

1.44 × 105

1

Ca2+

10

9.771

2.29

187.49

768

Mg2+

10

9.879

1.21

97.98

1470

_________________________________________________________________________________

Table 2. Adsorption of MOF 1 toward the Mixed Ions _________________________________________________________________________________ Mixed ions

C0 (ppm)

Ce (ppm)

Removal (%)

Kd (mL g−1)

SCu/M

_________________________________________________________________________________ Cu2+

10

0.696

93.04

1.07 × 105

1

Ca2+

100

98.44

1.56

126.78

844

Mg2+

100

97.67

2.33

190.85

561

_________________________________________________________________________________

17



(a)

(b) Figure 1. (a) View of the metallocyclic [(Zn3L3(H2O)6] unit and the coordination environment of the Zn centers in MOF 1. (b) View of the 3D supramolecular architecture in MOF 1 looking down the c axis. Atom color codes: Zn, cyan; Na, yellow; O, red; N, blue; C, gray; H, green. All H atoms except those related to H-bonding interactions are omitted for clarity.

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Figure 2. PXRD patterns of MOF 1 after immeresing in aqueous solution at pH = 3, 4, 6, 8, 10 (24 h).

Figure 3. (a-b) AFM images of MOF 1 after dispersing in aqueous solution. (c-d) The height of profiles across the blue lines in (b).

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Figure 4. Effects of coexisting ions on the removal of Cu2+ by MOF 1.

(a)

(b)

Figure 5. (a) Cu2+ adsorption isotherm for MOF 1. (b) Langmuir adsorption mode fitting for the adsorption of Cu2+ by MOF 1.

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(a)

(b)

Figure 6. (a) The fluorescence spectra of 1 in aqueous solution with Cu2+ at different concentrations (λex = 305 nm). (b) Linear relationship of the fluorescence intensity at 397 nm as a function of Cu2+ ion concentration (0.16-127 ppm).

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For Table of Contents Use Only

Efficient and Selective Removal of Copper(II) from Aqueous Solution by a Highly Stable H-Bonded Metal-Organic Framework Caixia Yu,†,‡ Zhichao Shao,† Leilei Liu,*,‡ and Hongwei Hou*,†

A H-bonded MOF with high stability was elaborately constructed. The uncoordinated carboxylate oxygen atoms in the channels of MOF were designed as active sites to recognize Cu2+ and further coordinate with it. Without pre-treatment, this MOF demonstrated a relative high uptake capacity. Even in the presence of various metal ions, highly selective adsorption of Cu2+ can also be achieved.

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from Aqueous Solution by a Highly Stable Hydrogen-Bonded Metal

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