Comparison of adsorption properties for anionic dye by metal organic frameworks with different metal ions

Journal Pre-proof Comparison of adsorption properties for anionic dye by metal organic frameworks with different metal ions Yi Liu, Yongfeng Liu, Rongjun Qu, Chunnuan Ji, Changmei Sun

PII:

S0927-7757(19)31254-3

DOI:

https://doi.org/10.1016/j.colsurfa.2019.124259

Reference:

COLSUA 124259

To appear in:

Colloids and Surfaces A: Physicochemical and Engineering Aspects

Received Date:

26 April 2019

Revised Date:

29 September 2019

Accepted Date:

19 November 2019

Please cite this article as: Liu Y, Liu Y, Qu R, Ji C, Sun C, Comparison of adsorption properties for anionic dye by metal organic frameworks with different metal ions, Colloids and Surfaces A: Physicochemical and Engineering Aspects (2019), doi: https://doi.org/10.1016/j.colsurfa.2019.124259

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Comparison of adsorption properties for anionic dye by metal organic frameworks with different metal ions

Yi Liu, Yongfeng Liu* [email protected], Rongjun Qu*, Chunnuan Ji, Changmei Sun College of Chemistry and Materials Science, Ludong University, Shandong 264025, People’s Republic of China

Corresponding authors. (Y.F. Liu).

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Graphical abstract

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Effect of ionic strength on adsorption. Effect of ionic strength on adsorption of Cu-BDC was promotive while that of Zn-BDC and NiBDC was suppressed, and that of Zn-BDC was gentle. Considering adsorption efficiency, Cu-BDC and Zn-BDC were suitable for the removal of the anionic dye from aqueous solution with high concentration of salts while Ni-BDC not.

Abstract Two dimensional MOFs materials with different metal ions were prepared through a facile and mild method at an ambient temperature and characterized to verify successful preparation of the materials. The MOFs materials were used to remove anionic dye alizarin yellow GG from aqueous solution in comparison with each other. Several parameters such as contact time, initial concentration, temperature and ionic strength affecting adsorption efficiency were systematically investigated. It was found that the adsorption capacity of the MOFs materials with zinc as linker

for the dye was the highest, indicating type of metal ion greatly influence adsorption efficiency. It was surprising to find that effect of ionic strength on adsorption of the material with copper linker was promotive while that of the materials with zinc and nickel liners was inhibited which may be due to different chemical structures of the adsorbents. The dye loaded MOFs materials could be regenerated with simple method and the materials had superior stability and reusability during the five adsorption-desorption cycles. Furthermore, the MOFs materials could selectively enrich anionic dyes from contaminated effluents with cationic and anionic dyes. The MOFs materials prepared were efficient and potential adsorbents to remove anionic dyes from aqueous solution. Keywords: metal organic frameworks, different metal ions, adsorption, anionic dye, regeneration

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Introduction Recent years, the problem of toxic dyes solution directly discharged into the environment have aroused worldwide attention due to these dyes contaminant aroused fatal damage to biological organisms and human bodies. Several technologies such as biological [1, 2], chemical [3] and physical [4] methods have been used to remove dyes from aqueous solution, among which adsorption is widely applied because of its simplicity, easy operation and low cost. It is known that adsorption efficiency of an adsorbent is largely depended on the structure of the adsorbent. Therefore design and preparation of an adsorbent is very important to achieve high adsorption efficiency. Metal organic frameworks (MOFs) with superior properties like high surface area, high porosity and regulated chemistry properties, have wide application in catalysis, sensing and storage and separation of gas, and so. MIL-101-Cr was prepared and used to remove reactive yellow 15, reactive black 5, reactive red 24 and reactive blue 2 from aqueous solution, and it found that the MOF material exhibited high adsorption efficiency with adsorption capacities in the range of 377397 mg/g [5], suggesting the MOF material was a potential and promising adsorbent to remove reactive dyes from aqueous solution and MOFs could be used as efficient adsorbents to enrich dyes. Ren et al [6] fabricated MIL-PVDF blend ultrafiltration membranes, and the membranes were employed for adsorption and catalytic oxidation of methylene blue. The results showed that the effective treatment volume of 67-MIL-PVDF membrane increased by 9 times with more than 75% dye uptake in comparison with traditional blend ultrafiltration membrane. Fe3O4NH2@HKUST-1@PDES was synthesized and could be used to selectively separate cationic dyes MG and CV from complex systems containing multiple dyes, showing high extraction ability for MG and CV [7]. According to references reported, the MOFs materials used as adsorbents to remove dyes were in the consideration of design of organic ligands with novel structures, supported MOFs, MOFs composites, and so on. However, effect of different metal ions on adsorption efficiency of the MOFs materials for dyes were few reported. Alizarin yellow GG, an anionic dye, as azo dye, is usually used as chromatographic reagent, acid-base indicator, sperm staining and so on. Due to its structure, it is highly carcinogenic, genotoxic and toxic dye to high chemical oxygen demand (COD) value [8]. The contaminated water containing alizarin yellow GG must be treated before it was discharged. Modified macroporous adsorption resins were prepared by us and used to enrich alizarin yellow GG [9]. The results showed that the resins could be regenerated and the desorption condition was mild and facile. The adsorption capacities of LZ-0, LZ-1 and LZ-2 for alizarin yellow GG were 9.78, 14.76

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and 5.41 mg/g, respectively, indicating the adsorption efficiency was relatively low. Thus materials with high adsorption efficiency, valid adsorption and fast adsorption rate for alizarin yellow GG are highly needed to meet the demand of practical application. In this study, the MOFs materials with terephthalate as organic linker and copper, zinc and nickel as metal ions were designed and prepared, and corresponding adsorption properties for alizarin yellow GG was systematically investigated. Adsorption mechanism was also speculated. Materials The materials used such as 1,4-benzenedicarboxylic acid (BDC), copper sulfate pentahydrate (CuSO4·5H2O), zinc acetate dihydrate (Zn(CH3COO)2·2H2O), nickel chloride hexahydrate (NiCl2·6H2O), N,N-dimethylformamide, triethylamine, anhydrous ethanol, alizarin yellow GG, malachite green and methylene blue were bought from Sinopharm Chemical Reagent Co., Ltd (Shanghai, China) and used without purification. Distilled water was used throughout the experiment. Preparation The preparation processes of the MOFs materials were facile and mild, listed as follows: 0.02 mol metal salt (CuSO4·5H2O, Zn(CH3COO)2·2H2O and NiCl2·6H2O) and 0.02 mol BDC were dissolved in anhydrous ethanol of 50 mL with the help of ultrasound. The solution was stirred and 5 mL triethylamine was added drop by drop. The reaction was lasted for 6 h, washed with ethanol and dried under vacuum until a constant weight. The materials obtained were named as Cu-BDC, Zn-BDC and Ni-BDC with color of dark blue, white and light green, respectively. Characterization The FTIR spectra of the prepared MOFs materials and alizarin yellow GG loaded MOFs materials were performed by FTIR spectroscopy in the range of 4000-400 cm-1 with a Nicolet 6700 FTIR spectrometer using KBr pressed pallet. The surface area and pore volume of the MOFs materials prepared were obtained by the means of N2 adsorption-desorption isotherms conducted on a Micromeritics Surface Area and Porosity Analyzer (ASAP 2020). N2 adsorption-desorption isotherm curve and pore diameter distribution were shown in Fig. S1. X-ray diffraction was performed on a Rigaku D/max-2500VPC equipped with a Cu Kα radiation source. The morphologies of the MOFs materials were characterized by high resolution field emission scanning electron microscopy (FESEM, Hitachi SU8010). Thermogravimetric analysis (TGA)

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was conducted on NETZSCH STA409PC from 30 to 650 °C in nitrogen atmosphere at a constant heating rate of 10 °C/min. The analyses of XRD, FESEM, TGA characterization (Figs. S2-4)

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were given in supporting information. Adsorption experiment In the present study, the factors affecting adsorption efficiency like contact time, initial dye concentration and temperature were systematically investigated to explore the potential of the prepared MOFs materials used as adsorbents for alizarin yellow GG uptake. The initial and final concentrations of alizarin yellow GG solution could be computed by measuring the absorbance at maximum absorption wavelength of 352 nm using a 752 ultraviolet-visible spectrophotometer on the basis of standard curve equation. To obtain equilibrium adsorption time, 25 mg adsorbent contacted with 25 mL dye solution with initial concentration of 800 mg/L, shook at constant temperature of 25 °C with stirring speed of 100 rpm. The supernatant was collected and

determined at predetermined time intervals until the concentration of residues unchanged. The effects of initial concentration and temperature on adsorption was investigated with a series of dye solutions with initial concentrations in the range of 300-800 mg/L and temperatures of 30, 40 and 50 °C, respectively. Each adsorption experiment was conducted triplicate throughout the experiment. For effect of ionic strength, NaCl concentration in the range of 0.01-0.09 mol/L, alizarin yellow GG concentration of 900 mg/L, and contact time of 240 min were applied. The adsorption capacity q can be calculated according to the equation, given as:

q

C0 Ct V W

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where C0 and Ct are initial and final concentration of dye solution (mg/L), W the weight of adsorbent used (g) and V the volume of dye solution applied in the adsorption process (L). Reusability and regeneration For an adsorbent with excellent adsorption performance, except for high adsorption capacity and fast adsorption rate, reusability is also an important factor for practical application. For the desorption experiments, the dye-loaded MOFs materials were desorbed by 95% ethanol, acetone, and 0.01 mol/L HCl, and then optimum desorbing agent was selected. Subsequently, the adsorption and desorption experiments were repeated five times.

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Results and discussion FTIR characterization The composition of the MOFs materials was investigated by the means of FTIR spectra, as shown in Fig. 1. It can be seen that The characteristic absorption peaks at 3621 and 3570 cm-1 for Cu-BDC (3606 and 3423 cm-1 for Zn-BDC, 3591 and 3433 cm-1 for Ni-BDC) were possible ascribed to bridged hydroxyl group (i.e. Cu-OH-Cu, Zn-OH-Zn, Ni-OH-Ni) [10, 11]. The peak at 1691 cm-1 for Cu-BDC (1656 cm-1 for Zn-BDC, 1607 cm-1 for Ni-BDC) corresponded to stretching vibration of single -COOH group of BDC molecules coordinated with metal ions. The characteristic absorption peaks at 1581 and 1508 cm-1 corresponded to asymmetric stretching vibration of carboxyl group, and 1398 cm-1 were due to symmetric stretching vibration of carboxyl group of Cu-BDC [11]. The bands at 1287 and 1062 cm-1 were due to C-O-C stretching vibration. The band at 1108 cm-1 was ascribed to C-O-Cu stretching vibration, and the band at 736 cm-1 could be considered as the characteristic absorption band of Cu-BDC [12, 13]. The band at 883 cm-1 for Cu-BDC (889 cm-1 for Zn-BDC, 883 cm-1 for Ni-BDC) was for CH wagging of 1,4disubstituted aromatic structure. The peak at 527 cm-1 was for Ni-O stretching vibration of NiBDC [14]. The bands in the range of 658-1098 cm-1 may related to Zn-O vibrations [15], which may be overlapped with absorption peaks of other bonds like CH wagging. In addition, it can be seen that the absorption peaks of Ni-BDC were similar to those of Zn-BDC, while they are different from those of Cu-BDC, suggesting different structures between the former two adsorbents and the latter one adsorbent, which may result in different adsorption behaviors. The analyses mentioned above hinted the MOFs materials were successfully synthesized. Furthermore, on the basis of references reported [13, 16, 17], the MOFs prepared in this study were two dimensional materials. According to the BET characterization (Table 1), the values of surface area and micropore area of the three MOFs materials were all lower than 20 m2/g and 0.09

cm3/g, respectively. However, the value of surface area was very large for three dimensional MOFs materials [18]. In this case, the MOFs synthesized were all two dimensional materials.

t qt

t qt

1 2 k2 q2e

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lg(q1e - qt ) = lg q1e - k1t

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Adsorption performance Effect of contact time and adsorption kinetics Adsorption time is an important factor for practical application, as adsorption equilibrium time is one of vital factors to verify whether the adsorbent is efficient. Consequently, effect of contact time on adsorption was investigated, as shown in Fig. 2. It was obvious that the adsorption for alizarin yellow GG was a fast process for the three adsorbents. In the first stage with contact time lower than 60 min, the dye removal was in the order of Zn-BDC>Cu-BDC>Ni-BDC, and for adsorbent Zn-BDC, the adsorption process already reached an equilibrium state, while for CuBDC and Ni-BDC not, which may be ascribed to different structures of the adsorbents. For CuBDC, with contact time lower than 120 min, the adsorption rate was very fast, due to available enough adsorption sites, and with contact time increasing, adsorption sites decreased and adsorption rate reduced, adsorption process gradually reaching an equilibrium state. Adsorption equilibrium time for Zn-BDC, Ni-BDC and Cu-BDC was 30, 60 and 300 min, respectively, indicating that for the first two adsorbents, it was a fast adsorption process while for the latter adsorbent, it was a slow adsorption process [19-21]. It is known that properties depend on the structure of the adsorbent. In this case, it was possible that different structures of the three adsorbents resulted in different adsorption behaviors. The adsorption capacity was in the order of Zn-BDC>Cu-BDC>Ni-BDC, and the adsorption capacity was all above 500 mg/g with contact time of 300 min, indicating the three adsorbents were promising adsorbents to remove anionic dyes like alizarin yellow GG from aqueous solution. To well understand adsorption mechanism, two widely used kinetic models pseudo-first-order and pseudo-second-order kinetic equations [22-24] were given as below, respectively to analyze adsorption kinetic data.

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where q1e and q2e (mg/g) are equilibrium adsorption capacity for pseudo-first-order and pseudosecond-order kinetics, accordingly; k1 (min-1) and k2 (mg/(g min)) are rate constants for pseudofirst-order and pseudo-second-order kinetics, respectively; qt (mg/g) is the adsorption capacity at time t (min). For pseudo-second-order kinetic model, initial adsorption rate h (mg/(g min)) was expressed as [25, 26]:

h

2 k2 q2e

where the parameters k2 and q2e were same as defined above. The adsorption kinetic data were analyzed using the equations mentioned above, and corresponding parameters obtained were tabulated in Table 2. It can be seen that for Cu-BDC, both kinetic models could be applied to depict the adsorption process due to high correlation coefficient (R2). However, for Zn-BDC and Ni-BDC, pseudo-second-order kinetic model fitted the

adsorption process because of excellent correlation coefficient, suggesting electrostatic interaction may be involved in the adsorption process, like several anionic dyes removal by TMU-16 and TMU-16-NH2 [27], and it hinted that Zn-BDC and Ni-BDC could be employed to the treatment of dyes with lower concentration [28, 29]. The different adsorption behaviors may be ascribed to different structure of the adsorbents. In addition, the value of q2e obtained from theoretical calculation was in the order of Zn-BDC>Cu-BDC>Ni-BDC, which was in line with the results in Fig. 2. The adsorption capacities of the three adsorbents for alizarin yellow GG were all higher than 600 mg/g, suggesting excellent adsorption efficiency and potential adsorbents to enrich anionic dyes such as alizarin yellow GG.

Ce qm

1 K L qm

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Effect of initial concentration at different temperatures Adsorption isotherm is important to obtain maximum adsorption capacity for an adsorbent and then it can predict that appropriate initial concentration range is applicable for the adsorbent in practical application. Effect of initial concentration on adsorption at different temperatures was investigated, as shown in Fig. 3. It can be seen that the adsorption capacity for alizarin yellow GG increased with initial concentration increasing for the three adsorbents, possibly due to high adsorption drive with high concentration gradient [30, 31]. For Cu-BDC, it was obvious that temperature exhibited little influence on the adsorption capacity, which was favorable in practical application, while for Zn-BDC and Ni-BDC, the adsorption capacity decreased with increasing temperature with low initial concentration and that increased with increasing temperature with high initial temperature. The adsorption capacity was in the same order as the effect of contact time with high initial concentration. Furthermore, the adsorption capacities of the prepared MOFs materials for alizarin yellow GG were compared to other adsorbents [32-37], and the results were tabulated in Table 3. It was observed that the three adsorbents showed excellent adsorption efficient for the dye in comparison with other adsorbents reported, indicating they could be used effectively to treat wastewater containing anionic dyes like alizarin yellow GG. Adsorption isotherm can give the information concerning equilibrium adsorption capacity of an adsorbent at certain temperature and concentration range. Langmuir and Freundlich isotherm models are commonly used. Langmuir isotherm model assumes that adsorption process happens on the homogeneous adsorption sites of an adsorbent and thus adsorbates adsorbed have no interactions with each other. The linear form of Langmuir isotherm is given as [38]:

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where Ce (mg/L) is equilibrium concentration of adsorbate solution; qe and qm (mg/g) are equilibrium adsorption capacity and maximum adsorption capacity to form a monolayer, accordingly; KL (L/mg) is Langmuir constant. An important factor of Langmuir isotherm as dimensionless separation factor (RL) is given as below [39]:

RL

(1 Co / KL )

1

where Co (mg/L) is initial concentration and KL is the same as defined above. Freundlich isotherm model describes that adsorption occurs in the form of multiple-layer on the heterogeneous adsorption sites. The Freundlich isotherm equation is expressed as [38]:

lg qe

lg K F

1 Ce n

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Where the parameters Ce and qe are the same as above; KF ((mg/g)(L/mg)1/n) and 1/n are Freundlich constants, corresponded to adsorption capacity and adsorption intensity, respectively. The value of 1/n was in the range of 0 to 1 indicated the adsorption process was favorable. The adsorption equilibrium data were analyzed by widely used Langmuir and Freundlich isotherm models (the equations were listed in the supporting information), and the results were shown in Table 4. For Cu-BDC, Freundlich isotherm could be used to describe the adsorption process in the temperature range investigated because of high correlation coefficient, while for ZnBDC and Ni-BDC, Langmuir isotherm model fitted the adsorption process, indicating monolayer adsorption of dye molecule onto both adsorbents [38], which furthermore verify different behaviors of the three adsorbents, same as adsorption kinetic. Furthermore, the values of KL and 1/n were all lower than one, suggesting the adsorption was favorable [40]. Furthermore, it was interesting that the MOFs materials used exhibited almost no adsorption efficiency for cationic dyes malachite green and methylene blue (the chemical structures of the three dyes were shown in Fig. S5). On the basis of analyses by ChemBio3D Ultra software, the molecular size of alizarin yellow GG, malachite green and methylene blue are 11.49, 13.31 and 14.16 angstrom, respectively. It may be due to that the steric hindrance of the dyes like malachite green and methylene blue was comparatively larger than that of alizarin yellow GG, and meantime due to the cationic property of malachite green and methylene blue, electrostatic repulsion between the MOFs materials and the dyes may exist, suggesting electrostatic interaction (Lewis acid-base interaction) played important role in the removal of alizarin yellow GG. Therefore the MOFs materials may be used to selectively adsorb anionic dyes from aqueous solution containing anionic and cationic dyes.

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Effect of ionic strength Existence of salt is common in dyes contaminants. In this condition, effect of NaCl concentration on dye removal was studied, as shown in Fig. 4. It was unexpected to find that adsorption efficiency of Cu-BDC increased and then remained an unchanged state with NaCl concentration increasing which may be due to all the accessible adsorption sites were occupied. However, for the other two MOFs materials, it was opposite, suggesting that the chemical structure of Cu-BDC was different from those of the other two adsorbents. It was in accordance with the analyses of adsorption kinetics. Meantime, for Ni-BDC, adsorption efficiency for the dye was very sensitive to ionic strength, while the ionic strength exhibited gentle influence on adsorption capacity of Zn-BDC for the dye. It has been reported that in the adsorption process, two kinds of surface complexes may be formed: covalent bond complex (inner sphere complex) and non-covalent bond complex (outer sphere complex) [41, 42]. Ionic strength exhibited almost undetectable effect on adsorption for covalent bond complex, while for outer sphere complex ionic strength may result in promotive or negative effect on adsorption [42]. NaCl concentration increasing led to increasing ionic strength. On the one hand, more Cl- ions can screen the positive adsorption sites of the adsorbents, and thus from the point of theory increase in ionic strength was not favorable for adsorption. On the other hand, the electronegativity of Cl was lower than that of O, and thus carboxyl group of alizarin yellow GG was more prone to contacting with positive adsorption sites of the adsorbents. And the equation is given as

Kө=a(Na+)*a(dye-)/a(dye)=γ+[Na+]*γ_[dye-]/[dye], where Kө is activity product, a the activity, γ activity coefficient, dye- and dye the anionic form and molecular form of alizarin yellow GG, respectively. With NaCl concentration increasing, ionic strength increased, leading to γ+ and γ_ decreasing. Due to the values of Kө and [dye] were constant for the designated system at certain temperature and pressure, and thus the values of [Na+] and [dye-] would turn to be large, which was favorable for the adsorption according to electrostatic interaction. For Cu-BDC, the latter factor dominated the adsorption while the former was predominant for Zn-BDC and Ni-BDC. Considering adsorption efficiency, Cu-BDC and Zn-BDC were suitable for the removal of the anionic dye from aqueous solution with high concentration of salts while Ni-BDC not.

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Desorption and regeneration Desorption ability is favorable to understand adsorption mechanism and to determine the feasibility of an adsorbent. 95% ethanol, acetone and 0.01 mol/L HCl were used as desorbing agents to regenerate the MOFs materials and 95% ethanol was selected as optimum desorbing agent due to desorption ratio was higher than 98%. In addition, according to our previous report, 95% ethanol was also good desorbing agent for the regeneration of the microporous adsorption resin with alizarin yellow GG as an adsorbate [9]. An adsorbent with excellent reusability is desirable and essential from the view of economy and environmental protection. The weights of the three MOFs materials after adsorption of the dye did not change, demonstrating super stability [43]. In addition, the FTIR spectra of untreated and

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treated in distilled water with temperature of 70 °C for 8 h and 95% ethanol for 12 h were

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illustrated in Fig. S6, which validated excellent stability of the MOFs materials under the experimental conditions. Taking the adsorbent Zn-BDC as an example, the result found that it exhibited excellent regeneration and negligible decrease in adsorption capacity could be found during the five adsorption-desorption cycles (Fig. 5). With 95% ethanol as desorbing agent, CuBDC and Ni-BDC all had superior recyclability (Fig. S7). The dye could be recycled and ethanol could be obtained under distillation under reduced pressure with 95% ethanol as desorbing agent. In all, the MOFs materials were promising in the removal of the anionic dyes like alizarin yellow GG and exhibited excellent reusability.

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Adsorption mechanism To better understand adsorption mechanism, the FTIR spectra of Cu-BDC before and after adsorption of the dye were investigated, as illustrated in Fig. 6. The FTIR spectra of Zn-BDC and Ni-BDC before and after adsorption were shown in Figs. S8 and S9. 1530 and 1353 cm-1 were the asymmetric and symmetric stretching vibration of -NO2, respectively, and the first band may be overlapped with the stretching vibration of carboxyl group, deformation vibration of O-H and C-C stretching vibration of aromatic ring. The bands of 1353 and 1319 cm-1 appeared in the spectrum of dye loaded Cu-BDC. The absorption peaks at 1691, 1581 and 1508 cm-1 shifted after the dye adsorption, which may be due to the formation of hydrogen bond between carboxyl of Cu-BDC and hydroxyl group of alizarin yellow GG. The band at 1250 cm-1 was ascribed to the stretching vibration of C-OH in the spectrum of the dye and appeared in the spectrum of dye loaded CuBDC. The bands at 883 cm-1 due to the CH wagging of 1,4-disubstituted aromatic ring of Cu-BDC was shifted after adsorption of the dye, suggesting π-π interaction may participate in the

adsorption. Furthermore, electrostatic attraction between metal cation of MOFs materials and carboxyl carboxylate anion may exist in the adsorption process. In all, hydrogen bond, electrostatic attraction (Lewis acid-base interaction) and π-π were involved in the adsorption process [44, 45], and electrostatic attraction (Lewis acid-base interaction) was predominant.

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Conclusion The MOFs materials (Cu-BDC, Zn-BDC and Ni-BDC) were prepared through a facile and mild method and employed to enrich anionic dye alizarin yellow GG from aqueous solution. Due to different metal ions, the three MOFs materials exhibited different morphologies (rectangle sheet for Cu-BDC, irregular sheet for Zn-BDC and peony-like for Ni-BDC) and different adsorption behaviors for alizarin yellow GG. For Cu-BDC, it obeyed pseudo-first-order and pseudo-secondorder kinetics, while for Zn-BDC and Ni-BDC, pseudo-second-order kinetics could be used to describe the adsorption process. The results of adsorption equilibrium data of Cu-BDC for the dye fitted Freundlich isotherm at the temperature investigated while those for Zn-BDC and Ni-BDC obeyed Langmuir isotherm. Effect of ionic strength on adsorption of Cu-BDC was promotive while that of Zn-BDC and Ni-BDC was suppressed, and that of Zn-BDC was gentle. Furthermore, the prepared MOFs materials could be regenerated by calcination or desorbing by 95% ethanol, suggesting super stability and recyclability. It was interesting to find that the MOFs materials could be used to selectively enrich anionic dyes rather than cationic dyes.

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Declaration of interests

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The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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The authors of the manuscript (COLSUA-D-19-01093) declare that we have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement The authors sincerely acknowledge the financial support of this work by the National Natural Sciences Foundation of China (NSFC No. 21605150 and 21544013).

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Figure captions

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Fig. 1 FTIR spectra of Cu-BDC, Zn-BDC and Ni-BDC.

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Fig. 2 Effect of contact time on adsorption.

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Fig. 3 Effect of initial concentration of alizarin yellow GG on adsorption capacity of Cu-BDC (a), Zn-BDC (b) and Ni-BDC (c) at different temperatures.

Fig. 4 Effect of ionic strength on adsorption.

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Fig. 5 The relationship between times for reuse versus adsorption capacity.

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Fig. 6 FTIR spectra of alizarin yellow GG, Cu-BDC and alizarin yellow GG loaded Cu-BDC.

Table 1 The physical property parameters of the prepared MOFs materials. Surface area

Micropore area

Pore volume

Micropore volume×105

Average pore width

m2/g

m2/g

cm3/g

cm3/g

nm

Cu-BDC

14.41

1.72

0.086

5.80

23.98

Zn-BDC

15.07

5.77

0.020

250

5.21

Ni-BDC

4.60

1.32

0.028

54

24.08

Adsorbents

Table 2 kinetic parameters obtained from pseudo-first-order and pseudo-second-order kinetic models. Adsorbents

×103

q1e

k1

Pseudo-second-order kinetics

R2

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Pseudo-first-order kinetics q2e

k2×105

h

R2

mg/g

mg/(g min)

mg/(g min)

min-1

Cu-BDC

296.55

6.04

0.9869

709.22

9.85

49.53

0.9970

Zn-BDC

87.08

3.51

0.6404

714.29

33.16

169.20

0.9986

Ni-BDC

329.14

7.50

0.8007

657.89

3.56

15.41

0.9914

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Table 3 Comparison of adsorption capacity for alizarin yellow GG (or alizarin yellow or alizarin

Adsorbents

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yellow R) with different adsorbents.

Adsorption capacity (mg/g)

Reference

400 15.87 121.95 39.0 72 37.7 47.8 710.02 764.79 621.12

[32] [33] [34] [35] [36] [37] [37] This study This study This study

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Ar@MCM Modified polymer Fe3O4@MCM@Cu–Fe–LDH γ-alumina nZVI/PANI/APT γ-Alumina DNPH-γ-Alumina Cu-BDC Zn-BDC Ni-BDC

Table 4 Adsorption isotherm parameters calculated from Langmuir and Freundlich isotherm models at different temperatures. Langmuir isotherm Adsorbents

qm

KL

mg/g

mg/L

R2

Freundlich isotherm RL

1/n

KF (mg/g)(L/mg)1/n

R2

Zn-BDC (30 °C) Ni-BDC (30 °C) Cu-BDC (40 °C) Zn-BDC (40 °C) Ni-BDC (40 °C) Cu-BDC (50 °C) Zn-BDC (50 °C)

30.34

0.8709

0.036-0.094

0.64

48.80

0.9856

764.79

194.61

0.9312

0.19-0.40

0.80

8.70

0.7632

621.12

353.93

0.9217

0.31-0.55

0.21

39.71

0.8788

669.67

39.44

0.8585

0.047-0.12

0.70

35.24

0.9885

656.60

251.85

0.9189

0.24-0.46

0.11

295.75

0.8656

648.09

263.91

0.9698

0.25-0.47

0.42

375.70

0.8923

647.63

66.98

0.8245

0.077-0.19

0.76

19.65

0.9712

613.12

140.37

0.9252

0.15-0.32

0.18

44.14

0.8851

638.53

173.16

0.9734

0.18-0.37

0.16

33.02

0.8758

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Ni-BDC (50 °C)

710.02

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Cu-BDC (30 °C)