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Facile synthesis of metal-organic framework UiO-66 for adsorptive removal of methylene blue from water
Journal Pre-proofs Facile Synthesis of Metal-Organic Framework UiO-66 for Adsorptive Removal of Methylene Blue from Water Xue Song, Pan Yang, Dongxue Wu, Pengxiang Zhao, Xiaochong Zhao, Lijun Yang, Yuanlin Zhou PII: DOI: Reference:
S0301-0104(19)31209-1 https://doi.org/10.1016/j.chemphys.2019.110655 CHEMPH 110655
To appear in:
Chemical Physics
Received Date: Revised Date: Accepted Date:
9 October 2019 4 December 2019 9 December 2019
Please cite this article as: X. Song, P. Yang, D. Wu, P. Zhao, X. Zhao, L. Yang, Y. Zhou, Facile Synthesis of MetalOrganic Framework UiO-66 for Adsorptive Removal of Methylene Blue from Water, Chemical Physics (2019), doi: https://doi.org/10.1016/j.chemphys.2019.110655
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Β© 2019 Published by Elsevier B.V.
Facile Synthesis of Metal-Organic Framework UiO-66 for Adsorptive Removal of Methylene Blue from Water Xue Songa,b, Pan Yangb, Dongxue Wub, Pengxiang Zhaoc, Xiaochong Zhaoc*, Lijun Yangb* , Yuanlin Zhoua*. a. State Key Laboratory of Environment-Friendly Energy Materials, Southwest University of Science and Technology, Mianyang 621010, China. b. Institute of Materials, Chinese Academy of Engineering Physics, Jiangyou 621908, China c. Science and Technology on Surface physics and Chemistry Laboratory, Jiangyou 621907, China. Corresponding author Email: [email protected] (Xiaochong Zhao), [email protected], and [email protected] (Yuanlin Zhou) Abstract Metal-organic frameworks have remarkable advantages of high specific surface area, tunable pore structure, species diversity and superior stability causing it be a good adsorbent for methylene blue removal. Here, UiO-66 was prepared by two-step simple method at room temperature, then the effects of water on morphology, crystallinity and adsorption properties of UiO-66 were studied. UiO-66 exhibits good adsorption performance of MB with maximum adsorption amount of 543.48 mg g-1 and good cycling stability.
Key words: metal-organic frameworks; removal; methylene blue. 1. Introduction Metal-organic frameworks (MOFs), 1-6a promising nanoporous material, has been gotten great attention and investigations. MOFs are composed of metal ions or clusters (as nodes) and organic ligands (as linkages) via self-assembly. These porous crystalline materials possess wonderful properties of high specific surface area, tunable pore structure and species diversity, which have been applied in a wide of fields such as gas storage and separation7, 8, catalysis9-11, drug loading12, 13 and adsorption removal14, 15, etc. Specially, various MOFs as adsorbents have been devoted to capture various toxic metal ions and dyes from water, and gain a certain progress over past decades6, 16-21. UiO-66, 22one kind of MOFs, possesses superior stability and chemical endurance that allow it be a suitable adsorbent to remove dyes in water.6, 15, 23-25 Herein, a facile and accessible method with two steps at room temperature is employed to prepare UiO-66 rather than solvothermal method. After that, the effects of water content on morphology and crystallinity of UiO-66 are investigated. Then the prepared UiO-66 with different water amount are utilized as adsorbents and adsorption performance of methylene blue (MB) as target organic pollutant are studied. Moreover, the effects of some influential parameters are studied and optimized the conditions. As a result, UiO-66 with high specific surface area exhibits good adsorption capacity, the maximum value is up to 543.48 mg g-1.
2. Experimental 2.1 Materials Zirconium (IV) propoxide solution, acetic acid (HAc), N, N-dimethylformamide (DMF), terephthalic acid (H2BDC,99%) are purchased from Aladdin Ltd in shanghai. Methylene blue is
obtained from kelong in chengdu. There is not any further purification for all above chemicals and deionized water is used in all experiments.
2.2 Synthesis of UiO-66 UiO-66 was prepared at room temperature in two-step according to a report with some modification.26 Firstly, 71ul of 70 % zirconium propoxide solution, 7 mL DMF and 4 mL acetic acid were added to a 20 ml vial. The solution was heated at 150 Β°C for 2 h under the wrapping of aluminum foil and the color turned yellow. Second, a magnetic stirrer and 75 mg terephthalic acid (H2BDC) were added to above solution after cooling down, the solution was sonicated for 30 s and stirred at 300 rpm for 18 h at 25 oC. Finally, the crystal was separated by centrifugation, washed several times with DMF and acetone and dried at 80 oC under a vacuum to get the white powder. This was defined as UiO-66 or UiO-66(0). UiO-66 (x) samples with various H2O/Zr molar ratio were prepared by adding water at first step, they were denoted as UiO-66(x) (x=10, 30, 60, 100).
2.3 Characterization The morphologies and structures of UiO-66 were investigated by scanning electron microscopy (SEM, Hitachi S4800) and powder X-ray diffraction (XRD, Bruker D8), respectively. The specific surface area was determined by N2 adsorption-desorption isotherms employing a Quantachrome surface area analyzer at 77 K. The concentration of MB was measured by UV-vis.
2.4 Adsorption experiments of MB All adsorption experiments were conducted at 25 oC in general environment. 10 mg UiO-66 was added to glass vial containing MB solution. The pH was adjusted by 0.1mol L-1 HCl and NaOH solutions ranging from 3 to 11 and initial concentration of MB was 60-130 mg L-1. Solution was sonicated for 5 min and stirred for different time (0-5h). Then, the concentration of residual MB was measured via UV-vis spectrophotometer at 664 nm. The adsorption capacity was calculated by Eq. (1-2). (πΆ0 β πΆπ)π ππ = (1) π (πΆ0 β πΆπ‘)π ππ‘ = (2) π Where qe is the equilibrium adsorption capacity in mg g-1, qt (mg/g) and Ct (mg L-1) is the adsorption capacity and concentration of MB at time t, C0 and Ce are initial and equilibrium concentration of MB solution in mg L-1, respectively, V is the volume of MB solution (mL), m is the mass of UiO-66 (mg), the same below. After first adsorption for MB (60 mg L-1) on UiO-66, the adsorbent was separated and washed with ethanol and HCl (0.1 M). The desorbed UiO-66 was used for next cycling at the same condition and repeated for 5 times.
3. Results and discussion 3.1 Characterization UiO-66 (x) were synthesized successfully at room temperature. The morphologies of adsorbents are determined by SEM images in Fig.1 (a-d). UiO-66 shows smooth cube shape and the surface of UiO-66 (x) become irregular as increasing water amount while the particle size become bigeer, which may result from the formation of defect. The XRD pattern is shown in Fig.2a. It can be found that peak positions are unchanged and the intensity declines in presence of water, which indicate that the incorporation of water does not
affect the structure but the crystallinity. The results of N2 adsorption-desorption isotherms of UiO-66 (x) were presented in Fig.2b and detail parameters in Table.1. The BET surface area of raw UiO-66 is the biggest up to 1684.295 m2 g-1 and the value decreases along with more water. This agrees to the results of SEM. While the pore diameter increases and following declines, and all diameter are less than 4 nm. The reason for this may be the defect of structure caused by water.
Fig.1 SEM images of (a)UiO-66, (b) UiO-66 (10), (c) UiO-66 (60), (d) UiO-66 (100).
Fig.2 (a) XRD patterns, (b) N2 adsorption-desorption isotherms and pore size distribution of UiO-66 (x).
Table.1 Surface and pore parameters of UiO-66(x).
adsorbent
SBET (m2οg-1)
Pore diameter (nm)
UiO-66 UiO-66(10)
1684.295 1469.082
3.387 3.792
UiO-66(60) UiO-66(100)
1364.183 1162.573
3.790 3.394
3.2 Removal of MB from water UiO-66 (x) were used to adsorb MB in water. As shown in Fig.3, it can be found that the adsorption amount and removal rate of UiO-66 (x) on MB declines as water content increases. UiO-66 has the best adsorption ability and removal efficiency among all, which may be attributed to the higher specific surface area and the presence of bigger pore. It indicates that the higher specific surface area is crucial for improving adsorption performance of UiO-66 on MB solution.
Fig.3 The plots of (a) adsorption capacity (b) efficiency of UiO-66 (x) on MB adsorption.
Fig.4 effect of pH on UiO-66 for MB adsorption.
The effect of pH in the range of 3-11 on adsorption capacity for MB removal by UiO-66 is shown in Fig.4. The adsorption capacity and removal rate improve gradually as pH increases and reaches equilibrium ultimately. The higher adsorption amount is obtained at higher pH value. This reason may be that MB molecules have positive charges, while the more negative charges are on the surface of UiO-66 at higher pH, promoting electrostatic attraction and contact between adsorbent and cationic dye MB.27 These indicated that pH is important in the adsorption process, which affected the interaction force between them. The pH value is selected as 10 in the following experiments.
Fig.5 (a) effect of initial concentration, (b) Langmuir isotherm and (c) Freundlich isotherm for MB adsorption on UiO-66. Table.2 coefficient of isotherm model.
Adsorbent UiO-66
Langmuir model qm
KL
(mg g-1)
(L mg-1)
543.48
0.049
Freundlich model R2
KF
n
R2
2.26
0.987
(L g-1) 0.996
69.74
The relationship between adsorption amount and initial concentration is plotted in Fig.5a. It can be seen that the adsorption capacity increases significantly as increasing MB concentration until achieving balance and the capacity is up to 375.70 mg g-1 at 130 mg L-1. This result may be caused by the strong driving force at higher concentration resulting in the more interaction between MB and adsorbent. The adsorption sites are definite at a fixed adsorbent usage. In this regard, almost adsorption sites of adsorbent are occupied and extra MB molecules remain in solution when the concentration reaches a certain value, leading to the adsorption equilibrium. Then the adsorption isotherms are predicted by Langmuir isotherm and Freundlich isotherm model Eq.(3,4)27,28, which are shown in Fig.5b,c. πΆπ πΆπ 1 + = (3) ππ πΎπΏππππ₯ ππππ₯ 1 ππππ = πππΎπΉ + πππΆπ (4) π where qmax is the maximum adsorption capacity in mg g-1, KL is Langmuir constant (L mg-1), KF is Freundlich constant, n indicates the adsorption intensity. Obviously, the Langmuir isotherm is more suitable to simulate MB adsorption comparing the results shown in Fig5b,c and Table.2. This demonstrates that the form of MB adsorption on UiO-66 is mainly single monolayer adsorption.28-30 In addition, the maximum adsorption capacity of 543.48 mg g-1 at room temperature is obtained, which is higher than that of reported literatures.23,24,31-34 Effect of contact time on MB adsorption of UiO-66 could be observed in Fig.6a and kinetic data are summarized in Table.3. The adsorption capacity is found to increase rapidly at beginning and then slow down gradually until reaching equilibrium. This reason is that the fixed number adsorption sites lessen with more contact time and eventually become saturated, and the efficient interactions changed accordingly. The kinetic behavior of MB adsorption is described by pseudo-first and pseudo-second order model as follows:27,28 ππ(ππ β ππ‘) = ππππ β πΎ1π‘ (5)
π‘ ππ‘
=
1 πΎ2π2π
+
π‘ ππ
(6)
Where K1 and K2 are rate constant of corresponding model. K1, K2 and qe can be evaluated from Eq.5 and 6 and results are presented in Fig.6b,c and Table.3. The results show that the fit of pseudo-second order model is more appropriate to describe the adsorption process. Moreover, it can be seen that the calculated qe of 242.13 mg g-1 is closer to the experimental value of 236.83 mg g-1 and R2 is closer to 1 in results of pseudo-second order model as compared with that of first order model. It means that the pseudo-second order model can be used to predict the adsorption capacity of MB onto UiO-66.
Fig.6 (a)time evolution, kinetics fits of (b) pseudo-first order (c) pseudo-second order for MB adsorption on UiO-66. Table.3 coefficient of kinetic model.
Adsorbent UiO-66
Pseudo-first-order model qe
K1
(mg g-1)
(min-1)
131.20
0.0166
R2 0.935
Pseudo-second-order model qe
K2
(mg g-1)
(g mg-1 min-1)
242.13
0.0005
R2 0.9989
The adsorption trend of MB on UiO-66 with different dosages is shown in Fig.7a. On the contrary, increasing adsorbent mass, the adsorption amount is reduced. This reason may be that the adsorption capacity of UiO-66 becomes saturated at low concentration of MB solution, but the mass increases leading the value of qe declines. Fig.7b shows five adsorption-desorption cycles. Compared with first adsorption efficiency of UiO-66, the removal rate reaches 72% of initial value after five cycles. This may because that some active sites are still occupied by MB molecules after desorption. Moreover, XRD analysis of the adsorbent after adsorption and desorption is shown in Fig.7c. It can be seen that the peak position of UiO-66 is unchanged and intensity declines after adsorption or desorption, which shows the good stable structure. These results indicate that the adsorbent has good stability and cycle abilities for removing MB dyes.
Fig.7 (a) effect of adsorbent dosage on adsorption capacity, (b) reusability of UiO-66, (c) XRD pattern of UiO-66 after
adsorption process.
Meanwhile, the SEM images of adsorbent after adsorption and desorption are presented in Fig.8. The morphology remains raw cube shape after adsorption process. These results above indicate that UiO-66 with good stability can be recycled for MB removal.
Fig.8 SEM image of UiO-66 (a) after adsorption, (b) after desorption.
4. Conclusion In summary, UiO-66 was synthesized via two-steps, the morphology and crystallinity change in the presence of water. UiO-66 performs the best adsorption capacity with maximum capacity of 543.48 mg g-1 for MB removal at room temperature. The good properties of the adsorbent may be attributed to its high specific surface area offering many adsorption sites. Furthermore, the adsorption progress follows the pseudo-second-order model. The adsorbent exhibits well recoverable ability after five cycles of adsorption-desorption.
Acknowledgements This work is supported by the Project of State Key Laboratory of Environment-friendly Energy Materials, Southwest University of Science and Technology (No.18zxhk20)
Conflicts of interest There are no conflicts to declare.
Reference [1] S. Yuan, L. Feng, K. Wang, J. Pang, M. Bosch, C. Lollar, Y. Sun, J. Qin, X. Yang, P. Zhang, Q. Wang, L. Zou, Y. Zhang, L. Zhang, Y. Fang, J. Li, H.C. Zhou, Adv Mater. 2018, 30, 1704303. [2] X. Han, S. Yang, M. SchrΓΆder, Nat Rev Chem. 2019, 3, 108-118. [3] Y. Cui, B. Li, H. He, W. Zhou, B. Chen, G. Qian, Acc Chem Res. 2016, 49, 483-93. [4] A.J. Howarth, Y. Liu, P. Li, Z. Li, T.C. Wang, J.T. Hupp, O.K. Farha, Nat Rev Mater, 2016, 1. [5] B. Li, H.M. Wen, Y. Cui, W. Zhou, G. Qian, B. Chen, Adv Mater, 2016, 28, 8819-8860. [6] J. Li, X. Wang, G. Zhao, C. Chen, Z. Chai, A. Alsaedi, T. Hayat, X. Wang, Chem Soc Rev. 2018, 47, 2322-2356. [7] S. Friebe, B. Geppert, F. Steinbach, J. Caro, ACS Appl Mater Inter. 2017, 9, 12878-12885. [8] H. Li, K. Wang, Y. Sun, C.T. Lollar, J. Li, H.-C. Zhou, Mater Today. 2018, 21, 108-121. [9] A. Dhakshinamoorthy, Z. Li, H. Garcia, Chem Soc Rev. 2018, 47, 8134-8172. [10] A.M. Abdel-Mageed, B. Rungtaweevoranit, M. Parlinska-Wojtan, X. Pei, O.M. Yaghi, R.J.
[11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34]
Behm, J Am Chem Soc. 2019, 141, 5201-5210. H. Tabassum, W. Guo, W. Meng, A. Mahmood, R. Zhao, Q. Wang, R. Zou, Adv. Energy Mater. 2017, 7. B. Lei, M. Wang, Z. Jiang, W. Qi, R. Su, Z. He, ACS Appl Mater Inter. 2018, 10, 16698-16706. H. Zheng, Y. Zhang, L. Liu, W. Wan, P. Guo, A.M. Nystrom, X. Zou, J Am Chem Soc. 2016, 138, 962-8. N.S. Bobbitt, M.L. Mendonca, A.J. Howarth, T. Islamoglu, J.T. Hupp, O.K. Farha, R.Q. Snurr, Chem Soc Rev. 2017, 46, 3357-3385. R.J. Drout, L. Robison, Z. Chen, T. Islamoglu, O.K. Farha, Trend in Chem. 2019, 1, 304-317. J.M. Yang, J Colloid Interf Sci. 2017, 505, 178-185. P.A. Kobielska, A.J. Howarth, O.K. Farha, S. Nayak, Coordin Chem Rev. 2018, 358, 92-107. M. Oveisi, M.A. Asli, N.M. Mahmoodi, J Hazard Mater, 2018, 347, 123-140. Q. Gao, J. Xu, X.-H. Bu, Coordin Chem Rev. 2019, 378, 17-31. Q. Yang, R. Lu, S. Ren, C. Chen, Z. Chen, X. Yang, Chem Eng J. 2018, 348, 202-211. C. Palomino Cabello, M.F.F. PicΓ³, F. Maya, M. del Rio, G. Turnes Palomino, Chem Eng J, 2018, 346, 85-93. Y. Bai, Y. Dou, L.H. Xie, W. Rutledge, J.R. Li, H.C. Zhou, Chem Soc Rev. 2016, 45, 2327-67. J. Qiu, Y. Feng, X. Zhang, M. Jia, J. Yao, J Colloid Interf Sci. 2017, 499, 151-158. J.M. Yang, R.J. Ying, C.X. Han, Q.T. Hu, H.M. Xu, J.H. Li, Q. Wang, W. Zhang, Dalton T. 2018, 47, 3913-3920. Q. Zhang, X. Jiang, A.M. Kirillov, Y. Zhang, M. Hu, W. Liu, L. Yang, R. Fang, W. Liu, ACS Sustain Chem Eng. 2019, 7, 3203-3212. M.R. DeStefano, T. Islamoglu, S.J. Garibay, J.T. Hupp, O.K.J.C.o.M. Farha, Chem Mater. 2017, 29, 1357-1361. Q. Wang, J. Ju, Y. Tan, L. Hao, Y. Ma, Y. Wu, H. Zhang, Y. Xia, K. Sui, Carbohydr Polym. 2019, 205, 125-134. J. Abdi, M. Vossoughi, N.M. Mahmoodi, I. Alemzadeh, Chem Eng J. 2017, 326, 1145-1158. X. Wan, Y. Zhan, Z. Long, G. Zeng, Y. He, Chem Eng J. 2017, 330, 491-504. X. Zhao, K. Wang, Z. Gao, H. Gao, Z. Xie, X. Du, H. Huang, Ind Eng Chem Res. 2017, 56, 4496-4501. F. Marrakchi, M.J. Ahmed, W.A. Khanday, M. Asif, B.H. Hameed, Int J Biol Macromol. 2017, 98, 233-239. X.P. Luo, S.Y. Fu, Y.M. Du, J.Z. Guo, B. Li, Micropor Mesopor Mat. 2017, 237, 268-274. C. Liu, A.M. Omer, X.K. Ouyang, Int J Biol Macromol. 2018, 106, 823-833. J. Zhang, F. Li, Q. Sun, Appl Surf Sci. 2018, 440, 1219-1226.
Declaration of interests β 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. βThe authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
UiO-66(x) with different water content were prepared specific surface area.
UiO-66
by a two-step simple method at room temperature, which owns high
performs pretty adsorption capacity with maximum adsorption amount of 543.48 mg g-1 and cycle
stability for methylene blue removal from water because of its better surace area.
Highlights:
ο¬ ο¬ ο¬ ο¬
UiO-66 was prepared by a facile method at room temperature. UiO-66 with different water content was studied. The maximum adsorption capacity of MB removal is 543.48 mg g-1. The adsorbent has good stability and durability at room temperature.
S0301-0104(19)31209-1 https://doi.org/10.1016/j.chemphys.2019.110655 CHEMPH 110655
To appear in:
Chemical Physics
Received Date: Revised Date: Accepted Date:
9 October 2019 4 December 2019 9 December 2019
Please cite this article as: X. Song, P. Yang, D. Wu, P. Zhao, X. Zhao, L. Yang, Y. Zhou, Facile Synthesis of MetalOrganic Framework UiO-66 for Adsorptive Removal of Methylene Blue from Water, Chemical Physics (2019), doi: https://doi.org/10.1016/j.chemphys.2019.110655
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Β© 2019 Published by Elsevier B.V.
Facile Synthesis of Metal-Organic Framework UiO-66 for Adsorptive Removal of Methylene Blue from Water Xue Songa,b, Pan Yangb, Dongxue Wub, Pengxiang Zhaoc, Xiaochong Zhaoc*, Lijun Yangb* , Yuanlin Zhoua*. a. State Key Laboratory of Environment-Friendly Energy Materials, Southwest University of Science and Technology, Mianyang 621010, China. b. Institute of Materials, Chinese Academy of Engineering Physics, Jiangyou 621908, China c. Science and Technology on Surface physics and Chemistry Laboratory, Jiangyou 621907, China. Corresponding author Email: [email protected] (Xiaochong Zhao), [email protected], and [email protected] (Yuanlin Zhou) Abstract Metal-organic frameworks have remarkable advantages of high specific surface area, tunable pore structure, species diversity and superior stability causing it be a good adsorbent for methylene blue removal. Here, UiO-66 was prepared by two-step simple method at room temperature, then the effects of water on morphology, crystallinity and adsorption properties of UiO-66 were studied. UiO-66 exhibits good adsorption performance of MB with maximum adsorption amount of 543.48 mg g-1 and good cycling stability.
Key words: metal-organic frameworks; removal; methylene blue. 1. Introduction Metal-organic frameworks (MOFs), 1-6a promising nanoporous material, has been gotten great attention and investigations. MOFs are composed of metal ions or clusters (as nodes) and organic ligands (as linkages) via self-assembly. These porous crystalline materials possess wonderful properties of high specific surface area, tunable pore structure and species diversity, which have been applied in a wide of fields such as gas storage and separation7, 8, catalysis9-11, drug loading12, 13 and adsorption removal14, 15, etc. Specially, various MOFs as adsorbents have been devoted to capture various toxic metal ions and dyes from water, and gain a certain progress over past decades6, 16-21. UiO-66, 22one kind of MOFs, possesses superior stability and chemical endurance that allow it be a suitable adsorbent to remove dyes in water.6, 15, 23-25 Herein, a facile and accessible method with two steps at room temperature is employed to prepare UiO-66 rather than solvothermal method. After that, the effects of water content on morphology and crystallinity of UiO-66 are investigated. Then the prepared UiO-66 with different water amount are utilized as adsorbents and adsorption performance of methylene blue (MB) as target organic pollutant are studied. Moreover, the effects of some influential parameters are studied and optimized the conditions. As a result, UiO-66 with high specific surface area exhibits good adsorption capacity, the maximum value is up to 543.48 mg g-1.
2. Experimental 2.1 Materials Zirconium (IV) propoxide solution, acetic acid (HAc), N, N-dimethylformamide (DMF), terephthalic acid (H2BDC,99%) are purchased from Aladdin Ltd in shanghai. Methylene blue is
obtained from kelong in chengdu. There is not any further purification for all above chemicals and deionized water is used in all experiments.
2.2 Synthesis of UiO-66 UiO-66 was prepared at room temperature in two-step according to a report with some modification.26 Firstly, 71ul of 70 % zirconium propoxide solution, 7 mL DMF and 4 mL acetic acid were added to a 20 ml vial. The solution was heated at 150 Β°C for 2 h under the wrapping of aluminum foil and the color turned yellow. Second, a magnetic stirrer and 75 mg terephthalic acid (H2BDC) were added to above solution after cooling down, the solution was sonicated for 30 s and stirred at 300 rpm for 18 h at 25 oC. Finally, the crystal was separated by centrifugation, washed several times with DMF and acetone and dried at 80 oC under a vacuum to get the white powder. This was defined as UiO-66 or UiO-66(0). UiO-66 (x) samples with various H2O/Zr molar ratio were prepared by adding water at first step, they were denoted as UiO-66(x) (x=10, 30, 60, 100).
2.3 Characterization The morphologies and structures of UiO-66 were investigated by scanning electron microscopy (SEM, Hitachi S4800) and powder X-ray diffraction (XRD, Bruker D8), respectively. The specific surface area was determined by N2 adsorption-desorption isotherms employing a Quantachrome surface area analyzer at 77 K. The concentration of MB was measured by UV-vis.
2.4 Adsorption experiments of MB All adsorption experiments were conducted at 25 oC in general environment. 10 mg UiO-66 was added to glass vial containing MB solution. The pH was adjusted by 0.1mol L-1 HCl and NaOH solutions ranging from 3 to 11 and initial concentration of MB was 60-130 mg L-1. Solution was sonicated for 5 min and stirred for different time (0-5h). Then, the concentration of residual MB was measured via UV-vis spectrophotometer at 664 nm. The adsorption capacity was calculated by Eq. (1-2). (πΆ0 β πΆπ)π ππ = (1) π (πΆ0 β πΆπ‘)π ππ‘ = (2) π Where qe is the equilibrium adsorption capacity in mg g-1, qt (mg/g) and Ct (mg L-1) is the adsorption capacity and concentration of MB at time t, C0 and Ce are initial and equilibrium concentration of MB solution in mg L-1, respectively, V is the volume of MB solution (mL), m is the mass of UiO-66 (mg), the same below. After first adsorption for MB (60 mg L-1) on UiO-66, the adsorbent was separated and washed with ethanol and HCl (0.1 M). The desorbed UiO-66 was used for next cycling at the same condition and repeated for 5 times.
3. Results and discussion 3.1 Characterization UiO-66 (x) were synthesized successfully at room temperature. The morphologies of adsorbents are determined by SEM images in Fig.1 (a-d). UiO-66 shows smooth cube shape and the surface of UiO-66 (x) become irregular as increasing water amount while the particle size become bigeer, which may result from the formation of defect. The XRD pattern is shown in Fig.2a. It can be found that peak positions are unchanged and the intensity declines in presence of water, which indicate that the incorporation of water does not
affect the structure but the crystallinity. The results of N2 adsorption-desorption isotherms of UiO-66 (x) were presented in Fig.2b and detail parameters in Table.1. The BET surface area of raw UiO-66 is the biggest up to 1684.295 m2 g-1 and the value decreases along with more water. This agrees to the results of SEM. While the pore diameter increases and following declines, and all diameter are less than 4 nm. The reason for this may be the defect of structure caused by water.
Fig.1 SEM images of (a)UiO-66, (b) UiO-66 (10), (c) UiO-66 (60), (d) UiO-66 (100).
Fig.2 (a) XRD patterns, (b) N2 adsorption-desorption isotherms and pore size distribution of UiO-66 (x).
Table.1 Surface and pore parameters of UiO-66(x).
adsorbent
SBET (m2οg-1)
Pore diameter (nm)
UiO-66 UiO-66(10)
1684.295 1469.082
3.387 3.792
UiO-66(60) UiO-66(100)
1364.183 1162.573
3.790 3.394
3.2 Removal of MB from water UiO-66 (x) were used to adsorb MB in water. As shown in Fig.3, it can be found that the adsorption amount and removal rate of UiO-66 (x) on MB declines as water content increases. UiO-66 has the best adsorption ability and removal efficiency among all, which may be attributed to the higher specific surface area and the presence of bigger pore. It indicates that the higher specific surface area is crucial for improving adsorption performance of UiO-66 on MB solution.
Fig.3 The plots of (a) adsorption capacity (b) efficiency of UiO-66 (x) on MB adsorption.
Fig.4 effect of pH on UiO-66 for MB adsorption.
The effect of pH in the range of 3-11 on adsorption capacity for MB removal by UiO-66 is shown in Fig.4. The adsorption capacity and removal rate improve gradually as pH increases and reaches equilibrium ultimately. The higher adsorption amount is obtained at higher pH value. This reason may be that MB molecules have positive charges, while the more negative charges are on the surface of UiO-66 at higher pH, promoting electrostatic attraction and contact between adsorbent and cationic dye MB.27 These indicated that pH is important in the adsorption process, which affected the interaction force between them. The pH value is selected as 10 in the following experiments.
Fig.5 (a) effect of initial concentration, (b) Langmuir isotherm and (c) Freundlich isotherm for MB adsorption on UiO-66. Table.2 coefficient of isotherm model.
Adsorbent UiO-66
Langmuir model qm
KL
(mg g-1)
(L mg-1)
543.48
0.049
Freundlich model R2
KF
n
R2
2.26
0.987
(L g-1) 0.996
69.74
The relationship between adsorption amount and initial concentration is plotted in Fig.5a. It can be seen that the adsorption capacity increases significantly as increasing MB concentration until achieving balance and the capacity is up to 375.70 mg g-1 at 130 mg L-1. This result may be caused by the strong driving force at higher concentration resulting in the more interaction between MB and adsorbent. The adsorption sites are definite at a fixed adsorbent usage. In this regard, almost adsorption sites of adsorbent are occupied and extra MB molecules remain in solution when the concentration reaches a certain value, leading to the adsorption equilibrium. Then the adsorption isotherms are predicted by Langmuir isotherm and Freundlich isotherm model Eq.(3,4)27,28, which are shown in Fig.5b,c. πΆπ πΆπ 1 + = (3) ππ πΎπΏππππ₯ ππππ₯ 1 ππππ = πππΎπΉ + πππΆπ (4) π where qmax is the maximum adsorption capacity in mg g-1, KL is Langmuir constant (L mg-1), KF is Freundlich constant, n indicates the adsorption intensity. Obviously, the Langmuir isotherm is more suitable to simulate MB adsorption comparing the results shown in Fig5b,c and Table.2. This demonstrates that the form of MB adsorption on UiO-66 is mainly single monolayer adsorption.28-30 In addition, the maximum adsorption capacity of 543.48 mg g-1 at room temperature is obtained, which is higher than that of reported literatures.23,24,31-34 Effect of contact time on MB adsorption of UiO-66 could be observed in Fig.6a and kinetic data are summarized in Table.3. The adsorption capacity is found to increase rapidly at beginning and then slow down gradually until reaching equilibrium. This reason is that the fixed number adsorption sites lessen with more contact time and eventually become saturated, and the efficient interactions changed accordingly. The kinetic behavior of MB adsorption is described by pseudo-first and pseudo-second order model as follows:27,28 ππ(ππ β ππ‘) = ππππ β πΎ1π‘ (5)
π‘ ππ‘
=
1 πΎ2π2π
+
π‘ ππ
(6)
Where K1 and K2 are rate constant of corresponding model. K1, K2 and qe can be evaluated from Eq.5 and 6 and results are presented in Fig.6b,c and Table.3. The results show that the fit of pseudo-second order model is more appropriate to describe the adsorption process. Moreover, it can be seen that the calculated qe of 242.13 mg g-1 is closer to the experimental value of 236.83 mg g-1 and R2 is closer to 1 in results of pseudo-second order model as compared with that of first order model. It means that the pseudo-second order model can be used to predict the adsorption capacity of MB onto UiO-66.
Fig.6 (a)time evolution, kinetics fits of (b) pseudo-first order (c) pseudo-second order for MB adsorption on UiO-66. Table.3 coefficient of kinetic model.
Adsorbent UiO-66
Pseudo-first-order model qe
K1
(mg g-1)
(min-1)
131.20
0.0166
R2 0.935
Pseudo-second-order model qe
K2
(mg g-1)
(g mg-1 min-1)
242.13
0.0005
R2 0.9989
The adsorption trend of MB on UiO-66 with different dosages is shown in Fig.7a. On the contrary, increasing adsorbent mass, the adsorption amount is reduced. This reason may be that the adsorption capacity of UiO-66 becomes saturated at low concentration of MB solution, but the mass increases leading the value of qe declines. Fig.7b shows five adsorption-desorption cycles. Compared with first adsorption efficiency of UiO-66, the removal rate reaches 72% of initial value after five cycles. This may because that some active sites are still occupied by MB molecules after desorption. Moreover, XRD analysis of the adsorbent after adsorption and desorption is shown in Fig.7c. It can be seen that the peak position of UiO-66 is unchanged and intensity declines after adsorption or desorption, which shows the good stable structure. These results indicate that the adsorbent has good stability and cycle abilities for removing MB dyes.
Fig.7 (a) effect of adsorbent dosage on adsorption capacity, (b) reusability of UiO-66, (c) XRD pattern of UiO-66 after
adsorption process.
Meanwhile, the SEM images of adsorbent after adsorption and desorption are presented in Fig.8. The morphology remains raw cube shape after adsorption process. These results above indicate that UiO-66 with good stability can be recycled for MB removal.
Fig.8 SEM image of UiO-66 (a) after adsorption, (b) after desorption.
4. Conclusion In summary, UiO-66 was synthesized via two-steps, the morphology and crystallinity change in the presence of water. UiO-66 performs the best adsorption capacity with maximum capacity of 543.48 mg g-1 for MB removal at room temperature. The good properties of the adsorbent may be attributed to its high specific surface area offering many adsorption sites. Furthermore, the adsorption progress follows the pseudo-second-order model. The adsorbent exhibits well recoverable ability after five cycles of adsorption-desorption.
Acknowledgements This work is supported by the Project of State Key Laboratory of Environment-friendly Energy Materials, Southwest University of Science and Technology (No.18zxhk20)
Conflicts of interest There are no conflicts to declare.
Reference [1] S. Yuan, L. Feng, K. Wang, J. Pang, M. Bosch, C. Lollar, Y. Sun, J. Qin, X. Yang, P. Zhang, Q. Wang, L. Zou, Y. Zhang, L. Zhang, Y. Fang, J. Li, H.C. Zhou, Adv Mater. 2018, 30, 1704303. [2] X. Han, S. Yang, M. SchrΓΆder, Nat Rev Chem. 2019, 3, 108-118. [3] Y. Cui, B. Li, H. He, W. Zhou, B. Chen, G. Qian, Acc Chem Res. 2016, 49, 483-93. [4] A.J. Howarth, Y. Liu, P. Li, Z. Li, T.C. Wang, J.T. Hupp, O.K. Farha, Nat Rev Mater, 2016, 1. [5] B. Li, H.M. Wen, Y. Cui, W. Zhou, G. Qian, B. Chen, Adv Mater, 2016, 28, 8819-8860. [6] J. Li, X. Wang, G. Zhao, C. Chen, Z. Chai, A. Alsaedi, T. Hayat, X. Wang, Chem Soc Rev. 2018, 47, 2322-2356. [7] S. Friebe, B. Geppert, F. Steinbach, J. Caro, ACS Appl Mater Inter. 2017, 9, 12878-12885. [8] H. Li, K. Wang, Y. Sun, C.T. Lollar, J. Li, H.-C. Zhou, Mater Today. 2018, 21, 108-121. [9] A. Dhakshinamoorthy, Z. Li, H. Garcia, Chem Soc Rev. 2018, 47, 8134-8172. [10] A.M. Abdel-Mageed, B. Rungtaweevoranit, M. Parlinska-Wojtan, X. Pei, O.M. Yaghi, R.J.
[11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34]
Behm, J Am Chem Soc. 2019, 141, 5201-5210. H. Tabassum, W. Guo, W. Meng, A. Mahmood, R. Zhao, Q. Wang, R. Zou, Adv. Energy Mater. 2017, 7. B. Lei, M. Wang, Z. Jiang, W. Qi, R. Su, Z. He, ACS Appl Mater Inter. 2018, 10, 16698-16706. H. Zheng, Y. Zhang, L. Liu, W. Wan, P. Guo, A.M. Nystrom, X. Zou, J Am Chem Soc. 2016, 138, 962-8. N.S. Bobbitt, M.L. Mendonca, A.J. Howarth, T. Islamoglu, J.T. Hupp, O.K. Farha, R.Q. Snurr, Chem Soc Rev. 2017, 46, 3357-3385. R.J. Drout, L. Robison, Z. Chen, T. Islamoglu, O.K. Farha, Trend in Chem. 2019, 1, 304-317. J.M. Yang, J Colloid Interf Sci. 2017, 505, 178-185. P.A. Kobielska, A.J. Howarth, O.K. Farha, S. Nayak, Coordin Chem Rev. 2018, 358, 92-107. M. Oveisi, M.A. Asli, N.M. Mahmoodi, J Hazard Mater, 2018, 347, 123-140. Q. Gao, J. Xu, X.-H. Bu, Coordin Chem Rev. 2019, 378, 17-31. Q. Yang, R. Lu, S. Ren, C. Chen, Z. Chen, X. Yang, Chem Eng J. 2018, 348, 202-211. C. Palomino Cabello, M.F.F. PicΓ³, F. Maya, M. del Rio, G. Turnes Palomino, Chem Eng J, 2018, 346, 85-93. Y. Bai, Y. Dou, L.H. Xie, W. Rutledge, J.R. Li, H.C. Zhou, Chem Soc Rev. 2016, 45, 2327-67. J. Qiu, Y. Feng, X. Zhang, M. Jia, J. Yao, J Colloid Interf Sci. 2017, 499, 151-158. J.M. Yang, R.J. Ying, C.X. Han, Q.T. Hu, H.M. Xu, J.H. Li, Q. Wang, W. Zhang, Dalton T. 2018, 47, 3913-3920. Q. Zhang, X. Jiang, A.M. Kirillov, Y. Zhang, M. Hu, W. Liu, L. Yang, R. Fang, W. Liu, ACS Sustain Chem Eng. 2019, 7, 3203-3212. M.R. DeStefano, T. Islamoglu, S.J. Garibay, J.T. Hupp, O.K.J.C.o.M. Farha, Chem Mater. 2017, 29, 1357-1361. Q. Wang, J. Ju, Y. Tan, L. Hao, Y. Ma, Y. Wu, H. Zhang, Y. Xia, K. Sui, Carbohydr Polym. 2019, 205, 125-134. J. Abdi, M. Vossoughi, N.M. Mahmoodi, I. Alemzadeh, Chem Eng J. 2017, 326, 1145-1158. X. Wan, Y. Zhan, Z. Long, G. Zeng, Y. He, Chem Eng J. 2017, 330, 491-504. X. Zhao, K. Wang, Z. Gao, H. Gao, Z. Xie, X. Du, H. Huang, Ind Eng Chem Res. 2017, 56, 4496-4501. F. Marrakchi, M.J. Ahmed, W.A. Khanday, M. Asif, B.H. Hameed, Int J Biol Macromol. 2017, 98, 233-239. X.P. Luo, S.Y. Fu, Y.M. Du, J.Z. Guo, B. Li, Micropor Mesopor Mat. 2017, 237, 268-274. C. Liu, A.M. Omer, X.K. Ouyang, Int J Biol Macromol. 2018, 106, 823-833. J. Zhang, F. Li, Q. Sun, Appl Surf Sci. 2018, 440, 1219-1226.
Declaration of interests β 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. βThe authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
UiO-66(x) with different water content were prepared specific surface area.
UiO-66
by a two-step simple method at room temperature, which owns high
performs pretty adsorption capacity with maximum adsorption amount of 543.48 mg g-1 and cycle
stability for methylene blue removal from water because of its better surace area.
Highlights:
ο¬ ο¬ ο¬ ο¬
UiO-66 was prepared by a facile method at room temperature. UiO-66 with different water content was studied. The maximum adsorption capacity of MB removal is 543.48 mg g-1. The adsorbent has good stability and durability at room temperature.