In situ modification of ZIF-67 with multi-sulfonated dyes for great enhanced methylene blue adsorption via synergistic effect

It is essential mean to adsorptive remove organic pollutants such dyestuff for water remediation. Herein in situ modification of the classic metal-organic framework ZIF-67 with –SO3 groups was easily achieved by the efficient adsorption of multi-sulfonated dyes due to the coordinative interaction between the unoccupied Co(II) of ZIF-67 and –SO3 of the dyes.

Microporous and Mesoporous Materials 303 (2020) 110304 Contents lists available at ScienceDirect Microporous and Mesoporous Materials journal homepage: http://www.elsevier.com/locate/micromeso In situ modification of ZIF-67 with multi-sulfonated dyes for great enhanced methylene blue adsorption via synergistic effect Yanfeng Liu a, Duoyu Lin a, Weiting Yang a, *, Xueying An a, Ahui Sun a, Xiaolei Fan b, **, Qinhe Pan a, *** a b Key Laboratory of Advanced Materials of Tropical Island Resources, Ministry of Education, School of Science, Hainan University, Haikou, 570228, PR China Department of Chemical Engineering and Analytical Science, School of Engineering, The University of Manchester, M13 9PL, UK A R T I C L E I N F O A B S T R A C T Keywords: Metal-organic frameworks (MOFs) ZIF-67 Multi-sulfonated dyes Methylene blue Synergistic effect It is essential mean to adsorptive remove organic pollutants such dyestuff for water remediation Herein in situ modification of the classic metal-organic framework ZIF-67 with –SOÀ3 groups was easily achieved by the effi­ cient adsorption of multi-sulfonated dyes due to the coordinative interaction between the unoccupied Co(II) of ZIF-67 and –SOÀ3 of the dyes Interestingly, highly efficient synergistic absorption of multi-sulfonated dyes toư wards methylene blue (MBỵ) upon ZIF-67 was discovered for the first time The improved adsorption capacity of ZIF-67 for MBỵ in presence of cotton blue (CB ) was measured with a record-high value of 5,857.9 mg/g The underlying mechanism of the synergistic adsorption was probed, showing that, after the initial coordination between the –SOÀ3 of the dyes and the unoccupied Co(II) of ZIF-67, the available –SOÀ3 groups of multi-sulfonated dyes can interact with Nỵ(CH3)2 in MBỵ and hence greatly improving the adsorption capacity of MBỵ Introduction The dyes are generally applied in many chemical industries such as textiles, plastic, prints, paper, cosmetics, etc [1] Most dyes are non-biodegradable, poisonous, as well as being carcinogenic The dyes are occasionally discharged into the environment as untreated waste, which affects the security of living species severely [2] As the essential demand of environmental conservation and ecological protection, it is extremely necessary to trap and separate the organic pollutants from wastewater effectively [3,4] Metal-organic frameworks (MOFs) have demonstrated much superiority in guest uptake/separation from exem­ plar mixtures due to the tunable host-guest interactions, including hydrogen bonds, Vander Waals interaction, ion exchange, π-π interac­ tion, electrostatic interaction, Lewis acid-base interaction, etc [5–11] Classical MOFs including MOF-5 [12], MIL-100 [13], Fe-MOF-235 [14], Co-ZIF-8 [15], Ni-MOF-199 [16], Cr-MIL-101 [17], and Ti-UiO-66 [18], have been revealed successfully in the adsorptive removal of various organic dyes from dye-containing aqueous systems Interestingly, MOFs functionalized with particular groups were discovered favorable in improving the adsorption of organic dyes For example, MOFs functionalized with amino group such as MIL-125-NH2 [19], MIL-101-NH2 [20], and UiO-66-NH2 [21], demonstrated the adsorption capacity improved for cationic dyes Compared with the pristine MIL-101(Cr), MIL-101(Cr)–SO3H was beneficial to trap the cationic dyes due to the presence of –SO3H groups [22,23] Considering the modifi­ cation of MOFs in situ using the functional groups in dyes (due to the coordinative interaction) after the initial adsorption, such synergy may be true as well for the subsequent adsorption of other dyes by the similar chemical and/or physical interactions So far various pristine and functionalized MOFs as well as MOF-based composite materials were used for the purification of dye-containing aqueous systems [5], how­ ever, the attempt of modification of MOFs using the dyes with particular functional groups for the synergistic adsorption of another dye was never reported In this work, ZIF-67 was selected as the candidate adsorbent for investigating the synergistic adsorption of the dyes in aqueous systems, due to its good stability, high specific surface area, large pore volume and the presence of unoccupied metal active sites [24,25] Additionally, the Co(II) centers in ZIF-67 can bind the organic dyes with –SOÀ3 groups [26] Moreover, MOFs modified with –SOÀ3 could improve the cationic * Corresponding author ** Corresponding author *** Corresponding author E-mail addresses: yangwt@hainanu.edu.cn (W Yang), xiaolei.fan@manchester.ac.uk (X Fan), panqinhe@163.com (Q Pan) https://doi.org/10.1016/j.micromeso.2020.110304 Received 16 February 2020; Received in revised form 22 April 2020; Accepted May 2020 Available online May 2020 1387-1811/© 2020 Elsevier Inc All rights reserved Y Liu et al Microporous and Mesoporous Materials 303 (2020) 110304 dyes adsorption via electrostatic attraction [22,23],which was poten­ tially beneficial to the possible synergistic absorption Accordingly, based on the considerations discussed above, MOFs after the in situ modification of the multi-sulfonated compounds may exhibit enhanced synergistic adsorption capacity especially for cationic dyes Thus, effi­ cient synergistic absorption towards cationic dyes with Nỵ(CH3)2 groups was studied by introducing multi-sulfonated dyes into ZIF-67 The experimental results showed that synergistic absorption of the multi-sulfonated dyes towards MBỵ upon ZIF-67 was true, yet very efficient Mechanistic analysis suggested that the electrostatic interacư tion between the respective SO3 and Nỵ(CH3)2 groups in the two dyes lead to the synergistic interaction This work demonstrates an efficient method to enhance the adsorption and separation performance of MOFs for dyes in aqueous media Meanwhile, it is innovative and easy to in situ modify MOFs with –SOÀ3 groups by coordination with dyes, compared with general functionalization about 0.9 μm as analyzed by SEM (Fig S2) The synthesized ZIF-67 was further characterized by FTIR spectroscopy, as seen in Fig S3, the IR bands at 3,133.9, 2,925.9, 1,171.9, and 425.4 cmÀ matched well with the previously reported data [28,29] The Brunauer–Emmett–Teller (BET) surface area via nitrogen adsorption was calculated to be 1,445 m2/g (Fig S4) 3.1 Performance of ZIF-67 for single component dye adsorption As illustrated in Fig 1, all the selected cationic and anionic dyes could be absorbed by ZIF-67, and the adsorption capacity ranged from 94.3 mg/g (for RhBỵ) to 1,250.0 mg/g (for CR ) Judging from the above adsorption behavior, the positive and negative charges of the dyes are not the critical factor for the quantity adsorbed In addition, as shown in Table S1, the calculated molecular sizes of the dyes are listed in order of MBỵ < MO < ACBK CB > FAÀ > EBBRÀ > CBBRÀ > CRÀ All of the in situ modification of the dyes on ZIF-67 resulted in the greatly enhanced absorption capacity of MBỵ, and the highest adsorbed quantity of MBỵ was measured at ~1,150.8 mg/g in the presence of ACBKÀ In com­ parison, the adsorption capacity of ZIF-67 for MBỵ is only ~103.4 mg/g in the single-component dye adsorption experiment Therefore, it is plausible that the greater enhanced MBỵ adsorption with ACBK , CBÀ , and FAÀ dyes than that with CBBRÀ , EBBRÀ and CRÀ dyes might be due to presence of the additional –SOÀ3 group, leading to the synergistic dyedye interaction Additionally, such synergetic effect was not measured for MBỵ with MOÀ which only possesses a single –SOÀ3 group These results demonstrate that the adsorption performance towards MBỵ can be enhanced via the synergistic dye-dye adsorption effect by the intro­ duction of multi–SOÀ3 groups-featured dyes, and the effect is a function of the number of –SOÀ3 groups in dyes 2.2 Dyes adsorption and modification of ZIF-67 with multi-sulfonated dyes ZIF-67 was synthesized according to a reported procedure [27] In order to achieve the adsorption performance of pristine ZIF-67 towards different organic dyes, 4.0 mg ZIF-67 with average particle size of ~0.9 μm was added into the aqueous solution of dyes (40 mL, 125 mg/L), respectively The dyes with different sizes and charges include, 1) cationic type with Nỵ(CH3)2 or Nỵ(CH2CH3)2 groups, methylene blue (MBỵ) and rhodamine B (RhBỵ); 2) anionic type with –SOÀ3 groups, methyl orange (MOÀ ), acid chrome blue K (ACBKÀ ), fuchsin acid (FAÀ ), cotton blue (CBÀ ), congo red (CRÀ ), coomassie brililiant blue R-250 (CBBRÀ ), eriochrome blue black R (EBBRÀ ) The details of the organic dyes were displayed in Table S1 Synergistic adsorption performance of several sulfonated dyes towards MBỵ upon ZIF-67 was conducted as follows Take CB for an example, 4.0 mg ZIF-67 was first added into the solution of CBÀ (125 mg/L) and stirred for 0.5 h to obtain CB @ZIF-67, subsequently mg MBỵ (125 mg/L) was added to allow the synergetic dye adsorption The trinary-component dye adsorptive experiments were carried out similarly with MBỵ/MO mixture being added instead The concentration of dyes was monitored by UV–vis spectroscopy 3.3 Adsorption performance of CBÀ upon ZIF-67 In all of the above multi-sulfonated dyes, CBÀ was selected as the model to perform the detailed study of the synergistic adsorption of MBỵ upon ZIF-67 due to the following considerations: 1) it features three –SOÀ3 groups, which would be favorable for the synergistic effect; 2) the fast adsorption kinetics; (5 to reach the adsorption equilibrium, pseudo-second-order adsorption rate, indicating chemical adsorption involving valence forces through sharing or exchanging of electrons between CBÀ and ZIF-67 as the rate-limiting step (Fig S6 & Table S2)); 3) the high uptake on ZIF-67 The correlation coefficient R2 of the Langmuir and Freundlich adsorption models are 0.997 and 0.994, respectively (Fig S7 & Table S3) This result illustrated the experimental Results and discussion The phase purity and crystallinity of the harvested ZIF-67 was veri­ fied by comparing the diffraction peaks to the simulated patterns of ZIF67 in the literature (Fig S1) The average particle size of ZIF-67 was Y Liu et al Microporous and Mesoporous Materials 303 (2020) 110304 Fig Adsorption performance of ZIF-67 towards dyes Fig Synergistic adsorption performance of several sulfonated dyes towards MBỵ upon ZIF-67 in aqueous solution (125 mg/L of single-component for MBỵ 125 mg/L of binary-component for MOÀ , CRÀ , CBBRÀ , EBBRÀ , FAÀ , ACBKÀ and CBÀ respectively mixed with MBỵ after being stirred with ZIF-67 for 0.5 h) data are better fitted with Langmuir model The maximum adsorption capacity of 6,004.94 mg/g calculated by the Langmuir model matches well with experimental data (5,860.1 mg/g) All the above results indicate that monolayer adsorption of ZIF-67 adsorbent is common As a result, binary-component adsorption investigations of CB and MBỵ were conducted in the following work added into each aqueous solution with the same concentration of CBÀ The color of the aqueous solution after adsorption became obviously lighter in sequential binary-component adsorption process, as shown in Fig S8 The adsorption capacity increased significantly with a record high capacity value of 5,857.9 mg/g for MBỵ (Fig & Table 1) The result indicates that the pre-adsorbed CBÀ has highly effective synergism for binding MBỵ The adsorption capacity of MBỵ increased significantly in the experiments with the initial concentration of CB and MBỵ ranged from 100 to 700 mg/L Nevertheless, the adsorption capacity of CBÀ in binary-component adsorption did not decrease compared with that in single-component experiments Therefore, based on the adsorption 3.4 Synergistic adsorption of MBỵ in presence of CB In binary-component dyes adsorption experiments, ZIF-67 was added in CBÀ aqueous solution, after being stirred for 10 min, MBỵ was Y Liu et al Microporous and Mesoporous Materials 303 (2020) 110304 Fig Single-component adsorption experiments of MBỵ or CB , and the synergistic adsorption performance of CB towards MBỵ upon ZIF-67 (Fig 4b) And the crystallinity of CBÀ @ZIF-67 was preserved well as evidenced by PXRD analysis (Fig S9) Table Comparison of the MBỵ adsorption capacity of CB @ZIF-67 with other adsorbents Adsorbents qmax (mg/ g) Ref CBÀ @ZIF-67 5,857.9 Calcium alginate membrane Carboxy methyl cellulose/poly(methyl acrylate) hydrogels SA nanofiber membranes Aminocarboxylate/maleic acid resin Lignocellulose-g-poly(acrylic acid)/montmorillonite hydrogel composites NaAlg-g-p(AA-co-St)/organo-I/S Poly(N-vinyl caprolactam-co-maleic acid) Fe3O4/HKUST-1 MIL-100 (Fe) GO/lignosulfonate aerogel NH2-MIL-125(Ti) Calcium alginatebentoniteactivated carbon composite beads Core@double-shell structured HNTs/Fe3O4/poly(DA ỵ KH550) nano-hybrids MOF-235 3,506.4 2,370 2,357.9 2,101 1,994.4 this work [30] [31] [32] [33] [34] 1,843.5 1,441 1,277 1,105 1,023.9 862 756.9 [35] [36] [37] [38] [39] [20] [40] 714.3 [41] 477 [14] 3.6 Synergistic and selective adsorption performance of dyes upon ZIF-67 To confirm the generic feature of such synergistic adsorption beư tween Nỵ(CH3)2 and SO3 , the sequential binary-component adsorpư tion of CBÀ with the dyes possessing the functional groups of N(CH3)2, Nỵ(CH2CH3)2 and Nỵ(CH3)2 on ZIF-67 was investigated, and MO and RhBỵ were selected, respectively The synergistic effect of CB / MO and CB /RhBỵ systems was barely measured (Fig 5a and b) While the CB /MBỵ system showed a significant improvement in adsorption performance Based on the results above, in situ modification of ZIF-67 with CBÀ can promote the adsorption capacity of ZIF-67 for MBỵ with Nỵ(CH3)2 groups Conversely, such synergistic effect for dyes with Nỵ(CH2CH3)2 and N(CH3)2 was notobserved Thus, the electrostatic interaction between the –SOÀ3 in dyes and Nỵ(CH3)2 in MBỵ might be responsible for the synergistic phenomenon While the steric hindrance of Nỵ(CH2CH3)2 and the lack of charge of –N(CH3)2 result in no such effect The selectivity of MBỵ over MO /RhBỵ associated with CB @ZIF-67 was further determined by the trinary-component adsorption experi­ ments The selective absorption performance of MBỵ by CB @ZIF-67 exhibited a similar trend The removal efficiency for MBỵ is 90.7% and 92.9%, respectively, under the conditions used, while only 6.3% for MO and 2.9% for RhBỵ were measured (Fig 5d) Therefore, the find­ ings suggest that CBÀ @ZIF-67 has comparatively good selectivity to MBỵ due to the synergistic adsorption amounts of both dyes, the molar ratio of adsorbed CBÀ to MBỵ is calculated to be about 1:2 The results demonstrate that after the coor­ dinative interaction between the Co(II) in ZIF-67 and –SOÀ3 in CBÀ , the electrostatic interaction occurs between the remaining two SO3 groups in CB and Nỵ(CH3)2 in MBỵ with the molar ratio of both functions being of 1:1 3.7 Mechanistic study 3.5 Recycling and reusability PXRD patterns of ZIF-67 before and after dye adsorption are illus­ trated in Fig S10 All the diffraction peaks of ZIF-67 (as-synthesized), CB @ZIF-67, MBỵ@ZIF-67, and MBỵ/CB @ZIF-67 are agreed with the reported patterns in literature [24] Thus, the crystallinity of ZIF-67 was unchanged after the adsorption of CB and MBỵ To explore the interaction mechanism between ZIF-67 and the dyes under study, FTIR spectra of ZIF-67, CB , MBỵ and dyes@ZIF-67 were compared together (Fig 6) In the spectrum of CBÀ (Fig 6a), the peak at Recycling and reusability of absorbents are the important factors in the dye adsorption properties Therefore, the release experiments were conducted by eluting the MBỵ/CB @ZIF-67 sample using CH3OH As shown in Fig 4a, MBỵ can be released into CH3OH solution from the saturated samples quickly in 60 In order to confirm the durability and reusability of CBÀ @ZIF-67 in the adsorption process, the adsorp­ tionÀ desorption experiments were performed alternatively for runs Y Liu et al Microporous and Mesoporous Materials 303 (2020) 110304 Fig a) Release experiments of MBỵ from the corresponding CBÀ @ZIF-67 adsorbed sample in the solution of CH3OH; b) the reusability of CB @ZIF-67 for MBỵ adsorption for times Fig UV–Vis spectra of several binary-component dyes during the adsorption process a) MOÀ /CBÀ , b) RhBỵ/CB , c) MBỵ/CB (The initial concentrations of CB , MO , RhBỵ and MBỵ were 120, 50, 60, and 25 mg/L, respectively.) d) Selectivity of MBỵ over MO /RhBỵ in trinary-component dyes adsorption (CB @ZIF-67 aqueous solution obtained after 120 mg/L CBÀ mixed with ZIF-67 stirred for 10 min, and then MBỵ/MO or MBỵ/RhBỵ were added with each single component concentration being 50 mg/L) 1,337.2 cmÀ is ascribed to asymmetric S–O stretching vibrations, and the peak at 1,169.1 cmÀ is associated with aromatic C–N stretching vibrations [42] In the spectrum of MBỵ (Fig 6b), a band appears at 3, 425.6 cmÀ 1, attributable to the O–H stretching vibration The characư teristic bands of MBỵ at 1,354.2 and 1,184.3 cmÀ are attributed to the stretching mode of C–N from the aromatic ring and the aliphatic chain of Nỵ(CH3)2, respectively According to Fig 6c, a characteristic band of ZIF-67 at 425.4 cmÀ is attributed to the Co–N stretching vibration [43, – N at 44] The stretching vibration peaks of C–N at 1171.9 cmÀ and C– 1579.1 cmÀ are also observed [45,46] Y Liu et al Microporous and Mesoporous Materials 303 (2020) 110304 Fig FTIR spectra of a) CB , b) MBỵ, c) ZIF-67, as well as that of d) CBÀ @ZIF-67, e) MBỵ@ZIF-67, and f) MBỵ/CB @ZIF-67 after adsorption of CB , MBỵ, or the mixture of CB and MBỵ, respectively As observed in Fig 6d, differences are observed obviously in the spectra of ZIF-67 and CBÀ @ZIF-67 The sharp peak of Co–N stretching vibrations at 425.4 cmÀ in ZIF-67 is shifted to 424.7 cmÀ in CBÀ @ZIF67, meanwhile, the vibration frequencies of the bands at 1,579.1 cmÀ – N and 1,171.8 cmÀ of C–N are shifted to 1,593.3 and 1,172.8 of C– cmÀ 1, respectively, which might be due to the interaction of –S(O2)–OÀ from CBÀ with Co(II) centers of ZIF-67 [26] Moreover, the bonding electron cloud of Co–N bond is far away from N core, the density of electron cloud around N core decreases, as well as the attraction of – N and bonding electron and the stretching vibration frequencies of C– C–N increases In the similar way, the interaction of –S(O2)–OÀ with Co (II) increases the donating electronic activity of negative oxygen ion, and the strength of S–O bond is weakened Therefore, the peak at 1, 337.2 cmÀ for asymmetric S–O stretching vibrations in CBÀ is shifted to 1,335.5 cmÀ in CBÀ @ZIF-67 IR analysis reveals the binding of CBÀ to the framework of ZIF-67 via chemisorption of –SOÀ3 group on Co(II) The open Co(II) centers in ZIF-67 are occupied by –OH, and the –OH group could be replaced by some stronger Lewis bases Consequently, the interaction between Lewis acidity of Co(II) in ZIF-67 and the Lewis basicity of –SOÀ3 group in CBÀ could occur by the replacement of –OH by –SOÀ3 [47,48] This illustrates that the chemisorption is dominant in the adsorption of CB on ZIF-67 In spectra of MBỵ and MBỵ@ZIF-67 (Fig 6b and e), OH and CoN bands from 3,425.6 cm and 425.4 cm in MBỵ shifted to 3,447.5 cmÀ and 424.5 cmÀ in MBỵ@ZIF-67, respectively The relevant wavelength shift might be caused by the formation of hydrogen-bonding and - stacking interactions between MBỵ and ZIF-67 [49,50] The Co–N peak at 424.7 cmÀ was unchanged after the adsorption of MBỵ on CB @ZIF-67 The bands at 1,335.5 cmÀ (S–O group), 1,593.3 cmÀ – N group) and 1,172.8 cmÀ (C–N group) in CBÀ @ZIF-67 are shifted (C– to 1,334.0, 1,598.2 and 1,173.5 cm in MBỵ/CB @ZIF-67, respectively (Fig 6e and f) The results suggest the interaction exists between Nỵ(CH3)2 in MBỵ and S(O2)O in CB , which is responsible for promoting the adsorption capacity of MBỵ upon ZIF-67 in the aqueous solution of MBỵ and CB @ZIF-67 XPS analysis of the several representative samples was investigated to further indentify the mechanism of the measured synergistic adsorption on ZIF-67 for CB and MBỵ As shown in Fig 7b, the Co 2P of ZIF-67 consists of Co 2p3/2 (781.2 eV) and Co 2p1/2 (796.7 eV) accompanied with two satellite peaks at 786.0 and 802.2 eV implying the presence of Co(II) phase [51] The Co 2p binding energies of MBỵ@ZIF-67 and ZIF-67 were similar While the Co 2p peaks shifted from 781.2 eV to 796.7 eV in ZIF-67 to 781.5 eV and 797.2 eV in CBÀ @ZIF-67, respectively, which resulted from the interaction between unoccupied Co(II) of ZIF-67 and the –SOÀ3 group in CBÀ [52,53] The binding energies S 2p at 167.9 and 169.0 eV in CBÀ @ZIF-67 originate from central sulphur atoms in –SO3-Co and –SO3-Na, respectively (Fig 7c) [54] The S 2p peaks in MBỵ/CB @ZIF-67 showed a slight downshift in comparison with that in CBÀ @ZIF-67, illustrating that the S chemical state had been changed by introducing MBỵ In the case of ZIF-67 and MBỵ@ZIF-67, signals related to S were not detected As shown in Fig 7d, the O 1s peak at 531.5 eV in ZIF-67 indicated the presence of surface –OH groups associated on Co(II) [55,56] The exis­ tence of hydrogen-bond interactions between ZIF-67 and MBỵ could be affirmed by O 1s peak shifting from 531.5 eV in pristine ZIF-67 to 531.3 eV in MBỵ@ZIF-67 [26,57] Coordination interactions also were formed between Co(II) and –SOÀ3 groups, which could be further confirmed by the presence of 531.7 eV (–SO3-Co) and 532.9 eV (–SO3-Na) in CBÀ @ZIF-67, as well as the absence of O 1s peak at 531.5 eV in pristine ZIF-67 [54] While the O 1s at 532.9 eV in CBÀ @ZIF-67 is shifted to lower binding energy at 532.1 eV in MBỵ/CB @ZIF-67, which should be caused by the interaction between SO3 in CB and Nỵ(CH3)2 in MBỵ Considering the analysis findings above, possible mechanism in the synergistic adsorption process for CB and MBỵ upon ZIF-67 is proposed as shown in Scheme In single-component adsorption of MBỵ upon ZIF67, hydrogen-bonding interaction is present between Nỵ(CH3)2 in MBỵ and –OH in active sites of ZIF-67 [49], meanwhile, the interaction be­ tween the benzene rings and the imidazole rings of them causes the Y Liu et al Microporous and Mesoporous Materials 303 (2020) 110304 Fig XPS spectra of ZIF-67, MBỵ@ZIF-67, CB @ZIF-67, and MBỵ/CB @ZIF-67 products a) XPS survey spectra, b) Co 2p, c) S 1s, d) O 1s Scheme Possible mechanism of the synergistic adsorption of multi-sulfonated dyes towards MBỵ upon ZIF-67 Y Liu et al Microporous and Mesoporous Materials 303 (2020) 110304 formation of π-π stacking [50] Significant differences appear in the adsorption of multi-sulfonated dyes upon ZIF-67, strong electrostatic attraction exists between –SOÀ3 groups in multi-sulfonated dyes and the Co(II) centers in ZIF-67 [58] Additionally, MOFs modified with –SOÀ3 groups also showed relatively strong affinity towards cationic dyes (like methylene blue and malachite green) [59] After the pre-adsorption of dyes with multi–SOÀ3 groups on ZIF-67, the electrostatic attraction be­ tween the available SO3 and Nỵ(CH3)2 in another dye resulted in significant enhancement on the uptake of the second dye Nevertheless, findings above exhibit that ZIF-67 functionalized with multi–SOÀ3 groups can synergistically adsorb other cationic dyes with Nỵ(CH3)2 groups in aqueous media, which contributes to the great improvement on the adsorption capacity of ZIF-67 adsorbent [3] [4] [5] [6] [7] Conclusions [8] In summary, ZIF-67 can be used as an optional adsorbent for removing organic dyes from aqueous media Interestingly, ZIF-67 preferred to adsorb multi-sulfonated dyes and was easily functional­ ized with –SOÀ3 groups due to the coordinative interaction The adsorption capacity of ZIF-67 towards CBÀ was very high at 5,860.1 mg/ g Importantly; the synergistic absorption of multi-sulfonated dyes and MBỵ upon ZIF-67 was discovered for the first time Specifically, a considerable increase in the adsorption capacity of ZIF-67 for MBỵ (5,857.9 mg/g) occurred by pre adsorbing CBÀ on ZIF-67 in aqueous media The inherent mechanism of the synergistic adsorption of different dyes on ZIF-67 was proposed, that is, the pre-adsorption of multi-sulfonated dyes on ZIF-67 functionalized ZIF-67 with the addi­ tional SO3 groups which interact strongly with the Nỵ(CH3)2 group in MBỵ The synergistic adsorption effect of different organic dyes upon the adsorbent reveals a novel idea for the in situ modification of MOFs adsorbent in greatly enhancing the adsorption efficient of trapping and separating the organic compounds from waste water [9] [10] [11] [12] [13] [14] [15] [16] Declaration of competing interest [17] There are no conflicts to declare CRediT authorship contribution statement [18] Yanfeng Liu: Conceptualization, Methodology, Investigation, Re­ sources, Writing - original draft Duoyu Lin: Resources, Investigation Weiting Yang: Supervision, Resources, Writing - review & editing, Data curation Xueying An: Formal analysis, Visualization, Investigation Ahui Sun: Formal analysis Xiaolei Fan: Supervision, Writing - review & editing Qinhe Pan: Project administration, Writing - review & editing [19] [20] [21] Acknowledgements [22] This work was supported by the Natural Science Foundation of Hainan Province (218QN185 and 2019RC005), the National Natural Science Foundation of China (21761010), and Hainan University startup fund (KYQD(ZR) 1806) [23] Appendix A Supplementary data [25] Supplementary data related to this article can be found at https://doi org/10.1016/j.micromeso.2020.110304 [26] [24] [27] References [28] [1] C Sun, X Wang, C Qin, J Jin, Z Su, P Huang, K Shao, Solvatochromic behavior of chiral mesoporous metal-organic frameworks and their applications for sensing small molecules and separating cationic dyes, Chem Eur J 19 (2013) 3639–3645 [2] M Massoudinejad, M Ghaderpoori, A Shahsavani, M.M Amini, Adsorption of fluoride over a metal organic framework UiO-66 functionalized with amine groups [29] and optimization with response surface methodology, J Mol Liq 221 (2016) 279–286 Y 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Fig Adsorption performance of ZIF-67 towards dyes Fig Synergistic adsorption performance of several sulfonated dyes towards MBỵ upon ZIF-67 in aqueous solution (125 mg/L of single-component for. .. improvement in adsorption performance Based on the results above, in situ modification of ZIF-67 with CBÀ can promote the adsorption capacity of ZIF-67 for MBỵ with Nỵ(CH3)2 groups Conversely, such synergistic