Controlled Manipulation of MOFs Layers to Nanometer Precision

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Applications of Polymer, Composite, and Coating Materials

Controlled Manipulation of MOFs Layers to Nanometer Precision inside large Meso-channels of Ordered Mesoporous Silica for Enhanced Removal of Bisphenol A from Water Junyu Peng, Yun Li, Xiaoli Sun, Chaonan Huang, Jing Jin, Jincheng Wang, and Jiping Chen ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 07 Jan 2019 Downloaded from http://pubs.acs.org on January 7, 2019

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ACS Applied Materials & Interfaces

Controlled Manipulation MOFs Layers to Nanometer Precision inside Large Meso-channels of Ordered Mesoporous Silica for Enhanced Removal of Bisphenol A from Water Junyu Peng,a, b Yun Li,a Xiaoli Sun,c Chaonan Huang,a, b Jing Jin,a Jincheng Wang,a Jiping Chena,* a Key

Laboratory of Separation Science for Analytical Chemistry, Dalian Institute of

Chemical Physics, Chinese Academy of Sciences, Dalian, 116011, China. b University

c Lishui

of Chinese Academy of Science, Beijing, 100049,China

University, Lishui, 323000, China

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ABSTRACT Considerable attention has been endeavored on the design of hierarchical porous metal-organic framework (MOF) composites, which not only enhances the performance but also broadens the applications of MOFs. So far, controlled manipulation of nanometer-thick MOF layers in ordered meso-channels while retaining their respective intrinsic properties is still a main challenge, due to the difficulty of growing MOFs in confined space. Herein, using a step-by-step coordination method, the formation of a hierarchical micro-mesoporous hybrid with wall (channel wall and coating layer) thickness up to 8.0 nm and open pore size down to 7.7 nm has been achieved based on large mesoporous SBA-15, and the wall thickness with nanometer precision can be controlled by adjusting the growth cycles of zeolite imidazolate framework-8 (ZIF-8) coating layers. Compared to pure ZIF-8, the obtained ZIF-8@SBA-15 composites showed more than 2-fold enhancement in adsorption capacity and approximately 20-fold improvement in adsorption rate constant for bisphenol A in water, which could be ascribed to the synergistic effects of the high adsorption ability from ZIF-8 and the fast diffusion property from SBA15. More importantly, the degraded ZIF-8@SBA-15 composite can be completely restored by a simple immersion into 2-methylimidazole solution. The easy restorability and good reusability further enable ZIF-8@SBA-15 as a promising adsorbent for effectively removing organic contaminants from water.

KEYWORDS ZIF-8@SBA-15 composite, stepwise coordination, nanometer precision, BPA adsorption, fast mass transfer


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INTRODUCTION Metal–organic frameworks (MOFs) are an intriguing class of hybrid frameworks composed of inorganic node (metal or metal cluster sites) connected with organic linkers.1-4 The flexibility of the combination of organic and inorganic blocks yields multiple MOFs with desired structures and functionalities. Due to their unique properties, such as high surface area, uniform structured cavities and an abundant of adjustable surface functionalities, MOFs have a great range of applications in gas storage and separation,5, 6 catalysis,7, 8 chemical sensor9 and energy storage10, 11 and so on. Recently, the structural diversity and unique properties of MOFs have facilitated them as attractive adsorbents for removing various types of contaminants from aqueous solution, including toxic/radioactive metal ion,12-14 dyes,15 pharmaceuticals1618

and endocrine-disrupting compounds.19 However, due to the exsitence of restricted-

access micropores, their performance in adsorption removal was severely affected by the slow mass transfer, especially for the bulky molecule. And their adsorption efficiency towards organic pollutants mainly depended on the host-guest interaction between target molecule and the active moieties on MOFs external surface. To improve their adsorption performances for bulky molecules, significant efforts has been dedicated towards the synthesis of MOFs nanoparticles those provided with reduced diffusion barrier and increased external surface area.20-22 Although MOFs nanoparticles possess fast adsorption/desorption kinetics and high adsorption capacity, they always suffer from the two main drawbacks as following, (1) when applied in aqueous solutions, the strong aggregation tendency of MOFs nanoparticles diminishes their adsorption performance due to the enlarged particle size, reduced interfacial area and increased mass transfer resistance; (2) the difficulty of separating MOFs nanoparticles from aqueous solutions further restricts their regeneration and reuse at a relatively large scale. Therefore, immobilization of the MOF nanoparticles on a mesoporous or macroporous matrix to form a hierarchical composite can



diminish or even eliminate these abovementioned problems. Due to the combination of the porous structure of support and the nanoscale MOFs, the composites not only show enhanced adsorption properties but also broaden the applications of MOFs, compared to purely microporous MOFs. Some previous reports have indicated the significance of this strategy. For example, the polyoxometalate-based MOF-5 composite exhibited a fast adsorption rate and selective adsorption ability towards the cationic dyes in aqueous solution due to the introduction of mesopore.23 The microand mesoporous composite incorporating MOF-74 and mesoporous γ-Al2O3 possessed high adsorptive desulfurization efficiency under high fluidity.24 In addition, the micro- and macroporous MOF-monolith composites provided excellent adsorption performance and ease of practical operation for capturing malachite green dye 25 and methylchlorophenoxypropionic acid26 from water, respectively. Due to the steric hindrance in mesoporous support and low surface area of macroporous support, less surface area was utilized for MOFs incorporation, and therefore, the performance improvements of these composites could be compromised. The assembling of MOFs inside ordered mesoporous structure should be a more promising route since both of the large surface area and fast mass transfer from mesochanels can be efficiently utilized. As well known, the size of MOFs particles prepared using various methods (e.g. microwave and ultrasound) usually ranges from tens to hundreds of nanometers, and therefore, the incorporation of MOFs of such size is almost impossible using an ex situ impregnation method. To date, the introduction of MOFs on the interior surface of mesoporous materials has been reported using some synthetic routes based on in situ crystallization, double-solvent strategy27, solvothermal synthesis28 and microwave assisted method29. Nevertheless, the research of this field is still in its infancy, and it is difficult or even impossible for the precise manipulation of the MOFs growth inside mesopore using these current synthetic routes. The liquid-phase epitaxy growth (LPE) approach was a stepwise bottom-up protocol.30-33 The components of MOFs were adsorbed in a stepwise manner from the liquid phase to a surface and then sequentially coordinated on the surface. Due to its self-terminated layer-by-layer growth mechanism, the nucleation and growth of


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MOFs crystals were controlled and hence the thickness of the obtained MOFs coating layers could be adjusted by varying the coordination cycles.30 For example, the ultrathin MOFs coating layers with thickness ranging from 4 to 18 nm were obtained on the external surface of oxide particles through the LPE approach.34, 35 Such controlled manipulation of MOFs layers to nanometer precision shows that the LPE approach has great potential for controllable decoration of MOFs in meso-channels. Herein, the controlled growth of ZIF-8 coating layers to nanometer precision within meso-channels of SBA-15 were investigated, and the obtained composite using a LPE approach was denoted as ZIF-8@SBA-15. The adsorption performance of ZIF8@SBA-15 composites for bisphenol A (BPA) in water were explored in order to assess their performances in capturing bulky molecules. BPA is widely used as an important intermediate in many consumer products and extensively release into aquatic environment during its manufacturing, consumption and disposal process.36-38 Thus, BPA removal from water is important due to its adverse effects on the endocrine systems of humans and animals. Our results showed that the hierarchal micro-mesoporous ZIF-8@SBA-15 composites exhibited much higher adsorption capacity, faster adsorption rate, and better reusability than their individual components (pure ZIF-8 and SBA-15), which was mostly due to the combined merits of both ZIFs and meso-materials.

EXPERIMENTAL SECTION Chemicals All chemicals and solvents were commercially available for experimental use and they were used without further purification. The reagents for the preparation of SBA-15 mainly involved EO20PO70EO20 (P123) from Sigma-Aldrich (Milwaukee, USA), tetraethyl orthosilicate (TEOS) from J&K Chemical (Beijing, China), and hydrochloric acid (HCl), ammonium fluoride (NH4F) and hexane from Tianjin Kermel (Tianjin, China). Toluene and N-[3-(triethoxysiliyl) propyl]-4, 5dihydroimidazole (DHIM) used for functionalizing SBA-15 were obtained from Sinopharm (Shanghai, China) and Fluorochem (Glossop, UK), respectively. Zinc



nitrate hexahydrate (Zn (NO3)2·6H2O), 2-methylimidazole (2-MeIM) and methanol (analytical grade) used for synthesizing ZIF-8 were supplied by China National Pharmaceutical Group, J&K Chemical and Tianjin Kermel, respectively. Methanol (HPLC grade) was purchased from Sigma-Aldrich. Bisphenol A was supplied by TCI Chemical (Tokyo, Japan). The deionized water with a resistivity of 18.2 MΩ cm was obtained through a Milli-Q Advantage A10 water purification system (Burlington, USA). Synthesis of Imidazole-terminated SBA-15 (Im-SBA-15) SBA-15 was prepared according to the procedure reported previously in the literature.39 2.4 g of P123 and 0.027 g of NH4F were dissolved in 85 g of HCl solution (1.3 mol/L) to yield a clear solution. The premixed solution (13 mL hexane and 5.5 mL TEOS) was added into the above solution under stirring at 16.5 oC. After reacting for about 20 hours, the mixture was then transferred into an autoclave for further reaction at 100 oC for 48 hours. The highly ordered SBA-15 was obtained by filtration, dried at 60 oC for overnight, and calcined at 550 oC for 5 h. Then the calcined SBA-15 was activated with 10% HCl solution and functionalized with DHIM in toluene. Thus, the light-yellow Im-SBA-15 solids were obtained. Synthesis of ZIF-8@SBA-15 via the LPE strategy The ZIF-8@SBA-15 composites were prepared using a stepwise procedure similar to that reported previously with some modifications.35 Briefly, the Im-SBA-15 (1 g) was reacted with 42 mmol/L Zn (NO3)2.6H2O in 60 mL MeOH solution at 30 oC for 45 minutes using an oscillator. Subsequently, the separated solids by centrifugation were reacted with 152 mmol/L 2-MeIM in 60 mL MeOH solution under the same conditions to obtain the composite for the first growth circle (denoted as ZIF-8@SBA-15-1C). Between the two consecutive reactions, the solid was centrifuged and washed thoroughly with methanol. The product with given growth cycles (xC) was denoted as ZIF-8@SBA-15-xC. And the product ended up with 2MeIM indicated the product possessed integer-growth cycles, i.e. x was an integer,


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while the product ended up with Zn2+ indicated the product possessed a semi-growth circle, i.e. x was a decimal. Synthesis of ZIF-8 2-MeIM (3.3 g) was dissolved in 66 mL of MeOH (solution A). 1.5 g of Zn(NO3)2·6H2O was dissolved in 66 mL of MeOH (solution B). The mixture of solution A and B was stirred for 1 hour at room temperature. The ZIF-8 powders were collected from the white gel by centrifugation, washed with MeOH, and dried under vacuum at 75 ºC for 3 days. Characterizations Fourier transform infrared (FTIR) spectra were conducted on a Nicolet iS5 spectrometer (Thermo Fisher) in the range of 400-4000cm-1 using KBr plates. By means of a field emission scanning electron microscopy (FESEM, JEOL JSM-7800F) equipped with an energy-dispersive spectroscopy (EDS), the scanning electron micrographs (SEM) and elemental composition spectra were obtained. The transmission electron micrographs (TEM) were taken on a JEOLJEM-2100EX operating at 100 keV. The powder X-ray diffraction (XRD) patterns were performed on a Panalytical Empyrean diffractometer at room temperature using Cu radiation (60 kV and 55 mA) over the range 5−60° for characterizing the crystalline structure. The small angle X-ray scattering (SXRS) patterns were measured on a SAXSess mc2 small and wide angle X-ray scattering instrument (Anton Paar, Austria) over the range 0.4−5° to investigate the mesoporous structure. The N2 adsorption-desorption isotherms were carried out at 77 K using an Autosorb automated gas sorption analyzer (Quantachrome Instruments). The total surface area was analyzed by Brunauer– Emmett–Teller (BET) method and the pore-diameter distribution was calculated from the adsorption branch of the isotherm by Barrett−Joyner−Halenda (BJH) method. And the micropore volume and surface area were evaluated by t-plot method. Sorption and Desorption Experiments



To evaluate the adsorption/desorption properties of ZIF-8@SBA-15, ZIF-8, and SBA-15 for BPA, batch experiments were performed. The BPA concentration in aqueous solution before and after adsorption was determined through an Agilent 1200 HPLC system (Santa Clara, CA) equipped with a C18 column and a diode array detector. The pH of BPA aqueous solution was adjusted using 0.1 mmol/L NaOH or HCl to the desired value ranging from 3 to 10. For adsorption experiments, 5 mg of adsorbent was put into 10 mL of BPA aqueous solution with given concentration varying from 0.01 to 1.5 mmol/L. The mixture was shaken at 150 rpm for a pre-determined time at 25ºC and then centrifuged. The BPA pre-adsorbed adsorbent was collected and the supernatant was filtered with 0.22 μm Millipore membrane before HPLC analysis. For desorption experiments, the BPA pre-adsorbed adsorbent was washed with methanol under shaking. The solid was isolated by centrifugation and the concentration of BPA in supernatant was determined to investigate the desorption efficiency. For reusability experiments, the BPA pre-adsorbed adsorbent was regenerated using the designed regeneration procedure (shown in Figure S1) and dried in a vacuum oven for another adsorption cycle. The adsorption isotherms of ZIF-8@SBA-15, ZIF-8 and SBA-15 were fitted with Langmuir and Freundlich isotherm models, and the models were expressed as follows: 𝐶𝑒

𝐶𝑒 1 + 𝐾𝐿 𝑞𝑚𝑎𝑥 𝑞𝑚𝑎𝑥

(1)

1 ln𝑞𝑒 = ln 𝐾𝐹 + ln 𝐶𝑒 𝑛

(2)

𝑞𝑒

=

qe and qmax are the equilibrium and maximal adsorption capacities, respectively; Ce is the BPA concentration after equilibrium was reached; KL is the Langmuir equilibrium constant; KF is the Freundlich equilibrium constant; n is the heterogeneity factor.


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The adsorption kinetics of ZIF-8@SBA-15, ZIF-8 and SBA-15 were further analyzed by the pseudo-second-order and pseudo-first-order kinetics models, and the equations were expressed as follows: 𝑘1

𝑙𝑜𝑔 (𝑞𝑒 ― 𝑞𝑡) = 𝑙𝑜𝑔𝑞𝑒 ― 2.303𝑡 𝑡 𝑞𝑡

1

1

= 𝑘 𝑞 2 + 𝑞𝑒𝑡

(3) (4)

2 𝑒

k1 (min-1) and k2 (g mg-1 min-1) are the rate constants for pseudo-second-order and pseudo-first-order adsorption, respectively. qe (mg g-1) is the adsorption capacity at equilibrium, and qt (mg g-1) is the adsorption capacity at time t (min).

RESULTS AND DISCUSSION Synthesis and Characterization of ZIF-8@SBA-15 According to our previous work35, confined space was detrimental to the growth of ZIF-8 using the LPE method. Thus, large pore of the mesoporous silica support is critical for successful growth of ZIF-8 in meso-channels. The highly ordered SBA-15 synthesized at low temperature in the presence of hexane possesses a large pore diameter of 15.0 nm, which can provide enough space for the growth of ZIF-8 in the meso-channels. Figure 1 illustrates the stepwise growth of ZIF-8 inside the mesopores and on the external surface of SBA-15. The SBA-15 was firstly activated with HCl and then functionalized with imidazole group. The imidazole group offers strong affinity to Zn2+, which was beneficial for subsequent growth of ZIF-8. When the imidazole functionalized SBA-15 was dispersed in Zn(NO3)2 solution, the strong affinity of imidazole groups towards Zn2+ facilitated their coordination, thus creating the nucleation sites that initiated the stepwise growth of ZIF-8 crystals.



Figure 1. Illustration of the stepwise growth of ZIF-8 on the surface and inside the mesopores of SBA-15. As shown in Figure 2, the FTIR spectra exhibit that both of the imidazole modification of SBA-15 and the fabrication of ZIF-8 were successful. Compared with activated SBA-15 , the Im-SBA-15 demonstrated an obvious decrease in peak intensity of Si-OH asymmetric stretching at 958 cm-1 and the appearance of the characteristic peaks of C-H (2931 cm-1 for stretching mode and 1450 cm-1 for bending mode), which confirmed the successful functionalization of imidazole onto SBA-15. For ZIF-8@SBA-15, the appearance of the characteristic peaks of ZIF-8 (1580 cm-1 for C=N stretching mode of imidazole ring, 1145 cm-1and 990 cm-1 for C-N stretching mode and 420 cm-1 for Zn-N stretching mode) indicated the formation of ZIF-8 on SBA-15. The activated SBA-15, Im-SBA-15 and ZIF-8@SBA-15 all showed the vibrational modes of Si-O-Si network at 1080 cm-1, 799 cm-1 and 465 cm-1, indicating that the composition of SBA-15 substrate did not suffer damage after imidazole modification and subsequent ZIF-8 fabrication.


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Figure 2. FTIR spectra of the activated SBA-15 (OH-SBA-15), Im-SBA-15, ZIF8@SBA-15 and ZIF-8. As displayed in Figure 3, the differences in morphology and chemical composition between Im-SBA-15 and ZIF-8@SBA-15-12C were examined by TEM and SEM/EDS analysis. It can be observed from the TEM images of Figure 3a and 3b that both Im-SBA-15 and ZIF-8@SBA-15 exhibited highly ordered meso-structures with large unit cells (15.7 and 15.9 nm, respectively), in accordance with the result from the previous report.39 This indicated that the structural integrity of SBA-15 was well preserved after the ZIF-8 growth process. There appeared finely nanosized ZIF-8 crystals with irregular morphology inside the pore channels and on the external surface for ZIF-8@SBA-15-12C. A coarser morphology of ZIF-8@SBA-15 than ImSBA-15 observed from the SEM images (Figure 3c and 3d) further showed the successful formation of ZIF-8 crystals. Moreover, as shown in their EDS patterns (Figure 3e and 3f), in going from Im-SBA-15 to ZIF-8@SBA-15, the successful incorporation of ZIF-8 into SBA-15 was clearly demonstrated by the appearance of Zn peak and the increased intensity of N peak.



Figure 3. The morphological characterizations of Im-SBA-15 and ZIF-8@SBA-1512C. TEM images of (a) Im-SBA-15 and (b) ZIF-8@SBA-15-12C, SEM images of (c) Im-SBA-15 and (d) ZIF-8@SBA-15-12C, and EDS patterns of (e) Im-SBA-15 and (f) ZIF-8@SBA-15-12C. The crystal structures of ZIF-8@SBA-15-xC were characterized using XRD analysis (Figure 4a). It can be seen that ZIF-8@SBA-15-xC ended with 2-MeIM (2MeIM-ZIF-8@SBA-15-xC, x=3, 6, 9, 12) presented similar XRD patterns, involving a characteristic broad peak of silica matrix at 2θ=20–25° and sharp peaks belonging to ZIF-8 crystalline phase, whereas the XRD pattern of the [email protected] contained only one broad peak of silica matrix. This result revealed that during the stepwise process the ZIF-8 crystalline structure was well achieved for 2-MeIM-ZIF8@SBA-15-xC (x= an integer), but not for Zn2+-ZIF-8@SBA-15-xC (x= a decimal). It was also noted that the XRD signal intensities derived from ZIF-8 increases gradually with the number of growth cycles, which further confirm the stepwise growth of nanosized ZIF-8 crystals in mesopores. These findings indicated that controlling growth of ZIF-8 in confined space such as SBA-15 channels could be only achieved through the LPE method when the synthesis was ended with 2-MeIM rather than Zn2+.


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Figure 4. The structural characterizations of ZIF-8@SBA-15-xC. (a) XRD, (b) SAXS, (c) N2 adsorption/desorption isotherms, as well as (d) mesopore and (d inset) micropore size distributions. The SAXS patterns of ZIF-8@SBA-15-xC were also used to investigate their structural differences (Figure 4b). ZIF-8@SBA-15-0C (i.e. Im-SBA-15) possessed three well-resolved peaks indexed as (100), (110), (200), suggesting the well retained hexagonal meso-structure of SBA-15 phase after imidazole modification. The positions of scattering peaks were nearly identical for all ZIF-8@SBA-15-xC samples. Furthermore, both the interplanar spacings corresponding to (100) plane (d100) and the unit-cell parameters (a0) remained almost unchanged, as shown in Table 1. All of them indicated that the mesoporous structure of SBA-15 was not damaged by the growth of ZIF-8 inside the pores. However, a continuous decrease of the peak intensities was observed when increasing the growth cycles, which suggested that the long-range hexagonal order of SBA-15 was reduced as a result from the continuous increase of ZIF-8 inside mesopores.



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Table 1 Structural properties of ZIF-8@SBA-15 after different growth cycles. d100/

SBET/

Smicro/

DBJH/

Vtotal/

Vmicro/

Vmeso/

a0/

dwall/

nm

m2 g-1

m2 g-1

nm

cm3 g-1

cm3 g-1

cm3 g-1

nm

nm

0C

13.4

206

10

12.6

0.61

0.00

0.61

15.5

3.1

3C

13.5

331

158

12.3

0.53

0.06

0.47

15.6

3.3

6C

13.6

452

250

9.5

0.53

0.10

0.43

15.7

6.2

9C

13.6

594

403

9.4

0.57

0.17

0.40

15.7

6.3

12 C

13.6

722

532

7.7

0.58

0.21

0.37

15.7

8.0

Materials

Notation: d100, (100) interplanar spacing; SBET, BET specific surface area; Smicro,

micro-surface area, DBJH, BJH pore diameter; Vtotal, total pore volume; Vmicro, micropore volume, Vmeso, mesopore volume; a0, unit-cell parameter; dw, the wall thickness. The porous properties of ZIF-8 and ZIF-8@SBA-15-xC were investigated by N2 adsorption/desorption experiments. The N2 adsorption/desorption isotherms of ZIF-8 and ZIF-8@SBA-15-xC are respectively displayed in Figure S2a and Figure 4c, and their calculated parameters based on the adsorption branches are listed in Table 1. ZIF-8 showed a typical type I isotherm, which was an indication of microporous structure. The pure ZIF-8 has a high micropore surface area of 1882 m2/g and a high micropore volume of 0.656 cm3/g. ZIF-8@SBA-15-0C clearly showed a typical type IV isotherm with H1 hysteresis loop, indicating its mesoporous character. With the stepwise formation of ZIF-8@SBA-15-xC (x=3, 6, 9, 12), the hysteresis loops originating from the mesopores became more and more flattened until step-like isotherms were observed for the composites at higher growth cycles (6, 9 and 12). These results were mostly ascribed to the achieved hierarchical pore structure combining both micro- and meso-porosity as a result of the integration of ZIF-8 and SBA-15. As shown in Table 1, with increasing growth cycles from 0C to 12C, ZIF8@SBA-15 showed gradual increases of the BET surface area (from 206 to 722 m2 g-


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1),

micropore surface area (from 10 to 532 m2 g-1) and micropore volume (from 0.00

to 0.21 cm3 g-1) companied with a gradual decrease mesopore volume (from 0.61 to 0.37 cm g-1), which were correlated to the gradually increased content of ZIF-8. The pore size distributions for ZIF-8 and ZIF-8@SBA-15-xC were calculated from the adsorption branches using the BJH method (Table 1). The mesopore size distribution curve in Figure 4d showed that there was a continuous decrease in mesopore diameter for ZIF-8@SBA-15-xC when increasing growth cycles from 0, 3, 6, 9 to 12. As shown in Figure 4d inset, compared to the Im-SBA-15 (0C), there appeared a characteristic peak in the micropore range around 1.2 nm (in agreement with that for ZIF-8, Figure S2) for ZIF-8@SBA-15 xC (x=3, 6, 9, 12) and its intensity increased in accordance with the growth cycles. Due to the stepwise strategy, the nanosized ZIF-8 crystals could probably build up crystal layers with well-defined thickness in the meso-channels. This was confirmed by the continuous increased wall thickness (dwall, Table 1) of ZIF-8@SBA-15-xC from 3.1, 3.3, 6.2, 6.3 to 8.0 nm for 0C, 3C, 6C, 9C to 12C, respectively. The wall of the hierarchical composite is composed of the pore wall of SBA-15 and the ZIF-8 crystal layer. The result showed that the thickness of crystal layer could be controllably manipulated to nanometer precision by adjusting the growth cycles. It is also worth mentioning that the continuous decrease in mesopore diameter in our case is different from those found for other ZIF-8-mesoporous composites prepared using in situ method,40-43 where their mesopore diameters remained almost the same because ZIF-8 crystals/layers were formed on the external surface but not the interior of meso-substrates. In summary, compared to traditional in situ method, the LPE method allowed ZIF-8 crystal layers with well-defined thickness to gradually occupy but not block the mesochannels of SBA-15, thus both of the large surface area and fast mass transfer coming from meso-substrates could be efficiently utilized. Enhanced Adsorption Performance of ZIF-8@SBA-15 for BPA in Aqueous Solution



Efficient adsorptive removal of hazardous materials relies on rapid uptake, high adsorption capacity, and ready regeneration of the used adsorbents. The batch adsorption experiments of BPA on ZIF-8@SBA-15-xC, ZIF-8 and SBA-15 were carried out to explore the efficiency of hierarchical structure for removal of BPA from water. As shown in Figure 5, [email protected] displayed inferior adsorption for BPA compared with 2-MeIM-ZIF-8@SBA-15-xC (x= 3, 6, 9, 12), which was directly related to their structural and chemical composition differences (shown in Figure 4a). Noticeably, compared to pure SBA-15 and ZIF-8, the hierarchical micro-mesoporous composites ZIF-8@SBA-15-x C (x= 3, 6, 9, 12) showed enhanced adsorption capacities, and the capacities increased in accordance with the contents of ZIF-8 (i.e. growth cycles). As a result, ZIF-8@SBA-15-12C possessed the highest equilibrium adsorption capacity of 116.9 mg g-1, which was higher than the sum of SBA-15 and ZIF-8, revealing a synergistic effect between them. The increase in adsorption capacity until the 9th growth circle showed a remarkable increase but its increase became less from 9 C to 12 C. This observation might be attributed to the more and more confined space for ZIF-8 growth, as well as the reduced accessibility for BPA adsorption. In view of its highest adsorption capacity, ZIF-8@SBA-15-12C was chosen for the following adsorption experiments and was abbreviated as ZIF-8@SBA-15.

Figure 5. Adsorption capacities of BPA on ZIF-8@SBA-15-xC, ZIF-8 and SBA-15 (adsorption time = 12 h, initial concentration = 1 mmol L-1).


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It could be seen from the adsorption isotherms in Figure 6a that ZIF-8@SBA-15 composite showed substantially superior adsorption capacity compared with its component materials (ZIF-8 and SBA-15). More notable was that the qmax of ZIF8@SBA-15 calculated from Langmuir model was 135.1 mg g-1, which was more than twice the qmax of ZIF-8 (59.2 mg g-1). Such an enhanced adsorption capacity could be mainly attibuted to the large surface area of mesopores for ZIF growth and the reduced size of ZIF-8 crystals. Higher surface-to-volume ratio of nanoscale ZIF-8 crystals could enable more BPA adsorbed on them. Two typical isotherm models, Langmuir and Freundlich models, were introduced to analyze the isotherms of BPA concentration. As shown in Figure 6b and 6c, the adsorption data of BPA onto ZIF-8 and ZIF-8@SBA-15 fit better with Langmuir model, as evidenced by the better linear fitting and higher correlation coefficients, while Freundlich model described the adsorption data of BPA on SBA-15 better. The Langmuir constant (KL), the Freundlich constant (KF) and heterogeneity factor (n) of ZIF-8@SBA-15 are approximate to that of ZIF-8 and much higher than that of SBA-15 (Table S1). According to these results, it could be deduced that the adsorption thermodynamic properties of ZIF-8@SBA-15 composite mainly inherited from ZIF-8 rather than SBA-15.

Figure 6. Adsorption performances of BPA on ZIF-8@SBA-15, ZIF-8 and SBA-15 in aqueous solution. (a) adsorption isotherms (adsorption time = 12 h, initial



concentration = 0.01─1.5 mmol L-1), and linear fitting curves of (b) Langmuir isotherm and (c) Freundlich isotherm; (d) adsorption kinetics (initial concentration = 1 mmol L-1, contact time = 1─400 min), and linear fitting curves using (e) pseudosecond-order kinetic model and (f) pseudo-first-order kinetic model. As shown in Figure 6d, the adsorption capacities of all adsorbents increased rapidly during the initial contact time and then approached to equilibrium. The adsorption equilibrium of BPA on ZIF-8@SBA-15 was achieved within a very short time (~2 min), while ZIF-8 required much longer time (~100 min). Such a remarkable adsorption kinetics of ZIF-8@SBA-15 can be resulted from its well-ordered mesoporous structure that may allow BPA molecules to diffuse easily into the pores. Besides, scaling down the size of ZIF-8 crystals to tiny nanoscale regime provided increased external surface area and reduced diffusion barrier, which were very favorable for BPA adsorption. Two typical kinetic models, pseudo-first-order and pseudo-second-order models, were introduced to analyze the kinetics of the adsorption behavior. The kinetic curves (Figure 6e and 6f) and their corresponding parameters (Table 2) both revealed that the pseudo-second-order model was more appropriate in describing the adsorption process where the correlation coefficient was close to 1 and the calculated qe was matching better with the experiment results when compared with the pseudo-first-order model. The pseudo-second-order kinetic constant (k2) of ZIF-8@SBA-15 (1.1×10-1 g mg-1 min-1) was similar to that of SBA-15 (1.2×10-1 g mg-1 min-1) and far superior to those of ZIF-8 (6.0×10-3 g mg-1 min-1) and other preciously reported MOFs-based adsorbents (Table S2). These reults suggested that the adsorption kinetic properties of ZIF-8@SBA-15 composite mainly inherited from SBA-15 rather than ZIF-8. These findings indiacted that the synergistic effects of ZIF-8 and SBA-15 allowed ZIF-8@SBA-15 composite not only achieving better adsorption capacity than pure ZIF-8 but also perserving the fast mass transfer character of SBA-15. Table 2 Kinetic parameters for the adsorption of BPA on ZIF-8@SBA-15, ZIF-8 and SBA-15.


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pseudo-first-order rate model

pseudo-second-order rate model

Materials

qe (mg g-1)

k1 (min-1)

R2

qe (mg g-1)

k2 (g mg-1 min-1)

R2

ZIF-8@SBA-15

22.6

6.0×10-3

0.361

123.4

1.1×10-1

0.9999

ZIF-8

18.4

7.0×10-3

0.636

61.7

6.0×10-3

0.9996

SBA-15

3.2

5.0×10-3

0.396

13.8

1.2×10-1

0.9989

Due to the hierarchical micro-mesoporous structure of ZIF-8@SBA-15, the adsorption towards BPA (molecule size, 0.96 nm44, 45) occurs mostly on the external surface of ZIF-8 coating layer after entering the mesopores. The zeta potential of ZIF8 is positively below a pH of 10 and becomes negative at higher pH, which results in electrostatic interaction.46, 47 Furthermore, there are an abundant of functional moieties located on the ZIF-8 external surface, involving low-coordinated Zn atom, imidazole linkers and N moieties,48, 49 which corresponds to the possible coordination, π–π stacking and H-bonding interactions, respectively. BPA is a weak acid that contains two ionizable hydroxyl groups (pKa = 9.6 and 10.2). The neutral fraction of BPA is predominant under pH below 10. The negligible pH effect on adsorption capacity (shown in Figure S3) indicated that the electrostatic interaction can be insignificant on the adsorption of BPA onto ZIF-8@SBA-15 and ZIF-8. The degraded adsorption capacity at lower pH was mostly due to the structural collapse of ZIF-8 at lower pH.18 This result also showed that ZIF-8@SBA-15 had a better acid tolerance than pure ZIF-8. Moreover, as shown in Figure 5, the adsorption capacity of 2-MeIMZIF-8@SBA-15-12C was much higher than that of [email protected]. For ZIF-8@SBA-15 composites prepared using stepwise coordination, the imidazole linkers and metal nodes were predominant on the external surface for the 2-MeIMZIF-8@SBA-15-12C and [email protected] C composites, respectively. Therefore, it can be concluded that the π–π stacking interaction between imidazole moieties and BPA have a much more favorable contribution to BPA adsorption than the coordination interaction between the oxygen atoms of BPA and low-coordinated Zn atoms. Furthermore, due to the existence of OH groups in BPA molecules and the N moieties derived from the imidazole moieties on the external surface of ZIF-8, H-



bonding can be considered as another adsorption mechanism. Our results also showed that the adsorption capacity of ZIF-8@SBA-15 was promoted by not only its higher surface-to-volume ratio but also its higher content of imidazole moieties on the external surface compared to ZIF-8. In summary, our study well demonstrates the unique advantage of LPE approach that permits construction of precise hierarchical hybrid porous systems for given applications. In comparison with its purely microporous equivalent, the hierarchical micro-mesoporous structure of ZIF-8@SBA-15 has higher adsorption capacity and superior mass transfer property for adsorbing bulky molecule from aqueous solution, which are mostly related to the nanoscale MOFs and open ordered mesoporous structure, respectively. Reusability of ZIF-8@SBA-15 Composite The reusability of the spent adsorbent is an important indicator for evaluating its application potential. As shown in Figure S4, the adsorbed BPA could be easily desorbed from ZIF-8@SBA-15 by washing with methanol. The reusability of ZIF-8 and ZIF-8@SBA-15 regenerated by methanol washing (i.e. regeneration procedure 1 in Figure S1) was shown in Figure 7a and 7c. Both of the regenerated ZIF-8 and ZIF8@SBA-15 presented decreased adsorption capacity as the regeneration cycle increased, and the latter showed much less loss of adsorption efficiency than the former. This result was mostly related to the higher structure stability of ZIF-8@SBA15 than pure ZIF-8 after regeneration as confirmed by the following SEM/EDS and XRD analysis.


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Figure 7. (a) Reusability and (b) XRD patterns of ZIF-8 regenerated through procedure 1 (adsorption time = 2 h, initial concentration = 1 mmol L-1); (c) reusability and (d) XRD patterns of ZIF-8@SBA-15 regenerated through procedure 1 and 2 (adsorption time = 0.5 h, initial concentration = 1 mmol L-1). The ZIF-8 and ZIF-8 @SBA-15 after the fifth regeneration cycle using procedure 1 were denoted as ZIF-8-5re-1 and ZIF-8@SBA-15-5re-1, respectively. As observed from the SEM images (Figure S5a and S5b) and EDS spectra (Figure S5c and S5d), after 5 times of regeneration and reuse, the morphology of pure ZIF-8 adsorbent was transformed from regular polyhedral crystals (~80 nm) to large irregular particles, companied with a significant decrease of the N/Zn ratio from 6.32 to 1.28. The differences in XRD patterns between ZIF-8 and ZIF-8-5re (Figure 7b) suggested a structural transformation to ZnO at some degree after the multiple regeneration and reuse process, according to the significantly decreased peak intensities of ZIF-8 and the appearance of new peaks at the high 2θ angle region of 31.7°, 34.4°, and 36.2°, 47.5°, 56.6° (in good agreement with those belonging to ZnO particles50). This observation was similar to the results in some previous reports,



where ZIF-8 was instable and degraded to ZnO or ZnCO3 under mild acid condition.51-54 However, for ZIF-8@SBA-15-5re-1, only a less decreased intensity of the characteristic XRD peaks (shown in Figure 7d) was observed compared to pristine ZIF-8@SBA-15, and its EDS spectrum (Figure S5e and S5f) also exhibited a less decreased N/Zn ratio (3.44 vs. 6.77, Table S3). Despite its better regeneration performance than ZIF-8, ZIF-8@SBA-15 could not be efficiently regenerated by only methanol washing. It is worth noticed that the XRD profile and EDS spectrum of ZIF-8@SBA-155re were similar to those of [email protected] ended with Zn2+, which revealed a possible loss of 2-MeIM groups after the regeneration and reuse. Therefore, a new regeneration procedure 2 by immersing ZIF-8@SBA-15 in 2-MeIM solution (see Figure S1) was adopted. The regenerated ZIF-8@SBA-15 after the fifth regeneration cycle using procedure 2 was denoted as ZIF-8@SBA-15-5re-2. Figure 7c showed that the regenerated ZIF-8@SBA-15 still retained good adsorption efficiency after 5 regeneration cycles recycles. The XRD pattern (Figure 7d) of ZIF-8@SBA-15-5re-2 also indicated the well-preserved crystal structure. The results above showed that the regeneration procedure 2 was a facile and effective method to regenerate ZIF8@SBA-15 adsorbents. It can be concluded that the regenerability of its 2-MeIM functionalized counterparts using a simple immersion procedure and thus its excellent reusability further improved its value in technical applications.

Conclusions In summary, the modified stepwise coordination method guarantees that the ZIF8 coating layers gradually occupy while not obstruct the meso-channels (~15 nm) of SBA-15 and thus the thickness of coating layers with nanometer precision can be adjusted by the growth cycles. This strategy led to a production of nanosized ZIF-8 crystals inside the well-preserved meso-channels, which was correlated to about 2 and 20-fold enhancements in adsorption capacity and rate constant for BPA in aqueous solution, respectively, compared to purely microporous ZIF-8. It can be concluded that the hierarchical micro-mesoporous composite combined the merits of good


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adsorption ability of ZIF-8 and fast diffusion property of SBA-15. And the synergistic effect played a favorable role on achieving the elevated adsorption performance. Our results showed that π–π stacking and hydrogen bonding interactions were the main adsorption mechanisms. Excellent regenerability could be achieved by a simple immersion treatment with 2-MeIM solution. These results above reveal that such hierarchical micro-mesoporous composites integrating desirable component properties can be a promising candidate for bulky molecule capture, drug delivery as well as other applications because of an elimination of transport limitation.

ACKNOWLEDGEMENTS We acknowledge with the National Natural Science Foundation of China (Grant Nos. 21475130, 21705149, 21607067 and 21677143) for its support.

ASSOCIATED CONTENT Supporting Information More diagram and characterization and investigation results, including illustration of generation procedures of adsorbents, BET isotherm and BJH pore size distribution, effect of the pH on the adsorption capacity, BPA desorption efficiency, and SEM/EDX of the regenerated adsorbents. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. Notes The authors declare no competing financial interest.

REFERENCES (1) Farha, O. K.; Hupp, J. T. Rational Design, Synthesis, Purification, and Activation of MetalOrganic Framework Materials. Acc. Chem. Res. 2010, 43, 1166-1175.



(2) Wang, Z.; Cohen, S. M. Postsynthetic modification of metal-organic frameworks. Chem. Soc. Rev. 2009, 38, 1315-1329. (3) Deria, P.; Mondloch, J. E.; Karagiaridi, O.; Bury, W.; Hupp, J. T.; Farha, O. K. Beyond postsynthesis modification: evolution of metal-organic frameworks via building block replacement. Chem. Soc. Rev. 2014, 43, 5896-5912. (4) Vleet, M. J. V.; Weng, T; Li, X.; Schmidt, J. R. In Situ, Time-Resolved, and Mechanistic Studies of Metal-Organic Framework Nucleation and Growth. Chem. Rev. 2018, 118, 36813721. (5) Li, J. R.; Kuppler, R. J.; Zhou, H. C. Selective gas adsorption and separation in metalorganic frameworks. Chem. Soc. Rev. 2009, 38, 1477-1504. (6) Erucar, I.; Keskin, S. High-Throughput Molecular Simulations of Metal Organic Frameworks for CO2 Separation: Opportunities and Challenges. Front Mater 2018, 5. (7) Chen, Y. Z.; Zhang, R.; Jiao, L.; Jiang, H. L. Metal–organic framework-derived porous materials for catalysis. Coord. Chem. Rev. 2018, 362, 1-23. (8) Ranocchiari, M.; Bokhoven, J. A. V. Catalysis by metal-organic frameworks: fundamentals and opportunities. Phys. Chem. Chem. Phys. 2011, 13, 6388-6396. (9) Hu, Z.; Deibert, B. J.; Li, J. Luminescent metal-organic frameworks for chemical sensing and explosive detection. Chem. Soc. Rev. 2014, 43, 5815-5840. (10) Wang, L.; Han, Y.; Feng, X.; Zhou, J.; Qi, P.; Wang, B. Metal–organic frameworks for energy storage: Batteries and supercapacitors. Coord. Chem. Rev. 2016, 307, 361-381. (11) Xia, W.; Mahmood, A.; Zou, R.; Xu, Q. Metal–organic frameworks and their derived nanostructures for electrochemical energy storage and conversion. Enger. Enviton. Sci. 2015, 8, 1837-1866. (12) Mon, M.; Bruno, R.; Ferrando-Soria, J.; Armentano, D.; Pardo, E. Metal–organic framework technologies for water remediation: towards a sustainable ecosystem. J. Mater. Chem. A 2018, 6, 4912-4947. (13) Li, J.; Wang, X.; Zhao, G.; Chen, C.; Chai, Z.; Alsaedi, A.; Hayatf. T.; Wang, X. Metalorganic framework-based materials: superior adsorbents for the capture of toxic and radioactive metal ions. Chem. Soc. Rev. 2018, 47, 2322-2356. (14) Yang, Y.; Yan, X.; Hu, X.; Feng, R.; Zhou, M. In-situ growth of ZIF-8 on layered double hydroxide: Effect of Zn/Al molar ratios on their structural, morphological and adsorption properties. J. Colloid Interface Sci. 2017, 505, 206-212. (15) Lin, K. Y. A.; Chang, H. A. Ultra-high adsorption capacity of zeolitic imidazole framework67 (ZIF-67) for removal of malachite green from water. Chemosphere 2015, 139, 624-631. (16) Dai, J.; Xiao, X.; Duan, S.; Liu, J.; He, J.; Lei, J.; Wang, L. Synthesis of novel microporous nanocomposites of ZIF-8 on multiwalled carbon nanotubes for adsorptive removing benzoic acid from water. Chem. Eng. J. 2018, 331, 64-74. (17) Ahmed, I.; Bhadra, B. N.; Lee, H. J.; Jhung, S. H. Metal-organic framework-derived carbons: Preparation from ZIF-8 and application in the adsorptive removal of sulfamethoxazole from water. Catal. Today 2018, 301, 90-97. (18) Wu, C. S.; Xiong, Z. H.; Li, C.; Zhang, J. M. Zeolitic imidazolate metal organic framework ZIF-8 with ultra-high adsorption capacity bound tetracycline in aqueous solution. RSC Adv. 2015, 5, 82127-82137.


Page 24 of 28

Page 25 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(19) Park, E. Y.; Hasan, Z.; Khan, N. A.; Jhung, S. H. Adsorptive Removal of Bisphenol-A from Water with a Metal-Organic Framework, a Porous Chromium-Benzenedicarboxylate. j. Nanosci. Nanotechno. 2013, 13, 2789-2794. (20) Tsai, C. W.; Langner, E. H. G. The effect of synthesis temperature on the particle size of nano-ZIF-8. Microporous Mesoporous Mater. 2016, 221, 8-13. (21) Abbasi, A. R.; Karimi, M.; Daasbjerg, K. Efficient removal of crystal violet and methylene blue from wastewater by ultrasound nanoparticles Cu-MOF in comparison with mechanosynthesis method. Ultrason. Sonochem. 2017, 37, 182-191. (22) Wahiduzzaman; Allmond, K.; Stone, J.; Harp, S.; Mujibur, K. Synthesis and Electrospraying of Nanoscale MOF (Metal Organic Framework) for High-Performance CO2 Adsorption Membrane. Nanoscale Res. Lett. 2017, 12, 6. (23) Liu, X.; Gong, W.; Luo, J.; Zou, C.; Yang, Y.; Yang, S. Selective adsorption of cationic dyes from aqueous solution by polyoxometalate-based metal–organic framework composite. Appl. Surf. Sci. 2016, 362, 517-524. (24) Zhao, Z.; Zuhra. Z.; Qin, L.; Zhou, Y.; Zhang, L.; Tang, F.; Mu, C. Confinement of microporous MOF-74(Ni) within mesoporous γ-Al2O3 beads for excellent ultra-deep and selective adsorptive desulfurization performance. Fuel. Process. Technol. 2018, 176 276–282. (25) Lin, K. Y. A.; Chang, H. A. A zeolitic imidazole framework (ZIF)–sponge composite prepared via a surfactant-assisted dip-coating method. J. Mater. Chem. A 2015, 3, 2006020064. (26) Fu, Q.; Wen, L.; Zhang, L.; Chen, X.; Pun, D.; Ahmed, A.; Yang, Y.; Zhang, H. Preparation of Ice-Templated MOF-Polymer Composite Monoliths and Their Application for Wastewater Treatment with High Capacity and Easy Recycling. ACS appl. Mater. interfaces 2017, 9, (39), 33979-33988. (27) Kou, J.; Sun, L. B. Fabrication of Metal-Organic Frameworks inside Silica Nanopores with Significantly Enhanced Hydrostability and Catalytic Activity. ACS appl. Mater. Interfaces 2018, 10, 12051-12059. (28) Chen, C.; Li, B.; Zhou, L.; Xia, Z.; Feng, N.; Ding, J.; Wang, L.; Wan, H.; Guan, G. Synthesis of Hierarchically Structured Hybrid Materials by Controlled Self-Assembly of Metal-Organic Framework with Mesoporous Silica for CO2 Adsorption. ACS appl. Mater. interfaces 2017, 9, 23060-23071. (29) Tari, N. E.; Tadjarodi, A.; Tamnanloo, J.; Fatemi, S. One pot microwave synthesis of MCM-41/Cu based MOF composite with improved CO2 adsorption and selectivity. 2016, 231, 154-162. (30) Tu, M.; Wannapaiboon, S.; Fischer, R. A. Liquid phase stepwise growth of surface mounted metal–organic frameworks for exploratory research and development of applications. Inorg. Chem. Front. 2014, 1, 442-453. (31) Shekhah, O. Layer-by-Layer Method for the Synthesis and Growth of Surface Mounted Metal-Organic Frameworks (SURMOFs). Materials 2010, 3, 1302-1315. (32) Shekhah, O.; Wang, H.; Kowarik, S.; Schreiber, F.; Paulus, M.; Tolan, M.; Sternemann, C.; Evers, F.; Zacher, D.; Fischer, R. A.; Woll, C. Step-by-step route for the synthesis of metalorganic frameworks. J. Am. Chem. Soc. 2007, 129, 15118-15119.



(33) Chernikova, V.; Shekhah, O.; Eddaoudi, M. Advanced Fabrication Method for the Preparation of MOF Thin Films: Liquid-Phase Epitaxy Approach Meets Spin Coating Method. ACS Appl. Mater. Interfaces 2016, 8, 20459-20464. (34) Zhang, N.; Zhu, B.; Peng, F.; Yu, X.; Jia, Y.; Wang, J.; Kong, L.; Jin, Z.; Luo, T.; Liu, J. Synthesis of metal-organic-framework related core-shell heterostructures and their application to ion enrichment in aqueous conditions. Chem. Commun. 2014, 50, 7686-7689. (35) Peng, J.; Sun, X.; Li, Y.; Huang, C.; Jin, J.; Dhanjai; Wang, J.; Chen, J. Controllable growth of ZIF-8 layers with nanometer-level precision on SiO 2 nano-powders via liquid phase epitaxy stepwise growth approach. Microporous Mesoporous Mater. 2018, 268, 268-275. (36) Staples, C. A.; Dom, P. B.; Klecka, G. M.; O’Blook, S. T.; Harris, L. R. A Reviewe of the Environmental fate, effects, and exposures of bisphenol A Chemosphere 1998, 36, 21492173. (37) Baggiani, C.; Baravalle, P.; Giovannoli, C.; Anfossi, L.; Giraudi, G. Molecularly imprinted polymer/cryogel composites for solid-phase extraction of bisphenol A from river water and wine. Anal. Bioanal. Chem. 2010, 397, 815-822. (38) Yang, Y.; Lu, L.; Zhang, J.; Yang, Y.; Wu, Y.; Shao, B. Simultaneous determination of seven bisphenols in environmental water and solid samples by liquid chromatography-electrospray tandem mass spectrometry. J. Chromatogr. A 2014, 1328, 26-34. (39) Sun, J.; Zhang, H.; Ma, D.; Chen, Y.; Bao, X.; Klein-Hoffmann, A.; Pfander, N.; Su, D. S. Alkanes-assisted low temperature formation of highly ordered SBA-15 with large cylindrical mesopores. Chem. Commun. 2005, 5343-5345. (40) Naik, P. V.; Wee, L. H.; Meledina, M.; Turner, S.; Li, Y.; Tendeloo, G. V.; Martens, J. A.; Vankelecom, I. F. J. PDMS membranes containing ZIF-coated mesoporous silica spheres for efficient ethanol recovery via pervaporation. J. Mater. Chem. A 2016, 4, 12790-12798. (41) Sorribas, S.; Zornoza, B.; Tellez, C.; Coronas, J. Ordered mesoporous silica-(ZIF-8) coreshell spheres. Chem. Commun. 2012, 48, 9388-8390. (42) Sue, Y. C.; Wu, J. W.; Chung, S. E.; Kang, C. H.; Tung, K. L.; Wu, K. C. W.; Shieh, F. K. Synthesis of hierarchical micro/mesoporous structures via solid-aqueous interface growth: zeolitic imidazolate framework-8 on siliceous mesocellular foams for enhanced pervaporation of water/ethanol mixtures. ACS Appl. Mater. Interfaces 2014, 6, 5192-5198. (43) Fu, Y. Y.; Yang, C. X.; Yan, X. P. Fabrication of ZIF-8@SiO2 core-shell microspheres as the stationary phase for high-performance liquid chromatography. Chem. Eur. J. 2013, 19, 13484-13491. (44) Li, Y.; Yang, C. X.; Yan, X. P. Controllable preparation of core-shell magnetic covalentorganic framework nanospheres for efficient adsorption and removal of bisphenols in aqueous solution. Chemical communications 2017, 53, 2511-2514. (45) Sun, X.; Wang, J.; Li, Y.; Jin, J.; Yang, J.; Li, F.; Shah, S. M.; Chen, J. Highly class-selective solid-phase extraction of bisphenols in milk, sediment and human urine samples using welldesigned dummy molecularly imprinted polymers. J. Chromatogr. A 2014, 1360, 9-16 (46) Jiang, J. Q.; Yang, C. X.; Yan, X. P. Zeolitic imidazolate framework-8 for fast adsorption and removal of benzotriazoles from aqueous solution. ACS Appl. Mater. Interfaces 2013, 5, 9837-9842.


Page 26 of 28

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(47) Khan, N. A.; Jung, B. K.; Hasan, Z.; Jhung, S. H. Adsorption and removal of phthalic acid and diethyl phthalate from water with zeolitic imidazolate and metal-organic frameworks. J. Hazard. Mater. 2015, 282, 194-200. (48) Chizallet, C.; Lazare, S.; Bazer-Bachi, D.; Bonnier, F.; Lecocq, V.; Soyer, E.; Quoineaud, A. A.; Bats, N. Catalysis of Transesterification by a Nonfunctionalized Metal-Organic Framework: Acido-Basicity at the External Surface of ZIF-8 Probed by FTIR and ab Initio Calculations. J. Am. Chem. Soc. 2010, 132, 12365–12377. (49) Chizallet, C.; Bats, N., External Surface of Zeolite Imidazolate Frameworks Viewed Ab Initio: Multifunctionality at the Organic-Inorganic Interface. J. Phys. Chem. Lett. 2010, 1, 349–353. (50) Ahmed, A.; Forster, M.; Jin, J.; Myers, P.; Zhang, H., Tuning Morphology of Nanostructured ZIF-8 on Silica Microspheres and Applications in Liquid Chromatography and Dye Degradation. ACS Appl. Mater. Interfaces 2015, 7, 18054-18063. (51) Pang, S. H.; Han, C.; Sholl, D. S.; Jones, C. W.; Lively, R. P. Facet-Specific Stability of ZIF-8 in the Presence of Acid Gases Dissolved in Aqueous Solutions. Chem. Mater. 2016, 28, 69606967. (52) Liu, H.; Guo, P.; Regueira, T.; Wang, Z.; Du, J.; Chen, G. Irreversible Change of the Pore Structure of ZIF-8 in Carbon Dioxide Capture with Water Coexistence. J. Phys. Chem. C 2016, 120, 13287-13294. (53) Avci, C.; Arinez-Soriano, J.; Carne-Sanchez, A.; Guillerm, V.; Carbonell, C.; Imaz, I.; Maspoch, D. Post-Synthetic Anisotropic Wet-Chemical Etching of Colloidal Sodalite ZIF Crystals. Angew. Chem., Int. Ed. 2015, 54, 14417-14421. (54) Mottillo, C.; Friscic, T. Carbon dioxide sensitivity of zeolitic imidazolate frameworks. Angew. Chem., Int. Ed. 2014, 53, 7471-7474.



Table of Contents


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Controlled Manipulation of MOFs Layers to Nanometer Precision

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