Adsorptive Separation of Fructose and Glucose by MetalâOrganic

Subscriber access provided by - Access paid by the | UCSB Libraries

Separations

Adsorptive separation of fructose and glucose by metalorganic frameworks (MOFs): Equilibrium, kinetic, thermodynamic and adsorption mechanism studies Zhouliangzi Zeng, Jiafei Lyu, Peng Bai, and Xianghai Guo Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b00435 • Publication Date (Web): 27 Jun 2018 Downloaded from http://pubs.acs.org on June 28, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 23 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

Industrial & Engineering Chemistry Research

Adsorptive separation of fructose and glucose by metal-organic frameworks

(MOFs):

Equilibrium,

kinetic,

thermodynamic

and

adsorption mechanism studies

Zhouliangzi Zeng, Jiafei Lyu, Peng Bai, Xianghai Guo*

Department of Pharmaceutical Engineering, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300350, P.R. China Key Laboratory of Systems Bioengineering (Ministry of Education), Tianjin University, Tianjin, 300072, P.R. China *

Corresponding author.

Email: [email protected]

Abstract In this work, seven metal-organic frameworks [ZIF-8, MIL-53(Cr), MIL-96(Al), MIL-100(Cr), MIL-100(Fe), MIL-101(Cr) and UiO-66 ] were applied for adsorptive separation of fructose-glucose mixture. UiO-66 exhibited better performance in adsorption capacity and selective adsorption of fructose. The adsorptive process with UiO-66 was further investigated in detail including kinetic, isotherm and adsorption mechanism. The rate-determining step analysis based on film diffusion and intraparticle diffusion model suggested that the adsorption process was controlled by multiple steps, which fitted the pseudo-second-order model. The Freundlich model was fitting better than Langmuir model, which indicated multilayer adsorption on heterogeneous surface. The thermodynamic parameters (∆G, ∆H and ∆S) were calculated, indicating that adsorption process on UiO-66 was an endothermic and entropy increment process. UiO-66 can be a promising adsorbent for adsorptive separation of fructose and glucose. Keywords: Metal-organic frameworks; fructose; glucose; adsorption; separation

1. Introduction

ACS Paragon Plus Environment

Industrial & Engineering Chemistry Research 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

The separation of monosaccharide mixtures from fermentation or isomerization in carbohydrates production industry has received considerable attention in past decades. As important monosaccharides, fructose and its isomer glucose commonly coexist in industrial downstream products. Several properties of fructose make it a potential non-glucose sweetener due to postprandial glucose-lowering effect and relatively higher sweetness1. Besides the wide applications in food and nutrition industry, fructose is also attractive in 5-hydroxymethyl furfural (HMF) synthesis2, which is an important green platform chemical3, 4. Compared with other hexoses, fructose rows over in the reaction conversion where many catalytic systems are proved to be able to convert fructose into HMF almost quantitatively5-7. The main economic and convenient source of fructose is high-fructose corn syrup (HFCs) 8, 9, where abundant starch from grain crop is hydrolyzed, then the produced glucose is isomerized by enzyme to predominant HFCs containing about 42% fructose. Therefore, separation of fructose and glucose is widely observed for its application in both food industry and sustainable biochemical industry. Since fructose and glucose have similar structures and physical properties, it is a challenge to separate them efficiently. A number of methods for fructose-glucose mixture separation were reported, such as crystallization10, ion exchange membrane separation11, ionic liquid extraction12, and chromatographic method13. Among them, continuous chromatography method is one of the most important and mature way which is currently employed for fructose and glucose separation in industry14, 15. Fructose is usually enriched in the simulated moving bed (SMB) where a specific adsorbent is used as packing materials16. So far, a wide range of adsorbents have been studied as packing materials for separation of fructose and glucose including zeolite, alumina and cation exchange resins17-19. In these materials, ion-exchange resins, which are widely used in industrial scale20-22, are recognized as the most feasible adsorbent for separation of fructose-glucose mixture due to their irreplaceable features like good chemical inertness, relatively high capacity and good selectivity. However, considering the large amount of fructose-glucose mixture to be separated annually, aggressive progress is still needed to fulfill a sustainable endeavor. For this reason, studies on more effective adsorbents in fructose and glucose separation have attracted lots of attention in recent years23, 24.


Page 2 of 23

Page 3 of 23 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


Metal-organic frameworks (MOFs), a type of novel porous materials constructed by coordination bonds between different metal ions or clusters and organic ligands, have attracted great interest due to their large porosity, high specific surface area and chemical tenability, which also make them interesting candidates in gas storage, catalysis, optics, drug delivery, separation and chemical sensors25. However, many MOFs are moisture-sensitive because the weak metal-oxygen coordination bond are easily attacked by water molecule26. The water instability of MOFs severely limits the application of MOFs in aqueous solution. Nevertheless, recent researches of water-stable MOFs have achieved significant advance. A few of MOFs with high water-stability were reported, such as ZIF-8, UiOs, and MILs27-30, which makes it promising to employ MOFs in many applications where water is involved. Although some researches about using MOFs as adsorbents in saccharides separation31, 32 have been reported, study on water-stable MOFs in fructose and glucose adsorption is still deficient. In this report, seven water-stable MOFs have been studied for adsorptive separation of fructose and glucose in aqueous solution, which included ZIF-8, MIL-53(Cr), MIL-96(Al), MIL-100(Cr), MIL-100(Fe), MIL-101(Cr) and UiO-66. The best performed adsorbent of seven MOFs is UiO-66, which was further studied on adsorption equilibrium, kinetics, thermodynamics and mechanism. The results proved MOFs can be potential adsorbents in effective fructose-glucose separation, which opened a new page in the application of MOFs.

2. Materials and Methods 2.1 Chemicals α-D-(+)-glucose and β-D-(‒)-fructose were purchased from Aladdin (Shanghai), they were dissolved in deionized water to prepare monosaccharide solutions with different concentrations for adsorption experiments. For the synthesis of MOFs, ZrCl4 (Macklin, Shanghai), terephthalic acid (TCI, Shanghai), 1,3,5-benzenetricarboxylic acid (TCI, Shanghai), concentrated HCl (Jiangtian, Tianjin), 2-methylimidazole (J&K, Beijing), hydrofluoric acid (J&K, 40 w%), chromium powder (Aladdin, Shanghai), iron powder (Aladdin, Shanghai), nitric acid (Macklin, Shanghai, 67%), Al(NO3)3·9H2O (Macklin, Shanghai), Zn(NO3)2·6H2O (Aladdin, Shanghai,) and Cr(NO3)3·9H2O (Aladdin, Shanghai) were used for synthesis of ZIF-8, MIL-53(Cr), MIL-96(Al), MIL-100(Cr), MIL-100(Fe),



MIL-101(Cr) and UiO-66. N, N-dimethylformamide (DMF) (HWRK CHEM., Beijing) and ethanol (HWRK CHEM., Beijing) were used as solvent and washing reagent. All the mentioned chemicals were analytical grade and used without further purification. Acetonitrile (HPLC grade, Concord, Tianjin) and methanol (HPLC grade, Concord, Tianjin) were used in HPLC analysis, both of which have been filtered and degassed before using.

2.2 Preparation of materials All the seven MOFs were synthesized based on the reported methods with slight modification33-39. UiO-66 was synthesized by the following procedure: ZrCl4 (0.50 g, 2.16 mmol), N,N-dimethylformamide (20 mL) and concentrated HCl (4 mL) were added in sequence. For complete dissolution, The obtained mixture was sonicated for 20 min. Then, terephthalic acid (0.492 g, 3.0 mmol) and another 20 mL N,N-dimethylformamide were added to the mixture. Then the obtained mixture was sonicated for another 20 min for complete dissolution. The final mixture was sealed in a Teflon lined autoclave and placed in a preheated oven at 80 °C overnight. The microcrystalline powder was then isolated by centrifugation, and washed with N,N-dimethylformamide (30 mL×3) and ethanol (30 mL×3). At last, the material was activated at 100 °C under vacuum overnight. Detailed synthetic procedures of other six MOFs have been described in supporting information.

2.3 Characterization and analytical methods All seven prepared MOFs were analyzed by a X-ray diffractometer (D/MaX-2500 X-ray, Bruker, Germany) at room temperature, which has a Cu anode (λKα = 1.5418 Å, 2θ = 5-50°). The crystallite structure of seven MOFs were analyzed by a field emission scanning electron microscope (S-4800, Hitachi, Japan), which is operated at 3.0 kV. The Thermogravimetric analysis of seven MOFs were analyzed under O2 flow (60 mL·min-1) from room temperature to 800 oC at 5 oC/min heating rate (TGA, Mettler-Toledo). The nitrogen adsorption isotherms were measured at -196 oC with a Nova 1000 (Micrometrics, USA), and MOF samples were dried at 100 oC before measurement. The surface area SBET and average pore diameter were calculated by Brunauer–Emmett–Teller (BET) method (relative pressure P/P°: 0.06 ~ 0.25) and Density Functional Theory (DFT). The X-ray photoelectron spectroscopy (XPS) analysis


Page 4 of 23

Page 5 of 23 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


employed a PHI 1600 ESCA instrument (PE Company, USA) with a X-ray radiation source of Al Kα (hν = 1486.6 eV). The as-synthesized MOFs samples were exposed under a flow of H2 at 600 °C for 1 hour before XPS measurements, and the C 1s peak at 284.5 eV was used to standardize the binding energies. In adsorption experiments, the concentrations of sugar solutions were analyzed by HPLC equipped with a Baseline NH2 column (250×4.6 mm, NH2bonded spherical silica, 5 µm, BaseLine Chromtech Research Centre, Tianjin) and a KNAUER 2300 refractive index detector at a 1.0 mL/min flowrate at 303 K. The mobile phase is comprised of acetonitrile and water, the proportion of mobile phase is 70:30(acetonitrile: water ).

2.4 Adsorption experiments 2.4.1

Adsorption capacities and selectivity on seven MOFs

To determine different adsorption performance of two saccharides and the selectivity factor between fructose and glucose, 150 mg of ZIF-8, MIL-53(Cr), MIL-96(Al), MIL-100(Cr), MIL-100(Fe), MIL-101(Cr) and UiO-66 was added in a 5 mL centrifuge tube respectively, followed by 1.0 mL aqueous solution of fructose and glucose mixture (20.0 mg fructose and 20.0 mg glucose in 1.0 mL deionized water). The tubes were placed in a water bath shaker at 140 rpm under 30 °C for 24 h. The equilibrium adsorption capacity on seven MOFs was calculated by the mass balance equation:

qe =（C 0 - Ce）V / m

(1)

where C0 is initial concentration of saccharides in the liquid phase (mg·mL-1), Ce is the concentration of saccharides in the liquid phase at equilibrium (mg·mL-1), qe is equilibrium adsorption capacity (mg·g-1), V is liquid volume (mL), and m is mass of adsorbent (g). The distribution coefficient K (mL·g-1) of fructose and glucose on each MOF is expressed by linear isotherm model as following equation:

K = qe / Ce

(2)

The selectivity factor (α) was calculated to evaluate the separation efficiency of each adsorbent by comparing the distribution coefficient constants of fructose (KF) and glucose (KG) in each adsorbent according to following equation:



α F G = K F / KG

2.4.2

Page 6 of 23

(3)

Adsorption isotherms

The adsorption isotherms of fructose and glucose on UiO-66 have been determined by batch adsorption experiments. Both mono- and bi-component sugar solutions were prepared in a range of concentrations among 10.0 and 100.0 mg·mL-1, and adsorption capacities were tested with these solutions at 25 °C, 35 °C and 45 °C. In the bi-component system, the mass concentration of fructose was same as glucose. A certain amount of adsorbent and 1 mL prepared sugar solutions were placed in temperature controlled by water bath shaker at 140 rpm for 12 h. Both Langmuir and Freundlich models were employed for adsorption isotherm analysis. The Langmuir model is suitable for monolayer adsorption onto a surface with limited number of identical sites40. The Langmuir equation is expressed by the following equation:

qe = qm K LCe / (1 + K LCe )

(4)

where qm (mg·g-1) is maximum adsorption capacity of the adsorbent, KL is Langmuir constant (mL·g-1). Empirical Freundlich model is widely used for multilayer adsorption onto a heterogeneous surface with non-uniform distribution of adsorption energy41. The Freundlich equation is expressed by the following equation:

qe = K b Ce1/ n

(5)

where Kb (mg·g-1) and n are parameters of Freundlich model. The unitless n is a constant which can suggest the adsorption intendency of the adsorbent and the capacity of the adsorption process.The constants Kb and n also show the scale of the adsorption driving force.

2.4.3

Adsorption kinetics

The adsorption kinetic studies on UiO-66 were carried out using starting saccharides solutions with a known concentration of fructose (20.0 mg·mL-1), glucose (20.0 mg·mL-1) or mixture of two saccharides in which the fructose and glucose have same concentration of 20.0 mg·mL-1. A weighed amount of 1.00 g adsorbent was added into a 50 mL centrifuge tube,


Page 7 of 23 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


followed by 20.0 mL of saccharides solution (fructose, glucose or their equivalent mixture). The mixtures containing adsorbent and saccharide solution were placed in a water bath shaker at a constantly controlled temperature (30 °C). During the adsorption, samples of 1.0 mL saccharide solution were withdrawn at different intervals for concentration determination by HPLC until equilibrium was reached. The pseudo-second order, Weber-Morris intra-particle diffusion models and Boyd film diffusion model were applied to analyze the adsorption kinetic data. Pseudo-second order rate equation is expressed by following equation:

t / Qt = 1 / ( K1Qe 2 ) + t / Qe

(6)

where Qt and Qe are amounts of adsorbate adsorbed at t (h) and at equilibrium respectively, and K1 (g·mg-1·h-1) is pseudo-second-order rate constant. The Weber-Morris intraparticle diffusion model and Boyd film diffusion model is applied to determine the rate-limiting step of adsorptions. The intraparticle diffusion model equation is expressed by Equation (7).

Qt = K 2t 0.5 + C

(7)

Liquid film diffusion model is expressed by Equation (8).

ln(1 − Qt / Qe ) = K3t

(8)

where K2 [g·(mg·h)-1] and K3 are the diffusion rate constant and C indicates the thickness of the boundary layer.

2.4.4

Adsorption thermodynamics

The thermodynamic constants, known as Gibbs free energy (∆G)，enthalpy (∆H) and entropy (∆S) were determined by using the following equations.

ln Kc = ∆S /R − ∆H /RT ∆G = − RT ln K c

(9) (10)

where R (8.314 J·mol-1·K-1) is universal gas constant; T (K) is Kelvin temperature; KC is the thermodynamic equilibrium constant for adsorption process. The value of KC is obtained by plotting Ce/Qe versus Ce and extrapolating to zero Ce. Namely, KC is equal to the opposite



value of intercept of Ce/Qe versus Ce plot (equal to qmKL)42.

3. Results and discussion 3.1 Adsorption capacities and selectivity on seven MOFs The structures, morphology and pore properties of seven MOFs including ZIF-8, MIL-53(Cr), MIL-96(Al), MIL-100(Cr), MIL-100(Fe), MIL-101(Cr) and UiO-66 were confirmed by X-ray diffraction, scanning electron (SEM), nitrogen adsorption/sorption and thermogravimetric analysis. Detailed characterization data have been summarized in the supporting information (Section S1). The adsorption in the aqueous solution of fructose and glucose mixture was proceeded at 30 °C for 24 h to evaluate the adsorption capacity and selectivity on seven MOFs . When hexoses like fructose and glucose are dissolved in water, they become an equilibrium mixture of their furanoid and pyranoid carbasugar isomers (Figure 1). β-D-glucopyranose and β-D-fructopyranose are the dominant conformation in their equilibrium solution respectively43. The molecule size of fructose was reported to be 9.8 Å at long axis and 8.5 Å at short axis, and glucose is slightly smaller than fructose where it is 8.6 Å at long axis and 8.4 Å at short axis 44. According to the pore width information of seven MOFs in the supporting information, for ZIF-8 and MIL-53(Cr) adsorption existed mainly on the surface of the material due to the small pore width. However, for other five MOFs their apertures are large enough to accommodate the guest molecule during the adsorption process.

Figure 1. Isomers of fructose and glucose in aqueous solution


Page 8 of 23

Page 9 of 23 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


Figure 2. The sugar adsorption capacity (F: fructose, G: glucose) and selectivity factor of seven MOFs.

All the seven MOFs exhibited good adsorption capacity towards two saccharides (Figure 2). Specifically, ZIF-8, UiO-66 and MIL-100 (Fe) showed a fructose preference and exhibited higher selectivity factor than many previous reported adsorbents46. Some of the reported adsorbents with good adsorption performance were shown in Table S1. Even though an ion-exchange resin Dowex Monosphere 99/Ca has shown better adsorption capacity(289.7 mg·g-1), UiO-66 has higher selectivity factor 3.5, which selectivity factor of Dowex Monosphere 99/Ca is 2.14. ZIF-8 exhibited good adsorption capacity and high selectivity factor even if it has smaller surface area and pore diameter than MIL-101(Cr). It can be attributed to the smaller particle size of ZIF-8 [50 nm compared to 1 µm of MIL-101(Cr)], which can provide more exposed adsorption area for adsorbate molecules. Other four MOFs, MIL-96(Al), MIL-101(Cr), MIL-100(Cr) and MIL-53(Cr) presented glucose affinity. In industrial application, the adsorption capacity is intensively related to the annual production45. Although MIL-96(Al) showed better selectivity between fructose and glucose, low adsorption capacity limited its application in industry. Even though separation factor of UiO-66 (3.5) is



not as good as ZIF-8, MIL-100(Fe) and MIL-96(Al), it is clear that UiO-66 outperformed other materials by balancing high selectivity factor and adsorption capacity (25.5 mg·g-1 adsorption capacity on fructose)46. In addition, as 12-connected Zr-MOF UiO-66 has outstanding rigidity and stability, which makes UiO-66 promising for industrial application. According to this analysis, further studies on adsorption of fructose and glucose on UiO-66 were conducted including kinetics, isotherms, thermodynamics and mechanism.

3.2 Adsorption kinetics The adsorption kinetics of UiO-66 on fructose, glucose and their mixture at 30 oC were analyzed through the measurement of time-dependent adsorption capacities (Figure 3). The adsorption process on each MOF can reach equilibrium within 4 h in each case. Compared with mono component adsorption, the adsorption of fructose from binary mixture decreased due to existence of its isomer glucose, which suggested a competitive adsorption between fructose and glucose. Three kinetic models including Weber-Morris diffusion model, Boyd diffusion model and pseudo-second order model were employed for data analysis. The Weber-Morris and Boyd diffusion model were usually applied to determine the rate-limiting step of adsorption where liquid film diffusion and intraparticle diffusion are rate-limiting step in adsorption and mass action is negligible47. As shown in Figure 3b, by fitting with Weber-Morris model there was no linear relationship between Qt and t0.5, which indicated that the intraparticle diffusion was not the only rate-determining step in saccharides adsorption on UiO-66. Since the data points did not pass the origin, the adsorption rate was not only controlled by the intraparticle diffusion. These results suggested that the adsorption process could be divided into two parts: at the first step, boundary layer diffusion occurred on the external surface of UiO-66; then at the second step, the linear part was due to the intraparticle diffusion48. The Boyd model fitting was shown in Figure 3c. The Boyd film diffusion model gave better correlation coefficients than intraparticle diffusion model (Table 1). As the data points did not pass the origin, film diffusion was not the only rate-limiting step. The film and intraparticle diffusion might control the adsorption kinetic simultaneously. which was similar to the conclusion from Weber-Morris diffusion model.


Page 10 of 23

Page 11 of 23 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


Figure 3. Saccharide adsorption kinetics and Fitting of parameters on UiO-66. F or G represents single component fructose or glucose in 20 mg·mL-1 solution, F* or G* represents fructose or glucose in binary mixture solution. (a) Effect of adsorbing time on saccharide adsorption on UiO-66; (b) Weber-Morris diffusion model; (c) Boyd diffusion model; (d) Pseudo-second order kinetic model.

Table 1 Kinetic parameters of saccharides adsorption on UiO-66 at 30 °C Pseudo-second order Saccharides

Qe(exp.)

Qe(cal.)

K1

mg·g-1

mg·g-1

g·(mg·h)-1

R2

Weber-Morris diffusion K2

C

R2

Boyd film diffusion K3

intercept

R2

g·(mg·h)-1

Fructose(m)

63.2(±1.82)

61.7

0.1132

0.996

6.28

53.78 0.793 1.98

1.26

0.804

Glucose(m)

23.5(±1.21)

24.7

0.0879

0.997

2.94

24.28 0.342 0.50

0.35

0.989

Fructose

94.3(±0.08)

94.4

0.1331

0.999

1.46

89.33 0.237 3.29

0.45

0.928

Glucose

24.7(±1.71)

23.3

0.4004

0.997

3.43

16.90 0.209 0.75

0.18

0.907



As shown in Figure 3d, the pseudo-second order model presented linear correlation and the highest correlation coefficients (R2 ˃ 0.995). The calculated Qe according to pseudo-second order model was also very close to the experimental Qe (Table 1). Good fitting of pseudo-second order model indicated that the kinetics of saccharide adsorption on UiO-66 was suitably described by pseudo-second-model, and the adsorptive process may involve some chemisorption process49.

3.3 Adsorption Isotherms The adsorption isotherms were studied at concentration range from 10 to 100 mg·mL-1, at 25 °C ~ 45 °C for 24 h. It was observed that adsorption capacities of both fructose and glucose increased with increasing temperature (Figure 4). In this study, both Langmuir and Freundlich models were employed to describe adsorption equilibrium of fructose and glucose on UiO-66, for both mono-component and binary systems. The parameters of Langmuir and Freundlich models were summarized in Table 2 with good correlation coefficients (R2). In mono-component system, the adsorption isotherms were better fitted by the Freundlich model, which is able to effectively describe adsorption behavior of organics from aqueous solution. All the values of n were larger than unity in Freundlich model, which indicated heterogeneity of these adsorption systems in some degree. This heterogeneity was likely to be caused by irregular defects in the material and various properties of different sorbate isomers.


Page 12 of 23

Page 13 of 23 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


Figure 4. Adsorption isotherms of mono-component. (a) Langmuir and (b) Freundlich model of fructose adsorption; (c) Langmuir and (d) Freundlich model of glucose adsorption.

Figure 5. Adsorption isotherms of fructose and glucose binary mixture at 303 K. (a) Langmuir model; (b) Freundlich model.

Binary sugar adsorption on UiO-66 was evaluated with a mixed solution of fructose and glucose in an equal proportion of mass. An obvious decrease of fructose adsorption was



Page 14 of 23

observed compared with that of mono-component adsorption. In contrast, glucose adsorption showed slight increase (Figure 5). It could be attributed to the different adsorption sites of fructose and glucose on UiO-66. Similar with mono-component system, Freundlich model fitted adsorption data better than Langmuir model. The calculated isotherm parameters are shown in Table 3.

Table 2 Fitting of fructose and glucose adsorption isotherms Langmuir model Sugar

Fructose

Glucose

T(°C)

Freundlich model R2

n

R2

KL

qm

Kb

mL·g-1

mg·g-1

25

0.0377

62.4

0.991

3.15

10.92

0.999

35

0.0434

68.5

0.981

2.94

11.33

0.997

45

0.0534

78.6

0.974

3.22

15.74

0.999

25

0.0589

8.4

0.907

2.89

1.54

0.920

35

0.0710

11.9

0.999

3.12

2.50

0.996

45

0.1363

14.6

0.996

4.65

5.30

0.999

mg·g-1

Table 3 Fitting of adsorption isotherms of fructose and glucose mixture Langmuir model

Freundlich model

Sugar KL (mL·g-1)

qm (mg·g-1)

R2

n

Kb (mg·g-1)

R2

Fructose

0.0910

43.5

0.976

2.72

9.03

0.971

Glucose

0.0304

18.1

0.908

2.81

2.21

0.960

3.4 Adsorption thermodynamics Thermodynamic parameters were calculated for further study of adsorption process. Change of Gibbs free energy ∆G can be calculated by using Kc (Eq.10). Other thermodynamic constants like change in enthalpy (∆H) and entropy (∆S) were determined from the slope and intercept of Van’t Hoff equation (Eq.9 by plotting lnKc verses 1/T (Figure 6). The values of ∆H and ∆S for fructose and glucose in mono-component adsorption were presented in Table 4


Page 15 of 23 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


respectively.

Figure 6. The plot of Van’s Hoff equation: (a) fructose adsorption; (b) glucose adsorption

Table 4 Thermodynamic values for fructose and glucose adsorption on UiO-66 Compound

Fructose

Glucose

T(°C)

∆G(kJ·mol-1)

25

‒2.12

35

‒2.79

45

‒3.79

25

1.74

35

0.44

45

‒1.99

∆H(kJ·mol-1)

∆S(kJ·mol-1·K-1)

22.75

83.29

57.25

185.67

The positive values of enthalpy change in mono-component adsorption of fructose and glucose indicated that both two adsorption processes are endothermic, which is in accordance with the result that the adsorption capacities increased with increasing temperature. In addition, an endothermic adsorption process usually implies a chemisorption process involved, which is also in accordance with the conclusion of kinetic studies. The change in free energy (∆G) of fructose adsorption process is negative, suggesting the adsorption would occur spontaneously. Meanwhile, the ∆G of fructose (‒3.79 ~ ‒2.12 kJ·mol-1) is more negative than glucose, which is consistent with the preference of fructose adsorption on UiO-66. As for glucose adsorption process, the positive ∆G values at 25 °C and 35°C should be amended by the following Eq.(11):



∆G = − RT ln Kc + RT ln X

Page 16 of 23

（11）

where X can be expressed as mass action quotient before equilibrium. It is only hypothesis that ∆G values of glucose adsorption could be more negative after corrections50. Its higher adsorption heat than fructose adsorption process was agreed with the selectivity preference on UiO-66. Fructose molecules were easily adsorbed than glucose. The positive value of ∆S indicated the freedom degree of adsorbed saccharide molecules increase in the solid/liquid interface51.

3.4 Adsorption mechanism MOFs are constructed with metal ions or clusters and organic ligands by coordination bonds. Among seven MOFs in this research, UiO-66, MIL-53(Cr), and MIL-101(Cr) share the same organic ligand 1,4-dicarboxybenzene; MIL-96(Al), MIL-100(Fe), and MIL-100(Cr) are constructed by 1,3,5-tricarboxybenzene; while ZIF-8 is constructed by 2-methylimidazole (Figure S1). No rules of adsorption on the MOFs with same linker can be concluded. What is more, we observed that although the three MOFs containing Cr3+ were constructed by

different organic ligands, all of these three MOFs with chromium cluster presented a glucose affinity tendency. In addition, MIL-100(Fe) and MIL-100(Cr) which shared the same organic linker exhibited opposite affinity to fructose and glucose. It suggested that metal ions may play an important role in adsorptive selectivity. Difference in selectivity of fructose and glucose adsorption may mainly depend on the interactions between the different metal ions and adsorbates. The saccharide adsorption kinetics, isotherms and thermodynamics in this study suggested that the adsorptive process on UiO-66 may involve a chemisorption process. To further explain the saccharide adsorptive mechanism on UiO-66, FT-IR (Figure 7) and XPS (Figure 8) were performed to analyze the interaction between saccharide molecules and adsorptive sites of UiO-66. The FT-IR patterns did not change greatly after adsorption, which indicated that the chemical structure of UiO-66 was barely changed after adsorption. But the peaks of O-H stretching vibration at 3400 cm-1 and C-O stretching vibration at 1100 cm-1 were stronger after


Page 17 of 23 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


fructose and glucose adsorption, which meant the saccharide molecules were adsorbed onto the surface of UiO-66 successfully.

Figure 7. The FT-IR patterns of as-synthesized and adsorbed UiO-66



Figure 8. The XPS patterns of as-synthesized and adsorbed UiO-66

As shown in Figure 8, the XPS patterns showed that binding energy changed at Zr 3p, Zr 3d and O 1s peaks after fructose and glucose adsorption on UiO-66, which indicated an interaction between saccharide molecules and Zr6O4(OH)4 clusters. There are two kinds of hydroxyl on the Zr6 cluster including terminal hydroxyl which can coordinate with organic linkers and bridging hydroxyl connecting zirconium, which is shown in Figure 952. Although each Zr6 cluster in UiO-66 is coordinated with twelve COO‾ which gives no unsaturated terminal hydroxyl for interaction with saccharide, defects in the material from missing organic linkers providing uncoordinated hydroxyls may play a critical effect on the high adsorption capacity. Therefore, we hypothesized that the hydroxyl groups on polyhydroxy saccharide molecule could interact with terminal hydroxyl and bridging hydroxyls on Zr6 node of UiO-66 through hydrogen bond, which could be verified by the O 1s, Zr 3p and Zr 3d binding energy change in XPS patterns. The slight difference of O 1s binding energy change on fructose and glucose may be the reason for the selectivity of UiO-66 on fructose and glucose.

Figure 9. The structure of Zr6 cluster

4. Conclusion In this study, metal organic frameworks were proved to be promising for adsorptive separation of fructose and glucose. UiO-66 exhibited high fructose adsorption selectivity with


Page 18 of 23

Page 19 of 23 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


a selectivity factor of 3.5. The selectivity of fructose and glucose adsorption on UiO-66 might be attributed to their different conformation in solution and strong interactions between hydroxyl group of adsorbate and metal ion of UiO-66. The obtained kinetic data were described well by pseudo-second-order model, and the isotherms were described better by Freundlich model. The thermodynamic parameters were also calculated and the adsorption process was proved to be endothermic. It is convincible that UiO-66 is a potential adsorbent with good adsorption capacity and selectivity for fructose and glucose separation in aqueous solution.

Acknowledgments We gratefully acknowledge the funding for this work provided by the National Natural Science Foundation of China (No. 21202116), Independent Innovation Foundation of Tianjin University of China (No. 2017XZY-0052), and Natural Science Foundation of Tianjin of China (No. 16JCYBJC20300).

ASSOCIATED CONTENT Supporting Information The Supporting Information Available: Separation factor of fructose and glucose on various adsorbents. Syntheses and characterization and of all the employed materials including TGA, Powder X-ray diffraction, SEM and nitrogen isotherms. Surface area and porosity of seven synthesized metal-organic frameworks.

References (1) Nabors, L. O. B. Alternative Sweeteners 4th Ed; CRC Press: New York, 2012. (2) Dornath, P.; Fan, W. Dehydration of fructose into furans over zeolite catalyst using carbon black as adsorbent. Micropor Mespor Mat. 2014, 191, 10-17. (3) Chheda, J. N.; Románleshkov, Y.; Dumesic, J. A. Production of 5-hydroxymethylfurfural and furfural by dehydration of biomass-derived mono- and poly-saccharides. Green Chem. 2007, 9, 342-350. (4) RomanLeshkov, Y.; Chheda, J. N.; Dumesic, J. A. Phase modifiers promote efficient production of hydroxymethylfurfural from fructose. Science. 2006, 312, 1933-1937.



(5) Zhao, H.; Holladay, J. E.; Brown, H.; Zhang, Z. C. Metal chlorides in ionic liquid solvents convert sugars to 5-hydroxymethylfurfural. Science. 2007, 316, 1597-1600. (6) Shimizu, K. I.; Uozumi, R.; Satsuma, A. Enhanced production of hydroxymethylfurfural from fructose with solid acid catalysts by simple water removal methods. Catal. Commun. 2009, 10, 1849-1853. (7) Dibenedetto, A.; Aresta, M.; Pastore, C.; Bitonto, L. D.; Angelini, A.; Quaranta, E. Conversion of fructose into 5-HMF: a study on the behaviour of heterogeneous cerium-based catalysts and their stability in aqueous media under mild conditions. Rsc Adv. 2015, 5, 26941-26948. (8) Vuilleumier, S. Worldwide production of high-fructose syrup and crystalline fructose. Am. J. Clin. Nutr. 1993, 58, 733-736. (9) White, J. S. Sucrose, HFCS, and Fructose: History, Manufacture, Composition, Applications, and Production. Springer New York: 2014; p 13-33. (10) Kazuo, H.; Mistunobu, S.; Masanobu, S.; Shiro, N. Process for the crystallization of glucose, fructose, or mixture of glucose and fructose. In US3704168: 1972. (11) Tetsujiro, K.; Ryoki, T. Separation of fructose and glucose. In US3666647: 1972. (12) Carneiro, A. P.; Rodriguez, O.; Macedo, E. n. A. Fructose and Glucose Dissolution in Ionic Liquids: Solubility and Thermodynamic Modeling. Ind. Eng. Chem. Res 2013, 52, 3424-3435. (13) Klatt, K. U.; Hanisch, F.; Dцnnebier, G. Model-based control of a simulated moving bed chromatographic process for the separation of fructose and glucose. J. Process Control. 2002, 12, 203-219. (14) Barker, P. E.; Irlam, G. A.; Abusabah, E. K. E. Continuous chromatographic separation of glucose-fructose mixtures using anion-exchange resins. Chromatographia. 1984, 18, 567-574. (15) Luz, D. A.; Rodrigues, A. K.; Silva, F. R.; Torres, A. E.; Jr, C. C.; Brito, E. S.; Azevedo, D. C. Adsorptive separation of fructose and glucose from an agroindustrial waste of cashew industry. Bioresour. Technol. 2008, 99, 2455-2465. (16) Hanover, L. M.; White, J. S. Manufacturing, composition, and applications of fructose. Am. J. Clin. Nutr. 1993, 58, 724-726. (17) Ching, C. B.; Ruthven, D. M. A liquid phase chromatographic study of sorption and diffusion of glucose and fructose in NaX and KX zeolite crystals. Zeolites. 1988, 8, 68-73. (18) Heper, M.; Tцrker, L.; Kincal, N. S. Sodium, ammonium, calcium, and magnesium forms of zeolite Y for the adsorption of glucose and fructose from aqueous solutions. J. Colloid Interface Sci. 2007, 306, 11-15. (19) Singh, K.; Mohan, S., Adsorption behavior of selected monosaccharides onto an alumina interface. J. Colloid Interface Sci. 2004, 270, 21-28. (20) Ghim, Y. S.; Chang, H. N. Adsorption characteristics of glucose and fructose in ion-exchange resin columns. Ind. Eng. Chem. Res. 1982, 21, 369-374. (21) Leiser, R. S.; Liaw, G. C. Process and equipment for chromatographic separation of fructose/dextrose solutions. In US:4366060 1982. (22) Saska, M.; Clarke, S. J.; Wu, M. D.; Iqbal, K. Glucose-fructose equilibria on Dowex Monosphere 99 CA resin under overloaded conditions. J. Chromatogr. A. 1992, 590, 147-151. (23) Wang, Y.J.; Jiang, X.W.; Liu, Z.Q.; Jin, L.Q.; Liao, C.J.; Cheng, X.P.; Mao, B.X.; Zheng, Y.G. Isolation of fructose from high-fructose corn syrup with calcium immobilized strong acid cation exchanger: Isotherms, kinetics, and fixed-bed chromatography study. Can. J. Chem. Eng. 2016, 94, 537-546.


Page 20 of 23

Page 21 of 23 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


(24) Yang, G.; Li, X.; Zhou, L. Adsorption of fructose in Sn-BEA zeolite from periodic density functional calculations. Rsc Adv. 2016, 6, 8838-8847. (25) Furukawa, H.; Cordova, K. E.; O'Keeffe, M.; Yaghi, O. M. The chemistry and applications of metal-organic frameworks. Science 2013, 341, 974. (26) Yang, J.; Grzech, A.; Mulder, F. M.; Dingemans, T. J. Methyl modified MOF-5: a water stable hydrogen storage material. Chem. Commun. 2011, 47, 5244-5246. (27) Adeyemo, A. A. Metal Organic Frameworks as adsorbents for dye adsorption: overview, prospects and future challenges. Toxicol. Environ. Chem. 2012, 94, 1846-1863. (28) Wu, Y.; Chen, H.; Liu, D.; Xiao, J.; Qian, Y.; Xi, H. Effective ligand functionalization of zirconium-based metal-organic frameworks for the adsorption and separation of benzene and toluene: a multi-scale computational study. Acs Appl Mater. Interfaces. 2015, 7, 5775-87. (29) Xie, K.; Shan, C.; Qi, J.; Qiao, S.; Zeng, Q.; Zhang, L. Study of adsorptive removal of phenol by MOF-5. Desalin. Water Treat. 2015, 54, 654-659. (30) Lan, X.; Zhang, H.; Bai, P.; Guo, X. Investigation of metal organic frameworks for the adsorptive removal of hydrochloride from dilute aqueous solution. Micropor Mesopor Mat. 2016, 231, 40-46. (31) Yabushita, M.; Li, P.; Kobayashi, H.; Fukuoka, A.; Farha, O. K.; Katz, A. Complete furanics-sugar separations with metal-organic framework NU-1000. Chem. Commun. 2016, 52, 11791. (32) Gupta, K. M.; Zhang, K.; Jiang, J. Glucose recovery from aqueous solutions by adsorption in metal-organic framework MIL-101: a molecular simulation study. Sci. Rep. 2015, 5, 12821. (33) Torad, N. L.; Hu, M.; Kamachi, Y.; Takai, K.; Imura, M.; Naito, M.; Yamauchi, Y. Facile synthesis of nanoporous carbons with controlled particle sizes by direct carbonization of monodispersed ZIF-8 crystals. Chem. Commun. 2013, 49, 2521-3. (34) Katz, M. J.; Brown, Z. J.; ColцЁn, Y. J.; Siu, P. W.; Scheidt, K. A.; Snurr, R. Q.; Hupp, J. T.; Farha, O. K., A facile synthesis of UiO-66, UiO-67 and their derivatives. Chem. Commun. 2013, 49, 9449. (35) JW, Y.; YK, S.; YK, H.; JS, C.; H, L.; S, W.; P, B.; A, V.; M, D.; E, B. Controlled reducibility of a metal-organic framework with coordinatively unsaturated sites for preferential gas sorption. Angew. Chem. Int. Ed. 2010, 49, 5949-5952. (36) Serre, C.; Millange, F.; Thouvenot, C.; Nogues, M.; Marsolier, G.; Louer, D.; Ferey, G. Very large breathing effect in the first nanoporous chromium(III)-based solids: MIL-53 or Cr-III(OH)·{O2C-C6H4-CO2}·{HO2C-C6H4-CO2H}x· H2Oy. J. Am. Chem. Soc. 2002, 124, 13519. (37) Ferey, G.; Serre, C.; Mellot-Draznieks, C.; Millange, F.; Surble, S.; Dutour, J.; Margiolaki, I. A hybrid solid with giant pores prepared by a combination of targeted chemistry, simulation, and powder diffraction. Angew. Chem. 2004, 43, 6296-301. (38) Ferey, G.; Mellot-Draznieks, C.; Serre, C.; Millange, F.; Dutour, J.; Surble, S.; Margiolaki, I. A Chromium Terephthalate Based Solid with Unusually Large Pore Volumes and Surface Area. Science 2005, 309, 2040-2042. (39) Liu, D.; Liu, Y.; Dai, F.; Zhao, J.; Yang, K.; Liu, C. Size- and morphology-controllable synthesis of MIL-96 (Al) by hydrolysis and coordination modulation of dual aluminium source and ligand systems. Dalton Trans. 2015, 44, 16421. (40) Richards, T. W.; Rd, C. W. THE DENSITY OF LEAD FROM RADIOACTIVE MINERALS.



J. Am. Chem. Soc. 1916, 181, 439─440. (41) D., z.; Cupic; Kolar-Anic, L. Z.; Anic, S. R.; Macesic, S. R.; Maksimovic, J. P.; Pavlovic, M. S.; Milenkovic, M. C.; Nusa, I.; Bubanja, A. M.; Greco, E. Regularity of Intermittent Bursts in BriggsRauscher Oscillating Systems with Phenol. Helv. Chim. Acta. 2014, 97, 321-333. (42) Aksu, Z.; Kabasakal, E. Batch adsorption of 2,4-dichlorophenoxy-acetic acid (2,4-D) from aqueous solution by granular activated carbon. Sep. Purif. Techol. 2004, 35, (3), 223-240. (43) Kuptsevich, Y. E. Chromatographic Separation of Glucose and Fructose. Russ. Chem. Rev. 1987, 56, 510-522. (44) Lourvanij, K. Partial dehydration of glucose to oxygenated hydrocarbons in molecular-sieving catalysts. Glucose 1995. (45) Warren, L; Smith, J. C.; Peter, H. Unit Operations of Chemical Engineering; McGraw-Hill press: New York, 2005. (46) Bai P. Renewable Chemicals: Production or Purification by Adsorption Process. J. Disperision Sci. Technol, 2015, 36,1297-1308. (47) Inagaki, M.; Katsumoto, T.; Nanba, E.; Ohno, K.; Suehiro, S.; Takeshita, K. Intimate coupling of electro and biooxidation of tannery wastewater. Desalin. Water Treat. 2013, 51, 6617-6623. (48) Acharya, J.; Sahu, J. N.; Sahoo, B. K.; Mohanty, C. R.; Meikap, B. C. Removal of chromium(VI) from wastewater by activated carbon developed from Tamarind wood activated with zinc chloride. Chem. Eng. J. 2009, 150, 25-39. (49) Asfaram, A.; Ghaedi, M.; Hajati, S.; Goudarzi, A.; Bazrafshan, A. A. Simultaneous ultrasound-assisted ternary adsorption of dyes onto copper-doped zinc sulfide nanoparticles loaded on activated carbon: optimization by response surface methodology. Spectrochim. Acta, Part A. 2015, 145, 203. (50) Khan, A. S. A. Evaluation of thermodynamic parameters of cadmium adsorption on sand from Temkin adsorption isotherm. Turk. J. Chem. 2012, 36, 437-443. (51) Almeida, C. A. P.; Debacher, N. A.; Downs, A. J.; Cottet, L. Mello, C. A. D. Removal of methylene blue from colored effluents by adsorption on montmorillonite clay. J. Colloid Interface Sci. 2009, 332, 46. (52) Planas, N.; Mondloch, J. E.; Tussupbayev, S.; Borycz, J.; Gagliardi, L.; Hupp, J. T.; Farha, O. K.; Cramer, C. J. Defining the Proton Topology of the Zr6-Based Metal-Organic Framework NU-1000. J Phys Chem Lett. 2014, 5, 3716-23.


Page 22 of 23

Page 23 of 23 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


Table of Contents graphic Title: Adsorptive separation of fructose and glucose by metal-organic frameworks (MOFs): Equilibrium, kinetic, thermodynamic and adsorption mechanism studies Industrial & Engineering Chemistry Research Year, Volume, Page – Page Zhouliangzi Zeng, Jiafei Lyu, Peng Bai, Xianghai Guo*

Seven

water-stable

metal-organic

frameworks

[UiO-66,

ZIF-8,

MIL-101(Cr),

MIL-100(Cr), MIL-53(Cr), MIL-96(Al), MIL-100(Fe)] were applied for adsorptive separation of fructose-glucose mixture. UiO-66 exhibited better performance in both adsorption capacity and selectivity of fructose. The adsorptive process with UiO-66 was further investigated in detail including kinetic, isotherm and adsorption mechanism. UiO-66 can be a promising adsorbent for adsorptive separation of fructose and glucose.


Adsorptive Separation of Fructose and Glucose by MetalâOrganic

Recommend Documents

Adsorptive Separation of Fructose and Glucose by MetalâOrganic