Facile Synthesis of Boron Organic Polymers for Efficient Removal and

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Facile Synthesis of Boron Organic Polymers for Efficient Removal and Separation of Methylene Blue, Rhodamine B and Rhodamine 6G Xue Zhao, Dan Wang, Changjun Xiang, Fulin Zhang, Luchang Liu, Xiaohai Zhou, and Haibo Zhang ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b04049 • Publication Date (Web): 19 Oct 2018 Downloaded from http://pubs.acs.org on October 24, 2018

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ACS Sustainable Chemistry & Engineering

Facile Synthesis of Boron Organic Polymers for Efficient Removal and Separation of Methylene Blue, Rhodamine B and Rhodamine 6G Xue Zhao†, Dan Wang†, Changjun Xiang†, Fulin Zhang†, Luchang Liu†, Xiaohai Zhou*§ †,

Haibo Zhang *§ †

†

College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072(P.

R. China)

§

Engineering Research Center of Organosilicon Compounds ＆ materials Ministry of Education, Wuhan 430072 (P. R. China).

*

National Demonstration Center for Experimental Chemistry, Wuhan University, Wuhan 430072 (P. R. China). 1

ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering 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

*Corresponding

*E-mail:

Page 2 of 57

author.

[email protected], [email protected]

ABSTRACT

The Dodecahydro-closo-dodecaborate anion (B12H122-) Organic Polymers (BOPs) was facilely obtained from the aqueous solution via a simple and effective method. Single crystal X-ray diffraction results insinuated that the BOPs was formed by intermolecular forces between 4,4’-bipyridine and B12H122-. The presence of B12H122- gave the BOPs a certain degree of electronegativity, which possessed excellent stability and high adsorption capacity toward cationic dyes methylene blue (MB), rhodamine B (RB), and rhodamine 6G (RB6G). The adsorption capacity of BOPs for MB, RB and RB 6G dyes 2


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reached 3250 mg·g-1, 1388 mg·g-1 and 2033 mg·g-1, respectively. Through adsorption kinetics and adsorption isotherm results, BOPs exhibited rapid kinetic adsorption and ultra-high adsorption capacity. Moreover, the BOPs materials could separate MB/MO, MB/RB, MB/RB6G, RB/MO and RB6G/MO mixed components efficiently by adjusting the pH of the dye solution. It was worth mentioning that BOPs adsorbents could be easily and rapidly regenerated and being recycled at least five times without decreasing the adsorption capacity, indicating a potential application in dye pollutants removal.

KEYWORDS: BOPs, B12H122-, B-H...π bonds, Dye adsorption, Selectively separate.

3



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INTRODUCTION

With the rapid development of society, the random discharge of industrial wastes such as dyes had caused serious environmental problems, which are water pollution as mainly, posing a serious threat to human health.1-4 Therefore, it is essential for environmental governance to remove these dyes from wastewater by exploring an effective method. However, the polluted water often has the characteristics of complex composition, strong diffusivity, high chromaticity, and poor biodegradability. Therefore, it is difficult to deep disposal by efficient and simple approach.5 At present, there are many methods to remove the dye pollutants, such as adsorption,6-11 photocatalytic degradation,12-14 membrane separation and ion exchange,15-20 etc. Compare with other methods, adsorption has the advantages of fast speed, simple operation, low-cost and low energy consumption, it is often used as the removal method of dye in sewage.21-22 The ideal adsorbent for dye adsorption should have high adsorption capacity, fast adsorption kinetics, good chemical stability, good selectivity and easy preparation and regeneration.23 However, traditional adsorbents such as activated carbon,24 zeolite,25 4


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natural fibres,26 etc., due to their poor selective adsorption and weak adsorption capacity, limit their application for removal dyes and the adopted adsorbents is where the shoe pinches. Therefore, the suitable sorbents for dye uptake with high capacity load and fast selective adsorption has become a hot topic.

During the exploration of dye adsorbents, a series of new adsorbent materials emerged. In the aspect of porous organic polymers (POPs), Yu et al.27 synthesized a poly cation two-dimensional covalent organic matrix framework (PC-COF), which has good adsorption capacity for methyl orange dye. Wang et al.28 use pyromellitic dianhydride and melamine to synthesis a porous polyimide (PI), which with rich amine groups and adsorption capacity for methyl orange reached 609.8mg·g-1 at 318 K. Metal-organic frameworks (MOFs) or coordination polymers with permanent porosity are formed by coordination bonds connecting inorganic metal nodes and organic structural units, which also commonly used for the adsorption of dyes. Wang29-30 systematically summarized the interaction mechanism between MOF materials and environmental pollutants by macroscopic batch experiments and theoretical calculations, which 5



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provided theoretical support for the improvement of MOF materials. Huang31 synthesized an amino-modified Zr-based magnetic metal-organic framework composite (Zr-MFCs) and found that this MOFs can effectively remove metal ions or organic dyes from water, and have high adsorption capacity and rapid adsorption kinetics. Roushani et al.32-33 also synthesized the corresponding MOFs and applied to the adsorption of dyes. In recent years, biomass polymers are often treated as adsorbents for wastewater treatment. Kim et al.34 synthesized CCMDs (carboxymethyl chitosan-modified magnetic dendrimers) and used for the selective adsorption of dye molecule. The maximum adsorption amounts of MO and MB were 20.85 mg·g−1 and 96.31 mg·g−1; Cho et al.35 prepared a magnetic materials by nano-magnetite, cross-linked chitosan and hemi zeolite, and used as a adsorbent for MB and MO. The maximum adsorption capacities were 45.1 mg·g−1 and 149.2 mg·g−1, respectively. In addition, new types graphene materials have also been used to solve the problem of organic dye contaminants in water. Wang et al.

36-39studied

the adsorption mechanism of rGO (Reduced Graphene

Oxide) for dye synthesis precursors such as phenols and anilines by experiments and 6


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theoretical calculations. And systematically summarizes the progress of boron nitride (BN, similar structure to graphene) on the water pollutants removal, which is of great significance in environmental pollution management. Although POPs, MOFs, biomass polymers and rGO materials have certain advantages in dye adsorption, their preparation is still challenging, usually requiring high reaction temperatures and environmentally unfriendly organic solvents, which increases manufacturing costs and damages the environment. In addition, the preparation of MOFs often requires a large amount of precious metals and complicated synthesis processes, which limits the industrial application of these adsorbents.40-41 Furthermore, rapid separation and recovery of these adsorbents in water pollution control is also facing severe challenges.

As illustrated in Scheme 1. There were only two additives involved in our work, 4,4'dipyridine and cesium dodecaborate (Cs2[closoB12H12]) with a simple preparation method, a novel BOPs was synthesized via mixing these two aqueous solutions. Since the BOPs has a large conjugated structure and exhibits a strong electronegativity, it has a good adsorption capacity for cationic organic dyes such as MB, RB and RB 6G, and 7



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separated selectively these dyes from anionic dye methyl orange (MO). The adsorption mechanism was studied by kinetic analysis and isothermal adsorption analysis. Adsorption results showed that BOPs materials have fast adsorption kinetics and high adsorption capacity (the adsorption capacity is 3250 mg·g-1, 1388 mg·g-1 and 2033 mg·g-1 for MB, RB and RB6G from water, respectively.). In addition, the BOPs still have high adsorption capacity after 5 cycles. Compare with other types dye adsorbents, this new type BOPs adsorbent is expected to be widely used for the removal of dye contaminants from polluted water by its simple preparation process, high adsorption capacity, and good stability.

EXPERIMENTAL SECTION

Chemicals and materials Cesium closo-dodecaborate (Cs2[closo-B12H12], 98%) were purchased from Strem Chemicals (Newburyport, USA). Other starting reagents (analytical reagent) were purchased from Sinopharm Chemical Reagent Co., Ltd (Shanghai, China), and all

8


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reagents were used as received unless otherwise stated. All solutions was prepared by ultra-pure water (18 MΩ cm-1)

Preparation of BOPs 1.9520g (12.5mmol) 4,4'-bipyridine was added to a 500mL round-bottom flask with 150mL pH3 deionized water at 298 K. 1.0175g (2.5mmol) Cs2B12H12 was added to another 500mL round-bottom flask with 150mL pH3 deionized water at 298 K, then the CS2B12H12 solution was added slowly to the 4,4'-bipyridine solution with stirring for 30 min continuously. After the mixture system stand for 24 hours, the precipitate was obtained by filtration. The pale yellow crystals of BOPs were obtained in mixed solvent of dimethyl sulfoxide and ethanol.

Material characterization The morphology of the composite material BOPs was obtained through field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The X-ray powder diffraction (XRD) was identified by Bruker D8 diffractometer (Germany) with monochromatized Cu Kα radiation (40 kV, 40 mA). 1H NMR spectra 9



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were recorded on a Bruker Advance 400M spectrometer at 400 MHz. ESI-MS spectra were taken at room temperature on a mass spectrometer (Finnigan LCQ advantage; Thermo Fisher Scientific). Fourier transform infrared spectroscopy (FT-IR) spectra were collected by using a KBr tablet as a platform on FT-IR spectrometer (Thermo, USA). The concentrations of dyes were determined by UV-visible spectrometer (UV-vis) (UV3600 Plus, Shimadzu). Crystal data of BOPs were collected at 123.0(1) K on an Agilent Super-Nova diffracto-meter using mirror-monochromatized Cu-Kα (λ = 1.54184 Å) radiation. The crystals were mounted on a Hampton cryoloop with light oil to prevent water loss. The SHELX package (Bruker) is used to solve and improve the structure. Apply the SADABS program to empirical absorption correction. The structure is solved by a direct method, and the anisotropic thermal parameters of all the heavy atoms contained in the model are refined by the full matrix least squares method (Σw(| Fo | 2- | Fc | 2) 2). A hydrogen atom of an organic group is introduced at a geometrically calculated position. These data can be obtained free of charge from the Cambridge Crystallographic

Data

Center

via

www.ccdc.cam.ac.uk/data_request/cif

(code: 10


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1848576). The concentration of dyes (MB/RB/RB 6G) was identified at 662 nm, 552 nm, and 525 nm by using UV-vis spectrometer, respectively.

Adsorption experiments Effect of pH The initial pH was adjusted for dyes solution by 1.0 mol·L-1 HCl aqueous solution and 1.0 mol·L-1 NaOH aqueous solution, respectively. The pH3, pH7 and pH11 stock solutions of MB, RB and RB 6G were prepared, respectively. A dose of 5.0 mg BOPs was added to 20 ml of MB, RB and RB 6G stock solutions, respectively. The mixture was stirred at room temperature. At a certain time interval, a portion of the dispersed sample was taken, and centrifuged for determination the concentration of dye by UV-Vis spectrometer until the dye concentration remains unchanged. All the experiments were triplicate. The results presented were the mean values with a total error of less than 3%.

Adsorption kinetics Kinetic experiments were performed in the dye stock at pH3. 5.0 mg BOPs was added to stock solutions of 20 ml MB, RB and RB 6G, respectively. The mixture was stirred at

11



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room temperature. At a certain time interval, a portion of the dispersed sample removed, which was centrifuged and then take the supernatant solution for determination the concentration of dye in the system by UV-Vis spectrometer. The equilibrate adsorption capacity of BOPs to various dyes is calculated by equation (1).

qe 

V (C0  Ce ) m

(1)

Where C0 (mg·L−1) is the initial concentrations of dyes, Ce (mg·L−1) is the equilibrium concentrations of dyes, qe (mg·g−1) is the adsorption capacity. V (mL) is the dye solution volume, and m (g) is the mass of the BOPs.

Adsorption isotherms The isothermal adsorption experiments were performed in a pH3 dye solution at 298 K. The true initial concentration was determined by UV-vis spectrometer, the initial concentrations of MB, RB, and RB 6G were set up from 50mg·L-1 to 2500mg·L-1, 50mg·L-1 to 1050mg·L-1 and 65mg·L-1 to 1100mg·L-1, respectively. In the isothermal adsorption experiment, 5.0 mg BOPs adsorbent was added to the dye solution with different initial concentrations. After stirring for 450 minutes, the supernatant was taken 12


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and centrifuged, for determining the concentration of dye in the initial system by UV-vis spectrometer. (All the experiments were triplicate. The results presented were the mean values with a total error of less than 3%). The adsorption quantity is calculated by equation (1). The isothermal adsorption data was evaluated by Langmuir and Freundlich classical isothermal adsorption models, respectively.

Selectively separate Based on the adsorption capacity of MB, RB and RB 6G dyes by BOPs adsorbents at different pH ,and the results of kinetic tests, to investigate the selectivity separate of BOPs for cationic dyes removal, BOPs adsorbents were designed to selective separation for MB, RB, RB 6G dyes and anionic dyes methyl orange (MO). Furthermore, the selectivity separate of BOPs for cationic dyes at different pH also was investigated.

Recycling test As BOPs exhibited a robust adsorption capability and a good stability for cationic dyes adsorption, the regeneration property was further evaluated. The recycling adsorption of BOPs was performed in pH3 stock solution at room temperature. The adsorption time 13



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was set to 450 min based on the result of kinetic adsorption. (All the experiments were triplicate. The results presented were the mean values with a total error of less than 3%). The release of dyes from BOPs was achieved by soaking the sorbents in a methanol containing HCl solution (1mol ·L-1 ）, after vacuum drying, the regenerate BOPs was used again for the dye adsorption. The adsorption cycle of each dye was repeated five times.

RESULTS AND DISCUSSION Characterizations of materials The 1HNMR （400MHz; DMSO; Me4Si ）of the BOPs is shown in Figure 1, all peaks were well assigned to 4,4’-bipyridine and B12H122- in the 1HNMR spectra, and the peaks ( δ9.00 (4H, d, CH), δ8.33 (4H, d, CH)) belong to 4,4’-bipyridine shift to the low field. The phenomenon indicates that there is an inductive effect between molecules, resulting in a larger de-shielding effect, thus the conjugates to occur in the low field, indicating that the BOPs consists of 4,4’-bipyridine and B12H122-. FT-IR spectroscopy of

14


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the BOPs was shown in Figure S1, the peak near 3100cm-1 belongs to the C-H stretching vibration in 4,4’-bipyridine, and the peak near 2500cm-1 belongs to the B-H stretching vibration of B12H122-.

The peak near 1650cm-1 is attributed to the C=N

backbone vibration in 4,4’-bipyridine, the peak near 1500cm-1 and 1400cm-1 is attributed to the C=C backbone vibration in 4,4’-bipyridine, The peaks near 800cm-1 attributed to the out-of-plane deformation vibration of C-H in 4,4’-bipyridine. Infrared spectrum indicated that 4,4’-bipyridine was successfully complexed with B12H122- to form a BOPs assembly.

The mass spectrum of BOPs is shown in Figure S2. From the mass

spectrum, it can also be determined that the 4,4’-bipyridine and B12H122- clusters are bound together. The powder XRD patterns shown in Figure S3. It can be seen from the XRD patterns that the BOPs has a certain crystal form.

The Single crystal X-ray diffraction results shown in Figure 2, which provided further insights into the stereochemical structure of BOPs and the binding behaviour between 4, 4 '- bipyridine and B12H122-. The Single crystal structure shows that each B12H122cluster interacts with six 4,4'-bipyridine molecules and each 4,4'-bipyridine molecule 15



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interacts with six B12H122- cluster, 4,4'-bipyridine and B12H122- clusters interwoven to form BOPs assembly. That is, the stoichiometric ratio of 4,4'-bipyridines and B12H122clusters in this BOPs network is 1:1(molar ratio). The crystal packing further exposed short contacts between the partially negatively charged hydrogens on the B12H122clusters and the hydrogens on the pyridines, there exist C-H...H-B bonds (H...H bonds in the double hydrogen bond range from 1.7-2.4 Å; 2.7 Å) and B-H...π bonds(B-H...π has been reported, the distance between H...π is 2.40-2.76Å ),42-43 the bond length are shown in Figure S4. The Crystal data and structure refinement are shown in Table S1. All these Intermolecular weak interaction forces makes the B12H122- cluster and 4,4'bipyridyl closely packed to form the BOPs ordered network. As far as we know, this is the first report the formation of a structurally ordered BOPs material between B12H122and conjugated molecules by intermolecular forces.

As shown in Figure 3, the morphology of the BOPs was observed by FE-SEM and TEM. The micrographs showed that the BOPs material exhibits irregular network structure, which is similar to the morphology of some carbon organic framework 16


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structure and indicates that 4,4'-bipyridine and B12H122-

clusters constructed BOPs

through certain regular interaction.

In practical applications, the stability of materials has been deemed as one of the most important criterion. We tested the stability of BOPs at different pH conditions by soaking BOPs in aqueous solutions at different pH values for 48 hours. Subsequently, the material was characterized by infrared spectroscopy. The results shown in Figure 4, the BOPs are stable in both acidic and basic environments. Therefore, the BOPs can adapt to various pollution systems in practice, and will not be restricted by the acid and alkalinity of the pollution system.

Adsorption of dyes Adsorption effect of pH

The adsorption effect of BOPs adsorbent for dyes in different pH value is shown in Figure 5. The results demonstrate that BOPs had a good adsorption effect for MB at pH3, pH7 and pH11. At pH3, adsorption effect is the best, adsorption capacity could 17



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reach 3250 mg·g-1. At the conditions pH3 and pH7, adsorbent BOPs to RB also have favourable adsorption effect, the adsorption capacity could reach 1388 mg·g-1 at pH3, but almost no adsorption at pH11. In the adsorption experiment of RB6G, it also showed a good adsorption effect at pH3 and pH7, and the adsorption amount could reach 2033 mg·g-1, but almost no adsorption at pH11, which shows the BOPs has the potential for selective separation of these cationic dyes. Furthermore, the adsorption capacity of various materials reported for MB, RB and RB 6G are compared and listed in Table 1. The results showed that the BOPs exhibited the best adsorption performance.

Table 1. Adsorption capacity of various materials for MB, RB and RB6G Adsorbents

Adsorption capacity (mg˙g-1)

Ref.

MB

RB

RB6G

UIO-66-Urea-Based-1

0.42

-

-

44

UIO-66-Urea-Based-2

0.57

-

-

44

UIO-66-Urea-Based-3

0.91

-

-

44

Membrane with a-CS

10.31

8.26

-

45

CCMDs

96.31

-

-

34

MFC-O

116

-

-

31

18


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MFC-U

121

-

-

31

Fe3O4@N-Mc composite

185.1

178.8

-

46

EAC

288.18

281.69

-

47

312

395

-

48

333.33

133.34

-

49

529.1

-

-

50

NH2-MIL-101(Al)

762

-

-

51

MOPs

1153

-

-

23

CaO/g-C3N4

1915.8

-

-

52

NMIL-100(Fe)

-

0.0469

0.0492

53

ZIF-8

-

7.2

-

54

Membrane with CS

-

7.41

-

45

PolyHIPEs/GO

-

1054

-

55

3250

1388

2033

This works

Ni/PC-CNT composites SHBG Fe3O4@SiO2@CSGO

BOPs

TETA-

Adsorption kinetics

Adsorption kinetics was used to assess the adsorption performance. The adsorption kinetics curves of dye solution at pH3 are shown in Figure 5. The results demonstrate 19



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that the adsorption capacity increased rapidly and soon reached equilibrium with the increase of time, the adsorption equilibrium time of MB,RB and RB 6G was 50min, 20min and 50min, respectively.

To further investigate the adsorption rate and the possible mechanism, kinetics of MB, RB and RB6G adsorption on BOPs were studied using the pseudo-first order (Equation (2)) and the pseudo-second order (Equation (3)). 56

K 1 1  1  Qt Qet Qe

t 1 t   2 Qt K 2Qe Qe

(2)

(3)

Where Qe (mg·g-1) is the adsorption capacities at equilibrium, Qt (mg·g-1) is the adsorption capacities at time t (min). K1 (g·mg-1·min-1) is the rate constants of the pseudo-first order model, K2 (g·mg-1·min-1) is the rate constants of the pseudo-second order model.

20


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The experimental data plots based on pseudo first-order and pseudo second-order simulations are shown in Figure 6a and Figure 6b, respectively. It could be seen that the adsorption of dyes MB, RB and RB6G on the BOPs has a better linear relationship in pseudo second order model than in the pseudo first order model. The calculated parameters of pseudo-first order and pseudo-second order are listed in Table 2. All the

Qe values are very close to the theoretical value for complete adsorption capacity. From the calculation parameters, we can see that the pseudo-second-order model of adsorption data has a good linear relationship, the linear correlation (R2) of MB, RB and RB6G is 0.9999, 0.9962 and 0.9999, respectively, which indicating that the adsorption process was attributed to chemisorptions.57-58

Table 2 Adsorption kinetic model parameters for the adsorption of MB, RB and RB 6G on the BOPs Pseudo-first order Dyes

Qe,cal MB

Pseudo-second order

Qe,exp

3250

3333.333

K1(min-1) 4.667

R2 0.9636

Qe,cal 3333.333

k2(g·mg-1·min-1) 0.100

R2 0.9999

21



RB RB 6G

Page 22 of 57

1388

1250.000

2.125

0.7975

1428.571

0.085

0.9962

2033

2000.000

2.800

0.9477

2000.000

0.208

0.9999

Adsorption isotherm The adsorption isotherms to evaluate the adsorption performance of synthesized adsorbent, also used research the interaction between the adsorbate and adsorbent surface.59 As demonstrated in Figure 7, with the increasing of the initial concentrations of MB, RB and RB6G, the adsorption capacity of BOPs increased until a plateau at C0 = 570mg·L−1 of MB, C0 =400mg·L−1 of RB and C0 = 400 mg·L−1 of RB6G, at which the adsorptions of MB, RB and RB6G reached saturation by BOPs Adsorbents. The saturated adsorption capacity were 3333.3 (mg·g−1), 1428.0 (mg·g−1), and 2000.0 (mg·g−1) for MB, RB and RB6G, respectively.

To depict the adsorption process thoroughly, reveal the adsorption isotherm mechanism. Langmuir and Freundlich equations (Equation (4) and (5)) were applied to describe adsorption equilibria, which are two well-known isotherm equations.60

Langmuir equation: 22


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Ce C 1  e  Qe Qmax K L Qmax

(4)

Freundlich equation:

1 log Qe  log K F  log Ce n

(5)

Where Qe and Ce are defined to be the same as above; KF (L·mg-1) is the Freundlich constant; and n is the heterogeneity factor.

The fitting lines of Langmuir isotherm and Freundlich isotherm are shown in Figure 8a and Figure 8b, respectively. The calculated isotherm parameters are listed in Table 3. From the isotherm fitting curve, the linear correlation (R2) of the Langmuir isotherm is higher than that of Freundlich isotherm, which indicates that the adsorption isotherm data of MB, RB and RB 6G by BOPs is more in line with the Langmuir model, the adsorption process of among MB, RB and RB6G on the surface of BOP was the monolayer adsorption. That is, single dye molecule corresponds to one site on the

23



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adsorbent, all surface sites on the adsorbent have the same affinity for the dye, and there is no interaction between the dyes.61

Table 3 Langmuir and Freundlich constants for the adsorption of MB, RB and RB 6G on the BOPs Langmuir

Freundlich

Dyes qmax (mg·g-1)

KL(L·mg-1)

R2

1/n

KF(L·mg-1)

R2

MB

3154

3.052*10-3

0.9667

0.6067

39.129

0.8672

RB

1475

6.342*10-3

0.9837

0.5174

50.107

0.9028

2055

4.156*10-3

0.9381

0.6852

23.774

0.9227

RB 6G

Selectively separation

To investigate the selectivity of BOP for different dyes removal, a mixture of cationic dyes and anionic dye MO was prepared and spiked with 5.0 mg of BOPs. From the Figure 9 ，the results clearly showed that BOPs could efficiently selective separate MB, RB, and RB6G from MO. Moreover, when the pH value is 11, BOPs can well separate MB from MO, RB and RB6G.

Adsorption mechanism 24


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BOPs exhibited rapid kinetic adsorption and superior adsorption capacity. And BOPs could efficiently separate MB/MO, MB/RB, MB/RB6G, RB/MO and RB6G/MO mixed components by adjusting the pH of the dye solution, we think this is based on result of the anion-cation interaction. The ≡RN(CH3)2 is prone to protonation to form ≡RNH+(CH3)2, which enhances the electropositivity of MB, while the inherent electronegativity of B12H122- cluster in BOPs makes the existence anion-cation interaction between BOPs and MB. Therefore, BOPs have good adsorption to MB. In neutral and alkaline conditions, the ≡RN(CH3)2 of MB is difficult to protonate, which makes the electropositive of MB weakened, thus anion - cation interaction between BOPs and MB is weakened , but its own ≡RN+(CH3)2 still exists. Therefore, BOPs still have a certain adsorption capacity for MB, and the adsorption amounts are not much different in PH7 and PH11 conditions. RB has two different existence forms in aqueous solution.62-63 In acidic conditions, in addition to the presence of ≡RN+(CH3)2, ≡RN(CH3)2 will also protonate to form ≡RNH+(CH3)2, enhancing the electropositive of RB only. With the weakening of acidity, ≡RNH+(CH3)2 is gradually deprotonated, the hydrolysis is 25



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gradually enhanced of carboxyl groups on RB , makes the RB exists with zwitterions forms, result in the conditions of anion-cations interaction is lost between BOPs and RB. Therefore, the adsorption of RB by BOPs is showed: acidic > neutral > alkaline (almost no adsorption) .In aqueous solution, RB6G also has different existence forms.64 In acidic and neutral conditions, RB6G exists in the forms of its own ≡NH+C2H5 cation. In the alkaline state, the H+ of ≡RNH+C2H5 is captured by OH-, RB6G turns into electrically neutral state from cationicity state, and no anion-cation interaction between BOPs and RB6G at this time. Therefore, BOPs have almost no adsorption to RB6G in alkaline conditions, but exhibit a certain adsorption amount in acidic and neutral conditions. In the adsorption process of MB, RB, RB6G dyes, BOPs showed different adsorption capacity for MB, RB, RB6G dyes. In addition to the anion-cation interaction, it may be also related to the size of the three molecules. According to the results of isothermal adsorption curve, BOPs are more inclined to langumiur adsorption for MB, RB, RB6G dyes. In the case of monolayer adsorption, the molecular size of methylene blue is smaller than that of RB and RB6G, there are more adsorption sites on BOPs. Therefore, 26


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it has the highest adsorption amount. However, the adsorption difference of RB and RB6G is small by BOPs, which might be the two methyl groups of ≡RN+(CH3)2 on RB make it difficult for BOPs to approach the positive electric center, but the RB6G's ≡RNH+C2H5 has only one ethyl group, BOPs can better approach the positive electric center, so that the adsorption amount of BOPs to RB6G is slightly higher than that of RB.

MO belongs to typical anionic dye, the presence of -SO3- causes electrostatic repulsion of MO and B12H122-, and thus BOPs have almost no adsorption to MO. Although MO is partially protonated (≡RN(CH3)2 + H+ → ≡RNH+(CH3)2) at pH

Facile Synthesis of Boron Organic Polymers for Efficient Removal and

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