Al2O3 ratio

Ecotoxicology and Environmental Safety 148 (2018) 585–592

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Study on adsorption of rhodamine B onto Beta zeolites by tuning SiO2/Al2O3 ratio

MARK

⁎

Zhi-Lin Cheng , Yan-xiang Li, Zan Liu School of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou 225002, China

A R T I C L E I N F O

A B S T R A C T

Keywords: Beta zeolite Dynamics Isotherms Adsorption Rhodamine B

The exploration of the relationship between zeolite composition and adsorption performance favored to facilitate its better application in removal of the hazardous substances from water. The adsorption capacity of rhodamine B (RB) onto Beta zeolite from aqueous solution was reported. The relationship between SiO2/Al2O3 ratio and adsorption capacity of Beta zeolite for RB was explored. The structure and physical properties of Beta zeolites with various SiO2/Al2O3 ratios were determined by XRD, FTIR, TEM, BET, UV–vis and so on characterizations. The adsorption behavior of rhodamine B onto Beta zeolite matched to Langmuir adsorption isotherm and more suitable description for the adsorption kinetics was a pseudo-second-order reaction model. The maximum adsorption capacity of the as-prepared Beta zeolite with SiO2/Al2O3 = 18.4 was up to 27.97 mg/g.

1. Introduction Rhodamine B (RB) as causing ecotoxicological effect is seriously threatening the survival environment of human due to its massive applications in textile, plastic, leather, dyeing, paper, and printing industries (Chen and Zhu, 2016). Therefore, it is imperative and preferential mission to eliminate RB from the industrial waste water before returning nature. To our knowledge, there were many treatment methods to be implemented for removing the eco-toxicity dyes from aqueous solutions, therein including coagulation, chemical oxidation, photo degradation, membrane filtration and adsorption. Among these methods, the adsorption was deemed to be high-efficient and cheap cost technology for removing those hazardous impurities from aqueous solutions. By far, due to low cost and energy consumption, adsorption was frequently chosen in separation process (Kyzas, 2012; Zhao et al., 2014; Wu et al., 2016a, 2016b; Yu et al., 2016; Jin et al., 2015; Zou et al., 2016). The high-performance adsorption materials mainly included activated carbon,nano metallic oxide, graphene, zeolite, “Greek coffee” grounds, etc. Zeolites have already found many applications because of their easy regeneration, low cost, environment-friendly material, thermal stability, higher cation-exchange capacity and larger surface area and so on (Zhou et al., 2016; Akgül and Karabakan, 2011). So far, many studies have exhibited a desirable prospective for the synthetic zeolites as a promising adsorbent for heavy metal ions and organic dyes from wastewater. The NaY zeolites derived of kaolin as adsorbents were addressed to get rid of methylene blue (MB) from ⁎

aqueous solution and the maximum adsorption capacity of MB obtained from Langmuir isotherms was up to 21.4 mg/g (EL-Mekkawi et al., 2016). The synthetic NaA zeolites were prepared by kaolin and the maximum adsorption capacity of iron ion attained 5.62 mg/g (Seliem and Komarneni, 2016). The dithizone-immobilized natural zeolite as adsorbent for the removal of Hg (II) ion in the river water was up to 99.36% of removal rate from the initial concentration of 8 mg/L (Mudasir et al., 2016). Beta zeolite as a kind of synthetic zeolite was one of the most widely used molecular sieves. The advantages of Beta zeolite were of higher Si/ Al ratio and three dimensional micropore channel (Blanch-Raga et al., 2016; Santos et al., 2016). A comparative study for kaolinite, activated carbon and Beta zeolite on eliminating ether amine from mining waste water showed that the adsorption capacity of kaolinite, activated carbon and Beta zeolite for ether amine was up to 33.5 mg/g, 65.5 mg/ g and 80.8 mg/g, respectively (Magriotis et al., 2014). As for the adsorption of heavy metal ions, Beta zeolite also exhibited a good adsorption ability for the removal of Pb2+, and the maximum adsorption capacity was up to 2.5 meq/g (Esfahani and Faghihian, 2014). However, the tunable SiO2/Al2O3 ratio was usually used to change the activity or the hydrophobic/hydrophilic nature of zeolite. In previous studied works, the catalytic performance of Beta zeolite was frequently associated with the SiO2/Al2O3 ratio (Tian et al., 2013). The adsorption isotherms of Triton X-100 (TX-100) onto seven types of zeolites (including Beta zeolite) showed that the adsorption capacity of zeolites for TX-100 were mainly determined by their pore sizes and surface hydrophobicity as determined by the SiO2/Al2O3 ratio

Corresponding author. E-mail address: [email protected] (Z.-L. Cheng).

https://doi.org/10.1016/j.ecoenv.2017.11.005 Received 25 September 2017; Received in revised form 31 October 2017; Accepted 3 November 2017 0147-6513/ © 2017 Elsevier Inc. All rights reserved.

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spectrophotometer (PE, America). The Zeta potentials of Beta zeolite in suspensions were measured using a Nano-ZS zetasizer (Malvern, UK) with electrophoretic light scattering mode. Suspensions were obtained by adding dry zeolite (0.25 g) powders into KNO3 (50 cm3, 10−3 M) and stirred for 30 min. After the ending, the upper liquid was taken out via pipette. As zeta potential measurements, the pH of the upper liquid was regulated in 1.5 − 9.0 by using NaOH solution (0.1 M) or HCl (0.1 M).

(Shahbazi et al., 2014). The SSZ-13 (CHA) zeolite membranes presented a good ability for the separation of the ethanol/water mixtures by pervaporation dehydration, which strongly depended on the SiO2/ Al2O3 ratio (Kosinov et al., 2015). For Beta zeolite with widely tunable SiO2/Al2O3, the exploration of the relationship between adsorption ability and SiO2/Al2O3 was of important significance for improving its performance to eliminate dye molecule from water. However, there are no relative reports found as yet. Herein, the as-prepared Beta zeolites with different SiO2/Al2O3 ratios were prepared by oxalic acid-dealumination method. The adsorption for RB onto them in aqueous solution was investigated. The relationship of between the adsorption of RB and the SiO2/Al2O3 ratio of Beta zeolite was discussed.

2.4. Adsorption experiments RB adsorption onto Beta zeolites was performed in a batch process to investigate the adsorption conditions. The adsorbents (0.01 g) were dispersed in the standard aqueous RB solution (10 mL) and then mechanically stirred at different temperatures. Then, a 0.45 µm membrane filter was used to separate the above suspension. The resulting filtrates were analyzed by using a UV–vis spectrophotometer at a wavelength of 354 nm. The RB concentrations were then calculated from a calibration curve. The RB adsorption capacity (q (mg/g)) were calculated from Eq. (1)

2. Experimental 2.1. Chemicals and reagents Oxalic acid dihydrate (C2H2O4﹒2H2O, 99.5%), sodium hydroxide (NaOH, 96%), sodium aluminate (NaAlO2, C.P.) were received from Sinopharm Chemical Reagent Co. LTD in China.

q= 2.2. Preparation of Beta zeolites with different SiO2/Al2O3 ratios

η = qn / q × 100%

3. Results and discussion 3.1. Characterizations of the as-prepared Beta zeolites with different SiO2/ Al2O3 ratios Fig. 1A shows the XRD patterns of the as-prepared Beta zeolites. As can be seen, all the samples are of the crystalline BEA structure (JCPDS47-0183）and no impurity is observed, suggesting that most of the crystalline structure of Beta zeolite is retained after dealuminizing by using oxalic acid with different concentrations. The characteristic diffraction peak has a slight shift from at 2θ = 22.28° of the parent Beta zeolite to at 22.54° of B-5, which suggests that the lattice of Beta zeolites took place a contraction due to the dealumination by oxalic acid (Wu et al., 2016b). The peak intensities of Beta zeolite decline and broaden with increase in the concentration of oxalic acid, suggesting that the bigger crystals could take place to fragment and turn into the nanosized crystals, which was affected by the dealumination. The FTIR spectra of the skeletal vibration of the as-prepared Beta zeolites with various SiO2/Al2O3 ratios are shown in Fig. 1B. The wavenumber in 820–750 cm−1 corresponding to the O-T-O (T = Si, Al) symmetric stretching vibration is increased with the decreasing of the framework aluminum content in zeolite structure. The shift of this wavenumber suggests the varying of the framework SiO2/Al2O3 ratio (Wu et al., 2016b). With regard to the parent Beta zeolite, the peak associated with the O-T-O symmetric stretching vibration locates at 788 cm−1, whereas those of the dealuminated Beta zeolites take place to shift towards the higher wavenumbers at 790 cm−1 (B-1), 794 cm−1 (B-2), 796 cm−1 (B3), 800 cm−1 (B-4) and 802 cm−1 (B-5), respectively. This should be due to the selective extraction of the framework aluminum species in acid medium, thus leading to the increasing of SiO2/Al2O3 ratio. Moreover, the weak characteristic adsorption peaks of the dealuminated Beta zeolite at 517 cm−1 and 565 cm−1 still exist, suggesting that most of the crystal structure in the dealuminated Beta zeolites is

The bulk SiO2/Al2O3 ratio was determined on LAB CENTER XRF1800X-ray fluorescence elemental analysis spectrometer (Shimadzu, Japan). XRD patterns were obtained with D8 advance X-ray diffraction with Cu Ka (λ = 0.154 nm) radiation (40 kV and 30 mA) (Bruker-AXS, Germany). The SEM images were recorded by S-4800 scanning electron microscope at an acceleration voltage of 15 kV. (Hitachi, Japan). Before observation, the samples were coated with a thin layer of Au. The TEM images were detected by Tecnai 12 transmission electron microscope (Philips, Netherlands). The FTIR spectra were measured on a IFS66/S type micro infrared spectrometer (Varian, America) in 400–4000 cm−1(KBr pellets in 1:99 ratios). The N2 adsorption-desorption isotherms were measured on Sorptomatic 1990 Thermo Finningen instrument (Thermo, America). The UV–vis adsorption spectrums were obtained with Lambda 850 UV–visible Table 1 The physical properties of the as-prepared Beta zeolites with different SiO2/Al2O3 ratios. Sbmeso, m2/g

Vcmicro,cm3/g

Vbmeso, cm3/g

Beta B-1 B-2 B-3 B-4 B-5

12.6 15.1 18.4 23.5 30.3 39.9

114 124 144 100 55 41

0.126 0.126 0.127 0.126 0.124 0.118

0.118 0.134 0.165 0.108 0.07 0.054

a b c

(2)

where qn and q are the adsorption capacity after the nth time recycling and the initial adsorption capacity, respectively.

2.3. Characterizations

SiO2/Al2O3a

(1)

Where C0 and C are the initial and equilibrium concentration of RB (mg/L), respectively; V is the volume of the solution (L) and W is the dry mass of the adsorbent (g). The recycling efficiency (η) of adsorbents was calculated from Eq. (2)

The parent Beta zeolite without template agent was synthesized by the seeding method (Zheng et al., 2014). The as-prepared Beta zeolites with different SiO2/Al2O3 ratios were obtained by oxalic acid-dealumination method (Giudici et al., 2000). Firstly, 3 g of Beta zeolite was dispersed into oxalic acid solution (60 mL) with different concentrations (0.05, 0.07, 0.12, 0.15 and 0.18 mol/L) at 70 °C for 3 h under stirring. Then, the suspension solutions were filtered. The solid residues were washed thoroughly with deionized water, then followed drying at 110 °C and calcining at 550 °C for 5 h. The resultant samples were represented to B-1, B-2, B-3, B-4, B-5,respectively. The physical properties of the as-prepared Beta zeolites are listed in Table 1.

Samples

(C0 − C ) V W

Measured by XRF. T-plot method. DFT method.

586

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22.28

beta

B-1

B-1

790

B-2

794

B-3

796

B-4

800

B-5

802

565 517

B-2 B-3 B-4

22.54

5

10

15

20

25

B-5

30

788

beta

Transmittance (%)

Intensity

7.8

35

1500

40

1000

150

beta B-1 B-2 B-3

Wavenumber (cm ) 0.20

A 0.15

B-4 B-5

100

0.10

0.05

50

0 0.0

beta B-1 B-2 B-3 B-4 B-5

B

dV/dD(cm3/g)

N2 volume adsorbed (cm3/g, STP)

200

500 -1

2θ(degree)

0.00

0.2

0.4

0.6

0.8

1.0

0

2

4

6

8

10

Pore diameter (nm)

Relative pressure (p/p0 )

Fig. 1. XRD patterns(A), FTIR spectra(B), N2 adsorption-desorption isotherms (C) and corresponding DFT pore size distributions (D) of the as-prepared Beta zeolite with different SiO2/ Al2O3 ratios.

crystals for these samples during the dealumination process due to higher acid concentration, which will result in decrease in the outer surface area and pore volume of Beta zeolite.

preserved. Figs. 1C and 1D shows the N2-physisorption isotherms and corresponding DFT adsorption pore size distributions of Beta zeolites with different SiO2/Al2O3 ratios. All the isotherms were attached to the typical type IV adsorption-desorption isotherm with showing a hysteresis loop type H3 at relative pressure p/p0 > 0.8 (Fig. 1 (C)), inferring the existence of the slitlike pores and mesopores in samples (Ma et al., 2017). However, the B-4 and B-5 samples (SiO2/Al2O3 = 30.3 and 39.9) have an evidently reduced uptake at low relative pressure, suggesting that the microporosity of two samples are declined due to the damage of the crystalline structure. The DFT pore size distributions of the B-1 and B-2 samples show that the mesopore diameters center at around 2.3 nm and 2.5 nm (Fig. 1D), indicating that a number of the smaller intracrystalline mesopores were produced during the dealumination. This conclusion also is demonstrated the Smeso values in Table 1. The B-2 sample with SiO2/Al2O3 = 18.4 has the most obvious hysteresis loop and the largest total pore volume of 0.292 cm3/g among all the samples. The SEM and TEM images of Beta zeolites with various SiO2/Al2O3 ratios are shown in Fig. 2. The B-1 and B-2 samples corresponding to SiO2/Al2O3 = 15.1, 18.4 and 23.5 still keep the similar crystal morphology with the parent Beta zeolite, indicating that oxalic acid solutions with those concentrations hardly affect the crystal integrity and the dealumination of the framework aluminum is dominant. However, with further increasing oxalic acid concentration, the crystal sizes of the dealuminated Beta zeolites (B-3, B-4 and B-5) become smaller while the crystal morphologies turn fuzzier and more irregular. There appears a lot of the crystal debris in crystal outside and the small holes in crystal interior. This result should be ascribed to the fragmentation of the

3.2. Adsorption of RB onto Beta zeolites with different SiO2/Al2O3 ratios Fig. 3A shows the adsorption capacities of the parent Beta zeolite for RB with the initial concentration of 5 mg/L depended on the adsorption time. As can be seen, the adsorption of RB on zeolite occurs rapidly prior to 10 min and afterwards turns slowly, ultimately attaining a relative equilibrium within 60 min. This phenomenon is of the typical feature of the physical adsorption. Fig. 3B shows the adsorption capacities of the parent Beta zeolite for RB depended on the adsorption temperature. The adsorption capacity of Beta zeolite is slightly increased with the adsorption temperature from 22 °C rising to 55 °C. This result suggests that the adsorption is the endothermic nature. Therefore, all following experiments were operated at 22 °C. Zeta potential analysis for the surface charge on the parent Beta zeolite is shown in Fig. 3C. There appears a distinct increase in the zeta potential with pH from 2 increasing to 9.0, exhibiting the negative zeta potential in the studied pH range. Fig. 3D illustrates the effect of initial pH value on the adsorption capacity of the parent Beta zeolite for RB. The maximum adsorption capacity is up to 4.408 mg/g at pH = 3. With increasing the initial pH value, the adsorption capacity slowly descends. Upon pH value up to 9, the adsorption capacity decreases to 4.26 mg/g. The surface of zeolite exhibits the negative zeta potential in the overall pH range (Yang et al., 2013). The negative charge is originated from either the replacement of Si4+ ions via Al3+ ions in the lattice of zeolite or the 587

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Fig. 2. SEM and TEM( Inset) images of A:Beta zeolite, B:B-1, C:B-2, D:B-3, E:B-4, F:B-5.

increasing in SiO2/Al2O3 ratio, the adsorption capacity are initially increased and then declined. Upon SiO2/Al2O3 = 18.4, the adsorption capacity reaches a maximum value of 4.808 mg/g. This is due to the augment of the hydrophobicity and intracrystalline mesopores of Beta zeolite with increasing SiO2/Al2O3 ratio. However, the fragmentation of the crystals of the B-3, B-4 and B-5 samples acted on the dealumination resulted in the loss of the intracrystalline mesopores despite possessing higher SiO2/Al2O3 ratio. Therefore, the number of the intracrystalline mesopores could decide on the adsorption of RB onto Beta zeolite. Fig. 4B shows the UV–vis adsorption spectra of RB aqueous solutions after the adsorption saturation of Beta zeolites with different SiO2/ Al2O3 ratios. The initial RB aqueous solution shows three strong adsorption peaks at λmax = 198 nm, 258 nm and 354 nm,respectively. After the adsorption of Beta zeolites, the characteristic adsorption peak at 354 nm turns small, and even disappears for B-2. The orderliness is consistent with the above results. Fig. 4C shows the effect of the initial

wreckage of the Si–O–Si bonds over the particle surface (Athanasiadis and Helmreich, 2005; Wang et al., 2012). While RB is dissolved in aqueous solution at pH < pHpzc (pH 3.0), it is firstly protonated the -Nfunctional groups (Cho et al., 1997). Next, there is the electrostatic attraction between the protonated RB and negative adsorbents, which is likely to being the rate-determining step (Adebayo et al., 2014). At pH > 3.0, RB can convert from a cationic form to a zwitterionic form due to the deprotonated form of the COOH groups in RB (Zhang et al., 2011; Mohammadi et al., 2010), which causes an electrostatic repulsion between RB and the negatively charged Beta zeolite, thereby decreasing its adsorption capacity. Furthermore, the zwitterionic form of RB in the solution can assemble into the big molecule aggregate, thus depressing the density of positive charge on RB resulting in the reducing of the adsorption capacity (Wu et al., 2009). Fig. 4A shows the effect of SiO2/Al2O3 ratio on adsorption capacity of Beta zeolite for RB with the initial concentration of 5 mg/L. With 588

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Fig. 3. Adsorption capacities of Beta zeolite for RB as a function of adsorption time (A) and adsorption temperature(B); Zeta potentials of Beta zeolite(C) and adsorption capacity (D) with varying pH (Beta zeolite:0.01 g, RB concentration:5 mg/L, Temperature: 22 °C, Solution volume:10 mL).

for the pseudo-second order model (R2 > 0.998) is larger than the pseudo-first order model (R2 > 0.903). Moreover, the qe (calc.) and qe (exp.) values are of good agreement with each other for pseudo-second order model. Thus, these results confirm that a more suitable description of the adsorption kinetics of rhodamine B onto Beta zeolite follows the pseudo-second order kinetic model. The k2 data show that the rate of initial adsorption for Beta zeolite was much higher at low RB concentrations. The diffusion of the intracrystalline mesopore contributed significantly to the overall mechanism of the adsorption process (Khan et al., 2012). The Langmuir isotherm is usually described to a homogeneous adsorption surface on which no molecular interaction exist between the adsorbate molecules as expressed in the following equation.

RB concentration on the adsorption capacity of B-2 (SiO2/Al2O3 = 18.4). The adsorption capacity of B-2 is hoisted distinctly at lower RB concentration and nevertheless shows a slow increase at higher concentration. Actually, the adsorption of RB onto zeolites can attains the equilibrium more rapidly than at higher concentrations. It should be ascribed to the studied result that the adsorption of RB soaked in those active sites of zeolite is a rate-limiting step at a higher concentration (Wu et al., 2009). In order to reducing application cost, it is crucial on the recycling performance of absorber. The recycling efficiency of B-2 with the recycling times is shown in Fig. 4D. The desorption experiment was carried out at 500 ℃ for 2 h. After recycling five times, the recycling efficiency of the B-2 slightly descends from 98.8% to 83.6%, exhibiting a good reusing ability. The adsorption dynamics of RB adsorption onto Beta zeolite were investigated by using the two well-known models of pseudo-first-order and pseudo-second-order as described in Eqs. (3) and (4), respectively (Ho, 2004).

log(qe − qt ) = log qe −

k1 t 2.303

t = 1/(k 2qe 2) + (1/ qe )⋅t qt

Ce C 1 = e + qe qm qm b

(5)

Where qm represents the maximum theoretical adsorption capacity (mg/g). Ce is the equilibrium concentration of RB (mg/L), b are the Langmuir constant related to adsorption mechanism of adsorption (L/ mg). According to Eq. (5), the slope and the intercept of the linear plots give the values of qm and b when the adsorption obeys the Langmuir equation, respectively. The Freundlich isotherm equation is often used to describe nonspecific adsorption. Thus, it can be applied to non-ideal adsorption on heterogeneous surfaces and multilayer adsorption. The Freundlich isotherm is expressed as follows:

(3)

(4)

where, qe (mg/g) and qt (mg/g) represent the amount of RB adsorbed onto per unit mass of zeolite at equilibrium time and at contact time t. The k1 and k2 are the pseudo-first order adsorption rate constant (1/ min) and the pseudo-second order rate constant (g/mg min),respectively. The rate constants k1 and k2 can be calculated from the intercept of the corresponding plots of log(qe-qt) vs. t and t/qt vs. t, respectively. As listed in Table 2, it can found that the correlation coefficient values

log qe = log Kf + 589

1 log Ce n

(6)

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Fig. 4. Effect of SiO2/Al2O3 ratios on adsorption capacity of Beta zeolite for RB adsorption(A) and UV–vis adsorption spectra of RB aqueous solutions before and after adsorption of Beta zeolites(B); effect of RB initial concentrations on adsorption of B-2 (C); recycling performance of Beta zeolite with SiO2/Al2O3 = 18.4 (D); Laugmuir (E) and Freundlich (F) adsorption isotherm models fitting to experimental date of RB adsorption onto B-2.

Table 2 The Pseudo-first order and pseudo-second order kinetic parameters of RB adsorption onto Beta zeolite. Sample

B2

RB(mg/L)

5 10 20 50

qe(exp)(mg/g)

4.80 8.27 14.33 19.53

Pseudo-first order model

Pseudo-second order model

k1(min−1)

qe(cal) (mg/g)

R2

k2(g/mg min)

qe(cal) (mg/g)

R2

0.022 0.02 0.045 0.049

1.11 1.17 3.03 3.59

0.907 0.903 0.966 0.949

0.30 0.32 0.061 0.051

4.28 7.69 13.99 19.23

1 1 0.998 0.998

590

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(PPZY2015B112).The data of this paper originated from the Test Center of Yangzhou University.

Table 3 The Langmuir and Freundlich isotherm parameters f RB adsorption onto Beta zeolite. Model

Langmuir Freundlich

Isotherm constants

References

qm (mg/g)

b (L/mg)

R2

27.97 Kf(L/mg) 2.54

0.0805 n 1.833

0.992 R2 0.879

Adebayo, M.A., Prola, L.D.T., Lima, E.C., Puchana-Rosero Cataluña, M.J., R., Saucier, C., Umpierres, C.S., Vaghetti, J.C.P., da Silva, L.G., Ruggiero, R., 2014. Adsorption of ProcionBlue MX-R dye from aqueous solutions by lignin chemically modified with aluminium and manganese. J. Hazard. Mater. 268, 43–50. Akgül, M., Karabakan, A., 2011. Promoted dye adsorption performance over desilicated natural zeolite. Microporous Mesoporous Mater. 144, 157–164. Athanasiadis, K., Helmreich, B., 2005. Influence of chemical conditioning on the ion exchange capacity and on kinetic of zinc uptake by clinoptilolite. Water Res. 39, 1527–1532. Blanch-Raga, N., Palomares, A.E., Martínez-Triguero, J., Valencia, S., 2016. Cu and Co modified Beta zeolite catalysts for the trichloroethylene oxidation. Appl. Catal. BEnviron. 187, 90–97. Chang, S.H., Wang, K.S., Li, H.C., Wey, M.Y., Chou, J.D., 2009. Enhancement of Rhodamine B removal by low-cost fly ash sorption with Fenton pre-oxidation. J. Hazard. Mater. 172, 1131–1136. Chen, J., Zhu, X., 2016. Magnetic solid phase extraction using ionic liquid-coated coreshell magnetic nanoparticles followed by high-performance liquid chromatography for determination of Rhodamine B in food samples[J]. Food Chem. 200, 10–15. Cho, S.J., Cui, C., Lee, J.Y., Park, J.K., Suh, S.B., Park, J., Kim, B.H., Kim, K.S., 1997. Nprotonation vs O-protonation in strained amides: ab initio study. J. Org. Chem. 62, 4068–4071. EL-Mekkawi, D.M., Ibrahim, F.A., Selim, M.M., 2016. Removal of methylene blue from water using zeolites prepared from Egyptian kaolins collected from different sources. J. Environ. Chem. Eng. 4, 1417–1422. Esfahani, S.M.B., Faghihian, H., 2014. Modification of synthesized β-zeolite by ethylenediamine and monoethanolamine for adsorption of Pb2+. J. Water Proc. Eng. 3, 62–66. Gad, H.M.H., El-Sayed, A.A., 2009. Activated carbon from agricultural by-products for the removal of Rhodamine-B from aqueous solution. J. Hazard. Mater. 168, 1070–1081. Giudici, R., Kouwenhoven, H.W., Prins, R., 2000. Comparison of nitric and oxalic acid in the dealumination of mordenite. Appl. Catal. A -Gen. 203, 101–110. Ho, Y.S., 2004. Selection of optimum sorption isotherm. Carbon 42, 2115–2116. Jin, Z.X., Wang, X.X., Sun, Y.B., Ai, Y.J., Wang, X.K., 2015. Adsorption of 4-n-nonylphenol and bisphenol-A on magnetic reduced graphene oxides: a combined experimental and theoretical studies. Environ. Sci. Technol. 49, 9168–9175. Khan, Tabrez A., Dahiya, Sarita, Ali, Imran, 2012. Use of kaolinite as adsorbent: equilibrium, dynamics and thermodynamic studies on the adsorption of Rhodamine B from aqueous solution. Appl. Clay Sci. 69, 58–66. Kosinov, N., Auffret, C., Borghuis, G.J., Sripathi, V.G.P., Hensen, E.J.M., 2015. Influence of the Si/Al ratio on the separation properties of SSZ-13 zeolite membranes. J. Membr. Sci. 484, 140–145. Kyzas, George Z., 2012. A decolorization technique with spent “Greek Coffee” grounds as zero-cost adsorbents for industrial textile wastewaters. Materials 5, 2069–2087. Ma, Y., Wu, X.Y., Zhang, G.K., 2017. Core-shell Ag@Pt nanoparticles supported on sepiolite nanofibers for the catalytic reduction of nitrophenols in water: enhanced catalytic performance and DFT study. Appl. Catal. B-Environ. 205, 262–270. Magriotis, Z.M., Leal, P.V.B., Sales, P.F.D., Papini, R.M., Viana, P.R.M., Arroyo, P.A., 2014. A comparative study for the removal of mining wastewater by kaolinite, activated carbon and Beta zeolite. Appl. Clay Sci. s 91–92 (2), 55–62. Mohammadi, M., Hassani, A.J., Mohamed, A.R., Najafpour, G.D., 2010. Removal of rhodamine b from aqueous solution using palm shell-based activated carbon: adsorption and kinetic studies. J. Chem. Eng. Data 55, 5777–5785. Mudasir, M., Karelius, K., Aprilita, N.H., Wahyuni, E.T., 2016. Adsorption of mecury(II) on dithizone-immobilized natural zeolite. J. Environ. Chem. Eng. 4, 1839–1849. Santos, L.R.M.D., Silva, M.A.P.D., Menezes, S.C.D., Jr, L.S.C., Lam, Y.L., 2016. Creation of mesopores and structural re-organization in Beta zeolite during alkaline treatment. Microporous Mesoporous Mater. 226, 260–266. Seliem, Moaaz K., Komarneni, Sridhar, 2016. Equilibrium and kinetic studies for adsorption of iron from aqueous solution by synthetic Na-A zeolites: statistical modeling and optimization. . Microporous Mesoporous Mater. 228, 266–274. Shahbazi, A., Gonzalez-Olmos, R., Kopinke, F.D., Zarabadi-Poor, Georgi, A., 2014. Natural and synthetic zeolites in adsorption/oxidation processes to remove surfactant molecules from water. Sep. Purif. Technol. 127, 1–9. Tian, F., Wu, Y., Shen, Q., Li, X., Chen, Y., Meng, C., 2013. Effect of Si/Al ratio on mesopore formation for zeolite Beta via NaOH treatment and the catalytic performance in α-pinene isomerization and benzoylation of naphthalene. Microporous Mesoporous Mater. 173, 129–138. Wang, S., Zhu, Z.H., 2006. Characterisation and environmental application of an Australian natural zeolite for basic dye removal from aqueous solution. J. Hazard. Mater. 136, 946–952. Wang, X., Ozdemir, O., Hampton, M.A., Nguyen, A.V., Do, D.D., 2012. The effect of zeolite treatment by acids on sodium adsorption ratio of coal seam gas water. Water Res. 46, 5247–5254. Wu, P., Wu, W., Li, S., Xing, N., Zhu, N., Li, P., Wu, J., Yang, C., Dang, Z., 2009. Removal of Cd2+ from aqueous solution by adsorption using Fe-montmorillonite. J. Hazard. Mater. 169, 824–830. Wu, X.F., Wang, W., Li, F., Khaimanov, S., Tsidaevac, N., Lahoubi, M., 2016a. PEG-assisted hydrothermal synthesis of CoFe2O4 nanoparticles with enhanced selective adsorption properties for different dyes. Appl. Surf. Sci. 389, 1003–1011.

where Kf is the Freundlich constant and 1/n is the heterogeneity factor. These values can be calculated from the slope and intercept of the lineralized Freundlich plots of logqe vs. logCe. As shown in Figs. 4E and 4F, the adsorption isotherms of RB onto the B-2 zeolite at pH = 3.0 are given. By fitting experimental equilibrium data,the correlation coefficients are evaluated according to each isotherm. The resulting data are listed in Table 3. The regression coefficient (R2 = 0.992) of the Langmuir model is larger than 0.95, indicating that the Langmuir model fit well. However, the regression coefficient of Freundlich model (R2 = 0.879) is smaller than 0.95. This suggests that the adsorption equilibrium behavior of RB onto the B-2 is compatibly described by the Langmuir adsorption isotherm. So, the adsorption of RB onto Beta zeolites should be considered up to the monolayer coverage on the surface of the adsorbents. The maximum adsorption capacity predicted by the Langmuir model of Beta zeolite (SiO2/Al2O3 = 18.4) is up to 27.97 mg/g. Except for graphene oxide (GO) adsorbent, the maximum adsorption capacity of Beta zeolite in this work is close to activated carbon reported by the references and higher than other type zeolites (Gad and El-Sayed, 2009; Wang and Zhu, 2006; Chang et al., 2009). More interestingly, the adsorption capacity of adsorbent is less dependent of BET surface area. The above results can be concluded that the adsorption capacity of Beta zeolite is significantly affected by the quantity of the intracrystalline mesopores in zeolite. Besides removal of framework Al, the other goal of the acid dealumination aims to create more quantity of the intracrystalline mesopores in zeolite. On the contrary, due to higher acid concentration, the fragmentation of the bigger crystals of zeolite resulted in the decline of the quantity of the intracrystalline mesopores. 4. Conclusions The Beta zeolites with various SiO2/Al2O3 ratios were successfully obtained by acid-dealumination method. Subsequently, the removal of RB from aqueous solution onto these zeolites was used to examine the adsorption ability. The maximum adsorption capacity of Beta zeolite with SiO2/Al2O3 = 18.4 was up to 27.97 mg/g at pH = 3 within reaching an equilibrium of 60 min. Furthermore, it also exhibited a good reusing ability. These experiment results also revealed that the quantity of the intracrystalline mesopores in zeolite was crucial factor for the adsorption of RB onto Beta zeolite. Acknowledgments This work was funded by the Talent Introduction Fund of Yangzhou University (2012-CZL), Zhenjiang High Technology Research Institute of Yangzhou University (2017-CZL), Key Research Project-Industry Foresight and General Key Technology of Yangzhou (YZ2015020), Innovative Talent Program of Green Yang Golden Phoenix (yzlyjfjh2015CX073), Yangzhou Social Development Project (YZ2016072), Jiangsu Province Six Talent Peaks Project (2014-XCL013) and Jiangsu Industrial-academic-research Prospective Joint Project (BY2016069-02). The authors also acknowledge the Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (2016-HXHG) and Top-notch Academic Programs Project of Jiangsu Higher Education Institutions 591

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characterization of gadolinium doped cobalt ferrite nanoparticles with enhanced adsorption capability for Congo Red. Chem. Eng. J. 250, 164–174. Zheng, B.M., Wan, Y.F., Yang, W.Y., Ling, F.X., Xie, H., Fang, X.C., Guo, H.C., 2014. Mechanism of seeding in hydrothermal synthesis of zeolite Beta with organic structure-directing agent-free gel, Chinese. J. Catal. 35, 1800–1810. Zhou, Y., Zhou, L., Zhang, X., Chen, Y., 2016. Preparation of zeolitic imidazolate framework-8 /graphene oxide composites with enhanced VOCs adsorption capacity. Microporous Mesoporous Mater. 225, 488–493. Zou, Y.D., Wang, X.X., Chen, Z.S., Yao, W., Ai, Y.J., Liu, Y.H., Hayat, T., Alsaedi, A., Alharbi, N.S., Wang, X.K., 2016. Superior coagulation of graphene oxides on nanoscale layered double hydroxides and layered double oxides. Environ. Pollut. 219, 107–117.

Wu, X.F., Wang, W., Song, N.N., Yang, X.J., Khaimanov, S., Tsidaeva, N., 2016b. From nanosphere to nanorod: tuning morphology, structure and performance of cobalt ferrites via Pr3+ doping. Chem. Eng. J. 306, 382–392. Yang, Y., Murthy, B.N., Shapter, J.G., Constantopoulos, K.T., Voelcker, N.H., Ellis, A.V., 2013. Benzene carboxylic acid derivatized graphene oxide nanosheets on natural zeolites as effective adsorbents for cationic dye removal. J. Hazard. Mater. 260, 330–338. Yu, S.J., Wang, X.X., Ai, Y.J., Tan, X.L., Hayat, T., Hu, W.P., Wang, X.K., 2016. Experimental and theoretical studies on competitive adsorption of aromatic compounds on reduced graphene oxides. J. Mater. Chem. A 4, 5654–5662. Zhang, R., Hummelgrd, M., Lv, G., Olin, H., 2011. Real time monitoring of the drug release of rhodamine B on graphene oxide. Carbon 49, 1126–1132. Zhao, X., Wang, W., Zhang, Y.J., Wu, S., Li, F., Liu, J.P., 2014. Synthesis and

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