Comparative adsorption of methylene blue by magnetic baker’s yeast and EDTAD-modified magnetic baker’s yeast: Equilibrium and kinetic study

Yunxue Xia; Qin Yao; Wei Zhang; Yunsong Zhang; Maojun Zhao

doi:10.1016/j.arabjc.2015.03.010

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Original article

12 (

); 2448-2456

doi:

10.1016/j.arabjc.2015.03.010

Comparative adsorption of methylene blue by magnetic baker’s yeast and EDTAD-modified magnetic baker’s yeast: Equilibrium and kinetic study

Yunxue Xia¹, Qin Yao¹, Wei Zhang, Yunsong Zhang, Maojun Zhao^⁎

College of Life and Science, Sichuan Agricultural University, Yaan 625014, PR China

⁎Corresponding author. Tel.: +86 835 2885782; fax: +86 835 2862227. 244842127@qq.com (Maojun Zhao)

Received: 2013-7-23, Accepted: 2015-3-13, Published: 2015-12-01

Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

1 These authors contribute equally to this work.

Abstract

Abstract

Adsorption mechanisms of methylene blue onto EDTAD-modified magnetic baker’s yeast (EMB) were deeply studied.
EMB showed super-paramagnetic characteristic of nano-Fe₃O₄ for isolation and recovery and good adsorption capacity of EDTAD for cationic dye.
Specific surface area of EMB was 94.972–499.85 m²/g which was around twice bigger than that of MB.

Abstract

Magnetic baker’s yeast (MB) was prepared using glutaraldehyde cross-linking method and chemical modification with ethylenediaminetetraacetic dianhydride (EDTAD). The fabricated EDTAD-modified magnetic baker’s yeast (EMB) was then employed to remove methylene blue. Comparative adsorption of methylene blue by EMB and MB was systematically investigated with respect to pH, contact time, initial concentration and reaction temperature. The mechanism of methylene blue adsorption by EMB and MB was investigated by SEM, FTIR and Special surface area using methylene blue method. The results revealed that Fe₃O₄ nanoparticles were steadily cross-linked/incorporated with baker’s yeast biomass and the EDTA was modified on the surface of the magnetic baker’s yeast. The equilibrium adsorption data were fitted better by Langmuir isotherm, and the specific surface areas were 42.953–226.07 m²/g for MB and 94.972–499.85 m²/g for EMB, respectively. Kinetic studies suggested that the pseudo-second-order model was suitable to describe the adsorption process. Thermodynamic studies indicated that the adsorption was feasible, spontaneous and endothermic. The recovery efficiencies were above 80% by using 0.1 M HCl.

Keywords

Baker’s yeast

EDTAD

Nano-Fe3O4

Methylene blue

Kinetic

Equilibrium isotherm

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1 Introduction

Dye contamination in wastewater can lead to a variety of environmental problems. Colored water can affect aquatic life and thus an entire ecosystem can be destroyed by contamination of various dyes in water. Methylene blue, as a typical cationic dye, can be widely used in industrial practices such as textile and printing (Hameed et al., 2007; Sajab et al., 2011; Wang et al., 2008 ). Because of its complex aromatic ring structure it is difficult to remove methylene blue from the environment (Wang et al., 2008). With the growing emphasis on green industry, it is important to discover cheaper and more efficient methods for cleaning industrial wastewater. Many physico-chemical methods such as adsorption, coagulation, oxidation and biodegradation, have been tested. Among them, adsorption is considered to be one of the efficient techniques. This is attributed to its low cost, easy availability, high efficiency, ease of operation and ability to treat dyes in more concentrated forms (Deng et al., 2011). In this respect, several types of natural and synthetic biomaterials such as commercial activated carbon, coal, activated carbon from agricultural and industrial and wheat straw, have been used as adsorbents to remove dyes from wastewater (Cherifi et al., 2013; Ebrahimian Pirbazari et al., 2014; Rafatullah et al., 2010; Yan et al., 2011 ). Recently, Saccharomyces, a safe, low-priced and easily available biological material, has shown great potential for removal of dyes (Farah et al., 2007; Pratibha et al., 2010). However, isolation and recovery have limited its application on a larger scale. The magnetic separation technique has been shown to be a potential application for solid–liquid phase separation. Nowadays, nano-Fe₃O₄ has been used for purifying wastewater from dyeing industry and the removal of heavy metals due to its super-paramagnetism (Fan et al., 2012; Geng et al., 2012; Yao et al., 2012a,b ). A research has been reported that the magnetic baker’s yeast (MB), prepared by crosslinking baker’s yeast and nano-Fe₃O₄, can be used as adsorbent to remove methyl violet in wastewater (Tian et al., 2010). Nevertheless, the adsorption capacity of MB for dyes was unsatisfied. The amount and species of functional groups on the surface of adsorbent have been confirmed to be significantly responsible for adsorption capacity when used to treat wastewater according the previous reports (Liu et al., 2010; Rafatullah et al., 2010; Shen et al., 2011 ). Ethylenediaminetetraacetic dianhydride (EDTAD) is a ramification of EDTA and an active agent containing two anhydride groups per molecule which can be employed to introduce chelating abilities to biomaterials through esterification/amidation reaction (Chen et al., 2012; Kołodyńska et al., 2008). Moreover, this reaction will introduce carboxylic and amine functional groups which possess high ability to form stable complexes with heavy metals or dyes. The exciting features of EDTAD inspire us to develop a facile approach for fabricating new adsorbents with superior adsorption capacity for heavy metals or dyes.

Herein, this work describes the fabrication of a new adsorbent from baker’s yeast using EDTAD and nano-Fe₃O₄ as modifying materials. The resulting EDTAD-modified magnetic baker’s yeast (EMB) was then utilized as absorbent for the removal of methylene blue in wastewater (shown in Fig. 1). It is desirable that the obtained EMB not only possesses the super-paramagnetic characteristic of nano-Fe₃O₄ for isolation and recovery, but also has the good adsorption capacity of EDTAD for cationic dye. The adsorption capacity for methylene blue on the prepared EMB (223.66 mg/g) was lower than that of polymer modified baker’s yeast (869.6 mg/g)(Yu et al., 2009b), however, EMB showed higher methylene blue adsorption capacity, compared with baker’s yeast (62.7 mg/g)(Yu et al., 2009a) and MB (110 mg/g).

Synthesis scheme of EMB and adsorption mechanism for methylene blue.

2 Materials and methods

2.1

2.1 Materials and reagents

The fresh baker’s yeast was purchased from Harbin Mali Ltd., China. In order to remove the nutritional ions and soluble impurities, the samples were repeatedly washed with deionized water till pH 7.0. After the suspension was centrifuged at 4000 r/min, deposit biomass was collected and dried at 80 °C for 24 h and then ground to granular material. Finally, the yeast was stored in an airer for further use.

Methylene blue was purchased from Tianjin Chemical Reagent No. 1 Plant, China. A stock solution of methylene blue was prepared by dissolving 1.0 g of methylene blue in 1 L of deionized water. Various working concentrations (50–400 mg/L) were obtained by dilution of the stock solution. The pH of the solution was adjusted to the ideal value by adding a small quantity of HCl (0.1 mol/L) or NaOH (0.1 mol/L).

2.2

2.2 Synthesis of EMB

2.2.1

2.2.1 Synthesis of MB

The magnetic nano-Fe₃O₄ was preformed according to a previous report (Shan et al., 2007). After the prepared nano-Fe₃O₄ (1.0 g) was dispersed in the deionized water (200 mL) by ultrasonication, dry baker’s yeast (5.0 g) and 100 mL glutaraldehyde solutions (1.5 wt.% in aqueous solution) were successively added into the suspension. Then the mixture was shaken for 18–24 h at room temperature. After the reaction, the nano-Fe₃O₄ biomass (MB) was separated magnetically and washed several times to remove the residual glutaraldehyde. Finally, the product was freeze-dried in high vacuum for 18–24 h and stored in a dryer.

2.3

2.3 Synthesis of EMB

2.0 g of EDTAD synthesized according to the previous report (Repo et al., 2011), was added to 100 mL of N,N-dimethylformamide (DMF) containing 5.0 g of MB in a three neck round bottom flask equipped with a condenser. The mixture was stirred at 60 °C for 3–5 h. Finally, the EMB was synthesized. The obtained EMB was separated from the mixture by an external magnet and washed thrice with DMF (200 mL), deionized water (500 mL) and 10% NaHCO₃ solution respectively. EMB was freeze-dried in a high vacuum for 24 h, and then preserved in a desiccator for further use.

2.4

2.4 Adsorption studies

Batch adsorption studies were conducted in 250 mL Erlenmeyer flasks. 0.1 g of each absorbent was added to methylene blue solution (100.0 mL). The suspension was agitated by a rotary shaker (DH2−DA China). Then the mixture was magnetically separated. After that, the supernatants were evaluated to decide the residual concentration of methylene blue by spectrophotometer (WFJ-7200 Spectrophotometer, China) at λ_max of 640 nm. The adsorption capacity and uptake efficiency were measured by the following equation:

(1)

q_{e} = \frac{(C_{0} - C_{e}) V}{m}

where q_e is the amount of adsorption capacity at equilibrium (mg/g), C₀ is the initial and concentration methylene blue (mg/L), C_e is the methylene blue concentration at time t (mg/L), V is the volume of the solution (L) and m is the mass of adsorbent (g).

2.5

2.5 Characterization

Scanning electron microscope (JEOLJSM-5900LV, Japan) was utilized to characterize the surface structure and morphology of nano-Fe₃O₄, baker’s yeast and EMB respectively. The magnetism of EMB was recorded using a digital camera. Infrared spectra of methylene blue, EMB before and after adsorption were identified using a Fourier transform infrared spectrophotometer (Shimadzu FTIR-8400s, Japan) within the region of 400–4000 cm⁻¹ via the KBr pressed-disk method.

3 Results and discussion

3.1

3.1 The experimental procedure

Fig. 1 shows the synthesis route to prepare EMB and provides a suggested mechanism for methylene blue adsorption or desorption. Four main steps were involved in the procedure. First, MB was composed by combining baker’s yeast and nano-Fe₃O₄ via glutaraldehyde as a cross-linking agent. Second, EDTAD molecules were integrated with the MB via formation of ester bond between EDTAD and hydroxyl on the surface of baker’s yeast cell wall. Third, after being rinsed by NaHCO₃ solution, the dissociative carboxyl groups on EMB surface were transformed into carboxylic acid sodium salts which would enhance the surface activity and water-solubility. Three of the four-carboxyl and two amino groups in each EDTA molecule bond with the surface of the magnetic baker’s yeast biomass (shown in Fig. 1). Finally, the resulting EMB was conducted as a recycling magnetic adsorbent for the removal of methylene blue in the aqueous solution.

3.2

3.2 Effect of pH on adsorption

The effect of solution pH on the amount of methylene blue absorbed was studied by varying initial pH under constant process parameters. As shown in Fig. 2, with increase in pH values, the adsorption capacity of methylene blue for two adsorbents was rapidly increased, which can be attributed to the increase in electrostatic attraction and the decrease of acid effect for the coordination bonds stability between methylene blue and functional groups at higher pH values (Padmavathy, 2008). The maximum adsorption capacities were attained at approximately pH 8.0 for both adsorbents, and the prepared EMB presented higher methylene blue adsorption capacity (223.66 mg/g) than MB (110.00 mg/g). More carboxyl groups (—COOH) were produced on EMB surface due to the introduction of EDTAD, which created more adsorption sites for methylene blue, resulting in the higher adsorption capacity of EMB for methylene blue.

3.3

3.3 Effect of contact time and kinetics analysis

Fig. 3a illustrates the effect of adsorption time on methylene blue uptake by MB and EMB. As for MB, the adsorption of methylene blue almost kept constant from 5 min to 45 min. In the first 20 min, the constant adsorption capacity could be attributed to the instant adsorption of functional groups on MB surface. After that, the limited binding sites for methylene blue on MB surface resulted in the constant adsorption capacity. As for MB, the adsorption capacity of methylene blue almost doubled because of the introduction of EDTAD, which brought more functional groups on EMB surface.

Effect of the contact time (a) and pseudo-second-order kinetic isotherms of MB and EMB (b).

In order to analyze the adsorption kinetics of methylene blue on MB and EMB, the pseudo-first-order and pseudo-second-order kinetic models were tested. The pseudo-first-order kinetic model and pseudo-second-order kinetic model were given in the following (Febrianto et al., 2009; Padmavathy, 2008):

(2)

\ln (q_{e} - q_{t}) = - k_{1} t + \ln q_{e}

(3)

\frac{t}{q_{t}} = \frac{1}{k_{2} q_{e}^{2}} + \frac{t}{q_{e}}

where q_e and q_t (mg/g) refer to the adsorption capacity at equilibrium and time t respectively, k₁ is the rate constant of pseudo-first-order equation (1/min), k₁ can be calculated from the slopes of the linear plot of ln(q_e − q_t) versus t. k₂ is the rate constant of pseudo-second-order equation (g/(mg min), and the slopes of the linear plot of t/q_t versus t represent k₂.

As shown in Fig. 3b, the linear plots of t/q_t versus t show good agreement between experimental (q_e_,_exp) and calculated (q_e_,_cal) values (shown in Table 1). The correlation coefficients (R²) for pseudo-second-order kinetics model are higher than that for pseudo-first-order kinetics model, indicating the better applicability of pseudo-second-order kinetics model. The results indicated that a chemisorption process was involved in this adsorption process in addition to physisorption. Additionally, the chemisorption process might be the rate-determining step where valency forces were involved because of electron sharing or exchange between the functional groups on adsorbents and methylene blue (Dogan et al., 2009).

Table 1 Pseudo-first- and pseudo-second-order constants for methylene blue adsorption by MB and EMB.

Adsorbents	q_e_,_exp	Pseudo-first-order kinetic model			Pseudo-second-order kinetic model
Adsorbents	(mg/g)	k₁ (min⁻¹)	R²	q_e_,_cal (mg/g)	k₂ (g/mg/min)	R²	q_e_,_cal (mg/g)
MB	100.48	0.03933	0. 9508	40.6	0.0016	0.9905	92.15
EMB	206.99	0.0377	0.9034	55.48	0.002562	0.9997	198.66

3.4

3.4 Effect of initial methylene blue concentration and adsorption isotherm

The initial concentration provides an important driving force to overcome all mass transfer resistance of all molecules between the aqueous and solid phases. Fig. 4a shows the effects of different initial dye concentrations on the amount of methylene blue adsorbed by MB and EMB. As shown, the removal of dye by adsorption on MB and EMB was found to be rapid at the initial period of methylene blue concentration and then to slow down with the increasing initial dye concentration. This phenomenon should be caused by the attractive forces between the dye molecule and the adsorbent such as van der Waals forces and electrostatic attraction. Afterward, fast diffusion onto the external surface was followed and the chemisorption of dye continued until reaching the equilibrium. The increase in loading capacity of the adsorbent for dye ions is probably due to a higher driving force for mass transfer. Then, a slower adsorption rate would occur as the surface adsorption sites gradually decrease (Abramian and El-Rassy, 2009).

Effect of the initial methylene blue concentration (a), Langmuir isotherm for adsorption of methylene blue on MB and EMB (b) and RL curves for methylene blue on MB and EMB (c).

The equilibrium data were modeled with Langmuir and Freundlich isotherms (Abramian and El-Rassy, 2009; Febrianto et al., 2009). The Langmuir isotherm is derived on the assumption of monolayer adsorption on a homogenous surface. A linear form of the Langmuir model is expressed by:

(4)

\frac{C_{e}}{q_{e}} = \frac{C_{e}}{q_{m}} + \frac{1}{{bq}_{m}}

The Freundlich isotherm is appropriate for the description of multilayer adsorption with interaction between adsorbed molecules. A linear form of Freundlich equation is given as:

(5)

\ln q_{e} = \frac{1}{n} \ln C_{e} + \ln K_{F}

where q_e and q_m are the equilibrium and maximum uptake capacities (mg/g), respectively. C_e is the equilibrium methylene blue concentration (mg/L), and b is the equilibrium constant. K_F (L/mg) is the Freundlich adsorption constant and 1/n is the heterogeneity factor.

As shown in Table 2, the greater R² values show the Langmuir isotherm fitted better to the adsorption data, which reveals that the adsorption process was based on monolayer adsorption and was mostly on the surface-active areas sites of MB and EMB. The linear plots of Langmuir isotherm for the adsorption of dye are shown in Fig. 4b.

Table 2 Results of isotherm models for methylene blue adsorption (biomass dose: 1 g/L; contact time: 60 min; pH: 8.0).

Adsorbents	Langmuir constant				Freundlich constant
Adsorbents	q_m (mg/g)	b (L/mg)	R²	R_L	1/n	k_F	R²
MB	107.99	0.03917	0.9967	0.05999	0.3034	19.63	0.8284
EMB	216.45	0.2485	0.997	0.009959	0.2391	71.73	0.7385

In order to find out whether adsorption is “favorable’’ or ‘‘unfavorable”, a dimensionless constant separation factor or equilibrium parameter, R_L was calculated using equation (Rao et al., 2007; Tian et al., 2010):

(6)

R_{L} = \frac{1}{1 + {bC}_{0}}

where C₀ is the initial methylene blue concentration (mg/L), and the value of R_L indicates the type of isotherm to be irreversible (R_L = 0), favorable (0 < R_L < 1), linear (R_L = 1) or unfavorable (R_L > 1).

As seen in Fig. 4c, 0 < R_L < 0.34 for two adsorbents at optimal condition reveals that the adsorption experiments of methylene blue for both MB and EMB are favorable. Moreover, R_L value decreases with increasing initial concentration (C₀), indicating that higher C₀ is conducive to adsorption reaction.

3.5

3.5 Specific surface area

It has been assumed that methylene blue forms a monolayer of adsorbed molecules on the surface of sorbent particles. From the maximum adsorption capacity values (Table 2), it is possible to determine the specific surface area of MB and EMB biomass according to the following expression (Vilar et al., 2007; Yukselen and Kaya, 2008):

(7)

S = \frac{q_{m} {NA}_{m}}{M}

where S is the specific surface area (m²/g), q_m the mass of adsorbed methylene blue in the monolayer (g/g), A_m the area occupied by one methylene blue molecule (m² per molecule), N the Avogadro’s number (6.02 × 10²³ molecule per mol) and M is the methylene blue molar mass (373.89 g/mol).

Methylene blue has a parallelepiped shape with approximately 1.7 nm × 0.76 nm × 0.33 nm. The adsorbent area covered by one methylene blue molecule probably changes as attachment can mainly be done with three orientations. Thus the surface covered area can be 1.30 × 10⁻¹⁸ m² per molecule, 6.6 × 10⁻¹⁹ m² per molecule and 2.47 m² × 10⁻¹⁹ m² per molecule. The uncertainty in the assumption of the covered area can significantly affect the estimation of specific surface area. The specific surface area range was evaluated and the results are listed in Table 3.

Table 3 Specific surface area calculated by methylene blue for two different adsorbents.

Adsorbents	Specific surface area (m²/g)
Adsorbents	S₁	S₂	S₃
MB	42.953	114.77	226.07
EMB	94.972	253.77	499.85

It is observed that the specific surface area for EMB in different orientations is 2 times higher than that of MB. This demonstrates that specific surface area of adsorbent plays the key role in affecting the adsorption capacity.

3.6

3.6 Effect of temperature and thermodynamic studies

Effect of temperature on the equilibrium adsorption capacity for methylene blue has been investigated in the range of 5–40 °C. As shown in Fig. 5, the adsorption capacities were basically unchanged with increasing temperature. This phenomenon should be caused by the following reasons. Although increase in the mobility of methylene blue molecules with temperature increasing could increase the adsorption capacity (Abramian and El-Rassy, 2009), a stronger escaping ability of dye molecules with a rise in temperature yet could lead to the decreased adsorption capacity. The amount of the non-protonated functional groups on the MB and EMB surface increased due to the increase in the dissociation constant of protonated carboxyl and amino groups with the rise of temperature while increasing the temperature swelled the internal structure of the yeast and enabled the dye ions to penetrate further. More importantly, as the hydrolysis degree of the ester bond between EDTAD and the baker’s yeast increased with the increase of reaction temperature, some EDTAD molecules could be released from the surface of biomass via hydrolysis. Based the interaction of these above factors, the adsorption capacity of methylene blue was basically constant with the rise of temperature in the adsorption process.

To determine whether the process is spontaneous, both energy and entropy factors were considered. The thermodynamic parameters were calculated by the following equation (Li et al., 2013):

(8)

Δ G ° = H ° - T Δ S °

(9)

\ln K_{C} = \frac{Δ S °}{R} - \frac{Δ H °}{RT}

(10)

Δ G ° = - RT \ln K_{C}

where b is the adsorption equilibrium constant. ΔS°, ΔH° and ΔG° are the changes of entropy (J/(K mol)), enthalpy (kJ/mol) and Gibbs energy (kJ/mol). T (K) is the temperature and R (J/(K mol)) is the idea gas constant. K_C (L/g) is the equilibrium constant which can be evaluated by the product of b (Langmuir equilibrium constant) and q_m (the maximum adsorption capacity at corresponding temperature). Thermodynamic parameters are shown in Table 4.

Table 4 Thermodynamic parameters for the adsorption of methylene blue by MB and EMB (initial concentration, 300 mg/L; volume, 100 mL; absorbent dose, 100 mg; contact time, 60 min; temperature, 5, 10, 20, 30, 40 °C; pH value, 8.0).

Absorbents	ΔH° (kJ/mol)	ΔS° (J/(K mol))	ΔG° (kJ/mol)
			5 °C	10 °C	20 °C	30 °C	40 °C
MB	0.8359	0.1204	−3.176	−3.223	−3.150	−3.411	−3.456
EMB	1.359	0.5494	−9.259	−9.270	−9.862	−10.14	−10.52

The negative values of ΔG° for two materials at different temperatures show that the adsorption process was spontaneous in nature. The negative ΔH° value for MB reveals the adsorption is exothermic. However, the positive ΔH° value for EMB suggests the adsorption is endothermic. This means chemisorption occurred between EMB and methylene blue. Moreover, the positive ΔS° value for both adsorbents shows an increased randomness in aqueous solution during the adsorption process as well as suggests that a better affinity of methylene blue toward EMB compared with MB.

3.7

3.7 Regeneration studies

The adsorption/desorption cycles of the methylene blue solutions (300 mg/L) were repeated three times with different eluants (0.1 mol/L HCl and absolute ethanol). The results are given in Table 5. It was found that the regeneration and recovery efficiency for two absorbents followed a decreasing order: HCl > absolute ethanol. The reasons for the decrease in regeneration efficiency were due to irreversible adsorption and the loss of methylene blue in the process of reuse. Meanwhile, ionized H⁺ ions from HCl solution would competitively occupy the adsorption sites on MB or EMB surface thereby releasing dye ions. As can be seen in Table 5, HCl (0.1 moL/L) solution was preferable for desorption of methylene blue on EMB. Both the HCl (0.1 moL/L) and absolute ethanol were feasible for MB. More importantly, new more functional groups were produced on EMB surface due to EDTAD decoration, and their uptake capacities for methylene blue were obviously fluctuant with the concentration of H⁺ ions in outer environment. Hence, compared with absolute ethanol, HCl solution was confirmed as the optimal eluant for EMB.

Table 5 Results of adsorption and desorption (methylene blue concentration: 300 mg/L; biomass doses: 1 g/L; contact time: 60 min; reaction temperature: 25 ± 1 °C; different eluants: 0.1 mol/L HCl and absolute C₂H₅OH).

Adsorbents	A/D cycle number	HCl		C₂H₅OH
Adsorbents	A/D cycle number	Dye adsorption capacity (mg/g)	Dye desorption efficiency (%)	Dye adsorption capacity (mg/g)	Dye desorption efficiency (%)
	1	100.48	91.03	100.53	88.42
MB	2	90.55	87.33	88.32	84.73
	3	82.11	84.21	82.25	81.31

	1	207	92.64	206.72	82.13
EMB	2	188.56	87.55	136.92	70.31
	3	172.33	81.31	85.2	50.15

3.8

3.8 Magnetic response analysis

The magnetic response characteristic of EMB is one of the most important characteristics for solid–liquid phase separation. Fig. 6 shows the magnetic response of EMB in methylene blue solution toward the applied magnetic field at the beginning (left) and after adsorption (right) respectively. The EMB gathered on the right side of ground-glass wall as well as the color of methylene blue obviously turned lighter (decreased from 300 mg/L to 76.44 mg/L) after adsorption. The magnetic response of EMB at 2.0 cm distance suggested that EMB still had a favorable magnetism at a relatively far distance. These phenomena reveal that the EMB prepared not only possessed ease of phase separation characteristic, but also had a preferable removal for methylene blue. This special advantage made efficient recovery and easy reuse possible. It would be predictable that the adsorbent material cost would be reduced and the problems about secondary pollution would be solved better then.

The magnetic response of EMB and adsorption efficiency.

3.9

3.9 SEM analysis

The nano-Fe₃O₄, baker’s yeast and EMB were analyzed by scanning electron microscopy (SEM) to study the surface structures and the results are given in Fig. 7. Fig. 7(a) shows that the sizes of these Fe₃O₄ particles were uniform, regular and fine. The average particle diameter was about 200 nm. As shown in Fig. 7(b), the baker’s yeast cells were oval and individual and their surfaces were smooth and even. The average length and width of the cells were about 6 μm and 4 μm, respectively. Fig. 7(c) displays that the surface of EMB was rather rough and some of biomasses were clung together. Because of the nano-Fe₃O₄ adhered on the baker’s yeast surface, as well as the esterification reaction between EDTAD and hydroxyl groups on the cell wall, therefore the baker’s yeast surface structure has changed. Moreover, the low temperature and high vacuum resulted in the production of pore channel on the baker’s yeast, and thus improving the permeability of EMB via sublimation and dehydration of baker’s yeast, which is beneficial for the adsorption and recovery.

SEM micrographs of nano-Fe3O4 (a), baker’s yeast (b) and EMB (c).

3.10

3.10 FTIR analysis

The spectra of MB, EMB and EMB adsorbed methylene blue are shown in Fig. 8a–c. The absorbance peaks at 3410 cm⁻¹, 1572 cm⁻¹, 1442 cm⁻¹, and 1140 cm⁻¹ were observed in the MB spectrum shown in Fig. 8a. The peak at 3410 cm⁻¹ attributed to —NH/—OH overlapped stretching vibration absorbance, while the peak at 2928 cm⁻¹ came from the symmetrical stretching C—H of —CH₂ band. The band at 1572 cm⁻¹ and 1442 cm⁻¹ belonged to the stretching band of C⚌O, C—N from the amide II and the symmetrical stretching band of carboxyl (—COOH), respectively. The strong peaks at 1140 cm⁻¹ and 854 cm⁻¹ indicated the bending band of N—H and C—N from the amide III band functional group (Burattini et al., 2008; Mahmoud et al., 2009).

FTIR spectra for MB (a), methylene blue (b) and EMB before (c) and after adsorption (d).

Compared with MB, several changes of EMB spectrum occurred. Firstly, the stretching band of —NH/—OH shifted from 3410 cm⁻¹ to 3444 cm⁻¹. Secondly, for EMB, not only did the increase in the adsorption intensity of carboxyl (—COOH) enhance, but the symmetrical stretching band of carboxyl (—COOH) moved from 1442 cm⁻¹ to 1433 cm⁻¹. This indicates that more —COOH groups were produced on EMB because of the introduction of EDTAD. All of these phenomena demonstrated that the EDTAD was successfully introduced to the MB surface via esterification reaction resulting in releasing of more carboxyl and amino groups. Finally, the adsorption peaks at around 540 cm⁻¹ on MB and EMB represented the characteristic stretching band of Fe—O from nano-Fe₃O₄ which suggested the existence of nano-Fe₃O₄ on the surface of two materials.

Fig. 8c shows the spectrum of EMB after adsorption, the peaks at 3444 cm⁻¹ (Fig. 8b) with respect to —NH/—OH absorbance disappeared. This means that —NH/—OH participated in the adsorption processes of methylene blue. Moreover, the absorbance at 1140 cm⁻¹ disappeared as well as the strength of adsorption peaks at 1579 cm⁻¹ and 1433 cm⁻¹ decreased obviously. These phenomena showed that C⚌O (—COOH) and N—H (—NH₂) participated in the adsorption of methylene blue. A new peak appeared at 1360 cm⁻¹ came from the strengthening of C—H asymmetric vibration peaks of —CH₃. This may be attributed to adsorption of methylene on EMB.

4 Conclusions

In this study, the EMB was prepared. It was found that the adsorption capacity of EMB was higher with pH range 4.0–8.0, compared with MB. The kinetic and equilibrium were well explained by the Langmuir isotherm and the pseudo-second-order kinetic, respectively. The result not only revealed that monolayer adsorption may exist in the adsorption process, but also indicated that the rate limiting step may be chemisorption. Higher specific surface area of EMB (94.972–499.85 m²/g) indicated the excellent adsorption capacity. Thermodynamic studies demonstrated that the adsorption of methylene blue onto EMB was spontaneous and endothermic. Regeneration studies confirmed HCl solution is the optimal eluant.

Acknowledgments

This research was supported by the Key Basic Research Program of the Sichuan Provincial Education Commission, PR China (Grant No. 10ZB034) and the Basic Research Program of the Science & Technology Department of Sichuan Province, PR China (Grant No. 2011ZR0067).

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Show Sections

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[Google Scholar]

[4] Cherifi H., Fatiha B., Salah H., . Kinetic studies on the adsorption of methylene blue onto vegetal fiber activated carbons. Appl. Surf. Sci.. 2013;282:52-59.
[Google Scholar]

[5] Deng H., Lu J., Li G., Zhang G., Wang X., . Adsorption of methylene blue on adsorbent materials produced from cotton stalk. Chem. Eng. J.. 2011;172(1):326-334.
[Google Scholar]

[6] Dogan M., Abak H., Alkan M., . Adsorption of methylene blue onto hazelnut shell: kinetics, mechanism and activation parameters. J. Hazard. Mater.. 2009;164(1):172-181.
[Google Scholar]

[7] Ebrahimian Pirbazari A., Saberikhah E., Habibzadeh Kozani S.S., . Fe₃O₄–wheat straw: preparation, characterization and its application for methylene blue adsorption. Water Resour. Ind.. 2014;7–8:23-37.
[Google Scholar]

[8] Fan W., Gao W., Zhang C., Tjiu W.W., Pan J., Liu T., . Hybridization of graphene sheets and carbon-coated Fe₃O₄ nanoparticles as a synergistic adsorbent of organic dyes. J. Mater. Chem.. 2012;22(48):25108.
[Google Scholar]

[9] Farah J.Y., El-Gendy N., Farahat L.A., . Biosorption of Astrazone Blue basic dye from an aqueous solution using dried biomass of Baker’s yeast. J. Hazard. Mater.. 2007;148(1–2):402-408.
[Google Scholar]

[10] Febrianto J., Kosasih A.N., Sunarso J., Ju Y.H., Indraswati N., Ismadji S., . Equilibrium and kinetic studies in adsorption of heavy metals using biosorbent: a summary of recent studies. J. Hazard. Mater.. 2009;162(2–3):616-645.
[Google Scholar]

[11] Geng Z., Lin Y., Yu X., Shen Q., Ma L., Li Z., . Highly efficient dye adsorption and removal: a functional hybrid of reduced graphene oxide–Fe₃O₄ nanoparticles as an easily regenerative adsorbent. J. Mater. Chem.. 2012;22(8):3527.
[Google Scholar]

[12] Hameed B.H., Din A.T., Ahmad A.L., . Adsorption of methylene blue onto bamboo-based activated carbon: kinetics and equilibrium studies. J. Hazard. Mater.. 2007;141(3):819-825.
[Google Scholar]

[13] Kołodyńska D., Hubicka H., Hubicki Z., . Sorption of heavy metal ions from aqueous solutions in the presence of EDTA on monodisperse anion exchangers. Desalination. 2008;227(1–3):150-166.
[Google Scholar]

[14] Li T.-T., Liu Y.-G., Peng Q.-Q., Hu X.-J., Liao T., Wang H., . Removal of lead(II) from aqueous solution with ethylenediamine-modified yeast biomass coated with magnetic chitosan microparticles: kinetic and equilibrium modeling. Chem. Eng. J.. 2013;214:189-197.
[Google Scholar]

[15] Liu Q.-S., Zheng T., Li N., Wang P., Abulikemu G., . Modification of bamboo-based activated carbon using microwave radiation and its effects on the adsorption of methylene blue. Appl. Surf. Sci.. 2010;256(10):3309-3315.
[Google Scholar]

[16] Mahmoud M.E., Yakout A.A., Osman M.M., . Dowex anion exchanger-loaded-baker’s yeast as bi-functionalized biosorbents for selective extraction of anionic and cationic mercury(II) species. J. Hazard. Mater.. 2009;164(2–3):1036-1044.
[Google Scholar]

[17] Padmavathy V., . Biosorption of nickel(II) ions by baker’s yeast: kinetic, thermodynamic and desorption studies. Bioresour. Technol.. 2008;99(8):3100-3109.
[Google Scholar]

[18] Pratibha R., Malar P., Rajapriya T., Balapoornima S., Ponnusami V., . Statistical and equilibrium studies on enhancing biosorption capacity of Saccharomyces cerevisiae through acid treatment. Desalination. 2010;264(1–2):102-107.
[Google Scholar]

[19] Rafatullah M., Sulaiman O., Hashim R., Ahmad A., . Adsorption of methylene blue on low-cost adsorbents: a review. J. Hazard. Mater.. 2010;177(1–3):70-80.
[Google Scholar]

[20] Rao G., Lu C., Su F., . Sorption of divalent metal ions from aqueous solution by carbon nanotubes: a review. Sep. Purif. Technol.. 2007;58(1):224-231.
[Google Scholar]

[21] Repo E., Warchol J.K., Bhatnagar A., Sillanpaa M., . Heavy metals adsorption by novel EDTA-modified chitosan-silica hybrid materials. J. Colloid Interface Sci.. 2011;358(1):261-267.
[Google Scholar]

[22] Sajab M.S., Chia C.H., Zakaria S., Jani S.M., Ayob M.K., Chee K.L., . Citric acid modified kenaf core fibres for removal of methylene blue from aqueous solution. Bioresour. Technol.. 2011;102(15):7237-7243.
[Google Scholar]

[23] Shen C., Shen Y., Wen Y., Wang H., Liu W., . Fast and highly efficient removal of dyes under alkaline conditions using magnetic chitosan-Fe(III) hydrogel. Water Res.. 2011;45(16):5200-5210.
[Google Scholar]

[24] Tian Y., Ji C., Zhao M., Xu M., Zhang Y., Wang R., . Preparation and characterization of baker’s yeast modified by nano-Fe₃O₄: application of biosorption of methyl violet in aqueous solution. Chem. Eng. J.. 2010;165(2):474-481.
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[25] Vilar V.J., Botelho C.M., Boaventura R.A., . Methylene blue adsorption by algal biomass based materials: biosorbents characterization and process behaviour. J. Hazard. Mater.. 2007;147(1–2):120-132.
[Google Scholar]

[26] Wang L., Pan X., Wang F., Yang L., Liu L., . Structure–properties relationships investigation on the azo dyes derived from benzene sulfonamide intermediates. Dyes Pigments. 2008;76(3):636-645.
[Google Scholar]

[27] Yan H., Zhang W., Kan X., Dong L., Jiang Z., Li H., . Sorption of methylene blue by carboxymethyl cellulose and reuse process in a secondary sorption. Colloids Surf. A: Physicochem. Eng. Aspects. 2011;380(1–3):143-151.
[Google Scholar]

[28] Yao Y., Miao S., Liu S., Ma L.P., Sun H., Wang S., . Synthesis, characterization, and adsorption properties of magnetic Fe₃O₄@graphene nanocomposite. Chem. Eng. J.. 2012;184:326-332.
[Google Scholar]

[29] Yao Y., Miao S., Yu S., Ma L.P., Sun H., Wang S., . Fabrication of Fe₃O₄/SiO₂ core/shell nanoparticles attached to graphene oxide and its use as an adsorbent. J. Colloid Interface Sci.. 2012;379(1):20-26.
[Google Scholar]

[30] Yu J.-X., Li B.-H., Sun X.-M., Jun Y., Chi R.-A., . Adsorption of methylene blue and rhodamine B on baker’s yeast and photocatalytic regeneration of the biosorbent. Biochem. Eng. J.. 2009;45(2):145-151.
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[31] Yu J.X., Li B.H., Sun X.M., Yuan J., Chi R.A., . Polymer modified biomass of baker’s yeast for enhancement adsorption of methylene blue, rhodamine B and basic magenta. J. Hazard. Mater.. 2009;168(2–3):1147-1154.
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[32] Yukselen Y., Kaya A., . Suitability of the methylene blue test for surface area, cation exchange capacity and swell potential determination of clayey soils. Eng. Geol.. 2008;102(1–2):38-45.
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[33] Shan Z., Zhang W.S.Y.X., Huang Q.M., Ye H., . Preparation and characterization of carboxyl-group functionalized superparamagnetic nanoparticles and the potential for bio-applications. Braz. Chem. Soc.. 2007;18(7):1329-1335.
[Google Scholar]

Comparative adsorption of methylene blue by magnetic baker’s yeast and EDTAD-modified magnetic baker’s yeast: Equilibrium and kinetic study

Abstract

Abstract

Abstract

Keywords

Baker’s yeast

EDTAD

Nano-Fe3O4

Methylene blue

Kinetic

Equilibrium isotherm

1 Introduction

2 Materials and methods

2.1 Materials and reagents

2.2 Synthesis of EMB

2.2.1 Synthesis of MB

2.3 Synthesis of EMB

2.4 Adsorption studies

2.5 Characterization

3 Results and discussion

3.1 The experimental procedure

3.2 Effect of pH on adsorption

3.3 Effect of contact time and kinetics analysis

3.4 Effect of initial methylene blue concentration and adsorption isotherm

3.5 Specific surface area

3.6 Effect of temperature and thermodynamic studies

3.7 Regeneration studies

3.8 Magnetic response analysis

3.9 SEM analysis

3.10 FTIR analysis

4 Conclusions

Acknowledgments

References

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