The ability of Sargassum hemiphyllum to remove methylene blue (MB) from aqueous solution was evaluated. Batch experiments were conducted to examine the effects of parameters such as initial pH, contact time, biomass dose and initial dye concentration on adsorption capacity. S. hemiphyllum before and after MB adsorption was characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The Langmuir isotherm model provided the best correlation with experimental data, and the monolayer biosorption capacity was 729.93 mg·g−1 within 120 min using 0.5 g·L−1 algal biomass and pH of 5. The pseudo-second-order kinetic model accurately described the adsorption kinetics data. Thermodynamic parameters (ΔG0, ΔH0 and ΔS0) at temperature ranges of 293–313 K demonstrated that biosorption is an endothermic and spontaneous reaction. FT-IR analysis showed that the hydroxyl, amine and carboxyl functional groups on the surface of the algae were the most important functional groups for biosorption of MB. XPS analysis indicated that the algal biomass combined with MB molecules through –NH2 groups. These results suggest that S. hemiphyllum is a favorable biosorbent for removing MB dye from wastewater.

INTRODUCTION

More than 0.7 million tons of synthetic dyes are used for textiles, plastics, rubber and packaging worldwide every year (Chen et al. 2003). Dye wastewater contains large amounts of organic pollutants that increase the chemical oxygen demand of the water. The dye effluents discharged into the environment are highly detrimental, which can irritate the skin and even result in carcinogenicity (Gupta & Suhas 2009). In addition, dyes also affect the photosynthesis of aquatic organisms, disturbing the ecological balance (Ali 2010). Therefore, dye wastewater treatment has been targeted as one of the significant issues in industrial wastewater treatment. Various traditional technologies exist for the treatment of dye wastewater, including flocculation, oxidation, membrane separation, electrochemistry, ion exchange and ozonation. However, they have some disadvantages, such as high cost, high energy consumption, or difficulty in disposing of the dye wastewater effectively (Kaushik & Malik 2009).

As a potential method for treating dye wastewater, biosorption has previously been investigated (Srinivasan & Viraraghavan 2010). A wide variety of materials, such as plant (Balci & Erkurt 2016), fungi (Abdallah & Taha 2012), chitosan (Wang et al. 2010), algae (Cengiz & Cavas 2008), rice husk (Saroj et al. 2015) and cotton waste (Goel et al. 2015), have been used to remove dyes from wastewater. Among these materials, algae have been proved to be a potential material for the adsorption of dyes because of their ubiquitous occurrence in nature, low cost, and availability. Previous studies have indicated that the green algae Enteromorpha spp. and Spirogyra rhizopus have impressive adsorption capacities for methylene blue (MB) and Acid Red 274, respectively (Özer et al. 2006a; Ncibi et al. 2009). Guler & Sarioglu (2013) also confirmed that raw and pretreated Spirogyra sp. can remove MB effectively. The brown macroalgae Nizamuddina zanardini (Esmaeli et al. 2013) and Laminaria japonica (Wang et al. 2009) have also been found to be potentially proper biosorbents with high removal rates in dye wastewater treatment. This is mainly attributed to functional groups such as hydroxyl, carboxylic and sulfonic groups on the algal cell wall, as well as their high binding affinity for dye (Nemr et al. 2015). The biosorption capacity depends on the species of biomass and sorbate, along with several factors such as pH, contact time and ionic concentration (Guler & Sarioglu 2013). In addition, many studies have shown that nonliving biomass appears to have a greater potential than living biomass because the nonliving biomass sorption is not needed for nutrient supply and is not affected by the toxicity in wastewater treatments (Sheng et al. 2004).

The brown macroalga Sargassum hemiphyllum is widely distributed in the South China Sea; however, only a small part is used for food or as a phycocolloid. Little attention has been paid to its use as a biosorbent. MB, a basic dye, is used for dyeing paper, wool and cotton (Vadivelan & Kumar 2005). In this study, we aimed to test the feasibility of using S. hemiphyllum as a dye adsorbent. The parameters affecting biosorption were investigated, including initial pH, adsorption time, sorbent dosage and initial dye concentration. To gain a better comprehension of the biosorption mechanisms, isotherm, kinetic and thermodynamics studies were conducted. The surface structure and functional groups were characterized based on scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) analyses.

MATERIALS AND METHODS

Biosorption preparation

S. hemiphyllum was obtained from Nan'ao Bay (23° 44′ N, 117° 03′ E) in Shenzhen in March 2014. The untreated algae were washed with deionized water three times to remove impurities and salts, then dried at 333 K for 24 h. The dried algae were smashed and sieved to a particle size of 96–180 μm.

Dye solution

MB was purchased from Guangzhou Chemical Reagent Factory (China). Its molecular formula is C16H18ClN3S·3H2O; its chemical structure is shown in Figure 1. Different concentrations of dye solution were prepared by diluting from a 1,000 mg L−1 stock solution.
Figure 1

Chemical structural formula of MB.

Figure 1

Chemical structural formula of MB.

Biosorption studies

Batch experiments under varied conditions, such as initial pH (2–10), biomass dosage (0.05–2 g·L−1) and initial dye concentration (30–1,000 mg·L−1) were conducted in 100 mL Erlenmeyer flasks containing 50 mL dye solution, while the experiment of contact time (0–180 min) was performed in 1,000 mL Erlenmeyer flasks containing 500 mL dye solution. Erlenmeyer flasks were shaken at 200 rpm in the dark. The experiments were repeated three times for all conditions.

Analytical procedure

Samples were centrifuged at 3,000 rpm for 5 min. The supernatant was analyzed using a UV-spectrophotometer (Shimadzu, UV-1800, Japan) at a wavelength of 664 nm to determine the dye concentration. The removal efficiency (η) was calculated using the initial and residual MB concentration as follows: 
formula
1
The adsorption capacity at equilibrium in S. hemiphyllum was determined using the following equation: 
formula
2
where qe is the equilibrium adsorption capacity of dye (mg·g−1), Co is the dye initial concentration (mg·L−1), Ce is the equilibrium concentration of dye (mg·L−1), m is the biosorbent mass (g), and V is the solution volume (L).

Biosorption isotherms

Isotherm experiments were conducted using 0.5 g·L−1 biomass and 50 mL dye solution with different initial concentrations (30–1,000 mg·L−1) in 100 mL Erlenmeyer flasks at 303 K for 120 min. The initial solution pH was maintained at 5. Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherms were used to fit the experimental data.

The Langmuir model is based on the conception of monolayer sorption onto a surface with limited active sites. The Langmuir isotherm is given by the following equation: 
formula
3
where qo is the monolayer sorption capacity (mg·g−1) and KL is the Langmuir constant related to the binding energy (L·mg−1).
The basic characteristics of the Langmuir isotherm can be described in terms of RL, a dimensionless constant called the equilibrium parameter. RL is expressed as follows: 
formula
4
The value of RL indicates the type of the isotherm: RL = 0, adsorption is irreversible; 0<RL<1, adsorption is favorable; RL = 1, adsorption is linear, RL>1, adsorption is unfavorable.
The Freundlich model is an empirical model used to describe the multilayer adsorption. The linear form of the Freundlich model is expressed in Equation (5): 
formula
5
where n is the biosorption intensity, between 1 and 10, indicating that biosorption was favorable under selected experimental conditions, and KF is the Freundlich constant related to the sorption capacity (mg1-(1/n)·L1/n·g−1).
The nature of the sorption process was also analyzed by the D-R isotherm to estimate the adsorption characteristics. The D-R isotherm model is expressed as follows: 
formula
6
where qe is amount of adsorbing dye per gram of adsorbent at equilibrium (mg·g−1), qm is the maximum adsorption capacity at equilibrium (mg·g−1), β is the D-R isotherm constant related to the sorption energy (mol2·kJ−2), and ɛ is the Polanyi potential described as follows: 
formula
7
where R is the ideal gas constant (8.314 J·mol−1·K−1) and T is the temperature (K).
The free energy of biosorption was obtained from the following equation: 
formula
8

The E (kJ·mol−1) value can be used to determine the biosorption mechanism for a physical or a chemical reaction. If it falls in the range of 8–16 kJ·mol−1, the biosorption process is a chemical reaction, while if E < 8 kJ·mol−1, a physical reaction takes place in the biosorption process.

Biosorption kinetics

The biosorption mechanism and potential rate-controlling steps were investigated using pseudo-first-order, pseudo-second-order and intraparticle diffusion models. The kinetics study was carried out in 1,000 mL Erlenmeyer flasks containing 0.5 g·L−1 biosorbent and 500 mL dye solutions at pH 5 for different times (0–180 min). Samples were removed at each predetermined time to determine the liquid residue solution concentration (Ce) and to calculate the dye sorption capacity (qe) at different adsorption times. The pseudo-first-order kinetic model is given by: 
formula
9
where qe is the adsorption capacity in equilibrium (mg·g−1), qt is the adsorption capacity at time t (mg·g−1), k1 is the equilibrium rate constant of the pseudo-first-order model (min−1), and t is the adsorption time (min).
The pseudo-second-order kinetic model is expressed by the following equation: 
formula
10
where k2 is the equilibrium rate constant of the pseudo-second-order model (g mg−1·min−1).
The rate of adsorption was used to elucidate the rate-controlling step. The intraparticle diffusion model has been greatly explored in this regard. The intraparticle diffusion model equation can be calculated from the following equation: 
formula
11
where ki is the rate constant of intraparticle diffusion (mg·g−1·min−1/2) and C is the intercept. If the intraparticle diffusion model can be plotted linearly and passes through the origin, the biosorption process is controlled only by intraparticle diffusion.

Biosorption thermodynamics

Biosorption of MB onto S. hemiphyllum was conducted at different temperatures (293 K, 303 K, and 313 K) under optimized conditions. The biosorption equilibrium constant of the Gibbs free energy was represented by the following equation: 
formula
12
where T is the thermodynamic temperature (K) and Kd is the equilibrium adsorption distribution constant. ΔG0 is related to the heat of biosorption and entropy change at constant temperature and is calculated as follows: 
formula
13
The changes in the standard entropy (ΔS0) and enthalpy (ΔH0) can be related to the equilibrium adsorption-distribution constant using the following equation: 
formula
14

Analysis of SEM, FT-IR and XPS

The surface morphology of the algal biomass was obtained from SEM (Jeol, JSM-7001F, Japan) under vacuum after a thin layer of gold was covered on the samples using a sputter coater. The FT-IR spectra were obtained using a FT-IR (Bruker, Tensor 27, Germany) in the range of 4,000–400 cm−1. The surface functionalization was analyzed by XPS (Thermo-VG Scientific, ESCALAB 250, USA). The binding energies were calibrated to the major C 1 s peak at 284.6 eV.

RESULTS AND DISCUSSION

Effect of pH

The initial solution pH played a key role in algal biosorption. Figure 2 shows the effect of the initial pH on the biosorption of MB in S. hemiphyllum. The adsorption capacity increased from 116.89 mg·g−1 to 187.04 mg·g−1 as the solution pH rose from 2 to 4 and remained constant over pH ranges of 4–10. Similar behavior had been reported by Ulothrix sp. (Doğar et al. 2010) and Enteromorpha spp. (Ncibi et al. 2009) for the biosorption of MB. Algal walls are mainly constituted of proteins, alginate, and fucan, which contain different functional groups, such as carboxyl, sulfate and amine (Nemr et al. 2015). At lower pH, the algal surface charge may become positively charged, causing hydrogen ions to compete with dye cations, resulting in a decrease in dye adsorption. At a higher pH, the algal polymeric composition may become negatively charged, which increases the biosorption capacity through electrostatic attractions (Ncibi et al. 2009). However, the active sorption sites were limited, therefore the sorption capacity was not continuously elevated as the pH became higher.
Figure 2

Effect of initial pH on adsorption capacity of S. hemiphyllum for MB. t = 120 min; biomass dosage = 0.5 g·L−1; dye concentration = 100 mg·L−1; T = 303 K.

Figure 2

Effect of initial pH on adsorption capacity of S. hemiphyllum for MB. t = 120 min; biomass dosage = 0.5 g·L−1; dye concentration = 100 mg·L−1; T = 303 K.

Effect of contact time

The effect of contact time on MB biosorption was investigated at different times (0–180 min). As shown in Figure 3, adsorption capacity increased rapidly within the first 5 min; thereafter, it slowly rose and attained a constant value. The adsorption capacity was 188.45 mg·g−1 at 90 min. A large number of available free surface sites was certainly responsible for the initial high sorption rate at the beginning, while the subsequent deceleration was observed when the available sites became saturated (Esmaeli et al. 2013).
Figure 3

Effect of contact time on adsorption capacity of S. hemiphyllum for MB. pH = 5; biomass dosage = 0.5 g·L−1; dye concentration = 100 mg·L−1; T = 303 K.

Figure 3

Effect of contact time on adsorption capacity of S. hemiphyllum for MB. pH = 5; biomass dosage = 0.5 g·L−1; dye concentration = 100 mg·L−1; T = 303 K.

Effect of biomass dosage

The effects of biosorbent dosage on adsorption capacity and removal efficiency are presented in Figure 4. The removal efficiency increased as the biosorbent dosage increased, while the adsorption capacity was gradually reduced. Similar behavior had been observed in Posidonia oceanica fibers for MB adsorption (Ncibi et al. 2007). The elevated removal efficiency can be attributed to the increased available adsorption sites with the elevated biosorbent dosage. The adsorption capacity of the adsorbent was lower, because adsorption sites remained unsaturated, and less commensurate increase in adsorption quality occurred as the adsorbent in adsorption was increased (Manohar et al. 2002).
Figure 4

Effect of biomass dosage on adsorption capacity and removal efficiency of S. hemiphyllum for MB. pH = 5; t = 120 min; dye concentration = 100 mg·L−1; T = 303 K.

Figure 4

Effect of biomass dosage on adsorption capacity and removal efficiency of S. hemiphyllum for MB. pH = 5; t = 120 min; dye concentration = 100 mg·L−1; T = 303 K.

Effect of initial dye concentration

The influence of initial MB concentration on biosorption by the nonliving biomass of S. hemiphyllum is presented in Figure 5. The adsorption capacity rapidly increased from 58.18 to 657.59 mg·g−1 as the dye concentration increased from 30 to 400 mg·L−1 and then remained constant. Similar results had been reported for the adsorption of Acid Blue 290 and Acid Blue 324 by Spirogyra rhizopus (Özer et al. 2006b). The results may be attributed to increase in the driving force and the collisions between sorbents and sorbates at lower initial dye concentrations (30–400 mg·L−1) (Esmaeli et al. 2013), and then no further increase in adsorption capacity implied that the available sites on the biosorbent are limited in higher initial dye concentrations (Özer et al. 2006b).
Figure 5

Effect of initial dye concentration on adsorption capacity of S. hemiphyllum for MB. pH = 5; t = 120 min; biomass dosage = 0.5 g·L−1; T = 303 K.

Figure 5

Effect of initial dye concentration on adsorption capacity of S. hemiphyllum for MB. pH = 5; t = 120 min; biomass dosage = 0.5 g·L−1; T = 303 K.

Biosorption isotherms

Langmuir, Freundlich and D-R models were used to explain the experimental data. The determination coefficients and the adsorption parameters are shown in Table 1. The experimental data were well represented by the Langmuir isotherm with high correlation coefficient (R2 = 0.99), suggesting the monolayer biosorption process could exist under the experimental condition. The monolayer biosorption capacity was 729.93 mg·g−1 according to the Langmuir model, which was compared with other materials and summarized in Table 2. From Table 2, S. hemiphyllum exhibited higher adsorption capacities than other materials. The value of the Langmuir separation factor RL was between 0 and 1, and the adsorption intensity (n) was between 1 and 10, which indicated the adsorption was favorable under the selected experimental conditions (Ncibi et al. 2009; Sivasamy et al. 2012). The D-R model did not fit the experimental data well, suggesting the involvement of dye sorption mechanisms other than the van der Waals force (Basha et al. 2008). The E value was 0.86 kJ·mol−1 (<8 kJ·mol−1), indicating that the biosorption of MB onto S. hemiphyllum mainly proceeds by physical sorption (Esmaeli et al. 2013).

Table 1

Comparison of the isotherm models adsorption constants for MB

ModelParametersValue
Langmuir qo (mg·g−1729.93 
KL (L·mg−10.07 
R2 0.99 
RL 0.014 
Freundlich KF (mg1-(1/n)·L1/n·g−184.15 
2.65 
R2 0.90 
Dubinin-Radushkevich qm (mg·g−1459.95 
E (kJ·mol−10.86 
R2 0.63 
ModelParametersValue
Langmuir qo (mg·g−1729.93 
KL (L·mg−10.07 
R2 0.99 
RL 0.014 
Freundlich KF (mg1-(1/n)·L1/n·g−184.15 
2.65 
R2 0.90 
Dubinin-Radushkevich qm (mg·g−1459.95 
E (kJ·mol−10.86 
R2 0.63 

pH = 5; t = 120 min; biomass dosage = 0.5 g·L−1; T = 303 K.

Table 2

Comparison of the monolayer adsorption capacities of various materials for MB

Adsorbentqo (mg g−1)References
Wheat shells 21.50 Bulut & Aydın (2006)  
Aspergillus fumigatus 125.00 Abdallah & Taha (2012)  
Cellulose sludge 100.00 Orlandi et al. (2017)  
Montmorillonite clay 300.30 Almeida et al. (2009)  
Caulerpa lentillifera 417.00 Marungrueng & Pavasant (2007)  
Activated carbon 238.00 Marungrueng & Pavasant (2007)  
Rice husk 40.59 Vadivelan & Kumar (2005)  
Spirogyra sp. 50.70 Guler & Sarioglu (2013)  
Enteromorpha spp. 273.73 Ncibi et al. (2009)  
S. hemiphyllum 729.93 This study 
Adsorbentqo (mg g−1)References
Wheat shells 21.50 Bulut & Aydın (2006)  
Aspergillus fumigatus 125.00 Abdallah & Taha (2012)  
Cellulose sludge 100.00 Orlandi et al. (2017)  
Montmorillonite clay 300.30 Almeida et al. (2009)  
Caulerpa lentillifera 417.00 Marungrueng & Pavasant (2007)  
Activated carbon 238.00 Marungrueng & Pavasant (2007)  
Rice husk 40.59 Vadivelan & Kumar (2005)  
Spirogyra sp. 50.70 Guler & Sarioglu (2013)  
Enteromorpha spp. 273.73 Ncibi et al. (2009)  
S. hemiphyllum 729.93 This study 

Kinetic study

The adsorption kinetics of biosorption are available to explain the biosorption process. In order to describe the kinetics of the reactions, three kinetic models were used to fit the experimental data. The parameters and determination coefficients of the adsorption kinetics are listed in Table 3. The values of R2 for the pseudo-first-order (0.97) and pseudo-second-order (0.99) kinetic models were high. The calculated adsorption capacities were compared with the experimental value, suggesting that the pseudo-second-order model was more appropriate than the pseudo-first-order model. Thus, the pseudo-second-order model was more useful for describing the biosorption kinetic process. A similar biosorption process had been reported for Acidic Black 1 biosorption by Sargassum glaucescens and Stoechospermum marginatum (Daneshvar et al. 2012). The results suggest that the adsorption of MB by S. hemiphyllum probably took place through surface exchange reactions until the active sites were fully occupied; then, dye molecules diffused into the algal biomass network for further interactions (Kousha et al. 2012). The intraparticle diffusion model was used to verify the ‘rate-controlling step’ of MB dye onto S. hemiphyllum; however, it did not fit the experimental data well, indicating that this diffusion mechanism was not playing the major role in the control of kinetics.

Table 3

Kinetics parameters obtained from kinetics models

ModelParametersValue
Pseudo-first-order qcal (mg·g−162.64 
k1 (min−10.033 
R2 0.97 
Pseudo-second-order qcal (mg·g−1194.17 
k2 (g·mg−1·min−11.48 × 10−3 
R2 0.99 
Intraparticle diffusion ki (mg·g−1·min−0.59.36 
C (mg·g−192.29 
R2 0.61 
 qexp (mg·g−1190.04 
ModelParametersValue
Pseudo-first-order qcal (mg·g−162.64 
k1 (min−10.033 
R2 0.97 
Pseudo-second-order qcal (mg·g−1194.17 
k2 (g·mg−1·min−11.48 × 10−3 
R2 0.99 
Intraparticle diffusion ki (mg·g−1·min−0.59.36 
C (mg·g−192.29 
R2 0.61 
 qexp (mg·g−1190.04 

pH = 5; biomass dosage = 0.5 g·L−1; dye concentration = 100 mg·L−1; T = 303 K.

Thermodynamic study

The thermodynamic parameters of ΔG0, ΔH0 and ΔS0 were obtained from the plot of lnKd values vs 1/T (Figure 6) and are shown in Table 4. The calculated values of Gibbs free energy (ΔG0) were −3.53, −3.85 and −4.29 KJ·mol−1 at 293, 303 and 313 K, respectively. The negative value of ΔG0 indicates the spontaneous nature of the biosorption. Furthermore, the enthalpy change was 7.46 KJ·mol−1, indicating that adsorption is an endothermic process. The positive values of ΔS0 (37.45 J·mol−1) correspond to the increased randomness at the solid-solution interface during MB adsorption by S. hemiphyllum. The positive values of ΔS0 may be attributed to a decrease in the number of water molecules surrounding the dye molecules, thus the degree of freedom of the water molecules increases (Gürses et al. 2004). A similar result had been reported for Acidic Black 1 adsorption in Sargassum glaucescens and Stoechospermum marginatum (Daneshvar et al. 2012).
Table 4

| Thermodynamic parameters for MB adsorption onto S. hemiphyllum at different temperatures

Temperature (K)ΔG0 (kJ·mol−1)ΔH0 (kJ·mol−1)ΔS0 (J·mol−1)
293 −3.53   
303 −3.85 7.46 37.45 
313 −4.29   
Temperature (K)ΔG0 (kJ·mol−1)ΔH0 (kJ·mol−1)ΔS0 (J·mol−1)
293 −3.53   
303 −3.85 7.46 37.45 
313 −4.29   
Figure 6

Plot of ln Kd vs 1/T for the biosorption of MB by S. hemiphyllum biomass. pH = 5; t = 120 min; biomass dosage = 0.5 g·L−1; dye concentration = 400 mg·L−1.

Figure 6

Plot of ln Kd vs 1/T for the biosorption of MB by S. hemiphyllum biomass. pH = 5; t = 120 min; biomass dosage = 0.5 g·L−1; dye concentration = 400 mg·L−1.

SEM analysis

Figure 7 shows the morphology and surface structure of S. hemiphyllum before and after biosorption of MB by SEM micrographs. The surface of S. hemiphyllum before loading MB featured lamellar protuberances, and became smoother after loading MB, which is consistent with reports by Guler & Sarioglu (2013) on Spirogyra sp. This phenomenon may arise from the MB molecules attaching around the algal surface and filling the pores.
Figure 7

SEM micrographs (×1,000 magnification) of S. hemiphyllum (a) before and (b) after biosorption of MB.

Figure 7

SEM micrographs (×1,000 magnification) of S. hemiphyllum (a) before and (b) after biosorption of MB.

FT-IR study

The FT-IR study provided a deeper understanding of the interaction between the biomass cell surface and dye molecules. FT-IR spectra of the biosorbents before and after dye adsorption are shown in Figure 8. The strong vibration and broadband at approximately 3,500–3,200 cm−1 represents the O–H group from cellulose and N–H groups from proteins in the algae. The peak at 2,925.84 cm−1 could be assigned to symmetric and asymmetric C–H stretching vibrations of the aliphatic groups. The peak at around 1,620.11 cm−1 could be attributed to the stretching vibration of carboxyl groups. The peak at 1,033.78 cm−1 could be related to the C–O stretching vibration of carboxylic acids and alcohols. This was in agreement with a large number of hydroxyl and carboxyl groups in brown algae (Leal et al. 2008). After MB adsorption, the peaks shifted to 3,388.73, 2,923.91, 1,600.82 and 1,035.71 cm−1, respectively. The significant change of the peaks showed that several functional groups on the surface of the algae interacted with the dyes. However, the large shift and the reduction of the peak at approximately 3,500–3,200 cm−1 indicated that the amine and hydroxyl groups were the most important functional groups for biosorption of MB. The significant reduction in the peak at 1,600.82 cm−1 showed that carboxyl groups also devoted to the binding of MB. The FT-IR analysis showed that hydroxyl, amine and carboxyl groups on the algal surface are responsible for the biosorption of MB.
Figure 8

FT-IR spectra of S. hemiphyllum biomass (a) before and (b) after biosorption of MB.

Figure 8

FT-IR spectra of S. hemiphyllum biomass (a) before and (b) after biosorption of MB.

XPS study

XPS was used to study the atomic composition and chemical environment of the surface and ensure the surface coverage accurately. The XPS wide scan spectra of S. hemiphyllum before and after MB adsorption are presented in Figure 9. The peaks shown in the spectra arose from the spectral lines of C 1 s (~284.8 eV), O 1 s (~532.7 eV) and N 1 s (~400 eV) peaks are discernible. The adsorption interaction between S. hemiphyllum with MB was investigated by N 1 s. The XPS spectra of N 1 s are shown in Figure 10. One peak at 399.9 eV was observed before adsorption. After adsorption dye, the spectra can be divided into two components (399.2 eV and 399.9 eV). A new peak at 399.2 eV appeared, and the area of 399.9 eV decreased. Actually, the N 1 s photoelectron peak which is close to 400 eV can be attributed to the nitrogen in the organic matrix (Serro et al. 2006). The binding energy of MB is 399.2 ± 0.2 eV (Hoppe et al. 1993). The results are consistent with the FT-IR study, a finding that demonstrated the interaction of MB with S. hemiphyllum through the –NH2 group.
Figure 9

XPS spectra (a) before and (b) after MB adsorption.

Figure 9

XPS spectra (a) before and (b) after MB adsorption.

Figure 10

XPS high resolution N 1 s spectra (a) before and (b) after MB adsorption.

Figure 10

XPS high resolution N 1 s spectra (a) before and (b) after MB adsorption.

CONCLUSION

In the present study, biosorption of MB by S. hemiphyllum from aqueous solutions was investigated. The adsorption capacity was influenced by the solution pH, contact time, biomass dosage and initial dye concentration. The isotherm study showed a good fit with the Langmuir model. The monolayer biosorption capacity fitted by the Langmuir isotherm was 729.93 mg·g−1 within 120 min using 0.5 g·L−1 algal biomass at pH 5 and 303 K. The value of the equilibrium parameter (RL) and the adsorption intensity (n) indicated that adsorption is favorable under selected experimental conditions. The pseudo-second-order model could be used as a successful model for the biosorption kinetics. The positive value of biosorption enthalpy change suggested that the process is endothermic, whereas the negative value of the Gibbs free energy established that it is a spontaneous process at temperature ranges of 293–313 K. The FT-IR analysis showed that hydroxyl, amine and carboxyl groups on the surface of the algae are responsible for the biosorption of MB. The XPS study indicated that the algae combine with MB molecules through the –NH2 group. It was concluded that the brown macroalga S. hemiphyllum could be a potential biosorbent to adsorb MB from wastewater.

ACKNOWLEDGEMENTS

This study was supported by the National Natural Science Foundation of China (No. 41376156), Foundation for High-level Talents in Higher Education of Guangdong, China and Guangzhou Science and Technology Program (201510010204).

REFERENCES

REFERENCES
Ali
H.
2010
Biodegradation of synthetic dyes – a review
.
Water Air and Soil Pollution
213
,
251
273
.
Almeida
C. A. P.
Debacher
N. A.
Downs
A. J.
Cottet
L.
Mello
C. A. D.
2009
Removal of methylene blue from colored effluents by adsorption on montmorillonite clay
.
Journal of Colloid and Interface Science
332
(
1
),
46
53
.
Chen
K. C.
Wu
J. Y.
Liou
D. J.
Hwang
S. C. J.
2003
Decolorization of the textile dyes by newly isolated bacterial strains
.
Journal of Biotechnology
101
,
57
68
.
Daneshvar
E.
Kousha
M.
Jokar
M.
Koutahzadeh
N.
Guibal
E.
2012
Acidic dye biosorption onto marine brown macroalgae: isotherms, kinetic and thermodynamic studies
.
Chemical Engineering Journal
204–206
,
225
234
.
Doğar
Ç.
Gürses
A.
Açıkyıldız
M.
Özkan
E.
2010
Thermodynamics and kinetic studies of biosorption of a basic dye from aqueous solution using green algae Ulothrix sp
.
Colloids and Surfaces B: Biointerfaces
76
,
279
285
.
Esmaeli
A.
Jokar
M.
Kousha
M.
Daneshvar
E.
Zilouei
H.
Karimi
K.
2013
Acidic dye wastewater treatment onto a marine macroalga, Nizamuddina zanardini (Phylum: Ochrophyta)
.
Chemical Engineering Journal
217
,
329
336
.
Gupta
V. K.
Suhas
2009
Application of low-cost adsorbents for dye removal – a review
.
Journal of Environmental Management
90
,
2313
2342
.
Gürses
A.
Karaca
S.
Doğar
Ç.
Bayrak
R.
Açıkyıldız
M.
Yalçın
M.
2004
Determination of adsorptive properties of clay/water system: methylene blue sorption
.
Journal of Colloid and Interface Science
269
(
2
),
310
314
.
Hoppe
R.
Schulz-Ekloff
G.
Wöhrle
D.
Shpiro
E. S.
Tkachenko
O. P.
1993
X.p.s investigation of methylene blue incorporated into faujasites and AIPO family molecular sieves
.
Zeolites
13
,
222
228
.
Kaushik
P.
Malik
A.
2009
Fungal dye decolourization: recent advances and future potential
.
Environment International
35
,
127
141
.
Kousha
M.
Daneshvar
E.
Dopeikar
H.
Taghavi
D.
Bhatnagar
A.
2012
Box–Behnken design optimization of Acid Black 1 dye biosorption by different brown macroalgae
.
Chemical Engineering Journal
179
,
158
168
.
Leal
D.
Matsuhiro
B.
Rossi
M.
Caruso
F.
2008
FT-IR spectra of alginic acid block fractions in three species of brown seaweeds
.
Carbohydrate Research
343
(
2
),
308
316
.
Marungrueng
K.
Pavasant
P.
2007
High performance biosorbent (Caulerpa lentillifera) for basic dye removal
.
Bioresource Technology
98
(
8
),
1567
1572
.
Ncibi
M. C.
Mahjoub
B.
Seffen
M.
2007
Kinetic and equilibrium studies of methylene blue biosorption by Posidonia oceanica (L.) fibres
.
Journal of Hazardous Materials
B139
,
280
285
.
Ncibi
M. C.
Ben Hamissa
A. M.
Fathallah
A.
Kortas
M. H.
Baklouti
T.
Mahjoub
B.
Seffen
M.
2009
Biosorptive uptake of methylene blue using Mediterranean green alga Enteromorpha spp
.
Journal of Hazardous Materials
170
,
1050
1055
.
Orlandi
G.
Cavasotto
J.
Machado
F. R. S.
Colpani
G. L.
Magro
J. D.
Dalcanton
F.
Mello
J. M. M.
Fiori
M. A.
2017
An adsorbent with a high adsorption capacity obtained from the cellulose sludge of industrial residues
.
Chemosphere
169
,
171
180
.
Özer
A.
Akkaya
G.
Turabik
M.
2006b
Biosorption of Acid Blue 290 (AB 290) and Acid Blue 324 (AB 324) dyes on Spirogyra rhizopus
.
Journal of Hazardous Materials
B135
,
355
364
.
Serro
A. P.
Gispert
M. P.
Martins
M. C. L.
Brogueira
P.
Colaço
R.
Saramago
B.
2006
Adsorption of albumin on prosthetic materials: implication for tribological behavior
.
Journal of Biomedical Materials Research Part A
78
,
581
589
.
Srinivasan
A.
Viraraghavan
T.
2010
Decolorization of dye wastewaters by biosorbents: a review
.
Journal of Environmental Management
91
,
1915
1929
.