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Potential biosorbent, Haloxylon recurvum plant stems, for the removal of methylene blue dye
⁎Corresponding author. Fax: +92 42 99230998. Ufq44@hotmail.com (Umar Farooq)
-
Received: ,
Accepted: ,
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.
Peer review under responsibility of King Saud University.
Abstract
Conventional technologies for the removal of dyes from the waste water are proving expensive due to non-regenerable materials used and their high costs. The use of dried biomass from Haloxylon recurvum plant stems (HRS) was studied for the removal of methylene blue, a textile dye, from its aqueous solution. FTIR studies revealed a variety of functional groups on the plant surface including carboxyl and amino groups. The pH at the point of zero charge (pHpzc) was found to be 6.3. The dye uptake by the plant increased with increasing pH, time of contact and dye concentration. Lagergren Pseudo first order and the Ho’s pseudo second order models were used to study the kinetics. The Langmuir and Freundlich equilibrium models were studied and the qmax was 22.93 mg/g. The changes in the values of free energy (ΔGo) and enthalpy (ΔHo) indicated the spontaneous, feasible and exothermic nature of the sorption process. H. recurvum plant is locally available in large quantities, so the powdered stems can act as a cost-effective and ecofriendly biosorbent for the removal of the dye from its aqueous solutions.
Keywords
Haloxylon recurvum
Methylene blue
Pseudo second order
Freundlich model
Desert plant
1 Introduction
In developing countries, environmental pollution caused due to the discharge of industrial waste water is of major concern. Usually, untreated and/or partially treated industrial effluents are being discharged into the natural ecosystem. These industrial effluents act as major water pollutants. The dyes, an important class of pollutants, are the compounds which are organic in nature and present in the industrial effluents. The presence of the dyes in the water ways is easily detectable even when released in small concentrations. Synthetic dyes are being produced on large scale than that of the natural dyes and are frequently being used in industries. Due to their extensive applications, the synthetic dyes can cause considerable environmental pollution and serious health risks. The presence of dyes in water bodies is toxic to aquatic as well as human lives, due to the presence of an aromatic structure; in some cases, metals in their structure. The dye-contaminated water is mutagenic, carcinogenic and causes many water-born diseases such as nausea, hemorrhage, ulceration of skin and mucous membrane etc. (Yesilada et al., 2003).
Among various methods in operation, adsorption using activated carbon (AC) is the most common choice but the cost of AC limits its use. Hence, there is a constant need to the search for efficient and cost-effective alternatives to activated carbon to remove dyes from industrial effluents (Garg et al., 2003).
Biosorption is a promising biotechnology for pollutant removal from their solutions. The materials of biological origin are used as sorbents in order to remove dyes from the solution. These ‘biosorbents’ contain a variety of functional groups which can complex dyes. Research in the field of biosorption suggests a number of advantages over other techniques such as: the material can be found easily as waste or by-products, materials can be recycled, no need of costly growth media, methods are simple, and requires less investment. Moreover, the process is ecofriendly, rapid, easy to operate and independent of the physiological constraints of living cells (Farooq et al., 2010).
In recent years a large number of biosorbents have been experimented on for use in the removal of dyes, such as Lentil straw (Celekli et al., 2012), rice husk ash (Chowdhury et al., 2009), activated carbons of sunflower hull (Thinakaran et al., 2008), tamarind fruit shell (Saha et al., 2010), Cucumis sativa Fruit peel (Santhi and Manonmani, 2011), Xanthoceras sorbifolia seed coat (Yao et al., 2009), vine stem (Ayan et al., 2011), cotton seed husk (Zhou et al., 2011) and Castor Seed Hull (Sen et al., 2010).
The objectives of the present study were to examine the sorption characteristics of powdered Haloxylon recurvum stems (HRS), under optimum conditions, for the removal of methylene blue dye from aqueous solution so as to facilitate comparison with other adsorbents. The H. recurvum is one of the dominant halophytic species of the salt desert plant abundantly available in the Cholistan Desert (Bahawalpur, Pakistan). It is mostly distributed in Egypt, Palestine, Jordan, Iraq, Kuwait, Iran and Pakistan (Ahmad, 2006). To the best of our knowledge, no report other than by Bestani et al. (2008) is available in the literature on the use of desert plants for the dye removal. The feasibility of the use of HRS, as low cost adsorbent, to determine the kinetics and equilibrium batch sorption parameters will predict the maximum possible sorption capacity and add a scientific basis to traditional uses of this desert plant.
2 Materials and methods
2.1 Preparation and characterization of powdered HRS biomass
All the chemicals and reagents used were of analytical grade, obtained from Merck (Germany) and were used as such without further purification. The H. recurvum plant stems (HRS) were collected from the Cholistan Desert in the district of Bahawalpur, Pakistan. The stems were cut into segments, thoroughly washed with tap water to remove dirt and then dried in open shade. The dried HRS were then ground in a domestic grinder and screened to different fractions of mesh size i.e., >800, 800–400, 400–200, 200–100 and <100 μm. The fractions were soaked in distilled water for two days to remove any soluble materials, then filtered and dried in the laboratory at room temperature. These dried fractions were stored in airtight plastic bottles. No other physical and chemical treatments were performed prior to batch sorption experiments. Methylene blue (MB), the adsorbate, was obtained from Sigma Aldrich. It is also named as Basic Blue 9 (C.I: 52015), basic in nature having the chemical formula C16H18N3SCl (Fig. 1) and molecular weight of 319.85 g/mol.
Elemental analysis was performed by using Vario EL III Elementar using Corn gluten as standard. FTIR spectrum of HRS biomass was scanned in the range of 4000–400 cm−1 using Perkin Elmer FTIR by standard Nujol mull method (Fig. 2a). Thermal analysis was performed using Perkin Elmer TGDTA by adopting the standard method, using a pre-defined heating program from 25 °C to 645 °C at a rate of 10 °C/min (Fig. 2b). The point of zero charge pH (pHpzc) of HRS biomass was determined (Fig. 2c) as described by (Abia and Asuquo, 2007).
2.2 Batch experiments
The batch experiments were carried out to optimize the experimental parameters like effect of time of contact, dose of biosorbent, concentration of dye, pH, temperature of dye solution and particle size of biomass. In all the experiments, measuring flasks of 100 mL were used containing 50 mL of dye solution of known concentration. A known amount of HRS biomass was added to the solution and then agitated on an orbital shaker (OS 2B Yellow line) at a constant speed of 400 rpm for a specific period of time. After this, the samples were withdrawn, centrifuged (EBA 20 Hettich) for 5 min at 3500 rpm and the supernatant of each sample was analyzed for remaining dye concentration at 660 nm (λmax) by using UV–Vis spectrophotometer (GallenKamp, SP-50). The difference between initial and final dye concentrations was considered to be sorbed by the biomass (HRS).
The amount of the dye adsorbed per unit mass of HRS biomass was calculated by using the following formula
2.2.1 Equilibrium models
The Langmuir and Freundlich models were used to study the equilibrium of the process. The linearized equation for the Langmuir sorption isotherm model is as follows;
The linearized Freundlich equation is as follows.
2.3 Sorption kinetics
Lagergren’s pseudo first order kinetic model and the Ho’s pseudo second order kinetic model were applied to elucidate the kinetics of the sorption process of the MB dye on the surface of the HRS biomass. The linear equations of these models are given as follows .
2.3.1 Thermodynamic modeling
The data obtained from temperature studies were used to determine the thermodynamic parameters, by using the following equation.
ΔGo = −RT lnKd = change in standard Gibb’s free energy and Kd = qe/Ce
ΔHo = Change in standard enthalpy and ΔSo = Change in standard entropy.
A graph was plotted between ΔGo and T. The values of ΔSo and ΔHo were calculated from the slope and intercept respectively (Fig. 6b).
2.4 Analytical methods
The wavelength of maximum absorption (λmax) was determined by measuring the absorbance of 20 mg/L solution of dye at different wavelengths using UV–Vis spectrophotometer (GallenKamp, SP-50). All the graphs were plotted by using Microsoft® Excel 2003. Regression analysis has also been performed to investigate the suitability of certain types of mathematical models.
3 Results and discussion
3.1 Characterization of biomass
The elemental analysis of powdered HRS biomass was performed using a “Vario EL III Elementar” using corn gluten as standard (C = 45.27%, N = 10.38%, S = 0.85%, H = 5.98%) indicating that the sorbent contains C = 43.07%, N = 2.104%, S = 0.13% and H = 6.09%.
The selective FTIR bands of HRS are shown in Fig. 2a. A broad peak at 3321.80 cm−1 represents the –OH stretching vibrations of carboxylic groups. The –NH asymmetric stretching of amino groups also occurs in this region. The peak at 1622.23 cm−1 represents C⚌O stretching vibrations of carbonyl compounds on the surface of the biomass. The peak at 1315.74 cm−1 represents the COO− symmetric stretching vibrations as well as the C–N stretching vibrations. The peak at 1243.44 cm−1 represents the symmetric SO3 stretching vibrations whereas the peak at 1027.93 cm−1 represents the C–OH stretching vibrations respectively which were due to several functional groups present on the surface of the biomass. The peak at 570.26 cm−1 represents O–C–N scissoring vibrations. The peaks around 1100–1000 cm−1 are known to be characteristics for all sugar derivatives (Bayramoglu and Arica, 2007; Won et al., 2009). The FTIR spectrum gives the indication of the poly functional nature of the biosorbent.
The thermal analysis shows that as the biomass was heated from room temperature to 100 °C, the moisture in the biomass was vaporized out. A little degradation occurred until about 200 °C. It might be possible that free radical mechanism occurred to eliminate water and to produce the volatile gases up to that temperature. It has been observed that between 300–375 °C, the majority of the carbohydrate polymers degraded and only lignin remained. The hemicellulose components started to decompose at about 225 °C and were almost completely degraded by 325 °C. Both the acid lignin and milled wood lignin start to decompose at about 200 °C, but are much more stable to thermal degradation as compared to the carbohydrate polymers (Rowell, 2005) (Fig. 2b).
To assess the ideal pH for dye sorption, it would be very helpful to determine the point of zero charge pH of the biosorbent (i.e., pHpzc). When biomass is kept in solution having a pH less than pHpzc of the biomass, it behaves as a positively charged poly matrix. This attracts the negatively charged ions present in the solution. An increase in the pH above this point makes the biomass type deprotonate and act as negative species and thus it binds the positive ions. This can be shown as follows where –BH represents the biomass type bearing zero charge (Farooq et al., 2010).
The point of zero charge pH was determined by drawing a plot ΔpH (pHi–pHf) vs. initial pH (pHi) (Fig. 2c). Initially, the pH dropped and then rose smoothly to a maximum value at pHi 11. The curve intersected the X-axis at pHi = 6.3, indicating that at this point the biomass type bears no charge. Hence, the pHpzc of HRS biomass was 6.3. At pH below 6.3 (pH < pHpzc), the surface of the biomass possesses a positive charge whereas at pH values above the pHpzc (pH > pHpzc) the surface possesses a negative charge.
3.2 Batch sorption studies
3.2.1 Equilibrium models – effect of initial dye concentration
In the sorption process, initially the solute molecules have to encounter the boundary layer effect. Then it has to diffuse from boundary layer to film onto the adsorbent surface. Finally, it has to diffuse into the porous structure of the adsorbent (Demirbas, 2009). Fig. 3a showed that the plot was a straight line indicating that the amount of dye sorbed per unit weight of the sorbent increased with the increase in the initial dye concentrations. The experimental qe value increased from 2.44 mg/g to 20.35 mg/g with increase in initial dye concentration.
At lower concentrations, the ratio of the dye molecule to the adsorbent sites is higher; therefore all the dye molecules can interact with the binding sites which cause an increase in the color removal. At higher concentrations lower adsorption yield is due to the saturation of adsorption sites (Iscen et al., 2007; Ozer et al., 2005).
Adsorption isotherms are used to investigate the relationship between the concentration of sorbed species and the sorption capacity of the sorbing species (Farooq et al., 2010). The Langmuir and Freundlich adsorption isotherm models are commonly applied to batch adsorption systems.
The Langmuir isotherm theory assumes a monolayer coverage of adsorbate over a homogenous adsorbent surface i.e., once a dye molecule occupies a site; no further adsorption can take place at that site (Hameed, 2009c).
The equilibrium data was used to investigate the fitting of the Langmuir model for the biosorption of MB onto the HRS biomass (Fig. 3b). The values of the constants determined from the plot are shown in Table 1. The value of coefficient of determination R2 was 0.9625, which is very close to 0.98 (the sorption system follows a specific mathematical model if the R2 value exceeds 0.98 (Farooq et al., 2010). The value of KL is very high, indicating a strong adsorption of the dye molecule onto the biomass surface. A very close R2 value indicates that the molecules adsorb on the biomass surface forming a mono layer. The monolayer sorption capacity (qmax) was found to be 22.94 mg/g.
| Langmuir model parameters | Freundlich model parameters | |||||
|---|---|---|---|---|---|---|
| qmax(mg/g) | KL (L/mg) | R2 | RL | n | KF (mg/g) | R2 |
| 22.94 | 134.58 | 0.9625 | 7.4 × 10−5 | 2.16 | 5.33 | 0.9936 |
The Langmuir adsorption constant KL is used in the calculation of the dimensionless equilibrium parameter or separation factor RL, which expresses the feasibility of the model. The value of RL indicates the type of the adsorption isotherm to be either unfavorable (RL > 1), favorable (0 < RL < 1), linear (RL = 1) or irreversible (RL = 0) (Hameed et al., 2009). It is defined as
The equilibrium data were used to study the Freundlich model (Fig. 3c) and the parameters are given in Table 1. The shape of the curve (a straight line) and the R2 value (0.9936) indicated that the MB-HRS system followed the Freundlich model. The Freundlich parameter 1/n was quite less than 1, indicating that the adsorption was quite feasible.
Being a lignocellulosic material, the HRS biomass is poly functional and porous in nature. Thus its surface favors the sorption of dye molecules in a multiple layer way rather than a monolayer manner.
3.2.2 Effect of pH of dye solution
The biosorbent consists of biopolymers with many functional groups, so that the net charge on the biosorbent, is also pH dependent (Maurya et al., 2006). When the pH of the system increases above the pHpzc, the number of negatively charged sites on the biosorbent increase, due to increase in the hydroxyl ion concentration where as the number of positively charged sites decrease (Iqbal and N., 2007). Therefore at higher pH, the surface of the adsorbent gets more negatively charged by losing protons (deprotonation of different functional groups on the surface of the biosorbent) and thus favors the uptake of positively charged (cationic) dyes due to increased electrostatic force of attraction (Ponnusami et al., 2009). Fig. 4a shows the biosorption of cationic dye MB. The shape of the curve is in agreement with the fact that pHpzc is playing an important role in the biosorptive removal of the dye. The decrease in qe value at lower pH is due to the less number of negatively charges cites at the HRS surface. The lower sorption of MB at lower pH was probably due to the presence of the excess H+ ions competing with the cationic groups on the dye for sorption sites (Hameed, 2008). The maximum sorption of the MB (cationic or positively charged dye) dye was observed at pH 8. The decrease in the biosorption of MB after pH was insignificant.
3.2.3 Effect of biomass dose
The adsorption of MB on HRS was studied by varying the amount of HRS biomass from 1–10 g/L while pH = 8, temperature (298 K) and solution concentration (10 mg/L) were kept constant (Fig. 4b). It was observed that with increase in the sorbent dose from 1 to 2 g/L, the sorption of the dye increased. After the dose was increased above 2 g/L, qe value decreased significantly. The lower sorption capacity (mg/g) of biomass at higher sorbent dose may be due to the splitting effect of flux (i.e., concentration gradient) between the sorbate and sorbent with increasing sorbent dose, causing a decrease in the amount of dye sorbed onto the unit mass of the adsorbent. Another reason of lower uptake of dyes would likely to be the inter particle interaction, such as aggregation, resulting from high sorbent concentration. Such aggregation would lead to a decrease in the total surface area of the sorbent and an increase in diffusion path length (Ozer et al., 2006). Moreover, the dye concentration is constant but the amount of HRS is increased. This increases the number of sites for a limited number of dye molecules. Hence, for a dye solution (10 mg/L), 2 g of biosorbent per liter of solution is found to be the optimum value.
3.2.4 Effect of particle size of biomass
The sorbent particle size is an important factor in sorption kinetics because it determines the time required for transport of sorbate within the pore to the sorbent sites (Tunc et al., 2009). The effect of particle size on sorption of MB dye was studied by conducting a series of experiments with different particle sizes ranging less than 100–800 μm. Fig. 4c shows that the sorption of the dye was less when the particle size was greater than that of 800 μm. In the experimental qe values the value decreased from 4.84 to 4.32 mg/g of biomass with an increase in biomass particle size.
The greater sorption at smaller particle size is due to the fact that the smaller particles move faster in solution than the larger particles. For larger particles, the diffusion resistance to mass transport is higher and most of the internal surface of the particle may not be utilized for sorption and consequently, the amount of dye adsorbed is small (Ong et al., 2007). Moreover increasing the surface area due to small particle size also increases the number of sites, and indirectly increases the sorption capacity (Tunc et al., 2009).
3.2.5 Effect of contact time – kinetic studies
The contact time is one of the important parameters for successful employment of the biosorbents for practical application (Iscen et al., 2007). The equilibrium time indicates the possible diffusion control mechanism between the sorbate as it moves toward the sorption surface (Abia and Asuquo, 2007).
The effect of change in the time of contact has been shown in Fig. 5a. The initial rapid rise in the slope of the curve (in the initial 30 min) pointed to the rapid binding of the dye with the HRS surface (rapid adsorption region). The higher sorption rate in the initial periods was due to greater number of vacant sites available on HRS biomass and due to the strong attractive forces between the dye molecule and the adsorbent (Jaikumar and Ramamurthi, 2009). This rapid increase during initial stages showed that the nature of binding was a physical one (Farooq et al., 2010). With the passage of time, the number of vacant sites decreased resulting in the decreased rate of dye binding (Uddin et al., 2009). After it, the slope became less sharp (transition region) indicating the slow sorption rate up to 40 min. After 40 min of contact, the curve became parallel to the x-axis i.e., there is no considerable change in the dye binding with the biomass type. This pointed to the establishment of equilibrium within MB-HRS system and the equilibrium time was 40 min.
The equilibrium times of 90 min to 12 h have been reported for MB sorption on various biomass types from higher plants (Bestani et al., 2008; Hameed, 2009a,b; Hameed et al., 2009; Han et al., 2007; Oladoja et al., 2008; Oliveira et al., 2008; Tsai et al., 2008; Zhou et al., 2011). The time of contact of MB on HRS is significantly shorter than previously reported ones and thus points to the possible use of HRS for the removal of MB from aqueous solutions as an alternative material.
Lagergren Pseudo first order (Lagergren, 1898) and Ho’s pseudo second order kinetic models (Ho and McKay, 1999) are mostly applied to study the kinetics of the biosorption system. Lagergren Pseudo first order kinetics indicates that the process of sorption occur at a rate proportional to the dye concentration, which is particularly suitable for low concentrations. The second order kinetics is thought to derive from sorption processes in which the rate controlling step is an exchange reaction (Bayramoglu and Arica, 2007).
The data obtained from the effect of time of contact studies are used to plot the graphs for both the kinetic models (Fig. 5b and c). The slopes and intercepts are calculated from the equation of the straight line obtained. Kinetic data and R2 values are presented in Table 2. The sorption system will follow a specific kinetic model if the R2 value exceeds 0.98 and the calculated qe value is comparable to that of the experimental value (Farooq et al., 2010). The comparison of R2 values showed that the Ho’s pseudo second order kinetic model was able to explain the kinetics of the process. The experimental and calculated qe values were relatively closer for the Ho’s pseudo second order model rather than for the Lagergren Pseudo first order model. This is in accordance with the previous studies that biosorption by agricultural materials followed a Ho’s pseudo second order kinetic model.
| Lagergren Pseudo first order kinetic model | Experimental | Ho’s pseudo second order kinetic model | ||||
|---|---|---|---|---|---|---|
| K1 (min−1) | R2 | qe(cal) (mg/g) | qe(exp)(mg/g) | qe(cal)(mg/g) | k2 (g mg−1 min−1) | R2 |
| 0.084 | 0.977 | 3.9590 | 4.8403 | 5.5866 | 0.0244 | 0.984 |
3.2.6 Effect of temperature of dye solution – thermodynamic parameter
A study of the temperature dependence of sorption reaction gives valuable information about the enthalpy change during adsorption. In addition, changing temperature will change the equilibrium capacity of the adsorbent for a particular adsorbate (Dogan et al., 2009).
The plot of the effect of the sorption of MB dye shows that the sorption of the dye decreased with increase in the temperature of the dye solution. The experimental qe values of the biomass decreased significantly from 4.82 to 1.46 mg/g with increase in the temperature of the dye solution from 298 to 343 K. This indicated that the sorption process was an exothermic process and that HRS biomass can be effectively used for removal of the dye at room temperature. The influence of temperature on the sorption of MB dye has been shown in Fig. 6a.
The effect of change in temperature on the MB dye sorption system was studied to determine the thermodynamic parameter and to investigate the nature of the process. The thermodynamic parameter, Gibb’s free energy change (ΔGo) (J/mol) was calculated by using the following equation.
A plot of ΔGo vs. T yields a straight line (Fig. 6b) and the values of ΔHo (kJ/mol) and ΔSo (J/mol K) were calculated from the intercept and the slope respectively in the graph plotted.
The negative value of ΔGo at the given temperature indicates the spontaneous nature of the sorption and confirms the energy free feasibility of the sorption process. The negative value of ΔHo (−210.38 J/mol K) and that of ΔSo (−65.88KJ/mol) is an implication of the exothermic nature of the sorption process and decrease in randomness or increased in orderness at the adsorbate–adsorbent interface respectively. The sorption capacities of the HRS biomass decreased with the increasing temperature, showing the exothermic adsorption process. The value of ΔHo suggests that the adsorption process might be considered as physical adsorption in nature (Farooq et al., 2010).
3.3 The comparison of experimental sorption capacities of H. recurvum stems (HRS) to some sorbents
In this study the removal of methylene blue by HRS was studied at various initial dye concentrations, pH and temperatures for an initial time period of 40 min. Under all conditions studied the most sorption occurred at 298 K, at pH 8.
The maximum amounts of dye adsorbed by various adsorbents in equilibrium time vary as a function of experimental conditions (Table 3). Especially the contact time has a very important effect on the estimation of the maximum amounts of dye adsorbed per unit adsorbent. Some of the biomasses have much less sorption capacity as compared to the HRS biomass, in spite of all this the time period is much greater for equilibrium to reach, e.g., Salsola vermiculata (desert plant), Cereal chaff, Cotton stalk, Cotton waste, Cotton dust, Orange peel, and Banana peel.
| Biomass | Bisorption capacity qmax (mg g−1) | Equilibrium time (min) | Equilibrium model | Kinetic model | References |
|---|---|---|---|---|---|
| Xanthoceras sorbifolia seed coat | 178.6 | 180 | Langmuir | PSO | Yao et al. (2009) |
| Azolla filiculoides | 166.7 | – | Langmuir | PSO | Padmesh et al. (2008) |
| Spent Cottonseed Husk Substrate | 143.5 | 240 | Langmuir | PSO | Zhou et al. (2011) |
| Pleurotus ostreatus (Jacq.) P. Kumm.; | 70 | – | Langmuir | İslek et al. (2008) | |
| Haloxylon recurvum stem (HRS) | 22.94 | 40 | Freundlich | PSO | Present work |
| Salsola vermiculata (desert plant) | 22 | 65 | Langmuir | _ | Bestani et al. (2008) |
| Cereal chaff | 20.3 | – | – | – | Han et al. (2007) |
| Orange peel | 15.9 | 20 | Langmuir | IPDM | Annadurai et al. (2002) |
| Cotton stalk, Cotton waste, Cotton dust | 5.95, 14.04, 15.78 | 90 | Freundlich | – | Ertas et al. (2010) |
| Banana peel | 13.9 | 20 | Freundlich | IPDM | Annadurai et al. (2002) |
| Rice Husk Ash | – | 60 | Temkin | PSO | Chowdhury et al. (2009) |
PSO = Pseudo second order.
IPDM = Intraparticle diffusion model.
4 Conclusion
The present study is an attempt to explore the possible use of HRS biomass type for the removal of MB from aqueous solution. FTIR analysis and the thermal studies revealed that the presence of carboxyl, hydroxyl, amino groups, cellulose and hemicelluloses in the biomass as major components. The equilibrium time for sorption of the dye was 40 min. MB-HRS sorption system could be explained by the electrostatic attraction between the negative charge surface of biomass and the positive charge dye molecule in basic medium. The removal efficiency of the dye was highly temperature dependent. The adsorption process was spontaneous and exothermic in nature which was further confirmed by the studies of thermodynamic parameters. A very good agreement with experimental data indicated that the sorption of dye on HRS biomass followed the Lagergren Pseudo first order kinetics. The sorption capacity and other parameters of the used biomass was compared with other reported biomasses and concluded that the H. recurvum stems could be employed as a low cost and eco-friendly biosorbent. It can be used as an alternative to the expensive methods of removing MB dye from the textile and leather industries effluents.
Conflict of interest
The authors have declared no conflict of interest.
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