Adsorptive removal of Methyl Orange and Reactive Red 198 ... - NOPR

Indian Journal of Chemical Technology Vol. 21, March 2014, pp. 105-113

Adsorptive removal of Methyl Orange and Reactive Red 198 dyes by Moringa peregrina ash Edris Bazrafshan1, Amin Allah Zarei1,*, Hossein Nadi1 & Mohammad Ali Zazouli2 1

Health Promotion Research Center, Zahedan University of Medical Sciences, Zahedan, Iran Department of Environmental Health Engineering, Faculty of Health and Health Sciences Research Center, Mazandaran University of Medical Sciences, Sari, Iran

2

Received 10 September 2012; accepted 1 July 2013 In the present study, a low-cost adsorbent derived from Moringa peregrina plant has been used for its ability to remove two common textile dyes, namely Methyl Orange (MO) and Reactive Red 198 (RR-198) from aqueous solutions. The effect of various operating parameters such as initial concentration of dye (10-150 mg L-1), contact time (10-150 min), adsorbent dosage (1-13 g L-1) and pH (2-11) is investigated. At an optimum pH of 2, approximately 96% removal of dye (50 mg L-1) is obtained for an adsorbent dose of 7.0 g L-1 after a 70 min contact time. The equilibrium assessment reveals that the Langmuir model is better than Freundlich model for the experimental data. The thermodynamic properties (∆Gº, ∆Hº and ∆Sº) show that the adsorption of RR-198 and MO dyes onto Moringa peregrina tree shell ash (MPTA) is spontaneous, endothermic and feasible in the temperature range of 293-313 K. Also, the magnitude of enthalpy change indicates that the adsorption is physical in nature. Finally it can be concluded that the MPTA can be used as a low-cost adsorbent for the removal of different concentrations of anionic dyes from aqueous solutions. Keywords: Adsorption, Anionic dyes, Moringa peregrine, Thermodynamic properties

Synthetic dyes have been used increasingly in the textile and dyeing industries because of their ease and cost-effectiveness in synthesis, high stability to light, detergent, temperature and microbial attack. This has resulted in the discharge of highly polluted effluents1. About 10,000 different commercial dyes and pigments are being manufactured, and over 7×108 kilograms are produced annually world-wide. It has been estimated that about 10-20% of these dyes are released as effluents during the dyeing processes2,3. Since dyes are stable, recalcitrant, colorant, and even potentially carcinogenic and toxic, their release into the environment poses serious environmental, aesthetical and health problems4,5. Thus, industrial dye-laden effluents are an increasingly major concern and need to be effectively treated before being discharged into the environment in order to prevent these potential hazards. The removal of dyes from wastewater is one of the major problems because conventional wastewater treatment systems are not effective to remove color from industrial effluents6. Unsuitable treatment and disposal of colored wastewaters from textile, dyeing, printing, ink, and related industries have provoked serious environmental —————— *Corresponding author. E-mail: [email protected]

concerns all over the world7,8. For the removal of dye materials from contaminated water, several methods such as physical, chemical and biological methods have been investigated9,10. The conventional treatment process of textile effluents involves numerous stages due to the characteristics of the production process11. Conventional treatment involves a process of coagulation/ flocculation. This is a versatile process, which can be used alone or combined with biological treatments, as a way of removing suspended solids and organic material, as well as promoting the extensive removal of dyes from textile industry effluents12,13. However, this approach presents the disadvantage of generating a large volume of sludge. This sludge is rich in dyes, as well as other substances used in the textile process. This is a problem, as the waste must be discarded properly to avoid environmental contamination11. Also, although biological degradation methods are one of the most economic processes for wastewater treatment, they are often unsuccessful to degrade molecules of refractive nature, like those present in textile industry wastewaters. Also, the survival of anaerobic biomass in the presence of high concentration of azo dyes is a difficult task. Therefore, for the treatment of this type of wastewaters other alternative methods have been proposed in the literature14.

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Other various techniques that have been used to remove dyes from colored wastewater, including enzymatic treatment15, ozone treatment16, nanoparticles17, photochemical and sonochemical processes18 coagulation by natural coagulants19 and membrane processes20 were used for removal of dye from textile effluents. However, some of these methods are limited due to their high operational costs and problems. Adsorption is an efficient alternative process for the treatment of contaminated wastewater and the most effective procedure for removal of synthetic dyes from industrial effluents, because the dye species are transferred from the water effluent to a solid phase, diminishing the effluent volume to a minimum. Subsequently, the adsorbent can be regenerated or kept in a dry place without direct contact with the environment21. Also, adsorption has proven to be a reliable treatment methodology due to its low capital investment cost, simplicity of design, ease of operation and insensitivity to toxic substances, but its application is limited by the high price of some adsorbents and the large amounts of wastewater normally involved. In order to reduce preparation cost, the use of low cost starting materials (industrial or agricultural residues) for activated carbon preparation has emerged as a potential alternative22. Besides the cost reduction, the conversion of agriculture waste in low cost adsorbents also added value to this residues and solve the problem of biomass disposal. Agricultural waste-based carbon has the advantage of exhibiting low ash content, reasonable hardness and high surface area and/or adequate porous structures20,23. The choice of activated carbon precursor largely depends on its availability, cost, and purity, but the manufacturing process and intended applications of the product are also important considerations24. Therefore, evaluation of biomass is getting increased attention in all over the world as it is renewable, widely available, cheap, and environmental friendly25. Moringa peregrina is a desert species; its occurrence in Iran is restricted to the southeast of the Sistan and Baluchestan province. Globally, it grows in Northeast Africa and Southwest Asia. The ground where Moringa peregrina grows is usually covered with coarse rock debris, which characterizes the upstream runnels at the mountain bases and slopes26. Methyl orange (MO), is one of the well-known acidic/anionic dyes, and has been widely used in textile, printing, paper, food and pharmaceutical

industries and research laboratories27. Methyl orange, an anionic dye belongs to the azo group of dyes. The azo group of dyes has nitrogen in molecule. The presence of azo group (N=N) on MO and low biodegradability makes it an issue of concern for environmental science27. Also, Reactive Red 198 is one of the most representative and commonly used dyes to dyeing the textile goods. This dye has several functional groups such as vinylsulfone [-SO2-CH2CH2-O-SO3Na] and monochlorotriazine. The chemical structures of MO and RR-198 dyes are shown in Fig. 1. In present study, adsorption of two dyes namely MO and RR-198 from aqueous solutions on Moringa peregrina tree shell ash (MPTA) has been studied. The dyes were selected based on availability of more complete study on efficiency of adsorbent (MPTA) for dyes removal. The effects of different parameters including initial pH, adsorbent dosage, initial dye concentration, and contact time were also studied. Additionally, the sorption isotherm was explored to describe the experimental data. Experimental Procedure Chemicals and reagents

Reactive Red 198 (RR-198) is an anionic dye with molecular weight 968.21 g mol-1 and maximum absorption (λmax) 530 nm. The RR-198 [C27H18ClN7Na4O15S5] dye used in this work was the analytical grade (Merck, Germany). Analytical grade (Merck, Germany) of MO [C14H14N3NaO3S], also used in this study, is an anionic dye with molecular weight 327.34 g mol-1 and maximum absorption (λmax) 465 nm. For treatment experiments, the dye solutions with concentrations in the range 10-150 mg L-1 were prepared by successive dilution of the stock solution (1000 mg L-1) with distilled water. All other chemicals used in this study were of analytical grade.

Fig.1─Structures of (a) Reactive Red 198, and (b) Methyl Orange dyes

BAZRAFSHAN et al.: ADSORPTIVE REMOVAL OF MO & RR-198 DYES BY M PEREGRINA ASH

Adsorbent preparation

Moringa peregrina tree shells were collected around the vicinity of Nikshahr city (26◦68' N, 59◦71' E), Sistan and Baluchestan province, Iran. This natural wastes were firstly washed with distilled water to remove impurity such as sand and leaves and soluble and colored components, dried at 110°C for 24 h, burned at 700°C for 2 h, crushed in a domestic grinder and sieved to obtain particle size (30-100 mesh). The powdered adsorbent was stored in an airtight container until use. No other chemical or physical treatments were used prior to adsorption experiments. An FTIR spectrum of Moringa peregrina tree shells powder (after carbonization) is shown in Fig. 2. Several peaks were observed from the spectra, indicating that MPTA is composed of various functional groups which are responsible for binding of anionic dyes RR-198 and MO. Dye removal experiments

Dye removal experiments with the MPTA were carried out as batch tests in 250 mL flasks under magnetic stirring. Each test consisted of preparing a 100 mL of dye solution with a desired initial concentration and pH by diluting the stock dye solution with distilled water, and transferring it into the beaker on the magnetic stirrer. The pH of the solution was adjusted using 1N [HCl] or [NaOH] solutions. A known mass of MPTA (adsorbent dosage) was then added to the solution, and the obtained suspension was immediately stirred for a predefined time. After the desired contact time, the samples were withdrawn from mixture by using a micropipette and centrifuged for 5 min at 5000 rpm. After centrifuged, supernatants were analyzed for the

Fig. 2─FTIR spectra of Moringa peregrina tree shells powder after carbonization

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determination of the final concentration of dye by using an UV–VIS spectrophotometer (T80 PG Instruments Ltd) set at a wave-length of 464 nm and 525 nm for MO and RR-198, respectively. Then the amount of dye adsorbed (qe, mg g-1) was obtained using the following relationship: qe =

(C0 − Ce )V M

… (1)

where C0 and Ce are the initial and equilibrium liquid phase concentration of dye (mg L-1) respectively; V, the volume of the solution (L); and M, the amount of adsorbent used (g). To express the % of dye removal, the following equation was used: Dye removal (% ) =

(C0 − C f ) C0

× 100

… (2)

where C0 and Cf represent the initial and final (after adsorption) dye concentrations respectively. All tests were performed in duplicate to ensure the reproducibility of the results; the mean of the two measurements was reported. All experiments were performed at room temperature (~20ºC). The investigated ranges of the experimental variables were as follows: dye concentration (10-150 mg L-1), pH of solution (2-11), MPTA dosage (1-13 g L-1) and mixing time (10-150 min). Results and Discussion Effect of initial pH

It is well known that the solution pH can affect the surface charge of the adsorbent, the degree of ionization of the different pollutants, the dissociation of functional groups on the active sites of the adsorbent as well as the structure of the dye molecule28. So the solution pH is an important parameter during the dye adsorption process. In present study, the effect of initial pH on the MO and RR-198 dyes adsorption capacities of the MPTA has been studied at various pH (2-11) with 50 mg L-1 fixed initial dye concentrations and adsorbent dosage 3 g L-1 for 60 min and the results are shown in Fig. 3. For both MO and RR-198 dyes, a decrease in pH from 11 to 2 causes a significant increase in the amount of dye adsorbed by MPTA. On the other hand, the adsorption of MO and RR-198 dyes onto MPTA is intimately dependent on solution pH. It could be seen that the uptake of dyes increases with decreasing pH form 11 to 2 until the equilibrium is obtained. The

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maximum adsorption capacity of the MPTA is found to be 14.03 and 15.29 mg g-1 at pH 2 for MO and RR198 dyes respectively, when 84.16% and 91.76% of the dyes were removed. Also, as it can be seen from Fig. 3, residual concentrations of dyes increase with rising of solution pH. The results of this study are according to findings of most researchers who have similarly reported attaining maximum adsorption onto different adsorbents in the acidic pH4,6,29,30. At acidic conditions, binding sites of the adsorbent would be closely associated with the hydrogen ions which act as bridging ligands between the adsorbent surface and the dye molecule. The lower pH values can be suitable for the adsorption of anionic dyes31-34.

However, as it can be seen from Fig. 4, when the adsorbent dosage is increased, percentage removal of dyes also increases but amount of adsorbed dyes of per gram adsorbent decreases (34.63 and 36.27 mg g-1 are reached to 3.54 and 3.61 mg g-1 for MO and RR-198 dyes respectively). It is due to the high number of unsaturated sorption sites during adsorption process. Similar results have previously been reported by other researchers6,35,36. Effect of contact time

Because adsorption is mainly a surface phenomenon, the amount of surface available for adsorption process and consequently the mass of adsorbent can considerably affect adsorption efficiency. Hence, the effect of MPTA dosage on dyes (MO and RR-198) removal has been investigated at an optimum pH of 2, dye concentration of 50 mg L-1 and contact time of 60 min. Figure 4 represents the removal percentages and adsorption capacity of MO and RR-198 dyes as a function of MPTA dosage. The removal of dye at a dose of 1.0 g L-1 is found to be 69.26% and 72.54% for MO and RR-198 respectively; removal improves to 92.44 and 94.16% when the adsorbent dosage is increased to 7.0 g L-1 and remains almost unchanged thereafter. The increasing adsorption efficiency with the increase in MPTA dose can be attributed to the increase in surface area and, by extension, the greater number of exchangeable sites available for interaction with dyes molecules.

The contact time is one of the most important parameters for practical application. The removal efficiency and residual dye concentration of MO and RR-198 adsorbed onto the MPTA at an optimum pH of 2, dye concentration of 50 mg L-1 and adsorbent dose of 7 g L-1 is shown as a function of time (0–150 min) in Fig. 5. The per cent removal of MO and RR-198 dyes onto the MPTA drastically increases during the initial adsorption stage and then continues to increase at a relatively slow speed with contact time until a state of equilibrium is attained after 70 min. The rapid adsorption of studied dyes is probably due to the abundant availability of active sites on the sorbent surface during the first 20 min, hence 67.38% and 74.02% removal efficiency is attained after only 20 min for MO and RR-198 dyes respectively. Also, the maximum removal efficiency (approximately 96%) for both dyes is obtained at contact time 70 min. Generally, the removal rate of sorbate is rapid initially, but gradually it decreases with time until it attains equilibrium. This phenomenon is attributed to the fact that a large number of vacant surface sites is available for adsorption at the initial stage, and after

Fig. 3─Effect of initial pH on MO and RR-198 dyes adsorption onto MPTA

Fig. 4─Effect of adsorbent dose on MO and RR-198 dyes adsorption onto MPTA

Effect of adsorbent dosage


Fig. 5─Effect of contact time on adsorption of MO and RR-198 dyes onto MPTA

a lapse of time, the remaining vacant surface sites are difficult to be occupied due to repulsive forces between the solute molecules on the solid and bulk phases. Similar finding was reported by other researchers6,35,37 also. Effect of initial dye concentration

The initial adsorbate concentration provides a critical driving force to overcome all mass transfer resistance of dyes between the aqueous and solid phases38. The influence of varying initial dye concentration (10 - 150 mg L-1) on adsorption process has been investigated at pH 2 and 7 g L-1 adsorbent concentration for 70 min. Based on data plotted in Fig. 6, when the initial dye concentration is increased, the removal efficiency for both the dyes decreases, so the removal of dye depends on the concentration of the dye. For example, when the initial dye concentration increases from 10 mg L-1 to 150 mg L-1, the removal efficiency of MPTA decreases from 97.6% to 80.21% and from 98.8% to 77.65% for MO and RR-198 dyes respectively. However, the values of qe (mg g-1) increase from 1.39 mg g-1 to 17.19 and from 1.41 mg g-1 to 16.64 mg g-1 with increasing the initial dye concentration for MO and RR-198 dyes respectively. This is probably due to high driving force for mass transfer. Similar trends have also been observed for Basic Red 46 dye removal from aqueous solution by pine tree leaves35 and Methylene blue dye sorption onto bamboo-based activated carbon39. The reduction of dye removal as a function of its concentration can be explained by the limitation of available free sites for adsorption of dye with the increase in dye concentration in bulk solution for a fixed mass of adsorbent, as well as by the increase in intraparticle diffusion.

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Fig. 6─Effect of initial dye concentration on adsorption of MO and RR-198 dyes onto MPTA Adsorption isotherms

The equilibrium adsorption isotherm is important in the design of adsorption systems that can describe how an adsorbate interacts with adsorbent. The isotherm provides a relationship between the concentration of dye in solution and the amount of dye adsorbed on the solid phase when both phases are in equilibrium. In this study, the Langmuir isotherm, and Freundlich isotherm models are employed to characterize the adsorption isotherms of MO and RR-198 dyes in single solute systems. The Langmuir isotherm model, which is a non-linear model based on the assumption of a monolayer uptake of the adsorbate on a homogenous surface with identical and equivalent adsorption sites40, has been the most frequently employed model in fitting experiment data. It can be expressed as the following equation:

qe =

qm K l Ce 1 + K l Ce

… (3)

where qe is the amount of metal adsorbed per specific amount of adsorbent (mg g-1); Ce, equilibrium concentration of the solution (mg L-1); and qm, is the maximum amount of MO and RR-198 dyes required to form a monolayer (mg g-1). The Langmuir equation can be rearranged to linear form for the convenience of plotting and determining the Langmuir constants (KL) and maximum monolayer adsorption capacity of MPTA (qm). The values of qm and KL can be determined from the linear plot of 1/qe versus 1/Ce, as shown below:

1 1 1 1 = + q e q m qm K l Ce

… (4)


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Langmuir isotherm. Therefore, dyes molecules are presumed to have been adsorbed as a monolayer on adsorption sites that are homogeneously distributed43 on the surface of MPTA with no interaction between the adsorbed dyes, i.e. all molecules show equal activation energy44. The favorability of the Langmuir model was further assessed using the equilibrium dimensionless parameter, RL (Eq. 5). Considering the obtained Langmuir constant, the calculated value for RL falls between 0 and 1, confirming the favorability of MO and RR-198 dyes adsorption onto MPTA. Moreover, the constant n in the plot of the Freundlich isotherm is greater than unity (between 1 and 10), which proves that MPTA is an appropriate and beneficial adsorbent45 for both studied dyes. Jalil et al.46 have also obtained a better fit using the Langmuir isotherm for experimental data for MO dye adsorption onto calcined Lapindo volcanic mud. Maximum adsorption capacity of some adsorbents for different dyes is presented at Table 2.

A dimensionless separation factor (RL), defined by Weber and Chakravorti41, can be used to predict the affinity between the adsorbate and the adsorbent. RL is calculated by the following equation:

RL =

1 1 + K l C0

… (5)

The value of RL indicates the adsorption nature to be either unfavorable (RL > 1), linear (RL = 1), favorable (0 < RL < 1) or irreversible (RL = 0). The Freundlich isotherm, which is the earliest relationship describing the non-idea and reversible sorption, is an empirical model assuming adsorption on heterogeneous surface and active sites with different energy42. It can be applied to multilayer adsorption. The Freundlich isotherm model can be represented by the following equation: 1

qe = K f Ce n

… (6)

where Kf and 1/n are the Freundlich constants related to adsorption capacity and adsorption intensity respectively. The Freundlich equilibrium constants are evaluated from the intercept and the slope respectively of the linear plot of log qe versus log Ce based on experimental data. The Freundlich equation can be linearized in logarithmic form for the determination of the Freundlich constants, as shown below: log q e = log K f +

1 log Ce n

Effect of temperature on dyes adsorption

To understand the effect of temperature on the removal of RR-198 and MO dyes by MPTA, experiments were carried out at 293, 303 and 313 K using pH 2 and adsorbent dosage 7 g L-1 and at different initial concentrations (10-150 mg L-1). Figure 7 shows that the removal efficiency of RR-198 and MO dyes for all initial dye concentrations increases, when the temperature is increased from 293 K to 313 K. Increasing the temperature is known to increase the rate of diffusion of the adsorbate molecules across the external boundary layer and in the internal pores of the adsorbent particle, owing to the decrease in the viscosity of the solution. In addition, changing temperature will change the equilibrium capacity of the adsorbent for a particular adsorbate58. Similar findings are also reported by Khodaie et al.59.

… (7)

The isotherms based on the experimental data and the parameters obtained from nonlinear regression by both models at different temperatures are listed in Table 1. The correlation coefficient (R2) of the Langmuir model is found to be higher than that of the Freundlich model for both studied dyes, suggesting that the equilibrium adsorption of MO and RR-198 dyes onto MPTA could be best described with the

Table 1─Isotherm parameters for adsorption of MO and RR-198 onto MPTA Temperature, K

Dyes

Langmuir isotherm -1

293 303 313

MO RR-198 MO RR-198 MO RR-198

-1

Freundlich isotherm 2

qm, mg g

Kl, L mg

R

Kf

n

R2

15.43 13.61 15.78 12.47 13.46 12.57

0.41 0.98 1.02 1.59 1.28 2.1

0.9959 0.9933 0.9762 0.9935 0.9817 0.9925

3.75 4.62 4.85 5.32 5.93 6.08

1.87 2.59 1.73 2.23 1.7 2.22

0.9607 0.9375 0.9870 0.9591 0.9938 0.9580


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Table 2─Maximum adsorption capacity of some adsorbents for different dyes Adsorbent

Adsorbate

MWCNTS Activated carbon (poplar wood) Activated rice husk carbon Eggshell Raw Kaolinite Montmorillonite Brazilian pine-fruit shell Cumin herb wastes Salvadora persica stems ash Bone char Cetyltrimethylammonium bromide modified zeolit High lime fly ash MPTA MPTA

Acid Red 18 Acid Red 18 Acid yellow 36 Reactive Red 123 Acid Red 18 Acid Red 18 Reactive Red 194 Reactive Red-120 Methylene blue Reactive Black 5 Reactive Black 5 Reactive Black 5 Methyl Orange Reactive Red 198

Maximum adsorption capacity, mg/g 166.67 3.9 86.9 1.26 29 19 20.8 47.88 22.78 160 12.93 7.94 15.43 13.61

References 47 48 49 50 51 51 52 53 54 55 56 57 Present study Present study

Table 3─Thermodynamics parameters for RR-198 and MO dyes adsorption on MPTA [∆Hº = 28.98 KJ/mol (RR198) and 43.13 KJ/mol (MO). ∆Sº = 0.1 kJ/mol K (RR198) and 0.14 kJ/mol K (MO)] Dyes

Temperature, K

∆Gº, kJ/mol

293 303 313 293 303 313

0.04921384 -1.16821184 -1.9307302 2.171934802 -0.04988563 -0.64239954

RR198

MO

enthalpy change (∆H°) and entropy change (∆S°) for the adsorption processes are calculated using the following equations: ∆G 0 = - R T ln K a … (8) ∆G 0 = ∆ H 0 - T ∆ S 0

Fig. 7─Effect of temperature on (a) RR-198 and (b) MO dyes adsorption onto MPTA

Thermodynamic considerations of an adsorption process are necessary to conclude whether the process is spontaneous or not. Gibb’s free energy change (∆G°) is the fundamental criterion of spontaneity. Reactions are spontaneously at a given temperature if ∆G° is a negative value. The thermodynamic parameters of Gibb’s free energy change (∆G°),

… (9)

where R is universal gas constant (8.314 J/mol/K); and T, the absolute temperature in K. Gibb’s free energy change (∆G°) was calculated using Ka obtained from Langmuir Eq. (3) (Table 3). The negative values of ∆G° confirm the feasibility of the process and also the spontaneous nature of adsorption with a high preference of RR-198 and MO dyes by MPTA. Furthermore, the decrease in the negative value of ∆G° with an increase in temperature indicates that the adsorption process of RR198 and MO dyes on MPTA becomes more favorable at higher temperatures60. The enthalpy change (∆H°) and the entropy change (∆S°) for the adsorption process were obtained from the intercept and slope of Eq. (9) and are found to be 28.98 and 43.13 kJ/mol and 0.1 and 0.14 kJ/mol/K for the removal of RR198 and MO dyes respectively.


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Adsorption process can be classified as physical adsorption and chemisorption by the magnitude of the enthalpy change. It is accepted that if magnitude of enthalpy change is less (84 kJ/mol), adsorption is physical. However chemisorption takes place in the range from 84 to 420 kJ/mol61. The positive value of ∆H° indicates that the adsorption reaction is endothermic. The positive value of ∆S° suggests that some structural changes occur on the adsorbent and the randomness at the solid/liquid interface in the adsorption system increases during the adsorption process62. Finally, it can be concluded that according to the thermodynamic properties (∆Gº, ∆Hº and ∆Sº) adsorption of RR198 and MO dyes onto MPTA is spontaneous, endothermic and feasible in the temperature range 293-313 K. Conclusion It is found that a new adsorbent Moringa peregrina tree shell ash (MPTA) is a promising new low cost adsorbent for the removal of MO and RR-198 dyes from aqueous solutions (removal efficiency ~ 96%). The equilibrium data analysis show that the Langmuir model is suitable for describing the adsorption equilibrium of MO and RR-198 dyes onto MPTA. The thermodynamic properties (∆Gº, ∆Hº and ∆Sº) show that the adsorption of RR-198 and MO dyes onto MPTA is spontaneous, endothermic and feasible in the temperature range 293-313 K. Also, the magnitude of enthalpy change indicates that the adsorption is physical in nature. References 1 2 3 4 5 6 7 8 9 10 11 12 13 14

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