This article was downloaded by: [Monash University Library]On: 10 March 2014, At: 17:15Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK

Separation Science and TechnologyPublication details, including instructions for authors and subscription information:http://www.tandfonline.com/loi/lsst20

Removal of Methyl Violet Dye from Aqueous Solution bysf Platanus Carpinifolia Tree Leaves as Highly EfficientSorbent: Multivariate Optimization, Isotherm Modeling,and Kinetic StudiesJavad Zolgharnein a , Fateme Gholami a , Neda Asanjarani a , Peyman Zolgharnein b &Gholamhasan Azimi ca Chemistry Department, Faculty of Science , Arak University , Arak , Iranb Textile Engineering Department, Faculty of Science , Islamic Azad University , ArakBranch , Arak , Iranc Central Laboratory , Isfahan University , Isfahan , IranAccepted author version posted online: 13 Nov 2013.Published online: 07 Mar 2014.

To cite this article: Javad Zolgharnein , Fateme Gholami , Neda Asanjarani , Peyman Zolgharnein & Gholamhasan Azimi(2014) Removal of Methyl Violet Dye from Aqueous Solution by sf Platanus Carpinifolia Tree Leaves as Highly Efficient Sorbent:Multivariate Optimization, Isotherm Modeling, and Kinetic Studies, Separation Science and Technology, 49:5, 752-762, DOI:10.1080/01496395.2013.862547

To link to this article: http://dx.doi.org/10.1080/01496395.2013.862547

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) containedin the publications on our platform. However, Taylor & Francis, our agents, and our licensors make norepresentations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of theContent. Any opinions and views expressed in this publication are the opinions and views of the authors, andare not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon andshould be independently verified with primary sources of information. Taylor and Francis shall not be liable forany losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoeveror howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use ofthe Content.

This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in anyform to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

Separation Science and Technology, 49: 752–762, 2014Copyright © Taylor & Francis Group, LLCISSN: 0149-6395 print/1520-5754 onlineDOI: 10.1080/01496395.2013.862547

Removal of Methyl Violet Dye from Aqueous Solution by PlatanusCarpinifolia Tree Leaves as Highly Efficient Sorbent: MultivariateOptimization, Isotherm Modeling, and Kinetic Studies

Javad Zolgharnein,1 Fateme Gholami,1 Neda Asanjarani,1 Peyman Zolgharnein,2 andGholamhasan Azimi31Chemistry Department, Faculty of Science, Arak University, Arak, Iran2Textile Engineering Department, Faculty of Science, Islamic Azad University, Arak Branch, Arak, Iran3Central Laboratory, Isfahan University, Isfahan, Iran

This study introduces a novel and highly efficient biosorbentcalled Platanus Carpinifolia tree leaves to remove Methyl violetfrom aqueous solution. A Box-Behnken design of experimentbased on three main factors (initial concentration (Cd�, sorbentamount (S), and pH) through the response surface methodologyapproach was chosen to model the removal efficiency (R%)of Methyl violet. The optimum conditions were found fromthe obtained model as Cd =500mg/L and S=0.11g/L with nopH significant influences. Langmuir, Freundlich, and Temkinisotherms were applied to scrutinize the equilibrium aspect ofbiosorption by fitting the adsorption experimental data withisotherms. The adsorbent’s maximum capacity uptake (qmax) wasobtained to be 555.5mg/g from the Langmuir model, whichhas shown better description of the equilibrium process. Kineticof biosorption was studied with making use of the pseudo-first order and pseudo-second order models along with intra-particle diffusion. The results showed that the adsorption processbehaves in accordance with the pseudo-second order model,and intraparticle diffusion is not solely the rate-limiting step.Regarding the thermodynamical investigation, �G�, �H�, and�S� respectively, were predicted to be 1.96, 37.34kJ/mol, and132 J/mol. This implies that chemisorption is the predominantportion of adsorption mechanism.

Keywords biosorption; Box-Behnken design; methyl violet;optimization; Platanus Carpinifolia

INTRODUCTIONDyeing is one of the key processes in textile industries,

which offers a wide range of garment designs and impartsbeauty. In this process, decolorization of dyeing bath has to bedone for providing higher efficiency of dyeing and producingthe regular shape of apparels. A substantial part of the above-mentioned process deals with pigments, which are released to

Received 3 April, 2013; accepted 24 October 2013.Address correspondence to J. Zolgharnein, Chemistry Department,

Faculty of Science, Arak University, Arak, 38156-8-8349, Iran. E-mail: J-zolgharnein@araku.ac.ir

Colors versions of one or more of the figures in this article can befound online at www.tandfonline.com/lsst.

the environment after decolorization due to incomplete dyefixing (1, 2). Due to having a synthetic origin and complexchemical compartments of most dyes, they are usually denotedto be highly toxic substances. They raise concerns in practicalinvestigation while they have higher stability upon heatingand oxidation agents along with a complicated biodegradationprocess (3–6). Regardless of complex structures, their residueperverts resources, for instance it reduces the water brightness.It may even happen at low concentration of basic dyes, which itinherently becomes deleterious while microorganism processessuch as photosynthesis are completely disrupted (4).

Methyl violet is a basic dye whose continuing existencein effluent causes a serious impact on the human body (7).Therefore, many efforts have been chemically, physically, orbiologically tried out to reduce its existence in resources.Already several experimental considerations have beenfundamentally carried out on the adsorption process of Methylviolet, such as using agricultural waste (7), granulated wastematerials (8), membranes (9), hydrogels (10), sepiolite (11), flyash (12), chitosan (13), perlite (14,15), and powdered activatedcarbon (16). Despite the encouraging results of these processes,cost effectiveness, and restriction of the adsorption process inlarge scale is predominantly a drawback according to somereports (16,17). Lately research has focused on alternative lowcost, readily preparable and available adsorbents in nature arefound in large scale (2–4,7, 17). Biosorption implementationhas drawn more attention due to the new known breakthroughof sorbent application (especially tree leaves) for removingsome particular contaminations (18–23).

In conventional methods of optimization, evaluation ofeffective parameters in a chemical process takes a long timeand consumes a large scale of reagent to run the experiments.Furthermore, considering the possible interaction betweenvariables and obtaining optimum conditions give benefitsfor inducing the best adsorption capacity. So, multivariateoptimization methodology plays an important role in abiosorption process due to being an efficient and economical

752

Dow

nloa

ded

by [

Mon

ash

Uni

vers

ity L

ibra

ry]

at 1

7:15

10

Mar

ch 2

014

REMOVAL OF METHYL VIOLET DYE 753

technique (18–22,24,25). Simultaneous optimization of severalvariables is the other capability of this method (18–22,24,25).Experimental design methodology based on the number ofvariables and responses in the adsorption system can be derivedfor testing the large number of factors with having just a tinyassortment of observations. The main aim of the current studyis to present the biosorption process for removing the Methylviolet dye from aqueous solution using Platanus Carpinifoliatree leaves as a novel sorbent. Following this, finding the mainfactors that affect on absorption and optimizing the processat the highest adsorption capacity are carried out. Moreover,equilibrium modeling of experimental data, thermodynamic,and kinetic studies of adsorption process are also investigated.

EXPERIMENTALMaterials

The Platanus Carpinifolia tree leaves used in current workwere gathered from local groves. The collected species werewashed by twice-distilled water for several times in orderto eliminate any mud and grime. After proper drying atroom temperature they were ground and sieved to obtain ageometrical range lower than the 60 mesh. Prepared sampleswere finally stored in a firmly isolated washed glass bottle forfuture use.

All chemicals used in this study were of analytical reagentgrade (Merck, Darmstadt, Germany) and were used withoutfurther purification. The Methyl violet dye with generalchemical structure of C24H28N3larCl had a molecular massabout 393.95g/mol and maximum absorbance wavelength(�max� of 586nm. The accurately weighed samples of dyewere used for preparing the solutions by dissolving in distilledwater to give a concentration of 1000mg/L. For optimizationof initial pH of solution the NaOH and HNO3 0.1mol/L wereused in this experiment.

MethodsThe experiment was performed in a batch system by shaking

0.1g of sorbent at 10mL of dye solution (i.e., 100 g/L). Sincethe solubility of Methyl violet in the water is not readilyattainable, a standing allowance of dye solution was takenfor 1–2 days until the absorbance of the solutions becomesconstant.

Studies were conducted at 25�C and samples were shakenat 300 rpm on the vibrator for one hour. The pH domain, theamount of sorbent (S), and initial Methyl violet concentration(Cd� that were taken according to the experimental designmethodology, are shown in Table 1. The samples then werecentrifuged at a high rate (300 rpm) for 2 minutes and thesorbent was separated from the solution. In the end, theresidual concentration of Methyl violet was evaluated byUV-Vis spectrophotometer Cecile 3000 at the wavelength of400–900nm.

TABLE 1Factors and level used in the Box-Behnken design

Factors Low (−1) Center (0) High (+1)

pH 3 5�5 8Dye concentration 500 1500 2500(Cd:mg/L)

Sorbent Concentration 0.02 0�09 0.16(S:mg/g)

For determination of removal percentage of Methyl violet(R%) and adsorption capacity of the sorbent (q) in aqueoussolution, the Eqs. (1) and (2) were used as follows (18):

R% =(Ci − Ce

Ci

)× 100 (1)

where Ci (mg/L) is initial concentration, Cf (mg/L) is the finalconcentration of dye in solution and also:

q = �C0 − Ce�

m× V (2)

where q is the capacity uptake of biosorbent (mg/g), C0 and Ce

are the initial and equilibrium concentrations of dye (mg/L),respectively, V is the volume of the solution (L), and S is theweight of the biomass (g).

Optimization StrategyExperimental design approach was employed to evaluate

the influences of significant factors and obtain the optimumlevel of biosorption conditions of Methyl violet onto PlatanusCarpinifolia tree leaves. Therefore, a Box-Behnken designalong with response surface methodology was used and theresults were analyzed making use of MINITAB 15 as statisticalsoftware.

RESULTS AND DISCUSSIONSEquilibrium Isotherms Studies

For investigation of sorbent-sorbate behavior theexperimental adsorption data through fitting the equilibriumisotherms are generally considered. Three most commonisotherms such as Langmuir, Freundlich, and Temkin wereutilized in the fixed experimental condition for instance, 7.5g/Lof sorbent concentration, 60 minutes contact time (it is a propertime that has been found during primary study), and 3000 rpmof the shaker while the initial dye concentration varied from50 to 3000mg/L (Fig 1). The solution was then centrifugedunder 2000 rpm for 2minutes.

The Langmuir IsothermThe Langmuir isotherm has been predominantly used to

evaluate adsorption processes. The basic assumption in the

Dow

nloa

ded

by [

Mon

ash

Uni

vers

ity L

ibra

ry]

at 1

7:15

10

Mar

ch 2

014

754 J. ZOLGHARNEIN ET AL.

FIG. 1. Equilibrium adsorption capacity of Methyl violet with PlatanusCarpinifolia tree leaves sorbent versus equilibrium concentrati.

current theory is generally that the adsorption process doesnot happen due to the lateral interaction between the sorbedmolecules; instead of that, a monolayer of solute molecules on

the adsorbent surface is the main target to be occupied with dyemolecules. In addition, when the dye molecules are located toindividual sites, adsorption may be suppressed for recent sites.Therefore, the homogenous adsorption may gradually occurin terms of occupying the other sites with left dye molecules(7, 8, 12, 13). The Langmuir model is described by its linearform as the following expression:

Ceq

qeq= 1

bqmax

+ Ceq

qmax

(3)

where qeq (mg/g) and Ceq (mg/L), respectively, are the amountof adsorbed dye per unit mass of sorbent and adsorbed dyeconcentration in solution at equilibrium. The qmax is the greateramount of dye per sorbent’s unit mass to form a completemonolayer on the surface bound at high Ceq , and b is an affinityrelated constant of the binding sites (L/mg). The straight linemay be plotted using Eq. (3) where variation of Ceq /qeq versusCeq gives the slope from 1/qmax and an intercept of 1/(bqmax�.Figure 2a shows the data that are fitted appropriately withthe Langmuir model according to the linear fitting and theestimated parameters are listed in Table 2. The maximumcapacity uptake (qmax�=555.50mg/g and b=0.0085 L/mg hasbeen obtained. For knowing the feasibility of the adsorption

FIG. 2. Equilibrium isotherms for Methyl violet sorption onto Platanus Carpinifolia tree leaves, a) Langmuir, b) Freundlich, c) Temkin.

Dow

nloa

ded

by [

Mon

ash

Uni

vers

ity L

ibra

ry]

at 1

7:15

10

Mar

ch 2

014

REMOVAL OF METHYL VIOLET DYE 755

TABLE 2The Langmuir, Freundlich, and Temkin isotherm models constants for adsorption of Methyl violet onto Platanus Carpinifolia

tree leaves

Langmuir Freundlich Temkin

Isotherm qmax(mg/g) b(L/mg) R2 KF 1/n R2 Kt(L/mg) B R2

Parameters 555.5 0.0085 0.993 49.4 0.319 0.972 1.512 0.0127 0.977

process, a dimensionless constant of the separation factor(RL = 1

�1+bC0�

)is introduced as an important characteristic

of the Langmuir isotherm. The C0 is the maximum initialconcentration of sorbate (mg/L) and b (L/mg) is Langmuirconstant. The parameter RL presents the nature of shape ofisotherms (7,14). When RL is greater than one, the adsorptionis not favorable. However, when its value lies between zeroand one, the adsorption process would be rather favorable.In the mean time, when RL is equal to zero the irreversibleadsorption would happen and the linear trend occurs whenits value takes one. Figure 3 illustrates the results and showsdecreasing the constant separation factor due to increasingthe initial concentration of Methyl violet (10 to 2500mg/L).At the highest level of initial concentration, the value of theseparation factor is significantly low, its corresponding valuehas been found between the range of 0.5 to 4 × 10−4, whichis placed between zero and one (0 < RL < 1). This amountmight be assumed to be zero, which means that the adsorptionprocess was carried out in a favorable manner (7,14).

FIG. 3. The separation factor versus highest initial concentration of Methylviolet.

The Freundlich IsothermThe Freundlich isotherm may be attributed to an adsorption

process, which occurs on heterogeneous surfaces of sorbentas an empirical equation. In addition, the concentration ofthe sorbate (Methyl violet) at equilibrium may dominate theadsorption capacity. This isotherm can be simplified as a linearform of the general expression as follows (7,8,12,13):

ln qeq = lnKF +(1n

)lnCeq (4)

where KF (mg/g) and n can be calculated from the interceptand slope of the linear plot. They are approximate indicatorsof adsorption capacity and adsorption intensity, respectively.Regarding the isotherm shape, favorability of the adsorptionmay also be explained by the magnitude of the exponent,1/n. Values of Kf and 1/n were found to be 49.4 and 0.39,respectively. An adsorption is usually favorable when the valueof 1/n is between zero and one. The obtained results from theFreundlich isotherm (Eq. 4) are shown in Fig. 2b and the linearregression correlation (R2 =0.972) is given in Table 2.

The Temkin IsothermIn adsorption, the heat of process of all molecules in the

layer would decrease linearly with coverage. It is attributedto some indirect sorbate-sorbent interactions on adsorptionisotherms. This phenomenon was presented and suggested byTemkin and Pyzhev and may be re-written in linear form:

qe = B lnKt + B lnCe (5)

where b is the Temkin constant associated with the heat ofsorption (J/mol); Kf is the Temkin isotherm constant (L/g), Ris the gas constant (8.31 J/mol K), T is the absolute temperature(K), and B is the constant term (RT/bt� in Eq. (5). As aresult of plotting qeversus ln C0 that is shown in Fig. 2c,the constants are attainable from the slope and intercept ofthe linear variations. The constants Kt and B with the R2

values are listed in Table 2, and their value was found tobe 1.512 (L/mg) and 0.0127, respectively. Table 2 collectsthe results of the isotherm constants for each one of theabove-mentioned equilibrium isotherms. With evaluating thecoefficient of determination (R2�, the Langmuir isotherm hasshown reasonably better fitting with the equilibrium adsorptiondata (R2 =0.993) in comparison with other isotherms. Fitted

Dow

nloa

ded

by [

Mon

ash

Uni

vers

ity L

ibra

ry]

at 1

7:15

10

Mar

ch 2

014

756 J. ZOLGHARNEIN ET AL.

values from the Langmuir isotherm comply firmly with theresults from the literature for adsorption of Methyl violet ontoMansonia wood sawdust (3), bagasse fly ash (12), perlite (14),and Basic violet 1 and 10 onto sugarcane dust (30). Owing tothis fact that the Langmuir isotherm assumes the homogenousadsorption happens in the surface of the sorbent, the recentobtained proper correlation may be justified. Experimental datawere also fitted with Freundlich and Temkin isotherms withcoefficients of determination in range of R2 = 0�97.

Table 3 compares the capacities uptake (qmax� from variousadsorbents utilized for removal of Methyl violet with currentwork. The value of (qmax� in this study is remarkably largerthan that obtained from previous works (3,7,11,12,31–33).

Multivariate Optimization StrategyIn order to find out the effective factors on the biosorption

process, main variables that in the previous study were foundas dominant are being considered in the current study (18–25).Acidity of medium (pH), the initial concentration of Methylviolet (Cd�, and biosorbent dosage (S) are defined as themain variables and their influences on the removal percentage(R%) and capacity of sorbent (q) were evaluated. In theadsorption process other variables such as speed of agitationand temperature, respectively, were kept identical at 300 rpmand 25�C throughout the experiment. A Box-Behnken designwith three factors was recruited to investigate the effectivefactors and their interactions. Table 1 presents the amounts ofthree selected factors along with their values in the adsorptionprocess. The number of experiments (N) required for runningof Box-Behnken design is N=2k (k− 1)+C0. The k denotesthe number of factors and C0 is the number of center points.Fifteen trials were performed at a block in three replicationsfor center point. The design was conducted at random orderto evaluate pure error of the method and minimize the effectof possible uncontrolled variable(s), respectively. One of themain advantages of the Box-Behnken design matrix is thatit does not contain combinations for which all factors are

simultaneously at their highest or lowest levels. Therefore, thisdesign is useful to avoid experiments performed under extremeconditions (26–28, 34). Factors were coded as −1 (low), 0(center point), and +1 (high). The results are listed in Table 4with coded and real values, removal percentage (R%), andmaximum adsorption capacity q (mg/g).

The main effects and interactions were consideredaccording to the statistical tests. Regression coefficientsand their significance for the response of Box-Behnken aresummarized in Table 5. When the influence of a factor ispositive, the removal efficiency increases with a changingfactor from lower to higher level. However, if the effectsare negative, a reduction in removal efficiency occurs for thehigher level of the same factor. According to the obtainedresults the initial concentration of Methyl violet (Cd�, andbiosorbent dosage (S) were found as significant factors at5% level (P<0.05) from the regression analysis (Table 5).The acidity of the medium (pH) does not play a significantrole in the adsorption process. In addition, the interactioneffect of biosorbent dosage (m) was also found to be aneffective parameter. Figures 4a and 4b show the main andinteraction effects of the factors on the biosorption of Methylviolet onto Platanus Carpinifolia tree leaves. It is depictedfrom Fig. 4a that effect of the amount of sorbent (S) is muchhigher throughout the biosorption process on the removalefficiency of Methyl violet. This higher influence could beattributed to the increasing of available adsorption sites, whichremained unsaturated during the removal process (18). Thus,the removal process of Methyl violet may be dominated by theamount of sorbent (S) rather than other factors such as initialconcentration of dye (Cd� or acidity of the medium (pH). Sincethe Methyl violet is bulky cationic dye, with increasing pHthe competition between protons and dye for same functionalgroups decreases (18,28). As an expectation, with increasingthe initial concentration of dye the adsorption rate would behindered. It is revealed properly in the same figure that theamount of adsorption was drastically decreased with usinghigher concentration of Methyl violet. These variations can

TABLE 3Comparison of sorption capacities of various adsorbents for and Methyl violet

Adsorbent Dye qmax(mg/g) Reference

Platanus Carpinifolia tree leaves Methyl violet 555.5 This workCrosslinked amphoteric starch Methyl violet 333.33 �31�Sunflower seed hull Basic violet 1 92.59 �7�Sugarcane dust Basic violet 1 50.40 �30�Bagasse fly ash Methyl violet 26.25 �12�Mansonia Sawdust Methyl violet 16.11 �3�Sugarcane dust Basic violet 10 13.90 �30�Cellulose-based wastes Methyl violet 11.50 �32�Sepiolite Methyl violet 2.60 �33�Sepiolite Methyl violet 2.33 �11�

Dow

nloa

ded

by [

Mon

ash

Uni

vers

ity L

ibra

ry]

at 1

7:15

10

Mar

ch 2

014

REMOVAL OF METHYL VIOLET DYE 757

TABLE 4Box-Behnken response surface design and results obtained for Methyl violet onto Platanus

Carpinifolia

Coded values Real values

Experiment pH S Cd pH S Cd R%

1 0 0 0 5.5 0.09 1500 78.002 −1 1 0 3.0 0.16 1500 98.303 1 −1 0 8.0 0.02 1500 37.904 −1 −1 0 3.0 0.02 1500 55.005 0 0 0 5.5 0.09 1500 77.356 0 1 −1 5.5 0.16 500 98.867 1 0 −1 8.0 0.09 500 97.408 −1 0 −1 3.0 0.09 500 97.569 −1 0 1 3.0 0.09 2500 63.2010 1 1 0 8.0 0.16 1500 97.2011 1 0 1 8.0 0.09 2500 72.0012 0 −1 1 5.5 0.02 2500 35.0013 0 −1 −1 5.5 0.02 500 60.7514 0 0 0 5.5 0.09 1500 76.3415 0 1 1 5.5 0.16 2500 90.14

TABLE 5Statistical parameters for Box-Behnken design

Term Coef SE Coef T P

Constant 77�23 3�487 22�15 0.000pH −1�194 2�135 −0�559 0.600S 24�476 2�135 11�463 0.000Cd −11�78 2�135 −5�517 0.003pH×pH 3�102 3�143 0�987 0.369S×S −8�243 3�143 −2�633 0.047Cd×Cd 2�2 3�143 0�7 0.515S×pH 4 3�02 1�325 0.243Cd×pH 2�247 3�02 0�744 0.490Cd×S 4�258 3�02 1�41 0.218

be related to the saturation of all adsorption sites due to thehigher initial concentration of dye. The presence of interactionmeans that factors may influence on the response factor (R%)interactively but not in an independent way (Fig 4b). Theircombined effect might be greater or less than that expected forthe straight addition of the effects (35,36). These synergisticeffects would not be detected in a univariate optimizationof the system (24, 25). Figure. 4b illustrates that there is noconsiderable interaction between the factors, especially wherethe pH is one of the members of this interaction. However,for unparallel effect, lines of interaction for S ×Cd illustratethat there is rather a strong two-way interaction betweeninitial concentration of dye (Cd� and amount of sorbent (S).

Meanwhile the interaction of pH with S and Cd is relativelyweak, because the effect lines are nearly parallel. It can alsobe concluded that when initial concentration of dye is low,increasing the sorbent mass has a greater effect and the removalpercentage is relatively high.

Finding Model and Determining Optimal ConditionThe initial concentration of dye (Cd� and amount of

sorbent(S) were determined as effective factors, optimizationof which has to be carried out for obtaining the bestcondition to have higher removal efficiency of Methyl violetfrom aqueous solution. According to the response surfacemethodology the optimization of these factors is carried out.The multiple regression analysis on the resultant responsesled to the following second-order polynomial equation, whichexplains the relation between the removal efficiency andeffective parameters as well as interactions:

R= 52�209+ 666�36S − 0�01178Cd − 1759�44S2 (6)

where R is the predicted value of the removal percentage,S and Cd are values of the amount of sorbent and initialconcentration of sorbent, respectively. The adequacy of themodel was checked using the analysis of variances (ANOVA)which was tested using Fisher’s statistical analysis; the resultsare shown in Table 6. The F value of 56.61 implies that themodel is significant. There was no chance that the F valuecould occur due to noise because the P-value of the modelwas <0.0001, which also confirms the high significance ofthe model. The results obtained by the analysis of variance

Dow

nloa

ded

by [

Mon

ash

Uni

vers

ity L

ibra

ry]

at 1

7:15

10

Mar

ch 2

014

758 J. ZOLGHARNEIN ET AL.

FIG. 4. Main effects (a) and Interaction effects (b) plots for removalefficiency (R%) of Methyl violet onto Platanus Carpinifolia tree leaves.

show that the P-value for lack-of-fit (0.353) is not significant(P>0.05) either and regression is completely meaningful

(Table 6). The coefficient of determination (R2� was reportedfor evaluating the goodness-of-fit for this model. In thiscase, fitting of experimental data with suggested model(Eq. 6) was very good (R2 =93.9%) and only (6.1%) oftotal variance has not been explained by the model. Thehigh value of adjusted regression coefficient (R2 =92.3%) alsoindicates high significance of the proposed model. This meansthat the regression model provided an excellent explanationof the relationship between the independent variables andresponse (removal efficiency). Investigation of residuals maygive useful information about adequacy of the model andclarifying whether further statistical procedure is required.It was evaluated according to the Anderson-Darling test asa powerful statistical analysis, which generates a normalprobability plot and performs a hypothesis test to examinewhether the observations follow a normal distribution. Theresult obtained for residuals is shown in Fig. 5. The Pvalue (0.675>0.05) shows that residuals followed the normaldistribution. Meanwhile the model adequacy was justifiedusing the examination of the residuals versus fitted values.With plotting the standardized residuals versus the predictedvalues the possible existence of outliers, which is not shownhere, are illustrated. If a point lies far from the majority ofpoints, it may be an outlier. It is important to identify theoutliers, because they can have a significant influence on themodel, providing potentially misleading or incorrect results.The response surface was also drawn as three-dimensionalplots of two factors while the others were kept constant(at the center point). The response surface plot shown inFig. 6 clearly indicates the influence of significant factorsand their interactions on the removal efficiency (R%). Theoptimal conditions according to RSM were estimated to beCd =500mg/L and S=0.11g/L.

Temperature Effect and Thermodynamical ParametersConsidering the temperature effects and thermodynamical

aspects as important parameters for efficiency of everyadsorption process can give beneficial information. In thisstudy, the biosorption process was carried out at four

TABLE 6Analysis of variance for suggested second-order model

Source DF Seq SS Adj SS Adj MS P F

Regression 3 6180�33 6180�33 2060�11 56�61 0.000Linear 2 5902�14 5902�14 2951�42 81�10 0.000Square 1 277�48 277�48 277�48 7�63 0.019Residual Error 11 400�30 400�30 36�39 — —Lack-of-Fit 5 213�18 213�18 42�64 1�37 0.353Pure Error 6 187�12 187�12 31�19 — —Total 14 6580�63 — — — —

*DF: degree of freedom, Seq SS: sum of square. Adj SS: adjusted sum of square.Adj MS: adjusted mean square.

Dow

nloa

ded

by [

Mon

ash

Uni

vers

ity L

ibra

ry]

at 1

7:15

10

Mar

ch 2

014

REMOVAL OF METHYL VIOLET DYE 759

FIG. 5. Normal probability plot for residuals through running BBD.

steps of temperature from 25, 35, 45, and 55�C. Theinitial dye concentration was adjusted to 2000mg/L inthe pH=3, 7.5g/L of sorbent and 60 minutes of contacttime. Due to the increasing of temperature around 20�Cin the biosorption process of methyl violet onto PlatanusCarpinifolia, the adsorption rate is considerably changedaround 25%. However, further substantial promotion inadsorption did not take place after increasing the temperaturefrom 45�C to 55�C.

The thermodynamic investigations are usually ascertainedfor understanding the behavior of biosorption process andwhether it occurs spontaneously. The basic criterion for this

FIG. 6. Response surface plot for removal efficiency(R%) of Methyl violetonto Platanus Carpinifolia tree leaves.

evaluation may be expressed by Gibbs free energy change,�G�. The negative value of the variation related to this criterionjustifies that the process is led by a spontaneous manner.The following expression is defined for the biosorptionprocess, which can be presented as a reversible process andheterogeneous equilibrium (19).

K′c =

Cad�eq

Ceq

(7)

where K′c is the apparent equilibrium constant of the

biosorption, Cad�eq is the dye concentration on the adsorbent atequilibrium, and Ceq is the dye equilibrium concentration inthe solution. The value of this apparent constant can be givenwhere the Gibbs free energy (�G�� is being determined usingthe equation below for the biosorption process (12):

�G� = − RT lnK ′c (8)

The Van’t Hoff equation (�G� = �H�–T�S�� is usedto determine the other thermodynamic parameters such asenthalpy (�H�� and entropy (�S�� from the slope and interceptof the �G� versus T . In these equations, �G� is standardfree energy change (J), R is the universal gas constant (8.314J/mol K), and T is the absolute temperature (K). The ultimateapparent equilibrium constant could be derived as (12):

lnKc =�H�

RT+ �So

R(9)

In the recent expression, the thermodynamic parameters ofthe biosorption process are calculated by plotting the ln Kc

versus 1/T. As shown in Fig. 7 the plot of Ln Kc as a function

FIG. 7. van’t Hoff plot for the adsorption of Methyl violet onto PlatanusCarpinifolia tree leaves.

Dow

nloa

ded

by [

Mon

ash

Uni

vers

ity L

ibra

ry]

at 1

7:15

10

Mar

ch 2

014

760 J. ZOLGHARNEIN ET AL.

TABLE 7Thermodynamic parameters of Methyl violet adsorption

T(�C) �G� (kJ/mol) �H� (kJ/mol) �S� (J/mol)

25 −1�96 37.34 13235 −3�6345 −4�9555 −6�27

of 103/T is a straight line. The values of �G� at differenttemperatures 300–330 K as well as the values of �H� and �S�

acquired from the slope and intercept of the plot are listed inTable 7.

According to the Table 7, the value for Gibbs free energy(�G�)is negative, which shows the biosorption process wascarried out spontaneously. Also, from the enthalpy of thereaction, the magnification of its value describes that thebiosorption was run either as chemical or physical process.Generally, the value of enthalpy for physical adsorption is lessthan 4.184kJ/mol, but for chemical adsorption, the value isgreater than 20.93kJ/mol (3, 7, 8, 12). As a result, the valueof enthalpy (Table 7) is much larger than 20.93kJ mol−1

and it seems that the biosorption process of Methyl violet(37.34kJmol−1) was chemically performed.

Kinetics of AdsorptionThe kinetic of adsorption indicates information concerning

the controlling mechanism of the process such as mass transfer,diffusion control, and chemical reaction.

The pseudo-first-order, pseudo-second-order, andintraparticle diffusion were employed to elucidate themechanism of biosorption of Methyl violet (11, 29, 30).

Pseudo-First-Order ModelOne of the simplest kinetic models is the pseudo-first-order

or Lagergren model (11,29,30,37). The transient behavior ofdye sorption process with following this kinetic model can beintroduced by the linear form below:

ln�qe − qt� = ln qe − K1t (10)

where qt and qe represent, respectively, the amount of dyeadsorbed (mg/g) at any time t and at equilibrium time. K1 isthe sorption rate constant (1/min). Therefore, the rate constantcan be obtained by plotting ln (qe−qt� versus time t as a lineartrend. Fig. 8a shows the variation of ln (qe−qt� versus time t inorder to evaluate the kinetic parameters of adsorption processof Methyl violet onto Platanus Carpinifolia tree leaves.

Pseudo-Second-Order ModelThe other straightforward model, which has been

extensively used for describing the kinetic analysis of the

FIG. 8. Kinetic of adsorption for Methyl violet onto Platanus Carpinifoliatree leaves at 25�C a) Pseudo-first-order, b) Pseudo-second-order.

adsorption process, is generally called pseudo-second-order.It is usually based on the solid phase’s biosorption capacity.The linear form of the equation is described in the followingexpression (11,29,30):

t

qt= 1

K2q2e

+ t

qe(11)

where K2 is the sorption rate constant (g/mg min), qe is theamount of dye adsorbed at equilibrium (mg/g), and qt isthe amount of dye adsorbed at time t (mg/g). The essentialassumption of this model is that one metal ion is adsorbed ontotwo surface sites, as indicated by the following equation (20):

2S�Solid� + dyeaqueous → S2dye�adsorbed phase� (12)

where S is the biosorbent site. The plotting qt against t givesthe slope and intercept for obtaining the rate parameters,K2 and qe. Figure 8b illustrates the linear plot of theequation (11). The rate parameter constants, predicted qe,and R2 were calculated from the slope and intercept of thelinear curve fitting that are: K1 =0.022; K2= 0.054, R2

1 =0.790;R2

2= 0.999, qe1 =1.7 (mg/g); qe2= 49.5(mg/g). As a result,the second-order model shows complete linear fitting withperfect coefficient of determination (R2 =0.999). It meansthat the experimental data were impeccably laid throughthe linear equation. It is also revealed that the estimatedqe was observed to be quite similar to the experimentalqexp�e = 49�5 (mg/g). According to this observation, the pseudo-second-order model represented the adsorption kinetics andrecommended that the overall rate of the Methyl violetadsorption process can be dominated by chemical process.The rate constant of adsorption from the second-order model(K2 = 0�055) was found to be much higher than that from thefirst-order, which may be introduced as a beneficial adsorptionprocess in terms of the time of mechanism. Figure 8a showsthe adsorption kinetic data did not fit properly with thepseudo-first-order model (R2 = 0�79). It may also be indicatedthat the amount of the experimental equilibrium capacityuptake qexp�e through the pseudo-second model (49.5mg/g) hasconsiderable deviation with the amount which was estimatedby the pseudo-first-order model (1.7mg/g). A comparison of

Dow

nloa

ded

by [

Mon

ash

Uni

vers

ity L

ibra

ry]

at 1

7:15

10

Mar

ch 2

014

REMOVAL OF METHYL VIOLET DYE 761

kinetic studies for adsorption of Methyl violet onto differentbiosorbents such as: Sunflower seed hull (6), Sepiolite (11),Bagasse fly ash (12), Perlite (15), Organomminral sorbent-iron humate (38),Manosonia wood sawdust (39), and PlatanusCarpinifolia tree leaves (current study) shows good kineticbehavior via the second-order model.

Intra-Particle Diffusion ModelingSince the pseudo-first-order and pseudo-second-order

models are not able to identify the diffusion mechanism, theintraparticle diffusion concept may give the different kindof insight about the adsorption process. It is based on thesorbate mass transfer through the sorbent structure related tothe thickness of the layer’s boundaries. This process has beenmodeled by an empirical expression such as the Weber-Morrisplot which is drawn as Fig. 9 according to the expressionbelow (40–43):

qt = Kidt1/2 + C (13)

where Kid is the intra-particle diffusion rate constant, qt isthe amount of dye adsorbed (mg/g) at time t (sec) and C asintercept. The effect of the boundary layer’s thickness maybe described from the intercept of the above expression (42,43). Due to the greater boundary layers, the intercept generallyattains the higher value (40).

Three general steps could usually take place duringintraparticle diffusion according to the basic definitionfor biosorption mechanism (8,12,15,39,41–43). It is veryimportant to understand which one is the rate-controlling step.The first step attributes to the particles that are surrounded bythe external boundary layer of liquid and the mass transfermay occur amongst the macropore. The next step, which

FIG. 9. Intraparticle diffusion of Methyl violet onto Platanus Carpinifoliatree leaves.

may happen instantaneously, is related to the sorption of theparticles at a site on the surface (42,43). The last part of processtakes place in order to diffuse the sorbate molecules into asorption site as a micro-pore (41). In Fig. 9, the first step, whichis due to mass transfer, happens so fast that it could not bereadily monitored and is not shown in this figure. The secondand third steps are presented and it is clearly found that the plotof intraparticle diffusion did not pass the origin and it meansthis step is not the only rate-controlling for the biosorption ofMethyl violet onto Platanus Carpinifolia (42,43).

Adsorption of Methyl Violet MechanismBiosorption mechanism can be explained by considering

different kinds of chemical and physical interactions among thefunctional groups present on the biosorbent and sorbate (heavymetal, dye, etc.) in solution (7,19,21,22). Due to the complexityof structure and behavior of the biosorbent, biosorptionmay not necessarily consist of a single mechanism (44). Inmany sorption processes, mechanisms could take place aschemisorption and physisorption. Therefore, proposing themechanism of adsorption of Methyl violet onto biosorbent isnot simply possible (44). However, according to the resultsobtained in this study the chemisorption has a predominantportion on the adsorption mechanism. This observation canbe justified with the following argument; the better fittingof experimental data to the Langmuir isotherm (R2 = 0�993),which could be an indication of chemical coverage of sorbentaccompanied with proper enthalpy of chemical loading (37.34>20.93kJ/mol), and better description of kinetic data bypseudo-second order model (R2 = 0�999).

Effect of Salt Concentration on Biosorption ProcessThe influence of four different kinds of salts such as NaNO3,

Mg (NO3�2, Ca(No3�2, and KNO3 on the biosorption wasinvestigated. No significant interference on the removal ofMethyl violet has been observed in the presence of the above-mentioned salts.

CONCLUSIONThe Platanus Carpinifolia tree leaves were appropriately

employed to remove the Methyl violet (2B) as a basic dyefrom aqueous solution. A Box-Behnken design with threefactors and the Response Surface Methodology were appliedto consider the removal efficiency of Methyl violet. Theoptimal conditions according to RSM were estimated andthe maximum absorption capacity of the sorbent was foundaccording to the Langmuir adsorption isotherm, which wasconsiderably comparable with the literature. It is also reportedfrom kinetic and equilibrium studies that the adsorption processis performed predominantly as chemisorption rather thanphysisorption and the process is thermodynamically favorable.Ultimately, based on the studies it comes to a conclusionthat Platanus Carpinifolia tree leaves are quite appropriatesubstances as highly efficient biosorbent for removing theMethyl violet dye from aqueous solutions.

Dow

nloa

ded

by [

Mon

ash

Uni

vers

ity L

ibra

ry]

at 1

7:15

10

Mar

ch 2

014

762 J. ZOLGHARNEIN ET AL.

REFERENCES1. Guaratini, C.C.I., Zanoni, M.V.B. (2000) Textile dyes. Quim Nova.

23(1):71–78.2. Pearce, C.I., Lioyd, J.R., Guthrie, J.T. (2003) The removal of color from

textile wastewater using whole bacterial cells: A review. Dyes Pigm., 58:179–196.

3. Ofomaja, A.E., Ho, Y.S. (2008) Effect of temperature and pH on methylviolet biosorption by Mansonia wood sawdust. Bioresour. Technol., 99:5411–5417.

4. Aksu, Z. (2005) Application of biosorption for the removal of organicpollutants: A review. Process Biochem., 40: 997–1026.

5. Sun, Q., Yang, L. (2003) The adsorption of basic dyes from aqueoussolution on modified peat-resin particle. Water Res., 37: 1535–1544.

6. Fu, Y., Viraraghavan, T. (2001) Fungal decolorization of wastewaters: Areview. Bioresour. Technol., 79: 251–262.

7. Hameed, B.H. (2008) Equilibrium and kinetic studies of methyl violetsorption by agricultural waste J. Hazard. Mater., 154: 204–212.

8. Mittal, A., Gajbe, V., Mittal, J. (2008) Removal and recovery of hazardoustriphenylmethane dye, Methyl Violet through adsorption over granulatedwaste materials J. Hazard. Mater., 150: 364–375.

9. Wu, J.-S., Liu, C.-H., Chu, K.-H., Suen, S.-Y. (2008) Removal ofcationic dye methyl violet 2B from water by cation exchange membranesJ. Membr. Sci., 309: 239–245.

10. Olpan, D.S., Kolge, Z. (2006) Adsorption of methyl violet in aqueoussolutions by poly (Nvinylpyrrolidone- co-methacrylic acid) hydrogelsRadiat. Phys. Chem., 75: 120–128.

11. Dogan, M., Ozdemir, Y., Alkan, M. (2007) Adsorption kinetics andmechanism of cationic methyl violet and methylene blue dyes ontoSepiolite Dyes Pigm., 75: 701–713.

12. Mall, I.D., Srivastava, V.C., Agarwal, N.K. (2006) Removal of Orange-Gand Methyl Violet dyes by adsorption onto bagasse fly ash-kinetic studyand equilibrium isotherm analyses Dyes Pigm., 69: 210–223.

13. Crini, G., Badot, P.-M. (2008) Application of chitosan, a naturalaminopolysaccharide, for dye removal from aqueous solutions byadsorption processes using batch studies: A review of recent literatureProg. Polym. Sci., 33: 399–477.

14. Dogan, M., Alkan, M. (2003) Removal of methyl violet from aqueoussolution by perlite J. Colloid Interf. Sci., 267: 32–41.

15. Dogan, M., Alkan, M. (2003) Adsorption kinetics of methyl violet ontoperlite Chemosphere, 50: 517–528.

16. Dai, M. (1998) Mechanism of adsorption for dyes on activated carbonJ. Colloid Interface. Sci., 198: 6–10.

17. Forgacs, E., Ceshati, T., Oros, G. (2004) Removal of synthetic dyes fromwaste waters: A review. Environ. Inter., 30: 953–971.

18. Zolgharnein, J. Adhami, Zh. Shahmoradi, A., Mmousavi, S.N. (2010)Optimization of removal of methylene blue byPlatanus tree leaves usingresponse surface methodology. Anal. Sci., 26 (1): 111–116.

19. Zolgharnein, J., Asanjarani, N., Mmousavi, S.N. (2011) Optimizationand Characterization of Tl(I) Adsorption onto modified Ulmuscarpinifolia tree leaves. CLEAN-Soil. Air. Water, 39(3): 250–258.

20. Zolgharnein, J., Shahmoradi, A. (2010) Adsorption of Cr(VI)onto Elaeagnus Tree leaves: Statistical optimization, equilibriummodeling, and kinetic studies. J. Chem. Eng. Data., 55(9): 3428–3437.

21. Zolgharnein, J., Shahmoradi, A., Sangi, M.R. (2008) Optimization ofPb(II) biosorption by Robinia tree leaves using statistical design ofexperiments.Talanta, 76(3): 528–532.

22. Zolgharnein, J., Shahmoradi, A. (2010) Characterization of sorptionisotherms, kinetic models, and multivariate approach for optimization ofHg(II) adsorption onto Fraxinus tree leaves. J. Chem. Eng. Data., 55(11):5040–5049.

23. Sangi, M.R., Shahmoradi, A., Zolgharnein, J., Azimi, Gh. H.Ghorbandoost, M. (2008) Removal and recovery of heavy metals fromaqueous solution using Ulmus carpinifolia and Fraxinus excelsior treeleaves. J. Hazard. Mater., 155(3): 513–522.

24. Massart, D.L., Vandeginste, B.G.M., Buydens, L.M.C., de Jong, S.,Lewi, P.J., Smeyers-Verbeke, J. (2003) Handbook of Chemometrics andQualimetrics, Part A; Elsevier: Amsterdam.

25. Montgomery, D.C. (2001) Design and Analysis of Experiments, 5th ed.;Wiley: New York.

26. Ferreira, S.L.C., Bruns, R.E., Ferreira, H.S., Matos, G.D., David, J.M.,Brandao, G.C., da Silva, E.G.P., Portugal, L.A., dos Reis, P.S., Souza,A.S., dos Santos, W.N.L. (2007) Box-Behnken design: An alternative forthe optimization of analytical methods. Anal. Chim. Acta., 597: 179–186.

27. Souza, S.A., dos Santos, W.N.L., Ferreira, L.C.S. (2005) Application ofBox-Behnken design in the optimization of an on-line pre -concentrationsystem using knotte reactor for cadmium determination by flame atomicabsorption spectrometry. Spectrochim. Acta, Part B., 60: 737–742.

28. Cristovao, R.O., Tavaresa, A.P.M., Loureiroa, J.M., Boaventuraa, R.A.R., Macedoa, E.A. (2008) Optimization of reactive dye degradationby laccase using box-behnken design.Environm. Technol., 29(12):1357–1364.

29. Ho, Y.S., McKay, G. (1998) Sorption of dye from aqueous solution bypeat, Chem. Eng. J., 70: 115–124.

30. Ho, Y., Chiu, W., Wang, Ch. (2005) Regression analysis for the sorptionisotherms of basic dyes on sugarcane dust, Bioresour. Technol., 96:1285–1291.

31. Xua, S., Wang, J., Wu, R., Wang, J., Li, H. (2006) Adsorption behaviorsof acid and basic dyes on crosslinked amphoteric starch. Chem. Eng. J.,117: 161–167.

32. Annadurai, G., Juang, R., Lee, D. (2002) Use of cellulose-based wastesfor adsorption of dyes from aqueous solutions. J. Hazard. Mater., B92:263–274.

33. Ozdemir, Y., Dogan, M., Alkan, M. (2006) Adsorption of cationic dyesfrom aqueous solutions by sepiolite. Micropor. Mesopor. Mater. 96:419–427.

34. Macedo, S.M., de Jesus, R.M., Garcia, K.S., Hatge, V., Queiroz,A.F.D.,Ferreira, S.L.C. (2009) Determination of total arsenic and arsenic(III) in phosphate fertilizers and phosphate rocks by HG-AAS aftermultivariate optimization based on Box-Behnken design. Talanta, 80:974–979.

35. Anderson, R.L. (1978)Practical Statistics for Analytical Chemists; VanNostrand Reinhold: New York.

36. Miller, J.N., Miller, J.C. (2000)Statistics and Chemometrics for AnalyticalChemistry, 4th ed.; Dorset Press: Dorchester.

37. Lagergren, S. (1898) About the theory of so-called adsorption of solublesubstances. Kungliga Svenska Vetenskapsakademiens Handlingar, 24 (4):1–39.

38. Janos, P., Smidova, V. (2005) Effect of surfactants on the adsorptiveremoval of basic dyes from water using an organomineral sorbent-ironhumate. J. Colloid Interface Sci., 291: 19–27.

39. Ofomaja, A.E. (2008) Kinetic study and sorption mechanism of methyleneblue and methyl violet onto mansonia (Mansonia altissima) wood sawdust.Chem. Eng. J., 143: 85–95.

40. Weber, Jr. W.J., Morris, J.C. (1963) Kinetics of adsorption on carbonfrom solution. J. Sanit. Eng. Div. ASCE., 89(SA2): 31–59.

41. Vaghetti, J.C.P., Lima, E.C., Royer, Betina., Cardoso, Natali F., Martins,B., Calvete, T. (2009) Pecan nutshell as biosorbent to remove toxic metalsfrom aqueous solution Sep. Sci. Technol, 44: 615–644.

42. Wang, L., Zhang, J., Zhao, R., Li, Y., Li, C., Zhang, C. (2010) Adsorptionof Pb(II) on activated carbon prepared from Polygonum orientale Linn.:Kinetics, isotherms, pH, and ionic strength studies Bioresour. Technol.,101: 5808–5814

43. Zhang, J., Li, Y., Zhang, C., Jing,Y. (2008) Adsorption of malachitegreen from aqueous solution onto carbon prepared from Arundo donaxroot J. Hazard. Mater., 150: 774–782.

44. Macfie, S.M., Welbourn, P.M. (2000) The cell wall as a barrier to uptakeof metal ions in the unicellular green alga Chlamydomonas reinhardtii(Chloro- phyceae). Arch. Environ. Contam. Toxicol., 39: 413–419.

Dow

nloa

ded

by [

Mon

ash

Uni

vers

ity L

ibra

ry]

at 1

7:15

10

Mar

ch 2

014