A Novel Pretreatment Method of Lignocellulosic Material

A Novel Pretreatment Method of Lignocellulosic Materialas Adsorbent and Kinetic Study of Dye Waste Adsorption

Ling Wei Low & Tjoon Tow Teng & Anees Ahmad &

Norhashimah Morad & Yee Shian Wong

Received: 8 June 2010 /Accepted: 23 September 2010 /Published online: 9 October 2010# Springer Science+Business Media B.V. 2010

Abstract Sulphuric acid-modified bagasse has beenused as low-cost adsorbent for the removal of methyleneblue (MB) dye from aqueous solution. In order toremove organic compounds that contribute to chemicaloxygen demand (COD), pretreatment with thoroughwashing of adsorbent using boiling distilled water wasperformed instead of conventional washing usingdistilled water at room temperature only. This hasresulted in the highest efficiency of color removal of99.45% and COD reduction of 99.36% for MB dyesolution at pH 9. Effects of initial pH, dye concentration,adsorbent dosage, temperature, and contact time havebeen studied. The adsorption of MB dye was pHdependent. Langmuir and Freundlich isotherm modelswere tested on the adsorption data. The kineticexperimental data were analyzed using pseudo-firstorder, pseudo-second order, and the intraparticle diffu-sion model in order to examine the adsorption mecha-nisms. The adsorption process followed the Langmuirisotherm as well as the Freundlich isotherm and pseudo-second-order kinetic model. The process was found tobe endothermic in nature.

Keywords Bagasse . Chemical oxygen demand .

Isotherm . Kinetics . Thermodynamics

1 Introduction

Dyes can be classified as anionic (direct, acid, andreactive dyes), cationic (basic dyes), and non-ionic(disperse dyes) (Mall et al. 2006). The increased use ofsynthetic dyes in process industries, such as the textile,the leather, the printing, and the plastic industry hasresulted in generation of effluents that contain highlytoxic and carcinogenic compounds (Hameed et al.2008). Discharge of dyes into water resources not onlyaffect aesthetic nature but also destroys aquatic life dueto strong color, high chemical oxygen demand (COD)and total organic carbon (TOC) (Wang et al. 2008).The highest rates of toxicity were found among basicand diazo direct dyes (Robinson et al. 2001).

Methylene blue (MB) is an important basic dye,which is widely used in textile industries to dye cottonand silk (Muthuraman et al. 2009). MB can causepermanent injury to the eyes of humans and animals,irritation to the gastrointestinal tract with symptoms ofnausea, vomiting, and diarrhea. MB will also causemethemoglobinemia, cyanosis, dyspnea, convulsions,and tachycardia. Contact of MB with the skin causesirritation (Hamdaoui and Chiha 2007).

In the past few decades, physical, chemical, andbiological treatments have been used for theremoval of dyes from the aqueous solutions, suchas coagulation–flocculation (Tan et al. 2000), Fenton

Water Air Soil Pollut (2011) 218:293–306DOI 10.1007/s11270-010-0642-3

L. W. Low : T. T. Teng (*) :A. Ahmad :N. MoradSchool of Industrial Technology, Universiti Sains Malaysia,11800 Penang, Malaysiae-mail: [email protected]

Y. S. WongSchool of Environmental Engineering,Universiti Malaysia Perlis,Kompleks Pusat Pengajian Jejawi 3,02600 Arau, Perlis, Malaysia

process (Behnajady et al. 2007), electrochemicaldegradation (Fan et al. 2008), and advance oxidationprocess (Lim et al. 2009). The adsorption process usingactivated carbon is one of the most effective andwidely used techniques in decolorizing different typesof coloring materials (Crini 2006). This process is awell-known equilibrium separation process which iseffective in removing suspended solids, odors, organicmatter, and oil from aqueous solutions. However, theusage of activated carbon has been limited due to highcost. Therefore, a number of inexpensive alternativeadsorbents from available materials, biosorbent, andwaste materials from industry and agriculture, such aspeanut hull (Gong et al. 2005), mansonia woodsawdust (Ofomaja 2008), Indian rosewood (Garg etal. 2004b), apple pomace, and wheat straw (Robinsonet al. 2002) are being used as adsorbents for dyesremoval from aqueous solutions.

In the present study, an agro-lignocellulosic mate-rial (bagasse) was modified with sulphuric acid to beused as adsorbent for the removal of MB dye from theaqueous solution. Bagasse consists mainly of threecomponents namely, the pith, the fiber, and the rindmixed in different proportions. Bagasse does notcontain large amount of toxic metals as comparedwith the other industrial by-products (Crini 2006).

Most previous studies only emphasize on thedecolorization of dye aqueous solutions. In this paper,COD reduction has been taken into consideration asCOD is a crucial parameter for evaluating theconcentration of organic contaminants in water bodies(Li and Song 2009). According to Li et al. (2003) asthe degradation of organic compounds involvesoxygen, their concentrations can be figured by theamount of oxygen needed.

In previous works, incomplete pretreatment of thelignocellulosic materials has resulted in large differ-ences between percentage of color removal and CODreduction. Sayan (2006) had reported that 99.90% ofcolor had been removed but only 85.22% of COD hadbeen reduced. According to Ahmad and Hameed(2009) 91.84% of color removal and 75.21% of CODreduction were obtained. In fact, the percentage ofcolor removal and COD reduction should relativelybe close to each other. Therefore, in the present study,a novel method is used to increase the efficiency ofadsorbents in COD reduction.

The adsorption kinetics and thermodynamics werecarried out under various experimental conditions and

the adsorption equilibria were investigated in orderto determine which isotherm model fitted well tothe experimental data. A novel discussion onkinetic data has been carried out. Finally, regenerationof spent adsorbent (bagasse after adsorption) wasexamined.

2 Experimental

2.1 Preparation of Sulphuric Acid-Modified Bagasse

Sulphuric acid-modified bagasse was preparedaccording to the method reported by Garg et al.(2004a). Bagasse was collected from a local sugar-cane juice seller in Penang. Bagasse was washed afew times with distilled water to remove impuritiesand the bagasse was then dried under sunlight. Driedbagasse was then ground to a fine powder using theRetsch Mill Grinder. In order to get rid of the residualorganic substances in the bagasse or to increase thepercentage of COD reduction for dye aqueoussolution, the bagasse powder was then washed withboiling distilled water until the yellowish residualwater became clear, indicating that the residualorganic substances had been removed from thebagasse.

The sulphuric acid modification of bagasse wasmade by mixing 1 g of dried bagasse with 1 mL ofconcentrated sulphuric acid (95–98%). The mixturewas dried in an oven for 24 h at 105°C. The driedbagasse was then cooled to room temperature andwashed with boiling distilled water followed bysoaking in 1% sodium bicarbonate overnight toremove residual acid. The treated bagasse was thenwashed repeatedly with boiling distilled water toremove residual sodium bicarbonate until the pHvalue of the washed solution reached 6.0–7.0. Thetreated bagasse was then dried in an oven at 105°Cfor 24 h and sieved to obtain the particle sizes of 63–125 μm, 125–250 μm, and 250–500 μm. Theadsorbent were dried at 110°C overnight before use.

2.2 Methylene Blue

The basic dye, methylene blue (CI 52015, chemicalformula=C16H18ClN3S.2H2O, FW=319.00 g/mol,nature=basic blue, λmax=665 nm) was obtainedfrom MF Chemicals.

294 Water Air Soil Pollut (2011) 218:293–306

2.3 Experimental Methods and Measurements

In order to determine the most suitable adsorbent sizeto be used throughout the experiment, the experimentwas performed by sieving the adsorbent to differentsizes (63–125 μm, 125–250 μm, and 250–500 μm).Different dye concentrations ranging from 50 to250 mg/L, pH ranging from 2.0 to 10.0, temperaturesfrom 20°C to 60°C, and adsorbent dosages rangingfrom 0.2 g to 0.8 g were used.

For each run, 100 mL of dye solution of knownconcentration and pH was added to a 250-mLErlenmeyer flask containing the desired amount ofadsorbent. The flask was then shaken in a Wise-Cube incubator shaker at 160 rpm at specifictemperature. The flask was then withdrawn fromthe shaker at predetermined time intervals. Thesupernatant liquid portion was withdrawn from theflask and was centrifuged at 4,000 rpm for 30 min.Shimadzu UV Visible spectrophotometer (ModelUV-1601PC) was used to measure the dye concen-tration before and after treatment at 665 nm. ThepH of the initial dye solution was adjusted by theaddition of dilute 0.1 M HCl or 0.1 M NaOHsolutions.

The COD was determined according to theprocedures in the APHA Standard Methods (APHA2005), Method No. 5220D (closed reflux, colorimetricmethod). Samples were placed in vials and this wasfollowed by the addition of COD digestion solutionand small amount of mercury sulphate. The vialswere inverted several times to ensure completemixing before being placed in a COD reactor(HACH), which was preheated to 150°C. Sampleswere kept refluxed for 2 h, and they were thencooled down to room temperature followed byCOD measurement at 620 nm by a spectrophotometer(HACH DR/2010). Digested distilled water was usedas the blank reference solution and the differencebetween the absorbance of the digested blank sampleand the digested sample was the COD measurement ofthe sample.

Each experiment was repeated three times. In orderto account for color leached by the adsorbent andadsorbed by the glass containers, blank runs with onlythe adsorbents in 100 mL of doubly distilled waterand 100 mL of dye solution without any adsorbentwere conducted simultaneously at similar conditions(Hameed et al. 2008).

The amount of MB adsorbed onto the adsorbentwas calculated by the mass balance relationship asrepresented in the equation,

qe ¼ ðC0 � CeÞVW

ð1Þ

The decolorization and COD reduction efficiencieswere calculated by the formula:

peð%Þ ¼ 100ðC0 � CeÞC0

ð2Þ

where qe and pe are the amount (mg/g) and percentage(%) of MB adsorbed at equilibrium, C0 and Ce are theinitial and equilibrium liquid-phase concentration ofMB, respectively (mg/L), V is the volume of solution(L) and W is the mass of the adsorbent (g).

The equilibrium data were then fitted to theLangmuir and Freundlich isotherm models.

2.4 Fourier Transform Infrared

The Fourier transform infrared (FT-IR) spectroscopymethod is used to investigate the presence of certainfunctional groups in a molecule. The FT-IR spectra ofMB dye, raw bagasse, sulphuric acid-treated bagasse,and spent adsorbent were recorded on a Perkin–ElmerSpectrum 2000 spectrophotometer over the wave-length region between 4,000 and 400 cm−1. Each ofthe spectra is a result of four scans. FT-IR spectra ofsamples were determined by using the potassiumbromide disc technique.

The scanning electron microscopy was used todetermine the morphology of the adsorbent surfaceand is suitable for conductive surfaces. Morphologicalanalysis was done using a Model Leo Supra 50 VPField Emission scanning electron microscope (SEM)equipped with an Oxford INCA 400 EnergyDispersiveX-rayMicroanalysis system. In this study, SEM test wasconducted under a voltage of 20 kV and magnificationrange of 50–2,000. Bagasse samples with the size of125–150 μmwere mounted on a carbon tape attached toan aluminum stab.

2.5 Regeneration of Adsorbent

Fifteen grams of used bagasse was first added with150 mL of 1 M NaOH solution. The mixture was

Water Air Soil Pollut (2011) 218:293–306 295

stirred with a magnetic stirrer for 1 day. After NaOHtreatment, the bagasse was washed with boilingdistilled water and was soaked in 150 mL of 1 M HCland stirred for 1 h. It was then washed with distilledwater and dried in an oven at 110°C. The dried bagassewas sieved to 125–150 μm for use (Gupta and Babu2009). Batch experiment has been carried out todetermine the effectiveness of the regenerated bagasse.The experiment was done under various initial dyeconcentrations ranging from 50 to 250 mg/L, 0.4 g ofadsorbent, and initial pH value of 9.0 at roomtemperature (27±1°C) for 3 h equilibrium time.

3 Results and Discussion

3.1 Effect of Thorough Washing in the AdsorbentPretreatment Steps and the Effect of Initial SolutionpH Value on Color Removal and COD Reduction

The initial pH value of the solution is an importantprocess controlling parameter in affecting the cationicdye adsorption (Lata et al. 2007). MB is basic innature; it releases colored dye cations in solution. Theadsorption of MB onto solid surface is influenced bythe surface charge of the adsorbent and the initialpH value of the solution (Wang et al. 2008). Inorder to study the effect of pH on MB adsorption onsulphuric acid-treated bagasse, experiments wereconducted at the varying pH range of 2.0–10.0,100 mg/L initial dye concentration with 0.4 gadsorbent at the room temperature (27±1°C) for the3 h equilibrium time. The highest percentage ofcolor removal was 99.45% and COD reduction was99.36% at pH 9.0. The removal and reductionefficiency of the color and COD were almost thesame. These results show that, the dye species thatmade some contributions to the COD has beencompletely removed. The conventional sulphuricacid pretreating method has been modified andboiling distilled water was used in place of roomtemperature distilled water for the washing purposeof lignocellulosic materials. Table 1 shows thecomparison between the conventional sulphuric acidmethod and the thorough pretreatment method on theeffect of the pH value on color removal and CODreduction of MB dye on bagasse. The results suggestthat, using room temperature distilled water foradsorbent washing will not thoroughly remove the

residual organic matter in the bagasse, which con-tributes to the COD.

Acidic condition in the pH range 2.0–6.0 wasunfavorable for MB adsorption by sulphuric acid-treated bagasse. This is because when the solutionwas in the acidic condition, the number of negativelycharged adsorbent sites decreased and positivelycharge increased which did not favor the adsorptionof positively charged dye cations (Nainasivayam andKadirvelu 1994). At low pH, adsorption of MB waslow due to the presence of excess H+ ions competingwith dye cations for adsorption. Hence, pH 9.0 waschosen for studying the effect of other systemvariables.

3.2 Effect of Adsorbent Particle Size on ColorRemoval and COD Reduction

Different adsorbent particle sizes have differenteffects on color removal and COD reduction. Threeadsorbent particle sizes (63–125 μm, 125–250 μm,and 250–500 μm) were selected to determine thedye adsorption capacity of sulphuric acid-modifiedbagasse (0.4 g) for 100 mg/L dye concentration atpH 9.0. Table 2 shows the percentage of colorremoval and COD reduction recorded for differentsizes of adsorbent used. The adsorbent size of 63–125 μm gives the best percentage of color removaland COD reduction which are 99.47% and 99.39%,respectively. This shows that adsorption capacityreduces with adsorbent size. Several investigationshave shown similar observation for other adsorbents(Gupta et al. 2003). However, it is interesting to notethat the differences in percentage color removal andCOD reduction for 63–125 μm and 125–250 μmwere not very significant. Hence, the adsorbent sizeof 125–250 μmwas chosen for subsequent experimentsdue to their sufficient adsorption capacity.

3.3 Effect of Dye Concentration on Color Removaland COD Reduction

To study the effect of dye concentration on colorremoval and COD reduction, the experiment wascarried out at fixed adsorbent dosage (0.4 g/100 mL),room temperature (27±1°C), pH 9.0, 160 rpm shakingspeed and at different initial concentrations of MB (50,100, 150, 200, 250 mg/L) for different time intervals(15, 30, 45, 60, 90, 120, 150, 180 min). Figure 1a, b


indicate the effect of initial dye concentration oncolor removal and COD reduction, respectively.Both figures show that the percentage of colorremoval and percentage of COD reduction ofsulphuric acid-treated bagasse decreased with initialdye concentration. However, the actual amount ofdye adsorbed per unit mass of adsorbent increasedwith dye concentration. Unit adsorption, a measurefor weight of dye adsorbed per unit weight ofadsorbent used, increased from 12.44 to 43.91 mg/gas the concentration increased from 50 to 250 mg/L,respectively. Therefore, uptake of MB in the solutionremains constant after 150 min. During the adsorptionprocess, a dye molecule first has to reach the boundarylayer and then diffuses onto adsorbent surface andfinally diffuses into the tiny pores of the adsorbent.This phenomenon takes relatively longer contacttime. The time profile of dye uptake is a single,smooth and continuous curve leading to saturation,indicating the possible monolayer coverage of dyeon the surface of adsorbent (Malik 2003).

Table 1 The comparison between the conventional sulphuric acid preparation method and the thorough pretreatment methods on the effectof the pH value on color removal and COD reduction of MB on bagasse (the results shown are the average of three replication studies)

pH Conventional sulphuric acid-modified method Thorough sulphuric acid pretreatment method

% color removal % COD reduction % color removal % COD reduction

2 38.46 29.13 39.26 38.79

3 53.69 41.69 53.49 53.09

4 70.46 62.53 70.19 69.23

5 79.63 70.31 80.58 80.51

6 85.26 73.49 85.03 85.29

7 92.39 80.96 92.67 92.39

8 98.87 88.82 98.89 98.13

9 99.42 89.19 99.45 99.36

10 99.49 90.00 99.51 99.41

Table 2 Effect of adsorbent size on color removal and CODreduction

Adsorbent Size (μm) % color removal % COD reduction

63 99.47 99.39

125 99.45 99.36

250 87.07 85.98 Fig. 1 a Effect of initial dye concentration on color removal. bEffect of initial dye concentration on COD reduction


3.4 Effect of Adsorbent Dosage on Color Removaland COD Reduction

The effect of adsorbent dosage was studied byvarying the adsorbent dosage (0.2, 0.4, 0.6, and0.8 g/100 mL) in the test solution, for a fixed initialdye concentration of 100 mg/L, room temperature(27±1°C), 160 rpm shaking speed, and pH 9.0.Figure 2a, b show the effect of adsorbent dosage oncolor removal and COD reduction, respectively. Thepercentage of color removal increased from 61.46%to 99.82% as the adsorbent dosage increased from 0.2to 0.8 g/100 mL, respectively, at equilibrium time asshown in Fig. 2a. The corresponding COD reductionis from 61.25% to 99.75%, as shown in Fig. 2b.Increasing adsorbent dosage increases the surfacearea of the adsorbent and hence more adsorptionsites are available to adsorb MB from aqueous

solution. This results in shorter equilibrium time athigher adsorbent dosage (Garg et al. 2004a). However,unit adsorption decreased with adsorbent dosage. Unitadsorption decreased from 19.27 to 12.48 mg/g,respectively, as the adsorbent dosage increased from0.2 to 0.8 g/100 mL. This may be attributed tooverlapping or aggregation of adsorbent surface areaavailable to MB and an increase in diffusion pathlength (Garg et al. 2004a).

3.5 Effect of Temperature on Adsorption Equilibrium

The effect of temperature on adsorption was performedunder various MB concentrations (50–250 mg/L), 0.4 gadsorbent, various temperatures (room temperature 27±1°C, 30°C, 40°C, 50°C, 60°C), 160 rpm, pH 9.0, 3 hequilibrium time. Figure 3 shows the amount of MBadsorbed at equilibrium qe versus temperature (T) atvarious initial MB concentrations. At low MB concen-tration, the effect of temperature on the adsorptionequilibrium was not significant. However, for higherMB concentrations of 200 and 250 mg/L, the amountof MB adsorbed at equilibrium increased with temper-ature. The qe value increased from 41.82 to 48.26 mg/gand 43.81 to 57.04 mg/g, for the initial MB dyeconcentrations of 200 and 250 mg/L, respectively,when the temperature increased from 300 to 333 K.This indicates the endothermic nature of the adsorptionreaction. At higher temperatures, the adsorption capacitywas enhanced by the increased rate of intraparticlediffusion of MB molecules into the pores of theadsorbent (Karthikeyan et al. 2005).

Fig. 2 a Effect of adsorbent dosage on color removal. b Effect ofadsorbent dosage on COD reduction

0

10

20

30

40

50

60

290 300 310 320 330 340

T (K)

qe (

mg/

g)

50 mg/L100 mg/L

150 mg/L200 mg/L

250 mg/L

Fig. 3 Effect of temperature on adsorption equilibrium


3.6 Adsorption Isotherm

The adsorption isotherm gives the relationshipbetween mass of adsorbate adsorbed per unit weight ofadsorbent in equilibrium and liquid-phase equilibriumconcentration of the adsorbate (Lata et al. 2007).Adsorption data were analyzed with two adsorptionisotherm models, namely Langmuir and Freundlich.

Langmuir adsorption model (Langmuir 1918) isbased on the assumption that maximum adsorptioncorresponds to a saturated monolayer of solutemolecules on the adsorbent surface. Langmuir modelis given by the following equation:

qe ¼ Q0KLCe

1þ KLCeð3Þ

where Q0 is the maximum amount of the adsorbeddye per unit mass of sorbent to form a completemonolayer on the surface bound at high Ce (mg/g),and KL (L/mg) is the Langmuir constant related to theaffinity of the binding sites. Langmuir model can berepresented in linear form as:

Ce

qe¼ 1

Q0KLþ Ce

Q0ð4Þ

The Langmuir isotherm was studied by varying thedye solution temperature (300, 303, 313, 323, and333 K) at pH 9.0 with initial concentration of 300 mg/L,0.2 g adsorbent dosage, 160 rpm shaking speed, and at3 h equilibrium time.

The linear plot of Ceqe

versus Ce with high r2 valuessuggests the applicability of Langmuir model forthe present system. This shows the formation ofmonolayer coverage of the adsorbate at the outersurface of adsorbent. The values of Q0 and KL weredetermined from the linear plot and their values aregiven in Table 3.

The essential characteristics of Langmuir isothermcan be expressed in terms of separation factor RL, adimensionless constant (Hall et al. 1966), which isgiven by:

RL ¼ 1

ð1þ KLC0Þ ð5Þ

A value of RL between 0 and 1 shows favorableadsorption conditions. In the present system, the valueof RL is 0.01, which indicates that the adsorption ofMB on sulphuric acid-treated bagasse is favorable.

Freundlich model is an empirical equation thatassumes heterogenous adsorption due to the diversityof adsorption sites (Hameed et al. 2008). TheFreundlich equation is given as:

qe ¼ KFC1=ne ð6Þ

where KF is Freundlich constant, an indicator foradsorption capacity and 1/n is the adsorption intensity.A value of n>1 represents favorable adsorptionconditions (Hameed et al. 2008). Logarithmic formfor Freundlich equation is given as:

ln qe ¼ lnKF þ 1

n

� �lnCe ð7Þ

Values of KF and n as shown in Table 3 are calculatedfrom the intercept and slope of the plot ln qe versusln Ce at various temperatures. The values of n arebetween 4.5 and 6.0, which indicate favorableadsorption condition (McKay et al. 1980).

Langmuir isotherm shows a very high regressioncoefficient (0.95–0.99) as compared with Freundlichisotherm (0.88–0.95). Though the relatively higher r2

values of Langmuir isotherm indicates it is morepreferable than Freundlich adsorption but the closenessof these values indicates that both of them are almostequally obeyed. It can be concluded that probably thesurface of the bagasse contains heterogenous moietieswhich are uniformly distributed on the surface whichaccounts for both Langmuir and Freundlich adsorptionisotherms (Mohammed et al. 1998).

3.7 Adsorption Kinetics

Pseudo-first-order and pseudo-second-order kineticmodels were applied to the experimental data in orderto analyze the adsorption kinetics of MB on sulphuricacid-treated bagasse.

Pseudo-first order was proposed by Langergrenand Svenska (1898). The pseudo-first-order equationcan be written as:

dqtdt

¼ k1ðqe � qtÞ ð8Þ

Integrating this for the boundary conditions t=0 to t=tand qt=0 to qt=qt, gives

ln ð1� qtqeÞ ¼ �k1t ð9Þ


where k1 is the rate constant (h−1), qe (mg/g) is theamount of solute adsorbed on the surface at equilibrium,qt (mg/g) is the amount of solute adsorbed at any timet, and is given by Eq. 10.

qt ¼ ðC0 � CtÞVW

ð10Þ

Pseudo-second-order equation (Ho and McKay1998) based on equilibrium adsorption can beexpressed as:

1

qt� 1

qe¼ 1

k2qe 2tð11Þ

where k2(g/mgh) is the pseudo-second-order rateconstant. Both k1 and k2 values can be calculatedfrom the slopes of the plots ln ð1� qt

qeÞversus t and

1qt� 1

qeversus 1

t , respectively.The parameters of the pseudo-first-order and pseudo-

second-order models are summarized in Table 4 whichshows the comparison of adsorption kinetics data forboth models with different initial MB concentrationsat different times. The linear plots must passthrough the origin (0,0). The qt values calculated,qt,cal from both models are compared with theexperimental values qt,exp. Most previous studiesobtained the values of k1 and k2 from the plots of ln(qe–qt) versus t and t

qtversus t, respectively (Mall et al.

2006; Mane et al. 2007; Tan et al. 2007; Hameed et al.2008; Tan et al. 2008; Hameed 2009). For the pseudo-first order plot, a measured value of qe in ln(qe–qt)wasused to determine k1value (Jalil et al. 2010; Mall et al.2006). Furthermore, measured qe value has also beenused in isotherm studies (Langmuir and Freundlich

plots). Accordingly, the measured qe value should alsobe used in the pseudo-second order. Hence, we suggestthat the k1 and k2 values should be obtained from theslopes of the plots lnð1� qt

qeÞversus t for pseudo-first-

order model and 1qt� 1

qeversus 1

t for pseudo-second-order model, respectively. The results of these plots(Table 4) show that pseudo-second-order model fits theexperimental data better. Usually pseudo-first-orderequation does not fit well to the whole range of contacttime and is generally applicable after the initial stageof the adsorption process (McKay and Ho 1999).Although the r2 values obtained in both models arehigh, there are appreciable differences between theqt,exp and qt,cal values in pseudo-first-order model atthe initial stage of adsorption process. The second-order rate constant values show that this adsorptionsystem is a pseudo-second-order model as the valuesof qt,exp and qt,cal are very close from the initial stageof the adsorption process until the final stage.

Weber and Morris (1962) proposed the theory ofintraparticle diffusion model, since the pseudo-first-order and pseudo-second-order cannot identify thediffusion mechanism. Hence, diffusion mechanismwas determined by the equation:

qt ¼ kit1=2 þ C ð12Þ

where ki is the intraparticle diffusion rate constant(mg/g.h1/2) and C (mg/g) is a constant which gives anidea about the thickness of boundary layer. The valuesof ki and C can be obtained from the slope andintercept of the plot of qt versus t1/2 as shown inFig. 4. The larger the C value the greater the boundary

Isotherms Solution temperature (K) Constants r2

Q0 (mg/g) KL (L/mg) KF (mg/g(L/mg)1/n n

Langmuir 300 44.44 0.72 0.99

303 47.39 0.63 0.99

313 49.75 0.64 0.99

323 54.95 0.69 0.98

333 56.50 0.83 0.95

Freundlich 300 20.20 4.87 0.88

303 21.27 4.75 0.91

313 22.58 4.69 0.92

323 25.09 4.58 0.95

333 31.76 6.00 0.90

Table 3 Langmuir andFreundlich isotherm modelconstants and correlationcoefficients for adsorptionof MB onto sulphuricacid-treated bagasse


layer effect becomes. A non-zero C value indicatesthat there is an initial boundary layer resistance(Kavitha and Namasivayam 2007). In this study,Weber–Morris plots of qt versus t1/2 (Fig. 4) showalmost straight lines. Therefore the adsorption processcan be considered as intraparticle diffusion controlled(Hameed et al. 2008).

3.8 Adsorption Thermodynamics

The thermodynamic parameters that must be takeninto consideration to determine the adsorption processare: changes in standard enthalpy (ΔH 0), standardentropy (ΔS 0), and standard free energy (ΔG0) due totransfer of unit mole of solute from solution onto the

Table 4 Comparison of the pseudo-first-order and pseudo-second-order adsorption rate constants and calculated and experimental qtvalues obtained at different initial MB concentrations at different times

Initial dye concentration Time (h) qt,exp (mg/g) Pseudo-first-order(qt, cal (mg/g))

Pseudo-second-order(qt, cal (mg/g))

50 mg/La 0.25 11.2921 6.8594b 11.1613c

0.50 11.5819 9.9363b 11.7656c

0.75 11.7629 11.3164b 11.9818c

1.00 11.9371 11.9354b 12.0929c

1.30 12.2877 12.2466b 12.1711c

2.00 12.3924 12.4186b 12.2635c

2.30 12.4313 12.4312b 12.2861c

3.00 12.4390 12.4382b 12.3215c

100 mg/Ld 0.25 20.2714 10.5978e 19.5907f

0.50 20.7733 16.6001e 21.7483f

0.75 21.5646 19.9997e 22.5772f

1.00 22.4770 21.9251e 23.0157f

1.30 23.1704 23.1687e 23.3295f

2.00 23.7567 24.1812e 23.7065f

2.30 24.2717 24.3092e 23.7997f

3.00 24.4400 24.4134e 23.9461f

150 mg/Lg 0.25 26.6711 15.3903h 25.6391i

0.50 27.8216 23.9724h 29.5220i

0.75 29.5889 28.7581h 31.0916i

1.00 31.1376 31.4268h 31.9406i

1.30 32.6575 33.1218h 32.5561i

2.00 33.9274 34.4656h 33.3049i

2.30 34.7173 34.6295h 33.4915i

3.00 34.7909 34.7594h 33.7859i

200 mg/Lj 0.25 31.1938 17.4427k 29.5238l

0.50 32.7663 27.6338k 34.6589l

0.75 33.6815 33.5881k 36.7919l

1.00 35.7605 37.0671k 37.9601l

1.30 38.6842 39.3908k 38.8132l

2.00 41.2295 41.3866k 39.8583l

2.30 41.7264 41.6573k 40.1199l

3.00 41.9563 41.8899k 40.5339l

250 mg/Lm 0.25 34.2671 16.1001n 32.8711o

0.50 36.1230 26.2971n 37.5977o


solid–liquid interface (Manju et al. 1998). The valuesof ΔH o and ΔS o can be calculated from adsorptiondata at different temperatures, using Van’t Hoffequation (Afzal et al. 1992).

ð13Þ

where R is the universal gas constant (8.314 J/mol.K),T (K) the absolute temperature and KL is theLangmuir constant in L/mmol at T. The values ofΔH 0 and ΔS 0 are calculated from the slope andintercept of the plot of ln KL versus 1/T. Adsorption atvarious temperatures as shown in Table 3 werestudied. ΔG0 can be calculated using the equation:

ð14Þ

Positive value of ΔH0 (6,226.28 J/mol) shows theendothermic nature of adsorption interaction. FromTable 3, the maximum monolayer adsorption capacity

of MB onto the sulphuric acid-treated bagasseincreased from 44.44 mg/g to 56.50 mg/g withincrease in solution temperature (27°C–60°C). Thisfurther confirms the endothermic nature of theadsorption process. The negative values of ΔG0 showthe feasibility of the process and the spontaneousnature of adsorption with a high preference of MBonto sulphuric acid-treated bagasse. Positive value ofΔS0 (64.73 J/mol.K) shows the affinity of the bagassefor MB and the increasing randomness at the solid-solution interface during adsorption process (Tanet al. 2008).

3.9 Regeneration Test

Spent bagasse was regenerated and was reused for theremoval of MB at different initial MB concentrationsin the range of 50–250 mg/L. Percentage of colorremoval for fresh adsorbent was 99.44% comparedto 95.41% using regenerated bagasse at MB concen-tration of 50 mg/L, a differences of 2.01 mg/L color

Table 4 (continued)

Initial dye concentration Time (h) qt,exp (mg/g) Pseudo-first-order(qt, cal (mg/g))

Pseudo-second-order(qt, cal (mg/g))

0.75 37.2918 32.7555n 39.4905o

1.00 39.2853 36.8460n 40.5102o

1.30 40.5077 39.8273n 41.2476o

2.00 41.9083 42.7749n 42.1425o

2.30 43.0621 43.2546n 42.3652o

3.00 43.9119 43.7289n 42.7163o

a qe=12.439 mg/gb k1=3.2069; r

2 =0.8666c k2=2.8090; r

2 =0.8616d qe=24.44 mg/ge k1=2.2740; r

2 =0.6959f k2=0.6612; r

2 =0.7794g qe=34.7909 mg/gh k1=2.3362; r

2 =0.8887i k2=0.3221; r

2 =0.8456j qe=41.9563 mg/gk k1=2.1496; r

2 =0.9411l k2=0.2264; r

2 =0.7649m qe=43.9119 mg/gn k1=1.8269; r

2 =0.7212o k2=0.2712; r

2 =0.825


lnKL ¼ ΔS0=R�ΔH0=RT

ΔG0 ¼ �RT lnKL

concentration. Similar trend has been obtained forother MB concentrations. COD reduction between freshand spent adsorbent shows similar results. Theseindicate that it is possible to regenerate or reuse thespent bagasse.

3.10 FT-IR of Bagasse

Surface functional groups of bagasse adsorbentsignificantly experienced chemical changes duringacid modification. The spectra show a number of

Fig. 4 Plots for evaluatingintraparticle diffusion rateconstant for sorption of MBonto sulphuric acid-treatedbagasse

4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400.01.8

5

10

15

20

25

30

35

40

45

50

55

60.4

cm-1

%T Raw Bagasse

Sulphuric Acid Treated Bagasse

Methylene Blue Dye

Sulphuric Acid Treated Bagasse (After Adsorption)

3736

3434

3018

2926

2861

2082

1606

1494

1451

14031079

1050

859

824

687 605

429

3406

2901

1733 1605

1515

1428

1376

1248

1164

1053

833

609

3384 17081605 1366 1215

782 652

16441587 1485

1385 1133 821 666

Fig. 5 IR spectra of methylene blue dye, raw bagasse, sulphuric acid-treated bagasse, and sulphuric acid-treated bagasse afteradsorption


adsorption peaks, indicating the complex nature of theadsorbents (Hameed et al. 2008).

Figure 5 shows IR spectra of methylene blue dye,raw bagasse, sulphuric acid-treated bagasse, andsulphuric acid-treated bagasse after adsorption.Peaks of MB dye are at 1,644 and 1,587 cm−1 forketone C=O group, at 1,485 cm−1 for aromaticcompounds; C=C stretch, at 1,385 cm−1 for alkylR–, at 1,133 cm−1 for C–N–, at 821 cm−1 for CH=Cand at 666 cm−1 for C–O–H twist.

After sulphuric acid modification, a few peakswhich also appeared in raw bagasse such as aromaticcompounds C=C stretch, alkyl R–, O–H stretchgroups had shifted. Some new functional groups suchas C=O stretch (1,708 cm−1), SO3–H (1,215 cm−1),sulfates C–O–S stretch (782 cm−1), and thios C–Sstretch groups (652 cm−1) were observed. Accordingto the spectroscopic results, it suggests that sulphuricacid modification could effectively convert bagasse tohighly adsorbing materials.

Peaks of MB dye were also found in the peaks ofH2SO4 treated bagasse after adsorption. They are ketonegroup, alkyl R group, and C–N– group. Other newgroups such as NH3

+, methyl CH3, isothiocynate −N=C=O, –NH4

+, chloro C–Cl and amines R′–NHR wereformed. This is due to MB dye adsorption.

The surface structure of bagasse was analyzed bySEM before and after sulphuric acid modificationand after adsorption process with a magnification of500×. Figure 6a shows that before sulphuric acidmodification, the surface of bagasse was smooth (asshown by the arrows). However, after sulphuric acidmodification, surface morphological changes can beseen in Fig. 6b (showing porous surface by thearrows). The surface was uneven. Figure 6c showsthe SEM photographs of bagasse after adsorptionprocess. The surface became rough because it wascovered by dye molecules (as shown by the arrows).

4 Conclusions

Thorough pretreatment of sulphuric acid-modifiedbagasse could effectively eliminate the residualorganic matter in the bagasse and hence lead tohigher reduction in COD. This novel pretreatmentmethod may effectively convert the bagasse becomehighly adsorbing low-cost adsorbent in terms of highpercentage of color removal and COD reduction. The

adsorption kinetics is well described by the pseudo-second-order model. The adsorption data fitted wellwith Langmuir isotherm as well as the Freundlichadsorption isotherms because the adsorbent contains

Fig. 6 a Scanning electron microscope of raw bagasse(magnification, 500×). b Scanning electron microscope ofsulphuric acid-modified bagasse (magnification, 500×). cScanning electron microscope of sulphuric acid-modifiedbagasse after adsorption (magnification, 500×)


heterogeneous moieties which are uniformly distrib-uted on the surface of the adsorbents. The positiveΔH 0 value indicates the endothermic nature of theadsorption interaction; the negative ΔG 0 valuesindicate the feasibility and the spontaneous nature ofthe adsorption of MB onto sulphuric acid-treatedbagasse; and the positive ΔS 0 value shows theincreased randomness at the solid-solution interfaceduring the adsorption process.

Acknowledgment The authors acknowledge the researchgrant provided by Malayan Sugar Manufacturing Companyunder Kuok Foundation Berhad and the research facilities ofUniversiti Sains Malaysia (USM).

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