Removal of methylene blue and crystal violet from

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Desalination 272 (2011) 225–232

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Desalination j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / d e s a l

Removal of methylene blue and crystal violet from aqueous solutions by palm kernel fiber Gamal Owes El-Sayed ⁎ Chemistry Department, Faculty of Science, Benha University, Benha, Egypt

a r t i c l e

i n f o

Article history: Received 10 September 2010 Received in revised form 7 January 2011 Accepted 11 January 2011 Keywords: Adsorption Methylene blue Crystal violet Palm kernel fiber

a b s t r a c t The ability of palm kernel fiber (PKF) to adsorb methylene blue (MB) and crystal violet (CV) from aqueous solutions has been studied. Adsorption studies were carried out at different initial dye concentrations (20, 40, 80 and 160 mg/L), contact time, pH (1.0–11.0) and sorbent doses (0.4, 2.0, 4.0 and 8.0 g/L). Other factors affecting the absorption process as stirring rate, ionic strength and temperature of the initial dye solution were also examined. Adsorption data were modeled using Langmuir, Freundlich and Temkin adsorption isotherms. Equilibrium data of the biosorption process fitted very well to the Freundlich model (R2 = 0.997 and 0.991 for MB and CV, respectively). The thermodynamic parameters such as ΔH°, ΔS° and ΔG° were evaluated. The dye adsorption process was found to be endothermic for the two dyes. The maximum adsorption capacity Qo was 95.4 mg/g for MB and 78.9 mg/g for CV at an optimum pH. Adsorption kinetic was verified by pseudo-first-order and pseudosecond-order models. The results indicated that the dye uptake process followed the pseudo second-order and saturation type rate expressions for each dye. © 2011 Elsevier B.V. All rights reserved.

1. Introduction The textile industry plays an important role in the economical development of many countries in the world. Various kinds of synthetic dyestuffs appear in the effluents of wastewater in various industries such as dyestuff, textiles, and leather. The effluents containing dyes are highly colored and cause serious water pollution. Today there are more than 10,000 dyes with different chemical structures available commercially. Dyes are broadly classified as anionic, cationic and non-ionic depending on the ionic charge on the dye molecules. Cationic dyes are more toxic than anionic dyes [1]. From an environmental point of view, the removal of synthetic industrial dyes is of great concern, since most of these dyes and their degradation products may be carcinogens and toxic. In the last decades, the removal of color synthetic organic dyestuff from waste effluents becomes an environmental challenge. It is rather difficult to treat dye effluents because of their synthetic origins and their mainly aromatic structures, which are biologically non-degradable. Different biological and physical/ chemical methods have been applied for dye wastewater treatment. These methods include anaerobic/aerobic treatment [2], coagulation/flocculation [3], oxidation/ozonation [4], membrane separation [5] and sorption [6]. Among several chemical and physical methods, adsorption process is one of the effective

⁎ Tel.: +20105618278; fax: +20133222578. E-mail address: [email protected]. 0011-9164/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2011.01.025

techniques that have been successfully employed for color removal from wastewater. Activated carbon is an effective but expensive adsorbent due to its high costs of manufacturing. It is also can't be used to treat a large quantity of effluents because of economic consideration. Many natural adsorbents have been tested to reduce dye concentrations from aqueous solutions. Among the natural materials used as adsorbents for artificial dyes, agricultural byproducts are considered to be low-cost products. Palm kernel fiber is an agricultural waste product in the production of palm oil. Agricultural waste products are complex materials containing cellulose and lignin as major constituents. Chemical adsorption can occur by the polar functional groups of lignin, which include alcohols, aldehydes, ketones, phenolic hydroxides and ethers which could increase the affinity of the sorbent material towards organic molecules. Earlier researches have shown that palm kernel fiber can be effectively applied as adsorbent for the removal of lead [7], copper [8], anionic dye [9] and basic dye [10] from an aqueous solution. Methylene blue (MB) and crystal violet (CV) are two basic dyes, which have been shown to have harmful effects on living organisms on short periods of exposure. The aim of the present investigations has been to evaluate the efficiency of the removal of methylene blue and crystal violet from aqueous solutions using palm kernel fiber as an easily available and cheap adsorbent. The effects of contact time, initial dye concentration, pH, ionic strength and temperature of dye solution and adsorbent dose on the adsorption percentage have been investigated to optimize the conditions leading to maximum removal efficiency.

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2. Experimental 2.1. Adsorbent Palm kernel fiber (PKF) (Phoenix dactylifera) used as an adsorbent in this study was obtained from Benha City, Egypt. The palm kernel fiber was allowed to dry for about three months. The raw fiber was washed several times with distilled water and then dried in an oven at 80 °C overnight, ground and screened through a set of sieves to obtain particles of size 50–80 μm. The sieved fiber was kept dry in a closed container until required. No chemical or physical treatments were performed prior to adsorption experiments. It was ensured that there was no color produced by the PKF when it was in contact with the dye solution. FTIR spectroscopy provides structural and compositional information on the functional groups presented in the samples. The proximate composition of the PKF was investigated by Fourier transform infrared (FTIR) spectra. The spectra were recorded by a spectroscope (FTIR 2000, PerkinElmer) in the range of 4000 to 400 cm− 1 using a KBr disk containing 1% of finely ground sample. The mixture was pressed into a KBr wafer under vacuum conditions and used as such for IR studies. As shown in Fig. 1, the spectra display a number of absorption peaks, indicating the complex nature of PKF.

Fig. 2. The structure of methylene blue (MB) and crystal violet (CV).

and the relation between the initial and final pH values was drawn and the pHzpc was evaluated to be 7.2. 2.4. Adsorption studies Sorption studies were performed by the batch technique to obtain equilibrium data. In each experiment, 0.05 g of adsorbent was added to a 25 ml dye solution of known concentration in a 250 mL Erlenmeyer flask of desired concentration, temperature, and pH. The mixture was stirred on an electromagnetic stirrer at a constant speed (200 rpm). All the experiments were carried out in duplicate. After equilibrium, the final dye concentration (Ce) was measured and the percentage removal of dye was calculated using the following relationship:

2.2. Adsorbate The dyes methylene blue (MB) and crystal violet (CV) (Fig. 2) were obtained from Sigma-Aldrich and their stock solutions (160 mg/L) were prepared in double distilled water. All reagents used in the present work were of analytical grade. To prepare various solutions at desired concentrations from the stock solution, double distilled water was used for the necessary dilutions. MB and CV concentrations were analyzed by measuring the absorbance values after and before each experiment with a Jasco V-530 (UV–Vis) spectrophotometer (Japan) at 664 nm and 586 nm, respectively.

2.3. Point of zero charge Point of zero charge (pHzpc) was determined for the dried grounded PKF. To a series of 250 mL Erlenmeyer flask, 50 mL of distilled water was transferred. The initial pH values of the solution were roughly adjusted to 1.5–11 by adding either 0.1 N HCl or 0.1 N NaOH. 0.5 g of crushed biomass was added to all flasks. The suspensions were then manually shaken and allowed to equilibrate for 24 h with intermittent manual shaking. The pH values of the supernatant liquids were noted,

%Dye removal =

Ci −Ce × 100 Ci

ð1Þ

where Ci and Ce are the initial and final (equilibrium) concentrations of dye (mg/L), respectively. The amount of dye adsorbed qe (mg/g), onto PKF was calculated from the mass balance equation as follows: qe = ðCi −Ce Þ

V W

ð2Þ

where V is the volume of dye solution (L), and W is the mass of the adsorbent used (g). Batch adsorption experiments were carried out at initial pH values ranging from about 2.5 to 11.5; initial pH was adjusted by addition of dilute HCl or NaOH solutions. The pH values were measured by using a pH-meter model HI 8014, Hanna Instruments (Italy). The effects of temperature on the adsorption data were carried out by performing the adsorption experiments at various temperatures (25, 35, 45 and 55 °C). The equilibrium data have been analyzed using the Langmuir, Freundlich and Temkin isotherms and the characteristics parameters for each isotherm have been determined.

Fig. 1. FTIR spectra of PKF before dye adsorption.

G.O. El-Sayed / Desalination 272 (2011) 225–232

3. Results and discussion 3.1. Effect of contact time and initial dye concentration Fig. 3 represents the adsorption capacity (mg dye/g adsorbent) versus the contact time for varying initial concentrations (20, 40, 80 and 160 mg/L) of dye (MB and CV, respectively) at an optimum pH. Both dyes showed a fast rate of sorption during the first 30 min of contact between the two phases and the equilibrium was attained in about 60 min. The rate of percent removal and adsorption capacity are higher in the beginning due to the large surface area of the adsorbents available for the adsorption of the dye. An increase in the initial dye concentration leads to an increase in the adsorption capacity of the dye on PKF due to the increase in the driving force of the concentration gradient. The adsorption capacity at equilibrium increases from 9.4 to 64.5 mg/g for MB and from 8.8 to 52.9 mg/g with an increase in the initial dye concentration from 20 to 160 mg/L.

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the adsorption process. The effect of pH in the acidic solutions on dye removal is greater for MB than CV. In the case of MB the % removal increased from 72.8% (at pH 2.4) to 96.3% (at pH 7.0), while it increased from 79.1% (at pH 2.4) to 87.5% (at pH 7.0) in the case of CV. Similar observations have been reported for the adsorption of MB [11] and CV [12] using different biosorbents. Lower adsorption of MB and CV at an acidic pH may be due to the presence of excess H+ ions competing with dye cations for the adsorption sites. The influence of the solution pH on the dye uptake could be explained on the basis of pH zero point charge (pHzpc). For amphoteric molecules which contain both positive and negative charges, the net surface charge is influenced by the pH of their surrounding environment. By either loosing or gaining protons (H+) they can become more negatively or more positively charged [11]. At a higher pH the surface of the PKF particles may get negatively charged, which enhances the positively charged dye cations through electrostatic attraction [13]. For the two dyes, neutral or slightly alkaline solutions were used for further experiments as they lead to maximum removal of the dyes.

3.2. Effect of pH 3.3. Effect of stirring rate The pH value of the initial solution is an important parameter in the adsorption process. In order to establish the effect of pH in the adsorption of MB and CV dyes, the batch equilibrium studies at different pH values were carried out in the range of 2.4–11.5. The experiments were carried out at 20 mg/L initial dye concentration with 0.05 g/25 mL adsorbent dosage at 25 ± 1 °C for 90 min of equilibrium time and a constant stirring speed of 200 rpm. As shown in Fig. 4, the adsorption of the two dyes increased as the pH of the solution increased in acidic media, while further increase of pH in alkaline solutions had no effect on

The effect of stirring rate was studied by varying the stirring speed between 50 and 350 rpm at a constant dye concentration (20 mg/L) and stirring time of 60 min. As shown in Fig. 4, the sorption of both dyes on PKF increases with the increase of stirring rate. The increase of stirring rate increases the removal efficiency by decreasing the thickness of the diffusion layer around the adsorbent surface. Similar results were reported for cationic dyes [14]. 3.4. Effect of salt concentration The effect of salt concentration on the biosorption process of dyes was tested by the addition of different amounts of sodium chloride to the initial solutions. The concentration of NaCl used ranged from 0 to 1.0 g/25 mL solution. As seen in Fig. 4, increasing the ionic strength of solution decreases the adsorption of dyes. This behavior could be attributed to the inhibition of the nearness of the active sorption sites and dye molecules [15]. 3.5. Effect of adsorbent dose The removal of MB and CV with PKF was studied at different adsorbent dosages (0.01–0.25 g/25 mL) of dye solution at a constant dye concentration (20 mg/L), stirring speed (200 rpm), pH (7.2) and contact time (60 min). The results (Fig. 4) indicate that an increase in the adsorbent dose resulted in a higher removal of both dyes. Maximum removal was observed with an adsorbent dose of 0.20 g/ 25 mL for MB and 0.15 mg/L for CV. The increase in the percentage removal with an increase in the adsorbent dosage is due to the increase in the number of adsorption sites. The adsorption capacity was lesser at higher adsorbent doses. This is due to greater availability of the exchangeable sites or surface area at a higher concentration of the adsorbent [16]. 3.6. Effect of temperature

Fig. 3. Effect of contact time on the equilibrium sorption capacity of different concentrations of (a) MB and (b) CV on PKF.

The temperature dependence of MB and CV sorption onto PKF was studied with a constant initial concentration of 20 mg/L at 200 rpm and pH 7.2. The effect of temperature on the sorption of MB and CV by PKF after saturation (at 60 min) is shown in Fig 4. The % of dye removal increases slightly from to 91.4% to 93.5% for MB and from 81.5% to 88.7% for CV, when the solution temperature increases from 25 to 55 °C. Since the adsorption increased when temperature increased, the system is considered to be endothermic. This behavior can be explained by the increase of the mobility of the dye molecules with a rise in the temperature implying a kinetically controlling

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Fig. 4. Effect of (a) solution pH, (b) stirring rate, (c) NaCl, (d) adsorbent dose and (e) temperature adsorption of MB and CV on PKF.

process, as found in many other systems [17]. It can be suggested also that the dye molecule should interact more effectively with the active sites on PKF. 3.7. Adsorption isotherms The adsorption isotherm indicates how the adsorption molecules distribute between the liquid phase and the solid phase when the adsorption process reaches an equilibrium state. The time required to attain this equilibrium state is termed the equilibrium time, and the amount of dye adsorbed at equilibrium reflects the maximum adsorption capacity of the adsorbent under the operating conditions. The analysis of the isotherm data by fitting them to different isotherm

models is an important step to find the suitable model for the case studied [18]. The Langmuir, Freundlich and Temkin models were used to describe the data derived from the adsorption of the two dyes by PKF over the entire concentration range studied. The Langmuir model assumes monolayer sorption on a surface with a finite number of identical sites [19]. While, the Freundlich isotherm model assumes heterogeneous surface energies, in which the energy term in the Langmuir equation varies as a function of the surface coverage and hence does not assume monolayer capacity [20]. The Temkin model is based on the assumption that the heat of adsorption would decrease linearly with the increase of the coverage of the adsorbent [21]. The applicability of the three isotherm equations were compared by evaluating the correlation coefficients, R2.

G.O. El-Sayed / Desalination 272 (2011) 225–232

3.7.1. Langmuir isotherm The linear form of the Langmuir's isotherm model is given by the following equation: Ce 1 C + e = Qo b qe Qo

ð3Þ

where Ce is the equilibrium concentration of the dye (mg/L), qe is the amount of adsorbate adsorbed per unit mass of adsorbent (mg/g), and Qo and b are the Langmuir constants related to adsorption capacity and rate of adsorption, respectively. The plot of Ce/qe against Ce gave straight lines with slope 1/Qo for MB and CV. This result indicated that the adsorption of MB and CV on PKF follows the Langmuir isotherm and demonstrated the formation of monolayer coverage of dye molecules at the outer surface of PKF. The Langmuir constants b and Qo for MB and CV were calculated from this isotherm and their values are given in Table 1. The essential characteristics of the Langmuir isotherm can be expressed in terms of a dimensionless equilibrium parameter (RL) [22], which is defined by: RL = 1 = ð1 + bC0 Þ

ð4Þ

where, b is the Langmuir constant and C0 is the highest dye concentration (mg/L). The value of RL indicates the type of the isotherm to be either unfavorable (RL N 1), linear (RL = 1), favorable (0b RL b 1) or irreversible (RL = 0). Values of RL were found to be 0.611–0.164 for MB and 0.612–0.165 for CV in the concentration range studied. These results confirmed that the PKF is favorable for the adsorption of MB and CV dyes under the experimental conditions used. 3.7.2. Freundlich isotherm The linear form of the Freundlich isotherm model can be defined by the following equation [20]: ln qe = ln KF +

1 lnCe n

ð5Þ

where KF [mg/g (L/mg)n] is the Freundlich isotherm constant related to adsorption capacity (represents the quantity of dye adsorbed onto the adsorbent) and n is the Freundlich isotherm constant related to adsorption intensity (giving an indication of how favorable the adsorption process). The applicability of the Freundlich sorption isotherm was analyzed by plotting lnqe versus lnCe. This plot gives straight lines for the two dyes with slope ‘1/n’, indicating that the adsorption of MB and CV follow the Freundlich isotherm. The slope 1/n ranging between 0 and 1, is a measure of adsorption intensity or surface heterogeneity. It becomes more heterogeneous as its value gets closer to zero and a value for 1/n below one indicates a normal Langmuir isotherm while 1/n above one is indicative of cooperative adsorption [23]. Accordingly, the Freundlich constants (KF and n) and the related correlation coefficients were calculated and recorded in Table 1.

where R is the general gas constant (8.314 J/mol. K), T the absolute temperature (K), B is a constant related to the heat of adsorption (J/ mol) and A is the Temkin isotherm constant (L/g). B and A could be calculated (Table 1) from the linear plot of lnCe against qe. This isotherm assumes that the heat of adsorption of all molecules in the layer decreases linearly with coverage due to the adsorbent– adsorbate interaction. It assumes also that adsorption is characterized by a uniform distribution of binding energies up to some maximum value [24]. The data obtained for the Langmuir, Freundlich and Temkin isotherms were well fitted with the Freundlich model when compared with the other models under the different concentrations studied. Langmuir and Temkin models do not describe the saturation behavior of the biosorbent as well as the Freundlich model. That implies that heterogeneous surface conditions exist under the used experimental conditions. The maximum adsorption capacities (Qo) of PKF adsorbent for MB and CV were compared with those reported in literature for different adsorbents used for MB and CV adsorption systems as shown in Table 2. Such adsorption data were derived from the Langmuir equation. As seen in Table 2, the adsorption capacities of both dyes onto PKF are comparable with those of other adsorbents of activated carbon (AC) or low-cost biosorbents. Variation in adsorption capacities and affinities is mainly attributed to the differences in experimental condition conducted and properties of adsorbent such as the specific surface area, pore size in AC and functional groups in biosorbents. 3.8. Thermodynamic parameters The increase in adsorption with a rise in temperature reveals an endothermic process which can be explained thermodynamically by evaluating parameters such as change in free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°). These parameters were calculated using the following equations: ΔG- = −RT lnðKL Þ

lnKL = −

ð6Þ

Table 1 Constants of adsorption isotherms of MB and CV on PKF. Dye Langmuir

Freundlich

Q0 b RL (mg/g) (L/mg) (L/mg) MB CV

95.4 78.9

0.0317 0.0316

R

2

KF

n

Temkin R

2

A

B

R2

0.611–0.164 0.918 8.67 1.77 0.997 1.166 15.7 0.903 0.612–0.165 0.948 5.10 1.70 0.991 0.574 14.2 0.927

ð7Þ

ΔGΔHΔS=− + RT RT RT

ð8Þ

Table 2 Comparison of the maximum adsorption of MB and CV from this study with different various adsorbents. Dye Adsorbent

Qo Reference (mg/g)

MB

Activated carbon (walnut shells) Activated carbon from pistachio shells Activated carbon from Euphorbia rigida Tomato plant root Wood apple Activated carbon from sunflower oil cake Activated carbon from hazelnut shell Activated carbon (coir pith) Activated carbon from apricot stones Activated carbon from almond shell Palm kernel fiber

315.0 129.0 114.4 83.3 40.1 16.4 8.8 5.8 4.1 1.3 95.4

CV

Tomato plant root Sulphuric acid activated carbon (male flowers coconut tree) Treated ginger waste Phosphoric acid activated carbon (male flowers coconut tree) Pinus bark powder Wood apple Sugarcane dust Neem sawdust Palm kernel fiber

3.7.3. Temkin isotherm The Temkin isotherm is given in a linearized form as: qe = B lnA + B lnCe

229

94.3 85.8

[25] [26] [27] [28] [29] [30] [31] [32] [31] [31] Present study [29] [33]

64.9 60.4

[28] [33]

32.8 19.8 3.8 3.8 78.9

[16] [34] [35] [36] Present study

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where KL equals to Q ob, the equilibrium constant of the adsorption process (L/mg). R and T are gas constant and absolute temperature, respectively. The plot of lnKL as a function of 1/T (Fig. 5) yields a straight line (R2 = 0.998 for MB and 0.992 for CV) from which ΔH° and ΔS° were calculated from the slope and intercept, respectively. The values of Gibbs free energy change of adsorption for MB and CV adsorption on PKF as calculated from the Langmuir constant were found to be negative for the experimental range of temperatures (Table 3), corresponding to a spontaneous process. The positive values of ΔH° for MB (+39.78 kJ/mol) and CV (+33.81 kJ/mol) confirm the endothermic nature of the overall adsorption process. This means that as the temperature increases, more energy is available to enhance the adsorption [37]. The negative values of ΔS° for the two dyes indicate that the two systems have a decreased randomness at the solid/solution interface [38]. 3.9. Adsorption kinetics The study of adsorption kinetics describes the solute uptake rate which controls the residence time of adsorbate uptake at the solid/ solution interface. The kinetics of MB and CV adsorption on the PKF were analyzed using pseudo first-order and pseudo second-order kinetic models [39]. The linear pseudo-first-order equation is given as follows: logðqe −qt Þ = logqe −

k1 t 2:303

ð9Þ

where qe and qt are the adsorption capacity at equilibrium and at time t, respectively (mg/g), k1 is the rate constant of the pseudo first-order adsorption (1/min). A plot of log (qe − qt) versus t (Fig. 6) should give a linear relationship from which k1 and qe can be determined from the slope and intercept of the plot, respectively. The shape of the lines indicates that the first-order Lagergren equation did not fit well to the whole range of the adsorption process and was generally applicable over the initial stage of the contact time [40]. The linear pseudo second-order equation is given as follows: t 1 t = + qt qe k2 q2e

Table 3 Thermodynamic parameters for the adsorption of MB and CV onto PKF. Dye

MB CV

ΔH°

39.78 33.81

−ΔS°

0.116 0.103

−ΔG° 298 K

303 K

313 K

323 K

5.210 3.117

3.966 2.086

2.889 1.056

1.729 0.026

for the pseudo first-order model, indicating a better fit with the pseudo second order model. The calculated qe values also agree very well with the experimental data. These results indicate that the adsorption system studied belongs to the second-order kinetic model. 4. Conclusion The adsorption of basic dyes (methylene blue and crystal violet) from aqueous solution onto palm kernel fibers has been studied. Adsorption experiments were carried out as a function of contact time, adsorbent dosage, stirring rate, solution temperature, salinity, pH and dye concentration. The adsorption experiments indicated that palm kernel fibers were effective in removing basic dyes such as methylene blue and crystal violet from aqueous solutions. The removal percent decreased with the increasing initial concentration of dye in the solution and increased with the increasing adsorbent dosage. The results also indicated that with temperature increasing, the ability of adsorption increased indicating an endothermic process. The adsorption data was well described by the Freundlich isotherm equation. The rates of sorption were found to conform to pseudo-second-order kinetics with

ð10Þ

where k2 is the pseudo-second-order rate constant (1/min g 1/mg). The slopes of the plots t/qt versus t give the value of qe, and from the intercept, k2 can be calculated. The plot of t/qt versus t (Fig. 7) yields very good straight lines for different initial MB and CV concentrations. The results of fitting experimental data with the pseudo first-order and pseudo second-order models for adsorption of MB and CV on PKF are presented in Table 4. As can be seen, the correlation coefficients (R2) are 0.99 at least for the pseudo second-order model and less than that

Fig. 5. Thermodynamic parameters for adsorption of MB and CV on PKF.

Fig. 6. First order plot of adsorption of (a) MB and (b) on PKF at different dye concentrations (20, 40, 80 and 160 mg/L dye).

G.O. El-Sayed / Desalination 272 (2011) 225–232

KL k1 k2 KF n qe qt Qo R R2 RL t T V W ΔG° ΔH° ΔS°

231

equilibrium constant at temperature T rate constant of pseudo-first-order adsorption (1/min) rate constant of pseudo-second-order adsorption (g/mg min) Freundlich constant Freundlich constant adsorption capacity at equilibrium (mg/g) adsorption capacity at time t (mg/g) Langmuir's constant related to capacity of adsorption (mg g− 1) ideal gas constant (kcal K/mol) regression coefficient equilibrium parameter, dimensionless time (1/min) absolute temperature (K) volume of dye solution to be treated (L) mass of adsorbent (g) standard free energy change (kJ/mol) standard enthalpy change (kJ/mol) standard entropy change (kJ/Kmol)

References

Fig. 7. Plot of pseudo-second-order model at different (a) MB and (b) CV concentrations, pH 7.2, temperature 24 ± 1 °C.

good correlation. The present study concludes that palm kernel fiber could be employed as a low-cost adsorbent for the removal of basic dyes from aqueous solutions. Nomenclature b Langmuir's constant related to energy of adsorption (L/mg) B constant related to the heat of adsorption (J/mol) Co initial concentration of dye (mg/L) Ce equilibrium concentration of dye (mg/L)

Table 4 Kinetic parameters for biosorption of MB and CV on PKF at different temperatures. Dye C0a Pseudofirst-order kinetics (mg L−1) k1c R2d q eb (mg g− 1) (min− 1) MB

CV

a b c d e

20 40 80 160 20 40 80 160

7.673 7.224 27.22 31.26 4.032 4.183 6.427 17.26

0.0741 0.1073 0.1045 0.0801 0.1339 0.1376 0.1483 0.2159

0.984 0.975 0.971 0.992 0.983 0.982 0.987 0.973

Pseudosecond-order kinetics qe k2e R2 (mg g− 1) (g mg− 1 min− 1) 12.344 15.623 36.309 66.309 8.687 15.411 22.928 42.935

Initial dye concentration. Adsorption capacity at equilibrium. Rate constant of pseudo first-order adsorption. Correlation coefficient. Rate constant of pseudo second-order adsorption.

0.1862 0.1215 0.0566 0.1026 0.2003 0.1220 0.0731 0.0345

0.990 0.999 0.998 0.988 0.999 0.999 0.999 0.998

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