Accepted Manuscript Title: Exploring the adsorption behavior of cationic and anionic dyes on industrial waste shells of egg Author: M.A. Abdel-Khalek M.K. Abdel Rahman A.A. Francis PII: DOI: Reference:
S2213-3437(16)30437-7 http://dx.doi.org/doi:10.1016/j.jece.2016.11.043 JECE 1356
To appear in: Received date: Revised date: Accepted date:
25-8-2016 27-11-2016 29-11-2016
Please cite this article as: M.A.Abdel-Khalek, M.K.Abdel Rahman, A.A.Francis, Exploring the adsorption behavior of cationic and anionic dyes on industrial waste shells of egg, Journal of Environmental Chemical Engineering http://dx.doi.org/10.1016/j.jece.2016.11.043 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Exploring the adsorption behavior of cationic and anionic
dyes on industrial waste shells of egg
M.A. Abdel-Khalek, M. K. Abdel Rahman and A. A. Francis*
Central Metallurgical Research and Development Institute- CMRDI , Cairo , Egypt
Corresponding author: adel_fra[email protected]
Abstract The objective of this work is to investigate the feasibility of using the whole eggshell matrix (eggshell + membrane) as a potential and low-cost bio-sorbent for color removal from dyes. The two tested dyes (Methylene blue, MB & Congo red, CR) revealed different adsorption behaviors reflecting the complex nature of the interaction between the adsorbent surface and these molecules. The functional groups and surface morphologies of untreated eggshell powder and adsorbed Eggshell were analyzed by Fourier transform infrared spectroscopy (FTIR) and field emission scanning electron microscopy (FESEM). The electrical double layer mechanism explained the adsorption behavior of MB cations onto the eggshell surface, whilst that of the CR anions favored the electrostatic attraction on the positively charged surface of eggshell at lower pH. The adsorption of dyes on the surface of eggshell follows a second order kinetics, while the adsorption isotherm obeys the Freundlich model and exhibits multilayer adsorption. The maximum adsorption capacity was estimated to be 94.9 mg/g and 49.5 mg/g for MB and CR respectively for a concentration of 1000mg/l at room temperature. The heterogeneity of the eggshell surface may cause rearrangement of dye molecules once they are primarily adsorbed. The free energy of adsorption showed an increase with temperature, indicating the occurrence of physical adsorption. The present results indicate the suitability of bio-composite eggshell wastes to be used as adsorbent for the removal of dyes.
Keywords: Industrial waste shells of egg; adsorption kinetics; equilibrium isotherms; Thermodynamics; SEM
1. Introduction From the environmental point of view, adsorption process has been considered to be an effective method to treat effluents and for the removal of different color from aqueous solutions . Since the last two decades, significant number of works has been reported on the use of activated carbon as one of the most popular adsorbent for treating effluents and dye-containing waste solutions [2-3]. However, its cost of disposal  has diverted the
attention to the use of cheap or natural adsorbents such as shale oil ash , chitosan , sunflower stalk , natural clay [8-9, 3], orange peel and soy meal hull [10-11] In the present work, we are exploring the adsorption potential of bio-composite eggshell as a common household byproduct toward the basic and acid dyes (methylene blue and congo red). There have been a number of interesting studies that revealed the adsorption capabilities of industrial waste shells of egg [12-17]. These investigations have been focused on the feasibility of using eggshells (ES) as a low cost bio-sorbent for the removal of dyestuffs from aqueous solution such as reactive red 123 , methylene blue , Malachite Green , Direct Red 28 , Reactive Yellow 205 , Direct Red 80 and Acid Blue 25 . Liao et al.  and De Paula et al.  have mentioned that derivatives from industrial waste shells of egg could be used to remove toxic metals (e.g. lead, cadmium and copper) from aqueous solution. Eggshell wastes had also been exploited as an alternative to calcium carbonate for the immobilization of heavy metals in soils . Avrami et al  evaluated the adsorption effectiveness of both Acid Red and Acid Blue onto the Egg shell membrane with respect to initial dye concentrations, pH, contact time, particle sizes and bio-sorbent doses at room temperature. These results may then be used in conjunction with the work of Otun et al  and Ahmad et al  on the use of eggshell wastes for the removal of heavy metals e.g. Cd (II), Cu (II), Cr (III), Fe (III), Ni (II) and Pb (II) from aqueous solutions. A detailed investigation on the adsorption behavior, kinetics and equilibrium for the effective removal of color from basic and acid dyes using the industrial waste shells of egg has been discussed. The effects of dye concentrations, pH, and contact time on the adsorption of both dyes onto the whole eggshell matrix (eggshell + membrane) were analyzed by Langmuir and Freundlich adsorption isotherms. Based on isotherms adsorption data, thermodynamics parameters such as free energy, enthalpy, and entropy of adsorption were also evaluated. The present work continues on the general theme of exploring the environmental, social, technological and economic advantages of this waste material not only for the removal of dye pollution or metal-contaminated wastewater, but also for the implementation of cleaner production processes and converting waste into industrially viable resources . It should be noted that the antibacterial activities of ESM against various types of bacteria, including Escherichia coli, and the ability of eggshell membrane (ESM) proteins to interact and disrupt the membrane integrity of bacteria were demonstrated by Poland et al. and Mine et al respectively [25-26]. The use of the whole eggshell matrix (ESM &ES) is a major advantage in terms of cost, energy and process requirement. While no process is perfect, reducing the need for calcination and washing of eggshells or even separation of ESM from ES prior to 3
processing has a major impact on cost-benefits and efficiency of adsorption process. Consequently, this work has a particular focus in the use of the whole Eggshell matrix without pretreatment as initiative to promote its application as low-cost adsorbent for the removal of dyes from waste solutions. A more detailed investigation concerning the treatment of industrial wastewater effluents generated from painting industry using eggshell wastes is the focus of an on-going study.
2. Experimental The Eggshells (EG) were collected from household kitchens and then crushed to fine powder by using planetary ball mill (Frisch 4). The average median diameter (d50) of eggshell powder was determined to be 1 μm . The milling operation of eggshells is just carried out to provide a uniform sufficient particle size feedstock for efficient adsorption. The functional groups on the surface of eggshell powder, methylene dye and adsorbed eggshell were analyzed by Fourier transform infrared spectroscopy (FTIR-6300, JASCO, Japan) in the range of 1000–4000cm-1. The morphology of the untreated raw Eggshell and adsorbed EG with methylene blue was examined with a field emission scanning electron microscope (FESEM, Quanta-FEG-250, Holland). Two different dyestuffs (methylene blue and congo red) were used as adsorbate on the bio-sorbent Eggshell. Methylene blue (C16H18ClN3S) is an important basic dye used for printing calico, dyeing cotton and leather. Congo red (C32H22N6Na2O6S2) is an acid dye used in biology and as a pH indicator. Adsorption experiments were conducted using 1 g of EG with 100 ml of solution containing dye of desired concentration at normal pH and room temperature (25C) in 200 ml rounded bottom flask. The flask was shaken at 200 rpm for 1 h. A stock solution of 2000 mg/l (ppm) was prepared by dissolving 2 g of solid dye in 1 Liter of deionized water. Samples were centrifuged at 3000 rpm for 5 min and analyzed by UV–Vis/NIR spectrophotometer (Lambda-1050) to determine the remaining dye concentration. To investigate the mechanism and order of adsorption, the initial dye concentrations and contact times were varied over wide ranges of 50-1000 mg/l and 10-120 min respectively. The amount of dyes adsorbed on the surface at equilibrium per unit mass of eggshell, qe (mg/g), is determined using the following relationship:
C -C q i exV e W
Where V is the solution volume in liter (l), W is the weight of eggshell (g), and Ci and Ce are the initial and equilibrium of dyestuff concentrations (mg/l of dye) respectively. The percent removal of dyes was calculated using the following equation:
C C Re moval % 0 - e x 100 C0
Both C0 and Ct (mg/ L) correspond to the initial and final concentration of dyes (mg/l) in solution respectively.
3. Results and Discussion The porous nature of eggshell and its valuable application in many industrial and scientific sectors has attracted a lot of attention since it can be used as a low-cost adsorbent for removal of ionic pollutants from aqueous solutions [27-29]. Efforts are being made to protect the environment from the harmful effects and non-biodegradability of dyes using the adsorption process as a non-destructive technique. It is worthy of note that the pH solution, temperature, concentration and contact time are the most important parameters which affect the adsorption process.
3.1. Impact of pH As expected, the adsorption of MB and CR onto Eggshells was highly dependent on the pH solution. Figure 1 shows the adsorbed values of both MB and CR (mg/g) on the surface of Eggshell within the pH range of 2-12. It is observed that the uptake increased slightly from 16.77 to 19.87 mg/g for MB and jumped quickly for CR from 9.45 to 18.71 mg/g when pH went from the more alkaline region to the more acidic region. Several investigations [30-32] reported that the adsorption of MB on various adsorbents preferred higher solution pH values and that´s contradict our results. Basically, the presence of excess H+ ions at low pH should compete with the cationic group of the MB dye causing a decrease in the amount of dye adsorbed. However, the presence of OH - on the surface of eggshell at high pH should favor the adsorption of cationic dye (MB). This behavior of MB is inconsistent with the known fact that the adsorption increases with increasing pH for cationic dyes . Therefore, the electrical double layer that maintains electrical neutrality of the system has been suggested to explain the adsorption behavior of MB onto the adsorbent 5
surface. It has been suggested [34-35] that the pores in between the interwoven fibers of collagen and glycoprotein present in the membrane of eggshell are effective in controlling the movement of ions. The organic matter of eggshell and shell membrane contains proteins as major constituents with small amounts of carbohydrates and lipids . It should be noted that eggshell membrane is comprised of various functional groups, such as hydroxyl, amine, and carbonyl which could also be affected by the pH of the solution . When the eggshell powder is mixed with the dyeʼs solution, calcium salts may partially dissolve and release Ca2+, HCO3-, CO32- and OH- ions . The released ions may be adsorbed onto the surface of the eggshell particles and formed a negative charge . The solution contains also alkali and alkaline ions (Na+, Mg2+ and K+) which may be adsorbed onto the surfaces of eggshell, forming an electrical double layer, with the surface of the eggshell acquiring a positive charge . Ions in the solution are attracted and absorbed to the negatively-charged membrane surface, forming the so-called Stern layer. However, the favorable adsorption of CR in acidic media is attributed to the electrostatic interactions between the SO3 group of the dye and the eggshell whose surface exhibits a positive charge at low pH.
3.2. Impact of temperature on dye removal The effect of temperature on the adsorption of both MB and CR onto EG was investigated with an initial dye concentration of 200 mg/l at the initial pH solution of 5.23 and 7.09 for MB & CR respectively. As can be seen from Figure 2, the amount of adsorbed dyes decreased gradually with temperature, and that´s due to the increasing mobility of dye ions and their escape from the solid phase (eggshell) to the liquid phase . This behavior might arise from the weaker van der Waals and dipole forces which are accompanied with low heat of bio-sorption [40-41]. In order to evaluate the spontaneity of the sorption process, thermodynamics parameters such as enthalpy (ΔHo), entropy (ΔSo), and Gibb’s free energy (ΔG o) for the sorption have been calculated and presented in Table 1. Both the equilibrium constant Kc and ΔGo were determined using the following two equations. (3) & (4)
S H ln K c R RT
G - RT ln K c
The values of ΔH° and ΔS° have been taken from the slope (ΔH°/R) and intercept (ΔS°/R) of the plot ln Kc vs 1/T , which should give a straight line with acceptable coefficient of determination for MB (R2= 0.8787) and CR (R2= 0.9829), Figure 3 . T is the temperature in degree K, and R is the gas constant (8.314 J/mol K). The negative values of ΔG0 at lower temperatures for both anionic and cationic dyes indicated the spontaneity of the adsorption process. Furthermore, the values of both ΔH0 and ΔS0 implied the occurrence of favorable adsorption. Based on the tabulated results, the adsorption process for MB is spontaneous and favorable at all temperatures however the adsorption was completely different for CR which is only feasible at 298 and 313 K. On the other hand, the negative values of entropy change (ΔS) suggest the decrease in randomness at the solid/liquid interface during the adsorption of Both MB and CR eggshells.
3.3. Impact of contact time The effect of contact time at room temperature and up to 120 min was studied using solutions containing 200 mg/l concentration of dyestuffs at initial pH of 5.23 for MB and 7.09 for CR. It can be deduced from Figure 4 that the adsorption process comprised of two phases: a primary rapid phase and a second slow phase. The first rapid phase lasted approximately 40 min and this is due to the availability of a large number of vacant surface sites for adsorption. However, a plateau value is reached in approximately 50 min and that´s due to the saturation of the active sites. The rate at which the dyes is adsorbed from an aqueous solution on the surface of Eggshell has been analyzed using both the Lagergren pseudo-first order equation based on solid capacity  and pseudo-second order equation based on solid phase sorption . The pseudo-first order equation of Lagergren can be expressed as Eq. (5):
log q e - q t log q e -
k1 t 2.303
Where the plot of log (qe − qt) versus time should give straight line. The slope is equal to k1 and the intercept equal log q e . The pseudo-second order reaction rate equation has the 2.303
t 1 1 t q t k 2q e2 q e
Where qt and qe are the adsorbed amount of dyes (mg/g) at time t (min) and at equilibrium respectively. k1 (min−1) is the rate constant of the pseudo-first order adsorption (min−1), and k2 (g/mg min-1) is the second order reaction rate constant for adsorption. The qe and k2 can be determined from the slope (1/qe) and intercept (1/k2q2e) of the plot t/qt versus time. The adsorption data presented in Figure 4 were used to fit the above-mentioned kinetic models at the initial pH solutions. Plots for pseudo-first and second-order models are shown in Figure 5.
The parameter values calculated using the pseudo-first order and the pseudo-second order models for the adsorption of both dyes were summarized in Table 2. Based on the values of correlation coefficient (R2 ≥ 0.999) and reaction rate constant (k2≥0.019), the second-order kinetic model is higher and fits the data better than the first-order kinetic model.
Field emission scanning electron microscope (FESEM) was employed for examining the surface morphology of eggshell and adsorbed eggshell with MB. A comparative SEM images showed a clear change in the textural structure of eggshell particles following the sorption experiment (Figure 6). The surface morphology indicates that the eggshells are porous and consist of irregular particles of different sizes. These findings indicated that the adsorption of MB onto the surfaces of eggshell is likely due to the physical adsorption mode.
For the sake of comparison, the surface characteristics of the adsorbed eggshell, methylene blue and untreated eggshell were examined by FTIR. Figure 7 confirmed that the two well defined peaks at 1395 cm-1 and 713 cm-1 belong to the C–O stretching and bending modes of calcium carbonate as major constituent in the eggshell matrix . The weak band at 817 cm1
is related to OCO out of plane of vibration mode . The 2 weak peaks between 2800-2900 8
cm-1 reflects the C=O5 group .The broad region at 3100-3500 cm-1 can be assigned to overlapping of O–H and N–H stretching vibration. The presence of OH group indicates that eggshell has moisture adsorption capacity. Bands at 1633 cm-1, 1540 cm-1 correspond to the carbonyl group stretching (amide group) and N–H bending respectively . FTIR spectrum of methylene blue reveals that the 2 peaks at 3718 and 2241 cm-1 are due to NH2 group and CC ring respectively. The 2 bands at 1236 and 1205 cm-1 are associated with aromatic and C-N amine group. While the aromatic C-H bending showed two peaks at 886 and 810 cm-1, bands at 1457 and 1313 cm-1 correspond to NH2 and CH2 groups. However, the adsorbed eggshell (Figure 7III) revealed the presence of 2 significant peaks belonging to MB at 3718 and 2241cm-1. The decrease in the intensities and the shift in wavenumbers are attributed to the adsorption of MB on the surface of eggshell.
3.4. Impact of concentrations on adsorption In order to optimize the design of an adsorbent-adsorbate system, various isotherm equations have been used to describe the equilibrium relationships between adsorbent and adsorbate, and consequently determine the ratio between the amount adsorbed and that remaining in the solution at room temperature and for a constant contact time of 60 min. The equilibrium adsorption data were analyzed with both the Langmuir  and the Freundlich isotherms . The used isotherms were expressed by the following 2 equations (7) and (8), respectively.
Ce C 1 e q e q max b. q max ln q e ln K F
1 n f ln Ce
Where KF , nf, are constants related to adsorption capacity and adsorption intensity, and qmax is the maximum amount of adsorbed dye on the adsorbent surface. The representation of the Freundlich isotherm (ln qe versus ln Ce) for the dyes gave straight lines with a slope of 1/n f and intercept of ln KF. As shown in Figure 8, the adsorption capacity (qe) for MB and CR increased from 4.8 to 94.9 mg/g and from 4.4 to 49.5 mg/g respectively, with increasing the concentration of dyes up to 1000 mg/l. It is noticed that the available sites of sorption became abundant and accommodate more dye molecules with the increase of dye concentrations which indicate the dependence of adsorption capacity (qe) on the initial dye concentration. 9
However, the removal percentage of MB showed almost a constant trend at all initial MB concentration in comparison to the CR. This phenomenon is consistent with our findings that the electrical double layer mechanism predominates the adsorption of MB onto the surface of Eggshell. A comparison of the isotherm constants in combination with the regression coefficients (R2) is illustrated in Table 3. It can be concluded that the Freundlich isotherm model describe better the sorption process of both dyes on the surface of eggshell.
The linearized form of Freundlich isotherm was found to be linear over the entire concentration range Figure 9, and the Freundlich constant, n, is equal to 2.0354 and 1.2738 for CR and MB respectively. Based on the work of Ho and McKay  and Basha and Murty , values of n between 1 and 10 indicate that both MB and CR dyes are favorably adsorbed onto Eggshell at all initial dye concentrations. Furthermore, the high correlation coefficient (R2) validated the appropriateness of Freundlich isotherm than the Langmuir isotherm to describe sorption of both dyes. The Freundlich model assumes a heterogeneous surface with a non–uniform distribution of heat of adsorption over the surface and the adsorption might be occurred as multiple-layer . The resulting fitting curves from the Langmuir isotherm are not illustrated, but the constants are tabulated in Table 3.
For the sake of comparison, Table 4 showed the adsorbent capacities of synthetic and natural adsorbents for the adsorption of different dyestuffs.
Conclusions Industrial waste shells of egg were a promising adsorbent for Methylene blue and Congo red. The effect of temperature on the adsorption capacity of eggshell was attributed to the mobility of dye ions that slipped away from the solid phase to the liquid phase. The impact of pH on the sorption capacity was firstly ascribed to the ionic interactions between the surface of eggshell and Congo red, and secondary to the electrical double layer mechanism for the adsorption of MB on the surface of eggshell. The FTIR spectrum of the adsorbed Eggshell confirmed the presence of significant peaks belonging to the MB adsorbate onto the surface of eggshell. The negative values of free energy and enthalpy indicated the spontaneity, feasibility and exothermic nature of the sorption process at room temperature. The high uptake capacity of eggshell with increasing initial dye concentrations from 50 to 1000 mg/l may be ascribed to the augmentation of collisions between the adsorbate and adsorbent. The 10
Freundlich isotherm model was the best for the description of the adsorption equilibrium of both dyes onto the eggshell, and characterized by a multilayer adsorption with a non-uniform distribution of adsorption over the surface which is accompanied by interactions between the adsorbed molecules. The adsorption of both MG and CR occurred spontaneously at a lower temperature.
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Figure 1 variation of the adsorbed amount MB and CR on eggshells with pH
Figure 2 Effect of temperature on the amount of adsorbed MB and CR on eggshells
Figure 3 Plot for (ln Kc) versus (1/T), gives a linear plot with a positive slope ΔH and the intercept is ΔS.
Figure 4 Effect of contact time on the adsorbed amounts of MB &CR at normal pH
Figure 5 First and second-order kinetic model for the adsorption of dyes on eggshell. a: plots of first order model log (qe - qt) versus Time, b: Plots of second order equation t/qt versus Time
Figure 6 SEM images of a) untreated eggshell, and b) adsorbed MB on Eggshell at low magnification c) adsorbed MB on Eggshell at high magnification
Figure 7: FTIR of I) untreated eggshell , II) MB, and III) MB adsorbed on eggshell
Figure 8 Effect of initial concentration of dyes on the amount adsorbed (mg/g) and their removal percentage at room temperature and pH normal.
Figure 9 Plots of linear Freundlich equation ln qe versus ln Ce for the estimation of isotherm constants. qe= adsorption density , Ce = equilibrium concentration
Table 1: Thermodynamics parameters for the adsorption of CR and MB on EG (Acid dye) Congo Red Temp., K 298
ΔG° J/mole -1630.07
323 333 343
(Basic dye) Methylene Blue
ΔG° J/mole -8949.28
Table 2: Kinetic parameters for the adsorption of MB & CR on the surface of eggshell. Pseudo first order
Pseudo second order
Table 3: Langmuir and Freundlich isotherms constants. Langmuir model
Table 4: Comparison between the adsorption capacities and kinetic models for the removal of various dyes by eggshell, eggshell membrane and other alternative adsorbents Adsorbent Adsorbate (dye) Kinetic Adsorption capacity, models qe(mg/g) G-Fe3O4/CaAlginate Composite Methylene blue Pseudo 2nd 38.12 order NH2-SBA15-ox Methylene blue Pseudo 2nd 445 order Eggshell biocomposite beads[55 ] Reactive red dye Pseudo 2nd 46.9 order & Elovich Calcined eggshell[56 ] Basic yellow28 Pseudo 2nd 28.87 order Eggshell powder[ 27] Anionic acid orange 51 Pseudo 2nd 112.36 order Vegetal fiber activated carbons Methylene blue Pseudo 2nd 33.7496 order Eggshell+Eggshell membrane [ this Methylene blue Pseudo 2nd 94.9 work] order Eggshell+Eggshell membrane [ this Congo red Pseudo 2nd 49.5 work] order