Kinetic Model Parameters

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Removal of Pb(II) from aqueous solutions by using chitosan coated zero valent Iron nano particles

Manuscript Type:

Complete List of Authors:

Original Article 06-Jan-2014

Madala, Suguna; Sri Venkateswara University, Department of Chemistry Chitosan coated zero valent Iron nano particles, adsorption, kinetics, isotherms

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Keywords:

LSST-2013-7120.R1

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Date Submitted by the Author:

Separation Science and Technology

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Manuscript ID:

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Removal of Pb(II) from aqueous solutions by using chitosan coated zero valent Iron nano particles Madala Suguna,*1 Nadavala Siva Kumar,2 Vudagandla Sreenivasulu,1 and Abburi Krishnaiah1 , *1Biopolymers and Thermo physical Laboratories, Department of Chemistry, Sri Venkateswara University, Tirupati – 517 502, A.P., India. 2

Department of Biological & Agricultural Engineering, Faculty of Engineering, University Putra

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Malaysia, Serdang, Selangor Darul Ehsan, Malaysia. ______________________________________________________________________________ ABSTRACT

This study reports the synthesis, characterization and application of chitosan coated zero

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valent Iron nanoparticles (CTS-Fe0) in the removal of Pb(II) from aqueous medium. This nano

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adsorbent showed a high adsorption capacity and efficient adsorption towards Pb(II) in aqueous medium. Adsorption of Pb(II) on

CTS-Fe0 obeyed pseudo-second order kinetics and was

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controlled by a film diffusion process. Among the various isotherm models the experimental data followed Langmuir isotherm and the maximum adsorption capacity was found to be 666.6 mg/g

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at pH 5.0 and 318 K. The sorption mean free energy from D-R isotherm was found to be 72, 131

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and 177 J/mol at 298, 308 and 318 K respectively, indicating a physical sorption. The percentage

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of Pb(II) removal by CTS-Fe0 particles is more than 90% at 318 K. The calculated thermodynamic parameters showed that the adsorption of Pb(II) is feasible, spontaneous and

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endothermic in nature. Experimental results indicated that the CTS-Fe0 appears to be a promising adsorbent for the removal of Pb(II) from aqueous media. Key Words: Chitosan coated zero valent Iron; adsorption; kinetics: Isotherms; Thermodynamics ______________________________________________________________________________ *Address Correspondence: Tel: +91-9493225460; E-mail: [email protected]

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INDRODUCTION Water pollution by heavy metals, through the discharge of industrial effluents, is a worldwide problem especially in some areas where a significant percentage of the population depends on ground water for drinking (1). Lead is hazardous heavy metal because once it gets into human body it disperses throughout the body immediately causing numerous diseases (2).

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According to US Environmental Pollution Agency, it is a highly toxic cumulative element, causing a variety of negative effects on humans, even at low dosages. For example, it can damage the red blood cells and limit their ability to carry oxygen to the organs and tissues. It can also affect the nervous system, kidneys and hearing (3). Hence, rigorous standards for lead

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concentrations in industrial effluents have been established by local legislations. According to

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US Environmental Protection Agency, the maximum contaminant level for Pb(II) in drinking water is 0.015 mg/L.

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A great deal of effort has been devoted to the effective removal of heavy metals from water. The traditional methods commonly used for heavy metal removal from aqueous solution

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include chemical precipitation, ion-exchange, solvent extraction, nano-filtration, reverse

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osmosis. The adsorption process is one of the popular methods for the removal of organics as

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well as inorganics from wastewaters (4-11). In the last decade, zero valent iron (ZVI) has been increasingly used in ground water remediation and hazardous waste treatment. Nano zerovalent

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iron is being used successfully to treat various metallic ions due to large specific surface area and more active sites (12,13). Recently many researchers have prepared several nanoparticles for removal of heavy metals because of the ease of modifying their surface functionality and their high surface area to- volume ratio for increased adsorption capacity and efficiency (14-17). Applications to aqueous medium require the zero valent nanoparticles to be stable in water.

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However due to van der Waals forces and magnetic interactions, these nanoparticles tend to agglomerate and grow rapidly to micrometer or millimeter scale particles, thereby diminishing their mobility and chemical reactivity. On the other hand ZVI particles show high activity in presence of aqueous medium and oxidized to ferrous or ferric iron. Eventually, ferric or ferrous may precipitate as a solid or remain in the solution depending on the solution pH. Mineral

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precipitates of carbonates, sulphides and oxides may farm coating on the reactive grains thereby inhibit the performance of iron. This oxidation of ZVI particles remains hurdle, especially in oxygen rich environments. While another disadvantage of this material is the separation and recovery of the fine particles after usage. Therefore, intensive efforts have been made to coat and

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protect ZVI particles from oxidation in order to overcome this problem (18,19).

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Chitosan is a natural polysaccharide with many useful properties such as biocompatibility, biodegradability and nontoxicity (20). Previous investigations demonstrated

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that chitosan can be used as protecting polymer for the preparation of metal nanoparticles in aqueous solutions including silver (Ag), gold (Au), platinum (Pt) and palladium (Pd). A number

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of nanoscale inorganic particles offer favorable properties in regard to selective removal of target

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contaminants. Polymer supported nano particles have been prepared and used for selective

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removal of target arsenic compounds and heavy metal ions. Geng et al., (2009) studied the removal of hexavalent Chromium by using a novel nano adsorbent Fe0-chitosan by borohydride

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reduction of Fe(III) in aqueous solutions (21). Chitosan can inhibited the formation of Fe(III)Cr(III) precipitation due to high ability to chelate Fe(III). Gupta et al., 2012 have demonstrated the applicability of zerovalent iron encapsulated chitosan nano spheres for the removal of total inorganic arsenic (22). These nano particles provide a promising single step treatment option to treat heavy metal contaminated natural water, which requires no pre-treatment. Qi and Xu,

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(2004) reported lead sorption from aqueous solution on chitosan nano particles (23).

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experiments showed that chitosan nano particles can sorb lead ions from aqueous solution effectively and sorption capacity has been improved greatly. Teng et al., (2013) have been reported the reduction of Cr(VI) to Cr(III) by using nano zero- valent Iron which is stabilized by sodium dodecyl sulfate (24).

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In this study, chitosan coated Iron nano particles (CTS-Fe0) were prepared, characterized and used for the removal of toxic metal ion such as Pb(II) in the pH range from 2.0-6.0. The synthesized sample is characterized by Fourier Infrared Transform Spectroscopy (FTIR), Scanning electron microscopy (SEM) and Energy dispersive X-ray (EDAX) analysis. The

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influence of experimental conditions such as pH, contact time, initial metal ion concentration,

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adsorbent dose and temperature were studied. The Freundlich, Langmuir, DubininRadushkevich (D-R) and Temkin equations were used to fit the equilibrium isotherms. The

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adsorption rates were analyzed on the basis of first- and second-order kinetic models. The thermodynamic parameters such as ∆Go, ∆Ho and ∆So for adsorption process were evaluated.

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MATERIALS AND METHODS

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Materials

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Chitosan with molecular weight 9.9 ×105 g mol-1 was purchased from Sigma-Aldrich, St. Louis, MO, U.S.A. Aqueous solutions were prepared using double distilled water. All the

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necessary chemicals are of analytical grade and obtained from Sigma-Aldrich, St. Louis, MO, U.S.A. Stock solution (1000 mg/L) was prepared by dissolving Pb(NO3)2.4H2O. This was further diluted to obtain the desired concentration for practical use.

The pH of the solution was

measured with a Digisun electronics digital pH meter using solid electrode calibrated with a standard buffer solution. A flame atomic absorption spectrophotometer (Shimadzu AA-6300,

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Japan) with deuterium background corrector was used. All measurements were carried out in an air/acetylene flame. A 10cm long slot burner head, a lamp and an air-acetylene flame were used. The operating parameters for working elements were set as recommended by the manufacturer. The FTIR spectra were recorded using Thermo-Nicolet FTIR, Nicolet IR- 200 series, Germany. Scanning Electron Microscopy (Model Evo15, CarlZeiss, England) has been used to study the

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surface morphology of the adsorbent. The sample composition and element contents were analyzed by using energy dispersive analysis system of X-ray (EDAX) (EDAX, Ltd., USA). Synthesis of Chitosan –stabilized zero valent Fe nano particles CTS-Fe0 was synthesized in solution by reducing Fe(II) to Fe0 using KBH4 in the

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presence of chitosan as a stabilizer. A 10 mL of solution containing 0.2978 g of FeSO4.7H2O

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was introduced in to 3 mL of 0.5% Chitosan solution. The mixed solution was stirred for 60 min under an inert atmosphere of nitrogen. Then 5 mL of freshly prepared aqueous solution

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containing 0.3467 g KBH4 was added drop wise into the mixture resulting in formation of black Fe0 nano particles and evolution of H2. After the gas evolution, the mixed solution was kept

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stirring for another 2 h until the entire reduction of metal. The resulted CTS-Fe0 were separated

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with magnet and washed with deoxygenated water thrice to eliminate excess chemicals. The entire process was carried out in a nitrogen atmosphere. Batch Studies

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Batch adsorption experiments were carried in Erlenmeyer flasks by adding 0.1 g of adsorbent in 100 mL of aqueous metal solution at desired initial pH, metal ion concentration and temperature. The initial pH was adjusted with solutions of 0.1M HCl or 0.1M NaOH. The flasks were gently agitated in a temperature controlled water bath shaker at 200 rpm for a period of 3h. All the experiments were performed in triplicates at the desired initial conditions and the

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concurrent value was taken. The content of flask was separated from adsorbent by filtration, using Whatman No. 42 filter paper and the filtrate was analyzed for remaining metal concentration in the sample using atomic adsorption spectrophotometer. The amount of metal ion sorbed per unit mass of the adsorbent (mg/g) was evaluated by using the following equation:

 C − Ce  Qe =  i  v  m 

(1)

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where Qe (mg/g) is the adsorption capacity at equilibrium, Ci and Ce denote respectively the initial and equilibrium concentrations of metal ion (mg/L), V (L) is volume of adsorbate in liters and m is the amount of adsorbent in grams. To study the effect of initial pH on metal ion

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uptake by adsorbent, sorption experiments were performed by using 100 mL of solution with

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initial metal ion concentration of 100 mg/L and adsorbent dose of 0.1 g at 298 K by varying the pH of the solution. The effect of adsorbent dose on adsorption of Pb(II) was studied by agitating

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100 mL of 100 mg/L metal solution with different amounts of adsorbent. Effect of initial concentration of was studied by varying the concentrations (100, 200, and 300 mg/L) and 0.1 g

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of adsorbent; pH was kept at 5.0. The effect of contact time on removal of metal ion was studied

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by varying the contact time from 30 to 240 min at 298 K. The synthetic solutions were prepared

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by diluting Pb(II) standard stock solutions (concentration 1000 ± 2 mg/L). Fresh dilutions were used in each experiment.

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STATISTICAL EVALUATION OF THE KINETIC PARAMETERS Marquardt’s percent standard deviation (MPSD)

The MPSD error function is employed in this study to find out suitable kinetic model to represent the experimental data (25). The MPSD error function has been used previously by a number of researchers (26).

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Ferro r ( % ) = 100 х

p

∑ i

 q i m od el − q i exp  q i exp 

  

2

 1  .   p −1

(2)

where qimodel is each value of q predicted by the fitted model and qiexp is each value of q measured experimentally and p is the number of experiments performed. RESULTS AND DISCUSSION

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SEM-EDAX analysis

Adsorption capacity of the adsorbent is mainly depends on the shape and size. SEM image of the CTS-Fe0 particles before adsorption of Pb(II) in Fig. 1a-i, shows that adsorbent is

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porous in nature. Fig. 1b-i indicates the SEM image of CTS-Fe0 after adsorption of Pb(II). The sample composition and element contents were analyzed by energy dispersive analysis system

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(EDAX). The EDAX spectrum for CTS-Fe0 particles shown in Fig. 1a-ii, indicates the presence of Fe, C, O, and S, but not Pb(II) ions on the surface of freshly synthesized CTS-Fe0 particles.

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An EDAX spectrum of Pb(II) loaded CTS-Fe0 is shown in Fig. 1b-ii. The EDAX spectrum gives

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characteristic peaks for Pb at 2.5, 6.5 and 10.5 keV. This confirms the binding of Pb(II) to CTS-

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Fe0. Surface morphology of SEM with EDAX of unloaded CTS-Fe0 (Fig. 1a-iii) is different from the metal loaded CTS-Fe0 (Fig. 1b-iii). It is also evident from the SEM pictures of loaded and un

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loaded CTS-Fe0 (Fig. 1a-i and Fig. 1b-ii). FTIR characterization

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FTIR spectra of CTS-Fe0 particles before and after adsorption Pb(II) is shown in Fig. 2. The peak at 3408.5 cm-1 is due to the –OH and N-H group stretch, a weak band at 2924.3 cm-1 (C-H stretch), 1631.93cm-1 (N-H bending vibration), 1111.1 and 1030.4 cm-1 are due to the skeletal vibration of C-O stretch. In Fig. 2 several noticeable changes occur in the spectrum of CTS-Fe0 (Fig. 2.a) in comparison with the spectrum of CTS-Fe0 loaded with Pb(II) (Fig.2.b). The

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stretching bands of the hydroxyl and amino groups shift from 3420 cm-1 for CTS-Fe0 to 3408 cm1

for CTS-Fe0 loaded with Pb(II) and clearly measurable change in wave number indicates that

N-H and O-H vibrations are affected due to Pb(II) adsorption on CTS-Fe0. The N-H bending band of CTS-Fe0 at 1647cm-1 is shifted to 1631.9 cm-1. In Fig. 2. (b), the peak at 545 cm-1 ascribe to Fe-O group, bands at 893 and 800 cm-1 corresponds to the bonding of Pb(II) and Fe.

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All these changes indicate that nitrogen and oxygen atoms are the binding sites for CTS-Fe0. Effect of pH

Adsorption of Pb(II) on CTS-Fe0 is found to be pH dependent as revealed from Fig. 3. In order to optimize the pH for maximum removal efficiency, experiments were conducted at

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different temperatures (From 298, 308 and 318 K) and employing 100 mL of Pb(II) ion solution

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of 100 mg/L initial concentration containing 0.1 g of CTS-Fe0 over the pH range 2.0-6.0. The maximum uptake of Pb(II) ions takes place at pH 5.0 at all temperatures studied. At low pH the

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surface sites are protanated and the surface becomes positively charged resulting in electrostatic repulsion between adsorbate and adsorbent. As pH increases deprotanation starts and the Pb(II)

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ion undergo complex with oxidized iron and chitosan. The pH could not maintain above 6.0 as

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the Pb(II) tendency to precipitate at higher pH.

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Effect of adsorbent dosage

The effect of dosage on the removal of Pb(II) on CTS-Fe0 is presented in Fig. 4. To

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understand the effect of amount of adsorbent on adsorption of Pb(II), the experiments were performed at pH 5.0 with 100 mL of sorbate solution by varying the amount of adsorbent from 0.05 to 0.5 g. It is observed that the removal of lead increased rapidly with increasing dosage from 0.05 to 0.5 g, after certain adsorbent dosage the removal efficiency does not increase significantly and reaches maximum at of 0.5 g. The increase in percent removal with increase in

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CST-Fe0 dose may be attributed to the increase in the availability of active sites and effective surface area. Effect of contact time The results obtained from time-dependent experiments for the removal of Pb(II) by CTSFe0 are shown in Fig. 5. It is evident from the figure that the adsorption capacity dependent on

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the equilibrium time. The extent of adsorption increases with time and attained equilibrium for all the concentrations of Pb(II) studied (100-300 mg/L) at 150 min. In the initial stages the removal efficiencies of the adsorbent increase rapidly due to the abundant availability of active binding sites on the biomass, and with gradual occupancy of these sites, the sorption became less efficient in the later stages. Adsorption kinetic models

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The adsorption kinetic models are very important in the process of removal of toxic

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heavy metals from the aquatic environment. In this study pseudo-first order model and pseudosecond order models have been used:

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 K  log(qe − qt ) = log qe −  1  t  2.303 

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(2)

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t 1 1 = + t 2 qt K 2 q e q e

(3)

The qe and qt are the adsorption capacity at equilibrium and time at t, respectively (mg/g) and K1

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(min-1) and K2 (mg/g/min) are rate constants of pseudo-first order and second order kinetic models. The second order sorption rate constants (K2) can be determined experimentally by plotting of t/Qt vs t.

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The intra-particle diffusion model is used to investigate the diffusion controlled adsorption system. The probability of the intra-particle diffusion was explored by using the following equation (27):

qt = kid t1/2 + C

(4)

where qt (mg/g) is the adsorption capacity at any time t (min), kid is the intraparticle diffusion

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rate constant (mg/g. min1/2), C is the value of intercept which gives an idea about the boundary layer thickness, i.e., the larger intercept; the greater is the boundary effect. The constants obtained from the plots of qt vs t0.5 (square root of time) at different concentrations are shown in

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Table 1. The plots are not linear over the whole time range, indicating that more than one step is involved in the adsorption of metal ions. If the intra-particle diffusion is the only rate-controlling

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step then the plot should pass through the origin, else the boundary layer diffusion affects the adsorption to some degree. The plots are not passing through origin indicating that the intra

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particle diffusion is not the only rate determining factor.

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The mathematical treatment recommended by Boyd was employed to recognize whether

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the sorption proceeds via film diffusion or particle diffusion mechanism. The model can be expressed in the following form (28): F = (1 -

6 Π2

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) exp(- B ) t

(5)

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where F = qt/qe; qe is the amount of metal ions adsorbed at equilibrium (mg/g), qt represents the amount of ions adsorbed at any time t (min) and Bt is a mathematical function of F. Eq. (5) can be rearranged by taking the natural logarithm to obtain the equation: Bt = -0.4977 - ln(1 - F)

(6)

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The plots of Bt vs. t at different initial concentrations of Pb(II) are shown in Fig. 6, which are linear with correlation coefficient (R2) close to unity and not passing through the origin. The results suggest that the adsorption process is controlled by film diffusion. The Elovich equation is often used to interpret the kinetics of chemisorption on highly heterogeneous sorbents. It can be expressed as

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1 1 q t =   ln( ab ) + ln t b b

(7)

where a (mg/g/min) is the initial sorption rate and b (g /mg) is the desorption constant related to extent of surface coverage and activation energy respectively for chemisorption. The values of

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parameters a and b, obtained from the slope and intercept of the linear plot of qt vs ln t (Figure not shown) are given in Table.1. Based on the correlation coefficients and MPSD error function

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values, the adsorption of Pb(II) on CS-Fe0 is best described by pseudo-second order. Adsorption isotherm modeling

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The data on adsorption of Pb(II) on CTS-Fe0 were correlated with Langmuir, Freundlich,

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D–R and Temkin isotherm models. The adsorption isotherms are fundamental in describing the

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interactive behavior between solute and adsorbent. The isotherm parameters illustrate the surface properties and affinity of the adsorbent. The Langmuir equation is expressed as

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1 1 1 = + qe qm K LC e qm

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(8)

where qe (mg g-1) is the amount of metal ion adsorbed per unit mass of adsorbent, Ce (mg L-1) is the equilibrium concentration of metal ions, qm is the maximum monolayer adsorption capacity of the adsorbent (mg/g) and KL (mg/L) is the Langmuir equilibrium constant. The plot of 1/qe vs 1/Ce (Figure not shown) at different temperature was used to determine qm and KL and the values

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were shown in Table 2. The Langmuir isotherm gave R2 values close to unity indicating that the adsorption of Pb(II) onto CTS-Fe0 is best described by Langmuir model. The Freundlich model is given as

lo g q e = lo g K

F

+

1 lo g C e n

(9)

where KF ((mg/g)(L/mg)1/n) is relating the adsorption capacity and 1/n is an empirical parameter

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relating the adsorption intensity. Values of n and KF for Pb(II) were calculated at different temperatures (298, 308 and 318 K) from the slope and intercept of log ce vs log qe and are presented in Table 2. The R2 values of Freundlich isotherm indicate that this model is unable to

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describe adequately the relationship between the amount of Pb(II) adsorbed by the CTS-Fe0 and its equilibrium concentration in the solution. The values of KF are found to increase with increase

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in temperature suggesting that adsorption process is endothermic in nature. The values of 1/n are less than 1 represents a favorable sorption.

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The equilibrium data were examined by using Dubinin-Radushkevich isotherm in order

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to determine the nature of the adsorption process as physical or chemical (29). The D–R sorption

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isotherm is more general than the Langmuir isotherm. The linear presentation of D–R isotherm equation is expressed as ln q e = ln q m − βε

On

2

(10)

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where qe is the amount of metal ions adsorbed per unit mass of biomass (mg g-1), qm is the maximum adsorption capacity (mg g-1), β is the activity coefficient related to adsorption mean free energy (mol2/kJ2) and ε the Polanyi potential ( ε = RT ln(1 + 1/Ce)), R and T are the universal gas constant (kJ/mol/K) and the absolute temperature (K) respectively. The constant β gives the mean free energy E (kJ/mol) of sorption per molecule of sorbate. The Dubinin-

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Radushkevich isotherm parameters for Pb(II) ions at three temperatures are listed in Table 2. E is related to the mean free energy of the sorption per mole of the sorbate (kJ/mol), as follows: E =

1 − 2β

(11)

E is used to estimate the type of adsorption process. If E < 8 kJ/mol, adsorption process is of a physical nature whereas, if value 8 < E > 16 kJ/mol, the adsorption process can be explained by

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ion exchange mechanism (30). The plots of Ce vs ε2 have no linear correlation between Ce and ε2, but the first six data points for each temperature gives linear correlation. E values are 72, 131 and 177 J/mol at 298, 308 and 318 K temperatures respectively, indicates that the process of

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adsorption of Pb(II) onto CTS-Fe0 is a physisorption. Temkin isotherm assumes that due to the adsorbent–adsorbate interactions, the heat of

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adsorption of all the molecules in the layer would decrease linearly rather than logarithmically (31). The adsorption is characterized by a uniform distribution of binding energies, up to some

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maximum binding energy. The linear form of the Temkin isotherm is expressed as:

e

(12)

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 RT   RT  qe =   ln A +   ln C  bT   bT 

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where RT/bT = B (J /mol), which is the Temkin constant related to heat of sorption whereas A

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(L/g) is the equilibrium binding constant corresponding to the maximum binding energy. The constants bT and A were calculated from the plot of Ln Ce vs. qe and are depicted in Table 2. The

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lower R2 values at all the temperatures, indicate that adsorption of Pb(II) on CTS-Fe0 does not follow Temkin model. The Langmuir isotherm gave R2 values close to unity indicating that the adsorption of Pb(II) on the CTS-Fe0 is best described by Langmuir model. CTS-Fe0 particles showed comparable biosorption capacity towards Pb(II) with previous literature results as shown in Table 3.

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Thermodynamic Study The thermodynamic parameters such as enthalpy change (∆H0), entropy change (∆S0) and Gibbs free energy change (∆G0) for the sorption process were calculated from the variation of Langmuir constant (KL) with temperature (T) using well known relations, ∆G 0 = − RT ln K L

(13)

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∆G 0 = ∆H 0 − T∆S0 ln K L =

(14)

∆S 0 ∆H 0 − R RT

(15)

Change in enthalpy and entropy due to adsorption of metal ions on CTS-Fe0 over the temperature

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range studied can be determined from the linear plots of ln KL against 1/T using the least squares analysis (Figure not shown). The values of ∆G0, ∆H0 and ∆S0 for sorption of Pb (II) by CTS-Fe0

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at different temperature (298-318 K), given in Table 4, show that ∆G0 is small and negative but

ev

decreases with increasing temperature. The negative values of ∆G0 demonstrate the process to be spontaneous and positive values of ∆H0 indicate that the process require some energy input from

ie

the outside. Hence the process of removal of Pb(II) on CTS-Fe0 is endothermic in nature. The

w

positive value of ∆S0 suggested the increase of randomness at the solid/solution interface during the adsorption of metal ions on CTS-Fe0.

On

CONCLUSIONS

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Chitosan coated iron nano particles (CTS-Fe0) have been proven to be an effective adsorbent for the removal of Pb(II). The metal ion adsorption on surface of CTS-Fe0 was observed via SEM, EDAX and FTIR analysis. The adsorption process strongly depends on the experimental parameters such as initial concentration of Pb(II), contact time, adsorbent dose, pH and temperature. The percentage of Pb(II) removal by CTS-Fe0 particles is more than 90%. The adsorption process follows Langmuir isotherm model and maximum adsorption capacity of

14

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Separation Science and Technology

adsorbent at 318 K temperature is 666.6 mg/g. Adsorption of Pb(II) onto CTS-Fe0 obeyed the pseudo-second order kinetic model. The thermodynamic results show the feasibility, spontaneous and endothermic nature of adsorption process.

ACKNOWLEDGEMENTS One of us (MS) thankful to DST, New Delhi, India for the award of Women Scientist and the

rP Fo

financial support of this research project, SR/WOS-A/CS/76/2011 and another (AK) is grateful to UGC, New Delhi for the award of BSR faculty fellowship.

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ee

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chemical deposition of air stable nano particles on mono dispersed carbon spherules. Chem. Mat., 15: 1378-1384. 19.

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Boguslavsky, Y.; Margel, S. (2008) Synthesis and characterization of poly (divinyle benzene) - coated magnetic iron oxide nanoparticles as precursor for the formation of air-

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stable carbon-coated iron crystalline nano particles. J. Colloid Interface Sci., 317: 101-

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Calvo, P.; Remunan-Lopez, C.; Vila-Jato, J.L.; Alonso, M.J.J. (1997) Novel hydrophilic Chitosan-polyethylene oxide nanoparticles as protein carriers. J. Appl. Poly. Sci., 63:

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Teng, H.; Xu, S.; Zhao, C.; Lv, F.; Liu, H. (2013) Removal of hexavalent chromium from aqueous solutions by sodium dodecyl sulfate stabilised nano zero valent iron: A kinetics, Equilibrium, thermodynamic stydy. Sep. Sci. Technol., 48: 1729-1737.

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Vaghetti, J.C.P.; Lima, E.C.; Royer, B.; Cunha, B.M.; Cardoso, N.F.; Brasil, J.L.; Dias, S.L.P. (2009) Pecan nutshell as biosorbent to remove Cu(II), Mn(II) and Pb(II) from

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and humic acids on the adsorption of metal cations to SiO2 nanoparticles. Colloids Surf.,

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functionalized Fe3O4 magnetic nano-particles. Chem. Eng. J., 91: 104– 111. 36.

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nano-TiO2 matrix. J. Environ. Sci., 21: 1722–1729. 37.

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Afkhami, A.; Saber-Tehrani, M.; Bagheri, H. (2010) Simultaneous removal of heavymetal

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with

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Sheela, T.; Arthoba Nayaka, Y. (2012) Kinetics and thermodynamics of cadmium and lead ions adsorption on NiO nanoparticles. Chem. Eng. J., 191: 123– 131.

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Xi, Y.; Megharaj, M.; Ravendra, N. (2010) Reduction and adsorption of Pb2+ in aqueous solution by nano-zero-valent iron—A SEM, TEM and XPS study. Mater. Res. Bull., 45: 1361–1367.

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Song, J.; Kong, H.; Jang, J. (2011) Adsorption of heavy metal ions from aqueous solution by polyrhodanine-encapsulated magnetic nano particles. J. Colloid Interface Sci., 359:

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505-511.

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Legends to tables

1. TABLE 1 Values of the parameters of kinetic models for Pb(II) on CTS-Fe0

Fo

2. TABLE 2 Langmuir, Freundlich, D-R, Temkin isotherm constants for adsorption of Pb(II) on CTS-Fe0 at different temperatures.

rP

3. TABLE 3 Comparison of maximum adsorption capacity (mg/g) of CTS-Fe0 for Pb(II) on different adsorbents from the literature

ee

rR

4. TABLE 4 Values of thermodynamic parameters for the adsorption of Pb(II) onto CTS-Fe0

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TABLE 1 Values of the parameters of kinetic models for Pb(II) on CTS-Fe0 Kinetic Model

Parameters

Fo

rP

Pseudo-first-order

Pseudo-second-order

100

200

300

qe,exp (mg/g)

58.4

71.5

87.7

qe, cal (mg/g)

36.4±1.1

56.6±3.9

59.6±1.6

K1

0.014±0.002

0.018±0.009

0.014±0.004

R2

0.998

0.964

0.987

MPSD (%)

26.6

14.7

22.6

qe, cal (mg/g)

58.8±1.5

74.9±0.7

90.0±1.2

0.27±0.03

0.48±0.06

0.73±0.22

0.998

0.998

0.998

0.4

3.3

1.8

qe, cal (mg/g)

53.7±0.53

68.6±0.61

84.67±1.31

a (g/mg/min

179.6±1.72

47±0.56

44.1±1.08

b (g/min)

0.05±0.002

0.06±0.005

0.07±0.001

MPSD (%)

5.7

2.9

qe, cal (mg/g)

55.4±0.5

68.1±0.7

Kid

3.9

3.6

C

7.8

24.6

49.1

R2

0.936

0.945

0.957

MPSD (%)

3.6

3.4

2.8

ee K2×10-3 R2

rR

MPSD (%) Elovich model

Weber- Morris model

Concentration of Pb(II) (mg/L)

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2.5 84.3±1.3

2.9

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TABLE 2 Langmuir, Freundlich, D-R, Temkin isotherm constants for adsorption of Pb(II) on CTS-Fe0 at different temperatures

Temp K 298 308 318

Langmuir qmax b (mg/g) (L/mg) 0.004± 416.6±1.7 0.001 0.016± 555.5±2.2 0.03 0.006± 666.6±1.2 0.003

Freundlich

Fo

KF (mg/g)

R2

rP

0.999

0.999 0.994

1/n

0.747 ±0.4 0.819 11.4±4.8 ±0.1 0.878 18.7±4.3 ±0.2 5.2±2.9

ee

qm (mg/g) 213.8± 3.5 236.7± 10.2 245.0± 4.2

R2 0.985 0.989 0.992

rR

Dubinin-Ruduskevick β E (mol2 /kJ2) (J/mol)

R2

bT (L/mg)

Temkin AT (J/mol)

R2

96.76±4.2

72±2.5

0.918

34.9±3.0

5.42±0.8

0.949

29.05±4.5

131±4.5

0.974

32.9±2.0

2.79±0.7

0.939

15.89±2.9

177±4.3

0.989

35.1±2.9

2.93±0.1

0.917

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TABLE 3 Comparison of maximum adsorption capacity (mg/g) of CTS-Fe0 for Pb(II) on different adsorbents from the literature

Adsorbent

Adsorption Capacity

References

(mg/g) low silica nano-zeolite X

909.09

(32)

CeO2 nano particles

189.9

(33)

Fe3O4 nano particles

83.0

TiO4 nano particles

159.0

SiO2 nano particles

41.9

Humic acid coated SiO2 nano

104.8

particles

ee

rP Fo

(34)

Fulvic acid coated SiO2 nano particles.

90.6

Amino functionalized Fe3O4

40.10

(35)

Pb(II)-imprinted polymer in

ev

rR

22.7

(36)

100.0

nano-TiO2 matrix

ie

(37)

NiO nanoparticles

909.0

(38)

Nano-zero-valent iron

401.8

Polyrhodanine encapsulated

179.0

Nano-alumina modified with

w

2,4-dinitrophenylhydrazine

Chitosan nano particles

398.0

CTS-Fe0

666.6

(39) (40)

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magnetic nano particles

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(23)

Present Study

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TABLE 4 Values of thermodynamic parameters for the adsorption of Pb(II) onto CTSFe0 Temperature (K)

0

-∆ G (kJ/mol)

298

6.9

308

5.4

∆ H0

∆ S0

R2

(kJ/mol)

(kJ/mol K)

54.47

0.159

0.991

rP Fo

318

3.5

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Legends Figures FIG. 1. (a) Unloaded CTS-Fe0 (i) SEM Image (ii) EDAX analysis (iii) SEM image with EDAX. (b) CTS-Fe0 Loaded with Pb(II) (i) SEM Image (ii) EDAX analysis (iii) SEM image with EDAX. FIG. 2. FTIR spectra (a) Unloaded CTS-Fe0 (b) CTS-Fe0 Loaded with Pb(II) FIG. 3. Effect of pH on the adsorption of Pb(II) onto CTS-Fe0 (initial concentration: 100 mg/L, contact

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time: 3h, agitation speed: 200rpm, temperature: 298-318 K, adsorbent dose: 0.1 g). FIG. 4. Effect of adsorbent dose on the adsorption of Pb(II) onto CTS-Fe0 particles (Conditions; initial concentration: 100 mg/L, contact time: 3h, pH: 5.0). FIG. 5. Effect of contact time on the adsorption of Pb(II) onto CTS-Fe0 particles (Conditions; adsorbent dose:

ee

0.1 g, pH: 5, Temperature;298 K).

rR

FIG. 6. Boyd model plots for the adsorption of Pb(II) onto CTS-Fe0 particles.

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ie

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(a)

Fo

rP

ee

rR

ev (i)

iew

Element C O S Fe

Weight% 8.07 20.07 7.33 5.99

Atomic% 30.25 59.26 5.2 5.33

Totals

42.09

99.99

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(ii) (iii) 2

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(b)

Fo

rP

ee

rR

ev (i)

Element

Weight%

O Si S Fe Zn As Pb

24.99 0.25 1.52 18.15 0.02 0.12 7.87

Totals

52.92

Atomic%

iew 77.74 0.45 2.35 15.96 0.02 0.08 3.41

100.01

On

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(ii) (iii) 0

FIG. 1. (a) Unloaded CTS-Fe (i) SEM Image (ii) EDAX analysis (iii) SEM image with EDAX

(b) CTS-Fe0 Loaded with Pb(II) (i) SEM Image (ii) EDAX analysis (iii) SEM image with EDAX

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w

ie

ev

rR

ee

rP Fo FIG. 2. FTIR spectra (a)

Unloaded CTS-Fe0

(b)

CTS-Fe0 Loaded with Pb(II)

4

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rR

ee

rP Fo 0

FIG. 3. Effect of pH on the adsorption of Pb(II) onto CTS-Fe (initial conc:

100 mg/L, contact time: 3h, agitation speed: 200rpm: adsorbent dose: 0.1 g).

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rR

ee

rP Fo FIG. 4. Effect of adsorbent dose on the adsorption of Pb(II) onto CTS-Fe

0

particles (Conditions; initial concentration: 100 mg/L, contact time: 3h, pH: 5.0, Room temperature).

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rR

ee

rP Fo 0

FIG. 5. Effect of contact time on the adsorption of Pb(II) onto CTS-Fe

ev

particles (conditions; adsorbent dose: 0.1 g, pH: 5, Room temperature).

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rR

ee

rP Fo 0

FIG. 6. Boyd model plots for the adsorption of Pb(II) onto CTS-Fe particles.

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