Synthesis, Characterization, and Silver Adsorption Property of

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Synthesis, Characterization, and Silver Adsorption Property of Magnetic Cellulose Xanthate from Acidic Solution: Prepared by One Step and Biogenic Approach Mostafa Hossein Beyki, Mehrnoosh Bayat, Simin Miri, Farzaneh Shemirani,* and Hassan Alijani School of Chemistry, University College of Science, University of Tehran, P.O. Box 14155-6455, Tehran, Iran S Supporting Information *

ABSTRACT: In this work magnetic cellulose xanthate was prepared with two different routes, i.e., fabrication of Fe3O4@ cellulose followed by preparation of xanthate, and a one step approach by adding iron source to cellulose xanthate solution. The cellulose acts as both as reducing agent to convert Fe3+ ions to Fe2+ and template for growth of Fe3O4. The prepared composites were characterized by SEM, XRD, VSM, EDS, TGA, and FT-IR techniques. Magnetic sorbents were applied for adsorption of silver from acidic medium, and results revealed that the one step prepared composite has better performance in comparison with Fe3O4@cellulose xanthate, as the maximum adsorption capacity within 5 min extraction time was 166 and 15.6 mg g−1, respectively. The relative selectivity factor (αr) of Ag+ with respect to other cations, such as Zn2+, Cr3+, Co2+, Ni2+, Pb2+, and Pd2+, is 252, 74.8, 2543, 924, 3837, and 26.6, respectively. Moreover, the reusability of the sorbent was investigated by elution the adsorbed ions with 3.0 mL of 0.4 mol/L Na2S2O3 solution. It was found that the recovery was (90−97%) after 3 cycles of sorption and desorption. Finally this method was applied to analyze the silver ions in tap water, dental radiology agent, and synthetic samples.

1. INTRODUCTION Microcrystalline cellulose is a partially depolymerized cellulose. It can be prepared by treating α-cellulose from corn cob, rice, and other fibrous plant materials with mineral acids.1,2 Cellulose is cheap and renewable, and can provide a permanent form of environmentally safe source of materials. Its structure is composed of a large number of hydroxyl groups which serve as active sites to bind desired materials such as metal ions, organic dyes, and proteins; hence, it has found wide applications in the fields of textiles, food processing, biomedicine, and environmental remediation.3−9 There are several distinct methodologies for improvement of the physiochemical properties of cellulose. In some cases, this biopolymer can be conjugated with a different organic or inorganic compound such as crown esters, amines, sulfur, and nanoparticles to yield a hybrid grafting compound with intrinsic properties.10−15 The xanthate method of grafting is one of the most promising for industrial applications because these maerials are highly insoluble, have high stability constant values of the metal complexes, and can be prepared with relatively inexpensive reagents. Cellulose can react with carbon disulfide in alkaline solution under caustic condition to form water-soluble cellulose xanthate.16,17 Xanthate salts are intermediates in the elimination process. They are used to control radical polymerization process, as flotation agents in mineral processing, and also for macromolecular design via interchange of xanthate. The sulfur fragment of xanthate has a soft Lewis base character; hence, toward naked cellulose the cellulose xanthate has higher ion exchange or adsorption capacity and can be employed as an efficient sorbent of soft heavy metals in environmental protection or other certain application.18 The collection and recycling of solid mass from reaction media, especially from a large sample solution, is a challenge when the adsorbent was made at the nanoscale. Hence, recently, magnetic © 2014 American Chemical Society

separation technology is gaining growing attention. By applying a magnetic field, magnetic nanocarriers can be easily manipulated; moreover, magnetic nanocomposites can improve the surface property and can reduce the required dosage.19,20 Besides, pure nanoparticles are easy to aggregate into large particles via the interparticle dipolar force, leading to the decrease of specific surface area. Therefore, to avoid the agglomeration, many materials have been used as the template to disperse the magnetic nanoparticles. Among many matrix materials, cellulose is an ideal candidate in order to avoid the agglomeration of magnetic nanoparticles owing to the fact that it is one of the most abundant row organic biomasses in the earth.21 In general, magnetic cellulose materials can be prepared with different morphologies, such as films, fibers, microspheres, etc. Moreover, they exhibit different magnetic responses because of the different natures and structures which can be employed in a wide range of potential applications.22 There are several reports about employing magnetic cellulose for heavy metal adsorption. Liu et al. used magnetic chitosan−cellulose hydrogel for copper adsorption as the stability and adsorption capacity of dispersed nanoparticles is greatly enhanced by preventing their aggregation and oxidation.23 Donia et al. used nanomagnetic cellulose for fast adsorption of Hg(II), Cu(II), and Ag(I) with good reusability and stability.24 Moreover, Min et al. employed magnetic cellulose composite for cadmium adsorption that was obtained with blending method.25 Herein, we have reported two approaches to synthesize magnetic Fe3O4/cellulose xanthate (MCX). In the first approach, Received: Revised: Accepted: Published: 14904

May 15, 2014 August 17, 2014 August 27, 2014 August 27, 2014 dx.doi.org/10.1021/ie501989q | Ind. Eng. Chem. Res. 2014, 53, 14904−14912

Industrial & Engineering Chemistry Research

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bath along with mechanical stirring. About 10 mL of Fe3+ solution (0.025 mol) was added dropwise into xanthate solution. After 2 h reaction time, the black precipitate was filtered with filter paper and washed several times with distilled water. The obtained magnetic composite was dried at 60 °C for 4 h and then stored until it was used. In the second approach for preparation of MCX2, 1.0 g of cellulose and 0.025 mol of Fe3+ were added to 50 mL of distilled water and stirred for 10 min in order to trap metal ions on cellulose structure. Then, NaOH solution (2.0 mol/L) was added to it, and the suspension was kept under ultrasound radiation for 1 h at 80 °C. The prepared composite was dried at 80 °C for 3 h. To prepare xanthate, 1.0 g of magnetic cellulose was dispersed in 50 mL of NaOH solution (2 mol/L) and stirred for 1 h at room temperature. After this step, 4 mL of CS2 was added to it and stirred for another 1 h, and then, the prepared xanthate separated with filter paper and then collected after washing with distilled water is dried at 60 °C for 4 h. The processes for preparation of MCX are represented in Scheme 1.

MCX1 was prepared by applying one step and biogenic route based on the dissolving of cellulose in NaOH and carbon disulfide followed by adding Fe3+ ions as the only iron source. The cellulose acts as the reducing agent and the template to promote the growing of nanoparticles. The other approach is based on the preparing of magnetic cellulose following by preparation of xanthate (MCX2). The prepared composite is a candidate for uptake of soft metal ions such as silver. The silver is a valuable and important substance in commerce and is widely used in jewelry, medicine, alloys, and photography.26,27 High levels of silver are toxic to human cells, which can slow healing in the case of wound care. On the other hand, recent information about the interaction of silver with essential nutrients, especially selenium, copper, vitamin E, and vitamin B12, has focused attention on its potential toxicity.28−33 Thus, due to the high economical value of silver and the toxicity of its compound, the recovery of it from waste solutions is important as well as its sensitive determination.34−39 In this view, the applicability of this method was investigated for analysis of the silver ions in acidic media. Finally this method was applied for determination of the silver ions, in tap water, dental radiology agent, and synthetic samples.

Scheme 1. Synthetic Approach to Prepare MCX

2. EXPERIMENTAL SECTION 2.1. Reagents and Solutions. All chemicals used in this work were of analytical reagent grade. Cellulose microcrystalline powder and Na2S2O3 were obtained from Merck (Merck, Darmstadt, Germany) and were used without further purification. Carbon disulfide (CS2), NaOH, and Fe(NO3)3·9H2O were used for synthesis of magnetic cellulose xanthate (MCX). The standard solution of silver ions (1000 mg L−1) was prepared by dissolving AgNO3 salt in an appropriate volume of distilled water before use. Different concentrations of HNO3 solution were prepared by dilution of concentrated HNO3 (65%). All the plastic and glassware were cleaned by soaking in diluted HNO3 or HCl and rinsed with distilled water prior to their use. 2.2. Instruments. Preparation of magnetic sorbent was assisted with an ultrasound clean bath operating at 40 Hz with a power of 340 W (Elmasonic, D-78224 Singen/utw, typ S, Germany). Separation was assisted by using a strong neodymium−iron− boron (Nd2Fe12B) magnet (1.31 T). The powder X-ray diffraction (p-XRD) analysis was carried out on a Phillips powder diffractometer X′ Pert MPD using PW3123/00 curved Cufiltered Cu Ka (λ = 1.540 589 Å) radiation. Fourier transform infrared spectra (FT-IR) were measured with Equinox 55 Bruker with ATR method over the wavelength range 400−4000 cm−1. Surface morphology analysis of the adsorbents was carried out using a scanning electronic microscope (SEM) (Philips XL30, Eindhoven Netherlands). Energy dispersive X-ray spectrometry (EDS) and TGA results are recorded with Oxford ED-2000 (England) and TA-Q-50, respectively. A Varian model AA-400 atomic absorption spectrometer (Varian, Musgrave, Australia), equipped with a deuterium lamp background and a hollow cathode lamp, was used for determination of silver. All measurements were carried out in a peak height mode. Operating parameters were set as recommended by the manufacturer. 2.3. Preparation of Magnetic Composite. In the first approach, about 1.0 g of cellulose and 4 mL of CS2 were added to 50 mL of NaOH solution (2.0 mol/L) and magnetically stirred for 1 h at room temperature. Then, the reaction mixture was distilled gently in water bath for 15 min until excess carbon disulfide was removed and an orange clear solution was obtained. The second step was carried out at 80 °C in an ultrasound clean

2.4. Adsorption Procedure. Batch adsorption experiments were carried out in 50 mL of HNO3 solution (0.1 mol/L) which contains 2- 50 μg of silver ions and 20 mg of adsorbent. The mixture was shaken for 5 min in order to complete the adsorption process. Silver concentration in supernatant or eluted phase (3.0 mL of 0.4 mol/L Na2S2O3 solution) was determined with FAAS, and recovery or adsorption efficiency was calculated with the following equations: % recovery = (Celuent /Pf *C0)*100

(1)

Qe = (C0 − Ce)V /m

(2)

Celuent, Pf, C0, and Ce are metal concentration in eluent phase after elution process, preconcentration factor (initial volume/ eluent volume), and initial and equilibrium concentration, respectively. The V and m equal sample volume (mL) and adsorbent dosage (mg) respectively.

3. RESULTS AND DISCUSSION 3.1. Characterization of Adsorbent. According to the surface morphology image (Figure 1a), the cellulose consists of rod shaped particles with diameter of 20−30 μm and length of 100−200 μm. Some agglomeration was observed in SEM image of MCX1 (Figure 1b), but the majority of this composite is spherical-like particles with diameter in the range 30−80 nm. The results display that the rod cellulose microcrystals are not observable and have been converted to nanoparticles which will increase the number of active sites in the surface of prepared composite. The image for MCX2 (Figure 1c) displays that the composite is in microscale and Fe3O4 may be present in the matrix of cellulose. 14905

dx.doi.org/10.1021/ie501989q | Ind. Eng. Chem. Res. 2014, 53, 14904−14912


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to the amount of volatile elements (carbon and hydrogen) in the structure of cellulose, was 26.0% and 44.2%. This result proves that the magnetic nanoparticles have been synthesized in cellulose matrix with high density and our attempt for preparation of magnetic cellulose composite was successful. The magnetic hysteresis loops of prepared magnetic composites are shown in Figure 2c. Due to the existence of organic layers on the surface of Fe3O4 nanoparticles the saturation magnetization values for MCX1 and MCX2 were 10.2 and 11.3 emu/g, respectively, which is in same level. The remanence (MR) values are 0.86 and 1.2 emu/g and indicate that the prepared composites exhibit superparamagnetic behavior and possess a sensitive magnetic response with an external magnetic field. The FT-IR spectra for cellulose and MCX are shown in Figure 2d. In the cellulose spectrum, the broad absorption peaks at around 3364 cm −1 correspond to the OH stretching vibrations due to the inter- and intramolecular hydrogen bonding of cellulose macromolecular, and the peak at 1374 cm−1 is due to the OH bending vibration. The band at 2923 cm−1 corresponds to the CH tensile vibration. The absorption peaks at 1441, 1164, 1111, and 1034 cm−1 relate to the CH2 symmetric scissoring, CO antisymmetric bridge stretching, COC pyranoid ring vibration, and the symmetric stretching vibrations of COH of alcoholic groups, respectively. The peak observed at 1683 cm−1 is the bending mode of the absorbed water.41,42 Some distinct changes are noted in the spectrum of MCX1, but the spectrum of MCX2 is dominant with the bands of magnetic cellulose because of low loading of sulfur fragments. New peaks at 500−574 cm−1 can be attributed to the vibration of FeO for Fe3O4. Due to the overlapping bands around 600 cm−1 in cellulose and the MCX composites, the other characteristic peaks at 500−600 cm−1 for CS, SCS groups and Fe3O4 are not visible separately. The presence of sulfur groups in the MCX has been identified by the appearance of new peaks at 600−1000 cm−1. 3.2. Synthesis Mechanism. Cellulose consisting of a linear chain of several (1,4)-linked β-D-glucose species. It can partially hydrolyze into glucose that has aldehyde functional groups; hence, cellulose can act as reducing agent, causing partial reduction of Fe3+ ions to Fe2+, that is required for preparation of Fe3O4 nanoparticles (Scheme 2). The second stage is a typical chemical coprecipitation in alkali solution. Moreover, gluconic acid is one of the byproducts of reduction steps; therefore, cellulose can act as a capping agent in order to form nanoscale particles. 3.3. Effect of Acid Concentration. Metal ions are pHdependently adsorbed onto nonspecific and specific sorbents. This effect is related to both the ionization state of the functional groups of the sorbent which affects availability of binding sites and the metal chemistry in the solution. The effect of pH on the value of Qe was studied in the presence of various amount of nitric acid (0.001−0.3 mol/L). According to the results in Figure 3, the adsorption reaction proceeds in the acidic media and the Qe increased with an increase in the acid concentration up to 0.1 mol/L and remained nearly constant at higher concentrations; therefore, 0.1 mol/L nitric acid was used as the optimum concentration. 3.4. Adsorption Mechanism. On the basis of hard and soft acid−base theory, silver has high affinity for self-assembly with sulfur groups; hence, complexation may be the dominant adsorption mechanism. Complex formation may occur between two sulfur atoms and one monovalent silver ion, because silver has empty orbitals that can be occupied by electrons

Figure 1. SEM images of cellulose and MCX.

The XRD analysis (Figure 2a) also used to verify the magnetic nanocomposite. The characteristic peaks due to the cubic Fe3O4 show scattering at 2θ° = 30.12, 35.5, 43.22, 53.52, 57.21, and 62.94 corresponding to the (220), (311), (400), (422), (511), and (440) planes of Fe3O4 crystal which match well with the standard spectra (00-003-0863.CAF). Moreover the composite material exhibits diffraction peaks for cellulose at 2θ = 14.05 (101), 15.80 (101−), 22.43 (002), and 34.06 (040) that are assigned to the typical structure of cellulose I40 suggesting that Fe3O4 has been successfully prepared in the cellulose matrix. The quantitative analysis by EDS (Figure 2b) gives weight ratios of Fe (44.3 and 52.0%), Si (0.65%, 0.73%), P (0.12%, 0.088%), and S (27.0 and 2.5%) for MCX1 and MCX2, respectively. The value of LOI (loss on ignition), corresponding 14906



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Figure 2. XRD pattern (a), EDS spectra (b), VSM (c), and FT-IR spectra (d) for MCX.

Scheme 2. Biogenic Rout Applied for Synthesis of MCX

to form a complex. Moreover, the xanthate can adsorb metal ions through ion exchange;43 within this process, one negatively charged sulfur atom of MCX participates in capturing one metal ion which is accompanied by release of Na+ ions (Scheme 3). 3.5. Effect of Time and Kinetic Models. In order to investigate the effect of time on the extraction efficiency, general procedure was performed for 50 mL of solution which contains 10.0 mg L−1 of silver ions, and time was varied from 1 to 10 min. The value of Qe increased rapidly in the first 2 min and then slowed down as equilibrium was approached. The increase in the Qe value was not significant after 5 min. Therefore, a time of 5 min was selected for further work. The high initial uptake rate

Figure 3. Effect of acid concentration on Qe value. Condition: concentration of silver ions, 10 mg L−1; sample volume, 50 mL; amount of sorbent, 30 mg; extraction time, 5 min.

may be due to the availability of a large number of active sites for chelation with silver ions. As the sites are gradually filled up, adsorption becomes slow, and the kinetics will be more 14907



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model expresses that the rate of adsorption is in direct proportion to the difference value of equilibrium adsorption capacity and the adsorption capacity at any time t; moreover, the adsorption was controlled by a diffusion step.44 The plots of kinetic models for adsorption of Ag+ with MCX are shown in Figure 4a−d and indicate that the second-order plots have better linearity; moreover, the results in Table 1 display that the Qe values obtained on the basis of the first-order model have high deviation with respect to the experimental value. According to these results, the second-order model can be accepted as the kinetic mechanism for Ag+ adsorption and confirms that the silver ions have been adsorbed via chemical reactions.45 This observation is consistent with the fact that sulfur groups on the surface of the MCX can adsorb the silver ions via complexation reaction. 3.6. Evaluation of Adsorption Isotherm Models. The equilibrium adsorption isotherm is important for designing an adsorption system; moreover, these models can describe the interactive behavior of the solution and the adsorbent.46,47 Two equilibrium models, i.e., Langmuir and Freundlich isotherms, were investigated for adsorption isotherms. The Langmuir model can be expressed as

Scheme 3. Mechanism for Silver Adsorption on MCX

dependent on the rate at which the analyte is transported from the bulk phase to the actual adsorption sites. The pseudo-first- and second-order kinetic models can be expressed as the following equations: ln(Qe − Qt) = ln Qe − K1t

(3)

t /qt = 1/(k 2Qe 2) + t /qe

(4)

Here, k1, k2, Qe, and Qt are the pseudo-first-order adsorption rate constant (min−1), the second-order rate constant (g mg−1 min−1), and the values of the amount adsorbed per unit mass at equilibrium and at any time t, respectively. The first-order kinetics

Ce/Qe = 1/(Qmb) + Ce/Qm

(5)

where Qe is the amount of metal ions sorbed per unit mass of the sorbent (mg g−1) and Ce the amount of metal ions in the liquid

Figure 4. First- and second-order plots of silver adsorption using MCX1 (a, b) and MCX2 (c, d).

Table 1. First-Order and Second-Order Rate Constants for Silver Adsorption at 303 K first-order

second-order

sorbent

k1

R

Qe (mg g )

k2

R2

Qe (mg g−1)

exptl Qe (mg g−1)

MCX1 MCX2

0.51 0.34

0.94 0.80

1.05 1.24

1.03 0.63

0.996 0.994

15.62 5.2

15.13 5.0

2

−1

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are energetically uniform on the solid surface, (ii) no interactions between adsorbed species, (iii) formation of a monolayer in saturation state. The essential characteristics of the Langmuir isotherm can be explained in terms of a dimensionless constant separation factor (RL), calculated by use of the equation

phase at equilibrium. The Qm is maximum adsorption capacity, and b is the Langmuir coefficient. Three assumptions of this model include the following: (i) presence of identical sites which Table 2. Adsorption Isotherm Model Constants and Correlation Coefficients for the Adsorption of Silver Ions values adsorption isotherm

Langmuir

Freundlich

RL = 1/(1 + bC i)

isotherm constant

MCX1

MCX2

Qm (mg g−1) b (L mg−1) RL RMSE R2 χ2 Kf (mg1−1/n g−1) (L)1/n n R2 RMSE χ2

166.0 0.33 0.029−0.23 0.31 0.979 12 42.5 2.31 0.951 0.13 4.33

15.62 0.13 0.2−0.6 0.029 0.995 0.19 2.67 2.0 0.990 0.019 0.14

(6)

where Ci is the initial concentration of metal ions and RL describes the type of Langmuir isotherm, irreversible (RL = 0), favorable (0 < RL < 1), linear (RL = 1), or unfavorable (RL > 1). Since the RL value lies between 0 and 1, this indicates favorable sorption of Ag+ ions on this sorbent. The Freundlich model is represented as Qe = K f Ce1/ n

(7)

where n and Kf are the Freundlich coefficients which are evaluated from the slopes and intercepts of the linear plot. This model assumes a heterogeneous adsorption surface and active

Figure 5. Langmuir and Freundlich adsorption isotherm mode for silver ions on MCX1 (a, b) and MCX2 (c, d). The theoretical model fitted with experimental data using MCX1 (e) and MCX2 (f). 14909



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(Table 2 and Figure 5), the linear Langmuir isotherm model has better linearity, but it was observed that the Langmuir equation gives higher values of the χ2 and RMSE test compared to Freundlich isotherm and suggests that the Freundlich model is the better model describing sorption behavior. 3.7. Selectivity of the Sorbent. Competitive enrichment of silver ions with respect to some heavy metals from 50 mL of solution containing 10 mg L−1 of each ion was also investigated, and the relevant parameters were calculated as the following equations:

sites with different energy. Moreover, this suggests the adsorption− complexation reactions in the adsorption process. The magnitude of the Freundlich constant, n, gives a measure of favorability of adsorption. The value of n (2.31) between 1 and 10 (i.e., 1/n < 1) represents a favorable sorption. The Freundlich isotherm is linear if 1/n = 1, and as 1/n decreases, the isotherm becomes more nonlinear. In order to determine the best-fitting model, three statistical functions have been used to evaluate isotherm model fitness, namely, the correlation coefficient of determination (R2), the root-mean-square error (RMSE), and the nonlinear chi-squared (χ2) test.48,49 The RMSE and χ2 can be defined mathematically as RMSE = χ2 =

∑ (Q e,exp − Q e,cal/Q e,exp)2

D = 1000Q /Ce

(10)

αAg /αM = DAg /DM

(8)

(11) −1

∑ [(Q e,exp − Q e,cal)2 /Q e,cal]

D is the distribution ratio (mL g ), αAg/αM is the selectivity coefficient, and DAg and DM represent the distribution ratios of Ag+ and Mn+.50 The results are listed in Table 3. It can be seen that the values of distribution factor for Ag+ are significantly higher than those of other metals. This means that silver can be separated even in the presence of interference. 3.8. Desorption and Reusability. From a practical point of view, regeneration or desorbing of the target analyte from the sorbent material makes the sorption process more economical. Hence to evaluate the regeneration possibility of the sorbent for trace analysis of silver, different eluents were tested. According to results for effect of pH, elution with acidic solution cannot be favorable because the adsorption was more efficient in acidic medium. According to hard and soft acid−base theory, eluents which contain sulfur atoms can be favorable for desorption of silver ions. The results for this study (Table 4) indicated that, by using 3 mL of 0.4 mol/L of Na2S2O3 solution, more than 98% of silver ions were desorbed from the sorbent surface. Moreover, in order to evaluate the reusability of MCX, it was subjected to several loadings with the sample solution and subsequent elution. It was found that the recovery remained constant (90−98%) after 3 cycles of sorption and desorption (Figure 6a). In order to evaluate the stability of magnetic iron composite in acidic pH, 20 mg of the adsorbent was suspended in 50 mL of HNO3 solution (0.1 mol/L). After shaking for 5 min, the adsorbent was separated and amount of dissolved iron ions in the supernatant solution was determined by FAAS. The percents of dissolved iron ions in each cycle are shown in Figure 6b. It can be seen that after three cycles only 3.5−4% iron was dissolved which shows good stability for magnetic composite.

(9)

where Qe,exp and Qe cal are the experimental data and the value calculated from nonlinear models. According to the results Table 3. Relative Selectivity Factor (αr) of Ag+ with Respect to Other Cations Uusing MCX1 analyte

Q

D

αr

Ag+ Pb2+ Co2+ Ni2+ Zn2+ Pd2+ Cr3+

16.31 0.2 0.3 0.8 2.6 10.6 6.4

77 666 20.24 30.54 84.03 308 2912 1038

3837 2543 924 252 26.6 74.8

Table 4. Elution Recovery for Silver Ions Adsorbed on MCX1 eluent

volume (mL)

recovery (%)

HCl (1 M) thiourea (3%) in HCl (1 M) thiourea (6%) in HCl (1 M) acetonitrile Na2S2O3 (0.3 M) Na2S2O3 (0.4 M) Na2S2O3 (0.4 M) Na2S2O3 (0.4 M) Na2S2O3 (0.4 M) Na2S2O3 (0.4 M)

5 5 5 5 5 5 4 3 2 1

38.3 87.5 91.3 15.4 90.1 98.9 98.5 98.6 89.6 80.2

Figure 6. Efficiency of MCX for silver adsorption after three cycle of sorption and desorption (a) and amount of released iron from composite structure in acidic condition (b). 14910



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drate Polymer for Removal of Ni (II) Ions from Aqueous Solutions. Int. J. Biol. Macromol. 2013, 54, 99. (8) Monier, M.; Akl, M. A.; Al, W. M. Modification and Characterization of Cellulose Cotton Fibers for Fast Extraction of some Precious Metal Ions. Int. J. Biol. Macromol. DOI: 10.1016/j.ijbiomac.2014.01.068. (9) El-Hamshary, H.; Fouda, M. M.G.; Mohideen, M.; Al-Deyab, S. S. Removal of Heavy Metal Using Poly (N NN N-vinylimidazole)-graftedcarboxymethylated Starch. Int. J. Biol. Macromol. DOI: 10.1016/ j.ijbiomac.2014.02.047. (10) Filho, E. C. S.; Melo, J. C.P.; Fonseca, M. G.; Airoldi, C. Cation Removal Using Cellulose Chemically Modified by a Schiff Base Procedure Applying Green Principles. J. Colloid Interface Sci. 2009, 340, 8. (11) Lima, I. S.; Lazarin, A. M.; Airoldi, C. Favorable Chitosan/ Cellulose Film Combinations for Copper Removal from Aqueous Solutions. Int. J. Biol. Macromol. 2005, 36, 79. (12) Sharma, S.; Rajesh, N. 2-Mercaptobenzothiazole Impregnated Cellulose Prepared by Ultrasonication for the Effective Adsorption of Precious Metal Palladium. Chem. Eng. J. 2014, 241, 112. (13) Sun, X.; Yang, L.; Li, Q.; Zhao, J.; Li, X.; Wang, X.; Liu, H. AminoFunctionalized Magnetic Cellulose Nanocomposite as Adsorbent for Removal of Cr(VI): Synthesis and Adsorption Studies. Chem. Eng. J. 2014, 241, 175. (14) Filho, E. C. S.; Melo, J. C.P.; Fonseca, M. G.; Airoldi, C. Cation Removal Using Cellulose Chemically Modified by a Schiff Base Procedure Applying Green Principles. J. Colloid Interface Sci. 2009, 340, 8. (15) Ji, F.; Li, C.; Tang, B.; Xu, J.; Lu, G.; Liu, P. Preparation of Cellulose Acetate/Zeolite Composite Fiber and Its Adsorption Behavior for Heavy Metal Ions in Aqueous Solution. Chem. Eng. J. 2012, 209, 325. (16) El-Hady, B. A.; Ibrahim, M. M. Graft Copolymerization of Acrylamide onto Carboxymethyl cellulose with the Xanthate Method. J. Appl. Polym. Sci. 2004, 93, 271. (17) Sha, L.; Xue-yi, G.; Ning-chuan, F.; Qing-hua, T. Effective Removal of Heavy Metals from Aqueous Solutions by Orange Peel Xanthate. Trans. Nonferrous Met. Soc. Chin. 2010, 20, 187. (18) Kamel, S.; Hassan, E. M.; El-Sakhawy, M. Preparation and Application of Acrylonitrile-Grafted Cyanoethyl Cellulose for the Removal of Copper (II) Ions. J. Appl. Polym. Sci. 2006, 100, 329. (19) Li, G.; Jiang, Y.; Huang, K.; Ding, P.; Chen, J. Preparation and Properties of Magnetic Fe3O4−Chitosan Nanoparticles. J. Alloys Compd 2008, 466, 451. (20) Bastami, T. R.; Entezari, M. H. Sono-Synthesis of Mn3O4 Nanoparticles in Different Media Without Additives. Chem. Eng. J. 2010, 164, 261. (21) Yu, X.; Tong, S.; Ge, M.; Zuo, J.; Cao, C.; Song, W. One-Step Synthesis of Magnetic Composites of Cellulose@iron Oxide Nanoparticles for Arsenic Removal. J. Mater. Chem. 2013, 1, 959. (22) Liu, S.; Luo, X.; Zhou, J. Magnetic Responsive Cellulose Nanocomposites and Their Applications. In CelluloseMedical, Pharmaceutical and Electronic Applications; InTech: Rijeka, Croatia, 2013. (23) Liu, Z.; Wang, H.; Liu, C.; Jiang, Y.; Yu, G.; Mu, X.; Wang, X. Magnetic Cellulose−Chitosan Hydrogels Prepared from Ionic Liquids as Reusable Adsorbent for Removal of Heavy Metal Ions. Chem. Commun. 2012, 48, 7350. (24) Donia, A. M.; Atia, A. A.; Abouzayed, F. I. Preparation and Characterization of Nano-magnetic Cellulose with Fast Kinetic Properties towards the Adsorption of Some Metal Ions. Chem. Eng. J. 2012, 191, 22. (25) Min, L.; Xiao-hui, G.; De -zhou, W. Removing Cd2+ by Composite Adsorbent Nano-Fe3O4/Bacterial Cellulose. Chem. Res. Chin. Univ. 2011, 27, 1031. (26) Hajiagha-Babaei, L.; Ghasemi, Z.; Darviche, F.; Shamsipur, M.; Raoufi, F.; Ganjali, M. R. Solid Phase Extraction of Ultra-Trace Amounts of Ag+ by Using Octadesyl Silica Membrane Disks Modified with New Fluvalen Derivative. Anal. Sci. 2001, 17, 1305. (27) Yu, H.; Sun, W.; Zhu, X.; Zhu, X.; Wei, J. Determination of Silver with On-Line Preconcentration Using Dithiozone Chelate and Carbon

4. CONCLUSIONS The magnetic cellulose xanthate was prepared by two approaches and applied for silver adsorption from acidic media. Preparation of sorbent is simple, and it shows good dispersity and superparamagnetic property. According to results, MCX1 has better performance with respect to MCX2, as the maximum adsorption capacity of MCX1 was 11 times greater than that of MCX2. This result can be explained according to SEM and EDS analysis. On the basis of the SEM image, MCX1 has better dispersity and lower dimension which increase the surface area and better accessibility of functional groups. Moreover, the EDS analysis showed that the amount of sulfur in the structure of MCX1 is 13 times greater with respect to MCX2. Hence, it has more functional groups. The sorbents showed a relatively fast adsorption rate within 5 min. Moreover, the sorbent has good stability and reusability as after three cycles of sorption and desorption the recovery of silver ions was quantitative. Finally, the MCX1 was applied for adsorption of Ag+ from dental radiology agent and synthetic samples, and the results indicate the capability of the method for selective adsorption of silver from complicated matrices.

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ASSOCIATED CONTENT

S Supporting Information *

Data for TGA analysis, enrichment of silver from high volume, effect of coexisting ions, application of method, and comparison with other methods. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected], shemiran@khayam. ut.ac.ir. Tel.: +98 21 61112481. Fax: +98 21 66405141. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Support of this investigation by the Research Council of University of Tehran through grants is gratefully acknowledged. REFERENCES

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Synthesis, Characterization, and Silver Adsorption Property of

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