Polyaniline-Coated Filter Papers: Cost Effective Hybrid Materials for

Article pubs.acs.org/jced

Polyaniline-Coated Filter Papers: Cost Effective Hybrid Materials for Adsorption of Dyes Sibani Majumdar, Upasana Saikia, and Debajyoti Mahanta* Department of Chemistry, Gauhati University, Guwahati, Assam 781014, India ABSTRACT: In this study, polyaniline-coated filter papers PANI (ES)-FP and PANI (EB)-FP have been synthesized by chemical oxidation polymerization. This is a cost-effective and simple method of preparing PANI film on an inexpensive filter paper. The PANI coated filter papers were characterized by UV−vis, IR, thermogravimetric analysis and scanning electron microscopy. These composite materials have been effectively used for adsorption of seven different dyes from aqueous medium. It has been observed that these are good materials for anionic and cationic dye adsorption. Detailed equilibrium and kinetic studies have been reported here by taking Eosin yellow and Methylene blue as anionic and cationic model dyes. The experimental data for Eosin yellow and Methylene blue adsorption were best fitted in Freundlich and Langmuir adsorption models, respectively. The Langmuir adsorption capacity of Eosin yellow and Methylene blue on PANI (ES)-FP and PANI (EB)-FP were 4.3 and 1.3 mg g−1, respectively, at neutral pH. Adsorption of both dyes follows second order kinetic model.

1. INTRODUCTION Since its discovery, conducting polymer has attracted the attention of researchers and technologists because of its promising electronic and optical properties.1,2 Conducting polymers have a wide range of applications such as in polymer solar cells,3−5 field effect transistors,6−8 light emitting diodes,9−11 and chemical sensors,12 etc. Polyaniline (PANI) is known to be one of the most widely studied conducting polymers because of its low cost synthesis from aniline by simple chemical or electrochemical methods. The high environmental stability and the simple doping/dedoping of PANI by acid/base treatment have made it one of the most promising members of conducting polymer family.13 The main limitation in the application of PANI is due to its insolubility in all organic solvents in the doped form.14,15 It is soluble only in N-methyl pyrolidone (NMP) in undoped form. The insolubility of PANI has restricted the easy film formation of the material for various device applications.16 Therefore, the hybrid materials of PANI with other organic and inorganic materials have been identified as a potential class of materials for a wide range of applications.17,18 Organic dyes are major components of the effluents from industries such as textile plants, printing, dying, and paper making, etc.19 The coloration of groundwater causes serious environmental pollution, and it is reported that the presence of dyes increases the COD and BOD levels of aquatic sources.20 Some dyes have a tendency to chelate metal ions which may cause microtoxicity to aquatic lives.21 Moreover, lots of textile dyes are not easily photodegradable or biodegradable, so it is extremely important to develop some effective methods to remove organic dyes from wastewater.22 Many methods are © XXXX American Chemical Society

known to be investigated for the removal of organic dyes from aqueous medium. Adsorption, photodegradation, precipitation, coagulation, and membrane filtration, etc. are the most widely used techniques for decolouration of water.23−26 Among them, adsorption is known to be the most efficient, easy to handle, and low cost technique employed for dye contaminated wastewater treatment. Activated carbon-based materials are generally used for this purpose.27 Researchers have investigated many other low cost or waste materials as adsorbents such as coconut coir, olive stone, orange peel, banana pith, rice husk, and corncob, etc. for removal of dyes.28 PANI emeraldine salt is reported as a useful adsorbent material for the removal of anionic dyes.29,30 Similarly, PANI emeraldine base can remove cationic dyes from wastewater.31 In this study, we prepared both PANI emeraldine salt (ES) and PANI emeraldine base (EB)-coated filter paper (PANI (ES)-FP and PANI (EB)-FP respectively) by modification of the method developed by Chattopadhyay et al.32 The PANI coated low cost filter paper has been used for removal of a wide range of organic dyes. Generally, in the case of powder adsorbents, it becomes difficult to separate the adsorbent particles from the aqueous medium after adsorption. But in this case, the low cost adsorbents can be removed easily by just removing the PANI-coated filter papers from the aqueous medium after completion of adsorption. It has been observed that even a small amount of PANI can tremendously enhance the adsorption capacity of cellulose-made filter paper. We have Received: July 26, 2015 Accepted: October 16, 2015

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DOI: 10.1021/acs.jced.5b00645 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

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Figure 1. Structure of different dyes used for adsorption experiment.

PANI emeraldine salt on the surface of the cellulose fibers of the filter paper. The green PANI (ES)-coated filter papers were washed with distilled water for several times to remove the uncoated PANI (ES) followed by drying in air at room temperature and finally kept in a desiccator. Polyaniline emeraldine salt-coated filter papers [PANI (ES)-FP] were converted into polyaniline emeraldine base-coated filter papers [PANI (EB)-FP] by treating PANI (ES)-FP with 1 M NH4OH solution for 2 h followed by washing with distilled water for several times. The amount of PANI coated on the hybrid filter paper had been determined by a simple gravimetric method. Four pieces of filter papers of dimension (1 × 3) cm2 were weighed before and after PANI formation. The amounts of PANI coated on the filter paper were determined by subtracting the weight of blank filter papers from that of the PANI-coated filter papers. The process of determination of PANI weight on the filter paper was repeated for five sets and the average weight of PANI in each filter paper was determined. It should be noted that there is very small deviation on the values of each set. Thus, the average mass of PANI coated on (1 × 1) cm2 filter paper was 0.3 mg. The average mass of a composite filter paper of dimension (1 × 1) cm2 was found to be 0.01 g.

investigated detailed equilibrium and kinetic behavior of dye adsorption by these materials.

2. EXPERIMENTAL SECTION 2.1. Materials. Whatman-40 filter paper was used for all the experiments. Aniline (Merck, India) was purified by distillation before use. Ammonium persulfate (APS) and hydrochloric acid (HCl) were bought from Merck, India, and used as received. The dyes Eosin blue, Eosin yellow, Methylene blue, Orange G, Orange II, Reactive orange-14 and Rhodamin B were purchased from, Merck, India, and used as received. Distilled water was used for all the experiments. 2.2. Preparation of PANI-Coated Filter Paper (PANIFP). Whatman-40 filter papers were cut into small pieces of size (1 × 3) cm2. Solutions of aniline and APS were prepared by dissolving 0.5 g of aniline and 1.225 g of APS in 25 mL of 1 M HCl solution, respectively. A quantity of 200 μL of anilinium chloride was poured dropwise over the surface of the filter paper piece using a pipet and 5 min was allowed for complete adsorption of anilinium chloride on the filter paper. Then 200 μL of APS was poured on the anilinium chloride-containing filter paper in the same manner. The conversion of color of the filter paper from white to green indicates the formation of B



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2.3. Dyes Used for Adsorption Experiment. All seven dyes used for the adsorption experiments are listed in Figure 1. 2.4. Adsorption Experiment. In this study, all the adsorption experiments have been performed in the UV cuvate itself. Stock solutions of all the dyes (1000 mg/L) were prepared in distilled water. The experimental solutions with desired dye concentration were obtained by successive dilution of these stock solutions with distilled water. For adsorption experiments, the required amount of PANI (ES)-FP and PANI (EB)-FP was added to 3 mL of different dye solutions having different initial concentrations ranging from 1 ppm to 25 ppm. These solutions were shaken, and the adsorption was studied for 2 h duration. Then the concentrations of the dyes were determined by UV−visible absorption spectrometer (UV-1800 Shimadzu spectrophotometer) at different intervals of time ((0, 2, 6, 10, 20, 30, 60, and 120) min respectively). The dye concentrations were calibrated with Beer−Lambert law at λmax values of (480, 517, 516, 664, 483, 554, and 420) nm for Orange G, Eosin yellow, Eosin blue, Methylene blue, Orange II, Rhodamin B, and Reactive orange 14, respectively. The effect of initial concentration of the dye, adsorbent dose, and the effect of pH on adsorption of the dye were studied by using Eosin yellow and Methylene blue as anionic and cationic model dyes, respectively.

adsorption of Eosin yellow and Methelyne blue, respectively. These are the characteristic peaks of Eosin yellow and Methylene blue. Thus, UV−visible spectra confirm the coating of PANI on the filter paper and adsorption of Eosin yellow and Methylene blue on PANI (ES)-FP and PANI (EB)-FP, respectively. 3.2. FTIR Analysis. The FTIR spectra of blank filter paper (Blank-FP), PANI (ES)-FP, and PANI (EB)-FP were recorded by IR Affinity-1 Shimadzu (Figure 3). Fibers of the blank and

Figure 3. FTIR spectra of blank FP, PANI (ES)-FP, and PANI (EB)FP.

3. RESULTS AND DISCUSSIONS 3.1. UV−Visible Analysis. The UV−vis absorption spectra of the composite filter papers before and after adsorption of the respective dyes were recorded by U-4100 Hitachi spectrophotometer (Figure 2). The UV−visible absorption spectrum of

hybrid filter papers were mixed well with dry KBr, and pellets were made to record the FTIR spectra. It was observed that the hybrid FP samples have characteristic peaks at 1550 cm−1 and 1640 cm−1 due to the emeraldine form of PANI, the peaks of which are not present in the blank filter paper.32 The bands appearing at around 1640 cm−1 and 1550 cm−1 corresponded to CC and CN stretching of quinoid and the benzoid rings of PANI, respectively. The peaks appearing at around 1420 cm−1 corresponded to the aromatic C−N stretching mode. The peak observed at around 1164 cm−1 in the case of PANI (EB)-FP had red-shifted to 1155 cm−1 in the spectrum of PANI (ES)-FP. These peaks correspond to a vibration mode of the −NH+ structure. Almost all peaks of PANI (EB)-FP have slightly red-shifted in PANI (ES)-FP, which is consistent with the previous reports.34−36 The FTIR spectroscopy confirms the presence of PANI (ES) and PANI (EB) in PANI (ES)-FP and PANI (EB)-FP, respectively. 3.3. TGA Analysis. A METTLER TOLEDO thermogravimetric analyzer (model TGA/DSC-1) was used for recording the thermogravimetric data. The thermal stabilities of blank FP, PANI (ES)-FP and PANI (EB)-FP were investigated by thermogravimetric analysis (TGA). From the TGA thermograms it has been observed that the blank FP shows around 80 % weight loss at 320 °C. This is due to degradation of cellulose chains. In the literature it is reported that PANI (ES) shows some weight loss at around 200 °C due to loss of the dopant HCl molecule.37 The second weight loss is at around 400 °C. In the case of PANI (EB), the major weight loss is only 14.23 % in the temperature range 475 °C to 600 °C.38 Moreover, in the composite samples the amount of PANI is only about 3 %; therefore, it is difficult to get a PANI signature from the TGA thermograms. But from Figure 4 it is observed that the PANI (EB)-FP has the same thermal stability as blank FP. In blank FP 100 % weight loss occurs at 600 °C but in PANI (EB)-FP, 5 % weight is still there at 600 °C or even more than that. This may be due to PANI (EB) present in the sample PANI (EB)-FP.

Figure 2. Defuse reflectance UV−vis spectra of PANI (ES)-FP and PANI (EB)-FP before and after Eosin yellow and Methylene blue adsorption.

the PANI (ES)-FP indicates that emeraldine salt is formed with its characteristic absorption peaks at around 700 and 400 nm. The formation of electrical conducting PANI (ES) on the filter paper was characterized by the appearance of the peak at 700 nm. Again in the absorption spectrum of PANI (EB)-FP two peaks appeared at around 600 and 300 nm corresponding to molecular exciton transition and π → π* transition, respectively.33 The spectra observed for the green and blue forms of the filter paper are similar to emeraldine salt and base form of bulk PANI prepared in the solution phase under the same experimental condition.32 Again in the spectra of PANI (ES)-FP and PANI (EB)-FP, two additional peaks at 517 and 664 nm were observed after C



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were filled up by PANI (ES) in the PANI (ES)-FP sample (Figure 5b). 3.5. Adsorption Study. 3.5.1. Adsorption of Different Anionic and Cationic Dyes. Adsorption experiments were performed with blank filter paper as an adsorbent material for both anionic and cationic dyes and the results have been compared with that of PANI (ES)-FP and PANI (EB)-FP (Figure 6). Eosin yellow and Methylene blue were taken as model dyes for comparison. (1 × 1) cm2 of adsorbents were taken for anionic and cationic dye adsorption. It was observed that PANI (ES)-FP adsorbs anionic dyes while PANI (EB)-FP acts as a good adsorbent material only for cationic dyes. For both anionic and cationic dyes the adsorption by blank filter paper is negligible. Thus, the adsorption is due to electrostatic interaction of deposited PANI on the filter paper. The positive and negative charge densities on PANI (ES)-FP and PANI (EB)-FP were responsible for adsorption of anionic and cationic dyes, respectively. A schematic diagram for the adsorption of dyes by PANI (ES)-FP and PANI (EB)-FP are shown in Scheme 1 Adsorption experiments were carried out with different types of anionic and cationic dyes by using [PANI (ES)-FP] and [PANI (EB)-FP] respectively. Figure 7(a) and 7(b) show the variation of concentration of different anionic and cationic dyes in the presence of PANI (ES)-FP and PANI (EB)-FP as adsorbents with time. It was observed that with the increase in time the concentration of dyes in the solution decreases due to effective adsorption. Among the dyes anionic dye Orange II and cationic dye Methylene blue were found to show maximum adsorption. 3.5.2. Effect of Initial Concentrations. To study the adsorption phenomenon further, experiments were conducted with different initial concentrations of Eosin yellow and Methylene blue in the presence of (1 × 0.5) cm2 and (1 × 1) cm2 PANI (ES)-FP and PANI (EB)-FP, respectively. Figure 8 panel a and b show the concentration profiles of Eosin yellow (ranging from 5 ppm to 25 ppm initial concentration) and Methylene blue (ranging from 2 ppm to 10 ppm initial concentration) at different time intervals. It was observed that the adsorption of the dye increases with an increase in initial concentration. At higher concentration, large number of dye molecules completely occupies the binding sites of the adsorbent materials which were not possible in the case of low dye concentration. 3.5.3. Effect of Adsorbent Dose. We have performed the adsorption experiments to ascertain the effect of various amounts of adsorbent on the uptake of the dye. Figure 9 panels a and b show the variation of concentration of Eosin yellow and Methylene blue with time for different amount of adsorbent at constant initial concentration 25 and 10 ppm, respectively. Experiments were done by using (1 × 0.5), (1 × 1), (1 × 2), and (1 × 3) cm2sized pieces of PANI (ES)-FP and PANI (EB)-FP samples. It was observed that the adsorption of dye increases with increase in the amount of adsorbent. The number of binding sites on the adsorbent surfaces increases with the amount of adsorbent materials. Thus, greater number of dye molecules can bind if the amount of adsorbent is more. 3.5.4. Effect of pH. The effect of pH on anionic and cationic dye adsorption by PANI (ES)-FP and PANI (EB)-FP is shown in Figure 10 panels a and b, respectively. The anionic and cationic dyes exist in aqueous solution in the form of negative and positive charged ions, respectively. The anionic dye molecules are adsorbed by PANI (ES)-FP due to the partial

Figure 4. TGA of blank FP, PANI (ES)-FP, and PANI (EB)-FP.

The most significant observation is the lower thermal stability of PANI (ES)-FP. It shows around 60 % weight loss in the range of 250 °C to 350 °C. Thus, it has lower thermal stability than PANI (ES), PANI (EB), PANI (EB)-FP, and blank filter paper. This may be due to the partial acid degradation of cellulose in PANI (ES)-FP samples. 3.4. Morphology Study. The SEM images of blank FP and PANI (ES)-FP have been shown in Figure 5. The long-range fibrous network of PANI (ES) on the cellulose fibers of filter paper was observed from the morphology of PANI (ES)-FP. Large pores were observed in the blank FP (Figure 5a) but when the same paper was coated with PANI (ES), the pores

Figure 5. Scanning electron micrographs of (a) blank FP; (b) PANI (ES)-FP. D



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Figure 6. Concentration profiles of (a) Eosin yellow and (b) Methylene blue in the presence of blank FP, PANI (ES)-FP, and PANI (EB)-FP with time.

of PANI (EB)-FP are in undoped (PANI-EB) form. Thus, at basic pH the adsorption on the surface of PANI (EB)-FP is high due to high negative charge density on the adsorbent surface which is responsible for binding with more cationic dye molecules by electrostatic interaction. When the pH becomes acidic, the PANI (EB) on the surface of PANI (EB)- FP gradually converted into PANI (ES) which introduce positive charge density on the adsorbent surface. This leads to decrease in cationic dye adsorption by PANI (EB)-FP at acidic pH. The percentage removal of the dye was calculated by using eq 1.

Scheme 1. Schematic Diagram for Adsorption of Anionic and Cationic Dyes by PANI (ES)-FP and PANI (EB)-FP

⎛ C − Ce ⎞ percentage removal = ⎜ 0 ⎟ × 100 ⎝ C0 ⎠

(1)

3.6. Adsorption Isotherms. The most studied adsorption isotherm models are Langmuir, Freundlich, and Temkin isotherm models. It is necessary to carry out adsorption isotherm studies to apply the adsorption technique for a practical purpose. A relationship can be established between qe, the amount of adsorption of the adsorbate per unit weight of the adsorbent (mg/g), and Ce, the equilibrium concentration of the adsorbate (mg/L). 3.6.1. Langmuir Isotherm. The Langmuir isotherm model is applicable for many adsorption processes. This model predicts the monolayer adsorption onto the adsorbent surface with a finite number of identical sites which are homogeneously distributed over the adsorbent surface and no further adsorption thereafter. It represents chemisorptions on a set of

positive charge on the PANI (ES) chain. At acidic pH, the PANI present on the surface of PANI (ES)-FP is in the doped form (PANI-ES form). Thus, at low pH, the positive charge density on the PANI (ES)-FP is high which is responsible for greater adsorption of anionic dyes. But at basic pH, the surface PANI molecules were converted from PANI (ES) form to PANI (EB) form with introduction of negative surface charge density. The repulsion between negatively charged surfaces of adsorbent with the anionic dye molecules is the reason for the sudden decrease in anionic dye adsorption by PANI (ES)-FP at basic pH. Similarly, at basic pH, PANI molecules on the surface

Figure 7. Concentration profile of various (a) anionic and (b) cationic dyes in the presence of [PANI (ES)-FP] and [PANI (EB)-FP], respectively. E



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Figure 8. Concentration profiles of (a) Eosin yellow and (b) Methylene blue for different initial concentrations.

Figure 9. Effect of adsorbent dose on the adsorption of (a) Eosin yellow and (b) Methylene blue.

Figure 10. Effect of pH on the percentage adsorption of (a) Eosin yellow and (b) Methylene blue.

qe as a function of the equilibrium concentration Ce of the dye Eosin yellow and Methylene blue, respectively. The equilibrium uptake was calculated by using the eq 4.

well-defined localized adsorption sites, where no adsorption takes place after saturation.39 The Langmuir model is expressed by eq 2.

qe =

bQ 0 1 + bCe

qe =

(2)

(4)

where Co is the initial concentration of the dye solution, Ce is the equilibrium concentration of the dye solution, V is the volume of the solution, and W is the mass of the adsorbent. 3.6.2. Freundlich Isotherm. As in the Langmuir isotherm model, the Freundlich model does not restrict the adsorption to a monolayer surface. According to this model adsorption of the dye will increase with increase in dye concentration in the solution, as there is no saturation of the adsorbent surface.40 Equation 5 describes the Freundlich model for the adsorption of solutes from a liquid to a solid surface

A linear form of this expression is given by eq 3.

ce c 1 = + e qe Q 0b Q0

(C0 − Ce)V W

(3)

The constant Q0 and b are called Langmuir constants where Q0 represents the adsorption capacity in mg/g and b represents the adsorption constant in L/mg. Values of Q0 and b are calculated from the slope and intercept of the plot of Ce/qe versus Ce. Figure 11 panels a and b show the amount adsorbed F



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Figure 11. Variation of equilibrium amount adsorbed qe with equilibrium dye concentration Ce of (a) Eosin yellow and (b) Methylene blue. The insets show the variation of Ce/qe with Ce for both the dyes.

Figure 12. Freundlich adsorption isotherm for (a) Eosin yellow and (b) Methylene blue.

Figure 13. Temkin adsorption isotherm for (a) Eosin yellow and (b) Methylene blue.

log qe = log KF +

1 log Ce n

qe =

(5)

RT (ln ACe) b

(6)

where A is the equilibrium binding constant in L/mg and corresponds to the maximum binding energy and b is related to heat of adsorption in J/mol. The linear form of the Temkin model is expressed by eq 7

where KF and n are the Freundlich constants, related to adsorption capacity and adsorption intensity, respectively. In Figure 12 panels a and b, a linear plot of log Ce versus log qe was shown for Eosin yellow and Methylene blue, respectively. The constants KF and n can be derived from the intercepts and slope of these straight lines. 3.6.3. Temkin Isotherm. The Temkin isotherm model can be expressed by eq 6

qe = B(ln A) + B(ln Ce)

(7)

where B = (RT/b); R is the universal gas constant (8.314 J/mol K) and T is the absolute temperature in Kelvin. The intercept and slope obtained from the linear plot of qe versus ln Ce gives the isotherm constants, A and B, respectively.41 G



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Table 1. Isotherm Constants and R2 Values for Adsorption of Eosin Yellow and Methylene Blue Langmuir isotherm

Freundlich isotherm

Temkin isotherm

dye used

Q0/(mg/g)

B/(L/mg)

R2

KF

n

R2

B

A/(L/mg)

R2

Eosin yellow Methylene blue

4.26 1.26

0.273 0.785

0.930 0.983

1.32 0.47

2.94 1.84

0.960 0.939

0.7656 0.259

4.943 9.38

0.882 0.940

Figure 14. Kinetic study for removal of (a) Eosin yellow and (b) Methylene blue by PANI (ES)- FP and PANI (EB)- FP, respectively.

The Temkin adsorption isotherm for Eosin yellow and Methylene blue are shown in Figure 13 panels a and b, respectively. The different isotherm constants obtained from the slope and intercepts of the plots and the R2 values for all the isotherms are given in Table 1. It can be suggested from the correlation coefficients of all three adsorption isotherms that the adsorption process of Eosin yellow is better explained by the Freundlich isotherm, and for Methylene blue, the Langmuir model exhibited better fitting compared to the other two models. The surface charge of PANI (ES)-FP changes from positive to negative in PANI (EB)-FP due to the structural changes in PANI chains. Moreover, in PANI (ES)-FP negatively charged Eosin yellow ions are adsorbed, whereas the positively charged methylene blue ions are adsorbed on the surface of PANI (EB)-FP. Thus, the two adsorptions are quite different in nature. For this reason the two adsorptions may follow two different adsorption models. 3.7. Kinetics Studies. A study of kinetics of adsorption is desirable as it provides information about the mechanism of adsorption, which is important for efficiency of the process. A second order model for adsorption is expressed by eq 8

dq t dt

= ks(qe − qt)2

Table 2. Kinetic Parameter for Adsorption

dye Eosin yellow

Methylene blue

Equation 9 is the linear form of eq 8 (9) −1

set set set set set set

2 3 4 1 2 4

qe

ks

mg L−1

mg g−1

g mg−1 min−1

21.1 15.7 10.5 9.59 8.04 2.12

7.55 6.50 4.50 1.13 0.73 0.33

0.011 0.012 0.02 0.07 0.24 0.30

in Figure 15 panels a and b, respectively. It was observed that the amount adsorbed remained almost constant for all four cycles. For this experiment we have used (1 × 1) cm2 of PANI (ES)-FP and PANI (EB)-FP and 15 ppm Eosin yellow and 10 ppm Methylene blue solution, respectively. The composite filter papers were then dipped in respective dye solutions (3 mL) and shaken for 2 h duration. The concentrations of dye solutions were determined before and after adsorption. After complete adsorption, the filter papers were washed with distilled water. Then for desorption, 1 M NH4OH solution (3 mL) and 1 M HCl solution (3 mL) were used for PANI (ES)-FP and PANI (EB)-FP, respectively. After complete desorption, 3 mL of 1 M HCL solution was added to PANI (ES)-FP to regenerate the vacant sites. Similarly 3 mL of 1 M NH4OH was added to the PANI (EB)-FP. We have repeated this process for four cycles to check the reusable capacity of the PANI-coated filter papers.

(8)

t 1 1 = + t 2 qt qe ksq e

set

initial concentration (C0)

−1

where ks is the rate constant in g mg min and qt is the amount adsorbed at time t in mg/g. Thus, a plot of t/qt versus t for various initial concentrations should be linear as shown in Figure 14 panels a and b. The values of ksqe2 and qe can be determined from the intercept and slope of the plot; respectively.29 The kinetic parameters obtained from the plots are given in Table 2. 3.8. Reusability. Regeneration of the sorbent is very important for industrial purposes. We have checked the reusability of the PANI-coated filter papers for four cycles. The efficiency of PANI (ES)-FP and PANI (EB)-FP are shown

4. CONCLUSION In this work, PANI has been synthesized on the surface of filter paper by chemical oxidation of aniline. The PANI formed on the filter paper could be reversibly converted between emeraldine salt (ES) and emeraldine base (EB) forms by a simple acid−base treatment. It has been observed that PANI (ES)-FP and PANI (EB)-FP act as good and cost-effective adsorbent materials for anionic and cationic dyes, respectively. These materials have several advantages such as increased adsorption capacity with a coating of very small amount PANI H



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Figure 15. Adsorption of dyes by recycled composite filter papers (a) Eosin yellow by PANI (ES)-FP and (b) Methylene blue by PANI (EB)-FP.

on the low cost filter papers, easy removal of adsorbent after adsorption, excellent reusability, and usefulness of the materials for both anionic and cationic dyes just by interconversion of materials with simple acid−base treatment, etc. Thus, these materials may act as promising adsorbent materials for different charged species in solution. As PANI coated on the filter papers acts as an active material for adsorption of anionic and cationic species, these hybrid filter papers may be used for the separation of different charged species from solutions. The detail adsorption and kinetic studies have been done by using Eosin yellow and Methylene blue as model anionic and cationic dye, respectively. The Langmuir adsorption capacity of Eosin yellow and Methylene blue on PANI (ES)-FP and PANI (EB)FP are 4.3 and 1.3 mg g−1, respectively, at neutral pH. Kinetic studies show that both dyes follow second-order kinetics. The second order rate constants for Eosin yellow and Methylene blue are 0.011 g mg−1 min−1 and 0.07 g mg−1 min−1 at initial concentrations 21 mg L−1 and 9.6 mg L−1, respectively.

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*Tel.: +91-9864579037. Fax: +91-0361-2700311. E-mail: [email protected], [email protected]. Funding

We thank the University Grant Commission (UGC), India, for financial support. Notes

The authors declare no competing financial interest.

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REFERENCES

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Polyaniline-Coated Filter Papers: Cost Effective Hybrid Materials for

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