Removal of azo dye from aqueous solution using an

Journal of Industrial and Engineering Chemistry 21 (2015) 387–393

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Removal of azo dye from aqueous solution using an anionic polymeric urethane absorbent (APUA) Azam Pirkarami a, Mohammad Ebrahim Olya a,*, Farhood Najafi b a b

Department of Environmental Research, Institute for Color Science and Technology, Tehran, Iran Department of Resin and Additives, Institute for Color Science and Technology, Tehran, Iran

A R T I C L E I N F O

Article history: Received 29 October 2013 Accepted 25 February 2014 Available online 2 March 2014 Keywords: Food Red 17 Adsorption Anionic polymeric urethane absorbent (APUA) UV irradiation.

A B S T R A C T

This paper is a report on an original research which investigated the effect of a number of experimental parameters on the removal of Food Red 17 (FR17) from an aqueous solution using anionic polymeric urethane absorbent (APUA) as an adsorbent. The optimum value of adsorbent dose was found to be 35 mg L1. Further, maximum dye removal took place at pH 3 and 45 8C. The fourth parameter, stirring the solution during the treatment, also resulted in significant removal improvement. The amount of FR17 adsorbed on APUA surface was quantified using the Langmuir equation. UV irradiation was also found to have a positive effect on the removal process. The efficiency of the treatment was verified using FT-IR spectrometry results for APUA, FR17, and APUA-FR17. Finally, the adsorbent was subjected to SEM characterization. ß 2014 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

1. Introduction The presence of the organic dyes in surface water resources is esthetically unpleasant and threatens living organisms by reducing sunlight penetration and absorbing the oxygen dissolved in water. These dyes can even release toxic, mutagenic, and carcinogenic materials [1–5]. Numerous methods have been developed to treat colored effluents. Chief among these methods are coagulation, flocculation, biological treatment, ozone treatment, membrane filtration, colloidal gas aphrons, chemical oxidation, photocatalytic removal, and ion exchange [6–11]. However, these methods are not without their disadvantages. As an instance, some dyes are resistant to physico-chemical and biological methods [12], chemiocoagulation causes pollution [13], chemical oxidation is slow and needs reactive materials which are hazardous [14], and oxidation methods are expensive and uneconomical [15]. For these reasons, researchers have turned to adsorption because it is highly effective and economical [5]. Many adsorbents have been tried in previous studies: zeolites, clays (kaolinite, bentonite), siliceous material (perlite, alunite,

silica beads), industrial waste products (metal hydroxide sludge, waste carbon slurries), agricultural products and wastes (hazelnut shell, bagasse pith, macro-fungus, maize cob, kidney bean, coconut shell, rice husk), bio adsorbents (peat, chitosan, biomass), cyclodextrin, starch, and cotton [16,17]. Some modification processes have been used to improve adsorbent materials and adsorption performance [18,19]. The present study is a report on an attempt to remove Food Red 17 (FR17) from an aqueous solution using anionic polymeric urethane absorbent (APUA) as the adsorbent. Three operating parameters were explored: adsorbent dosage, initial pH, and temperature. In all the experiments, the effect of time was a key concern. Furthermore, the effect of stirring on the adsorption of FR17 onto APUA was investigated. The Langmuir model was used to quantify the amount of adsorption. We also addressed the effect of UV irradiation on the removal process. The efficiency of the treatment was studied via FT-IR spectrometry, and APUA efficiency was studied using the SEM technique. 2. Materials and methods 2.1. Adsorbent synthesis

* Corresponding author at: Department of Environmental Research, Institute for Color Science and Technology, P.O. Box: 16765-654, Tehran, Iran. Tel.: +98 2122944184. E-mail address: [email protected] (M.E. Olya).

APUA was synthesized in three steps. First, 0.1 mol of isophorone diisocyanate (IPDI), 0.1 mol of hydroxyethyl methacrylate (HEMA), and 0.1 mol of dimethylpropionic acid (DMEA)

http://dx.doi.org/10.1016/j.jiec.2014.02.050 1226-086X/ß 2014 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

[(Fig._1)TD$IG]

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A. Pirkarami et al. / Journal of Industrial and Engineering Chemistry 21 (2015) 387–393

Fig. 1. The synthesis of APUA.

were combined at 45 8C in the presence of 2 drops of dibutyltin dilaurate (DBTDL) as the catalyst and 100 ml of acetone as the reaction solvent. This solution was allowed to stand for 2 h to achieve urethane acrylate with a tertiary amine terminal group. Then, cationic polymerizable urethane acrylate was synthesized via quaternization of tertiary amine groups of urethane acrylate with 1, 8-diboromooctane at 55 8C for 2 h. Finally, APUA was synthesized via radical polymerization of cationic polymerizable urethane acrylate in the presence of tert-butyl hydroperoxide (TBHP) (70% solution in water) and sodium formaldehydesulfoxylate (SFS) as redox radical initiators at 75 8C for 2 h. The entire process of synthesizing APUA is shown in Fig. 1. It is noteworthy at this point that APUA is not soluble in water and can be readily removed via filtration. The resulting APUA residue was used in subsequent runs of the experiment. 2.2. Materials and equipment FR17, also called Allura Red AC, used to prepare the aqueous [(Fig._2)TD$IG] solution was procured from an Iranian supplier Alvan sabet (Iran).

This cationic dye is extensively used as a colorant in foodstuffs, soft drinks, cosmetics, children’s medications, and tattoo inks [20,21]. Although FR17 has fewer health risks associated with it in comparison with other azo dyes, some studies [22,23],have found some adverse health effects for the dye. H2SO4 (98.079 g mol1) and NaOH (39.9971 g mol1) used to adjust the pH of the aqueous solution were purchased from the German company of Merck. The water bath used for controlling the temperature was a Memmert WB 14, Schutzart DIN 40050-IP 20 (Germany). The morphological features and surface characteristics of APUA were studied using a scanning electron microscope (SEM) unit (HITACHI-3000 SH Model, Japan). 2.3. Procedure The aqueous solution was prepared by dissolving 40 mg L1 of dye into 1 L of deionized water in a beaker. At the next step, APUA was poured into the solution. Then, the pH of the aqueous solution was adjusted, and the solution was magnetically stirred at 150 rpm at room temperature for 4 h.

Fig. 2. (a) Effect of the adsorbent dose on the removal of FR17 (dye concentration: 40 mg L1, pH: 3, temperature: 35 8C, stirring speed: 150 rpm). (b) Electrostatic force between the positively charged FR17 molecule and negatively charged APUA.


The goal was to examine the effect of adsorbent dosage, initial pH, and temperature as the operating parameters on the efficiency of removing the azo dye. To determine the effect of adsorbent dosage on removal efficiency, seven concentrations of APUA were considered: 5, 10, 15, 20, 25, 30, and 35 mg L1. For the effect of pH, the pH of the solution was adjusted at 12 values: (3, 3.3, 4, 4.3, 4.7, 5, 5.3, 5.7, 6, 6.5, 7, and 7.5). To study the effect of temperature, three degrees were applied (25, 35, and 45 8C). For this purpose, a beaker was placed in a water bath. The effect of time was of concern to the authors in all the experiments. Another matter of interest was the effect of stirring speed on the adsorption of FR17 onto APUA. To this end, the experiment was conducted in two homogeneous (with stirring) and heterogeneous (without stirring) modes. Lastly, as APUA is insoluble in water and highly viscous, it deposited in solid form and was easily reusable from the dye solution. 2.4. Evaluation of treatment efficiency To determine the efficiency of dye removal, aliquots were taken out from the solution and were placed inside a UV–Vis spectrophotometer (Camspec M-350 Double Beam, UK) to measure the maximum adsorption of the dye. Dye concentration was measured using absorbance values at 504 nm (the maximum

[(Fig._3)TD$IG]

389

absorbance wavelength of FR17). The linear relationship between efficiency of dye removal (denoted by R and expressed in a percentage) and dye concentration was obtained using Eq. (1): Rð%Þ ¼

A0 A 100 A

(1)

where A0 and A are the light absorbance of the dye before and after electrocoagulation, respectively. The FT-IR technique was employed to evaluate the efficiency of the treatment. This was accomplished by characterizing the adsorbent, the dye, and the combination thereof (i.e., APUA + FR17). The samples were mixed with spectroscopically pure KBr in the ratio of 2:100 to make pellets, which were then placed in the Shimadzu 8300 FT-IR (Perkin-Elmer, Spectrum one). FT-IR spectroscopy was accomplished in the range of 500– 3500 cm1 for the intact dye and degraded dye. 3. Results and discussion The removal of FR17 from the aqueous solution was studied at

lmax 504 nm. Adsorbent dose of 30 mg L1, pH of 3, and temperature level of 35 8C were found to be the optimal conditions for decolorization. The parameters under investigation and the effect of stirring will be further discussed below.

Fig. 3. (a) Effect of pH on the removal of FR17 (adsorbent dose: 35 mg L1, temperature: 35 8C, stirring speed: 150 rpm); (b) the associated mechanism.

[(Fig._4)TD$IG]

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[(Fig._5)TD$IG]


Fig. 4. Effect of temperature on the removal of FR17 (APUA dose: 35 mg L1, pH: 3, contact time: 4 h, stirring speed: 150 rpm).

Fig. 5. Effect of stirring on the removal of FR17 (APUA dose: 35 mg L1, pH: 3, temperature: 25 8C, contact time: 4 h, stirring speed: 150 rpm).

3.1. Effect of adsorbent dose

caused at 35 mg L1. It was also observed that as more of the adsorbent was used, more adsorption of FR17 occurred. This could be attributed to the appearance of more active sites in the solution and the expansion of the polymer network as a result of introducing more adsorbent. To explain the adsorption of FR17

As for the effect of adsorbent dosage on dye removal, seven concentrations of APUA were applied: 5, 10, 15, 20, 25, 30, and 35 [(Fig._6)TD$IG] mg L1. As Fig. 2a shows, maximum decolorization (90.5%) was

Fig. 6. Effect of UV irradiation on the removal of FR17 (a) and the proposed mechanism (b) (APUA dose: 35 mg L1, pH: 3, temperature: 25 8C, contact time: 4 h, stirring speed: 150 rpm).


onto APUA, it can be argued that since the dye molecule and the polymer are oppositely charged, the positive charge of FR17 interacts with the negative charge of APUA (Fig. 2b). This interaction is mainly a result of the electrostatic force generated by the two opposite charges. Of course, the existence of the van der Waals force cannot be ignored, but it is thought that this force is not as effective [24]. 3.2. Effect of pH Fig. 3a shows the effect of different values of pH on the efficiency of the removal of FR17: 3, 3.3, 4, 4.3, 4.7, 5, 5.3, 5.7, 6, 6.5, 7, and 7.5. Maximum adsorption (90%) was observed at the pH value of 3 after 4 h of treatment. This phenomenon may be attributed to the fact that with a decrease in pH, the concentration of H+ increases. The H+ ions react with CO2 on the surface of the polymer and are converted into COOH, which creates an electrostatic bond with the positive charge of the dye molecule. This bond increases the adsorption of the dye on the polymer surface [25–27]. The reactions are displayed in Fig. 3b.

(0 < RL < 1), or irreversible (RL = 0). For FR17 in this research, the value of RL is within the 0.618–0.163 concentration range. These results confirm that APUA is favorable for the adsorption of FR17 under the optimized experimental conditions. 3.6. Effect of UV irradiation The aqueous solution was subjected to UV light under the optimum conditions obtained (contact time: 4 h, APUA dose: 35 mg L1, pH: 3, temperature: 25 8C, stirring speed: 150 rpm). Fig. 6a presents the FR17 removal percentage in the absence and presence of UV irradiation: APUA and APUA + UV, respectively. As can be seen, significantly more removal took place when UV light was present. Fig. 7b portrays a tentative mechanism for the removal of FR17 in the presence of UV light. Upon UV illumination, the electrons on COOH surface are excited from the valence band (VB) to the

[(Fig._7)TD$IG]

3.3. Effect of temperature Another important parameter in the removal process is temperature. Three levels of 25, 35, and 45 8C were subjected to analysis. Fig. 4 shows the effect of temperature on the efficiency of removing FR17 from the aqueous solution. It can be observed that the highest degree of dye removal (89%) was obtained at 45 8C after 4 h of treatment. This agrees with El-Khaiary (2007), who also found that temperature significantly affects the adsorption of the dye. 3.4. Influence of stirring We also explored the effect of stirring at 150 rpm on the adsorption of FR17 onto APUA. As Fig. 5 shows, stirring the aqueous solution led to significantly more adsorption. To explain this, it can be said that stirring increases the number of active sites in the solution and consequently intensifies the contact between the polymer and the dye. 3.5. Langmuir equation The Langmuir adsorption equation is commonly used to quantify the adsorption of the molecules of an adsorbate on to the surface of an adsorbent [28]. Eq. (2) states this model: Ce 1 Ce þ ¼ qe Q O b Q O

(2)

where Ce is the equilibrium concentration of the dye (mg L1), qe is the amount of dye adsorbed per unit mass of the adsorbent (mg g1), and Qo and b are the Langmuir constants related to adsorption capacity and adsorption rate, respectively. The plot of Ce/qe against Ce yielded straight lines with a slope = 1/Qo for FR17. That is, FR17 was adsorbed on to APUA. Also, a layer of dye covered the outer surface of APUA. For FR17, the constants b and Qo were calculated to be 0.0316 mg L1 and 90.5 mg g1, respectively. The main characteristics of the Langmuir isotherm can be stated in terms of a dimensionless equilibrium parameter (RL) [29] expressed in Eq. (3) below: RL ¼

1 ð1 þ bC o Þ

(3)

where b is the Langmuir constant, and C0 is the maximum dye concentration (mg L1). The value of RL shows that the isotherm is one of four types: unfavorable (RL > 1), linear (RL = 1), favorable

391

Fig. 7. The FT-IR spectra of FR17 (a), APUA (b), and APUA-FR17 (c).


392

4. Characterization and analysis

occurring during the adsorption process. The broad peak at 3458 cm1 is attributable to the presence of O–H stretching. The peak at 1633 cm1 can be assigned to the combination of the carbon of the naphthalene ring with the C5 5N group [32]. The intense peak at 1491 cm1 indicates an –N5 5N– group. A comparison was also drawn between the FT-IR spectra of APUA (Fig. 7b) and those of the APUA-FR17 combination (Fig. 8c). In Fig. 7b, IPDI appeared at the peak at 2495 cm1. In addition, the sharp bands at 1722 cm1 and 1153 cm1 respectively indicate the C5 5O and C–O stretching vibrations of HEMA and urethane. Furthermore, the peaks at 1308 cm1 and 1364 cm1 are due to the C–H bending vibrations of CH3, and the band at 1459 cm1 represents the C–H bending vibration of CH2. Lastly, the peak at 1580 cm1 is an indication of the N–H bending vibration of urethane [33]. In Fig. 7c, it can be seen that the peak for the NCO stretching vibration of IPDI (2495 cm1) has disappeared, suggesting that IPDI has been completely blocked by HEMA and DMPA. Another observation is the shifting of peak for O–H stretching shifted from 3458 cm1 to 3451 cm1. Furthermore, the peak representing the C5 5N group shifted from 1633 cm1 to 1624 cm1, possibly due to the fact that the dye molecule adsorbed water. Another observed shift is for the peak indicating the –N5 5N– group: from 1491 cm1 1 to 1499 cm . This, too, can be attributed to water adsorption. All these changes confirm the adsorption of the dye molecule on the APUA surface as a result of the treatment.

4.1. FT-IR spectral analysis

4.2. SEM characterization

conduction band (CB), thus generating electron-hole pairs (Eqs. (4) and (5) below) [30]. hv

COOH !COOH ðeCB Þ þ COOH hþ VB

(4)

CO2 ðeÞ þ COOH ðeCB Þ ! reduction reaction

(5)

Furthermore, as Eq. (6) states, the H ions reacting with CO2 may trap electrons and hamper the recombination of photo-generated electrons and holes. CO2 þ COOHðeÞ ! CO2 ðeÞ þ COOH

(6)

In the meantime, the reactions in the aqueous solution produce H2O2, which is thought to expedite the process of dye removal by generating more hydroxyl and superoxide radicals responsible for attacking the dye molecules (Eq. (7)–(10)) [31]. H2 O2 þ COOHðeÞ ! OH þ OH

(7)

þ

(8)

OH þ OH2 ! H2 O þ O2

(9)

OH þ O2 þ Dye ! mineral products

H2 O2 þ hVB ! OH2 þ H

(10)

The efficiency of the treatment can be identified using the FT-IR

[(Fig._8)TD$IG]spectra of FR17 (Fig. 7a). This figure shows some structural changes

The surface texture of APUA was analyzed prior to (Fig. 8a) and following (Fig. 8b–f) adsorption using the SEM technique. As can be

Fig. 8. SEM images of pre-treatment APUA (a), APUA after 20 min of adsorption (b, c), and APUA after 1 h of adsorption (d); APUA after 4 h of adsorption in the presence of UV (e, f).


seen, the nanoparticles in Fig. 8a have sharp and amorphous edges. In Fig. 8b and c, pores can be seen on the surface of the APUA soaked in the aqueous solution. Fig. 8d shows amorphous short thin strips of noodle. Lastly, Fig. 8e and f show that dye molecules were adsorbed onto polymer surface after 4 h of treatment as a result of the electrostatic force. 5. Conclusions This study aimed to optimize the removal of an azo dye, FR17, from aqueous solution employing APUA as an adsorbent. The experimental parameters were APUA dose, pH, temperature, and stirring. The optimum adsorbent dose observed for efficient dye removal was 35 mg L1. Further, a pH value of 3 brought about maximum adsorption. It was also observed that the highest degree of dye removal is possible at 45 8C. Finally, it was found that stirring significantly maximizes efficiency of dye removal. The Langmuir model was used to quantify the amount of FR17 adsorption. UV illumination turned out to have a positive effect on the removal process. To verify the efficiency of the treatment, we obtained FT-IR spectra of APUA, FR17, and the combination thereof. APUA was characterized using the SEM technique. References [1] [2] [3] [4]

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