Journal of Industrial and Engineering Chemistry 19 (2013) 1371–1376
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Dye sorption characters of gamma irradiated foamed ethylene propylene diene monomer (EPDM) rubber/clay composites Mahmoud S. Hassan, Khaled F. El-Nemr * Radiation Chemistry Department, National Center for Radiation Research and Technology, P.O. Box 29, Nasr City, Cairo, Egypt
A R T I C L E I N F O
Article history: Received 2 October 2012 Accepted 31 December 2012 Available online 3 January 2013 Keywords: Rubber composites Dye sorption Gamma radiation
A B S T R A C T
Composites based on gamma irradiated ethylene propylene diene monomer rubber in foam structure, loaded with different types of clays were used as adsorbents for different classes of dyestuffs (basic, acid, reactive and disperse) from aqueous solutions. The clays under investigation were Aswan clay (ASC) and sodium montmorillonite (Na-MMT). The effect of adsorbent composition, irradiation dose, pH and contact time on dye sorption was studied. It was found that the rubber composites loaded by Na-MMT gave maximum adsorption of the basic dye (42%) in aqueous solution, while the rubber composites loaded by AS clay gave maximum adsorption (28%) of the acidic dye. On the other hand, both type of clays did not show no affinity toward reactive and disperse dyes. The efficiency of dye removal was found to increase with increasing the pH and contact time. It was also observed that the irradiation dose (50 kGy) was the optimum dose for the removal of dyes for all rubber composites. ß 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
1. Introduction In modern industries, synthetic dyes are widely used to color products such as textiles and papers. These dyes as an effluent, even in small amounts, are highly visible and have undesired effects, not only on the environment, but also on living organisms. In addition, the degradation products of some dyes may be carcinogenic, toxic, and consequently they are important sources of water pollution and their treatment becomes a major problem for environmental managers. Adsorption is one of the most efficient methods to remove pollutants from waste water. Many studies have been made on the possibility of using adsorbents based on activated carbon [1], clay minerals [2–4], crosslinked amphoteric starch [5], weeds [6], fly ash [7,8], Indian rosewood sawdust [9], and crosslinked chitosan beads [10]. Clay minerals represent a cheap and environmentally safe source of raw material for the preparation of low-cost adsorbents that may be useful for the removal of pollutants from waste water. Removal efficiency and adsorption capacity were found to be the highest for RAC (commercial activated carbon). RAC is the most popular adsorbent and has been used with great success, but is expensive. Experimental results have shown that adsorption capacity of RAC activated carbon obtained from shell of hazelnut
* Corresponding author. Tel.: +202 22748246; fax: +202 22749298. E-mail address:
[email protected] (K.F. El-Nemr).
was comparatively lower than those of clays such as raw kaolinite (KC) and montmorillonite (MMC). These experiments indicate that raw kaolinite and montmorillonite were effective in removing direct dyes from aqueous solution in the range of the concentrations investigated. Because these types of clays are plentiful and inexpensive adsorbents, these could be considered for removing direct dyes from an aqueous solution [11]. Diatomite clay was used as an adsorbent for the removal of methylene blue dye from water. The adsorption equilibrium revealed that diatomite can uptake 42 mmol dye/100 g in relatively low concentration in aqueous medium. This naturally occurring material could substitute the use of activated carbon as adsorbent due to its availability and its low cost [12]. Natural Jordanian Tripoli is abundant low-cost clay, can be used as adsorbent for the removal of methylene blue dye (MB) from aqueous solutions [13]. The amount of dye adsorbed was found to vary with initial pH, Tripoli dose, MB concentration and contact time. It was found the high adsorption yield was obtained at pH 8–10, the maximum adsorption efficiency was 97% at pH 8; also the results showed that, with increase in the adsorbent concentration, from 0.1 to 0.5 g 100 mL1, the amount of adsorbed MB removal increases from 45 to 97%. On the other hand, the percent removal of MB decreased from 97 to 33% as the initial MB concentration increased from 50 to 250 mg/L. The sorption efficiency of MB increases with the increase of shaking time up to 120 min. The removal of acid red 183 from aqueous solution onto activated carbon, raw kaolinite and montmorillnite was studied [14]. The results indicated that the adsorption capacity of RAC obtained from shell of hazelnut was comparatively lower than
1226-086X/$ – see front matter ß 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jiec.2012.12.042
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RAC but was higher than based on clays such as raw kaolinite and montmorillonite (MMT). These results indicated that raw kaolinite and montmorillonite are effective in removing acid red 183 from aqueous solution in the range of concentrations studied. So, because this type of clays is plentiful and cheap adsorbents they could be used to remove dyestuff from aqueous solution. Removal efficiency could be made better by increasing the amount of clay used. The aim of the present work is to study the gamma irradiation effect on the potential application of composites based on ethylene propylene diene monomer (EPDM) foam rubber/clay for removal of different types of dyes from aqueous solutions. The factors which, affecting adsorption, such as type of dye, irradiation dose, pH and contact time were evaluated. The rubber composites were prepared in the foam structure to increase the surface area of irradiated composites and hence increase the dye sorption.
2. Materials and methods 2.1. Materials Ethylene propylene diene monomer (EPDM) rubber used in this work is the commercial trade vistalon 5600 and was obtained from Exxon Chemical Company (Belgium). It has ethylene content 60%, specific gravity 0.86, ash content 0.3 wt%, and mooney viscosity ML1+4 at 100 8C of 45. The chemical blowing agent used in this work was azodicarbonamide (ADC) has gas yield 220 mL/g, decomposition temperature 160 8C, and was supplied from Haihong Chemical, China. Aswan clay, supplied by General Company for Ceramics, Cairo, Egypt has the chemical composition: SiO2 (47%), Al2O3 (% 30%), Fe2O3 (8.24%), CaO (2.89%), MgO (1.08%) and alkaline (Na2O + K2O) of 0.83%. Na-montmorillonite was supplied by the Egypt Bentonite and Dreivatives, Egypt. 1,2-Dihydro-2,2,4-trimethyl quinoline (TMQ) as antioxidant was obtained from Intatrade Chemicals (GmbH), Germany. The ingredients, i.e. zinc oxide and stearic acid were of commercial grades. The basic dye (Remacryl blue 3G–Basic blue 3) was supplied by Hoechst, Germany. The acid dye (Nylson navy N-RBL–Acid blue 13) was supplied by Sandoz, Switzerland. The reactive dye (Remazol brilliant blue BB–Reactive blue 19) was supplied by Hoechst, Germany. The dispersive dye (Samaron red 2BSL–Disperse red 60) was supplied by Hoechst, Germany. All the dye solutions used were at 1% dye concentration. 2.2. Preparation of rubber/clay composites EPDM was first masticated on a laboratory two-roll mill for 2 min followed by addition of ingredients, antioxidant (TMQ), stearic acid, ZnO, and finally the different clay types were added at a constant concentration of 30 phr (part per hundred part of rubber). The nip-gap, mill roll speed ratio and the number of passes were kept constant for all mixtures. Compounds were finally sheeted in the rolling direction into slabs of 1 mm thickness. The sheets were transferred to foam structure by pressing in clean molds of an electric press. The molds were brought to 160 8C and held at this temperature for 15 min at a pressure of 160 kg/cm2. The different formulations of prepared specimens are shown in Table 1. 2.3. Gamma irradiation The samples were irradiated in the Cobalt-60 Gamma cell source (made in Russia) installed at National Center for Radiation Research and Technology (NCRRT), Cairo, Egypt. Irradiation was done at a dose rate of 3 kGy/h.
Table 1 The different formulations of prepared specimens. Formulation
A
B
C
EPDM Stearic acid ZnO TMQ Aswan clay Na-montmorillonite ADC
100 1 5 1 – – 5
100 1 5 1 30 – 5
100 1 5 1 – 30 5
2.4. Soluble fraction (SF) The soluble fractions of different irradiated EPDM rubber composites were determined as follows: accurate weight of sample (Wo) was placed in stainless grids. The grids containing samples were extracted with benzene under reflux for 24 h. After extraction, the samples were dried to constant weight (W1) in dry oven at 50 8C. The soluble fraction was calculated as follows: SF ¼
Wo W1 Wo
(1)
2.5. Swelling ratio (Q) The swelling ratio of different irradiated EPDM rubber composites was determined by immersing extracted samples at room temperature in benzene for 48 h to insure equilibrium state. The insoluble part swollen with solvent in equilibrium was weighed at room temperature (W2), the swelling ratio (Q) can be calculated as follows: Q¼
ðw1 =dp Þ þ ðw2 w1 Þ=ds w1 =dp
(2)
where w1 is the weight of the sample after extraction and before swelling, w2 is the weight of the swelled sample, dp is the density of the EPDM and ds is the density of benzene. 2.6. Water absorption Swelling behavior in water was carried out as follows: a dry weight of the insoluble composite (W1) was soaked in water for different periods of times: one, two and 4 weeks at room temperature. The sample was then removed and blotted on a filter paper to remove the excess water on the surface and reweighed (W2). The percentage swelling was calculated according to the following equation: Swelling ð%Þ ¼
W2 W1 100 W1
(3)
2.7. Dye sorption measurements The percentage sorption of the different dyestuffs by different rubber composites was performed using a UV/Vis spectrophotometer (Unicom UV2 series). Standard curves were first made representing a relation between different known concentrations from each dye and the corresponding light absorption as shown in Fig. 1. In this procedure, a certain concentration from each dye under investigation was first dissolved in boiled water. The relations representing these curves are as follows: For basic dye ðl ¼ 660 nmÞ : concentration ðmg=LÞ ¼
light absorbance 0:1751
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Fig. 2. The characteristic wavelengths of different used dyes.
Fig. 1. UV/Vis absorbance of different concentrations of the basic dye (Remacryl blue 3G), acid dye (Nylson navy N-RBL), reactive dye (Remazol brilliant blue BB) and disperse dye (Samaron red 2BSL).
For acid dye ðl ¼ 560 nmÞ : concentration ðmg=LÞ ¼
light absorbance 0:0653
For reactive dye ðl ¼ 520 nmÞ : concentration ðmg=LÞ ¼
light absorbance 0:2042
the soluble fraction up to 50 kGy and then tends to level off with increasing irradiation dose. These trends were observed for the rubber composites containing Aswan or montmorillonite clays. It was found that the composites loaded with MMT gave lower values of soluble fraction than those for ASC at any irradiation dose. It is known that the clay as a filler has low reinforcing ability to rubber due to the presence of low silanol groups on its surface [15,16]. The effect of irradiation dose on the swelling ratio of EPDM foams loaded with different types of clays is shown in Fig. 4. It can be seen that the increase of the irradiation dose leads to a decrease in the swelling ratio up to 150 kGy. The same trend was obtained for rubber composites containing ASC or MMT. It was obviously observed that incorporation of MMT gave lower decrease in the swelling ratio for the composites loaded with ASC. This is due to the MMT have higher interaction and adhesion with EPDM rubber matrix. From Figs. 3 and 4, it can be concluded that the irradiation
For disperse dye ðl ¼ 500 nmÞ : concentration ðmg=LÞ ¼
light absorbance 0:0306
where (l) expression for the characteristic wavelengths of different used dyes at constant concentrations (1 mg/L) as shown in Fig. 2. After that, a constant weight of the rubber composites was immersed in the different dye solutions and the uptake by the rubber composites was determined by measuring the light absorption of the residual dye solution. The percentage sorption of dyes by rubber composites was determined according to the following equation: CR (4) 100 Dye sorption ð%Þ ¼ Co where CR is the dye concentration on rubber composite and Co is initial dye concentration. 3. Results and discussion 3.1. Soluble fraction and swelling ratio Fig. 3 shows the effect of irradiation dose on the soluble fraction of foamed EPDM rubber loaded with different types of clays. It can be observed that the soluble fraction decreased with increasing irradiation dose. This can be explained on the basis of the crosslinking effect of gamma radiation on the rubber composites. The increase of irradiation dose was companied by a decrease in
Fig. 3. Effect of irradiation dose on the soluble fraction of EPDM rubber composites loaded with different types of clays.
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Fig. 4. Effect of irradiation dose on the swelling ratio of EPDM foam composites loaded with different types of clays.
dose of 50 kGy is the optimum dose for soluble fraction and swelling ratio. 3.2. Water absorption The effect of irradiation dose on water absorption (%) after different periods for different EPDM composites is shown in Fig. 5. It can be seen that the type of clay plays an important role on water absorption, regardless irradiation dose. However, it is obvious that the highest water absorption (%) was obtained for EPDM loaded with MMT, followed by ASC. On the other hand, the EPDM that not loaded with clays exhibit the lower values of water absorption. For all composites of EPDM either unloaded or loaded with clay, the values of water absorption decreased with increasing the irradiation dose, as a result of the crosslinking by radiation. MMT and ASC clays are three layers clay mineral, having a negative charge on the surface of the layers. This negative charge is responsible for the capability of cation exchange (adsorption of Naor Ca-cations). Depending on the type of the adsorbed ions, the MMT is designated as Na- or Ca-MMT. When water is available, the cations can hydrate and the distance between the layers will widen; this is called inner crystalline swelling, a typical property of montmorillonite or Aswan clays. 3.3. Effect of clay type on dye sorption by EPDM rubber composites The different EPDM rubber composites irradiated at 50 kGy were examined as substrates for different classes of dyestuffs. Fig. 6 illustrates the percentages sorption of basic, acid, reactive and disperses dyes from their solutions by the different rubber composites loaded with constant concentrations of clays of 30 phr for definite time (24 h). It was found that the percentage of dye sorption by EPDM rubber composite (A) was 0.0, 12.2, 2.45 and 4.35% for basic, acid, reactive and disperses dyes, respectively. The percentage of dye sorption by EPDM rubber composite (B), which contains Aswan clay was 5.0, 57.3, 7.78 and 3.48% for basic, acid, reactive and disperse dyes, respectively. Whereas, the percentage of dye sorption by EPDM rubber composite (C), which contains
Fig. 5. Effect of irradiation dose on water absorption (%) after different periods for EPDM composites: (A) unloaded, (B) loaded with Aswan clay and (C) loaded with Na-MMT clay.
montmorillonite clay was 42, 14.6, 4.1 and 0.87% for basic, acid, reactive and disperse dyes, respectively. From Fig. 6, it can be concluded that, the EPDM rubber composite (B), which contains Aswan clay gave the highest dye sorption toward acid dye (28%). Whereas, the EPDM rubber composite (C), which contains montmorillonite clay gave the highest dye sorption toward basic dye (42%). It can be also seen that the different EPDM rubber composites did not give a considerable dye sorption percentage for reactive and disperse dyestuffs. 3.4. Effect of irradiation dose on the dye sorption by EPDM rubber composites The effect of irradiation dose on dye sorption of the different EPDM rubber composites (B) and (C) on the dye sorption efficiency toward acid and basic dyes was studied as shown in Fig. 7. It can be seen that the dye sorption was affected by the irradiation dose. The increasing of irradiation dose onto rubber composites was accompanied by decreasing in the dye sorption up to 25 kGy and then tends to decreasing sharply with increasing of the irradiation dose up to 100 kGy, regardless of dye type and clay. That could be attributed to the effect of irradiation doses onto the rubber composite swelling, which is responsible for the dye sorption. At higher irradiation doses, the crosslinking of the rubber
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Fig. 8. Effect oEffect of pH on the sorption of the basic dye by EPDM rubber composite (C) and acid dyes by EPDM rubber composite (B).
Fig. 6. Dye sorption of different dyestuffs by different EPDM rubber composites.
composites increase causing a decreasing in the swelling ratio, which leads to decreasing of the dye sorption. From Figs. 3, 4 and 7, it was found that the best irradiation dose, which gives good dye sorption efficiency, beside enhancing of the soluble fraction and swelling ratio of different used EPDM rubber composites, was 50 kGy.
different rubber composites loaded with clays, may be explained on the basis of surface hydroxylation, acid base dissociation and surface complexation. The broken Si–O bonds and Al–OH bonds along the surface of the clay crystals, result in hydrolysis [17]. In aqueous systems, at low pH range, the reaction might be as follows: SiOH þ Hþ ! SiOH2 þ at high pH range, the reaction will be:
3.5. Effect of pH on the dye sorption by EPDM rubber composites
SiOHþ þ OH ! SiO þ H2 O
The effect of pH on dye sorption at room temperature by the gamma irradiated EPDM rubber composites at 50 kGy was studied as shown in Fig. 8. It can be seen that the dye sorption percentage of gamma irradiated rubber composite (C) toward the basic dye was enhanced in the basic medium, compared to the initial dye solution. The dye sorption by composite (C) was 59.0, 45.0 and 37.5% in basic, natural and acid medium, respectively. The dye sorption percentage of gamma irradiated rubber composite (B) toward the acid dye was 34.6, 27.1 and 0.6% in basic, natural and acid medium, respectively. The increase in sorption depends on the surface properties and dye structure. The effect of pH range on the dye sorption of
So, the dye sorption could be reached to the maximum in the alkaline medium, due to the contacting of dye solution with the basal oxygen surface of the tetrahedral sheet which will contain excess hydroxyls. The surface will then exhibit a cation exchange capacity. Similar explanation has been reported for the sorption of acid and basic dyes on Aswan and montmorillonite clays, respectively [18].
Fig. 7. Effect of irradiation dose on the sorption of the basic dye by EPDM rubber composite(C) and acid dyes by EPDM rubber composite (B).
Fig. 9. Effect of immersing time on the sorption of the basic EPDM rubber composite (C) and acid dyes by EPDM rubber composite (B).
3.6. Effect of immersion time on dye sorption The effect of immersing time on dye sorption percentage at room temperature (pH = 11) by the gamma irradiated EPDM
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3.7. Scanning electron microscopy (SEM) Fig. 10(A) shows the SEM micrographs of the fracture surfaces of EPDM rubber composites. It can be seen clearly the foam structure which full of holes with large cell size. However the incorporation of Aswan clay to EPDM as shown in Fig. 10(B) improved the compatibility between rubber and clay, and this observed in the decrease of cell size. Fig. 10(C) demonstrates that the addition of montmorillonite to EPDM made the cell size smaller and more uniform. 4. Conclusion - The crosslink density for all rubber composites increased by increasing irradiation dose, and this was shown by the results of soluble fraction and swelling ratio. - The Na-montmorillonite gave maximum adsorption affinity toward basic dye; meanwhile, the Aswan clay gave maximum affinity toward acid dye. - Both types of clay were not shown any response toward reactive and disperse dyes. - The results were shown that the radiation dose at 50 kGy was the optimum for removal of dyes, with keeping of the improvement of soluble fraction and swelling ratio of EPDM rubber composites with clays. - Generally the removal of dyes increased with increasing the pH and contact time.
References
Fig. 10. Scanning electron micrograph at 50 kGy for (A) EPDM, (B) EPDM loaded by AS clay and (C) EPDM loaded by Na-MMT. All the rubber composites were irradiated at 50 kGy dose of gamma radiation.
rubber composites at 50 kGy was studied as shown in Fig. 9. It can be seen that the dye sorption percentage of basic dye by rubber composite (C) increased with increasing the immersing time, compared with the initial dye solution, which gave 43.5, 52.5, and 57.5% after immersing for 1, 5 and 10 days, respectively. The same trend was noticed for the dye sorption by the rubber composite (B) toward acid dye which gave 28.6, 31.5 and 33.49% after immersing for 1, 5 and 10 days, respectively.
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