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Hindawi Publishing Corporation Journal of Chemistry Volume 2013, Article ID 938374, 8 pages Research Article Decolorisation of Reactive Red 120 Dye by Using Single-Walled Carbon Nanotubes in Aqueous Solutions Edris Bazrafshan, 1 Ferdos Kord Mostafapour, 1 Ali Reza Hosseini, 1 Ataolah Raksh Khorshid, 1 and Amir Hossein Mahvi 2, 3, 4 1 Health Promotion Research Center, Zahedan University of Medical Sciences, Zahedan, Iran 2 School of Public Health, Tehran Uni
  Hindawi Publishing CorporationJournal of Chemistry Volume 2013, Article ID 938374, 8 pages Research Article DecolorisationofReactiveRed120DyebyUsingSingle-WalledCarbonNanotubesinAqueousSolutions EdrisBazrafshan, 1 FerdosKordMostafapour, 1  AliRezaHosseini, 1  AtaolahRakshKhorshid, 1 andAmirHosseinMahvi 2,3,4 1 Health Promotion Research Center, Zahedan University of Medical Sciences, Zahedan, Iran 2 School of Public Health, Tehran University of Medical Sciences, Tehran, Iran 3 Center for Solid Waste Research, Institute for Environmental Research, Tehran University of Medical Sciences, Tehran, Iran 4 National Institute of Health Research, Tehran University of Medical Sciences, Tehran, Iran Correspondence should be addressed to Amir Hossein Mahvi; ahmahvi@yahoo.comReceived 2 June 2012; Revised 14 July 2012; Accepted 15 July 2012Academic Editor: Mohammad A. Al-GhoutiCopyright © 2013 Edris Bazrafshan et al. is is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the srcinal work is properly cited.Dyes are one of the most hazardous chemical compound classes found in industrial effluents and need to be treated since theirpresence in water bodies reduces light penetration, precluding the photosynthesis of aqueous ora. In the present study, single-walled carbon nanotubes (SWCNTs) was used as an adsorbent for the successful removal of Reactive Red 120 (RR-120) textile dyefrom aqueous solutions. e effect of various operating parameters such as initial concentration of dye, contact time, adsorbentdosage and initial pH was investigated in order to �nd the optimum adsorption conditions. Equilibrium isotherms were used toidentify the possible mechanism of the adsorption process. e optimum pH for removing of RR-120 dye from aqueous solutionswas found to be 5 and for this condition maximum predicted adsorption capacity for RR-120 dye was obtained as 426.49mg/g.Also, the equilibrium data were also �tted to the Langmuir, Freundlich and BET equilibrium isotherm models. It was found thatthe data �tted to BET (  2 = 0.9897 ) better than Langmuir (  2 = 0.9190 ) and Freundlich (  2 = 0.8819 ) model. Finally it wasconcluded that the single-walled carbon nanotubes can be used for dye removal from aqueous solutions. 1.Introduction Environmental pollution has recently become a severe prob-lem worldwide [1]. Dyes are one of the most hazardouschemical compound classes found in industrial effluentsand need to be treated since their presence in water bodiesreduces light penetration, precluding the photosynthesis of aqueous ora [2, 3]. ey are also aesthetically objectionablefor drinking and other purposes [4] and can cause allergy,dermatitis,skinirritation[5]andalsoprovokecancer[6]andmutation in humans [7].Reactive dyes represent an important portion of thecommercial synthetic dyes, mainly because of their excellentbinding ability initiated by the formation of a covalent bondbetween their reactive groups and the surface groups of thetextileandcellulose�bers.eyareusedextensivelyintextileindustries, and their release in the ecosystem representsincreasing environmental danger, because of their toxicity,mutagenicity, and nonbiodegradability [8–10]. Also, reactivedyes are, in general, the most problematic among other dyes,as they tend to pass through conventional treatment systemsunaffected [10, 11]. Additionally, reactive dyes are resistantto natural biodegradation, due to the aromatic rings in theirstructure [12]. Among dyes used in textile industry, ReactiveRed-120(RR-120)isoneofthefrequentlyuseddyesintextileindustriesandisapotentialthreattotheaquaticenvironmentdue to its poor biodegradability [1].Improper treatment and disposal of dye-contaminatedwastewaters from textile, dyeing, printing, ink, and relatedindustries have provoked serious environmental concerns allover the world [13, 14]. Removal of dye in wastewater hasbeen made by physical, physicochemical, biological, and/orchemicalprocesses[15–17].econventionaltreatmentpro-cess of textile effluents involves numerous stages due to the  2 Journal of Chemistry  T 1: Some characteristics of the investigated dye.Characteristic Reactive Red-120 (RR-120)Molecular formula C 44 H 24 C 12 N 14 Na 6 O 20 S 6 Color index name Reactive Red-120Molecular weight 1469,34g/molWater solubility 70 (gL −1 )  max  515Class Diazo (–N=N– bond) characteristics of the production process [18]. Conventionaltreatment involves a process of coagulation/occulation.is is a versatile process, which can be used alone orcombined with biological treatments, as a way of removingsuspended solids and organic material, as well as promotingthe extensive removal of dyes from textile industry effluents[19, 20]. However, this approach presents the disadvantageof generating a large volume of sludge. is sludge is rich indyes, as well as other substances used in the textile process.is is a problem, as the waste must be discarded properly to avoid environmental contamination [18]. Also, biologicaltreatmentandenzymatictreatment[21–23],ozonetreatment[24, 25], chemical oxidation, photocatalytic processes [14,26], sonochemical processes [27], nanoparticles [28], andmembrane processes [29] were used for removal of dye fromtextile effluents. However, some of these methods are limiteddue to their high operational costs and problems.e most efficient procedure for removal of syntheticdyes from industrial effluents is the adsorption procedure,because the dye species are transferred from the watereffluent to a solid phase, diminishing the effluent volume to aminimum. Subsequently, the adsorbent can be regeneratedor kept in a dry place without direct contact with theenvironment [3]. Also, adsorption has proven to be a reliabletreatment methodology due to its low capital investmentcost, simplicity of design, ease of operation, and insensitivity to toxic substances, but its application is limited by thehigh price of some adsorbents and the large amounts of wastewater normally involved. Activated carbon [30, 31],mesoporous carbon [8], clay minerals [32], hydrotalcite [11],biopolymers such as chitosan beads [33] and quaternary chitosan [9], and agricultural by-products [34, 35] are a few of the adsorptive materials that have been tested for thetreatment of wastewaters.Carbon nanotubes (CNTs), ever since their discovery,haveattracted extensive attention dueto their unique physic-ochemical and electrical properties. CNTs include single-walledcarbonnanotubes(SWCNTs)andmultiwalledcarbonnanotubes (MWCNTs) depending on the number of layerscomprising those [36]. CNTs, which are considered to beextremely superior adsorbents due to their high speci�csurface area and large micropore volume, have been utilizedfor the sorption of a number of different organic compoundsand inorganic ions [37–45], since the �rst report of theirsuccessful removal of dioxin [46]. For the �rst time Longand Yang reported that CNTs could be used as superioradsorbents for dioxin and the removal capacity of CNTs wasfound to be higher than that of activated carbon [46].In the present study, single-walled carbon nanotubes(SWCNTs) were chosen as sorbent for removal of RR-120dye. e aim of this study is to investigate the adsorption of RR-120 dye on single-walled carbon nanotubes (SWCNTs)under various conditions. So, the inuence of several oper-ating parameters such as initial concentration, contact time,adsorbentdosage,andinitialpHofsolutionwasinvestigated.Equilibrium isotherms were used to identify the possiblemechanism of the adsorption process. is information willbe useful for designing and operating color removal systemsbased on different local water qualities. 2. Experimental 2.1. Chemicals and Reagents.  e model textile reactive dye(Reactive Red 120) was purchased from Merck Company (Germany). e chemical structure and some properties of the Reactive Red-120 dye are presented in Table 1 and Figure1. Also, all other chemicals and reagents used were analyticalgrade(MerckCompany,Germany).StocksolutionofRR-120dye (1000mg/L) was prepared by dissolving the dye in 1Ldouble distilled water. For treatment experiments, the dyesolutions with concentrations in the range of 10–200mg/Lwere prepared by successive dilution of the stock solutionwith double distilled water. 2.2. Adsorbent Preparation.  SWCNTs (provided fromResearch Institute of Petroleum Industry (RIPI), Tehran,Iran) were selected as adsorbents to study the adsorptioncharacteristics of RR-120 dye from aqueous solutions. Onthe basis of the information provided by the manufacturer,the SWCNTs were synthesized by catalytic chemical vapordeposition (CVD) method. e morphologies of SWCNTswere examined by using SEM (JEOL microscope, modelJSM-6700F) (see Figure 2). e size of the outer diameterfor the SWCNTs was 1-2nm. e length of SWCNTs was10  m. Furthermore, speci�c surface area of SWCNTs wasmore than 700m 2 /g, and the mass ratio of the amorphouscarbon of SWCNTs was less than 5 % .Because carbon nanotubes had the amorphous carbonand therefore the adsorption rate is very low, therefore,carbonnanotubeshouldbepuri�ed.InordertofunctionalizeSWCNTs, 0.3g of the SWCNTs was dispersed in 25mL of nitricacid(65wt % )ina100mLroundbottomaskequippedwith a condenser and the dispersion was reuxed undermagnetic stirring for 48h. Aer that, the resulting dispersionwas diluted in water and �ltered. e resulting solid waswasheduptoneutralpH,andthesamplewasdriedinvacuumat 40 ∘ C overnight. 2.3. Dye Removal Experiments.  Dye removal experimentswith the synthesized SWCNTs were carried out as batch testsin 250mL asks under magnetic stirring. e experimentswere conducted individually for each of the model dyes, butthesameprocedurewasusedforboth,asdetailedbelow.Eachtest consisted of preparing a 100mL of dye solution with a  Journal of Chemistry 3 T 2: Isotherm parameters for adsorption of RR-120 onto SWCNTs at 23  ±  2 ∘ C.Langmuir isotherm Freundlich isotherm BET isotherm    (mg/g)     (L/mg)   2      2     (mg/g)   2 2500 0.031 0.9190 134.8 1.07 0.8819 384.6 0.00025 0.9897 NNOH NHClNNNNHNHN NNClNHNOHNNaSO 3 NaSO 3 SO 3 NaSO 3 NaSO 3 NaSO 3 Na F 1: e chemical structure of the Reactive Red-120.F 2: SEM image of SWCNTs sample. desiredinitialconcentrationandpHbydilutingthestockdyesolutions with double distilled water, and transferring it intothebeakeronthemagneticstirrer.epHofthesolutionwasadjusted using 0.1 NHCl or NaOH solutions by a pH metermodelE520 (MetrohmHerisau, Switzerland). A known massof SWCNTs powder (adsorbent dosage) was then added tothe solution, and the obtained suspension was immediately stirred for a prede�ned time. Aer the mixing time elapsed,the suspension was allowed to settle and the supernatantwasanalyzedusingadoublebeamUV/visspectrophotometer(Shimadzu,Tokyo,Japan;Model1601)at515nmforReactiveRed-120. en the amount of dye (RR-120 dye) adsorbed,    (mg/g), was obtained as follows:    =  0  −    ,  (1)where   0  and     are the initial and equilibrium liquid phaseconcentration of dye (mg/L), respectively.    is the volume of the solution (L) and    is the amount of adsorbent used (g).To express the percent of dye removal, the followingequation was used: % =  0  −    0 × 100,  (2)where   0  and     represent the initial and �nal (aeradsorption) dye concentrations, respectively. All tests wereperformed in duplicate to insure the reproducibility of theresults; the mean of the two measurements is reported. Fur-thermore, all experiments were performed at room tempera-ture (23  ±  2 ∘ C). e investigated ranges of the experimental variables were as follows: dye concentration (10, 50, 100, 150,200mg/L), initial pH of solution (3–12), SWCNTs dosage(0.01–0.05g/L), and mixing time (30, 60, 90, 120, 150, 180,210, 240min). 3. Results and Discussion 3.1. Effect of Initial pH.  It is known that the solution pHcan affect the surface charge of the adsorbent, the degree  4 Journal of Chemistry  320340360380400420440505560657075808590951000 1 2 3 4 5 6 7 8 9 10 11 12 13 14    D  y  e  r  e  m  o  v  a    l  e    ffi  c   i  e  n  c  y    (   %    ) Initial pHDye removal (%)Adsorbed dye (mg/g)                                      F 3: Effect of initial pH on the adsorption of RR-120 toSWCNTs. (  0  = 50mg/L, contact time = 180min, adsorbentdosage = 0.01g/L, temperature = 23  ±  2 ∘ C). 050010001500200025003000350040004583.58484.58585.58686.58787.588.50 0.01 0.02 0.03 0.04 0.05 0.06    D  y  e  r  e  m  o  v  a    l  e    ffi  c   i  e  n  c  y    (   %    ) Dye removal (%)Adsorbed dye (mg/g)Adsorbent dosage (g/L)                                      F 4: Effect of adsorbent dosage on RR-120 adsorption ontoSWCNTs. (  0  = 50mg/L, contact time = 180min, pH = 5, tempera-ture = 23  ±  2 ∘ C). of ionization of the different pollutants, the dissociation of functional groups on the active sites of the adsorbent as wellas the structure of the dye molecule [38]. e solution pHwould affect both aqueous chemistry and surface bindingsites of the adsorbent. So the solution pH is an importantparameter during the dye adsorption process.At present study, the effect of pH on the RR-120 dyeadsorption capacities of the SWCNTs was conducted at varying pH (pH 3–12) with 50mg/L �xed initial dye con-centrations and adsorbent dosage 0.01g/L for 180min. Ascan be seen from Figure 3, the adsorption of RR-120 dyeonto SWCNTs is intimately dependent on initial pH of solution. e adsorption capacity of RR-120 dye increaseswith increasing solution pH from 3 to 5 and decreasesslightly when solution pH is above 5. erefore, in order tocontinue the adsorption studies, the initial pH was �xed at5. e maximum adsorption capacity of the SWCNTs was426.49mg/gatpH5,initialdyeconcentrationof50mg/Land 23±2 ∘ C, when 85.3 %  of the dye was removed. Similar resultswere reported by other researchers [47–50]. 505560657075808590950200400600800100012000306090120150180210240270Contact time (min)    D  y  e  r  e  m  o  v  a    l  e    ffi  c   i  e  n  c  y    (   %    ) Dye removal (%)Adsorbed dye (mg/g)                                      F 5: Effect of contact time on RR-120 adsorption ontoSWCNTs. (  0  = 50mg/L, adsorbent dosage = 0.04g/L, pH = 5,temperature = 23  ±  2 ∘ C). 506070809010005001000150020002500300035004000050100150200250Initial dye concentration (mg/L)    D  y  e  r  e  m  o  v  a    l  e    ffi  c   i  e  n  c  y    (   %    ) Dye removal (%)Adsorbed dye (mg/g)                                      F 6: Effect of initial dye concentrations on RR-120 adsorptiononto SWCNTs. (Adsorbent dosage = 0.04g/L, contact time =180min, pH = 5, temperature = 23  ±  2 ∘ C). It is well known that the surface of CNTs contains someoxygen groups such as carboxylic groups (–COOH) andhydroxyl groups (–OH) aer acid treatment [51]. At lowerpH values, due to the protonation of electron    rich regionson the surface of SWCNTs, the positive surface charge canbe formed. Under these conditions, the uptake of negativecharged dyes (RR-120) will be high. When pH increases, thecarboxylicgroupsareionizedandthenegativechargedensity onthesurfaceincreases,resultinginreducedremovalofdyes. 3.2. Effect of SWCNTs Dosage.  e adsorbent concentrationis an important parameter because this determines thecapacity of the adsorbent (SWCNTs) for a given initial RR-120 dye concentration. In order to attain the optimal amountof SWCNTs for the adsorption of RR-120 dye, 0.01–0.05g/Ladsorbent(SWCNTs)wasusedforadsorptionexperimentsat�xed initial pH (pH 5), initial dye concentration (50mg/L),and temperature (23  ±  2 ∘ C) for 180min.
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