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Photocatalytic degradation of food dye by Fe 3 O 4 –TiO 2 nanoparticles in presence of peroxymonosulfate: The effect of UV sources

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A B S T R A C T Food dyes are extensively used in food industry and their residual in aquatic environment makes environmental problems. In this study, F 3 O 4-TiO 2 nanoparticles (FTNs) were prepared and their characteristics were evaluated by X-ray
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  Contents lists available at ScienceDirect Journal of Environmental Chemical Engineering  journal homepage: www.elsevier.com/locate/jece Photocatalytic degradation of food dye by Fe 3 O 4 – TiO 2  nanoparticles inpresence of peroxymonosulfate: The e ff  ect of UV sources Mohammad Ali Zazouli a , Farshid Ghanbari b,c, ⁎ , Maryam Youse 󿬁 d , Soheila Madihi-Bidgoli e a  Department of Environmental Health Engineering, Health Sciences Research Center, Mazandaran University of Medical Sciences, Sari, Iran b  Student Research Committee, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran c  Environmental Technologies Research Center, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran d  Student Research Committee, Mazandaran University of Medical Sciences, Sari, Iran e  Division of Food Safety, Department of Environmental Health Engineering, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran A R T I C L E I N F O  Keywords: PhotocatalysisMagnetic TiO 2 Food dyePeroxymonosulfateSulfate radical A B S T R A C T Food dyes are extensively used in food industry and their residual in aquatic environment makes environmentalproblems. In this study, F 3 O 4 -TiO 2  nanoparticles (FTNs) were prepared and their characteristics were evaluatedby X-ray powder di ff  raction (XRD),  󿬁 eld emission scanning electron microscope (FESEM), vibrating samplemagnetometer (VSM), Brunauer – Emmett – Teller (BET) speci 󿬁 c surface area and energy dispersive spectroscopy(EDS). The catalytic activity of FTNs was tested for Brilliant Blue FCF decolorization in FTNs/UVA system in thepresence of peroxymonosulfate (PMS) as electron acceptor. The results showed that 100% decolorizationoccurred under the condition of pH = 6.0, PMS = 2.0 mM, 0.8 g/L FTNs and 60 min reaction time. First-orderkinetic was  󿬁 tted for FTNs/UVA/PMS with rate constant of 0.059 min − 1 . PMS exhibited a superiority comparedto other electron acceptors (persulfate and hydrogen peroxide). FTNs maintained its activity in 4th cycle andshowed a dual catalytic behavior; photocatalyst and PMS activation via Fe 3 O 4 . The e ff  ects of UV sources wereinvestigated and the results indicated that UVC region and the use of LED (Light-emitting diode) accelerated thedecolorization considerably. Compared to UVA, UVC increased hydroxyl radical contribution in degradation of the dye. Mineralization was also tested by total organic carbon and the order of mineralization follows: FTNs/UVA/PMS < FTNs/UVC/PMS ≤ FTNs/UVA-LED/PMS < FTNs/UVC-LED/PMS. 1. Introduction The use of dyes for di ff  erent products is unavoidable especially intextile, cosmetic and food industries since we consume the products byour eyes. Hence, the color plays a key role in consumption of theproducts. The U.S. Food and Drug Administration (FDA) has reportedthat  󿬁 ve times increase of consumption in dyes is observed since 1955to 2009 [1]. Brilliant Blue FCF (BBF) or E113 is a food additive dyewhich is widely used for ice cream, baked goods, cereals, beverages,blue raspberry  󿬂 avored products, dessert powders and various dairyproducts [2,3]. The health e ff  ects of BBF on human and animals havebroadly been reported including gastrointestinal tumors, neurologicaldisorders, and severe allergies [4]. BBF is highly soluble since itsmolecular structure consists of three sulfonic acid groups [3,5]. Thepresence of even small amount of dye makes water resources coloringwhich is aesthetically unfavorable [6]. Apart from, the presence of colorin water resource decreases dissolved oxygen and it causes death of aquatic organisms consequently [7,8]. There is a variety of newtechnologies for the degradation of dyes. Advanced oxidation processes(AOPs) are promising technologies which are established based onreactive radicals such as hydroxyl radical (HO % ) [9]. Photocatalysisprocess is well-known as a green technology for the degradation of organic contaminants. In photocatalysis process, a semiconductor isexcited by light irradiation and an electron is migrated from valancebond to conduction bond and a hole is remained in valance bond whichare the corresponding agents of generating free radicals (super oxideand hydroxyl radical) [10,11]. Nano TiO 2  is the most conventionalphotocatalyst in environmental applications. However, TiO 2  su ff  ers animportant drawback which is related to its separation from aqueoussolution [12]. Accordingly, doping of magnetic materials has beenproposed for easier re-collection of photocatalyst in magnetic  󿬁 eld. Inthis way, ferriferrous oxide (Fe 3 O 4 ) can be doped on semiconductors forthis purpose [13,14]. Moreover, recombination of conduction electron(e − ) and hole (h + ) limits the function of photocatalysis process. Toovercome this limitation, an electron acceptor has been usually used forreaction with conduction electron. Amongst the electron acceptors, http://dx.doi.org/10.1016/j.jece.2017.04.037Received 19 December 2016; Received in revised form 18 April 2017; Accepted 20 April 2017 ⁎ Corresponding author at: Student Research Committee, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran.  E-mail address:  Ghanbari.env@gmail.com (F. Ghanbari). Journal of Environmental Chemical Engineering 5 (2017) 2459–2468Available online 23 April 20172213-3437/ © 2017 Elsevier Ltd. All rights reserved. M R  oxygen, hydrogen peroxide and persulfate have been widely used inphotocatalytic degradation [13,15,16]. In last decade, the applicationof peroxymonosulfate (PMS) in degradation of environmental pollu-tants has received great attention. PMS is an asymmetrical oxidantwhich is activated by transition metals, UV irradiation, ultrasound,heat, and carbon-based catalyst [17,18]. PMS can generate sulfate andhydroxyl radicals through activation by conduction electron i.e. PMSacts as an electron acceptor in photocatalytic treatment based on Eq. (2)[19,20].Semiconductor + hv → e CB − + h + (1)HSO 5 − + e CB − → OH − + SO 4 % − or HO % + SO 42 − (2)Sulfate radicals (E 0 = 2.5 – 3.1 V) and hydroxyl radicals(E 0 = 2.8 V) are reactive oxidants which can e ff  ectively degrade theorganic compounds [21,22]. In fact, the presence of PMS acceleratesthe photocatalytic degradation of organic compounds by the simulta-neous production of hydroxyl and sulfate radicals. Fe 3 O 4 – TiO 2  nano-particles (FTNs) have been broadly synthesized and used for variouspollutants as a photocatalyst or adsorbent. The presence of iron in FTNsgives a dual role to the catalyst in a way that FTNs can be both aphotocatalyst and a PMS activator. Besides, FTNs is a magneticseparable composite encouraging the scientists for the application of them in pollution control. The performance of FTNs in the presence of PMS and UV has not been studied yet. Moreover, the mechanisms of sulfate or hydroxyl radical generation have not been su ffi cientlyinvestigated. In this study, we aimed to report the performance of Fe 3 O 4 -TiO 2 /UV in the presence of PMS for BBF removal with focus onthe main operating parameters such as pH, PMS and catalyst dosages.Besides, the e ff  ect of UV sources on BBF removal is also considered inFe 3 O 4 -TiO 2 /UV/PMS system. Finally, the quenching experiments wereconducted for the determination of mechanism of BBF degradation inphotocatalysis process. 2. Materials and methods  2.1. Chemical and reagents Brilliant Blue FCF (BBF) (C 37 H 34 N 2 Na 2 O 9 S 3 ) was purchased fromAlvan Sabet Company (Iran) with 98% purity. The dye characteristicsare presented in Table 1. Ferric chloride (FeCl 3 ·6H 2 O), ferrous chloride(FeCl 2 ·4H 2 O), ammonia (28%) (NH 3 ·H 2 O), hydrogen peroxide (30%),potassium hydroxide (KOH) and sulfuric acid (96%) (H 2 SO 4 ) wereobtained from Merck Company. Sodium persulfate (Na 2 S 2 O 8 ) waspurchased from Fluka Company. Oxone (2KHSO 5 ·KHSO 4 ·K 2 SO 4 ) wasprovided from Sigma-Aldrich. Nano TiO 2  (P25) was purchased fromEvonic Company.  2.2. Preparation of Fe 3 O 4  –  TiO  2  and its characteristics The preparation of Fe 3 O 4 – TiO 2  nanoparticles (FTNs) was conductedby simple method based on precipitation titration using ammonia. First,1.0 g TiO 2  (P25) was added to 20 mL deionized water and it wassonicated for 15 min. 0.707 g FeCl 2 ·4H 2 O and 1.98 g FeCl 3 .6H 2 O weredissolved in 15 mL and 30 mL deionized water respectively. Two ironsolutions were added to TiO 2  suspension while mixture was stirred withthe speed of 1000 rpm for 20 min. The ratio of Ti:Fe and Fe 2+ :Fe 3+ was1:1 and 1:2 for FTNS respectively. The 28% NH 3 ·H 2 O was dropwiseadded to the mixture until a black precipitate was formed and it wasseparated by a magnet. The precipitates were placed in oven at 185 °Cfor 12 h. The obtained powder was washed by ethanol and water for 󿬁 ve times and then the precipitate was dried at 105 °C for 2 h. Fe 3 O 4 nano particles were synthesized as the same condition without TiO 2 .XRD analysis was applied to determine the type of crystals of FTNsby a di ff  ractometer (Bruker D8-Advanced X-ray) by Cu K α  photon(k = 1.5418 Å) with the conditions of 40 kV voltage and 30 mAcurrent. The textural and morphological structures of the FTNs weredetermined by  󿬁 eld emission scanning electronic microscopy (FESEM)(Mira 3-Xmu). The integrated energy-dispersive X-ray spectroscopy(EDS) was used to analyze the dispersion of the elements in the FTNS.The magnetism of FTNs was measured by vibrating sample magnet-ometer (VSM-MDK-Iran). The Brunauer – Emmett – Teller (BET) speci 󿬁 csurface area and pore volume were measured by the N 2  adsorption/desorption with a Beckman Coulter 3100. The pore size distributionwas calculated using the BJH (Barrett, Joyner&Halenda) method.  2.3. Photocatalysis experiments All photocatalysis experiments were conducted in a cylindricalreactor made of quartz with height of 15 cm and diameter of 7. TheBBF solution (25 mg/L in all experiments) with volume of 300 mL waspoured in the reactor. The pH of the solution was adjusted by H 2 SO 4 and KOH (0.1 M). And then the known amount of FTNs was added tothe solution after that a certain amount of PMS as electron acceptor wasintroduced to the solution. A mechanical stirrer was applied for mixingthe solution. The temperature of solution was kept in range of 24 – 26 °C.Two low pressure UVA lamps (6 W-Philips) were used as UV source forlight irradiation which were placed in two sides of the reactor withdistance of 2 cm. UV lamps warmed up for 10 min before starting thephotodegradation. The samples were taken every 10 min and measuredimmediately. In order to compare di ff  erent UV sources, two lowpressure UVC lamps (6 W-Philips), 12 UVA-LEDs (1 W, 365 – 370 nm)and 12 UVC-LEDs (1 W, 254 – 258 nm) were used for light irradiationunder similar conditions with photocatalysis experiments with lowpressure UVA lamps. The diameter of UV-LED was 0.5 mm. All LEDswere installed on an electronic chip which was operated by a DC power(2.0 A, 30.0 V). In LED photocatalysis, two chips were used that eachone had six LEDs and located in two sides of reactor as the same UVAphotocatalysis experiments. The UV light intensities were measuredwith a radiometer (Lux-UV-IR meter, Leybold Didactic GMBH-666-230). The UV light intensities in center of the empty reactor were 2.52,2.70, 2.85 and 2.95 mW/cm 2 for low pressure UVA lamp, low pressureUVC lamp, UVA-LEDs and UVC-LEDs respectively. All experiments wereconducted in triplicate and average values were used in the results.  2.4. Analytical methods The Brilliant Blue FCF (BBF) concentration in the solutions wasmeasured using a spectrophotometer (DR5000, HACH) at wavelengthof 628 nm. Total organic carbon (TOC) was analyzed by a TOC analyzer Table 1 The characteristics of Brilliant Blue FCF.Dye Brilliant Blue FCFStructureChemical formula C 37 H 34 N 2 Na 2 O 9 S 3 Molecular weight(g/mol)792.85Color index No. 42090CAS No 3844-45-9E number E133Solubility in water(g/L)30.0 – 50.0  M.A. Zazouli et al.  Journal of Environmental Chemical Engineering 5 (2017) 2459–2468 2460  (Shimadzu) and the accuracy of TOC values was checked by potassiumhydrogen phthalate (KHP). The concentration of the oxidants wasmeasured by iodometric titration [23]. Total iron concentrations weredetermined by atomic absorption spectrophotometer (AAS) (Perkin-Elmer Model 303). All anions and total dissolved solids (TDS) weremeasured based on Standard Methods [24]. Fig. 1.  (a) XRD patterns of Fe 3 O 4 /TiO 2  (b) EDS of FTNs (c) magnetization hysteresis loop of FTNs.  M.A. Zazouli et al.  Journal of Environmental Chemical Engineering 5 (2017) 2459–2468 2461  3. Results and discussions 3.1. FTNs characteristics Fig. 1a shows the XRD pattern of FTNs. The di ff  raction peaks withplanes of (110), (101), (111) and (211) were at 2 θ  angels of 27.78°,36.16°, 41.60° and 54.63° respectively con 󿬁 rming the titanium oxidecrystals. The di ff  raction peaks which are marked to (220), (311), (400),and (440) planes, are related to 2 θ  angels of 30.50°, 35.71°, 43.53° and61.13° respectively. These peaks were well match with Fe 3 O 4  revealingthe coated iron species on TiO 2  in form of magnetite. Fig. 1b indicatesthe EDS along with weight percentage of elements in FTNs. As shown,the weight percentage of titanium (27.05%) was relatively equal withthat of iron (25.60%) indicating the synthesis of FTNs was successfuland no impurity was observed in mapping elements. Fig. 1c presentsmagnetization hysteresis loop of FTNs. The saturation magnetization(M s ) was found to be 52.6 emu/g indicating Fe 3 O 4  was successfullycoated on TiO 2 . In other words, the presence of Fe 3 O 4  on the surface of TiO 2  gave a magnetic property to the photocatalyst.Fig. 2a and b shows the morphology and texture of TiO 2  and FTNs.As can be seen, TiO 2  nanoparticles (TNs) had homogeneity in the sizeand their surface were smooth and  󿬂 at while some dots were observedin FTNs which were corresponded to the nanoparticles of magnetite.The results of FESEM images, XRD analysis and EDS proved thesynthesis of composite of Fe 3 O 4 – TiO 2 . Fig. 2c shows synthesizedFe 3 O 4  nanoparticles (FNs). A sphere-like morphology was observedwith a size range between 40 and 70 nm. Moreover, the nanoscaleFESEM images showed that the FTNs and FNs were relatively synthe-sized in the same size.Table 2 shows the obtained results from BET analysis. As can beseen, the surface area and pore volume of TiO 2  were 35.3 m 2 /g and0.2566 cm 3 /g while these value was reduced to 24.76 m 2 /g and0.2151 cm 3 /g with coating Fe 3 O 4  onto TiO 2  (FTNs). This reduction insurface area and pore volume was due to magnetic nanoparticlessupported on TiO 2 . On the other hand, the pore size of threenanoparticles was less than 40 nm indicating mesoporous particleswere synthesized. 3.2. The e  ff  ect of operational parameters The solution pH is a critical parameter in chemical reactionsparticularly in oxidative process. The e ff  ect of pH was investigated inrange of 3.0 – 11.0 under the conditions of 1.5 mM PMS, 0.4 g/L FTNSand irradiation time of 60 min. Fig. 3a displays the results of solutionpH e ff  ect on BBF decolorization. As can be seen, more decolorizationoccurred in pH = 6.0. The e ffi ciency of the FTNs/PMS/UV dropped inacidic and alkaline conditions. Indeed, decrease or increase in pH valuehad a negative e ff  ect on BBF decolorization. In acidic pH values,excessive H + can play the role of a scavenger for hydroxyl and sulfateradicals based on Eqs. (3) and (4) [25,26]. HO % + H + + e − → H 2 O (3)SO 4 % − + H + + e − → HSO 4 − (4)On the other hand, a signi 󿬁 cant decrease in decolorization wasobserved in alkaline conditions. In alkaline media, PMS may bedecomposed in non-radical pathway [27]. The adsorption of pollutantand PMS onto the catalyst depends on the surface charge of the catalyst.Since zero point charge (pH zpc ) of FTNs was found at pH 6.9, thecatalyst surface was positively charged at pH below 6.9, whereas at pHvalues above 6.9, it was negatively charged. Therefore, there was arepulsion behavior between HSO 5 − and FTNs at alkaline conditionsreducing PMS activation to generate sulfate radical. Hence, the abilityof the system in degradation of BBF decreased. Moreover, it isworthwhile to express that oxidation potential of the radicals reducedin alkaline conditions. Regarding the results, pH = 6.0 provided thehighest e ffi ciency of BBF removal with 61% decolorization.The e ff  ect of FTNs dosage was studied under the conditions of pH = 6.0, PMS = 1.5 mM and 60 min reaction time and their resultsare presented in Fig. 3b. As expected, with increase of FTNs loading, thedecolorization of BBF enhanced linearly (Fig. 3b). In this way,decolorization e ffi ciencies were 37.8, 48.6, 61.3, 74.6, 88.9 and87.9% for 0.1, 0.2, 0.4, 0.6, 0.8, 1.0 g/L FTNs respectively. Thisincrease in e ffi ciency was related to the fact that the increasing of thequantity of FTNs increased the number of active sites on the surface of FTNs, which in turn enhanced the amount of free radicals generatedthrough activation of PMS. Furthermore, the increase of FTNs increasedamount of photons absorption on the catalyst surface which acceleratesphotocatalytic degradation of BBF. In addition, when no catalyst wasused, the e ffi ciency of the system was negligible indicating PMS cannotbe e ff  ectively activated by UVA irradiation. After 0.8 g/L FTNs, removale ffi ciency was slightly reduced which could be attributed to theincrease in opacity of the suspension and the enhancement of the lightre 󿬂 ectance as a consequence of excess FTNs. With respect to the results, Fig. 2.  FESEM image (a) TiO 2  (b) FTNs (c) Fe 3 O 4  nanoparticles. Table 2 The surface area, average pore diameter and pore volume of TiO 2 , Fe 3 O 4 – TiO 2  and Fe 3 O 4. Properties TiO 2  Fe 3 O 4 – TiO 2  Fe 3 O 4 BET surface area (m 2 /g) 35.3 24.76 45.1Average pore diameter (nm) 34.89 35.2 28.6Pore volume (cm 3 /g) 0.2566 0.2151 0.2821  M.A. Zazouli et al.  Journal of Environmental Chemical Engineering 5 (2017) 2459–2468 2462  0.8 g/L of FTNs was chosen as optimum loading of FTNs.In order to study the PMS dosage, a series of experiments wasconducted for PMS in range of 0 – 2.0 mM under the conditions of pH = 6.0, FTNs of 0.8 g/L. It can be clearly seen from Fig. 3c thatdegradation of BBF was highly in 󿬂 uenced by PMS concentration. Onthe other hand, in the absence of PMS, photocatalytic activity of FTNsprovided 53.2% decolorization during 60 min reaction time. Theincrease of PMS dosage raised the amount of sulfate and hydroxylradicals resulting in more degradation of BBF [28]. In this way, at2.0 mM of PMS, complete decolorization was achieved during 60 minreaction time. 3.3. The comparison of the processes The comparison of the systems can help to understand the mechan-ism and function of photocatalytic degradation of BBF. Fig. 4 depictsthe decolorization of BBF in di ff  erent systems. One can see that soleapplying UV, PMS and FTNs had a negligible in 󿬂 uence on BBF Fig. 3.  The e ff  ect of operational parameters on decolorization of BBF (a) pH e ff  ect (FTNs = 0.4 g/L, PMS = 1.5 mM and reaction time = 60 min) (b) FTNs dosage e ff  ect (pH = 60,PMS = 1.5 mM and time = 60 min) (c) PMS dosage e ff  ect (pH = 60, FTNs = 0.8 g/L and time=60 min).  M.A. Zazouli et al.  Journal of Environmental Chemical Engineering 5 (2017) 2459–2468 2463
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