Accepted Manuscript Degradation of Crystal Violet by catalytic ozonation using Fe/activated carbon catalyst Jie Wu, Hong Gao, Shuo Yao, Lu Chen, Yaowen Gao, Hui Zhang PII: DOI: Reference:
S1383-5866(15)00246-4 http://dx.doi.org/10.1016/j.seppur.2015.04.022 SEPPUR 12304
To appear in:
Separation and Purification Technology
Received Date: Revised Date: Accepted Date:
19 November 2014 3 April 2015 16 April 2015
Please cite this article as: J. Wu, H. Gao, S. Yao, L. Chen, Y. Gao, H. Zhang, Degradation of Crystal Violet by catalytic ozonation using Fe/activated carbon catalyst, Separation and Purification Technology (2015), doi: http:// dx.doi.org/10.1016/j.seppur.2015.04.022
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Degradation of Crystal Violet by catalytic ozonation using Fe/activated carbon catalyst Jie Wu a,b, Hong Gao a,c, Shuo Yao a, Lu Chen a, Yaowen Gao a, Hui Zhang a, a
Department of Environmental Engineering, Wuhan University, Wuhan 430079, China
b
Fuzhou Environmental Monitoring Center, Fuzhou 350011, China
c
School of Chemical Engineering and Pharmacy, Wuhan Institue of Technology, 693
Xiongchu Avenue, Wuhan 430079, China
Abstract: An active Fe/activated carbon was prepared and used in catalytic ozonation of Crystal Violet. The catalyst was characterized by SEM and XRD, and the results showed that the iron loaded on activated carbon existed in α-FeOOH phase. An improved effect was achieved in the decolorization of Crystal Violet via catalytic ozonation in the presence of Fe/activated carbon compared with ozonation alone. Almost complete decolorization (>96%) of 400 mg/L Crystal Violet was achieved after 30 min reaction under the conditions 4.44 mg/min ozone dosage, 300 mL/min gas flow rate, 2.5 g/L catalyst dosage and pH 7, while 57% COD removal efficiency was obtained when the reaction time was prolonged to 90 min. The acute toxicity to Daphnia magna decreased during 90 min of catalytic ozonation. The main intermediates were separated and identified by gas chromatography-mass spectrometry (GC-MS) technique and an initial degradation pathway of Crystal Violet was proposed. Keywords: Catalytic ozonation, Crystal Violet, Fe/activated carbon, decolorization, GC-MS
1. Introduction The dye wastewater has long been a major environmental problem all over the world. The main sources of dye wastewater are from textile, dying, printing and other related industries [1-2]. Among various dyes, Crystal Violet, also known as C.I. Basic Violet 3, is a kind of
Corresponding author. Tel: + 86-27-68775837; fax: + 86-27-68778893. E-mail address:
[email protected] (H. Zhang) 1
cationic triphenylmethane dye. It is widely used for textile dying, paper printing, biological staining, dermatological agent, veterinary medicine, intestinal parasites and fungus, etc [3,4]. Crystal Violet is a mutagen and mitotic poison, and its presence in water will cause a serious risk to aquatic life and constitute a potential human health hazard. As one of the most effective methods, advanced oxidation processes (AOPs) have been used for the decolorization of Crystal Violet, including photo-catalysis [3-5], UV/H2O2 oxidation [6], Fenton and Fenton-like systems [6,7], electro-Fenton method [8,9] and electrochemical oxidation [10,11]. Compared with these AOPs, ozonation has proven to meet the strict color discharge limits of many industrialized countries [12-15]. It is well known that ozone is a strong oxidant, the oxidation potential of which is 1.52 times higher than that of chlorine [16]. Through a direct reaction of molecular ozone or a radical reaction involving the hydroxyl radical generated by the ozone decomposition, chromophoric dye molecules can be broken into smaller non-chromophoric ones [17,18]. However, there are a few drawbacks which limit industrial applications of ozonation. First of all, the installation of ozone generation unit and the cost of electricity give rise to the high production cost of ozone [19]. Secondly, the poor mass transfer rate of ozone leads to the low ozone utilization. Furthermore, the limit oxidizing power of ozone (E0 = 2.07 V) results in the low mineralization efficiency [20,21]. Fortunately, catalytic ozonation can improve the ozone utilization and mineralization degree through the transformation of ozone into more reactive species [16,22,23]. Activated carbon not only has excellent adsorption capacity, but also exhibits high catalytic activity due to its high surface area and surface chemical properties [17,24-26]. Metal oxides are also used for the catalytic ozonation [16], and iron type catalysts are normally employed due to their relatively low price and high catalytic activity [27-29]. Moreover, iron oxide loaded on the activated carbon could further improve the catalytic activity [30-32]. To the best of our knowledge, there is no report on the degradation of Crystal Violet by heterogeneous catalytic ozonation with Fe/activated 2
carbon catalyst. Therefore, in this study, Fe/activated carbon was prepared and used for the catalytic ozonation of Crystal Violet. The effect of operation condition such as catalyst dosage, initial dye concentration, pH, temperature, gas flow rate and ozone dosage on the decolorization of Crystal Violet was investigated. The degradation of Crystal Violet in terms of COD removal and the variation of acute toxicity to Daphnia magna during the heterogeneous catalytic ozonation process were also investigated. 2. Materials and methods 2.1. Materials The reagents used in this study were analytical grade. Crystal Violet (C 25H31N3) was obtained from Shenyang No. 3 Chemicals Reagent Factory (China) and used without further purification. Crystal Violet solution was prepared in a 0.05 mol/L phosphate buffer solution. 2.2. Catalyst preparation and characterization The catalyst used in this study was iron oxides supported on activated carbon (AC), which was prepared by incipient wetness impregnation [33]. Activated carbon was subjected to pretreatment with HNO3 and NaOH to modify its porous structure and surface chemistry. Then one gram of dry based carbon was equilibrated with 30 mL 1.0 M N2-purged ferrous sulfate solution for 24 h to prevent the formation of iron hydroxide. After adsorption saturation, oxygen was bubbled through the slurry with magnetic stirring. The dispersion was then aged for 48 h, and the impregnated activated carbon samples were separated from the mixture, rinsed with de-ionized water for three times, and dried at 60C. The morphology of samples was obtained using a scanning electron microscopy (Quanta 200, FEI, Netherlands). X-ray powder diffraction (XRD) analysis was investigated to identify the crystalline phases of Fe/activated carbon catalyst. Diffraction data were obtained by step-scans using CuKα radiation generated at 30 kV and 30 mA, scanning from 10 to 80 and a position-sensitive detector using a step size of 0.02. The pH at the point of zero charge 3
(pHpzc) was measured with a mass titration method [32]. 2.3. Methods In each run, Fe/activated carbon was added into the reactor containing 100 mL solution. The mixture was then stirred at 500 r/min for 30 minutes to reach adsorption equilibrium [33]. Thereafter, ozone was continuously bubbled into the solution. Ozone was generated by using an ozone generator (XFZ-5BI, China). The gas flow rate Q was determined with a bubble flow meter. The gaseous ozone concentration [O3]g was monitored by the iodometric method with potassium iodide solution [34]. At pre-selected time intervals, 1 mL sample was withdrawn from the reactor and then filtered through 0.45-m membrane filters before analysis. The absorbance of the sample was measured at λmax = 584 nm using a Shimadzu UV-1600 spectrophotometer (Shimadzhu, Japan). Decolorization efficiency was calculated according to Eq. (1): Decolorization efficiency (%) = (A0 At)/A0 × 100%
(1)
where A0 and At are the absorbencies at time 0 and t, respectively. Chemical oxygen demand (COD) was determined using closed reflux spectrophotometric method based on the Standard of the People’s Republic of China for Environmental Protection [35]. The intermediate products during the reaction were detected by gas chromatography-mass spectrometry (GC-MS) (Shimadzu GCMS-QP2010 Plus). Samples for GC-MS analysis were prepared as follows [7,11]: 100 mL dye solution was extracted with dichloromethane (total volume 100 mL) ten times, and the extracts were then concentrated by rotary evaporator at 40°C to about 1 mL before being analyzed by GC-MS. A HP-5 MS capillary column (30 m length × 0.25mm ID × 0.25 μm film thickness) was employed for GC separation. The GC equipment was operated in a temperature programmed mode with an initial temperature of 4
40°C held for 4 min, then ramped first to 80°C with a 4°C min-1 rate and held for 2 min; then ramped to 280°C at 8°C min-1 and held at that temperature for 9 min. Helium was used as a carrier gas at a flow rate of 5.79 mL min -1. Electron impact (EI) mass spectra were scanned from 10-300 m/z. The injector, ion source and interface temperatures were set at 280, 220 and 280C, respectively. The active toxicity was determined with Daphnia magna immobilization test [36]. Daphnia magna was cultured in laboratory for more than three generations. The acute toxicity experiments were repeated four times using 24-h-old Daphnia magna in 100-mL-capacity test beakers. They were set in the incubator along with testing samples. The incubator was kept at 20°C in a 16 h light-8 h dark cycle. No food was given during the acute toxic test. Surviving and mobile Daphnia magna was counted after 24 h. 3. Results and discussion 3.1. Characterization of the catalysts A small amount of iron oxides (56 mg g1 Fe content) was immobilized on the activated carbon, and the catalysts with diameters of 250-300 μm were used in the catalytic ozonation processes. The results of textural properties for Fe/activated carbon catalyst were given in Table 1, and the SEM images of the fresh catalyst sample were shown in Fig. 1. It can be seen that the catalyst has an irregular surface (Fig. 1a), and some large druses (small spherical particles, the average particle size was about 10 μm) were dispersed in the uneven surface (Fig. 1b). Fig. 2 displayed X-ray powder diffraction patterns of Fe/activated carbon catalyst. The main diffraction peaks located at 21.30°, 34.72°, 41.16°, 58.94° and 61.44° of 2θ were correspond to α-FeOOH [37], supposing a high catalytic activity for Fe/activated carbon catalyst in the ozonation process [38-44]. 3.2. The effect of catalyst dosage In order to determine the effect of the catalyst dosage on the decolorization of Crystal Violet 5
by heterogeneous ozonation process, experiments were performed at various catalyst dosages. As can be seen in Fig. 3, catalytic ozonation could achieve higher decolorization rate than ozonation alone. The α-FeOOH has three different types of surface functional groups (≡Fe-OH2+,≡Fe-OH, ≡Fe-O-) depending on the solution pH, which could enhance ozone decomposition to generate hydroxyl radicals via the following reactions [38,44,45], ≡FeOH2+ + O3 → ≡FeOH•+ + •OH + O2
(2)
≡FeOH•+ + H2O → ≡FeOH2+ + HO•
(3)
≡FeOH + O3 → ≡FeO• + HO• + O2
(4)
≡FeO• + O3 → ≡FeOH + HO• + O2
(5)
Consequently, the decolorization rate could be improved compared with ozonation alone. With the increase in catalyst dosage, the surface active sites increased accordingly, and more ozone molecules would be transformed into hydroxyl radicals [38,40]. As a result, the decolorizaton rate of Crystal Violet increased with an increase in catalyst dosage from 1.0 to 2.5 g/L. Nevertheless, further increasing catalyst dosage to 4.0 g/L would only lead to a slight improvement of the decolorization rate. This may due to the fact that the 2.5 g/L catalyst could catalyze ozone to generate sufficient reactive radicals and oxidize Crystal Violet. At higher catalyst dosage than 2.5 g/L, the excess hydroxyl radicals may undergo recombination reaction (Eq. (6)) or react with ozone (Eq. (7)) [6,16]: HO• + HO• → H2O2
(6)
HO• + O3 → O2 + HO2•
(7)
Therefore, the excessively generated hydroxyl radicals would be consumed ineffectively and an insignificant improvement of the decolorization rate was observed at catalyst dosage of 4.0 g/L. Since there was little difference of the decolorization rate between 2.5 and 4.0 g/L catalyst dosage, 2.5 g/L of catalyst dosage was used in the following experiments. 3.3. The effect of pH value 6
The pH of textile effluent varies to a great extent and the chemical characteristics of Crystal Violet would change accordingly. The effect of pH on the decolorization of Crystal Violet was investigated at pH 4, 7 and 10, respectively. As observed in Fig. 4, the decolorization rate increased with pH. The decolorization efficiencies rose from 77.7% to 88.1% after 10 min reaction when pH increased from 4 to 10. The point of zero charge (pHpzc) of the catalyst was found to be 7.95 given by the intersection of titration curve with x-axis as illustrated in Fig. S1. At this pH, the catalyst surface was mostly zero charged and the catalytic activity of Fe/activated carbon reached its maximum [32]. When the solution pH was higher than pH pzc of Fe/activated carbon, the catalyst became negatively charged. The cationic structure of Crystal Violet favors electrostatic attraction of positive charge of Crystal Violet and negative charge of the catalyst. Therefore, the increase in pH value would result in the higher color removal of Crystal Violet in the first 15 min of reaction. Despite of this, the decolorization efficiencies at 30 min were almost the same (96.0-98.5%), indicating the catalytic ozonation in the presence of Fe/activated carbon was efficient for the decolorization of Crystal Violet at the pH range investigated. 3.4. The effect of reaction temperature Three different reaction temperatures (25, 35 and 45°C) were tested to investigate the influence of temperature on color removal. As shown in Fig. 5, the decolorization rates were nearly the same and the decolorization efficiencies varied only from 96.6% to 97.5% after 30 min reaction with temperature ranging from 25 to 45°C. It indicated that temperature exhibited little effect on the removal of Crystal Violet during heterogeneous catalytic ozonation process. Based on the two-film theory, mass transfer rate of ozone from gas phase to liquid phase can be described as a function of volumetric mass transfer coefficient and mass transfer driving force [46,47]. The solubility of ozone would decrease with temperature, which results in the decrease of mass transfer driving force, and the mass transfer rate of 7
ozone from gas phase to liquid phase would be dropped consequently [46,47]. In the meanwhile, chemical reaction rate usually decreases with temperature. The opposite effects of temperature on mass transfer rate of ozone and chemical reaction rate could cancel each other. Therefore, the influence of temperature on the decolorization rate was unpronounced in the heterogeneous ozonation process. 3.5. The effect of gas flow rate The gas flow rate plays an important role during the heterogeneous catalytic ozonation process, and its effect was investigated at 200, 300 and 400 mL/min, respectively. It can be seen in Fig. 6 that the decolorization efficiencies increased from 81.9% to 90.6% in the first 10 min of reaction with gas flow rate increasing from 200 to 400 mL/min. The volumetric mass transfer coefficient is dependent on the interfacial area. The increase in the flow rate corresponds to a larger net surface area for mass transfer of ozone to the liquid phase, and consequently a higher volumetric mass transfer coefficient of ozone. On the other hand, the gaseous ozone concentration decreased as the gas flow rate increased at constant ozone dosage. It led to the decrease of equilibrium ozone concentration in the liquid phase and thus the mass transfer driving force. The extent of the increase in volumetric mass transfer coefficient was greater than the decrease in mass transfer driving force. Therefore, the decolorization rate increased with the increase of gas flow rate. 3.6. The effect of ozone dosage The effect of ozone dosage was investigated in the range of 1.68 to 4.44 mg/min. It can be seen in Fig. 7 that the decolorizaton efficiency of Crystal Violet increased from 65.1% to 84.7% with an increase in ozone dosage from 1.68 to 4.44 mg/min in the first 10 min of reaction. At the same gas flow rate, the increasing ozone dosage increased the equilibrium ozone concentration in the aqueous phase and improved the mass transfer driving force accordingly [46,47]. It resulted in the increase of mass transfer rate of ozone from gas phase to liquid 8
phase. Thus, the decolorization rate increased with the increasing ozone dosage. 3.7. The effect of initial Crystal Violet concentration The effect of initial Crystal Violet concentration on color removal was investigated at 200, 400 and 600 mg/L, respectively. As shown in Fig. 8, the decolorization efficiencies decreased from 87.4% to 76.3% after 10 min reaction with initial dye concentration increasing from 200 to 600 mg/L. A higher initial dye concentration would lead to more amount of intermediate products. The available oxidizing species would be consumed both for oxidation of parent compound as well as its intermediate products [48]. Therefore, the decolorization rate decreased with initial dye concentration in the first 10 min of reaction. As the catalytic ozonation process proceeded, most of the original Crystal Violet would be degraded. The deolorization efficiencies were all above 96% after 30 min reaction when the initial Crystal Violet concentration ranged from 200 to 600 mg/L. This indicated that catalytic ozonation could achieve a nearly complete decolorization even if the initial dye concentration increased to 600 mg/L. 3.8. The degradation pathway of Crystal Violet To clarify the changes in molecular and structural characteristics of Crystal Violet as a result of the heterogeneous catalytic ozonation process, UV-visible (vis) spectra changes in the dye solution as a function of reaction time were depicted in Fig. 9. As can be observed from these spectra, before the oxidation, the absorption spectrum of Crystal Violet in water was characterized by one main band in the visible region, with its maximum absorption at 584 nm, and by two other bands in the UV region located at 250 and 300 nm, respectively. The peaks at 250 and 300 nm were associated with aromatic structures in the molecule, and that at 584 nm originated from an extended chromophore. The disappearance of the visible band over time was due to the fragmentation of the aromatic rings links by oxidation. In addition to this rapid decolorization effect, the decay of the absorbance at 250 or 300 nm was considered as 9
evidence of aromatic fragment degradation in the dye molecule and its intermediates. GC-MS was employed to further identify the intermediate products formed during the reaction, and the main intermediate products were detected and shown in Table S1. Based on the results and previous studies [10,11,49], an initial degradation pathway was proposed. As can be seen in Fig. 10, the oxidizing species attacked the central carbon portion of the Crystal Violet (A) to form the compounds 4-(N,N-dimethylamino)-4’-(N’.N’-dimethylamino) benzophenone (B) and 4-(N,N-dimethylamino)-4’-(N’.N’-dimethylamino) diphenylmethane (C) [10,49]. Then the central carbon of compound (C) was successively attacked by the active radicals to generate compound (B) [10]. Reaction of hydroxyl radicals with the ketonic group of compound (B) resulted in the generation of 4-(N,N-dimethylamino)-4’-(N’,N’-dimethylamino) dimethylaniline (D) [10]. Finally, the gradual cleavage of the aromatic intermediates would lead to the formation of carboxylic acids prior to conversion into carbon dioxide. 3.9. Changes of COD and toxicity with reaction time It was clearly seen from Fig. 11 that the COD removal efficiency reached 57% at 90 min by catalytic ozonation process, while only 41% COD removal efficiency was achieve by ozonation alone. The presence of Fe/activated carbon could enhance the generation of hydroxyl radicals from ozone decomposition, and then improve the COD removal efficiency of Crystal Violet in the ozonation process. Since COD was not completely removed after 90 min reaction, the change of acute toxicity to Daphnia magna was monitored during the treatment. The Daphnia magna immobilization rate of the initial Crystal Violet was 100% after 24 h exposition. It indicated that the original Crystal Violet solution was extremely toxic [50,51]. After 30 min treatment, the Daphnia magna immobilization rate decreased to 95%. When the reaction time was extended to 90 min, the immobilization rate could further decrease to 75%. This illustrated that the acute toxicity of the dye solution could be reduced to some extent after catalytic ozonation. 10
4. Conclusion The presence of Fe/activated carbon catalyst significantly enhanced the decolorization efficiency and COD removal efficiency during ozonation of Crystal Violet. The decolorization rate increased with pH, gas flow rate and ozone dose, but decreased with initial dye concentration. The reaction temperature had little effect on color removal. The decolorization rate increased with catalyst dosage, but the increase became insignificant after catalyst dosage exceeded 2.5 g/L. The UV-vis spectra indicated that the chromophore and aromatic fragment was almost destroyed after 30 min treatment. It indicated that catalytic ozonation in the presence of Fe/activated carbon is a promising technique for the degradation of dye contaminants.
Acknowledgements This study was supported by Natural Science Foundation of China (Grant No. 20977069, 21211130108).
References [1] C. O’Neill, F.R. Hawkes, D.L. Hawkes, N.D. Lourenço, H.M. Pinheiro, W. Delée Colour in textile effluents-sources, measurement, discharge consents and simulation: a review, J. Chem. Technol. Biotechnol. 74 (1999) 1009-1018. [2] G. Moussavi, M. Mahmoudi, Degradation and biodegradability improvement of the reactive red 198 azo dye using catalytic ozonation with MgO nanocrystals, Chem. Eng. J. 152 (2009) 1-7. [3] C. Sahoo, A. K. Gupta, A. Pal, Photocatalytic degradation of Crystal Violet (C.I. Basic Violet 3) on silver ion doped TiO2, Dyes Pigment. 66 (2005) 189-196. [4] A.K. Gupta, A. Pal, C. Sahoo, Photocatalytic degradation of a mixture of Crystal Violet 11
(Basic Violet 3) and Methyl Red dye in aqueous suspensions using Ag+ doped TiO2, Dyes Pigment. 69 (2006), 224-232. [5] C.C. Chen, F.D. Mai, K.T. Chen, C.W. Wu, C.S. Lu, Photocatalyzed N-de-methylation and degradation of crystal violet in titania dispersions under UV irradiation, Dyes Pigment. 75 (2007) 434-442. [6] F.A. Alshamsi, A.S. Albadwawi, M.M. Alnuaimi, M.A. Rauf, S.S. Ashraf, Comparative efficiencies of the degradation of Crystal Violet using UV/hydrogen peroxide and Fenton’s reagent, Dyes Pigment. 74 (2007) 283-287. [7] H.J. Fan, S.T. Huang, W.H. Chung, J.L. Jan, W.Y. Lin, C.C. Chen, Degradation pathways of Crystal Violet by Fenton and Fenton-like systems: condition optimization and intermediate separation and identification. J Hazard. Mater. 171 (2009) 1032-1044. [8] I. Sirés, E. Guivarch, N. Oturanm, M.A. Oturan, Efficient removal of triphenylmethane dyes from aqueous medium by in situ electrogenerated Fenton’s reagent at carbon-felt cathode, Chemosphere 72 (2008) 592-600. [9] C.I. Brinzila, R. Ciobanu, E. Brillas, Effect of experimental parameters on crystal violet mineralization by electro-Fenton processes, Environ. Eng. Manage. J. 11 (2012) 517-523. [10] R.E. Palma-Goyes, F.L. Guzmán-Duque, G. Peñuela, I. González, J.L. Nava, R.A. Torres-Palma, Electrochemical degradation of crystal violet with BDD electrodes: Effect of electrochemical parameters and identification of organic by-products, Chemosphere 81 (2010) 26-32. [11] H. Zhang, J. Wu, Z.Q. Wang, D.B. Zhang, Electrochemical oxidation of Crystal Violet in the presence of hydrogen peroxide, J. Chem. Technol. Biotechnol. 85 (2010) 1436-1444. [12] M.T.F. Tabrizi, D. Glasser, D. Hildebrandt, Wastewater treatment of reactive dyestuffs by ozonation in a semi-batch reactor, Chem. Eng. J. 166 (2011) 662-668. [13] H. Zhang, W.J. Wang, Oxidation of C.I. Acid Orange 7 with ozone and hydrogen 12
peroxide in a hollow fiber membrane reactor, Chem. Eng. Comm. 198 (2011) 1530-1544. [14] C. Tizaoui, N. Grima, Kinetics of the ozone oxidation of Reactive Orange 16 azo-dye in aqueous solution, Chem. Eng. J. 173 (2011) 463-473. [15] A.C. Gomes, L.R. Fernandes, R.M.S. Simões, Oxidation rates of two textile dyes by ozone: Effect of pH and competitive kinetics, Chem. Eng. J. 189-190 (2012) 175-181. [16] B. Kasprzyk-Hordern, M. Ziółek, J. Nawrocki, Catalytic ozonation and methods of enhancing molecular ozone reactions in water treatment, Appl. Catal. B-Environ. 46 (2003) 639-669. [17] O.S.G.P. Soares, P.C.C. Faria, J.J.M. Órfão, M.F.R. Pereir, Ozonation of textile effluents and dye solutions in the presence of activated carbon under continuous operation, Sep. Sci. Technol. 42 (2007) 1477-1492. [18] H. Zhang, L.J. Duan, D.B. Zhang, Decolorization of methyl orange by ozonation in combination with ultrasonic irradiation, J. Hazard. Mater. 138 (2006) 53-59. [19] T. Sreethawong, S. Chavadej, Color removal of distillery wastewater by ozonation in the absence and presence of immobilized iron oxide catalyst, J. Hazard. Mater. 155 (2008) 486-493. [20] H. Zhang, Y. J. Lv, F. Liu, D.B. Zhang, Degradation of C.I. Acid Orange 7 by ultrasound enhanced ozonation in a rectangular air-lift reactor, Chem. Eng. J. 138 (2008) 231-238. [21] X.Y. Liu, Z.M. Zhou, G.H. Jing, J.H. Fang, Catalytic ozonation of Acid Red B in aqueous solution over a Fe-Cu-O catalyst, Sep. Purif. Technol. 115 (2013) 129-135 [22] Q.Z. Dai, J.Y. Wang, J. Chen, J.M. Chen, Ozonation catalyzed by cerium supported on activated carbon for the degradation of typical pharmaceutical wastewater, Sep. Purif. Technol. 127 (2014) 112-120. [23] S.N. Zhu, K.N. Hui, X.T. Hong, K.S. Hui, Catalytic ozonation of basic yellow 87 with a reusable catalyst chip, Chem. Eng. J. 242 (2014) 180-186. 13
[24] F. Gholami-Borujeni, K. Naddafi, F. Nejatzadeh-Barandozi, Application of catalytic ozonation in treatment of dye from aquatic solutions, Desalin. Water Treat. 51 (2013) 6545-6551. [25] J. Altmann, A.S. Ruhl, F. Zietzschmann, M. Jekel, Direct comparison of ozonation and adsorption onto powdered activated carbon for micropollutant removal in advanced wastewater treatment, Water Res. 55 (2014) 185-193. [26] C.A. Guzman-Perez, J. Soltan, J. Robertson, Kinetics of catalytic ozonation of atrazine in the presence of activated carbon, Sep. Purif. Technol. 79 (2011) 8-14. [27] F.J. Beltran, F.J. Rivas, R. Montero-de-Espinosa, Iron type catalysts for the ozonation of oxalic acid in water, Water Res. 39 (2005) 3553-3564. [28] L.W. Hou, H. Zhang, L.G. Wang, L. Chen, Y.D Xiong, X.F Xue, Removal of sulfamethoxazole from aqueous solution by sono-ozonation in the presence of a magnetic catalyst, Sep. Purif. Technol. 117 (2013) 46-52. [29] L.W. Hou, H. Zhang, L.G. Wang, L. Chen, Ultrasound-enhanced magnetite catalytic ozonation of tetracycline in water, Chem. Eng. J. 229 (2013) 577-584. [30] W.C Ling, Z.M. Qiang, Y.W. Shi, T. Zhang, B.Z. Dong, Fe(III)-loaded activated carbon as catalyst to improve omethoate degradation by ozone in water, J Mol. Catal. A: Chem. 342-343 (2011) 23-29. [31] C.M. Chen, H.S. Chen, X. Guo, S.H. Guo, G.X. Yan, Advanced ozone treatment of heavy oil refining wastewater by activated carbon supported iron oxide, J. Ind. Eng. Chem. 20 (2014) 2782-2791. [32] Y.X. Huang, C.C. Cui, D.F Zhang, L. Li, D. Pan, Heterogeneous catalytic ozonation of dibutyl phthalate in aqueous solution in the presence of iron-loaded activated carbon, Chemosphere 119 (2015) 295-301. [33] H. Zhang, H. Gao, C. Cai, C.Y. Zhang, L. Chen. Decolorization of Crystal Violet by 14
ultrasound/heterogeneous Fenton process, Water Sci. Technol. 68 (2013) 2515-2520. [34] D.L. Flamm, Analysis of ozone at low concentration with boric acid buffered KI, Environ. Sci. Technol. 11 (1977) 978-983. [35] Standard of the People’s Republic of China for Environmental Protection, Water quality – determination of the chemical oxygen demand – fast digestion – spectrophotometric method, HJ/T 399-2007. [36] OECD, Organization for Economic Cooperation and Development, Daphnia sp. Acute Immobilization Test. Test Guideline No. 202, OECD Guidelines for Testing of Chemicals, 2004. [37] Y. Wang, Y.W. Gao, L. Chen, H. Zhang, Goethite as an efficient heterogeneous Fenton catalyst
for
the
degradation
of
methyl
orange,
Catal.
Today
(2015),
http://dx.doi.org/10.1016/j.cattod.2015.01.012 [38] J.S. Park, H. Choi, J. Cho, Kinetic decomposition of ozone and para-chlorobenzoic acid (pCBA) during catalytic ozonation, Water Res. 38 (2004) 2284-2291. [39] J.S. Park, H. Choi, K.-H. Ahn, J.-W. Kang, Removal mechanism of natural organic matter and organic acid by ozone in the presence of goethite, Ozone Sci. Eng. 26 (2004) 141-151. [40] M. Muruganandham, J.J. Wu, Granular -FeOOH - A stable and efficient catalyst for the decomposition of dissolved ozone in water, Catal. Commun. 8 (2007) 668-672 [41] T. Zhang, C.J. Li, J. Ma, H. Tian, Z.M. Qiang, Surface hydroxyl groups of synthetic α-FeOOH in promoting •OH generation from aqueous ozone: Property and activity relationship, Appl. Catal. B-Environ. 82 (2008) 131-137. [42] T. Zhang, J. Ma, Catalytic ozonation of trace nitrobenzene in water with synthetic goethite, J. Mol. Catal. A-Chem. 279 (2008) 82-89. [43] T. Zhang, J. Lu, J. Ma, Z. Qiang, Comparative study of ozonation and synthetic 15
goethite-catalyzed ozonation of individual NOM fractions isolated and fractionated from a filtered river water, Water Res. 42 (2008) 1563-1570. [44] M.H. Sui, L. Sheng, K.X. Lu, F. Tian, FeOOH catalytic ozonation of oxalic acid and the effect of phosphate binding on its catalytic activity, Appl. Catal. B: Environ. 96 (2010) 94-100. [45] Y. Wang, H. Zhang, L. Chen, Ultrasound enhanced catalytic ozonation of tetracycline in a rectangular air-lift reactor, Catal. Today 175 (2011) 283-292. [46] H. Zhang, L. Ji, F. Wu, J. Tan, In-situ ozonation of anthracene in unsaturated porous media, J. Hazard. Mater. , 120 (2005) 143-148. [47] V. Yargeau, C. Leclair, Impact of operating conditions on decomposition of antibiotics during ozonation: A review, Ozone Sci. Eng. 30 (2008) 175-188. [48] L.S. Li, W.Y. Ye, Q.Y. Zhang, F.G. Sun, P. Lu, X.K. Li, Catalytic ozonation of dimethyl phthalate over cerium supported on activated carbon, J. Hazard. Mater. 170 (2009) 411-416. [49] F. Guzman-Duque, C. Pétrier, C. Pulgarin, G.Peñuela, R.A. Torres-Palma, Effects of sonochemical parameters and inorganic ions during the sonochemical degradation of crystal violet in water, Ultrason. Sonochem. 18 (2011) 440-446. [50] E.
Zablocka-Godlewska,
W.
Przystaś,
E. Grabińska-Sota,
Decolourization of
triphenylmethane dyes and ecotoxicity of their end products, Environ. Prot. Eng. 35 (2009) 161-169. [51] J. Bae, H.S. Freeman, Aquatic toxicity evaluation of new direct dyes to the Daphnia magna, Dyes Pigments 73 (2007) 81-85.
16
Figure captions Fig. 1 SEM image for the catalyst (a) 500 times (b) 5000 times Fig. 2 XRD pattern of the Fe/activated carbon catalyst Fig. 3 The effect of catalyst dosage (C0 = 400 mg/L, Q = 300 mL/min, ozone dosage = 4.44 mg/min, temperature = 25C, pH 7) Fig. 4 The effect of pH (C0 = 400 mg/L, Q = 300 mL/min, ozone dosage = 4.44 mg/min, catalyst dosage = 2.5 g/L, temperature = 25C) Fig. 5 The effect of temperature (C0 = 400 mg/L, Q = 300 mL/min, ozone dosage = 4.44 mg/min, catalyst dosage =2.5 g/L, pH 7) Fig. 6 The effect of gas flow rate (C0 = 400 mg/L, ozone dosage = 4.44 mg/min, catalyst dosage = 2.5 g/L, temperature = 25C, pH 7) Fig. 7 The effect of ozone dosage (C0 = 400mg/L, Q = 300 mL/min, catalyst dosage = 2.5 g/L, temperature = 25C, pH 7) Fig. 8 The effect of initial dye concentration (Q = 300 mL/min, ozone dosgae = 4.44 mg/min, catalyst dosage = 2.5 g/L, temperature = 25C, pH 7) Fig. 9 UV–vis spectral changes with reaction time (C0 = 200 mg/L, Q = 300 mL/min, ozone dosage = 4.44 mg/min, catalyst dosage = 2.5 g/L, temperature = 25C, pH 10) Fig. 10 Initial degradation pathway of Crystal Violet (C0 = 400 mg/L, Q = 300 mL/min, ozone dosage = 4.44 mg/min, catalyst dosage = 2.5 g/L, temperature = 25C, pH 7) Fig. 11 Changes of COD in (■) ozonation and (●) catalytic ozonation processes with reaction time. (C0 = 400mg/L, Q = 300 mL/min, ozone dosage = 4.44 mg/min, catalyst dosage = 2.5 g/L, temperature = 25C, pH 7)
17
(b)
(a)
Figure 1
18
Intensity a.u
JCPDS Card 29-0713: Goethite
10
20
30
40
50 2
Figure 2
19
60
70
80
90
Decolorization efficiency (%)
100 80 60 40
0 g/L 1.0 g/L 2.5 g/L 4.0 g/L
20 0 0
5
10
15 Time (min)
Figure 3
20
20
25
30
Decolorization efficiency (%)
100 80 60 40 pH = 4 pH = 7 pH = 10
20 0 0
5
10
15 Time (min)
Figure 4
21
20
25
30
Decolorization efficiency (%)
100 80 60 O
25 C O 35 C O 45 C
40 20 0 0
5
10
15 Time (min)
Figure 5
22
20
25
30
Decolorization efficiency (%)
100 80 60 200 mL/min 300 mL/min 400 mL/min
40 20 0 0
5
10
15 Time (min)
Figure 6
23
20
25
30
Decolorization efficiency (%)
100 80 60 40
1.68 mg/min 3.84 mg/min 4.44 mg/min
20 0 0
5
10
15 Time (min)
Figure 7
24
20
25
30
Decolorization efficiency (%)
100 80 60 40
200 mg/L 400 mg/L 600 mg/L
20 0 0
5
10
15 Time (min)
Figure 8
25
20
25
30
1.2 0 min 5 min 10 min 15 min 20 min 25 min 30 min
Absorbance
1.0 0.8 0.6 0.4 0.2 0.0 200
300
400
500
600
Wavelength (nm)
Figure 9
26
700
800
H3C
CH3
N
H 3C H 3C
N CH3
A
CH3 N CH3
CH3 N CH3
N CH3
C
O H3C
H 3C N H 3C
CH3
N CH3
N CH3
CH3 N CH3
D
B
Figure 10
27
COD removal efficiency (%)
60 50 40 30 20 Ozonation Catalytic ozonation
10 0 0
15
30
45 Time (min)
Figure 11
28
60
75
90
Table 1. The textural properties of the Fe/activated carbon catalysts. Textural properties Particle size Catalysts (μm)
Fe/AC
250-300
Pore volume
Average pore
(cm3/g)
size(nm)
0.1645
3.374
BET area (m2/g)
195.0
29
Highlights Fe/activated carbon promoted the degradation of Crystal Violet during ozonation The effect of operating parameters on the decolorization was investigated The initial degradation pathway of Crystal Violet was proposed The changes of COD and the acute toxicity during the treatment were monitored
30
