International Journal of Environment Science and Technology Center for Environment and Energy Research and Studies (CEERS) ISSN: 1735-1472 EISSN: 1735-2630 Vol. 5, Num. 1, 2008, pp. 17-26

International Journal of Enviornmental Science and Technology, Vol. 5, No. 1, Winter 2008, pp. 17-26

Photocatalytic ozonation of 2, 4-dichlorophenoxyacetic acid in water with a new TiO₂ fiber

¹*R. R. Giri; ²H. Ozaki; ¹S. Taniguchi; ¹R. Takanami

¹New Industrial R and D Center, Osaka Sangyo University, 3-1-1 Nakagaito, Daito City, 574-8530 Osaka, Japan
² Department of Civil Engineering, Osaka Sangyo University, 3-1-1 Nakagaito, Daito City, 574-8530 Osaka, Japan
*Corresponding Author Email: rabindra@cnt.osaka-sandai.ac.jp Tel.: +81 72875 3001; Fax: +81 72875 3076

Received 1 September 2007; revised 12 October 2007; accepted 9 November 2007; available online 26 December 2007

Code Number: st08003

ABSTRACT

More effective techniques are required to mineralize the increasing number of recalcitrant organic contaminants at low concentrations in the water environment using advanced oxidation process. Though relatively new, photocatalytic ozonation (O₃/UV/TiO₂) is considered superior to ozonation (O₃) and photocatalysis (UV/TiO₂), due to synergistic effects and use of immobilized TiO₂ photocatalysts is a milestone in advance oxidation process. This article aimed to elucidate 2, 4-dichlorophenoxyacetic acid (2, 4-D) mineralization characteristics in low aqueous solutions by O₃/UV/TiO₂ using the world’s first high-strength TiO₂ fiber catalyst in laboratory experiments. 2, 4-D degradation and TOC removal in O₃, UV/TiO₂ and O₃/UV/TiO₂ followed pseudo-first order reaction kinetic. The removal rates for 2, 4-D and TOC in O₃/UV/TiO₂ were respectively about 1.5 and 2.4-fold larger than the summation of the corresponding values in O₃ and UV/TiO₂. The O₃/UV/TiO₂ process was characterized by short-lived few aromatic intermediates, faster degradations of aliphatic intermediates and dechlorination as a major step in 2, 4-D mineralization. The significantly enhanced 2, 4-D mineralization in the process was attributed to increased ozone decomposition and reduced electron-hole recombination on TiO₂ surface resulting to a large number of ^. OH generation. The O₃/UV/TiO₂ process with the TiO₂ fiber catalyst was very promising with respect to the major challenges being faced in AOP involving TiO₂, namely separation of powder catalyst in suspension and reduced efficiency of immobilized catalysts (e.g. TiO₂ film/fiber).

Key words: Photocatalysis, degradation, hydroxyl radical, intermediates, rate constant, total organic carbon

Ever-increasing use of chemicals and discovery of new recalcitrant organic contaminants in water environment have remained as major challenges in developing effective treatment methods for water and wastewater. A large number of organic contaminants are hazardous even at low concentration levels and stringent regulations are being enforced, especially in the industrialized nations for both conventional and non-conventional pollutants. Therefore, more effective methods are necessary for treating contaminated water and wastewater to meet the challenges. Ozonation (O₃) and photocatalysis (UV/TiO₂) are widely investigated advanced oxidation processes (AOP) for treating contaminated waters (Djebbar and Sehili, 1998; Yao, et al., 1998; Drzewicz, et al., 2004; Singh and Muneer, 2004). Ozonation alone is less effective, since its reaction with organic contaminants is selective (Brillas, et al., 2003;Agustina, et al., 2005; Li, et al., 2005) and generation of free radicals from its decomposition takes place only at elevated pH conditions (Munter, 2001). Oxidation of contaminants in UV/TiO₂ system involves free hydroxyl radical (·OH), but separation of TiO₂ catalyst in suspension has been a major obstacle. Although recent developments in TiO₂ film and fiber catalysts can overcome the problem, mere photocatalysis is reported to be less efficient for several organic contaminants(Agustina, et al., 2005; Li, et al., 2005; Terashima, et al., 2006). Photocatalytic ozonation (O₃/UV/TiO₂) isemerging as a morepromising oxidation method for refractory organic contaminants due to a large number of ·OH generation (Agustina, et al., 2005; Beltran, et al., 2005;Li ,et al., 2005; Farre, et al., 2005). Few literatures are available on the O₃/UV/TiO₂ process,because its use is relatively new, while successful use of TiO₂ fiber catalyst is expected to be a milestone in practical applications of the UV/TiO₂ and O₃/UV/TiO₂ processes. This article aimed to investigate degradation characteristics of low concentration (≈ 45 µM) 2, 4-dichlorophenoxyacetic acid (2, 4-D) in aqueous solution by the O₃/UV/TiO₂ process using the world’s first high-strength TiO₂ fiber catalyst (Ishikawa, 2004) developed by Ube Industries Ltd., Japan, with laboratory batch-experiments.

The 2, 4-D standard (Cica-Reagent) was obtained from Kanto Chemical Co., Inc. Na₂SO₃ solution (1.0 g/L) and Spectroquant^® Picco Colorimeter test kit (Merck, Germany) which were respectively used to quench and measure residual dissolved ozone in samples in O₃ and O₃/UV/TiO₂ experiments. Other reagents were of HPLC grade obtained from Wako Pure Chemicals Ltd., Japan. Carrier gas flow from ozone generator to reactor was regulated with a flow meter, while O₃ concentration in the carrier gas was continuously monitored using an ozone measuring device (EG-600, EBARAJITSUGYO Co.Ltd., Japan).A Pyrex glass reactor (8.0 l capacity, ID: 18.4 cm, h: 30 cm) with centrally placed tubular jacket (OD: 6.2 cm) and six circular ports (OD: 2.8 cm) at the top was used for batch experiments. TiO₂ fiber catalyst (20 cm × 25 cm sheets) was supplied by Ube Industries Ltd., Japan. A cylindrical catalyst module (OD: 18.4 cm, h: 30 cm) was prepared using the catalyst and stainless steel wire mesh (3 mm ×3 mm opening). Ozone was generated by passing air (21% O₂ + 79% N₂) through an ozone generator (Nippon Ozone Co., Ltd.). A UV tube lamp (10 W, 254 nm, UVL10DL-12, SEN Lights Corporation, Japan) was the source of irradiation in UV/TiO₂ and O₃/UV/TiO₂ processes. Headspace gas in the reactor was continuously pumped, dried and passed through a packed tower to absorb residual O₃ gas.

Seven and half liter of about 45 µM 2, 4-D solution without initial pH adjustment was poured into the reactor. Ozone generator, carrier gas flow meter, ozone concentration monitoring device, reactor, pump and absorption tower were connected in series. The solution was continuously mixed with a magnetic stirrer with the same speed in all the experiments. The samples were taken at 20 min. interval for analysis, while all of the experiments were carried out for a duration of 2 h. The catalyst module was placed inside the reactor in the UV/TiO₂ and O₃/UV/TiO₂ experiments. Carrier gas flow rate and ozone concentration in it were respectivly maintained at 1.0 L/min. and 2.0 mg/L throughout the experiments in the O₃ and O₃/UV/TiO₂ processes. The ozone concentration in carrier gas was regulated by varying electric voltage in ozone generator.

The samples were analyzed for remaining 2, 4-D and both aromatic and aliphatic intermediates using HPLC with UV detector (Model: D-7000, Hitachi, Japan). Inertsil ODS-3V column (150 mm × 3 mm ID × 5 µm) with 35 ^oC oven temperature, 20 µL sample volume and CH₃CN: H₂O: CH₃COOH = 50: 49: 1 (v/v) mobile phase at 0.40 mL/min. flow rate was employed for aromatic intermediates including 2, 4-D at 254 nm. Supelcogel C-610H (30 cm × 7.8 mm ID × 9 µm) together with Supelguard C-610H (5 cm × 4.6 mm ID) columns with 30^oC oven temperature, 20 µL sample volume and 0.1% H₃PO₄ in water (v/v) mobile phase at 0.50 mL/min. flow rate were used for aliphatic intermediates at 210 nm. The detected intermediates of 2, 4-D oxidation were identified by matching peak retention time (RT) of oxidized 2, 4-D samples with the peaks of various known standards. Total organic carbon (TOC) analyzer (TOC-V_CSH, Shimadzu, Japan) was used to measure TOC while Ion Chromatograph with conductivity detector (Model: L-7000, Hitachi, Japan), GL-IC-A25 column (150 mm × 4.6 mm ID), 40 ºC oven temperature and 4.0 mM Na₂CO₃ solution (in water) mobile phase at 1.0 mL/min. flow rate were used to measure chloride ion concentration in the samples. Residual aqueous phase ozone in the samples was measured by photometric diphenylen-diamine-based (DPD) method at 528 nm UV wave length.

All the experiments were carried out in triplicate and average values of the results are presented in figures while the error bars in the figures indicate standard deviations. Average initial pH values of about 45 µM 2, 4-D solutions in O₃, UV/TiO₂ and O₃/UV/TiO₂ processes were 4.36, 4.32 and 4.33, respectively, which gradually decreased during a 2 h. oxidation. The O₃/UV/TiO₂ and UV/TiO₂ processes have the most and least efficiencies respectively for 2, 4-D oxidation (Fig. 1). About 54% and 83% of 2, 4-D was oxidized in UV/TiO₂ and O₃ at the end of the 2 h. oxidation, while one hundred percent of the 2, 4-D degraded in less than two hours in O₃/UV/TiO₂. The half-life periods for 2, 4-D in the O₃, UV/TiO₂ and O₃/UV/TiO₂ processes were about 60, 110 and 28 min., respectively. 2, 4-D oxidations in all of the three processes were well described by pseudo-first order reaction kinetic (Fig. 1). The degradation rate (k) values in UV/TiO₂, O₃ and O₃/UV/TiO₂ were 0.39, 0.89 and 1.93/h, respectively. The value for O₃/UV/TiO₂ was about 1.5 times higher than the summation of the values for the other two processes. Thus, O₃/UV/TiO₂ using TiO₂ fiber catalyst was found to be a very effective process to degrade the model pollutant in low aqueous solution. Though a positively charged hole on TiO₂ surface in UV/TiO₂ process is mentioned to possess the highest oxidation power (Munter, 2001), its role on oxidation of micropollutants is not well explained. Therefore, ·OH is considered to be the sole oxidizing species, which has the second highest oxidation power (Munter, 2001). Despite the non-selective reaction and high oxidation power of ·OH, UV/TiO₂ with fiber catalyst was found to be rather a slow process in this investigation, which is consistent with the earlier results with TiO₂ fiber, powder and film catalysts (Beltran, et al., 2005; Li, et al., 2005; Terashima, et al., 2006). Generation and utilization of ·OH are two important steps in oxidations involving ·OH. However, the quantification of ·OH in a process is quite complicated due to its very short life. Chloride ions at high concentrations are reported to have scavenging effect on ·OH (Kiwi, et al., 2000). Theoretically, about 90.48 µM of chloride ions can be liberated from 45 µM of 2, 4-D oxidation. Photocatalytic oxidation experiments with 45 µM 2, 4-D, TiO₂ fiber catalyst and various initial chloride ion concentrations (0, 56, 85, 113 and 141 µM) were also carried out. The results (not shown) exhibited no significant effect of chloride ions on 2, 4-D oxidation. The slow 2, 4-D oxidation in the UV/TiO₂ process was presumably due to a less number of ·OH generation. Recombination of electrons and positive holes formed on TiO₂ surface are considered as a possible reason for a less number of ·OH in the process (Agustina, et al., 2005; Farre, et al., 2005). The 2, 4-D degradation rates in O₃ and O₃/ UV/TiO₂ were about 2.3 and 4.9 times of UV/TiO₂, while the value for O₃/UV/TiO₂ was about 2.2 times of O₃. Since the oxidations took place below 4.36 pH value in the O₃ process, direct ozonation of 2, 4-D was most likely a major degradation mechanism (Beltran, et al., 2005). The enhanced degradation in O₃/UV/TiO₂ can be attributed to ozone decomposition resulting in an increased ·OH production (Agustina, et al., 2005; Beltran, et al., 2005). Dissolved residual ozone concentrations in O₃/UV/TiO₂ were significantly smaller than that in O₃ and almost constant throughout the experiments (Fig. 2). This presumably is the result of its decomposition, while the values in the O₃ process drastically increased during the first-half of the experiment and then remained almost stagnant. Farre, et al., (2005) also argued that the presence of dissolved ozone in irradiated TiO₂ aqueous suspension not only increases ·OH production but also decreases the recombination of electrons and positive holes on the TiO₂ surface.

Since all the detected intermediates were not identified, their abundance profiles with time are used for discussion in this section. Ozonation was characterized by the largest number of intermediates including eight aromatics (Fig. 3) and ten aliphatics (Fig. 4). The two identified aromatics (2, 4dichlorophenol (2, 4-DCP) and benzyl alcohol (BA)) were relatively at low concentrations while the two unknowns (RT ≈ 4.5 and 6.6 min.) appeared to be the main (Fig. 3). The least number of intermediates was detected in the UV/TiO₂ process (Fig. 5), where 2, 4-DCP was the main aromatic intermediate while benzyl alcohol at low concentrations was also detected at the end of the experiments. Maleic acid and one unknown (RT ≈15.1 min.) were aliphatic intermediates in the process. Three aromatics (2, 4-DCP, BA and one unknown (RT ≈ 4.1 min.)) and nine aliphatics, including the four unknowns (Fig. 6), were detected in the O₃/ UV/TiO₂ process, where the number was larger than that in UV/TiO₂ and smaller than that in O₃. 2, 4-DCP, which is more toxic than the parent compound and was the major aromatic byproduct in the UV/TiO₂ process. Despite increased toxicity due to the 2, 4-DCP formation, the least number of intermediates may be interpreted as a result of shorter paths for 2, 4-D degradation. The increasing intensity profiles of both aromatic and aliphatic intermediates until the end of the experiments (Fig. 5) exhibited that UV/TiO₂ is a slow process in terms of 2, 4-D mineralization. In contrast to UV/TiO₂, most of the aromatic intermediates detected in ozonation reached to their highest intensity values, and then decreased before the end of the experiments (Fig. 3). But the intensity values for all of the aliphatic intermediates continued its increasing to the end (Fig. 4). The largest number of aliphatic intermediates was attributed to the selective reaction of ozone at acidic or neutral pH conditions resulting in the formation of carboxylic acids as the end products (Agustina, et al., 2005). The slow degradations of the carboxylic acids were also presumably due to the selective reaction. Though several aliphatic intermediates were not identified (Fig. 4), the formation of saturated carboxylic acids in the process could have resulted in the slow oxidation, since the unsaturated carboxylic acids are relatively unstable and get oxidized more easily than the saturated ones (Jung, 2001). Low concentrations of the three aromatic intermediates in O₃/UV/TiO₂ (not shown) were present for a short period indicating their fast oxidations. Despite a relatively large number of aliphatic intermediates in the process, their intensities reached to the peak values at the middle of the experiments and decreased significantly by the end (Fig. 6). Thus, the detected intermediates in the O₃/UV/TiO₂ process were oxidized faster than that in the other two processes presumably due to the increased ·OH generation and its effective use in the oxidation. In contrast to ozonation, the nature of aliphatic intermediates did not appear to be an important factor for their oxidation in the O₃/UV/TiO₂ process.

Though 2, 4-D oxidation in O₃ was more than two folds larger than that in UV/TiO₂, no significant difference in TOC removals between these two processes was observed through the first half of the experiments (Fig. 7). Ozonation then appeared to be less efficient compared to UV/TiO₂ and the difference between them gradually increased till the end. TOC removals in these processes by the end of the experiments were about 17% and 23%, respectively. Similar to 2, 4-D degradation, O₃/UV/TiO₂ was the most effective in terms of TOC removal among the three processes (Fig. 7), where the removal was about 67% at the end of the 2 h. oxidation. But the O₃ and UV/TiO₂ processes appeared to be very inefficient in terms of TOC removal. TOC removals by the three processes were well described by pseudo first-order reaction kinetic (inset of Fig. 7). The removal rate k values for O₃, UV/TiO₂ and O₃/UV/TiO₂ were about 0.09, 0.14 and 0.56/h, respectively. The k value for O₃/UV/TiO₂ was about 2.4 folds higher than the summation of k values for the remaining two processes. Thus, 2, 4-D mineralization in the O₃/UV/TiO₂ process using TiO₂ fiber catalyst was very effective due to the synergistic effects of photocatalysis and ozonation. Two possible mechanisms are proposed for the enhanced mineralization of organics in the combined process (Agustina, et al., 2005). Dissolved ozone can easily accept electrons produced on TiO₂ surface, which reduces the possibility of their recombination with positive holes resulting in a large number of ·OH formation. A large number of hydrogen peroxide and ·OH can also be produced from dissolved ozone as a result of UV irradiation. More than one parallel path for ·OH generation is proposed in the combined process (Beltran, et al., 2005).

Though ozone photolysis is a slow process in the beginning, it is considered to be an important mechanism for ·OH generation after a few minutes. With high extinction coefficient value of ozone at 254 nm wave length (ε = 3300/M/cm), a significantly large number of ·OH is generated from its photolysis (Munter, 2001). The presence of TiO₂ implies some adsorption steps followed by surface reactions though there is a lackof kinetic information (Beltran, et al., 2005). Reaction between ozone and titanium yields adsorbed ozonide ion radical (O₃^-x), which is another source of ·OH. Thus, three parallel paths of ·OH generation are available in the O₃/UV/TiO₂ process in addition to direct photolysis and ozonation of 2, 4-D and its intermediates. The almost constant and significantly smaller dissolved residual ozone values for the process (Fig. 3) were presumably the result of ozone photolysis and/or adsorption followed by its decomposition. Reactions of organics containing C-H or C-C multiple bonds with ·OH generally proceed with larger rate constants (∼ 10¹⁰/M/S) and therefore their oxidations are usually limited by ·OH generation and reaction with ·OH scavengers (Haag and Yao, 1992). Carbonate, bicarbonate and high concentrations of chloride ions are considered as ·OH scavengers, but their scavenging effects in these experiments were presumably insignificant. Reaction rates of ozone with aromatics including phenols are very small (by 6 ∼ 11-log orders) compared to ·OH (Munter, 2001). Therefore, the generation of a large number of ·OH from the parallel paths and high reaction rates of ·OH with 2, 4-D and its degradation intermediates presumably resulted in the enhanced 2, 4-D mineralization in the O₃/UV/TiO₂ process.

The chloride content in hazardous organics is considered as a measure of their toxicity and hence dechlorination is a very important step in their oxidations. Dechlorination in a sample was calculated as the ratio of free chloride ion concentration in the sample to the theoretical chlorine content in 2, 4-D before oxidation. Dechlorination profiles for the three oxidation processes in this investigation (Fig. 8) exhibited that O₃ was more efficient than UV/TiO₂ and O₃/UV/TiO₂ was the most efficient. Dechlorination values for the O₃, UV/TiO₂ and O₃/UV/TiO₂ processes at the end of the 2 h. experiments were about 35, 63 and 81%, respectively. The average dechlorinations during the experiments in O₃/UV/TiO₂ and O₃ were about three and two folds the value for the UV/TiO₂ process, respectively. But, with respect to the values in UV/ TiO₂, the dechlorination ratios in O₃ and O₃/UV/TiO₂ started to decline from 80 min. and continued to the end. Since the detected aliphatic intermediates were carboxylic acids, presumably only the aromatic intermediates were chlorinated. The smallest dechlorinations in UV/TiO₂ can be attributed to a very slow 2, 4-D decay and formation of 2, 4-DCP, which was the only aromatic intermediate and considered to be more resistant to degradation than 2, 4-D. The enhanced dechlorination in O₃, despite the selective reaction of ozone with organic compounds, may be attributed to relatively large ozone supply rate (≈ 2.0mg/L/min.). The two apparentlymajor unidentified aromatics (RT ≈4.5 min. and 6.6 min.) in the O₃ process (Fig. 4) could be chlorinated in addition to 2, 4-DCP. The relatively slow 2, 4-D decay and the formation of possibly chlorinated aromatics in significant amounts in O₃ resulted in smaller dechlorinations compared to the values in O₃/UV/TiO₂. Detection the aromatic intermediates, including 2, 4-DCP, only for a short period and at very low concentrations, exhibited that dechlorination was presumably the first and/or major step in the O₃/UV/TiO₂ process. The largest dechlorination values in O₃/UV/TiO₂ can obviously be attributed to a large number of ·OH generation, its high oxidation potential and non-selective reactions with 2, 4-D and its chlorinated aromatic intermediates. Despite complete disappearance of 2, 4-D and its aromatic intermediates, the dechlorination values were less than 90% in the O₃/UV/TiO₂ process by the end of the experiments. Reaction between chloride ions and ·OH resulting in the reduced chloride concentrations may be ruled out in this case because the reaction is considered to be significant at high (≥ 0.1 M) chloride concentrations only (Kiwi, et al., 2000). The dechlorination values could have been underestimated, since the background chloride concentrations (before oxidation), which varied between 5% and 7%, were taken as zero in all of the experiments. The relatively larger background chloride concentrations may be the result of agitation of 2, 4-D solution due to mixing (all experiments) and air flow (experiments involving O₃) before commencing the experiments.

In aqueous solution, mineralization of low concentration 2, 4-D (≈ 45 µM) by the O₃, UV/TiO₂ and O₃/UV/TiO₂ processes was investigated, using the world’s first high-strength fiber catalyst. 2, 4-D degradation and TOC removal followed pseudo firstorder reaction kinetic while the mineralization was greatly enhanced in O₃/UV/TiO₂. The removal rates for 2, 4-D and TOC in O₃/UV/TiO₂ were about 1.5 and 2.4-folds larger than the summation of the corresponding values for O₃ and UV/TiO₂. The O₃/UV/ TiO₂ process was characterized by a few aromatic intermediates and their short lives, fast degradations of the aliphatic intermediates despite their presence in a relatively larger number and dechlorination as a major step in the mineralization. The enhanced dechlorination and 2, 4-D mineralization in the O₃/UV/TiO₂ process were due to the increased ozone decomposition and the reduced electron-hole recombination on TiO₂ surface resulting in a large number of ·OH generation. The results exhibited that photocatalytic ozonation with TiO₂ fiber catalyst is very promising to overcome the problems being faced in AOP using TiO₂ as a photocatalyst: separation of catalyst in suspension and reduced efficiency of immobilized catalyst (e.g. TiO₂ film/fiber).

The authors would like to thank Ube Industries Ltd., Yamaguchi, Japan, for providing the TiO₂ fiber catalyst used in this investigation.

• Agustina, T. E.; Ang, H. M.; Vareek, V. K., (2005). A review of synergistic effect of photocatalysis and ozonation on wastewater treatment. J. Photoch. Photobio. C., 6, 264-273.
• Brillas, E.; Calpe, J. C.; Cabot, P., (2003). Degradation of the herbicide 2,4-dichlorophenoxyacetic acid by ozonation catalyzed with Fe²⁺ and UVA light. Appl. Catal. B., 46, 381-391.
• Beltran, F. J.; Rivas, F. J.; Gimeno, O., (2005). Comparison between photocatalytic ozonation and other oxidation processes for the removal of phenols from water. J. Chem. Tech. Biotech., 80, 973-984.
• Djebbar, K.; Sehili, T., (1998). Kinetics of heterogeneous photocatalytic decomposition of 2,4-dichlorophenoxyacetic acid over titanium dioxide and zinc oxide in aqueous solution. Pestic. Sci., 54, 269-276.
• Drzewicz, P.; Trojanowicz, M.; Zona, R.; Solar, S.; Gehringer, P., (2004). Decomposition of 2,4-dichlorophenoxyacetic acid by ozonation, ionizing radiation as well as ozonation combined with ionizing radiation. Radiat. Phys. Chem., 69, 281-287.
• Farre, M. J.; Franch, M. I.; Malato, S.; Ayllon, J. A.; Peral, J.; Domenech, X., (2005). Degradation of some biorecalcitrant
  pesticides by homogeneous and heterogeneous photocatalytic ozonation. Chemosphere, 58, 1127-1133.
• Ishikawa, T., (2004). Photocatalytic fiber with gradient surface structure produced from a polycarbosilane and its applications. Int. J. Appl. Ceram. Tech., 1(1), 49-55.
• Haag, W. R.; Yao, C. C. D., (1992). Rate constants for reaction of hydroxyl radicals with several drinking water contaminants. Environ. Sci. Tech., 26, 1005-1013.
• Jung, O., (2001). Destruction of 2-chlorophenol from wastewater and investigation of byproducts by ozonation. Bull. Korean Chem. Soc., 22(8), 850-856.
• Kiwi, J.; Lopez, A.; Nadtochenko, V., (2000). Mechanism and kinetics of the OH-radical intervention during Fenton
  oxidation in the presence of a significant amount of radical scavenger (Cl^- ). Environ. Sci. Tech., 34, 2162-2168.
• Li, L.; Zhu, W., Chen, L.; Zhang, P.; Chen, Z., (2005). Photocatalytic ozonation of dibutyl phthalate over TiO₂
  film. J. Photoch. Photobiol. A, 175, 172-177.
• Munter, R., (2001). Advanced oxidation processes: current status and prospects. Proc. Estonian Acad. Sci., Chem.,
  50(2), 59-80.
  
• Singh, H. K.; Muneer, M., (2004). Photodegradation of a herbicide derivative, 2, 4-dichlorophenoxyacetic acid in
  aqueous suspension of titanium dioxide. Res. Chem. Intermediat., 30(3), 317-329.
  
• Terashima, Y.; Ozaki, H.; Giri, R. R.; Tano, T.; Nakatsuji, S.; Takanami, R.; Taniguchi, S., (2006). Photocatalytic
  oxidation of low concentration of 2, 4-D solution with new TiO₂ fiber catalyst in a continuous flow reactor. Water Sci. Tech., 54(8), 55-63.
  
• Yao, J.; Huang, Z.; Masten, S. J., (1998). The ozonation of
  pyrene: pathway and product identification. Water Res.,
  32(10), 3001-3012.

AUTHOR (S) BIOSKETCHES

Giri, R. R., Ph.D., Researcher, New Industrial R and D Center, Osaka Sangyo University, 3-1-1 Nakagaito, Daito City, 574-8530 Osaka, Japan. Email: rabindra@cnt.osaka-sandai.ac.jp

Ozaki, H., D.Eng, Professor, Department of Civil Engineering, Osaka Sangyo University, 3-1-1 Nakagaito, Daito City, 574-8530 Osaka, Japan. Email: ozaki@ce.osaka-sandai.ac.jp

Taniguchi, S., M.Sc., Researcher, New Industrial R and D Center, Osaka Sangyo University, 3-1-1 Nakagaito, Daito City, 574-8530 Osaka, Japan, Email: taniguch@cnt.osaka-sandai.ac.jp

Takanami, R., M.Sc., Researcher, New Industrial R and D Center, Osaka Sangyo University, 3-1-1 Nakagaito, Daito City, 574-8530 Osaka, Japan. Email: r-nami@cnt.osaka-sandai.ac.jp

This article should be referenced as follows:

Giri, R. R.;Ozaki, H.; Taniguchi, S.;Takanami,R., (2008). Photocatalyticozonation of 2,4-dichlorophenoxyacetic acid in water with a new TiO₂ fiber. Int. J. Environ. Sci. Tech., 5(1), 17-26.

The following images related to this document are available:

Photo images