Photo catalytic degradation of spill oils on TiO2 nanoparticles in the strait of Singapore

Photo catalytic degradation of spill oils on TiO2 nanoparticles in the strait of Singapore

List of Symbols

XRD X-ray diffractometer

TEM transmission electron microscope wavelength

R² coefficient of determination

The TiO2 nanoparticles with anatase form was prepared and analysed by X-ray diffractometer (XRD) and transmission electron microscope (TEM). In this study, TiO2 was used with and without sunlight for the degradation toluene. About 37.8% of toluene (representing aromatics in the oil spills) in sea water (strait of Singapore) can be photocatalytically degraded under sunlight after 120 min. On an average, , the effectiveness of TiO2 for photocatalytic degradation of toluene in the oil spill sea water is around 0.38 mg toluene/g TiO2 h under sun light radiation. It is expected that oil spills in the harbors or seashores can be adsorbed and photocatalytically degraded with the TiO2 nanoparticles.

Keywords: Oil spill, TiO2 nanoparticle, toluene, photo catalyst, degradation.

The heterogeneous photo-catalysis has been the subject of a vast amount of studies related to environmental abatement in both liquid and gas phase environments2,7,8,12,14. Photocatalytic decomposition of water contaminants on semiconductor catalysts, such as TiO2, is a potential technique for improving indoor air quality4. Recently, a large quantity of work has been devoted to this field3, because of its low-cost production, high specific surface area, and many applications in photo catalytic process. Among different semiconductors nanorod with wide band gaps and titanate or titanium oxide have been prepared over the past decades15.

The primary oil pollutant in ocean may be caused by leaking of oil from the shipwreck, prospecting and excavating of oil from the sea, subsidence of oil gas in the atmosphere, shipping maintenance industry and offshore industry or harbour contamination1. In addition to the release

of the toxic substances from oil spills , the oil slick may cover the sea surface to reduce the photosynthesis of alga and dissolve oxygen

therein5. The negative impacts of oil spill to the ecosystem of ocean or environment of sea surface may be very serious and unexpected13.

The fate and behaviour of spilled oil in the environment depends on a number of physicochemical and biological factors including evaporation, dissolution, microbial degradation, photo oxidation, interaction between oil and

sediments13. Many previous studies revealed

toluene as one of the most hazardous compound present in the oil5. In this study, TiO2 was used for the degradation of toluene in oil under two conditions: with and without sunlight. The Singapore Strait is 105-kilometer long, 16- kilometer wide strait between the Strait of

Malacca in the west and south China Sea in the east. The Malaysia-Singapore border lies along the length of the straits and one oil spill took place in 2010, so for the current research seawater was selected from this area.

2. Titanium Oxide was characterized for its shape, size and distribution. The phase recognition was done using X-ray diffractometer (XRD, Bruker D-8 Advance) using the Cu K radiation of wavelength = 1.5406A. Fine powder of titanium nanoparticles was applied for sample preparation, at first the sample was put in a sample holder and then the powder was pushed into the trough with a glass side to get an even dispensation of the powder.

   The transmission electron microscopy (TEM) was performed to get high resolution images of the specimen. During the sample preparation, the samples were first diluted and then a droplet of the liquid sample was directly placed on a copper microscope grid covered with a carbon film. The size, shape, distribution and poly dispersity of the maghemite nano particles were verified using JEOL-JSM 639OL.

The solution preparation was carried out using sea water and then, toluene that is considered to be one of the most toxic and hazardous material in the oil was added to seawater samples with various ratios of (5, 10 and 15%V/V) in the laboratory.

All the reactions were performed under sunlight irradiation.1g of TiO2 was placed in 100 ml of seawater which includes oil in a 250 ml conical flask. 5 ml of sample was withdrawn at every 20 minutes up to l20 minutes and were analysed for oil concentration. The prepared samples prepared were then tested for oil concentration using model of Jenway 6300

spectrophotometer. Toluene wavelength for spectrophotometer is 365nm from before studies5. Furthermore, all the reactions were carried out without sunlight for comparing degradation result of toluene. The photo catalyst set up is shown in

Fig. 1.

The XRD patterns of the powders obtained from the hydrothermal treatment are shown in Fig. 2. The peaks of the powdered material are identified to originate from (1 0 1), (0 0 4), (2 0

0), (1 0 5), (2 1 3), (1 1 6), (2 1 5) and (3 0 3)

reflections. All the reflection of peaks can be readily indexed to anatase TiO2 with lattice constants of a = 3.784 A and c = 9.512 A (JCPDS: no. 84-1286). No characteristic peak was associated with other crystalline forms as detected in the XRD pattern.

The low and high magnification FESEM images of the prepared powder sample are shown in Fig. 3(a, b). The nanoparticles are uniformly distributed throughout the sample and the sizes of the particles are relatively small. To find the average size HRTEM study was performed. The low and high magnification HRTEM images of the sample are shown in Fig. 3 (c,d) respectively, which shows the uniform formation of TiO2 nanoparticles. The average particle size was 12 nm as seen from Fig. 3(d). The minimum and maximum particle sizes are lying closer to the average particle size. The inset of Fig. 3(d) shows the lattice image of TiO2 nanoparticles with d value (3.52A) corresponding to (1 0 1) planes.

Fig. 2. XRD patterns of the prepared TiO2 nanoparticles

The standard concentration curve of solution was constructed by measuring the absorbance of several different known concentrations of the solution and graphing the results by plotting absorbance on the Y-axis and concentration on the X-axis. The spectrophotometer can be used to

measure the absolute or relative concentration of a characterized substance in solution9,11. To determination of the absolute concentration of a pure substance was carried out, by constructing a standard concentration curve from known

concentrations and then taking the absorbance reading of the unknown concentration. The unknown concentration was further determined from the standard curve by drawing a horizontal line on the graph parallel to the X-axis and through the point on the Y-axis which corresponds to the absorbance. This line will intersect the standard curve; at this intersection, a vertical line was dropped to the X-axis and the concentration is read from the X-axis as shown in (Table 1 and Fig. 4).

Toluene concentration (%)

Absorbance from spectrophotometer (nm)

0 0

5 0.635

10 1.21

15 1.48

20 1.78

2

Absorbance

Absorbance

1.5

1

0.5

y = 0.088x + 0.14 R² = 0.963

Fig. 3. The different magnification of TiO2 nanoparticles (a), (b) FESEM images (c), (d)

TEM images

0

0 5 10 15 20 25

Concentration

The photo reduction of toluene in the absence

and presence of TiO2 is shown in Table 2. It is

observed that the concentration of toluene is constant and unchanged under sunlight irradiation in the absence of TiO2. However in the presence TiO2 nanoparticles, toluene was found be degraded after 20 min of exposure to sunlight irradiation. The addition of titanium oxide nanoparticles has enhanced degradation of toluene within 20

minutes, and 37. 8% of the toluene was degraded. If the system was not exposed to sunlight irradiation, the toluene reduction was only about 26.6% (Fig. 5). The results illustrated that

illumination energy is significant in determining the toluene degradation 6.

40

35

30

Degradation

Degradation

25

20

15

10 5 (%) with Sunlight

10(%) with Sunlight

5 15(%) with Sunlight

5(%) without Sunlight

0

0 50 100 150

Time (min)

Fig. 5. The degradation for TiO2 at various time intervals

The overall findings of this study are very attractive as titanium dioxide exhibits excellent photo catalytic activity. From the experiments performed it clearly shows that TiO2 prepared are far more superior in terms of performance and robustness. A series of batch experiments were performed in two conditions; titanium dioxide with and without sunlight. The light energy seems to be vital in oil degradation, as it has significant inference on the photo catalytic activity. As it is visible, with the increasing amount of toluene in solution the effects of photo catalytic activity for degradation also decreased. The overall finding shows that the effect of titanium dioxide on degradation line slopes of toluene. The increment of toluene from 5 to 10 and 10 to 15 percent degradation had declined from 22.1 to 18.1 and

18.1 to 16.3 in 20 minutes of sunlight exposure time, also without sunlight exposure is from 15.1 to 12.2 and from 12.2 to 9.9 respectively.

1. Adolf K.Y. Ng, Su Song, The environmental impacts of pollutants generated by routine shipping operations on ports, Ocean & Coastal Management, 53 (2010) 301-311.

2. Akira Fujishima, Xintong Zhang, Donald. A. Tryk, Heterogeneous photocatalysis: From water photolysis to applications inenvironmental cleanup, International Journal of Hydrogen Energy, 32 (2007) 2664 2672.

3. Bullen, H. A, and S. J. Garrett, TiO2 nanoparticle arrays prepared using a nanosphere lithography technique, NANO LETTERS, 2 (2002)739-745.

4. Cao, L., Z. Gao, S. L. Suib, y. S. O. H. Timothy N. Obee and J. D. Freihaut, Photocatalytic oxidation of toluene on nanoscale TiO2 catalysts: studies of deactivation and regeneration." Journal of Catalysis, 196 (2000) 253261.

5. Hsu, Y.-Y., T.-L. Hsiung, H. P. Wang, Y. Fukushima, Y.-L. Wei and J.-E. Chang, Photocatalytic degradation of spill oils on TiO2 nanotube thin films, Marine Pollution Bulletin, 57 (2008) 873876.

6. Idris, A., N. Hassan, N. S. Mohd Ismail, E. Misran,

   N. Mohd Yusof, A. F. Ngomsik and A. Bee, Photocatalytic magnetic separable beads for chromium(VI) reduction, Water research, 44 (2010)1683-1688.

7. Jim Van Durme, Jo Dewulf, Christophe Leys, Herman Van Langenhove, Combining non-thermal plasma with heterogeneous catalysis in waste gas treatment: A review, Applied Catalysis B: Environmental, 78 (2008) 324333.

8. Nick Serpone, Relative photonic efficiencies and quantum yields in heterogeneous photocatalysis, Journal of Photochemistry and Photobiology A: Chemistry, 104 (1997) 1-12.

9. O. Zielinski, D. Voß, B. Saworski, B. Fiedler, A. Körtzinger, Computation of nitrate concentrations in turbid coastal waters using anin situ ultraviolet spectrophotometer, Journal of Sea Research, 65 (2011) 456460.

10. Sang-Keun Song, Zang-Ho Shon, Yoo-Keun Kim, Yoon-Hee Kang, Ki-Hyun Kim, An oil spill accident and its impact on ozone levels in the surrounding coastal regions, Atmospheric Environment, 45 (2011) 1312- 1322.

11. S K Jain , N D Mathur, T K Pushpakaran and P Kumawat, Assembly and use of Permanent secondary standards for calibration of Infrared spectrophotometer for determination of isotropic purity of nuclear grade heavy water, Journal of Scientific & Industrial Research, 58 (1999) 861-863.

12. Roger I. Bickley, Heterogeneous photocatalysis at liquidsolid interfaces. Oxidative dehydrogenation of propan-2-ol as a method of assessing photocatalytic activity, Journal of Photochemistry and Photobiology A: Chemistry, 216 (2010) 256260.

13. Wang, Z., M. Fingas and D. S. Page, Oil spill identification, Journal of Chromatography A, 843 (1999)369411.

14. Xander Van Doorslaera, Kristof Demeesterea, Philippe M. Heynderickxa, Marieke Caussyn, Herman Van Langenhove, Frank Devlieghereb, An Vermeulen, Jo Dewulfa, Heterogeneous photocatalysis of moxifloxacin: Identification of degradation products and determination of residual antibacterial activity, Applied Catalysis B: Environmental, 138 139 (2013) 333-341.

15. Zhao, H., W. Fu, H. Yang, Y. Xu, W. Zhao, Y. Zhang, H. Chen, Q. Jing, X. Qi, J. Cao, X. Zhou and Y. Li, Synthesis and characterization of TiO2/Fe2O3 core shell nanocomposition film and their photoelectrochemical property, Applied Surface Science, 257 (2011)8778 8783.