FIELD OF INVENTION

This invention relates to the development of a nano sized N-doped TiO2 photo catalyst and capable of removing insecticides like methyl parathion, dichlorvos and lindane under solar radiation, which is commonly present in the drinking water sources. The N-doped TiO2 is capable of removing microorganisms as well. The immobilized N-doped TiO2 can be reused for several times without regeneration. The material has high photo catalytic activity and stay stable even under prolonged exposure to water.

PRIOR ART:

The uncontrolled use of pesticides all over the world has led to the pollution of all compartments of the environment with pesticide residues. Several organochlorine and organophosphorous pesticides like Methyl parathion (0,0-dimethyl-0-4-nitrophenyl phosphorothioate), dichlorvos (2,2- dichlorovinyl-0-O-dimethyl phosphate) and lindane (1a,2a,3p,4a,5a,6p-hexachloro cyclohexane) are the most commonly used insecticides in India for increasing agricultural productivity. Because of their widespread use, they are detected in various environmental matrices such as soil, water and air. Most of these pesticides are known to resist biodegradation and therefore they can be concentrated through food chain. Sankararamakrishnan, N. Sharma, A. K. Sanghi, R. Organochlorine and organophosphorous pesticide residues in groundwater and surface waters of Kanpur, Uttar Pradesh India. Environment International. 2005, 31, 113-120. Even when present in small quantities, their variety, toxicity and persistence have an adverse effect on ecological systems such as birds, fish and trees with which human welfare is inseparably bound. Gupta, P.K., Pesticide exposure Indian scene. Toxicology, 2004, 198(1-3), 83-90. They are ubiquitous and found even in the most remote areas, far from any industrial activity. Li, Y.F. Macdonald, R.W. Sources and pathways of selected organochlorine pesticides to the Artic and the effect of pathway divergence on the HCH trends in biota: A review. Science of the Total Environment, 2005 342, 87-106. Direct applications of insecticides, rain water runoff from agricultural systems, disposal of out dated stocks and discharge of wastewater from industries are the major sources of insecticides contamination in water bodies in India. However, leaching from agricultural fields is the single and most important non-point source of pollution to the aquatic environment.

PESTICIDES CONTAMINATION PROBLEMS IN INDIA

LINDANE

In India, unsystematic and indiscreet use of organochlorine pesticides has led to the contamination of water bodies, rivers and estuarine bodies. Lindane concentrations in the range of 10-100 ng/L have been reported in major rivers in north India. Guzzella, L. Roscioli, C. Vigano, L. Saha, M. Sarkar, S.K. Evaluation of the concentration of HCH, DDT, HCB, RGB and PAH in the sediments along the lower stretch of Hugli estuary. West Bengal, northeast India Bhattacharya. Environment International, 2005, 31(4), 523-534. Lindane (259 ng/L) and malathion (2618 ng/L) were detected in surface water samples collected from the river Ganges. Sankararamakrishnan, N. Sharma, A. K. Sanghi, R. Organochlorine and organophosphorous pesticide residues in groundwater and surface waters of Kanpur, Uttar Pradesh India. Environment International, 2005, 31, 113-
120. Concentrations of organochlorine residues in water and sediment samples of river Gomti ranged between 2.16-567.49 ng/L and 0.92-813.59 ng/g, respectively. Malik, A. Singh, K. P. Ojha, P. Residues of organochlorine pesticides in fish from the Gomti River, India. Bulletin of Environmental Contamination and Toxicology, 2007, 78(5), 335-340. Out of top five brands and other less popular brands of packed drinking water have been tested by Centre for Science and Environment (CSE) 2003, India for 12 organochlorine pesticides and 8 organophosphorus pesticides, most of the bottled water samples were contaminated with pesticide residues. A seven year study of pesticide residues in milk in 12 Indian states was studied by Indian Council of Medical Research and they found that a high proportion of milk samples of human and others had residues of HCH and DDT. The occurrence and distribution of y-hexachloro-cyclohexane (y-HCH) was studied in vegetation samples of a highly contaminated area in Lucknow. y-HCH was present in all samples in the concentration ranges of 1-9 ng/g. Abhilash, P.C. Jamil, S. Vandana, S. Amita, S. Nandita, S. Srivastava, S.C. Occurrence and distribution of hexachloro-cyclohexane isomer in vegetation sample from a contaminated area. Chemosphere, 2008, 72(1), 79-86

METHYL PARATHION

Methyl parathion is an organophosphorus pesticide widely used for agricultural purposes and due to its low environmental persistence and strong biocidal properties; methyl parathion is used on almost 70 different crops including vegetables, fruits and cereals. Amaya-Chavez, A. Martinez-Tabche, L. Lopez-Lopez, E. Galar-Martinez, M. Methyl parathion toxicity to and removal efficiency by Typha latifolia in water and artificial sediments. Chemosphere, 2006, 63(7), 1124-129. Pesticide contamination of fields, crops, water and air occurs through off-target spraying as a consequence of agricultural and forestry activities. Guzzella, L. Roscioli, C. Vigano, L. Saha, M. Sarkar, S.K. Evaluation of the concentration of HCH, DDT, HCB, PCB and PAH in the sediments along the lower stretch of Hugli estuary, West Bengal, northeast India Bhattacharya. Environment International, 2005, 31(4), 523-534. Twelve samples each of soil and groundwater were collected from paddy-wheat, paddy-cotton, sugarcane fields and tube wells from fields around Hisar, Haryana, India during 2002-2003 to monitor pesticide residues. Among organophosphorus pesticides, chlorpyriphos (2-172 ng/g), methyl parathion (2-8 ng/g) and quinalphos (1-10 ng/g) were detected. Kumari, B. Madan, V. K. Kathpal, T. S. Status of insecticide contamination of soil and water in Haryana, India. Environmental Monitoring and Assessment, 2008,136, 1-3.

DICHLORVOS

Dichlorvos is an organophosphorous insecticide. Since 1961, it has been commercially manufactured and used throughout the world. Dichlorvos breaks down rapidly by both a-biotic and biotic processes in humid air, water and soil. It may persist for a longer time (39 % remaining after 33 days) on hard dry surfaces such as wood. Ural, M.S. Calta, M. Acute toxicity of dichlorvos (DDVP) to fingerling mirror carp, Cyprinus carpio L. Bulletin of Environmental Contamination Toxicology, (2005), 75(2), 368-373. Dichlorvos degrades mainly to dichloroethanol, dichloroacetaldehyde, dichloroacetic acid, dimethylphosphate, dimethylphosphoric acid and other water-soluble compounds which are eventually mineralized. Dwivedi, N. Bhutia, Y. D. Kumar, V. Yadav, P. Kushwaha, P. Swarnkar, H. Flora, S. J.S. Effects of combined exposure to dichlorvos and monocrotophos on blood and brain biochemical variables in rats. Human and Experimental Toxicology, (2010), 29(2), 121-129.

REMEDIAL MEASURES

Different treatment technologies are available for removing pesticide contamination from surface and groundwater. Among these techniques, advanced oxidation technique (AOP) such as photo oxidation is most effective because it does not leave any by-products and pesticide residue in the system and it is very effective in low concentration of pesticides. Chiron, S. Fernandez-Alba, A. Rodriguez, A. Garcia-Calvo, E. Pesticide chemical oxidation: state-of-the-art. Water Research, (2000), 34(2), 366-377. Several researchers have tried the degradation of methyl parathion, dichlorvos and lindane from drinking water sources using TiO2 under UV light. Senthilnathan, J. Philip, L. Removal of mixed pesticides from drinking water system by photodegradation using suspended and immobilized TiO2, Journal Environmental Science and Health-Part B, (2009) 44, 262-70. Dionysiou, D.D. Khodadoust, A.P. Kern, A.M. Suidan, M.T. Baudin, I. Laine, J.M. Continuous mode photocatalytic degradation of chlorinated phenols and pesticides in water using a bench scale TiO2 rotating disk reactor. Applied Catalyst B: Environment, (2000) 24, 139-155. Evgenidou, E. Konstantinou, I. Fytianos, K. Pouliosc, I. Albanisd, T. Photocatalytic oxidation of methyl parathion over TiO2 and ZnO suspension. Catalysis Today, (2007), 124(3-4), 156-162. Evgenidou, E. Konstantinou, I. Fytianos, K. Albanis, T. Study of the removal of dichlorvos and dimethoate in a titanium dioxide mediated photocatalytic process through the examination of intermediates and the reaction mechanism. Journal of Hazardous Materials, (2006), B137, 1056-1064. Although advanced oxidation process with TiO2 photo catalysts have been shown to be an effective alternative in this regard, the vital snag of TiO2 semiconductor is that it absorbs a small portion of solar spectrum in the UV region (band gap energy of TiO2 is 3.2eV). To utilize maximum solar energy, it is necessary to shift the absorption threshold towards visible region. Chatterjee, D. Mahata, A. Evidence of superoxide radical formation in the photodegradation of pesticide on the dye modified TiO2 surface using visible light. Journal of Photochemistry and Photobiology A: Chemistry, (2004), 165, 19-23. Asahi, R. Morikawa, T. Ohwaki, T. Aoki, K. Taga, Y. Visible-Light photocatalysis in nitrogen-doped titanium oxides. Science, (2001), 293, 269-271. Only a few studies have been reported on degradation of methyl parathion, dichlorvos and lindane under solar
radiation. Vidal, A. Developments in solar photocatalysts for water purification. Chemosphere, 1998, 36(12), 2593-2606. Shifu, C. Gengyu, C. Photocatalytic degradation of organophosphorus pesticides using floating photocatalyst TiO2:Si02/beads by sunlight. Solar Energy, 2005, 79, 1-9.

PHOTODEGRADATION OF ORGANIC POLLUTANTS USING N-DOPED TIO2 UNDER VISIBLE AND SOLAR RADIATION

TiO2 absorption towards the visible light with non-metallic elements such as nitrogen (N), sulphur (8), carbon (C) and phosphorus (P) has been reported by many researchers (Ohno et al., 2004; Sato et al., 2005; Kobayakawa et al., 2005; Chen et al., 2005; Valentin et al., 2007; Kitano et al., 2007; Nishijima et al., 2007; Liu et al., 2009; Dong et al., 2010). Asahi et al. (2001) were the first to show an absorption increase in the visible region upon nitrogen doping. This opened the way to study TiO2 doping with non-metallic elements. Asahi et al. (2001) have reported that the insertion of N or S atoms on TiO2 produces localized states within the band gap just above the valence band. Thus, when N or S doped TiO2 is exposed to visible light, electrons are promoted from these localized states to the conduction band (Valentin et al., 2007). The substitutional (N-Ti-0) doping of N was most effective compared to S, P and C. This is because N p states contribute to the band-gap narrowing by mixing with O 2p states (Xing et al., 2009; Ashai et al., 2001).

a) Asahi, R. Morikawa, T. Ohwaki, T. Aoki, K. Taga, Y. Visible light photocatalysis in nitrogen-doped titanium oxides. Science, 2001, 293,269-271.

b) Chen, X. Lou, Y. Samia, A.C.S. Burda, C. Cole, J.L. Formation of oxinitride as the photocatalytic enhancing site in nitrogen doped titania nanocatalysts: Compare to a commercial nano powder. Advanced Functional Materials, 2005 15, 41- 49.

c) Dong, F. Wang, H. Wu, Z. Qiu, J. Marked enhancement of photocatalytic activity and photochemical stability of N-doped TiO2 nanocrystals by Fe3+ VFe2+ surface modification. Journal of Colloid and Interface Science, 2010, 343(1), 200-208.

d) Kitano, M. Matsuoka, M. Ueshima, M. Anpo, M. Recent developments in titanium oxide-based photocatalysts. Applied Catalyst A: General, 2007, 325, 1-14.

e) Kobayakawa, K. Murakami, Y. Sato, Y. Visible-light active N-doped TiO2 prepared by heating of titanium hydroxide and urea. Journal of Photochemistry and Photobiology A: Chemistry, 2005,170, 177-179.

f) Liu, S. Yang, L. Xu, S. Luo, S. Cai, Q. Photocatalytic activities of C-
N-doped TiO2 nanotube array/carbon nanorod composite. Electrochemistry Communications, 2009,11(9), 1748-1751.

g) Nishijima, K. Ohtani, B. Yan, X. Kamai, T. Chiyoya, T. Tsubota, T. Murakami, N. Ohno, T. Incident light dependence for photocatalytic degradation of acetaldehyde and acetic acid on S-doped and N-doped TiO2 photocatalysts. Chemical Physics, 2007, 339(1-3), 64-72.

h) Ohno, T. Akiyoshi, M. Umebayashi, T. Asai, K. Mitsui, T. Matsumura, M. Preparation of S-doped TiO2 photocatalysts and their photocatalytic activities under visible light. Applied Catalyst A: General, 2004, 265, 115-121.

i) Sato, S. Nakamura, R. Abe, S. Visible-light sensitization of TiO2
photocatalysts by wet method N doping. Applied Catalyst A: General, 2005, 284, 131-137.

j) Valentin, C. D. Finazzi, E. Pacchioni, G. Selloni, A. Livraghi, S. Paganini, M. C. Giamello, E. N-doped TiO2: Theory and Experiment. Chemical Physics, 2007, 339, 44-56.

k) Xing, M. Zhang, J. Chen, F. New approaches to prepare nitrogen-doped TiO2 photo catalysts and study on their photo catalytic activities in visible light. Applied Catalyst B: Environment, 2009, 89, 563-569.

Xing et al. (2009) have reported that N-doped TiO2 synthesized using ammonium nitrate and ammonia as nitrogen sources showed maximum photocatalytic activity for the degradation of 2,4-dichlorophenol (initial concentration 100 mg/L) within 5 h of irradiation under visible light. Xing, M. Zhang, J. Chen, F. New approaches to prepare nitrogen doped TiO2 photocatalysts and study on their photocatalytic activities in visible ligHt. Applied Catalyst B: Environment, 2009, 89, 563-569. Ananpattarachai et al. (2009) have reported that the degradation of 2-chlorophenol (initial concentration 25mg/L) using N-doped TiO2 under visible light followed pseudo first order reaction and complete degradation was achieved within 50 min of irradiation. Ananpattarachai, J. Kajitvichyanukul, P. Seraphin, S. Visible light absorption ability and photocatalytic oxidation activity of various interstitial N-doped TiO2 prepared from different nitrogen dopants. Journal of Hazardous Materials, 2009, 168, 253-261. Similar study was conducted by Cong et al. (2007) with 2, 4-dichlorophenol (lOOmg/L) and rhodamine B (20mg/L) using N-doped TiO2 under visible light and complete degradation was obtained within 5h and 1h of irradiation, respectively. Cong, Y. Zhang, J. Chen, F. Anpo, M. Synthesis and characterization of nitrogen doped TiO2 nanophotocatalyst with high visible light activity. Journal of Physical Chemistry C, 2007, 111, 6976-6982. Huan et al. (2007) have studied the decomposition of 4-chlorophenol (13 mg/L) using N-doped TiO2 under visible light and achieved 63.5% degradation within 6h of irradiation time. Huan, Y. Xuxu, Z. Zhongyi, Y. Feng, T. Beibei, F. Keshan, H. Preparation of nitrogen-doped TiO2 nanoparticle catalyst and its catalytic activity under visible light. Chinese Journal of Chemical Engineering, 2007, 15, 802-807. Kun et al. (2009) have studied the photocatalytic activity of phenol (0.5mM/L) under visible light with N-doped TiO2 and found that acid treated N-doped TiO2 showed higher catalytic activity within 2h of irradiation. Kun, R. Tarjan, S. Oszko, A. Seemann, T. Zollmer, V. Busse, M. Dekany, I. Preparation and characterization of mesoporous N-doped and sulfuric acid treated anatase TiO2 catalysts and their photocatalytic activity under UV and visible illumination. Journal of Solid State Chemistry, 2009, 182, 3076-3084.

PRIOR ART RELATED TO PESTICIDES REMOVAL BY N-DOPED TIO2 UNDER VISIBLE AND SOLAR RADIATION

a) Sathish, M. Viswanathan, B. Viswanath, R.P. Characterization and photocatalytic activity of N-doped TiO2 prepared by thermal decomposition of Ti-melamine complex. Applied Catalyst B: Environment, 2007, 74, 307-312.

b) Michalow, K. A. Logvinovich, D. Weidenkaff, A. Amberg, M. Fortunate, G. Heel, A. Graule, T. Rekas, M. Synthesis, characterization and electronic structure of nitrogen-doped TiO2 nano powder. Catalyst Today, 2009, 144, 7-12.

c) Wu, Z. Dong, F. Zhao, W. Guo, 8. Visible light induced electron transfer process over nitrogen doped TiO2 nano crystals prepared by oxidation of titanium nitride. Journal Hazard Materials, 2008, 157, 57-63.

d) Chen, 8. Zhang, P. Zhuang, D. Zhu, W. Investigation of nitrogen doped TiO2 photocatalytic films prepared by reactive magnetron sputtering. Catalyst Communication, 2004, 5, 677-680.

e) Zuyuan, W. Fuxiang, Z. Yali, Y. Jie, C. Qing, 8. Naijia, G. One-pot synthesis of visible-light-responsive TiO2 in the presence of various amines. Chinese Journal of Catalysis, 2006, 27, 1091-1095.

f) Yu, J. Wang, J. Zhang, J. He, Z. Liu, Z. Ai, X. Characterization and photoactivity of TiO2 sols prepared with tri-ethylamine. Materials Letters, 2007, 61, 4984-4988.

DESCRIPTION OF THE INVENTION:

In the following, we present the synthesis, characterization and water purification applications of a nano sized N-doped TiO2 prepared by sol-gel process. The process of synthesis was conducted by hydrolysis of titanium tetraisopropaxide in acid and base medium. The nitrogen doping was carried out with ethylamine, urea, triethylamine and ammonium hydroxide in alcohol medium. The nature of N doping in TiO2 lattice was established with different advanced instruments like X-ray diffraction (XRD), semi electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectrometer (XPS) and UV-visible spectrometer. The uptake test results of a few contaminants like methyl parathion, dichlorvos and lindane from drinking water by immobilized N-doped TiO2 using batch and continuous reactor under solar radiation were presented. However, the result presented here should not be construed as limiting the scope of the invention.

ANALYTICAL METHODS

Concentrations of methyl parathion, dichlorvos and lindane were analyzed by using Perkin Elmer Clarus 500 gas chromatograph (GC), with electron capture detector (GC/ECD) equipped with auto-sampler, an on-column, split/split less capillary injection system and with Perkin Elmer (PE)-5 capillary column. The intermediates formed during the degradation of methyl parathion, dichlorvos and lindane were monitored using a GC-MS, supplied by Agilent, USA. The mineralized end products of NO3-', S042- PO43- and or ions formed during the degradation of methyl parathion dichlorvos and lindane were analyzed using Ion Chromatography (IC) supplied by Dionex, USA, with Electro Chemical Detector (ED 50).

MATERIAL CHARACTERIZATION

Crystalline structure modification of doped and undoped TiO2 was examined by X-ray diffraction (XRD) analysis using Copper K alpha radiation with Lynx detector at an operating voltage of 35 kV and current of 25 milliamps, supplied by Bruker-Axs, USA (model D8 Discover). Varian Cary-5E UV-VIS-NIR, Scan range 185-3000nm (UV-VIS-NIR) high resolution spectrophotometer was used to find the UV and visible light absorption pattern of anatase and doped TiO2. The surface morphology and crystalline size of doped and undoped TiO2 was monitored using a scanning electron microscope (SEM), equipped with a field emission gun (JEOL, JSM-6380, Japan) and high resolution transmission electron microscopy (HRTEM) using JEOL 3010 UHR instrument. The effective particle size of N-doped TiO2 was monitored by using particle size analyzer, supplied by Brookhaven Instrument Corporation, Model 90 Plus, USA. This can be detecting the particles between the sizes of 3 microns and 1 nm. X-ray photoelectron spectroscopy (XPS) measurements were carried out using an Omicron Nanotechnology spectrometer with polychromatic Al KaX-rays (hv=1486.6eV). Binding energy (BE) was calibrated with respect to C-1s (285.OeV). The Raman spectrum and corresponding imaging were carried out using a Witec Gmb Hconfocal, Raman spectrometer equipped with 514.5 and 532 nm sources with a spot size <1 μ m.

SPECIFICATION AND OPERATING CONDITIONS OF BATCH AND CONTINUOUS REACTORS

Photodegradation of methyl parathion, dichlorvos and lindane were carried out In both batch and continuous reactors under solar radiation. Oxygen flow rate of 300 mL/min and a stirring rate of 150 rpm were maintained in all the batch reactor experiments. 200 mg/L of N-doped TiO2 used for batch reactor in suspended form for all the experiments. The length and width of the continuous reactor was 80 cm and 30 cm, respectively, with an effective length of 74 cm separated by glass plates of 0.6 cm height and 0.5 cm width. The effective volume of the reactor was 1350 cm2 . Four glass plates (30 cm wide and 18.2 cm long) were used for coating photocatalyst. After coating, the plates were placed inside the continuous reactor. Samples were collected at regular intervals from continuous photo reactor, extracted with HPLC grade hexane and analyzed for residual pesticide concentrations using GO. A flow rate of 12.5 mL/min and residence time of 108 min was maintained in all the studies in the continuous reactor. Experiments on photo degradation of pesticides under solar radiation were carried out between 10.00 am and 4.00 pm during the month of April and May, 2010. The solar radiation pattern was monitored by using solar sensor (Pyranometer) supplied by Environment S.A., France.

PHOTODEGRADATION OF PESTICIDES UNDER VISIBLE AND SOLAR RADIATION

Photodegradation of commercial grade methyl parathion, dichlorvos and lindane were carried out using N-doped TiO2 under solar radiation. Commercial grade 2,2-dichlorovinyl dimethyl phosphate (DDVP) 76% EC contains 83% w/w of dichlorvos, 8% w/w xylene, 1% w/w epichlorohydrin, 7% w/w emulsifier, 0.9% w/w triethanolamine and 0.1% w/w methylene blue. Similarly, 50% w/w of methyl parathion is present in Folidon 50% E.C and remaining 50% is constituted by adjuvant, emulsifier, stabilizer, solvent and other fillers. Technical grade lindane contains 90% w/w of HCH isomers and remaining 10% w/w are fillers. Commercial grade and technical grade of methyl parathion, dichlorvos and lindane were standardized against pure methyl parathion, dichlorvos and lindane and were used for degradation studies. The photodegradation studies of methyl parathion, dichlorvos and lindane were carried out by using three different concentrations such as 50, 100 and 250 μ g/L of each pesticide. The samples were collected at regular interval of time for GC-MS analysis using syringe filter. The degradation pattern of each pesticide and intermediates formed during the reaction were identified. The samples were collected at regular intervals of time using syringe filter and extracted with n-Hexane. The organic phase was used for GC-MS analysis and aqueous phase was used for the ion chromatography (IC) analysis.

PHOTODEGRADATION OF MIXED PESTICIDES WITH BATCH AND CONTINUOUS REACTOR

Mixed pesticides degradation studies were carried out by using commercial grade of methyl parathion (purity 50%), dichlorvos (purity 70%) and lindane (purity 90%). Two different concentrations of (50 μ g/L and 250 μ g/L) mixed pesticides were used for batch and continuous reactor. For batch reactor 50 μ g/L concentration of each pesticide and total concentration of 150 μ g/L were used. Similarly, for 250 μ g/L concentration of mixed pesticides, 83.33 μ g/L concentrations of each pesticide were taken for continuous reactor.

EXAMPLE 1

This example describes the preparation of N-doped TiO2 (non metal doped TiO2) was carried out by the hydrolysis of titanium isopropoxide. 2.4 mL of titanium isopropoxide was dissolved in 20mL ethyl alcohol and suitable ratio of nitrogen containing organic compounds (ethylamine, urea, triethylamine and ammonium hydroxide) was added to it. 20 mL of 0.1 M of HCI was added to the above solution and stirred to get a clear yellow. The above solution was autoclaved at 80°C for 12h. The suspension was centrifuged at 8000 rpm and residue was dried at 100°C. The dried sample was calcined at 550°C for 4h. The characterization studies were carried out to find nature of doping and particle size of N-doped TiO2.

EXAMPLE 2

Four glass plates with a width of 30 cm and a length of 18.2 cm were used for immobilizing the photocatalyst for the continuous thin film photoreactor. Before coating, the surfaces of the glass plates were treated with 5 % (v/v) hydrofluoric acid for 30 min to get a rough surface and washed with distilled water. The glass plate coating was carried out using N-doped T1O2. N-doped TiO2 and isopropanol suspension (1 % solution) were used for the coating of all the four plates. Before coating, the suspension was sonicated for 15 min. The glass plate was inserted slowly into the sonicated suspension and allowed to stay in the suspension for 1 min. The coated catalyst was taken out and dried in an oven for 30 min at 150°C. This procedure was repeated for each plate.

EXAMPLE 3

The effect of nitrogen concentration on photocatalytic activity of TiO2 modified with triethylamine was investigated. The nature of doping of nitrogen in to the crystal lattice of anatase TiO2 was examined using XPS, XRD and Raman spectrometer. The SEM and HRTEM analysis of N-doped TiO2 was used to find the surface morphology particle size of N-doped TiO2.The reduction in band gap energy of N-doped TiO2 was monitored using UV-visible absorption spectrometer. The change in surface area of anatase TiO2 before and after nitrogen doping was monitored.

EXAMPLE 4

This example is to show that the N-doped TiO2 as-synthesized material is capable of removing pesticides from water in both single and mixed pesticide condition. The batch and continuous photo reactor with N-doped TiO2 were capable of bring down the pesticides concentration to the permissible limits recommended by the European (0.5 μ g/L) and Indian standard (1.0 μ g/L) under solar radiation. The coated N-doped TiO2 with continuous photo reactor was repeatedly used for several cycles in continuous reactor and with out loss of photo catalytic activity. The photo degradation of mixed pesticides (methyl parathion, dichlorvos and lindane) was carried out in batch and continuous reactor under solar radiation. Complete mineralization was observed for all the three pesticide in batch continuous reactor under solar radiation.

DESCRIPTION WITH REFERENCE TO DRAWINGS AND TABULATED DATA:

Flgure.1 Schematic diagram of photo reactor
1) Water circulating pump, 2) oxygen cylinder, 3) Organic solvent, 4) cooling water inlet, 5) cooling water outlet, 6) purging gas outlet, 7) oxygen gas inlet , 8) sample collection port, 9) condenser, 10) UV lamp, 11) coated Pyrex tube, 12) oxygen gas inlet, 13) magnetic pellet, and 14) O2 gas regulator

Figure.2 Solar energy patterns for the months of April and May, 2010

Figure.3 Kinetics of methyl parathion degradation by N-doped TiO2 prepared using various nitrogen containing organic compounds (Initial methyl parathion concentration = 100 μ g/L; oxygen purging rate = 300 mL/min, doping concentration = 1:2 molar ratio of N/Ti)

Figure.4 UV-Visible absorption of N-doped TiO2 (N-doped TiO2 ratios = 1:1.2 and 1:1.6)

Figure.5 XRD for analysis of N-doped TiO2 and anatase TiOa (N-doped TiO2 ratio = 1:1.6)

Figure.6 SEM (A) TEM (B, C and D) analysis of N-doped TiO2 (N-doped TiO2 ratios = 1:0.8 and 1:1.6)

Flgure.7 Particle Size Analysis of N-doped TiO2 (DLS) (a) Particle dispersed with surfactant (b) Particle dispersed without surfactant

Figure.8 Raman spectrums of anatase and N-doped TiO2 (N-doped TiO2 = 1:1.6 ratio)

Figure.9 XPS of pure anatase and N-doped TiO2 nano-particles (N-doped TiO2 ratios = 1:0.8 and 1:1.6)

Figure.10 Kinetics of photodegradation of various concentrations of methyl parathion using N-doped TiO2 under solar radiation (Methyl parathion 50, 100 and 250 μ g/L; 200 mg/L of 1:1.6 ratio of N doped TiO2; oxygen purging flow rate = 300 mL / min)

Flgure.11 Kinetics of photodegradation of various concentrations of dichlorvos using N-doped TiO2 under solar radiation (dichlorvos 50, 100 and 250 μ g/L; 200 mg/L of 1:1.6 ratio of N doped TiO2; oxygen purging flow rate = 300 mL/min)

Figure.12 Kinetics of photodegradation of various concentrations of lindane using N-doped TiO2 under solar radiation (lindane = 50, 100 and 250 μ g/L; 200 mg/L of 1:1.6 ratio of N doped TiO2; oxygen purging rate = 300 mL/min)

Figure.13 Kinetics of photodegradation of mixed pesticides by N-doped TiO2 under solar irradiation (Co = 83.3 μ g/L each of lindane, methyl parathion and dichlorvos; TiO2 was used in suspension form; oxygen purging rate = 300 mL/min; stirring rate = 150 rpm).

Figure.14 Block diagram of thin film continuous photoreactor

Figure.15 Photodegradation of mixed pesticides under UV and visible light with continuous photoreactor (pesticides concentration 50 μ g/L each; total reaction time 24 h; Degussa P-25 TiO2 used under UV light; N-doped TiO2 used under visible light; sample collected after 110 min of retention time and monitored every 120 min)

DETAILED DESCRIPTION WITH REFERENCE TO DRAWINGS AND TABULATED DATA:

The batch photoreactor for the degradation of methyl parathion, dichlorvos and lindane with suspended and immobilized N-doped TiO2 is given in Figure 1. Solar radiation pattern was monitored in the month of April and May, 2010 from 6.00 am to 4.00 pm and their radiation patterns are given in Figure.2. These experiments were carried out on all the days of April, 2010 except 6th and 15th. On these two days, the maximum radiation recorded was 851.47 and 872.46 W/m2 , respectively. The maximum radiation of more than 1000 W/m2 was recorded on all the 28 days in the month of April, 2010. Similarly in the month of May, 2010, minimum solar radiation recorded on 16th 17th 18th 19th and 20th were 950, 852, 516, 482 and 570 W/m2 respectively. On remaining days, solar radiation more than 1000 W/m2 was recorded. There was not much variation in the minimum and average solar radiation pattern.

N-doped TiO2 was prepared using triethylamine, urea, ethylamine and ammonium hydroxide by sol-gel process. Photodegradation studies were carried out with methyl parathion (100 μ g/L), dichlorvos (100 μ g/L) and lindane (100 pg/L) by using N-doped TiO2 prepared by different nitrogen containing compounds and the performances were compared. The photodegradation methyl parathion with different N containing organic compound are given in Figure.3. Photocatalytic activity was much higher for triethylamine doped TiO2 as compared to urea, ethyl amine and ammonium hydroxide doped TiO2 for all the three pesticides. Similar trend was reported by other researchers also. Ananpattarachai, J. Kajitvichyanukul, P. Seraphin, S. Visible light absorption ability and photocatalytic oxidation activity of various interstitial N-doped TiO2 prepared from different nitrogen dopant. Journal of Hazardous Materials, (2009), 168, 253-261. Cong, Y. Zhang, J. Chen, F. Anpo, M. Synthesis and characterization of nitrogen doped TiO2 nano photo catalyst with high visible light activity. Journal of Physical Chemistry C, (2007), 111, 6976-6982. Yu, J. Wang, J. Zhang, J. He, Z. Liu, Z. Ai, X. Characterization and photo activity of TiO2 sols prepared with tri-ethylamine. Materials Letters, (2007), 61, 4984-4988. Triethylamine doped TiO2 used for the rest of the studies.

UV-Vis absorption spectrum for N-doped TiO2 (1:1.2 and 1:1.6 ratio), were studied and the results are presented in Figure.4. The optical absorption edges of the N-doped TiO2 shifted to the lower energy region and the absorption of light in the wavelengths ranging from 400 to 600 nm was stronger after nitrogen doping. Furthermore, the absorption increased with increasing doping concentration from 1:1.2 to 1:1.6. Results also showed that band gap energies of N-doped TiO2 were lower than those of anatase TiO2. The reduction in the band gap energy of the N-doped TiO2 sample was determined by the following equation. O'Regan, B. Gratzel, M. A low cost, high-efficiency solar cell based on dye-sensitized colloidal TiOz films. Nature, (1991) 353, 737-740.

Eg = 1239.8/A (1)

Where Eg is the band gap (eV) and A is the wavelength (nm) of the absorption edge in the spectrum. The band gap was shifted from 3.20 eV to 2.84eV for (1:1.6 ratio) N-doped TiO2. This decrease in band width will enhance the transfer of electron from valance band to conduction band under visible light. This may be the reason for the better performance of N-doped TiO2 under visible and solar radiation.

X-ray diffraction patterns (XRD) for different ratio of N-doped TiO2 are presented in Figure.5. The N-doped TiO2 samples showed X-ray line broadening connpared to TiO2 samples, representing the formation of nano particles. The broadening of the XRD peaks is inversely proportional to the crystalline size of the N-doped TiO2 nano particles. Cong, Y. Zhang, J. Chen, F. Anpo, M. Synthesis and characterization of nitrogen doped TiO2 nano photo catalyst with high visible light activity. Journal of Physical Chemistry C, (2007), 111, 6976-6982. This indicates that N doping was introduced into the lattice of the TiO2 without altering the average unit cell dimension. Khan, S.U.M. Al-Shahry, M. Ingler, W.B. Efficient photochemical water splitting by a chemically modified n-TiO2. Science, (2002), 297, 2243-2245. Crystalline sizes of anatase TiO2 and N-doped TiO2 were determined using Scherrer equation. The values of (3 and G are taken for crystal plane (1 0 1) of anatase phase. The crystal grain size of anatase TiO2 was 70.3 nm and by adding the amount of N-doping into the TiO2 lattice, the crystallite size decreased to 25.4 nm. Cong, Y. Zhang, J. Chen, F. Anpo, M. Synthesis and characterization of nitrogen doped TiO2 nano photo catalyst with high visible light activity. Journal of Physical Chemistry C, (2007), 111, 6976-6982.

The particle size of N-doped TiO2 was further confirmed by SEM and TEM analysis. The SEM and TEM analysis of N-doped TiO2 are given in Figure. 6. SEM analysis showed the surface morphology of N-doped TiO2 and TEM analysis showed the particle size of N-doped TiO2 was in the range of 25 nm. The d space value of N doped TiO2 was 0.341 nm and it was very close to the d space (0.354nm) value of anatase TiO2. This clearly indicates nitrogen doping was not altering the crystalline structure of N-doped TiO2, whereas slight change in d space value was observed. The N-doped TiO2
nanoparticles in reaction solution can aggregate into larger particles. The effective particle size of N-doped TiO2 in solution can differ from the size measured initially with TEM analysis. Zhao, Y. Qiu, X. Burda, C. The effects of sintering on the photocatalytic activity of N-doped TiO2 nanoparticles. Chemistry Materials, (2008), 20, 2629-2636. Therefore, it is important to know the particle size and size distribution also in solution. Effective particle size of N-doped TiO2 was carried out with particle size analyzer. One portion of N-doped TiO2 sample was dispersed in water with surfactant (Tween 80) and another portion was dispersed in water with out surfactant. The effective particle size of N-doped TiO2 which dispersed in surfactant showed 191 nm, whereas N-doped TiO2 dispersed in water showed 384 nm. Veronovski, N. Andreozzi, P. La-Mesa, C. Sfiligoj-mole, M. Ribitsch, V. Use of Gemini surfactants to stabilize TiO2 P-25 colloidal dispersions, Colloid Polymer Science. (2011), 288, 387-394. The particle size analyses of N-doped TiO2 dispersed in surfactant and with out surfactant are given in Figure.7.

The Raman spectrum of TiO2 peaks visible over the 400-700 cm-1 range are characteristic of anatase and rutile crystalline structures. Tang, H. Prasad, K. Sanjinbs, R. Schmid, P. E. Levy, F. Electrical and optical properties of TiO2 anatase thin films. Journal of Applied Physics, (1994), 75, 2042-2047. Robert, T.D. Laude, L.D. Geskin, V.M. Lazzaroni, R. Gouttebaron, R. Micro Raman spectroscopy study of surface transformations induced by excimer laser irradiation of TiO2. Thin Solid Films, (2003), 440, 268-277. TiO2 of anatase crystalline structure shows six Raman active fundamental modes correspondingly at 144 cm-1 (Eg), 197 cm"'' (Eg), 397 cm-1 (Big), 518 cm''' (Aig+Big) and 640 cm-1 Eg) for crystalline anatase TiO2. For rutile TiO2, there are four Raman active modes at 144 cm-1 (Big), 448 cm-1 (Eg), 613 cnT^ (Aig) and 827 cnT^ (B2g), respectively. Robert, T.D. Laude, L.D. Geskin, V.M. Lazzaroni, R. Gouttebaron, R. Micro Raman spectroscopy study of surface transformations induced by excimer laser irradiation of TiO2. Thin Solid Films, (2003), 440, 268-277. The anatase TiO2 and N-doped TiOa displayed Raman vibrations at around 146 cm-1 199 cm-1 400 cm-1 519 cm-1 and 636 cm-1 All peaks were corresponding to anatase crystalline structure and no rutile peak was observed. Small peak shift was observed while comparing anatase TiO2 and N-doped TiO2. This is because of different crystalline sizes of the anatase and N-doped TiO2. The formation of 0-Ti-N bond in N-doped TiO2 does not lead to any new Raman band. Bernard, M. Deneuville, A. Thomas, O. Gergaud, P. Sandstrom, P. Birch, J. Raman spectra of TiN/AIN super lattices. Thin Solid Films, (2000), 380, 252-255. There could be a small change in the Raman vibration modes due to the partial replacement of O with N, which is too small to be detected. The Raman spectrum of anatase TiO2 and N-doped TiO2 (two different ratios) are given in Figure.8.

X-ray photoelectron spectrometer (XPS) analysis of for anatase TiO2 and N-doped TiO2 samples were examined for three areas of the XPS spectrum, the Ti 2p region near 460eV, the O 1s region near 530eV and the N Is region near 400eV. Most of the N Is binding energies are found in between 396eV and 408eV. Diwald, 0. Thompson, T.L. Zubkov, T.E. Goralski, G. Walck, S.D. Yates, J.T. Photochemical activity of nitrogen-doped rutile TiO2 (111) in visible light. Journal of Physical Chemistry B, (2004), 108, 6004-6008. However, the binding energy of the N 1s is highly dependent on the synthetic method used for the preparation of N TiO2 and N Is binding energies found around 396-397eV are attributed to substitutional N in Ti-N, while peaks at higher binding energies (400eV) as observed in the present study are usually ascribed to a generic interstitial site (0-Ti-N). Saha, N.C. Tomkins, H.C. Titanium nitride oxidation chemistry: An x-ray photoelectron spectroscopy study. Journal Applied Physics, (1992), 72, 3072-3079. This clearly indicates that the N-doped TiO2 prepared by sol-gel process in the present study did not have N-Ti-N form where as 0-Ti-N form was present in the catalyst. XPS analysis of anatase TiO2 and N-doped TiO2 (1:0.8 and 1:1.6 ratio) are given in Figure. 9. Both varieties (difference in T/N ratio) of N-doped TiO2 showed peak at 400eV after carbon correction. The peak at 400eV indicates the incorporation of N atoms in to the TiO2 lattice and it was observed that a peak towards 400 eV could be assigned to Ti bound to O or to the 0-Ti-N formation. Chen, X. Lou, Y. Samia, A.C.S. Burda, C. Cole, J.L. Formation of oxinitride as the photocatalytic enhancing site in nitrogen doped titania nanocatalysts: Compare to a commercial nano powder. Advanced Functional Materials, (2005), 15, 41-49. From the above observations, it can be concluded that the chemical states of the nitrogen doped into TiO2 may be various and coexist in the form of N-Ti-0 and Ti-O-N.

Photodegradation of methyl parathion, dichlorvos and lindane were carried out with suspended form of N-doped TiO2 batch reactor and photodegradation were carried out with three different concentrations 50, 100 and 250 μ g/L under solar radiation. The experiments was carried out only for 300 min reaction time as effective solar radiation was available only for 6 h i.e., from 10 am to 4 pm as mentioned earlier. Complete degradation of methyl parathion was obtained within 45, 75 and 105 min for 50,100 and 250 μ g/L concentrations, respectively. Complete degradation of dichlorvos was obtained within 20, 35 and 50 min for 50, 100 and 250 μ g/L concentrations, respectively. Similarly, complete degradation of lindane was achieved for 50, 100 and 250 μ g/L within 145, 275 and 450 min respectively. The photodegradation of methyl parathion, dichlorvos and lindane under solar radiation with N-doped TiO2 are given in Figure. 10, Figure. 11 and Figure. 12. The rate of photodegradation was related to the formation of OH radicals which are formed through the reaction of valance band holes with adsorbed H2O and OH'. At high concentration of pesticides, adsorbed OH" ions might have been replaced by pesticides which might have reduced the production of OH radicals. This may be the reason for the reduction in reaction rate with increase in concentration of pesticide. Kormann, C. Bahnemann, D.W. Hoffmann, M.R. Photolysis of chloroform and other organic molecules in aqueous TiO2 suspensions. Environmental Science and Technology, (1991), 25, 494-500. Mixed pesticides degradation studies were carried out by using commercial grade of methyl parathion, dichlorvos and lindane. 250 μ g/L concentration of mixed pesticides, 83.3 μ g/L concentration of each of the pesticide was taken for photodegradation with N-doted TiO2 under solar radiation. The time required for the complete degradation of 83.3 pg/L of each pesticide was much higher compared to 250 μ g/L of methyl parathion, dichlorvos and lindane in individual pesticide systems. The degradation kinetics of 83.3 pg/L of each pesticide is given in Figure. 13.
Photodegradation of methyl parathion, dichlorvos and lindane were carried out with continuous reactor using immobilized form of N-doped TiO2. The block diagram of continuous photoreactor is given in Figure. 14. Photodegradation were carried out with three different concentrations, 50, 100 and 250pg/L under visible and solar radiation. N-doped TiO2 showed complete degradation, for initial concentrations of 50, 100 and 250 pg/L of methyl parathion, dichlorvos and lindane, respectively under visible and solar radiation. GC-MS analysis was carried out to find the intermediate compounds present in the reactor outlet during the degradation of methyl parathion, dichlorvos and lindane. Results showed that no intermediate was identified from the outlet of the reactor.

Photodegradation studies of mixed pesticides were carried out using identical mass concentrations of methyl parathion, dichlorvos and lindane (5O μ g/L). The reasons for taking 50 μ g/L of each pesticides was the concentration of methyl parathion, dichlorvos and lindane present in the river and ground water sources are in the range of 10 ng/L to 100 μ g/L. Guzzella, L. Roscioli, C. Vigano, L. Saha, M. Sarkar, S.K. Evaluation of the concentration of HCH, DDT, HCB, PCB and PAH in the sediments along the lower stretch of Hugli estuary, West Bengal, northeast India Bhattacharya. Environment International, (2005), 31 (4), 523-534. Sankararamakrishnan, N. Sharma, A. K. Sanghi, R. Organochlorine and organophosphorous pesticide residues in ground water and surface waters of Kanpur, Uttar Pradesh, India. Environment International, (2005) 31, 113-120. Kumari, B. Madan, V. K. Kathpal, T. S. Status of insecticide contamination of soil and water in Haryana, India. Environmental Monitoring and Assessment, (2008), 136, 1-3. Therefore, a low concentration of (50 μ g/L) methyl parathion, dichlorvos and lindane was employed for the photodegradation mixed pesticides. The photodegradation of mixed pesticides with N-doped TiO2 under solar radiation was carried out with identical experimental conditions as mentioned earlier. Under solar radiation, 100% removal was achieved for all the three pesticides. Residual concentrations of pesticides, intermediates and formulation compounds were not identified by GC-MS analysis. Similar experiment was carried out using N-doped TiO2 under visible light with identical experimental conditions. Residual concentrations of 0.23, 0.25 and 1.13 pg/L were obtained in the out let of the continuous reactor for dichlorvos, methyl parathion and lindane, respectively. Percentage removals of dichlorvos, methyl parathion and lindane were 99.54%, 99.50% and 97.74%, respectively. The photodegradation of mixed pesticide under visible light are given in Figure. 15.

We Claim:

1) A process for purifying a water feedstock containing an oxidizable compounds like pesticides, comprising the steps of mixing the water feedstock with N-doped TiO2having particles size in the range of 0.025 - 1.0 micron and in an amount of between 0.01 - 0.2% by weight of the water, exposing said water and N-doped TiO2semiconductor to UV, visible and solar radiation for contact time sufficient to effect the oxidation of the oxidizable contaminant compound(s) and thereby to purify said water.

2) A process as defined in claim 1 wherein the said, N-doped TiO2is immobilized on glass tube or glass plate through dip coating at a loading range of 0.01-1.0% and the as-immobilized N-doped TiO2is used for detoxifying a water feedstock containing an oxidizable compounds like pesticides by exposing the said water and the immobilized N-doped TiO2to UV, visible and solar radiation for contact time sufficient to effect the oxidation of the compound(s) and thereby to purify said water.

3) A process as defined in claim 1 and 2, including the step of adding oxygen gas to the water and N-doped TIO2 mixture during exposure to UV, visible and solar radiation.

4) A method according to claim 1 and 2, wherein the said N-doped TiO2is utilized for the degradation of pesticides like methyl parathion, dichlorvos and lindane individually and in combination under UV, visible, and solar radiation.

5) A process as defined in claim 1, wherein the N-doped TiO2is recycled in the process after separation from the purified water.

6) A process as defined in claim 2, wherein the immobilized N-doped TiO2is recycled in the process after separation from the purified water.

7) A process as defined in claim 2, wherein the N-doped TiO2is immobilized on substrates like rayon, nylon, polyester, teflon, metal sheet, latex, cellulose, activated alumina, activated carbon, sand, clay, wood, rice husk, their derivatives and combination thereof.

8) A process as defined in claim 1, wherein the N-doped TiO2can be used in batch or continuous mode for the oxidation of the pesticide(s) in contaminated water.

9) A process as defined in claim 2, wherein the N-doped TiO2 can be used in batch or continuous mode for the oxidation of the pesticide(s) in contaminated water.

10) A process as defined in claim land 2, wherein the N-doped TiO2can be used for removing, reducing or detoxifying organic pollutants other than pesticides or killing microorganisms in water.

11) A process as defined in claim 1 and 2, wherein the N-doped TIO2 is exposed under visible light ranging from wavelength of 400 to 800 nm and UV radiation ranging from wavelength of 200-380 nm.

12) A method is according to claim 1 or 2, wherein the N-doped TiO2 can be used in various forms of reactors including suspended, fluidized, and packed bed reactors.

13) A method according to claim 1 and 2, wherein the N- doped TiO2is used to remove pesticides, microorganism and other organic pollutants other than drinking water including organic pollutant in air, industrial waste, agriculture runoff water, polluted water reservoirs or oil spills.

14) A chemical reactor, comprising: a thin film photocatalytic reactor made up of metal, glass and plastic, comprising N-doped TiO2immobilizing on surface of the thin film reactor, N-doped TiO2having a particle size in the range of 0.025-1.0 micron and in an amount of between 0.01-1.0% by weight of the suspended catalyst used for the costing, exposed to the artificial visible light or solar radiation, reaction medium is passed through the from an inlet of the reactor to outlet of the reactor, continuous reactor is partitioned in between the reactor to maintain the fixed residence time for the particular flow rate.

15) The methods according to claim 14, the N-doped TiO2coated on the bottom of the reactor, contaminants are passed through the coated surface of the catalyst in a liquid phase.