Boron doped TiO(2) thin films have been successfully deposited on glass substrate and silicon wafer at 30 degrees C from an aqueous solution of ammonium hexa-fluoro titanate and boron trifluoride by liquid phase deposition technique. The boric acid was used as an F(-) scavenger. The resultant films were characterized by XRD, EDAX, UV and microstructures by SEM. The result shows the deposited film to be amorphous which becomes crystalline between 400 and 500 degrees C. The EDAX and XRD data confirm the existence of boron atom in TiO(2) matrix and a small peak corresponding to rutile phase was also found. Boron doped TiO(2) thin films can be used as photocatalyst for the photodegradation of chlorobenzene which is a great environmental hazard. It was found that chlorobenzene undergoes degradation efficiently in presence of boron doped TiO(2) thin films by exposing its aqueous solution to visible light. The photocatalytic activity increases with increase in the concentration of boron

Begum, N.

Farveez Ahmed, H.M.

Hussain, O.M.

Bulletin of Materials Science

Boron doped TiO2 thin films have been successfully deposited on glass substrate and silicon wafer at 30Â°C from an aqueous solution of ammonium hexa-fluoro titanate and boron trifluoride by liquid phase deposition technique. The boric acid was used as an F- scavenger. The resultant films were characterized by XRD, EDAX, UV and microstructures by SEM. The result shows the deposited film to be amorphous which becomes crystalline between 400 and 500Â°C. The EDAX and XRD data confirm the existence of boron atom in TiO2 matrix and a small peak corresponding to rutile phase was also found. Boron doped TiO2 thin films can be used as photocatalyst for the photodegradation of chlorobenzene which is a great environmental hazard. It was found that chlorobenzene undergoes degradation efficiently in presence of boron doped TiO2 thin films by exposing its aqueous solution to visible light. The photocatalytic activity increases with increase in the concentration of boron. Â© Indian Academy of Sciences

Begum, N.S.

ePrints@Bangalore University

Characterization and photocatalytic activity of boron-doped TiO2 thin films prepared by liquid phase deposition technique

Bull.  Mater.  Sci.,  Vol.  31,  No.  5,  October  2008,  pp.  741–745.  ©  Indian  Academy  of  Sciences.   741Characterization and photocatalytic activity of boron-doped TiO2 thin films prepared by liquid phase deposition technique NOOR  SHAHINA  BEGUM*,  H  M  FARVEEZ  AHMED  and  O  M  HUSSAIN† Department of Studies in Chemistry, Central College Campus, Bangalore University, Bangalore 560 001, India †Department of Physics, Sri Venkateswara University, Tirupati 517 502, India MS received 28 December 2007; revised 16 March 2008 Abstract. Boron doped TiO2 thin films have been successfully deposited on glass substrate and silicon wafer at 30°C from an aqueous solution of ammonium hexa-fluoro titanate and boron trifluoride by liquid phase deposition technique. The boric acid was used as an F– scavenger. The resultant films were characterized by XRD, EDAX, UV and microstructures by SEM. The result shows the deposited film to be amorphous which becomes crystalline between 400 and 500°C. The EDAX and XRD data confirm the existence of boron atom in TiO2 matrix and a small peak corresponding to rutile phase was also found. Boron doped TiO2 thin films can be used as photocatalyst for the photodegradation of chlorobenzene which is a great environmental hazard. It was found that chlorobenzene undergoes degradation efficiently in presence of boron doped TiO2 thin films by exposing its aqueous solution to visible light. The photocatalytic activity increases with increase in the concen-tration of boron.  Keywords. B-TiO2 thin film; LPD technique; photodegradation. 1. Introduction Since TiO2 was found to be a well known photocatalyst, intense research was concentrated on anatase TiO2 photo-catalysis. However, this material is only active upon UV excitation because of its large energy bandgap of 3⋅2 eV. Recently, many researchers’ work on the doping of TiO2 with non-metal atoms has received a lot of attention (Asahi et al 2001; Khan et al 2002; Burda et al 2003; Irie et al 2003a, b; Lindgren et al 2003; Sakthival and Kisch 2003a, b; Umebayashi et al 2003; Gole et al 2004; Noor Shahina Begum and Farveez Ahmed 2008).  For example, Asahi et al (2001) and Khan et al (2002) reported that doping TiO2 with nitrogen or carbon can lower its bandgap and shift its optical response to the visible region. Zhao et al (2004) observed remarkable improvement in the rate of degradation by doping TiO2 with metal and non-metal atoms.  Here we report the photocatalytical activity of B-doped TiO2 thin films grown by a simple technique known as liquid phase deposition (LPD). The LPD method is a unique soft solution process, and is performed by very simple procedures. In this method, metal oxide or hydroxide thin films are formed on the substrate through the ligand-exchange (hydrolysis) equilibrium reaction of metal-fluoro complex species. Addition of boric acid or aluminium metal acts as a free F – scavenger and shifts the equili-brium to one side (Nagayama et al 1988; Richardson and Rubin 2000; Deki et al 2001; Noor Shahina Begum and Farveez Ahmed 2008).  Our findings suggest that incorporation of B into TiO2 can extend the spectral response to the visible region and that the photocatalytic activity is greatly enhanced. 2. Experimental 2.1 Preparation of boron doped TiO2 thin films Ammonium hexa-flurotitanate and boric acid were dis-solved in distilled water so that the concentration of Ti ion was about 0⋅15 mol/dm3 and boric acid concentration, about 0⋅05 mol/dm3. A boron trifluoride solution was mixed with the above precursor in different proportions (TiO2-X, X = 1, 2 and 3% of B). The substrates [glass and Si wafer (111)] were degreased and washed ultrasonically and subsequently kept immersed vertically in treatment solution at 30°C for 40 h. After 40 h, the substrate was taken out, washed and dried at lab temperature. Calcina-tion of the films was also carried out at various tempera-tures. 2.2 Photocatalytic degradation B-doped TiO2 thin film was settled in a solution of chlorobenzene of concentration, 10 ppm. The solution *Author for correspondence (noorsb@rediffmail.com) Noor  Shahina  Begum,  H  M  Farveez  Ahmed  and  O  M  Hussain  742  Figure 1. EDAX spectra of TiO2 thin film doped with a. 2% B, grown on glass substrate and annealed at 500°C and b. 3% B, grown on glass substrate annealed at 500°C.   Figure 2. XRD pattern of B-doped TiO2 thin films annealed at different temperatures: (a) as-deposited film, and films an-nealed at (b) 200 and (c) 500°C.   was exposed to sunlight at different irradiation times. The solution was bubbled frequently with air during irradiation. The concentration of chlorobenzene was determined with a UV-visible spectrophotometer by measuring the absor-bance between 300 and 1200 nm. 3. Characterization of deposited films X-ray diffraction spectra were obtained from an X-ray diffractometer (type PW 3710 based tube anode: CuKα1: 1⋅54056 and Kα2: 1⋅54439). Optical properties were studied by using UV-vis-NIR, scanning spectrophotometer (type, Shimadzu-2003, Japan) in the wavelength range 300–1400 nm. The structural properties and elemental analysis of coating were studied using scanning electron micro-scope and EDAX (type: Leica Cambridge Ltd./Leica S440i for SEM and Oxford link software for EDAX). 4. Results and discussion 4.1 EDAX analysis The elemental analysis of boron doped TiO2 thin film was analyzed by taking EDAX. Figures 1a and b show the EDAX spectra of experimental films calcined at 500°C with 2% and 3% boron dopants, respectively. The elemen-tary analysis reveals the peaks for Ti, O and B but boron concentration was found to be very less. 4.2 Structure and surface morphology Figure 2 shows XRD pattern of B-doped TiO2 thin films annealed at different temperatures. The as deposited film and the film annealed at 200°C are amorphous in nature (curves a and b). Crystallinity begins only after 200°C (curve c). X-ray diffraction analysis also reveals that a structure composed only of anatase phase formed after calcinations at 500°C and that there was no observable structural difference between pure TiO2 thin films and boron-doped TiO2.  X-ray data reveals that there is slight change in lattice parameter of B-doped TiO2 thin films (TiO2-X, X = 3%B)Characterization  and  photocatalytic  activity  of  boron-doped  TiO2  thin  films  743 Figure 3. Scanning electron micrographs of (a) as deposited TiO2 thin film doped with 3% B, grown on glass sub-strate showing amorphous background, (b) B-doped TiO2 thin films (3% B), grown on glass substrate and annealed at 400°C showing the segregation of B atoms, (c) B-doped TiO2 thin films (3% B), grown on glass substrate and annealed at 500°C showing the segregation of B atoms, (d) B-doped TiO2 thin films (2% B), grown on Si wafer and annealed at 600°C showing the B atoms segregated like roots and (e) B-doped TiO2 thin films (3% B), grown on Si wafer and an-nealed at 600°C showing the B atom segregated like roots.   at c-axis when compared to pure TiO2, this confirms the existence of B atoms in TiO2 thin films (9⋅5958) for pure TiO2 and (9⋅6263) for B-doped TiO2 (Zhao et al 2004; Chen et al 2006). However, a small peak (figure 2) corre-sponding to rutile phase was observed with the orienta-tion [200].  Surface morphology of B-doped TiO2 thin films was studied by using Leica S440i scanning electron micro-scope with Oxford link software used to evaluate surface topology of experimental films.  Figures 3(a)–(d) show scanning electron micrographs of 3% B-doped TiO2 thin films grown on glass substrate and Noor  Shahina  Begum,  H  M  Farveez  Ahmed  and  O  M  Hussain  744 annealed at different temperatures. The as deposited film is homogeneous with the amorphous background (figure 3(a)). The films annealed at 400°C and 500°C show the compact structure with the segregation of B atoms (figures 3(b)–(c)) and the average grain size of about 50 nm. However, B-doped TiO2 thin films grown on Si wafer and annealed at 600°C show roots like morphology (figures 3(d) and (e)). These structures show the B on Si wafer to be segregated and not uniformly distributed. 4.3 Optical property Figure 4 shows the UV-vis transmittance spectra of bare TiO2 (curve a) and B-doped TiO2 thin film samples (curve b), grown on glass substrate and annealed at 500°C. It was observed that the optical absorption edge of B-doped TiO2 thin films (3% B) is significantly shifted towards visible region when compared to undoped TiO2. The energy bandgap calculation of pure and doped TiO2 shows remark-able changes in the bandgap. The graph of (αhν)1/2 × hν    Figure 4. UV-vis transmittance spectra of (a) bare TiO2 and (b) 3% B-doped TiO2 thin films, grown on glass substrate and annealed at 500°C.   Figure 5. Bandgap energy of pure TiO2 and B-doped TiO2 thin films grown on glass substrate and annealed at 500°C. shows bandgap energies of pure TiO2, 3⋅2 eV and B-doped TiO2, 2⋅95 eV (figure 5). From this observation, it is clear that the photocatalysis is possible under visible light. However, no significant differences were found in UV-vis transmittance spectra of 2% B-doped TiO2 thin films when compared to bare TiO2 thin films. 4.4 Photodegradation studies Photocatalytic activity of bare TiO2 and B-doped TiO2 films, grown on glass substrate and annealed at 500°C, were studied by taking chlorobenzene (Hussain 1991; Hoffmann et al 1995; Cheng et al 2004) which is envi-ronmentally hazardous. Figure 6 shows that B-doped TiO2 exhibits much greater activity than pure TiO2 thin films in the visible region. From the graph it can be con-cluded that the TiO2 thin film with 3% boron dopant ex-hibits photocatalytic activity much efficiently when compared to 2% B-doped TiO2 and bare TiO2 thin films, respectively.  The mechanism of photocatalytic activity of B-TiO2 was suggested by Grey et al (1996) that boron incorporation to TiO2 leads to the partial reduction of Ti4+ to Ti3+, which could improve the photocatalytic activity of TiO2. Since Ti3+ sites could act as the photogenerated electron traps and thus facilitate the charge separation. This increases the stability of electron–hole pair and minimizes the re-combination phenomena. In addition to that doping of B remarkably decreases the bandgap. It is also believed that segregation of boron in TiO2 thin films may partially in-crease the surface area and hence photocatalytic activity is enhanced. 5. Conclusions Boron-doped TiO2 thin films have been prepared by a simple novel technique known as liquid phase deposition    Figure 6. Photodegradation of chlorobenzene by bare TiO2 and B-doped TiO2 thin films, grown on glass substrate and an-nealed at 500°C. a. 3% B-doped TiO2 thin film, b. 2% B-TiO2 thin film and c. bare TiO2 thin film. Characterization  and  photocatalytic  activity  of  boron-doped  TiO2  thin  films  745technique. The prepared films were homogeneous and well adhered to the substrate and showed amorphous background. At higher temperature the films turn into crystalline form. The SEM images show the distribution of B atoms in the TiO2 matrix. The root like morphology was observed for the films grown on silicon wafer. EDAX and XRD data confirm the existence of B in TiO2 thin films. A small peak corresponding to rutile phase with the orientation [200] was observed. The photodegra-dation studies reveal that TiO2 doped with 3% B degraded the chlorobenzene effectively when compared to 2% B-doped TiO2 and bare TiO2 thin films under visible light irradiation. Acknowledgements The authors are grateful to Dr K R Gunasekar, Indian Institute of Science, Bangalore and Mr D Basavaraj and Mr Kalyan Raj, BMS College of Engineering, Bangalore, for providing technical support. References Asahi R, Morikawa T, Ohwaki T, Aoki K and Taga Y 2001 Science 293 269 Burda C, Lou Y, Chen X, Samia A C S, Stout J and Gole J L 2003 Nano Lett. 3 1049 Chen Daimai, Wang Dong Yang and Jiang Zhongyi 2006 Ind. Eng. Chem. 45 4110 Cheng Jen-hao 2003 A study on photocatalytic oxidation of aque-ous chlorobenzene solution by nanostructured film of TiO2, Master Thesis, National Sun Yat-Sen University, Taiwan Deki S, Henin Yu Yu Ko, Fujita T, Akamatsu K, Mizuhata X and Kajinami A 2001 Eur. Phys. J.D 16 325 Gole J L, Stout J D, Burda C, Lou Y and Chen X 2004 J. Phys. Chem. B108 1230 Grey I E, Li C and Macrae C 1996 J. Solid State Chem. 127 240 Hoffmann M R, Martin S T, Choi W and Bahnemann D W 1995 Chem. Rev. 95 69 Hussain Al-Ekabi 1991 Proc. of workshop on ‘Potential appli-cations of concentrated solar energy’, USA, p. 28 Irie H, Washizuka S, Yoshino N and Hashimoto K 2003a Chem. Commun. 11 1298 Irie H, Watanabe Y and Hashimoto K 2003b J. Phys. Chem. B107 5483 Khan S U M, Al-Shahry M and Ingler W B Jr 2002 Science 297 2243 Lindgren T, Mwabora J M, Avendano E, Jonsson J, Hoel A, Granqvist C and Lindquist S 2003 J. Phys. Chem. B107 5709 Nagayama H, Honda H and Kawahara H 1988 J. Electrochem. Soc. 135 2013 Noor Shahina Begum and Farveez Ahmed H M 2008 Bull. Mater. Sci. 31 43 Richardson T J and Rubin M D 2000 4th Int. mtg. on electro-chromism, Uppsala, Sweden Sakthivel S and Kisch H 2003a Angew. Chem., Int. Ed. 42 4908 Sakthivel S and Kisch H 2003b Chem. Phys. Chem. 4 487 Umebayashi T, Yamaki T, Tanaka S and Asai K 2003 Chem. Lett. 32 330 Zhao Wei, Ma Wanhong, Chen Chuncheng, Zhao Jincai and Shuai Zhigang 2004 J. Am. Chem. Soc. 126 4782     

Characterization and photocatalytic activity of boron-doped TiO(2) thin films prepared by liquid phase deposition technique

http://eprints-bangaloreuniversity.in/7118/1/noor.pdf

Characterization and photocatalytic activity of boron-doped TiO(2) thin films prepared by liquid phase deposition technique

Abstract

Similar works

Full text

Available Versions

ePrints@Bangalore University

ePrints@Bangalore University