Photocatalytic activity of bare colloidal TiO2 nanoparticles (NPs, d~45Å) and
surface modified with dopamine was obtained following degradation reaction of
herbicide RS-2-(4-chloro-o-tolyloxy)propionic acid (mecoprop, MCPP, C10H11ClO3)
under UV light irradiation. Results indicated that inner sphere charge transfer (CT)
complex is formed on the surface of TiO2 NPs due to modification with dopamine
which induced decreasing of the photocatalytic efficacy of TiO2 NPs

Abramović, Biljana F.

Despotović, Vesna N.

Janković, Ivana A.

Radoičić, Marija B.

Čomor, Mirjana

Šaponjić, Zoran

Šojić, Daniela V.

Repository of the Vinča Nuclear Institute (VinaR)

       PHYSICAL CHEMISTRY 2010  10th International Conference on Fundamental and Applied Aspects of Physical Chemistry  Proceedings      The Conference is dedicated to the 100th Anniversary of the academician Pavle Savić birthday and 20th Anniversary of the Society of Physical Chemists of Serbia         21-24 September 2010 B E L G R A D E                            ISBN 978-86-82475-17-0 Title: Physical Chemistry 2010. (Proceedings) Editors: S. Anić and Ž. Čupić Published by: Society of Physical Chemists of Serbia, Studentski trg 12-16 P.O.Box 47, 11158 Beograd, 218, Srbija Publisher: Society of Physical Chemists of Serbia For Publisher: S. Anić, President of Society of Physical Chemists of Serbia Printed by: “Jovan” Printing and Publishing Company; 200 Copies; Number of pages 16 + 388, Format: B5; Printing finished in September 2010.  Text and Layout: “Jovan”  200 - Copy printing    II   The Society of Physical Chemists of Serbia  in co-operation with   Institute of Catalysis, Bulgarian Academy of Sciences  Boreskov Institute of Catalysis, Siberian Branch of  the Russian Academy of Sciences  Faculty of Physical Chemistry, University of Belgrade, Serbia  Institute of Chemistry Technology and Metallurgy, University of Belgrade, Serbia  Vinča Institute, University of Belgrade, Serbia   Institute of General and Physical Chemistry, Serbia                         IV  International Organizing Committee  Chairman:             S. Anić (Serbia) Vice-chairman:     N. Stepanov (Russia)                                B. Adnađević (Serbia)  Members: M. Gabrovska (Bulgaria), N. Cvijetićanin (Serbia), T. Grozdić (Serbia),  D. Jovanović (Serbia), M. Lalić (BiH), D. Marković (Serbia), B. Milosavljević (USA), N. Miljević (Serbia), M. Mojović (Serbia), N. Ostrovski (Serbia), C. Pona (Italy), B. Simonović (Serbia), D. Stanisavljev (Serbia), A. G. Stepanov (Russia), V. Vasić (Serbia), N. Vukelić (Serbia), V. Vukojević (Sweden)   International Scientific Committee  Chairman:              Ž. Čupić (Serbia) Vice-chairmans:     V. N. Parmon (Russia)                                 M. Franko (Slovenia)  V. Vasić (Serbia)  Members: A. Antić-Jovanović (Serbia), G. Bačic (Serbia), R. Cervellati (Italy), R. Compton (United Kingdom), V. Gaspar (Hungary),  M. Jeremić (Serbia), A. L. Kawczyñski (Poland), Lj. Kolar-Anić (Serbia), S. Kuchanov (Russia), R. Leblanc (USA),  S. Mentus (Serbia), S. Milonjić (Serbia), Lj. Morozova-Roche (Sweden),  D. Moscone (Italy), J. Nedeljković (Serbia), Z. Noszticzius (Hungary), M. Perić (Serbia), V. Petruševski (Macedonia), M. Plavšić (Serbia), G. Smulevich (Italy),  G. Schmitz (Belgium), I. Schreiber (Czech), P. Ševčik (Slovakia), N. Stepanov (Russia), M. Trtica (Serbia), D. Veselinović (Serbia)  Local Executive Committee  Chairman:              B. Adnadjević Vice-chairmans:    S. Blagojević                                 A. Ivanović  Members: A. Abu Rabi-Stanković, P. Banković, N. Begović, S. N. Blagojević,  N. Cvjetičanin, M. Daković, A. Đerić, A. Ignjatović, Lj. Ignjatović, A. Jović,  J. Krstić, S. Kuprešak, D. Lončarević, J. Maksimović, V. Marković, M. Milenković, M. Milojević, Z. Mojović, B. Nedić, I. Pašti, N. Pejić, A. Popović-Bjelić, M. Petković, N. Potkonjak, D. Ranković, R. Ranković, M. Stević,  I. Stojković, B. Šljukić, M. Vujković    VPHOTOCATALYTIC ACTIVITY OF TiO2 NANOPARTICLES MODIFIED WITH DOPAMINE   M. Radoičić1, I. Janković1 ,V. Despotović2, D. Šojić2, Z. Šaponjić1,  B. Abramović2 and M. I. Čomor*1  1Vinča Institute of Nuclear Sciences, P. O. Box 522, 11001 Belgrade, Serbia 2Department of Chemistry, Faculty of Sciences, University of Novi Sad, Trg D. Obradovića 3, 21000 Novi Sad, Serbia  Abstract Photocatalytic activity of bare colloidal TiO2 nanoparticles (NPs, d~45Å)  and surface modified with dopamine was obtained following degradation reaction of herbicide RS-2-(4-chloro-o-tolyloxy)propionic acid (mecoprop, MCPP, C10H11ClO3) under UV light irradiation. Results indicated that inner sphere charge transfer (CT) complex is formed on the surface of TiO2 NPs due to modification with dopamine which induced decreasing of the photocatalytic efficacy of TiO2 NPs.   Introduction Titanium dioxide is the photocatalytic material which has been studied extensively over the past decade because it is inexpensive, nontoxic, and photostable. The absorption of photons with energy greater than band gap energy of TiO2 (3.2 eV, λ< 390 nm) promotes electron from the valence band to conduction band, leaving a positively charged hole in the valence band. Most of the charges recombine either radiatively or noniradiatively, while only a small fraction of the charges moves to the surface and react with adsorbed species or be trapped in the midgap surface states [1]. One of the possible ways to minimize charge recombination is to enlarge separation distances before desired redox reaction occurs. This can be done by surface modification of TiO2 NPs with electron-accepting/donating species [2]. In the nanosize regime, because of the large curvature of TiO2 particles, the surface reconstruct in such a way that distorts the crystalline environment of surface Ti atoms forming coordinatively unsaturated Ti atoms, coordination change from octahedral (bulk, inside the NP) to square-pyramidal for NP surface. Formation of charge-transfer complex at the surface of NPs can adjust their coordination to octahedral geometry and change the electronic properties of TiO2 [3]. This type of electronic coupling yields to instantaneous separation of photogenerated charges, the holes localize on organic modifier and electrons delocalize in the conduction band of TiO2 NPs.  In the scope of this work, we wanted to study the effect of fast and enlarged separation distance of photogenerated charges induced by surface modification of TiO2 NPs and formation of CT complex, on photocatalytic activity of TiO2 NPs. Photocatalytic degradation of herbicide RS-2-(4-chloro-o-tolyloxy)propionic acid (mecoprop, MCPP, C10H11ClO3) was used as model reaction because of its wide use all over the world and usual occurrence in drinking water [4]. 143Experimental All chemicals used were of the highest purity available. All solutions were prepared with triply distilled water. The TiO2 NPs were prepared by controlled hydrolysis of titanium (IV) chloride (Fluka), as described elsewhere [3]. Particle size was determined using a transmission electron microscope, JOEL CXII. The surface modification of TiO2 NPs was accomplished by dissolution of Dopamine (3-hydroxytyramine, puriss, Fluka) in TiO2 colloidal solution. Spectrophotometric measurements were carried out on a Evolution 600 UV-VIS spectrophotometer. Photocatalytic degradation was carried out in a way described previously [4]. The kinetics of MCPP degradation were studied by liquid chromatography- diode array detection, Agilent Technologies 1100 Series, details as in ref. [4].  Results and Discussion The absorption spectra of bare and surface modified TiO2 NPs are presented in Figure 1.    Fig.1. Absorption spectra of bare, surface modified TiO2 NPs and pure Dopamine (DAM), concentrations and surface coverage are presented in inset.      350 400 450 500 550 600 650.00.20.40.6absorbancewavelength, nm1.03 mM Tisurf + DAM , pH 2 0 % 25 % 50 % 90 % 1.03 mM DAM   It can be seen that the optical properties of bare TiO2 NPs are changed due to CT formation with Dopamine. We used three concentrations of Dopamine which produced 25 %, 50% and 90% coverage of surface, undercoordinated Ti atoms (for NPs with d~ 45 Å, about 30% of Ti atoms are on the surface).  As can be seen in Fig. 2, MCPP can be decomposed with all applied photocatalysts under UV irradiation. The best results were obtained with bare TiO2 NPs. Modified TiO2 NPs showed lower photocatalytic activity, without linear dependence with surface coverage of TiO2 NPs with CT complex with Dopamine. As the matter of fact, all applied coverages had almost the same photocatalytic activity. One of the possible reasons for such results can be decreased adsorption of MCPP on the surface of modified TiO2. This fact must be considered for 50% and 100% of coverage, but even 25 % of coverage reduced photocatalytic actitity.   The other reason can be based on the nature of the formed CT complex. Namely, all concentration of CT complex on the surface of TiO2 NPs was capable to extract photogenerated positive holes from TiO2 NPs. Obviously, extracted holes are not 144able to produce OH radicals which can oxidize MCPP and it seems that only electrons from TiO2 conduction band participate in the degradation of MCPP. As can be seen in Fig. 1, surface modification induced red shift of the absorption onset and charge transfer interaction between the modifier and surface Ti atoms also induced fine tuning of the electrochemical potential of semiconductor NPs indicating changes in oxidizing/reducing abilities. As already stressed in literature [3], TiO2 conduction band potential is kept constant while valence band potential is moved due to modification, to lower potential and holes extracted through CT complex are not capable to react with MCPP.          Fig.2. Kinetics of photocatalytic degradation of MCPP in the presence  of bare (a) and surface modified TiO2 NPs. 0 20 40 60 80 100 120 140 160 180 2000.00.20.40.60.81.0  time (min)c/c 0abcda- TiO2b- TiO2+ 25% DAMc- TiO2+ 50% DAMd- TiO2+ 100% DAM Conclusions Binding of the Dopamine molecules to undercoordinated surface Ti atoms (defect sites) results in formation of inner-sphere charge-transfer complex, observed by changes in the onset of absorption and effective band gap. Photocatalytical degradation of herbicide MCPP was followed as model reaction for evaluation of photocatalytic activity of applied catalysts. Modified TiO2 NPs showed reduced photocatalytic activity compared to bare TiO2 NPs. Observed results can be explained by reduced TiO2 surface after modification, at which MCPP can be adsorbed and inappropriate potential of holes extracted from TiO2 NPs in Dopamine molecule, for direct oxidation of MCPP molecule.  References [1]  A. J. Nozik, Annu.Rev. Phys.Chem., 1978, 29, 189-193. [2]  Z. V. Šaponjić, N. M. Dimitrijević, D. M. Tiede, J. A. Goshe, X. Zuo, L. X. Chen, A. S. Barnard, P. Zapol, L. Curtiss,T. Rajh, Adv. Mater., 2005, 17, 965-971. [3]  I. A. Janković, Z. V. Šaponjić, M. I. Čomor, J. M. Nedeljković, J. Phys. Chem. C, 2009, 113, 12645-12652. [4]  D.V. Šojić, V.N. Despotović, N.D. Abazović, M.I. Čomor, B.F. Abramović, J. Hazard. Mater., 2010, 179, 49-56.  145

Photocatalytic activity of TiO2 nanoparticles modified with dopamine

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Photocatalytic activity of TiO2 nanoparticles modified with dopamine

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