204 J. Adv. Oxid. Technol. Vol. 18, No. 2, 2015 ISSN 1203-8407 © 2015 Science & Technology Network, Inc. The Photocatalytic Performance of Benzene- Modified TiO 2 Photocatalysts under UV-vis Light Irradiation Ewelina Kusiak- Nejman*, Agnieszka Wanag, Łukasz Kowalczyk, Beata Tryba, Joanna Kapica-Kozar, Antoni W. Morawski West Pomeranian University of Technology, Szczecin, Institute of Chemical and Environment Engineering, Pułaskiego 10,70-322 Szczecin, Poland Abstract: In this study a photocatalytic performance of new carbon-modified titanium dioxide photocatalysts was discussed. Benzene was used as carbon precursor. It was found that the photocatalytic activity of obtained samples increases with the increase of modification temperature and decrease of carbon concentration present in TiO 2 /C samples. This could be related to the kind of interactions between TiO 2 surface and carbon from thermal decomposition of benzene. The higher calcination temperature the less carbon deposits on the surface of modified samples and the higher probability of the Ti and C interaction confirmed by means of UV-vis/DR studies. It was proved that the photocatalytic activity of carbon modified titania nanomaterials strongly depends on carbon content in TiO 2 /C photocatalysts. Modification of starting TiO 2 with benzene is a promising method especially by taking into account the mineralization of phenol and the co-products of its degradation. Keywords: photocatalysis, carbon-modified TiO 2 , benzene precursor, phenol photodegradation, UV-vis light Introduction Among various semiconductors, TiO 2 is widely known as the most useful photocatalyst because of its special optical and electronic properties, low cost, chemical stability and nontoxicity. However, because of its large band gap of 3.20 eV only the small fraction (UV) of solar light (about 2-3%), can be utilized. In order to increase the efficiency of photo- catalytic processes in the presence of titanium dioxide many studies have been carried out. There are many ways to improve TiO 2 properties and one of them is carbon modification. This process can be carried out with several methods (1): heating or combustion of Ti/TiO 2 in a carbonaceous gas atmosphere, pyrolysis of precursors containing Ti and carbon or carbonization of different carbonaceous species deposited on the surface of TiO 2 . For this purpose many of the carbon precursors can be used, such as: n-hexane (2-4), poly(vinyl alcohol) or poly(ethylene terephthalate) (5-9), citric acid (10), cellulose (11-12), glucose (13), sucrose (14-15), poly(divinylbenzene) (16) and formaldehyde polymers (17-20). Commonly used method to introduce carbon into TiO 2 lattice is thermal treatment. Khan et al. (21) used for this purpose combustion of Ti metal sheet in a natural gas flame with controlled amounts of oxygen. Thereby obtained reduction of the energy gap to 2.3 eV. Whereas other researchers *Corresponding author; E-mail: Ewelina.Kusiak@zut.edu.pl used combustion of Ti precursors with various fuels (22-24). Thanks to that it was possible to obtain photocatalyst able to be activated in visible light region and 3-times more efficient in phenol degradation under solar light irradiation compared to commercial TiO 2 P25. Thermal treatment was also applied by Hahn et al. (25), to receive C/TiO 2 photo- catalyst able to absorb whole range of visible light. They used acetylene as a carbon precursor. Carbon can be also added to TiO 2 by heating TiO 2 or its precursors in the vapour of cyclohexane (26), ethanol (27-29) or with other alcohols (30-35). Carbon-doped titania obtained this method (26) has much better photocatalytic activity for gas-phase photo-oxidation of benzene under irradiation of artificial solar light than pure titania. The photocatalytic activity in azo dyes decomposition of modified P25 (29) was two times higher than for unmodified P25. Moreover, after the process such prepared photocatalysts showed better sedimentation and filtration. It is due to the change of their surface character from hydrophilic to hydrophobic (27). Modified TiO 2 photocatalysts were also used for NO x oxidation in air (34). The experi- mental results showed that up to 70% of NO x could be oxidized in a continuous flow type reaction system under irradiation with visible light. Other researchers modified TiO 2 by calcinations of hydrolysis product from Ti precursors and heat treatment with urea and thiourea (36-38) or tetrabutylammonium hydroxide (39-42). These studies showed that carbon addition to Unauthenticated Download Date | 7/28/18 7:25 AM