PHOTODEGRADATION OF METHYLENE BLUE ON VISIBLE LIGHT IRRADIATED TIO_2 IN THE PRESENCE OF NITROGEN MODIFIED ORGANIC MATERIALS

摘要

Introduction Titanium dioxide, particularly in anatase phase has great potential for many applications such as photocatalysis, solar energy conversion, gas sensor and photolysis of water. It is well known that TiO_2 is the best photocatalysts; however, several attends have been used to increase its photoefficiency and among them adding an inert co-adsorbent such as activated carbon (AC). A synergy effect between both solids has been observed in the photocatalytic degradation of model pollutants [1,2]. Our group performed the work on degradation of aromatic molecules such as phenol and 4-chlorophenol on UV-irradiated TiO_2-AC binary materials showing that functionalization of activated carbon's surface plays an important role upon the photoactivity of TiO_2 [3,4]. It was also shown that the both texture and surface pH of activated carbons are responsible to induce remarkable changes in the product distributions during the photooxidation of 4-chlorophenol [5]. Moreover, Lettmann and coworkers suggested that the specific functional groups on the carbon surface can photo-assist the oxidation process occurring at the TiO_2 surface [6]. It has been demonstrated that doping TiO_2 with nitrogen was one of the most effective approaches to improve photocatalytic activity, of TiO_2 on the visible region [7]. Continuing on that, Asahi et al. prepared nitrogen doped TiO_2 films by sputtering TiO_2 in a N_2/Ar gas mixture, and concluded that the doped Ν atoms narrowed the band gap of TiO_2 by mixing Ν 2p and O 2p states, therefore showed photocatalytic activity for the decomposition of organic compound such as acetone and methylene blue in wavelengths up to 550nm [8]. Particularly, it was indicated that MB degradation model experiments showed that the N-doped TiO_2 nanotube arrays presented a significantly enhancement of the photocatalytic activity comparing with the pure TiO_2 nanotube arrays under the visible light irradiation.