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In situ synthrsis of the novel PANI/TiO2 photocatalysts for azo dye degradation in wastewater

Titanium dioxide (TiO2 ; Aeroxide® P25) is one of the most famous commercial photocatalyst. TiO2 is non-toxic [1], environment friendly but with relatively high band gap of 3.2 eV that restricts its photocatalytic activity under the visible light. There were several attempts to increase the TiO2 activity under the visible light (> 400 nm) by doping and by controlling the surface/particle size [1]. However, the above attempts require the novel TiO2 preparation. The most promising solution is to prepare P25- compostites by using conductive (-conjugated) polymers such as polyaniline (PANI) [2], since they are non-toxic, thermally stable and they have a high absorption coefficient in the visible light region. When the PANI/TiO2 composite is irradiated by visible light, the PANI excited- state electrons are formed which are easily injected into the TiO2 conduction band (CB) [2]. Consequently, the injected electrons produce the superoxide radicals that oxidize the organic (dye) pollutant. The above mechanism, which enables the TiO2 photoactivity under the visible light, is one part of the synergic PANI/TiO2 effect. PANI/TiO2 composites can be prepared by chemical in situ oxidation of aniline (An) in the presence of TiO2 [3] by using ammonium persulfate (APS). However, the PANI conductivity is governed by the experimental conditions that should be carefully chosen: concentration of An and APS, m(An):m(TiO2), n(An):n(APS), type of acid, pH, etc. [2]. Obtained photocatalytic results (Fig.1) show achieved synergic PANI/TiO2 effect as the dye removal is higher for 10% PANI/TiO2 than for the pure TiO2.

titanium dioxide ; polyaniline ; composite ; photocatalyst ; azo dye

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