Preparation of effective TiO2/Bi^sub 2^O3 photocatalysts for water treatment

Photocatalytic oxidation using semiconductors is one of the advanced oxidation processes for degradation of organic pollutants in water and air. TiO2 is an excellent photocatalyst that can mineralize a large range of organic pollutants such as pesticides and dyes. The main challenge is to improve the efficiency of the TiO2 photocatalyst and to extend TiO2 light absorption spectra to the visible region. A potential solution is to couple TiO2 with a narrow band gap semiconductor possessing a higher conduction band such as bismuth oxide. Therefore, here we prepared Bi2O3/TiO2 heterojunctions by the impregnation method with different Bi/Ti ratio. The prepared composites have been characterized by UV-Vis diffused reflectance spectra and X-ray diffraction. The photocatalytic activity of the heterojunction has been determined from the degradation of orange II under visible and UV light. Results show that Bi2O3/TiO2 heterojunctions are more effective than pure TiO2-anatase under UV-A irradiation, with an optimum for the Bi/Ti ratio of 5 %, for the photocatalytic degradation of Orange II. However, the photocatalytic activity under irradiation at [lambda] higher than 420 nm is not much improved. Under UV-visible radiation, the two semiconductors are activated. We propose a mechanism explaining why our products are more effective under UV-visible irradiation. In this case the charge separation is enhanced because a part of photogenerated electrons from the conduction band of TiO2 will go to the conduction band of bismuth oxide. In this composite, titanium dioxide is the main photocatalyst, while bismuth oxide acts as adsorbent photosensitizer under visible light.