Destruction of emerging organic contaminants and bacteria in water by TiO2- based photocatalysts under visible-light led irradiation

• Main Author: Wang, Xiaoping.
• Other Authors: Lim Teik Thye
• Format: Theses and Dissertations
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Environmental engineering::Water treatment
• Online Access: http://hdl.handle.net/10356/52458
• Institution: Nanyang Technological University

TiO2-assisted heterogeneous photocatalysis has been proved to be a very promising technique for water treatment and purification such as degradation of recalcitrant organic contaminants and disinfection. However, the widespread and practical applications of TiO2 photocatalysis are rather limited, since the wide band gap of TiO2 restricts its photoexcitation to the UV region. In order to effectively utilize visible light or indoor light to initiate photocatalysis, this study aims to fabricate various types of visible-light active TiO2-based photocatalysts for destruction of aqueous emerging organic contaminants and/or pathogens. In the first part of this study, anatase Fe-C codoped TiO2 (Fe-C-TiO2) was synthesized by a facile solvothermal method. The synergistic effects of Fe and C codoping resulted in improved photocatalytic activities of Fe-C-TiO2 for degradation of bisphenol A (BPA) and clofibric acid (CA) as compared to C-TiO2, Fe-TiO2 and Degussa P25 under visible-light LED and simulated solar light irradiation. The toxicities of BPA solutions gradually decreased throughout BPA mineralization. The photocatalytic activity of the Fe-C-TiO2 was maintained effectively even after several cyclic experiments. The hypothesized photocatalytic mechanisms over the Fe-C-TiO2 under visible light and UV irradiation are presented. The next phase of study involved solvothermal synthesis of C-N codoped TiO2 (C-N-TiO2) for BPA degradation under visible light irradiation. The synthesis conditions including source of dopants, dopant concentration, and temperatures of solvothermal treatment and calcinations were evaluated. The C-N-TiO2 showed a much higher BPA removal efficiency than that of C-TiO2, N-TiO2 and P25 under white LED irradiation. Under the simulated solar light and UV irradiation, BPA was almost completely mineralized by the C-N-TiO2 within 5 h. After 5 h of reaction, generally the BPA solution became almost non-toxic irrespective of the light sources used. The C-N-TiO2 was still able to remove a small fraction of BPA even under yellow LED irradiation. The effects of pH and inorganic anions were also examined. The pretreatment of the solution by simply reducing the pH could prevent deactivation of the C-N-TiO2 by silica. Additionally, the formation and roles of various oxidative species in the BPA degradation were studied with the use of appropriate scavengers. Finally, photocatalytic mechanism of BPA degradation by the C-N-TiO2 under visible light irradiation is proposed.