Dual phase titanate/titania photocatalyst for degradation of organic pollutants under visible light

• Main Author: Cheng, Yu Hua
• Other Authors: Chen Zhong
• Format: Theses and Dissertations
• Language: English
• Published: 2012
• Subjects: DRNTU::Engineering::Materials::Energy materials; DRNTU::Engineering::Materials::Material testing and characterization
• Online Access: https://hdl.handle.net/10356/48676
• Institution: Nanyang Technological University

This research focuses on the design and development of a unique efficient dual phase photocatalyst material suitable for efficient degradation of harmful organic pollutants under visible light. Existing photocatalyst materials are ineffective as they have poor surface adsorption, are only responsive to UV light and experience fast charge recombination which impedes breakdown of organic pollutants. The thesis begins with a study on synthesis variations and its influence on the properties of the photocatalyst. The material that has high efficiency under visible light was determined to be a dual phase mixture of nanoscaled titanate and titania (anatase). Using a combination of theoretical and experimental techniques, the complete structure solution was achieved and the dual phase structure was confirmed by x- ray diffraction and high resolution transmission electron microscopy. Another key accomplishment of this thesis is the study of phase transition of the dual phase material and its evolution in crystal structure, surface area, optical absorption and chemical composition with change in synthesis temperature and duration. The titanate phase was found to dominate at lower temperatures and anatase phase at higher temperatures. This simple synthesis method also leads to doping of nitrogen in the titanate phase which effectively narrows its wide band-gap. Photo-activity of the dual phase photocatalyst is demonstrated in a systematic study of methylene blue (MB) dye degradation under visible light. This work highlights the importance of surface adsorption and distinguishes its contribution in overall photo- degradation process. Dual phase photocatalyst S160 exhibited superior performance over a commercial reference, Degussa P25. Its efficiency stems from its synergistic “adsorption- degradation” mechanism. In addition to capturing visible light, the titanate phase also plays the role of an adsorbent to attract organics such as MB molecules onto its surface. Intimate interfacial contact with the anatase phase allows easy band to band electron- hole transfer that retards charge recombination leading to faster degradation of organic compounds. In this study, demineralization of MB and its intermediates was studied in detail to make a distinction between dye sensitization and photocatalysis. Degradation of phenol under visible light was studied as well and the dual phase photocatalyst showed remarkable results compared to P25. In summary, this thesis introduces the development of a nitrogen doped dual phase photocatalyst and demonstrates its use in efficiently breaking down two organic targets under visible light. Essentially, the experimental advances realized in this work will have a direct impact in functionalizing photocatalysis in practical solar- driven wastewater degradation of organic pollutants.