Materials for Energy, Efficiency and Sustainability: TechConnect Briefs 2016Materials for Energy, Efficiency and Sustainability TechConnect Briefs 2016

Water Technologies Chapter 7

In-situ generation of radicals in photocatalytic reactor with TiO2 nanotube plate

D. Pak, H. Ku, Y. Lee
Seoul National University of Science and Technolog, Korea

pp. 205 - 208

Keywords: OH radical, photocatalytic reactor, TiO2 nanotube, anodization 

In-situ generation of radicals in photocatalytic reactor with TiO2 nanotube plate Daewon Pak, Haemin Ku, Yongho Lee Graduate School of Energy and Environment, Seoul National University of Science and Technology, 232 Gongneungro, Nowon-gu, Seoul, Korea, daewon@seoultech.ac.kr In recent years, photocatalytic oxidation processes have shown great potential as a low-cost, environmental friendly treatment technology in the water and wastewater industry [1, 2]. This oxidation technology has been widely demonstrated to have the ability to remove persistent organic compounds and microorganisms in water [3, 4]. The rationale for this advanced oxidation technology is based on the in-situ generation of highly reactive transitory species (i.e. OH, H2O2, O2, O3) for oxidation of refractory organic compounds and disinfection of water pathogens. A photocatalytic reactor employing TiO2 nanotubes grown on Ti plate was designed and operated. In order to synthesize TiO2 nanotubes on a Ti plate, self-organized oxide nanotube layers were grown by anodization in a glycerol based electrolyte. The ultimate conditions for the synthesis of the TiO2 nanotube array on the Ti plate were investigated by comparing the morphology, length, and inner diameter of the nanotubes. They were significantly affected by the applied anodic voltage, anodization time, and composition of the electrolyte such as the water and fluoride ion concentration. The crystallographic structures of TiO2 nanotubes before and after annealing were compared. The photocatalytic reactor used in this study consisted of two parallel and closely spaced TiO2 nanotube plates. The plates were squares while a UV lamp was inserted perpendicularly to them. OH radical generation in the photocatalytic reactor was monitored by using a probe compound, parachlorobenzoate (pCBA). The steady state OH radical concentration was compared depending on the length of nanotubes and crystallographic structure. The longer the nanotubes, the higher the steady state OH radical concentration. During the electrochemical synthesis of TiO2 nanotube arrays it was observed that the morphology, length, and inner diameter of the nanotube array were influenced by the electrolyte composition, applied anodic voltage, and anodizing time. The length and inner diameter of the nanotube array increase with anodization potential between 30 and 80 V. The nanotube length and inner diameter can be controlled by the anodization time. The concentration of ammonium fluoride and water in glycerol electrolyte has to be optimized for the formation of TiO2 nanotubes with a desirable morphology. As-prepared TiO2 nanotube arrays have an amorphous structure but can be converted to anatase by annealing at 400 oC. Above 500 oC, the rutile phase starts to appear. In the photocatalytic reactor with a TiO2 nanotube array plate, the longer the nanotube, the higher the steady-state OH radical concentration formed.