Sonocatalytic facilitation of hydroxyl radical generation in the presence of TiO2

• Published in: Ultrasonics sonochemistry Vol. 15; no. 6; pp. 988 - 994
• Main Authors: SHIMIZU, Nobuaki, OGINO, Chiaki, MAHMOUD FARSHBAF DADJOUR, NINOMIYA, Kazuaki, FUJIHIRA, Atsushi, SAKIYAMA, Kazumichi
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier 01.09.2008
• Subjects: Aluminum Oxide - chemistry; Catechols - chemistry; Chemistry; Chromatography, High Pressure Liquid; Electrochemistry; Electron Spin Resonance Spectroscopy; Exact sciences and technology; Free Radical Scavengers - chemistry; Gases - chemistry; General and physical chemistry; Hydroxybenzoates; Hydroxyl Radical - chemistry; Hydroxyl Radical - radiation effects; Physical chemistry of induced reactions (with radiations, particles and ultrasonics); Salicylates - chemistry; Salicylates - radiation effects; Spin Trapping; Titanium - chemistry; Titanium - radiation effects; Ultrasonic chemistry; Ultrasonics; X-Ray Diffraction; Binary compound; Sonochemistry; Transition element compounds; Ultrasonic irradiation;Titanium dioxide;Hydroxyl radical;Salicylic acid;Cavitation bubble;Radical scavenger; Titanium oxide; Ultrasound; Hydroxyl
• ISSN: 1350-4177; 1873-2828
• DOI: 10.1016/j.ultsonch.2008.04.011

The generation of hydroxyl (OH) radicals was investigated during ultrasonic irradiation and in the presence of TiO(2). The effect of TiO(2) on an ultrasonic system's oxidation power was evaluated by examining the oxidation of salicylic acid. The generation of the salicylic acid derivatives, 2,3-dihydroxybenzoic acid (DHBA) and 2,5-DHBA, was measured by high-performance liquid chromatography coupled with electrochemical detection under different experimental conditions. The presence of TiO(2) enhanced the generation of DHBA during ultrasonic irradiation, thus indicating a higher oxidation power in the ultrasonic system. Al(2)O(3) also increased the generation of DHBA during irradiation; however, the effect of TiO(2) was found to be higher than that of Al(2)O(3). The addition of OH radical scavengers such as dimethylsulfoxide (DMSO), methanol and mannitol significantly suppressed the production of DHBA, and DMSO was found to have the highest suppressive effect among all scavengers. The effects of dissolved gases on the generation of OH radicals were further studied, and their power was found to be in the order Xe > Ar > O(2) > N(2). The degassing of the irradiation solution completely suppressed the generation of OH radicals. These results indicate that the presence of TiO(2) accelerates the generation of OH radicals during ultrasonic irradiation, and that the process may be mediated through the induction of cavitation bubbles in irradiating solutions.