Applicability of coumarin for detecting and measuring hydroxyl radicals generated by photoexcitation of TiO2 nanoparticles

• Published in: Applied catalysis. B, Environmental Vol. 81; no. 3-4; pp. 295 - 302
• Main Authors: Czili, Hajnalka, Horváth, Attila
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 24.06.2008; Elsevier
• Subjects: Catalysis; Chemistry; Colloidal state and disperse state; Coumarin; Exact sciences and technology; Fluorescent probe; General and physical chemistry; Heterogeneous photocatalysis; Hydroxyl radical; Photochemistry; Physical and chemical studies. Granulometry. Electrokinetic phenomena; Physical chemistry of induced reactions (with radiations, particles and ultrasonics); Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; TiO2; Coumarin; Heterogeneous photocatalysis; Hydroxyl radical; Fluorescent probe; TiO2; Binary compound; Nanoparticle; Photocatalysis; Transition element compounds; Heterogeneous catalysis; Titanium oxide; Hydroxyl; Environmental protection
• ISSN: 0926-3373; 1873-3883
• DOI: 10.1016/j.apcatb.2008.01.001

Applicability of coumarin (COU) as fluorescent probe to detect and measure hydroxyl radicals generated by UV irradiation of aqueous suspension of TiO2 was investigated under aerobic and anaerobic conditions. The fluorescent 7-hydroxycoumarin (7HC) was formed in argon-saturated suspension when silver ion was used as electron acceptor. The luminescence intensity increased with irradiation time until the deposition of silver on the surface of TiO2 was completed and then the luminescence intensity was constant and proportional to the initial concentration of the silver ion. The low yield of 7HC related to the deposited silver (0.32%) indicates the appearance of efficient side reactions of hydroxyl radicals and holes. It has also been demonstrated that efficient electron donors reacting directly with photogenerated holes such as oxalic acid significantly reduce the yield of 7HC. Using oxalic acid of relatively high concentration in aerated suspension leads to the production of hydroxyl radical in thermal reactions followed by primary electron transfer steps.