Heterogeneous Interaction of H2O2 with TiO2 Surface under Dark and UV Light Irradiation Conditions

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• 作者：Manolis N. Romanias ; Atallah El Zein ; Yuri Bedjanian
• 刊名：The Journal of Physical Chemistry A
• 出版年：2012
• 出版时间：August 9, 2012
• 年：2012
• 卷：116
• 期：31
• 页码：8191-8200
• 全文大小：406K
• 年卷期：v.116,no.31(August 9, 2012)
• ISSN：1520-5215

文摘

The heterogeneous interaction of H₂O₂ with TiO₂ surface was investigated under dark conditions and in the presence of UV light using a low pressure flow tube reactor coupled with a quadrupole mass spectrometer. The uptake coefficients were measured as a function of the initial concentration of gaseous H₂O₂ ([H₂O₂]₀ = (0.17鈥?20) 脳 10¹² molecules cm^鈥?), irradiance intensity (J_NO2 = 0.002鈥?.012 s^鈥?), relative humidity (RH = 0.003鈥?2%), and temperature (T = 275鈥?20 K). Under dark conditions, a deactivation of TiO₂ surface upon exposure to H₂O₂ was observed, and only initial uptake coefficient of H₂O₂ was measured, given by the following expression: 纬₀(dark) = 4.1 脳 10^鈥?/(1 + RH^0.65) (calculated using BET surface area, estimated conservative uncertainty of 30%) at T = 300 K. The steady-state uptake coefficient measured on UV irradiated TiO₂ surface, 纬_ss(UV), was found to be independent of RH and showed a strong inverse dependence on [H₂O₂] and linear dependence on photon flux. In addition, slight negative temperature dependence, 纬_ss(UV) = 7.2 脳 10^鈥? exp[(460 卤 80)/T], was observed in the temperature range (275鈥?20) K (with [H₂O₂] 鈮?5 脳 10¹¹ molecules cm^鈥? and J_NO2 = 0.012 s^鈥?). Experiments with NO addition into the reactive system provided indirect evidence for HO₂ radical formation upon H₂O₂ uptake, and the possible reaction mechanism is proposed. Finally, the atmospheric lifetime of H₂O₂ with respect to the heterogeneous loss on mineral dust was estimated (using the uptake data for TiO₂) to be in the range of hours during daytime, i.e., comparable to H₂O₂ photolysis lifetime (1 day), which is the major removal process of hydrogen peroxide in the atmosphere. These data indicate a strong potential impact of H₂O₂ uptake on mineral aerosol on the HO_x chemistry in the troposphere.