Nitrite Reduction to Nitrous Oxide and Ammonia by TiO2 Electrons in a Colloid Solution via Consecutive One-Electron Transfer Reactions

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• 作者：Sara Goldstein ; David Behar ; Tijana Rajh ; Joseph Rabani
• 刊名：Journal of Physical Chemistry A
• 出版年：2016
• 出版时间：April 21, 2016
• 年：2016
• 卷：120
• 期：15
• 页码：2307-2312
• 全文大小：333K
• 年卷期：0
• ISSN：1520-5215

文摘

The mechanism of nitrite reduction by excess electrons on TiO₂ nanoparticles (e_TiO2^–) was studied under anaerobic conditions. TiO₂ was loaded with up to 75 electrons per particle, induced by γ-irradiation of acidic TiO₂ colloid solutions containing 2-propanol. Time-resolved kinetics and material analysis were performed, mostly at 1.66 g L^–1 TiO₂. At relatively low nitrite concentrations (R = [e_TiO2^–]_o/[nitrite]_o > 1.5), e_TiO2^– decays via two consecutive processes; at higher concentrations, only one decay step is observed. The stoichiometric ratio Δ[e_TiO2^–]/[nitrite]_o of the faster process is about 2. This process involves the one-electron reduction of nitrite, forming the nitrite radical (k₁ = (2.0 ± 0.2) × 10⁶ M^–1 s^–1), which further reacts with e_TiO2^– (k₂) in competition with its dehydration to nitric oxide (NO) (k₃). The ratios k₂/k₃ = (3.0 ± 0.5) × 10³ M^–1 and k₂ > 1 × 10⁶ M^–1 s^–1 were derived from kinetic simulations and product analysis. The major product of this process is NO. The slower stage of the kinetics involves the reduction of NO by e_TiO2^–, and the detailed mechanism of this process has been discussed in our earlier publication. The results reported in this study suggest that several intermediates, including NO and NH₂OH, are adsorbed on the titanium nanoparticles and give rise to inverse dependency of the respective reaction rates on the TiO₂ concentration. It is demonstrated that the reduction of nitrite by e_TiO2^– yields mainly N₂O and NH₃ via consecutive one-electron transfer reactions.