Laboratory of Environmental Chemistry, Paul Scherrer Institut, 5232, Villigen, Switzerland.
Laboratory for Catalysis and Sustainable Chemistry, Paul Scherrer Institut, 5232, Villigen, Switzerland.
Nat Commun. 2017 Sep 26;8(1):700. doi: 10.1038/s41467-017-00823-x.
Oxidation of bromide in aqueous environments initiates the formation of molecular halogen compounds, which is important for the global tropospheric ozone budget. In the aqueous bulk, oxidation of bromide by ozone involves a [Br•OOO] complex as intermediate. Here we report liquid jet X-ray photoelectron spectroscopy measurements that provide direct experimental evidence for the ozonide and establish its propensity for the solution-vapour interface. Theoretical calculations support these findings, showing that water stabilizes the ozonide and lowers the energy of the transition state at neutral pH. Kinetic experiments confirm the dominance of the heterogeneous oxidation route established by this precursor at low, atmospherically relevant ozone concentrations. Taken together, our results provide a strong case of different reaction kinetics and mechanisms of reactions occurring at the aqueous phase-vapour interface compared with the bulk aqueous phase.Heterogeneous oxidation of bromide in atmospheric aqueous environments has long been suspected to be accelerated at the interface between aqueous solution and air. Here, the authors provide spectroscopic, kinetic and theoretical evidence for a rate limiting, surface active ozonide formed at the interface.
溴在水相环境中的氧化作用会引发分子卤代化合物的形成，这对于全球平流层臭氧预算非常重要。在水相中，臭氧氧化溴涉及[Br·OOO]络合物作为中间体。在这里，我们报告了液体射流 X 射线光电子能谱测量结果，这些结果为臭氧化物提供了直接的实验证据，并确定了其在溶液-蒸气界面上的倾向。理论计算支持这些发现，表明水稳定了臭氧化物并降低了中性 pH 值时过渡态的能量。动力学实验证实了在低浓度、与大气相关的臭氧浓度下，这种前体通过非均相氧化途径的主导地位。总之，我们的结果提供了一个强有力的案例，说明在水相-蒸气界面上发生的反应的反应动力学和机制与在水相本体中不同。
在大气水相环境中，溴的非均相氧化作用在水溶液与空气之间的界面处一直被怀疑会加速。在这里，作者提供了光谱、动力学和理论证据，证明在界面处形成了一种具有反应活性限制的表面活性臭氧化物。
