Eatoo Muzzamil Ahmad, Mishra Himanshu
Environmental Science and Engineering (EnSE) Program, Biological and Environmental Science and Engineering (BESE) Division, King Abdullah University of Science and Technology (KAUST) 23955-6900 Thuwal Kingdom of Saudi Arabia.
Water Desalination and Reuse Center (WDRC), King Abdullah University of Science and Technology (KAUST) 23955-6900 Thuwal Kingdom of Saudi Arabia
Chem Sci. 2024 Jan 24;15(9):3093-3103. doi: 10.1039/d3sc06534k. eCollection 2024 Feb 28.
Recent reports on the spontaneous formation of hydrogen peroxide (HO) at the air-water and solid-water interfaces challenge our current understanding of aquatic chemistry and have ramifications on atmosphere chemistry models, surface science, and green chemistry. Suggested mechanisms underlying this chemical transformation include ultrahigh instantaneous electric fields at the air-water interface and the oxidation of water and reduction of the solid at the solid-water interface. Here, we revisit this curious problem with NMR spectroscopy (with an HO detection limit ≥50 nM) and pay special attention to the effects of nebulizing gas, dissolved oxygen content, and the solid-water interface on this chemical transformation in condensed and sprayed water microdroplets. Experiments reveal that the reduction of dissolved oxygen at the solid-water interface predominantly contributes to the HO formation (not the oxidation of hydroxyl ions at the air-water interface or the oxidation of water at the solid-water interface). We find that the HO formation is accompanied by the consumption (, reduction) of dissolved oxygen and the oxidation of the solid surface, , in the absence of dissolved oxygen, the formation of HO(aq) is not observed within the detection limit of ≥50 nM. Remarkably, the tendency of the solids investigated in this work towards forming HO in water followed the same order as their positions in the classic Galvanic series. These findings bust the prevailing myths surrounding HO formation due to the air-water interface, the ultrahigh electric fields therein, or the micro-scale of droplets. The hitherto unrealized role of the oxidation of the solid surface due to dissolved oxygen in the formation of HO is exposed. These findings are especially relevant to corrosion science, surface science, and electrochemistry, among others.
最近有关过氧化氢（HO）在气-水和固-水界面自发形成的报道，对我们目前对水生化学的理解提出了挑战，并对大气化学模型、表面科学和绿色化学产生了影响。这种化学转化背后的潜在机制包括气-水界面处的超高瞬时电场以及固-水界面处水的氧化和固体的还原。在这里，我们利用核磁共振光谱法（HO检测限≥50 nM）重新审视这个有趣的问题，并特别关注雾化气体、溶解氧含量以及固-水界面在凝聚和喷雾水微滴中对这种化学转化的影响。实验表明，固-水界面处溶解氧的还原主要促成了HO的形成（而非气-水界面处氢氧根离子的氧化或固-水界面处水的氧化）。我们发现HO的形成伴随着溶解氧的消耗（即还原）和固体表面的氧化，也就是说，在没有溶解氧的情况下，在≥50 nM的检测限内未观察到HO（aq）的形成。值得注意的是，这项工作中所研究的固体在水中形成HO的倾向与其在经典电动序中的位置顺序相同。这些发现打破了围绕因气-水界面、其中的超高电场或微滴的微观尺度而形成HO的普遍误解。揭示了溶解氧导致固体表面氧化在HO形成过程中迄今未被认识到的作用。这些发现尤其与腐蚀科学、表面科学和电化学等领域相关。
