Department of Chemistry, Stanford University, Stanford, CA 94305.
Department of Mechanical Engineering, Stanford University, Stanford, CA 94305.
Proc Natl Acad Sci U S A. 2019 Sep 24;116(39):19294-19298. doi: 10.1073/pnas.1911883116. Epub 2019 Aug 26.
We show HO is spontaneously produced from pure water by atomizing bulk water into microdroplets (1 μm to 20 µm in diameter). Production of HO, as assayed by HO-sensitve fluorescence dye peroxyfluor-1, increased with decreasing microdroplet size. Cleavage of 4-carboxyphenylboronic acid and conversion of phenylboronic acid to phenols in microdroplets further confirmed the generation of HO The generated HO concentration was ∼30 µM (∼1 part per million) as determined by titration with potassium titanium oxalate. Changing the spray gas to O or bubbling O decreased the yield of HO in microdroplets, indicating that pure water microdroplets directly generate HO without help from O either in air surrounding the droplet or dissolved in water. We consider various possible mechanisms for HO formation and report a number of different experiments exploring this issue. We suggest that hydroxyl radical (OH) recombination is the most likely source, in which OH is generated by loss of an electron from OH at or near the surface of the water microdroplet. This catalyst-free and voltage-free HO production method provides innovative opportunities for green production of hydrogen peroxide.
我们展示了通过将大块水雾化成微液滴（直径为 1 微米至 20 微米），HO 可以自发地从纯水中产生。HO 产量，如通过对过氧荧光染料 peroxyfluor-1 的敏感性荧光测定来评估，随着微液滴尺寸的减小而增加。4-羧基苯硼酸的裂解和苯硼酸向苯酚的转化进一步证实了 HO 的生成。通过与草酸钾滴定法确定，生成的 HO 浓度约为 30 µM（约百万分之一）。将喷雾气体改为 O 或在微液滴中鼓泡 O 会降低 HO 的产率，表明纯水滴在空气中或溶解在水中时，无需 O 的帮助即可直接产生 HO。我们考虑了 HO 形成的各种可能机制，并报告了许多不同的实验来探索这个问题。我们认为羟基自由基（OH）的重组是最有可能的来源，其中 OH 是通过 OH 在水微液滴表面或附近失去电子而产生的。这种无催化剂和无电压的 HO 生产方法为过氧化氢的绿色生产提供了创新的机会。
