Zhou Limin, Wang Xingya, Shin Hyun-Joon, Wang Jian, Tai Renzhong, Zhang Xuehua, Fang Haiping, Xiao Wei, Wang Lei, Wang Chunlei, Gao Xingyu, Hu Jun, Zhang Lijuan
Shanghai Synchrotron Radiation Facility, Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201204, People's Republic of China.
Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, People's Republic of China.
J Am Chem Soc. 2020 Mar 25;142(12):5583-5593. doi: 10.1021/jacs.9b11303. Epub 2020 Mar 11.
To understand the unexpected and puzzling long-term stability of nanoscale gas bubbles, it is crucial to probe their nature and intrinsic properties. We report herein synchrotron-based scanning transmission X-ray microscopy (STXM) evidence of highly condensed oxygen gas molecules trapped as surface nanobubbles. Remarkably, the analysis of absorption spectra of a single nanobubble revealed that the oxygen density inside was 1-2 orders of magnitude higher than that in atmospheric pressure, and these bubbles were found in a highly saturated liquid environment with the estimated oxygen concentration to be hundreds of times higher than the known oxygen solubility in equilibrium. Molecular dynamics simulations were performed to investigate the stability of surface nanobubbles on a heterogeneous substrate in gas-oversaturated water. These results indicated that gas molecules within confinement such as the nanobubbles could maintain a dense state instead of the ideal gas state, as long as their surrounding liquid is supersaturated. Our findings should help explain the surprisingly long lifetime of the nanobubbles and shed light on nanoscale gas aggregation behaviors.
为了理解纳米级气泡出人意料且令人费解的长期稳定性，探究其本质和固有属性至关重要。我们在此报告基于同步加速器的扫描透射X射线显微镜（STXM）证据，证明有高度凝聚的氧气分子被困作表面纳米气泡。值得注意的是，对单个纳米气泡吸收光谱的分析表明，其内部的氧气密度比大气压下的氧气密度高1至2个数量级，并且这些气泡存在于高度饱和的液体环境中，估计氧气浓度比已知的平衡态氧气溶解度高数百倍。进行了分子动力学模拟，以研究气体过饱和水中异质基底上表面纳米气泡的稳定性。这些结果表明，只要纳米气泡周围的液体处于过饱和状态，受限在纳米气泡等环境中的气体分子就能保持密集状态，而非理想气体状态。我们的研究结果应有助于解释纳米气泡惊人的长寿命，并阐明纳米级气体聚集行为。
