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Ultrahigh Density of Gas Molecules Confined in Surface Nanobubbles in Ambient Water
journal contribution
posted on 2020-03-11, 18:33 authored by Limin Zhou, Xingya Wang, Hyun-Joon Shin, Jian Wang, Renzhong Tai, Xuehua Zhang, Haiping Fang, Wei Xiao, Lei Wang, Chunlei Wang, Xingyu Gao, Jun Hu, Lijuan ZhangTo 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.