Zhang Pengchao, Chen Changsheng, Feng Muye, Sun Chao, Xu Xuefei
Center for Combustion Energy, Department of Energy and Power Engineering, and Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Tsinghua University, Beijing 100084, China.
School of Mechanical and Power Engineering, Nanjing Tech University, Nanjing 211816, China.
J Am Chem Soc. 2024 Jul 17;146(28):19537-19546. doi: 10.1021/jacs.4c06641. Epub 2024 Jul 1.
It has been widely recognized that the pH environment influences the nanobubble dynamics and hydroxide ions adsorbed on the surface may be responsible for the long-term survival of the nanobubbles. However, understanding the distribution of hydronium and hydroxide ions in the vicinity of a bulk nanobubble surface at a microscopic scale and the consequent impact of these ions on the nanobubble behavior remains a challenging endeavor. In this study, we carried out deep potential molecular dynamics simulations to explore the behavior of a nitrogen nanobubble under neutral, acidic, and alkaline conditions and the inherent mechanism, and we also conducted a theoretical thermodynamic and dynamic analysis to address constraints related to simulation duration. Our simulations and theoretical analyses demonstrate a trend of nanobubble dissolution similar to that observed experimentally, emphasizing the limited dissolution of bulk nanobubbles in alkaline conditions, where hydroxide ions tend to reside slightly farther from the nanobubble surface than hydronium ions, forming more stable hydrogen bond networks that shield the nanobubble from dissolution. In acidic conditions, the hydronium ions preferentially accumulating at the nanobubble surface in an orderly manner drive nanobubble dissolution to increase the entropy of the system, and the dissolved nitrogen molecules further strengthen the hydrogen bond networks of systems by providing a hydrophobic environment for hydronium ions, suggesting both entropy and enthalpy effects contribute to the instability of nanobubbles under acidic conditions. These results offer fresh insights into the double-layer distribution of hydroxide and hydronium near the nitrogen-water interface that influences the dynamic behavior of bulk nanobubbles.
人们普遍认识到，pH环境会影响纳米气泡的动力学，吸附在表面的氢氧根离子可能是纳米气泡长期存活的原因。然而，在微观尺度上了解大量纳米气泡表面附近水合氢离子和氢氧根离子的分布以及这些离子对纳米气泡行为的影响仍然是一项具有挑战性的工作。在本研究中，我们进行了深度势分子动力学模拟，以探索氮纳米气泡在中性、酸性和碱性条件下的行为及其内在机制，并且我们还进行了理论热力学和动力学分析，以解决与模拟持续时间相关的限制。我们的模拟和理论分析表明，纳米气泡溶解的趋势与实验观察到的相似，强调了大量纳米气泡在碱性条件下的有限溶解，在碱性条件下，氢氧根离子往往比水合氢离子离纳米气泡表面稍远，形成更稳定的氢键网络，从而保护纳米气泡不被溶解。在酸性条件下，水合氢离子优先有序地聚集在纳米气泡表面，驱动纳米气泡溶解以增加系统的熵，而溶解的氮分子通过为水合氢离子提供疏水环境进一步加强了系统的氢键网络，这表明熵和焓效应都导致了酸性条件下纳米气泡的不稳定性。这些结果为影响大量纳米气泡动态行为的氮 - 水界面附近氢氧根和水合氢离子的双层分布提供了新的见解。
