Wang Qiang, Qu Zhiguo, Zhang Xu, Chen Liang
MOE Key Laboratory of Thermal-Fluid Science and Engineering, School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, China.
ACS Appl Mater Interfaces. 2022 Aug 24;14(33):37608-37619. doi: 10.1021/acsami.2c06687. Epub 2022 Aug 2.
Osmotic energy conversion features directional ion migration in selective nanochannels, dominated by interfacial effects, temperature, and concentration. Current efforts emphasize membrane modification for superior reliability and durability, whereas the origin and implication of interfacial effects are unclear. This work performs ab initio molecular dynamics simulations for hydrated ion-graphene oxide interfaces by regulating the temperature and concentration. The interfacial effects associated with their induced anisotropic ion diffusion and ion selectivity are revealed. The scientific essence of the interfacial effects is an electron transfer triggered by hydrated ion-functional group interactions. The interfacial effects are clarified to include dynamic solvation structures, interfacial H-bonds, and chemical reactions. Ions possess incomplete hydration shells, and their arrangements vary from ordered to disordered to overlapped. Interfacial H-bonds restrict hydrated ions by constraining water molecules, whereas continuous reactions provide lateral pathways to generate anisotropy. Cation selectivity is further clarified by negative surface charges from hydroxyl deprotonation. Besides, temperature rise induces disordered hydrated ions as well as frequent and violent reactions, enhancing ion diffusion, selectivity, and anisotropy; excessive concentrations produce overlapped hydrated ions, more H-bonds, and inferior reactions, weakening ion diffusion, selectivity, and anisotropy. Finally, the bottom-up concept for osmotic energy conversion is summarized, and elevated temperature combined with low concentration is found to boost ion diffusion and ion selectivity synergistically. This work provides an in-depth understanding of interfacial phenomena and ion behaviors in nanochannels.
渗透能转换的特点是在选择性纳米通道中存在定向离子迁移，其主要受界面效应、温度和浓度的影响。目前的研究重点是对膜进行改性以提高可靠性和耐久性，然而界面效应的起源和影响尚不清楚。这项工作通过调节温度和浓度，对水合离子-氧化石墨烯界面进行了从头算分子动力学模拟。揭示了与其诱导的各向异性离子扩散和离子选择性相关的界面效应。界面效应的科学本质是由水合离子-官能团相互作用引发的电子转移。界面效应被阐明包括动态溶剂化结构、界面氢键和化学反应。离子具有不完整的水合壳，其排列从有序到无序再到重叠。界面氢键通过限制水分子来约束水合离子，而连续反应提供横向途径以产生各向异性。阳离子选择性通过羟基去质子化产生的负表面电荷进一步阐明。此外，温度升高会导致水合离子无序化以及反应频繁剧烈，增强离子扩散、选择性和各向异性；过高的浓度会产生重叠的水合离子、更多的氢键和较差的反应，削弱离子扩散、选择性和各向异性。最后，总结了渗透能转换的自下而上概念，发现升高温度与低浓度相结合可协同促进离子扩散和离子选择性。这项工作深入理解了纳米通道中的界面现象和离子行为。
