Zhu Zhenghao, Sokolov Alexei P, Paddison Stephen J
Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA.
Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996, USA.
J Chem Phys. 2024 Oct 21;161(15). doi: 10.1063/5.0222398.
The solvation and transport of protons in aqueous solutions of phosphoric acid (PA), sulfuric acid (SA), and nitric acid (NA) were studied using ab initio molecular dynamics simulations. Systems with acid-to-water ratios of 1:1 and 1:3 were examined to understand the similarities and differences in transport mechanisms. The solvation structure of H3O+ in these systems is similar to that in slightly acidic water, with variations in the strength of hydrogen bonds (H-bonds) accepted by acid molecules. In aqueous PA systems, strong H-bonds between PA molecules are slightly affected by water, leading to significantly greater H3O+ diffusion compared to aqueous SA and NA systems. This enhanced diffusion is attributed to the participation of PA molecules in H3O+ transport, where the PA molecule can shuttle a proton for H3O+, facilitating a large displacement via collective proton hopping. This shuttling mechanism is prominent in aqueous PA but rare in aqueous SA and absent in aqueous NA. Moreover, the decomposition of H3O+ diffusion into vehicular and structural components indicates that the higher diffusion in aqueous PA is primarily due to the structural mechanism with the aid of PA molecules. In the aqueous NA systems, the vehicular diffusion is dominant at low water contents and the increase in water content improves the structural diffusion by forming connected H-bonds within water molecules. Our findings elucidate the role of acid molecules in proton transport within their aqueous solutions, thereby advancing the fundamental understanding of proton transport mechanisms.
使用从头算分子动力学模拟研究了质子在磷酸（PA）、硫酸（SA）和硝酸（NA）水溶液中的溶剂化和传输。研究了酸与水比例为1:1和1:3的体系，以了解传输机制的异同。这些体系中H3O+的溶剂化结构与微酸性水中的相似，酸分子接受的氢键（H键）强度有所变化。在PA水溶液体系中，PA分子之间的强H键受水的影响较小，导致与SA和NA水溶液体系相比，H3O+的扩散显著更大。这种增强的扩散归因于PA分子参与H3O+传输，其中PA分子可以为H3O+穿梭质子，通过集体质子跳跃促进大的位移。这种穿梭机制在PA水溶液中很突出，但在SA水溶液中很少见，在NA水溶液中不存在。此外，将H3O+扩散分解为载体扩散和结构扩散成分表明PA水溶液中较高的扩散主要是由于在PA分子帮助下的结构机制。在NA水溶液体系中，在低含水量时载体扩散占主导，含水量的增加通过在水分子内形成连接的H键改善了结构扩散。我们的研究结果阐明了酸分子在其水溶液中质子传输中的作用，从而推进了对质子传输机制的基本理解。
