In situ investigation of water on MXene interfaces
In situ investigation of water on MXene interfaces
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DOI：
10.1073/pnas.2108325118
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发表时间：
2021-11
期刊：
影响因子：
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通讯作者：
W. Zaman;Ray A. Matsumoto;M. Thompson;Yu-Hsuan Liu;Y. Bootwala;Marm B. Dixit;S. Nemšák;E. Crumlin;M. Hatzell;P. Cummings;K. Hatzell
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作者：
W. Zaman;Ray A. Matsumoto;M. Thompson;Yu-Hsuan Liu;Y. Bootwala;Marm B. Dixit;S. Nemšák;E. Crumlin;M. Hatzell;P. Cummings;K. Hatzell
意义固液界面的水组织在吸附、膜分离、储能和催化等一系列应用中起着关键作用。目前，我们对固体界面处的分子水的理解仅限于宏观和体积测量方法。这些审讯技术缺乏必要的空间和时间分辨率，以检测水如何与当地的异质性化学微环境的表面化学，溶质等。这项工作揭示了水和二维MXenes之间的相互作用，结合原位环境压力X射线光电子能谱（XPS）和分子动力学模拟。这项工作演示了溶质（阳离子）的大小如何控制在受限的纳米通道内的运输和溶质的水合能控制暴露表面的水吸附/解吸性质。水种群的连续体可以存在于纳米级层状材料中，其影响与分离、吸附和电荷存储过程相关的传输现象。水结构和组织的量化和直接询问对于设计具有新兴能源和水应用的分子水平控制的材料是重要的。通过结合分子模拟与环境压力X射线光电子能谱，X射线衍射和漫反射红外傅里叶变换光谱，我们直接探测水化机制在受限和非受限区域的纳米层过渡金属碳化物材料。疏水性（K+）阳离子降低水的流动性内的封闭夹层和加速水在非封闭表面的去除。亲水性阳离子（Li+）增加水的流动性内的封闭夹层和减少水的去除率在非封闭的表面。溶质，而不是表面终止基团，被证明是更有影响力的水吸附和解吸的动力学。巨正则分子动力学的计算表明，亲水性阳离子（Li+）积极帮助在MXene界面的水吸附。相比之下，疏水阳离子（K+）与水的相互作用较弱，导致更高程度的水有序（取向）和更快的去除在高温下。
Significance Water organization at solid–liquid interfaces plays a critical role in a range of applications related to adsorption, membrane separations, energy storage, and catalysis. Currently, our understanding of molecular water at solid interfaces is limited to macroscopic and bulk measurement approaches. These interrogation techniques lack the spatial and temporal resolutions necessary to detect how water interacts with local heterogeneous chemical microenvironments governed by surface chemistry, solutes, etc. This work reveals the interaction between water and two-dimensional MXenes by combining in situ ambient-pressure X-ray photoelectron spectroscopy (XPS) and molecular dynamics simulation. This work demonstrates how the size of a solute (cation) governs transport within confined nanochannels and the hydration energy of the solute governs water adsorption/desorption properties at exposed surfaces. A continuum of water populations can exist in nanoscale layered materials, which impacts transport phenomena relevant for separation, adsorption, and charge storage processes. Quantification and direct interrogation of water structure and organization are important in order to design materials with molecular-level control for emerging energy and water applications. Through combining molecular simulations with ambient-pressure X-ray photoelectron spectroscopy, X-ray diffraction, and diffuse reflectance infrared Fourier transform spectroscopy, we directly probe hydration mechanisms at confined and nonconfined regions in nanolayered transition-metal carbide materials. Hydrophobic (K+) cations decrease water mobility within the confined interlayer and accelerate water removal at nonconfined surfaces. Hydrophilic cations (Li+) increase water mobility within the confined interlayer and decrease water-removal rates at nonconfined surfaces. Solutes, rather than the surface terminating groups, are shown to be more impactful on the kinetics of water adsorption and desorption. Calculations from grand canonical molecular dynamics demonstrate that hydrophilic cations (Li+) actively aid in water adsorption at MXene interfaces. In contrast, hydrophobic cations (K+) weakly interact with water, leading to higher degrees of water ordering (orientation) and faster removal at elevated temperatures.