Pore size effects upon adsorption of PFAS in covalent organic frameworks: molecular dynamics study

IF 4.4 Q3 ENGINEERING, ENVIRONMENTAL
Timothy C. Ricard, Timothy C. Schutt, Caitlin G. Bresnahan and Manoj K. Shukla
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Abstract

Per- and polyfluoroalkyl substances (PFAS) are a large class of industrial chemicals whose diversity, spread, and environmental/health impacts have recently become a major concern for environmental and health policy makers. This concern is further exacerbated by their pervasiveness and chemical resilience, which complicates their removal from watersheds and other contaminated environments. Due to the chemical stability of the carbon–fluoride bonds, they are difficult to degrade. Instead, an alternative presents itself in the form of adsorption, concentration, and then removal of PFAS from contaminated sites. Both metal organic frameworks (MOFs) and covalent organic frameworks (COFs) have recently come under significant investigation as possible adsorption media which could be adapted for the removal of PFAS from contaminated sites. To gain greater insight into the adsorption capabilities of COFs for the removal of PFAS from waterways, we have studied the adsorption of PFAS molecules in COFs of differing pores sizes using molecular dynamics simulations. We examine the absorption of aqueous PFBA, PFOA, and PFOS into Covalent Triazine-Based Frameworks (CTF) of different pore sizes. This mechanistic adsorption data shows that a goldilocks zone occurs in pores with diameters of around 8 Å where the PFAS thread through the pores smoothly. Kinetic factors from diffusion into these nanopores favors the adsorption of short chain PFAS even though larger PFAS are thermodynamically favored. Each pore tends to initially adsorb only one PFAS, occupying the mouth of the pore, until the local COF surface is saturated and then multiple occupancy per pore can occur. Discussion on the impacts of PFAS concentration and interaction with the pores will inform design principles for enhanced selectivity and capacity for PFAS adsorbent material.

Abstract Image

孔径对共价有机骨架中PFAS吸附的影响:分子动力学研究
全氟和多氟烷基物质(PFAS)是一类大型工业化学品,其多样性、扩散和对环境/健康的影响最近已成为环境和健康决策者关注的主要问题。它们的普遍存在和化学恢复力进一步加剧了这种担忧,这使得从流域和其他受污染的环境中清除它们变得复杂。由于碳氟键的化学稳定性,它们很难降解。相反,另一种方法是吸附、浓缩,然后从污染地点去除PFAS。金属有机框架(mof)和共价有机框架(COFs)作为一种可能的吸附介质,可用于去除污染场所的PFAS,近年来受到了广泛的研究。为了更深入地了解COFs去除水道中PFAS的吸附能力,我们使用分子动力学模拟研究了不同孔隙大小的COFs对PFAS分子的吸附。我们研究了水溶液PFBA, PFOA和PFOS在不同孔径的共价三嗪基框架(CTF)中的吸收。这一吸附机理数据表明,在直径约为8 Å的孔隙中存在一个适居带,PFAS可以顺利地穿过孔隙。扩散到这些纳米孔的动力学因素有利于短链PFAS的吸附,尽管大的PFAS在热力学上是有利的。每个孔最初倾向于只吸附一个PFAS,占据孔口,直到局部COF表面饱和,然后每个孔可以发生多个占用。讨论PFAS浓度的影响及其与孔隙的相互作用将为提高PFAS吸附材料的选择性和容量的设计原则提供信息。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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CiteScore
1.90
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