Department of Chemical & Environmental Engineering, University of Arizona, 1133 E James E Rogers Way, Harshbarger 108, Tucson, AZ, 85721-0011, USA.
Department of Chemical & Environmental Engineering, University of Arizona, 1133 E James E Rogers Way, Harshbarger 108, Tucson, AZ, 85721-0011, USA; Hazen and Sawyer, Tempe, AZ, 85282, USA.
Water Res. 2020 Aug 15;181:115897. doi: 10.1016/j.watres.2020.115897. Epub 2020 May 19.
In this study, magnetic ion exchange (MIEX) resin was evaluated to remove six carboxylic and three sulfonic PFAS at environmentally relevant concentrations (∼300 ng/L) in groundwater with low organic content and aromaticity (0.78 mg/L of dissolved organic carbon, DOC and 0.96 L mgm of specific UV absorbance, SUVA). In order to evaluate PFAS adsorption, the apparent equilibrium constant for PFAS adsorption in a dilute system was derived as an indicator of the adsorption capacity of MIEX. In adsorption of PFAS, hydrophobic interactions induced by difluoromethylene and trifluoromethyl groups are known to be effective. However, the hydrophobic and charge interactions caused by such functional groups are not easily differentiable from each other since both are additive with respect to the chain length. In this study, the total negative atomic charge [∑Q(-)] was calculated using density functional theory (DFT) calculation and correlated with the apparent equilibrium constants. The negative atomic charge showed better correlation than the hydrophobicity (log D at pH 7) of PFAS, suggesting that the charge interaction would be a more plausible role of fluorinated moieties for adsorption in the MIEX process than the hydrophobic interaction. This was also bolstered by the similar adsorption kinetics and equilibrium of PFOS (log D = 3.05) and its less hydrophobic isomer (log D = 2.79), but with almost identical total negative atomic charge (8.05 and 8.06 of ∑Q(-), respectively). The regeneration efficiency of MIEX was also assessed. Almost complete restoration of PFAS adsorption capacity was achieved after 30 min of a regeneration process with a 10% w/w NaCl solution as a regenerant. The efficient regeneration was attributed to the effective desorption of dissolved organic matter that occupied sorptive sites predominantly.
在这项研究中，评估了磁性离子交换（MIEX）树脂在低有机芳香度（DOC 为 0.78mg/L，SUVA 为 0.96Lmgm）的地下水环境相关浓度（约 300ng/L）下去除六种羧酸和三种磺酸全氟羧酸的能力。为了评估全氟羧酸的吸附，从稀溶液体系中推导了全氟羧酸吸附的表观平衡常数，作为 MIEX 吸附容量的指标。在全氟羧酸的吸附中，已知二氟亚甲基和三氟甲基基团引起的疏水力是有效的。然而，由于这些官能团引起的疏水力和电荷相互作用彼此不易区分，因为它们都随链长而增加。在这项研究中，使用密度泛函理论（DFT）计算计算了总负原子电荷[∑Q(-)]，并与表观平衡常数相关联。负原子电荷的相关性优于全氟羧酸的疏水性（pH7 时的 logD），这表明在 MIEX 过程中，带电荷的相互作用比疏水力更有可能是氟化物部分吸附的作用。这也得到了 PFOS（logD=3.05）及其疏水性较低的异构体（logD=2.79）相似的吸附动力学和平衡的支持，但它们的总负原子电荷几乎相同（∑Q(-)分别为 8.05 和 8.06）。还评估了 MIEX 的再生效率。在使用 10%w/w 的 NaCl 溶液作为再生剂的 30min 再生过程后，几乎完全恢复了 MIEX 的全氟羧酸吸附能力。有效的再生归因于主要占据吸附位的溶解有机质的有效解吸。
