Helmholtz Centre for Environmental Research - UFZ, Department of Environmental Engineering, D-04318 Leipzig, Germany.
Helmholtz Centre for Environmental Research - UFZ, Department of Environmental Engineering, D-04318 Leipzig, Germany.
Chemosphere. 2021 Jun;273:128520. doi: 10.1016/j.chemosphere.2020.128520. Epub 2020 Oct 5.
Various activated carbon products show wide variability in adsorption performance towards perfluoroalkyl acids (PFAAs) and predictive tools are largely missing. In order to gain a better understanding on the adsorption mechanisms of PFAAs, perfluorooctanoic acid (PFOA) was compared with its fluorine-free analogon octanoic acid (OCA) as well as phenanthrene (nonionic) in terms of their response towards changes in carbon surface chemistry. For this approach, a commercial activated carbon felt (ACF) with high content of acidic surface groups was modified by amino-functionalisation as well as thermal defunctionalisation in H (yielding DeCACF). While improvement by amino-functionalisation was moderate, defunctionalisation drastically enhanced adsorption of PFOA and other PFAAs. In comparison, OCA and phenanthrene were much less affected. Electrostatic interactions and charge compensation provided by positively charged surface sites (quantified by their anion exchange capacity) are obviously more crucial for PFAAs than for common organic acids (such as the tested OCA). A possible reason is their exceptionally strong acidity with pK < 1. Nevertheless, at the best modified ACF material (DeCACF) the sorption coefficients (K) for PFOA and perfluorooctylsulfonic acid (PFOS) at environmentally relevant concentrations reach the range of 10 L/kg which is outstanding. DeCACF provides a surface with overall low polarity (low O-content), low density of acidic sites causing electrostatic repulsion, but nevertheless a sufficient density of charge-balancing sites for organic anions. The results of the present study contribute to an optimized selection of adsorbents for PFAA adsorption from water considering also various salt matrices and the presence of natural organic matter.
各种活性炭产品对全氟烷基酸（PFAAs）的吸附性能差异很大，而且缺乏预测工具。为了更好地了解 PFAAs 的吸附机制，本研究比较了全氟辛酸（PFOA）与其无氟类似物辛酸（OCA）以及非离子型菲（phenanthrene）在碳表面化学变化方面的响应。为此，采用氨基功能化和 H 热脱功能化的方法对商业活性炭毡（ACF）进行了改性，得到了含大量酸性表面基团的改性活性炭毡（DeCACF）。氨基功能化的改性效果适中，但脱功能化极大地增强了 PFOA 和其他 PFAAs 的吸附。相比之下，OCA 和菲的吸附受影响较小。带正电荷的表面位点（通过阴离子交换容量定量）提供的静电相互作用和电荷补偿对 PFAAs 显然比对常见有机酸（如测试的 OCA）更为重要。一个可能的原因是它们具有异常强的酸性，pK < 1。然而，在最佳改性的 ACF 材料（DeCACF）上，环境相关浓度下的 PFOA 和全氟辛基磺酸（PFOS）的吸附系数（K）达到了 10 L/kg 的范围，这是非常出色的。DeCACF 提供了一个整体低极性（低 O 含量）的表面，低密度的酸性位点导致静电排斥，但仍有足够数量的电荷平衡位点用于有机阴离子。本研究的结果有助于优化选择用于从水中吸附 PFAA 的吸附剂，同时考虑到各种盐基质和天然有机物的存在。
