Efficient removal of short-chain and long-chain PFAS by cationic nanocellulose
Efficient removal of short-chain and long-chain PFAS by cationic nanocellulose
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DOI：
10.1039/d3ta01851b
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发表时间：
2023-04-18
影响因子：
11.9
通讯作者：
Hsiao, Benjamin S.
中科院分区：
文献类型：
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作者：
Li, Duning;Lee, Cheng-Shiuan;Hsiao, Benjamin S.
尽管大多数制造商已停止使用长链全氟和多氟烷基物质（PFASs），包括全氟辛酸（PFOA）和全氟辛烷磺酸（PFOS），但短链PFASs仍被广泛应用。短链PFASs的毒性鲜为人知，且其吸附行为与长链PFASs不同。先前的研究表明，与吸附剂的静电相互作用是去除短链PFASs的主要机制。在本研究中，我们设计了一种高电荷密度的阳离子季铵化纳米纤维素（QNC），以提高从受污染水中去除短链和长链PFASs的效果。使用QNC吸附剂进行了系统的批量吸附试验，以比较其对不同链长和官能团的PFASs的去除效率。动力学研究表明，全氟丁酸（PFBA）、全氟丁烷磺酸（PFBS）和全氟辛烷磺酸（PFOS）的吸附速率很快，在1分钟至15分钟内达到接近平衡值（去除率>95%），而全氟辛酸（PFOA）达到平衡所需时间相对较长，为2小时（15分钟内去除率达到90%）。根据等温线结果，QNC吸附剂的最大吸附容量（Q(m)）呈现以下趋势：PFOS（Q(m)=559毫克/克或1.12毫摩尔/克）>PFOA（Q(m)=405毫克/克或0.98毫摩尔/克）>PFBS（Q(m)=319毫克/克或1.06毫摩尔/克）>PFBA（Q(m)=121毫克/克或0.57毫摩尔/克）。这种吸附顺序大体上与四种PFASs的疏水性趋势相符，而疏水性与PFASs的链长和官能团均有关。在竞争研究中，预先吸附的短链PFASs会被长链PFASs迅速解吸，这表明分子的疏水性在QNC的吸附过程中起着重要作用。最后，对所开发的QNC吸附剂处理受PFAS污染的地下水进行了测试，结果表明，即使吸附剂用量低至32毫克/升，该吸附剂对长链PFASs（C7 - C9）仍具有出色的去除效率（>95%）。然而，由于地下水中存在竞争成分，QNC吸附剂对短链PFASs（即PFBA和全氟戊酸（PFPeA））的去除效果不佳（去除率分别为0%和10%）。对照实验进一步证实了这一点，实验表明，在离子强度（NaCl）升高时，QNC对短链PFASs的去除性能下降，但对长链PFASs则不然，这可能是由于PFASs的阴离子官能团被无机阳离子中和了电荷。总体而言，QNC吸附剂的PFAS吸附能力有所提高，去除PFAS的效果几乎是颗粒活性炭的两倍，尤其是对短链PFASs。我们认为，QNC可与活性炭或离子交换树脂等常用处理方法配合使用，以去除多种PFAS污染物，朝着彻底修复PFAS污染的方向迈进。
Although most manufacturers stopped using long-chain per- and polyfluoroalkyl substances (PFASs), including perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), short-chain PFASs are still widely employed. Short-chain PFASs are less known in terms of toxicity and have different adsorption behavior from long-chain PFASs. Previous studies have shown electrostatic interaction with the adsorbent to be the dominant mechanism for the removal of short-chain PFASs. In this study, we designed a high charge density cationic quaternized nanocellulose (QNC) to enhance the removal of both short- and long-chain PFASs from contaminated water. Systematic batch adsorption tests were conducted using the QNC adsorbent to compare its efficiency against PFASs with varying chain lengths and functional groups. From the kinetic study, PFBA (perfluorobutanoic acid), PFBS (perfluorobutanesulfonic acid) and PFOS showed rapid adsorption rates, which reached near equilibrium values (>95% of removal) between 1 min to 15 min, while PFOA required a relatively longer equilibration time of 2 h (it obtained 90% of removal within 15 min). According to the isotherm results, the maximum adsorption capacity (Q(m)) of the QNC adsorbent exhibited the following trend: PFOS (Q(m) = 559 mg g(-1) or 1.12 mmol g(-1)) > PFOA (Q(m) = 405 mg g(-1) or 0.98 mmol g(-1)) > PFBS (Q(m) = 319 mg g(-1) or 1.06 mmol g(-1)) > PFBA (Q(m) = 121 mg g(-1) or 0.57 mmol g(-1)). This adsorption order generally matches the hydrophobicity trend among four PFASs associated with both PFAS chain length and functional group. In competitive studies, pre-adsorbed short-chain PFASs were quickly desorbed by long-chain PFASs, suggesting that the hydrophobicity of the molecule played an important role in the adsorption process on to QNC. Finally, the developed QNC adsorbent was tested to treat PFAS-contaminated groundwater, which showed excellent removal efficiency (>95%) for long-chain PFASs (C7-C9) even at a low adsorbent dose of 32 mg L-1. However, short-chain PFASs (i.e., PFBA and perfluoropentanoic acid (PFPeA)) were poorly removed by the QNC adsorbent (0% and 10% removal, respectively) due to competing constituents in the groundwater matrix. This was further confirmed by controlled experiments that revealed a drop in the performance of QNC to remove short-chain PFASs at elevated ionic strength (NaCl), but not for long-chain PFASs, likely due to charge neutralization of the anionic functional group of PFASs by inorganic cations. Overall, the QNC adsorbent featured improved PFAS adsorption capacity at almost two-fold of PFAS removal by granular activated carbons, especially for short-chain PFASs. We believe, QNC can complement the use of common treatment methods such as activated carbon or ionic exchange resin to remove a wide range of PFAS pollutants, heading towards the complete remediation of PFAS contamination.