Sorptive removal of per- and polyfluoroalkyl substances from aqueous solution: Enhanced sorption, challenges and perspectives

Synthesis and characterization of amine functionalized silylated clay for heavy metal adsorption: Thermodynamic and kinetic studies on Fe(III) ion

Amine functionalized bentonites were used as adsorbents for the bioremoval of Fe(III) ions, which led to the inclusion of functional groups such as -OH, -NH2, -OCH3, etc. FTIR, XRD, SEM, AFM, TG, BET, XRF, and CHNS analyzer were used to analyze the surface and textural characteristics. The influence of adsorption factors, such as pH, contact time, temperature, and initial concentration, have been investigated and tailored in batch adsorption experiments of Fe (III) metal ions. The maximum adsorption efficiency and capacity of modified BNT-APTMS is 100.90 % and 103.91 mg/g respectively. The adsorption process is best fit with Freundlich model (R2=0.998) than Langmuir model (R2=0.788) and the Temkin model D-R isotherm parameters indicating a physisorption process. A mechanism of spontaneous complexation was accomplished, because of the heterogeneity of the surface, electrostatic forces, pore filling, and π-π stacking. Follows PSO kinetics and favours Freundlich isotherm. The adsorbent substance showed a remarkable capacity for regeneration, assuring the substance's stability and reusability.

Covalent Organic Framework-Involved Sensors for Efficient Enrichment and Monitoring of Food Hazards: A Systematic Review

The food safety issues caused by environmental pollution have posed great risks to human health that cannot be ignored. Hence, the precise monitoring of hazard factors in food has emerged as a critical concern for the food safety sector. As a novel porous material, covalent organic frameworks (COFs) have garnered significant attention due to their large specific surface area, excellent thermal and chemical stability, modifiability, and abundant recognition sites. This makes it a potential solution for food safety issues. In this research, the synthesis and regulation strategies of COFs were reviewed. The roles of COFs in enriching and detecting food hazards were discussed comprehensively and extensively. Taking representative hazard factors in food as the research object, the expression forms and participation approaches of COFs were explored, along with the effectiveness of corresponding detection methods. Finally, the development directions of COFs in the future as well as the problems existing in practical applications were discussed, which was beneficial to promote the application of COFs in food safety and beyond.

Efficient adsorption of short-chain perfluoroalkyl substances by pristine and Fe/Cu-loaded reed straw biochars

As the substitutes of legacy long-chain per-/polyfluoroalkyl substances (PFASs), short-chain PFASs have been widely detected in the environment. Compared to long-chain PFASs, short-chain PFASs have smaller molecules and are more hydrophilic. Therefore, they are more likely to experience long-distance transport and pose lasting environmental impacts. In this study, Fe-doped (R-Fe) and Cu-doped biochars (R-Cu) were prepared using reed straw biochar (R). The results showed that the PFBA and PFPeA sorption capacities of R-Fe were 25.81 and 43.59 mg g-1, 1.65 and 1.55 times higher than those of R, respectively. The PFBA and PFPeA sorption capacities of R-Cu were 19.34 and 33.69 mg g-1, 1.24 and 1.20 times higher than those of R, respectively. In addition, R, R-Fe, and R-Cu exhibited higher PFBA and PFPeA sorption capacities than the biochars previously reported. The excellent PFAS sorption performances of the biochars were attributed to the highly porous structure of R, which provided rich adsorption sites. Ion-pair sorption, pore filling, electrostatic interaction between the Fe/Cu and cationic groups on biochar and the anionic groups of PFASs, and hydrophobic interaction between the hydrophobic surface of biochar and the fluorinated tails of PFASs were the underlying sorption mechanisms. The biochars presented high removal rates (>86 %) of multiple PFASs (∑PFAS: 350 μg L-1) from synthetic wastewaters, including legacy and emerging PFASs of different chain lengths and with different functional groups. The biochars reported in this study are promising candidate adsorbents for treating waters contaminated with short-chain PFASs.

Understanding the Selective Removal of Perfluoroalkyl and Polyfluoroalkyl Substances via Fluorine-Fluorine Interactions: A Critical Review

As regulatory standards for per- and polyfluoroalkyl substances (PFAS) become increasingly stringent, innovative water treatment technologies are urgently demanded for effective PFAS removal. Reported sorbents often exhibit limited affinity for PFAS and are frequently hindered by competitive background substances. Recently, fluorinated sorbents (abbreviated as fluorosorbents) have emerged as a potent solution by leveraging fluorine-fluorine (F···F) interactions to enhance selectivity and efficiency in PFAS removal. This review delves into the designs and applications of fluorosorbents, emphasizing how F···F interactions improve PFAS binding affinity. Specifically, the existence of F···F interactions results in removal efficiencies orders of magnitude higher than other counterpart sorbents, particularly under competitive conditions. Furthermore, we provide a detailed analysis of the fundamental principles underlying F···F interactions and elucidate their synergistic effects with other sorption forces, which contribute to the enhanced efficacy and selectivity. Subsequently, we examine various fluorosorbents and their synthesis and fluorination techniques, underscore the importance of accurately characterizing F···F interactions through advanced analytical methods, and emphasize the significance of this interaction in developing selective sorbents. Finally, we discuss challenges and opportunities associated with employing advanced techniques to guide the design of selective sorbents and advocate for further research in the development of sustainable and cost-effective treatment technologies leveraging F···F interactions.

Enhanced sorption and destruction of PFAS by biochar-enabled advanced reduction process

The biochar-enabled advanced reduction process (ARP) was developed for enhanced sorption (by biochar) and destruction of PFAS (by ARP) in water. First, the biochar (BC) was functionalized by iron oxide (Fe3O4), zero valent iron (ZVI), and chitosan (chi) to produce four biochars (BC, Fe3O4-BC, ZVI-chi-BC, and chi-BC) with improved physicochemical properties (e.g., specific surface area, pore structure, hydrophobicity, and surface functional groups). Batch sorption experimental results revealed that compared to unmodified biochar, all modified biochars showed greater sorption efficiency, and the chi-BC performed the best for PFAS sorption. The chi-BC was then selected to facilitate reductive destruction and defluorination of PFAS in water by ARP in the UV-sulfite system. Adding chi-BC in UV-sulfite ARP system significantly enhanced both degradation and defluorination efficiencies of PFAS (up to ∼100% degradation and ∼85% defluorination efficiencies). Radical analysis using electron paramagnetic resonance (EPR) spectroscopy showed that sulfite radicals dominated at neutral pH (7.0), while hydrated electrons (eaq-) were abundant at higher pH (11) for the efficient destruction of PFAS in the ARP system. Our findings elucidate the synergies of biochar and ARP in enhancing PFAS sorption and degradation, providing new insights into PFAS reductive destruction and defluorination by different reducing radical species at varying pH conditions.

Perfluoroalkyl acid adsorption by styrenic β-cyclodextrin polymers, anion-exchange resins, and activated carbon is inhibited by matrix constituents in different ways

Perfluoroalkyl acids (PFAAs) are ubiquitous environmental contaminants of global concern, and adsorption processes are the most widely used technologies to remove PFAAs from water. However, there remains little data on the ways that specific water matrix constituents inhibit the adsorption of PFAAs on different adsorbents. In this study, we evaluated the adsorption of 13 PFAAs on two styrene-functionalized β-cyclodextrin (StyDex) polymers, an activated carbon (AC), and an anion-exchange resin (AER) in the absence and presence of specific water matrix constituents (16 unique water matrices) in batch experiments. All four adsorbents exhibited some extent of adsorption inhibition in the presence of inorganic ions and/or humic acid (HA) added as a surrogate for natural organic matter. Two PFAAs (C5-C6 perfluorocarboxylic acids (PFCAs)) were found to exhibit relatively weak adsorption and five PFAAs (C6-C8 perfluorosulfonic acids (PFSAs) and C9-C10 PFCAs) were found to exhibit relatively strong adsorption on all four adsorbents across all matrices. Adsorption inhibition was the greatest in the presence of Ca2+ (direct site competition) and HA (direct site competition and pore blockage) for AC, NO3- (direct site competition) and Ca2+ (chemical complexation) for the AER, and SO42- (compression of the double layer) for the StyDex polymers. The pattern of adsorption inhibition of both StyDex polymers were similar to each other but different from AC and AER, which demonstrates the distinctive PFAA adsorption mechanism on StyDex polymers. The unique performance of each type of adsorbent confirms unique adsorption mechanisms that result in unique patterns of adsorption inhibition in the presence of matrix constituents. These insights could be used to develop models to predict the performance of these adsorbents in real water matrices and afford rational selection of adsorbents based on water chemistry for specific applications.

Natural mineral and industrial solid waste-based adsorbent for perfluorooctanoic acid and perfluorooctane sulfonate removal from surface water: Advances and prospects

PER: and polyfluorinated alkyl substances, especially perfluorooctanoic acid and perfluorooctane sulfonic acid (PFOX), have attracted considerable attention lately because of their widespread occurrence in aquatic environment and potential biological toxicity to animals and human beings. The development of economical, efficient, and engineerable adsorbents for removing PFOX in water has become one of the research focuses. This review summarized the recent progress on natural mineral and industrial solid based adsorbent (NM&ISW-A) and removal mechanisms concerning PFOX onto NM&ISW-A, as well as proposed the current challenges and future perspectives of using NM&ISW-A for PFOX removal in water. Kaolinite and montmorillonite are usually used as model clay minerals for PFOX removal, and have been proved to adsorb PFOX by ligand exchange and electrostatic attraction. Fe-based minerals, such as goethite, magnetite, and hematite, have better PFOX adsorption capacity than clay minerals. The adsorbent prepared from industrial solid waste by high temperature roasting has great potential application prospects. Fabricating nanomaterials, amination modification, surfactant modification, fluorination modification, developing versatile composites, and designing special porous structure are beneficial to improve the adsorption performance of PFOX onto NM&ISW-A by enhancing the specific surface area, positive charge, and hydrophobicity. Electrostatic interaction, hydrophobic interaction, hydrogen bond, ligand and ion exchange, and self-aggregation (formation of micelle or hemimicelle) are the main adsorption mechanisms of PFOX by NM&ISW-A. Among them, electrostatic and hydrophobic interactions play a considerable role in the removal of PFOX by NM&ISW-A. Therefore, NM&ISW-A with electrostatic functionalities and considerable hydrophobic segments enables rapid, efficient, and high-capacity removal of PFOX. The future directions of NM&ISW-A for PFOX removal include the preparation and regeneration of engineerable NM&ISW-A, the development of coupling technology for PFOX removal based on NM&ISW-A, the in-depth research on adsorption mechanism of PFOX by NM&ISW-A, as well as the development of NM&ISW-A for PFOX alternatives removal. This review paper would be helpful the comprehensive understanding of NM&ISW-A potential for PFOX removal and the PFOX removal mechanisms, and identifies the gaps for future research and development.

Fabrication of molecularly imprinted carbon nanotubes integrating ionic liquids for efficient detection of perfluoroalkyl carboxylic acid in environmental water

It is extremely significant while challenging to accurately detect low-levels of perfluoroalkyl carboxylic acid compounds (PFCAs) in environmental water. Herein, adopting perfluorotetradecanoic acid as the dummy template, selective molecularly imprinted composites (CNTs@ILs@MIPs) grafted carbon nanotubes integrating hydrophilic ionic liquids were successfully prepared via surface imprinting and dummy-template imprinting techniques. The obtained CNTs@ILs@MIPs were applied as selective extraction adsorbent for specifically extract PFCAs in environmental water coupled with gas chromatography-mass spectrometry quantification. Detailed studies were conducted on the main preparation parameters and extraction conditions. The CNTs@ILs@MIPs displayed excellent adsorptivity, and the established method exhibited low LODs (0.60-1.64 ng L-1), wide linearity with R2 above 0.9994, and satisfactory adsorption recoveries (80.5-112.5%) for seven PFCAs. This proposed method provides a new applicable approach for the detection of targeted pollutants in environmental water by utilizing the high affinity and recognition ability of molecularly imprinted carbon nanotube functional materials modified with ionic liquids.

Surface Modification of Graphene Oxide for Fast Removal of Per- and Polyfluoroalkyl Substances (PFAS) Mixtures from River Water

Per- and polyfluoroalkyl substances (PFAS) make up a diverse group of industrially derived organic chemicals that are of significant concern due to their detrimental effects on human health and ecosystems. Although other technologies are available for removing PFAS, adsorption remains a viable and effective method. Accordingly, the current study reported a novel type of graphene oxide (GO)-based adsorbent and tested their removal performance toward removing PFAS from water. Among the eight adsorbents tested, GO modified by a cationic surfactant, cetyltrimethylammonium chloride (CTAC), GO-CTAC was found to be the best, showing an almost 100% removal for all 11 PFAS tested. The adsorption kinetics were best described by the pseudo-second-order model, indicating rapid adsorption. The isotherm data were well supported by the Toth model, suggesting that PFAS adsorption onto GO-CTAC involved complex interactions. Detailed characterization using scanning electron microscopy-energy dispersive X-ray spectroscopy, Fourier transform infrared, thermogravimetric analysis, X-ray diffraction, and X-ray photoelectron spectroscopy confirmed the proposed adsorption mechanisms, including electrostatic and hydrophobic interactions. Interestingly, the performance of GO-CTAC was not influenced by the solution pH, ionic strength, or natural organic matter. Furthermore, the removal efficiency of PFAS at almost 100% in river water demonstrated that GO-CTAC could be a suitable adsorbent for capturing PFAS in real surface water.

Roles of varying carbon chains and functional groups of legacy and emerging per-/polyfluoroalkyl substances in adsorption on metal-organic framework: Insights into mechanism and adsorption prediction

Metal-organic frameworks (MOFs) are promising adsorbents for legacy per-/polyfluoroalkyl substances (PFASs), but they are being replaced by emerging PFASs. The effects of varying carbon chains and functional groups of emerging PFASs on their adsorption behavior on MOFs require attention. This study systematically revealed the structure-adsorption relationships and interaction mechanisms of legacy and emerging PFASs on a typical MOF MIL-101(Cr). It also presented an approach reflecting the average electronegativity of PFAS moieties for adsorption prediction. We demonstrated that short-chain or sulfonate PFASs showed higher adsorption capacities (μmol/g) on MIL-101(Cr) than their long-chain or carboxylate counterparts, respectively. Compared with linear PFASs, their branched isomers were found to exhibit a higher adsorption potential on MIL-101(Cr). In addition, the introduction of ether bond into PFAS molecule (e.g., hexafluoropropylene oxide dimeric acid, GenX) increased the adsorption capacity, while the replacement of CF2 moieties in PFAS molecule with CH2 moieties (e.g., 6:2 fluorotelomer sulfonate, 6:2 FTS) caused a decrease in adsorption. Divalent ions (such as Ca2+ and SO42-) and solution pH have a greater effect on the adsorption of PFASs containing ether bonds or more CF2 moieties. PFAS adsorption on MIL-101(Cr) was governed by electrostatic interaction, complexation, hydrogen bonding, π-CF interaction, and π-anion interaction as well as steric effects, which were associated with the molecular electronegativity and chain length of each PFAS. The average electronegativity of individual moieties (named Me) for each PFAS was estimated and found to show a significantly positive correlation with the corresponding adsorption capacity on MIL-101(Cr). The removal rates of major PFASs in contaminated groundwater by MIL-101(Cr) were also correlated with the corresponding Me values. These findings will assist with the adsorption prediction for a wide range of PFASs and contribute to tailoring efficient MOF materials.

Industrializable and pH-tolerant electropositive imidazolium chloride polymer for high-efficiency removal of perfluoroalkyl carboxylic acids from aqueous solution

In recent years, various materials have been used to adsorb and remove perfluoroalkyl compounds from water. However, most of these materials have limited applications due to their high cost, complex synthesis, inadequate selectivity and sensitivity, and, even worse, the possibility of introducing secondary pollution. Here, under mild conditions, we prepared an inexpensive imidazolium chloride and nitrogen-rich polymer (TAGX-Cl) with a high cationic loading rate and a high yield (>82%). The adsorbent exhibits excellent pH tolerance (pH=1-9) and achieves nearly 99.9% removal of nine perfluoroalkyl carboxylic acids (PFCAs) within 120 min. Experimental data and theoretical simulations confirmed that synergistic electrostatic interactions, hydrogen bonds, and P-π interactions control the adsorptive ability of TAGX-Cl. This work provides a practical strategy for PFCAs removal.

Sorption of per- and poly-fluoroalkyl substances and their precursors on activated carbon under realistic drinking water conditions: Insights into sorbent variability and PFAS structural effects

Recent stringent drinking water quality standards create challenges for water utilities to meet these standards. Advanced treatment techniques will have to be applied on many drinking water production locations to meet these quality standards. This study investigated the sorption of per- and polyfluorinated-alkyl substances (PFAS) onto granular activated carbon (GAC). The study was performed at environmentally relevant PFAS concentrations and a realistic water-to-GAC ratio, providing a realism often overlooked in existing studies. Three different forms of GAC were evaluated, differing in micropore and mesopore structures. Tap water spiked with 5 ng/L of each of 31 PFAS was used in the sorption experiments, i.e. perfluorocarboxylic acids (C4-C12), perfluorosulfonic acids (PFSA, C5-C10) including linear and branched isomers, and three groups of PFAS precursors (per-/polyfluoroalkyl ether acids, sulfonamides, and sulfonamide acetic acids). The three studied GAC did not exhibit distinct differences in PFAS sorption. The removal of PFAS was below 50 % for most studied PFAS, except for the short-chain PFAS precursors. Sorption was affected by both the carbon chain length and functional groups for PFAS, while this was not observed for PFAS precursors. The presence of ether linkages and sulfonamide groups notably enhanced sorption. Linear and branched PFSA demonstrated similar sorption behavior, whereas branched isomers of the sulfonamide acetic acid precursors exhibited significantly higher sorption. This indicates that sorption was determined by both hydrophobic and electrostatic interactions. Given the relatively low PFAS removal by GAC under environmentally relevant test conditions, further improvements in sorbents are required to ensure that PFAS concentrations in produced drinking water comply with drinking water standards.

Porous polypyrrole with a vesicle-like structure for efficient removal of per- and polyfluoroalkyl substances from water: Crucial role of porosity and morphology

Herein, a vesicle-like and porous polypyrrole (pPPy) was fabricated by in suit self-template method to efficiently capture per- and polyfluoroalkyl substances (PFASs) and the important role of porosity and morphology in PFAS removal was explored. Compared to solid PPy (sPPy), the porosity and vesicle-like morphology of pPPy endowed it with excellent properties such as large specific surface area (108.9 m2/g vs. 22.3 m2/g), suitable pore sizes (17.4 nm), dispersity, and high hydrophilicity, which facilitated mass transfer and enhanced PFAS sorption performance. The estimated sorption capacities of pPPy for perfluorooctanoic acid (PFOA) and perfluorooctanesulfonate (PFOS) were 509 mg/g and 532 mg/g, respectively, which were ∼2 times higher than sPPy. Furthermore, pPPy demonstrated PFAS removal of ≥ 90% across a wide pH range (3-9) and varying humic acid concentrations (0-50 mg/L). In actual water matrices, pPPy efficiently removed 12 short-chain (C-F number: 3-6) and long-chain PFASs (>90% removal for major PFASs), outperforming sPPy by ∼1.2-2.5 times. Notably, the enlarged porosity and regular morphology of pPPy significantly enhanced the removal of short-chain PFASs by ∼2 times. The spent pPPy could be regenerated and reused over 5 times. This research provides valuable insights for designing efficient PFAS sorbents by emphasizing control over porosity and morphology.

Adsorption of per- and polyfluoroalkyl substances (PFAS) by ionic liquid-modified clays: Effect of clay composition and PFAS structure

Organically modified clays have been reported as a promising class of adsorbents for the treatment of per- and polyfluoroalkyl substances (PFAS), a group of emerging contaminants of widespread concerns. Here, we reported the development and evaluation of ionic liquid (IL)-modified clays prepared with various natural clays to explore the role of clay substrate in the adsorption of eight persistent perfluoroalkyl acids (PFAAs). Based on detailed adsorption isotherm study, we found that the adsorption capacities of PFAAs were closely related to the cation exchange capacities of the raw clays and correspondingly the IL loadings of the modified clays. Additionally, a positive correlation was observed between the adsorption affinity of PFAAs onto IL-modified clays and the octanol-water distribution coefficient (Dow) of PFAAs. Adsorption free energy analysis suggested that both electrostatic and hydrophobic interactions played important roles in the adsorption of PFAAs onto IL-modified clays. Although electrostatic interactions were more predominant, the contribution of hydrophobic interactions increased with the increasing carbon number of perfluoroalkyl moiety of PFAAs, resulting in more favorable adsorption of long-chain PFAAs than their short-chain homologs. The performance of IL-modified clays was further demonstrated for the removal of PFAA mixtures under environmentally relevant conditions. Overall, results of this work can provide important insights into guiding the design of organically modified clay adsorbents for PFAS treatment.

An Overview on Recent Advances in Biomimetic Sensors for the Detection of Perfluoroalkyl Substances

Per- and polyfluoroalkyl substances (PFAS) are a class of materials that have been widely used in the industrial production of a wide range of products. After decades of bioaccumulation in the environment, research has demonstrated that these compounds are toxic and potentially carcinogenic. Therefore, it is essential to map the extent of the problem to be able to remediate it properly in the next few decades. Current state-of-the-art detection platforms, however, are lab based and therefore too expensive and time-consuming for routine screening. Traditional biosensor tests based on, e.g., lateral flow assays may struggle with the low regulatory levels of PFAS (ng/mL), the complexity of environmental matrices and the presence of coexisting chemicals. Therefore, a lot of research effort has been directed towards the development of biomimetic receptors and their implementation into handheld, low-cost sensors. Numerous research groups have developed PFAS sensors based on molecularly imprinted polymers (MIPs), metal-organic frameworks (MOFs) or aptamers. In order to transform these research efforts into tangible devices and implement them into environmental applications, it is necessary to provide an overview of these research efforts. This review aims to provide this overview and critically compare several technologies to each other to provide a recommendation for the direction of future research efforts focused on the development of the next generation of biomimetic PFAS sensors.

In situ self-sacrificial synthesis of polypyrrole/biochar composites for efficiently removing short- and long-chain perfluoroalkyl acid from contaminated water

Efficient removal of perfluoroalkyl acids (PFAAs), especially short-chain ones, from contaminated water is of great challenge and is urgently called for so as to safeguard the ecosystem and human health. Herein, polypyrrole (PPy) functionalized biochar (BC) composites were innovatively synthesized by an in situ self-sacrificial approach to allow efficient capture of PFAAs with different chain lengths. Compared with conventional PPy-based composites synthesized by direct polymerization using FeCl3 as an oxidizing agent, PPy/BC composites were fabricated utilizing freshly generated Fe3+ as an oxidizing agent from self-sacrificial Fe3O4 for pyrrole monomers in situ polymerizing on BC. As a result, with the support of BC and gradual release of Fe3+, PPy overcame its tendency to aggregate and became uniformly dispersed on BC, and meanwhile, PPy could well tailor the surface chemistry of BC to endow its positively charged surface. Consequently, the composites exhibited strong sorption capacities of 3.89 and 1.53 mmol/g for short-chain perfluorobutanoic acid (PFBA) and perfluorobutane sulfonic acid (PFBS), 2.55 and 1.22 mmol/g for long-chain perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), respectively, which were superior to those of pristine BC, commercial activated carbon, and anion exchange resins reported. Additionally, they could effectively remove 17 different classes of per- and polyfluoroalkyl substances (PFAS) (removal >95%) from actual PFAS-contaminated water, and the spent sorbent could be well regenerated and reused at least 5 times. An integrated analysis indicated that such an outstanding PFAA sorption performance on PPy/BC composites could be mainly attributed to surface adsorption enhanced by electrostatic attractions (anion exchange interaction) with the traditional hydrophobic interaction and pore filling of less contribution, particularly for short-chain analogues. These results are expected to inform the design of BC with greater ability to remove PFAS from water and the new sorbent could help water facilities comply with PFAS regulations.

The Specific Removal of Perfluorooctanoic Acid Based on Pillar[5]arene-Polymer-Packed Nanochannel Membrane

The conspicuous surface activity and exceptional chemical stability of perfluorooctanoic acid, commonly referred to as PFOA, have led to its extensive utilization across a broad spectrum of industrial and commercial products. Nonetheless, significant concerns have arisen regarding the environmental presence of PFOAs, driven by their recognized persistence, bioaccumulative nature, and potential human health risks. In the realm of sustainable agriculture, a pivotal challenge revolves around the development of specialized materials capable of effectively and selectively eliminating PFOA from the environment. This study proposes harnessing the exceptional properties of a pillar[5]arene polymer to construct a nanochannel membrane filled with tryptophan-alanine dipeptide pillar[5]arene polymer. Through the functionalization of these nanochannel membranes, we achieved a PFOA removal rate of 0.01 mmol L-1 min-1, surpassing the rates observed with other control chemicals by a factor of 4.5-15. The research on PFOA removal materials has been boosted because of the creation of this highly selective PFOA removal membrane.

Revealing the factors resulting in incomplete recovery of perfluoroalkyl acids (PFAAs) when implementing the adsorbable and extractable organic fluorine methods

Per- and polyfluoroalkyl substances (PFASs) are environmental contaminants of concern. Techniques that quantify total organic fluorine (TOF) such as the adsorbable organic fluorine (AOF) and extractable organic fluorine (EOF) methods are important for PFAS risk assessments. The objective of this study was to systematically evaluate each step of the AOF (loading, washing, combustion) and EOF (loading, washing, elution, combustion) methods for the recovery of ten ultrashort-, short-, and long-chain unsubstituted perfluoroalkyl acids (PFAAs). We measured the overall recovery of fluoride for each method for each PFAA, and the recovery of each PFAA around the loading, washing, and elution steps. We also measured the combustion efficiency of each PFAA by direct combustion. The overall AOF and EOF recovery ranged from 9.3%-103.3% to 21.0%-108.1%, respectively, with higher recoveries measured for PFAAs with increasing chain length in both methods. The three ultrashort-chain PFAAs (trifluoroacetic acid, perfluoropropionic acid, and perfluoropropanesulfonic acid) exhibited the lowest overall recoveries from 9.3-25.2% for AOF and 21.0-51.5% for EOF. We found that decreases in the overall recovery are the result of losses of ultrashort- and short-chain PFAAs during the washing step and the incomplete mineralization of perfluoroalkyl sulfonic acids during combustion for AOF and incomplete elution of short- and long-chain PFAAs and the loss of ultrashort-chain PFAAs during the washing step for EOF. Our data suggest that the EOF method is more appropriate than the AOF method for measuring TOF in samples containing ultrashort- and short-chain PFAAs and that methodological improvements are possible with a focus on the washing, elution, and combustion steps.