Adsorption Of Perfluorooctanoic Acid Research Articles

Fast Perfluorooctanoic Acid (PFOA) Removal with Honeycomb-like Nitrogen-Doped Carbon Nanosheets: Mechanisms for the Selective Adsorption of PFOA over Competing Contaminants/Water Matrix

Fast Perfluorooctanoic Acid (PFOA) Removal with Honeycomb-like Nitrogen-Doped Carbon Nanosheets: Mechanisms for the Selective Adsorption of PFOA over Competing Contaminants/Water Matrix

Removal of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) by coagulation: Influence of coagulant and dosing conditions

Per- and polyfluoroalkyl substances (PFAS) pose significant risks to the environment and human health. Perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) are two of the most frequently detected PFAS in the environment. In most surface water drinking water treatment works (WTW), coagulation is the first processes exposed to a range of contaminants, including PFAS. While not designed to be a process for removal of micropollutants, it is important to understand the fate of PFAS in coagulation processes, intended or otherwise, to determine whether water treatment sludge can be a significant sink for this group of micropollutants. This work advances understanding of PFAS removal in coagulation processes by comparing the removal of PFOA and PFOS by four metal coagulants (Zr, Zn, Fe, and Al) from real water matrices. The coagulant performance followed the order Al > Fe > Zr > Zn. Al was taken forward for further evaluation, with significant removal of PFAS (>15 % for PFOA and > 30 % for PFOS) being observed when the pH<5.5 and the dose was > 5 mg Al·L-1. The adsorption of PFOA and PFOS onto flocs through hydrophobic interaction was the primary removal route. The impacts of background matrix on the mechanisms of coagulation for PFAS were explored using five organic compounds. Macromolecular organic compounds contributed to an increase in removal due to the sorption of PFAS and subsequent removal of the organic-PFAS aggregate during coagulation. Low molecular weight organic matter inhibited the removal of PFAS due to the ineffective removal of these compounds during coagulation.

Removal of per- and polyfluoroalkyl substances (PFAS) from water using magnetic cetyltrimethylammonium bromide (CTAB)-modified pine bark

Per- and polyfluoroalkyl substances (PFAS) have gained global attention in recent years due to their adverse effect on environment and human health. In this study, a novel and cost-effective sorbent was developed utilizing forestry by-product pine bark and tested for the removal of PFAS compounds from both synthetic solutions and contaminated groundwater. The synthesis of the adsorbent included two steps: 1) loading of cetyltrimethylammonium bromide (CTAB) onto the pine bark and followed by 2) a simple coating of magnetite nanoparticles. The developed sorbent (MC-PB) exhibited 100 % perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) removal from synthetic solution (10 µg/L PFOA and PFOS) and enabled quick magnetic separation. A rapid removal of PFOA (> 80 %) by MC-PB was observed within 10 min from synthetic PFOA solution and the adsorption equilibrium was reached within 4 h, achieving > 90 % removal of PFOA (dosage 2 g/L, PFOA 10 mg/L, initial pH 4.2). The PFOA adsorption kinetics fitted well to an optimized pseudo-order model (R2=0.929). Intra-particle diffusion and Boyd models suggested that the adsorption process was not governed by pore diffusion. The maximum PFOA adsorption capacity was found to be 69 mg/g and the adsorption isotherm was best described by the Dual Mode Model (R2=0.950). The MC-PB demonstrated > 90 % PFOA and PFOS removal from contaminated groundwater. Furthermore, both short- and long-chain perfluorosulfonic acids and 6:2 fluorotelomer sulfonate were efficiently removed resulting in 83.9 % removal towards total PFAS (2 g/L dosage).

Removal of PFOA from water by activated carbon adsorption: Influence of pore structure

Activated carbon (AC) adsorption is a practical process for the removal of perfluorooctanoic acid (PFOA) in aquatic environments, but the relationship between its pore structure and adsorption performance is not well understood. In this study, the KOH-activated carbons (KACs) with different tailored pore structures were prepared, and presented a 2.61-fold higher adsorption capacity and a 2.21-fold higher adsorption rate than the raw AC. An in situ characterization method and a modified adsorption model were introduced to investigate the impact of pore size, which demonstrated that the ultra-micropores (<1.2 nm) and small mesopores (2.0–3.0 nm) contributed significantly to the adsorption of PFOA, with the highest mean contribution factor (k) of 0.45 and the second highest of 0.39, respectively. Molecular dynamics simulations revealed that PFOA molecules tend to attach to the pore walls at various pore sizes. The adsorption of PFOA in the ultra-micropores was dominated by enhanced interactions due to the overlapping potentials of the bilateral pore walls (maximum of −567.32 Kcal·mol−1) and hydrophobic interactions. PFOA micelles or hemi-micelles could be formed in the small mesopores, allowing them to function as both the molecule transportation channels and strong adsorption sites. This study would guide the development of activated carbon tailored for the selective adsorption of PFOA from water.

3D-printed indium oxide monoliths for PFAS removal

More efficient removal methods for per- and polyfluoroalkyl substances (PFAS), anthropogenic compounds with high persistence in the environment, are urgently needed due to their significant adverse health effects. Current technologies for PFAS removal in water are limited by incomplete degradation or practical concerns about the use of slurry-based adsorbents. In this study, self-supported indium oxide (In2O3) monoliths were produced via extrusion-based 3D printing and used for the removal of perfluorooctanoic acid (PFOA) via adsorption in a recirculating flow system. A detailed study of the sintering temperature, monolith geometry, and flow rate allowed maximising PFOA adsorption due to the improvement of PFOA diffusion and the increased number of active sites on the monolith, resulting in 53 % of PFOA removal with fast adsorption kinetics in 3 h. Additionally, a low-temperature pyrolysis process at 500 °C effectively regenerated the In2O3 monoliths, allowing reusing the monoliths for three adsorption cycles, while also improving the PFOA removal to 75 % in 3 h. The regenerated In2O3 monoliths not only have a high adsorption capacity (0.16 mg g−1), but also required a much shorter time to reach the adsorption equilibrium compared with other adsorbents reported in the literature. The effectiveness, robustness and reusability of the 3D printed In2O3 monoliths highlight their potential as an efficient and sustainable adsorbent for PFAS removal. The approach presented here represents an effective strategy for the fabrication of complex adsorbents, which are reusable and can be easily handled, eliminating the expensive downstream removal required for slurries while offering a clear route for scale-up towards industrial use.

Vesicles exhibit high-performance removal of per-and polyfluoroalkyl substances (PFAS) depending on their hydrophobic groups

The removal of per- and polyfluoroalkyl substances (PFAS) from drinking water is urgently needed. Here, we demonstrated high performance of vesicles on PFAS adsorption. Vesicles used in this study were enclosed amphiphile bilayers keeping their hydrophobic groups inside and their hydrophilic groups outside in water. The distribution coefficient Kd of perfluorooctane sulfonic acid (PFOS) for vesicles was 5.3 × 105 L/kg, which is higher than that for granulated activated carbon (GAC), and Kd of perfluorooctanoic acid (PFOA) for vesicles was 103–104 L/kg. The removal efficiencies of PFOA and PFOS adsorption on DMPC vesicles were 97.1 ± 0.1% and 99.4 ± 0.2%, respectively. The adsorption behaviors of PFOA and PFOS on vesicles were investigated by changing the number of cis-double bonds in the hydrophobic chains of the vesicle constituents. Moreover, vesicles formed by membranes in the different phases were also tested. The results revealed that, when vesicles are formed of a membrane in the liquid-crystalline (liquid-like) phase, the adsorption amounts of both PFOA and PFOS increased as the cis-double bond in the hydrocarbon chains decreased, which is considered due to molecular shape similarity. When vesicles are formed of a membrane in the gel (solid-like) phase, they do not adsorb PFAS as much as in the liquid-crystalline phase, even though the hydrocarbon chains do not have any cis-double bond. Our findings demonstrate that vesicles can be utilized as PFAS adsorbents by optimizing the structure of vesicle constituents and their thermodynamical phase. Indeed, the vesicles (DMPC) were demonstrated that they can adsorb PFOA and PFOS, and be coagulated by a coagulant even in environmental water. The coagulation will enable the removal of PFOA and PFOS from the water after adsorption.

Adsorption behaviors of perfluorooctanoic acid on aged microplastics.

The presence of perfluoroalkyl substances (PFAS) in the environment poses a significant threat to ecological safety and environmental health. Widespread microplastics (MPs) have been recognized as vectors for emerging contaminants due to human activities. However, the adsorption behaviors of PFAS on MPs, especially on aged MPs, have not been extensively investigated. This study aimed to investigate the adsorption behaviors of perfluorooctanoic acid (PFOA) on aged MPs (polystyrene, polyethylene, and polyethylene terephthalate) treated with UV irradiation and persulfate oxidation under salinity and dissolve organic matter (DOM) condition. Carbonyl index values of MPs increased after the aged treatment, indicating the production of oxygen-containing groups. The PFOA adsorption on aged MPs was impacted by the co-existence of Na+ ions and DOM. As PFOA adsorption onto aged MPs was mainly controlled by hydrophobic interaction, the electrostatic interaction also made a contribution, but there was no significant change in PFOA adsorption behavior between the pristine and aged MPs. While these findings provide insight into PFAS adsorption on aged MPs, further research is necessary to account for the complexity of the real environment. PRACTITIONER POINTS: Adsorption behaviors of perfluorooctanoic acid (PFOA) on aged microplastics were investigated. Hydrophobic interaction mainly controlled PFOA adsorption on aged microplastics (MPs). Co-existence dissolve organic matter and salinity influenced PFOA adsorption behaviors on aged MPs.

Zirconium-Based Metal-Organic Frameworks with Free Hydroxy Groups for Enhanced Perfluorooctanoic Acid Uptake in Water.

Perfluorooctanoic acid (PFOA) is a highly recalcitrant organic pollutant, and its bioaccumulation severely endangers human health. While various methods are developed for PFOA removal, the targeted design of adsorbents with high efficiency and reusability remains largely unexplored. Here the rational design and synthesis of two novel zirconium-based metal‒organic frameworks (MOFs) bearing free ortho-hydroxy sites, namely noninterpenetrated PCN-1001 and twofold interpenetrated PCN-1002,are presented. Single crystal analysis of the pure ligand reveals that intramolecular hydrogen bonding plays a pivotal role in directing the formation of MOFs with free hydroxy groups. Furthermore, the transformation from PCN-1001 to PCN-1002 is realized. Compared to PCN-1001, PCN-1002 displays higher chemical stability due to interpenetration, thereby demonstrating an exceptional PFOA adsorption capacity of up to 632mgg-1 (1.53mmolg-1), which is comparable to the reported record values. Moreover, PCN-1002 shows rapid kinetics, high selectivity, and long-life cycles in PFOA removal tests. Solid-state nuclear magnetic resonance results and density functional theory calculations reveal that multiple hydrogen bonds between the free ortho-hydroxy sites and PFOA, along with Lewis acid-base interaction, work collaboratively to enhance PFOA adsorption.

Comparison of perfluoroalkyl substance adsorption performance by inorganic and organic silicon modified activated carbon

Owing to the persistence and increasingly stringent regulations of perfluoroalkyl substances (PFAS), it is necessary to improve their adsorption capacities using activated carbon (AC). However, their adsorption capacities are suppressed by dissolved organic matter (DOM). In this study, two ACs modified with organic silicon (C-OS) and inorganic silicon (C-IS) were synthesized and used for the adsorption of PFAS in raw water (RW). The results showed that the PFAS adsorption capacity of C-IS was much less influenced by DOM than that of the original AC (C-virgin). In RW, perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) adsorption capacities on C-IS were 15.08 and 3.65 times higher than those on C-virgin, respectively. DOM had less influence on the PFOA and PFOS adsorption kinetics of C-IS than C-OS and C-virgin. Under multi-PFAS condition, C-IS also exhibited slower desorption of short-chain PFAS and breakthrough in batch and column tests, respectively. Characterization of the ACs before and after adsorption and independent gradient modelling indicated that hydrogen bond interactions between the O-Si of C-IS and the –COOH or –CSO3H groups of PFAS contributed to PFAS adsorption. Density functional theory calculations demonstrated that the adsorption energy of C-IS was much lower than that of C-OS and C-virgin. The arrangement of PFAS molecules on C-OS was chaotic owing to the hydrophobic siloxane chain, whereas the arrangement of PFAS on C-IS was orderly in multi-layer or semi-micelle status and more favorable to PFAS adsorption. This study provides a new strategy for avoiding adverse effects of DOM on PFAS adsorption.

Investigation of Kinetic, Equilibrium, and Thermodynamic Modeling of Perfluorooctanoic Acid (PFOA) Adsorption in the Presence of Natural Organic Matter (NOM) by Dielectric Barrier Discharge Plasma-Modified Granular Activated Carbon (GAC)

Perfluorooctanoic acid (PFOA) contamination in water sources poses significant environmental and health concerns. The kinetic, equilibrium, and thermodynamic features of PFOA adsorption in the existence of natural organic matter (NOM) were thoroughly investigated in this work using granular activated carbon (GAC) modified by dielectric barrier discharge (DBD) plasma. The impacts of DBD plasma parameters on the adsorption process were systematically examined. The results demonstrated that GAC modified by DBD plasma exhibited enhanced adsorption performance for PFOA, even in the presence of NOM. The optimal condition for plasma-treated GAC was achieved with 20 min of plasma treatment time and 100 W of plasma power, resulting in 92% PFOA removal efficiency in deionized water (DIW) and 97% removal efficiency in Chao Phraya River water (CPRW). A kinetic investigation using the pseudo-first-order model (PFOM), the pseudo-second-order model (PSOM), and the Elovich model (EM) indicated that plasma treatment time and NOM presence influenced the adsorption capacity and rate constants of PFOA with the PSOM having emerged as the most fitting kinetic model. The Langmuir isotherm model indicates monolayer adsorption of PFOA on plasma-treated GAC, with higher maximum adsorption capacity while NOM is present. The Redlich–Peterson and Sips isotherm models indicated varying adsorption capacity and heterogeneity in the adsorption system. The Sips model was determined as the most fitting isotherm model. Furthermore, the favorable and spontaneous character of PFOA adsorption onto plasma-treated GAC was validated by thermodynamic analysis, with endothermic heat absorption during the process. Overall, this comprehensive investigation provides valuable insights into the adsorption characteristics of PFOA in the existence of NOM using GAC modified by DBD plasma.

Adsorptive removal of perfluorooctanoic acid from aqueous matrices using peanut husk-derived magnetic biochar: Statistical and artificial intelligence approaches, kinetics, isotherm, and thermodynamics

Removal of perfluorooctanoic acid (PFOA) from water matrices is crucial owing to its pervasiveness and adverse ecological and human health effects. This study investigates the adsorptive removal of PFOA using magnetic biochar (MBC) derived from FeCl3-treated peanut husk at different temperatures (300, 600, and 900 °C). Preliminary experiments demonstrated that MBC600 exhibited superior performance, with its characterization confirming the presence of γ-Fe2O3. However, efficient PFOA removal from water matrices depends on determining the optimum combination of inputs in the treatment approaches. Therefore, optimization and predictive modeling of the PFOA adsorption were investigated using the response surface methodology (RSM) and the artificial intelligence (AI) models, respectively. The central composite design (CCD) of RSM was employed as the design matrix. Further, three AI models, viz. artificial neural network (ANN), support vector machine (SVM), and adaptive neuro-fuzzy inference system (ANFIS) were selected to predict PFOA adsorption. The RSM-CCD model applied to optimize three input process parameters, namely, adsorbent dose (100–400 mg/L), pH (3–10), and contact time (20–60 min), showed a statistically significant (p < 0.05) effect on PFOA removal. Maximum PFOA removal of about 98.3% was attained at the optimized conditions: adsorbent dose: 400 mg/L, pH: 3.4, and contact time: 60 min. Non-linear analysis showed PFOA adsorption was best fitted by pseudo-second-order kinetics (R2 = 0.9997). PFOA adsorption followed Freundlich isotherm (R2 = 0.9951) with a maximum adsorption capacity of ∼307 mg/g. Thermodynamics and spectroscopic analyses revealed that PFOA adsorption is a spontaneous, exothermic, and physical phenomenon, with electrostatic interaction, hydrophobic interaction, and hydrogen bonding governing the process. A comparative analysis of the statistical and AI models for PFOA adsorption demonstrated high R2 (>0.99) for RSM-CCD, ANN, and ANFIS. This research demonstrates the applicability of the statistical and AI models for efficient prediction of PFOA adsorption from water matrices using MBC (MBC600).

Co-Removal of Perfluorooctanoic Acid and Nitrate from Water by Coupling Pd Catalysis with Enzymatic Biotransformation.

PFAS (poly- and per-fluorinated alkyl substances) represent a large family of recalcitrant organic compounds that are widely used and pose serious threats to human and ecosystem health. Here, palladium (Pd0)-catalyzed defluorination and microbiological mineralization were combined in a denitrifying H2-based membrane biofilm reactor to remove co-occurring perfluorooctanoic acid (PFOA) and nitrate. The combined process, i.e., Pd-biofilm, enabled continuous removal of ∼4 mmol/L nitrate and ∼1 mg/L PFOA, with 81% defluorination of PFOA. Metagenome analysis identified bacteria likely responsible for biodegradation of partially defluorinated PFOA: Dechloromonas sp. CZR5, Kaistella koreensis, Ochrobacterum anthropic, and Azospira sp. I13. High-performance liquid chromatography-quadrupole time-of-flight mass spectrometry and metagenome analyses revealed that the presence of nitrate promoted microbiological oxidation of partially defluorinated PFOA. Taken together, the results point to PFOA-oxidation pathways that began with PFOA adsorption to Pd0, which enabled catalytic generation of partially or fully defluorinated fatty acids and stepwise oxidation and defluorination by the bacteria. This study documents how combining catalysis and microbiological transformation enables the simultaneous removal of PFOA and nitrate.

Fixed-bed adsorption of perfluorooctanoic acid from water by a polyamine-functionalized polychlorotrifluoroethylene-ethylene polymer coated on activated carbon

Perfluorooctanoic acid (PFOA) has received extensive attention because of its ubiquitous presence in the aqueous environmental phase and concerns of its impact on human health. An economical and effective adsorption method is in demand to help resolve the issue. In this study, a polyamine-functionalized polychlorotrifluoroethylene-ethylene polymer coated activated carbon (AC) was synthesized via a two-step reaction. The fluoropolymer based on the repeating unit ethylene-chlorotrifluoroethylene (ECTFE) was applied as the binding medium to connect activated carbon with polyethyleneimine (PEI). Hence a dual grafted activated carbon-based sorbent AC-ECTFE-PEI was generated. Through the adsorption evaluation of packed columns by on-line detection flow analysis, the optimum synthetic stoichiometry parameters to produce AC-ECTFE-PEI, based on the longest adsorption breakthroughs, were determined to be the 5:2 AC/ECTFE and 1:1 AC-ECTFE/PEI mass ratios. The new adsorbent has shown a strongly enhanced initial adsorption breakthrough to PFOA compared to AC, 270 min vs. 110 min, under the same adsorption conditions. AC-ECTFE-PEI was also characterized by attenuated total reflectance infrared spectroscopy, BET surface area analysis, and scanning electron microscopy. The functional group alterations during the reactions and the morphology information of the sorbent have also been elucidated. The Thomas, Adams-Bohart, and Yoon-Nelson models respectively were used to describe the adsorption behavior, indicating an PFOA adsorption capacity of 380 mg/g sorbent, 120 mg/L sorbent column, and a 50% average breakthrough time of 350 min for 100 mg/L PFOA removal, under a 1 mL/min flow rate and a 2 cm bed height. The regeneration study of AC-ECTFE-PEI of more than five adsorption-desorption cycles indicates good sustainability and stability. Both electrostatic and hydrophobic interactions of PFOA were justified using selective solvent compositon of the mobile phase as the two main adsorption mechanisms. The electrostatic forces of PFOA on AC-ECTFE-PEI, AC-ECTFE, and AC were also evaluated by their zeta-potential values.

Separation of Perfluorooctanoic Acid from Water Using Meso- and Macroporous Syndiotactic Polystyrene Gels.

Per- and polyfluoroalkyl substances are an emerging class of contaminants that are environmentally persistent, bioaccumulative, and noxious to human health. Among these, perfluorooctanoic acid (PFOA) molecules are widely found in ground and surface water sources. A novel high surface area, meso- and macroporous syndiotactic polystyrene (sPS) wet gel is used in this work as the adsorbent of PFOA molecules from water at environmentally relevant PFOA concentrations (≤1 μg/L) and cleanse water to below the U.S. EPA's 2023 health advisory limit of 4 parts per trillion (ppt). The sigmoidal shape of the PFOA adsorption isotherm indicates a two-step adsorption mechanism attributed to the strong affinity of PFOA molecules for the sPS surface and molecular aggregation at solid-liquid interfaces or within the pores of the sPS wet gel. The adsorption kinetics and the effects of sPS wet gel porosity, pore size, and pore volume on the removal efficiency are reported. The adsorption kinetics is seen to be strongly dependent on pore size and pore volume.

Electrosorption approach removing PFOA from wastewater using a MXene-polyaniline film

Perfluorooctanoic acid (PFOA) is a persistent organic pollutant found in various industrial effluents, posing significant environmental and health risks. Electrosorption of PFOA on MXene-polyaniline film from water was studied. The results of electrosorption kinetics showed that the functionalized MXene film with polyaniline resulting in an approximately 100 % increase in electrosorption capacitance for PFOA due to increasing of the MXene film's volumetric capacitance and modifying of surface chemistry of MXene. The maximum adsorption of PFOA on MXene and MXene-polyaniline films were 358.5 mg/g and 966.1 mg/g, respectively, at an initial concentration of 100 mg/L upon application of +1.0 V. Moreover, humic acid (HA) competing with the adsorption sites, sodium chloride through the double-layer compression effect, and pH affecting the amine or amide functional groups on MXene-polyaniline which inhibited PFOA adsorption onto MXene-polyaniline film were thoroughly examined. Lastly, the reversible adsorption–desorption cycles show that the MXene–polyaniline film possesses the potential to be used continuously. To address PFAS pollution in water sources, we think our approach can help build effective and long-lasting technology.

Efficient removal of per/polyfluoroalkyl substances from water using recyclable chitosan-coated covalent organic frameworks: Experimental and theoretical methods

Covalent organic frameworks (COFs) demonstrate remarkable potential for adsorbing per/polyfluoroalkyl substances (PFAS). Nevertheless, the challenge of recycling powdered COFs hampers their practical application in water treatment. In this research, a quaternary amine COF with inherent positive surface charge was synthesised to adsorb perfluorooctanoic acid (PFOA) via electrostatic interactions. The COF was then combined with chitosan (CS) through a simple dissolution-evaporation process, resulting in a composite gel material termed COF@CS. The findings indicated that the adsorption capacity of COF@CS significantly surpassed that of the original COF and CS. According to the Langmuir model, COF@CS achieved a maximum PFOA capacity of 2.8 mmol g−1 at pH 5. Furthermore, the adsorption rate increased significantly to 6.2 mmol g−1 h−1, compared to 5.9 mmol g−1 h−1 for COF and 3.4 mmol g−1 h−1 for CS. Notably, COF@CS exhibited excellent removal efficacy for ten other types of PFAS. Moreover, COF@CS could be successfully regenerated using a mixture of 70% ethanol and 1 wt% NaCl, and it exhibited stable reusability for up to five cycles. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) characterisation, and theoretical calculations revealed that the quaternary amine functional group in COF served as the primary adsorption site in the composite gel material, while the protonated amino group on CS enhanced PFOA adsorption through electrostatic interaction. This study highlights the significant practical potential of COF@CS in the removal of PFAS from aqueous solution and environmental remediation.

Electrochemical Reduction of Perfluorooctanoic Acid (PFOA): An Experimental and Theoretical Approach.

Perfluorooctanoic acid (PFOA) is an artificial chemical of global concern due to its high environmental persistence and potential human health risk. Electrochemical methods are promising technologies for water treatment because they are efficient, cheap, and scalable. The electrochemical reduction of PFOA is one of the current methodologies. This process leads to defluorination of the carbon chain to hydrogenated products. Here, we describe a mechanistic study of the electrochemical reduction of PFOA in gold electrodes. By using linear sweep voltammetry (LSV), an E0' of -1.80 V vs Ag/AgCl was estimated. Using a scan rate diagnosis, we determined an electron-transfer coefficient (αexp) of 0.37, corresponding to a concerted mechanism. The strong adsorption of PFOA into the gold surface is confirmed by the Langmuir-like isotherm in the absence (KA = 1.89 × 1012 cm3 mol-1) and presence of a negative potential (KA = 3.94 × 107 cm3 mol-1, at -1.40 V vs Ag/AgCl). Based on Marcus-Hush's theory, calculations show a solvent reorganization energy (λ0) of 0.9 eV, suggesting a large electrostatic repulsion between the perfluorinated chain and water. The estimated free energy of the transition state of the electron transfer (ΔG‡ = 2.42 eV) suggests that it is thermodynamically the reaction-limiting step. 19F - 1H NMR, UV-vis, and mass spectrometry studies confirm the displacement of fluorine atoms by hydrogen. Density functional theory (DFT) calculations also support the concerted mechanism for the reductive defluorination of PFOA, in agreement with the experimental values.

Size-selective trapping and photocatalytic degradation of PFOA in Fe-modified zeolite frameworks

Removal and destruction of perfluorooctanoic acid (PFOA) are challenging due to its extreme persistence and dilute concentrations. This study investigated dual-function adsorptive-photocatalytic zeolite materials to selectively adsorb and degrade PFOA via tuning pore structures and doping transition metals. It is found that the pore opening is critical in the size-selective trapping of PFOA, while the iron doped zeolites present excellent adsorption of PFOA (>80 mg g−1) combining hydrophobic and electrostatic interactions. The formation of PFOA-iron complexes has reduced bond dissociation energy of C−F, calculated from density functional theory, for favorable stepwise defluorination (over 60% defluorination in 4 hours) by superoxide radicals and ligand-to-metal charge transfer. This mechanistic investigation extends the potential of the concentrate-and-degrade concept to remove PFOA selectively and effectively from contaminated water.

Fluorinated Nonporous Adaptive Cages for the Efficient Removal of Perfluorooctanoic Acid from Aqueous Source Phases.

Per- and polyfluoroalkyl substances (PFAS) accumulate in water resources and pose serious environmental and health threats due to their nonbiodegradable nature and long environmental persistence times. Strategies for the efficient removal of PFAS from contaminated water are needed to address this concern. Here, we report a fluorinated nonporous adaptive crystalline cage (F-Cage 2) that exploits electrostatic interaction, hydrogen bonding, and F-F interactions to achieve the efficient removal of perfluorooctanoic acid (PFOA) from aqueous source phases. F-Cage 2 exhibits a high second-order kobs value of approximately 441,000 g mg-1 h-1 for PFOA and a maximum PFOA adsorption capacity of 45 mg g-1. F-Cage 2 can decrease PFOA concentrations from 1500 to 6 ng L-1 through three rounds of flow-through purification, conducted at a flow rate of 40 mL h-1. Elimination of PFOA from PFOA-loaded F-Cage 2 is readily achieved by rinsing with a mixture of MeOH and saturated NaCl. Heating at 80 °C under vacuum then makes F-Cage 2 ready for reuse, as demonstrated across five successive uptake and release cycles. This work thus highlights the potential utility of suitably designed nonporous adaptive crystals as platforms for PFAS remediation.

Apple Pomace-Derived Cationic Cellulose Nanocrystals for PFAS Removal from Contaminated Water

Per- and poly-fluoroalkyl substances (PFAS) are concerning contaminants due to their ubiquity, persistence, and toxicity. Conventional PFAS water treatments such as granular activated carbon are limited by low adsorption rates and capacities. Carbon-based nano-adsorbents with enhanced surface areas address these limitations but are hindered by their high cost and toxicity. Cellulose nanocrystals (CNC) are promising PFAS adsorbents due to sustainable sourcing, large surface areas, and amenable surface properties. In this study, CNC was synthesized from the agro-food waste, apple pomace (APCNC), and coated with Moringa oleifera cationic protein (MOCP) aqueous extract to produce MOCP/APCNC for the removal of perfluorooctanoic acid (PFOA) from water. APCNC and MOCP/APCNC were manufactured, characterized, and utilized in PFOA batch adsorption kinetics and equilibrium trials. APCNC was successfully produced from apple pomace (AP) and determined through characterization and comparison to commercial CNC (CCNC). APCNC and MOCP/APCNC exhibited rapid PFOA adsorption, approaching equilibrium within 15 min. MOCP coatings inverted the MOCP/CNC surface charge to cationic (−15.07 to 7.38 mV) and enhanced the PFOA adsorption rate (2.65 × 10−3 to 5.05 × 10−3 g/mg/s), capacity (47.1 to 61.1 mg/g), and robustness across varied water qualities. The sustainable sourcing of APCNC combined with a green surface coating to produce MOCP/CNC provides a highly promising environmentally friendly approach to PFAS remediation.