Sorption Of Perfluorooctane Sulfonate Research Articles

Transport parameters for PFOA and PFOS migration through GCL's and composite liners used in landfills

The effect of applied stress (20, 60, and 150 kPa) on the diffusion of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) through a geosynthetic clay liner (GCL) is examined. The diffusion coefficients deduced from GCL diffusion tests for PFOA and PFOS decrease linearly with decreasing final bulk GCL void ratio (increasing applied stresses). The different components of the same GCL are also tested for PFOA and PFOS sorption. No statistically significant sorption of PFOA is observed for any of the components of the GCL. However, some sorption of PFOS onto the cover and carrier geotextiles of the GCL is observed with in an average distribution coefficient, Kd ∼2.22 ml/g for the GCL. Permeants containing different PFAS compounds are tested to assess their impact on the Geomembrane (GMB) - GCL interface transmissivity in composite liners. Results show PFAS concentrations up to 20 ppm had negligible impact on the GMB-GCL interface transmissivity. Lastly, the GCL specimens extracted from the diffusion tests are tested for hydraulic conductivity. No impact of PFAS is seen on the hydraulic conductivity of GCLs subjected to high applied loads, but a small increase is seen on the GCLs subjected to relatively low applied stresses.

Impact of Variable Water Chemistry on PFOS-Goethite Interactions: Experimental Evidence and Surface Complexation Modeling.

Perfluorooctanesulfonate (PFOS) has become a major concern due to its widespread occurrence in the environment and severe toxic effects. In this study, we investigate PFOS sorption on goethite surfaces under different water chemistry conditions to understand the impact of variable groundwater chemistry. Our investigation is based on multiple lines of evidence, including (i) a series of sorption experiments with varying pH, ionic strength, and PFOS initial concentration, (ii) IR spectroscopy analysis, and (iii) surface complexation modeling. PFOS was found to bind to goethite through a strong hydrogen-bonded (HB) complex and a weaker outer-sphere complex involving Na+ coadsorption (OS-Na+). The pH and ionic strength of the solution had a nontrivial impact on the speciation and coexistence of these surface complexes. Acidic conditions and low ionic strength promoted hydrogen bonding between the sulfonate headgroup and protonated hydroxo surface sites. Higher electrolyte concentrations and pH values hindered the formation of strong hydrogen bonds upon the formation of a ternary PFOS-Na+-goethite outer-sphere complex. The findings of this study illuminate the key control of variable solution chemistry on PFOS adsorption to mineral surfaces and the importance to develop surface complexation models integrating mechanistic insights for the accurate prediction of PFOS mobility and environmental fate.

Mechanistic understanding of perfluorooctane sulfonate (PFOS) sorption by biochars

Biochar has recently emerged as a cost-effective solution to combat per- and polyfluoroalkyl substances (PFAS) pollution in water, but mechanistic understanding of which physicochemical properties of biochars dictate PFAS sorptive removal from water remains elusive. Herein, 15 biochars were pyrolyzed from five feedstocks (corn, Douglas fir, eucalyptus, poplar, and switchgrass) at three pyrolysis temperatures (500, 700, and 900 °C) to investigate their removal efficiencies and mechanisms of perfluorooctane sulfonate (PFOS) from water. A commercial biochar was also included for comparison. Biochar physiochemical properties, including elemental composition, pH, specific surface area (SSA), pore structure, hydrophobicity, surface charge, surface functional groups, and crystalline structure were systematically characterized. Batch sorption data showed that the Douglas fir 900 biochar (Douglas fir and 900 are the feedstock type and pyrolysis temperature, respectively; this naming rule applies to other biochars), poplar 900 biochar, and commercial biochar can remove over 95% of PFOS from water. Structural equation model (SEM) was used to elucidate which biochar properties affect PFOS sorption. Interestingly, biochar pore diameter was identified as the most critical factor controlling PFOS removal, but pore diameter/pore volume ratio, SSA, pyrolysis temperature, hydrophobicity, and elemental composition all played variable roles. Hypothetically, biochars with small pore diameters and large pore volumes had a narrow yet deep pore structure that traps PFOS molecules inside once already sorbed, resulting in an enhanced PFOS sorption. Biochars with small pore diameter, low nitrogen content, and high pyrolysis temperature were also favorable for enhanced PFOS sorption. Our findings advance the knowledge of using biochars with optimized properties to remove PFOS and possibly other similar PFAS compounds from water.

The effects of soil properties and sorbent amendments on immobilization of perfluorooctane sulfonate (PFOS) in contrasting soils: Experimental and numerical study

Per- and polyfluoroalkyl substances (PFAS), a class of manmade organo-fluorine chemicals, are a serious challenge to water supplies. In this study, the effects of physicochemical properties of Florida topsoil and Ringold formation Hanford site sediment as well as the influence of immobilizers on the sorption behavior of PFOS were tested. Activated charcoal (AC) and food waste compost amendments were added to the soil and sediment at 0.1 and 3 wt% concentration, respectively. The PFOS adsorption fits best to pseudo second-order kinetic and Freundlich isotherm models. PFOS uptake was greater in Florida topsoil compared to Hanford site sediment, indicating that organic matter played a key role in the retention of PFOS. The food waste compost amendment at 3 wt% had no impact on PFOS uptake. However, AC amendment at 0.1 wt% enhanced PFOS sorption in Florida topsoil by 80% and Hanford site sediment by 99% through increasing the soil/water partitioning coefficients (kd value). A one-dimensional model was used to simulate the influence of AC in Florida topsoil on the leaching of PFOS to the groundwater by the percolation of rainwater over time. The results demonstrated the addition of 0.1 wt% AC, to the soil dramatically inhibits or delays the leaching of PFOS for up to one year under certain conditions to below the guideline for maximum concentration level (0.02 ng/L). The amendment could control PFOS release for more than 10 years by increasing the kd value by 10 times.

Sorption and partitioning of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) onto sediments of Diep and Plankenburg river systems Western Cape, South Africa

Partitioning behaviour of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) in sediments obtained from river systems were investigated in this study. The partitioning coefficient (log K OC ) and distribution coefficient (log K D ) of PFOA and PFOS between sediments and the aqueous solution were estimated from the sorption data. Levels of PFOA and PFOS in the sediment samples ranged between 30.01–191.96 ng/g dw and 0.50–248.14 ng/g dw, respectively. The kinetic study showed that the time required for equilibrium was <400 min for the compounds. Sediment samples SS-C provided the highest sorption capacities (0.11 and 0.13 mg/g) for both PFOA and PFOS. Sorption studies revealed that the removal kinetics fitted well into the Elovich rate equation (R 2 = 0 . 98 and 0.92) followed by the pseudo-second-order kinetic model (R 2 = 0 . 91 and 0.89) for PFOA and PFOS, respectively. Mean values for the partitioning coefficient (log K OC ) in the river systems were 1.04 ± 0.26 and 1.85 ± 0.65 (cm 3 /g) for PFOA and PFOS respectively. Partitioning coefficient (log K OC ) significantly (p < 0.05) increased over time. This study represents the first report on partitioning and distribution of PFOA and PFOS in sub-Sahara Africa, which provide data and a scientific base to understand the fate and sorption of PFOA and PFOS in an aquatic system. The findings showed that lower pH values and increasing ionic strength favours sorption and partitioning of perfluoroalkyl substances (PFAS) in aqueous solution onto sediments; hence, plays an important role in their availability in water. Presence of PFAS in the aquatic system sediments is a potential risk to organisms. • Maximum concentration of PFOA and PFOS in the sediments from the river systems were 191.9 and 248.1 ng/g dw, respectively. • Mean values for the log K OC in the river systems were 1.04 ± 0.2 and 1.85 ± 0.6 (cm 3 /g) for PFOA and PFOS respectively. • Sorption kinetics for PFOA and PFOS fitted well into the elovich rate equation for the investigated sediment samples. • Lower solution pH and increase in Ca 2 + concentration favours the sorption and partitioning behaviour of PFOA and PFOS.

Sorption and desorption kinetics of PFOS to pristine microplastic

The sorption processes of persistent organic pollutants on microplastics particles are poorly understood. Therefore, the present study investigated the sorption processes of perfluorooctanesulfonate (PFOS) on polyethylene (PE) microplastic particles (MPs) which are representing a prominent environmental pollutant and one of the most abundant microplastic polymers in the aquatic environment, respectively. The focus was set on the investigation of the impact of the particle size on PFOS sorption using four different PE MPs size ranges. The sorption kinetics for 6 months was studied with one selected size range of PE MPs. Besides, the desorption of PFOS from PE MPs under simulated digestive conditions was carried out by using artificial gut fluid mimicking the intestinal juice of fish. The investigation of the size effects of particles over 6 months demonstrated a linear increase of PFOS concentration sorbed onto PE with a decrease of the particle size. Thus, our findings implicate efficient sorption of PFOS onto PE MPs of different sizes. The results showed that PFOS desorbed from the PE MPs into the artificial gut fluid with a rate of 70 to 80%. Besides, a longer exposure of PE MPs to PFOS leads to a higher concentration adsorbed by PE MPs, which may favor the ingestion of higher concentration of PFOS, and thus represents a higher risk to transfer relevant concentrations of PFOS during digestion.

Efficient sorption of perfluoroalkyl acids by ionic liquid-modified natural clay

Contamination caused by per- and polyfluoroalkyl substances (PFAS), including perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), is a big concern worldwide due to their persistence in the environment. Removal of PFAS represents a special challenge for water/wastewater treatment because of their diverse structures and unique physicochemical properties such as high water solubility and high stability of the C-F bond. In this study, we primarily investigated the removal of PFOA and PFOS from water through sorption with ionic liquid (IL)-modified natural clay. A series of ILs with varied alkyl chain lengths were applied for clay modification, and the successful intercalation of ILs was verified with X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), zeta potential measurement, and elemental analysis. The structure and properties of IL-modified clays were strongly affected by the IL chain lengths. Specifically, long-chain IL not only changed the surface potential of clay, but also expanded the interlayers of clay, both of which greatly facilitated PFOA and PFOS sorption. Clay modified with the long-chain IL exhibited both fast kinetics for PFOA and PFOS sorption and high PFOA and PFOS removal efficiency under various water chemistry conditions. Furthermore, long-chain IL-modified clay was very effective for the removal of a suite of perfluorinated carboxylic and sulfonic acids with various chain lengths of the perfluoroalkyl moiety. IL-modified natural clay may be potentially applied for PFAS pollution control.

Sorption of Perfluorooctane sulfonate (PFOS) including its isomers on hydrargillite as a function of pH, humic substances and Na2SO4

Perfluorooctane sulfonate (PFOS) is a persistent organic pollutant (POP) and emergent contaminant that are widespread in the environment. Understanding the mechanisms controlling the distribution of PFOS and its isomers between hydrargillite and the water phase is important in order to study their redistribution and mobility in the environment. This study investigated the effects of pH, humic acid, fulvic acid and Na2SO4 on sorption of PFOS isomers to hydrargillite. A mixture of PFOS isomers was spiked into water and hydrargillite was added to the system and shaken for one day; the system was tested with different aqueous composition. Concentrations of PFOS isomers in the aqueous phase were quantified using an ultra-performance liquid chromatograph coupled to a triple quadrupole mass spectrometer. Our results showed that the distribution coefficients of PFOS isomers were found to be 0.76, 0.71, 0.93 and 0.90 at pH 6.5, for 3-/4-/5- PFOS, 6-/2-PFOS, L-PFOS and total PFOS respectively. The distribution coefficients increased at lower pH and decreased at alkaline conditions. The presence of humic substances (HS) increased the sorption slightly at the environmental pH of 6.5, although a competition effect was observed during acidic conditions. A tendency of PFOS distribution to hydrargillite in the presence of Na2SO4 was like its behavior in the presence of HS although the mechanisms behind the sorption were interpreted differently. This study revealed that L-PFOS was readily sorbed when no other chemicals were added or in 20 mg/L FA or 100 mg/L Na2SO4. We suggest that an increase in PFOS sorption in the presence of HS may be due to hydrophobic mechanisms while Na2SO4 contributed to increased sorption through ionic strength effects.

Enhanced sorption of perfluorooctane sulfonate and perfluorooctanoate by hydrotalcites

Perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) are recalcitrant compounds that are toxic to humans and ecosystems. Hydrotalcite-like compounds have emerged as promising PFOS and PFOA sorbents due to their high anion exchange capacity and high specific surface area. In this study, hydrotalcite (HT) compounds were intercalated with nitrate and carbonate ions (HT-CO 3 and HT-NO 3 ) and their specific surface area and particle aggregate size modified by treatment with acetone (AHT-CO 3 and AHT-NO 3 ). Sorption experiments with AHT-NO 3 indicated that sorption equilibrium was reached faster with PFOS (< 5 min) compared to PFOA (< 20 min), and that sorption capacity for PFOS (1,610.0 mg/g) was substantially higher compared to PFOA (909.0 mg/g). The sorption yields are explained by anion exchange occurring at higher PFOS and PFOA concentrations, along with surface adsorption, and by PFOS having a higher affinity for the HT interlayer. In comparison to AHT-NO 3 , PFOS and PFOA sorption by AHT-CO 3 was slower (equilibration times ≥ 20 min) and the maximum capacities were generally lower, because anion exchange is hindered by the affinity of the carbonate ion for the HT interlayer. As such, surface adsorption dominated across a large PFOS and PFOA concentration range (up to 2,000 mg/L). The presence of non-ionic species (trichloroethylene) did not affect the sorption capacity, while alkaline pH conditions and the presence of other anionic species (dodecyl sulfate) reduced the sorption capacity of AHT compounds towards PFOS and PFOA. Compared to untreated HT compounds, acetone treated HT exhibited improved sorption properties towards PFOA and PFOS removal from groundwater, particularly AHT-CO 3 . Overall, AHT compounds outperform activated carbon sorbents in terms of PFOA and PFOS sorption kinetics and capacities, thus could be promising new sorbents for PFAS removal from contaminated waters. • Acetone-treated hydrotalcites (AHT) show modified physical properties. • Nitrate-intercalated AHT show fast equilibration time (<1 h) towards PFOS and PFOA. • The maximum sorption uptake for PFOS is 1,610 mg/g by nitrate-intercalated AHT. • XPS and other techniques are used to evaluate the sorption mechanism. • Alkaline pH and other anions impact the sorption capacity of PFOS and PFOA by AHT.

Dynamics, thermodynamics, and mechanism of perfluorooctane sulfonate (PFOS) sorption to various soil particle-size fractions of paddy soil

Soil is an important sink for perfluorooctane sulfonate (PFOS) that is a typical persistent organic pollutant with high toxicity. Understanding of PFOS sorption to various particle-size fractions of soil provides an insight into the mobility and bioavailability of PFOS in soil. This study evaluated kinetics, isotherms, and mechanisms of PFOS sorption to six soil particle-size fractions of paddy soil at environmentally relevant concentrations (0.01–1 μg/mL). The used soil particle-size fractions included coarse sand (120.4–724.4 mm), fine sand (45.7–316.2 mm), coarse silt (17.3–79.4 mm), fine silt (1.9–39.8 mm), clay (0.5–4.4 mm), and humic acid fractions (8.2–83.7 mm) labeled as F1~F6, respectively. PFOS sorption followed pseudo-second-order kinetics related to film diffusion and intraparticle diffusion, with speed-limiting phase acted by the latter. PFOS sorption isotherm data followed Freundlich model, with generally convex isotherms in larger size fractions (F1~F3) but concave isotherms in smaller size fractions (F4 and F5) and humic acid fraction (F6). Increasing organic matter content, Brunner−Emmet−Teller surface area, and smaller size fractions were conducive to PFOS sorption. Hydrophobic force, divalent metal ion-bridging effect, ligand exchange, hydrogen bonding, and protein-like interaction played roles in PFOS sorption. But hydrophobic force controlled the PFOS sorption, because its relevant organic matter governed the contribution of the soil fractions to the overall PFOS sorption. The larger size fractions dominated the PFOS sorption to the original soil because of their high mass percentages (~80%). This likely caused greater potential risks of PFOS migration into groundwater and bioaccumulation in crops at higher temperatures and ce values, based on their convex isotherms with an exothermic physical process.

The effects of soil properties and co-contaminants on sorption of perfluorooctane sulfonate (PFOS) in contrasting soils

Abstract Sorption plays an important role in controlling the fate and behaviour of per- and polyfluoroalkyl substances (PFAS) in soils. However, there is no consensus on the influence of key soil properties on sorption of perfluorooctane sulfonate (PFOS) in the current literature. In particular, the effects of soil mineral components on sorption have not been fully investigated. In this study the sorption isotherms of PFOS under different electrolytes (Na + and Ca2＋) was investigated using eight contrasting soils that varied in pH, total organic carbon (TOC) content, clay content and other physico-chemical properties. In addition the sorption behaviour of PFOS was studied at different pH values (3–9) and ionic strengths (0.03 and 0.3 M NaNO3) to determine the role of hydrophobic and electrostatic interactions on PFOS sorption. The effects of possible co-contaminants, lead (Pb) (20.8 mg/L Pb 2 + ) and dissolved organic carbon (DOC, 11.5 mg/L as humic acid) and perfluorooctanoic acid (114 μ g/L PFOA) on sorption of PFOS were also investigated. A strongly significant linear relationship (p + or Ca2＋. The presence of DOC, and other common co-contaminants like PFOA, and Pb 2 + in solution generally increased PFOS sorption by the soils. Sorption of PFOS at different ionic strengths and pH demonstrated that the sorption was dominated by hydrophobic interactions when the TOC content was high, but electrostatic interactions dominated at lower pH values and in soils with smaller TOC contents. This study demonstrates the role of both organic matter and surface chemical properties of soils as key factors influencing PFOS sorption. The use of multiple soil properties to explain the sorption is required.

Adsorption of Perfluorooctane sulfonate (PFOS) onto metal oxides modified biochar

Perfluorooctane sulfonate (PFOS) is a persistent organic pollutant (POP), which poses potential toxicity to biotic and abiotic ecosystem. Adsorption of PFOS from soil and water has emerged as promising remediation practice due to low cost, high removal performance, low environmental impact, and recalcitrant to induce secondary contamination. In this study, red mud modified sawdust (RMSDN600) and unmodified sawdust (SDN600) were prepared for sorption of PFOS from aqueous solution. The presence of magnetites (Fe 3 O 4 ), ferrihydrites, and desilicated minerals are identified in the RMSDN600 using XRD (X-ray diffraction) and XANES (X-ray absorption near-edge structure). Sorption isotherm for RMSD600 and SDN600 showed close-fitting with Langmuir and Freundlich model demonstrated monolayer and multilayer sorption of PFOS over the active sites of the adsorbents. The potential formation of micelles and hemi-micelles can occur in interparticle porous biochars as the concentration of PFOS exceeds critical hemi-micelle concentration (4.57–45.7 mg/L). The kinetic study followed Pseudo-second-order model for both adsorbents, demonstrated both physisorption and chemisorption of PFOS. The results revealed the adsorption of PFOS was governed by both hydrophobic and electrostatic interaction, with hydrophobic interaction as the dominant sorption mechanism. The higher adsorption capacity for RMSDN600 (194.6 mg/g) was recorded than that for SDN600 (178.6 mg/g) at pH 3.1 due to the abundance of protonated metal-based functional groups, and more ordered graphitic carbon structure resulting from catalytic degradation and transformation of cellulose and hemicellulose. Aromatic structure can potentially enhance PFOS sorption by non-ionic interaction. In contrast, metal-based and other oxygen-containing functional groups of adsorbents enhance adsorption capacity through electrostatic interaction and ion exchange reactions. Lower solution pH and smaller particle size of the adsorbents could also enhance sorption of PFOS from aqueous phase. • Carbon content, surface area, and porosity of biochar reduced after modification with metal oxides. • Iron minerals in red mud transformed to magnetites, and ferrihydrites in RMSDN600. • Highly pyrolyzed (600 °C) hydrophobic biosorbents favor PFOS adsorption. • Metal oxide modified biochar has more ordered aromatic structure than the raw biochar. • The adsorption capacity was 178.1 and 194.6 mg/g for SDN600 and RMSDN600.

Evaluation of the effects of PFAS soil adsorption and transformation in the presence of divalent cations under ambient conditions

AbstractA bench‐scale study was conducted to evaluate the effect of divalent cations on the adsorption of perfluoroalkyl and polyfluoroalkyl substances (PFAS) onto soil particles. The study entailed batch testing of a synthetic soil mixture under a range of Epsom salt (soluble magnesium sulfate heptahydrate) concentrations. The synthetic soil was produced using a mix of sand, silt, clay, and organic matter that then was mixed and saturated with water collected from a PFAS‐impacted water source. The results indicate that variable concentrations of magnesium (divalent cation) had a minor effect on the sorption of perfluorooctane sulfonate with the highest sorption occurring in the strongest solution of Epsom salt. An unanticipated result of the test involved apparent biomediated transformation of polyfluorinated alkylated sulfonates (fluorotelomers or FTS) to perfluorooctanoic acid, perfluoroheptanoic acid (PFHpA), and perfluorononanoic acid. We believe this is the first time the complete transformation of 6:2 FTS to PFHpA has been observed and reported under ambient surface water‐like conditions within 6 months, a relatively short timeframe.

Effect of corn straw biochar application to sediments on the adsorption of 17α-ethinyl estradiol and perfluorooctane sulfonate at sediment-water interface

The immobilization of organic contaminants in sediment-water systems is of growing concern. Using biochar as sorbent amendment to reduce the mobility of pollutants in the sediment-water interface is becoming increasingly popular as a low-cost and environmentally friendly option. In this study, we mixed sediment from the Weishan Lake with biochar (0%, 2%, and 5% (w/w)) derived from corn straw to investigate the adsorption of perfluorooctane sulfonate (PFOS) and 17α-ethinyl estradiol (EE2). Biochar addition significantly improved the adsorption rates and capacities of EE2 and PFOS on sediments by the factors 1.7–3.5; the organic carbon concentration in the sediment was the main factor influencing this process. The sorption of EE2 and PFOS to sediment was near-linear (Freundlich exponent 1/n of 0.799–0.805), but non-linear for biochar (0.430–0.476) and sediment+biochar (0.370–0.421). The mobility of PFOS in the water-sediment system after biochar addition was significantly reduced, with a considerable increase (about three times) in the sediment-water distribution coefficient Kd. Compared to EE2, PFOS is anionic compound and contains hydrophobic C–F chains and hydrophilic S–O groups, making it more susceptible pH influences and resulting in interactions with–OH, –C=O, Si–O–Si, –O–Si, and –Al–O–Al groups via hydrogen bonding, ligand exchange, and surface complexation. We suggest that biochar amendment at ～5% is a viable approach to immobilize EE2 and PFOS at the sediment-water interface.

Highly Defective UiO-66 Materials for the Adsorptive Removal of Perfluorooctanesulfonate

Perfluorooctanesulfonate (PFOS) is a persistent organic pollutant that is bioaccumulative and toxic. While its use in most countries has been restricted to certain industrial applications due to environmental and health concerns, chrome plating and semiconductor manufacturing facilities are industrial point sources of PFOS-containing wastewater. Current remediation technologies are ineffective at treating these highly concentrated industrial effluents. In this work, UiO-66 metal–organic frameworks (MOFs) of several defect concentrations were studied as sorbents for the removal of PFOS from concentrated aqueous solutions. PFOS sorption isotherms indicated that defective UiO-66, prepared with HCl as a modulator, had a maximum Langmuir sorption capacity of 1.24 mmol/g, which was ∼2× greater than powdered activated carbon (PAC), but ∼2× less than that of a commercial ion-exchange resin. Defective UiO-66 adsorbed PFOS 2 orders of magnitude faster than the ion-exchange resin. Large pore defects (∼16 and ∼20 A) ...

Effects of sediment components and TiO2 nanoparticles on perfluorooctane sulfonate adsorption properties

Here, the roles of sediment components in perfluorooctane sulfonate (PFOS) adsorption onto aquatic sediments and relevant adsorption mechanisms were investigated in terms of adsorption isotherms and influences of TiO2 nanoparticles (NPs) contamination. Due to the complexity of the sediments, instead of randomly selecting different component sediments, the selective dissolution method was used to better explore the effects of sediment compositions, such as sediment organic matter (SOM) and ferric oxides (dithionite–citrate–bicarbonate [DCB] Fe), and TiO2 NPs pollution on PFOS adsorption. Mathematical equations (Freundlich, Langmuir, and Temkin) were used to describe the adsorption behavior of PFOS on different sediments and adsorption mechanisms of multiple pollutant interactions. Moreover, the characterization methods of zeta potential, nitrogen (N2) adsorption–desorption, and scanning electron microscopy (SEM) analysis, as well as Fourier transform infrared (FT-IR) spectroscopy, explained effects of the sediment components and TiO2 NPs on PFOS adsorption properties in view of physicochemical theories. The adsorption isotherms of PFOS on six tested sediments were all nonlinear (Freundlich model, R2 = 0.992~1.000). The Freundlich sorption affinities (KF) of PFOS on S (original sediments), S1 (sediment organic matter (SOM)-removed S), and S2 (ferric oxides (DCB Fe)-removed S1) were 0.232, 0.179, and 0.120, respectively. Both SOM and DCB Fe influenced the physicochemical properties of the sediments, e.g., zeta potential, specific surface area, and permanent negative charge. The addition of TiO2 NPs increased the KF of PFOS for S, S1, and S2 by approximately 9.9%, 14.5%, and 26.7%, respectively, by increasing the zeta potential and specific surface area (SBET, Sext, and Smicro) and by changing the water and oil properties of the three sediments. However, the addition of TiO2 NPs decreased the linearity of the sorption isotherm (1/n). FT-IR spectroscopy showed that hydrophobicity, ion exchange, surface complexation, and hydrogen bonding interactions (non-fingerprint region) could all play a role in PFOS sorption onto tested sediments. However, the hypothesis of hydrogen bonding to promote PFOS adsorption on sediment layer silicates (fingerprint region) should be studied further. The content of both SOM and DCB Fe affected the physicochemical properties of sediment. Both SOM and DCB Fe showed a positive relationship with sorption of PFOS on sediment. The addition of TiO2 NPs increased PFOS sorption by altering the sediment surface properties. Hydrophobic interactions certainly impelled and ligand and ion exchange and hydrogen bonding (non-fingerprint region) could promote PFOS sorption on the sediments.

Unraveling adsorption behavior and mechanism of perfluorooctane sulfonate (PFOS) on aging aquatic sediments contaminated with engineered nano-TiO2.

Engineered nano-TiO2 (Enano-TiO2) have inevitably discharged into aquatic sediments that resulted from their widespread use. The physicochemical characteristics of sediments might be changed because of remarkable properties of Enano-TiO2 and affected by the aging of sediments, thereby altering the environmental behavior and bioavailability of other pollutants such as perfluorooctane sulfonate (PFOS) in sediments. Here, adsorption behavior and mechanism of PFOS on aging aquatic sediments spiked with Enano-TiO2 at a weight ratio of 5.0% were investigated. The results showed that Enano-TiO2 significantly altered zero points of charge (pHzpc) and pore surface properties of sediments, manifested as pHzpc, the total surface area (SBET), the micro-pore surface area (Smicro), and the external surface area (Sext) of sediment particles contaminated with Enano-TiO2 clearly increased, instead average pore size decreased. Rapid intra-particle diffusion processes were well fitted by the pseudo-second-order rate model with the sorption rate (K2) following the order single (5.764mg/(g·h)) > binary systems (3.393mg/(g·h)). Freundlich model best described the sorption isotherm data with the larger sorption capacity (KF) and sorption affinity (1/n) of sediments spiked with Enano-TiO2 than that of sediments only. Additionally, Enano-TiO2 changed the adsorption thermodynamics of PFOS on the sediments with the absolute value of ∆G0, ∆H0, and ∆S0 increased. Fourier transform infrared (FT-IR) spectroscopy suggested possible formation of a negative charge-assisted H-bond between PFOS and the functionalities on sediment surfaces, including O-H of carboxyl, alcohol, phenols, and chemisorbed H2O as well as carbonyl groups (C=O) of ketone groups. Furthermore, the multilayer sorption of PFOS on sediments contaminated with Enano-TiO2 is plausible because of bridging effect of Cu2+ and Pb2+.

Environmentally Friendly β-Cyclodextrin–Ionic Liquid Polyurethane-Modified Magnetic Sorbent for the Removal of PFOA, PFOS, and Cr(VI) from Water

Emerging contaminants such as perfluorinated compounds (PFCs) and heavy metals are of increasing concerns due to their detrimental effects on environment and human health. Their mixtures are often present at contaminated sites that pose a challenge in water remediation. Herein, we report a multifunctional magnetic sorbent (Fe3O4-CDI-IL MNPs) that was prepared by modifying the magnetic Fe3O4 nanoparticle with β-cyclodextrin–ionic liquid (β-CD-IL) polyurethanes for the removal of perfluorooctanesulfonate (PFOS), perfluorooctanoic acid (PFOA), and Cr(VI) from aqueous solution. The successful grafting of the β-CD-IL polymer on magnetic nanoparticles was confirmed by FTIR, ζ -potential, TGA, and VSM. The sorption behaviors of Fe3O4-CDI-IL MNPs were investigated in terms of sorption kinetics, isotherms, simultaneous removal capability, and reusability. The kinetic results showed that the sorption of PFOS, PFOA, and Cr(VI) reached equilibrium within 4, 6, and 3 h, respectively, and the pseudo-second-order kineti...

Behavior and mechanisms for sorptive removal of perfluorooctane sulfonate by layered double hydroxides

Perfluorooctane sulfonate (PFOS) is known to be extremely persistent and is toxic to wildlife and humans. In this study, we evaluated the sorptive removal behavior of PFOS from aqueous solution using three forms of layered double hydroxides (LDHs), namely, nitrate-, carbonate- and chloride-intercalated LDHs. Batch experiments showed that the sorption process was very fast with an equilibrium time of 10–60 min. The nitrate-LDH had the greatest ability to remove PFOS with a removal rate of 99.7% at an initial concentration of 100 mg/L and the maximum uptake capacity reached 865 mg/g. The sorption kinetic and equilibrium data could be fitted well with the pseudo-second-order model and Langmuir model, respectively. The intraparticle diffusion model suggests that both external diffusion and intraparticle diffusion are the rate-limiting processes for PFOS sorption onto the LDHs. The initial pH, background electrolyte concentration and coexisting ions influenced the sorption of PFOS by the LDHs. It was concluded that both surface adsorption and anion exchange were involved in the PFOS sorption onto the LDHs.

Sorption kinetics, isotherms and mechanisms of PFOS on soils with different physicochemical properties

Perfluorooctane sulfonate (PFOS), an emerging contaminant, is environmentally persistent, bioaccumulative and toxic to human health and ecosystems. It has been widely detected in groundwater, surface water, soil and sediment. So far, very few research has reported on the PFOS sorption behaviors onto soils, one of the primary processes that influence its fate and transport in the subsurface. In this study, the sorption and desorption of PFOS onto six soils with different physicochemical properties were investigated. Kinetic and equilibrium studies of PFOS sorption onto six soils were carried out in batch experiment. The sorption kinetics of PFOS on the six soils demonstrated that PFOS sorption reached equilibrium within 48h, and the well-fitted pseudo-second-order kinetic model to experimental data suggested that chemisorption was involved in PFOS sorption on soils. The intraparticle diffusion model results indicated that both film diffusion and intraparticle diffusion were the rate-limiting steps for five of the six soil samples, while the intraparticle diffusion was the only limiting step in the PFOS sorption on the sixth soil. PFOS sorption isotherms can be described by the Freundlich model well for all six soils (R2=0.979–0.999). The correlation analysis between KF of PFOS and the physicochemical properties of the soils showed that a positive correlation between KF and Al2O3, SOC and Fe2O3. The FTIR data demonstrated hydrophobic interaction, ion exchange, surface complexing and hydrogen bonding might all play a role in the PFOS sorption onto soil samples. PFOS sorption onto soil minerals, especially iron oxide minerals, needs to be further explored in future.