Perfluorooctane sulfonate (PFOS) adsorption on Fe-rich mineral assemblages and soils: experiments and surface complexation modeling

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.

Novel MOF-808 metal–organic framework as highly efficient adsorbent of perfluorooctane sulfonate in water

Perfluorooctanesulfonate (PFOS) is a hazardous chemical, and its presence in surface and groundwater poses a risk to environmental quality and human health. Containment is often applied to immobilize PFOS to stop or minimize the exposure. Mineral-based materials became promising adsorbents. However, there is scope to develop adsorbents using locally available minerals and understand their adsorption mechanisms. Here, we developed oleylamine-modified composites using naturally occurring Iranian zeolite and diatomaceous earth (DE). The mineralogy and surface properties of materials were fully characterized, and the adsorption of PFOS from simulated wastewater was linked to it. Clinoptilolite in zeolite sample, calcite and kaolinite in DE were main mineral assemblages. The raw samples also contained silica as a main constituent of them. Thermogravimetric analysis suggested that the materials were successfully modified with the oleylamine molecules in the material's structure and surfaces. These were further supported by scanning electronic microscopy (SEM), Fourier transmission infrared spectroscopy (FTIR), and surface and pore size analysis. After adsorption at various pHs, the isotherm of adsorption was also performed at ambient temperature. Modified DE and zeolite tend to adsorb PFOS (14.1 and 25.5 mg/g, respectively) more than their raw counterparts (4.72 and 0.39 mg/g, respectively). Adsorption models suggest monolayer and, in rare cases multilayer binding capacities and affinities toward PFOS. We analyzed the post-adsorption materials and discovered that electrostatic and hydrophobic interaction was likely the main cause of PFOS adsorbed to the material. This research helps to improve our knowledge of how PFOS adheres to untreated and surfactant-altered zeolite and DE in aquatic environments.

Perfluorooctane sulfonate adsorption on powder activated carbon: Effect of phosphate (P) competition, pH, and temperature

Mechanistic study of PFOS adsorption on kaolinite and montmorillonite

The fate and bioavailability of perfluorooctane sulfonate (PFOS) in soils is significantly influenced by its interactions with dissolved organic matter (DOM), which is elevated in soil solutions due to the land application of organic amendments. Evaluating the effects of DOM chemical properties on PFOS affinity and adsorption-desorption processes in soil is essential to better predict PFOS behavior in soils. We studied the interactions between PFOS and DOM from locally sourced and commercial organic amendments, including biosolids, animal manure, composts, and humic acid. Additionally, we measured PFOS adsorption on a kaolinitic Ultisol (Gwinnett) and adsorption-desorption on a smectitic Vertisol (Vaiden). PFOS affinity for DOM was strongly correlated with the humification index (HIX, r2=0.94), protein-like fluorophores (C3, r2=0.76), and aromaticity (specific UV absorption at 254nm [SUVA254], r2=0.71). The presence of 100mgC L⁻¹ DOM from biosolids and animal waste enhanced PFOS adsorption by up to 90%, whereas DOM from plant and terrestrial sources reduced adsorption by as much as 40%. Strong correlations were observed between PFOS adsorption enhancement on Gwinnett and C3 (r2=0.72), SUVA254 (r2=0.68), and HIX (r2=0.62). In contrast, PFOS adsorption on Vaiden was substantially lower and less influenced by DOM, though DOM type still affected PFOS adsorption-desorption hysteresis on Vaiden. This study offers a framework for using easily measurable DOM chemical properties to predict DOM's impact on PFOS fate and behavior in soils.

Polystyrene micro and nanoplastics attenuated the bioavailability and toxic effects of Perfluorooctane sulfonate (PFOS) on soybean (Glycine max) sprouts

Superhigh adsorption of perfluorooctane sulfonate on aminated polyacrylonitrile fibers with the assistance of air bubbles

Poly- and perfluoro alkyl substances (PFAS) are a group of man-made, notoriously persistent, and highly toxic contaminants in the environment reported worldwide. Many adsorbents including granular activated carbon, graphene, biochar, zeolites, and clay minerals have been tested for PFAS removal from water, but most of these materials suffer from high cost and/or poor removal performance. Here, we synthesized, characterized, and examined the efficiency of PCN-222(Fe), a new porous metal organic framework (MOF) with high water stability, for adsorptive removal of a frequently occurring PFAS, perfluorooctane sulfonate (PFOS), from water. The adsorption isotherm and kinetic studies revealed high PFOS adsorption capacity of PCN-222 (2257 mg/g), with rapid PFOS removal rate (within 30 min). The structure of PCN-222 was unaffected in water in the pH range of 2–10 but disintegrated and lost its PFOS removal ability at pH > 10. The PFOS adsorption on PCN-222 was an endothermic reaction. Electrostatic attraction was a dominant mechanism for PFOS adsorption at < 1694 mg/g PFOS concentration, while hydrophobic interaction accompanied with hydrogen-bonding was responsible at ≥ 1694 mg/g PFOS concentration. The interlayer morphology of PCN-222 did not change due to increasing PFOS loading. The findings of this study demonstrated superior features of PCN-222 over other conventional adsorbents for its potential application in removing PFOS from contaminated water to reduce PFOS transfer from water to living organisms.

Effect of solution chemistry on the adsorption of perfluorooctane sulfonate onto mineral surfaces

The adsorption of PFOS by activated sludge and EPS-removed sludge was conducted to investigate the adsorption mechanism of activated sludge and the effect of EPS on this adsorption process. The experimental results indicated that the adsorption process of PFOS onto activated sludge and EPS-removed sludge fitted the pseudo-second-order model, with equilibrium absorption capacities (qe) of 0.46 mg·g-1 and 0.38 mg·g-1, respectively. The sorption isotherm accorded well with the Freundlich, Langmuir, and Temkin models. Chemisorption played an important role in the adsorption of PFOS on the activated sludge. Ca2+ and Cu2+ contributed to PFOS adsorption on the activated sludge through an ion-bridging effect. Adsorption efficiency was better on the normal activated sludge compared to the EPS-removed sludge. FTIR and XPS were used to analyze the variations of functional groups before and after sorption. The results showed that the amount of functional groups such as hydroxyl, carboxyl, and amidogen on EPS-removed sludge was lower; however, these functional groups were found to have participated in the PFOS adsorption process. It is concluded that carboxyl and amidogen contained in protein of EPS provided reaction sites for PFOS adsorption, thus EPS components played a vital role in PFOS adsorption on the activated sludge.

Experimental and molecular dynamic simulation study of perfluorooctane sulfonate adsorption on soil and sediment components

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.

Adsorption of perfluorooctane sulfonate (PFOS) on corn straw-derived biochar prepared at different pyrolytic temperatures

Coupling effects of tide and salting-out on perfluorooctane sulfonate (PFOS) transport and adsorption in a coastal aquifer