Perfluoroalkyl Substances Degradation Research Articles

PFAS Degradation from Water by Using Metal Oxide as Photocatalyst

The recalcitrant nature of perfluoroalkyl substances (PFAS) urge scientists to discover solutions to permanently remove PFAS contaminations from water with less energy in contrast to incineration. In this presentation, we will introduce a duo-functional tri-metallic-oxide (f-TMO) hybrid photocatalyst that was synthesized via a facile process, which displayed both high adsorption capacity and high defluorination rate of a series of PFAS including PFOA, PFOS, PFHpA, PFHxA and PFBA due to the generated holes/electrons (h+/e-) and multi-radicals such as O2 •- and SO4 •- (Samuel, Shang, Niu. Chemosphere , 293 (2022) 133568). The Langmuir adsorption capacities up to 827.84 and 714.46 mg g-1 along with the adsorption efficiency of 99.8% and 99.4% for PFOS and PFOA were respectively achieved. A defluorination ratio of as high as 74.8% with PFOA and a ratio up to 67.6% with PFOS were respectively received. Over 98% PFOA molecules were degraded within as fast as 15 min under initial concentrations ranging from 1 ppb to 1000 ppb, which demonstrates an excellent degradation kinetics. After degradation, the PFOA residuals were as low as 10 ng L-1 in industrial wastewater with an initial concentration of 1 ppb. Moreover, as high as 95.5% degradation efficiency of PFOS was obtained within 300 min. The high physical adsorption capacity and high defluorination rate make this f-TMO catalyst promising applications in removing PFAS from a broad range of water sources. Keywords: Perfluoroalkyl substances (PFAS); Photocatalytic degradation; Water Remediation

New Indole Derivative Heterogeneous System for the Synergistic Reduction and Oxidation of Various Per-/Polyfluoroalkyl Substances: Insights into the Degradation/Defluorination Mechanism.

The hydrated electron (eaq-) system is typically suitable for degrading perfluoroalkyl substances (PFASs). To enhance eaq- utilization, we synthesized a new indole compound (DIHA) that forms stable nanospheres (100-200 nm) in water via a supramolecular assembly. Herein, the DIHA nanoemulsion system exhibits high degradation efficiencies toward a broad category of PFASs, regardless of the headgroup, chain length, and branching structure, under UV (254 nm) irradiation. The strong adsorption of PFAS on the DIHA surface ensures its effective degradation/defluorination. Quenching experiments further demonstrated that the reaction took place on the surface of DIHA nanospheres. This specific heterogeneous surface reaction unveiled novel PFAS degradation and defluorination mechanisms that differ from previously reported eaq- systems. First, the photogenerated surface electrons nonselectively attacked multiple C-F bonds of the -CF2- chain. This plays a dominant degrading/defluorinating role in the DIHA system. Second, abundant hydroxyl radicals (•OH) were also produced, leading to synergistic reduction (by surface electron) and oxidation (by surface •OH) in a single system. This facilitates faster and deeper defluorination of different structured PFASs through multiple pathways. The new mechanism inspires the design of innovative organo-heterogeneous eaq- systems possessing synergistic reduction and oxidation functions, thereby making them potentially effective for treating PFAS-contaminated water.

Durable water- and oil-repellent textiles without long- or short-chain perfluoroalkylated substances

For decades, the water and oil repellency of textiles was achieved using long-chain (CnF2n+1, n ≥ 7) perfluoroalkyl substances (PFAS). However, due to their proven bioaccumulative nature and toxic impacts on the environment and human health, these substances have been phased out of industrial production and/or legally banned in many countries. There is some evidence that a shorter carbon chain leads to less bioaccumulation and toxicity, and accordingly short-chain PFAS have been widely used as a replacement in recent years. Nevertheless, short-chain PFAS exhibit inferior surface properties due to their less crystalline and more loosely packed polymer chains, as compared to their long-chain counterparts. Moreover, surface properties become worse with decreasing chain length. Here we develop an alternative method for obtaining durable water and oil repellency on a nylon fabric using a liquidlike perfluoropolyether (PFPE) brush coating. The coating demonstrates excellent water and oil repellency, on par with the banned long-chain PFAS finishes, although its longest PFAS degradation product would have a chain length of L = 3, i.e. an ultra-short-chain PFAS. The PFPE-treated nylon exhibits superior surface properties compared to state-of-the-art, short-chain PFAS finished fabrics used in industry currently, even after laundering and 10,000 cycles of abrasion. The comfort of the treated fabrics is also maintained. The PFPE coatings developed here could replace the toxic, short-chain PFAS in use worldwide today.

Degradation of perfluoroalkyl substances using UV/Fe0 system with and without the presence of oxygen

ABSTRACT The wide presence of per- and poly-fluoroalkyl substances (PFAS) in the environment is a global concern, thus their degradation is an imminent task. In this study, oxidative and/or reductive degradation of three representative PFAS – perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), and perfluorooctane sulfonate (PFOS) was achieved using nanoscale zero-valent iron (Fe0 NPs) under ultraviolet (UV) light, both with and without the presence of oxygen. Higher degradation and defluorination rates were obtained for a longer chain PFNA compared to PFOA, and a higher removal of PFAS was achieved without the presence of O2 compared to that with O2. The degradation followed first-order reaction kinetics, and obtained the highest rates of 97.6, >99.9, and 98.5% without the presence of O2 for PFOA, PFNA, and PFOS, respectively. The degradation rates increased with an increase in the nanoparticle concentrations in the range of 1–100 mg/L. In addition to fluoride ions, shorter chain perfluorocarboxylic acids (PFCAs) were detected as the main intermediates during PFAS degradation; PFHpS and 6:2 FTS were also detected during PFOS degradation. Hydroxyl radicals (·OH) and superoxide radicals (·O2 −) were not involved in the degradation of PFOA, but likely involved in the degradation of PFOS. Emerging contaminants PFAS degradation using the UV/Fe0 system is a cost-effective technology owing to the low cost and recyclability of Fe0 nanomaterials, low energy consumption in the system, and its capability to degrade PFAS both with and without the presence of oxygen. This technology can be potentially applied to treat PFAS-contaminated waters in the environment.

Degradation of PFOS and PFOA in soil and groundwater samples by high dose Electron Beam Technology

Remediation technologies are urgently needed to degrade poly – and per fluoroalkyl substances (PFAS) in groundwater and soils. Since high energy electron beam (eBeam) technology involves rapid oxidation and reduction reactions it has the potential to breakdown PFAS. In this study, the technology was applied to PFAS-contaminated groundwater and soil samples to degrade PFOS and PFOA and other PFAS. An eBeam dose of 2000 kGy (kGy) reduced PFOS and PFOA concentrations in groundwater by 87.9% and 53.7% respectively. In soils with 10% moisture content, PFOS and PFOA concentrations were reduced by 99.9% and 86.5%, respectively. Out of 17 different PFAS that were detected in the soil sample, the 2000 kGy dose was able to degrade 10 PFAS to below detectable levels: PFNA (initially 19.4 ng/g), PFDA (3.9 ng/g), PFPeS (12.1 ng/g), PFHxS (365 ng/g), PFHpS (18.0 ng/g), PFNS (4.3 ng/g), 4:2 FTS (16.6 ng/g), 6:2 FTS (146.1 ng/g), 8:2 FTS (165.6 ng/g) and PFOSA (171.8 ng/g). Of the remaining 7 PFAS, the removal efficiency ranged between 49% and 99.9%. It appears that eBeam degradation of PFAS in soil is more effective at reduced soil moisture content.

PFAS Degradation in Ultrapure and Groundwater Using Non-Thermal Plasma.

Perfluoroalkyl substances (PFAS) represent one of the most recalcitrant class of compounds of emerging concern and their removal from water is a challenging goal. In this study, we investigated the removal efficiency of three selected PFAS from water, namely, perfluorooctanoic acid (PFOA), perfluorohexanoic acid (PFHxA) and pefluorooctanesulfonic acid (PFOS) using a custom-built non-thermal plasma generator. A modified full factorial design (with 2 levels, 3 variables and the central point in which both quadratic terms and interactions between couple of variables were considered) was used to investigate the effect of plasma discharge frequency, distance between the electrodes and water conductivity on treatment efficiency. Then, the plasma treatment running on optimized conditions was used to degrade PFAS at ppb level both individually and in mixture, in ultrapure and groundwater matrices. PFOS 1 ppb exhibited the best degradation reaching complete removal after 30 min of treatment in both water matrices (first order rate constant 0.107 min−1 in ultrapure water and 0.0633 min−1 in groundwater), while the degradation rate of PFOA and PFHxA was slower of around 65% and 83%, respectively. During plasma treatment, the production of reactive species in the liquid phase (hydroxyl radical, hydrogen peroxide) and in the gas phase (ozone, NOx) was investigated. Particular attention was dedicated to the nitrogen balance in solution where, following to NOx hydrolysis, total nitrogen (TN) was accumulated at the rate of up to 40 mgN L−1 h−1.

Facing the Challenge of Poly- and Perfluoroalkyl Substances in Water: Is Electrochemical Oxidation the Answer?

Electrochemical treatment systems have the unique ability to completely mineralize poly- and perfluoroalkyl substances (PFASs) through potential-driven electron transfer reactions. In this review, we discuss the state-of-the-art on electrooxidation of PFASs in water, aiming at elucidating the impact of different operational and design parameters, as well as reported mechanisms of PFAS degradation at the anode surface. We have identified several shortcomings of the existing studies that are largely limited to small-scale laboratory batch systems and unrealistic synthetic solutions, which makes extrapolation of the obtained data to real-world applications difficult. PFASs are surfactant molecules, which display significant concentration-dependence on adsorption, electrosorption, and dissociation. Electrooxidation experiments conducted with high initial PFAS concentration and/or in high conductivity supporting electrolytes likely overestimate process performance. In addition, the formation of organohalogen byproducts, chlorate and perchlorate, was seldom considered. Nevertheless, the first step toward advancing from laboratory-scale to industrial-scale applications is recognizing both the strengths and limitations of electrochemical water treatment systems. More comprehensive and rigorous evaluation of novel electrode materials, application of scalable proof-of-concept studies, and acknowledgment of all treatment outputs (not just the positive ones) are imperative. The presence of PFASs in drinking water and in the environment is an urgent global public health issue. Developments made in material science and application of novel three-dimensional, porous electrode materials and nanostructured coatings are forging a path toward more sustainable water treatment technologies and potential chemical-free treatment of PFAS-contaminated water.

Efficient Reductive Destruction of Perfluoroalkyl Substances under Self-Assembled Micelle Confinement.

Recently, perfluoroalkyl substances (PFASs) have received great attention from both academia and the industry due to their persistence and health risks. Here, we developed a simple ternary self-assembled micelle composite, consisting of a photosensitive substance (indole acetic acid, IAA), cationic surfactant (cetyltrimethylammonium bromide), and contaminant (PFAS). Owing to the rapid hydrated electron transfer from IAA to the PFAS in the micelle, the PFAS degradation and defluorination were greatly enhanced even under ambient conditions. After 2.5 h UV irradiation, the perfluorooctanoic acid (PFOA) concentration decreased from 10 mg L-1 to ∼60 ng L-1, which is below the drinking water health advisory level of the United States Environmental Protection Agency for the combined concentration of PFOA and perfluorooctane sulfonate (70 ng L-1). Meanwhile, the dissolved organic carbon content of the reaction solution was also reduced to ∼3 mg L-1 due to the quick settlement and automatic separation of the micelle. Furthermore, the newly developed composite was also adaptable to a wide pH range (pH 4-8), attributing to the barrier created by the ternary micelle system. This novel self-assembly method is expected to directly treat industrial PFAS-containing wastewater or PFAS-enriched concentrates derived from adsorption processes. The conceptually new advanced reduction technique represents a major breakthrough toward PFAS rapid destruction and efficient usage of hydrated electrons and might also shed light on other environmental applications.

Highly Efficient Degradation of Perfluorooctanoic Acid over a MnOx‐Modified Oxygen‐Vacancy‐Rich In2O3 Photocatalyst

AbstractDestructive removal of perfluoroalkyl substances (PFASs) from water has been an emerging concern, as the C−F bond cleavage requires energy‐consuming advanced oxidation approaches. The conventional photocatalyst materials exhibit insufficient PFAS degradation due to either a weak absorption ability towards PFASs or a limited reaction oxygen species (ROS) generation. Herein, In2O3, which has an excellent absorption ability towards perfluorooctanoic acid (PFOA), is chosen as the main catalyst materials. Oxygen vacancies are then generated on the surface of In2O3 to assist the PFOA adsorption. Further depositions of the MnOx cocatalyst on the surface of In2O3 are performed to enhance the ROS generation efficiency. Based on the above design, the MnOx‐modified oxygen‐vacancy‐rich In2O3 photocatalyst shows a remarkably improved PFOA photodegradation and defluorination efficiencies under the solar light irradiation as compared with the pristine and commercial In2O3. The photodegradation pathway of PFOA is investigated. The experimental results from the PFOA adsorption analysis and electron spin resonance (ESR) spectra confirm the enhanced adsorption ability and the higher ROS generation efficiency, respectively. The catalyst is further tested in the presence of different anions and cations, where rapid degradation of PFOA is also observed, indicating the potential of the composite materials applied in the practical treatment of PFAS‐contaminated water.

Rapid Degradation and Mineralization of Perfluorooctanoic Acid by a New Petitjeanite Bi3O(OH)(PO4)2 Microparticle Ultraviolet Photocatalyst

Water treatment techniques for destructive removal of perfluoroalkyl substances (PFAS) have only recently begun to emerge in the research literature, comprising unconventional advanced oxidation and reduction methods. Photocatalytic degradation of PFAS has not been widely pursued, which is a result of the limited ability of common semiconductor materials to induce C–F bond cleavage in aqueous systems. Herein, degradation of perfluorooctanoic acid (PFOA) by bismuth phosphate photocatalysts under ultraviolet irradiation has been investigated for the first time, including the relatively well-known monoclinic BiPO4 wide band gap semiconductor, as well as a novel Bi3O(OH)(PO4)2 (BOHP) composition. Compared to BiPO4 and a β-Ga2O3 nanomaterial reference catalyst, BOHP microparticles achieved dramatically faster PFOA degradation and mineralization, despite both a smaller surface area and a lower band gap energy. The rate constant for degradation of PFOA by BOHP in a pure water solution was ∼15 times greater than those of both BiPO4 and β-Ga2O3 (∼20–30 times greater when normalized for surface area) and was on the same order of magnitude as that of phenol degradation by P25 TiO2 in the same photoreactor. The superior performance of BOHP was primarily related to the surface charge and adsorption behavior of PFOA, in combination with the favorable redox potentials of BOHP charge carriers. The catalyst was further tested at low PFOA concentrations (i.e., microgram per liter range) in the presence of natural organic matter, and rapid degradation of PFOA was also observed, indicating the potential of BOHP to enable practical ex situ destructive treatment of PFAS-contaminated groundwater.

1,2-Fluorine Radical Rearrangements: Isomerization Events in Perfluorinated Radicals.

Devising effective degradation technologies for perfluoroalkyl substances (PFASs) is an active area of research, where the molecular mechanisms involving both oxidative and reductive pathways are still elusive. One commonly neglected pathway in PFAS degradation is fluorine atom migration in perfluoroalkyl radicals, which was largely assumed to be implausible because of the high C-F bond strength. Using density functional theory calculations, it was demonstrated that 1,2-F atom migrations are thermodynamically favored when the fluorine atom migrated from a less branched carbon center to a more branched carbon center. Activation barriers for these rearrangements were within 19-29 kcal/mol, which are possible to easily overcome at elevated temperatures or in photochemically activated species in the gas or aqueous phase. It was also found that the activation barriers for the 1,2-F atom migration are lowered as much as by 10 kcal/mol when common oxidative degradation products such as HF assisted the rearrangements or if the resulting radical center was stabilized by vicinal π-bonds. Natural bond orbital analyses showed that fluorine moves as a radical in a noncharge-separated state. These findings add an important reaction to the existing knowledge of mechanisms for PFAS degradation and highlights the fact that 1,2-F atom shifts may be a small channel for isomerization of these compounds, but upon availability of mineralization products, this isomerization process could become more prominent.