Enhanced removal and destruction of per- and polyfluoroalkyl substances (PFAS) with magnetic modified clay and photoreductive degradation

Abstract

Magnetic modified clay (MMC) is used as an adsorbent for removing a wide range of per- and polyfluoroalkyl substances (PFAS) from the environment, including soil and water. Subsequent photoreductive degradation is optimized to enhance PFAS breakdown under UV light. The MMC can be regenerated and reused for the sustainable treatment of PFAS-contaminated soil and water.

Description

ENHANCED REMOVAL AND DESTRUCTION OF PER- AND POLYFLUOROALKYL SUBSTANCES (PFAS) WITH MAGNETIC MODIFIED CLAY AND PHOTOREDUCTIVE DEGRADATIONCROSS-REFERENCE TO RELATED APPLICATION

[0001] This invention claims the benefit of US Provisional Application Serial No. 63 / 704,735, filed on October s, 2024, and US Provisional Patent Application Serial No. 63 / 548,316, filed on November 13, 2023, the entireties of which are hereby incorporated herein by this reference.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0002] This invention was made with government support under grant number CBET2225596, awarded by the National Science Foundation. The government has certain rights in the invention.BACKGROUND OF THE INVENTION

[0003] 1 . Field of the Invention

[0004] The present invention generally relates to methods and substances for removal of pollutants from the environment. More particularly, the present invention utilizes magnetic modified clay (MMC) as an adsorbent for per- and polyfluoroalkyl substances (PFAS) pollution along with photoreductive degradation for removal of the PFAS from the environment.

[0005] 2. Description of the Related Art

[0006] PFAS compounds encompass a vast array of synthetic organic compounds where the carbon backbones are either fully or partially fluorinated. The distinctive characteristics of PFAS have facilitated their extensive utilization in various industrial operations and consumer goods, such as surfactants for mining and oil wells, coatings for textiles and food packaging, foams for aqueous film formation, cosmetics and personal care items, cleaning agents, and numerous other applications. PFAS, which have been in production for more than six decades and are now widely detected in the environment, are recognized as posing high risks to human health. Thus, there has been a tremendous interest in technologies and methods for eliminating PFAS contamination from the environment.

[0007] Several approaches have been examined for treating PFAS, such as physical adsorption / filtration, chemical / electrochemical destruction, and biological degradation. Adsorption is a cost-effective and efficient method for rapidly removing PFAS especially from polluted water sources. Adsorbents used for PFAS removalconsist of carbon-based materials, ion exchange resins, biosorbents, and clay-based materials. Activated carbons (ACs), such as granular and powdered AC (GAC and PAC), carbon nanotubes (CNTs), and biochar, are widely recognized as the primary carbon-based materials utilized for the adsorption of PFAS. Among these materials, PAC and CNTs have demonstrated notable efficacy in adsorption capacity. The hydrophobic adsorption of PFAS is facilitated by the presence of non-polar functional groups in carbon-based adsorbents. In contrast to the adsorption of long-chain PFAS, the adsorption of short-chain PFAS presents a distinct challenge due to their increased hydrophilicity and reduced affinity with adsorbents.

[0008] Clay-based materials represent an additional classification of adsorbents for PFAS. Numerous investigations have been conducted on the adsorption of PFAS using a diverse range of naturally occurring clays, including montmorillonite (Mt), kaolinite, alumina, boehmite, and hematite. The surfaces of natural clays exhibit hydrophilic properties due to the hydration of inorganic cations at the exchange sites and this hydration process leads to a negative charge on the clay surfaces, reducing their efficiency in adsorbing hydrophobic and anionic PFAS. As a result, the adsorption of PFAS is enhanced by modifying natural clays with surfactants, thereby converting the hydrophilic surface to a lipophilic one

[0009] Generally, due to modification by cationic surfactants, the positively charged surfaces are inclined towards anionic PFAS due to electrostatic interactions. Mt, belonging to the smectite group, exhibits a structural arrangement consisting of two tetrahedral silicate layers enclosing an aluminum oxide / hydroxide layer (referred to as a 2:1 layered structure). This configuration facilitates a significant cation exchange capacity (CEC) and specific surface area. Previous research has utilized quaternary ammonium compounds to modify the surface of Mt to enhance its ability to adsorb PFAS. In a study, modifications to Mt using the cationic surfactant hexadecyltrimethylammonium bromide (HDTMAB) led to adsorption capacities of approximately 62 mg / g and 339 mg / g for perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), respectively, when the HDTMAB to CEC ratio was 0.5. Another study modified Mt by incorporating quaternary ammonium compounds, specifically L-carnitine and choline to enhance adsorption capacity for PFOA, PFOS, undecafluoro-2-methyl-3-oxahexanoic acid (GenX), and perfluorobutane sulfonate (PFBS). However, complete separation of modified clayparticles from an aqueous solution post-adsorption is challenging owing to their limited mechanical stability and pronounced dispersion.

[0010] Magnetic adsorbents derived from clay minerals have been of significant scientific interest due to their ability to combine distinctive adsorption properties with the cost-effectiveness of clays. Moreover, these adsorbents offer the advantage of easy and fast separation from an aqueous suspension upon exposure to a magnetic field. Numerous articles are dedicated to magnetic adsorbents with a matrix composed of bentonite, montmorillonite, kaolin, zeolite, and other clays, which are applied to remove dyes, heavy metals, and pharmaceuticals. These adsorbents are generally produced through a coprecipitation technique. Magnetite-based clay adsorbents have demonstrated notable affinity and fast adsorption kinetics in the removal of hazardous metal ions. Furthermore, these adsorbents have shown exceptional performance in engineering research and have been successfully employed in industrial and pilot-scale applications. However, there has been a notable absence of research specifically addressing the use of magnetic modified clay (MMC) for the adsorption of PFAS mixtures in real-world environments.

[0011] Additionally, in recent years, photocatalytic degradation has been investigated for breaking down PFAS due to that method’s relatively inexpensive energy needs and high transformation efficiency. Photodegradation can be divided into photooxidation and photoreduction. PFAS undergo oxidative degradation by undergoing one electron transfer to photo-induced oxidants, resulting in the detachment of functional groups and the shortening of the carbon chain. Prior research has recorded the breakdown of PFAS by photooxidation when exposed to UV or visible light in the presence of semiconductor photocatalysts, such as TiC>2 and Ga2Os. Within this system, the breakdown of PFAS is thought to be associated with photo-induced holes (hVb+) that possess a potent oxidation capability. The general oxidation pathways of perfluorocarboxylic acids (PFCAs; CnF2n+iCOO')may be characterized by the acid transforming into an unstable CnF2n+iCOO' radical, which then undergoes decarboxylation to form a perfluoroalkyl radical CnF2n+i. During liquid-phase photocatalytic reactions, the hydroxyl radical (HO-) is produced by splitting water when exposed to UV or visible light. This HO' then combines with the perfluoroalkyl radical to create CnF2n+iOH in the water.

[0012] However, HO’ is unable to break down PFCAs like perfluorooctanoic acid (PFOA) for two reasons. Firstly, the carbon chain of PFCAs does not have any hydrogen atoms that can be removed. Secondly, the oxidation potential of HO’ is lower than the average energy required to break a C-C bond, which is 276.0 kJ / mol compared to 347.0 kJ / mol.

[0013] Recently, UV photochemical reactions that produce hydrated electrons (eaq-) have been recognized for their ability to effectively degrade both PFCAs and perfluorosulfonic acids (PFSAs). While several photosensitizers and inorganic anions such as dithionite have been employed to enhance the efficiency of eaq- toward the breakdown of PFAS, I- and SO32-are the most often used. The generation of eaq- in the UV / I- system occurs via the photoexcitation of I-, forming an excited iodide species (I’HsO-*). This species then undergoes a transformation into a caged complex (I*, e-) consisting of an iodine atom and an electron, or it may decay back to the ground state (I-). The caged complex dissociates, producing eaq-. The iodine atom produced in this process undergoes further reactions with l~, resulting in the formation of many additional iodine species that have the ability to consume eaq-- SO3* and eaq- may be generated in a UV / SO32-system that is operated under alkaline conditions.

[0014] In a recent study, it was discovered that the presence of P ions greatly speeds up the breakdown of PFSAs and PFCAs in the UV / SO32-aqueous system (UV / SO32-+ I-). This is due to the higher concentration of eaq- and greater consumption of SO32-ions, resulting in improved degradation. Additionally, the use of power and chemicals in the UV / SOs2-+ I- system was much less compared to the UV / SO32-system while removing an equivalent quantity of PFSAs or PFCAs.BRIEF SUMMARY OF THE INVENTION

[0015] Briefly described, the present invention is an innovative approach to PFAS removal and destruction using a system and method for adsorption that can also use photoreductive degradation. A mixture of a magnetic modified clay (MMC) is employed as an adsorbent for PFAS, achieving high adsorption efficiencies. Then subsequent photoreductive degradation can be optimized, from both reductant concentrations and pH to enhance PFAS breakdown under a UV light. Thus, the MMC effectively adsorbs PFAS and facilitate their degradation through thephotochemical process, achieving substantial defluorination and removal efficiencies. The MMC can also be regenerated and reused for the sustainable treatment of PFAS-contaminated water and soil.

[0016] The present invention offers a cost-effective and environmentally friendly solution for mitigating PFAS pollution. In an embodiment, a UV / SOs2-+ I- system is able to destroy PFAS in spent sorbent and thus leads to regeneration and reuse of the sorption material.

[0017] The MMC has outstanding PFAS adsorption ability and is made from inexpensive clay minerals that have unique adsorption properties and ease of separation in water under a magnetic field. The present invention therefore outperforms powdered activated carbon in PFAS removal efficiency and the magnetic feature allows fast and easy sorbent harvesting and prevents potential secondary contamination.

[0018] In one embodiment, the invention includes a magnetic modified clay (MMC) that is made from an adsorbent clay and a magnetizable metal mixed with the adsorbent clay. The mixture of adsorbent clay and magnetizable metal is further subject to a predetermined magnetic modification process such that the mixture is configured to attract and bind PFAS. The adsorbent clay can be made of montmorillonite K10, an Na2COs solution, and hydrochloric acid. The MMC can also include a solution having a cation exchange capacity, such as one or both of cetrimonium chloride and cetyltrimethylammonium chloride.

[0019] The predetermined magnetic modification process of the MMC can be adding FeCl3-6H2O to the adsorbent clay mixture, and adding FeCl2-4H2O, adding NF OH, and exposing the mixture to a magnetic field for a predetermined period. The MMC can also be configured to be reusable by selectively releasing bound PFAS and then reused to attract and bind PFAS. The MMC can also be subject to a predetermined period of drying. Moreover, the MMC can be configured to remove PFAS from water or soil.

[0020] In another embodiment, the magnetic modified clay is optimized for photoreductive degradation of PFAS), with the mixture including an adsorbent clay, a magnetizable metal, and a photoreductive enhancing solution mixed with the adsorbent clay. The mixture of adsorbent clay and magnetizable metal further subject to a predetermined magnetic modification process such that the mixture isconfigured to attract and bind PFAS. The photoreductive enhancing solution can be a solution of Na2SOs and KI. The photoreductive enhancing solution can be further modified to a predetermined pH.

[0021] The invention can also include a method for removing PFAS from substances by the steps of adding a magnetic modified clay to a PFAS-containing substance to create a PFAS-containing mixture thereof, the magnetic modified clay including an adsorbent clay, and a magnetizable metal mixed with the adsorbent clay, wherein the mixture of adsorbent clay and magnetizable metal further subject to a predetermined magnetic modification process such that the mixture is configured to attract and bind PFAS. A photoreductive enhancing solution is also added. The method continues with exposing the PFAS-containing mixture to a UV source for a predetermined duration to photochemically degrade the PFAS.

[0022] The method can include removing the magnetic modified clay from the PFAS-containing mixture, as well as removing PFAS from the magnetic modified clay to create a cleaned magnetic modified clay, and reusing the clean magnetic modified clay by adding the clean magnetic modified clay to a PFAS containing substance to create a PFAS-containing mixture thereof. The method can also include modifying the photoreductive enhancing solution to a predetermined pH.

[0023] The present invention therefore provides an advantageous system and method to remove pollutant PFAS from the environment, and especially from water and soil. Further, the present invention is industrially application in pollution remediation and environmental restoration. Other objects, advantages and features of the present invention will be apparent to one of skill in the art.BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Fig.1 is series of graphs that illustrate the adsorption performance comparison among modified clay and commercially available clay-based adsorbents for PFAS at different contact times.

[0025] Fig. 2 is a series of graphs illustrating the effects of environmental factors on adsorption of PFAS by unmodified and modified clays.

[0026] Fig. 3A is a graph of the recovery of MMC after use for PFAS removal.

[0027] Fig. 3B is a graph of the reuse of MMC for PFAS adsorption.

[0028] Fig. 4 is a graph of the adsorption performance of PFAS by magnetic modified clay in pure water.

[0029] Fig. 5A is an image of the MMC before adsorption,

[0030] Fig. 5B is a graph of the compositional analysis of the MMC of Fig. 5A.

[0031] Fig. 5C is an image of the MMC after adsorption.

[0032] Fig. 5D is a graph of the compositional analysis of the MMC of Fig. 5C.

[0033] Fig. 6A is a graph of FTIR spectra of pristine MMC and spent MMC.

[0034] Fig. 6B is a graph of the XRD pattern of pristine MC and pristine MMC.

[0035] Fig. 7 is a series of graphs illustrating the adsorption of PFAS spiked to snowmelt by magnetic modified clay and GAC.

[0036] Fig. 8 is a graph 80 of the adsorption of the six regulated PFAS by magnetic modified clay after 48 h.

[0037] Fig. 9 is a series of graphs illustrating photodegradation of PFAS in aqueous solutions without and with pristine magnetic modified clay (MMC).

[0038] Fig. 10 is a series of graphs illustrating the photodegradation of PFAS in aqueous solutions with magnetic modified clay adsorbed with individual GenX, PFOA, and PFOS.

[0039] Fig.11 is a series of graphs illustrating the photoreductive degradation of adsorbed PFAS in MMC at various reductant concentrations.

[0040] Fig. 12 is a graph of the overall defluorination efficiency (%) for each parent PFAS in the photodegradation 366 of adsorbed PFAS in MMC at various reductant concentrations.

[0041] Fig. 13 is a series of graphs of the photoreductive degradation of adsorbed PFAS in MMC at various conditions.

[0042] Fig. 14 is a graph of the overall defluorination efficiency (%) for each parent PFAS in the photodegradation of adsorbed PFAS in MMC at various conditions.

[0043] Fig. 15 is a graph of the mass balance of fluorine before and after photodegradation of adsorbed PFAS in MMC at various conditions.

[0044] Fig. 16 is a graph of the reuse of magnetic modified clay after photochemical degradation of the adsorbed PFAS at different contact times.DETAILED DESCRIPTION OF THE INVENTION

[0045] With reference to the figures in which like numerals represent like elements throughout the several views, in an embodiment, the invention includes a magneticmodified clay (MMC) that is made from an adsorbent clay and a magnetizable metal mixed with the adsorbent clay. The mixture of adsorbent clay and magnetizable metal is further subject to a predetermined magnetic modification process such that the mixture is configured to attract and bind PFAS.

[0046] To synthesize the MMC, in this embodiment, a two-step process was employed, starting with the addition of montmorillonite K10 (Alfa Aesar, Haverhill, MA, USA) to a Na2COs solution and stirring for 3 h. Then, a few drops of concentrated hydrochloric acid were added to the mixture, which was followed by rinsing with deionized (DI) water, and drying overnight to generate the unmodified clay. The obtained solids were then mixed with a CTAC solution at a CTAC / CEC ratio of 0.85 and stirred at 80 °C for 2 h. This was followed by rinsing with DI water and drying overnight to produce the MC adsorbent.

[0047] In one embodiment, the MMC was prepared in the following way. At first, 4.41 g FeCl3-6H2O was dissolved in 200 ml DI water, to which 4.67 g MC was dispersed in. The mixture was ultrasonicated for 10 min. Then, 1 .61 g FeCl2-4H2O was dissolved in the obtained dispersion. After heating to 90 °C, the pH was adjusted to -10 with a NH4OH solution (-28%) under stirring. The mixture was maintained under the same condition for another 1 h. The solids were then collected and rinsed carefully using DI water until the pH reached neutrality. The solids were dried at 90 °C overnight and stored for further use.

[0048] Thus, the predetermined magnetic modification process of the MMC can be adding FeCi3-6H2O to the adsorbent clay mixture, and adding FeCl2-4H2O, adding NH4OH, and exposing the mixture to a magnetic field for a predetermined period. The MMC can also be configured to be reusable by selectively releasing bound PFAS and then reused to attract and bind PFAS. The MMC can also be subject to a predetermined period of drying. Moreover, the MMC can be configured to remove PFAS from water or soil.

[0049] The adsorbent clay can be made of montmorillonite K10, an Na2COs solution, and hydrochloric acid. The MMC can also include a solution having a cation exchange capacity, such as one or both of cetrimonium chloride and cetyltrimethylammonium chloride.

[0050] To demonstrate the efficacy of the present invention, Fourier transform infrared spectroscopy (FTIR; PerkinElmer Spectrum 100, Waltham, MA, USA) wasused to analyze the functional groups in the adsorbent samples both before and after PFAS adsorption. The spectral data were collected within the 4,000-650 cm-1spectral region, with a resolution of 1 cm-1. To understand adsorbents’ surface morphology and elemental composition, a scanning electron microscope (SEM) (Zeiss LEO 1550, Oberkochen, Germany) equipped with energy dispersive X-ray spectroscopy (Bruker Quantax XFIash 6, Billerica, MA, USA) was used. The crystal structure of the samples was examined using a powder X-ray diffractometer (XRD; Rigaku MiniFlex 6G, Rigaku Corporation, Tokyo, Japan). The particle size distribution and zeta potential were quantified using a Malvern Zetasizer Nano-ZS analyzer (Malvern Panalytical Ltd, Malvern, UK) at a neutral pH and room temperature.

[0051] Here, adsorption studies were conducted in a batch manner and were replicated three times using 50-mL polypropylene centrifuge tubes (Corning Inc., Corning, NY, USA). To each tube, a PFAS mixture consisting of nine short- and long-chain perfluoroalkyl acids (PFAAs) (C6-C11 perfluorocarboxylic acids (PFCAs) and C4, C6, C8 perfluorosulfonic acids (PFSAs)), GenX, and two precursors, namely 6:2 fluorotelomer sulfonic acid (6:2 FTSA) and 2-N-ethyl perfluorooctane sulfonamido acetic acid (N-EtFOSAA) was added. The starting concentration for each PFAS was 10 ppb and the dose of each adsorbent was 100 mg / L. All tubes with or without an adsorbent were agitated at 150 rpm at room temperature.Subsamples were collected at seven specific time intervals, namely 0, 1 , 2, 4, 8, 24, and 48 h and examined for amounts of PFAS following centrifugation, filtering the supernatant through 0.2 pm nylon syringe filters and analyzing these compounds using a LC-MS-MS as detailed below. Additionally, the adsorption of PFAS in a snowmelt was investigated using a similar methodology, except that each PFAS was spiked at 1 , 5, or 10 ppb. Furthermore, a comparison of adsorption performance was conducted between the MC, MMC and five commercially available adsorbents, namely FS, FS-F, MAT, MAT-P, and GAG. Moreover, the impacts of three environmental factors, including pH (2, 5, 7, 9, and 12), natural organic matter (NOM) (0, 2, 5, 10, 20, 50, and 100 mg / L humic acid), and ionic strength (0, 5, 10, 50, 100, and 200 mM NaCI) were evaluated on the adsorption of PFAS by both unmodified and modified clays with an initial concentration of 100 ppb for each PFAS mentioned above.

[0052] In a regeneration step for the MMC, 5 ml_ of methanol with 0.1 M NF OH was added to the spent MMC. The mixture was vortexed for 30 s, sonicated at 35 °C for 30 min, and centrifuged at 4500 rpm for 10 min. The supernatant was then collected. The above extraction steps were repeated twice, and the extract for each round was 5 mL. The residual solids were rinsed using DI water thrice and dried at 90°C overnight. The solids generated from the recovery step were mixed and reacted with a CTAC solution, rinsed with DI water, and dried in an oven as detailed above. The regenerated adsorbent was then used to remove a PFAS mixture according to the aforementioned steps to investigate their reusability performance.

[0053] PFAS in the melted snow were quantified following EPA Method 537.1. Briefly, a surrogate of 30 pL (30 ng, 1 ppm) 13C-perfluorohexanoic acid (PFHxA) was spiked to each sample of 400 mL. The spiked sample was then loaded to a Hypersep C18 cartridge conditioned by methanol and DI water. Following elution of the PFAS retained on the C18 cartridges and before measurement, the samples were supplemented with 13C-PFOS and 13C-PFOA as internal standards.Quantification of the target PFAS in the prepared samples was performed using an Agilent Technologies 1290 Infinity II LC system paired with a 6470 Triple Quad Mass Spectrometer (LC-MS / MS, Santa Clara, CA, USA). Supernatant samples derived from the adsorption tests were subject to similar analysis except that the solid phase extraction (SPE) step was eliminated. Overall, making PFAS measurements using the LC-MS / MS would be known to one of skill in art.

[0054] The anions in the snowmelt were analyzed using a 930 Compact IC Flex instrument (Metrohm, Herisau, Switzerland) equipped with a conductivity detector. Anions were separated using a Metrosep SUPP 5 column (Metrohm). The elution process included the use of a 1 :1 combination of 1.8 mM Na2COs and 1.7 mM NaHCOs as the eluent, with a flow rate of 0.7 mL / min. Subsequently, a solution of H2SO4 with a concentration of 0.05 M was used as a regenerating agent to mitigate the conductivity. A standard mixture (Thermo Fisher Scientific Inc., USA) consisting of seven anions, including CI-, F-, Br-, SO42", NO2-, NO3-, and PO43-, was employed to build calibration curves in the range of 1-500 pg / L.

[0055] To compare the adsorption performance of MC with those of commercially available clay-based adsorbents, namely FS, FS-F, MAT, and MAT-P, PFAS concentrations in the subsamples collected at 1 , 4, 8, and 48 h were measured andPFAS’ removal efficiencies were calculated as shown in Figure 1. The main observation is that MC had excellent adsorption performance, i.e. , 100% removal within 1 h for all 12 PFAS. No desorption occurred for MC, at least in the studied time interval of 1-48 h, which confirmed the strong binding of MC with all target PFAS compounds. In contrast, in addition to the low adsorption performance of the commercial clay adsorbents, desorption of some PFAS from all four commercial adsorbents occurred as time increased (Figure 1). For instance, FS showed desorption for PFDA, perfluoroundecanoic acid (PFUnA), PFOS, 6:2 FTSA, and N- EtFOSAA.

[0056] Fig. 1 is a series of graphs that illustrate adsorption performance comparison among modified clay and commercially available clay-based adsorbents for PFAS at different contact times (1 , 4, 8, and 48 h). Error bars represent the standard deviations of triplicate measurements. To compare the adsorption performance of MC with those of commercially available clay-based adsorbents, namely FS, FS-F, MAT, and MAT-P, PFAS concentrations in the subsamples collected at 1 , 4, 8, and 48 h were measured and PFAS’ removal efficiencies were calculated as shown in Fig. 1 . The main observation is that MC had excellent adsorption performance, i.e., 100% removal within 1 h for all 12 PFAS. No desorption occurred for MC, at least in the studied time interval of 1-48 h, which confirmed the strong binding of MC with all target PFAS compounds. In contrast, in addition to the low adsorption performance of the commercial clay adsorbents, desorption of some PFAS from all four commercial adsorbents occurred as time increased (Fig. 1). For instance, FS showed desorption for PFDA, perfluoroundecanoic acid (PFUnA), PFOS, 6:2 FTSA, and N-EtFOSAA.

[0057] The impact of varying pH levels (2, 5, 7, 9, and 12) on the adsorption of a PFAS mixture by both unmodified clay and MC was explored. Fig. 2 is a series of graphs illustrating the effects of environmental factors on adsorption of PFAS by unmodified and modified clays. Error bars represent the standard deviations of triplicate measurements.

[0058] As shown in Fig. 2, (a) and (b), both clays displayed pH sensitivity in their adsorption behavior. The unmodified clay exhibited limited adsorption capabilities for all examined PFAS, suggesting that the clay’s intrinsic properties alone were not sufficient to effectively remove PFAS from aqueous solutions. As pH changed,removal efficiencies remained low for most PFAS. In contrast, the modification of clay significantly enhanced its adsorption capacity for PFAS across all pH levels. Notably, at pH 2 and 5, MMC achieved nearly complete removal for most PFAS. As pH increased, the removal efficiency showed a decreasing trend in general. This can be attributed to the dominance of negatively charged hydroxide ions (OH-) in the solution, which compete with negatively charged PFAS for adsorption sites on the clay surface. The results also showed that the impacts of pH on PFAS adsorption were dependent on the chain length of PFAS, exhibiting a more significant impact on short-chain PFAS. Especially, as pH increased, removal efficiencies for short-chain PFAS, including PFHxA, perfluoroheptanoic acid (PFHpA), PFBS, and GenX, were dramatically reduced, while the impacts were slight for the adsorption of long-chain PFAS, such as perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDA), PFOS, and N-EtFOSAA.

[0059] The influence of ionic strength on PFAS adsorption by both unmodified clay and MC was also investigated at varying NaCI levels (Fig. 2, (c) and (d)). The ionic strength exhibited a generally negative effect on the adsorption of PFAS by both clays. For the unmodified clay, as the ionic strength increased, removal efficiencies of all PFAS decreased, even resulting in nearly no removal for some PFAS, such as PFOS and PFDA. This indicated the highly negative impact of ionic strength on the adsorption performance of unmodified clay for all PFAS, regardless of their chain lengths and functional groups. Conversely, the increasing ionic strength only affected the adsorption of short-chain PFAS, i.e., PFHxA, PFHpA, PFBS, GenX, and 6:2 FTSA for the modified clay. For the long-chain PFAS, no obvious impacts were observed. This resilience to ionic strength fluctuations underscored the potential of MC as a robust solution for efficient PFAS removal under diverse environmental conditions, with implications for practical remediation strategies.

[0060] The natural organic matter (NOM) effect, represented by humic acid, showed an evident impact on PFAS adsorption performance of both unmodified clay and MC (Fig. 2, (e) and (f)). This phenomenon was more pronounced for the unmodified clay, where increasing humic acid generally led to reduced removal efficiencies for all PFAS, except N-EtFOSAA, suggesting competition between humic acid and PFAS for adsorption sites on the unmodified clay surface. MMC consistently demonstrated good adsorption performance across all tested humic acid doses. Even in thepresence of high NOM levels, the MMC maintained near-complete or complete removal of all long-chain PFAS. This shows that the clay modification process enhanced its affinity for PFAS, allowing it to effectively compete with humic acid for adsorption sites. This finding suggested that the MC held promise for effective PFAS remediation in natural waters where NOM is commonly present.

[0061] Fig. 3A is a graph 30 of the recovery of MMC after use for PFAS removal. Fig. 3B is a graph 32 of the reuse of MMC for PFAS adsorption. Error bars represent the standard deviations of triplicate measurements. Despite the widespread use of adsorption processes for PFAS removal, one of their full-scale application’s main drawbacks is the difficulty to regenerate the spent materials when their adsorption capacity has been exhausted. Regeneration must allow complete removal of adsorbed PFAS to restore the adsorption capacity of the spent materials through technologies that have economic viability and environmental security. For this purpose, this study conducted three rounds of extraction by basic methanol (0.1 M NH4OH) at room temperature. As shown in Fig. 3A all adsorbed PFAS were recovered after three rounds. The regenerated MMC was found to have similar adsorption performance as the original MC (Fig. 3B). Thus, the MMC can be regenerated and reused repeatedly.

[0062] Although MC has excellent and super-fast adsorption performance for all target PFAS, its powder form brings an issue of separation when it is used in suspension. To facilitate separation of MC from water, MMC was synthesized by adding the magnetic property. Video S2 showed that MMC can be separated fast and easily in water by a magnetic bar. The adsorption of a mixture of 12 PFAS by MMC was tested in pure water.

[0063] Fig. 4 is a graph 40 of the adsorption performance of PFAS by magnetic modified clay in pure water. The initial concentrations were 10 ppb for each PFAS, the dose of adsorbent was 100 mg / L, and the pH was unadjusted. As shown in Fig. 4, at an initial individual concentration of 10 ppb, the adsorption of all PFAS reached a high removal efficiency (> 89%) within 1 h. Specifically, for the four short-chain PFAS, i.e. , PFHxA, PFHpA, PFBS, and GenX, removal efficiencies ranged from 89.4% to 97.0% within 1 h and kept rising to nearly 100% as the contact time increased to 48 h. In comparison, for the six long-chain PFCAs (C8-C11 ) and PFSAs (C7-C8), as well as the two precursors (6:2 FTSA and N-EtFOSAA),saturated adsorption was attained with 100% removal efficiency within the initial hour and no desorption was observed during the exposure duration of 48 h. These findings show the excellent adsorption performance of MMC for both short- and long- chain PFAS including precursors. Additionally, in comparison with previously documented magnetic PFAS adsorbents, the MMC exhibited comparable or better performance for PFAS adsorption, as shown below in Table 1 .Table 1

[0064] Table 1 shows the adsorption performance of the synthesized MMC in the present study with the magnetic PFAS adsorbents reported in the literature. This shows that the present MMC could serve as a highly effective adsorbent for PFAS in water.

[0065] SEM-EDS was utilized to examine the morphology and elemental composition of the MMC before and after PFAS adsorption. Fig. 5A is an SEM image 50 of the MMC before adsorption. Fig. 5B is a graph 52 of the compositional analysis of the MMC of Fig. 5A. As shown in Figs. 5A and 5B, before adsorption, sizable particles were agglomerated and possessed irregular shapes. The EDS analysis indicated that oxygen (O), iron (Fe), silicon (Si), and aluminum (Al) were the predominant elements, constituting more than 90% of the overall elemental compositions. These findings aligned with previous research regarding the structural formula of Mt.

[0066] Following the adsorption process, the adsorbent surface became smooth and heterogeneous, characterized by the presence of mineral and crystalline phases. Fig. 5C is an SEM image 54 of the MMC after adsorption. Fig. 5D is a graph 56 of the compositional analysis of the MMC of Fig. 5C. The metallic elements Fe, Al, and Ti were present on the surface of the MMC, as seen in Figs. 5C and 5D. The presence of empty spaces inside the interparticle cavities among the smaller particles resulted in the formation of macroporous structures in the larger aggregated clay particles. These structures are believed to have a notable impact on the adsorption of PFAS by promoting the movement of the adsorbate through the cavities. Further, the principal elements exhibited minor fluctuations due to the exchange of ions between PFAS compounds and water molecules coordinated with Fe. Moreover, the existence of PFAS on the MMC can be seen based on the EDSspectrum, which identified the presence of fluorine (F) (3.99%) originating from the adsorbed PFAS, as shown in Figs. 5C and 5D.

[0067] The surface of MC was positively charged and the zeta potential of MMC was determined to be 11 .13 mV. This observation suggested that the process of magnetic modification did not compromise the positively charged property of the adsorbent surface, which was beneficial for PFAS adsorption. Furthermore, it was observed that the particle size underwent a reduction after the magnetic modification process, with values of 5.43 pm for MC and 3.59 pm for MMC. In general, the physicochemical features of MMC indicated its suitability for use in environmental matrices where PFAS are often found to possess a negative charge. Previous research has also shown that adsorbents with a greater positive charge and smaller particle size have a greater affinity for adsorbing PFAS.

[0068] The functional groups of the pristine and spent MMC were investigated using FTIR. Fig. 6A is a graph 60 of FTIR spectra of pristine MMC and spent MMC. Fig. 6B is a graph 62 of the XRD pattern of pristine MC and pristine MMC. As shown in Fig. 6A, the FTIR spectra of MMC showed a minute band at 3,391 cm-1 associated with the stretching vibration of the O-H (adsorbed water) in the CTAC and clay layer, while the bending vibrations of O-H were observed at 1 ,644 cm-1. The strong stretching vibrations of Si-0 functional groups of the MC in MMC appeared at 1 ,019 cm-1. Next, the minute FTIR bands at 580-560 cm-1were attributed mainly to the stretching vibrations of Fe-0 and are typical of magnetite. The main observations in the FTIR spectra of PFAS-laden MMC were: 1 ) FTIR bands of MMC reappeared with altered signals, and a few new bands appeared due to PFAS adsorption; 2) The stretching vibration of Fe-0 almost disappeared after PFAS adsorption due to the interactions between Fe3+and anionic head groups such as COO' and SOs' of PFAS; 3) The FTIR band intensity in the stretching vibration of C-H hydrophobic segment of MMC at 2,925 cm-1was affected slightly suggesting the minor hydrophobic interactions between MMC and PFAS molecules; 4) The new FTIR bands at 1 ,365 and 1 ,216 cm'1corresponded to the stretching vibrations of -CF2- and -CF3 groups from organic fluorine, indicating the strong interactions of the PFAS compounds with MMC.

[0069] XRD analysis of the MC and MMC is illustrated in Fig. 6B. In the XRD pattern of MC, the main characteristic reflection peak of the montmorillonitecrystalline structure was observed at 20 = 8.87°, corresponding to the inter-layer spacing (d) of 0.99 nm. The same characteristic peak also appeared in the magnetic iron oxide loaded-MC at 20 = 8.95° (d = 0.98 nm) and indicated that the incorporation of magnetic particles into the MC did not affect the structure of MC. The highest sharp XRD peak at 20 = 26.62 (d = 49.1 nm) was due to the Si-0 particles in the MC. Additionally, the sharp peak at 20 - 35.05 (d = 14.7 nm) became broad after loading with magnetic particles, as shown in the XRD pattern of MMC at 20 = 35.73 (d = 7.53 nm). The decrease in the layer spacing from 14.7 nm to 7.53 nm was due to the intercalation of iron oxide particles into MC clay layers. Several other XRD peaks attributed to different impurities were detected in the MC and MMC diffractogram, which can be omitted.

[0070] To assess the efficacy of MMC more precisely in practical scenarios, experiments were conducted to evaluate its adsorption of PFAS in snowmelt. The findings indicated that a rapid adsorption process occurred during the first hour of contact time, as seen in Fig. 7. Fig. 7 is a series of graphs illustrating the adsorption of PFAS spiked to snowmelt by magnetic modified clay and GAC. At the starting concentrations of 1 and 5 ppb, the adsorption process reached its maximum within 1 h with removal efficiencies for all PFAS between 90% and 100% (Fig, 7). With initial concentration of 10 ppb for each PFAS, the effect of carbon chain length on adsorption was observed. Notably, PFAS with longer carbon chains exhibited higher removal than their short chain counterparts.

[0071] In snowmelt, the short-chain PFAS, including PFHxA 70, PFBS 72, and GenX 76 exhibited incomplete adsorption in 8 h and had removal efficiencies varying between 84% and 96%. The adsorption performance of the material is slightly lower than that in pure water, as seen in Fig. 4, with a range of 89.4% to 97%. This observation implies that the presence of chemicals in snowmelt has a negative effect on the performance of the adsorbents. The chemical analysis of snowmelt indicated the presence of two types of anions, namely bromide at 6 ng / L and phosphate at 1 ng / L. Besides, the concentration of TN of 0.10 ± 0.10 mg / L and TOC of 31.34 ± 2.28 mg / L was high compared to other types of precipitation, such as rainwater and stormwater. The TOC, in particular, is much higher than the global mean concentration of TOC in lake water at 5.578 mg / L. Anions and TOC are known to compete for the adsorption sites with PFAS and negatively impact the effectivenessof adsorption. Our findings thus exhibit a significant correlation with prior studies that have shown a reduced efficacy in the removal of PFAS in natural water (Parker et al., 2023; Pritchard et al., 2023). Given the

[0072] small decrease in removal efficiency of MMC for PFAS in snowmelt, the MMC reported in this study has great potential in capturing PFAS in aquatic environments.

[0073] A comparative analysis was conducted to assess the adsorption efficiency of MMC in snowmelt, in parallel with GAC, which is a commonly used commercial adsorbent in practical applications. According to Fig. 7, GAC had slow removal of all PFAS with the highest rate of 60% during the 8-h contact period. Therefore, compared to the MMC, GAC is not a good option for removing PFAS in snowmelt at least in suspension systems. Compared to other adsorbents, MMC was proven superior in terms of PFAS removal from natural precipitation medium.Table 2

[0074] Table 2 is a comparison of adsorption performance of MMC in removal of PFAS in precipitation with reported data.

[0075] The invention can also include a method for removing PFAS from substances by the steps of adding a magnetic modified clay to a PFAS-containing substance to create a PFAS-containing mixture thereof and then use photoreductive degradation of the contaminated MMC. As described above, the magnetic modified clay includes an adsorbent clay and a magnetizable metal mixed with the adsorbent clay, wherein the mixture of adsorbent clay and magnetizable metal further subject to a predetermined magnetic modification process such that the mixture is configured to attract and bind PFAS. Further, a photoreductive enhancing solution is also added as described herein. The method continues with exposing the PFAS- containing mixture to a UV source for a predetermined duration to photochemically degrade the PFAS.

[0076] The adsorption experiments with MMC were conducted using mixtures containing the six regulated PFAS that then were photodegraded. The MMC dose was 2 g / L, and the initial concentration of each PFAS was approximately 1 mg / L. The mixtures were agitated at 150 rpm at room temperature for 48 h. Following this, the MMC was collected by centrifugation, and the PFAS in the supernatant were determined using an Agilent Technologies 1290 Infinity II LC system paired with a 6470 Triple Quad Mass Spectrometer (LC-MS / MS, Santa Clara, CA, USA). Additionally, individual adsorption experiments were performed for three PFAS, i.e., GenX, PFOA, and PFOS, with initial concentrations of 5.17, 5.62, and 6.62 mg / L, respectively. All other experimental conditions remained the same as those in the PFAS mixture adsorption experiments.

[0077] The spent MMC from these adsorption experiments was subsequently used for photodegradation experiments. After photodegradation, a portion of the residual MMC with adsorbed PFAS mixtures was rinsed by deionized (DI) water and subjectto further adsorption experiments to assess the reusability of regenerated MMC. In these experiments, a PFAS mixture including PFOA, PFNA, PFDA, perfluoroundecanoic acid (PFUnA), PFOS, 6:2 FTSA, and 2-N-ethyl perfluorooctane sulfonamide acetic acid (N-EtFOSAA), each at a starting concentration of 10 pg / L, was used with an adsorbent dose of 100 mg / L. Subsamples were collected for PFAS analysis at six time points, i.e., 0, 1 , 4, 8, 24, and 48 h.

[0078] Photodegradation experiments were conducted in 250-mL high-density polyethylene cylinders wrapped with aluminum foil. A 10 W low-pressure mercury 254-nm ultraviolet (UVC) lamp (GPH212T5L / 4P; Light Spectrum Enterprises Inc., Southampton, PA, USA) in a quartz sleeve was placed vertically in the center of each cylinder, irradiating 80 mL of aqueous solutions containing 5 mM NaHCOs and predetermined concentrations of NasSOs and KI, with or without MMC. The initial pH of all solutions was adjusted to 12 using 1 M NaOH, and the pH was either maintained at 12 or left uncontrolled throughout the experiments. The temperature of the aqueous matrices was kept at approximately 20°C using a circulated cooling water system.

[0079] During the photodegradation process with MMC, a magnetic stirrer was placed at the bottom of the reaction cylinder to agitate the mixture at 450 rpm. Aqueous samples were collected and centrifuged at predetermined intervals. The supernatant samples were subject to analysis of F- and PFAS. The pellet left after the centrifugation was returned to the corresponding cylinder system. At the conclusion of the experiments, residual MMC and the aqueous phase were separated by centrifugation for further treatment and analysis. The remaining PFAS and fluoride ions (F-) in the residual MMC were extracted through three rounds of methanol extraction with 0.1 M ammonium hydroxide. The basic methanol extract was then analyzed for PFAS and F- content.

[0080] Parent PFAS and transformation products (TPs) in the collected supernatant samples and methanol extracts were quantified using the Agilent LC-MS / MS. The analysis focused on perfluoroalkyl acids (PFAAs) as the TPs. Prior to analysis, samples were spiked with 13C-PFOS and 13C-PFOA as internal standards. The non-extractable total fluorine content, including organofluorine and inorganic fluorine in the residual MMC after methanol extraction, was analyzed using a combustion ion chromatography (CIC) system, consisting of a combustion module with an Auto BoatDrive (ABD) and a 930 Compact IC Flex instrument (Metrohm, Herisau, Switzerland) equipped with a conductivity detector. A Metrosep SUPP 5 column (Metrohm) was used for the separation of anions. The eluent for the elution process was a carbonate buffer consisting of 1.8 mM Na2COs and 1.7 mM NaHCO3 (1 :1) with a flow rate of 0.7 mL / min.

[0081] To mitigate conductivity, a solution of 0.05 M H2SO4 was used as a regenerating agent. Calibration samples were prepared using a PFOA standard dissolved in methanol. The fluoride ions (F-) in the aqueous phase were measured using a Thermo Scientific Orion Dual Star two-channel pH / ISE meter with a 9609BNWP Sure-Flow fluoride ion-selective electrode (Waltham, MA, USA). Standards were prepared from a NaF standard solution in DI water.

[0082] Prior to the photodegradation of PFAS adsorbed onto MMC, the adsorption of six different regulated PFAS was performed with MMC. Fig. 8 is a graph 80 of the adsorption of the six regulated PFAS by magnetic modified clay after 48 h. The initial concentration of each tested PFAS was around 1 .2 mg / L, and the MMC dose was 2 g / L (0.1 g in 50 mL). The PFAS solution pH was unadjusted. Error bars represent the standard deviations of triplicate tests. The numbers above each bar are the residual PFAS concentrations in ng / L, and zero indicates a residual concentration lower than the limit of detection for each PFAS shown.

[0083] According to Fig. 8, all PFAS were captured with about 100% removal efficiency at an initial individual concentration of ca. 1 .28 mg / L, and no desorption was seen over the 48-h exposure. These results demonstrated that MMC had superior adsorption capabilities for both long- and short-chain PFAS and is strong evidence that MMC has the potential to be an excellent PFAS adsorbent in water.

[0084] The inventive method can therefore include removing the magnetic modified clay from the PFAS-containing mixture, as well as removing PFAS from the magnetic modified clay to create a cleaned magnetic modified clay, and reusing the clean magnetic modified clay by adding the clean magnetic modified clay to a PFAS containing substance to create a PFAS-containing mixture thereof. The method can also include modifying the photoreductive enhancing solution to a predetermined pH.

[0085] The efficiency for photoreductive degradation of the six regulated PFAS in aqueous solutions both in the absence and presence of pristine MMC was evaluated. Fig. 8 validates the photodegradation of the parent PFAS under reductiveconditions with Na2SOs and KI. The C2-C7 PFAAs were selected as the primary TPs during the photodegradation. The rationale for focusing on these shorter-chain PFAAs as TPs was grounded in the well-documented degradation pathways of long- chain PFAS under reductive conditions, particularly those involving eaq“ generated in UV / sulfite systems. It has been demonstrated that during reductive defluorination of PFAS, the breakdown of the parent molecules typically involved sequential cleavage of the terminal CF2groups, resulting in the stepwise formation of shorter-chain PFAAs (e.g., C2-C7) as stable intermediates. The chain-length distribution of these TPs reflected the progressive defluorination and 5 carbon chain shortening process characteristic of advanced reduction treatments. However, it is important to acknowledge the limitations in detecting only these shorter chain PFAAs as TPs. It has been shown that the complexity of PFAS degradation can lead to the formation of a wide variety of partially defluorinated intermediates and byproducts, some of which may not be fully captured in the analysis of C2-C7 PFAAs alone. While C2-C7 PFAAs may not encompass all TPs formed during the process, they can still serve as useful indicators of degradation.

[0086] Fig. 9 is a series of graphs that illustrate the Photodegradation of PFAS in aqueous solutions without ((a), (b)) and with ((c), (d)) pristine magnetic modified clay. Fig. 9 (a), (c) show the change in percentage of spiked concentration (%) of each parent PFAS. Fig. 9 (b),(d) show the total concentrations (pg / L) of C2-C7 PFAA transformation products. The initial concentrations of the parent PFAS were around 0.8-1.0 mg / L, and the MMC dose in (c) and (d) were 2.5 g / L (0.2 g in 80 mL). Photodegradation conditions were: 50 mM Na2SO3, 10 mM KI, and 5 mM NaHCOs at the initial pH of 12 (uncontrolled throughout the experiments) and around 20°C. Error bars represent the standard deviations of duplicate tests.

[0087] Fig. 9 illustrates the degradation trends for the six parent PFAS and the total formation of C2-C7 PFAAs as TPs under conditions of 50 mM Na2SOs and 10 mM KI. Without MMC, a noticeable decrease in the concentration of all six parent PFAS was observed, indicating their effective breakdown over the photodegradation period. This was further supported by the high defluorination efficiency (deF%) and decay efficiency of pure PFOA and PFOS in solutions, with deF% of 96.0 ± 1.0% and 99.4 ± 0.7%, respectively / . However, the photodegradation rates varied among the different PFAS. The short-chained PFBS showed the slowest degradation rate,with the remaining percentage of 46.3 ± 4.2% at the end of experiment (48 h) (Fig. 9, (a)) Previous research also demonstrated that PFBS was the most difficult to decay among the six regulated PFAS because of its shorter carbon chain length, robust molecular structure, and higher chemical stability. All other five PFAS exhibited much higher degradation rates, especially within the initial 2 h, achieving nearly 100% decay efficiency at 48 h.

[0088] Fig. 9, (b) details the total concentrations of C2-C7 PFAA TPs formed during the photodegradation process. The formation of total by-products increased over the initial 2 h, sharply decreased to zero at 4-8 h, and increased slowly again until 48 h. This trend may be due to the very high degradation rates of the parent PFAS and the slower breakdown of the shorter-chain TPs at the initial time, leading to the accumulation of TPs in the beginning.

[0089] Previous studies have demonstrated that the use of Mt clays, particularly organo-modified variants, can enhance the photodegradation of PFAS due to their ability to stabilize and extend the persistence of the reactive species (e.g., eaq") generated during the process. For instance, Mt modified with hexadecyltrimethyl ammonium (HDTMA) has been shown to adopt a tilted conformation within the clay interlayers, which effectively isolated and shielded eaq" from quenching by oxygen. This protection promoted the defluorination of PFOA under UV irradiation

[0090] In contrast, in the present study, the use of MMC did not lead to the same enhancement in PFAS degradation. The results indicated that the presence of pristine MMC led to high removal efficiency of PFAS in aqueous solutions. However, the removal included photodegradation and adsorption. The further analysis of defluorination revealed that in the presence of pristine MMC, the deF% was 18.5 ± 0.2% at the end of experiment, compared to 79.6 ± 1 .4% for the PFAS mixture solution without MMC.

[0091] This suggested that MMC may inhibit the photodegradation process, possibly due to the adsorption of PFAS onto the pristine MMC, which reduced their availability for photodegradation compared to the PFAS mixture solution. The discrepancy between our findings and previous studies indicates that the specific modifications and the nature of the clay material play critical roles in influencing the efficiency of photochemical processes. The interlayer spacing and surface chemistry of MMC likely differ from those of organo-modified clays, which could affect theinteraction between the clay and PFAS molecules, as well as the generation and stabilization of reactive species.

[0092] The photochemical degradation of PFAS adsorbed onto MMC was systematically investigated under various conditions. Fig. 10 is a series of graphs illustrating the photodegradation of PFAS in aqueous solutions with magnetic modified clay adsorbed with individual GenX, PFOA, and PFOS. The photodegradation of PFAS in aqueous solutions with magnetic modified clay adsorbed with individual GenX (Fig. 10(a), (b); PFOA (Fig. 10 (c), (d); and PFOS Fig. 10(e), (f). Fig. 10 (a), (c), (e) show the changes in concentration (pg / L; left Y- axis) and percentage of adsorbed concentration (%; right Y-axis) in photodegradation. Fig. 10 (b),(d),(f) show the concentration (pg / L) of each PFAA transformation product. The initial adsorbed masses of GenX, PFOA, and PFOS in MMC were 3.07, 2.81 , and 3.30 mg / g, respectively. All the doses of MMC in the three aqueous solutions in photodegradation were 2.5 g / L (0.2 g in 80 mL).Photodegradation conditions were: 10 mM Na2SO3, 2 mM KI, and 5 mM NaHCOs at the initial pH of 12 (uncontrolled throughout the experiments) and around 20 °C. Error bars represent the standard deviations of duplicate tests.

[0093] Fig. 10 illustrates the changes in concentration and percentage of adsorbed GenX, PFOA, and PFOS individually, as well as their transformation products (TPs), during photodegradation with 10 mM Na2SOs and 2 mM KI at an initial pH of 12. The initial adsorbed masses of GenX, PFOA, and PFOS in MMC were 3.07, 2.81 , and 3.30 mg / g, respectively, with MMC doses of 2.5 g / L. For all three PFAS, the concentrations in the aqueous phase showed a rapid initial increase, with GenX exhibiting a higher aqueous concentration than PFOA and PFOS (Fig. 10 (a),(c),(e). This indicated that GenX was desorbed more readily, resulting in significantly higher levels of TPs (Fig. 10 (b),(d),(f).

[0094] Regarding the defluorination efficiency for GenX, PFOA, and PFOS when adsorbed onto MMC, GenX exhibited the highest defluorination efficiency of 66.3 ± 18.0%, followed by PFOA with 42.2 ± 1 .5% and then PFOS with 26.7 ± 1 .9%. However, this did not necessarily indicate that GenX was more readily photodegraded. Previous research has shown that GenX was actually more recalcitrant to decay compared to PFOA and PFOS. The higher defluorination percentage of GenX observed in our study could be attributed to its greater tendencyto desorb, resulting in higher aqueous concentrations of GenX available for photodegradation compared to PFOA and PFOS. The lower deF% of PFOA and PFOS may be attributed to the stronger interactions of PFOA and PFOS with the MMC compared to GenX, which could also enhance their resistance to photochemical decay. The stronger binding of PFOA and PFOS to MMC could result in a higher proportion of these compounds being retained and subsequently degraded within the MMC matrix, compared to the more readily desorbed GenX.

[0095] This study highlights the complex interplay between adsorption characteristics and photodegradation efficiency for different PFAS compounds. The influence of different reductant concentrations on the photoreductive degradation of adsorbed PFAS mixtures in MMC was also examined, as shown in Figs. 11 and 12.

[0096] Fig.1 1 is series of graphs illustrating the photoreductive degradation of adsorbed PFAS in MMC at various reductant concentrations. Fig.11 graphs show the photoreductive degradation of adsorbed PFAS in MMC at various reductant concentrations: Fig. 11 (a),(b) 10 mM Na2SO3 and 2 mM KI; Fig. 11 (c),(d) 20 mM Na2SO3 and 4 mM KI; Fig. 11 (e),(f) 50 mM Na2SO3 and 10 mM KI. Fig. 11 (a),(c),(e). The changes in concentration (pg / L; left Y-axis) and percentage of adsorbed concentration (%; right Y-axis) in photodegradation; Fig. 11 (b),(d),(f).Total concentrations (pg / L) of C2-C7 PFAA transformation products. The total initial adsorbed mass of PFAS was 3.64 mg / g, with each PFAS accounting for approximately the same amount. The MMC dose in aqueous solution was 2.5 g / L (0.2 g in 80 mL). Other chemical reagent and conditions for all groups were: 5 mM NaHCOs at the initial pH of 12 (uncontrolled throughout the experiments) and around 20 °C. Error bars represent the standard deviations of duplicate tests.

[0097] Three sets of reductant concentrations were tested: 10 mM Na2SOs and 2 mM KI, 20 mM Na2SOs and 4 mM KI, and 50 mM Na2SOs and 10 mM KI. The total initially adsorbed mass of six PFAS was 3.64 mg / g, with each PFAS accounting for approximately the same amount. The results showed higher reductant concentrations led to lower PFAS in aqueous phase, except for PFBS. Fig. 11 (a),(c),(e). This trend suggested that increasing the availability of reductants enhanced the generation of reactive species, thereby accelerating the photodegradation process.

[0098] Additionally, the lower total concentrations of C2-C7 PFAA TPs, as well as each TP, were observed at higher reductant concentrations (Fig. 11 (b),(d),(f), indicating that higher doses of Na2SOs and KI facilitated the more extensive breakdown of both parent and daughter PFAS molecules.

[0099] Fig. 12 is a graph 120 of the overall defluorination efficiency (%) for each parent PFAS in the photodegradation of adsorbed PFAS in MMC at various reductant concentrations: 10 mM Na2SOsand 2 mM KI, 20 mM Na2SOsand 4 mM KI, and 50 mM Na2SOs and 10 mM KI. The total initial adsorbed mass of PFAS was 3.64 mg / g, with each PFAS accounting for approximately the same amount. The MMC dose in aqueous solution was 2.5 g / L (0.2 g in 80 mL). Other chemical reagent and conditions for all groups were: 5 mM NaHCOs at the initial pH of 12 (uncontrolled throughout the experiments) and around 20 °C. Error bars represent the standard deviations of duplicate tests.

[0100] Fig. 12 summarizes the total defluorination efficiency for each parent PFAS at the three reductant concentrations tested. The results confirmed that increasing the concentration of reductants enhanced both the defluorination and removal efficiencies, with the highest concentrations (50 mM Na2SOs and 10 mM KI) achieving the most effective PFAS destruction. As the reductant concentrations increased, the overall defluorination efficiencies rose from 20.9 ± 0.8%, to 32.1 ± 6.2%, and to 58.7 ± 2.0%, respectively. The enhanced defluorination and removal efficiencies at higher reductant concentrations can be attributed to the increased production of reactive species, which facilitates the breakdown of PFAS molecules. This was consistent with the above results indicating that higher concentrations of reductants improved the photoreductive degradation efficiency.

[0101] Besides the reductant concentrations, pH was also found to be influential on the photoreductive degradation of PFAS. Thus, different concentrations of Na2SOs and KI, as well as the impact of pH control on the photochemical degradation of PFAS adsorbed on MMC was investigated to optimize conditions. As shown in Fig. 11 and Fig. 13, further increasing concentrations of Na2SOs and KI from 50 and 10 mM to 100 and 20 mM, respectively, did not significantly change the photodegradation profiles of PFAS mixtures. Additionally, the overall deF% just increased slightly to 60.5 ± 2.8% as the concentrations rose (Fig. 10 and Fig. 12). These findings were consistent with the similar PFAS photodegradation profilesobserved when doubling the concentrations of Na3SO3and KI from 50 and 10 mM, respectively, at the stable pH of 12, as shown in Fig. 13.

[0102] Fig. 13 is a series of graphs of the photoreductive degradation of adsorbed PFAS in MMC at various conditions: Fig. 13 (a),(b),100 mM Na2SO3and 20 mM KI at initial pH 12 (uncontrolled); Fig. 13 (c),(d), 50 mM Na3SO3and 10 mM KI at stable pH 12; Fig. 13 (e),(f), 100 mM Na2SO3and 20 mM KI at stable pH 12. Fig.13(a),(c),(e), show the changes in concentration (pg / L; left Y-axis) and percentage of adsorbed concentration (%; right Y-axis) in photodegradation; Fig. 13 (b),(d),(f) show the total concentrations (pg / L) of C2-C7 PFAA transformation products. The total initial adsorbed mass of PFAS was 3.1 mg / g, with each PFAS accounting for approximately the same amount. The MMC dose in aqueous solution was 438 2.5 g / L (0.2 g in 80 mL). Other chemical reagent and conditions for all groups were: 5 mM 439 NaHCOs at around 20 °C. Error bars represent the standard deviations of duplicate tests.

[0103] Fig. 14 is a graph 140 of the overall defluorination efficiency (%) for each parent PFAS in the photodegradation of adsorbed PFAS in MMC at various conditions: 100 mM Na3SO3and 20 mM KI at initial pH 12 (uncontrolled), 50 mM Na2SO3and 10 mM KI at stable pH 12, and 100 mM Na2SO3and 20 mM KI at stable pH 12. The total initial adsorbed mass of PFAS was 3.1 mg / g, with each PFAS accounting for approximately the same amount. The MMC dose in aqueous solution was 2.5 g / L (0.2 g in 80 mL). Other chemical reagent and conditions for all groups were: 5 mM NaHCO3at around 20 °C. Error bars represent the standard deviations of duplicate tests.

[0104] Interestingly, the overall deF% decreased from 66.5 ± 1 .1 % to 59.9 ± 2.7% as the concentrations increased 386 (Fig. 14). These findings suggested that while both Na2SO3 and KI played a role in the photoreductive degradation of PFAS, there appeared to be a threshold beyond which additional increases in their concentrations did not significantly enhance the degradation efficiency. This plateau effect indicated that other factors, such as the saturation of reactive intermediates, mass transfer limitations, or the limitations imposed by the reaction kinetics, might be influencing the overall degradation process.

[0105] Furthermore, the role of pH control was examined to elucidate its influence on the photochemical degradation of PFAS, particularly in systems where eaq“ play acrucial role. In the comparison of degradation at 50 mM Na2SOs and 10 mM KI at an initial pH of 12 with and without pH stabilization, it was evident that maintaining a stable pH at 12 notably affected the degradation process (Fig. 13 (c)-(d)), compared to that without pH control which ended with a final pH of 9.6 ± 0.1 % (Fig. 13). This was attributed primarily to the increased availability of eaq", as the high pH environment minimized the protonation of these reactive species, thereby preserving their concentration and reactivity. Specifically, at a stable pH of 12, the lower consumption of eaq- by H+facilitated a more effective cleavage of strong C-F bonds in PFAS, leading to a higher overall deF% as shown in Figs. 12 and 14. The enhanced degradation can be ascribed to the more favorable conditions for nucleophilic attack by eaq“, which has been identified as the primary mechanism driving the reductive defluorination of PFAS, particularly for PFCAs.

[0106] However, when the reductant concentrations were elevated to 100 mM Na2SC>3 and 20 mM KI, the effect of pH stabilization at 12 was less significant, as shown in Fig.13 (a),(b) and (e)-(f). This was also consistent with the similar overall deF% between the two groups (Fig. 14). Additionally, an excess of I" can result in the formation of reactive iodine species, such as 12, I2-, and I3-, which are potent scavengers of eaq“, thereby reducing the system’s dependency on pH at higher reductant levels.

[0107] The mass balance of fluorine before and after photodegradation under the three different conditions was also investigated, as displayed in Fig. 15. Fig. 15 is a graph 150 of the mass balance of fluorine before and after photodegradation of adsorbed PFAS in MMC at various conditions: 100 mM Na2SOs and 20 mM KI at initial pH 12 (uncontrolled), 50 mM Na2SOs and 10 mM KI at stable pH 12, and 100 mM Na2SOs and 20 mM KI at stable pH 12. The total initial adsorbed mass of PFAS was 3.1 mg / g, with each PFAS accounting for approximately the same amount. The MMC dose in aqueous solution was 2.5 g / L (0.2 g in 80 mL). Other chemical reagent and conditions for all groups were: 5 mM NaHCOs at around 20 °C. Error bars represent the standard deviations of duplicate tests.

[0108] All organofluorine and fluoride were derived from PFAS sorbed to MMC, from which the theoretical total organofluorine was calculated. After photodegradation, the organofluorine could be in: (1) the parent and daughter PFAS in the aqueous solution; (2) the same set of PFAS in the leachate of the residualMMC by basic methanol; (3) the same set of PFAS in the MMC residual after methanol extraction. The organofluorine concentration in (1) and (2) was calculated based on PFAS quantified in each stream. Those in (3) were quantified by CIC which converts organofluorine to fluoride. Solutions from (1 ) and (2) were also subjected to measurement of inorganic fluoride by a fluoride ion-selective electrode. The deF% was calculated by dividing the sum of all organoflurorine from the three sources and inorganic fluoride from the two types of solution by the total theoretical organofluorine concentration. The CIC results showed that a significant fraction of non-extractable organofluorine was retained in the residual MMC for all three conditions. Interestingly, the presence of non-extractable PFAS in the residual MMC did not negatively affect the reusability of MMC.

[0109] Despite adsorption technique’s extensive usage in PFAS removal, the difficulty of renewing these materials when their adsorption ability is depleted is a major limitation of their full-scale deployment. Restoring the adsorption capacity of the spent materials requires regeneration procedures that are both economically viable and environmentally secure, allowing for the virtually full removal of adsorbed PFAS. Thus, additional tests were carried out on MMC to examine its possible reutilization following photochemical degradation. The tests measured adsorption efficiency at an initial concentration of 10 pg / L for each tested PFAS, with a dose of 100 mg / L of regenerated MMC administered under varying contact times (1 , 4, 8, 24, and 48 h).

[0110] Fig. 16 is a graph 160 illustrating the reuse of magnetic modified clay after photochemical degradation of the adsorbed PFAS at different contact times (1 , 4, 8, 24, and 48 h). The initial concentration of each tested PFAS was 10 pg / L, and the dose of regenerated MMC was 100 mg / L (5 mg in 50 mL). The PFAS solution pH was unadjusted. Error bars represent the standard deviations of triplicate tests. The findings show that PFOA and 6:2 FTSA had a lower removal efficiency (about 70%), and desorption happened after 48 h, but PFHxA, PFDA, PFUnA, PFOS, and N- EtFOSAA were seen with nearly 100% capture (Fig. 16). This suggests that MMC could be regenerated by effective photodegradation of pre-concentrated PFAS, allowing for reuse without the need for further chemical regeneration. Overall, this key property highlights the distinct benefit of MMC compared to more traditional adsorbents such as AC or ion-exchange resins which requires either thermal orchemical regeneration, respectively. Aside from difficulties in regeneration, use of these conventional sorbents needs to address the challenge of disposing properly the concentrated regenerant waste.

[0111] The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below, if any, are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of one or more aspects of the invention and the practical application, and to enable others of ordinary skill in the art to understand one or more aspects of the invention for various embodiments with various modifications as are suited to the particular use contemplated.

Claims

CLAIMSWhat is claimed is:1 . A magnetic modified clay, comprising: an adsorbent clay; and a magnetizable metal mixed with the adsorbent clay; wherein a mixture of adsorbent clay and magnetizable metal further subject to a predetermined magnetic modification process such that the mixture is configured to attract and bind per- and polyfluoroalkyl substances (PFAS).

2. The magnetic modified clay of claim 1 , wherein the adsorbent clay is comprised of: montmorillonite K10; an Na2CC>3 solution; and hydrochloric acid.

3. The magnetic modified clay of claim 2, further including a solution having a cation exchange capacity.

4. The magnetic modified clay of claim 3, further wherein the solution is one or both of cetrimonium chloride and cetyltrimethylammonium chloride.

5. The magnetic modified clay of claim 1 , wherein the predetermined magnetic modification process is: adding FeC -6H2O; adding FeCb-4H2O; adding NH4OH; and exposing the mixture to a magnetic field for a predetermined period.

6. The magnetic modified clay of claim 1 , wherein the mixture of adsorbent clay and magnetizable metal is subject to a predetermined period of drying.

7. The magnetic modified clay of claim 1 , wherein the mixture is configured to be reusable by selectively releasing bound PFAS and then reused to attract and bind PFAS.

8. The magnetic modified clay of claim 1 , further configured to remove PFAS from water.

9. A magnetic modified clay optimized for photoreductive degradation of per- and polyfluoroalkyl substances (PFAS), comprising: an adsorbent clay; a magnetizable metal mixed with the adsorbent clay, wherein the mixture of adsorbent clay and magnetizable metal further subject to a predetermined magnetic modification process such that a mixture is configured to attract and bind PFAS; and a photoreductive enhancing solution.

10. The magnetic modified clay of claim 9, wherein the photoreductive enhancing solution is a solution of Na2SOs and KI.11 . The magnetic modified clay of claim 9, wherein the photoreductive enhancing solution further modified to a predetermined pH.

12. A method for removing per- and polyfluoroalkyl substances (PFAS) from substances, comprising: adding a magnetic modified clay to a PFAS-containing substance to create a PFAS-containing mixture thereof, the magnetic modified clay comprising: an adsorbent clay; a magnetizable metal mixed with the adsorbent clay, wherein the mixture of adsorbent clay and magnetizable metal further subject to a predetermined magnetic modification process such that the mixture is configured to attract and bind PFAS; and a photoreductive enhancing solution; and exposing the PFAS-containing mixture to a UV source for a predetermined duration to photochemically degrade the PFAS.

13. The method of claim 12, further comprising removing the magnetic modified clay from the PFAS-containing mixture.

14. The method of claim 13, further comprising: removing PFAS from the magnetic modified clay to created cleaned magnetic modified clay; and reusing the clean magnetic modified clay by adding the clean magnetic modified clay to a PFAS containing substance to create a PFAS-containing mixture thereof15. The method of claim 12, wherein the magnetic modified clay is created from a mixture of: montmorillonite K10; an Na2CC>3 solution; and hydrochloric acid.

16. The method of claim 12, further adding a solution having a cation exchange capacity to the magnetic modified clay.

17. The method of claim 15, further adding a solution comprised of one or both of cetrimonium chloride and cetyltrimethylammonium chloride.

18. The method of claim 12, further modifying the photoreductive enhancing solution to a predetermined pH.

19. The method of claim 12, wherein the PFAS-containing substance is soil.

20. The method of claim 12, wherein the PFAS-containing substance is water.

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