Removal Of PFOA Research Articles

Effective removal of perfluorooctanoic acid from water using PVA@UiO-66-NH2/GO composite materials via adsorption

This study introduces an innovative approach using highly efficient nanocomposite materials to effectively remove PFAS from water, demonstrating remarkable adsorption capabilities. The nanocomposite was synthesized by integrating a zirconium-based metal-organic framework (MOF) called UiO-66 with graphene oxide (GO) within a polyvinyl alcohol (PVA) matrix. The resulting PVA@UiO-66/GO material features flower-like UiO-66 MOF crystals embedded in the PVA and GO matrix. Various kinetic models were applied to determine the rate constants and adsorption capacities, with the Langmuir isotherm indicating an adsorption capacity of 9.904 mg/g. Thermodynamic analysis confirmed the process's spontaneity and exothermic nature. The UiO-66-NH2/GO/PVA composite also demonstrated high reusability, maintaining substantial PFOA removal efficiency across multiple cycles, with optimal reduction occurring at approximately pH 5. Overall, the PVA@UiO-66/GO composites offer an effective, sustainable, and environmentally friendly solution for PFAS removal in water purification.

Zinc oxide@citric acid-modified graphitic carbon nitride nanocomposites for adsorption and photocatalytic degradation of perfluorooctanoic acid

Perfluorooctanoic acid (PFOA) is a highly persistent organic pollutant of global concern. A novel nanocomposite composed of ZnO nanoparticles and citric acid-modified g-C3N4 was synthesized by ball milling process. The synthesized nanocomposite was more efficient than pure ball-milled ZnO nanoparticles for PFOA elimination under visible light irradiation. The optimal hybrid photocatalyst, produced by the addition of 5 wt% of citric acid-modified g-C3N4, demonstrated significantly better performance for PFOA removal than pure ZnO nanoparticles under UV irradiation, with the apparent rate constants of 0.468 h−1 and 0.097 h−1, respectively. The addition of peroxymonosulfate (0.53 g L−1) significantly increased PFOA removal, clarifying the crucial effect of sulfate radicals on PFOA photodegradation. In comparison, citric acid-modified g-C3N4 was not effective for PFOA elimination under visible light irradiation, even with the addition of peroxymonosulfate. Further experiments under dark conditions identified surface adsorption on hybrid photocatalyst as a key process in total PFOA removal. In summary, PFOA removal by ZnO@citric acid-modified graphitic carbon nitride nanocomposites is due to the combined action from adsorption and photodegradation, with adsorption as the dominating mechanism.

Installation of synergetic binding sites in β-Cyclodextrin-Bipyridine ionic liquid based magnetic sorbent for simultaneous removal of anionic PFAS and Cr (Ⅵ) in water matrix

Herein, we develop a versatile strategy for developing a Fe3O4-NH-β-CD-BP ILs based sorbent by installing synergistic bonding sites for simultaneous removal of per- and polyfluoroalkyl substances (PFASs) and heavy metals from contaminated water. This sorbent with its quaternary ammonium cation achieved remarkable removal efficiency (∼99 %)for both short and long chain anionic PFASs in pure water as compared to previous β-CD based materials. Moreover, when subjected to a challenging metal salt matrix, the adsorbents revealed that long-chain PFASs primarily relied on electrostatic and hydrophobic interactions, while short-chain PFASs depended solely on electrostatic attractions. The results indicate that the sorbent exhibits outstanding adsorption capacities for PFCAs, PFSAs and Cr (VI) coupled with fast adsorption kinetics featuring equilibrium times 5, 4 and 2 h, respectively. The simultaneous removal of PFOA, PFOS and Cr (VI) in multi-component systems (electroplating plant wastewater) was also determined due to their dual sites rendered by cationic and β-CD groups. The adsorption of PFCAs and Cr (VI) was significantly influenced by the initial pH compared to the sorption of PFSAs. Additionally, the viologen based sorbent also showed better photocatalytic hydrogen evolution activity. In summary, these results revealed the outstanding adsorption capacity and convenient regeneration process make the adsorbent as a promising candidate for efficient and rapid removal of PFASs from other pollutants.

Bioremediation of rapid sand filters for removal of organic micropollutants during drinking water production

Rapid sand filtration (RSF) is used during drinking water production for removal of particles, possible harmful microorganisms, organic material and inorganic compounds such as iron, manganese, ammonium and methane. However, RSF can also be used for removal of certain organic micropollutants (OMPs). In this study, it was investigated if OMP removal in columns packed with sand from full scale RSFs could be stimulated by bioaugmentation (i.e. inoculating RSFs with sand from another RSF) and/or biostimulation (i.e. addition of nutrients, vitamins and trace-elements that stimulate microbial growth). The results showed that removal of PFOA, carbamazepine, 1-H benzotriazole, amidotrizoate and iopamidol in the columns was low (< 20 %). Propranolol and diclofenac removal was higher (50–60 %) and propranolol removal likely occurred via sorption processes, whereas for diclofenac it was unclear if removal was a combination of physical-chemical and biological processes. Moreover, bioaugmentation and biostimulation resulted in 99 % removal of gabapentin and metoprolol after 38 days and 99 % removal of acesulfame after 52 days of incubation. The bioaugmented column without biostimulation showed 99 % removal for gabapentin and metoprolol after 52 days, and for acesulfame after 80 days. In contrast, the non-bioaugmented column did not remove gabapentin, removed < 40 % metoprolol and showed 99 % removal of acesulfame only after 80 days of incubation. Removal of these OMPs was negatively correlated with ammonium oxidation and the absolute abundance of ammonia-oxidizing bacteria. 16S rRNA gene sequencing showed that OMP removal of acesulfame, gabapentin and metoprolol was positively correlated to the relative abundance of specific bacterial genera that harbor species with a heterotrophic and aerobic or denitrifying metabolism. These results show that bioaugmentation of RSF can be successful for OMP removal, where biostimulation can accelerate this removal.

Efficient PFOA removal from drinking water by a dual-functional mixed-matrix-composite nanofiltration membrane

Drinking water contamination by per- and polyfluorinated alkyl substances (PFAS) is a global concern. Nanofiltration is a promising PFAS removal technology due to its scalability and cost-effectiveness. However, nanofiltration cannot typically reduce PFAS concentrations below current drinking water recommendations. To enhance PFAS removal, we developed mixed-matrix-composite nanofiltration (MMCNF) membranes—an active nanofiltration layer on porous adsorptive support that synergetically combines filtration and adsorption. We synthesized MMCNF membranes comprising thin polyelectrolyte multilayer films deposited on thick (~400 µm) polyethersulfone supports incorporating β-cyclodextrin microparticles. These membranes achieved near complete removal (>99.9%) of model PFAS (PFOA: perfluorooctanoic acid) for significantly longer filtration times compared to a control membrane without β-cyclodextrin, but otherwise identical. The spent MMCNF membrane was regenerated using ethanol, and high PFOA removal performance was regained during three filtration cycles. Perfluorooctanoic acid was concentrated 38-fold in the ethanol eluent. Further concentration by evaporation is straightforward and can enable eluent recycling and effective PFAS removal.

Understanding the synergistic effect of hydrated electron generation from argon plasma catalysis over Bi2O3/CeO2 for perfluorooctanoic acid dehalogenation: Mechanism and DFT study

Pseudo-photocatalysis driven by argon-plasma-system (AP) is a new approach toward the promotion of reactive species production for water remediation. Here, we investigated the synergistic effect between AP and catalyst by altering the oxygen vacancies (OV) concentration of CeO2/Bi2O3 for stimulating the hydrated electrons (eaq–) production for PFOA removal. The soft X-ray total fluorescence yield (TFY) analysis and DFT calculation revealed the formation of the built-in electric field in the Bi/Ce0.43 interface can enhance interfacial electron migration with direction from Bi2O3 toward CeO2, simultaneously promoting the eaq– generation. Notably, AP-Bi/Ce0.43 (0.1488 min−1, EEO = 0.43 kW mg−1) exhibited excellent PFOA removal kinetic performance with almost 5.7 times faster and 72.6% lower energy consumption than sole AP (0.0261 min−1, EEO = 1.57 kW mg−1), respectively. The multiple-plasma-jet continuous-flow-experiments results illustrated the scalability of AP-Bi/Ce0.43 for PFOA destruction. Our findings demonstrate fundamental insights into the synergistic effect of PFOA removal in AP catalysis.

Enhanced coagulation coupled with cyclic IX adsorption-ARP regeneration for removal of PFOA in drinking water treatment.

Laboratory investigations were conducted to demonstrate a potentially transformative, cost-efficient per- and polyfluoroalkyl substances (PFAS) treatment approach, consisting of enhanced coagulation and repeated ion exchange (IX)-advanced reduction process (ARP) for concurrent PFAS removal and IX resin regeneration. Enhanced alum coagulation at the optimal conditions (pH6.0, 60 mg/L alum) could preferentially remove high molecular-weight, hydrophobic natural organic matter (NOM) from 5.0- to ~1.2-mg/L DOC in simulated natural water. This facilitated subsequent IX adsorption of perfluorooctanoic acid (PFOA, a model PFAS in this study) (20 μg/L) using IRA67 resin by minimizing the competition of NOM for functional sites on the resin. The PFOA/NOM-laden resin was then treated by ARP, generating hydrated electrons (eaq - ) that effectively degraded PFOA. The combined IX-ARP regeneration process was applied over six cycles to treat PFOA in pre-coagulated simulated natural water, nearly doubling the PFOA removal compared with the control group without ARP regeneration. This study underscores the potential of enhanced coagulation coupled with cyclic IX-ARP regeneration as a promising, cost-effective solution for addressing PFOA pollution in water. PRACTITIONER POINTS: Enhanced alum coagulation can substantially mitigate NOM to favor the following IX removal of PFOA in water. Cyclic IX adsorption-ARP regeneration offers an effective, potentially economical solution to the PFOA pollution in water. ARP can effectively degrade PFOA during the ARP regeneration of PFOA/NOM-laden resin.

Ultrasonic assisted activation of persulfate for the treatment of spent porous biochar: Degradation of adsorbed PFOA and adsorbent regeneration

In this work, the regeneration of spent biochar adsorbent and the degradation of adsorbed PFOA by the system of ultrasonic assisted activation of persulfate were explored. The effects of ultrasound, persulfate and biochar on PFOA removal were investigated through a series of regeneration and degradation experiments. Meanwhile, the degradation mechanism and reaction pathways of PFOA were investigated with electron paramagnetic resonance (EPR) and high-resolution quadrupole orbitrap mass spectrometer. The results showed that PFOA adsorbed by biochar could be degraded efficiently with the synergistic effect of ultrasound and persulfate. The degradation of PFOA in biochar could be finished in 4 h, while the defluorination took longer, with a defluorination efficiency of 50.6% after 4 h and 99.6% after 10 h. In this process, PFOA was degraded and defluorinated gradually by thermal decomposition caused by cavitation bubbles and degradation caused by the attack of SO4•ˉ and •OH. Two different free radicals controlled different degradation pathways, with SO4•ˉ playing a dominant role. In this system, the regeneration of the waste biochar adsorbent was achieved by eliminating PFOA, which could be recycled more than three times. The application potential of the system was evaluated using real water sample, and it was found that the removal of PFOA in real water sample was satisfactory even with the influence of inorganic ions and organic matter, indicating that it has promising application prospects. This work provided new insight into the degradation of adsorbed PFOA and adsorbent regeneration.

The Specific Removal of Perfluorooctanoic Acid Based on Pillar[5]arene-Polymer-Packed Nanochannel Membrane.

The conspicuous surface activity and exceptional chemical stability of perfluorooctanoic acid, commonly referred to as PFOA, have led to its extensive utilization across a broad spectrum of industrial and commercial products. Nonetheless, significant concerns have arisen regarding the environmental presence of PFOAs, driven by their recognized persistence, bioaccumulative nature, and potential human health risks. In the realm of sustainable agriculture, a pivotal challenge revolves around the development of specialized materials capable of effectively and selectively eliminating PFOA from the environment. This study proposes harnessing the exceptional properties of a pillar[5]arene polymer to construct a nanochannel membrane filled with tryptophan-alanine dipeptide pillar[5]arene polymer. Through the functionalization of these nanochannel membranes, we achieved a PFOA removal rate of 0.01 mmol L-1 min-1, surpassing the rates observed with other control chemicals by a factor of 4.5-15. The research on PFOA removal materials has been boosted because of the creation of this highly selective PFOA removal membrane.

Iron slag permeable reactive barrier for PFOA removal by the electrokinetic process

The efficacy of the Standalone Electrokinetic (EK) process in soil PFAS removal is negligible, primarily due to the intersecting mechanisms of electromigration and electroosmosis transportation. Consequently, the redistribution of PFAS across the soil matrix occurs, hampering effective remediation efforts. Permeable reactive barrier (PRB) has been used to capture contaminants and extract them at the end of the EK process. This study conducted laboratory-scale tests to evaluate the feasibility of the iron slag PRB enhanced-EK process in conjunction with Sodium Cholate (NaC) biosurfactant as a cost-effective and sustainable method for removing PFOA from the soil. A 2 cm iron slag-based PRB with a pH of 9.5, obtained from the steel-making industry, was strategically embedded in the middle of the EK reactors to capture PFOA within the soil. The main component of the slag, iron oxide, exhibited significant adsorption capacity for PFOA contamination. The laboratory-scale tests were conducted over two weeks, revealing a PFOA removal rate of more than 79% in the slag/activated carbon PRB-EK test with NaC enhancement and 70% PFOA removal in the slag/activated carbon PRB-EK without NaC. By extending the duration of the slag/AC PRB-EK test with NaC enhancement to three weeks, the PFOA removal rate increased to 94.09%, with the slag/AC PRB capturing over 87% of the initial PFOA concentration of 10 mg/L. The specific energy required for soil decontamination by the EK process was determined to be 0.15 kWh/kg. The outcomes of this study confirm the feasibility of utilizing iron slag waste in the EK process to capture PFOA contaminants, offering a sustainable approach to soil decontamination. Combining iron slag PRB and NaC biosurfactant provides a cost-effective and environmentally friendly method for efficient PFOA removal from soil.

PFOA remediation from aqueous media using CTAB impregnated activated carbon: A closed-loop sustainable study with comprehensive selectivity analysis

PFASs have been attracting worldwide attention in recent years. In this study, a novel surface-impregnated activated carbon (AC) has been optimally synthesized utilizing waste Karanja shells. Surface functional group modification has been performed using Cetyltrimethylammonium bromide (CTAB). PFOA-selectivity analysis of the adsorbent against different background species present at typical river water concentration was performed. To make the process sustainable, the development of regenerant specifications as well as recovery of the regenerant and PFOA from the spent regenerant solution were investigated. A biomass/acid ratio of 1:2.5, temperature 450 °C, and 1 % CTAB solution was found to be optimum synthesis parameters for the CTAB-modified AC (CTAB_K-AC) for PFOA removal. By CTAB-impregnation, the PFOA uptake capacity of the adsorbent increased up to threefold. The maximum PFOA adsorption capacities exhibited by Karanja AC (K_AC) and CTAB_K-AC were 157.1 mg/g & 455.8 mg/g, respectively. The adsorbent exhibited high PFOA selectivity against all background co-contaminants i.e., NOM (humic acid), clay (bentonite), anions, and cations, and removed ~90 % PFOA. The regenerant (50 % ethanol with 1 % NH4OH aqueous solution) showed 80–90 % PFOA recovery. The distillation process at ~80 °C temperature recovered ~90 % PFOA and 80–90 % of the regenerant reagents from the spent regenerant solution. The packed-bed column run of the adsorbent showed high PFOA removal capacity from the river water matrix and the breakthrough data was well fitted with Thomas and Yoon Nelson Model with R2 values of 0.97 for both the models. The results showed that novel CTAB_K-AC can be an effective adsorbent for PFOA adsorptive remediation from aqueous media with high treatment selectivity towards the PFOA in a materially closed-loop sustainable process.

Comparison of eco-improvement on constructed wetlands with nano zero valent iron introduction under different levels of PFOA stress: Perspectives on plant, microbe, and PFOA removal

The ecological hazards of perfluoro octanoic acid (PFOA, a typical perfluoroalkyl substances) have been continually reported in constructed wetlands (CWs) for wastewater treatment. In present study, nano zero valent iron (nZVI) was adopted to alleviate PFOA stress at different levels (1 and 10 mg/L) in CWs. It was revealed that the effects of nZVI on specific ecological parameters varied at different PFOA dosages. PFOA influenced plant photosynthetic and antioxidant parameters with significant concentration-dependence. NZVI addition caused more obvious promotion of chlorophyll (25.30–31.84 %) and reduction of catalase (172.64 %) and malondialdehyde (83.01 %) with 10 mg/L PFOA exposure. For microbe, nZVI was prone to stimulate enzyme activities under 1 mg/L PFOA, in which the relative activity of dehydrogenase, urease, phosphatase, and four nitrogen cycling enzymes increased by 86.25–375.56 %, 43.10–71.16 %, 1.52–29.38 %, and 4.49–315.18 %. However, nZVI caused more abundant of functional bacteria (like nitrifying bacteria and phosphorus-accumulating organisms) and function genes (like amoA, hao, and ppx) with PFOA at 10 mg/L. On the whole, changes in bacterial community confirmed the enhancement potential of nZVI on ammonium and phosphorous removal. PFOA removal at 10 mg/L was higher compared to 1 mg/L, resulting from higher abundance of class Gammaproteobacteria, and nZVI addition further contributed to the highest removal efficiency (73.54 %). This study provided evidence on nZVI as a possible manner for optimizing eco-function in CWs with PFOA stress at different levels.

PFAS Characteristics and Treatment for Landfill Leachate

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) are manmade chemicals which has been extensively used, resulting in great potential for human and environmental accumulation due to high persistence. PFASs can be divided to two parts, terminal and precursor compounds, based on how many fluorine atoms link to the carbon bonds. Many studies have examined the removal ability of method including activated carbon (AC), Foam fractionation (FF), chemical oxidation and boron-doped diamond anodes (BBD). This paper focus on introducing advanced remedial technology for PFAS treatment from landfill leachate. The details about PFASs are introduced, including the chemical structure, source, and properties. Then, different types of PFASs from landfill leachate are demonstrated. Some of PFAS, especially short-chain, are prone to stay as liquid phase. Activated carbon, a great model of adsorption, shows excellent performance on removal of PFOS and PFOA. In addition, boron-doped diamond anodes technique which belongs to the electrochemical anodic oxidation, have a great potential on landfill leachate in the future. Last but not least, the conclusion makes a summary and shows possible treatment to landfill in the future.

Rechargeable stormwater biofilters: In situ regeneration of PFAS removal capacity by using a cationic polymer, polydiallyldimethylammonium chloride

Conventional stormwater biofilter media such as sand and compost have limited capacity to remove PFAS due to the exhaustion of attachment sites with pollutants and other stormwater constituents. Replacing exhausted filter media is expensive whereas in situ regeneration of their adsorption capacity can be cost-effective. This study demonstrates that in situ application of cationic polymers such as polydiallyldimethylammonium chloride (PDADMAC), a drinking water coagulant, could regenerate the filter media capacity to remove anionic PFAS. The benefit of PDADMAC increased with a decrease in PFAS carbon chain length: the removal of PFBA increased by 9.9 ± 1.8 times while the removal of PFOA only increased by 0.3 ± 0.03 times. The result indicates the application of the cationic polymer can help remove short-chain PFAS, the ones that are most difficult to remove by typical organic amendments such as activated carbon and biochar. Despite being used as coagulants, the addition of PDADMAC did not negatively affect the clogging rate of the biofilters in the presence of suspended sediments. Surprisingly, biofilters exposed to PDADMAC required 35.3% more suspended sediments than the biofilters without PDADMAC to reduce the hydraulic conductivity below half of the initial value. PDADMAC application reduced the release of colloids from the biofilter media during intermittent flow, thereby decreasing the potential of the colloid-facilitated release of adsorbed PFAS. The adsorbed PDADMAC in the biofilter was not degraded, indicating that applied PDADMAC could last long and continue to remove PFAS in the biofilter. Thus, in situ application of cationic polymers can help regenerate the PFAS removal capacity of conventional biofilters.

Effect of electron shuttles on typical perfluoroalkyl substance removal via iron oxide reduction in wetland sediment

Perfluoroalkyl substance (PFAS) had been widely detected in water environment and caused extremely toxicity. The Fe(Ⅲ) reduction process had been confirmed with potential effect on organic pollutants removal. Many substances can be served as electron shuttles that played important role in Fe(Ⅲ) reduction and the removal or distribution of PFAS. Considering the complex organic characteristics in wetland sediment, this study explored the effect of diverse electron shuttles, including activated carbon (AC), sucrose, humic acid (HA), organic acid (OA) and NH4+, on typical PFAS (PFOA and PFOS) removal under the Fe(Ⅲ) reduction conditions. Results showed that, the Fe(Ⅲ) contents reduced with the removal of PFAS. The addition of NH4+, AC and sucrose enhanced PFOA and PFOS removal in sediment. And the addition of NH4+ achieved best PFOA removal, which had 30.2% lower content than that in control. The characteristics of organic carbon changed with these electron shuttles and thus influenced the performance and distribution of PFAS. Among the organic matter components, the proportions of fulvic acid-like and humic-like materials increased, which could promote Fe(Ⅲ) reduction. Increased proportions of Firmicutes, Proteobacteria and Pseudomonas were detected with various electron shuttles. These microbes could survival under PFAS pollution and have potential to defluorination of PFAS. The electron shuttles highly improved the proportions of iron-reduction bacteria, which were more than 86.0% higher than that in control. This study provided a key information for better understanding the role of electron shuttles in PFAS removal via Fe(Ⅲ) reduction process, which could be useful for effective PFAS remediation in sediment.

Trace Co coupled and tourmaline doped g-C3N4 for visible-light synergistic persulfate system for degradation of perfluorooctanoic acid

Removal of perfluorinated compounds (PFCs) from the environment is a major challenge due to their refractory, persistent and bioaccumulative properties. In this study, trace Co coupled via Co–P coordination and tourmaline (TM) doped g-C3N4 was fabricated (marked as Co/TM/g-C3N4) and used as the catalyst for activating peroxymonosulfate (PMS) to remove emerging PFOA under visible light irradiation. Several affecting parameters were systematically investigated, inlcuding Co/TM/g-C3N4 dosage, PMS concentration, initial pH, as well as coexisting Cl−, HCO3−, H2PO4−, NO3− and humic acid. Under the conditions of 0.5 g/L Co/TM/g-C3N4, 2.5 g/L PMS and pH 3.0, the developed synergistic system had the ability for 81.11% removal of PFOA within 4 h, 67.64% removal after the fourth run, and also could be effectively applied in actual water bodies. During the degradation process, π-π*, N–CN and graphite N played the vital role, with the final defluorination rate of 31.12% at 4 h. Free radical quenching and quantitative analysis, as well as electron paramagnetic resonance was used to verify the free radical and non-free radical pathways for PFOA removal, with the findings that SO4•− (2.61 μM at 1 h), •OH (0.067 μM at 4 h), O2•−, h+, and O12 were involved with possible time-dependent. By liquid chromatography-mass spectrometry analysis, the short-chain intermediates of C3–C7 were proposed and identified. From this study, trace Co coupled and TM doped g-C3N4 demonstrated higher catalytic potential to activate PMS for visible-light synergistic PFOA removal, with the expectation of achieving a cleaner water environment for human beings.

Enhanced adsorption and photocatalytic removal of PFOA from water by F-functionalized MOF with in-situ-growth TiO2: Regulation of electron density and bandgap

PFOA has caused enormous environmental risks with recalcitrance, toxicity, and bioaccumulation, while the degradation of PFOA is still a challenging topic related to the high energy of CF bonds. However, the conventional methods such as biological oxidation, electrochemical oxidation and membrane separation have their own drawbacks. Actually, adsorption-photocatalysis is considered a potential treatment due to effectiveness and thoroughness. Instead of preparing the composite material by adding TiO2, the method to in-situ grow TiO2 in the MOF (MIL-125(Ti)) was carried out, which achieved narrowed band gap and improved the photoresponse ability, simultaneously. Furthermore, the surface F-functionalized MOF provided more available special adsorption sites for PFOA enrichment. Linked fluorine groups not only improved the adsorption capacity (185.151 μmol/g) but also enhanced the photocatalytic rate (1.221 E−4/s) by altering the electronic density of VB and CB. The constructed F-TiO2@MIL-125 stepwise degraded PFOA through a dominant ·OH attack pathway and maintained the oxidize ability of h+ to PFOA. As a bifunctional material for adsorption and photocatalysis, F-TiO2@MIL-125 was able to be applied in various water environments repeatedly, which has unlimited environmental application potential.

Rapid removal of PFOA and PFOS via modified industrial solid waste: Mechanisms and influences of water matrices.

Emerging perfluoroalkyl and polyfluoroalkyl substances contaminate waters at trace concentrations, thus rapid and selective adsorbents are pivotal to mitigate the consequent energy-intensive and time-consuming issues in remediation. In this study, coal combustion residuals-fly ash was modified (FA-SCA) to overcome the universal trade-off between high adsorption capacity and fast kinetics. FA-SCA presented rapid adsorption (teq = 2 min) of PFOX (perfluorooctanoic acid and perfluorooctanesulfonic acid, collectively), where the dynamic adsorption capacity (qdyn = qm/teq) was 2-3 orders of magnitude higher than that of benchmark activated carbons and anion-exchange resins. Investigated by advanced characterization and kinetic models, the fast kinetics and superior qdyn are attributed to (1) elevated external diffusion driven by the submicron particle size; (2) enhanced intraparticle diffusion caused by the developed mesoporous structure (Vmeso/Vmicro = 8.1); (3) numerous quaternary ammonium anion-exchange sites (840 μmol/g), and (4) appropriate adsorption affinity (0.031 L/μmol for PFOS, and 0.023 L/μmol for PFOA). Since the adsorption was proven to be a synergistic process of electrostatic and hydrophobic interactions, effective adsorption ([PFOX]ini = 1.21 μM, concentration levels of highly-contaminant-sites) was obtained at conventional natural water chemistries. High selectivity (>85.4% removal) was also achieved with organic/inorganic competitors, especially compounds with partly similar molecular structures to PFOX. In addition, >90% PFOX was removed consistently during five cycles in mild regeneration conditions (pH 12 and 50 °C). Overall, FA-SCA showed no leaching issues of toxic metals and exhibits great potential in both single-adsorption processes and treatment train systems.

Flexible construct of N vacancies and hydrophobic sites on g-C3N4 by F doping and their contribution to PFOA degradation in photocatalytic ozonation

N vacancies, hydrophobic sites and electron rich zone were simply regulated by doping F into g-C3N4 (CN) to accelerate photocatalytic ozonation of PFOA. Activity of F-CN was superior to that of CN, with 74.3% PFOA removal by F-CN/Vis/O3 but only 57.1% by CN/Vis/O3. Experimental results and theory simulations suggested that the photogenerated hole (hvb+) oxidation with the help of N vacancies was vital for PFOA degradation. N vacancies on both CN and F-CN would trap O atom of PFOA and seize electron from α –CF2 group, which made PFOA more easily to be oxidized. Doping of F narrowed band gap, lowered the valence band position and enhanced the oxidation potential of hvb+. The hydrophobic sites would accelerate the mass transfer of O3 and PFOA, enhance O3’s single electron reduction with ecb- to generate hydroxyl radicals (•OH) and reduce the recombination of hvb+-ecb-. Under the joint function of hvb+, N vacancies and •OH, PFOA degradation in F-CN/Vis/O3 proceeded through the gradually shortening of perfluoroalky chain and loss of CF2 unit. The acute and chronic toxicity of generated short-chain perfluorocarboxylic acid toward fish, green algae daphnid were predicted by ECOSAR. And the toxicity change of solutions was examined by luminescent bacteria.

Preparation of magnetic covalent triazine frameworks by ball milling for efficient removal of PFOS and PFOA substitutes from water

Recyclable magnetic COFs/Fe3O4 synthesized using ball-milling showed fast and high adsorption for two PFOS and PFOA substitutes in water.