Complete Defluorination and Mineralization of Perfluorooctanoic Acid by a Mechanochemical Method Using Alumina and Persulfate

Innovative techniques for combating a common enemy forever chemicals: A comprehensive approach to mitigating per- and polyfluoroalkyl substances (PFAS) contamination

The pervasive presence of per and polyfluoroalkyl substances (PFAS), commonly referred to as "forever chemicals," in water systems poses a significant threat to both the environment and public health. PFAS are persistent organic pollutants that are incredibly resistant to degradation and have a tendency to accumulate in the environment, resulting in long-term contamination issues. This comprehensive review delves into the primary impacts of PFAS on both the environment and human health while also delving into advanced techniques aimed at addressing these concerns. The focus is on exploring the efficacy, practicality, and sustainability of these methods. The review outlines several key methods, such as advanced oxidation processes, novel materials adsorption, bioremediation, membrane filtration, and in-situ chemical oxidation, and evaluates their effectiveness in addressing PFAS contamination. By conducting a comparative analysis of these techniques, the study aims to provide a thorough understanding of current PFAS remediation technologies, as well as offer insights into integrated approaches for managing these persistent pollutants effectively. While acknowledging the high efficiency of adsorption and membrane filtration in reducing persistent organic pollutants due to their relatively low cost, versatility, and wide applicability, the review suggests that the integration of these methods could result in an overall enhancement of removal performance. Additionally, the study emphasizes the need for researcher attention in key areas and underscores the necessity of collaboration between researchers, industry, and regulatory authorities to address this complex challenge.

Mechanochemical remediation of contaminated soil: A review

Mechanochemical techniques have been garnering growing attention in remediation of contaminated soil. This paper summarizes the performance, mechanism, influential factors, and environmental impacts of mechanochemical remediation (MCR) for persistent organic pollutants (POPs) contaminated soil and heavy metal(loid) s (HMs) contaminated soil. Firstly, in contrast to other technologies, MCR can achieve desirable treatment of POPs, HMs, and co-contaminated soil, especially with high-concentration pollutants. Secondly, POPs undergo mineralization via interaction with mechanically activated substances, where aromatic and aliphatic pollutants in soil may go through varied degradation routes; inorganic pollutants can be firmly combined with soil particles by fragmentation and agglomeration induced by mechanical power, during which additives may enhance the combination but their contact with anionic metal(loid)s may be partially suppressed. Thirdly, the effect of MCR primarily hinges on types of milling systems, the accumulation of mechanical energy, and the use of reagents, which is basically regulated through operating parameters: rotation speed, ball-to-powder ratio, reagent-to-soil ratio, milling time, and soil treatment capacity; minerals like clay, metal oxides, and sand in soil itself are feasible reagents for remediation, and alien additives play a crucial role in synergist and detoxification; additionally, various physicochemical properties of soil might influence the mechanochemical effect to varying degrees, yet the key influential performance and mechanism remain unclear and require further investigation. Concerning the assessment of soil after treatment, attention needs to be paid to soil properties, toxicity of POPs' intermediates and leaching HMs, and long-term appraisement, particularly with the introduction of aggressive additives into the system. Finally, proposals for current issues and forthcoming advancements in this domain are enumerated in items. This review provides valuable insight into mechanochemical approaches for performing more effective and eco-friendly remediation on contaminated soil.

Current trends and patterns of PFAS in agroecosystems and environment: A review

Per- and polyfluoroalkyl substances (PFASs) are one of the more well-known highly persistent organic pollutants with potential risks to agroecological systems. These compounds are of global concern due to their persistence and mobility, and they often lead to serious impacts on environmental, agricultural, and human health. In the past 20 years, the number of science publications on PFAS has risen; despite this, certain fundamental questions about PFAS occurrence, sources, mechanism of transport, and impacts on agroecosystems and the societies dependent on them are still open and evolving. There is a lack of systematic and comprehensive analysis of these concerns in agroecosystems. Therefore, we reviewed the current literature on PFAS with a focus on agroecosystems; our review suggests that PFASs are nearly ubiquitous in agricultural systems. We found the current research has limitations in analyzing PFAS in complex matrices because of their small size, distribution, and persistence within various environmental systems. There is consistency in the properties and composition of PFAS in and around agroecosystems, suggesting evidence of shared sources and similar components within different tropic levels. The introduction of new and varied sources of PFAS appear to be growing, adding to their residual accumulation in environmental matrices and leading to possible new types of chemical compounds that are difficult to assess accurately. This review determines existing research trends, understands mechanisms and incidence of PFAS within agroecosystems and their impact on human health, and thereby recommends further studies to remedy research gaps.

3D structure-functional design of a biomass-derived photocatalyst for antimicrobial efficacy and chemical degradation under ambient conditions

Surface sterilization and hazardous chemical degradation under ambient conditions can provide significant benefits for public and environmental health. Materials with sterilization and chemical degradation capacity under sunlight can efficiently reduce infectious disease incidence rates and toxic chemical exposure. Utilizing renewable energy for sustainable sterilization and degradation is more desirable as it reduces the potential secondary contamination. Herein, we report functional structure design using lignin, a renewable carbon heterogeneous polymer, to synthesize a highly efficient and stable photocatalyst that degrades environmentally hazardous organic compounds rapidly. Through a hydrolysis reaction between Ti-OH and the hydroxyl groups of lignin, Ti-O-C and Ti-O-Ti bonds were established and a lignin based photocatalyst with a hollow sphere structure (Clignin@H-TiO2) was formed. The presence of a homozygous carbon modified TiO2 structure contributes to the enhanced photodegradation activity with solar light. The close hetero-interfacial contact between carbonized lignin and TiO2 further improves the photocatalytic efficiency by facilitating effective charge carrier separation. After synthesis optimization, the resulting Clignin@H-TiO2 photocatalyst exhibits excellent performance in the degradation of atenolol under solar light irradiation with 100% degradation within five minutes. Additionally, it efficiently removes approximately 50% of PFOA and kills about 90% of bacteria within three hours. The uniform distribution of lignin within the crosslinking structures ensures a durable carbon modified TiO2 framework, which remains stable after 10 cycles of usage. The robustness of the lignin-based photocatalyst enables incorporating the catalyst into diversified material formats and various usages. Coating of the photocatalyst onto device surfaces shows bacterial killing efficacy under sunlight. The photocatalysts based on lignin valorization present a green chemistry approach for environmental remediation and surface sterilization, which has long-term environmental protection benefits, with broad applications in toxin treatment and health protection against pathogen infection.

PFOA-contaminated soil remediation: a comprehensive review

Soil and groundwater contamination has been raised as a concern due to the capability of posing a risk to human health and ecology, especially in facing highly toxic and emerging pollutants. Because of the prevalent usage of perfluorooctanoic acid (PFOA), in industrial and production processes, and subsequently the extent of sites contaminated with these pollutants, cleaning up PFOA polluted sites is paramount. This research provides a review of remediation approaches that have been used, and nine remediation techniques were reviewed under physical, chemical, and biological approaches categorization. As the pollutant specifications, environmental implications, and adverse ecological effects of remediation procedures should be considered in the analysis and evaluation of remediation approaches, unlike previous research that considered a couple of PFAS pollutants and generally dealt with technical issues, in this study, the benefits, drawbacks, and possible environmental and ecological adverse effects of PFOA-contaminated site remediation also were discussed. In the end, in addition to providing sufficient and applicable understanding by comprehensively considering all aspects and field-scale challenges and obstacles, knowledge gaps have been found and discussed.

Unlocking New Avenues: Solid-State Synthesis of Molecularly Imprinted Polymers

Molecularly imprinted polymers (MIPs) are established artificial molecular recognition platforms with tailored selectivity towards a target molecule, whose synthesis and functionality are highly influenced by the nature of the solvent employed in their synthesis. Steps towards the "greenification" of molecular imprinting technology (MIT) has already been initiated by the elaboration of green MIT principles; developing MIPs in a solvent-free environment may not only offer an eco-friendly alternative, but could also significantly influence the affinity and expected selectivity of the resulting binding sites. In the current study the first solvent-free mechanochemical synthesis of MIPs via liquid-assisted grinding (LAG) is reported. The successful synthesis of the imprinted polymer was functionally demonstrated by measuring its template rebinding capacity and the selectivity of the molecular recognition process in comparison with the ones obtained by the conventional, non-covalent molecular imprinting process in liquid media. The results demonstrated similar binding capacities towards the template molecule and superior chemoselectivity compared to the solution-based MIP synthesis method. The adoption of green chemistry principles with all their inherent advantages in the synthesis of MIPs may not only be able to alleviate the potential environmental and health concerns associated with their analytical (e.g., selective adsorbents) and biomedical (e.g., drug carriers or reservoirs) applications, but might also offer a conceptual change in molecular imprinting technology.

Cutting-edge technologies and relevant reaction mechanism difference in treatment of long- and short-chain per- and polyfluoroalkyl substances: A review

Per- and polyfluoroalkyl substances (PFAS) are emerging contaminants. Compared with short-chain PFAS, long-chain PFAS are more hazardous. Currently, little attention has been paid to the differences in reaction mechanisms between long-chain and short-chain PFAS. This pressing concern has prompted studies about eliminating PFAS and revealing the mechanism difference. The reaction rate and reaction mechanism of each technology was focused on, including (1) adsorption, (2) ion exchange (IX), (3) membrane filtration, (4) advanced oxidation, (5) biotransformation, (6) novel functional material, and (7) other technologies (e.g. ecological remediation, hydrothermal treatment (HT), mechanochemical (MC) technology, micro/nanobubbles enhanced technology, and integrated technologies). The greatest reaction rate k of photocatalysis for long- and short-chain PFAS high up to 63.0 h-1 and 19.7 h-1, respectively. However, adsorption, membrane filtration, and novel functional material remediation were found less suitable or need higher operation demand for treating short-chain PFAS. Ecological remediation is more suitable for treating natural waterbody for its environmentally friendly and fair reaction rate. The other technologies all showed good application potential for both short- and long-chain PFAS, and it was more excellent for long-chain PFAS. The long-chain PFAS can be cleavaged into short-chain PFAS by C-chain broken, -CF2 elimination, nucleophilic substitution of F-, and HF elimination. Furthermore, the application of each type of technology was novelly designed; and suggestions for the future development of PFAS remediation technologies were proposed.

Enhanced piezoelectric catalysis of BaTiO3 by ZVAl for mechanochemical defluorination of PFOA: Promotion of electron transfer

Mechanochemical (MC) destruction of pollutants is effective; however, the emerging electron transfer mechanism is ambiguous owing to a lack of systematic evaluation. Therefore, this study aims to evaluate the contribution of electrons to perfluorooctanoic acid (PFOA) defluorination during MC process. A synergistic effect was obtained by activating BaTiO3 to generate piezoelectrons and applying zero-valence aluminum (ZVAl) to facilitate electron transfer, with 95.66% PFOA defluorination and reaction time decreasing from 6 h to 3 h. The mechanism of piezoelectric catalysis of the BaTiO3/ZVAl system was further investigated through kinetic analyses and intersystem comparisons. The major contribution of piezo-excited electrons was revealed through probe detection and quantitative determination. A positive correlation between electron generation and PFOA defluorination was ascertained, and the calculation of the electron utilization ratio revealed an electron transfer mechanism. The detached fluorides were confirmed to be bonded directly to the additives. Furthermore, PFOA decomposition was identified as a cyclical process with constant dissociation of the CF2 groups.

Zero-valent iron-peroxydisulfate as synergistic co-milling agents for enhanced mechanochemical destruction of 2,4-dichlorophenol: Coupling reduction with oxidation

Mechanochemical (MC) remediation with zero-valent iron (ZVI) as co-milling agent enables the non-combustion and solvent-free disposal of solid halogenated organic pollutants (HOPs) via solid-phase reaction, but suffers from incomplete dechlorination (especially for less chlorinated chemicals). Herein, a reduction-oxidation coupling strategy using ZVI and peroxydisulfate as synergistic (ZVI-PDS) co-milling agents was investigated, with 2,4-dichlorophenol (2,4-DCP) as probe contaminant. By revisiting the MC destruction process of 2,4-DCP by ZVI, the contribution of both reductive and oxidative routes is confirmed, and the inefficient •OH generation is addressed. With ball-to-material and reagent-to-pollutant mass ratios of 30:1 and 13:1, respectively, ZVI-PDS achieves higher dechlorination ratio (86.8%) for 2,4-DCP within 5 h, outcompeting sole ZVI (40.3%) or PDS (33.9%), due to the accumulation of numerous SO4•-. As suggested by a two-compartment kinetic model, the optimal ZVI/PDS molar ratio of 4:1 is determined, which balances the relative contribution of reductive/oxidative routes and leads to a maximum mineralization efficiency of 77.4%. The analysis on product distribution verifies the generation of dechlorinated, ring-opening and minor coupling products (with low acute toxicity). This work validates the necessity to couple reduction with oxidation in MC destruction for solid HOPs, and may provide information on reagent formulation.

Differences between reductive defluorination of perfluorooctanoic acid by chlorination, bromination, and iodization in the vacuum-ultraviolet/sulfite process

The introduction of iodide (I-) has broad perspectives on the decomposition of perfluorocarboxylates (PFCAs, CnF2n+1COO-). However, the iodinated substances produced are highly toxic synthetic chemicals, hence, it is urgent to find a similar alternative with less toxicity. In this work, the defluorination of perfluorooctanoic acid (PFOA) by I-, bromide (Br-) and chlorine (Cl-) was systematically compared in the VUV/sulfite process. Results indicated that the PFOA defluorination rates increased with increasing nucleophilicity of halogens (I > Br > Cl). Meanwhile, the introduction of I-, Br-, and Cl- reduced the interference of the coexisting water matrix on the degrading influence of PFOA. The in situ produced eaq-, SO3•-, H•, and HO• were recognized, among the addition of I- maximized the relative contribution of eaq- but Br- and Cl- decreased that of H• and other radicals. Additionally, HPLC/MS analysis revealed the presence of I-, Br-, and Cl- had a vital impact on the difference in product concentrations, while they had a negligible effect on the change in the pathway of degradation. Overall, this study demonstrated the similarities and differences between I-, Br-, and Cl-, which has significant implications for further understanding VUV/sulfite degradation.

Peroxymonosulfate assisted mechanochemical remediation of high concentration DDTs contaminated soil

DDTs (DDT and its metabolites) contaminated sites urgently need to be treated efficiently and greenly. In this study, a horizontal planetary mechanochemical method with co-milling additives was developed aiming at efficiently degrading high-concentration DDTs in historical contaminated soil (∼7500 mg/kg). Peroxymonosulfate (PMS) was firstly used to the mechanochemical degradation of DDTs in historical contaminated soil, with a degradation efficiency of over 95% after 1 h of milling under the optimal milling conditions (CR = 30:1, r = 500 rpm, R = 1:4). Mechanism study indicated that DDTs in soil were partially dechlorinated and mineralized. The main products formed might be chlorinated aliphatic hydrocarbons, which need further treatment by ball milling or other methods. Under the action of mechanical energy, PMS could oxidize DDTs in soil through non-radical way rather than common radical way. Then, a comprehensive assessment of this remediation method was conducted by analyzing the changes in soil properties and acute biotoxicity after ball milling. Although PMS had a great performance on the degradation of DDTs, especially p, p'-DDE, it would cause the acidification and salinization of soil. Therefore, further pH adjustment and desalination treatment were suggested to reduce the negative impacts. This work successfully presents a practical approach to mechanochemical remediation of DDTs contaminated sites.

Mechanochemical remediation of lindane-contaminated soils assisted by CaO: Performance, mechanism and overall assessment

Soil contamination caused by persistent organic pollutants (POPs) has been a worldwide concern for decades. With lindane-contaminated soil as the target, a mechanochemical method assisted by CaO was comprehensively evaluated in terms of its remediation performance, degradation mechanism and overall assessment. The mechanochemical degradation performance of lindane in cinnamon soil or kaolin was determined under different additives, lindane concentrations and milling conditions. 2,2-Diphenyl-1-(2,4,6-trinitrophenyl) hydrazinyl free radical (DPPH^•) and electron spin resonance (ESR) tests evidenced that the degradation of lindane in soil was caused mainly by the mechanical activation of CaO to produce free electrons (e^-) and the alkalinity of the generated Ca(OH)₂. Dehydrochlorination or dechlorination by elimination, alkaline hydrolysis, hydrogenolysis and the subsequent carbonization were the main degradation pathways of lindane in soil. The main final products included monochlorobenzene, carbon substances and methane. The mechanochemical method with CaO was proved to also efficiently degrade lindane in three other soils and other hexachlorocyclohexane isomers and POPs in soil. The soil properties and soil toxicity after remediation were assessed. This work presents a relatively clear discussion of various aspects of the mechanochemical remediation of lindane-contaminated soil assisted by CaO.

Mechanochemical destruction of per- and polyfluoroalkyl substances in aqueous film-forming foams and contaminated soil

Per- and polyfluoroalkyl substances (PFASs) are a class of synthetic chemicals of concern that exhibit extreme persistence within the environment and possess physicochemical properties that are resistant to targeted degradation. Comprising substantial concentrations of PFASs, aqueous film-forming foams (AFFFs) present a major exposure pathway to the environment having been applied to land at firefighting-training sites globally for decades. This has led to significant contamination of environmental media. Herein, we demonstrate that mechanochemical destruction (MCD) is an effective method for the destruction of PFASs in an AFFF concentrate and an authentic sample of PFAS-contaminated soil derived from a decommissioned firefighting training facility. Both targeted analysis and non-targeted analysis were used in this study to evaluate the degradation of PFASs in complex substrates during MCD treatment. Destruction efficiencies of target PFAS subgroups ranged from 99.88% to 100%. The only additive employed for MCD treatment was quartz sand, which was used only for the liquid AFFF sample, with no additives required for the destruction of PFASs in the contaminated soil. This confirms the viability of MCD for both the remediation of PFAS-contaminated land and the destruction of stockpiled AFFFs.

Insight into mechanochemical destruction of PFOA by BaTiO3: An electron-dominated reduction process

Perfluorooctanoic acid (PFOA) is a representative persistent organic pollutant and its disposal by mechanochemical (MC) technology emerges in recent years. However, degradation mechanism of PFOA especially rupture of C-F bonds during MC process is still unclear. Therefore, we innovatively employed barium titanate as co-milling reagent in MC system to disclose an electron-dominated reduction process. By stimulating piezoelectric effect of BaTiO₃ under MC impact, free electrons were generated. The results implied more than 95.00% degradation and 60.00% defluorination efficiency were obtained after 6 h' ball milling. DPPH• was used as probe to confirm the existence of piezo-excited electrons, which were further verified to be major reactive species by atmosphere experiments. Thus, PFOA destruction was dominated by reduction process, characterizing by breakage of C-F bonds induced by electrons. Accordingly, the fate of organic fluorides was explored and BaF₂ was identified as final product. The cleavage of carboxyl group initiated PFOA decomposition, following by successive removal of CF₂ groups and elimination of F^-. Moreover, the practical experiments and reusable trials implied promising application of this method. Overall, this paper provides a novel perspective for reductive decomposition of PFOA by MC technology and reveals the major role of electrons during reaction process.

Degradation of Perfluorooctanoic Acid on Aluminum Oxide Surfaces: New Mechanisms from Ab Initio Molecular Dynamics Simulations

Perfluorooctanoic acid (PFOA) is a part of a large group of anthropogenic, persistent, and bioaccumulative contaminants known as per- and polyfluoroalkyl substances (PFAS) that can be harmful to human health. In this work, we present the first ab initio molecular dynamics (AIMD) study of temperature-dependent degradation dynamics of PFOA on (100) and (110) surfaces of γ-Al₂O₃. Our results show that PFOA degradation does not occur on the pristine (100) surface, even when carried out at high temperatures. However, introducing an oxygen vacancy on the (100) surface facilitates an ultrafast (<100 fs) defluorination of C-F bonds in PFOA. We also examined degradation dynamics on the (110) surface and found that PFOA interacts strongly with Al(III) centers on the surface of γ-Al₂O₃, resulting in a stepwise breaking of C-F, C-C, and C-COO bonds. Most importantly, at the end of the degradation process, strong Al-F bonds are formed on the mineralized γ-Al₂O₃ surface, which prevents further dissociation of fluorine into the surrounding environment. Taken together, our AIMD simulations provide critical reaction mechanisms at a quantum level of detail and highlight the importance of temperature effects, defects, and surface facets for PFOA degradation on reactive surfaces, which have not been systematically explored or analyzed.

Engineered ball-milled colloidal activated carbon material for advanced oxidation process of ibuprofen: Influencing factors and insights into the mechanism

This study explores a simple and efficient, physically modified ball-milled activated carbon (AC_BM) preparation from granular activated carbon (GAC), which can be demonstrated for groundwater application. The colloidal stability of the AC_BM plays a vital role in the activation of peroxymonosulfate (PMS) and the degradation of pollutants. Adsorption kinetics and isotherm studies explain that the AC_BM has more active sites and maximum adsorption capacity (q_max = 509 mg g^-1) on the surface of the materials than GAC. The 92% of ibuprofen degradation was achieved at 240 min along with 0.1 g L^-1 of AC_BM, 5 mM of PMS, and 6.3 of initial solution pH. A chemical scavenger and electron spin resonance spectra also confirmed the formation of reactive oxygen species such as radicals (O₂^•-, HO^•, SO₄^•-) and non-radical (¹O₂) in the AC_BM/PMS system. Three major degradation pathways, hydroxylation, demethylation, and decarboxylation involved in ibuprofen degradation. Nearly 13 degradation by-products were detected during the AC_BM/PMS oxidation of ibuprofen. The toxicity analysis of oxidation by-products of ibuprofen was also discussed by computational simulation employing the ecological structure-activity relationships software. The AC_BM/PMS system was successfully applied to the natural groundwater system for ibuprofen degradation. Hence, the AC_BM/PMS system is an excellent catalyst for real groundwater applications.

Solvent-Free Nonthermal Destruction of PFAS Chemicals and PFAS in Sediment by Piezoelectric Ball Milling

Studies on the destruction of solid per- and polyfluoroalkyl substances (PFAS) chemicals and PFAS-laden solid wastes significantly lag behind the urgent social demand. There is a great need to develop novel treatment processes that can destroy nonaqueous PFAS at ambient temperatures and pressures. In this study, we develop a piezoelectric-material-assisted ball milling (PZM-BM) process built on the principle that ball collisions during milling can activate PZMs to generate ∼kV potentials for PFAS destruction in the absence of solvents. Using boron nitride (BN), a typical PZM, as an example, we successfully demonstrate the complete destruction and near-quantitative (∼100%) defluorination of solid PFOS and perfluorooctanoic acid (PFOA) after a 2 h treatment. This process was also used to treat PFAS-contaminated sediment. Approximately 80% of 21 targeted PFAS were destroyed after 6 h of treatment. The reaction mechanisms were determined to be a combination of piezo-electrochemical oxidation of PFAS and fluorination of BN. The PZM-BM process demonstrates many potential advantages, as the degradation of diverse PFAS is independent of functional group and chain configurations and does not require caustic chemicals, heating, or pressurization. This pioneering study lays the groundwork for optimizing PZM-BM to treat various PFAS-laden solid wastes.

Mechanochemical Preparation of Edge-Selectively justify Hydroxylated Graphene Nanosheets Using Persulfate via a Sulfate Radical-Mediated Process

The production of water-dispersed graphene with low defects remains a challenge. The dry ball milling of graphite with additives produces edge-selectively functionalized graphene. However, the "inert" additives require a long milling time and cause inevitable in-plane defects. Here, the mechanochemical reaction of graphite with persulfate solved the above drawback and produced edge-selectively hydroxylated graphene (EHG) nanosheets through a 2 h ball-milling and a subsequent 0.5 h sonication. The mechanochemical cleavage of persulfate yielded SO₄ ⋅^- to spontaneously oxidize graphite to form the carbon radical cations selectively at edges, followed by hydroxylation with water of moisture. Because the O-O bond dissociation energy of persulfate is 20 % of the graphitic C-C bond, the rather low milling energy allowed the hydroxylation of graphite at edges with nearly no in-plane defects. The obtained EHG showed high water-dispersibility and excellent photothermal and electrochemical properties, thereby opening up a new door to fabricate graphene-based composites.

Solvent-Free, Ambient Temperature and Pressure Destruction of Perfluorosulfonic Acids under Mechanochemical Conditions: Degradation Intermediates and Fluorine Fate

Perfluorosulfonic acids (PFSAs) are a recalcitrant subclass of per- and polyfluoroalkyl substances (PFASs) linked to numerous negative health effects in humans. Scalable technologies that effectively destroy PFSAs will greatly reduce the future health and ecological impact of these "forever chemicals". Herein, we show that several PFSAs undergo facile mechanochemical destruction (MCD) in the presence of quartz sand (SiO₂). This process operates in the absence of solvent, at ambient temperature and pressure, generating a benign solid byproduct. Quantitative analysis of milled samples revealed high destruction efficiencies of 99.95% to 100% for five different PFSAs subjected to MCD conditions in the presence of SiO₂ only. Extensive nontargeted analysis showed that, during degradation, other PFASs form and are ultimately destroyed upon extended mechanochemical treatment. Direct polarization (DP) and cross-polarization (CP) solid-state nuclear magnetic resonance (SSNMR) spectroscopy showed abundant silicon-fluorine (Si-F) bond formation post-MCD, indicating that fluorine was secured in a stable reservoir. Collectively, these results identified the degradation profile for an environmentally sound and effective PFSA degradation process that is amenable to scale-up.

Review of influence of critical operation conditions on by-product/intermediate formation during thermal destruction of PFAS in solid/biosolids

Poly- and perfluoroalkyl substances (PFAS) are a large group of synthetic organofluorine compounds. Over 4700 PFAS compounds have been produced and used in our daily life since the 1940s. PFAS have received considerable interest because of their toxicity, environmental persistence, bioaccumulation and wide existence in the environment. Various treatment methods have been developed to overcome these issues. Thermal treatment such as combustion and pyrolysis/gasification have been employed to treat PFAS contaminated solids and soils. However, short-chain PFAS and/or volatile organic fluorine is produced and emitted via exhaust gas during the thermal treatment. Combustion can achieve complete mineralisation of PFAS at large scale operation using temperatures >1000 °C. Pyrolysis has been used in treatment of biosolids and has demonstrated that it could remove PFAS completely from the generated biochar by evaporation and degradation. Although pyrolysis partially degrades PFAS to short-chain fluorine containing organics in the syngas, it could not efficiently mineralise PFAS. Combustion of PFAS containing syngas at 1000 °C can achieve complete mineralisation of PFAS. Furthermore, the by-product of mineralisation, HF, should also be monitored due to its low regulated atmospheric discharge values. Alkali scrubbing is normally required to lower the HF concentration in the exhaust gas to acceptable discharge concentrations.

Interface hydrogen bonding dominated perfluorooctanoic acid (PFOA) accumulation by iron particles in drinking water pipes

Iron particle is one of the key factors inducing discoloration in drinking water distribution system (DWDS), but the mechanism of iron particles on the accumulation of trace organic pollutants in DWDS is not clear. Here, iron-based pipes from real DWDS were used to investigate the perfluorooctanoic acid (PFOA) accumulation mechanisms in DWDS. Results showed that old unlined pipes had a much higher accumulation capacity for PFOA than new pipes. Among the corrosion products in old pipes, Fe₂O₃ and Fe₃O₄ did not have obvious accumulation for PFOA, while FeOOH exhibited a strong accumulation effect for PFOA. Furthermore, the in-situ formed iron particles contributed more to PFOA accumulation than pre-formed iron particles. Interestingly, PFOA caused an increase in turbidity and particle size of in-situ formed iron particles. Mulliken charge of F-bonded Fe increased from +1.28 e to +1.30 e, which indicated that the oxidation state of Fe-center was strengthened by PFOA. When dissolved oxygen existed, a PFOA-FeOOH-O₂ linkage could form through COO-Fe coordination and O₂ interface adsorption, which enhanced cytotoxicity due to the generation of •OH radicals. These findings implied that interface hydrogen bonding dominated PFOA accumulation by iron particles in DWDS, which would increase the risks of discoloration.

Applications of crushing and grinding-based treatments for typical metal-containing solid wastes: Detoxification and resource recovery potentials

Metal-containing solid wastes can induce serious environmental pollution if managed improperly, but contain considerable resources. The detoxification and resource recoveries of these wastes are of both environmental and economic significances, being indispensable for circular economy. In the past decades, attempts have been made worldwide to treat these wastes. Crushing and grinding-based treatments have been increasingly applied, the operating apparatus and parameters of which depend on the waste type and treatment purpose. Based on the relevant studies, the applications of crushing and grinding on four major types of solid wastes, namely spent lithium-ion batteries (LIBs) cathode, waste printed circuit boards (WPCBs), incineration bottom ash (IBA), and incineration fly ash (IFA) are here systematically reviewed. These types of solid wastes are generated in increasing amounts, and have the potentials to release various organic and inorganic pollutants. Despite of the widely different texture, composition, and other physicochemical properties of the solid wastes, crushing and grinding have been demonstrated to be universally applicable. For each of the four wastes, the technical route that involving crushing and grinding is described with the advantages highlighted. The crushing and grinding serve either mainstream or auxiliary role in the processing of the solid wastes. This review summarizes and highlights the developments and future directions of crushing and grinding-based treatments.

Complete mechanochemical defluorination of perfluorooctanoic acid using Al2O3 and Al powders through matching electron-mediated reduction with decarboxylation

This work reports a mechanochemical (MC) method for complete defluorination of perfluorooctanoic acid (PFOA) by using Al and Al₂O₃ as milling agents. Both the Al/Al₂O₃ molar ratio ( [Formula: see text] ) and the pre-thermal treatment of Al₂O₃ strongly influenced the defluorination of PFOA. When commercial γ-Al₂O₃ was pre-treated at 1200 °C, the use of Al and heat-treated γ-Al₂O₃ with [Formula: see text] of 1: 1 led to PFOA defluorination of 100% after ball milling for 26 min at 350 rpm, being much higher than those (8.3%-58.1%) for using singlet milling agents or binary milling agents containing γ-Al₂O₃ pre-heated at temperatures lower than 700 °C. It was clarified that the carboxylate-mediated adsorption of PFOA on Al₂O₃ was essential for the MC decarboxylation as a degradation initiation step, and the in-situ generated electron on milled Al consequently caused the reductive dissociation of C-F bonds in the decarboxylation intermediate. A larger [Formula: see text] increased the in-situ electron generation rate (r_e), and a higher heat-treatment temperature decreased OH^-/H₂O adsorbed on Al₂O₃ to low the PFOA decarboxylation rate (r_dec). The r_e/r_dec ratio determined defluorination pathways, and the percentage of the defluorination of PFOA in its total degradation including the generation of any degradation intermediates increased linearly with increasing r_e/r_dec.

Horizontal planetary mechanochemical method for rapid and efficient remediation of high-concentration lindane-contaminated soils in an alkaline environment

Lindane is a persistent organic pollutant that has attracted worldwide attention because of its threat to human health and environmental security. A horizontal planetary mechanochemical method was developed for rapid and efficient degradation of lindane in soil in an alkaline environment. Under the condition of a very low reagent-to-soil ratio (R = 2%), ball-to-powder ratio (C_R = 6:1), rotation speed (r = 300 rpm) and high soil single treatment capacity (S_C = 60 g), the lindane in four typical soils (~ 100 mg/kg) can be degraded up to 96.30% in 10 min. This method can also remediate high-concentration lindane-contaminated soil (833 ± 26 mg/kg). The experimental results and theoretical calculations proved that the stepwise dechlorination and final carbonization of lindane in soil are mainly attributed to the combined action of mechanical energy and alkalinity. The bimolecular elimination (E2) reaction was the first step of lindane destruction. Subsequently, the unimolecular elimination (E1) reaction tended to occur with the weakening of alkalinity. Then, benzene was obtained through stepwise hydrogenolysis reaction. The last was the generation of carbon substances by fragmentation or condensation of benzene rings. This work proposes a practical remediation technology for organic contaminated soil and improves the understanding of the degradation pathways of lindane in soil in alkali-assisted mechanochemical system.

Functional group modified 1D interpenetrated metal-organic frameworks on perfluorooctanoic acid adsorption: Experimental and theoretical calculation study

Functional groups modified metal-organic frameworks (MOFs) was synthesized via a pre-tailor method and served as an adsorbent for perfluorooctanoic acid (PFOA) removal. The material was characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction and N₂ sorption-desorption. Monte Carlo simulation and molecular dynamics are derived to predict the possible molecular packing and adsorption mechanism. The Hirshfeld surface with reduced density gradient analysis demonstrates that PFOA is adsorbed on MOF-X mainly affected by van der Waals interactions and steric effects. Adsorption kinetics and isotherms were investigated on the basis of a static experiment. The pseudo-second-order kinetic model and Langmuir isotherm were fitted well to characterize adsorption process. Hereinto, amino-modified MOFs reached the highest adsorption efficiency and the maximum capacity was 185.6 mg/g. Combing the experimental data with theoretical simulation, results indicated that functional group modification is an effective approach to alter the crystal structure and then affect the adsorptive properties of MOFs.

Efficient photodegradation of PFOA using spherical BiOBr modified TiO2 via hole-remained oxidation mechanism

Photo-induced holes (h⁺) oxidation is an efficient approach for perfluorooctanoic acid (PFOA; C₇F₁₅COOH) removal. To maintain a high amount of h⁺ on the surface of photocatalysts participating in the PFOA photodegradation could be a critical issue. Herein, a highly efficient spherical BiOBr-modified nano-TiO₂ (P25) was synthesised and used for PFOA photodegradation through direct oxidation with h⁺. A high number of h⁺ could be generated and remain on the surface of P25/BiOBr due to the appropriate position of the conduction band (CB) and valence band (VB) levels between P25 and BiOBr. Meanwhile, PFOA molecules were coordinated to the P25/BiOBr's surface via unidentate binding, being directly activated and oxidised by h⁺, resulting in a decomposition yield of 99.5% (100 mg/L) under simulated solar light irradiation within 100 min, at the initial pH condition (3.5). A stepwise photodegradation pathway was proposed due to the significant intermediates detected as the short-chain perfluorinated carboxylic acids (C2-C7). Reactive oxygen species (ROS) generation, scavenging and trapping analysis indicated that the direct oxidation on h⁺ followed PFOA degradation. In a real aqueous environment of Tangxun lake (adjusted pH 3.5), stable common anions and natural organic matter (NOM) would restrain the PFOA photodegradation. However, adding 10 mg/L of NO₃^- or HA could reduce the inhibition effect of PFOA photodegradation. These findings gave an alternative strategy to drive an h⁺ directly oxidation to treat PFOA contaminated water bodies.

Emerging technologies for PFOS/PFOA degradation and removal: A review

Perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) are highly recalcitrant anthropogenic chemicals that are ubiquitously present in the environment and are harmful to humans. Typical water and wastewater treatment processes (coagulation, flocculation, sedimentation, and filtration) are proven to be largely ineffective, while adsorption with granular activated carbon (GAC) has been the chief option to capture them from aqueous sources followed by incineration. However, this process is time-consuming, and produces additional solid waste and air pollution. Treatment methods for PFOS and PFOA generally follow two routes: (1) removal from source and reduce the risk; (2) degradation. Emerging technologies focusing on degradation are critically reviewed in this contribution. Various processes such as bioremediation, electrocoagulation, foam fractionation, sonolysis, photocatalysis, mechanochemical, electrochemical degradation, beams of electron and plasma have been developed and studied in the past decade to address PFAS crisis. The underlying mechanisms of these PFAS degradation methods have been categorized. Two main challenges have been identified, namely complexity in large scale operation and the release of toxic byproducts. Based on the literature survey, we have provided a strength-weakness-opportunity-threat (SWOT) analysis and quantitative rating on their efficiency, environmental impact and technology readiness.

Mechanochemical destruction and mineralization of solid-phase hexabromocyclododecane assisted by microscale zero-valent aluminum

Hexabromocyclododecane (HBCD) has been listed in Annex A of the Stockholm Convention as a persistent and bio-accumulative chemical. While HBCD is often present in the solid form for its low solubility, cost-effective technologies have been lacking for the degradation of solid-phase HBCD. In this work, mechanochemical (MC) destruction of high-energy ball milling was employed for direct destruction of solid-phase HBCD, where a strong reducer, microscale zero-valent aluminum (mZVAl), was used as the co-milling agent. The new mZVAl-assisted MC process achieved complete debromination and mineralization of HBCD within 3 h milling. The optimal operating parameters were determined, including the milling atmosphere, the milling speed, the mZVAl-to-HBCD molar ratio, and the ball-to-mZVAl mass ratio. Fourier transform infrared spectrometry and Raman analyses revealed that the organic structures of HBCD were destroyed and organic bromine was completely converted into inorganic bromide, accompanied by the generation of amorphous and graphite carbon. Analysis of the milled samples by GC-MS demonstrated the absence of obvious organic matter after MC treatment, also indicating the complete degradation and conversion of HBCD to inorganic compounds. Further X-ray photoelectron spectroscopic analysis indicates that the fresh surface of mZVAl was generated upon the MC treatment, and Al(0) served as a strong reducing agent (e-donor) for reductive debromination and destruction of the carbon skeleton. The mZVAl-assisted MC milling appears promising as a non-combustion approach for effective destruction and carbonization/mineralization of solid-phase HBCD or potentially other persistent organic pollutants.

Developing innovative treatment technologies for PFAS-containing wastes

The release of persistent per- and polyfluoroalkyl substances (PFAS) into the environment is a major concern for the United States Environmental Protection Agency (U.S. EPA). To complement its ongoing research efforts addressing PFAS contamination, the U.S. EPA's Office of Research and Development (ORD) commissioned the PFAS Innovative Treatment Team (PITT) to provide new perspectives on treatment and disposal of high priority PFAS-containing wastes. During its six-month tenure, the team was charged with identifying and developing promising solutions to destroy PFAS. The PITT examined emerging technologies for PFAS waste treatment and selected four technologies for further investigation. These technologies included mechanochemical treatment, electrochemical oxidation, gasification and pyrolysis, and supercritical water oxidation. This paper highlights these four technologies and discusses their prospects and the development needed before potentially becoming available solutions to address PFAS-contaminated waste.Implications: This paper examines four novel, non-combustion technologies or applications for the treatment of persistent per- and polyfluoroalkyl substances (PFAS) wastes. These technologies are introduced to the reader along with their current state of development and areas for further development. This information will be useful for developers, policy makers, and facility managers that are facing increasing issues with disposal of PFAS wastes.

Application of Hydrothermal Alkaline Treatment for Destruction of Per- and Polyfluoroalkyl Substances in Contaminated Groundwater and Soil

Hydrothermal alkaline treatment (HALT) can effectively degrade per- and polyfluoroalkyl substances (PFASs) present in aqueous film-forming foam (AFFF). However, information is lacking regarding the treatment of PFASs in actual groundwater and soil from AFFF-impacted sites, especially for complex soil matrices. Given the lack of studies on direct soil treatment for PFAS destruction, we herein applied HALT to two groundwater samples and three soil samples from AFFF-impacted sites and characterized the destruction of PFASs using high-resolution mass spectrometry. Results showed that the 148 PFASs identified in all collected field samples, including 10 cationic, 98 anionic, and 40 zwitterionic PFASs, were mostly degraded to nondetectable levels within 90 min when treated with 5 M NaOH at 350 °C. The near-complete defluorination, as evidenced by fluoride release measurements, confirmed the complete destruction of PFASs. While many structures, including perfluoroalkyl carboxylic acids and polyfluorinated substances, were readily degraded, perfluoroalkyl sulfonates (PFSAs, C_nF_2n+1-SO₃^-), most notably with short chain lengths (n = 3-5), were more recalcitrant. Rates of PFSA destruction in groundwater samples were similar to those measured in laboratory water solutions, but reactions in soil were slow, presumably due to base-neutralizing properties of the soil. Further, the degradation of PFASs in groundwaters and soils was found to be a function of reaction temperature, NaOH concentration, and reaction time. These findings have important implications for the remediation of AFFF-impacted sites.

Degradation of tris(1-chloro-2-propanyl) phosphate by the synergistic effect of persulfate and zero-valent iron during a mechanochemical process

This study revealed a dual pathway for the degradation of tris(1-chloro-2-propanyl) phosphate (TCPP) by zero-valent iron (ZVI) and persulfate as co-milling agents in a mechanochemical (MC) process. Persulfate was activated with ZVI to degrade TCPP in a planetary ball mill. After milling for 2 h, 96.5% of the TCPP was degraded with the release of 63.16, 50.39, and 42.01% of the Cl^-, SO₄^2-, and PO₄^3-, respectively. In the first degradation pathway, persulfate was activated with ZVI to produce hydroxyl (·OH) radicals, and ZVI is oxidized to Fe(II) and Fe(III). A substitution reaction occurred as a result of the attack of ·OH on the P-O-C bonds, leading to the successive breakage of the three P-O-C bonds in TCPP to produce PO₄^3-. In the second pathway, a C-Cl bond in part of the TCPP molecule was oxidized by SO₄·^- to carbonyl and carboxyl groups. The P-O-C bonds continued to react with ·OH to produce PO₄^3-. Finally, the intermediate organochloride products were further reductively dechlorinated by ZVI. However, the synergistic effect of the oxidation (·OH and SO₄·^-) and the reduction reaction (ZVI) did not completely degrade TCPP to CO₂, resulting in a low mineralization rate (35.87%). Moreover, the intermediate products still showed the toxicities in LD₅₀ and developmental toxicant. In addition, the method was applied for the degradation of TCPP in soil, and high degradations (> 83.83%) were achieved in different types of soils.

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 (h_vb⁺) 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 h_vb⁺. The hydrophobic sites would accelerate the mass transfer of O₃ and PFOA, enhance O₃'s single electron reduction with e_cb^- to generate hydroxyl radicals (•OH) and reduce the recombination of h_vb⁺-e_cb^-. Under the joint function of h_vb⁺, 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.

Thermal decomposition of perfluorinated carboxylic acids: Kinetic model and theoretical requirements for PFAS incineration

Thermal decomposition of high-fluorine content PFAS streams for the disposal of old generations of concentrates of firefighting foams, exhausted ion-exchanged resins and granular activated carbon, constitutes the preferred method for destruction of these materials. This contribution studies the thermal transformation of perfluoropentanoic acid (C₄F₉C(O)OH, PFPA), as a model PFAS species, in gas-phase reactions over broad ranges of temperature and residence time, which characterise incinerators and cement kilns. Our focus is only on gas-phase reactions, to formulate a gas-phase submodel that, in future, could be used in comprehensive simulation of thermal destruction of PFAS; such comprehensive models will need to comprise fluorine mineralisation on flyash and in clinker material. Our submodel consists of 56 reactions and 45 species, and includes new pathways that cover the initial decomposition channels of PFPA, including those that lead to the formation of the n-C₄F₉ radical, the abstraction of hydroxyl H by O/H radicals, the fragmentation of the n-C₄F₉ radical, reactions between HF and perfluoropentanoic acid, as well as between HF and heptafluorobutanoyl fluoride (C₃F₇COF), and the cyclisation reactions. The model illustrates the formation of a wide spectrum of small C_nF_m and C_nHF_m compounds in the temperature window of 800-1500 K, 2 and 25 s residence time in a plug flow reactor, providing theoretical estimates for the operating conditions of PFAS thermal destruction systems. The initiation reactions involve the loss of HF and formation of the transition α-lactone species that converts to C₃F₇COF, with C₄F₉C(O)OH completely decomposed at 1020 K for 2 s residence time. At 1500 K, we predict the emission of ꞉CF₂ (biradical difluorocarbene), HF, CO₂, CO, CF₄, C₂F₆, and C₂F₄, but at < 1400 K, we note the formation of 1H-nonafluorobutane (C₄HF₉), phosgene (COF₂), and heptafluorobutanoyl fluoride (C₃F₇COF), with 1-C₄F₈, 2-C₄F₈ and C₃HF₇ persisting to 1500 K. We demonstrate that, the gas-phase pyrolysis processes by themselves convert PFAS to HF and short-chain fluorocarbons, with similar product distribution for short (2 s) and long (25 s) residence times, as long as the treatment temperature exceeds 1500 K. These residence times reflect those encountered in incinerators and cement kilns, respectively. Thermokinetic and mechanistic insights revealed herein shall assist to innovate PFAS thermal disposal technologies, and, from a fundamental perspective, to accelerate research progress in modelling of gas/solid reactions that mineralise PFAS-derived fluorine.

Thin interfacial film spontaneously produces hydrogen peroxide: mechanism and application for perfluorooctanoic acid degradation

We have unambiguously demonstrated spontaneous formation of hydrogen peroxide (H2O2) in thin film formats by evaporating almost all the water and its effective for perfluorooctanoic acid (PFOA) degradation without catalysts.

Improved fractal kinetic model to predict mechanochemical destruction rate of organic pollutants

Mechanochemical destruction of organic pollutants by high energy milling with inorganic reagents is considered a promising non-thermal technology to detoxify hazardous waste. However, due to complex nature of the physicochemical phenomena involved, pollutant destruction kinetics heavily depends on the used reagents and operating parameters, thus varying case by case. In the present work, a fractal model was validated as flexible tool to interpolate pollutant mechanochemical destruction data satisfactorily. In addition, such model was expanded to estimate the contributions of the inorganic reagent and the pollutant to the overall reaction rate. Specifically, the kinetic constant associated to mechanical activation of the co-milling reagent and that related to pollutant destruction reaction were calculated. Their values resulted to depend only on the specific compound, hence, the tabulated data could be used to predict the pollutant mechanochemical degradation rate for any kind of mixture.

Development of a hydroxyl group-mediated biosynthetic schwertmannite as a persulfate activator for efficient degradation of RhB and Cr(VI) removal

Recently, sulfate radical-based advanced oxidation processes (SR-AOPs) have shown broad potential for restoring the water environment. However, the application of SR-AOPs to simultaneously remove organic pollutants and Cr(VI) has rarely been reported. Herein, we developed a modified schwertmannite (Sch-PVA) synthesized via the mediation of Acidithiobacillus ferrooxidans in the introduction of polyvinyl alcohol (PVA). This modification significantly changed the morphology and structure of the schwertmannite (Sch). The specific surface area and the density of functional sites also increased. Sch-PVA significantly increased the persulfate (PDS) activation efficiency. Even in 100 mg L^-1 rhodamine B (RhB) conditions, 96.3% of RhB was eliminated by 0.5 g L^-1Sch-PVA and 6 mM PDS in 120 min. Moreover, excellent performance was exhibited over a wide pH range. The dissolution of the passivation layer facilitated the exposure of new adsorption and reduction sites, thereby enhancing the simultaneous removal of RhB and Cr(VI). Quenching experiments and electron spin resonance (ESR) measurements verified that sulfate and hydroxyl radicals were generated. The hydroxyl groups on the Sch-PVA surface played a key role in the bonding with and the activation of PDS. In conclusion, Sch-PVA provides new insights into the catalyst application for simultaneous removal of organic pollutants and Cr(VI).

Electrochemical adsorption of perfluorooctanoic acid on a novel reduced graphene oxide aerogel loaded with Cu nanoparticles and fluorine

Perfluorooctanoic acid (PFOA) is widely concerned because its serious toxicity to the environment and ecosystems. In order to effectively and conveniently remove PFOA from aqueous solutions, reduced graphene oxide aerogel modified by Cu nanoparticles and fluorine (Cu/F-rGA) was prepared by the microbubble template method as an electrode in electrosorption. The removal capacity of Cu/F-rGA electrode to PFOA was 489% and 45.9% higher at + 0.8 V than that of open circuit and unmodified electrode, respectively. These significant improvements can be attributed to the advantages of Cu/F-rGA in ligand exchange reaction and electrostatic attraction under voltage assistance. The regeneration of Cu/F-rGA electrode maintained 75.51% capacity after 10 times electrosorption-desorption by applying reverse voltage. These properties provided potential for the reuse and application of Cu/F-rGA electrode. The electrosorption isotherm and model results showed that PFOA tended to be parallel to the adsorption site at low temperature and perpendicular at high temperature. The number of PFOA molecules connected to each adsorption site was 0.72-1.76, and the number of adsorption layers of PFOA on the electrode was between 1.46 and 2.87. Findings from this study provide a green and effective strategy to remove PFOA from aqueous solutions with low energy consumption.

Direct and efficient reduction of perfluorooctanoic acid using bimetallic catalyst supported on carbon

A variety of metal elements have exhibited strong reductive and dehalogenative capabilities for the removal of persistent organic pollutants, owing to electron transfer or electron-hole activation through various methods. Herein, a bimetallic C_Ni-Al₂O₃ structure (AlC_Ni) was successfully synthesized to simultaneously function as sorbent and catalyst in the reduction of perfluoroalkyl carboxylic acids (PFOA) polluted wastewater. Using a reaction period of 3 h, 98% of PFOA was removed by AlC_Ni through a mechanochemical stirring method and 70.43% of fluorine ions was released from PFOA anchored onto the surface of AlC_Ni. Both thermocatalysis and photocatalysis technologies were incorporated and compared when utilized in tandem with AlC_Ni to mitigate the PFOA. In addition, peroxymonosulfate (PMS) and sodium sulfite (Na₂SO₃) were also integrated into experiments, separately, as a strong oxidant and reductant to improve the degradation effect of PFOA. However, the degradation efficiency of both were lower than that of AlC_Ni, even when assisted by elevated temperatures and ultraviolet irradiation. The feasibility of employing AlC_Ni for PFOA degradation was further investigated at various temperature and pH conditions. The data obtained from HPLC-MS/MS, TOC, and IC with multiple characterizations of AlC_Ni/PFOA, proposed the predominant degradation pathways comprising adsorption, defluorination-hydroxylation, and decarboxylation. This study provides a valuable remediation method without utilizing chemical agents and special activation for PFOA by AlC_Ni, which can be suitable for large-scale sewage treatment applications.

Mechanochemical remediation of perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) amended sand and aqueous film-forming foam (AFFF) impacted soil by planetary ball milling

Per- and polyfluoroalkyl substances (PFAS) are manmade, fluorinated organic chemicals which have been identified as persistent organic pollutants. PFAS have surface active properties that have made them suitable for applications in oil- and water-resistant products, as well as many firefighting foams. No on-site remediation strategies exist to treat PFAS impacted soils. Mechanochemical remediation of PFOS- and PFOA-amended sand via a planetary ball mill was studied. The effect of sand mass, KOH as a co-milling reagent, and water saturation on the degradation of PFOA and PFOS was evaluated. By 4 h of milling concentrations were reduced by up to 98% for PFOS-amended dry sand and 99% for PFOA-amended dry sand without the addition of a co-milling reagent. Water saturation was determined to be a significant hindrance on the mechanochemical destruction of PFOS and PFOA. A maximum of 89% of fluoride was recovered from PFOS-amended sand when KOH was used as a co-milling reagent. It is hypothesized that reactive particles generated from the fracture of sand grains react with PFAS molecules to initiate destruction, which can result in full defluorination. Milling experiments were also conducted on soils from a Canadian firefighting training area (FFTA), demonstrating that PFOS concentrations can be reduced by up to 96% in site soils. For the first time, ball milling for the remediation of PFAS in environmental media has been demonstrated using amended sand and legacy soils from a FFTA.

Copper Nanoparticle Loading and F Doping of Graphene Aerogel Enhance Its Adsorption of Aqueous Perfluorooctanoic Acid

Perfluorooctanoic acid (PFOA) persists in the environment for a long time due to its stable physical and chemical properties, and it is harmful to the environment and biological system. In order to effectively remove PFOA from aqueous solution, Cu nanoparticles and fluorine-modified graphene aerogel (Cu/F-rGA) were fabricated by the microbubble template method. Compared with unmodified aerogels (rGA), the adsorption rate of PFOA on Cu/F-rGA was enhanced 2.68-fold. These significant improvements were assumed to benefit from the ligand exchange reaction and hydrophobic and F-F interactions. The regeneration of Cu/F-rGA maintained 73.26% with ethanol as the desorption solvent after 10 times adsorption-desorption. The fitting results of the statistical physics model showed that PFOA tended to be parallel to the adsorption site at low temperature and perpendicular at high temperature. The number of PFOA molecules connected to each adsorption site was 0.53 to 1.41, and the number of adsorption layers of PFOA on the Cu/F-rGA was between 1.63 and 2.51. Compared with the response surface methodology and artificial neural network, an adaptive neuro-fuzzy inference system had more accurate analysis and prediction results. These results provide an effective and alternative strategy to remove PFOA from aqueous solution with environment-friendly consumption.

Hydrothermal Alkaline Treatment for Destruction of Per- and Polyfluoroalkyl Substances in Aqueous Film-Forming Foam

The widespread use of aqueous film-forming foam (AFFF) for firefighting activities (e.g., fire training to extinguish fuel-based fires at aircraft facilities) has led to extensive groundwater and soil contamination by per- and polyfluoroalkyl substances (PFASs) that are highly recalcitrant to destruction using conventional treatment technologies. This study reports on the hydrothermal alkaline treatment of diverse PFASs present in AFFFs. Quantitative and semiquantitative high-resolution mass spectrometry analyses of PFASs demonstrate a rapid degradation of all 109 PFASs identified in two AFFFs (sulfonate- and fluorotelomer-based formulations) in water amended with an alkali (e.g., 1-5 M NaOH) at near-critical temperature and pressure (350 °C, 16.5 MPa). This includes per- and polyfluoroalkyl acids and a range of acid precursors. Most PFASs were degraded to nondetectable levels within 15 min, and the most recalcitrant perfluoroalkyl sulfonates were degraded within 30 min when treated with 5 M NaOH. ¹⁹F NMR spectroscopic analysis and fluoride ion analysis confirm the near-complete defluorination of PFASs in both dilute and concentrated AFFF mixtures, and no stable volatile organofluorine species were detected in reactor headspace gases by the gas chromatography-mass spectrometry analysis. These findings indicate a significant potential for application of hydrothermal treatment technologies to manage PFAS waste streams, including on-site treatment of unused AFFF chemical stockpiles, investigation-derived wastes, and concentrated source zone materials.

Decomposition of highly persistent perfluorooctanoic acid by hollow Bi/BiOI1-xFx: Synergistic effects of surface plasmon resonance and modified band structures

Perfluorooctanoic acid (PFOA) is highly stable due to the strong CF bond and extremely difficult to be removed by conventional photocatalysts. In this study, Bi doped BiOI_1-xF_x solid solutions with hollow microsphere structure were prepared through a facile one-step hydrothermal method. Compared with pure BiOI and BiOF, the band gap of the Bi/BiOI_1-xF_x solid solutions was significantly reduced, thus promoting the visible light absorbance. The cavity structure of the BiOI_1-xF_x solid solutions enhanced the surface areas and active sites for reaction. The local electromagnetic field dominated by surface plasmon resonance (SPR) effect of Bi metal on the surface favored the separation of the photoinduced charge pairs. As a consequence, Bi/BiOI_0.8F_0.2 (x = 0.20, the doping amount of fluorine was 20 %) composite displayed the best photocatalytic performance for decomposing PFOA, and 40 mg/L PFOA could be removed within 2 h illumination. The degradation rate constant (k = 0.0375 min^-1) of PFOA by Bi/BiOI_0.8F_0.2 was about tenfold of that by pure BiOI and BiOF. Superoxide radical (·O₂-) predominated in the degradation of PFOA by Bi/BiOI_0.8F_0.2, and the possible degradation pathway of PFOA by Bi/BiOI_0.8F_0.2 was proposed. This work provides a highly efficient catalyst for the practical application in removal of highly persistent PFOA.

Reductive Defluorination and Mechanochemical Decomposition of Per- and Polyfluoroalkyl Substances (PFASs): From Present Knowledge to Future Remediation Concepts

Over the past two decades, per- and polyfluoroalkyl substances (PFASs) have emerged as worldwide environmental contaminants, calling out for sophisticated treatment, decomposition and remediation strategies. In order to mineralize PFAS pollutants, the incineration of contaminated material is a state-of-the-art process, but more cost-effective and sustainable technologies are inevitable for the future. Within this review, various methods for the reductive defluorination of PFASs were inspected. In addition to this, the role of mechanochemistry is highlighted with regard to its major potential in reductive defluorination reactions and degradation of pollutants. In order to get a comprehensive understanding of the involved reactions, their mechanistic pathways are pointed out. Comparisons between existing PFAS decomposition reactions and reductive approaches are discussed in detail, regarding their applicability in possible remediation processes. This article provides a solid overview of the most recent research methods and offers guidelines for future research directions.

Mechanochemical treatment with CaO-activated PDS of HCB contaminated soils

Mechanochemical methods with co-milling reagents have been widely used to degrade organic pollutants. In this study, calcium oxide and persulfate were employed as co-milling reagents in a mechanochemical process that showed highly effective degradation of hexachlorobenzene in contaminated soil. The influences of soil particle size and organic matter content were also investigated. The interaction between different factors was analyzed by response surface methodology, and a multi-variate regression equation was obtained relating the soil-to-oxidant mass ratio, rotation speed and organic matter content. The existence of SO₄^- and OH during the mechanochemical reaction was proved by the indirect detection of benzoquinone and p-hydroxybenzoic acid for the first time, providing a new method for testing free radicals in solid-phase reactions. Finally, a possible activation mechanism and hexachlorobenzene degradation pathway were proposed. This study successfully presents a mild degradation method in the field of hexachlorobenzene contaminated site remediation.

Mechanochemical degradation of perfluorohexane sulfonate: Synergistic effect of ferrate(VI) and zero-valent iron

Perfluorohexane sulfonate (PFHxS) has been newly recommended to be added into the Stockholm Convention on persistent organic pollutants (POPs). As one of the major perfluoroalkyl pollutants, its long half-time in human serum and neurotoxicity are cause for significant concern. Although mechanochemical degradation has been evaluated as a promising ecofriendly technology to treat pollutants, the extraordinary stability of poly- and perfluoroalkyl substances (PFASs) raises harsh requirements for co-milling reagents. In the present study, zero-valent iron (ZVI) and ferrate(VI) were for the first time used as the co-milling reagents to degrade PFHxS. When ZVI and ferrate(VI) were used alone, both the degradation and defluorination efficiencies were low. However, after milling at the optimum ratio (ferrate(VI):ZVI = 1:2) for 4 h, the synergistic effect of ZVI and ferrate(VI) resulted in almost complete degradation (100%) and defluorination (95%). Two points can account for this excellent performance: (1) the mechanochemical energy input in the system initiates and prominently promotes related reactions; and (2) the active species generated from the reactions among ZVI, ferrate(VI) and other high-valent iron species will accelerate the process of electron transfer. The sulfonate group comprises the favorable attack sites, as corroborated by both the identified intermediates and quantum chemical calculations. The homolysis of the C-S bond is not only the triggering step, but also the rate-limiting step. In summary, the present work confirms the feasibility and underlying mechanism of the ZVI-ferrate(VI) co-milling system to defluorinate PFHxS, which might be a promising technology to treat PFASs in solid wastes.

Enhanced adsorption of perfluorooctanoic acid (PFOA) from water by granular activated carbon supported magnetite nanoparticles

A new composite material (Fe₃O₄@GAC, Fe₃O₄ nanoparticles loaded on a commercial granular activated carbon (GAC)) was prepared through a facile hydrothermal process at controlled Fe²⁺:Fe³⁺ molar ratios in air. Fe₃O₄@GAC was thoroughly characterized and tested for adsorption of perfluorooctanoic acid (PFOA) in water. Fe₃O₄@GAC(2:1), prepared at an Fe²⁺:Fe³⁺ molar ratio of 2:1, showed the best PFOA removal and offered 28.8% higher adsorption capacity than the parent GAC at final pH 4.0. The enhanced adsorption of PFOA was attributed to concurrent hydrophobic, electrostatic and complexation interactions between PFOA, GAC and Fe₃O₄. GAC in the composite played an important role for PFOA adsorption. The presence of Ca²⁺ ions (10 mM) at final pH 5.0-10.0 more than doubled the PFOA equilibrium uptake of PFOA by Fe₃O₄@GAC(2:1) due to the calcium bridging effect between PFOA and the Si-OH or Fe-OH groups in Fe₃O₄@GAC(2:1), and because of the Ca²⁺-modification induced formation of PFOA hemi-micelles on the surface or in the relatively large pores (2.27 nm) of Fe₃O₄@GAC(2:1). Fe₃O₄@GAC(2:1) was amenable to efficient regeneration using a mixture of NaOH solution and methanol. Fe₃O₄@GAC holds the potential to be used as a simple and low-cost adsorbent for enhanced adsorption of PFOA, especially in waters of high hardness and alkalinity.

Insights into electrochemical decomposition mechanism of lipopolysaccharide using TiO2 nanotubes arrays electrode

Electrochemical decomposition of lipopolysaccharide (LPS) was firstly investigated over titania nanotubes (TNTs) arrays electrode. The TNTs layer of this electrode consisted of numerous tubular structures which arranged tightly, and the average diameter of each nanotube is 100 ± 5 nm. The degradation of LPS and polysaccharides followed pseudo-first-order kinetics. The optimal LPS removal ratio was nearly 80 %. The endotoxin toxicity of LPS steadily decreased during the electrolysis process. The acute toxicity of the intermediates increased suddenly at the beginning of electrochemical degradation process (< 5 min), then maintained high inhibition ratio (> 95 %) for about 150 min, and decreased significantly (< 10 %) after electrolysis for 240 min. After 20 min of electrolysis, LPS with molecular weight of 116,854 Da was transformed into small molecular compounds with molecular weights of 59,312 - 12,209 Da. Possible degradation and detoxification mechanisms of LPS including electric-field-force-driving accumulation, adsorption and direct electron transfer on TNTs arrays electrode, and •OH oxidation were proposed. This study underscores that electrochemical technique can be applied to eliminate and decrease the toxicity of LPS from contaminated water.

Mechanochemical degradation of brominated flame retardants in waste printed circuit boards by Ball Milling

Degradation of brominated flame retardants (BFRs) in waste printed circuit boards (WPCBs) occurred due to mechanical force during the crushing process. In this study, a planetary ball-milling simulation experiment was designed to explore the mechanochemical debromination process of BFRs in WPCBs. The results showed that CaO had a better debromination performance than MgO and the mixture of Fe + SiO₂, and high revolution speed and low mass ratio of WPCBs to CaO promoted the degradation of BFRs. After milling for 1 h, the particle size distribution was stable while the debromination efficiency increased with the increase of milling time. Ball milling promoted the migration of bromine from the inside to the new surface of WPCBs powder, and submicron particles adhered to the micron size aggregates. The polybrominated diphenyl ethers (PBDEs) detection showed that the concentrations of most PBDE congeners decreased with the increase of milling time, and a possible degradation pathway was proposed according to the experimental results. All the results provided new data for the mechanism of degradation of BFRs in WPCBs during the mechanical crushing process.

Facilely synthesized cobalt doped hydroxyapatite as hydroxyl promoted peroxymonosulfate activator for degradation of Rhodamine B

Hydroxyapatite (HAP) is a promising supporter of catalyst due to its potential in immobilizing metals stably. HAP supported cobalt-based catalyst (Co-HAP) was synthesized via a facile ion exchange-calcination method to reduce the Co leaching. The synthesized Co-HAP was characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscope (TEM), Brunauer-Emmett-Teller (BET) analysis and X-ray photoelectron spectroscopy (XPS). Cobalt ions were incorporated into HAP structure and Co₃O₄ on HAP surface. Co-HAP showed satisfactory performance in peroxymonosulfate (PMS) activation for eliminating Rhodamine B (RhB) in aqueous solution. Co-HAP even revealed a better activity than that of CoFe₂O₄. •OH, SO₄^•- and ¹O₂ were all involved in RhB degradation and ¹O₂ played a leading role. High content of surface oxygen groups could be found on Co-HAP after RhB degradation, which might be resulted from the high amounts of hydroxyl groups. The presence of hydroxyl groups performed the co-catalytic activity of PMS activation in Co-HAP/PMS system.

TiO2 quantum dots loaded sulfonated graphene aerogel for effective adsorption-photocatalysis of PFOA

With the pollution of perfluoroalkyl substances (PFASs) became increasingly serious, the researches focused on removal of PFASs by adsorption-photocatalysis method has attracted considerable attention. To make the catalyst TiO₂ disperse uniformly as quantum dots onto hydrophobic surface which was liable to attract perfluorooctanoic acid (PFOA), the surfactant sodium dodecyl sulfate (SDS) were used in this work, which not only connected the hydrophilic TiCl₃ to the hydrophobic sulfonated graphene (SG) nanosheets, but also behaved as the molecular template for controlled nucleation and growth of the nanostructured TiO₂. After 3D SG-TiO₂ QD nanosheets were fabricated, a series of 3D SG-TiO₂ QD aerogels were self-assembled by ice-template. TiO₂ uniformly distributed on the surface of SG aerogel at QD size level (2-3 nm) and the size of TiO₂ could be effectively regulated by concentration of SDS. Compared with aggregated TiO₂ material, 3D SG-TiO₂ QD aerogels owned higher adsorption and photocatalytic performance. Benefiting from the hydrophobic surface of 3D SG as well as dispersed TiO₂ QDs, 3D SG-TiO₂ QD could enrich PFOA instantaneously (0.0381/s) and photocatalytic decomposed them effectively (1.898 E^-4/s). PFOA degradation by hole and hydroxyl radicals proceeded via a stepwise mechanism. The column made of 3D SG-TiO₂ QD could remove PFOA persistently in cycles of permeation. 3D SG-TiO₂ QD possessed powerful adsorption-photocatalytic decomposition capability of PFOA and steady reusability performance. The present work highlights the individual roles and synergistic effect of TiO₂ QD and 3D SG for effectively removing PFOA.