Modulating hierarchically microporous biochar via molten alkali treatment for efficient adsorption removal of perfluorinated carboxylic acids from wastewater

Synergistic adsorption and photocatalytic degradation of perfluorooctanoic acid in aqueous solution by a regenerable biochar-titania nanotube composite

Perfluorooctanoic acid (PFOA), a recalcitrant perfluoroalkyl substance, presents escalating challenges for aquatic decontamination due to its extreme persistence and bioaccumulation. A biochar-titania nanotube (TNTs@biochar) combining the advantages of biochar and TNTs was synthesized for the first time via an alkaline hydrothermal approach and explored for the adsorption and photodegradation of PFOA in aqueous solution. Titania nanotubes interacted with biochar to form TNTs@biochar. The optimal composite was obtained at a biochar : TiO2 mass ratio of 1 : 1 and a calcination temperature of 550 °C. The composite efficiently adsorbed ∼99% of PFOA through hydrophobic and anion-π interactions and hydrogen bonding, concentrating PFOA on photoactive sites. The incorporation of biochar with TNTs enhanced light absorption in the 200-700 nm range, lowered the band gap energy to 3.10 eV, improved the formation rate and separation efficiency of e--h+ pairs, and enhanced interfacial charge transfer, resulting in promoted photocatalytic activity. The degradation of pre-concentrated PFOA on TNTs@biochar reached up to 99%. The photodegradation also regenerated the composite, allowing for four successive adsorption-photodegradation cycles. Hydroxyl radical and h+-driven oxidation played a paramount part, leading to decarboxylation and C-F bond cleavage. The byproducts of the photodegradation demonstrated lower acute and chronic toxicity compared with PFOA. The composite exhibits synergistic adsorption and photocatalytic activity as well as offers efficiently and economically scalable solutions for PFOA-laden water remediation.

Functionalized biochar for the removal of poly- and perfluoroalkyl substances in aqueous media

Biochar has gained attention as a promising adsorbent for removing various environmental pollutants due to its availability, cost-effectiveness, eco-friendly nature, and high adsorption capacity. This review focuses on using biochar to remove poly- and perfluoroalkyl substances (PFAS), emerging contaminants that pose significant environmental and health risks due to their toxicity, persistence, and bioaccumulation potential. The classification of biochar and using pristine and functionalized biochar for pollutant removal are addressed, along with an overview of the various functionalization techniques employed to enhance biochar's adsorption capacity. Different factors influencing the removal of poly- and perfluoroalkyl substances (PFAS), such as pH, the molecular chain length of PFAS, and biochar characteristics like pyrolysis temperature, particle size, and dosage, are investigated. Long-chain PFAS, such as perfluoro octane sulfonate (PFOS) and perfluorooctanoic acid (PFOA), are more effectively adsorbed than short-chain PFAS, with competitive sorption effects observed in mixed-solution environments. A decrease in pH, smaller biochar particle sizes, and optimized pyrolysis temperatures have been found to enhance biochar's sorption capacity. Furthermore, biochar demonstrates higher efficiency in single-solution systems compared to mixed solutions when removing PFAS.

Mechanistic insights into adsorption-desorption of PFOA on biochars: Effects of biomass feedstock and pyrolysis temperature, and implication of desorption hysteresis

Adsorptive removal of the emerging organic pollutant perfluorooctanoic acid (PFOA) from contaminated water using biochar is a promising cost-effective approach. To determine the stability of PFOA adsorption on biochar, the thermodynamic analysis of the adsorption-desorption behavior is essential. This study comprehensively investigated the adsorption and desorption of PFOA on biochars derived from maple sawdust, peanut shells and corn stalks, pyrolyzed at peak temperatures of 400, 600 and 800 °C. The findings indicated that the micropore volume of the biochars was key to PFOA adsorption, with peanut shell biochar produced at 800 °C showing the highest adsorption capacity of 16.75 mg/g, attributed to its larger micropore volume (0.22 m3/g). Thermodynamic analysis showed that the negative values of ∆G0 of PFOA adsorption ranged from -2.24 to -5.38 kJ/mol, confirmed that the process was spontaneous and involved physical pore-filling. However, the close similarity between the adsorption and desorption isotherms, coupled with a low hysteresis coefficient, clarified that the PFOA adsorption was unstable and prone to desorption. The thermodynamic insights from this study highlighted that lignin-rich biochar produced at high temperature with high micropore content was very favorable for the effective adsorptive removal of PFOA, while the long-term adsorption stability should not be overlooked in the remediation applications.

Enhanced adsorption of aqueous perfluorooctanoic acid on iron-functionalized biochar: elucidating the roles of inner-sphere complexation

Perfluorooctanoic acid (PFOA) is ubiquitously detected in various water bodies, which raises the urgent need for developing effective and economic remediation methods in response to its health risks. The adsorptive removal of PFOA by biochar (BC) is regarded as a simple, effective, and economical technique. However, engineered BCs, including FeCl3-activated BC, for PFOA removal and adsorption mechanisms have been ill-studied. In this study, a FeCl3-activated dairy manure-derived biochar (Fe@MBC) was prepared via one-step pyrolysis/activation, and its properties and adsorption characteristics were compared with a pristine manure-derived biochar (P-MBC). The FeCl3 activation largely increased the surface area of Fe@MBC and the deposition of FexOy minerals on surface of Fe@MBC while significantly elevating the surface roughness of Fe@MBC. The maximum adsorption capacity of Fe@MBC for PFOA (233 mg·g-1) was five times higher than that of P-MBC (46 mg·g-1). PFOA adsorption was favorable at low solution pH and was independent on ionic strength, which supported the major contribution by inner-sphere complexation rather than out-sphere complexation. This mechanism was further confirmed by the disappearance of FeO peak on Fourier transform infrared spectrum and the blue-shift of Fe binding energies on X-ray photoelectron Fe 2p spectrum of Fe@MBC after PFOA adsorption. Fe@MBC maintained a near 100% adsorption capacity for PFOA after 4 cycles of chemical regeneration. Fe@MBC also exhibited efficient removal for PFOA and other PFAS compounds at trace levels in the lake water and wastewater treatment plant effluent. Thus, this study highlights a promising insight for selectively eliminating PFASs from water.

Progress on the removal of PFAS contamination in water by different forms of iron-modified biochar

Per- and polyfluoroalkyl substances (PFAS) contamination poses a significant threat to human health. Iron-modified biochar is an eco-friendly, cost-effective, and efficient adsorption material. There is a beneficial interaction between iron groups and biochar to remove PFAS from water through adsorption and degradation. The removal mechanism of the iron-modified biochar mainly includes advanced oxidation, iron group reduction, and adsorption. The adsorption mechanism shifted from being dominated by hydrophobic interactions to electrostatic interactions and ion exchange. Different forms of iron-modified biochar showed excellent removal of short-chain PFAS, which is not found in other modified biochar. Few existing studies have systematically investigated the role of various forms of iron-modified biochar in PFAS removal. Accordingly, this review explores the following areas, the synthesis methods of different forms of iron-modified biochar, the removal effect on long and short-chain PFAS, the key factors affecting removal capacity and the mechanisms of their interaction, the mechanism of PFAS removal, and the regeneration capacity of the composites. In this study, the potential of different forms of iron-modified biochar for PFAS remediation was explored in depth. To provide new ideas for subsequent studies of PFAS removal using iron-modified biochar.

Exploring the sources, occurrence, transformation, toxicity, monitoring, and remediation strategies of per- and polyfluoroalkyl substances: a review

Per- and polyfluoroalkyl substances (PFAS), a class of man-made chemicals, possess unique properties that have rendered them indispensable in various industries and consumer goods. However, their extensive use and persistence in the environment have raised concerns about their potential repercussions on human health and the ecosystem. This review provides insights into the sources, occurrence, transformation, impacts, fate, monitoring, and remediation strategies for PFAS. Once released into the environment, these chemicals undergo intricate transformation processes, such as degradation, bioaccumulation, and biomagnification, which result in their far-reaching distribution and persistence. Their chemical stability results in persistent pollution, with far-reaching ecological and human health implications. Remediation strategies for PFAS are still in their infancy, and researchers are exploring innovative and sustainable methods for treating contaminated environments. Promising technologies such as adsorption, biodegradation, and electrochemical oxidation have shown the potential to remove PFAS from contaminated sites, yet the search for more efficient and sustainable solutions continues. In conclusion, this review emphasizes the urgent need for continued research and innovation to address the global environmental challenge posed by PFAS. As we move forward, it is imperative to prioritize sustainable solutions that minimize the detrimental consequences of these substances on human health and the environment.

A critical review of biochar for the remediation of PFAS-contaminated soil and water

Per- and polyfluoroalkyl substances (PFAS) present significant environmental and health hazards due to their inherent persistence, ubiquitous presence in the environment, and propensity for bioaccumulation. Consequently, the development of efficacious remediation strategies for soil and water contaminated with PFAS is imperative. Biochar, with its unique properties, has emerged as a cost-effective adsorbent for PFAS. Despite this, a comprehensive review of the factors influencing PFAS adsorption and immobilization by biochar is lacking. This narrative review examines recent findings indicating that the application of biochar can effectively immobilize PFAS, thereby mitigating their environmental transport and subsequent ecological impact. In addition, this paper reviewed the sorption mechanisms of biochar and the factors affecting its sorption efficiency. The high effectiveness of biochars in PFAS remediation has been attributed to their high porosity in the right pore size range (>1.5 nm) that can accommodate the relatively large PFAS molecules (>1.02-2.20 nm), leading to physical entrapment. Effective sorption requires attraction or bonding to the biochar framework. Binding is stronger for long-chain PFAS than for short-chain PFAS, as attractive forces between long hydrophobic CF2-tails more easily overcome the repulsion of the often-anionic head groups by net negatively charged biochars. This review summarizes case studies and field applications highlighting the effectiveness of biochar across various matrices, showcasing its strong binding with PFAS. We suggest that research should focus on improving the adsorption performance of biochar for short-chain PFAS compounds. Establishing the significance of biochar surface electrical charge in the adsorption process of PFAS is necessary, as well as quantifying the respective contributions of electrostatic forces and hydrophobic van der Waals forces to the adsorption of both short- and long-chain PFAS. There is an urgent need for validation of the effectiveness of the biochar effect in actual environmental conditions through prolonged outdoor testing.

Novel pillar[n]arenes magnetic nanoparticles: Preparation and application in quantitative analysis of trace perfluorinated compounds from aqueous samples

BACKGROUND

Perfluorinated compounds (PFCs) are a class of widely manufactured and used emerging persistent pollutants. The recent discovered new class of macrocycles pillararenes have garnered significant attention for the applications in environmental pollutant adsorption, with abundant π electron cavities, a symmetrical rigid structure, and host-guest recognition capabilities.

RESULTS

In this work, we designed and synthesized novel cationic pillar [n]arenes magnetic nanoparticles (CWPA5@MNPs), and investigated its adsorption performance and mechanism as a type of new adsorbent for the enrichment of PFCs. The results indicate that CWPA5@MNPs exhibits selectively strong affinity for perfluorooctane sulfonate (PFOS) and long-chain (C9-C14) perfluorocarboxylic acids (PFCAs), with the adsorption efficiency exceeding 80 % within 12 min. The maximum adsorption capacity of CWPA5@MNPs for PFOS was measured to be 29.02 mg/g. CWPA5@MNPs can be rapidly isolated from the solution using external magnets, offering a quick and easy separation. Consequently, this study established a CWPA5@MNPs-assisted magnetic solid-phase extraction (MSPE) coupled with high-performance liquid chromatography-tandem mass spectrometry (CWPA5@MNPs-MSPE-HPLC-MS/MS) method for the rapid detection of trace levels of PFCs in environmental water samples. The analysis of 7 PFCs yielded recovery rates ranging from 86.1 % to 107.5 %, with intraday and interday relative standard deviations (RSD) of 3.6-6.4 % and 1.3-7.0 %, respectively.

SIGNIFICANCE AND NOVELTY

The study reveals the synthesis and application of novel cationic pillar [n]arenes magnetic nanoparticles (CWPA5@MNPs) as highly efficient adsorbents for selective perfluorinated compounds (PFCs) in water samples. It demonstrates the potential of the newly developed CWPA5@MNPs-MSPE-HPLC-MS/MS method for the quantitative analysis of PFCs in environment, with high sensitivity, accuracy and stability.

Rapid adsorptive removal of emerging and legacy per- and polyfluoroalkyl substances (PFASs) from water using zinc chloride-modified litchi seed-derived biochar

The present study successfully synthesized a novel biochar adsorbent (M-L-BC) using litchi seed modified with zinc chloride for PFASs removal in water. M-L-BC greatly enhanced removal of all examined PFASs (>95 %) as compared to the pristine biochar (<40 %). The maximum adsorption capacity was observed for PFOS, reaching 29.6 mg/g. Adsorption kinetics of PFASs followed the pseudo-second-order model (PSO), suggesting the predominance of chemical adsorption. Moreover, characterization and density functional theory (DFT) calculations jointly revealed involvement of surface complexation, electrostatic interactions, hydrogen bonding, and hydrophobic interactions in PFAS adsorption. Robust PFAS removal was demonstrated for M-L-BC across a wide range of pH (3-9), and coexisting ions had limited impact on adsorption of PFASs except PFBA. Furthermore, M-L-BC showed excellent performance in real water samples and retained reusability after five cycles of regeneration. Overall, M-L-BC represents a promising and high-quality adsorbent for efficient and sustainable removal of PFASs from water.

Treatment of aqueous per- and poly-fluoroalkyl substances: A review of biochar adsorbent preparation methods

Per- and poly-fluoroalkyl substances (PFAS) are synthetic chemicals widely used in everyday products, causing elevated concentrations in drinking water and posing a global challenge. While adsorption methods are commonly employed for PFAS removal, the substantial cost and environmental footprint of commercial adsorbents highlight the need for more cost-effective alternatives. Additionally, existing adsorbents exhibit limited effectiveness, particularly against diverse PFAS types, such as short-chain PFAS, necessitating modifications to enhance adsorption capacity. Biochar can be considered a cost-effective and eco-friendly alternative to conventional adsorbents. With abundant feedstocks and favorable physicochemical properties, biochar shows significant potential to be applied as an adsorbent for removing contaminants from water. Despite its effectiveness in adsorbing different inorganic and organic contaminants from water environments, some factors restrict its effective application for PFAS adsorption. These factors are related to the biochar properties, and characteristics of PFAS, as well as water chemistry. Therefore, some modifications have been introduced to overcome these limitations and improve biochar's adsorption capacity. This review explores the preparation conditions, including the pyrolysis process, activation, and modification techniques applied to biochar to enhance its adsorption capacity for different types of PFAS. It addresses critical questions about the adsorption performance of biochar and its composites, mechanisms governing PFAS adsorption, challenges, and future perspectives in this field. The surge in research on biochar for PFAS adsorption indicates a growing interest, making this timely review a valuable resource for future research and an in-depth exploration of biochar's potential in PFAS remediation.

Fluoro-functionalized plant biomass adsorbent: Preparation and application in extraction of trace perfluorinated compounds from environmental water samples

Perfluorinated compounds (PFCs) are toxic and widely present in the environment, and therefore effective adsorbents are required to remove PFCs from environmental water. In the present study, a new type of fluorinated biomass materials was synthesized via an ingenious fluorosilanization reaction. These adsorbents were applied for the adsorption of 13 typical PFCs, including perfluorocarboxylic acids (PFCAs) and perfluorosulfonic acids (PFSAs). By comparing their adsorption performance, Fluorinated cedar slag (FCS) was discovered to have the best absorption efficiency and enabled highly efficient enrichment of PFCs. The adsorption recovery of FCS with the investigated PFCs is greater than 90% under the optimal adsorption condition. Ascribed to the high affinity of F-F sorbent-sorbate interaction, FCS had good adsorption capacities of PFCs from aqueous solution, with the maximum adsorption capacity of 15.80 mg/g for PFOS and 10.71 mg/g for PFOA, respectively. Moreover, the adsorption time could be achieved in a short time (8 min). Using the FCS absorbent, an innovative FCS-solid phase extraction assisted with high performance liquid chromatography-electrospray-tandem mass spectrometry (FCS-SPE-HPLC-ESI-MS/MS) method was first developed to sensitively detect PFCs in the environmental water samples. The intra-day and inter-day recovery rates of the 13 compounds ranged from 90.7%-104.3%, with the RSD of 2.1%-4.7% (intra-day) and 2.5%-8.5% (inter-day), respectively. This research demonstrates the potential of the newly fluoro-functionalized plant biomass to adsorb PFCs from environmental water, with the advantages of high adsorption efficiencies, high anti-interference, easy operation and low economic cost.

Progress and perspectives on carbon-based materials for adsorptive removal and photocatalytic degradation of perfluoroalkyl and polyfluoroalkyl substances (PFAS)

Per- and polyfluoroalkyl substances (PFAS) (also known as 'forever chemicals') have emerged as trace pollutants of global concern, attributing to their persistent and bio-accumulative nature, pervasive distribution, and adverse public health and environmental impacts. The unregulated discharge of PFAS into aquatic environments represents a prominent threat to the wellbeing of humans and marine biota, thereby exhorting unprecedented action to tackle PFAS contamination. Indeed, several noteworthy technologies intending to remove PFAS from environmental compartments have been intensively evaluated in recent years. Amongst them, adsorption and photocatalysis demonstrate remarkable ability to eliminate PFAS from different water matrices. In particular, carbon-based materials, because of their diverse structures and many exciting properties, offer bountiful opportunities as both adsorbent and photocatalyst, for the efficient abatement of PFAS. This review, therefore, presents a comprehensive summary of the diverse array of carbonaceous materials, including biochar, activated carbon, carbon nanotubes, and graphene, that can serve as ideal candidates in adsorptive and photocatalytic treatment of PFAS contaminated water. Specifically, the efficacy of carbon-mediated PFAS removal via adsorption and photocatalysis is summarised, together with a cognizance of the factors influencing the treatment efficiency. The review further highlights the neoteric development on the novel innovative approach 'concentrate and degrade' that integrates selective adsorption of trace concentrations of PFAS onto photoactive surface sites, with enhanced catalytic activity. This technique is way more energy efficient than conventional energy-intensive photocatalysis. Finally, the review speculates the cardinal challenges associated with the practical utility of carbon-based materials, including their scalability and economic feasibility, for eliminating exceptionally stable PFAS from water matrices.

Recent advances in the application of magnetic materials for the management of perfluoroalkyl substances in aqueous phases

Perfluoroalkyl substances (PFASs) are a class of artificially synthesised organic compounds extensively used in both industrial and consumer products owing to their unique characteristics. However, their persistence in the environment and potential risk to health have raised serious global concerns. Therefore, developing effective techniques to identify, eliminate, and degrade these pollutants in water are crucial. Owing to their high surface area, magnetic responsiveness, redox sensitivity, and ease of separation, magnetic materials have been considered for the treatment of PFASs from water in recent years. This review provides a comprehensive overview of the recent use of magnetic materials for the detection, removal, and degradation of PFASs in aqueous solutions. First, the use of magnetic materials for sensitive and precise detection of PFASs is addressed. Second, the adsorption of PFASs using magnetic materials is discussed. Several magnetic materials, including iron oxides, ferrites, and magnetic carbon composites, have been explored as efficient adsorbents for PFASs removal from water. Surface modification, functionalization, and composite fabrication have been employed to improve the adsorption effectiveness and selectivity of magnetic materials for PFASs. The final section of this review focuses on the advanced oxidation for PFASs using magnetic materials. This review suggests that magnetic materials have demonstrated considerable potential for use in various environmental remediation applications, as well as in the treatment of PFASs-contaminated water.

Tetracycline-adsorbed biochar for solid biofuel usage to achieve waste utilization for environmental sustainability

Biochar is widely used to remove organic pollutants from the environment. Several studies have focused on pollutant removal via biochar adsorption. However, research on the subsequent processing of pollutant-adsorbed biochar is lacking. This study explored the potential of biochar for the adsorption of an aquatic organic pollutant (tetracycline) and its subsequent use as a solid biofuel. These results suggest that corn straw-derived biochar (torrefaction and pyrolysis) is suitable for two-stage utilization to achieve bioresource valorization for environmental sustainability. Tetracycline-adsorbed biochar, particularly biochar pyrolyzed at 600 °C, is suitable for use as a biofuel. The biochar produced via torrefaction (300 °C) and pyrolysis (600 °C) is the optimal choice, with surface area, contact angle, graphitization degree, calorific value, enhancement factor, and upgrading energy index values of 172.48 m2/g, 120.4°, 3.87, 26.983 MJ/kg, 1.58, and 33.72, respectively. This is supported by the results of expense calculation, comprehensive performance analysis, and life-cycle assessment. Overall, the biochar produced in this study is suitable for organic pollutant removal and as solid biofuel; thus, it can be used to realize waste utilization for environmental sustainability.

Removal of methylene blue by porous biochar obtained by KOH activation from bamboo biochar

A series of activated biochar (KBBC-700, KBBC-800 and KBBC-900) which were modified by KOH and pyrolysis at various temperatures from ball-milling bamboo powder were obtained. The physicochemical properties and pore structures of activated biochar were investigated by scanning electron microscopy (SEM), fourier transform infrared spectoscopy (FT-IR), X-ray diffraction (XRD) and N2 adsorption/desorption. The adsorption performance for the removal of methylene blue (MB) was deeply studied. The results showed that KBBC-900 obtained at activation temperature of 900 °C exhibited a great surface area which reached 562 m2/g with 0.460 cm3/g of total pore volume. The enhancement of adsorption capacity could be ascribed to the increase of surface oxygen-containing functional groups, aromatization and mesoporous channels. The adsorption capacity was up to 67.46 mg/g under the optimum adsorption parameters with 2 g/L of adsorbent dose, 11 of initial solution pH and 298 K of the reactive temperature. The adsorption capacity was 70.63% of the first time after the material was recycled for three cycles. The kinetics indicated that the adsorption equilibrium time for MB on KBBC-900 was of about 20 min with the data fitted better to the pseudo-second-order kinetics model. The adsorption process was mainly dominated by chemical adsorption. Meanwhile, the adsorption isotherm showed that the Langmuir model fitted the best, and thermodynamic parameters revealed that the adsorption reaction was the endothermic nature and the spontaneous process. Adsorption of MB mainly attributed to electrostatic interactions, cation-π electron interaction and redox reaction. This study suggested that the activated biochar obtained by KOH activation from bamboo biochar has great potentials in the practical application to remove MB from wastewater.

The application of Rumex abyssinicus based activated carbon for Brilliant Blue Reactive dye adsorption from aqueous solution

The environmental pollution and human health impacts associated with the discharge of massive dye-containing effluents necessitate a search for cost-effective treatment technology. Therefore, this research work is conducted with the objective of investigating the potential of Rumex abyssinicus-derived activated carbon (RAAC) for the adsorption of Brilliant Blue Reactive (BBR) dye from aqueous solutions. Chemical activation with H₃PO₄ followed by pyrolysis was used to prepare the adsorbent. Characterization of the developed adsorbent was done using proximate analysis, pH point of zero charge (pHpzc), scanning electron microscope (SEM), Fourier transform infrared spectrometer (FTIR), Brunauer, Emmett, and Teller (BET), and X-ray diffraction (XRD). The experimental design and the effect of independent variables including pH (2, 6, and 10), initial dye concentration (50, 100, and 150 mg/L), adsorbent dosage (0.05, 0.1, and 0.15 g/100 mL), and contact time (20, 50, and 80 min) were optimized using the response surface methodology (RSM) coupled with Box Behnken design (BBD). The analysis results revealed the exitance of high specific surface area of 524 m²/g, morphological cracks, and the presence of multiple functional groups like -OH, C=C, alkene, and amorphous structure. Maximum removal efficiency of 99.98% was attained at optimum working conditions of pH 2, contact time of 50 min, dye concentration of 100 mg/L, and adsorbent dosage of 0.15 mg/100 mL, reducing the pollutant concentration from 100 to 0.02 mg/L. Evaluation of the experimental data was done using Langmuir, Freundlich, Temkin, and Sips isotherm models, in which the Langmuir model was found to be the best fit with the experimental data at R² 0.986. This shows that the adsorbent surface is homogeneous and mono-layered. Furthermore, the kinetic study confirmed that the pseudo second-order model best describes the experimental data with R² = 0.999. In general, the research work showed that the low cost, environmental friendliness and high adsorption capabilities of the activated carbon derived from Rumex abyssinicus could be taken as an effective nt for the removal of BBR dye from aqueous solutions.

Synthesis and characterization of PCN-222 metal organic framework and its application for removing perfluorooctane sulfonate from water

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

Batch and fixed bed sorption of low to moderate concentrations of aqueous per- and poly-fluoroalkyl substances (PFAS) on Douglas fir biochar and its Fe3O4 hybrids

Per- and poly-fluoroalkyl substances (PFAS) can cause deleterious effects at low concentrations (70 ng/L). Their remediation is challenging. Aqueous μg/L levels of PFOS, PFOS, PFOSA, PFBS, GenX, PFHxS, PFPeA, PFHxA, and PFHpA (abbreviations defined in Table 1) multi-component adsorption (pH dependence, kinetics, isotherms, fixed-bed adsorption, regeneration, complex matrix) was studied on commercial Douglas fir biochar (BC) and its Fe₃O₄-containing BC. BC is a waste product when syn-gas is produced in a large scale from wet Douglas fir wood fed to gasification at 900-1000 °C and held for 1-20 s. This generates a relatively high surface area (∼700 m²/g) and large pore volume (∼0.25 cm³/g) biochar. Treatment of BC with FeCl₃/FeSO₄ and NaOH to chemically precipitate Fe₃O₄ onto BC. BC and its magnetic Fe₃O₄/BC analogue rapidly adsorbed (20-45 min equilibrium time) significant amounts of PFOS (∼14.6 mg/g) and PFOA (∼652 mg/g) at natural waters' pH range (6-8). Adsorption from μg/L concentrations has produced remediated aqueous PFAS concentrations of ∼50 ng/L or below the detection limits, which is closing in on EPA advisory limits. Column capacities of PFOS were 215.3 mg/g on BC and 51.9 mg/g Fe₃O₄/BC vs 53.0 mg/g and 21.8 mg/g, respectively, for PFOA. Hydrophobic and electrostatic interactions are thought to drive this sorption. Successful stripping regeneration by methanol was achieved. Thus, hydrophobic Douglas fir biochar produced by fast high temperature pyrolysis and its Fe₃O₄/BC analogue are adsorbent candidates for PFAS remediation from the dilute PFAS concentrations often found in polluted environments. Small Fe₃O₄/BC particles can be magnetically removed from batch treatments avoiding filtration.

Recovery, regeneration and sustainable management of spent adsorbents from wastewater treatment streams: A review

Adsorption is the most widely adopted, effective, and reliable treatment process for the removal of inorganic and organic contaminants from wastewater. One of the major issues with the adsorption-treatment process for the removal of contaminants from wastewater streams is the recovery and sustainable management of spent adsorbents. This review focuses on the effectiveness of emerging adsorbents and how the spent adsorbents could be recovered, regenerated, and further managed through reuse or safe disposal. The critical analysis of both conventional and emerging adsorbents on organic and inorganic contaminants in wastewater systems are evaluated. The various recovery and regeneration techniques of spent adsorbents including magnetic separation, filtration, thermal desorption and decomposition, chemical desorption, supercritical fluid desorption, advanced oxidation process and microbial assisted adsorbent regeneration are discussed in detail. The current challenges for the recovery and regeneration of adsorbents and the methodologies used for solving those problems are covered. The spent adsorbents are managed through regeneration for reuse (such as soil amendment, capacitor, catalyst/catalyst support) or safe disposal involving incineration and landfilling. Sustainable management of spent adsorbents, including processes involved in the recovery and regeneration of adsorbents for reuse, is examined in the context of resource recovery and circular economy. Finally, the review ends with the current drawbacks in the recovery and management of the spent adsorbents and the future directions for the economic and environmental feasibility of the system for industrial-scale application.

Magnetic adsorbent developed with alkali-thermal pretreated biogas slurry solids for the removal of heavy metals: optimization, kinetic, and equilibrium study

Discharge of effluents containing heavy metal without adequate treatment causes contamination of water resources and creates environmental and health issues. Adsorption could be applied to remediate heavy metals from wastewater effectively. In this study, a low-cost adsorbent was prepared by magnetic modification of pretreated biogas slurry solids (BSS) to remove heavy metals such as Cu²⁺, Cd²⁺, and Pb²⁺. The temperature (423 K) and time (1.5 h) of pretreatment, the BSS to KOH ratio (1:10 w/v), and the ratio of magnetic iron nanoparticle (MIN) to pretreated BSS (PSS) (1:2 w/w) were optimized for the preparation of adsorbent. The magnetically modified pretreated biogas slurry solid (MMPSS) adsorbent was characterized by BET isotherm, FTIR, XRD, FESEM, VSM, and EDX analysis. MMPSS attained equilibrium at 60 min and showed an adsorption capacity of 26.84 mg/g, 24.79 mg/g, and 23.86 mg/g with removal percentages 89.46%, 82.63%, and 79.54% for Cu²⁺, Cd²⁺, and Pb²⁺, respectively, at 310 K and pH 6 with an initial concentration of 150 mg/L. The adsorption process followed a pseudo second-order model with an R² value above 0.9 for all metals with a well-approaching equilibrium pattern. The good fit of experimental data by the Langmuir isotherm model implied monolayer adsorption. The metal ions adsorbed onto MMPSS were able to desorb effectively in the presence of HCl and retained 83.01%, 84.66%, and 81.83% of the initial adsorption capacity for Cu²⁺, Cd²⁺, and Pb²⁺ respectively after 5 consecutive cycles.

Evaluating the potential of KOH-modified composite biochar amendment to alleviate the ecotoxicity of perfluorooctanoic acid-contaminated sediment on Bellamya aeruginosa

Modified composite biochar offers a cost-effective solution for the remediation of contaminated sediments; however, few studies have evaluated the effects of modified composite biochar amendment on the ecotoxicity of contaminated sediment based on benthic macroinvertebrates. A 21-day sediment toxicity test was conducted using the freshwater snail Bellamya aeruginosa to examine the intrinsic ecotoxicity of a novel KOH-modified composite biochar (KOH-CBC) and its efficacy for reducing the bioavailability, uptake, and ecotoxicity of perfluorooctanoic acid (PFOA). It was found that KOH-CBC is toxic to B. aeruginosa, which may be attributed to its high polycyclic aromatic hydrocarbons (PAHs) content and alkalinity. The addition of KOH-CBC to PFOA-contaminated sediments can markedly reduce the bioavailability and uptake of PFOA by more than 90% and 50%, respectively, and subsequently alleviate the toxicity of PFOA to B. aeruginosa by at least 30%. Increasing the KOH-CBC dosage is not beneficial for further mitigating the toxicity of PFOA-contaminated sediments. Our findings imply that KOH-CBC is a promising sorbent for the in-situ remediation of PFOA-contaminated sediments. Application of acidified KOH-CBC at a dosage of approximately 1-3% will be sufficient to control the ecotoxicity of PFOA; however, its long-term environmental effects should be further validated.