Understanding the Selective Removal of Perfluoroalkyl and Polyfluoroalkyl Substances via Fluorine-Fluorine Interactions: A Critical Review.

As regulatory standards for per- and polyfluoroalkyl substances (PFAS) become increasingly stringent, innovative water treatment technologies are urgently demanded for effective PFAS removal. Reported sorbents often exhibit limited affinity for PFAS and are frequently hindered by competitive background substances. Recently, fluorinated sorbents (abbreviated as fluorosorbents) have emerged as a potent solution by leveraging fluorine-fluorine (F···F) interactions to enhance selectivity and efficiency in PFAS removal. This review delves into the designs and applications of fluorosorbents, emphasizing how F···F interactions improve PFAS binding affinity. Specifically, the existence of F···F interactions results in removal efficiencies orders of magnitude higher than other counterpart sorbents, particularly under competitive conditions. Furthermore, we provide a detailed analysis of the fundamental principles underlying F···F interactions and elucidate their synergistic effects with other sorption forces, which contribute to the enhanced efficacy and selectivity. Subsequently, we examine various fluorosorbents and their synthesis and fluorination techniques, underscore the importance of accurately characterizing F···F interactions through advanced analytical methods, and emphasize the significance of this interaction in developing selective sorbents. Finally, we discuss challenges and opportunities associated with employing advanced techniques to guide the design of selective sorbents and advocate for further research in the development of sustainable and cost-effective treatment technologies leveraging F···F interactions.

Superselective Hg(II) Removal from Water Using a Thiol-Laced MOF-Based Sponge Monolith: Performance and Mechanism.

Point-of-use (POU) devices with satisfying mercury (Hg) removal performance are urgently needed for public health and yet are scarcely reported. In this study, a thiol-laced metal-organic framework (MOF)-based sponge monolith (TLMSM) has been investigated for Hg(II) removal as the POU device for its benchmark application. The resulting TLMSM was characterized by remarkable chemical resistance, mechanical stability, and hydroscopicity (>2100 wt %). Importantly, the TLMSM has exhibited high adsorption capacity (∼954.7 mg g-1), fast kinetics (kf ∼ 1.76 × 10-5 ms-1), broad working pH range (1-10), high selectivity (Kd > 5.0 × 107 mL g-1), and excellent regeneration capability (removal efficiency >90% after 25 cycles). The high applicability of TLMSM in real-world scenarios was verified by its excellent Hg(II) removal performance in various real water matrices (e.g., surface waters and industrial effluents). Moreover, a fixed-bed column test demonstrated that ∼1485 bed volumes of the feeding streams (∼500 µg L-1) can be effectively treated with an enrichment factor of 12.6, suggesting the great potential of TLMSM as POU devices. Furthermore, the principal adsorption complexes (e.g., single-layer -S-Hg-Cl and double-layer -S-Hg-O-Hg-Cl and -S-Hg-O-Hg-OH) formed during the adsorption process under a wide range of pH were synergistically and systematically unveiled using advanced tools. Overall, this work presents an applicable approach by tailoring MOF into a sponge substrate to achieve its real application in heavy metal removal from water, especially for Hg(II).

Critical Review of Advances in Engineering Nanomaterial Adsorbents for Metal Removal and Recovery from Water: Mechanism Identification and Engineering Design.

Nanomaterial adsorbents (NAs) have shown promise to efficiently remove toxic metals from water, yet their practical use remains challenging. Limited understanding of adsorption mechanisms and scaling up evaluation are the two main obstacles. To fully realize the practical use of NAs for metal removal, we review the advanced tools and chemical principles to identify mechanisms, highlight the importance of adsorption capacity and kinetics on engineering design, and propose a systematic engineering scenario for full-scale NA implementation. Specifically, we provide in-depth insight for using density functional theory (DFT) and/or X-ray absorption fine structure (XAFS) to elucidate adsorption mechanisms in terms of active site verification and molecular interaction configuration. Furthermore, we discuss engineering issues for designing, scaling, and operating NA systems, including adsorption modeling, reactor selection, and NA regeneration, recovery, and disposal. This review also prioritizes research needs for (i) determining NA microstructure properties using DFT, XAFS, and machine learning and (ii) recovering NAs from treated water. Our critical review is expected to guide and advance the development of highly efficient NAs for engineering applications.

Highly Efficient and Selective Hg(II) Removal from Water Using Multilayered Ti3C2Ox MXene via Adsorption Coupled with Catalytic Reduction Mechanism.

Mercury (Hg) removal is crucial to the safety of water resources, yet it lacks an effective removal technology, especially for emergency on-site remediation. Herein, multilayered oxygen-functionalized Ti3C2 (Ti3C2Ox) (abbreviated as M-Ti3C2) nanosheets were prepared to remove Hg(II) from water. The M-Ti3C2 has demonstrated ultrafast adsorption kinetics (the concentration decreased from 10 400 to 33 µg L-1 in 10 s), impressively high capacity (4806 mg g-1), high selectivity, and broad working pH range (3-12). The density functional theory (DFT) calculations and experimental characterizations unveil that this exceptional Hg(II) removal is owing to the distinct interaction (e.g., adsorption coupled with catalytic reduction). Specifically, Ti atoms on the {001} facets of M-Ti3C2 prefer to adsorb Hg(II) in the form of HgClOH, which subsequently undergoes homolytic cleavage to form radical species (e.g., •OH and •HgCl). Immediately, the •HgCl radicals dimerize and form crystalline Hg2Cl2 on the edges of M-Ti3C2. Up to ∼95% of dimeric Hg2Cl2 can be efficiently recovered via facile thermal treatment. Notably, owing to the adsorbed •OH and energy released during the distinct interaction, M-Ti3C2 has been oxidized to TiO2/C nanocomposites. And the TiO2/C nanocomposites have shown to have better performance on the photocatalytic degradation of organic pollutants than Degussa P25. These exceptional features coupled with mercuric recyclable nature make M-Ti3C2 an outstanding candidate for rapid/urgent Hg(II) removal and recovery.

Refining hydrogel-based sorbent design for efficient toxic metal removal using machine learning-Bayesian optimization.

Hydrogel-based sorbents show promise in the removal of toxic metals from water. However, optimizing their performance through conventional trial-and-error methods is both costly and challenging due to the inherent high-dimensional parameter space associated with complex condition combinations. In this study, machine learning (ML) was employed to uncover the relationship between the fabrication condition of hydrogel sorbent and their efficiency in removing toxic metals. The developed XGBoost models demonstrated exceptional accuracy in predicting hydrogel adsorption coefficients (Kd) based on synthesis materials and fabrication conditions. Key factors such as reaction temperature (50-70 °C), time (5-72 h), initiator ((NH4)2S2O8: 2.3-10.3 mol%), and crosslinker (Methylene-Bis-Acrylamide: 1.5-4.3 mol%) significantly influenced Kd. Subsequently, ten hydrogels were fabricated utilizing these optimized feature combinations based on Bayesian optimization, exhibiting superior toxic metal adsorption capabilities that surpassed existing limits (logKd (Cu): increased from 2.70 to 3.06; logKd (Pb): increased from 2.76 to 3.37). Within these determined combinations, the error range (0.025-0.172) between model predictions and experimental validations for logKd (Pb) indicated negligible disparity. Our research outcomes not only offer valuable insights but also provide practical guidance, highlighting the potential for custom-tailored hydrogel designs to combat specific contaminants, courtesy of ML-based Bayesian optimization.

Overcoming metals redox rate limitations in spinel oxide-driven Fenton-like reactions via synergistic heteroatom doping and carbon anchoring for efficient micropollutant removal.

The transition metals redox rate limitations of spinel oxides during Fenton-like reactions hinder its efficient and sustainable treatment of actual wastewater. Herein, we propose to optimize the electronic structure of Co-Mn spinel oxide (CM) via sulfur doping and carbon matrix anchoring synergistically, enhancing the radicals-nonradicals Fenton-like processes for efficient water decontamination. Activating peroxymonosulfate (PMS) with optimised spinel oxide (CMSAC) achieved near-complete removal of ofloxacin (10 mg/L) within 6 min, showing 8.4 times higher efficiency than CM group. Significantly higher yields of SO4·- and high-valent metal species in CMSAC/PMS system provided exceptional resistance to co-existing anions, enabling efficient removal of various emerging contaminants in high salinity leachate. Specifically, sulfur coordination and carbon anchoring-induced oxygen vacancy synergistically improved the electronic structure and electron transfer efficiency of CMSAC, thus forming highly reactive Co sites and significantly reducing the energy barrier for Co(IV)=O generation. The reductive sulfur species facilitated the conversion of Co(III) to Co(II), thereby maintaining the stability of the catalytic activity of CMSAC. This work developed a synergistic optimization strategy to overcome the metals redox rate limitations of spinel oxides in Fenton-like reactions, providing deep mechanistic insights for designing Fenton-like catalysts suitable for practical applications.

Utilizing cost-effective pyrocarbon for highly efficient gold retrieval from e-waste leachate.

Addressing burdens of electronic waste (E-waste) leachate while achieving sustainable and selective recovery of noble metals, such as gold, is highly demanded due to its limited supply and escalating prices. Here we demonstrate an environmentally-benign and practical approach for gold recovery from E-waste leachate using alginate-derived pyrocarbon sorbent. The sorbent demonstrates potent gold recovery performance compared to most previously reported advanced sorbents, showcasing high recovery capacity of 2829.7 mg g-1, high efficiency (>99.5%), remarkable selectivity (Kd ~ 3.1 × 108 mL g-1), and robust anti-interference capabilities within environmentally relevant contexts. The aromatic structures of pyrocarbon serve as crucial electrons sources, enabling a hydroxylation process that simultaneously generates electrons and phenolic hydroxyls for the reduction of gold ions. Our investigations further uncover a "stepwise" nucleation mechanism, in which gold ions are reduced as intermediate gold-chlorine clusters, facilitating rapid reduction process by lowering energy barriers from 1.08 to -21.84 eV. Technoeconomic analysis demonstrates its economic viability with an input-output ratio as high as 1370%. Our protocol obviates the necessity for organic reagents whilst obtaining 23.96 karats gold product from real-world central processing units (CPUs) leachates. This work introduces a green sorption technique for gold recovery, emphasizing its role in promoting a circular economy and environmental sustainability.

Electronic structure modulation of iron sites with fluorine coordination enables ultra-effective H2O2 activation.

Electronic structure modulation of active sites is critical important in Fenton catalysis as it offers a promising strategy for boosting H2O2 activation. However, efficient generation of hydroxyl radicals (•OH) is often limited to the unoptimized coordination environment of active sites. Herein, we report the rational design and synthesis of iron oxyfluoride (FeOF), whose iron sites strongly coordinate with the most electronegative fluorine atoms in a characteristic moiety of F-(Fe(III)O3)-F, for effective H2O2 activation with potent •OH generation. Results demonstrate that the fluorine coordination plays a pivotal role in lowering the local electron density and optimizing the electronic structures of iron sites, thus facilitating the rate-limiting H2O2 adsorption and subsequent peroxyl bond cleavage reactions. Consequently, FeOF exhibits a significant and pH-adaptive •OH yield (~450 µM) with high selectivity, which is 1 ~ 3 orders of magnitude higher than the state-of-the-art iron-based catalysts, leading to excellent degradation activities against various organic pollutants at neutral condition. This work provides fundamental insights into the function of fluorine coordination in boosting Fenton catalysis at atomic level, which may inspire the design of efficient active sites for sustainable environmental remediation.

Macro-constructing zeolitic imidazole frameworks functionalized sponge for enhanced removal of heavy metals: The significance of morphology and structure modulation.

Rational synthesis of metal-organic frameworks (MOFs) via structural and morphology engineering are fundamental for enhanced heavy metal removal. Beyond tuning intrinsic characteristics, it is essential to address inseparability and instability issues of MOFs to fulfill the practical applications. Herein, we successfully constructed macroscopic zeolitic imidazole frameworks-functionalized melamine sponge (MS@ZIFx, x represents the ultrasonication duration) using a facile dip-coating method. By varying ultrasonication duration, the morphology and structure of the loaded ZIF were modulated from leaf-shaped phase to hollow mixed phase to achieve the excellent adsorption performance. The optimized MS-ZIF10 exhibited significantly enhanced performance for Pb(II) and Cu(II) adsorption. Specifically, the MS-ZIF10 combined high adsorption capacities (624.8 and 588.6 mg g-1 for Pb(II) and Cu(II), respectively), rapid kinetics, excellent anti-interfering capability (e.g., cations, dissolved organic matters) with outstanding reusability (removal efficiency > 91.8 % after 10 cycles). The MS-ZIF10 presented satisfactory performance on Pb(II) and Cu(II) removal in various real water matrices. Fixed-bed experiments were performed to assess the practicality of MS-ZIF10, and 1821 bed volumes (BVs) and 1630 BVs of feeding streams containing Pb(II) and Cu(II) were effectively treated. This work proposed a novel paradigm for promoting the MOF's performance and simultaneously boosting MOF's application in actual heavy metal removal.

Radix Astragali residue-derived porous amino-laced double-network hydrogel for efficient Pb(II) removal: Performance and modeling.

Valorizing solid waste for heavy metal adsorption is highly desirable to avoid global natural resources depletion. In this study, we developed a new protocol to valorize Radix Astragali residue (one of the Chinese medicine residues) into a low-cost, chemically robust, and highly permeable (ca. 90%) amino-laced porous double-network hydrogel (NH2-CNFs/PAA) for efficient Pb(II) adsorption. The NH2-CNFs/PAA showed (i) excellent Pb(II) adsorption capacity (i.e., 994.5 mg g-1, ~4.8 mmol g-1), (ii) fast adsorption kinetics (kf = 2.01 ×10-5 m s-1), (iii) broad working pH range (2.0-6.0), and (iv) excellent regeneration capability (~15 cycles). (v) excellent performance in various real water matrices on Pb(II) removal. Moreover, its high selectivity (distribution coefficient Kd ~2.4 ×106 mL g-1) toward Pb(II) was owing to the present of abundant amino groups (-NH2). Furthermore, the fix-bed column test indicated the NH2-CNFs/PAA can effectively remove 114.6 bed volumes (influent concentration ~5000 µg L-1) with an enrichment factor 10.9. The full-scale system modeling (i.e., pore surface diffusion model (PSDM)) has been applied to predict the NH2-CNFs/PAA performance on Pb(II) removal. Overall, we have provided an alternative "win-win" scenario that can resolve the Chinese medicine residues disposal issue by valorizing it into high performance gel-based adsorbents for efficient heavy metal removal.

Construction of metal-organic framework/polymer beads for efficient lead ions removal from water: Experiment studies and full-scale performance prediction.

Metal-organic frameworks (MOFs) show great promise in heavy metal removal; however, their applications are restricted by the poor separability and water instability. Herein, granular Zr-based MOF-polymer composite beads (MPCB(Zr)) (mean diameter âˆ¼ 1.74 mm) were synthesized using a facile dropping method, and applied on efficient lead ions (Pb(II)) removal. The as-prepared MPCB(Zr) demonstrated deep Pb(II) removal capability by reducing its concentration to âˆ¼ 0.002 mg L-1 after adsorption equilibrium at 360 min. The distribution coefficient for Pb(II) reached 8.0 × 106 mL g-1, and the theoretical adsorption capacity for Pb(II) was 144.5 mg g-1 (0.70 mmol g-1, 30 °C). The resulting MPCB(Zr) was highly selective for Pb(II), with the selectivity coefficient up to âˆ¼ 1.0-3.6 × 103 for the background cations (Na(I), K(I), Ca(II), and Mg(II)). Moreover, the MPCB(Zr) exhibited a broad working pH range (3.0-6.0) and satisfactory anti-interference to dissolved organic matters (humic acid and fuvic acid). Notably, the MPCB(Zr) also demonstrated excellent reusability with the Pb(II) removal efficiency over 99.0% after 20 cycles. Combined physicochemical characterizations unveiled that the thiol and oxygen-containing groups (e.g., hydroxyl, carboxylate) were responsible for the effective Pb(II) removal. To provide guidance for engineering application, the full-scale performance of the MPCB(Zr) under varying operation conditions was systematically evaluated via the validated pore surface diffusion model. This work provides an effective methodology to construct macroscopic MOF-polymer beads for effective Pb(II) removal, and promote the actual application of MOFs in water treatment.

Phase-Mediated Heavy Metal Adsorption from Aqueous Solutions Using Two-Dimensional Layered MoS2.

An understanding of the impacts regarding different phases of inorganic materials on heavy metal removal is indispensable, owing to the intrinsic structure of materials that can affect its properties. In this study, the distinct adsorption behaviors of heavy metals (Pb(II) and Cu(II)) on different phases of MoS2 (metallic phase (1T) and semiconducting phase (2H)) were theoretically and experimentally investigated. According to the computational results, both Pb(II) and Cu(II) have formed more stable complexes on 1T-MoS2 compared to those on 2H-MoS2 due to the lower adsorption energy (Ead). This phenomenon indicates that Pb(II) and Cu(II) were more preferably adsorbed onto 1T-MoS2. Based on the results of the computational studies, two-dimensional (2D) MoS2 nanosheets with identical 1T and 2H phases were synthesized via a facile hydrothermal reaction. As we surmised, 1T-MoS2 achieved excellent Pb(II) and Cu(II) adsorption capacities, which were 147.09 and 82.13 mg/g at 298 K, respectively, compared to those of 2H-MoS2 (i.e., 64.16 and 50.74 mg/g at 298 K). Moreover, 1T-MoS2 has shown other superior properties, such as (i) ultrafast adsorption kinetics and (ii) great anti-interference activity toward other existing cations, compared to 2H-MoS2. Extensive computations and characterizations of MoS2-Pb and -Cu adsorption complexes illustrated that the active S sites were indispensable for heavy metal adsorption. Overall, for the first time, we provide evidence that 1T-MoS2 is more functional in heavy metal removal compared to 2H-MoS2, which can guide and expand the applications of MoS2-based adsorbents in environmental remediation.