The persistence and ecological impact of per- and poly-fluoroalkyl substances (PFAS) in water sources necessitate effective and energy-efficient treatment solutions. This study introduces a novel approach using cerium dioxide (CeO2) electrodes enhanced with oxygen vacancy (Ov) to catalyze the defluorination of PFAS. By leveraging the unique affinity between cerium and fluorine-containing species, our approach enables adsorptive preconcentration and catalytic degradation at low oxidation potentials (1.37 V vs. SHE). Demonstrating high removal and defluorination efficiencies of perfluorooctanoic acid (PFOA) at 94.0 % and 73.0 %, respectively, our approach also proves effective in the environmental matrix. It minimizes the impacts of co-existing natural organic matter and chloride ions, crucial benefits of operating at lower oxidation potentials. The role of Ov in CeO2 is validated by both experimental results and density functional theory modeling, demonstrating that these sites can activate the C-F bond and substantially reduce the energy barriers for defluorination. Consequently, our CeO2-based method not only achieves defluorination efficiencies comparable to more energy-intensive techniques but does so while requiring less than 0.62 kWh/m3 per order. This positions our approach as a promising, cost-effective alternative for the remediation of PFAS-contaminated waters, emphasizing its relevance and effectiveness in environmental remediation scenarios.

The singlet oxygen (O-1(2))-based nonradical AOP process, realized in carbon materials after nitrogen and metal doping, has drawn much attention in recent years. However, the exclusive generation of O-1(2) in the specialized two-dimensional (2D) catalytic membranes and the associated contaminant degradation mechanisms remain unclear. Herein, a Fe-doped crystalline carbon nitride (Fe-CCN) material without additional nitrogen doping was developed to preferentially initiate O-1(2)-based nanoconfined oxidation of organic pollutants in the 2D Fe-CCN membrane/PMS system. Density functional theory calculation revealed that the Fe-O-N configuration formed after Fe doping altered the electronic structure of Fe centers, enhancing PMS adsorption and promoting the thermodynamically favorable generation of the -O* intermediate, leading to fast and highly selective O-1(2) generation. EPR characterization and ROS quenching experiment also confirmed that the Fe-CCN activated PMS, generating nearly 100 % O-1(2). The Fe-CCN membrane/PMS system exhibited excellent resistance to natural organic matter (NOM) interference and dramatically increased Bisphenol A (BPA) degradation kinetics, approximately 590 times faster than in conventional batch systems. Enhanced O-1(2) exposure concentration within the Fe-CCN membrane nanochannels was supported by EPR data and O-1(2) exposure simulations. Furthermore, The Fe-CCN membrane/PMS system showed wide pH tolerance, excellent pollutant degradation performance, and high stability. This work underscores the practical significance of O-1(2)-based oxidation reactions in membrane-confined AOPs for the rapid and efficient removal of organic contaminants from water.

The environmental redox transformation of CeO2 is crucial for evaluating its ecological risk and understanding the geochemical cycling of cerium (Ce). In this study, we examined the effects of crystallinity on CeO2 dissolution and monitored the structural evolution during redox transformations. The reductive dissolution and reoxidation behavior of CeO2 (100 mg/L) was examined in the presence of 200 μM citrate. Our findings indicate that ligand-induced dissolution is more pronounced in CeO2 with lower crystallinity under both dark and light conditions. This dependence is related to the intensive ligand complexation at oxygen vacancy sites, resulting in a higher complexation of Ce(III) and more efficient photoelectron generation for Ce(IV) reduction. During cyclic dissolution-reprecipitation, CeO2 notably transformed into an amorphous phase, progressively decreasing the crystallinity of the nanoparticles. Consequently, the dissolution fraction of well-crystallized CeO2 increased significantly from 1.2% in the first cycle to 11.4% in the third cycle, suggesting a transition to structures with higher interfacial reactivity. Similar transformation and dissolution behavior was observed in redox oscillations in a soil environment. Additionally, hydroponic exposure experiments with Arabidopsis thaliana, treated with 100 mg/L CeO2 for 7 days, demonstrated increased Ce uptake by roots post-transformation, with a higher proportion of CePO4 detected within the plants. This comprehensive study not only provides vital mechanistic insights into the transformation processes of CeO2 but also aids in assessing the ecological risks associated with engineered CeO2 nanomaterials.

Thin-film nanocomposite (TFN) membranes have garnered considerable attention for their potential to improve separation performance by incorporating nanomaterials. However, challenges such as these materials' uneven distribution and aggregation have hindered practical applications. While prior studies have largely concentrated on modifying nanosheets for compatibility with polymer matrices, the role of substrate pore size in influencing nanosheet distribution has been overlooked. In this work, MoS2 nanosheets were dispersed in an aqueous phase to fabricate TFN membranes, investigating the effect of substrate pore size relative to the nanosheets. By systematically varying the particle size of MoS2 and the pore size of the substrate, we reveal how these factors impact material distribution and structural uniformity within the membranes. Our findings reveal that larger substrate pores allow the MoS2-containing monomer solution to infiltrate more effectively, minimizing nanosheet aggregation. This enhances membrane performance by promoting better dispersion. Our results underscore the importance of considering the relative size of substrate pores and nanosheets in TFN membrane design, providing a pathway to improved material integration and higher membrane efficiency.

Understanding the behavior and fate of microplastics (MPs) in aquatic environment is crucial for assessing their potential risks. This study investigated the heteroaggregation behaviors of MPs with representative 2D nanosheets, MoS2 and graphene oxide (GO), under various conditions, focusing on the transport behavior of the resulting aggregates. It was found that the destabilization capabilities of 2D nanosheets are notably stronger than those of well-reported nanoparticles. More importantly, the deposition and transport of MPs are highly dependent on the configuration of the resulting aggregates. MoS2 nanosheets conformally coat MPs, forming compact and colloidally stable complexes that completely alter the MPs' surface to the negatively charged MoS2. The interaction resulted in high mobility and minimal deposition in environmental matrices. In contrast, GO nanosheets bridge MPs into large clusters, reducing transport and increasing deposition. This difference in aggregate configuration is attributed to the distinct interactions between the nanosheets and MPs: rigid MoS2 nanosheets adhere via strong van der Waals forces, while GO, with oxygen functional groups on its edges and surfaces, folds and crosslinks between particles upon adsorption. These findings underscore the critical role of 2D materials in shaping the environmental fate of MPs, advancing our knowledge on the aggregation process.

Selective capacitive deionization (SCDI) is a promising desalination process for preferentially removing specific ions from waters with complex compositions. Its selectivity towards certain species can be achieved through novel electrode materials with high affinities towards targeted ions. In this work, we studied the selective removal of fluoride ions from groundwater containing concentrated co-existing chloride ions. A carbon nanotube-CeO2 (CNT-CeO2) electrode was employed for electro-sorption of fluoride ions. When processing a F−/Cl− mixed solution containing 10 mg/L F− and 100 mg/L Cl−, the CNT-CeO2 electrode reduced the concentration of F− ions to 1.5 mg/L in 150 min, amounting to a 85% F− removal efficiency, while Cl− removal was below 2%. This corresponds to a separation factor of 4.16, which is 40x higher than that of conventional AC electrodes. The high affinity of CNT-CeO2 to fluoride could be attributed to the entrance of fluoride ions into the crystal lattice of the CeO2 and the subsequent substitution for lattice oxygen atoms. The addition of CNTs offers substantial improvements in conductivity of the electrode and restricts the aggregation of CeO2, accelerating ion diffusion and selective adsorption. In addition, a selective CDI adsorption-desorption transport model was developed to describe the defluoridation process.

The desalination of seawater/wastewater utilizing flow-electrode capacitive deionization (FCDI) has received significant interest. However, challenges like the low electrical conductivity of flow electrode and excessive energy consumption have prevented the scaling up of desalination operations. To overcome these issues, this study introduces a new FCDI system termed the two-stage FCDI (TS-FCDI) system, in which desalination modules are equipped with freestanding and flow electrode. The TS-FCDI system offers a graded desalination module design that produces an average salt removal rate (ASRR) of 113 mu g cm(2).min(-1). However, the TS-FCDI system requires substantially reduced infrastructure investment, device size, and energy expenses. Notably, the design allows for the simultaneous operation of freestanding and flow electrode and enables the transport of ions and charges in the electrode region. Experimental evidence from multiple device configurations (CDI, FCDI, and TSFCDI) supports this claim. Notably, the TS-FCDI system shows about twice the desalination performance over FCDI, with approximately 50 h of single-cycle (SC) operation. This enhancement links the freestanding electrode with the flow electrode, enabling the device to be well-suited for practical applications. The continuous flow of electrode particles in contact with the freestanding electrode initiates secondary ion transport, merging two different types of electrodes to enhance the active space of the electrode, effectively improving ion adsorption performance. In summary, the results of this study indicate the potential of the TS-FCDI system as a suitable desalination technology for scaling up applications.

Faced with worldwide mercury (Hg) contamination in groundwater, efficient in situ remediation technologies are urgently needed. Carboxymethyl cellulose (CMC) stabilized iron sulfide (CMC-FeS) nanoparticles have been found effective for immobilizing mercury in water and soil. Yet, the potential use of the nanoparticles for creating an in situ reactive zone (ISRZ) in porous geo-media has not been explored. This study assessed the transport and deliverability of CMC-FeS in sand media towards creating an ISRZ. The nanoparticles were deliverable through the saturated sand bed and the particle breakthrough/deposition profiles depended on the injection pore velocity, initial CMC-FeS concentration, and ionic strength. The transport data were well interpreted using an advection-dispersion transport model combined with the classical filtration theory. The resulting ISRZ effectively removed mercury from contaminated groundwater under typical subsurface conditions. While the operating conditions are yet to be optimized, the Hg breakthrough time can be affected by groundwater velocity, influent mercury concentration, dissolved organic matter, and co-existing metals/metalloids. The one-dimensional advection-dispersion equation well simulated the Hg breakthrough data. CMC-FeS-laden ISRZ effectively converted the more easily available Hg species to stable species. These findings reveal the potential of creating an ISRZ using CMC-FeS for in situ remediation of Hg contaminated soil and groundwater.

Mercury contamination in groundwater is a serious global environmental issue that poses threats to human and environmental health. While MoS2 nanosheets have been proven promising in removing Hg from groundwater, an effective tool for in situ groundwater remediation is still needed. In this study, we investigated the transport and retention behavior of MoS2 nanosheets in sand column, and employed the formed MoS2 in situ reactive zone (IRZ) for the remediation of Hg-contaminated groundwater. Breakthrough test revealed that high flow velocity and MoS2 initial concentration promoted the transport of MoS2 in sand column, while the addition of Ca ions increased the retention of MoS2. In Hg removal experiments, the groundwater flow velocity did not influence the Hg removal capacity due to the fast reaction rate between MoS2 and Hg. With an optimized MoS2 loading, MoS2 IRZ effectively reduced the Hg effluent concentration down to <1 mu g/L without apparent Hg remobilization. Additionally, flake-like MoS2 employed in this study showed much better Hg removal performance than flower-like and bulk MoS2, as well as other reported materials, with the Hg removal capacity a few to tens of times higher than those materials. These results suggest that MoS2 nanosheets have the potential to be an efficient IRZ reactive material for in situ remediation of Hg in contaminated groundwater.

Thin film nanocomposite (TFNi) membranes interlayered with 2D nanomaterials are promising for organic solvent nanofiltration (OSN) applications. However, swelling and drying problems can arise due to the instability of the 2D nanomaterial interlayer in different solvents and humidity conditions. To address this issue, covalently modified molybdenum disulfide (MoS2) nanosheets (MoS2-COOH and MoS2-CONH2) were used as interlayers in the fabrication of TFNi membranes. The covalent groups acted as spacers to stabilize the interlayer spacing of the MoS2 interlayer and regulate its structural stability in diverse solvents and drying conditions. The TFNi membranes interlayered with MoS2-COOH and MoS2-CONH2 nanosheets demonstrated excellent structural stability and maintained their high permeance even after exposure to various solvents and drying conditions. The TFNiMoS2-CONH2 membrane exhibited the highest permeance of 8.60 +/- 0.23 L m- 2 h-1 bar-1 for MeOH, with a high rejection of 87.1 +/- 1.3 % for Evans Blue (EB). Furthermore, the TFNi membranes exhibited sustained separation performance throughout the 72 h test, demonstrating their structural stability. This study highlights the potential of TFNi membranes interlayered with covalently modified MoS2 nanosheets for OSN applications, providing high permeance and structural stability in diverse solvents and drying conditions.

In groundwater, the efficiency of MoS 2 nanosheets for Hg( ii ) removal is significantly hindered by natural organic matter (NOM) at high molar ratios of Hg/MoS 2 , whereas at low ratios, NOM has minimal impact on Hg( ii ) removal.

The critical challenge of effectively removing Pb-EDTA complexes and Pb(II) ions from wastewater is pivotal for environmental remediation. This research introduces a cutting-edge bulk-MoS2/H2O2 system designed for the simultaneous decomplexation of Pb-EDTA complexes and extraction of free Pb(II) ions, streamlining the process by eliminating the need for subsequent treatment stages. The system exhibits outstanding efficiency, achieving 98.1% decomplexation of Pb-EDTA and 98.6% removal of Pb. Its effectiveness is primarily due to the generation of reactive oxygen species, notably •OH and O2•- radicals, facilitated by bulk-MoS2 and H2O2. Key operational parameters such as reagent dosages, Pb(II): EDTA molar ratios, solution pH, and the presence of coexisting ions were meticulously evaluated to determine their impact on the system's performance. Through a suite of analytical techniques, the study confirmed the disruption of Pb-O and Pb-N bonds, further elucidating the decomplexation process. It also underscored the synergistic role of bulk-MoS2's adsorption properties and the formation of PbMoO4-like precipitates in enhancing Pb elimination. Demonstrating the bulk-MoS2/H2O2 system as a robust, one-step solution that meets stringent Pb emission standards, this study provides in-depth insights into the removal mechanisms of Pb-EDTA, affirming its potential for broader application in wastewater treatment practices.

Nitrophenol wastewater treatment and extracting and reusing precious metals from electronic wastewater have recently gained considerable attention. In this study, polyaniline-based membranes showcased remarkable gold recovery capability from electronic wastewater, effectively reclaiming 100% of gold on the membrane surface even in the presence of competing metal cations. The prepared Au@PmPD membrane, characterized by its high specific surface area and abundant Au nanoparticles (NPs), demonstrated excellent catalytic activity and stability, maintaining near 100% conversion efficiency in reducing 4-NP to 4-AP in the presence of NaBH4 over extended durations. Compared with the conventional physical mixing method, our in situ formation of the Au@PmPD membrane highlights the superior distribution of Au NPs and active sites for enhanced catalytic efficiency. It eliminates the need for additional steps to load Au NPs onto the membrane, resulting in a more straightforward and efficient process. Overall, this research provides a sustainable approach to repurposing waste into precious resources and offers a promising solution for the efficient treatment of persistent organic pollutants in wastewater, aligning with the principles of a circular economy.

Recent studies reveal the enhancement in water permeability for thin-film nanocomposite (TFN) membranes that incorporate an interlayer (TFNi), mainly when developed using substrates with larger pores. Nevertheless, the impact of substrate pore size on the membrane's morphology and separation performance requires further exploration. The study systematically investigates how the pore size of polycarbonate track-etched (PCTE) substrates influences these factors. Findings suggest that larger pores lead to rougher membrane surfaces and higher water permeance by reducing hydraulic transport resistance. However, optimal performance on larger pores requires a thicker MoS2 interlayer, leading to a thinner polyamide layer. Specifically, on PCTE-200 substrates, the MoS2 interlayer made up of large MoS2 nanosheets creates a more tortuous path for water molecules, limiting permeance. Conversely, smaller pores than the MoS2 nanosheets' dimensions obstruct the storage and diffusion of PIP monomers, negatively affecting the polyamide film and salt rejection. These findings underscore the significance of choosing the suitable substrate and adjusting interlayer thickness for creating TFN membranes with desired separation characteristics. The study provides valuable insights into the role of substrate selection and interlayer thickness in TFNi membrane design, offering guidelines for developing high-performance membranes for various separation tasks.

Two-dimensional (2D) metal-organic frameworks (MOFs) membranes have recently gained attention as novel material membranes for advanced oxidation processes (AOPs). Nonetheless, the susceptibility of 2D MOFs to reactive oxygen species (ROS) limits 2D MOF membranes’ effectiveness in AOPs. In this study, we introduce a novel approach, fabricating a 2D Co-MOF-derived nanosheet membrane (referred to as Co@C NS), assembled from pyrolyzed and exfoliated Co-MOF nanosheets, for the activation of peroxymonosulfate (PMS) in the removal of bisphenol A (BPA). Crucially, the synthesis process involves the pyrolysis of a carbon layer, serving as a protective barrier. This barrier effectively prevents the release of Co ions, ensuring the long-term structural and catalytic stability of the Co@C NS membrane. Notably, the membrane exhibits remarkable capabilities in discriminating between natural organic matter (NOM) and BPA through size exclusion, significantly mitigating the impact of NOM competition for ROS. Additionally, our study demonstrates an exceptional removal efficiency, achieving 100% BPA removal at an ultrahigh permeance of 1100 L m−2 h−1 bar−1, corresponding to an exceedingly short retention time of 0.14 s. Our mechanistic investigation reveals the involvement of singlet oxygen and sulfate radicals in the removal of BPA within the nanochannels, facilitated by the nanoconfinement effect. This study introduces valuable strategies for the development of 2D MOF-derived nanosheet membranes characterized by high catalytic activity and excellent stability, underlining their practical potential in AOP applications.

The presence of excess fluoride ions in drinking water has raised widespread concerns, necessitating the development of effective methods for its removal. Cerium dioxide (CeO2) holds promise as a selective adsorbent for fluoride ions, due to its exceptional affinity for fluoride and stability across a wide pH range. However, the impact of intrinsic properties of CeO2 on its adsorption characteristics and mechanisms remains unclear. In this study, we prepared a range of CeO2 materials with diverse intrinsic properties by adjusting the annealing temperature and atmosphere. Through a series of characterization techniques, we discovered a correlation between the content of oxygen vacancies, Ce(III) species, and surface hydroxyl groups (-OH), all of which decreased simultaneously with increasing air annealing temperature. With respect to the adsorption performance, the highest fluoride adsorption capacity of 111.1 mg g-1 was observed in un-CeO2, representing the nanomaterials with the highest oxygen vacancies. This capacity gradually decreased to 29.1 mg g-1 in 800-CeO2. Following fluoride adsorption, the oxygen vacancy density, Ce(III) content, and surface -OH content of all CeO2 materials decreased. When CeO2 materials were annealed in H2 for 1 h, the F- adsorption density increased due to the formation of more oxygen vacancies and surface -OH. Based on our findings, we conclude that oxygen vacancies play a critical role in determining whether fluoride ions can successfully exchange with surface -OH groups and enter the crystal lattice of CeO2, which significantly affects the adsorption performance. The pivotal role of oxygen vacancies, as proposed in this study, provides a valuable direction for future research aimed at enhancing the fluoride adsorption performance of CeO2.

The economic value of recovering gold from electronic waste (e-waste) has generated significant interest, but selective capture of gold from complex acidic electronic leaching solutions remains challenging. Here, we synthesized poly-m-phenylenediamine (PmPD) nanoparticles with a positively charged surface and amino functional groups, resulting in an adsorption capacity of 2063 mg/g for Au(III) in acidic solutions, superior to most traditional adsorbents. Electrostatic adsorption and reduction were identified as the adsorption mechanism for Au(III) by zeta potential, X-ray diffraction, transmission electron microscope, Fourier transform infrared, and X-ray photoelectron spectroscopy analyses. To enable adsorbent recycling, PmPD nanoparticles were assembled into adsorptive membranes and used for gold recovery from e-wastewater via a continuous-flow membrane separation process. The PmPD membrane achieved a dynamic gold recovery capacity of approximately 530 mg/g and could be effectively regenerated after washing with a mixture of thiourea and HCl. We demonstrated the practical application of the adsorptive membranes by recovering about 100% of gold from the leaching solution of waste printed circuit boards of computers. Finally, the recovered gold nanoparticles on the PmPD membrane were used to catalyze the degradation of p-nitrophenol, showcasing the catalytic property of gold. The Au@PmPD membrane loaded with 4 mg gold exhibited a high catalytic reduction performance with an apparent rate constant of 0.59 min(-1), one of the highest catalytic degradation rate constants of p-nitrophenol reported to date. Our study presents an effective and economical approach for recovering gold from e-waste, providing a prototype of resource recovery and reuse.

The study reveals that the interaction with cations, colloidal stability and transport behavior of MoS2 rely on its phase compositions and geometric structures.

Matrix effects of groundwater have profound implications on the removal mechanism and efficiency of Hg by two-dimensional MoS2 nanosheets.