Nanobubble transport in porous media: Towards agro- and environmental applications.

Nanobubbles have been increasingly used in various applications involving porous media, such as groundwater remediation and irrigation. However, the fundamental scientific knowledge regarding the interactions between nanobubbles and the media is still limited. The interactions can be repulsive, attractive, or inert, and can involve reversible or irreversible attachment as well as destructive mechanisms. Specifically, the stability and mobility of nanobubbles in porous media is expected to be dependent on the dynamic conditions and the physicochemical properties of the porous media, solutions, and nanobubbles themselves. In this study, we investigated how changes in solution chemistry (pH, ionic strength, and valence) and media characteristics (size and wettability) affect the size and concentration of nanobubbles under dynamic conditions using column experiments. Quartz crystal microbalance with dissipation monitoring provided a deeper understanding of irreversible and elastic nanobubbles' interactions with silica-coated surfaces. Our findings suggest that nanobubbles are less mobile in solutions of higher ionic strength and valence, acidic pH and smaller porous media sizes, while the wettability of porous media has a negligible influence on the retention of nanobubbles. Overall, our findings provide insights into the underlying mechanisms of nanobubble interactions and suggest potential strategies to optimize their delivery in various applications.

One-pot green bio-assisted synthesis of highly active catalytic palladium nanoparticles in porcine gastric mucin for environmental applications.

In this work, palladium nanoparticles were synthesized using one-pot synthesis utilizing porcine gastric mucin glycoproteins as reducing and capping agents. It is shown that the particles exhibited noticeable catalytic activity through both nitrophenol reduction and Suzuki-Miyaura coupling reactions. The catalytic performance was demonstrated with exceptionally high product yield, a fast reaction rate, and low catalyst use. The palladium-mucin composites obtained could be used in particle solution and as hydrogel catalysts to increase their reusability for at least ten reaction cycles with minimum loss in their catalytic effectiveness.

Risk assessment framework for microplastic in marine environments.

Constantly raising microplastic (MP) contamination of water sources poses a direct threat to the gentle balance of the marine environment. This study focuses on a multifactor hazard evaluation of conventional (polyethylene - PE, polypropylene - PP, and polystyrene - PS) and alternative (polyethylene terephthalate with 25 % or 50 % recycled material and polylactic acid) plastics. The risk assessment framework explored included MP abundance, water acidification potential, surface oxidation, fragmentation, and bacterial growth inhibition. Based on MP monitoring campaigns worldwide, we conclude that PE-based plastics are the most abundant MPs in water samples (comprise up to 82 % the MP in those samples). A year-long weathering experiment showed that PS-based and PP-based plastics were oxidized to a higher extent, resulting in the highest water acidification with pH reduction of up to three orders of magnitude. Finally, our laboratory experiments showed that weathered PS was the most fragile plastic during mechanical degradation, while both PP- and PS-based plastic extracts showed a significant growth inhibition toward the marine microorganisms (Bacillus sp. and Pseudoaltermonas sp). Using the examined factors as weighted inputs into our framework, this holistic evaluation of hazards suggest that PP-based plastic products were the most hazardous compared to the other conventional and alternative plastic types.

Engineering the Performance and Stability of Molybdenum Disulfide for Heavy Metal Removal.

Molybdenum disulfide (MoS2) has recently emerged as one of the most promising water nano-based adsorbent materials for heavy metal removal with the potential to provide an alternative to conventional water decontamination technologies. In this study, we demonstrate the trade-off between mercuric removal capacity and overall MoS2 adsorbent stability, both driven by MoS2 synthesis parameters. A bottom-up hydrothermal synthesis setup at various growth temperatures was employed to grow flower-like MoS2 films onto planar alumina supports. A thorough material characterization suggests that an increase in growth temperature from 150 to 210 °C results in higher MoS2 crystallinity. Interestingly, elevated growth temperatures resulted in poor mercuric removal (525 mg g-1, K = 2.2 × 10-3 h-1), yet showed enhanced chemical stability (i.e., minimal molybdenum leaching during exposure to mercury). On the other hand, low growth temperatures produce amorphous supported MoS2, exhibiting superb mercuric removal capabilities (5158 mg g-1, K = 36.1 × 10-3 h-1) but displaying poor stability, resulting in substantial byproduct molybdate leaching. Mercuric removal by crystalline MoS2 was accomplished by adsorption and electrostatic attraction-based removal mechanisms, whereas redox reactions and HgS crystallization-based removal mechanisms were more dominant when using amorphous MoS2 for mercury removal. Overall, our study provides essential insights into the delicate balance between MoS2 mercuric removal capabilities and MoS2 degradation, both related to material synthesis growth conditions. Employment of nano-enabled water treatments in general, and MoS2 for heavy metal removal in particular, requires us to better understand these important fundamental trade-off behaviors to achieve sustainable, effective, and responsible implementation of nanotechnologies in large scale systems.

Mediterranean microplastic contamination: Israel's coastline contributions.

This study provides an analysis of the current state of microplastic (MP) contamination along the Mediterranean coastline of Israel. Six strategic sites were monitored in this study - each representing a unique coastal environment. We conclude that Tel Aviv and Hadera, both located near stream estuaries, were highly contaminated (18,777 particles/m3) with MP compared to the other locations. The MP detected included both secondary MP and pristine polymeric pellets. In-depth characterization of the MP illustrated a large percentage of both fragmented and film MP morphologies and the most common MP polymers were polyethylene and polypropylene. Further particle analysis showed that MPs were contaminated with biofilm, including microorganisms such as diatoms, as well as metal residues. Through the spatial analysis presented herein we suggest that local rivers are significant contributors to MP contamination along the Mediterranean Sea coastline of Israel and may pose a direct threat to environment and human health.

Slow release of copper from jellyfish-based hydrogels for soil enrichment.

Nanotechnology has shown great potential to increase global food production and enhance food security. However, large-scale application of nano-enabled plant agriculture necessitates careful adjustments in design to overcome barriers associated with targeted nanomaterial delivery and their safety concerns. The research herein proposes the delivery of copper (Cu) from immobilized and non-immobilized copper oxide nanoparticles (Cu2O), an active nanomaterial with antifungal and micro-nutrient properties. A benign and biodegradable jellyfish-based hydrogel was used as a platform during Cu2O delivery to soils. The delivery kinetics and Cu dissolution from the nanocomposite were compared to those obtained with crosslinked ionic Cu in hydrogel, which was found to be a less controlled composite. In addition, changing environmental conditions from DI to soil extracts resulted in a decrease in the Cu dissolution rate (from 0.025 to 0.015 h-1) and an increase in the overall normalized Cu release (0.27 to 0.76 mg g-1). Use of hydrogels from natural sources allowed biodegradability over several months, adding nutrients (in the form of elements such as sulfur, nitrogen, and carbon) back to the environment, which ultimately minimizes nanomaterial required for a given desired nanomaterial yield and enhances the overall performance. Altogether, this work demonstrates the potential of Cu2O embedded hydrogels as a benign composite for Cu slow-release and therefore bolsters the field of nano-enabled plant agriculture and supports its safe deployment at large scales.

The role of size, charge, and cholesterol of cell membrane models in interactions with graphene oxide.

The growing in manufacturing and applications of graphene oxide (GO), a two-dimensional nanomaterial, highlights the need for a better understanding of its environmental impact and toxicity. This work investigates the interaction of GO with cell membrane models as an indication for GO's potential harmfulness. A wide range of biologically-relevant membrane parameters (size, charge and, cholesterol content) and simple optical techniques were used to evaluate the outcome of interactions of vesicular cell membrane models with GO. Loss of membrane integrity was found to be positively correlated with electrostatic attraction and negatively correlated with cholesterol content. The size of vesicle-GO aggregates increased as a function of initial vesicle size, while cholesterol content was found to have a negligible effect on aggregation. Interestingly, charged vesicles reduced vesicle-GO aggregate size either by electrostatic repulsion of negatively charge vesicles or by GO folding following attachment of positively charge vesicles. Overall, by examining how key biologically-relevant parameters of membrane models affect interactions with GO, we have augmented the understanding of the potential threats of GO towards biological cell and to the environment.

Interactions of microplastics and organic compounds in aquatic environments: A case study of augmented joint toxicity.

High levels of persistent contaminants such as microplastics (MPs) and trace organic compounds (TrOCs) in the aquatic environment have become a major threat on the ecosystem and human health. While MP's role as a vector of environmental TrOCs is widely discussed in the literature, the corresponding implications of the interaction between these two compounds on human health (i.e., their joint toxic effect) have not been illustrated. Using a TrOCs model (Triclosan, TCS) and primary MPs (polystyrene microbeads), this work evaluates the sorption and desorption potential of TCS and MPs in simulated environmental and cellular conditions, respectively, and estimates the single and joint toxicity of these interactions toward human cells (Caco-2). Surface functionality of the microbeads highly increased their adsorption capacity of TCS, from 2.3 mg TCS for non-functionalized microbeads to 4.6 mg and 6.1 mg TCS per gram of microbeads for amino- and carboxyl-functionalized MPs, respectively. Using non-functionalized MPs, non-specific "hydrophobic-like" interactions and π-π interactions dominated the sorption mechanism of TCS; however, the addition of hydrogen interactions between functionalized microbeads and TCS increased the microbeads' overall sorption capacity. TCS was desorbed from both functionalized and non-functionalized MPs when changing from environmental conditions to cellular conditions. Desorption was found to be dependent on the matrix complexity and protein content as well as microbead functionality. Finally, toxicity tests suggested that while low concentrations of TCS and MPs (separately) have minor toxic effect toward Caco-2 cells, TCS-sorbed MPs at similar concentrations have an order of magnitude higher toxicity than pristine MPs, potentially associated with the close interaction of both MP and TCS with the cells. Overall, this study not only elucidates the role of MPs as a TrOC vector, but also demonstrates a realistic scenario in which co-presence of these environmental contaminants poses risks to the environment and human health.

Modeling the energy consumption of potable water reuse schemes.

Potable reuse of municipal wastewater is often the lowest-energy option for increasing the availability of fresh water. However, limited data are available on the energy consumption of potable reuse facilities and schemes, and the many variables affecting energy consumption obscure the process of estimating energy requirements. By synthesizing available data and developing a simple model for the energy consumption of centralized potable reuse schemes, this study provides a framework for understanding when potable reuse is the lowest-energy option for augmenting water supply. The model is evaluated to determine a representative range for the specific electrical energy consumption of direct and indirect potable reuse schemes and compare potable reuse to other water supply augmentation options, such as seawater desalination. Finally, the model is used to identify the most promising avenues for further reducing the energy consumption of potable reuse, including encouraging direct potable reuse without additional drinking water treatment, avoiding reverse osmosis in indirect potable reuse when effluent quality allows it, updating pipe networks, or using more permeable membranes. Potable reuse already requires far less energy than seawater desalination and, with a few investments in energy efficiency, entire potable reuse schemes could operate with a specific electrical energy consumption of less than 1 kWh/m3, showing the promise of potable reuse as a low-energy option for augmenting water supply.

Engineered Polystyrene-Based Microplastics of High Environmental Relevance.

Microplastic (MP) pollution-an emerging environmental challenge of the 21st century-refers to accumulation of environmentally weathered polymer-based particles with potential environmental and health risks. Because of technical and practical challenges when using environmental MPs for risk assessment, most available data are generated using plastic models of limited environmental relevancy (i.e., with physicochemical characteristics inherently different from those of environmental MPs). In this study, we assess the effect of dominant weathering conditions-including thermal, photo-, and mechanical degradation-on surface and bulk characteristics of polystyrene (PS)-based single-use products. Further, we augment the environmental relevance of model-enabled risk assessment through the design of engineered MPs. A set of optimized laboratory-based weathering conditions demonstrated a synergetic effect on the PS-based plastic, which was fragmented into millions of 1-3 µm MP particles in under 16 h. The physicochemical properties of these engineered MPs were compared to those of their environmental counterpart and PS microbeads often used as MP models. The engineered MPs exhibit high environmental relevance with rough and oxidized surfaces and a heterogeneous fragmented morphology. Our results suggest that this top-down synthesis protocol combining major weathering mechanisms can fabricate improved, realistic, and reproducible PS-based plastic models with high levels of control over the particles' properties. Through increased environmental relevancy, our plastic model bolsters the field of risk assessment, enabling more reliable estimations of risk associated with an emerging pollutant of global concern.

Questioning the suitability of available microplastics models for risk assessment - A critical review.

The rise of microplastic (MP) pollution in the environment has been bolstering concerns regarding MPs' unknown environmental fate, transport, and potential toxicity toward living forms. However, the use of real environmental plastics for risk assessment is often hindered due to technical and practical challenges such as plastics' heterogeneity and their wide size distribution in the environment. To overcome this issue, most available data in the field is generated using plastic models as surrogates for environmental samples. In this critical review, we describe the gaps in risk assessments drawn from these plastic models. Specifically, we compare physicochemical properties of real environmental plastic particles to synthesized polymeric micro-beads, one of the most commonly used plastic models in current literature. Several surface and bulk characteristics including size, surface chemistry, polymer type, and morphology are shown to not only be inherently different between environmental MP's and synthesized micro-beads, but also drive behavior in fate, transport, and toxicity assays. We highlight the importance of expressing real-world physicochemical characteristics in representative MP models and outline how current state-of-the-art models are limited in this regard. To address this issue, we suggest future areas of research such as combinations of mechanical, photochemical, and thermal degradation processes to simulate real-world weathering, all in an effort to increase realism of plastic modeling and allow more robust and reliable environmental MP risk assessment in the future.

Pseudoviruses for the assessment of coronavirus disinfection by ozone.

The COVID-19 pandemic has severely impacted public health worldwide. Evidence of SARS-CoV-2 transmission via aerosols and surfaces has highlighted the need for efficient indoor disinfection methods. For instance, the use of ozone gas as a safe and potent disinfectant against SARS-CoV-2 virus is of particular interest. Here we tested the use of pseudoviruses as a model for evaluating ozone disinfection of the coronavirus at ozone concentrations of 30, 100, and 1000 ppmv. Results show that ozone disinfection rate of pseudoviruses was similar to that of coronavirus 229E (HuCoV-229E) at short contact times, below 30 min. Viral infection decreased by 95% following ozone exposure for 20 min at 1000 ppmv, 30 min at 100 ppmv and about 40 min at 30 ppmv. This findings mean that ozone is a powerful disinfectant toward the enveloped pseudovirus even at low ozone exposure. We also showed that viral disinfection occurs on various contaminated surfaces, with a positive association between disinfection and surface hydrophilicity. Infected surfaces made of aluminum alloy, for example, were better disinfected with ozone as compared to brass, copper, and nickel surfaces. Lastly, we demonstrate the advantage of ozone over liquid disinfectants by showing similar viral disinfection on top, side, bottom, and interior surfaces. Overall, our study demonstrates the potential use of ozone gas disinfection to combat the COVID-19 outbreak.

Tunable Molybdenum Disulfide-Enabled Fiber Mats for High-Efficiency Removal of Mercury from Water.

The application of molybdenum disulfide (MoS2) for water decontamination is expanded toward a novel approach for mercury removal using nanofibrous mats coated with MoS2. A bottom-up synthesis method for growing MoS2 on carbon nanofibers was employed to maximize the nanocomposite decontamination potential while minimizing the release of the nanomaterial to treated water. First, a co-polymer of polyacrylonitrile and polystyrene was electrospun as nanofibrous mats and pretreated to form pristine carbon fibers. Next, three solvothermal methods of controlled in situ MoS2 growth of different morphologies were achieved on the surface of the fibers using three different sets of precursors. Finally, these MoS2-enabled fibers were extensively characterized and evaluated for their mercuric removal efficiency. Two mercury removal mechanisms, including reduction-oxidation reactions and physicochemical adsorption, were elucidated. The two nanocomposites with the fastest (0.436 min-1 mg-1) and highest mercury removal (6258.7 mg g-1) were then further optimized through intercalation with poly(vinylpyrrolidone), which increased the MoS2 interlayer distance from 0.68 nm to more than 0.90 nm. The final, optimal fabrication technique (evaluated according to mercuric capacity, kinetics, and nanocomposite stability) demonstrated five times higher adsorption than the second-best method and obtained 70% of the theoretical mercury adsorption capacity of MoS2. Overall, results from this study indicate an alternative, advanced material to increase the efficiency of aqueous mercury removal while also providing the basis for other novel environmental applications such as selective sensing, disinfection, and photocatalysis.

Shape-Dependent Interactions of Manganese Oxide Nanomaterials with Lipid Bilayer Vesicles.

Interactions of transition-metal-oxide nanomaterials with biological membranes have important environmental implications and applications in ecotoxicity and life-cycle assessment analysis. In this study, we quantitatively assess the impact of MnO2 nanomaterial morphology-one-dimensional (1D) nanowires, 2D nanosheets, and 3D nanoflowers-on their interaction with phospholipid vesicles as a model for biological membranes. Confocal microscopy suggests visual evidence for the interaction of undisrupted vesicles with dispersed MnO2 nanomaterials of different morphologies, and it further supports the observation that minimal dye leakage of the vesicle inner solution was detected during the interaction with MnO2 nanomaterials during the dye leakage assay. Upon titration of vesicles to dispersions of MnO2 nanowires, nanosheets, and nanoflowers, each roughly 10 times larger than the vesicles, dynamic light scattering reveals two diffusive time scales associated with aggregates in the mixture. While the longer time scale corresponds to the dispersed MnO2 control population, the appearance of a shorter timescale with vesicle addition indicates interaction between the dispersed metal oxide nanomaterials and the vesicles. The interaction is shape-dependent, being more pronounced for MnO2 nanowires than for nanosheets and nanoflowers. Furthermore, the shorter diffusive time scale is intermediate between the vesicle and nanomaterial controls, which may suggest a degree of metal oxide aggregate breakup. Vesicle adsorption isotherms and zeta potential measurements during titration corroborate vesicle attachment on the nanomaterials. Our results suggest that the dispersed nanomaterial shape plays an important role in mediating nondestructive vesicle-nanomaterial interactions and that lipid vesicles act as efficient surfactants for MnO2 nanomaterials.

1,4-Dioxane as an emerging water contaminant: State of the science and evaluation of research needs.

1,4-Dioxane has historically been used to stabilize chlorinated solvents and more recently has been found as a contaminant of numerous consumer and food products. Once discharged into the environment, its physical and chemical characteristics facilitate migration in groundwater, resulting in widespread contamination of drinking water supplies. Over one-fifth of U.S. public drinking water supplies contain detectable levels of 1,4-dioxane. Remediation efforts using common adsorption and membrane filtration techniques have been ineffective, highlighting the need for alternative removal approaches. While the data evaluating human exposure and health effects are limited, animal studies have shown chronic exposure to cause carcinogenic responses in the liver across multiple species and routes of exposure. Based on this experimental evidence, the U.S. Environmental Protection Agency has listed 1,4-dioxane as a high priority chemical and classified it as a probable human carcinogen. Despite these health concerns, there are no federal or state maximum contaminant levels for 1,4-dioxane. Effective public health policy for this emerging contaminant requires additional information about human health effects, chemical interactions, environmental fate, analytical detection, and treatment technologies. This review highlights the current state of knowledge, key uncertainties, and data needs for future research on 1,4-dioxane.

Electrospun silica nanofiber mats functionalized with ceria nanoparticles for water decontamination.

This study demonstrates the fabrication of nanoceria-immobilized silica nanofibers for efficient water decontamination with easy reuse and regeneration properties. Commercially-available ceria (CeO2) nanoparticles were immobilized on electrospun silica nanofiber mats. Optimal conditions for both oxidation of model trace organic compounds (TrOCs) and hydroxyl-radical formation were determined in batch experiments with ceria nanoparticles. Kinetic experiments showed comparable oxidation rates of positively- and neutrally-charged TrOCs (95 and 98%, respectively) by the nanofiber composites at pH 2 in 0.5 mM H2O2. We demonstrated the reuse properties of the ceria nanofiber composites, finding less than a 15% reduction in oxidation performance after 10 cycles. In addition to this oxidative performance, the electrospun CeO2 nanofiber composites are also applicable for adsorbing the persistent contaminant perfluorooctanesulfonic acid (PFOS) through electrostatic interactions. Regeneration of the fibers was enabled through a one-hour heat treatment at 550 °C in air. Overall, results from this study show that the nanoceria-immobilized silica nanofibers can be used as efficient oxidative and adsorptive media to treat TrOCs in acidic waters, without use of an additional catalyst separation stage from solution.

Reactive, Self-Cleaning Ultrafiltration Membrane Functionalized with Iron Oxychloride Nanocatalysts.

Self-cleaning, antifouling ultrafiltration membranes are critically needed to mitigate organic fouling in water and wastewater treatment. In this study, we fabricated a novel polyvinylidene fluoride (PVDF) composite ultrafiltration membrane coated with FeOCl nanocatalysts (FeOCl/PVDF) via a facile, scalable thermal-treatment method, for the synergetic separation and degradation of organic pollutants. The structure, composition, and morphology of the FeOCl/PVDF membrane were extensively characterized. Results showed that the as-prepared FeOCl/PVDF membrane was uniformly covered with FeOCl nanoparticles with an average diameter of 1-5 nm, which greatly enhanced membrane hydrophilicity. The catalytic self-cleaning and antifouling properties of the FeOCl/PVDF membrane were evaluated in the presence of H2O2 at neutral pH. Using a facile H2O2 cleaning process, we showed that the FeOCl/PVDF membrane can achieve an excellent water flux recovery rate of ∼100%, following organic fouling with a model organic foulant (bovine serum albumin). Moreover, the in situ catalytic production of active hydroxyl radicals by the FeOCl/PVDF membrane was elucidated by electron spin resonance (ESR) and UV analysis. The catalytic performance of the FeOCl/PVDF membrane was further demonstrated by the complete degradation of bisphenol A when H2O2 was dosed in the feed solution at neutral pH. Our results demonstrate the promise of utilizing this novel membrane for the treatment of waters with complex organic pollutants.

High Performance Nanofiltration Membrane for Effective Removal of Perfluoroalkyl Substances at High Water Recovery.

We demonstrate the fabrication of a loose, negatively charged nanofiltration (NF) membrane with tailored selectivity for the removal of perfluoroalkyl substances with reduced scaling potential. A selective polyamide layer was fabricated on top of a poly(ether sulfone) support via interfacial polymerization of trimesoyl chloride and a mixture of piperazine and bipiperidine. Incorporating high molecular weight bipiperidine during the interfacial polymerization enables the formation of a loose, nanoporous selective layer structure. The fabricated NF membrane possessed a negative surface charge and had a pore diameter of ∼1.2 nm, much larger than a widely used commercial NF membrane (i.e., NF270 with pore diameter of ∼0.8 nm). We evaluated the performance of the fabricated NF membrane for the rejection of different salts (i.e., NaCl, CaCl2, and Na2SO4) and perfluorooctanoic acid (PFOA). The fabricated NF membrane exhibited a high retention of PFOA (∼90%) while allowing high passage of scale-forming cations (i.e., calcium). We further performed gypsum scaling experiments to demonstrate lower scaling potential of the fabricated loose porous NF membrane compared to NF membranes having a dense selective layer under solution conditions simulating high water recovery. Our results demonstrate that properly designed NF membranes are a critical component of a high recovery NF system, which provide an efficient and sustainable solution for remediation of groundwater contaminated with perfluoroalkyl substances.

Formation and degradation of N-oxide venlafaxine during ozonation and biological post-treatment.

While ozonation is considered an efficient treatment to eliminate trace organic compounds (TrOCs) from secondary wastewater effluents, the presence and persistence of transformation products (TPs) resulting from ozonation of TrOCs is a major concern that should be assessed prior to effluent discharge to the environment. Venlafaxine (VLX), an environmentally relevant tertiary amine-containing TrOC, was chosen as the model for this study. TP analysis confirmed that the lone electron pair of the non-protonated amine are the predominant site of oxidant attack, and therefore strongly affected by pH value and VLX speciation. N-oxide VLX (NOV), the primary ozone-induced TP, was formed and degraded simultaneously during ozonation of VLX-containing secondary effluent and reached a maximum yield of 0.44 to 0.85 (NOV-to-VLX0 ratio), depending on pH and hydroxyl (OH) radical presence. Rate constants for the reaction of NOV with ozone (3.1×102M-1s-1) and OH radicals (5.3×109M-1s-1) were determined. A simple kinetic model was developed to fit the kinetics of formation and degradation of NOV during ozonation in secondary effluents, based on a known ozone-reaction kinetic equation. The biodegradability of NOV (degradation rate of 39%) was significantly lower than that of the parent compound (VLX, 92%) after 71days, as evaluated by modified Zahn-Wellens tests, suggesting that N-oxide products are not better removed than the parent compound in a simulated biological post-treatment, which may even result in partial reformation of the parent compound. Lessons learned from this study were supported by a pilot-scale demonstration at the Shafdan wastewater-treatment plant, confirming the presence of NOV after ozonation and its persistence in biological post-treatment. Removal of such persistent TP will require higher dosages or promotion of OH-radicals during ozonation. Nevertheless, further assessment of the toxicity of persistent TPs relative to the parent compound is needed for complete evaluation of concerned TPs.

Enhanced antibacterial activity through the controlled alignment of graphene oxide nanosheets.

The cytotoxicity of 2D graphene-based nanomaterials (GBNs) is highly important for engineered applications and environmental health. However, the isotropic orientation of GBNs, most notably graphene oxide (GO), in previous experimental studies obscured the interpretation of cytotoxic contributions of nanosheet edges. Here, we investigate the orientation-dependent interaction of GBNs with bacteria using GO composite films. To produce the films, GO nanosheets are aligned in a magnetic field, immobilized by cross-linking of the surrounding matrix, and exposed on the surface through oxidative etching. Characterization by small-angle X-ray scattering and atomic force microscopy confirms that GO nanosheets align progressively well with increasing magnetic field strength and that the alignment is effectively preserved by cross-linking. When contacted with the model bacterium Escherichia coli, GO nanosheets with vertical orientation exhibit enhanced antibacterial activity compared with random and horizontal orientations. Further characterization is performed to explain the enhanced antibacterial activity of the film with vertically aligned GO. Using phospholipid vesicles as a model system, we observe that GO nanosheets induce physical disruption of the lipid bilayer. Additionally, we find substantial GO-induced oxidation of glutathione, a model intracellular antioxidant, paired with limited generation of reactive oxygen species, suggesting that oxidation occurs through a direct electron-transfer mechanism. These physical and chemical mechanisms both require nanosheet penetration of the cell membrane, suggesting that the enhanced antibacterial activity of the film with vertically aligned GO stems from an increased density of edges with a preferential orientation for membrane disruption. The importance of nanosheet penetration for cytotoxicity has direct implications for the design of engineering surfaces using GBNs.