Chemical Mechanism Research Articles

Action of Low-Density Polyethylene Microspheres in the Transport of Metformin Hydrochloride in Aqueous Medium Through Adsorption and Desorption

The present study addresses the issue of transporting pharmaceuticals via microplastics in aquatic environments. For this purpose, the adsorption and desorption of metformin hydrochloride (MET), a hydrophilic compound, on polyethylene microspheres (PMEs) were studied via batch adsorption and desorption capacity and kinetics tests. The adsorption test results indicated minimal influence of pH values above 5, alongside a decrease in adsorption capacity with an increasing mass of PMEs. The Freundlich model best represented the adsorption capacity data; however, values of n < 1 (0.6) and low K suggest a decrease in the sorption affinity of MET with increasing initial MET concentration and a low affinity of MET for PM beads. The rate and equilibrium of adsorption were fast, and the results adequately fit the pseudo-first- and pseudo-second-order models, suggesting that physical and chemical mechanisms contributed to the adsorption of MET onto the PEMs under the conditions of this study. The desorption equilibrium result was 1.3 mg g−1 ± 0.04 mg g−1, without significant change, regardless of the initial amount of adsorbed MET. However, the desorption percentage varied between 26.14% and 7.01% as a function of the amount. of MET adsorbed onto the PMEs. These results suggest that PMEs could be potential vectors of MET transport in aquatic environments.

Development of seasonal ozone maximum reactivity scales for Beijing, China

We designed scenarios based on urban emissions to develop a Maximum Incremental Reactivity (MIR) scale for 41 conventional volatile organic compounds (VOCs) in Beijing and quantitatively analyzed the various factors affecting MIR in urban areas. We explored the effects of updating the representative urban atmosphere used for ozone reactivity calculations by incorporating updated meteorological data, emission rates, initial condition concentrations, and VOC profile compositions. A box model equipped with the Master Chemical Mechanism (MCM) was used to localize the MIR scale for Beijing based on urban emission model inputs, and this was compared with scenarios in the United States. The MIR differences for most VOC species were minimal; however, Beijing exhibited higher MIR values for aromatic hydrocarbons in the summer, attributed to the higher emission intensity of aromatics in the city. Due to differences in meteorological conditions and emission scenarios, the MIR showed significant seasonal characteristics across different months. It is necessary to calculate independent MIR scales for different urban agglomerations under specific ozone pollution seasons and emission conditions. This study provides recommendations for the application of the MIR scale and can serve as a reference for VOC control strategies in China and other countries facing ozone pollution.

Disentangling mechanisms by which microplastic films affect plant-soil systems: physical effects of particles can override toxic effects of additives

BackgroundMicroplastics, polymer-based particles < 5 mm, affect plant–soil systems positively or negatively, suggesting there are different modes of action. Microplastics, as particles, have physical effects but the leaching of additives likely contributes chemical mechanisms, both of which may be dependent on microplastic size. To disentangle such mechanisms, we established a controlled experiment involving polypropylene and polyethylene films of small, medium and large size, and we evaluated the individual and combined effect of plastic particles and additives (leachates from plastic particles) on soil properties and plant performance of the phytometer Daucus carota and on bare soils.ResultsWe find that additives better explained variation in soil properties (e.g., 44.6% vs 1.3%). Soil respiration and aggregation were negatively affected for additives, likely due to the presence of toxic substances. Overall, such effects increased as plastic size decreased. By contrast, plastic particles better explained plant biomass responses. The positive effect of particles on aeration which may promote root penetration and nutrient uptake, and microplastics itself as a source of carbon potentially promoting soil microbial activity, help explain the positive effect of particles on plant biomass. Plants mitigated the negative effects of additives on bare soils while enhancing the positive effects of particles. This improvement was likely linked to an increase in root activity and rhizodeposition, as plastic particles improved soil aeration. The combined effect of additives and particles, which mimics the microplastic found in the soil, mitigated their individual negative effects on plant–soil systems. As the negative effect of additives could have been masked by the positive effects of particles, simply reporting net positive effects would capture only part of the response.ConclusionsAdditives and plastic particles differently affect soil properties and plant biomass. Additives primarily negatively affect soil properties due to toxic substances, while plastic particles enhance plant biomass likely by improving soil aeration. When examining microplastics effects on terrestrial systems (i.e., the combined effect of additives and particles), the negative effect of additives may be masked by the positive effects of plastic particles. Reporting only net positive effects risks overlooking these underlying negative effects. Plants can mitigate the negative impacts of additives and amplify the positive effects of plastic particles. Our study emphasizes the importance of investigating both the individual and combined effects of additives and particles to fully understand and address the impacts of microplastics on terrestrial ecosystems.

Developing a high-fidelity reduced chemical kinetic mechanism for liquefied petroleum gas (LPG)

The current study aimed at developing an optimal and highly accurate reduced chemical kinetic mechanism for the Liquid Petroleum Gas (LPG). A three-stage reduction process including pre-processing, the main body reduction, and post-processing was utilized. In the main body reduction, a five-step reduction schematic was applied to the detailed mechanism including 980 species and 4972 reactions released by LLNL utilizing the Direct Relation Graph Error Propagation (DRGEP) method coupled with the isomer lumping and sensitivity analysis. Four different reduced mechanisms including 88, 73, 67, and 44 species were developed and compared with the experimental data. The laminar flame speed/equivalence ratio, ignition delay/temperature curves of the LPG combustion as well as 3D combustion parameters including in-cylinder pressure, mean temperature, heat release rate, and fuel consumption rate for an LPG-fueled opposed-piston engine were considered. It was seen that the 73 species mechanism results for the ignition delay/temperature and laminar flame speed/equivalence ratio matched with the experimental data with discrepancies of 3% and 5%, respectively. The 88 species and 73 species mechanisms showed good agreement in 3D modeling for all the considered parameters in comparison with the detailed mechanism with error values less than 2%. However, the 67 and 44 mechanisms results were not in accordance with the experimental data. Consequently, the developed 73-species mechanism was considered the optimal mechanism for LPG fuel.

Enhanced nitrogen fixation and Cd passivation in rhizosphere soil by biochar-loaded nitrogen-fixing bacteria: Chemisorption and microbial mechanism

This study developed a biochar-loaded Ac material and clarified its chemical and microbial mechanisms for cadmium (Cd) immobilization and plant growth promotion. Results showed that biochar-loaded nitrogen-fixing bacteria (Azotobacter chroococcum; BAc) enhanced Cd adsorption by forming stable complexes with bacterial secretions and activating biochar functional groups. Compared with BC and Ac, after BAc application, Ac successfully colonized the lettuce rhizosphere, tagged with green fluorescent protein. It improved plant nitrogen by 47.39–72.47 % and increased root and shoot biomass by 50.35–107.32 % through nitrogen fixation and amino acid release. BAc reduced soil Cd bioavailability by 16.67–46.42 % and Cd accumulation in root and shoot by 14.28–69.74 %. This occurred through increasing soil pH and converting exchangeable Cd to carbonate-bound and Fe/Mn oxide-bound fractions. Importantly, BAc improved the rhizosphere nutrient environment and promoted the deterministic assembly of the rhizosphere microbial community. It also increased microbial diversity and attracted taxa like Actinomycetales (7.59 %), Solirubrobacteriales (5.17 %), Rhizobiales (5.17 %), and Sphingomonadales (5.17 %), all associated with nitrogen fixation, plant growth promotion, and Cd immobilization. Structural equation modeling (SEM) confirmed that BAc increased nitrogen utilization efficiency in lettuce and facilitated biotic immobilization of soil Cd by optimizing the microbial structure. This study provides insights into how biochar-loaded Ac improve plant growth and control soil Cd pollution.

Clogging of Leachate Drains in Landfills due to Biochemical Precipitation: a Literature Review

Objective: Review the relevant literature and analyze the causes that lead to the clogging of leachate drains in landfills due to biochemical precipitation. Theoretical Framework: Although leachate drainage systems have greatly evolved in terms of performance, clogging can occur in all designs due to physical, biological, and chemical mechanisms. Method: To investigate the issue of clogging in leachate drainage systems, an extensive literature review was conducted through consultations on relevant websites. National and international technical papers were sought, as well as regulations from environmental agencies of different countries. Results and Discussion: The removal of Chemical Oxygen Demand (COD), primarily in the form of acetic acid, transforms this stronger acid into weaker acids such as carbonic acid, which results in an increase in the pH of the environment. The concentration of carbonate also increases, consequently accelerating the precipitation of calcium carbonate. These precipitates are usually mixed with the biofilm and exhibit very characteristic shapes and structures. Research Implications: The lifespan of a vertical landfill can be strongly determined by the clogging phenomena in the leachate drainage system. Therefore, the monitoring of this system must be carried out with great care. Originality/Value: This review stands out for addressing a relevant and underexplored topic, especially in the national technical literature. Understanding the processes that can lead to clogging of the leachate drainage system is of interest to everyone working in the field, particularly those who design and/or operate a landfill.

The regulatory effects of bioactive polysaccharides on intestinal function and bile acids: chemical structures, bioactivities, and mechanisms.

Polysaccharides are one of the important components of the human diet, offering a wide range of biological activities, especially in improving inflammation in the digestive system and addressing metabolic diseases. Among all the reported bioactivities of polysaccharides, their regulation effects on intestinal function and bile acids (BAs) are gradually attracting the attention of more researchers. Bile acids, the main components of intestinal lipid digestive fluid, are also key signal factors for metabolic homeostasis and impact overall health. Polysaccharides usually interact directly or indirectly with the gut and gut microbiota to participate in the regulation process of reabsorption, metabolism, and excretion of bile acids in humans, thereby exerting their role in the intervention of human diseases. In this review, we comprehensively reviewed the effects of bioactive polysaccharides on the regulation of intestinal function and bile acids. The chemical structures, bioactivities, and potential mechanisms for their activities were also reviewed. This study aimed to provide a comprehensive reference for future research on the activities and mechanisms of polysaccharides, as well as to offer important strategies and insights for the development of bioactive polysaccharides to prevent inflammatory and metabolic diseases.

Simple Parameters and Data Processing for Better Signal-to-Noise and Temporal Resolution in In Situ 1D NMR Reaction Monitoring.

In situ 1D NMR spectroscopic reaction monitoring allows detailed investigation of chemical kinetics and mechanism. Concentration versus time data are derived from a time series of NMR spectra. Each spectrum in the series is obtained by Fourier transform of the corresponding FID. When the spectrometer outputs FIDs recorded from multiple scans, the spectra benefit from an increase in signal-to-noise (S/N). However, this reduces the number of FIDs and, thus, kinetic data points. We report a simple alternative in which the same number of scans is acquired by the spectrometer, but each scan is saved independently. Signal averaging is then conducted by postacquisition processing. This leads to an increase in both the S/N and the number of kinetic data points and can avoid "overaveraging" effects. The entire series of single-scan FIDs spanning the reaction lifetime can be summed to yield a "total reaction spectrum" in which intermediates can be identified. The method can be applied in coherence with phase cycling to minimize spectral distortion during solvent signal suppression. Overall, the approach simplifies the preacquisition parameters to the estimation of the reaction duration and T1max and then the selection of the pulse angle, θ, and scan repetition time, τR, without the need to set the signal averaging before the experiment.

Nanodomains and Their Temperature Dependence in a Phosphonium-Based Ionic Liquid: A Single-Molecule Tracking Study.

Ionic liquids (ILs) exhibit a unique nanoscale structure (i.e., nanodomains) characterized by their organization into distinct domains. We present evidence of nanodomains in trihexyl(tetradecyl)phosphonium chloride, [P66614][Cl], using single-molecule tracking (SMT) and the maximum entropy method (MEM) to analyze single-molecule trajectories. The diffusion properties of ATTO 647N were assessed as the temperature of [P66614][Cl] increased from 20 °C (4020 cP), 35 °C (1239 cP), 45 °C (599 cP) to 50 °C (439 cP). The MEM analysis revealed a distinct two-population distribution of diffusion coefficients representing nanodomains in [P66614][Cl] at 20 °C (4020 cP). The slow population accounts for 16%, with a diffusion coefficient of 0.104 μm2/s, while the fast population constitutes 84% with a diffusion coefficient of 0.634 μm2/s. Two diffusing populations were also measured for the chemically different probes ATTO 647N, DiD, and Nile Blue chloride in [P66614][Cl] at 20 °C. In contrast, only a single fast population was measured in [P66614][Cl] at 50 °C. At a similar viscosity (640 cP) but a lower temperature of 20 °C, trihexyl(tetradecyl)phosphonium bis[(trifluoromethyl)-sulfonyl]imide, [P66614][NTf2], also showed only a single diffusing population. The elimination of the slow population and the presence of a single diffusing population in [P66614][Cl] as the temperature increases and the viscosity decreases is consistent with liquid-liquid phase separation (LLPS) as a mechanism of nanodomain formation. In addition, the measurement of two diffusing populations for three fluorophores with different chemical structures is also consistent with a physical mechanism, and not a chemical mechanism, for nanodomain formation.

Long-Range Charge Transport in Molecular Wires.

Long-range charge transport (LRCT) in molecular wires is crucial for the advancement of molecular electronics but remains insufficiently understood due to complex transport mechanisms and their dependencies on molecular structure. While short-range charge transport is typically dominated by off-resonant tunneling, which decays exponentially with molecular length, recent studies have highlighted certain molecular structures that facilitate LRCT with minimal attenuation over several nanometers. This Perspective reviews the latest progress in understanding LRCT, focusing on chemical designs and mechanisms that enable this phenomenon. Key strategies include π-conjugation, redox-active centers, and stabilization of radical intermediates, which support LRCT through mechanisms such as coherent resonant tunneling or incoherent hopping. We discuss how the effects of molecular structure, length, and temperature influence charge transport, and highlight emerging techniques like the Seebeck effect for distinguishing between transport mechanisms. By clarifying the principles behind LRCT and outlining future challenges, this work aims to guide the design of molecular systems capable of sustaining efficient long-distance charge transport, thereby paving the way for practical applications in molecular electronics and beyond.

Multi–class cyanobacterial toxin analysis using hydrophilic interaction liquid chromatography–mass spectrometry

Cyanobacteria produce diverse classes of toxins including microcystins, nodularins, anatoxins, cylindrospermopsins and saxitoxins, encompassing a range of chemical properties and mechanisms of toxicity. Comprehensive analysis of these toxins in cyanobacterial, environmental and biological samples generally requires multiple methods of extraction and analysis.In this work, a method was developed for the major classes of cyanotoxins, which comprised of a three-step liquid-solid extraction method using 75 % CH3CN with 0.1 % HCOOH and a hydrophilic interaction liquid chromatography (HILIC) elution gradient that provided retention of the less polar microcystins through to the highly polar saxitoxins. Detection was performed by tandem mass spectrometry in selected reaction monitoring mode with positive and negative polarity switching. Identification criteria included matching retention times and product ion ratios with available standards. In-house validation demonstrated good performance of the method including precision ranging from 1.5 (microcystin-LA) to 5.8 (gonyautoxin-2) % RSDs, and detection limits ranging from 0.01 (cylindrospermopsin) to 0.99 (gonyautoxin-3) µg/g in freeze dried material cyanobacteria. Recovery was assessed using spiked non-toxic cyanobacterial samples (Aphanizomenon sp.) and ranged from 83 (neosaxitoxin) to 107 % ([Dha7]microcystin-LR).As a demonstration of application, toxin profiles in cyanobacterial cultures, benthic and planktonic cyanobacteria field samples, and shellfish reference materials were successfully evaluated. The procedure is also amenable for extension to other polar toxin classes including domoic acid and guanitoxin. With increasing reports of cyanobacterial blooms globally, the method represents a powerful quantitative screening tool for measuring cyanotoxins across a broad range of samples.

Chemical Composition of Aerosols from the E-Cigarette Vaping of Natural and Synthetic Cannabinoids.

Vaping cannabinoids in electronic (e)-cigarette devices is rapidly increasing in popularity, particularly among adolescents, although the chemistry affecting the composition of the vape aerosol is not well understood. This work investigates the formation of aerosol mass, bioactive hydroxyquinones, and harmful or potentially harmful carbonyls from the e-cigarette vaping of natural and synthetic cannabinoids e-liquids in propylene glycol and vegetable glycerin (PG/VG) solvent at a 50 mg/mL concentration in a commercial fourth-generation vaping device. The following cannabinoids were studied: cannabidiol (CBD), 8,9-dihydrocannabidiol (H2CBD), 1,2,8,9-tetrahydrocannabidiol (H4CBD), cannabigerol (CBG), and cannabidiolic acid (CBDA). Quantification of analytes was performed using liquid chromatography coupled to accurate mass spectrometry. The addition of cannabinoids significantly increased aerosol and carbonyl formation compared with the PG/VG solvent alone. All cannabinoids in the study formed hydroxyquinones during vaping (up to ∼1% mass conversion) except for CBDA, which primarily decarboxylated to CBD. Hydroxyquinone formation increased and carbonyl formation decreased, with a decreasing number of double bonds among CBD and its synthetic analogues (H2CBD and H4CBD). During the vaping process, ∼3-6% of the cannabinoid mass can be observed as carbonyls under the study conditions. Oxidation of the terpene moiety on the cannabinoids is proposed as a major contributor to carbonyl formation. CBD produced significantly higher concentrations of formaldehyde, acetaldehyde, acrolein, diacetyl, and methylglyoxal compared with the other cannabinoid samples. CBG produced significantly higher levels of acetone, methacrolein, and methylglyoxal. Conversion of CBD to tetrahydrocannabinol (THC) was not observed under the study conditions. The chemical mechanism basis for these observations is discussed. Compared with other modalities of use for CBD and other cannabinoids, vaping has the potential to adversely impact human health by producing harmful products during the heated aerosolization process.

Reductive Photocatalytic Proton-Coupled Electron Transfer by a Zirconium-Based Molecular Platform.

Reductive proton-coupled electron transfer (PCET) has important energetic implications in numerous synthetic and natural redox processes. The development of catalytic systems that can mediate such transformations has become an attractive target, especially when light is used to generate the reactive species towards solar-to-chemicals conversion. However, such approach becomes challenged by kinetic competition with H2 evolution. Here we describe the excited state reactivity of a molecular Zr-based platform under visible light irradiation for the efficient reduction of multiple bonds. Mechanistic investigations shine light on a charge separation process that colocalizes an excited electron and an acidic proton to promote selective PCET. We further leveraged this reactivity for the photocatalytic reduction of a variety of organic substrates. Our results demonstrate the promise of this molecular platform to design strong photocatalytic PCET mediators for reductive transformations. More broadly, we also show the potential relevance of PCET mechanisms in the (photo)redox chemistry of Zr-based molecular materials.

Reductive Photocatalytic Proton‐Coupled Electron Transfer by a Zirconium‐Based Molecular Platform

AbstractReductive proton‐coupled electron transfer (PCET) has important energetic implications in numerous synthetic and natural redox processes. The development of catalytic systems that can mediate such transformations has become an attractive target, especially when light is used to generate the reactive species towards solar‐to‐chemicals conversion. However, such approach becomes challenged by kinetic competition with H2 evolution. Here we describe the excited state reactivity of a molecular Zr‐based platform under visible light irradiation for the efficient reduction of multiple bonds. Mechanistic investigations shine light on a charge separation process that colocalizes an excited electron and an acidic proton to promote selective PCET. We further leveraged this reactivity for the photocatalytic reduction of a variety of organic substrates. Our results demonstrate the promise of this molecular platform to design strong photocatalytic PCET mediators for reductive transformations. More broadly, we also show the potential relevance of PCET mechanisms in the (photo)redox chemistry of Zr‐based molecular materials.

Scalp condition improvement with botanical extracts possessing chemical and physical antioxidant activity.

Oxidative stress is implicated in scalp and hair health manifesting in several ways, including skin barrier, hair retention, healthy hair appearance and scalp sensation. We previously linked markers of oxidative damage to dandruff and skin barrier impairment and have linked key anti-dandruff technologies to the resolution of these issues. Here we expand the therapeutic space demonstrating many botanical extracts offer protective benefits against ROS stress via both chemical and biological antioxidant mechanisms. Chemical antioxidant activity of 10 botanical extracts was measured using oxygen radical absorbance capacity (ORAC) and biological antioxidant activity was measured using a Nrf-2 cell assay. A three-dimensional human keratinocyte skin equivalent model from MatTek was used to measure efficacy of reducing reactive oxygen species (ROS) from both the botanicals added as a solution and from a shampoo product. A 4-week consumer study with 56 panels was conducted with a leave-on treatment containing a botanical extract. Measurement of the oxidized lipids (9 and 13-Hydroxy-10E 12Z-octadecadienoic acid, HODE) extracted from scalp tape strips was made using gradient reversed-phase high-performance liquid chromatography with tandem mass spectrometry (HPLC/MS/MS). We demonstrated invitro that many botanical extracts exert antioxidant activity by quenching radicals in ORAC testing as well as activating biological antioxidant pathways via nrf-2 up-regulation in a cellular reporter system. Furthermore, we demonstrate these antioxidant activities for these botanicals in 3D skin models and ultimately show the reduction of lipid oxidation products in a consumer use context with a rosemary extract. Improved scalp condition can be achieved with incorporation of botanicals having the potential to exert antioxidant activity in hair/scalp care products.

Mechanisms of Biocontrolling Action of Yeasts in Post-Harvest Fruit: A Review

Objective: The aim of the research is to address the biological control developed by yeasts in the post-harvest of fruits, based on a brief literature review on the subject. Theoretical Framework: The use of chemical control mechanisms and biocontrol is based on the increasing need for sustainable agricultural practices that ensure human health and environmental preservation. While synthetic fungicides are effective in combating fungal diseases, their excessive use raises concerns about pathogen resistance and public health risks. In this context, the development of biocontrol agents, such as yeasts, emerges as a viable and ecological alternative, promoting food safety and crop protection with a lower environmental impact. Method: A narrative literature review was conducted using major scientific databases to collect articles on the biological control of yeasts in the post-harvest of fruits. Key studies were evaluated to measure effectiveness and understand the mechanisms related to the biocontrol action of these yeasts. Results and Discussion: The predominant chemical control for fungal diseases is being replaced by sustainable alternatives, such as yeast-based biofungicides, which demonstrate effectiveness against pathogens in post-harvest settings. Mechanisms such as killer activity and the production of hydrolytic enzymes stand out in biocontrol. Although promising, further research is needed to deepen the understanding of biocontrol agents and their applications.

An updated aerosol simulation in the Community Earth System Model (v2.1.3): dust and marine aerosol emissions and secondary organic aerosol formation

Abstract. Aerosols constitute important substance components of the Earth's atmosphere and have a profound influence on climate dynamics, radiative properties, and biogeochemical processes. Here we introduce updated emission schemes for dust, sea-salt, and marine primary organic aerosols (MPOA), as well as augmented secondary organic aerosol (SOA) formation pathways within the Community Earth System Model (CESM; version 2.1.3). The modified dust emission scheme shifts the original hotspot-like dust emission to a more continuous distribution, improving the dust aerosol optical depth (DAOD) simulations at stations in north Africa and central Asia. This update also reduces dust residence time from 4.1 to 1.6 d, enhancing concentration simulations downwind of dust source regions. For sea-salt emissions, we incorporate an updated sea surface temperature (SST) modulation and introduce a relative-humidity-dependent correction factor for sea-salt particle size, with SST having a significantly larger impact on sea-salt emissions (16.1 %) compared to the minor effect of humidity (−0.3 %). We then extend our modelling to incorporate emissions of marine primary organic aerosols (MPOA) as mixed externally with sea-salt aerosols, coupled offline with the ocean component Parallel Ocean Program (POP2). The results underscore the substantial influence of phytoplankton diversity on MPOA emissions, with 148 % variability simulated among different phytoplankton types, highlighting the role of biological variability in aerosol modelling. Furthermore, we refine the model's chemical mechanisms by including the irreversible aqueous uptake of dicarbonyl compounds as a new pathway for SOA formation, contributing an additional 37 % to surface SOA concentrations. These improvements enrich the ability of the CESM to use intricate linkages between different components of the Earth system, thereby enabling a more comprehensive description of natural aerosol emissions, chemical processes, and their impacts.

Single-molecule profiling of per- and polyfluoroalkyl substances by cyclodextrin mediated host-guest interactions within a biological nanopore.

Biological nanopores are increasingly used in molecular sensing due to their single-molecule sensitivity. The detection of per- and polyfluoroalkyl substances (PFAS) like perfluorooctanoic acid and perfluorooctane sulfonic acid is critical due to their environmental prevalence and toxicity. Here, we investigate selective interactions between PFAS and four cyclodextrin (CD) variants (α-, β-, γ-, and 2-hydroxypropyl-γ-CD) within an α-hemolysin nanopore. We demonstrate that PFAS molecules can be electrochemically sensed by interacting with a γ-CD in a nanopore. Using HP-γ-CDs with increased steric resistance, we can identify homologs of the perfluoroalkyl carboxylic acid and the perfluoroalkyl sulfonic acid families and detect common PFAS in drinking water at 0.4 to 2 parts per million levels, which are further lowered to 400 parts per trillion by sample preconcentration. Molecular dynamics simulations reveal the underlying chemical mechanism of PFAS-CD interactions. These insights pave the way toward nanopore-based in situ detection with promises in environmental protection against PFAS pollution.

Numerical study on flow and combustion properties of oblique detonation engine in a wide speed range

Ensuring safe flight is a fundamental prerequisite for developing hypersonic propulsion systems. A comprehensive investigation of the steady boundary associated with oblique detonation wave in a wide speed range was conducted, with the aim of exploring the feasibility of oblique detonation engine across a diverse array of flight conditions. In this study, the wedge angle applicable in a wide-speed range was acquired via the analysis of oblique detonation wave polar curve. The configuration of the internal injection oblique detonation engine was subsequently designed and established, considering the effect of fuel-air inhomogeneity and complex wave system interactions within a confined combustor. The compressible Euler equations coupled with a 9-species and 19-step chemical reaction mechanism are employed to simulate the oblique detonation process. Ultimately, the safe flight envelope of an air-breathing vehicle equipped with the internal injection oblique detonation engine is mapped across a broad range of Mach numbers, demonstrating the engine’s capability to operate within the Mach 8 to 12 range. Furthermore, the findings reveal that decreasing either the flight Mach number or altitude results in unsteady oblique detonation wave within the internal injection oblique detonation engine combustor, however, reducing the equivalence ratio can stabilize the oblique detonation wave once again. This study provides valuable guidance for the design and wide-speed-range operation of an internal injection oblique detonation engine.

All-In-One Epoxy/MXene Nanocomposites with Bead-Type Polymeric Imidazole Latent Curing Agent for Enhancing Storage Stability and Flame Retardancy.

Developing a single-component epoxy system is challenging but crucial for advanced thermoset applications. Unfortunately, conventional latent curing agents using chemical or physical passivation do not provide satisfactory storage stability and the necessary property requirements. Here, it is demonstrated that all-in-one epoxy/MXene nanocomposite system, comprising epoxy resin, polymeric imidazole latent curing agent beads (PILCAB), and Ti3C2Tx MXene, exhibits excellent storage stability, improved flame retardancy, and enhanced mechanical strength. PILCABs, prepared through a Diels-Alder (DA) crosslinking reaction between furan groups of poly(imidazolyl methacrylate)-random poly (furfuryl methacrylate) (PIm-r-PFu) copolymer and bismaleimide (BMI), exhibit excellent storage stability, as stable as under 60 °C storage due to the imidazole reactivity being suppressed synergistically by both physical and chemical passivation mechanisms. Ti3C2Tx MXene flakes, surface-functionalized with alkylated 3,4-dihydroxyl-L-phenylalanine, exhibit excellent compatibility with the epoxy matrix. Consequently, the enhanced storage stability, flame retardancy, and mechanical strength of the all-in-one epoxy/MXene nanocomposite are attributed to the strong DA bond formation in latent curing agent, efficient charring capability of MXene and BMI, and the catalytic effect of the MXene. This study opens new avenues for designing and developing single-component epoxy systems that satisfy demanding requirements, including storage stability, mechanical strength, and flame retardancy, which are essential for practical applications.