Transport Mechanism Research Articles

Sources and transport of organic matter in the Ganges-Brahmaputra-Meghna River system of Bengal Basin, Bangladesh

This study aimed to understand the sources and transport mechanism of organic matter (OM) in the Ganges-Brahmaputra-Meghna (GBM) river system in Bangladesh. We conducted analyses of total organic carbon (TOC), total nitrogen (TN), their stable isotopes (δ13C and δ15N), and sediment grain size. The results reveal a heterogeneous mixture of OM derived from terrestrial plants, aquatic environments, and anthropogenic sources. The Brahmaputra River exhibited higher concentrations of TOC and TN, with δ13C and δ15N values indicating that the OM is primarily sourced from C3 plants. Conversely, the Ganges River demonstrated lower TOC levels and higher isotopic values, reflecting significant anthropogenic inputs. The Lower Meghna showed a mixture of terrestrial and marine sources. Variations in the TOC/TN ratios across the river system underscore the complex interplay between natural and anthropogenic factors. Additionally, sediment grain size plays a crucial role, with finer sediments in the Brahmaputra River associated with increased OM concentrations, while coarser sediments in the Ganges River correlate with lower TOC and TN levels.

Mathematical modeling of 18F-Fluoromisonidazole (18F-FMISO) radiopharmaceutical transport in vascularized solid tumors

18F-Fluoromisonidazole (18F-FMISO) is a highly promising positron emission tomography radiopharmaceutical for identifying hypoxic regions in solid tumors. This research employs spatiotemporal multi-scale mathematical modeling to explore how different levels of angiogenesis influence the transport of radiopharmaceuticals within tumors. In this study, two tumor geometries with heterogeneous and uniform distributions of capillary networks were employed to incorporate varying degrees of microvascular density. The synthetic image of the heterogeneous and vascularized tumor was generated by simulating the angiogenesis process. The proposed multi-scale spatiotemporal model accounts for intricate physiological and biochemical factors within the tumor microenvironment, such as the transvascular transport of the radiopharmaceutical agent, its movement into the interstitial space by diffusion and convection mechanisms, and ultimately its uptake by tumor cells. Results showed that both quantitative and semi-quantitative metrics of 18F-FMISO uptake differ spatially and temporally at different stages during tumor growth. The presence of a high microvascular density in uniformly vascularized tumor increases cellular uptake, as it allows for more efficient release and rapid distribution of radiopharmaceutical molecules. This results in enhanced uptake compared to the heterogeneous vascularized tumor. In both heterogeneous and uniform distribution of microvessels in tumors, the diffusion transport mechanism has a more pronounced than convection. The findings of this study shed light on the transport phenomena behind 18F-FMISO radiopharmaceutical distribution and its delivery in the tumor microenvironment, aiding oncologists in their routine decision-making processes.

Observation of voltage dependent negative differential resistance (NDR) in SnS2-GO nanocomposites

This study investigates the structural, optical, and electrical properties of tin disulfide (SnS2) and SnS2-graphene oxide (GO) nanosheets synthesized via chemical bath deposition method (CBD). Structural characterization confirms the formation of hexagonal crystal phases with nanosheet morphology. It shows a well distribution of nanosheet average square sizes of 10 nm for SnS2 and 6 nm for SnS2-GO. Optical analysis shows blue shifts in absorption edges compared to bulk SnS2, attributed to quantum confinement effects. Photoluminescence emission peaks exhibit different energy levels in SnS2-GO originated to native defects. The composites show a sharp reduced of PL intensity due to enhanced charge carrier separation. Electrical measurements on SnS2-GO thin films demonstrate negative differential resistance (NDR) behavior in both planar and sandwich contact configurations, suggesting electron injection/extraction mechanisms. The NDR phenomenon exhibits a dependence on voltage scan rate, indicating the involvement of electronic and ionic elements in charge transport mechanisms. Overall, this study provides insights into the NDR properties of SnS2-GO nanocomposite, laying the groundwork for their potential applications in optoelectronics and nanoelectronics.

Influence of nitrogen exchange in the core-shell structure of naphthalenediimide molecules on the advancement of quantum electronic properties

This study explores how nitrogen substitution and gold electrodes collectively influence the electronic characteristics of naphthalenediimide (NDI) molecules (M = 1, 2, and 3) through theoretical analysis. Utilizing ELF, LOL, QTAIM, and NCI analyses, we reveal significant alterations in NDI's electronic structure and interactions upon bonding with gold electrodes (Au-M-Au). Both ELF and LOL analyses demonstrate increased electron localization and delocalization on the NDI surface due to gold electrodes, with a stronger effect on nitrogen-doped molecules (M = 2, 3). QTAIM analysis confirms favorable non-covalent interactions, including evident hydrogen bonding, between NDI molecules and gold electrodes, notably intensified in doped molecules, especially the Au…O interaction. NCI analysis provides insight into the diverse interactions within the molecular system. Overall, this research highlights the crucial role of gold electrodes and nitrogen substitution in fine-tuning NDI molecules' electronic properties. The observed modulation of electron behavior and formation of beneficial interactions with gold electrodes hint at promising applications for doped NDI-gold systems requiring efficient charge transport mechanisms.

Band gap engineering of novel double perovskites Na2LiYX6 (X=Cl, Br) through halide ion replacement for solar cell and energy harvesting applications

Using the Perdew − Burke − Ernzerhof-generalized-gradient approximation (PBE-GGA) and PBE+SOC exchange − correlation functional, this work investigates the physical properties and energy storage capacity of novel double perovskite Halides Na2LiYX6 (X=Cl and Br) through Density Functional Theory (DFT) and semiclassical transport theory under ideal conditions. Thermal stability has been verified through the computation of thermodynamic parameters and formation energies. Brittle and anisotropic nature has been confirmed by the calculation of elastic and mechanical parameters. With PBE+SOC, the band gaps (Eg) for Na2LiYCl6 and Na2LiYBr6 are 2.90 and 3.76 eV, respectively, whereas with PBE-GGA, they are 3.061 and 3.824 eV, respectively. The analysis of the computed optical characteristics determines whether double perovskite halides are suitable for use in photovoltaic applications. The calculations for the transport properties were carried out using the BoltzTraP code. The effectiveness and transport mechanism for thermal energy conversion have been studied by determining the thermoelectric properties. To assess the stability at high temperatures and suitability for industrial applications, thermal properties such as heat capacity, entropy, Debye temperature, and thermal expansion are investigated. Overall, evaluations of the compounds’ thermoelectric characteristics show that they have a high-power factor and remarkably low thermal conductivity, which makes them ideal for energy harvesting devices.

Ion Transport at Polymer-Argyrodite Interfaces.

Solid-state electrolytes, particularly polymer/ceramic composite electrolytes, are emerging as promising candidates for lithium-ion batteries due to their high ionic conductivity and mechanical flexibility. The interfaces that arise between the inorganic and organic materials in these composites play a crucial role in ion transport mechanisms. While lithium ions are proposed to diffuse across or parallel to the interface, few studies have directly examined the quantitative impact of these pathways on ion transport and little is known about how they affect the overall conductivity. Here, we present an atomistic study of lithium-ion (Li+) transport across well-defined polymer-argyrodite interfaces. We present a force field for polymer-argyrodite interfacial systems, and we carry out molecular dynamics and enhanced sampling simulations of several composite systems, including poly(ethylene oxide) (PEO)/Li6PS5Cl, hydrogenated nitrile butadiene rubber (HNBR)/Li6PS5Cl, and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)/Li6PS5Cl. For the materials considered here, Li-ion exhibits a preference for the ceramic material, as revealed by free energy differences for Li-ion between the inorganic and the organic polymer phase in excess of 13 kBT. The relative free energy profiles of Li-ion for different polymeric materials exhibit similar shapes, but their magnitude depends on the strength of interaction between the polymers and Li-ion: the greater the interaction between the polymer and Li-ions, the smaller the free energy difference between the inorganic and organic materials. The influence of the interface is felt over a range of approximately 1.5 nm, after which the behavior of Li-ion in the polymer is comparable to that in the bulk. Near the interface, Li-ion transport primarily occurs parallel to the interfacial plane, and ion mobility is considerably slower near the interface itself, consistent with the reduced segmental mobility of the polymer in the vicinity of the ceramic material. These findings provide insights into ionic complexation and transport mechanisms in composite systems, and will help improve design of improved solid electrolyte systems.

Comprehensive Analysis of the Gradient Porous Transport Layer for the Proton-Exchange Membrane Electrolyzer.

A reasonable porous transport layer (PTL) is crucial to decreasing the mass-transfer loss in proton-exchange membrane water electrolyzers (PEMWEs). In this study, it was experimentally demonstrated that the gradient porosity PTL is beneficial in improving the performance of electrolyzers. The research comprehensively investigates the impact of gradient porosity PTL structures on the performance of the PEMWE, considering mass transfer and interfacial contact. It offers insights into the two-phase (oxygen-water) flow transport mechanisms within the PTLs using a 2D numerical model based on the actual PTL geometry. At the microscopic level, it analyzes how the interfacial contact impacts proton and electron transport mechanisms, affecting not only the contact resistance but also the number of effective catalytic sites for the oxygen evolution reaction. Experimental results demonstrate that the cis-gradient porosity PTL leads to a performance enhancement of 9.3% at 2.2 A/cm2. Numerical simulations reveal that the drivers of oxygen transport include the surface tension of the fibers and the pressure drop influenced by the local PTL porosity. Further analysis indicates that the lower oxygen saturation in the bottom region of the PTL with cis-gradient porosity favors a lower oxygen coverage area in the catalyst layers (CL) since the narrower pore space and higher capillary pressure increase the number of water flow paths into the CL. Overall, this study provides valuable insights for designing high-performance PTLs for use in electrolyzers.

Hygroscopic hydrogel-based cooling system for photovoltaic panels: An experimental and numerical study

Thermal management is an essential aspect of photovoltaic (PV) system design because of the negative effects of high temperatures on the efficiency of PV panels. The use of hygroscopic hydrogels for the evaporative cooling of PV panels is an emerging technique that has attracted attention owing to the high latent heat and recyclability of these materials. However, a comprehensive understanding of the heat and mass transport mechanisms in hygroscopic hydrogels is necessary. Factors that would ensure the long-term performance of PV panel/hydrogel (PV/HG) systems under real-world conditions are still poorly understood, and the intrinsic properties of hydrogels and the effect thereof on their cooling performance have hitherto remained unexplored. Herein, we propose a mathematical model for hydrogel-cooled PV panels to study the heat and mass transfer mechanisms of PV/HG systems in practical environments. The model is used to examine the impact of the thermal conductivity, diffusion coefficient, and thickness of the hydrogel on the performance of the PV/HG system. Unlike previously reported approaches to enhance the efficiency, in this study, the external heat transfer resistance and internal mass transfer resistance were identified as the primary controlling factors. Enhancement of the thermal conductivity of the hydrogel is shown to have a limited effect on the performance, whereas improving the water diffusion within the hydrogel significantly boosts the system efficiency. Optimally, the thickness of the hydrogel must be such that it balances the heat and mass transfer distances with the available water volume. During the summer in Guangzhou, China, a 6-mm thick layer of hydrogel lowered the temperature of a PV cell by up to 7.5 °C to increase the daily power generation by 2.1%. Analysis of the nationwide situation showed that hydrogels have substantial potential for lowering the peak PV panel temperatures (by as much as 19.3 °C) to mitigate fluctuations in the output power. Our findings offer valuable insights into the design of PV/HG systems towards improving their performance.

Proton Transport Scenarios in Sulfuric Acid Explored via Ab Initio Molecular Dynamics Simulations.

Sulfuric acid (H2SO4), a highly reactive reagent containing intrinsic protonic charge carriers, has been studied via ab initio molecular dynamics simulations. Specifically, we explore the solvation shell structure of the protonic defects, H1SO4- and H3SO4+, as well as the underlying proton transport mechanisms in both the neat and hydrated H2SO4 solutions. Our findings reveal a significant contraction of the dynamic hydrogen-bonded network around the protonic defects, which resembles features seen in water. The simulations provide estimates of the structural relaxation time scales for proton release from both the covalent O-H bonds (∼23 ps) and the hydrogen bonds (∼0.4 ps). In contrast to water, our analysis of the proton transfer scenarios in sulfuric acid reveals correlated events mediated by the formation of longer (up to four) hydrogen-bonded Grotthuss chains.

Numerical simulation of melting heat transport mechanism of Cross nanofluid with multiple features of infinite shear rate over a Falkner‐Skan wedge surface

Numerical simulation of melting heat transport mechanism of Cross nanofluid with multiple features of infinite shear rate over a Falkner‐Skan wedge surface

Atom layer deposited TiO2 electron transport layer for silicon heterojunction solar cells to achieve high performance

Silicon/compound heterojunction (SCH) solar cells based on p-type and n-type c-Si wafers using atom layer deposition-TiO2 and low work function metal as the electron transport layer and rear electrode are fabricated. Efficiencies of 20.6 % and 21.6 % are achieved on p-type and n-type silicon solar cells, respectively. High Voc exceeding 700 mV have been realized on both kinds of Si wafers. Special attention has been paid to the SCH solar cells based on p-type c-Si wafers in which the TiO2 electron transport layer serves as the emitter. Carrier transport mechanisms and junction characteristics of the SCH solar cells are analyzed based on dark J-V measurement. The formation of a strong inversion layer at the Si surface region is determined, which implies the high Voc potential of the SCH solar cells based on p-type Si. An optical loss analysis is performed along with a possible solution to further improve the Jsc. The feasibility of TiO2 applied as an efficient electron transport layer (emitter) in p-type SCH solar cells with high performance has been showed.

Hierarchical Branched TiO2 Photo/Photoelectrocatalyst with Directed Charge Transfer for Efficient Hydrogen Production from Seawater.

The directed electron transport channel design in semiconductors, which could promote charge utilization, is attractive but rarely reported. Hierarchical branched titanium dioxide (HB-TiO2), possessing a charge cascade transfer channel, was constructed by assembling titanium-defected TiO2 nanobranches on oxygen-defected TiO2 nanobelts. The interfacial Ti/O vacancies have been detected by X-ray photoelectron and electron paramagnetic resonance spectroscopies, and the vacancies act as the "bridge" of photogenerated carrier transport. This structure maintained high photoactivity in H2 production in different mass fractions of NaCl solutions. The photocurrent density of the HB-TiO2 photoanode in natural seawater is 3.9, 2.1, and 2.6 times that of oxygen-defected TiO2 nanobelts, titanium-defected TiO2 nanobranches, and their mixture, respectively. Besides, the charge transport mechanism from the inner lattice to the TiO2 surface is proposed.

Current trends and patterns of PFAS in agroecosystems and environment: A review.

Per- and polyfluoroalkyl substances (PFASs) are one of the more well-known highly persistent organic pollutants with potential risks to agroecological systems. These compounds are of global concern due to their persistence and mobility, and they often lead to serious impacts on environmental, agricultural, and human health. In the past 20 years, the number of science publications on PFAS has risen; despite this, certain fundamental questions about PFAS occurrence, sources, mechanism of transport, and impacts on agroecosystems and the societies dependent on them are still open and evolving. There is a lack of systematic and comprehensive analysis of these concerns in agroecosystems. Therefore, we reviewed the current literature on PFAS with a focus on agroecosystems; our review suggests that PFASs are nearly ubiquitous in agricultural systems. We found the current research has limitations in analyzing PFAS in complex matrices because of their small size, distribution, and persistence within various environmental systems. There is consistency in the properties and composition of PFAS in and around agroecosystems, suggesting evidence of shared sources and similar components within different tropic levels. The introduction of new and varied sources of PFAS appear to be growing, adding to their residual accumulation in environmental matrices and leading to possible new types of chemical compounds that are difficult to assess accurately. This review determines existing research trends, understands mechanisms and incidence of PFAS within agroecosystems and their impact on human health, and thereby recommends further studies to remedy research gaps.

Optimization of hollow fiber membrane contactor system for CO2 mineralization using seawater brine: Comparative analysis of performance and transport mechanisms

Carbon mineralization is a promising approach for carbon capture, utilization, and storage (CCUS) but still faces technical and economic challenges. This study reports on CO2 mineralization using various hollow fiber membrane contactors (HFMCs) to optimize the system and understand the mass transport mechanism. We conducted a quantitative comparative assessment through theoretical and experimental approaches to evaluate the performance of three HFMC types with different morphological and chemical characteristics at various gas and liquid velocities. Results showed that the in-house developed highly porous hollow fiber (HF) membrane exhibited superior CO2 capture efficiency compared to commercial membranes. In contrast to other HFMCs showing a sharp decline in CO2 flux due to internal fouling caused by pore wetting and external fouling, the highly porous HF membrane with surface modification maintained stable performance during continuous operation due to its superhydrophobicity and surface roughness. The HF membrane also achieved the highest overall mass transfer coefficients, closely matching the theoretical non-wetted mode due to negligible partial wetting. We expect that this study will provide insights into optimizing HFMCs for enhanced carbon mineralization efficiency.

The negative differential resistance of nitrogen implanted TiO2

The microstructure and negative differential resistance (NDR) effect of nitrogen implanted rutile TiO2 were investigated by measuring the XPS, Raman spectra and current voltage curves. It was found that the light illumination has large influence on the NDR effect. Under the illumination of 60 mW laser light, a large NDR with a small electric field (1250 V/cm) is obtained. This electric field is about three orders smaller than that reported in literature (1×106 V/cm). The electric field induced tunneling is the possible mechanism of electric transport at higher field region. The NDR is thought to be related to the light and nitrogen dopant induced reaction including the destroying of water, the scavenging of electron, and the surface oxidation transform of non-stoichiometric TiO2−x to stoichiometric insulating state. The results of this paper are not only useful in understanding the mechanism of NDR, but also useful in providing an effective method in manipulation NDR.

Mechanism Exploration of the Photoelectrochemical Immunoassay for the Integration of Radical Generation with Self-Quenching.

Photoelectrochemical (PEC) sensing mechanisms based on enzyme-catalyzed strategies primarily achieve the quantitative analysis of biomolecules through the enhancement or attenuation of photocurrent signals. However, there are still no reports that delve into the principles of photocurrent signaling conversion in the reaction between photoactive materials and the biomolecules. In this work, we demonstrated that indium oxysulfide InOS-0.5 heterojunction has excellent peroxidase activity to catalyze the reaction of H2O2-generated hydroxyl radicals (•OH) with the self-generated electrons, thereby resulting in synergistic quenching of the photocurrent signal. Based on the above principles, we coupled InOS-0.5 with a sandwich-type immunoassay to introduce H2O2 production catalyzed by glucose oxidase for the development of a PEC immunosensing platform. H2O2 reacted with InOS-0.5 to produce •OH with strong oxidizing properties, thus quenching the photogenerated electrons and realizing the PEC detection of the carcinoembryonic antigen (CEA, as a model analyte). The photocurrent intensity decreases with the logarithmic increase in CEA concentration (0.02-50 ng mL-1), with a remarkable limit of detection of 8.9 pg mL-1 (S/N = 3). This study further investigates the mechanism of hydrogen peroxide-induced photocurrent quenching, providing deeper insights into the mechanisms of electron-hole transport in hollow porous semiconductor materials and paving the way for the development of efficient PEC sensors.

Design of multiple-function matrix encapsulated with Marjoram extract to support cellular functions, stimulate collagen synthesis and decrease infection in wound

This study aimed to assess the role of the combination of design techniques of the engineered substrates, and the effect of encapsulating Marjoram (Origanum Majorana L.) into the matrix network was studied. To this end, PVA-PEG matrices were designed through 3 techniques of freeze–thaw (FT), the combination of both methods of freeze-drying and freeze-thawing(FT-FD), and ternary technique(freeze-drying,freeze-thawing,cross-linking(FT-FD/CL)), by combining equal volume ratios of both polymers. The results indicated the ternary technique can provide better physicochemical properties(porosity: 96%, lower degradation rate, higher modulus) compared to FT and FT-FD methods. Afterward, encapsulation of Marjoram-extracted bio-actives in the matrix network designed with the ternary technique demonstrated that the increase in the extract concentration up to 3% can increase encapsulation efficiency. The encapsulation also caused a more cohesive network by better bonding between functional groups in herbal biomolecules and polymer chains of the matrix. Mass transport mechanisms and release kinetics of matrix-encapsulated bio-actives indicated a deviation from Fickian diffusion and the release by diffusion and swelling process. Biologically, matrix-loaded herbal carbohydrate(Epi-alpha-Cadinol) improved fibroblast adhesion and distribution on the substrate surface, and led to the better synthesis of collagen fibers, especially in 3% herbal extract, and antibacterial activities owing to the controlled release of sesquiterpenoids and N-Acetyl-l-proline.

Transport mechanism and structural pharmacology of human urate transporter URAT1.

Urate is an endogenous product of purine metabolism in the liver. High urate levels in the blood lead to gout, a very common and painful inflammatory arthritis. Excreted urate is reabsorbed in the kidney mainly by URAT1 antiporter, a key target for anti-gout drugs. To uncover the mechanisms of urate transport and drug inhibition, we determined cryo-EM structures of human URAT1 with urate, counter anion pyrazinoate, or anti-gout drugs of different chemotypes-lesinurad, verinurad, and dotinurad. We captured the outward-to-inward transition of URAT1 during urate uptake, revealing that urate binds in a phenylalanine-rich pocket and engages with key gating residues to drive the transport cycle. In contrast to the single binding site for urate, pyrazinoate interacts with three distinct, functionally relevant sites within URAT1, a mechanism that has not yet been observed in other anion antiporters. In addition, we found that while all three drugs compete with substrates and halt the transport cycle, verinurad and dotinurad further hijack gating residues to achieve high potency. These insights advance our understanding of organic anion transport and provide a foundation for designing improved gout therapeutics.

Emerging Two-Dimensional Materials for Proton-Based Energy Storage.

The rapid diffusion kinetics and smallest ion radius make protons the ideal cations toward the ultimate energy storage technology combining the ultrafast charging capabilities of supercapacitors and the high energy densities of batteries. Despite the concept existing for centuries, the lack of satisfactory electrode materials hinders its practical development. Recently, the rapid advancement of the emerging two-dimensional (2D) materials, characterized by their ultrathin morphology, interlayer van der Waals gaps, and distinctive electrochemical properties, injects promises into future proton-based energy storage systems. In this perspective, we comprehensively summarize the current advances in proton-based energy storage based on 2D materials. We begin by providing an overview of proton-based energy storage systems, including proton batteries, pseudocapacitors and electrical double layer capacitors. We then elucidate the fundamental knowledge about proton transport characteristics, including in electrolytes, at electrolyte/electrode interfaces, and within electrode materials, particularly in 2D material systems. We comprehensively summarize specific cases of 2D materials as proton electrodes, detailing their design concepts, proton transport mechanism and electrochemical performance. Finally, we provide insights into the prospects of proton-based energy storage systems, emphasizing the importance of rational design of 2D electrode materials and matching electrolyte systems.

Tree Rings Mercury Controlled by Atmospheric Gaseous Elemental Mercury and Tree Physiology.

Tree rings are an emerging atmospheric mercury (Hg) archive. Questions have arisen, though, regarding their mechanistic controls and reliability. Here, we report contrasting tree-ring Hg records in three collocated conifer species: Norway spruce (Picea abies), Scots pine (Pinus sylvestris), and European larch (Larix decidua), which are from a remote boreal forest. Centennial atmospheric Hg trends at the site, derived from varved lake sediments, peats, and atmospheric monitoring, indicated a steady rise from the 1800s, peaking in the 1970s, and then declining. Prior to ca. 2005, larch and spruce tree rings reproduced the peak in the atmospheric Hg trend, while pine tree rings peaked in the 1930s, likely due to the prolonged sapwood period and ambiguity in the heartwood-sapwood boundary of pine. Since ca. 2005, tree rings from all species showed increasing Hg concentrations in the physiologically active outer rings despite declining atmospheric Hg concentrations. The good agreement between Hg and nitrogen concentrations in active tree-ring cells indicates a similar transport mechanism and cautions against their applicability as atmospheric Hg archives. Our results suggest that tree-ring Hg records are controlled by atmospheric Hg and tree physiology. We provide recommendations for using tree-ring Hg archives that take tree physiology into account.