Mass Transport Research Articles

Numerical Analysis of the Submerged Horizontal Plate Device Subjected to Representative Regular and Realistic Irregular Waves of a Sea State

This study numerically analyzes a submerged horizontal plate (SHP) device subjected to both regular and irregular waves. This device can be used either as a breakwater or a wave energy converter (WEC). The WaveMIMO methodology was applied for the numerical generation and wave propagation of the sea state of the Rio Grande coast in southern Brazil. The finite volume method was employed to solve conservation equations for mass, momentum, and volume fraction transport. The volume of fluid model was employed to handle the water-air mixture. The SHP length (Lp) effects were carried out in five cases. Results indicate that relying solely on regular waves in numerical studies is insufficient for accurately determining the real hydrodynamic behavior. The efficiency of the SHP as a breakwater and WEC varied depending on the wave approach. Specifically, the SHP demonstrates its highest breakwater efficiency in reducing wave height at 2.5Lp for regular waves and 3Lp for irregular waves. As a WEC, it achieves its highest axial velocity at 3Lp for regular waves and 2Lp for irregular waves. Since the literature lacks studies on SHP devices under the incidence of realistic irregular waves, this study significantly contributes to the state of the art.

Whey protein and maltodextrin conjugated foam-mat dried honey powder: Functional, physicochemical, structural, rheological and thermal characterization

Honey in its natural form possesses considerable challenges in mass production and transportation owing to its viscosity and stickiness, making it prone to crystallization over time. Dried honey powder makes it convenient for handling and processing. In this study, foam mat dried powder (FMDP) was obtained by foam mat drying technique in which whey protein isolate (WPI) and maltodextrin (MD) were used as foaming agent and foam stabilizer, respectively. The obtained FMDP was characterized in terms of physical, chemical, functional, phytochemical, rheological and structural properties to study the impact of foaming agents. WPI was found to improve the functionality, stability and glass transition temperature and on the other hand, MD was found to enhance the stability, crystallinity and the color of the FMDP. FTIR helped in understanding the changes in the functional groups attributed to the foaming agents. The crystallinity and the microstructural changes in the FMDP were observed from X-ray diffractograms and SEM micrographs, respectively. The rheological characterization confirmed the viscous nature of honey. The study confirmed the interaction between proteins and polysaccharides, which subsequently improved the heat stability, functional properties, solubility, emulsifying capacity, antioxidant properties, and solubility. The dried honey samples demonstrated minimal caking, low cohesiveness (Hausner ratio: 1.16 ± 0.027–1.29 ± 0.041), good and fair flowability (ranging between 14.25 ± 2.02–22.52 ± 2.25). Therefore, it can be concluded that during this study, protein and polysaccharide conjugate FMDP was obtained with better quality attributes, which can be further incorporated during various product development in food industries.

Stratospheric Hydration Processes in Tropopause‐Overshooting Convection Revealed by Tracer‐Tracer Correlations From the DCOTSS Field Campaign

AbstractHydration of the stratosphere by tropopause‐overshooting convection has received increasing interest due to the extreme concentrations of water vapor that can result and, ultimately, the climate warming potential such hydration provides. Previous work has recognized the importance of numerous dynamic and physical processes that control stratospheric water vapor delivery by convection. This study leverages recent comprehensive observations from the NASA Dynamics and Chemistry of the Summer Stratosphere (DCOTSS) field campaign to determine the frequency at which each process operates during real events. Specifically, a well‐established analysis technique known as tracer‐tracer correlation is applied to DCOTSS observations of ozone, water vapor, and potential temperature to identify the occurrence of known processes. It is found that approximately half of convectively‐driven stratospheric hydration samples show no indication of significant air mass transport and mixing, emphasizing the importance of ice sublimation to stratospheric water vapor delivery. Furthermore, the temperature of the upper troposphere and lower stratosphere environment and/or overshoot appears to be a commonly active constraint, since the approximate maximum possible water vapor concentration that can be reached in an air mass is limited to the saturation mixing ratio when ice is present. Finally, little evidence of relationships between dynamic and physical processes and their spatial distribution was found, implying that stratospheric water vapor delivery by convection is likely facilitated by a complex collection of processes in each overshooting event.

Replication of soil analogues at the original scale by 3D printing: Quantitative assessment of accuracy and repeatability of the pore structural heterogeneity

The present study investigates the quality of four three-dimensional (3D) printing technologies to accurately reproduce the complex pore structure of a real undisturbed soil sample for laboratory experiments of transport in porous media at a 1:1 scale. Four state-of-the-art 3D printing technologies were evaluated (digital light synthesis, PolyJet with gel support material, low-force stereolithography, and PolyJet with water-soluble support material) using a combination of 3D image analysis from microtomopraphy and flow simulations of the pore structure produced with each 3D printing technique. Accuracy, as determined by matching solid and void volumes, permeability, connected porosity, specific surface area, and pore size distribution of the print against the original digital soil structure, was found to be substantially better for digital light synthesis, as compared to the other tested technologies. Repeatability, as determined by the same metrics but compared between identical prints, was found to be comparable across all printing technologies and did not significantly improve for prints at greater magnification (1.5×). Wettability of the samples was improved by plasma treatment of the prints. The thorough analysis herein presented demonstrates that advanced, yet relatively inexpensive 3D printing approaches can be used to generate real-scale high quality analogs of soils/rocks that are much needed for experimental laboratory work. Such a method can open countless opportunities for studying the coupling of pore-structure and hydrodynamics on reactive mass transport in environmental science and engineering, soil science, and other subsurface related fields.

Numerical simulation of heat transport mechanism in chemically influenced ternary hybrid nanofluid flow over a wedge geometry

Ternary hybrid nanofluid flow over a wedge surface facilitates optimization, promotes industrial processes such as heat transfer, temperature regulation, material compatibility, energy efficiency and is very useful in equipment design. Due to this attention the current study focalizes the heat diffusion and mass transportation in ternary hybrid (TiO2-AL2O3-SiO2) nanofluid flow over a stretching/shrinking wedge geometry. Additionally, Ternary hybrid flow is examined under the impact of activation energy together with chemical reactions. The nanofluid flow process is structured using Modified Boungiorno Model together with framed set of partial differential equation (PDEs). The resulting systems is altered into non dimensional form of ordinary differential equation (ODEs) using transform functions and linearization is obtained through shooting technique. MATLAB bvp4c solver scheme is utilized for numerical findings of the problem. Influence of key parameters are analyzed on velocity, temperature, and concentration field. Fluid concentration intensifies via augmentation in activation rate whereas wedge stretching due to larger values of wedge angle, lessens velocity of fluid. Heat transportation escalate with higher values of fluid index, whereas negative trend is seen in case of higher value of Brownian parameter.

Analysis of Entropy Generation via Non-Similar Numerical Approach for Magnetohydrodynamics Casson Fluid Flow with Joule Heating.

This analysis emphasizes the significance of radiation and chemical reaction effects on the boundary layer flow (BLF) of Casson liquid over a linearly elongating surface, as well as the properties of momentum, entropy production, species, and thermal dispersion. The mass diffusion coefficient and temperature-dependent models of thermal conductivity and species are used to provide thermal transportation. Nonlinear partial differential equations (NPDEs) that go against the conservation laws of mass, momentum, heat, and species transportation are the form arising problems take on. A set of coupled dimensionless partial differential equations (PDEs) are obtained from a set of convective differential equations by applying the proper non-similar transformations. Local non-similarity approaches provide an analytical approximation of the dimensionless non-similar system up to two degrees of truncations. The built-in Matlab (Version: 7.10.0.499 (R2010a)) solver bvp4c is used to perform numerical simulations of the local non-similar (LNS) truncations.

Evidence for littoral convergence and sediment delivery to Mattole submarine canyon, Northern California

At geologic timescales, a significant proportion of the sediment eroded from continents is transferred from rivers to littoral cells, then through submarine canyons to deep ocean basins. Accumulation and occasional discharge of sediment from canyon headwall regions is a likely driver for the sediment gravity flows believed to be responsible for much of this mass transport, but the responsible mechanisms and event timescales in canyon heads are imprecisely defined, largely due to the drowning of canyon heads since the last glaciation and the resulting dearth of modern depositional environments to observe. We investigated a littoral cell adjacent to Mattole submarine canyon in Northern California to better understand the influence of bathymetry and coast shape on sediment trajectories and hypothesize that canyon heads promote littoral sediment accumulation due to bathymetric sheltering of the adjacent coast from waves and convergence of littoral cells exposed to varying wave direction. The uppermost gullies of Mattole Canyon extend to the littoral cell, and a train of sediment waves within the uppermost thalweg of Mattole Canyon suggests that gravity-driven flows of shore-derived sediment may have recently occurred. Mattole Canyon and nearby Mendocino Canyon flow into the deep Mendocino Channel, which has the highest observed Late Holocene sediment accumulation rates in Northern California. We documented the beach slope, grain size, and sediment provenance along 15 km of coast adjacent to Mattole Canyon and conducted numerical wave modeling to infer the dominant direction and magnitude of sediment transport, relative wave sheltering by bathymetry, and estimated sediment mobility in the vicinity of the canyon head over a multi-year period. South of the canyon headwall, in the vicinity of the Mattole River outlet, coarser sediment rich in metasandstone clasts and steeper beach slopes coincide with decadal-scale beach accretion. North of the canyon head, sediments are generally finer, beaches are flatter, clast lithologies include more quartz and mudstone grains, and there is decadal-scale net erosion. Wave modeling suggests the Mattole headwall region is subject to sustained sheltering from waves due to canyon bathymetry, littoral sediment convergence above the canyon head for much of a typical year, and occasional bed entrainment of sediment in the canyon’s uppermost gullies by large waves. Larger winter waves from the northwest likely result in net southerly drift north of the canyon head, with a high likelihood of preferentially transporting fine-grained, more quartz-rich sediment towards the Mattole headwall. Smaller summer swells from the west and south likely results in net northerly transport of metasandstone clast-rich Mattole River-derived sediment towards the canyon head. The imbalance in seasonality in wave conditions, coast shape, and sediment delivery by the Mattole River and other coastal creeks is broadly consistent with the spatial patterns in grain size, mineralogy, slope, and beach width that we observe in the vicinity of the canyon, and the net delivery of sediment to the Mattole Canyon head. An approximate mass balance of sediment flux from coastal streams feeding Mattole River littoral cell suggests that sediment volumes likely accumulate in the canyon headwall region that could supply several density flow events in a typical decade. These findings highlight the importance of the connectivity of the canyon to the nearshore region for the processes and products in canyons and fans. We hypothesize that feedbacks between canyon bathymetry, sediment accumulation, and mass evacuating flows promotes the long-term persistence of canyon systems.

Surface Complexation and Packed Bed Mass Transport Models Enable Adsorbent Design for Arsenate and Vanadate Removal

Surface Complexation and Packed Bed Mass Transport Models Enable Adsorbent Design for Arsenate and Vanadate Removal

Assessing Road Users’ Preferences for Various Travel Demand Management Strategies for Adoption in Accra, Ghana

The rise in population density, vehicle ownership, and urban development has significantly influenced travel demand and altered travel patterns, leading to traffic congestion in rapidly growing urban centers such as Accra, Ghana. The traditional approach of expanding roadways to accommodate rising traffic is no longer environmentally sustainable. Instead, the emphasis has shifted toward travel demand management (TDM) strategies as a more sustainable solution. This study aimed to investigate a range of TDM strategies that can be adopted in Accra to improve traffic flow through the lenses of everyday road users. The study employed a questionnaire survey and a stratified sampling technique to gather data from 615 respondents for relative importance index (RII) ranking and Chi-square statistical analysis. The findings revealed that the topmost preferred strategies were mass transit improvements, walking and cycling improvements, and alternative work schedules. Notably, mass transit improvements emerged as the most preferred strategy. Conversely, strategies like efficient parking pricing, congestion pricing, and higher fuel and road taxes for private vehicles ranked lowest, garnering minimal preference. The study also revealed a statistically significant correlation between variables such as age, education level, marital status, income level, and mode of transportation and all the selected TDM preferences. However, no significant relationship was found between gender or car ownership and any of the selected TDM preferences. The study provides valuable insights into road users’ preferences for TDM strategies that can aid in planning future urban mobility systems to proactively manage travel demand, alleviate congestion, and promote sustainable transportation options for the city’s residents.

PH and potential-controlled multi-modal mass transport in block copolymer nanochannel membranes

Inspired by the hydrophobic gating for achieving fast and selective ion/molecular transport in cell membranes, wetting/dewetting transition in solid-state nanopores controlled by external stimuli such as voltage, pH, electrostatics, and light have attracted increasing attention. For an accurate and better understanding, a single nanopore or low-density array of nanopores was preferred to investigate the wetting and dewetting transitions owing to their well-defined chemical functions and physical structures. However, high-density nanochannel membranes capable of processing high-throughput and multi-modal mass transport are more beneficial with the aim of practical use. In this regard, pH- and potential-responsive nanochannel membranes consisting of a polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) block copolymer (BCP) are prepared to demonstrate a multi-modal transport system with high-throughput capability. At pH < pKa(P4VP) (pKa ∼ 4.8), the cylindrical P4VP nanodomains are hydrophilic and positively charged, acting as an anion-exchange membrane. In contrast, at pH > pKa(P4VP), the P4VP domains switch to be charge-neutral and hydrophobic, naturally blocking the mass transport through the nanochannels. Applying a sufficiently positive potential to a BCP membrane-coated electrode may induce oxidative wetting in the hydrophobic nanochannels to facilitate mass transport across the membrane with no charge-selectivity. Releasing the bias makes the hydrophobic nanochannel membranes retrieve the original dewetted state, blocking the transport again. In addition, direct observation of the wetting-dewetting transition dynamics in the hydrophobic nanochannels is investigated by monitoring potential-correlated electrochemiluminescence (ECL) signals arising from Ru(bpy)32+ and co-reactant tripropylamine (TPA) under potential modulations. ECL signals tend to decrease with increasing membrane thickness ranging from 0 nm to 820 nm because it requires higher potentials to induce wetting in the nanochannels due to elongated hydrophobic nanochannels. The multi-modal transport system developed in the present work will be useful for applications such as water treatment, biosensors, and smart valve systems like controlled drug release/delivery.

Dissecting the vital role of dietary changes in food security assessment under climate change

National and global food security depend on both supply and demand, yet the vast majority of studies on the impact of climate change on food security have focused somewhat myopically on the supply side. Here, we assess planetary implications of the changing climate for food supply, concurrently considering implications of shifts in dietary preferences on food security. From 1990 to 2018, climate change detrimentally impacted on the food production of 92% of nations assessed. During this time, demand decreased at a greater rate than food supply in 28% of countries; food security for 35% of the global population was unperturbed by climate change. On the other hand, 2% of the global population did not benefit from positive impacts of climate change on food production, due to dietary changes faster increasing food demand. If consumers shift dietary preferences en masse towards healthier diets, detrimental impacts of the climate crisis on food security may be abated, although en mass and/or abrupt transitions in dietary preferences are unlikely.

Accelerating the Hydrogen Evolution Kinetics with a Pulsed Laser-Synthesized Platinum Nanocluster-Decorated Nitrogen-Doped Carbon Electrocatalyst for Alkaline Seawater Electrolysis.

Efficient and durable electrocatalysts for the hydrogen evolution reaction (HER) in alkaline seawater environments are essential for sustainable hydrogen production. Zeolitic imidazolate framework-8 (ZIF-8) is synthesized through pulsed laser ablation in liquid, followed by pyrolysis, producing N-doped porous carbon (NC). NC matrix serves as a self-template, enabling Pt nanocluster decoration (NC-Pt) via pulsed laser irradiation in liquid. NC-Pt exhibits a large surface area, porous structure, high conductivity, N-rich carbon, abundant active sites, low Pt content, and a strong NC-Pt interaction. These properties enhance efficient mass transport during the HER. Remarkably, the optimized NC-Pt-4 catalyst achieves low HER overpotentials of 52, 57, and 53mV to attain 10mA cm-2 in alkaline, alkaline seawater, and simulated seawater, surpassing commercial Pt/C catalysts. In a two-electrode system with NC-Pt-4(-)ǀǀIrO2(+) as cathode and anode, it demonstrates excellent direct seawater electrolysis performance, with a low cell voltage of 1.63mV to attain 10mA cm-2 and remarkable stability. This study presents a rapid and efficient method for fabricating cost-effective and highly effective electrocatalysts for hydrogen production in alkaline and alkaline seawater environments.

Hierarchical Bifunctional NiO Electrocatalyst: Highly Porous Structure Boosting the Water Splitting Activity.

The development of an efficient, low-cost and earth-abundant electrocatalyst for water splitting is crucial for the production of sustainable hydrogen energy. However their practical applications are largely restricted by their limited synthesis methods, large overpotential and low surface area. Hierarchical materials with a highly porous three-dimensional nanostructure have garnered significant attention due to their exceptional electrocatalytic properties. These hierarchical porous frameworks enable the fast electron transfer, rapid mass transport, and high density of unsaturated metal sites and maximize product selectivity. Here the process involved obtaining monodispersed microrod-shaped Ni(OH)2 through a hydrothermal reaction, followed by a heat treatment to convert it into hierarchical microrod-shaped NiO materials. N2 sorption analysis revealed that the BET surface area increased from 9 to 89 m2/g as a result of the heat treatment. The hierarchical microrod-shaped NiO materials demonstrated outstanding bifunctional electrocatalytic water splitting capabilities, excelling in both HER and OER in basic solution. Overpotential of 347 mV is achieved at 10 mA/cm2 for OER activity, with a Tafel slope of 77 mV/dec. Similarly, overpotential of 488 mV is achieved at 10 mA/cm2 for HER activity, with a Tafel slope of 62 mV/dec.

Impact of nanoparticle movement on oil mobilization: Particles adsorbed at the oil–water interface versus particles dispersed in bulk fluid

Active colloid particles have been used in many fields due to their good performance in enhancing mass transport or modifying interfacial energy. Previous studies have shown that both nanoparticles adsorbed at oil–water interface and those dispersed in bulk fluid could enhance oil recovery during the oil production process. It is challenge to directly compare these results and clarify the effect of nanoparticle’s location on oil detachment from rock surface because different kinds of nanofluids were used in those work. Herein, the oil mobilization performance by nanoparticles adsorbed at oil–water interface and dispersed in the bulk phase were investigated from the pore-scale to core-scale by using one material. Two fluorescent quantum nanodots with different affinities for oil and water phases were synthesized using the same materials but with different compositions and solvents. Their locations were observed under the laser confocal microscopy. The nanoparticles adsorbed at the oil–water interface not only presented a lower interface tension, but also demonstrated a notable capability to change the wettability from oil-wet to water-wet due to its strong tendency to rock surface. The particles-laden interface can also increase the stability and shear viscosity of formed emulsions. Furthermore, it featured a larger swept area of 6.6 % in microfluidic flooding and a higher displacement efficiency of 1.7 % in the core flooding experiments. All these findings indicate that the particle-adsorbed at the oil–water interface is more favorable for enhanced oil recovery.

Elucidating the Transition of 3D Morphological Evolution of Binary Alloys in Molten Salts with Metal Ion Additives.

Molten salts serve as effective high-temperature heat transfer fluids and thermal storage media used in a wide range of energy generation and storage facilities, including concentrated solar power plants, molten salt reactors and high-temperature batteries. However, at the salt-metal interfaces, a complex interplay of charge-transfer reactions involving various metal ions, generated either as fission products or through corrosion of structural materials, takes place. Simultaneously, there is a mass transport of ions or atoms within the molten salt and the parent alloys. The precise physical and chemical mechanisms leading to the diverse morphological changes in these materials remain unclear. To address this knowledge gap, this work employed a combination of synchrotron X-ray nanotomography and electron microscopy to study the morphological and chemical evolution of Ni-20Cr in molten KCl-MgCl2, while considering the influence of metal ions (Ni2+, Ce3+, and Eu3+) and variations in salt composition. Our research suggests that the interplay between interfacial diffusivity and reactivity determines the morphological evolution. The summary of the associated mass transport and reaction processes presented in this work is a step forward toward achieving a fundamental comprehension of the interactions between molten salts and alloys. Overall, the findings offer valuable insights for predicting the diverse chemical and structural alterations experienced by alloys in molten salt environments, thus aiding in the development of protective strategies for future applications involving molten salts.

Enhancing mechanical properties of additively manufactured voronoi-based architected metamaterials via a lattice-inspired design strategy

Voronoi-based architected metamaterials have gained significant recognition as promising candidates for bone defect repair implants. However, the demanding requirements for reliable and adjustable load-bearing capacity pose challenges in applying irregular Voronoi-based architected metamaterials in implant applications. In this study, we propose a lattice-inspired design methodology for these metamaterials, enabling precise control over topologies and porosities to enhance their mechanical properties. We demonstrate the influence of unit cell topology on the printability, mechanical properties, and permeability of lattice-inspired Voronoi-based metamaterials (LIVMs) fabricated via laser powder bed fusion (LPBF) additive manufacturing. The LPBF-printed LIVMs exhibited yield strengths ranging from 3.35 to 17.59 MPa and specific energy absorption ranging from 3.81 to 14.29 J/g. Through finite element modeling and experimentation, we show that the deformation behavior of LIVMs with various topologies plays a crucial role in enhancing mechanical performance through mechanisms such as homogeneous load transfer between unit cells and multistage-contact strengthening within a unit cell. Additionally, we analyze the impact of unit cell type and porosity on the mass-transport behavior of LIVMs using computational fluid dynamics simulations. The LIVMs achieved experimental permeability values ranging from 3.88 × 10−9 to 16.83 × 10−9 m2 (consistent with trabecular bones), indicating that multiple fluid flow channels can be utilized to enhance mass transport by distributing flow pressure and increasing fluid mobility. The proposed design method effectively achieves a favorable combination of superior mechanical properties and tunable permeability in Voronoi-based architected metamaterials. These findings provide valuable theoretical guidance for the development of architected metamaterials for bone implant applications.

Design and Impact: Navigating the Electrochemical Characterization Methods for Supported Catalysts.

This review will investigate the impact of electrochemical characterization method design choices on intrinsic catalyst activity measurements by predominantly using the oxygen reduction reaction (ORR) on supported catalysts as a model reaction. The wider use of hydrogen for transportation or electrical grid stabilization requires improvements in proton exchange membrane fuel cell (PEMFC) performance. One of the areas for improvement is the (ORR) catalyst efficiency and durability. Research and development of the traditional platinum-based catalysts have commonly been performed using rotating disk electrodes (RDE), rotating ring disk electrodes (RRDE), and membrane electrode assemblies (MEAs). However, the mass transport conditions of RDE and RRDE limit their usefulness in characterizing supported catalysts at high current densities, and MEA characterizations can be complex, lengthy, and costly. Ultramicroelectrode with a catalyst-filled cavity addresses some of these problems, but with limited success. Due to the properties discussed in this review, the recent floating electrode (FE) and the gas diffusion electrode (GDE) methods offer additional capabilities in the electrochemical characterization process. With the FE technique, the intrinsic activity of catalysts for ORR can be investigated, leading to a better understanding of the ORR mechanism through more reliable experimental data from application-relevant high-mass transport conditions. The GDEs are helpful bridging tools between RDE and MEA experiments, simplifying the fuel cell and electrolyzer manufacturing and operating optimization process.

Relevance of the Iron Distribution in Natural Smectite Clays for the Thermal Stability of PMMA-Clay Nanocomposites.

Polymer-clay nanocomposites have greater thermal stability compared to the pristine polymer matrix. This can be attributed to the physical barrier provided by the inclusion of 2D clay nanoparticles (especially of the smectite group), together with radical trapping related to the distribution of specific 3d atoms in the inorganic phase. To elucidate the relevance of the Fe3+ distribution in this synergic effect, the iron atoms present in octahedral sheets of natural nontronite clay (Non, 5.6 wt % Fe) or in maghemite (M) nanoparticles (γ-Fe2O3) were incorporated in a poly(methyl methacrylate) (PMMA) matrix. Na-laponite (Lap) clay was used to evaluate the contribution of the diffusion barrier effect to the increased thermal stability of a PMMA-Lap nanocomposite, as evidenced by the upshift of the thermogravimetric (TGA) curve compared to that for PMMA. The contribution of radical trapping to the thermal stability of the PMMA-Non nanocomposite was evidenced by a significant shift of the Fe K-edge rising edge position by -4.5 eV after iron reduction by heating in N2, while similar treatment of pristine nontronite did not lead to a significant rising edge shift in the X-ray absorption spectra (XAS). This downshift demonstrated the reduction of Fe3+ to Fe0, induced by the sequestration of radicals formed by PMMA depolymerization. Raman spectroscopy analysis evidenced the formation of graphitic char deposits above 400 °C, further improving the thermal stability of PMMA-Non by providing an additional physical barrier to mass transport. A fourth contribution of well-dispersed iron was the abstraction of carbon from the char by the iron carburization reaction, which hindered CO2 formation by oxidative coking. In contrast, no relevant contribution of graphitic layer deposition was observed for the PMMA-M-Lap nanocomposite, where its improved thermal stability was only due to the combined contributions of the gas diffusion barrier effect and radical trapping by iron atoms. The maghemite effectively captured the radicals confined by the clay sheets, resulting in significant stabilization of the nanocomposite, with a shift of the mass loss of the PMMA-M-Lap nanocomposite compared to PMMA-Lap.

Analysis of a plasma reactor performance for direct nitrogen fixation by use of three-dimensional simulations and experiments

This study utilizes state-of-the-art in-situ measurements and advanced three-dimensional simulations to investigate the operation of a microwave plasma reactor for nitrogen fixation at a high subatmospheric pressure under various power inputs. It is shown that the system should be treated as a warm plasma due to negligible differences in vibrational and rotational temperatures and that it is required to account for chemical non-equilibrium. Complex flow field and significant temperature and concentration gradients are observed, emphasizing the need for three-dimensional simulations to accurately describe the interactions between mass, heat, and momentum transport and chemical reactions in non-equilibrium conditions. The innermost plasma regions reach temperatures close to 6000 K, while wall temperatures remain low due to presence of a low-temperature swirling flow field around the hot core. Analysis reveals that the swirling flow field around the hot core provides intrinsic partial quenching in regions with large temperature gradients which counteract the return to chemical equilibrium and enrich the flow surrounding the hot core. The inner flow exhibits a recirculation zone, stagnation point, and a transition into an increasingly parabolic flow profile closer to the reactor outlet. The agreement between the numerical modeling and the measurements is strong. In-situ Raman spectroscopy measurements confirm the calculated temperature field inside the reactor. Thermocouple measurements on the reactor wall are also in good agreement with the simulation. Additionally, Fourier-transform infrared spectroscopy measurements agree very well with the simulated amount of nitrogen oxide exiting the reactor at different microwave power inputs. The understanding and modeling capabilities are expected to support the development of future reactor designs that can facilitate higher yields.

Effective oxygen evolution of NCF@CoNiO2 with one-dimensional core-shell structure synthesized by induced effect of polymer nanofibers

The non-noble bimetallic oxides have recently received more and more attention in electrocatalytic oxygen evolution reaction (OER) because of their potential to replace traditional precious metal catalysts, but the low activity and stability limit their wide application. Herein, the bimetallic oxide CoNiO2 layers are decorated on the nitrogen-doped carbon nanofibers (NCF) through in situ grown of Ni(Co) bimetal organic frameworks (Ni(Co)-MOFs) on polyacrylonitrile nanofibers and subsequent pyrolysis process, so that a new NCF@CoNiO2 electrocatalyst with one-dimensional (1D) core-shell structure is synthesized by structural induced effect of polyacrylonitrile nanofibers. Importantly, the unique interconnected network formed in the 1D NCF@CoNiO2 electrocatalyst effectively improves electron mobility and mass transport capacity, thus exhibiting the glorious OER activity and long-term stability in alkaline solutions. As a result, the optimal NCF@CoNiO2-7 electrocatalyst requires an overpotential of 518 mV for OER at the current density of 100 mA cm−2, which is obvious lower than that of RuO2 (633 mV) and CoNiO2/C-7 as a contrast sample (569 mV), respectively. This work opens up a new path for structural control of 1D bimetallic oxides to improve OER activity and stability.