Lowest Potential Energy Research Articles

Effect of low molecular weight organic acids on the lead and chromium release from widely-used lead chromate pigments under sunlight irradiation

Lead chromate pigments are commonly used yellow inorganic pigments. They can pose environmental risks as they contain toxic heavy metals lead and chromium. Low molecular weight organic acids (LMWOAs), as widespread dissolved organic matter (DOM), affect the lead and chromium release from the pigment in water. In this work, the role of LMWOAs in the photodissolution of commercial lead chromate pigment was investigated. The pigment underwent significant photodissolution under simulated sunlight exposure with LMWOAs, and subsequently released Cr(III) and Pb(II). The photodissolution process is caused by the reduction of Cr(VI) by photogenerated electrons of the lead chromate pigment. The LMWOAs promoted photodissolution of the pigment by improving the electron-hole separation. The formation of Cr(III)-contained compounds leads to a slower release of chromium than lead. The photodissolution kinetics increase with decreasing pH and increasing LMWOAs concentration. The photodissolution of lead chromate pigment was basically positively related to the total number of hydroxyl and carboxyl groups in LMWOAs. The LMWOAs with stronger affinity to lead chromate pigment, lower adiabatic ionization potential (AIP) and higher energy of the highest occupied molecular orbital (EHOMO) are favorable to Cr(VI) reduction by photogenerated electrons and pigment photodissolution. 2.39% of chromium and 10.34% of lead released from the lead chromate pigment in natural conditions during a 6-h sunlight exposure. This study revealed the photodissolution mechanism of lead chromate pigment mediated by LMWOAs with different molecular structures, which helps understand the environmental photochemical behavior of the pigment. The present results emphasize the important role of DOM in the heavy metals release from commercial inorganic pigments.

Utilization of Molecular Simulation Applications for Stability Testing of Anthocyanin Compounds in Black Elderberry

Recently, many studies on the molecular activity of compounds have been carried out using simulations through computer programs or in silico simulations. Anthocyanins are one of the compounds that are often used as food coloring agents and can function as antioxidants to prevent blockage of blood vessels, as an anti-cancer that can prevent the development of cancer cells and tumors and have anti-inflammatory effects. The purpose of the research is to determine the stability of anthocyanins using molecular simulations and determine the best mixing sequence of ingredients to produce the most stable anthocyanin mixture. Based on the results of the simulations carried out, it can be proven that the final 3 sets (the modeled compound belonging to namely AP and AZ followed by a number based on the simulation order) selected are AP17, AP18, and AZ17. The AP17 set had the lowest potential energy at the end of molecular dynamics simulations, but molecular visualization showed structural instability indicated by the formation of gaps in the molecular conformation. The AP18 set had the second lowest potential energy at the end of molecular dynamics simulations and molecular visualization showed molecular conformation that tended to be stable during molecular simulations with no change in structure. The AZ17 set had the highest potential energy of the final 3 sets selected and molecular visualization showed a gap in the conformation at the beginning of the simulation, but over time the gap became denser, indicating that the molecule became more stable over time. Based on the research results, the AP18 set was chosen because it has relatively low potential energy and it can be proven that the structure visualization of this set tends to be more stable over time during molecular dynamics simulations.

Nanoscale Investigation of Bubble Nucleation and Boiling on Random Rough Surfaces.

Surface roughness is one of the significant factors affecting liquid-vapor phase change heat transfer. This paper explores the effect of surface roughness on bubble nucleation and boiling heat transfer, as well as the microscopic mechanism, by constructing random rough surfaces using molecular dynamics (MD) simulation. Bubbles randomly nucleate on a flat surface and tend to nucleate in pits on rough surfaces. The pits on the random rough surface gather more argon atoms than the protrusions, forming low potential energy regions on the surface, thus providing stable nucleation sites for bubbles. As the surface roughness increases, bubble generation, merging, and growth are advanced. In addition, rough surfaces offer a larger effective heat transfer area for the heat transfer process, increase the strength of solid-liquid coupling, and obtain smaller solid-liquid interaction energy. The critical heat flux (CHF) value positively correlates with surface roughness. As the roughness increases, the surface superheat at the onset of CHF decreases accordingly. This paper provides new insights into the mechanism of heat transfer enhancement on rough surfaces and surface design in thermal management.

High Areal-Capacity Aqueous Manganese-Based Batteries Enabled by Redox Mediators

Aqueous manganese batteries based on deposition-dissolution of Mn2+/MnO2 reactions have aroused great attention due to their intrinsic low cost, high potential, and high energy.1, 2 However, the incomplete dissolution and exfoliated dead MnO2 would inevitably lead to capacity loss and poor cyclability at high areal capacity application.3, 4 Herein, we apply a redox mediator strategy to dissolve the accumulated MnO2 via a spontaneous chemical reaction between redox mediators iodide and MnO2.5,6 During the discharge process, the iodide (I–) could react with the residual MnO2 and be oxidized to I3 – that could be further reduced back to I– on the electrode, continuing this process until fully dissolved the accumulated MnO2. We will discuss detailed reaction mechanisms verified by ex-situ UV-vis spectroscopy, scanning electron microscopy, and X-ray diffraction. The zinc-manganese (Zn-Mn) battery with iodide mediator showed improved cycling stability at 2.5 mAh cm–2 (400 vs. 100 cycles, static mode) and 15 mAh cm–2 (225 vs. 60 cycles, flow mode). Areal capacity is one of the most important parameters determining system energy for deposition-based batteries.7 The Zn-Mn flow cell could demonstrate a high areal capacity application at 50 mAh cm–2 for 50 cycles. We will discuss how to expand this strategy to other manganese-based batteries and broaden the horizon of aqueous batteries.AcknowledgmentThis work is supported by a grant from the Research Grant Council of the Hong Kong Special Administrative Region, China (project no. C1002-21G).Reference W. Chen, G. Li, A. Pei, Y. Li, L. Liao, H. Wang, J. Wan, Z. Liang, G. Chen, H. Zhang, J. Wang and Y. Cui, Nat. Energy, 2018, 3, 428-435. D. Chao, W. Zhou, C. Ye, Q. Zhang, Y. Chen, L. Gu, K. Davey and S.-Z. Qiao, Angew. Chem. Int. Ed. Engl., 2019, 58, 7823-7828. C. Liu, X. Chi, Q. Han and Y. Liu, Adv. Energy Mater., 2020, 10, 1903589. G. Liang, F. Mo, H. Li, Z. Tang, Z. Liu, D. Wang, Q. Yang, L. Ma and C. Zhi, Adv. Energy Mater., 2019, 9, 1901838. J. Lei, Y. Yao, Z. Wang and Y.-C. Lu, Energy Environ. Sci., 2021, 14, 4418-4426. J. Lei, Y. Yao, Y. Huang and Y.-C. Lu, ACS Energy Letters, 2022, DOI: 10.1021/acsenergylett.2c02524, 429-435. Y. Yao, J. Lei, Y. Shi, F. Ai and Y.-C. Lu, Nat. Energy, 2021, 6 (6), 582–588.

AIEgen configuration transition and aggregation enable dual prompt emission for single‐component nondoped white OLEDs

AbstractThe dual emission (DE) feature in materials holds great potential to revolutionize the development of one‐component system white organic light‐emitting diodes (WOLEDs). However, the reported DE materials remain scarce owing to the formidable challenge of breaking Kasha's rule and managing the intricate energy/charge transfer processes. Herein, we have introduced a groundbreaking DE AIEgen, 2CzAn‐TPE, which possesses a simple structure and undergoes Z‐to‐E isomerization and exhibits yellow and red fluorescence powders for pre‐ and post‐sublimation, respectively. With relatively lower potential energy, Z‐conformation ((Z)‐1,2‐diphenyl‐1,2‐bis(4‐(10‐(9‐phenyl‐9H‐carbazol‐3‐yl)anthracen‐9‐yl)phenyl)ethene) of 2CzAn‐TPE can be readily transformed into E‐conformation ((E)‐1,2‐diphenyl‐1,2‐bis(4‐(10‐(9‐phenyl‐9H‐carbazol‐3‐yl)anthracen‐9‐yl)phenyl)ethene) via vacuum sublimation. The utilization of X‐ray diffraction and grazing‐incidence‐wide‐angle X‐ray scattering techniques confirms the structural transformation, while the crystallographic analysis reveals the establishment of numerous intermolecular CH···π interactions between the tetraphenylethene (TPE) moiety and both the anthracene and carbazole units. This allows a densely packed molecular arrangement, thereby offering propitious conditions for excimer generation in the E‐conformation aggregated state. By utilizing the sublimated 2CzAn‐TPE as an emitter, a nondoped one‐component WOLED was prepared, exhibiting an exceptionally high external quantum efficiency (EQE) of 5.0%, which represents one of the highest performances among all one‐component WOLEDs. This research introduces a novel, simple, and efficient approach to realize highly efficient one‐molecule WOLEDs.

Enhanced proton conductivity of SPEEK membranes by constructing hydrogen bond network through doping ionic liquid and graphene oxide

AbstractSo as to improve proton conductivity at medium temperatures while reducing the loss of ionic liquids (ILs), this article fabricated a series of hybrid membranes with sulfonated poly (ether ether ketone) (SPEEK) as their base material, 1‐allyl‐3‐methylimidazolium chloride ([AMIM][Cl]) as their primary proton conductor, and graphene oxide (GO) as their filler. The characterization results showed that the –SO3H groups of SPEEK formed acid–base pairs with the imidazole ring of [AMIM][Cl] at the interface where electrostatic attraction inhibited the main‐chain migration of the SPEEK. At the same time, the large hydrogen bond network formed between [AMIM][Cl], GO and SPEEK provided more jump sites for proton transfer. Proton conduction of the prepared membranes was enhanced by way of low potential energy barriers. At 120°C, SPEEK/IL/GO‐2% exhibited a proton conductivity of 21.35 mS/cm, and the IL loss rate was 20.17%. The characterization results demonstrated that the prepared SPEEK/IL/GO composite membranes had excellent physicochemical properties, dimensional stability, high proton conductivity, and low IL loss, which were expected to be used in practical conditions at medium temperature.Highlights Large hydrogen bonding network provides additional proton hopping sites. Physical cross‐linking limits the leaching of ionic liquid. SPEEK/IL/GO‐2% membrane achieves a conductivity of 21.35 mS/cm at 120°C.

Heat transfer characteristics in nanochannels with rough walls based on capillary flow: A molecular dynamics study

Passive micro/nanoscale cooling based on capillary flow has become a promising and widely used thermal management technology for electronic devices. In this study, nanochannels with different surface roughness are established based on the chord function, and the capillary flow and heat transfer in different nanochannels are investigated by molecular dynamics simulation. Compared with smooth walls, rough walls retard capillary flow, and the heat transfer process also affects capillary flow to some extent. The region of low potential energy is much larger near rougher walls in nanochannels. When fluid flows through a depression on a wall, the velocity decreases, resulting in an uneven flow velocity. An analysis of the temperature field, Nusselt number and heat transfer amount shows that although rougher structure causes more atoms to gather, thus improving the heat transfer rate, it reduces the total heat transfer amount due to reduced capillary flux. The microscopic mechanism of the impact of surface roughness on capillary flow and heat transfer is revealed at the atomic scale by potential energy analysis. Furthermore, increasing solid-liquid interaction hinders capillary flow, but it increases the heat transfer rate at the solid-liquid interface.

Enhanced hydrogen production coupled with ethanol electrocatalytic oxidation by flow-through self-supporting electrode

Electrocatalytic oxidation of ethanol to value-added production is an ideal replacement of the conventional anodic oxygen evolution reaction (OER) for efficient hydrogen (H2) production due to the lower electric potential energy and higher safety. However, the sluggish mass transfer rate of reactants commonly is the crucial limitation of electrocatalytic oxidation efficiency. Here, Ni(OH)2 nanosheet is immobilized on nickel foam (NF) to fabricate a flow-through self-supporting electrode (Ni(OH)2/NF) served as anode for ethanol electrocatalytic oxidation, in coupling with high-purity H2 production at the cathode. The potential for electrocatalytic oxidation of ethanol and H2 evolution was significantly reduced by 200 mV compared to pure water splitting at 25 mA cm−2. The boundary layer thickness on the anodic electrode surface could be decreased from 86.66 μm to 66.21 μm with the flow rate increased from 0 to 0.82 cm min−1. Compared to the batch mode, The conversion rate of ethanol can be increased from 59 % to 100 % and the selectivity of acetic acid can be increased from 88 % to 100 % under the flow-through mode. The Faraday efficiency of the anode achieved an increase from 76 % to over 99 % and the H2 production of the cathode increased by 31 % under the flow-through mode.

Ultrathin liquid film phase change heat transfer on fractal wettability surfaces

Surface wettability is significant for the liquid–vapor phase change heat transfer. In this paper, patterned wettability surfaces are constructed from the perspective of fractal theory to comprehensively investigate the microscopic mechanism of surface wettability patterns affecting evaporation and bubble nucleation. The evaporation heat transfer rates of the hydrophilic fractal wettability surfaces are close to that of the pure hydrophilic surface. The solid–liquid interfacial heat transfer dominates the evaporation heat transfer. In contrast, the liquid–vapor interfacial heat transfer’s effect is insignificant. The hydrophobic points of the hydrophilic fractal wettability surfaces provide stable and abundant nucleation sites for the bubble nucleation process. The nucleation times of the hydrophilic fractal wettability surfaces are earlier than that of the pure hydrophilic surface. Hydrophobic fractal wettability surfaces can improve bubble nucleation. With increased hydrophilic points, nucleation sites are mainly concentrated in hydrophobic regions near the hydrophilic/hydrophobic contact boundary. The expanding low potential energy region near the contact boundary is the main reason for improving bubble nucleation. Critical heat flux (CHF) increases as the area proportion of the hydrophilic part increases, and surface superheats decrease when CHF occurs. The fractal wettability surfaces improve CHF, and the CHF of the hydrophilic fractal wettability surface is close to that of the pure hydrophilic surface.

Short- and long-duration cooperative energy storage system: Optimizing sizing and comparing rule-based strategies

Reasonable configuration of energy storage equipment could solve the mismatch problem between load demand and renewable power output. The energy storage devices could be classified into short-duration and long-duration storage according to the operation timescale. Short- and long-duration cooperative energy storage is a promising trend because of its complementary advantages. This work focuses on the systems of photovoltaics and wind farms combined with energy storage components, such as batteries, thermal energy storage (TES), and hydrogen energy storage (HS). The optimal design parameters are obtained by multi-objective optimization with the objective of levelized cost of energy and loss of power supply probability. The techno-economic performance of different short- and long-term cooperative energy storage systems are compared. The influence of rule-based strategies on the system performance is investigated. Results indicate that the system with batteries and TES has great competitiveness from an economic perspective, and the system with batteries and HS has a lower potential energy waste probability when the power-supply reliability is extremely high. The recommended discharging priority of the system with batteries and TES is TES first and then batteries, which could completely achieve power supply reliability.

Hybrid molecular dynamic Monte Carlo simulation and experimental production of a multi-component Cu–Fe–Ni–Mo–W alloy

High-entropy alloys are a class of materials intensely studied in the last years due to their innovative properties. Their unconventional compositions and chemical structures hold promise for achieving unprecedented combinations of mechanical properties. The Cu–Fe–Ni–Mo–W multicomponent alloy was studied using a combination of simulation and experimental production to test the possibility of formation of a simple solid solution. Therefore, Molecular Dynamics and hybrid Molecular Dynamic/Monte Carlo simulations from 10K up to the melting point of the alloy were analyzed together with the experimental production by arc furnace and powder milling. The Molecular Dynamics simulations starting with a bcc type-structure show the formation of a single-phase bcc solid solution type-structure, whereas using Monte Carlo one, generally produced a two-phase mixture. Moreover, the lowest potential energy was obtained when starting from a fcc type-structure and using Monte Carlo simulation giving rise to the formation of a bcc Fe–Mo–W phase and a Cu–Ni fcc type-structure. Dendritic and interdendritic phases were observed in the sample produced by arc furnace while the milled powder evidence an separation of two phases Cu–Fe–Ni phase and W–Mo type-structures. Samples produced by both methods show the formation of bcc and a fcc type-structures. Therefore, the Monte Carlo simulation seems to be closer with the experimental results, which points to a two-phase mixture formation for the Cu–Fe–Ni–Mo–W multicomponent system.

Pyrolytic Graphite for an In-Plane Force Study of Diamagnetic Levitation: A Potential Microdetector of Cracks in Magnetic Material.

The diamagnetic levitation technique can be applied in non-destructive testing for identifying cracks and defects in magnetic materials. Pyrolytic graphite is a material that can be leveraged in micromachines due to its no-power diamagnetic levitation on a permanent magnet (PM) array. However, the damping force applied to pyrolytic graphite prevents it from maintaining continuous motion along the PM array. This study investigated the diamagnetic levitation process of pyrolytic graphite on a permanent magnet array from various aspects and drew several important conclusions. Firstly, the intersection points on the permanent magnet array had the lowest potential energy and validated the stable levitation of pyrolytic graphite on these points. Secondly, the force exerted on the pyrolytic graphite during in-plane motion was at the micronewton level. The magnitude of the in-plane force and the stable time of the pyrolytic graphite were related to the size ratio between it and the PM. During the fixed-axis rotation process, the friction coefficient and friction force decreased as the rotational speed decreased. Smaller-sized pyrolytic graphite can be used for magnetic detection, precise positioning and other microdevices. The diamagnetic levitation of pyrolytic graphite can also be used for detecting cracks and defects in magnetic materials. We hope this technique will be used in crack detection, magnetic detection and other micromachines.

Rapid and durable oxygen reduction reaction enabled by a perovskite oxide with self-cleaning surface

The growth of electrochemically inert segregation layers on the surface of solid oxide fuel cell cathodes has become a bottleneck restricting the development of perovskite-structured oxygen reduction catalysts. Here, we report a new discovery in which enriched Ba and Fe ions on the near-surface of Nd1/2Ba1/2Co1/3Fe1/3Mn1/3O3−δ spontaneously agglomerate into dispersed Ba5Fe2O8 nanoparticles and maintain a highly active and durable perovskite structure on the surface. This unique surface self-cleaning phenomenon is related to the low average potential energy of Ba5Fe2O8, which is grown on the near-surface layer. The electrochemically inert Ba5Fe2O8 segregation layer on the near-surface of the perovskite catalyst achieves self-cleaning by regulating the formation energy of enriched metal oxides. This self-cleaned perovskite surface exhibits an ultrafast oxygen exchange rate, high catalytic activity for the oxygen reduction reaction, and good adaptability to the actual working conditions of solid oxide fuel cell stacks. This study paves a new way for overcoming the stubborn problem of perovskite catalyst surface deactivation and enriches the scientific knowledge of surface catalysis.

Influence of Cysteine 440 on the Active Site Properties of 3-Deoxy-d-Arabino-Heptulosonate 7-Phosphate Synthase in Mycobacterium tuberculosis (MtDAHPS).

The shikimate pathway, which produces aromatic amino acids and key intermediates, is critical to the viability of the tuberculosis-causing pathogen Mycobacterium tuberculosis. The enzyme 3-deoxy-d-arabino-heptulosonate 7-phosphate synthase (DAHPS) catalyzes the first committed step of this pathway and possesses regulatory functions. Its active site contains two cysteinyls: one (Cys87) bound to a metal ion, while the other (Cys440) is in proximity to the first but is located on a connecting loop. This arrangement seemingly appeared as a disulfide linkage. However, Cys440 is not metal binding, and its positioning indicates that it could collapse the disulfide linkage. Hence, its potential role may be more than simply structural support of the active site fold. Using a multiscale computational approach, molecular dynamics (MD) simulations, and DFT-based calculations, the influence of Cys440 on the active site properties has been investigated. MD simulations reveal an unusually long disulfide bond, more than 3.0 Å, whereas DFT calculations identified two stable active site conformers in the triplet and quintet spin states. Analysis of group spin density distribution identified antiferromagnetic coupling in each conformer, which suggests their relatively low potential energy and stable conformations. The conformer in the triplet spin state could favor enzyme reactivity due to its low HOMO-LUMO energy gap. In addition, reduction of the Cys440 thiolate group results in collapse of the active site metal-ligand configuration with large exothermicity. Hence, Cys440 could activate and inactivate the enzyme. For the first time, the study revealed the role of Cys440 as being vital for the catalytic activity of the enzyme rather than solely for the structural stabilization of its active site. Thus, the findings may lead to a novel basis for antituberculosis drug design and development that would disrupt the contributions of the Cys440.

Unintentional force drifts in the lower extremities.

We explored the phenomenon of unintentional force drift seen in the absence of visual feedback during knee extension contractions in isometric conditions. Based on the importance of knee extensors for the anti-gravity function, we hypothesized that such force drifts would be slower and smaller compared to those reported for the upper extremities. We also explored possible effects of foot dominance and gender on the force drifts. Young healthy persons produced isometric knee extension contractions to different levels, ranging from 15 to 25% of maximal voluntary contraction force, with the help of visual feedback, and then, the visual feedback was turned off. Force change over the time interval without visual feedback was quantified. In the absence of visual feedback, force drifted to smaller magnitudes. The drift magnitude expressed in percent of the initial force magnitude was smaller for smaller initial force levels, ranging between 8 and 15% of the initial force for the initial force magnitude of 15% and 25% of maximal voluntary contraction force. The time exponent of the force drift was independent of the initial force magnitude and was, on average, 6.45s. There were no significant effects of foot dominance or gender, although the male subjects tended to show stronger scaling of the drift magnitude with the initial force level compared to the female subjects. The results show that unintentional force drift is a common phenomenon across limbs and muscle groups. This conclusion fits the theory of control with spatial referent coordinates and the general tendency of all natural systems to drift to states with lower potential energy.

Adsorption-enhanced catalytic oxidation for long-lasting dynamic degradation of organic dyes by porous manganese-based biopolymeric catalyst

Improving the adsorption kinetics of metal-oxide catalysts is critical for the enhancement of catalytic performance in heterogeneous catalytic oxidation reactions. Herein, based on the biopolymer pomelo peels (PP) and metal-oxide catalyst manganese oxide (MnOx), an adsorption-enhanced catalyst (MnOx-PP) was constructed for catalytic organic dyes oxidative-degradation. MnOx-PP shows excellent methylene blue (MB) and total carbon content (TOC) removal efficiency of 99.5 % and 66.31 % respectively, and keeps the long-lasting stable dynamic degradation efficiency during 72 h based on the self-built continuous single-pass MB purification device. The chemical structure similarity and negative-charge polarity sites of the biopolymer PP improve the adsorption kinetics of organic macromolecule MB, and construct the adsorption-enhanced catalytic oxidation microenvironment. Meanwhile, the adsorption-enhanced catalyst MnOx-PP obtains lower ionization potential and O2 adsorption energy to promote the continuous generation of active substance (O2*, OH*) for the further catalytic oxidation of adsorbed MB molecules. This work explored the adsorption-enhanced catalytic oxidation mechanism for the degradation of organic pollutants, and provided a feasible technical idea for designing adsorption-enhanced catalysts for the long-lasting efficient removal of organic dyes.

Thin film composite nanofiltration membrane with tannic acid-Fe(III) complexes functionalized CNTs interlayer toward energy efficient remediation of groundwater

Tailoring nanofiltration (NF) membrane with low scaling potential and high energy efficiency is of critical importance to its practical implementation for groundwater remediation. In this study, interfacial polymerization was performed on the surface of an intermediate layer of TA-Fe/CNTs coated polyether sulfone (PES) substrate to obtain a loose NF membrane (TFNi-x) with negative surface charges and optimized water transport path for selective permeation of scaling ions and higher water permeance. The obtained TFNi-10 intermediated with a moderate amount of CNTs (10 μg/cm2) exhibited 80.5 % higher selectivity of Ca2+ over SO42− and 156 % higher water permeance compared to the control TFC while maintaining a high PFOA rejection (∼97.3 %). For the gypsum scaling measurements, TFNi-10 showed better anti-scaling behavior and 40 % less pressure energy consumption for the same recovered water volume (2.2 L), resulting in the higher water recovery and lower energy cost of specific volume of the permeate. It was contributed by the synergistic effects of the strong affinity of TA-Fe to piperazine monomer and the gutter effect of TA-Fe/CNTs interlayer. Our results paved a new way of fabricating novel NF membrane with tailored intermediate layer for optimized interfacial polymerization to realizing groundwater remediation in a cost-effective manner.

Study on the influence mechanism of mineral components in biochar on the adsorption of Cr(VI)

Cr(VI) is extremely harmful to the ecological environment. The secondary purification method of treating low concentrations is not satisfactory currently. In this paper, wheat straw were pyrolyzed at 800 °C to obtain biochar, which were used to explore the effect of minerals on adsorption effect as a precursor at different pH and 25 °C. The biochar was gradually eluted with HCl and HF to remove the ash, soon loaded with K+, Ca2+, Mg2+ and Fe3+, respectively. The results show that under the action of H+, the CO bonds left after mineral removal have lower potential energy than the original surface functional groups in terms of conversion to –OH and binding to Cr. The order of promotion of Cr(VI) adsorption by the four elements is Fe3+> Mg2+＞ Ca2+> K+. As the radius of metal ions decreases, so does the electronegativity of biochar and the surfactive site increases. The adsorption mechanisms of alkali metals, alkaline earth metals and transition metals to Cr(VI) are mainly based on ion exchange, precipitation and complexation, respectively. The adsorption of Cr(VI) by wheat straw biochar was consistent with the quasi-secondary kinetic model. Combined with the results of intraparticle diffusion model fitting, it shows that this process is a multi-stage adsorption process with the combined effect of physical and chemical adsorption.

Size effects on the structural and physical properties of Cu50Zr50 metallic glass nanoparticles

The large surface area to volume ratio of metallic glass on the nanoscale imparts unique properties that are active areas of research in material science. We performed extensive calculations to investigate the structural properties, vibrational properties and low-temperature heat capacity of the Cu 50 Zr 50 metallic glass nanoparticles. The low-frequency vibrational density of states was lower in the core region of the nanoparticles than that of the bulk metallic glass. Furthermore, the potential energy of the core region was lower than that of the bulk metallic glass, which confirms that the stability of the core region of the nanoparticles was different from the bulk. The fast dynamics of the surface atoms and curvature effects enhanced the stability of the core region. The fraction of Cu-centered icosahedral clusters increased in the core region of the nanoparticles and it was the structural origin of the enhanced stability. The low-temperature heat capacity of the metallic glass depended on the nanoparticle size and there was an obvious boson peak in nanoparticles with a radius of 54.9 Å. Our investigations are helpful for understanding the structural and vibrational properties of metallic glass nanoparticles. • We performed extensive calculations to explore the structure properties, vibrational properties and low-temperature heat capacity of Cu 50 Zr 50 MGNs. • The core region of the metallic glass nanoparticles have a lower potential energy, higher density and higher fraction of icosahedral clusters. • Fast surface dynamics and curvature effect benefited to the suppressed low-frequency VDOS of the core region of the nanoparticles. • An obvious boson peak was observed in the Cu 50 Zr 50 metallic glass nanoparticle.

Electronic nonadiabatic effects in the state-to-state dynamics of the H + H2 → H2 + H exchange reaction with a vibrationally excited reagent.

Out of the many major breakthroughs that the hydrogen-exchange reaction has led to, electronic nonadiabatic effects that are mainly due to the geometric phase has intrigued many. In this work we investigate such effects in the state-to-state dynamics of the H + H2 (v = 3, 4, j = 0) → H2 (v', j') + H reaction with a vibrationally excited reagent at energies corresponding to thermal conditions. The dynamical calculations are performed by a time-dependent quantum mechanical method both on the lower adiabatic potential energy surface (PES) and also using a two-states coupled diabatic theoretical model to explicitly include all the nonadiabatic couplings present in the 1E' ground electronic manifold of the H3 system. The nonadiabatic couplings are considered here up to the quadratic term; however, the effect of the latter on the reaction dynamics is found to be very small. Adiabatic population analysis showed a minimal participation of the upper adiabatic surface even for the vibrationally excited reagent. A strong nonadiabatic effect appears in the state-to-state reaction probabilities and differential cross sections (DCSs). This effect is manifested as "out-of-phase" oscillations in the DCSs between the results of the uncoupled and coupled surface situations. The oscillations persist as a function of both scattering angle and collision energy in both the backward and forward scattering regions. The origins of these oscillations are examined in detail. The oscillations that appear in the forward direction are found to be different from those due to glory scattering, where the latter showed a negligibly small nonadiabatic effect. The nonadiabatic effects are reduced to a large extent when summed over all product quantum states, in addition to the cancellation due to integration over the scattering angle and partial wave summation.