Hasil untuk "Physical and theoretical chemistry"

J. McCleverty, T. Meyer

Arroussi, Abdelaziz, Laksaci, Hamza, Djaafri, Mohammed et al.

The pollution of water resources by hazardous contaminants is a major obstacle to the provision of safe and potable water worldwide. Cost-effective, innovative, renewable, and environmentally friendly technologies are essential for wastewater treatment. In the current work, the potential of using raw date palm petiole (DPP) for the removal of Bezaktiv Marine S-BL (SBL) dye is investigated under a wide range of experimental conditions in batch mode. Experimental results show that the removal of SBL dye by DPP is highly dependent on contact time, initial pH, initial dye concentration, and temperature. The removal of SBL dye is relatively rapid where the equilibrium state is reached within a contact time of 120 min. Moreover, the biosorbent exhibits high stability in SBL adsorption ability over a wide pH range (4–12). Furthermore, the SBL dye adsorption increases with increase in initial concentration. The maximum adsorption capacity of the SBL dye on DPP is evaluated to be 110 mg/g, which is much higher than numerous other materials. In addition, a thermodynamic study indicates that the adsorption of SBL dye by DPP is a feasible exothermic and spontaneous process.The findings of the present study indicate that untreated DPP wastes can be considered effective materials for the treatment of textile dyes in wastewater in general and SBL in particular.

Kyriaki Barmpa, Claudia Saraiva, Diego Lopez-Pigozzi et al.

Abstract Parkinson’s disease, an aging-associated neurodegenerative disorder, is characterised by nigrostriatal pathway dysfunction caused by the gradual loss of dopaminergic neurons in the substantia nigra pars compacta of the midbrain. Human in vitro models are enabling the study of the dopaminergic neurons’ loss, but not the dysregulation within the dopaminergic network in the nigrostriatal pathway. Additionally, these models do not incorporate aging characteristics which potentially contribute to the development of Parkinson’s disease. Here we present a nigrostriatal pathway model based on midbrain-striatum assembloids with inducible aging. We show that these assembloids can develop characteristics of the nigrostriatal connectivity, with catecholamine release from the midbrain to the striatum and synapse formation between midbrain and striatal neurons. Moreover, Progerin-overexpressing assembloids acquire aging traits that lead to early neurodegenerative phenotypes. This model shall help to reveal the contribution of aging as well as nigrostriatal connectivity to the onset and progression of Parkinson’s disease.

Shalaunda M. Reeves, Kent J. Crippen, Erica D. McCray

K. Hirai, J. Hutchison, H. Uji‐i

Vibrational polaritonic chemistry is emerging as an exciting new sub-field of chemistry, one in which strong interactions with optical cavity vacuum fields are another degree of freedom alongside temperature, solvent, catalyst, and so on to modify thermochemical reactivity. The field stands at a fascinating juncture with experimental works on a variety of organic reactions continuing to blossom, just as many theoretical works appear which diverge significantly in their predictions compared to experiments. The outlook for the field is no doubt an exciting one as it seeks to unify the observed novel optical cavity-induced chemical phenomena with satisfying accompanying physical theory. In this minireview we highlight experimental works on vibrational polaritonic chemistry that have appeared most recently, focusing on the chemistry of the rate-limiting steps to provide mechanistic insight. We hope this review will encourage synthetic chemists to enter the field and we discuss the opportunities and challenges that lie ahead as polaritonic chemistry grows into the future.

S. Viti, J. Holdship

Databases of gas and surface chemical reactions are a key tool for scientists working in a wide range of physical sciences. In Astrochemistry, databases of chemical reactions are used as inputs to chemical models to determine the abundances of the interstellar medium. Gas chemistry and, in particular, grain surface chemistry and its treatment in gas-grain chemical models are however areas of large uncertainty. Many reactions - especially on the dust grains - have not been systematically experimentally studied. Moreover, experimental measurements are often not easily translated to the rate equation approach most commonly used in astrochemical modelling. Reducing the degree of uncertainty intrinsic in these databases is therefore a prime problem, but has so far been approached mainly by ad hoc procedures of essentially trial and error. In this chapter we review the problem of the determination of accurate and complete chemical networks in the wider context of Astrochemistry and explore the possibility of using statistical methods and machine learning (ML) techniques to reduce the uncertainty in chemical networks.

V. P. Srinivasan, Ch. Sandeep, C. Shanthi et al.

Electrical discharge machining is a thermo-physical-based material removal technique. 25 combinations of process variables were formulated with the aid of Taguchi technique for EDM of adsorbed Si3N4–TiN. Machining variables like pulse current, pulse-on time, pulse-off time, dielectric pressure, and spark gap voltage varied, and impact of each variables on the performance metrics (MRR, EWR, SR, ROC, θ, CIR, and CYL) was assessed. MCDM strategies like grey relational analysis and TOPSIS are utilized to find out the ideal arrangement of machining parameters to achieve most acute productivity of the multitude of reactions. Likewise, metaheuristic algorithm in particular GRA combined with teaching-learning-based optimization algorithm is utilized for getting global optimized input factors. Important factors like pulse current, pulse-on time, and spark gap voltage characteristically affect the outputs. It is recognized that the pulse-on time and the pulse current are the most significant input factors than others. The ideal machining parameters in view of GRA and TOPSIS techniques for acquiring better output factors are I, 12 amps; PON, 7 μsec; POFF, 4 μsec; DP, 12 kg/cm2; and SV, 36 volts.

A.P. Zajogin, N.H. Trinh, M.A. Malets et al.

A layer-by-layer analysis of metals and alloys has been carried out, and the possibility of deposition of nanofilms containing tin in their composition on various types of surfaces (metal, glass) under the action of dual laser pulses on a target in an air atmosphere has been studied. The experiments were carried out using the laser two-pulse multichannel atomic emission spectrometer LSS-1. The advantages of the pulsed laser deposition as a method for producing clusters and fractals are: versatility in relation to the material, the ability to exclude impurities, the flexibility of the method, and the ability of controlling the formation of film structures. The performed spectroscopic studies of the laser plasma formed by the action of two successive pulses on a target illustrate the development of methods for obtaining nanoclusters of various chemical elements. This method can be used to obtain nanofilms of not only pure metals, but also composite alloys. The possibility of obtaining nanofilms for creating gas-sensitive sensors is shown.

G. Futter, A. Latz, T. Jahnke

Abstract Chemical membrane degradation causes deterioration of critical membrane properties such as gas separation which finally causes failure of polymer electrolyte membrane fuel cells (PEMFCs). In order to identify the underlying physical processes, a physics-based model of chemical membrane degradation is implemented into the novel numerical framework NEOPARD-X [1]. The existing 2D PEMFC model is extended to incorporate the mechanisms of hydrogen peroxide formation and reduction, a redox cycle of iron contaminants in the ionomer phase, radical formation due to Fenton's chemistry and radical attack on the polymer structure. Unzipping of the polymer backbone and scission of the side chains are considered as degradation mechanism. The degradation model is validated against experimental data obtained in accelerated stress tests (ASTs). From theoretical considerations, the influence of chemical membrane degradation on the cell performance is revealed. The influence of pressure, relative humidity and cell voltage on the chemical degradation is rationalized. The operating conditions strongly influence the kinetics and spacial distribution of the membrane degradation. Degradation is found to be most pronounced at elevated pressure, high relative humidity and high cell voltage close to the interface of anode catalyst layer and PEM.

L. Pietanza, O. Guaitella, V. Aquilanti et al.

E. Coccia, J. Fregoni, Ciro Achille Guido et al.

The multidisciplinary nature of the research in molecular nanoplasmonics, i.e., the use of plasmonic nanostructures to enhance, control, or suppress properties of molecules interacting with light, led to contributions from different theory communities over the years, with the aim of understanding, interpreting, and predicting the physical and chemical phenomena occurring at molecular- and nano-scale in the presence of light. Multiscale hybrid techniques, using a different level of description for the molecule and the plasmonic nanosystems, permit a reliable representation of the atomistic details and of collective features, such as plasmons, in such complex systems. Here, we focus on a selected set of topics of current interest in molecular plasmonics (control of electronic excitations in light-harvesting systems, polaritonic chemistry, hot-carrier generation, and plasmon-enhanced catalysis). We discuss how their description may benefit from a hybrid modeling approach and what are the main challenges for the application of such models. In doing so, we also provide an introduction to such models and to the selected topics, as well as general discussions on their theoretical descriptions.

Qunfang Zhao, Shuqiong Zhang, Chang Wang et al.

As a promising cathode material for lithium-ion batteries (LIBs), olivine-structured LiFePO4 has been increasingly studied due to its high capacity, excellent thermal stability, cycling stability and environmental friendliness. Nevertheless, the main challenge of LiFePO4 is its poor conductivity and Li+ diffusion coefficient. Herein, a V-doped LiFePO4/C composite is prepared via a solid-state method. The electronic structures of the samples are obtained by first-principles calculations based on density functional theory. V2 exhibits enhanced electrochemical performance, demonstrating discharge capacities as high as 155.6, 150.2, 136.0, 122.4 and 93.1 mA h g-1 at 0.1, 0.2, 0.5, 1.0 and 3.0C, respectively, and approximately 100% capacity retention after 100 cycles at 1.0C.

Fang Ge, Xin Huang, Yi Zhang et al.

The corrosion behavior of 2205 duplex stainless steel (DSS) base metal (BM) and ER2209 weld metal (WM) in an ash/water suspension composed of deposited ash on the flue gas side of a low-temperature heat exchanger in a waste-to-energy plant and water was studied by polarization curve analysis, electrochemical impedance spectroscopy (EIS), localized electrochemical measurements, microscopic surface morphology observation, and metallographic analysis. The results showed that the corrosion resistance of both the BM and the WM decreased with the increase in immersion time. After 4 h of immersion, active sites where the current density increased suddenly appeared on the surface of the WM, and the surface roughness increased significantly, indicating the beginning of pitting on the WM surface. However, it took 8 h for the active sites to appear on the BM, and the pitting corrosion on the BM surface was obviously less than that of the WM surface under the same immersion time. The pitting corrosion resistance of the 2205 DSS BM was obviously better than that of the WM. According to the metallographic analysis results, the high proportion of dendritic ferrite in the metallographic structure of the WM may be the reason for its poor corrosion resistance.

T. Vidal, J. Loison, A. Jaziri et al.

Sulphur-bearing species are often used to probe the physical structure of star forming regions of the interstellar medium, but the chemistry of sulphur in these regions is still poorly understood. In dark clouds, sulphur is supposed to be depleted under a form which is still unknown despite numerous observations and chemical modeling studies that have been performed. In order to improve the modeling of sulphur chemistry, we propose an enhancement of the sulphur chemical network using experimental and theoretical literature. We test the effect of the updated network on the outputs of a three phases gas-grain chemical model for dark cloud conditions using different elemental sulphur abundances. More particularly, we focus our study on the main sulphur reservoirs as well as on the agreement between model predictions and the abundances observed in the dark cloud TMC-1 (CP). Our results show that depending on the age of the observed cloud, the reservoir of sulphur could either be atomic sulphur in the gas-phase or HS and H2S in icy grain bulks. We also report the first chemical model able to reproduce the abundances of observed S-bearing species in TMC-1 (CP) using as elemental abundance of sulphur its cosmic value.

M. Mugnai, Changbong Hyeon, M. Hinczewski et al.

By operating out of equilibrium, nanoscale biological machines execute many functions that do not take place in abiotic systems. Statistical physics, physical chemistry, and polymer physics principles are needed in elucidating the rules and constraints governing large-scale structural changes that occur when metabolizing molecular fuel. This paper reviews the advances in theories rooted in coarse graining the complex systems while reminding us that molecular details must be an integral part of a deeper understanding of processes in living systems.

S. Aouimer, M. Ameri, D. Bensaid et al.

The Elastic, Electronic and Thermodynamic Properties of a New Cd Based Full Heusler Compounds — A Theoretical Investigation Using DFT Based FP-LMTO Approach S. Aouimer, M. Ameri, D. Bensaida,c,∗, N.E. Moulay, A.Z. Bouyakoub, F.Z. Boufadi, I. Ameri and Y. Al-Douri Laboratory of Physical Chemistry of Advanced Materials, University of Djillali Liabes, BP 89, Sidi-Bel-Abbes 22000, Algeria Physics Department, Faculty of Science, University of Sidi-Bel-Abbes, 22000, Algeria Institute of Science, University Belhadj Bouchaib, BP 284, Ain-Temouchent, 46000, Algeria Nanotechnology and Catalysis Research Center (NANOCAT), University of Malaya, 50603 Kuala Lumpur, Malaysia

Jingwen Ai, Gaoxu Huang, Yuming Zhao et al.

Lithium metal batteries (LMBs) are promising energy storage system due to the lowest reduction potential and high specific capacity. However, the uncontrolled growth of Li dendrites during cycling processes might induce the low coulombic efficiency and severe safety hazards. Herein, our work focus on improving the performances of lithium metal batteries by constructing a new 3D current collector decorated with CuO nanowire array (CuO NWA@Cu). As a result, in contrast to the coulombic efficiency (about 90%) and voltage hysteresis (about 100 mV) of planar Cu after 10 cycles, the obtained CuO NWA@Cu has a higher coulombic efficiency (close to 98%) and lower voltage hysteresis (about 50 mV) at the current density of 0.5 mA cm-2 after 100 cycles. This work provides a simple and scalable method to obtain CuO NWA@Cu 3D anode current collector for dendrite-free and high coulomic efficiency LMBs.

Fanglong Yin, Xin Zhou, Songlin Nie et al.

To select appropriate combinations of antifriction and wear-resistant materials for key tribopairs in seawater hydraulic valves, the tribocorrosion behavior of six kinds of corrosion-resistant alloys sliding against a carbon fiber/polytetrafluoroethylene/graphite (CF/PTFE/graphite)-filled polyetheretherketone (CF-PEEK) composite under artificial seawater lubrication was comparatively investigated by using a pin-on-disk friction tester and electrochemical workstation. The results show that AISI 316, AISI 630 and chromium-plated Ti6Al4V exhibit better tribological behavior than Ti6Al4V and nitrided Ti6Al4V under dry friction, distilled water and artificial seawater conditions. Besides, Ti6Al4V exhibits better corrosion resistance than other corrosion-resistant alloys in both static corrosion and tribocorrosion conditions, and the chromium plating process significantly accelerates the Ti6Al4V corrosion rate in seawater. Moreover, the corrosion-induced wear is higher than the wear-induced corrosion. In addition, the contribution of corrosion-induced wear to synergetic weight loss is more than 85% for all the alloys under tribocorrosion in seawater. Consequently, material combinations of AISI 630/CF-PEEK and AISI 316/CF-PEEK could preferentially be used in seawater hydraulic valves.

I.S. Bagrysheva, N.N. Bolshakova, A.I. Ivanova et al.

The results of the study of dynamic processes of repolarization of crystals of pure and deuterated triglycine sulfate are presented. It is established that deuteration and an increase in the concentration of the L- α alanine impurity in deuterated crystals lead to a decrease in the relative and effective dielectric constants, switchable polarization and an increase in the coercive field and the displacement field. Deuteration and substitution of a part of glycine molecules into alanine allows obtaining a stable unipolar state in crystals.

Yu-Ching Weng, Zhao-Nan Wang, Shu-Yii Wu

Electrospun carbon nanofibers modified with Pd sensors have been developed for O2 sensing with high sensitivity. The average diameter of carbon nanofiber and Pd particle is about 251 and 20.5 nm, respectively. The sensing performances of the Pd decorated carbon nanofiber (Pd-CNF) electrode towards reduction of O2 were evaluated. The Pd-CNF electrode with a Pd loading of 4.7 mg/cm2 shows maximum sensitivity of 2.6 μAppm-1cm-2 in the O2 concentration region of 100-1000 ppm. The response and recovery times are less than 32 and 48 s, respectively. The high sensitivity, wide linear range and rapid response and recovery times make the Pd-CNF electrode a promising candidate for amperometric O2 sensors.