Frontiers of Chemical Science and Engineering

ISSN 2095-0179

ISSN 2095-0187(Online)

CN 11-5981/TQ

Postal Subscription Code 80-969

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, Volume 13 Issue 2

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EDITORIAL
Special Issue on future directions in plasma nanoscience
Erik C. Neyts
Front. Chem. Sci. Eng.. 2019, 13 (2): 199-200.  
https://doi.org/10.1007/s11705-019-1843-y

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REVIEW ARTICLE
Towards an integrated modeling of the plasma-solid interface
Michael Bonitz, Alexey Filinov, Jan-Willem Abraham, Karsten Balzer, Hanno Kählert, Eckhard Pehlke, Franz X. Bronold, Matthias Pamperin, Markus Becker, Dettlef Loffhagen, Holger Fehske
Front. Chem. Sci. Eng.. 2019, 13 (2): 201-237.  
https://doi.org/10.1007/s11705-019-1793-4

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Solids facing a plasma are a common situation in many astrophysical systems and laboratory setups. Moreover, many plasma technology applications rely on the control of the plasma-surface interaction, i.e., of the particle, momentum and energy fluxes across the plasma-solid interface. However, presently often a fundamental understanding of them is missing, so most technological applications are being developed via trial and error. The reason is that the physical processes at the interface of a low-temperature plasma and a solid are extremely complex, involving a large number of elementary processes in the plasma, in the solid as well as fluxes across the interface. An accurate theoretical treatment of these processes is very difficult due to the vastly different system properties on both sides of the interface: Quantum versus classical behavior of electrons in the solid and plasma, respectively; as well as the dramatically differing electron densities, length and time scales. Moreover, often the system is far from equilibrium. In the majority of plasma simulations surface processes are either neglected or treated via phenomenological parameters such as sticking coefficients, sputter rates or secondary electron emission coefficients. However, those parameters are known only in some cases and with very limited accuracy. Similarly, while surface physics simulations have often studied the impact of single ions or neutrals, so far, the influence of a plasma medium and correlations between successive impacts have not been taken into account. Such an approach, necessarily neglects the mutual influences between plasma and solid surface and cannot have predictive power.

In this paper we discuss in some detail the physical processes of the plasma-solid interface which brings us to the necessity of coupled plasma-solid simulations. We briefly summarize relevant theoretical methods from solid state and surface physics that are suitable to contribute to such an approach and identify four methods. The first are mesoscopic simulations such as kinetic Monte Carlo and molecular dynamics that are able to treat complex processes on large scales but neglect electronic effects. The second are quantum kinetic methods based on the quantum Boltzmann equation that give access to a more accurate treatment of surface processes using simplifying models for the solid. The third approach are ab initio simulations of surface process that are based on density functional theory (DFT) and time-dependent DFT. The fourths are nonequilibrium Green functions that able to treat correlation effects in the material and at the interface. The price for the increased quality is a dramatic increase of computational effort and a restriction to short time and length scales. We conclude that, presently, none of the four methods is capable of providing a complete picture of the processes at the interface. Instead, each of them provides complementary information, and we discuss possible combinations.

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Important parameters in plasma jets for the production of RONS in liquids for plasma medicine: A brief review
Anna Khlyustova, Cédric Labay, Zdenko Machala, Maria-Pau Ginebra, Cristina Canal
Front. Chem. Sci. Eng.. 2019, 13 (2): 238-252.  
https://doi.org/10.1007/s11705-019-1801-8

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Reactive oxygen and nitrogen species (RONS) are among the key factors in plasma medicine. They are generated by atmospheric plasmas in biological fluids, living tissues and in a variety of liquids. This ability of plasmas to create a delicate mix of RONS in liquids has been used to design remote or indirect treatments for oncological therapy by treating biological fluids by plasmas and putting them in contact with the tumour. Documented effects include selective cancer cell toxicity, even though the exact mechanisms involved are still under investigation. However, the “right” dose for suitable therapeutical activity is crucial and still under debate. The wide variety of plasma sources hampers comparisons. This review focuses on atmospheric pressure plasma jets as the most studied plasma devices in plasma medicine and compiles the conditions employed to generate RONS in relevant liquids and the concentration ranges obtained. The concentrations of H2O2, NO2, NO3 and short-lived oxygen species are compared critically to provide a useful overview for the reader.

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Plasma for cancer treatment: How can RONS penetrate through the cell membrane? Answers from computer modeling
Annemie Bogaerts, Maksudbek Yusupov, Jamoliddin Razzokov, Jonas Van der Paal
Front. Chem. Sci. Eng.. 2019, 13 (2): 253-263.  
https://doi.org/10.1007/s11705-018-1786-8

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Plasma is gaining increasing interest for cancer treatment, but the underlying mechanisms are not yet fully understood. Using computer simulations at the molecular level, we try to gain better insight in how plasma-generated reactive oxygen and nitrogen species (RONS) can penetrate through the cell membrane. Specifically, we compare the permeability of various (hydrophilic and hydrophobic) RONS across both oxidized and non-oxidized cell membranes. We also study pore formation, and how it is hampered by higher concentrations of cholesterol in the cell membrane, and we illustrate the much higher permeability of H2O2 through aquaporin channels. Both mechanisms may explain the selective cytotoxic effect of plasma towards cancer cells. Finally, we also discuss the synergistic effect of plasma-induced oxidation and electric fields towards pore formation.

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Plasma-catalysis: Is it just a question of scale?
J. Christopher Whitehead
Front. Chem. Sci. Eng.. 2019, 13 (2): 264-273.  
https://doi.org/10.1007/s11705-019-1794-3

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The issues of describing and understanding the changes in performance that result when a catalyst is placed into plasma are discussed. The different chemical and physical interactions that result and how their combination might produce beneficial results for the plasma-catalytic processing of different gas streams are outlined with particular emphasis being placed on the different range of spatial and temporal scales that must be considered both in experiment and modelling. The focus is on non-thermal plasma where the lack of thermal equilibrium creates a range of temperature scales that must be considered. This contributes in part to a wide range of inhomogeneity in different properties such as species concentrations and electric fields that must be determined experimentally by in situ methods and be incorporated into modelling. It is concluded that plasma-catalysis is best regarded as conventional catalysis perturbed by the presence of a discharge, which modifies its operating conditions, properties and outcomes often in a very localised way. The sometimes used description “plasma-activated catalysis” is an apt one.

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An overview of carbon nanotubes role in heavy metals removal from wastewater
Leila Ouni, Ali Ramazani, Saeid Taghavi Fardood
Front. Chem. Sci. Eng.. 2019, 13 (2): 274-295.  
https://doi.org/10.1007/s11705-018-1765-0

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The scarcity of water, mainly in arid and semi-arid areas of the world is exerting exceptional pressure on sources and necessitates offering satisfactory water for human and different uses. Water recycle/reuse has confirmed to be successful and promising in reliable water delivery. For that reason, attention is being paid to the effective treatment of alternative resources of water (other than fresh water) which includes seawater, storm water, wastewater (e.g., dealt with sewage water), and industrial wastewater. Carbon nanotubes (CNTs) are called the technology of 21st century. Nowadays CNTs have been widely used for adsorption of heavy metals from water/wastewater due to their unique physical and chemical properties. This paper reviews some recent progress (from 2013 to 2018) in the application of CNTs for the adsorption of heavy metals in order to remove toxic pollutants from contaminated water. CNTs are expected to be a promising adsorbent in the future because of its high adsorption potential in comparison to many traditional adsorbents.

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Phosphorene: Current status, challenges and opportunities
Anandarup Goswami, Manoj B. Gawande
Front. Chem. Sci. Eng.. 2019, 13 (2): 296-309.  
https://doi.org/10.1007/s11705-018-1783-y

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The field of 2-dimensional (2D) materials has witnessed a sharp growth since its inception and can majorly be attributed to the substantial technical and scientific developments, leading to significant improvements in their syntheses, characterization and applications. In the list of 2D materials, the relatively newer addition is phosphorene, which ideally consists of a single layer of black phosphorous. Keeping in mind the past, and ongoing research activities, this short account offers a brief overview of the present status and the associated challenges in the field of phosphorene-related research, with special emphasis on their syntheses, properties, applications and future opportunities.

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Carbon-based materials for photodynamic therapy: A mini-review
Di Lu, Ran Tao, Zheng Wang
Front. Chem. Sci. Eng.. 2019, 13 (2): 310-323.  
https://doi.org/10.1007/s11705-018-1750-7

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Carbon-based materials have been extensively applied in photodynamic therapy owing to the unique optical characteristics, good biocompatibility and tunable systematic toxicity. This mini-review mainly focuses on the recent application of carbon-based materials including graphene, carbon nanotube, fullerene, corannulene, carbon dot and mesoporous carbon nanoparticle. The carbon-based materials can perform not only as photosensitizers, but also effective carriers for photosensitizers in photodynamic therapy, and its combined treatment.

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COMMUNICATION
Molecular dynamics simulations of initial Pd and PdO nanocluster growth in a magnetron gas aggregation source
Pascal Brault, William Chamorro-Coral, Sotheara Chuon, Amaël Caillard, Jean-Marc Bauchire, Stève Baranton, Christophe Coutanceau, Erik Neyts
Front. Chem. Sci. Eng.. 2019, 13 (2): 324-329.  
https://doi.org/10.1007/s11705-019-1792-5

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Molecular dynamics simulations are carried out for describing growth of Pd and PdO nanoclusters using the ReaxFF force field. The resulting nanocluster structures are successfully compared to those of nanoclusters experimentally grown in a gas aggregation source. The PdO structure is quasi-crystalline as revealed by high resolution transmission microscope analysis for experimental PdO nanoclusters. The role of the nanocluster temperature in the molecular dynamics simulated growth is highlighted.

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RESEARCH ARTICLE
Multifunctional antimicrobial chlorhexidine polymers by remote plasma assisted vacuum deposition
Ana Mora-Boza, Francisco J. Aparicio, María Alcaire, Carmen López-Santos, Juan P. Espinós, Daniel Torres-Lagares, Ana Borrás, Angel Barranco
Front. Chem. Sci. Eng.. 2019, 13 (2): 330-339.  
https://doi.org/10.1007/s11705-019-1803-6

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Novel antibacterial materials for implants and medical instruments are essential to develop practical strategies to stop the spread of healthcare associated infections. This study presents the synthesis of multifunctional antibacterial nanocoatings on polydimethylsiloxane (PDMS) by remote plasma assisted deposition of sublimated chlorhexidine powders at low pressure and room temperature. The obtained materials present effective antibacterial activity against Escherichia coli K12, either by contact killing and antibacterial adhesion or by biocide agents release depending on the synthetic parameters. In addition, these multifunctional coatings allow the endure hydrophilization of the hydrophobic PDMS surface, thereby improving their biocompatibility. Importantly, cell-viability tes